From Marconi to Wireless Internet: The Wireless (R)evolution

Prof. Vijay K. Bhargava

Professor and Head,

Dept. of Electrical and Computer Engineering

The University of British Columbia

Vancouver, Canada

Email: vijayb@ece.ubc.ca

Website: http://www.ece.ubc.ca

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Presentation Outline

1. Historical Overview

2. The Three Generations

3. Beyond 3G/Wireless Internet

4. Enabling Techniques (Innovations from IT Society)

5. Malaise Afflicting the Wireless Industry

6. Possible Recovery Scenario

7. Conclusions

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4

Maxwell

Hertz

Popov

Fessenden

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6

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Signal Hill, December 12, 2001

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The Three Generations and Beyond (Overview)

First Generation : Analog Cellular

(Mainly Speech) Second Generation : Digital Cellular

(Digital Speech and messaging)

2.5G, 2.75G, … Third Generation : IMT2000

(Integrated Audio and Video)

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Beyond 3G

The true Wireless Internet

Internet connectivity anytime anywhere

Wireless and mobile extensions to the Internet

Wireless – Wireline BB Transparency

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Claude Elwood Shannon 

Father of Information Theory

Electrical engineer, mathematician, and native son of Gaylord. His creation of information theory,

the mathematical theory of communication, in the 1940s and 1950s inspired the revolutionary

advances in digital communications and information storage that

have shaped the modern world.

This statue was donated by the Information Theory Society of the Institute of

Electrical and Electronics Engineers, whose members follow gratefully in his footsteps.

Dedicated October 6, 2000 Eugene Daub, Sculptor

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Enabling Techniques (Innovations from IT Society)

Reed Solomon Codes

Viterbi Algorithm

Public Key Crytosystem

Compression Algorithm, Huffman, Lempel-Ziv, Algebraic Coding

Modem Design with Coded Modulation, Ungerböeck

Turbo Decoding approaches Shannon’s capacity limit by less than 0.5dB

Theory of CDMA and Multiuser Transmission

Space-Time Coding for Mobiles

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Cryptography

Secret Key System

Public Key System

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Digital Signature

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Source Coding for Voice and Video

Variants of Predictive Coding

For voice CELP, VCELP, RPE-LTP and other Variants

H.261 and H.263 Standards support low bit rate (30-64 kbps) Video for mobile communication

MPEG-4 (with Reed-Solomon Codes)

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Turbo Codes

Originally Turbo code encoder was built using a parallel concatenation of two (or more) relatively simple recursive systematic convolutional (RSC) codes with large interleaving

Although the component codes are weak, the output turbo codeword is very powerful due to the “Interleaver gain” which produces a random-like codeword

dk

RSC1

RSC2

Interleaver

dk

d1,k

d2,k

Turbo Code Encoder

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After miterations

Decoder1

Decoder2

rk

r1,k

r2,k

Turbo code Decoder

d

Turbo Codes (Iterative Decoding)

Soft Input/Soft Output MAP Decoder

Use “extrinsic information” produced from past decoder as á priori information

Gradually improvement of knowledge on transmitted information through iterations

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Turbo Codes

Turbo codes will be used in high data rate services in the next generation CDMA systems above 32 kbps

There are already existing standards for ½ and 1/3 coding rate turbo code for 3GPP systems

The same iterative decoding principle can be applied in various different areas

Turbo equalization

Turbo multiuser detection (for coded CDMA signals)

Turbo decoding with estimation of parameters of an unknown time-varying channel

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Multiuser Detection (MUD)

Signals from all users are considered useful instead of only interference to each other

MUD provides important performance gains over the conventional single-user receiver

Performance of single-user conventional receivers are limited in fading channel due to the near-far effect which necessitates use of strict power control

In certain cases multiuser receivers can even benefit from the diversity in powers of the received users and have better performances than in the case of equal received powers of users

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Multiuser Detection (MUD)

•In the single user approach, each detector focuses on extracting the data of a single user•Other users are considered as interference•Simple

h(t)

1st Rake Receiver

Kth Rake Receiver

Rx MultiuserDetector

b1

bK

oscillator

• •

•In the multi-user detection approach, the common detector uses available information from all users to detect each user•Complex

oscillator

Rxh(t)

1st Rake Receiver

Kth Rake Receiver

Detector

Detector

b1

bK

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Multiuser Detection (MUD)

