![CRC-45474 CH001.tex 26/6/2007 9: 24 Page 2
2 WiMAX: Applications
characterized by some as a threat to the long-term viability of several exist-
ing wireless technologies (including IEEE 802.11-based wireless local area
network [WLAN] technology, broadband residential Internet technologies
such as digital subscriber line [DSL] and cable), even viewed by some as a
competitor to third-generation (3G) cellular technologies. Others view 802.16
as a powerful complementary technology to these various tools. Regard-
less, 802.16 is seen by many in the commercial wireless industry as a key
enabling technology in the large-scale realization of the wireless Internet,
providing a tool that may potentially allow service providers to deliver high
data rates (i.e., tens of Mbps) to a variety of devices, such as handheld devices,
and enabling an entire new generation of applications (e.g., handheld,
high-resolution videophones).
The future success of WiMAX in the commercial marketplace and its poten-
tial emergence as a disruptive technology is still unknown. While WiMAX has
certainly generated a high degree of excitement within the commercial wire-
less industry, the marketplace always proves to be the final judge—that which
separates hype from reality. However, this determination is a complex matter
that is a function of numerous factors. The goal of this chapter is to provide an
overview of the evolution of WiMAX from three key perspectives: (1) usage
case, (2) technology, and (3) standardization.
1.2 WiMAX—An Overview
WiMAX is based upon the IEEE 802.16 WMAN technology family, which
provides specifications of the media access control (MAC) layer and the
physical (PHY) layer. The 802.16 specification further subdivides the MAC
sublayer into three sublayers: the convergence sublayer (CS), the common
part sublayer (CPS), and the security sublayer. The CS aims to enable
802.16 to better accommodate the higher layer protocols placed above the
MAC layer. The 802.16 specification assumes there will be two predominant
types of traffic transported across the 802.16 network: ATM and IEEE 802.3
(Ethernet). Thus, there are two CS specifications: ATM and packet. The CS
receives data frames from a higher layer and classifies the frame. On the basis
of this classification, the CS can perform additional processing, such as pay-
load header compression, before passing the frame to the MAC CPS. The CS
also accepts data frames from the MAC CPS. If the peer CS has performed any
type of processing, the receiving CS will restore the data frame before pass-
ing it to a higher layer. The CS is separate from the remainder of the 802.16
MAC such that vendors who wish to support other protocols can develop
specialized CSs.
The CPS is the central piece of the 802.16 MAC, defining the medium access
method (Figure 1.1). The CPS provides functions related to duplexing, net-
work entry and initialization, framing, quality of service (QoS), and channel
access. The security sublayer, also referred to as the privacy sublayer, has](https://image.slidesharecdn.com/83641-250214212221-eec94b53/85/WiMAX-Applications-1st-Edition-Syed-A-Ahson-2024-Scribd-Download-22-320.jpg)
![CRC-45474 CH001.tex 26/6/2007 9: 24 Page 7
WiMAX Past, Present, and Future 7
1.3 WiMAX—Evolving Usage Cases
Any successful technology must fit a key need in the marketplace. That is, a
technology must have a compelling usage case, a “killer niche’’ that it can fit
better than alternatives. And here, niche does not imply any type of limited
size of scale, but rather is viewed as analogous to the “killer app.’’ This is
often why the position of “first-to-market’’ is so attractive, because it elim-
inates competition from viable alternatives, leaving that technology as the
only choice to meet the compelling usage case. One needs to look no further
than the wildly successful IEEE 802.11 WLAN technology family to see the
importance of a killer niche. IEEE 802.11 found a niche in the marketplace for
localized hot-spot wireless connectivity, the ability to replace network cables
within localized regions, and has filled that niche with a family of highly
capable technologies that now approaches ubiquity. This original usage case
of IEEE 802.11 WLANs was simple and narrow in focus. Only now do later
revisions of the technology address more sophisticated usage cases, such as
QoS, mesh networking, and roaming.
Clearly, it is quite important for WiMAX to have a killer niche that it can
satisfy to enjoy long-term success in the marketplace. However, an agree-
ment on exactly what that compelling usage case is or should be has been
difficult to come to, even within the WiMAX community. Even up to this
point in time, the vision for how WiMAX will be or should be employed is
arguable.
Certainly, the dominant usage case scenarios have evolved over time as
WiMAX has continued to evolve from both a marketing and a technology
perspective. The original 802.16 specification [1] was clearly oriented toward
providing high-rate, PTP, LOS connectivity between fixed platforms. Here,
the driving usage scenario was that of interconnecting locations that do not
lend themselves to cabled solutions. A classic example of this usage scenario
is that of the remotely located transmission tower that is wirelessly back-
hauled to a fixed location attached to a larger wired network. There was,
and still is, a legitimate market within this problem space. However, this
market was continually hampered by poor interoperability between propri-
etary solutions. The goal of creating an interoperable technology to fit this
niche was the original inspiration of the 802.16 specification, the envisioned
backhaul technology of this problem space. In this envisioned usage case,
the primary competition to WiMAX is proprietary solutions. It is clear that,
in the long term, a standardized technology with strong industry support,
such as WiMAX, would enjoy tremendous success. However, this is the nar-
rowest of envisioned problem spaces for which WiMAX is often considered a
candidate.
Afterthefinalizationoftheoriginal802.16technologystandard, thescopeof
envisioned WiMAX usage scenarios was significantly expanded. Originally,
WiMAX was viewed as a PTP, LOS backhaul technology, envisioned to pro-
vide wireless bridging between fixed locations within network infrastructure.](https://image.slidesharecdn.com/83641-250214212221-eec94b53/85/WiMAX-Applications-1st-Edition-Syed-A-Ahson-2024-Scribd-Download-27-320.jpg)
![CRC-45474 CH001.tex 26/6/2007 9: 24 Page 8
8 WiMAX: Applications
The primary expansion of scope was to that of the direct support of end-user
networks. Here, WiMAX was envisioned to serve a role within the internet
service providers (ISP) problem space, interconnecting end-user networks
(e.g., homes)withnetworkinfrastructure. Thisexpansionofscopemakesvery
good logical sense, particularly given the still fixed nature of network nodes.
Here, the creators of WiMAX had created a wireless technology capable of
delivering very high data rates over very long distances. Indeed, this would
seem an ideal technology to apply to the problem space of the residential
wireless local loop, where low-rate wired infrastructure often limits the types
of capabilities that can be enjoyed by the residential consumer. The resultant
technology brought to bear in this problem space was the IEEE 802.16a speci-
fication [2], leading to the eventual IEEE 802.16d specification, which unified
the original 802.16 and 802.16a specifications. This 802.16d specification is also
often referred to as the IEEE 802.16-2004 specification and is the basis for fixed
WiMAX. However, this problem space contains much stiffer competition than
the original scope of employment in the form of both wire-line and wireless
technologies. Technologies such as DSL and cable modem are already firmly
entrenched within this market space, already enjoying significant consumer
bases. Additionally, there are other wireless technologies also contending
for this market, such as CDMA2000. The marketplace will ultimately deter-
mine the level of success any of these technologies will experience. However,
current conventional wisdom is that technologies such as WiMAX are more
likely to enjoy success in this problem space within markets that are not yet
fully developed (e.g., third-world markets) or in regions where other forms
of ISPs do not have a strong presence (e.g., rural areas within developed
countries).
The final evolution of the WiMAX usage scenario came in the form of mobil-
ity support. Here, the envisioned scenario has WiMAX serving as the air inter-
face for the actual radio access network, where both fixed and mobile users
access the WiMAX network. The developers of the technology had created a
technology capable of reasonably high data rates at reasonably long ranges.
If this technology could now be augmented to support the case of the mobile
users, then WiMAX could serve as a viable candidate for wide-area connec-
tivity. This usage case is the driving scenario behind the creation of the IEEE
802.16e technology standard [5], also referred to as IEEE 802.16-2005, the basis
of mobile WiMAX. This market arguably presents the stiffest competition
of all envisioned usage scenarios. Within this space, there are two potential
deployment scenarios: (1) employment of the WiMAX air interface by incum-
bent wireless service providers (WSPs) and (2) employment of the WiMAX
air interface by new-entry WSPs. Incumbent cellular providers have invested
enormous amounts of capital expenditures to reach current level of capabil-
ities that will not be easily equaled or surpassed by any new-entry technology.
Even next-generation cellular technologies, such as 3GPP and 3GPP2, have
experienced relatively slow deployment as cellular service providers have
not been quick to embrace these technologies over older technologies such](https://image.slidesharecdn.com/83641-250214212221-eec94b53/85/WiMAX-Applications-1st-Edition-Syed-A-Ahson-2024-Scribd-Download-28-320.jpg)
![CRC-45474 CH002.tex 16/7/2007 9: 47 Page 21
Overview of WiMAX Standards and Applications 21
specified in 802.16a to reduce such interference. The implementation of
DFS enables the mobile device to switch between different radio frequency
(RF) channels on the basis of certain channel measurement criteria, such as
signal-to-interference ratio. This standard is designed to support a maximum
data rate of 75 Mbps at a distance of up to 50 km. In the following sections,
the main new features introduced by 802.16a will be discussed.
2.2.2.1 Flexible Bandwidth
A problem existing in the original 802.16 standard is that it is often very
difficult for some power-sensitive devices, such as laptops and handheld
equipments, to transmit to the BS over long distances if the channel band-
width is too wide. It is solved in 802.16a by using flexible bandwidth choices,
including channel bandwidth between 1.25 and 28 MHz, which provides
the flexibility to operate in different frequency bands with varying chan-
nel requirements around the world. Because of the interference problem in
2–11 GHz bands, 802.16a systems are more attractive in rural and developing
markets where there are sufficient unlicensed spectrums available without
interference concerns.
2.2.2.2 Mesh Topology
In addition to PTP and PMP, 802.16a introduces the mesh topology, which is a
more flexible, effective, reliable, and portable network architecture based on
the multihop concept. Mesh networks are wireless data networks that give
the SSs more intelligence than traditional wireless transmitters and receivers.
In a PMP network, all the connections must go through the BS, while with
mesh topology, every SS can act as an access point and is able to route packets
to its neighbors by itself to enlarge the geographical coverage of a network.
The architecture of a mesh system is shown in Figure 2.3. The routing across
the network can be either proactive (using predetermined routing tables) or
reactive (generating routes on demand).
Mesh topology can be divided into two basic categories: switched mesh
and routed mesh [11]. In a switched mesh, a fixed route between two net-
work nodes is predetermined and all packets follow the same path during
the transmission. If the connection is down or the QoS of the link is degraded,
a new route will be established to replace the old one. However, in routed
mesh architecture, there is no fixed path from the source to the destination.
All packets are forwarded by intelligent network nodes on the basis of the
evaluation of link conditions measured by a number of parameters, such as
throughput, traffic density, packet loss, interference level, delay, and jitter.
Packets from the same source to the same destination may follow different
paths and arrive with various delays and jitters. The routed mesh can be fur-
ther divided into different forms. At one extreme, every node knows all the
other nodes in the network, which is called all-knowing mesh. At another
extreme, every node only knows its immediate neighbors. An all-knowing](https://image.slidesharecdn.com/83641-250214212221-eec94b53/85/WiMAX-Applications-1st-Edition-Syed-A-Ahson-2024-Scribd-Download-41-320.jpg)
![CRC-45474 CH002.tex 16/7/2007 9: 47 Page 25
Overview of WiMAX Standards and Applications 25
bands suitable for mobility must be below 6 GHz. IEEE 802.16e is also not
backward compatible with 802.16-2004 so that hardware/software updates
are required to implement it.
Compared with 802.16-2004, 802.16e has lower throughput (up to 15 Mbps),
butitsupportsbothhardandsofthandoffs. Hardhandoffsarebasedonbreak-
before-make concept, which leads to high latency while soft handoffs use
make-before-break approach to minimize the delay. The former is usually
used for data transfer, while the latter is more suitable for delay-sensitive
applications, such as VoIP and online games.
IEEE 802.16e uses OFDMA to enhance network performance. OFDMA is a
multiple-user version of OFDM and is a more flexible way to manage different
user devices with various antenna types and form factors. In OFDMA, the
whole carrier space is divided into N groups, where each of them includes M
carriers. All the carriers are then grouped into M subchannels, each with one
carrier per group.
In OFDM, only one user device can use the channel during a single time slot.
OFDMA allows multiple users to transmit data simultaneously. A number of
users can communicate at the same time using the subchannels allocated to
them.
