A Novel Parameterized QoS based Uplink and Downlink Scheduler for Bandwidth/Data Management over IEEE 802.16d Network

ACEEE International Journal on Network Security, Vol 1, No. 2, July 2010

A Novel Parameterized QoS based Uplink and
Downlink Scheduler for Bandwidth/Data
Management over IEEE 802.16d Network
R. Mahmood1, M. I. Tariq1 and M. S. H. Khiyal2
1
International Islamic University Islamabad Pakistan
rashidmahmood@live.com, imranchaudhry12@hotmail.com
2
Fatima Jinnah Women University Rawalpindi Pakistan
m.sikandarhayat@yahoo.com

Abstract: Recent developments in Broadband Wireless we discuss results. Finally, we conclude with a
Access (BWA), caused users to use multimedia, real–time summary in Section VI.
and high bandwidth intensive applications that lead to a
new era of research and development in wireless
II. BACKGROUND
networks. IEEE 802.16 standard has come forward as
BWA solution to fulfill the requirements of users. Even IEEE 802.16d [11] standard defines an air interface
though IEEE 802.16 standard defines scheduling service for fixed point to multipoint BWA that is competent of
flows and quality of service parameters, but scheduling of providing various services. The architecture mainly
these flows to maintain QoS and fairness among flows is
left open for researchers. In this paper we developed a
consists of two components, a Base Station (BS) and a
scheduling architecture for IEEE 802.16 in both uplink number of Subscriber Stations (SS). Figure 1 depicts
and downlink directions. Our scheduling architecture the BWA system architecture. Both BS and SS are
includes QoS parameters like maximum sustained rate, fixed, whereas users inside a building may be fixed or
maximum latency, tolerated jitter, minimum reserved mobile. Communication takes place from the BS to the
bandwidth, request transmission policy, traffic priority, SSs (Downlink (DL)) and from SS to BS (Uplink
burst size, SDU size and queue information for various (UL)). DL transmission is carried through Point to
scheduling service flows. We use First in First out (FIFO), Multipoint access method, and UL is conducted by
Earliest Deadline First (EDF) and Self Clocked Fair
Time Division Duplexing (TDD) on demand basis.
Queuing (SCFQ) to schedule different flows to achieve
QoS and efficient bandwidth utilization. IEEE 802.16d specifies physical layer that operates on
2-11 GHz and 10-66 GHz frequency bands. The data
Index Terms: IEEE 802.16, Quality of Service, Broadband rate supported by these two frequency bands is
Wireless Access, Medium Access Control, Self Clocked dependent upon the channel bandwidth and modulation
Fair Queuing technique.

I. INTRODUCTION
Broadband wireless access (BWA) has turned out
to be the best most efficient way to handle business and
home demand for fast internet access, voice/video
services, integrated data, resource sharing and
utilization, mass data transfer and multimedia
applications. It has advantages over its wired
competitors, such as fast deployment, ease of
implementation, lower maintenance cost, lower upgrade
cost, high data rate and high scalability. Figure 1. Broadband Wireless Access System Architecture
In this paper we develop an efficient scheduling
architecture that incorporates mandatory Quality of Orthogonal Frequency Division Multiple Access
Service (QoS) parameters. We have also evaluated the (OFDMA) is a potential multiple access scheme that
behavior of fragmentation under this scheduling can very efficiently cope with these impairments. It
architecture. The rest of this paper is organized as considerably reduces frequency fading and inter-symbol
follows. In the next section, we provide an overview of interference [7]. The MAC layer of IEEE 802.16 is
IEEE 802.16 standard (more specifically MAC layer) divided into three parts: Privacy sublayer, MAC
and describe some of their QoS related features. In common part sublayer and convergence sublayer. Each
Section II we discussed related work. We then propose packet has to be linked with a unique connection in the
our scheduling architecture in Section IV. In section V MAC layer. SSs the use bandwidth request mechanism
to specify UL bandwidth requirements to the BS. BS

