Evolution of Modern

Wireless Communication

Systems

Prof. Dr. Said E. El-Khamy,

Life Fellow IEEE

Email: elkhamy@ieee.org

1. Needs and Limitations of Wireless Multimedia

Communication Systems

2

Needs of Future Wireless Communications

• Wireless communications is attracting an increasing interest and investigations due to: – Rapid growth of the number of wireless voice subscribers and the

internet.

– Quickly increasing use of portable devices.

• Wireless internet multimedia access is expected to rise rapidly over the next few years.

• This increases the growing demand for reliable high data rate multimedia services .

3

Limitations

• The wireless channel impairments

• The large needed bandwidth

• Interference

• Security issues

4

Wireless Channels Impairments

– Fading.

– Channel-induced ISI (multipath).

– Co-Channel and Multi-User interference.

– Intended Interference, (Jamming in Radars).

5

Fading

• Fluctuation in the received signal amplitude

6

Multipath Propagation

7

Interference

8

Co-Channel Interference

in Cellular Systems

Mutiple-Acess

Interference in

Multipath Environment

Bandwidth Limitations:

• A Large bandwidth is needed to support multimedia signals (voice, images, video, data, ……).

9

Voice Video Data

Delay

Packet Loss

BER

Data Rate

Traffic

<100ms - <100ms

<1% 0 <1%

10-3 10-6 10-6

8-32 Kbps 1-100 Mbps 1-20 Mbps

Continuous Bursty Continuous

Multimedia Requirements

10

2. Duplexing Techniques (FDD-TDD)

11

TDD or FDD ?

3. Multiple-Access Techniques OFDMA versus TDMA & CDMA

12

Evolution In View of Multiple Access Methods

13

4. 2G SYSTEMS

14

Examples of Modern Wireless Communication Systems (2G) • Fixed Wireless Access

• Home RF

• Wide Area Wireless Data Services

• Cellular Mobile Systems

• Cordless Telephones

• Wireless LANs

• Satellite Systems

• Paging Systems

• Bluetooth

and more!!!!!!!!!!!!!! 15

Wireless Local Area Networks (WLANs)

WLANs connect “local” computers (100m range)

Breaks data into packets

Channel access is shared (random access)

Backbone Internet provides best-effort service

Poor performance in some apps (e.g. video)

01011011

Internet

Access

Point

0101 1011

16

Wireless LAN Standards • 802.11b (2G)

– Standard for 2.4GHz ISM band (80 MHz) – Frequency hopped spread spectrum (or DS SS) – 1.6-10 Mbps, 500 ft range

• 802.11a (2+ G) -WiFi – Standard for 5GHz NII band (300 MHz) – OFDM with time division – 20-70 Mbps, variable range – Similar to HiperLAN in Europe

• 802.11g (Emerging Generation) – Standard in 2.4 GHz and 5 GHz bands – OFDM – Speeds up to 54 Mbps

• 802.11n (New Standard)

17

Wi-Fi Architecture

18

8C32810.61-Cimini-7/98

Bluetooth

• Cable replacement RF technology (low cost)

• Short range (10m, extendable to 100m)

• 2.4 GHz band (crowded)

• 1 Data (700 Kbps) and 3 voice channels

• Widely supported by telecommunications, PC, and consumer electronics companies

• Interesting applications starting to emerge 19

• It consists of: – Base Station Controller ( BSC)

– Base Transceiver Stations (BTS(

CELLULAR MOBILE SYSTEMS

20

CELLULAR NETWORK COMPONENTS

GSM Specifications-1

• RF Spectrum

GSM 900

Mobile to BTS (uplink): 890-915 Mhz

BTS to Mobile(downlink):935-960 Mhz

Bandwidth : 2* 25 Mhz

GSM 1800

Mobile to BTS (uplink): 1710-1785 Mhz

BTS to Mobile(downlink) 1805-1880 Mhz

Bandwidth : 2* 75 Mhz

GSM Specification-II

• Carrier Separation : 200 Khz

• Duplex Distance : 45 Mhz

• No. of RF carriers : 124

• Access Method : TDMA/FDMA

• Modulation Method : GMSK

• Modulation data rate : 270.833 Kbps

Characteristics of GSM Standard

• Fully digital system using 900,1800 MHz frequency band. • TDMA over radio carriers(200 KHz carrier spacing.

• 8 full rate or 16 half rate TDMA channels per carrier.

• User/terminal authentication for fraud control.

• Encryption of speech and data transmission over the radio path.

• Full international roaming capability.

• Low speed data services (upto 9.6 Kb/s).

• Compatibility with ISDN.

• Support of Short Message Service (SMS).