Signal coding, modulation, and amplitude are set separately for each sub-
channel based on channel conditions to optimize the utilization of network
resources. From the user perspective, subchannelization allows different
subchannels to be allocated to different subscribers according to their require-
ments and channel conditions. One customer can be allocated two or more
subchannels. For service providers, subchannelization provides a flexible and
efficient bandwidth management solution and a flexible power transmission
method. Higher power can be allocated to those subchannels with bad radio
conditions.
Using OFDMA, fixed user devices can be supported with the same data rate
as OFDM, while mobile users trade off mobility against bandwidth. Com-
pared to OFDM, OFDMA supports larger FFT size of 1024 so that it enables
more flexible subcarrier bandwidth allocation [10].
The four main IEEE 802.16 family standards have been introduced in the
above sections. Table 2.2 summarizes their main features.
2.2.5 Other IEEE 802.16 Family Standards
In addition to the four main standards discussed before, there are some other
IEEE 802.16 family standards that will be briefly introduced in the following
sectionsforcompleteness. Ifreaderswanttolearnmoreaboutthesestandards,
please refer to Ref. 9.
2.2.5.1 802.16c
It was published in January 2003 as an amendment to 802.16. This standard is
aimed to develop the 10–66 GHz BWAsystem profiles and aid interoperability
specifications. It has already been replaced by the IEEE 802.16-2004 standard.](https://image.slidesharecdn.com/83641-250214212221-eec94b53/85/WiMAX-Applications-1st-Edition-Syed-A-Ahson-2024-Scribd-Download-45-320.jpg)
WiMAX Applications 1st Edition Syed A. Ahson 2024 Scribd Download
- 1. Visit https://ebookfinal.com to download the full version and explore more ebooks WiMAX Applications 1st Edition Syed A. Ahson _____ Click the link below to download _____ https://ebookfinal.com/download/wimax-applications-1st- edition-syed-a-ahson/ Explore and download more ebooks at ebookfinal.com
- 2. Here are some suggested products you might be interested in. Click the link to download Arabic for Beginners International Edition Hippocrene Language Studies Syed A. Ali https://ebookfinal.com/download/arabic-for-beginners-international- edition-hippocrene-language-studies-syed-a-ali/ Handbook of Photomask Manufacturing Technology 1st Edition Syed Rizvi https://ebookfinal.com/download/handbook-of-photomask-manufacturing- technology-1st-edition-syed-rizvi/ Islam Economics and Society Syed Nawab Haider Naqvi https://ebookfinal.com/download/islam-economics-and-society-syed- nawab-haider-naqvi/ Next Generation Knowledge Machines Design and Architecture 1st Edition Syed V. Ahamed (Auth.) https://ebookfinal.com/download/next-generation-knowledge-machines- design-and-architecture-1st-edition-syed-v-ahamed-auth/
- 3. LTE WiMAX and WLAN Network Design Optimization and Performance Analysis 1st Edition Edition Leonhard Korowajczuk https://ebookfinal.com/download/lte-wimax-and-wlan-network-design- optimization-and-performance-analysis-1st-edition-edition-leonhard- korowajczuk/ Security in Next Generation Mobile Networks SAE LTE and Wimax 1st Edition Anand R. Prasad https://ebookfinal.com/download/security-in-next-generation-mobile- networks-sae-lte-and-wimax-1st-edition-anand-r-prasad/ Polyphosphazenes for Biomedical Applications 1st Edition A. K. Andrianov https://ebookfinal.com/download/polyphosphazenes-for-biomedical- applications-1st-edition-a-k-andrianov/ Amines Synthesis Properties and Applications 1st Edition Stephen A. Lawrence https://ebookfinal.com/download/amines-synthesis-properties-and- applications-1st-edition-stephen-a-lawrence/ Bayesian Inference with ecological applications 1st Edition William A Link https://ebookfinal.com/download/bayesian-inference-with-ecological- applications-1st-edition-william-a-link/
- 5. WiMAX Applications 1st Edition Syed A. Ahson Digital Instant Download Author(s): Syed A. Ahson, Mohammad Ilyas ISBN(s): 9781420045475, 1420045474 Edition: 1 File Details: PDF, 3.69 MB Year: 2007 Language: english
- 7. CRC-45474 fm.tex 27/7/2007 18: 38 Page i WiMAX Applications
- 8. CRC-45474 fm.tex 27/7/2007 18: 38 Page ii CRC Press is an imprint of the Taylor & Francis Group, an informa business Boca Raton London New York WiMAX: Technologies, Performance Analysis, and QoS ISBN 9781420045253 WiMAX: Standards and Security ISBN 9781420045237 WiMAX: Applications ISBN 9781420045474 The WiMAX Handbook Three-Volume Set ISBN 9781420045350 The WiMAX Handbook
- 9. CRC-45474 fm.tex 27/7/2007 18: 38 Page iii CRC Press is an imprint of the Taylor & Francis Group, an informa business Boca Raton London New York WiMAX Applications Edited by SYED AHSON MOHAMMAD ILYAS
- 10. CRC-45474 fm.tex 27/7/2007 18: 38 Page iv CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2008 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 1-4200-4547-4 (Hardcover) International Standard Book Number-13: 978-1-4200-4547-5 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the conse- quences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www. copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Ahson, Syed. WiMAX : applications / Syed Ahson and Mohammad Ilyas. p. cm. Includes bibliographical references and index. ISBN 978-1-4200-4547-5 (alk. paper) 1. Wireless communication systems. 2. Broadband communication systems. 3. IEEE 802.16 (Standard) I. Ilyas, Mohammad, 1953- II. Title. TK5103.2.A4316 2008 621.384--dc22 2007012502 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com
- 11. CRC-45474 fm.tex 27/7/2007 18: 38 Page v Contents Preface ...................................................................................................................vii Editors .....................................................................................................................xi Contributors .........................................................................................................xiii 1. WiMAX Past, Present, and Future: An Evolutionary Look at the History and Future of Standardized Broadband Wireless Access .............................................................................................1 Jack L. Burbank and William T. Kasch 2. Overview of WiMAX Standards and Applications .............................15 Leijia Wu and Kumbesan Sandrasegaran 3. WiMAX Technology for Broadband Wireless Communication ........35 Neena Gupta and Gurjit Kaur 4. VoIP over WiMAX ......................................................................................55 Mainak Chatterjee and Shamik Sengupta 5. WiMAX Technology for Home Access ...................................................77 Giselle M. Galván-Tejada and Erickson Trejo-Reyes 6. WiMAX Enables Cyber Extension to Rural Communities ...............103 K.R. Santhi, G. Senthil Kumaran, and Albert Butare 7. WiMAX over GSM for Basic IP Access in African Rural Areas ................................................................................................133 Damien Chatelain and Barend J. van Wyk 8. Applications of Wi-Fi/WiMAX Technologies in the Emerging World .......................................................................................159 Vinoth Gunasekaran and Fotios C. Harmantzis v
- 12. CRC-45474 fm.tex 27/7/2007 18: 38 Page vi vi Contents 9. Connectivity and Load Distribution in WiMAX-Based Multihop Backhaul Networks ...............................................................175 Sayandev Mukherjee and Dan Avidor 10. Providing QoS to Real and Interactive Data Applications in WiMAX Mesh Networks .........................................................................195 Vinod Sharma and Harish Shetiya Index ....................................................................................................................221
- 13. CRC-45474 fm.tex 27/7/2007 18: 38 Page vii Preface The demand for broadband services is growing exponentially. Traditional solutions that provide high-speed broadband access use wired access tech- nologies, such as traditional cable, digital subscriber line, Ethernet, and fiber optic. It is extremely difficult and expensive for carriers to build and maintain wired networks, especially in rural and remote areas. Carriers are unwilling to install the necessary equipment in these areas because of little profit and potential. WiMAX will revolutionize broadband communications in the developed world and bridge the digital divide in developing coun- tries. Affordable wireless broadband access for all is very important for a knowledge-basedeconomyandsociety. WiMAXwillprovideaffordablewire- less broadband access for all, improving quality of life thereby leading to economic empowerment. Broadband wireless access is as important as waterways, railroads, and interstate highways of an earlier era. Broadband wireless access technical solutions and products have been available for some time. These technologies have primarily focused on providing high data rate connectivity wirelessly between fixed stationary sites. These technical solutions are proprietary in nature and suffer from poor interoperability with other broadband wireless access products and high cost due to the lack of economy of scale. The IEEE 802.16 BWA technology family, referred to as worldwide interoperability for microwave access (WiMAX), intends to provide a standardized broadband wireless access solution. WiMAX has a strong base of standardization and industry support that provides a strong evolutionary path of its capabilities. The IEEE 802.16 specifications continue to evolve and expand in capabilities in support of the evolving vision of WiMAX usage and deployment. WiMAX enables wireless broadband access anywhere, anytime, and on vir- tually any device and has generated unparalleled interest within the wireless networking community. WiMAX is the next step in the mobile technol- ogy evolution path; it competes with IEEE 802.11-based WLAN technology, broadband residential Internet technologies such as digital subscriber line and cable and third-generation cellular technologies. WiMAX offers numer- ous advantages, such as improved performance and robustness, end-to-end IP-based network, secure mobility, and broadband speeds for voice, data, and video. The WiMAX handbook provides technical information about all aspects of WiMAX. The areas covered in the handbook range from basic concepts to research-grade material including future directions. The WiMAX hand- book captures the current state of wireless local area networks, and serves as a source of comprehensive reference material on this subject. The WiMAX vii
- 14. CRC-45474 fm.tex 27/7/2007 18: 38 Page viii viii Preface handbook consists of three volumes: WiMAX: Applications; WiMAX: Standards and Security; and WiMAX: Technology, Performance Evaluation, and QoS. It has a total of 32 chapters authored by experts from around the world. WiMAX: Applications includes 10 chapters authored by 21 experts from around the world. Chapter 1 (WiMAX Past, Present, and Future: An Evolutionary Look at the History and Future of Standardized Broadband WirelessAccess) describes the logical architecture of IEEE 802.16 and summarizes technology specifications. An example of an IEEE 802.16 network comprising core network, base station, and subscriber station is presented. Evolving usage scenarios for “fixed’’ and “mobile’’ WiMAX and role of competing technologies are examined in detail. Chapter 2 (Overview of WiMAX Standards and Applications) introduces some of the main IEEE 802.16 family standards (802.16a, 802.16.2-2001, 802.16- 2004, 802.16.2-2004, 802.16c, 802.16e, and 802.16f-2005). The application of WiMAX for rural area broadband services is analyzed. An example of last- mile access for providing high-speed access to buildings using WiMAX is given. A comprehensive list of WiMAX applications for video surveillance, automatic teller machines, online gaming, multimedia communication, med- ical applications, vehicular voice and data, sensor networks, telematics, and telemetry is included. Chapter 3 (WiMAX Technology for Broadband Wireless Communication) compares WiMAX to Wi-Fi (IEEE 802.11a/b/g) with respect to coverage area, bandwidth, spectrum, technology, network deployment, and applications. Advantages of WiMAX technology such as high capacity, quality-of-service, flexible architecture, mobility, improved user connectivity, robust carrier class operation, scalability, nonline-of-sight connectivity, cost-effectiveness, and fixed and nomadic access are discussed. Cellular, military, medical, secu- rity, disaster recovery, public safety, and campus connectivity applications of WiMAX are described in detail. Chapter 4 (VoIP over WiMAX) studies the feasibility of supporting VoIP over WiMAX and discusses a combination of techniques that can be adopted not only to enhance the performance of VoIP but also to support more num- bers of VoIP calls. A simplified VoIP system architecture is presented. Perfor- mance of VoIP calls is studied with respect to an ITU-T E-Model R-score that combines different aspects of voice quality impairment. Chapter 5 (WiMAX Technology for HomeAccess) presents issues related to the use of WiMAX technology as an alternative to provide broadband access to residential users. The feasibility of WiMAX for home access is analyzed from different perspectives, including data rate, frequency, coverage, and cell planning. Chapter 6 (WiMAX Enables Cyber Extension to Rural Communities) illus- trates the advantages of WiMAX as a last-mile solution and evaluates the potential of WiMAX as a 4G technology of the future. WiMAX with Wi-Fi as an application is presented as a solution to enable rural information and com- munication technology infrastructure. Economic and technical advantages of WiMAX are summarized. Analysis done in this chapter shows that WiMAX
- 15. CRC-45474 fm.tex 27/7/2007 18: 38 Page ix Preface ix will win in the marketplace and will capitalize on this, and further supports the proliferation of VoIP devices and IP-based services. Chapter 7 (WiMAX over GSM for Basic IP Access in African Rural Areas) shows that basic but affordable Internet protocol connectivity can be pro- vided to rural communities by using spare capacity on GSM networks to carry WiMAX traffic. In general, rural areas in Africa are seen as unprofitable by operators and hence these areas do not benefit from typical wired Internet access. On the contrary, the global system for mobile communications has thoroughly penetrated Africa and in many cases unutilized capacity exists in rural areas. Since the main problem with wireless local area network in Africa is not the last mile, but rather finding a way to connect the wireless access point to an existing backbone network, a solution to integrate WiMAX with GSM is proposed. Chapter 8 (Applications of Wi-Fi/WiMAX Technologies in the Emerging World) proposes a strategic wireless framework to address challenges in three different sectors of a developing country. Deployment and implementation of an affordable communications infrastructure with emerging wireless tech- nologies are the first steps toward narrowing the digital divide. This chapter concludes that information and communication technology backed by mod- ern wireless technologies will take any developing country into a new age of information economy and wealth creation. Chapter 9 (Connectivity and Load Distribution in WiMAX-Based Multihop Backhaul Networks) examines the backhaul requirements of a large fixed wireless network providing high-speed data service to customer premises. Distribution of access point load is investigated and the required capacity of access-point-to-access-point and access-point-to-gateway links is character- ized such that the occurrence of overload conditions is limited. Defining the service requirements of a single customer as a “unit load,’’ the distribution of the load supported by a single access point is calculated. Chapter 10 (Providing QoS to Real and Interactive Data Applications in WiMAX Mesh Networks) considers the problem of centralized routing and scheduling for IEEE 802.16 mesh networks so as to provide quality of service to real and interactive data applications. This chapter presents scheduling algorithms that provide per flow QoS guarantees while utilizing the network resources efficiently. Admission control policies, which ensure that sufficient resources are available, are discussed. The targeted audience for the handbook includes professionals who are designers and planners for WiMAX networks, researchers (faculty members and graduate students), and those who would like to learn about this field. The handbook is expected to have the following specific salient features: • To serve as a single comprehensive source of information and as reference material on WiMAX networks • To deal with an important and timely topic of emerging communi- cation technology of today, tomorrow, and beyond