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polls SS by allocating bandwidth to them for the OFDMA/TDD based broadband wireless access
purpose of making bandwidth requests. Bandwidth can system, in which radio resources of both time and
be requested by sending a bandwidth request packet or frequency slots are dynamically shared by all users
by piggybacking it with a data packet. Requests can be [12]. Claudio Cicconetti et. al. in 2006, assessed the
aggregated or incremental. The IEEE 802.16 standard performance of IEEE 802.16 in two of the most
defines the following two ways for allocation of promising scenarios(residential and small and medium-
bandwidth grants: Grant per Connection (GPC) and sized enterprise (SME)) envisaged by the Wimax forum
Grant per Subscriber Station (GPSS). [7] and they also evaluated the effectiveness of rtPS,
The standard defines four types of scheduling nrtPS, and BE through simulation in [10]. Abhishek
services, each one with distinct QoS requirements. Each Maheshwari in 2006, proposed Weighted Fair Queue
connection is linked with a single scheduling service (WFQ) based MAC scheduling architecture for IEEE
and each scheduling service is linked with a set of QoS 802.16 WirelessMANs in both uplink and downlink
parameters that measure its behavior. The following directions [6]. Xiaojing Meng in 2007 proposed a
four scheduling services are supported by IEEE 802.16. scheduling algorithm for OFDM/TDMA based on
Unsolicited Grant Service (UGS), Real-Time Polling WiMAX network to extend proportional fairness
Service (rtPS), Non Real-Time Polling Service (nrtPS) scheme to multiple service types with diverse Quality
and Best Effort Service (BE) flows. The key service of Service requirements [9].
information elements (IEs) for the above mentioned In previous work, number of authors proposed
scheduling services the Maximum Sustained Traffic, scheduling architecture for IEEE 802.16 and most of
Minimum Reserved Traffic Rate, Maximum Latency, them concentrated on Uplink Scheduling. Some of them
Tolerated Jitter, Traffic Priority and also proposed downlink scheduling, but all these
Request/Transmission Policy. The scheduler is in scheduling architectures and mechanisms ignored the
charge of controlling the common UL bandwidth as QoS parameters defined by IEEE 802.16 to achieve
well as distributing resources to flows to maintain stringent quality of service. All authors used static
quality. Fragmentation, Piggybacking, Concatenation, weights for different scheduling algorithms, while the
and Contention processes are used to maintain QoS, dynamic calculation of weights was ignored. At present
resource utilization and bandwidth guarantee. there is a need for scheduling architecture, which will
use all mandatory parameters defined by the IEEE
III. PREVIOUS WORK 802.16 to schedule packets, and to achieve the QoS
requirements of different applications.
M. Hawa and D. W. Petr in 2002 suggested an
uplink scheduling architecture for IEEE 802.16 and
IV. SCHEDULING ARCHITECTURE
DOCSIS (standard for delivering broadband services
over Hybrid Fiber Coax) with GPC grant mode. They We proposed a scheduling architecture as shown in
are more focused on DOCSIS rather than IEEE 802.16 Figure 2 for the IEEE 802.16d in the mac layer that
[1]. Guosang Chu et. al. in July 2002, suggested incorporates the QoS parameter. Our proposed QoS
Weighted Round Robin (WRR) as uplink scheduling scheduling architecture is composed of a BS Uplink
algorithm with GPSS (Grant per Subscriber Station) Bandwidth Management Module, BS Downlink
grant mode [3]. They chose five priority queues with Bandwidth Management Module, SS Uplink Scheduler,
dynamic priority competitive ratio parameter BS Downlink Scheduler, Packet Ordering Module and
assignment. Aura Ganz and Kitti Wongthavarawat in Fragmentation Module. We designed this scheduling
2003, suggested uplink bandwidth allocation algorithms architecture to meet the QoS of each flow, and still
based on flow type and strict priority from highest to achieve high system bandwidth utilization under GPSS
lowest - UGS, rtPS, nrtPS and BE [5]. Victor Rangel1 (Grant per subscriber station).
et. al. in 2004, suggested a scheduling algorithm named
BS Uplink Bandwidth Management Module
EBSA that combines Early Deadline First and
Prioritization, Round Robin and Weighted Fair Queuing This module, as shown in figure 3, has the
to match CBR and VBR traffic over the IEEE 802.16 responsibility for allocating bandwidth to each SS flow
air interface [8]. Jianfeng Chen et. al. in 2005, for UL transmission. Its main function is to produce a
suggested Quality of Service (QoS) enhancement of UL map for all SS according to their bandwidth
IEEE 802.16 standard, based on cross layer requirements, to achieve excellent QoS for each flow
optimizations in PMP mode [4]. Supriya Maheshwari in under the limited information of each queue. It also
2005 has described a scheduling architecture based on keeps fairness among different flows and Subscriber
GPSS grant mode with WFQ for downlink scheduling Stations under overloaded conditions. It assures the
and min-max fair allocation for uplink scheduling [2]. delay guarantee to UGS and rtPS flows. Bandwidth is
Vandana Singh et. al. in 2006, developed new allocated to each SS in the following way:
scheduling algorithms for the IEEE 802.16d

