B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

11.9 MATLAB Exercises 657
The first MATLAB program, gold3 lcode . m, assigns four Gold sequences of length 31 to the
four QPSK modulated user signals:
% MATLAB PROGRAM <gold3 1code .m>
% to generate a table of 4 Gold sequence
% with length 31 each .
GPN= [l 1 1 -1
-1 1 -1 1
-1 -1 1 1
1 1 -1 -1
-1 -1 -1 -1
1 1 1 1
1 1 -1 -1
-1 -1 -1 1
-1 1 -1 -1
1 -1 -1 1
-1 -1 1 1
1 1 -1 1
1 -1 1 -1
-1 1 1 1
1 -1 1 1
-1 1 1 -1
-1 -1 1 -1
-1 1 1 -1
1 1 1 -1
1 -1 1 1
1 -1 1 -1
1 1 -1 -1
1 1 1 1
1 1 1 -1
-1 -1 -1 -1
1 1 -1 1
1 -1 -1 -1
-1 1 -1 1
1 1 -1 -1
1 1 1 1
1 1 1 1] ;
The main MATLAB program, Exl 1_3 . m, completes the spreading of the four user signals. The
four spread CDMA signals are summed together at the receiver before detection. Each of the four users
will apply the conventional despreader (matched filter) at the receiver before making the symbol-bysymbol
decision. We provide the resulting BER of all four users in Fig. 11.25 under additive white
Gaussian noise. We also give the single-user BER in AWGN channel as a reference. All four users have
the same BER. The small degradation of the multiuser BER from the single-user BER is caused by the
nonorthogonal spreading codes.
% MATLAB PROGRAM <Exll 3.m>
% This program provides simulation for multiuser DS-CDMA signaling using
% coherent QPSK for 4 users .
%
%clear;clf
Ldata=l0000;
Lc=31;
%User number 4;
% data length in simu lation; Must be divisible by 8
% spreading factor vs data rate