- 16. CRC-45474 fm.tex 27/7/2007 18: 38 Page x x Preface • To present accurate, up-to-date information on a broad range of topics related to WiMAX networks • To present the material authored by the experts in the field • To present the information in an organized and well-structured manner Although the handbook is not precisely a textbook, it can certainly be used as a textbook for graduate and research-oriented courses that deal with WiMAX. Any comments from the readers will be highly appreciated. Many people have contributed to this handbook in their unique ways. The first and the foremost group that deserves immense gratitude is the group of highly talented and skilled researchers who have contributed 32 chapters to this handbook. All of them have been extremely cooperative and professional. It has also been a pleasure to work with Nora Konopka, Helena Redshaw, Jessica Vakili, and Joette Lynch of Taylor & Francis and we are extremely gratified for their support and professionalism. Our families have extended their unconditional love and strong support throughout this project and they all deserve very special thanks. Syed Ahson Plantation, FL, USA Mohammad Ilyas Boca Raton, FL, USA
- 17. CRC-45474 fm.tex 27/7/2007 18: 38 Page xi Editors Syed Ahson is a senior staff software engineer with Motorola Inc. He has extensive experience with wireless data protocols (TCP/IP, UDP, HTTP, VoIP, SIP, H.323), wireless data applications (Internet browsing, multimedia mes- saging, wireless e-mail, firmware over-the-air update), and cellular telephony protocols (GSM, CDMA, 3G, UMTS, HSDPA). He has contributed signifi- cantly in leading roles toward the creation of several advanced and exciting cellular phones at Motorola. Prior to joining Motorola, he was a senior soft- ware design engineer with NetSpeak Corporation (now part of Net2Phone), a pioneer in VoIP telephony software. Syed is a coeditor of the Handbook of Wireless Local Area Networks: Applications, Technology, Security, and Standards (CRC Press, 2005). Syed has authored “Smartphones’’ (International Engineering Consortium, April 2006), a research report that reflects on smartphone markets and technolo- gies. He has published several research articles in peer-reviewed journals and teaches computer engineering courses as adjunct faculty at Florida Atlantic University, Florida, where he introduced a course on smartphone techno- logy and applications. Syed received his BSc in electrical engineering from India in 1995 and MS in computer engineering in July 1998 at Florida Atlantic University, Florida. Dr. Mohammad Ilyas received his BSc in electrical engineering from the University of Engineering and Technology, Lahore, Pakistan, in 1976. From March 1977 to September 1978, he worked for the Water and Power Development Authority, Pakistan. In 1978, he was awarded a scholar- ship for his graduate studies and he completed his MS in electrical and electronic engineering in June 1980 at Shiraz University, Shiraz, Iran. In September 1980, he joined the doctoral program at Queen’s University in Kingston, Ontario, Canada. He completed his PhD in 1983. His doctoral research was about switching and flow control techniques in computer communication networks. Since September 1983, he has been with the Col- lege of Engineering and Computer Science at Florida Atlantic University, Boca Raton, Florida, where he is currently associate dean for research and industry relations. From 1994 to 2000, he was chair of the Department of Com- puter Science and Engineering. From July 2004 to September 2005, he served as interim associate vice president for research and graduate studies. During the 1993–1994 academic year, he was on his sabbatical leave with the Depart- ment of Computer Engineering, King Saud University, Riyadh, Saudi Arabia. Dr. Ilyas has conducted successful research in various areas includ- ing traffic management and congestion control in broadband/high-speed xi
- 18. CRC-45474 fm.tex 27/7/2007 18: 38 Page xii xii Editors communication networks, traffic characterization, wireless communication networks, performance modeling, and simulation. He has published one book, eight handbooks, and over 150 research articles. He has supervised 11 PhD dissertations and more than 37 MS theses to completion. He has been a consultant to several national and international organizations. Dr. Ilyas is an active participant in several IEEE technical committees and activities. Dr. Ilyas is a senior member of IEEE and a member of ASEE.
- 19. CRC-45474 fm.tex 27/7/2007 18: 38 Page xiii Contributors Dan Avidor Bell Laboratories, Lucent Technologies Alcatel-Lucent Holmdel, New Jersey Jack L. Burbank Applied Physics Laboratory The Johns Hopkins University Laurel, Maryland Albert Butare Ministry of Infrastructure Kachiyuru, Kigali, Rwanda, Central Africa Damien Chatelain University of Technology Pretoria, South Africa Mainak Chatterjee University of Central Florida Orlando, Florida Giselle M. Galván-Tejada CINVESTAV-IPN Mexico City, Mexico Vinoth Gunasekaran Stevens Institute of Technology Hoboken, New Jersey Neena Gupta Punjab Engineering College Deemed University Chandigarh, India Fotios C. Harmantzis Stevens Institute of Technology Hoboken, New Jersey William T. Kasch Applied Physics Laboratory The Johns Hopkins University Laurel, Maryland Gurjit Kaur UniversityInstituteofEngineering and Technology Chandigarh, India G. Senthil Kumaran Kigali Institute of Science and Technology Kigali, Rwanda, Central Africa Sayandev Mukherjee Marvell Semiconductor Santa Clara, California Kumbesan Sandrasegaran University of Technology Sydney, Australia K.R. Santhi Kigali Institute of Science and Technology Kigali, Rwanda, Central Africa Shamik Sengupta University of Central Florida Orlando, Florida Vinod Sharma Indian Institute of Science Bangalore, India xiii
- 20. CRC-45474 fm.tex 27/7/2007 18: 38 Page xiv xiv Contributors Harish Shetiya Ittiam Systems Bangalore, India Erickson Trejo-Reyes Nextel de Mexico Mexico City, Mexico Barend J. van Wyk University of Technology Pretoria, South Africa Leijia Wu University of Technology Sydney, Australia
- 21. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 1 1 WiMAX Past, Present, and Future: An Evolutionary Look at the History and Future of Standardized Broadband Wireless Access Jack L. Burbank and William T. Kasch CONTENTS 1.1 Introduction ................................................................................................... 1 1.2 WiMAX—An Overview .............................................................................. 2 1.2.1 The WiMAX Standard ...................................................................... 3 1.2.2 Current WiMAX Product Market ................................................... 5 1.2.3 A Brief Overview of IEEE 802.16 Networking ............................. 5 1.3 WiMAX—Evolving Usage Cases ............................................................... 7 1.4 WiMAX—Evolution of the Technology .................................................. 10 1.5 Relevant Standardization Activities ........................................................ 12 1.6 Conclusion ................................................................................................... 13 References ............................................................................................................. 13 1.1 Introduction Broadband wireless access (BWA) technical solutions and products have been available for some time. Historically, these technologies have been primarily focused on providing high data rate connectivity wirelessly between fixed stationary sites. Examples of these types of applications include building- to-building bridging and providing high-rate connectivity to remote sites, such as broadcast towers, where the installation of wired infrastructure is not viable. However, these technical solutions have historically been proprietary in nature and have suffered from several of the negative characteristics often accompanying proprietary solutions, including poor interoperability with other BWA products and high cost due to the lack of economy of scale. The IEEE 802.16 BWA technology family, often referred to as world- wide interoperability for microwave access (WiMAX) or WirelessMAN, is intended to provide a standardized BWA solution to provide “broad- band wireless to the masses’’ and is so anticipated that it has even been 1
- 22. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 2 2 WiMAX: Applications characterized by some as a threat to the long-term viability of several exist- ing wireless technologies (including IEEE 802.11-based wireless local area network [WLAN] technology, broadband residential Internet technologies such as digital subscriber line [DSL] and cable), even viewed by some as a competitor to third-generation (3G) cellular technologies. Others view 802.16 as a powerful complementary technology to these various tools. Regard- less, 802.16 is seen by many in the commercial wireless industry as a key enabling technology in the large-scale realization of the wireless Internet, providing a tool that may potentially allow service providers to deliver high data rates (i.e., tens of Mbps) to a variety of devices, such as handheld devices, and enabling an entire new generation of applications (e.g., handheld, high-resolution videophones). The future success of WiMAX in the commercial marketplace and its poten- tial emergence as a disruptive technology is still unknown. While WiMAX has certainly generated a high degree of excitement within the commercial wire- less industry, the marketplace always proves to be the final judge—that which separates hype from reality. However, this determination is a complex matter that is a function of numerous factors. The goal of this chapter is to provide an overview of the evolution of WiMAX from three key perspectives: (1) usage case, (2) technology, and (3) standardization. 1.2 WiMAX—An Overview WiMAX is based upon the IEEE 802.16 WMAN technology family, which provides specifications of the media access control (MAC) layer and the physical (PHY) layer. The 802.16 specification further subdivides the MAC sublayer into three sublayers: the convergence sublayer (CS), the common part sublayer (CPS), and the security sublayer. The CS aims to enable 802.16 to better accommodate the higher layer protocols placed above the MAC layer. The 802.16 specification assumes there will be two predominant types of traffic transported across the 802.16 network: ATM and IEEE 802.3 (Ethernet). Thus, there are two CS specifications: ATM and packet. The CS receives data frames from a higher layer and classifies the frame. On the basis of this classification, the CS can perform additional processing, such as pay- load header compression, before passing the frame to the MAC CPS. The CS also accepts data frames from the MAC CPS. If the peer CS has performed any type of processing, the receiving CS will restore the data frame before pass- ing it to a higher layer. The CS is separate from the remainder of the 802.16 MAC such that vendors who wish to support other protocols can develop specialized CSs. The CPS is the central piece of the 802.16 MAC, defining the medium access method (Figure 1.1). The CPS provides functions related to duplexing, net- work entry and initialization, framing, quality of service (QoS), and channel access. The security sublayer, also referred to as the privacy sublayer, has
- 23. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 3 WiMAX Past, Present, and Future 3 Service-specific convergence sublayer (CS) MAC common part sublayer (MAC CPS) Physical layer (PHY) PHY SAP MAC SAP CSS SAP Security sublayer MAC PHY Management entity (PHY) Management entity (MAC CPS) Management entity service-specific CS Security sublayer Network management system Data plane Management plane Scope of 802.16 standard FIGURE 1.1 The logical architecture of IEEE 802.16. been designed to meet two primary goals: providing subscribers with privacy across the wireless network and providing operators with strong protection from theft of service. The PHY layer then converts MAC layer frames into signals to be transmitted across the air interface. Consequently, the security sublayer has two component protocols: an encapsulation protocol and a privacy key management protocol. The 802.16 technology family is actually composed of several distinct technology specifications. These specifications are summarized in Table 1.1. The term “WiMAX’’ is a marketing term that has become synonymous with 802.16-based BWA networks in much the same manner as “wireless fidelity’’or“Wi-Fi’’hasbecomesynonymouswithIEEE802.11-basedWLANs. The WiMAX Forum was formed in April 2001 as a nonprofit international organization to certify conformance and interoperability of products on the basis of the IEEE 802.16 and ETSI HIPERMAN standards. This forum is also heavily involved as an advocate for 802.16 technology. It has now grown to include over 420 member companies. The WiMAX-certified logo of the WiMAX Forum will be placed on the package of certified products, and is envisioned to become a key criterion for market viability in the same way that the Wi-Fi-certified logo of the Wi-Fi Alliance is a key criterion for market viability of 802.11 WLAN products. 1.2.1 The WiMAX Standard There is typically much confusion regarding the “WiMAX standard.’’ WiMAX is not a standard. WiMAX is a marketing term trademarked by the WiMAX
- 24. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 4 4 WiMAX: Applications TABLE 1.1 Summary of Various 802.16 Technology Specifications Year of Specification Reference Ratification Description 802.16 1 2001 MAC and PHY definition for fixed broadband wireless access in the 10–66 GHz frequency bands. 802.16a 2 2003 Amendment to the original specification. Contains new PHY definitions for the 2–11 GHz frequency bands. Also includes mesh network modes of operation. 802.16c 3 2002 System profiles for 10–66 GHz operations. 802.16d 4 2004 Contains 802.16, 802.16a, and various MAC enhancements. Commonly referred to as 802.16-2004. Considered the base 802.16 fixed broadband wireless specification. 802.16e 5 2006 Amendment to the 802.16d specification to provide explicit support for mobility. Incorporates WiBRO. Commonly referred to as 802.16-2005. Considered the base 802.16 mobile broadband wireless specification. 802.16f 6 2005 802.16 management information base. 802.16g N/A In progress Network management (management plane control procedures). 802.16h N/A In progress Coexistence in license-exempt frequency bands. 802.16i N/A In progress Mobile management information base. 802.16j N/A In progress Multihop relay specification. 802.16k N/A In progress 802.16 MAC-layer bridging. 802.20 N/A In progress Mobile broadband wireless access standards group. Initially formed as a standards group within the 802.16 Working Group, it consisted of a group of individuals who wished to develop a new technology focused solely on mobility. No other relation to WiMAX, other than perhaps competitive. WiBRO Korean wireless broadband standard incorporated into the 802.16e (802.16-2005) standard. Forum to describe 802.16-based technology. 802.16 is a technology standard. However, it is not uncommon for 802.16 and WiMAX to be referred to as sep- arate standards. The WiMAX standard refers to the set of capabilities within 802.16 that the WiMAX Forum will test against when performing conform- ance and interoperability testing in its equipment certification process. In this sense, the WiMAX Forum will indeed have significant impact on what functionality within the 802.16 standard will be brought to market by ven- dors, but it in itself is not a standard. Rather, the WiMAX standard refers to the subset of 802.16 capabilities that are likely to experience widespread implementation.