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Figure 2. Scheduling Architecture for IEEE 802.16

• Amount of bandwidth allocated to each SS in Traffic Priority is used as an ordering parameter. If two
regular intervals by the QoS parameters of flows are equal in Traffic priority, then priority will be
connection associated with each connection. given to that flow which has less bandwidth as
• Amount of bandwidth requested by each SS for UL compared to the other, and that is calculated from
transmission. Maximum Sustained Rate.
• Amount of bandwidth required periodically by SS’s
UGS flow.
BS distributed UL bandwidth among various SSs in the
following way. Bandwidth Allocation to UGS: BS
allocates bandwidth to each UGS UL flow according to
QoS parameters negotiated during connection setup.
These parameters include Maximum Sustained Rate
and SDU size to define the interval for allocating
bandwidth. If the number of UGS flow increases then
Tolerated Jitter is used as an ordering parameter. If two
flows are equal in Tolerated Jitter, then Maximum
Latency is used to break a tie. Bandwidth Allocation to
Figure 3. Uplink Bandwidth Scheduling
rtPS: BS fulfills the requirements of rtPS flow
whenever there is an entry in its queue. So BS provides
unicast polling request to each rtPS flow to meet the
QoS. BS fulfills the BW request of rtPS flows for
different SSs. Maximum Latency is used as an ordering
parameter. If two flows are equal in Maximum Latency
then priority will be given to that flow which has lower
Maximum Sustained Rate and Minimum Reserved
Traffic Rate. Bandwidth Allocation to nrtPS: BS
provides unicast request opportunities to each nrtPS
flow to meet the QoS. After fulfilling the requirements
of all UGS and rtPS flows, BS provides the requested
bandwidth to different SS for nrtPS flow and Traffic Figure 4. SS Uplink Scheduler
Priority parameter used as an ordering parameter. If
two flows are equal in Traffic priority then priority will SS Uplink Scheduler
be given to that flow which has lower Maximum After allocation of bandwidth from UL Bandwidth
Sustained Rate and Minimum Reserved Traffic Rate as Management module, SS uplink scheduler as shown in
compared to other nrtPS flows. Bandwidth Allocation figure 4, responsibility is to schedule packets from the
to BE: After fulfilling the requirements of all UGS, respective queues of UGS, rtPS, nrtPS and BE. First
rtPS, and nrtPS flows, BS fulfills the requirements of we schedule UGS packets, because there is fixed
all BE flows by allocating bandwidth according to bandwidth allocation from BS side. UGS packets are
Maximum Sustained Rate and Last Polling Time. The queued by FIFO mechanism. rtPS Packets are queued
parameter by Earlier Deadline First mechanism, and ordering
parameter is Maximum Latency. nrtPS Packets are

