Table Of ContentCODE DIVISION MULTIPLE ACCESS COMMUNICATIONS
CODE DIVISION
MULTIPLE ACCESS
COMMUNICATIONS
Edited by
SAVO G. GLISIC
and
PEN1TI A. LEPPANEN
University of Oulo,
Oulo, Finland
SPRINGER SCIENCE+BUSINESS MEDIA, B.V.
A C.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN 978-1-4613-5948-7 ISBN 978-1-4615-2251-5 (eBook)
DOI 10.1007/978-1-4615-2251-5
Printed an acid-free paper
AU Rights Reserved
@ 1995 Springer Science+Business Media Dordrecht
Origina11y published by Kluwer Academic Publishers in 1995
Softcover reprint ofthe hardcover Ist edition 1995
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical,
including photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
Thlrd Prlntlng 1999.
TABLE OF CONTENTS
Preface vii
Shift-Register Sequences and Spread-Spectrum Communications
S.w. Golomb ix
CHAPTER 1: Introduction
The Evolution of Spread-Spectrum Multiple-Access Communications
R.A. Scholtz 3
CHAPTER 2: Information Theory & Spread Spectrum
Towards an Information Theory of Spread-Spectrum Systems
J.L. Massey 29
Performance Limits of Error Correcting Coding in Multi-Cellular CDMA
Systems with and without Interference Cancellation
A.J. Viterbi 47
Optimum PN Sequences for CDMA Systems
D. V. Sarwate 53
Block Demodulation - An Overview
E. Biglieri, E. Bogani and M. Visintin 79
CHAPTER 3: Interference Suppression
Adaptive Multiuser Detection
S. Verda 97
Spatial and Temporal Filtering for Co-Channel Interference in CDMA
R. Kohno 117
Interference Suppression for CDMA Overlays of Narrowband Waveforms
L.B. Milstein and J. Wang 147
vi
OS/COMA Successive Interference Cancellation
J.M. Holtzman 161
CHAPTER 4: Performance Analysis
Rake Reception .for a COMA Mobile Communication System with
Miltipatb Fading
D.L. Noneaker and M.B. Pursley 183
Frequency Hopped Systems for PCS
D.E. Borth, P.D. Rasky, G.M. Chiasson and J.F. Kepler 203
Code Synchronization: A Review of Principles and Techniques
A. Polydoros and S. Glisic 225
CHAPTER 5: CDMA AppUcadons
Design Aspects of a COMA Cellular Radio Network
W. C. Y. Lee 269
Consumer Communications Based on Spread Spectrum Techniques
M. Nakagawa 283
Optimal Policies for Multi-Media Integration in COMA Networks
E. Geraniotis, Y.-w. Chang and W.-B. Yang 299
COMA for Mobile LEO Satellite Communications
R.L Pickholtz and B.R. Vo}cic 331
Standardization in a Wireless Environment
D.L. Schilling, J. Taylor and J. Garodnick 351
Index 359
PREFACE
Code division multiple access has become a main candidate for the next
generation of mobile land and satellite communication systems. Although
spread spectrum technique has been used for military applications for a half
of the century only recently it has been recognised that this technique
combined with some additional steps can provide higher capacity and better
flexibility for the mobile cellular radio communications. In these systems N
users use the same frequency band and assuming that all signals are of the
same power S, the bit energy per equivalent noise density become Yb =
Eb/Ne = STb/[S(N-l)lRc1 :: GIN where G = RclRb is the system
processing gain (ratio of the sequence chip rate and bit rate).In other words
the system capacity (the maximum number of users that can operate in the
same frequency band for a given signal to noise ratio Yb needed for a given
quality of communications ) is proportional to the system processing gain
and inversely proportional to Yb i.e. N == G/Yb.The first step to increase the
system capacity was to use powerful FEC that will decrease Yb needed for a
given probability of error. Shannon's limit suggests that theoretically in
limiting case if coding is powerful enough Yb might be even less than one
which makes N > G and automatically capacity of the CDMA becomes
larger than capacity of TDMA even at this stage.
In practice utilisation of convolution coding (e.g.constraint length K=7 and
rate R=1I3) would bring this parameter to N:: O.5G. If voice activity
monitoring is used the average level of interference will be reduced for a
factor a=3/8 so that we have Yb == 01 aN and the system capacity will
become now N = 01 aYb > O. Further improvements are due to cell
sectorization (factor 3) and frequency reuse (factor 7) so that the capacity of
CDMA in cellular network becomes considerably higher than the capacity
of any other multiple access technique.
Based on these results several systems have been already developed and
some standardisation documents ( IS-95 and a number of proposals for the
common air interface in 2GHz region) are in the final stage of preparation.
Having in mind the importance of this techniques and being in charge of
organising The Third IEEE International Symposium on Spread Spectrum
Techniques and Applications - IEEE ISSSTA'94 the editors of this book
have invited the most distinguished world scientist in the field to present
review type papers on some selected topics in spread spectrum. These
papers are collected in this book.