- 25. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 5 WiMAX Past, Present, and Future 5 1.2.2 Current WiMAX Product Market It is important to note at this point that there are relatively few WiMAX- certified products currently available on the market. Rather, many so-called WiMAX products currently available are proprietary in nature. The WiMAX Forum opened its laboratory only in mid-2005 to begin certifying confor- mance and interoperability for fixed equipments at 3.5 and 5.8 GHz, with additional spectrum channels to follow; the first certifications were issued only in early 2006 for fixed WiMAX products and no mobile WiMAX prod- ucts are yet certified. However, many vendors already offer products that they advertise as WiMAX-ready (both fixed and mobile). These products are based on potentially proprietary technologies but are advertised as capable of being brought into WiMAX conformance via software upgrade only. Whether an organization or individual decides to deploy this equipment with the future goal of interoperability with WiMAX-certified equipments, is an individual choice, and is largely a function of trust and confidence in the equipment vendor. 1.2.3 A Brief Overview of IEEE 802.16 Networking The 802.16 network architecture is predicated on the presence of fixed infra- structural sites. In fact, the architectural model of 802.16 is similar to the model employed within cellular telephone networks. Each 802.16 coverage area consists of one base station (BS) and one or more subscriber stations (SSs). BSs provide connectivity to core networks (CNs), whereas the SS is the suite of the equipment at the customer location, or customer premises equipment, whichprovidesaccessfortheenduserintothebroadbandwirelessnetwork.A single 802.16 coverage area is depicted in Figure 1.2. The architecture depicted in this figure represents a single cell of network coverage. These 802.16 cells BS SSs Core network Coverage area 802.16 FIGURE 1.2 The 802.16 coverage area.
- 26. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 6 6 WiMAX: Applications BS SSs Core network BS SSs BS SSs BS SSs BS SSs FIGURE 1.3 An example 802.16 network. can then be grouped together to form a larger 802.16 network, where the BS sites are interconnected via a CN, as depicted in Figure 1.3. In the 802.16 model, channel access is highly centralized; the BS is in complete control over how and when SSs access the wireless medium. Transmissions may be point-to-point (PTP), point-to-multipoint (PMP), or point-to-consecutive-point (PTCP) in nature, where PTCP involves the cre- ation of a closed loop through multiple PTP connections. In addition, 802.16a provides for a mesh networking capability in which SSs can act as routers, relaying data to nodes that may not have line-of-sight (LOS) connectivity with the BS. BSs typically employ one or more wide-beam antennas that may be partitioned into several smaller sectors, where all sectors sum to complete 360◦ coverage. This is analogous to BSs within the cellular model. SSs typic- ally employ highly directional antennas that are pointed toward the BS. This is a significant departure from the model employed within cellular communi- cations or the 802.11 WLAN communities, where low-gain, omnidirectional antennas are employed. This is one of the key reasons 802.16 achieves such higher data rates compared to other technologies. The BS-to-SS link is referred to as the downlink. The SS-to-BS link is referred to as the uplink. The proper routing of traffic to a BS is a function of the CN, which is not explicitly defined within the 802.16 specification. In fact, the 802.16 specification has provisions to accommodate a multitude of existing or future CN technologies. This CN is analogous to the DS of 802.11 networks.
- 27. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 7 WiMAX Past, Present, and Future 7 1.3 WiMAX—Evolving Usage Cases Any successful technology must fit a key need in the marketplace. That is, a technology must have a compelling usage case, a “killer niche’’ that it can fit better than alternatives. And here, niche does not imply any type of limited size of scale, but rather is viewed as analogous to the “killer app.’’ This is often why the position of “first-to-market’’ is so attractive, because it elim- inates competition from viable alternatives, leaving that technology as the only choice to meet the compelling usage case. One needs to look no further than the wildly successful IEEE 802.11 WLAN technology family to see the importance of a killer niche. IEEE 802.11 found a niche in the marketplace for localized hot-spot wireless connectivity, the ability to replace network cables within localized regions, and has filled that niche with a family of highly capable technologies that now approaches ubiquity. This original usage case of IEEE 802.11 WLANs was simple and narrow in focus. Only now do later revisions of the technology address more sophisticated usage cases, such as QoS, mesh networking, and roaming. Clearly, it is quite important for WiMAX to have a killer niche that it can satisfy to enjoy long-term success in the marketplace. However, an agree- ment on exactly what that compelling usage case is or should be has been difficult to come to, even within the WiMAX community. Even up to this point in time, the vision for how WiMAX will be or should be employed is arguable. Certainly, the dominant usage case scenarios have evolved over time as WiMAX has continued to evolve from both a marketing and a technology perspective. The original 802.16 specification [1] was clearly oriented toward providing high-rate, PTP, LOS connectivity between fixed platforms. Here, the driving usage scenario was that of interconnecting locations that do not lend themselves to cabled solutions. A classic example of this usage scenario is that of the remotely located transmission tower that is wirelessly back- hauled to a fixed location attached to a larger wired network. There was, and still is, a legitimate market within this problem space. However, this market was continually hampered by poor interoperability between propri- etary solutions. The goal of creating an interoperable technology to fit this niche was the original inspiration of the 802.16 specification, the envisioned backhaul technology of this problem space. In this envisioned usage case, the primary competition to WiMAX is proprietary solutions. It is clear that, in the long term, a standardized technology with strong industry support, such as WiMAX, would enjoy tremendous success. However, this is the nar- rowest of envisioned problem spaces for which WiMAX is often considered a candidate. Afterthefinalizationoftheoriginal802.16technologystandard, thescopeof envisioned WiMAX usage scenarios was significantly expanded. Originally, WiMAX was viewed as a PTP, LOS backhaul technology, envisioned to pro- vide wireless bridging between fixed locations within network infrastructure.
- 28. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 8 8 WiMAX: Applications The primary expansion of scope was to that of the direct support of end-user networks. Here, WiMAX was envisioned to serve a role within the internet service providers (ISP) problem space, interconnecting end-user networks (e.g., homes)withnetworkinfrastructure. Thisexpansionofscopemakesvery good logical sense, particularly given the still fixed nature of network nodes. Here, the creators of WiMAX had created a wireless technology capable of delivering very high data rates over very long distances. Indeed, this would seem an ideal technology to apply to the problem space of the residential wireless local loop, where low-rate wired infrastructure often limits the types of capabilities that can be enjoyed by the residential consumer. The resultant technology brought to bear in this problem space was the IEEE 802.16a speci- fication [2], leading to the eventual IEEE 802.16d specification, which unified the original 802.16 and 802.16a specifications. This 802.16d specification is also often referred to as the IEEE 802.16-2004 specification and is the basis for fixed WiMAX. However, this problem space contains much stiffer competition than the original scope of employment in the form of both wire-line and wireless technologies. Technologies such as DSL and cable modem are already firmly entrenched within this market space, already enjoying significant consumer bases. Additionally, there are other wireless technologies also contending for this market, such as CDMA2000. The marketplace will ultimately deter- mine the level of success any of these technologies will experience. However, current conventional wisdom is that technologies such as WiMAX are more likely to enjoy success in this problem space within markets that are not yet fully developed (e.g., third-world markets) or in regions where other forms of ISPs do not have a strong presence (e.g., rural areas within developed countries). The final evolution of the WiMAX usage scenario came in the form of mobil- ity support. Here, the envisioned scenario has WiMAX serving as the air inter- face for the actual radio access network, where both fixed and mobile users access the WiMAX network. The developers of the technology had created a technology capable of reasonably high data rates at reasonably long ranges. If this technology could now be augmented to support the case of the mobile users, then WiMAX could serve as a viable candidate for wide-area connec- tivity. This usage case is the driving scenario behind the creation of the IEEE 802.16e technology standard [5], also referred to as IEEE 802.16-2005, the basis of mobile WiMAX. This market arguably presents the stiffest competition of all envisioned usage scenarios. Within this space, there are two potential deployment scenarios: (1) employment of the WiMAX air interface by incum- bent wireless service providers (WSPs) and (2) employment of the WiMAX air interface by new-entry WSPs. Incumbent cellular providers have invested enormous amounts of capital expenditures to reach current level of capabil- ities that will not be easily equaled or surpassed by any new-entry technology. Even next-generation cellular technologies, such as 3GPP and 3GPP2, have experienced relatively slow deployment as cellular service providers have not been quick to embrace these technologies over older technologies such
- 29. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 9 WiMAX Past, Present, and Future 9 as GSM. It is unclear whether existing incumbents would embrace a tech- nology such as WiMAX. It is reasonable to expect that WiMAX would be a compelling technology for a new-entry WSP. However, a new-entry WSP faces enormous challenges in the marketplace. Spectrum is expen- sive, infrastructure is expensive, and reaching the economy of scale required to drive down equipment and service costs to a competitive level is very challenging. Originally, one of the key enablers for this type of usage sce- nario was that of offering wireless service in unlicensed frequency bands. Thus was born the promise of “anybody can be a service provider’’ and brought great hope that a new-entry WSP could compete with incumbents. However, this is not realistic given that the WiMAX Forum has no certifica- tion profiles for unlicensed (5.8 GHz) mobile WiMAX. Thus, the majority of deployments, particularly those within the United States, will utilize licensed spectrum. Indeed, it is envisioned that mobile WiMAX will make its largest impact within this problem space in the United States within the 2.5 GHz multichannel multipoint distribution service (MMDS) frequency bands by incumbent WSPs. It can be seen that the evolution of WiMAX usage cases can be character- ized by an increasing scope and scale, along with much stiffer competition from other technologies. This corresponds to the increasing confidence that the proponents of WiMAX have in the technology they have developed. Cer- tainly, there is a lot of excitement regarding WiMAX, and there is a lot of momentum building that favors rapid WiMAX adoption and deployment. This is evidenced by the escalating grandeur of the envisioned usage scenarios by the community. However, admittedly arguable and speculative, WiMAX will face significant difficulties in emerging as a serious competitor to 3G technologies. This is due to several complicating factors: (1) the evolution of other “competitive’’ technologies and (2) the lack of a “killer app’’ in the mobile data networking space. The evolution of 3GPP to high-speed down- link packed access renders the increased data rates of WiMAX merely an incremental increase. It is unclear if this incremental increase in data rate will motivate existing service providers to migrate to WiMAX. It should also be noted that WiMAX is only an air interface replacement, and that there remains the issue of deploying and maintaining a CN. Furthermore, it is unclear if WiMAX will mount a significant challenge to 802.11-based WLANs or residential broadband technologies such as DSL and cable. 802.11 is evolv- ing quickly to several hundred Mbps solutions, and has a rapidly evolving suite of technologies for aspects such as mobility and roaming support. Both 802.11 and 3G have a several-year lead time to market over WiMAX. Resi- dential broadband technologies such as DSL and cable are firmly entrenched in the market. For these reasons, it is envisioned by the authors that WiMAX will likely remain a complementary technology to these technologies, or shall remain a niche technology serving very specific usage cases. Most notably are (1) the original usage case of backhaul connectivity, (2) wireless local loop ser- vice to fixed locations in underdeveloped regions, and (3) mobile radio access in developing regions.
