Multiple access techniques
for
spread spectrum systems
by
Bogdan Cristea
(final year student in Military Technical Academy,
Bucharest, Romania)
Tutor: Daniel
Roviras
training period report, Toulouse, France
March – June 2001
Contents
Introduction  1 


I Comparison between multiple
access techniques 

I.1 Direct sequence code
division multiple access (DS CDMA)  2 
I.1.1 Binary maximal length
sequences (msequences)  2 
I.1.2 Gold sequences (Gold
codes)  6 
I.1.3 Elementary
model of a DS CDMA system  8 
I.2 Chaotic
CDMA  9 
I.2.1 Chaotic
generator based on logistic map  9 
I.2.2 Chaotic
generator based on Bernoulli map  13 
I.3
Random permutations as a multiple access technique  17 
I.3.1
Permutations for multiple access  18 
I.3.2 Chip interleaving for
multiple access  19 
I.3.3
Permutations followed by DS spreading  20 
I.4 Numerical
results  21 
I.4.1 Comparison between Gold
codes  21 
I.4.2 Comparison between chaotic
sequences  23 
I.4.3 Comparison between Gold
codes and chaotic signals  24 
I.4.4 Comparison between multiple
access techniques with permutations  25 
I.4.5 Comparison between Gold
codes and permutations  28 
I.4.6 Comparison between Gold
codes, chaotic signals and permutations  28 
References  30 


II Synchronisation
issues  31 
II.1 Baseband delay lock loop for
code tracking in DS CDMA systems  31 
II.1.1 Baseband delay lock loop
model  31 
II.1.2 Numerical
results  36 
II.2 Baseband delay lock loop for DS CDMA systems
with periodic chaotic
sequences  42 
II.2.1 Baseband delay lock loop
for chaos based DS CDMA systems  42 
II.2.2 Numerical
results  44 
II.3 Baseband DLL for code tracking in a multiple
access SS system with random
permutations  50 
II.3.1 Baseband DLL
model  50 
II.3.2 Numerical
results  53 
References  57 


Conclusions  58 

