Matlab中用于WBAN的BER计算中的路径损耗因子

Question

Can anyone please guide me how to include path loss value in BER calculation for wireless body area networks in Matlab? I am using qpsk modulation and Rayleigh channel.

If I simply multiply the channel with path loss value as:

y=x*(h*PL)+n

the result is that most of the values become zero.

Code (see calculation of rx, rx1, and rx2):

format long; bit_count = 1000000;

Eb_No = 0: 1: 30;

SNR = Eb_No + 10*log10(2);

for aa = 1: 1: length(SNR)

   T_Errors = 0;

   T_bits = 0;

   T_Errors1=0;

   T_Errors2=0;  

   while T_Errors < 10 && T_Errors1 < 10 && T_Errors2 < 10

      uncoded_bits  = round(rand(1,bit_count));

      B1 = uncoded_bits(1:2:end);

      B2 = uncoded_bits(2:2:end);

      qpsk_sig = ((B1==0).*(B2==0)*(exp(i*pi/4))+(B1==0).*(B2==1)...
      *(exp(3*i*pi/4))+(B1==1).*(B2==1)*(exp(5*i*pi/4))...
      +(B1==1).*(B2==0)*(exp(7*i*pi/4)));        

      h = sqrt(0.5*((randn(3,length(qpsk_sig))).^2+(randn(3,length(qpsk_sig))).^2));

      d1=50;

      PL1=43.22;

      PL2=67.77;

      PL3=69.8; 

      n=0.6^(SNR(aa)/0.6); 

      n1=0.7^(SNR(aa)/0.7); 

      n2=1/10^(SNR(aa)/10);  

      rx = (qpsk_sig.*h(1,:)*PL1)+ sqrt(n/2)*(randn(1,length(qpsk_sig))+i*randn(1,length(qpsk_sig)));  % Source to  Relay

      rx_re = real(rx);
      rx_im = imag(rx);      
      rxHat(find(rx_re < 0 & rx_im < 0)) = -1 + -1*j;

      rxHat(find(rx_re >= 0 & rx_im > 0)) = 1 + 1*j;

      rxHat(find(rx_re < 0 & rx_im >= 0)) = -1 + 1*j;

      rxHat(find(rx_re >= 0 & rx_im < 0)) = 1 - 1*j;
      rx1 = (rxHat.*h(2,:)*PL2) + sqrt(n1/2)*(randn(1,length(qpsk_sig))+i*randn(1,length(qpsk_sig)));  %Relay to Destination

      rx2=(qpsk_sig.*h(3,:)*PL3) + sqrt(n2/2)*randn(1,length(qpsk_sig))+i*randn(1,length(qpsk_sig)));  % Source to Destination

      %---------------------------------------------------------------

      rx = rx./h(1,:);

      rx1 = rx1./h(2,:);

      rx2 = rx2./h(3,:);

      B4 = (real(rx)<0);

      B3 = (imag(rx)<0);

      uncoded_bits_rx = zeros(1,2*length(rx));

      uncoded_bits_rx(1:2:end) = B3;

      uncoded_bits_rx(2:2:end) = B4;

      % Calculate Bit Errors

      diff = uncoded_bits - uncoded_bits_rx;

      T_Errors = T_Errors + sum(abs(diff));

      T_bits = T_bits + length(uncoded_bits);


      B8 = (real(rx1)<0);

      B7 = (imag(rx1)<0);

      uncoded_bits_rx1 = zeros(1,2*length(rx1));

      uncoded_bits_rx1(1:2:end) = B7;

      uncoded_bits_rx1(2:2:end) = B8;


      % Calculate Bit Errors
      diff1 = uncoded_bits - uncoded_bits_rx1;
      T_Errors1 = T_Errors1 + sum(abs(diff1));
      T_bits = T_bits + length(uncoded_bits);

      B6 = (real(rx2)<0);
      B5 = (imag(rx2)<0);

      uncoded_bits_rx2 = zeros(1,2*length(rx2));
      uncoded_bits_rx2(1:2:end) = B5;
      uncoded_bits_rx2(2:2:end) = B6;


      % Calculate Bit Errors
      diff2 = uncoded_bits - uncoded_bits_rx2;
      T_Errors2 = T_Errors2 + sum(abs(diff2));
      T_bits = T_bits + length(uncoded_bits);

   end

   % Calculate Bit Error Rate
   BER(aa) = T_Errors / T_bits;
   BER1(aa) = T_Errors1 / T_bits; 
   BER2(aa) = T_Errors2 / T_bits;
end

%------------------------------------------------------------ figure(1); semilogy(SNR,BER1,'bs-','LineWidth',2');

hold on;

xlabel('SNR');

ylabel('BER');

grid on;

figure(1);

semilogy(SNR,BER2,'*r');

hold on;

xlabel('SNR');

ylabel('BER');

grid on;

legend('Relay','Direct');

axis([0 30 10^-10 0.1])

Please help. Thanks You

Answer 1

I think the zeros are acceptable, since the source->relay->destination path has 0 bit errors on occasion, whereas the direct path has > 0. When plotting in log scale, this results in the data points showing up at -Inf (off the plot).