- 30. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 10 10 WiMAX: Applications Another issue facing mobile WiMAX is that of the lack of a “killer app’’ that draws the masses to fully mobile data networking. Certainly, this is not only an issue unique to WiMAX but also an important issue facing cellular service providers. Despite the significant emergence of wireless networking technologies, it is still unclear whether there is an overwhelming market for truly mobile data networking. There is certainly a strong marketplace for nomadic mobility, the ability to move from one location to another with con- nectivity achievable from either location. However, it is not yet clear whether there is an overwhelming demand for data networking that can provide seam- less connectivity while on the move. There are certainly examples where the motivation is quite strong. Military networks certainly need to be capable of operating in a seamless fashion while on the move. There are also the clas- sical mobile data networking scenarios of public transit vehicles providing network services (e.g., train). However, these usage cases do not necessarily constitute a mainstream need for on-the-move network connectivity. Rather, despite being quite arguable, nomadic mobility is likely still the driving demand from consumers. This is also often referred to as portability. It should be noted that fixed WiMAX has already experienced significant deployments in which nomadic mobility has been demonstrated. However, as always, the marketplace will make the final determination as to which usage scenarios are viable, and which are not. All else is speculation. One development to watch closely, which could provide significant insight into the viability of WiMAX in the mobile radio access network problem space, is the ongoing deployment of WiBRO in South Korea in the 2.3 GHz band. 1.4 WiMAX—Evolution of the Technology As the envisioned usage scenario has evolved over time, so has evolved the technological basis of WiMAX. The IEEE 802.16 technical specification has now evolved through three generations: • IEEE 802.16: High data rate, high-power, PTP, LOS, fixed SSs • IEEE 802.16-2004: Medium data rate, PTP, PMP, fixed SSs • IEEE 802.16-2005: Low-medium data rate, PTP, PMP, fixed or mobile SSs The first generation of IEEE 802.16 operates in microwave frequencies (hence the name) 10–66 GHz and utilizes single-channel (SC) modula- tion as it assumes LOS propagation is required for communications. This WirelessMAN-SC physical layer can employ QPSK, 16-QAM, or 64-WAM modulation, adaptively changing on the basis of channel conditions. The original 802.16 specification operates with channel bandwidths of 20–25 MHz in the United States and 28-MHz channel bandwidths in Europe.
- 31. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 11 WiMAX Past, Present, and Future 11 This technology employs highly directional antennas and high-power lev- els within licensed frequency bands to achieve simultaneously high data rates and long ranges. Security mechanisms within the original specifica- tion are somewhat rudimentary, with a reliance on antenna directionality to mitigate intrusion. As can be seen, this technology is well suited to a fixed point-to-fixed point backhaul type of application. The IEEE 802.16-2004 specification amends the original specification to operate in the 2–11 GHz, both licensed and license-exempt. This frequency band of operations, which was first addressed in the IEEE 802.16a specifica- tion, assumes non-LOS communications. This specification provides a total of three air interfaces: a. WirelessMAN-SC2—single-carrier modulation. b. WirelessMAN-OFDM—OFDM modulation with a 256-point fast fourier transform (FFT) with TDMA channel access. c. WirelessMAN-OFDMA—OFDM is employed with a 2048-point FFT. Multiple access is provided by addressing a subset of carriers to individual receivers. In addition to the forward error control (FEC) coding employed in the ori- ginal specification, the 2–11 GHz PHY specification also allows for the use of automatic retransmission requests as an optional capability. This technology incorporates numerous MAC-layer enhancements to the 802.16-2004 specifi- cation, including the support of multihop mesh networking to enable relaying between nodes to extend coverage areas of WiMAX BSs. This technology often operates using sectored omnidirectional antennas, decreasing dependence on precise antenna pointing and increasing the ability to provide entire cover- age areas of service. Furthermore, operation in the 2–11 GHz frequency band allows for adaptive antenna beam-forming techniques to improve interfer- ence and scalability performance. Numerous security enhancements, such as two-way authentication, were included in this update to the original specifi- cation. It is readily apparent that this technology was certainly designed for the wireless local loop type of application. The IEEE 802.16-2005 specification was developed with one primary goal: thesupportforalargenumberofmobileusers.AkeyenhancementoftheIEEE 802.16-2005 specification is the employment of scalable OFDMA (as opposed tothenonscalableversionemployedinthefixedWiMAXspecification), which technology proponents argue makes the technology highly robust to network congestion and highly graceful degradation in the presence of interference. Other key enhancements include the introduction of several state-of-the-art technologies, suchashybridautomaticretransmissionrequest, advancedFEC coding schemes such as turbo codes and low-density parity check codes, and multiple-input multiple-output. In general, the technological evolution of WiMAX has traded capacity and range for mobility support and scalability. Figure 1.4 illustrates the basic
- 32. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 12 12 WiMAX: Applications Range Mobility Number of users Data rate 802.16 802.16-2004 802.16-2005 FIGURE 1.4 Evolution of WiMAX technologies. capabilities of these various forms of WiMAX. From this figure, the trend is clearly toward compromising range and data rate for scalability and mobility support. An important point to make here is that these various flavors are not com- patible with one another. That is, an 802.16-2004 BS cannot interoperate with an 802.16-2005 SS, and vice versa. This could significantly constrain 802.16 deployment in the future. However, major chip manufacturers have already announced dual-mode chipsets that will support both standards. Thus, there will likely emerge products that can interoperate with both 802.16-2004 and 802.16-2005networks. Unfortunately, thereremainsnumerousregulatoryand coexistence issues that complicate if not prohibit heterogeneous Fixed and Mobile WiMAX networks. 1.5 Relevant Standardization Activities Another key for any successful technology is a strong evolution path. Cer- tainly, this has become a key attractive feature of IEEE 802.11 WLAN technology. The IEEE 802.11 working group is actively working to address numerous issues and deficiencies in existing WLAN technologies. Indeed, who wants to invest enormous amounts of capital resources on a network infrastructurethatisgoingtobecomeobsoletequickerthannecessary? Rather, one wishes to acquire a solution that will grow and evolve with the needs of
- 33. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 13 WiMAX Past, Present, and Future 13 the user. Thus, it is important to consider the strength of the industrial sup- port of a technology and the amount of standardization activity to ensure competition among vendors. This is an area in which WiMAX is very strong. WiMAX indeed enjoys enor- mous industry backing. The WiMAX Forum is a consortium of hundreds of companies, all proponents of the technology. Major industry players such as Intel (which certainly played a prominent role in the success of IEEE 802.11 with the success of its embedded Centrino chipset) are active in this forum and in the development of WiMAX devices and technology standards. The WiMAX Forum currently operates eight working groups: application, certifi- cation, global roaming, marketing, networking, regulatory, service provider, and technical. Each of these working groups are chartered to address particu- lar aspects of the WiMAX technology to help ensure its successful adoption and deployment. For example, the networking working group creates net- working specifications beyond that defined within the 802.16 specification as necessary to support fixed, nomadic, portable, and mobile WiMAX systems. As can be seen from Table 1.1, the IEEE 802.16 working group continues to be quite active in the development of refinements to the IEEE 802.16 technol- ogy base of WiMAX. There are currently six active groups within the IEEE 802.16 working group, each working on a unique aspect of 802.16, such as specifications for 802.16 multihop relaying. 1.6 Conclusion There are numerous factors that contribute to the success (or lack thereof) of a technology. WiMAX has generated a tremendous, almost unparalleled, amount of interest within the wireless networking community. Prior to its deployment, it was already being referred to as a disruptive technology. Time indeed will tell how disruptive it will become; it certainly has the potential to be landscape altering. WiMAX has a strong base of standardization and industry support that provides a strong evolutionary path of capabilities. Its technology base, the IEEE 802.16 specifications, has continued to evolve and expand in capabilities in support of the evolving vision of WiMAX usage and deployment. However, WiMAX faces very stiff competition from tech- nologies such as 3GPP and 3GPP2, as well as expanding metropolitan-scale deployments of 802.11 WLANs. It should be very interesting to watch how the role of WiMAX now evolves within the emerging wireless Internet. References 1. IEEE 802.16-2001, IEEE standard for local and metropolitan area networks—Part 16: Air interface for fixed broadband wireless access systems, 6 December 2001.
- 34. CRC-45474 CH001.tex 26/6/2007 9: 24 Page 14 14 WiMAX: Applications 2. IEEE 802.16a-2001, IEEE standard for local and metropolitan area networks— Part 16: Air interface for fixed broadband wireless access systems—Amendment 2: Medium access control modifications and additional physical layer specifications for 2–11 GHz, 1 April 2003. 3. IEEE 802.16c-2001, IEEE standard for local and metropolitan area networks— Amendment 1: Detailed system profiles for 10–66 GHz, 15 January 2003. 4. IEEE 802.16-2004, IEEE standard for local and metropolitan area networks: Air interface for fixed broadband wireless access systems, 1 October 2004. 5. IEEE 802.16E-2005, IEEE standard for local and metropolitan area networks— Part 16: Air interface for fixed and mobile broadband wireless access systems amendment for physical and medium access control layers for combined fixed and mobile operation in licensed bands, 28 February 2006. 6. IEEE 802.16f-2005, IEEE standard for local and metropolitan area networks— Part 16: Air interface for fixed broadband wireless access systems—Amendment 1—Management information base, 1 December 2005.