As an introduction, evolution of code division multiple access technique is
summarised by R. Scholtz.
In chapter 2 information theory aspects of spread spectrum are discussed by
J.Massey from the fundamental viewpoint of Shannon's information theory.
Performance limits of "error preventin~" or "error protecting" methods in
vii
viii
multi cellular COMA systems with and without interference cancellation is
discussed by A. Viterbi. A considearable work done by many researchers in
the past in the field of PN sequences for COMA systems is summarised by
O.Sarwate. The approach is based on the fact that most known methods for
the design of codes in frequency hopping and direct sequence spread
spectrum systems generate sequences that can be viewed as codewords
selected from low rate Reed Solomon codes. An overview of block
demodulation techniques is presented by E. Biglieri et a1.
Chapter 3 deals with interference suppression. Work in the field of adaptive
multiuser detection is summarised by S. Verdu. Since 1986 a considerable
number of the papers has been published in this field demonstrating a huge
improvement of the optimum performance compared with the performance
of the conventional single user detector which neglects the presence of
multiaccess interference. Spatial and temporal filtering of co-channel
interference in COMA network is presented by R.Kohno. Interference
suppression for COMA overlays of narrowband waveforms is presented by
L.Milstein et. aI. Using this concept a standard communication network with
narrowband users and COMA network can coexist in the same frequency
band. Such a system has been already built and field tested. Successive
interference cancellation that is assumed to reduce hardware complexity is
summarised by J.Holtzman.
Chapter 4 deals with performance analysis. Rake reception for COMA
mobile communication system with multipath fading is discussed by
M.Pursley and O. Honeaker. Frequency hopped systems for PCS are
discussed by O. Borth et al and code synchronisation by A. Polydoros and S.
Glisic.
The most of the work is concentrated in chapter 5 dealing with different
applications of COMA. Oesign aspects of a COMA cellular radio network
are presented by W.Lee. Consumer communications based on spread
spectrum techniques are summarised by M. Nakagawa. These applications
include power line communications, data carrier, radio remote control ISM
wireless LAN, vehicle to vehicle communications, digital TV broadcasting
and different devices and systems. Application of COMA in satellite
communications is discussed in two papers. E.Geraniotis et al discuss
optimal polices for multimedia integration in COMA networks and
R.Pickholtz et al discuss COMA for mobile LEO satellite communications.
Nowadays a number of projects are carried out in this field example being
Globalstar, Odyssey, Constellation. Ellypso, Archimedes, etc. Finally
progress in standardisation for wireless communications is presented by O.
Schilling. The main message from this work is that multiple standards
including TDMA and COMA should be expected and already are a reality.
We believe that material presented in this book summarises the main
problems in modern COMA theory and practice and represents a solid
starting point for studying this complex and still challenging field.
Editors
Like any other technical field, Spread Spectrum (or code Division
Multiple Access) has its own pioneers. One of them is Solomon Golomb.
We are glad to have his contribution within this book too.
Editors
smFT· REGISTER SEQUENCES AND
SPREAD·SPECTRUM
COMMUNICATIONS
Solomon W. Golomb
Forty years ago, when I began to study shift register sequences, digital
technology was in its infancy. The most advanced electronic computers still
used vacuum tubes. The integrated circuit was not even on the horizon. In
that environment, a two-tap linear shift register of length n, producing a
randomlooking binary bit stream of period 2n -I was an incredible device.
With only twenty active delayline positions, and only two of these positions
~ccessible, using no logical circuitry except a single "half adder", a binary
sequence with a period of more than one million bits could be generated!
The first problem I addressed was how to predict the periodicity of a linear
shift register from the feedback tap connections. I quickly discovered the
equivalence of this question with the primitivity of the roots of the
corresponding polynomials over the field of two elements. Gradually I
learned of the long mathematical history of this problem, in which
connection the names of L. Euler (ca. 1760), E. Lucas (ca. 1875), and 0.
Ore (ca. 1933) deserve special mention.
I also noticed that these "maximum-length linear shift register sequences",
named m-sequences by Neal Zieder, had several properties suggestive of
randomness. Three of these, which I designated "R-I It, "R-2", and "R-3",
were the following:
ix
S.G. Glisic and P.A. Leppiinen (eds.), Code Division Multiple Access Communications, ix-xii.
i\) 1995 Kluwer Academic Publishers.
x
R-l. In a binary sequence of period 2n-1, there are 2n-l ones and 2n-1
-1 zeroes. [The "balance property.]