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queued by Earlier Deadline First mechanism and flows that have not gotten bandwidth in the current
ordering parameter is Maximum Latency and Traffic frame will get it in the next.
Priority. BE Packets are queued by First Come First
Serve mechanism. We use a variant of WFQ scheduling
algorithm that is Self Clocked Fair Queuing (SCFQ), to
schedule rtPS, nrtPS and BE packets that avoid to
costly computation of round number in WFQ. A weight
is calculated dynamically for each class of scheduling
services by the size of the queue and a constant
(weight) priority connections with each flow and
bandwidth distributed among flows by calculated
weight.
BS Downlink Bandwidth Management Module
This module, as shown in figure 5, has Figure 5. Downlink Bandwidth Management
responsibility for allocating bandwidth to each SS for
DL transmission. Its main responsibility is to produce a
DL map for all SSs according to their bandwidth
requirements. To allocate DL bandwidth among
different SSs is easier than UL bandwidth allocation,
because BS has all information for each scheduled
service flow. It is also the responsibility of this module
to keep fairness among different flows and SS under
overloaded conditions. The module assures the delay
guarantee to UGS and rtPS flows as we increase the
number of flows. BS distributes UL bandwidth among
various SSs by the following strategies. Bandwidth
Figure 6. BS Downlink Scheduler
Allocation to UGS: BS fulfills the requirements of UGS
flow whenever a UGS packet is queued in its queue. BS
allocates bandwidth to flow according to packet size. If BS Downlink Scheduler
the number of UGS flow increases then Tolerated Jitter After bandwidth allocation from downlink
is used as an ordering parameter. If two flows are equal bandwidth management module, BS Downlink
in Tolerated Jitter, then Maximum Latency is used to Scheduler’s as shown in figure 6, responsibility is to
break a tie. Bandwidth Allocation to rtPS: BS satisfies schedule packets from the respective queues of UGS,
the requirements of rtPS flow whenever number of rtPS, nrtPS and BE according to allocated bandwidth.
rtPS-packets is in its queue. The parameter Maximum First we schedule UGS packets, because there is fixed
Latency is used as an ordering parameter. If two flows bandwidth allocation, so that it can meet QoS
are equal in Maximum Latency, then that flow has the efficiently. After scheduling UGS packets, the
priority, which has less allocated bandwidth, and it remaining bandwidth is allocated among rtPS, nrtPS
calculated from Maximum Sustained Rate and Minimum and BE flows. These packets are scheduled by SCFQ
Reserved Traffic Rate. While ordering flows, there is scheduling algorithm, which finds the finish number of
one important aspect where a flow, which is much each packet before its introduction into the respective
closer to maximum latency, is crossing a deadline. Here queue, and this algorithm also updates the round
it is better to drop the packets instead of allocating very number after each arrival and departure of packets.
costly bandwidth. Bandwidth Allocation to nrtPS: BS Weight is calculated by the mechanism described in SS
fulfills the requirements of all nrtPS flows according to Uplink Scheduler.
size of packets that are queued in its queue. The Fragmentation Module
parameter Traffic Priority is used as an ordering
parameter. If two flows are equal in Traffic priority, This module is mainly responsible for allowing
then that flow has the priority, which has, less allocated efficient use of granted bandwidth relative to the QoS
bandwidth as compared to the other, and that is requirements of a connection. We do not fragment the
calculated from Maximum Sustained Rate and Minimum UGS connection, because there is fixed allocation of
Reserved Traffic Rate. Bandwidth Allocation to BE: At bandwidth. This process is performed before BS
last it fulfills the requirements of all BE flows. Traffic scheduler and SS scheduler schedule the packets. Its
Priority is used as an ordering parameter to allocate main task is to fragmenting the packets whose size is
bandwidth among BE service flows. In the second greater than that allocated for a packet. In these cases
stage, BS allocates DL bandwidth to all SSs. Service header overhead increases, but this can be compensated

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for through efficient utilization of bandwidth allocated easily schedule packets. We concluded that to achieve
to each SS. quality of service, efficient utilization of bandwidth and
fairness, the best method is to design such an
V. RESULT architecture that incorporates all QoS parameters, so a
flow can meets its delay and bandwidth guarantee. This
We performed a number of simulation tests in Network
approach can save a BS from excessive computation
Simulator 2 (NS-2) to show the effectiveness and
and databases management overhead for each flow.
performance of our proposed scheme. Figures 7 and 8
Finally, we concluded that such architecture is best for
show the Mean Mac delay of scheduling service flows
the varied quality of service requirements of different
to SS (UL and DL) when the number of SSs increases
flows in UL and DL directions.
from 2 to 24. It is found that mean delay of all
scheduling flows in UL direction increases gradually
REFERENCES
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A Novel Parameterized QoS based Uplink and Downlink Scheduler for Bandwidth/Data Management over IEEE 802.16d Network

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