- 35. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 15 2 Overview of WiMAX Standards and Applications Leijia Wu and Kumbesan Sandrasegaran CONTENTS 2.1 Overview of WiMAX ................................................................................. 16 2.2 WiMAX Standards ...................................................................................... 16 2.2.1 802.16 ................................................................................................ 17 2.2.1.1 Network Topology .......................................................... 17 2.2.1.2 802.16 Protocol Stack ....................................................... 17 2.2.1.3 Modulation Technologies ............................................... 19 2.2.1.4 Duplexing Technologies ................................................. 19 2.2.1.5 Multiplexing Technologies ............................................. 20 2.2.1.6 Quality of Service ............................................................ 20 2.2.2 802.16a .............................................................................................. 20 2.2.2.1 Flexible Bandwidth ......................................................... 21 2.2.2.2 Mesh Topology ................................................................. 21 2.2.2.3 Orthogonal Frequency Division Multiplexing ............ 23 2.2.2.4 Adaptive Modulation ..................................................... 23 2.2.3 802.16-2004 ....................................................................................... 24 2.2.4 802.16e .............................................................................................. 24 2.2.5 Other IEEE 802.16 Family Standards ........................................... 25 2.2.5.1 802.16c ............................................................................... 25 2.2.5.2 802.16.2-2001 ..................................................................... 26 2.2.5.3 802.16.2-2004 ..................................................................... 26 2.2.5.4 802.16f-2005 ...................................................................... 27 2.2.5.5 IEEE Standard 802.16/Conformance01-2003 .............. 27 2.2.5.6 IEEE Standard 802.16/Conformance02-2003 .............. 27 2.2.5.7 IEEE Standard 802.16/Conformance03-2004 .............. 27 2.3 WiMAX Applications ................................................................................. 27 2.3.1 WMANs ........................................................................................... 28 2.3.2 Rural Area Broadband Services .................................................... 28 2.3.3 Last-Mile High-Speed Access to Buildings ................................. 29 2.3.4 Wireless Backhaul ........................................................................... 30 2.3.5 Enterprise/Private Networks ....................................................... 30 15
- 36. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 16 16 WiMAX: Applications 2.3.6 Wireless Video Surveillance .......................................................... 31 2.3.7 Other Applications ......................................................................... 31 2.4 Conclusion ................................................................................................... 32 References ............................................................................................................ 32 2.1 Overview of WiMAX The demand for broadband services is growing sharply today. The traditional solutions to provide high-speed broadband access is to use wired access tech- nologies, such as cable modem, digital subscriber line (DSL), Ethernet, and fiber optic. However, it is too difficult and expensive for carriers to build and maintain wired networks, especially in rural and remote areas. Broadband wireless access (BWA) technology is a flexible, efficient, and cost-effective solution to overcome the problems. The global deregulation of radio spec- trum also encourages the development of BWA technologies. WiMAX is one of the most popular BWA technologies today, which aims to provide high- speed broadband wireless access for wireless metropolitan area networks (WMANs). The air interface standard, IEEE 802.16, commonly referred to as WiMAX, is a specification for broadband wireless communication standards developed for WMANs, which supports fixed, nomadic, portable, and mobile broadband accesses and enables interoperability and coexistence of BWAsys- tems from different manufacturers in a cost-effective way. Compared to the complicated wired network, a WiMAX system only consists of two parts: the WiMAX base station (BS) and WiMAX subscriber station (SS), also referred to as customer premise equipments. Therefore, it can be built quickly at a low cost. Ultimately, WiMAX is also considered as the next step in the mobile technology evolution path. The potential combination of WiMAX and CDMA standards is referred to as 4G. This chapter gives an overview of the WiMAX standards and applications. 2.2 WiMAX Standards The purpose of developing 802.16 standards is to help the industry to provide compatible and interoperable solutions across multiple broadband segments and to facilitate the commercialization of WiMAX products. Cur- rently, WiMAX has two main variations: one is for fixed wireless applications (covered by IEEE 802.16-2004 standard) and another is for mobile wireless ser- vices (covered by IEEE 802.16e standard). Both of them are evolved from IEEE 802.16 and IEEE 802.16a, the earlier versions of WMAN standards. The 802.16 standards only specify the physical (PHY) layer and the media access control (MAC) layer of the air interface while the upper layers are not considered.
- 37. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 17 Overview of WiMAX Standards and Applications 17 In the following sections, we will introduce some of the main IEEE 802.16 family standards. 2.2.1 802.16 The IEEE 802.16 standard (also known as the air interface for fixed broadband wireless access (FBWA) systems or IEEE WMAN air interface) is the first version of 802.16 family standards (published in April 2002). It specifies fixed broadband wireless systems operating in the 10–66 GHz licensed spectrum, which is expensive but there is less interference at the high-frequency band and more bandwidth is available. Because radio waves in this band are too short to penetrate buildings, the 802.16 standard is only used for line-of-sight (LOS) connections. Compared to nonline-of-sight (NLOS) connections, LOS links are not so flexible but are stronger and more stable against transmission errors. IEEE 802.16 is interoperable with other wireless networks, such as cellular systems and wireless local area networks (WLANs). In the following sections, the main features of 802.16 will be introduced. 2.2.1.1 Network Topology 802.16 defines two WiMAX network topologies: point-to-point (PTP) and point-to-multipoint (PMP). The PTP link refers to a dedicated link that con- nects only two nodes: BS and subscriber terminal. It utilizes resources in an inefficient way and substantially causes high operation costs. It is usually only used to serve high-value customers who need extremely high band- width, such as business high-rises, video postproduction houses, or scientific research organizations. In these cases, a single connection contains all the available bandwidth to generate high throughput. A highly directional and high-gain antenna is also necessary to minimize interference and maximize security. Although PTP can be applied in the above special cases, it is too expensive for common customers. The PMP topology, where a group of subscriber ter- minals are connected to a BS separately (shown in Figure 2.1), is a better choice for users who do not need to use the entire bandwidth. Under PMP topology, sectoral antennas with highly directional parabolic dishes (each dish refers to a sector) are used for frequency reuse. The available bandwidth now is shared between a group of users, and the cost for each subscriber is reduced. 2.2.1.2 802.16 Protocol Stack The 802.16 standard covers the lowest two layers in the OSI model: MAC layer and PHY layer (shown in Figure 2.2). The MAC layer is responsible for determining which SS can access the network and is further divided into three sublayers: service-specific convergence sublayer (CS), MAC common part sublayer (CPS), and security sublayer. The CS transforms incoming data received from the CS service access point (SAP) into MAC data packets. The transformation maps external network information into IEEE 802.16 MAC
- 38. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 18 18 WiMAX: Applications Base station Subscriber station Subscriber station Subscriber station Subscriber station FIGURE 2.1 Point-to-multipoint WiMAX network topology. Scope of standard Data/control plane MAC layer Physical layer CS SAP Service-specific convergence sublayer (CS) MAC common part sublayer (MAC CPS) Management entity MAC common part sublayer Management entity PHY layer Management plane Network management system Management entity service-specific convergence sublayers Physical layer (PHY) MAC SAP PHY SAP Security sublayer Security sublayer FIGURE 2.2 IEEE 802.16 protocol stack. (Reprinted with permission from IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, © IEEE 2002.)
- 39. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 19 Overview of WiMAX Standards and Applications 19 information, such as service flow and connection identifier (CID). The cur- rent standard details two CS specifications: ATM CS and Packet CS. The CS is also responsible for preserving/enabling QoS and allowing bandwidth allocation. The CPS is responsible for access control functionality, bandwidth alloca- tion, connection establishment, and maintenance. Data, PHY control, and other management information are exchanged between the MAC CPS and PHY via the PHY SAP. The security sublayer is responsible for authentication, key exchange, and encryption. IEEE 802.16 PHY is responsible for data transmission and reception. It is specified for the 10–66 GHz spectrum assuming LOS between the BS and the SS. IEEE 802.16 PHY supports wide channel bandwidth of 20, 25, or 28 MHz. 2.2.1.3 Modulation Technologies IEEE 802.16 uses single-carrier modulation schemes in which all packets are sequentially transmitted through a single frequency carrier. Three modula- tion schemes are supported: QPSK (quadrature phase shift keying), 16QAM (quadrature amplitude modulation), and 64QAM. The higher order of mod- ulation allows more bits to be encoded per symbol to achieve higher data rate, but it is more prone to interferences (such as 64QAM). However, the lower order of modulation delivers low transmission speed but is more robust against interferences. Table 2.1 shows the bit rates for different modulation schemes under different channel sizes. 2.2.1.4 Duplexing Technologies 802.16 supports both frequency division duplexing (FDD) and time division duplexing (TDD). FDD requires two channels: one for transmission and one for reception while for TDD a single channel is shared by both the uplink and the downlink but separated by different time slots. FDD is designed only for symmetrical traffic with lower spectrum efficiency and higher cost but shorter delay. In contrast, TDD supports both symmetrical and asymmetrical traffic with better frequency usage, but it cannot transmit and receive at the TABLE 2.1 Bit Rates and Channel Sizes Bit Rate (Mbps) Channel Size (MHz) QPSK 16QAM 64QAM 20 32 64 96 25 40 80 120 28 44.8 89.6 134.4 Source: Reprinted with permission from IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, © IEEE 2002.
- 40. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 20 20 WiMAX: Applications same time. TDD is more efficient for data transmission while voice traffic can be handled by FDD with minimum delays. 2.2.1.5 Multiplexing Technologies The multiplexing technologies used in 802.16 are time division multiplexing (TDM)—for downlink channel and time division multiple access (TDMA)— for uplink channel. In TDM, subscribers share the same frequency band but are allocated by different time slots. TDMA is a flexible multiple access scheme in which time slots can be allocated to subscribers according to fixed or contention modes. 2.2.1.6 Quality of Service To allow quality-of-service (QoS) differentiation, the uplink traffic flows are grouped into four types of applications for 802.16 MAC: • Unsolicited grant services (UGS): UGS is designed to support con- stant bit rate services, such as T1/E1 emulation and voice over IP (VoIP) without silence suppression. • Real-time polling services (rtPS): It is used to support real-time vari- able bit rate services, such as MPEG video and VoIP with silence suppression. • Nonreal-time polling services (nrtPS): It is used to support nonreal- time variable bit rate services, such as FTP. • Best-effort (BE) services: With BE services, packets are forwarded on a first-in-first-out basis using the capacity not used by other services. Web browsing is one example of it. The 802.16 MAC is connection oriented and every traffic flow is mapped into a connection, which is identified by a CID and assigned to one of the above four service types with a set of QoS and traffic parameters. The UGS traffic flow has the highest priority while the BE service has the lowest. 2.2.2 802.16a IEEE 802.16a (published in April 2003) is an improved version of 802.16. This standard extends the 802.16 spectrum down to a lower frequency range from 2 to 11 GHz so that it can utilize both the unlicensed and licensed bands and enables NLOS transmission. LOS transmissions are not required in this case because radio waves at 2–11 GHz frequency bands can pen- etrate into and bend and reflect around buildings and other obstacles to some extent, which are more desirable in urban areas. However, the per- formance of NLOS is worse than LOS owing to the attenuation when passing through obstacles and the introduction of license-free bands that increase the interference. So, a dynamic frequency selection (DFS) mechanism is
- 41. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 21 Overview of WiMAX Standards and Applications 21 specified in 802.16a to reduce such interference. The implementation of DFS enables the mobile device to switch between different radio frequency (RF) channels on the basis of certain channel measurement criteria, such as signal-to-interference ratio. This standard is designed to support a maximum data rate of 75 Mbps at a distance of up to 50 km. In the following sections, the main new features introduced by 802.16a will be discussed. 2.2.2.1 Flexible Bandwidth A problem existing in the original 802.16 standard is that it is often very difficult for some power-sensitive devices, such as laptops and handheld equipments, to transmit to the BS over long distances if the channel band- width is too wide. It is solved in 802.16a by using flexible bandwidth choices, including channel bandwidth between 1.25 and 28 MHz, which provides the flexibility to operate in different frequency bands with varying chan- nel requirements around the world. Because of the interference problem in 2–11 GHz bands, 802.16a systems are more attractive in rural and developing markets where there are sufficient unlicensed spectrums available without interference concerns. 2.2.2.2 Mesh Topology In addition to PTP and PMP, 802.16a introduces the mesh topology, which is a more flexible, effective, reliable, and portable network architecture based on the multihop concept. Mesh networks are wireless data networks that give the SSs more intelligence than traditional wireless transmitters and receivers. In a PMP network, all the connections must go through the BS, while with mesh topology, every SS can act as an access point and is able to route packets to its neighbors by itself to enlarge the geographical coverage of a network. The architecture of a mesh system is shown in Figure 2.3. The routing across the network can be either proactive (using predetermined routing tables) or reactive (generating routes on demand). Mesh topology can be divided into two basic categories: switched mesh and routed mesh [11]. In a switched mesh, a fixed route between two net- work nodes is predetermined and all packets follow the same path during the transmission. If the connection is down or the QoS of the link is degraded, a new route will be established to replace the old one. However, in routed mesh architecture, there is no fixed path from the source to the destination. All packets are forwarded by intelligent network nodes on the basis of the evaluation of link conditions measured by a number of parameters, such as throughput, traffic density, packet loss, interference level, delay, and jitter. Packets from the same source to the same destination may follow different paths and arrive with various delays and jitters. The routed mesh can be fur- ther divided into different forms. At one extreme, every node knows all the other nodes in the network, which is called all-knowing mesh. At another extreme, every node only knows its immediate neighbors. An all-knowing
- 42. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 22 22 WiMAX: Applications Subscriber stations Subscriber stations Subscriber stations Base station FIGURE 2.3 Mesh network topology. mesh has better understanding of the whole network and can find the best path for data transmission. However, it is more complicated and expensive owing to the need for large memory size, high processing power, and complex routing algorithm. A trade-off is required to decide the appropriate mesh forms. Mesh topology is better than its single-hop and directional alternatives. It is more robust against system failure. In a single-hop network, if a single node goes down, so does the whole system. However, in a mesh network, if one node is out of work, the system continues to operate by simply routing packets through an alternative path. Mesh topology can also provide greater redundancy for traffic balancing. In single-hop networks, if too much traffic flows are transmitted simultaneously, a traffic jam may happen and the sys- tem will sharply slow down. Mesh networks solve this problem by routing data along an alternative path, where the traffic load is light so that the avail- able bandwidth can be used more efficiently. Another advantage of mesh is the saving of cost. Because network intelligence is distributed to each net- work node, the number of network management devices, such as BSs, central offices, routers, and switches can be significantly reduced. The backhaul is also no longer needed. In addition, mesh topology can also help the network to adapt to changes and navigate around large obstacles. However, some problems also arise with mesh topology. The latency increases with the number of network hops, which may degrade the quality of delay-sensitive applications, such as voice traffic. Mesh networks are inherently noisy because wireless mesh links are multidirectional broad- casters that may pick up extra signals. Increasing the number of mesh nodes may also cause scalability issues because the routing tables in them will become more complex.