R-2. In each period (of length 2n-l), there are 2n-2 runs of ones
alternating with 2n-2 runs of zeroes. Half the runs of each kind have
length 1, one-fourth of the runs of each type have length 2, and in
general -} of the runs of each type (i.e. 2n-k-2 runs of each type) have
length Ie, for 1 So k .s.. n-2. In addition, there is a single run of n - 1
zeroes, and a single run of n ones. [The "run property. "]
R-3. Compared with every non-identical cyclic shift of itself, the
sequence has 2n-Ll "agreements" and 2n-1 "disagreements." If we
regard the sequence as consisting of +l's and -l's (instead of O's and
I's), then its normalized autocorrelation function C(t) satisfies C(t) =
1 when t is a multiple of the period p = 2n-l, and C(t) = -lip for all
other values of t. [The "two-level correlation property. "]
These "randomness properties" made the m-sequences particularly useful in
many applications which have subsequently been referred to as "spread
spectrum", and more specifically "direct sequence spread spectrum." In the
last few years, in the context of digital cellular communications, these
sequences now form the basis of code diuision mUltiple access (CDMA)
technology .
There are several other properties of m-sequences which are worth noting.
One of these is:
The cycle-and-add property: '1f an m-sequence is added, term-by-term
modulo 2, to any non-identical cyclic shift of itself, the result is another
cyclic shift." This property actually characterizes the m-sequences. It can be
restated as follows: "The 2n-1 cyclic shifts of an m-sequence of period p =
2n-l, together with the sequence of 2n-l zeroes, regarded as a set of 2n
vectors of leneth 2n-l over the field GF(2) of two elements, form a subspace
of the space of all 2P binary vectors of length p = 2n-l." [The subspaoe
property.]
The "two-level correlation property", R-3, follows immediately from the
"cycle-and-add property" of m-sequences. However, the binary seqUences of
period p (not necessarily of the form p =2n-l) with two-level autocorrelation
(~ agreements and ~ disagreements with all non-identical cyclic shifts)
are a larger class, and correspond to the combinatorial objects called "cyclic
Hadamard difference sets." All known examples of cyclic Hadamard
difference sets have p 53 (mod 4) where either i) p = 2n-l, n > 1, ii) p=4t-l
is a prime, t ~ 1; or iii) p =r (r + 2) where rand r + 2 are both primes (the
twin-prime examples). Over thirty years ago, with little direct evidence, I
conjectured that all cyclic Hadamard difference sets must have periods of
one of these three types. The experimental evidence for this is now quite
xi
impressive, though there is still little theoretical basis for this conjecture.
Even in the case of cyclic Hadamard difference sets with period p = 2n-l,
which includes all the m-sequences, we do not yet know all of the
inequivalent constructions which yield examples. Several member of my
group (H.-Y. Song; D. Rutan; etc.) at USC, as well as my long-time
colleague Lloyd Welch, are actively investigating these unresolved
questions concerning the existence of two-level-correlation sequences.
The "run property", R.-2, follows easily from the fact that in an m-sequence
of period p = 2n-l, all possible subsequences of lellgth n, except for n
consecutive zeroes, occur within each period, each exactly once [the "span-
n" property]. There are only ; (2n-l)/n =2n/n different m-sequences of
2/1-1
period p =2 n-l, but there are 2 -n different span-n sequences with this
period, all obtainable from nonlinear shift registers of length n. (These differ
from the "de Bruijn sequences" of span n simply by omitting a single zero
from the unique run of n zeroes in the de Bruijn sequence.)
In their book Cipher Systems, H. Beker and F. Piper introduce the term G-
randomness for sequences with all three properties R-l, R-2, and R-3. It was
shown by U. Cheng that G-randomness is insufficient to characterize m-
sequences. (In particular, there is a sequence of period p =1 27 which has G-
randomness but is not an m-sequence.) However, the "span-n" property is
more restrictive than the "run property" R-2, and I have long conjectured
that the span-n property (modified de Bruijn sequences) together with R-3
(the two-level correlation property) can be satisfied only by m-sequences.
This conjecture has now been verified for n .s. 9 (period p S 29 -1 = 511), but
no proof is yet in sight.
Shift register sequences have becn used in both pulse and CW radar systems
for several decades. The first attempt at radar contact with another planet,
Venus, conducted by Lincoln Laboratories in the late 1950's, used pulse
radar modulated by an m-sequence of period 213_1 = 8191. The JPL
interplanetary ranging system, developed in 1959 - 60, used a CW signal
with binary phase modulation specified by a long sequence obtained as a
Boolean combination of several short-period shift register sequences.
Incidentally, it was at JPL that we had the first successful radar contact with
Venus, on March, 10, 1961.
Much of the early impetus for the use of "direct sequence spread spectrum"
was to make military communications relatively resistant to jamming. Using
only m-sequences for this purpose assumes a very unsophisticated jammer.
The "cycle-and-add" property enables the jammer, without even
"deciphering" the sequence, to generate a forward time-shift of the intended
modulating sequence, which might be used successfully to fool the receiver.
A trivial exercise in linear algebra over GF(2), "rediscovered" in numerous
algebraic coding/decoding contexts, enables one to determine the span and
the recursion of any linear sequence from a small number of its terms. To
achieve more jam resistance, or any degree of resistance to deciphering, it is