Edit : I modified your code slightly to plot higher SNRs (see updated graph). Also, I think the original usage of pathloss was incorrect. I presume the given pathloss constants were in dB. Those need to be converted to linear scale prior to applying them (multiplying) against the transmitted signal. Also, the pathloss values should be negative dB. The original code was essentially giving the signal a gain rather than a loss. Here's the modified code:

format long; 

bit_count = 1000000;

Eb_No = 20: 1: 100;

SNR = Eb_No + 10*log10(2);  % not sure about the 10*log10 part, ??
BER = zeros(size(SNR));
BER1 = zeros(size(SNR));
BER2 = zeros(size(SNR));
for aa = 1: 1: length(SNR)

   T_Errors = 0;

   T_bits = 0;

   T_Errors1=0;

   T_Errors2=0;  

   while T_Errors < 10 && T_Errors1 < 10 && T_Errors2 < 10

      uncoded_bits  = round(rand(1,bit_count));

      B1 = uncoded_bits(1:2:end);

      B2 = uncoded_bits(2:2:end);

      qpsk_sig = ((B1==0).*(B2==0)*(exp(1i*pi/4))+(B1==0).*(B2==1)...
      *(exp(3*1i*pi/4))+(B1==1).*(B2==1)*(exp(5*1i*pi/4))...
      +(B1==1).*(B2==0)*(exp(7*1i*pi/4)));        

      h = sqrt(0.5*((randn(3,length(qpsk_sig))).^2+(randn(3,length(qpsk_sig))).^2));

      d1=50;

      % Path losses in dB
      PL1=-23.22;

      PL2=-27.77;

      PL3=-49.8; 

      n=0.6^(SNR(aa)/0.6); 

      n1=0.7^(SNR(aa)/0.7); 

      n2=1/10^(SNR(aa)/10);  

      % Since we are multiplying pathloss by the input, pathloss needs to
      % be linear (not dB).  If we keep P.L. in dB, then we would subtract
      % P.L. from the signal (which would also need to be in dB).
      rx = (qpsk_sig.*h(1,:)*(10^(PL1/10)))+ sqrt(n/2)*(randn(1,length(qpsk_sig))+1i*randn(1,length(qpsk_sig)));  % Source to  Relay

      rx_re = real(rx);
      rx_im = imag(rx);  

      rxHat = zeros(size(rx));

      rxHat(find(rx_re < 0 & rx_im < 0)) = exp(5*1i*pi/4); %-1 + -1*j;

      rxHat(find(rx_re >= 0 & rx_im > 0)) = exp(1i*pi/4); % 1 + 1*j;

      rxHat(find(rx_re < 0 & rx_im >= 0)) = exp(3*1i*pi/4); % -1 + 1*j;

      rxHat(find(rx_re >= 0 & rx_im < 0)) = exp(7*1i*pi/4); % 1 - 1*j;

      % Same as above, convert pathloss from dB to linear
      rx1 = (rxHat.*h(2,:)*(10^(PL2/10))) + sqrt(n1/2)*(randn(1,length(qpsk_sig))+1i*randn(1,length(qpsk_sig)));  %Relay to Destination

      rx2=(qpsk_sig.*h(3,:)*(10^(PL3/10))) + sqrt(n2/2)*(randn(1,length(qpsk_sig))+1i*randn(1,length(qpsk_sig)));  % Source to Destination

      %---------------------------------------------------------------

      rx = rx./h(1,:);

      rx1 = rx1./h(2,:);

      rx2 = rx2./h(3,:);

      B4 = (real(rx)<0);

      B3 = (imag(rx)<0);

      uncoded_bits_rx = zeros(1,2*length(rx));

      uncoded_bits_rx(1:2:end) = B3;

      uncoded_bits_rx(2:2:end) = B4;

      % Calculate Bit Errors

      diff = uncoded_bits - uncoded_bits_rx;

      T_Errors = T_Errors + sum(abs(diff));

      T_bits = T_bits + length(uncoded_bits);


      B8 = (real(rx1)<0);

      B7 = (imag(rx1)<0);

      uncoded_bits_rx1 = zeros(1,2*length(rx1));

      uncoded_bits_rx1(1:2:end) = B7;

      uncoded_bits_rx1(2:2:end) = B8;


      % Calculate Bit Errors
      diff1 = uncoded_bits - uncoded_bits_rx1;
      T_Errors1 = T_Errors1 + sum(abs(diff1));
      T_bits = T_bits + length(uncoded_bits);

      B6 = (real(rx2)<0);
      B5 = (imag(rx2)<0);

      uncoded_bits_rx2 = zeros(1,2*length(rx2));
      uncoded_bits_rx2(1:2:end) = B5;
      uncoded_bits_rx2(2:2:end) = B6;


      % Calculate Bit Errors
      diff2 = uncoded_bits - uncoded_bits_rx2;
      T_Errors2 = T_Errors2 + sum(abs(diff2));
      T_bits = T_bits + length(uncoded_bits);

   end

   % Calculate Bit Error Rate
   BER(aa) = T_Errors / T_bits;
   BER1(aa) = T_Errors1 / T_bits; 
   BER2(aa) = T_Errors2 / T_bits;
end

%------------------------------------------------------------ 

figure(1); 

subplot(2,1,1);

semilogy(SNR,BER1,'bs-','LineWidth',2');

hold on;

xlabel('SNR');

ylabel('BER');

grid on;

figure(1);

semilogy(SNR,BER2,'*r');

hold on;

xlabel('SNR');

ylabel('BER');

grid on;

legend('Relay','Direct');

title('Bit Errors (log)')

xlim([min(SNR) max(SNR)])

subplot(2,1,2)

plot(SNR,BER1,'bs-');

hold on

plot(SNR,BER2,'*r')

hold off

title('Bit Errors (linear)')

xlabel('SNR')

ylabel('BER')

xlim([min(SNR) max(SNR)])