- 43. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 23 Overview of WiMAX Standards and Applications 23 FDM OFDM Guard band Frequency Saving frequency Frequency FIGURE 2.4 Comparison between FDM and OFDM in bandwidth utilization. 2.2.2.3 Orthogonal Frequency Division Multiplexing One important improvement of 802.16a is the usage of orthogonal fre- quency division multiplexing (OFDM) technology, which allows high-speed bidirectional wireless data transmission in a mobile environment. OFDM is based on the traditional frequency division multiplexing (FDM), which enables simultaneous transmission of multiple signals by separating them into different frequency bands (subcarriers) and sending them in parallel. In FDM, guard bands are needed to reduce the interference between dif- ferent frequencies, which causes bandwidth wastage (shown in Figure 2.4). Therefore, it is not a spectrum-efficient and cost-effective solution. How- ever, OFDM is a more spectrum-efficient method that removes all the guard bands but keeps the modulated signals orthogonal to mitigate the interference level. As shown in Figure 2.4, the required bandwidth in OFDM is signifi- cantly decreased by spacing multiple modulated carriers closer until they are actually overlapping. OFDM uses fast Fourier transform (FFT) and inverse FFT to convert serial data to multiple channels. The FFT size is 256, which means a total number of 256 subchannels (carriers) are defined for OFDM. In OFDM, the original signal is divided into 256 subcarriers and transmit- ted in parallel. Therefore, OFDM is referred to as a multicarrier mod- ulation scheme. Compared to single-carrier schemes, OFDM is more robust against multipath propagation delay owing to the use of nar- rower subcarriers with low bit rates resulting in long symbol periods. A guard time is introduced at each OFDM symbol to further mitigate the effect of multipath delay spread. For more details of OFDM, please refer to Refs. 10 and 12. 2.2.2.4 Adaptive Modulation Another new feature of 802.16a standard is adaptive modulation, which allows the provision of more flexible services to customers by enabling the BS
- 44. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 24 24 WiMAX: Applications to dynamically assign modulation schemes to the clients. Like 802.16, 802.16a supports different modulation technologies, including QPSK, 16QAM, and 64QAM. The higher the order of modulation, the higher is the bit rate achieved. However, high-order modulation techniques are more susceptible tointerferenceandnoise, whichcausehigherbiterrorratios(BERs). Theuseof adaptive modulation allows a wireless system to adjust modulation schemes depending on the channel conditions, distance between the BS and the user, weather, signal interference, and other transient factors. In good channel con- ditions, high-order modulations can be used to increase the data throughput and spectral efficiency. When the radio channel conditions become worse, low-order modulations should be used to maintain a certain BER. Using adaptive modulation, it is also able to provide a gradation of QoS depending on the distance from the user to the BS. The longer the distance between the BS and the SS, the lower the guarantee of QoS. A BS can choose the highest modulation scheme (64QAM) to increase the throughput of a customer close to it, while the modulation order may be reduced to 16QAM or even QPSK to serve a distant customer. It allows the BS to automatically extend its effective range at the expense of reduc- ing throughput or vice versa. Adaptive modulation maximizes the network performance while ensuring robust RF links in the quickly changing wireless environment. 2.2.3 802.16-2004 IEEE 802.16-2004 is a wireless access technology standard optimized for fixed and nomadic access, which was published in October 2004. It is a combined and improved version of IEEE 802.16, 802.16a, and 802.16c (these three stan- dards are replaced by 802.16-2004 now) in which both the 10–66 GHz and 2–11 GHz frequency bands are specified and the bandwidth can be as narrow as 1.25 MHz. IEEE 802.16-2004 is designed for fixed BWA systems to support multiple services. The goal of this standard is to enable global deployment of innovative, low-cost, and interoperable multivendor BWAproducts; increase the capacity of competition of BWAsystems against their wired counterparts; and facilitate global commercialization of BWA products. IEEE 802.16-2004 does not add any new models in addition to those covered by IEEE 802.16 and 802.16a. Its main features also remain the same and have already been discussed before. 2.2.4 802.16e All the above standards only focus on fixed broadband systems. How- ever, IEEE 802.16e standard published in February 2006 aims to provide portability and mobility to wireless devices and supports for higher layer handover, which are lacking in the previous standard. 802.16e also enhances the network performance in fixed environment by using orthogonal fre- quency division multiplexing access (OFDMA). However, the frequency
- 45. CRC-45474 CH002.tex 16/7/2007 9: 47 Page 25 Overview of WiMAX Standards and Applications 25 bands suitable for mobility must be below 6 GHz. IEEE 802.16e is also not backward compatible with 802.16-2004 so that hardware/software updates are required to implement it. Compared with 802.16-2004, 802.16e has lower throughput (up to 15 Mbps), butitsupportsbothhardandsofthandoffs. Hardhandoffsarebasedonbreak- before-make concept, which leads to high latency while soft handoffs use make-before-break approach to minimize the delay. The former is usually used for data transfer, while the latter is more suitable for delay-sensitive applications, such as VoIP and online games. IEEE 802.16e uses OFDMA to enhance network performance. OFDMA is a multiple-user version of OFDM and is a more flexible way to manage different user devices with various antenna types and form factors. In OFDMA, the whole carrier space is divided into N groups, where each of them includes M carriers. All the carriers are then grouped into M subchannels, each with one carrier per group. In OFDM, only one user device can use the channel during a single time slot. OFDMA allows multiple users to transmit data simultaneously. A number of users can communicate at the same time using the subchannels allocated to them. Signal coding, modulation, and amplitude are set separately for each sub- channel based on channel conditions to optimize the utilization of network resources. From the user perspective, subchannelization allows different subchannels to be allocated to different subscribers according to their require- ments and channel conditions. One customer can be allocated two or more subchannels. For service providers, subchannelization provides a flexible and efficient bandwidth management solution and a flexible power transmission method. Higher power can be allocated to those subchannels with bad radio conditions. Using OFDMA, fixed user devices can be supported with the same data rate as OFDM, while mobile users trade off mobility against bandwidth. Com- pared to OFDM, OFDMA supports larger FFT size of 1024 so that it enables more flexible subcarrier bandwidth allocation [10]. The four main IEEE 802.16 family standards have been introduced in the above sections. Table 2.2 summarizes their main features. 2.2.5 Other IEEE 802.16 Family Standards In addition to the four main standards discussed before, there are some other IEEE 802.16 family standards that will be briefly introduced in the following sectionsforcompleteness. Ifreaderswanttolearnmoreaboutthesestandards, please refer to Ref. 9. 2.2.5.1 802.16c It was published in January 2003 as an amendment to 802.16. This standard is aimed to develop the 10–66 GHz BWAsystem profiles and aid interoperability specifications. It has already been replaced by the IEEE 802.16-2004 standard.
- 46. Exploring the Variety of Random Documents with Different Content
- 47. DANDO UMA QUEDA Á VISTA DE UMA DAMA QUE SE ENTENDE SER A CELEBRADA BABÚ. Filena, o ter eu cahido Nenhum susto me tem dado, Porque a vossos pés prostrado Me julgo então mais subido: Direis que fiquei sentido, Mas sabei que não sentira, Inda que me não subira A cahir onde cahi, Si como no chão me vi, Com vosco em terra me vira. Porém que isso me succeda, Por mais quédas que inda dê, Não creio, pois vejo que Não tenho com vosco quéda. Vossa crueza me veda Este bem que eu tanto abraço: Quem viu similhante passo, Que encontre meu desvario, Filena, em vosso desvio A minha quéda embaraço.
- 48. Confesso que então cahido Fiz tenção de me sangrar, Mas não me quiz mais picar, Porque assaz fiquei corrido. Não andei pouco advertido, Fallo como quem vos ama; Porque eu sei, formosa dama, Que por mais que me sangrasse, Livre estou de que chegasse A vêr-me por vós na cama. E com toda essa desgraça Por satisfeito me dera Si com cahir merecêra Siquer cahir-vos em graça: Mas porque, Filena, faça D’esta quéda estimação, Inda sobeja razão, Si a quéda motivo é De prostar-me a vosso pé Para beijar-vos a mão. Dizeis que quereis tomar, Para dar, vosso conselho: Quereis conselho de velho? Nunca o tomeis para o dar: Os olhos se hão de fechar Para o dar, e abrir da mão, Com razão ou sem razão, Que os negocios que se tractam, Com conselhos que dilatam, Nunca se conseguirão.
- 49. Si conselhos não tomaes, Quando alvedrios rendeis, Como conselhos quereis, Quando alvedrios pagaes? Sem conselho me mataes, E daes-me a vida em conselho? Este estylo é já tão velho Na eschola da tyrannia, Que da mais tyranna harpia Podereis vós ser espelho.
- 50. JULGA O P. COM SUBTILEZA TODA A CULPA DE ACONTECIMENTOS INIQUOS NO TEMPO ABSTRACTO. ENTENDE-SE SER ESTA OBRA SATYRA AO GOVERNADOR ANTONIO DE SOUSA DE MENEZES, POR ALCUNHA O BRAÇO DE PRATA Tempo, que tudo trasfegas, Fazendo aos pelludos calvos, E pelos tornar mais alvos Até os bigodes lhe esfregas: Todas as caras congregas, E á cada uma pões mudas; Tudo acabas, nada ajudas: Ao rico pões em pobreza, Ao pobre dando riqueza, Só para mim te não mudas. Tu tens dado em malquerer-me, Pois vejo que dá em faltar-te Tempo só para mudar-te, Si é para favorecer-me: Por conservar-me e manter-me No meu infeliz estado, Até em mudar-te has faltado, E estás tão constante agora, Que para minha melhora De mudanças te has mudado.
- 51. Tu que esmaltas e prateias Tanta guedelha dourada, E tanta face encarnada Descoras, turbas e affeias: Que sejas pincel não creias, Si não dias já passados, Mas si esmaltes prateados Branqueam tantos cabellos, Como branqueando pellos, Não me branqueias cruzados? Si corres tão apressado, Como paraste commigo? Corre outra vez, inimigo, Que o teu curro é meu sangrado: Corre para vir mudado, Não pares por mal de um triste; Porque si pobre me viste, Paraste ha tantas Auroras, Si de tão infaustas horas, O teu relogio consiste? O certo é, que és um caco, Um ladrão da mocidade, Por isso nessa cidade Corre um tempo tão velhaco: Farinha, assucar, tabaco No teu tempo não se alcança; E por tua intemperança Te culpa o Brazil inteiro; Porque sempre és o primeiro Movel de qualquer mudança.