Benefits of using multiuser detection

More efficient spectrum utilization (in some situations we can expect ten fold increase in spectrum efficiency)

Reduced precision requirement for power control

More efficient power utilization

Main difficulties in implementing multiuser detection

Existence of the other-cell multiple-access interference (MAI)

Difficulty in implementing multiuser detection on the downlink (cost, size, weight are of much larger concern for mobile terminals)

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Multiuser Detection (MUD)

Some of the MUD algorithms areMaximum Likelihood (Optimal) Decoding (complexity increases exponentially with the number of users)Linear detectors (similar to the linear equalization techniques)

decor relating detectorMMSE detector

• MMSE detector can be implemented as an adaptive filter to reduce complexity

• Blind adaptive implementation of the MMSE detectorDecision Feedback Detectors where past decisions are used to improve the current ones

Conventional Decision Feedback or Successive Interference CancellationParallel Interference CancellationOptimum Decision Feedback Receiver (has the spectral efficiency equal to the optimum detector)

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Multiuser Detection (MUD)

Implementation examples of multistage parallel interference cancellation multiuser detection:

DSP implementation [Buehrer, Woerner, 1999]VLSI implementation [Aazhang et al., 2000]

The parallel interference cancellation is prefered due to its performance complexity tradeoffHowever, MUD research is still in a phase that would not justify to make it a mandatory feature for 3G WCDMA standardsMost probably, its practical implementation and standardization is going to be defered for 4G systems

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Space-Time Codes

Capacity of a multi-antenna systems far exceeds that of single-antenna system

Multiple transmit/receive antennas provide diversity in the space domain (space diversity)

Channel coding designed for wireless communication systems with multiple transmit/receive antennas provide both space and time diversity Space-time codes

Two categories of space-time coding

1) space-time trellis codes 2) space-time block codes

Decoding of space-time codes requires channel estimation

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Space-Time Codes

Informationsource

Space-timeencoder

Receivers(k)

c1(k)

cN(k)

r1(k)

rN(k)s’(k)

Space-time coding system

0

1

2

3

4

5

6

7

00,01,02,03,04,05,06,07

50,51,52,53,54,55,56,57

20,21,22,23,24,25,26,27

70,71,72,73,74,75,76,77

40,41,42,43,44,45,46,47

10,11,12,13,14,15,16,17

60,61,62,63,64,65,66,67

30,31,32,33,34,35,36,37

Input: 0 1 5 7 6 4

Tx 1: 0 0 5 1 3 6

Tx 2: 0 1 5 7 6 4

0

12

3

4

56

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Space-time trellis codes (8-PSK) with two transmit antennas

Space-time block codes with two transmit antennas (Alamouti’s scheme)

ConstellationMapper

s(k) [c1 c2]

*12

*21

cc

cc

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Space-Time Codes

Bandwidth and power efficient – a codeword is transmitted simultaneously from different antennas with the same total transmit power

Channel information is not necessary at the transmitter

Differential scheme is available when channel information is not known at the receiver

Can be concatenated with other codes such as Reed-Solomon, TCM, turbo code

Can be applied in broadband channel – CDMA, OFDM

Adopted in standards – IS-136, W-CDMA, CDMA2000

Tested in WLAN 802.11a. Increase in link layer throughput and improving TCP performance

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The Malaise Afflicting The Communications Industry*

A convergence of five key factors

1. Greed

2. Corporate Crime

3. Misguided Regulations

4. Too Much Debt

5. A Broken Business Model

Why did we, the engineers, allow business manipulators and bureaucrats to drive the show ?

*Peter A. Bernstein, IEEE Spectrum, January 2003

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Possible Recovery Scenario

“Nothing lasts forever”

“This too shall pass”

“Survival of the fattest”!

Broadband: Alive and Well Mobile, and Loving it If Each is Good, Both are Better If You Build it, Killer Apps will Come

*Steven M.Cherry, IEEE Spectrum, January 2003

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Conclusions

We have presented a historical overview of Wireless Communication

Innovations from IT Society have been discussed

Reliable high-speed mobile Internet Access will lead to innovative product and services

“It is dangerous to put limits on Wireless Communications”

29ISBN: 1-4020-7251-1 © 2003

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31WHY ARE THESE MEN SMILING ?

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