GSM 接收机实验

1，  实验题目：GSM接收机设计
2，  实验步奏
（1）  输入为BPSK 信号，+1, -1

（2）  包含Pilot （training  sequence)和 传输数据 (infobits)

（3）  Normal Busrt 假定不考虑Guard period

（4）train_seq = [0,0,1,0,0,1,0,1,1,1,0,0,0,0,1,0,0,0,1,0,0,1,0,1,1,1];

   




GSM接收机原理框图

3.信道部分
（1）产生一个5 径的多径信道   h=[h1 h2 h3 h4 h5]

 
（2）      产生一个高斯加性信道     W（n）~N(0,sigma^2)

                                                                                      

（3）      产生一个Rayleigh 多径信道

 Y(n)=namda(n)*A+W(n),

 W（n）~N(0,sigma^2)

namda(n)~R(1,sigma^2)

（4）GSM中的信道估计

Ax=r

(5) 基于维纳滤波器原理的均衡器设计

y=Hs

R=E[vv’]=H*H’

S’=R^(-1)*y

4.实验程序

%%%%%%%%%%%%% %%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%

% GSM Channel Estimation Using  LS estimation

%%%%%%%%%%%%% %%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%

 

clear

close all

n = 1;

 

s1=2*randint(1,58)-1;      %产生1，-1

s2=2*randint(1,58)-1;

train_seq =[0,0,1,0,0,1,0,1,1,1,0,0,0,0,1,0,0,0,1,0,0,1,0,1,1,1];

train_seq=2*train_seq-1;

%%%%%% BPSK modulation %%%%%%%%%%%%%

t_seq=[s1,train_seq,s2];

 

 

 

%%%%%% wireless multipath channel%%%%%%%%%%%%%

%%%%%% we need to estimate the wirelessmultipath channel %%%%%%%%%%%%%

x = [ 1 -0.5  1   0.5 0.3  0.2];     

 

for SNR = 30                  

   %%%%% Convoluation over wireless channel %%%%%%

   recv_seq = conv(t_seq, x);  %%multipath channel

   recv_seq = awgn(recv_seq, SNR) ;%%% Add AWGN noise %%

   

   

   b= recv_seq(64:84);      

    b =b.';

    %b is our received signal %%%%%%

   

   %%%%% LS  Equation %%%%%%%%%%

    %A*x = b   

   %%

    %A = [ train_seq(6)  train_seq(5)  train_seq(4) train_seq(3)  train_seq(2)  train_seq(1);

   %       train_seq(7)  train_seq(6) train_seq(5)  train_seq(4)  train_seq(3) train_seq(2);

   %       .....

   %       train_seq(26)  train_seq(25) train_seq(24)  train_seq(23)  train_seq(22) train_seq(21)]

   for row = 1 : 21

       for col = 1 : 6

           A(row,col) = train_seq(row+6-col);

       end

   end

   

   est_x = inv(A'*A)*A'*b;

 [x' est_x];

   

   figure(n);   

   stem([1:6], x, 'b-o'); hold on;

   stem([1:6], est_x, 'r-s');

       

   axis([0 7  -2 2]);

   xlabel('Channel taps', 'fontsize', 18)

   ylabel('Amplitude', 'fontsize', 18)   

   str = strcat('SNR=',num2str(SNR),'dB');

   title(str, 'fontsize', 18)    

   legend('True  x', 'Estmated x');

    n= n+1;

 s=zeros(142,147);               

 s=[fliplr(est_x'),zeros(1,141)];

  fori=2:142

     for j=2:147

         d=[zeros(1,i-1),fliplr(est_x'),zeros(1,142-i)];

     end

      s=[s;d];

  end

             

    Eq_out=inv(s'*s+0.01*eye(147))*s'*recv_seq(6:147)';%length(recv_seq)=147,s为142×147矩阵

   figure(2);   

   stem(Eq_out', 'b-o'); hold on;

   stem(t_seq, 'r-s');  

end

5.运行结果

信道估计参数与实际参数对比如图（1）



最小二乘估计序列与实际发送信息比特对比，如图（2）