Training period report

 






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 (m-sequences)

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





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