- 52. Não ha já quem te supporte, E quem armado te vê De fouce e relogio, crê Que és o precursor da morte: Vens adeante de sorte E com tão fino artificio Que á morte forras o officio; Pois ao tempo de morrer, Não tendo já que fazer, Perde a morte o exercicio. Si o tempo consta de dias, Que revolve o céu opaco, Como tu, tempo velhaco, Constas de velhacarias? Não temes que as carestias, Que de ti se hão de escrever, Te darão á aborrecer Tanto ás futuras edades, Que ouvindo as tuas maldades A cara te hão de trocer. Si porque penas me dês, Páras cruel e inhumano, O céu sancto e soberano Te fará mover os pés: Esse azul movel que vês Te fará ser tão corrente, Que não parando entre a gente Preveja a Bahia inteira Que has de correr a carreira Com pregão de delinquente.
- 53. Á LUIZ CESAR DE MENEZES GOVERNADOR DE ANGOLA, PEDINDO-LHE DE CARCONDA CERTO FAVOR OU DESPACHO POR TITULOS DE COMEDIAS Meu príncipe, d’esta vez Espero que o plectro obre, Ainda que para um pobre Tudo succede al revéz: O que tão raro me fez, Levante-me hoje de raso, Que é já meu timbre em tal caso Querer por solo querer, Porfiar hasta vencer Los empenos de un acaso. Tanta tragedia e inopia Tenho em Angola soffrido, Que em mim se vê el parecido Del mentir de la Ethiopia: De tal retrato e tal cópia Foi causa um general zêlo, Mas por divino modelo Quem tanto me fez cahir, Tanto me viu resurgir: Lo que juizios del cielo!
- 54. Senhor: favores tão grandes Nunca os poderei pagar: Mas eu hei de vos mandar Un valiente Negro en Flandes: Ao senhor Vasco Fernandes, A quem por fé tanto adoro, Por quien a Cruz Sancta imploro, Que lhe dê Sancta Cruz Neto, Tambem mandar-lhe prometto Un esclavo en grilhos de oro. Dois negros são não pequenos, Que offereço de antemão; E posto que só dois são Pocos bastan, si son buenos: A El-rei, quando não dê menos, Ao menos o servirei Com muita amigavel lei, E prometto desde aqui Que tenha em Carconda em mi El maior Amigo El-rei.
- 55. REDARGUE O P. A DOUTRINA OU MAXIMA DO BEM VIVER QUE MUITOS POLITICOS SEGUEM DE INVOLVER-SE NA CONFUSÃO DE HOMENS PERDIDOS E NESCIOS, PARA PASSAR COM MENOS INCOMMODO ESTA HUMANA VIDA Que nescio que eu era então Quando cuidava o não era! Mas o tempo, a edade, a era Puderam mais que a razão: Fiei-me na discrição, E perdi-me, em que me pez, E agora dando ao travez, Vem no cabo á conhecer Que o tempo veiu a fazer O que a razão nunca fez. O tempo me tem mostrado Que, por me não conformar Com o tempo e com logar, Estou de todo arruinado: Na politica de estado Nunca houve principios certos, E posto que homens expertos Alguns documentos deram, Tudo o que nisto escreveram São contingentes acertos.
- 56. Muitos por vias erradas Têm acertos mui perfeitos, Muitos por meios direitos Não dão sem erro as passadas: Cousas tão disparatadas Obra-as a sorte importuna, Que de indignos é columna. E si me ha de ser preciso Lograr fortuna sem sizo, Eu renuncio á fortuna. Para ter por mim bons fados Escuso discretos meios, Que ha muitos burros sem freios E bem afortunados: Logo os que andara bem livrados, Não é propria diligencia, É o ceu e sua influencia, São forças do fado puras, Que põem mentidas figuras No theatro da prudencia. De diques de agua cercaram Esta nossa cidadella, Todos se molharam nella, E todos tontos ficaram: Eu, á quem os céus livraram D’esta agua, fonte da asnia, Fiquei são da fantasia Por meu mal, pois nestes tratos Entre tantos insensatos Por sisudo eu só perdia.
- 57. Vinham tontos em manada, Um simples, outro doudete, Este me dava um moquete, Aquell’outro uma punhada: Tá: que sou pessoa honrada, E um homem de entendimento, Qual honrado ou qual talento? Foram-me pondo num trapo, Vi-me tornado um farrapo, Porque um tolo fará cento. Considerei logo então Os baldões que padecia, Vagarosamente um dia, Com toda a circumspecção: Assentei por conclusão Ser duro de os correger, E livrar do seu poder, Dizendo com grande magua: Si me não molho nesta agua, Mal posso entre estes viver. Eia: estamos na Bahia, Onde agrada a adulação, Onde a verdade é baldão, E a virtude hypocrisia: Sigamos esta harmonia De tão fatua consonancia, E inda que seja ignorancia Seguir erros conhecidos, Sejam-me a mim permittidos Si em ser besta está a ganancia.
- 58. Alto pois com planta presta Me vou ao Dique botar, E ou me hei de nelle afogar, Ou tambem hei de ser besta: Do bico do pé até a testa Lavei as carnes e os ossos: Ei-los vêm com alvoroços Todos para mim correndo, Ei-los me abraçam dizendo: «Agora sim que é dos nossos.» Dei por besta em mais valer, Um me serve, outro me presta, Não sou eu de todo besta, Pois tractei de o parecer: Assim vim á merecer Favores e applausos tantos Pelos meus nescios encantos, Que emfim e por derradeiro Fui gallo do seu poleiro E lhes dava os dias sanctos. Já sou na terra bem visto, Louvado e engrandecido, Já passei de aborrecido Ao auge de ser bemquisto: Já entre os grandes me alisto, E amigos são quantos topo: Estou fabula de Esopo, Vendo fallar animaes, E fallando eu que elles mais, Bebemos todos num copo.
- 59. Seja pois a conclusão, Que eu me puz aqui a escrever O que devia fazer, Mas que tal faça, isso não: Decrete a Divina mão, Influam malignos fados, Seja eu entre os desgraçados Exemplo da desventura, Não culpem minha cordura, Que eu sei que são meus peccados.
- 60. DESCREVE O RICO FEITIO DE UM CELEBRE GREGORIO DE NEGREIROS EM QUE VARIAS VEZES FALLA, MOÇO COM QUEM GRACEJAVA COM DIVERTIMENTO NAQUELLE SITIO ROMANCE Eu vos retrato Gregorio, Desde a cabeça á tamanca, Co’ um pincel esfarrapado Numa pobrissima tabua. Tão pobre é nossa gadelha, Que nem de lendias é farta, E inda que cheia de aneis, São aneis de piassaba. Vossa cara é tão estreita, Tão faminta e apertada, Que dá inveja aos Buçacos, E que entender ás Thebaidas. Tende dois dedos de testa Porque da frente á fachada Quiz Deus e a vossa miseria Que não chegue á pollegada. Os olhos dois ermitães, Que em uma lobrega estancia Sempre fazem penitencia Nas grutas da vossa cara. Dois arcos quizeram ser As sobrancelhas, mas para Os dois arcos se acabarem Até de pello houve falta. Vosso pae vos amassou, Porém com miseria tanta, Que tremeu a natureza
- 61. Que algum membro vos faltára. Deu-vos tão curto o nariz, Que parece uma migalha, E no tempo dos defluxos Para assoar-vos não basta. Vós devieis de ser feito No tempo em que a lua se acha Pobrissima já de luz, Correndo á minguante quarta. Pareceis homem meminho, Como o meminho da palma, O mais pequeno na rua, E o mais pobresinho em casa. Vamos aos vossos vestidos, E peguemos na casaca, Com tento, porque sem tento A leva qualquer palavra. Anda tão rota, senhor, Que tenho por coisa clara Que no Tribunal da Rota De Roma está sentenciada. A vossa grande pobreza Para perpetua lembrança Dedico á de Manuel Trapo, Que foi no mundo affamada.
- 62. Á HENRIQUE DA CUNHA CHEGANDO DO SITIO DA ITAPEMA Á CAJAHYBA ROMANCE Senhor Henrique da Cunha, Vós que sois lá na Itapema Conhecido pelo brio, Graça, garbo, e gentileza: Vós que aonde quer que estais Todo o mundo se vos chega A escutar a muita graça, Que vos chove á bocca cheia: Vós que partindo de casa, Ou seja ao remo, ou á vela, Bem que venhais sem velame, Vindes fiado na verga: E apenas tendes chegado A esta Cajahyba amena, Logo São Francisco o sabe, Logo Apollonia se enfeita: Logo chovem os recados, Logo a canôa se apresta, Logo vai, e logo encalha, Logo a toma, volta e chega: Logo vós a conduzis Para a Casa das galhetas, Onde o melado se adoça, Onde a garapa se azeda: Entra ella, e vós tambem, Assenta-se, e vós com ella E assentada lhe brindais Á saude das parentas. Vós: mas baste tanto vós,
- 63. Si bem que a Musa burlesca Anda tão desentoada, Que em vez de cantar, vozea. Ás vossas palavras vamos, Vamos ás vossas promessas, Que com serem infinitas, Não são mais que as minhas queixas. Promettestes-me, ha dois annos, De fazer-me aquella entrega Da viuva de Naim, Que hoje é gloria da Itapema. Não me mandastes comboy, Necessaria diligencia, Para um triste que não sabe Nem caminho, nem carreira. Tão penoso desde então Fiquei com tamanha perda, Que ou a pena ha de acabar-me, Ou ha de acabar-se a pena. Mas inda fio e confio Na Senhora Dona Tecla Que nas dez varas de hollanda Hei de amortalhar a peça. Disse amortalhar, mal disse, Melhor resurgir dissera, Que em capello tal resurge A mais defuncta potencia. Vós me tirastes o ganho: Sois meu amigo, paciencia; Por isso diz o rifão Que o maior amigo apega. Só vós soubestes logra-la, Que sois com summa destreza Grande jogador de gorra, Pela branca e pela negra. Jogais a negra e a branca, E tudo na eschola mesma,
- 64. Bem haja escrava e senhora, Que uma de outra se não zela. Esta é a queixa passada, Porém a presente queixa É que a todos os amigos Mandastes mimos da Terra. A uns peças de piassabas, A outros fizeste a peça, E eu já essa peça tomára, Por ter de vós uma prenda. Enviar-me alguma cousa, Mais que seja um pau de lenha, Terei um pau para os caens, Que é o que ha na nossa terra. Lembre-vos vosso compadre, Que o tal Duarte de Almeida Co’ a obra parou, emquanto A piassaba não chega. Mandae-me uma melancia, Que ainda que é fruita velha, Não importa o ser passada, Como de presente venha. Mandae-me um par de tipoyas, Das que se fazem na Terra, A dois cruzados cada uma, Que eu mandarei a moeda. Mandae-m’as sem zombaria, Que eu vo-las peço de veras, Porque não peço de graça Quanto a dinheiro se venda. Mandae-me boas novas vossas, E em que vos sirva e obedeça, Que como vosso captivo Irei por mar e por terra. Mandae-me novas da mãe, Das filhas muitas novellas, Pois em faze-las excedem
- 65. Cervantes e outros poetas. E perdoae disparates De quem tanto vos venera, Que por em tudo imitar-vos Vos quer seguir na pespega.
- 66. PEDINDO-SE A SOLTURA DE UM MULATO Á SEU SENHOR Não estamos nos Ilheos, Que é terra de meus peccados, Mas estamos melhorados Aqui na Madre de Deus: E si aquelles tabaréus Por vossa mesma verdade Dão tão geral liberdade Aos delinquentes da terra, Vós c’o peccador que erra Como usaes tal crueldade? Um castigo tão tyranno, Uma prisão tão severa, Satisfaria a uma fera, E eu cuidei que ereis humano: Ha pouco menos de um anno Que está esse peccador Purgando com grande dor, E com trabalho infinito, Á principio o seu delicto, E agora o de seu senhor.
- 67. Welcome to our website – the ideal destination for book lovers and knowledge seekers. With a mission to inspire endlessly, we offer a vast collection of books, ranging from classic literary works to specialized publications, self-development books, and children's literature. Each book is a new journey of discovery, expanding knowledge and enriching the soul of the reade Our website is not just a platform for buying books, but a bridge connecting readers to the timeless values of culture and wisdom. With an elegant, user-friendly interface and an intelligent search system, we are committed to providing a quick and convenient shopping experience. Additionally, our special promotions and home delivery services ensure that you save time and fully enjoy the joy of reading. Let us accompany you on the journey of exploring knowledge and personal growth! ebookfinal.com