wireless communication Chapter 1 Introduction.ppt

2
Subject Outline
 Introduction to Cellular Mobile Communications
 Radio Propagation : Large Scale Effects
 Path loss prediction models
 Shadowing
 Radio Propagation : Small Scale Effects
 Multi-path models : Rayleigh, Rician
 Doppler effect, power spectra and signal correlation
 Coherence time and bandwidth, flat and selective fading
channel
 Modulation Techniques
 Constant envelope and phase modulation
 QPSK, π /4 QPSK, FSK, GMSK

3
Subject Outline
 Equalization, Diversity and Coding Techniques
 Linear and non-linear equalization
 Selection, equal-gain and maximal ratio combining
 Interleaving and convolution coding
 Multiple Access Techniques
 FDMA, TDMA, CDMA, SDMA
 Packet radio and random access
 Cellular System Concepts
 Frequency reuse
 Channel assignment and control
 Cellular traffic
 Cellular coverage
 System expansion techniques

4
Subject Outline
 CDMA Cellular Systems
 Power Control and Interference
 Multi-user Detection
 Capacity and Enhancement
 More Advanced Topics (if time allows)
 Orthogonal Frequency Division Mulitplexing (OFDM)
 Multi-carrier CDMA System
 Speech Coding
Fundamentals of quantization, PCM, Vocoder
 Brief Overview of System Standards
GSM, IS-95, IMT2000

5
References
 Theodore S. Rappaport, Wireless Communications: Principles &
Practice, Prentice-Hall, 2nd Edition.
 Jon W Mark, Weihua Zhuang, Wireless Communications and
Networking, Prentice Hall.
 Simon R. Saunders, Antennas and Propagation for Wireless
Communication Systems, Wiley.
 William C. Y. Lee, Mobile Communications Engineering, McGraw-Hill.
 J. D. Parsons, The mobile radio propagation channel, Wiley, 2nd
Edition.
 Michel Daoud Yacoub, Foundations of Mobile Radio Engineering, CRC
Press.
 William C. Jakes, Microwave Mobile Communications, IEEE Press.

6
Wireless Communications
 Satellite
 TV
 Cordless phone
 Cellular phone
 Wireless LAN, WIFI
 Wireless MAN, WIMAX
 Bluetooth
 Ultra Wide Band
 Wireless Laser
 Microwave
 GPS
 Ad hoc/Sensor Networks

7
Europe Standards
 GSM
 CT2
 Dect

9
North American Major Standards
 PCS
 GSM
 Coreless
 FDMA
 TDMA
 CDMA
 Modulation
 FM
 QPSK
 GMSK
 BPSK
 QAM

10
Basic concepts
 Simplex, half-duplex, and full duplex
 Frequency division duplexing, FDD
 Most of system because of simplicity
 Time division duplexing, TDD:
 indoor system only, because of delay
 Different from FDMA and TDMA

13
Cordless phone
 Virtually all telephones now sold in the US use the 900 MHz, 2.4 GHz, or
5.8 GHz bands. There is no specific requirement for any particular
transmission mode on 900, 2.4, and 5.8, but in practice virtually all 900
MHz phones are inexpensive, bare-bones analog models; digital features
such as DSSS and FHSS are generally only available on the higher
frequencies.
 The recently allocated 1.9 GHz band is used by the popular DECT phone
standard from Europe

16
Introduction
 The target for mobile communications is to provide
communications for anyone, from anywhere, at any time.
 A demanding task. Technological challenges include:
 Time–varying, hostile communication channel.
 Location and tracking complexities due to mobility.
 Efficient use of scarce resources such as frequency spectrum
⇒ cellular structure. The amount of interference generated is
critical.
 Power restrictions due to health issues.

17
Introduction
 The exponential
growth of mobile
subscribers
worldwide is due
to the
decreasing
service charges
and diminishing
hardware costs.
The continuous
development of
the enabling
technologies is
the key.

18
Introduction
RF technologies (such as improved frequency stability in electronics)

19
Introduction
 IC design (size)
 Battery technology (weight and size)
 Higher order modulation is made possible due to
the use of more sophisticated advanced digital
signal processing techniques.
 Speech coding techniques – reduces the
required bandwidth per channel.

20
Cellular system
Example :
 Consider a system allocated total bandwidth of 12.5MHz
and each voice channel requires a 10kHz slot. We can only
support 12.5MHz/10kHz or 1250 simultaneous
conversations.
 Supposing the penetration rate in Singapore is 10%, for a
population of 3M+, this is equivalent to 300k users. What
happen if 1% of the users making call at the same time?
Channels need to be in someway reused or shared?

21
Cellular system
What can we do?
 Frequency bands are reused at different
locations. With this, higher user capacity in the
same frequency spectrum can be achieved.
 Technical challenge: interference issue, location
tracking, etc., needs to be overcome.

23
Cellular system
 Each cell has a base station (BS), providing the radio interface to
the mobile station (MS).
 A sophisticated switching technique called a handover enables a
call to proceed uninterrupted across cell boundaries.
 All the BS’s are connected to a mobile switching center (MSC)
which is responsible for connection users to the public switched
telephone network (PSTN).
 Control channels transmit and receive data messages that carry
call initiation and service requests, and are monitored by mobiles
when they do not have a call in progress. ~5% of total available
channels.

24
Cellular system
 Communication between the BS and the mobiles is
defined by a standard common air interface that
specifies 4 different physical channels
 Forward (Downlink) voice/data channel : BS to MS
 Reverse (Uplink) voice/data channel : MS to BS
 Forward (Downlink) control channel : BS to MS
 Reverse (Uplink) control channel : MS to BS
 A MS contains a transceiver, an antenna and control
circuitry. A BS consists of several transmitters and
receivers.

wireless communication Chapter 1 Introduction.ppt

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