Evolution Of GSM 2nd Generation

GSM -9.6 Kbps (data rate)

2.5 Generation ( Future of GSM)

HSPSD (High Speed packet Switched data)

Data rate : 76.8 Kbps (9.6 x 8 kbps)

GPRS (General Packet Radio service)

Data rate: 14.4 - 115.2 Kbps

EDGE (Enhanced data rate for GSM Evolution)

Data rate: 547.2 Kbps (max)

3 Generation

WCDMA(Wide band CDMA)

Data rate : 0.348 – 2.0 Mbps

5. ADVANCED TECHNIQUES FOR 3G AND 4G SYSTEMS

25

Why MIMO ?

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Frequency and time processing

are limited!

Space processing is

interesting because it does not

increase bandwidth

MIMO systems is a viable

approach to provide significant

capacity improvement

Transmit-Receive Diversity ( MIMO)

TMTR RCVR

Smart Antennas

Smart Arrays: Employ more than one antenna

element and exploit the spatial dimension in signal processing to improve some system operating parameters:

– Capacity, Quality, Coverage, and Cost.

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OFDM Basics

• Input symbols are divided into parallel streams

• Each Stream multiplied by an orthogonal carrier

• Process performed using IFFT

• Guard added to protect against ISI

frequency

28

x

+

0je

Seria

l to

Para

llel

x

x

1je

1Nje

IFFT

Add

Guard

guard

X1

XN -1

X1 XN -1

xn

xn

1

N k 0

N 1

Xnej

2 kn

N

52 Orthogonal carriers (48 Data + 4 Pilots)

Each carrier is narrow band

Easier to equalize against fading channels

802.11a Example

OFDM, OFDMA & SOFDMA

OFDMA

• Orthogonal Frequency Division Multiple Access

• Each user has a subset of subcarriers for a few slots

• OFDM systems use TDMA

• OFDMA allows Time+Freq DMA ⇒ 2D Scheduling

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6. 3G Systems

30

WiMAX • Features: High data rate

Over large distance: few kilometers

For large number of users: stationary, mobile

Alternative to DSL or T1 lines

• Big brother of WiFi

WLAN

WLAN

Hot Spots

Homes

DSL Service

Suburban

home

To business

WiMax Tower

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WiMAX Service

Model

WiMAX Service Models

32

Switch &

Data Base

WiMAX Mobile WiMAX Fixed

Evolution of 2G Cellular Systems to 2.5G, 3G & 4G

CDMA

(IS-95A) GSM

CDMA

(IS-95B)

cdma

2000

1xEV-DO

Rev 0/A/B

UMB

2G

2.5G

3G

3.5G

3.9G

(4G)

GPRS

E-GPRS

EDGE

HSDPA

FDD/TDD

TDMA

IS-136

WCDMA

FDD/TDD TD-SCDMA

LCR-TDD

HSUPA

FDD/TDD

HSPA+

LTE

IEEE

802.16

Fixed WiMAX

802.16d

Mobile WiMAX

802.16e

WiBRO

IEEE

802.11

802.11g

802.11a

802.11g

802.11n

CDMA GSM/UMTS IEEE Cellular IEEE LAN

33

3G Mobile Communication Standards

(CDMA Based)

• IMT-2000 in 1996

• Japan: WCDMA became central technology

in 1997.

• Europe:WCDMA (UMTS) (FDD model) and

TD-CDMA (TDD).

• America: CDMA-2000 Phase II

• China: TD-SCDMA(1998)

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35

UMTS: Modulation & Data Rates

• Quadrature Phase Shift Keying is used in UMTS as the modulation technique.

• It Provides different data rates like:

–144 kbits/s satellite and rural outdoor

– 384 kbits/s urban outdoor

– 2048 kbits/s indoor and low range outdoor

• USES OVSF Codes for multirate multimedia transmission

Optional Features of 3G PHY

• Optional Turbo Coding – Considerable performance improvement at the expense of

latency and complexity

• Space Time Codes (MIMO) – Achieving antenna diversity through multiple transmit and

receive antennas

• Adaptive Antenna Systems – Directing beams towards one or more user

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7. 4G SYSTEMS

37

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OFDMA technology is the cost-effective, next generation broadband solution

with Public Safety features and in-building coverage

3GPP Long Term Evolution systems

• 3GPP LTE systems will provide higher data rate services with better QoS than the current 3G systems.

• This requires reliable and high-rate communications over time-dispersive (frequency-selective) channels with limited spectrum and inter-symbol interference (ISI) caused by multi-path fading.

• OFDMA was chosen as the downlink air interface of 3GPP LTE systems due to its several advantages:

• high spectral efficiency, • simple receiver resign, • and robustness in a multi-path environment.

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LTE

WiMAX mobile, IEEE 802.16e

• Adds mobility to WiMAX

• Mobility Support features: Based on Scalable OFDMA (SOFDMA)

128, 512, 1024 or 2048 subcarriers (instead of 256)

Uplink open and closed loop power control

Support for hard and soft handoff

Support for sleep mode

Better support for MIMO and adaptive antenna systems using more mid-ambles

40