error for bit error rate

Good morning, I've realized this OFDM system, utilizing a function called "canale" that representes a multipath channel. The problem is that for each input and for each type of noise the ber was around a value of 0.5. Where is the mistake?! I can't see it!! Please help me

      %parametri per poter calcolare le diverse funzioni.
      s=300; %riflessioni sulla superficie
      b=1000; %riflessioni sul fondale
      R=1000; %distanza diretta tra rx e tx espressa in metri
      d1=4; %distanza del tx dalla superficie
      d2=7; %distanza del rx dalla superficie
      h=16; %altezza del fondale
      M = 4;                          %   QPSK signal constellation
      bittrasm = 1000;        %   have 64 data points
      block_size = 8;                 %   size of each ofdm block
      cp_len = ceil(0.1*block_size);  %   length of cyclic prefix
      no_of_ifft_points = block_size;           %   8 points for the FFT/IFFT
      no_of_fft_points = block_size;
      EbNo        = 0:5:40;
      sub_car=8;
      w=15; %velocità del vento espressa in metri/s
      f=1000; %frequenza portante espressa in herz
      >> 
      >> EsNo= EbNo + 10*log10(sub_car/no_of_fft_points)+ 10*log10(no_of_fft_points/80); % symbol to noise ratio

      snr= EsNo - 10*log10(no_of_fft_points/80); % snr as to be used by awgn fn.

      %   ---------------------------------------------
      %   B:  %   +++++   TRANSMITTER    +++++
      %   ---------------------------------------------
      %   1.  Generate 1 x 64 vector of random data points
      data_source =ones(1,1000)*2;
      figure(1)
      stem(data_source); grid on; xlabel('Data Points'); ylabel('Amplitude')
      title('Transmitted Data "O"')

      %   2.  Perform QPSK modulation
      qpsk_modulated_data = pskmod(data_source, M);
      scatterplot(qpsk_modulated_data);title('MODULATED TRANSMITTED DATA');

      %   3.  Do IFFT on each block
      %   Make the serial stream a matrix where each column represents a pre-OFDM
      %   block (w/o cyclic prefixing)
      %   First: Find out the number of colums that will exist after reshaping
      num_cols=length(qpsk_modulated_data)/block_size;
      data_matrix = reshape(qpsk_modulated_data, block_size, num_cols);

      %   Second: Create empty matix to put the IFFT'd data
      cp_start = block_size-cp_len;
      cp_end = block_size;

      %   Third: Operate columnwise & do CP
      for i=1:num_cols,
          ifft_data_matrix(:,i) = ifft((data_matrix(:,i)),no_of_ifft_points);
          %   Compute and append Cyclic Prefix
          for j=1:cp_len,
             actual_cp(j,i) = ifft_data_matrix(j+cp_start,i);
          end
          %   Append the CP to the existing block to create the actual OFDM block
          ifft_data(:,i) = vertcat(actual_cp(:,i),ifft_data_matrix(:,i));
      end

      %   4.  Convert to serial stream for transmission
      [rows_ifft_data cols_ifft_data]=size(ifft_data);
      len_ofdm_data = rows_ifft_data*cols_ifft_data;

      %   Actual OFDM signal to be transmitted
      ofdm_signal = reshape(ifft_data, 1, len_ofdm_data);
      figure(3)
      plot(real(ofdm_signal)); xlabel('Time'); ylabel('Amplitude');
      title('OFDM Signal');grid on;
      h=canale(s,b,R,d1,d2,h,bittrasm,w);
      after_channel=conv(ofdm_signal,h,'same');
      for ii=1:length(snr)
      recvd_signal =awgn(after_channel,snr(ii),'measured'); % awgn addition
      recvd_signal_matrix = reshape(recvd_signal,rows_ifft_data, cols_ifft_data);
      recvd_signal_matrix(1:cp_len,:)=[];
      for i=1:cols_ifft_data,
          %   FFT
          fft_data_matrix(:,i) = fft(recvd_signal_matrix(:,i),no_of_fft_points);
      end
      recvd_serial_data = reshape(fft_data_matrix, 1,(block_size*num_cols));
      qpsk_demodulated_data = pskdemod(recvd_serial_data,M);
      [no_of_error(ii),ratio(ii)]=biterr(data_source,qpsk_demodulated_data) ; % error rate calculation
      end
      semilogy(EbNo,ratio,'--or','linewidth',2);
      hold on;
      EbN0Lin = 10.^(EbNo/10);
      grid on

      xlabel('EbNo');
      ylabel('BER')
      title('Bit error probability curve for BPSK using OFDM');

also the function "canale":

    function [y] = canale(s,b,R,d1,d2,h,bittrasm,w)

tb=1/bittrasm; % tempo di bit

ts=tb/10; %consideriamo come tempo di campionamento un decimo del tempo di bit

ncampioni=tb/ts;
D00=sqrt(R^2-(d1-d2)^2);%distanza diretta
Dsb=sqrt(R^2+2*b*h+d1-d2*(-1)^(s-b));
Dbs=sqrt(R^2+2*b*h-d1+d2*(-1)^(b-s));
beta = 1; %valore fittizio
LaD00=10^-((D00/1000)*beta)/20; %perdite per assorbimento
LaDbs=10^-((Dbs/1000)*beta)/20;
LaDsb=10^-((Dsb/1000)*beta)/20;
sigma=sqrt(w*0.32*10^(-5));
teta=45; %angolo di incdenza sulla superficie
lambda=5; % lunghezza d'onda
k=2*3.14/lambda;
ro=2*k*sigma*sin(teta);
Lsr=exp(-ro^2);
tetabs=atan(R/(2*b*h-d1*d2*(-1)^(b-s)));
tetasb=atan(R/(2*b*h+d1*d2*(-1)^(s-b)));
r1=10; % densità del fondale
c1=23; %velocità dell'onda riflessa sul fondale
r=12; %densità del liquido
c=1500; % velocità del suono è di circa 1500 m/s
m=r1/r;
n=c/c1;
Lbrsb=abs([m*cos(tetasb)-sqrt(n^2-(sin(tetasb))^2)]/[m*cos(tetasb)+sqrt(n^2-(sin(tetasb))^2)]);
Lbrbs=abs([m*cos(tetabs)-sqrt(n^2-(sin(tetabs))^2)]/[m*cos(tetabs)+sqrt(n^2-(sin(tetabs))^2)]);
tausb=(Dsb-D00)/c;
taubs=(Dbs-D00)/c;

tausb1=ceil(tausb*1000);% poichè ogni posizione della risposta è espresso in millisecondi, trasformo il ritardo in millisecondi e mi sposto di tot posizioni intere

taubs1=ceil(taubs*1000); %stesso discorso di tausb

y=zeros(1,2*ncampioni); % poichè prendo come tempo di simulazione 2*tb, la mia risposta avrà 2*ncamp posizioni

y1=LaD00/D00;
y2=0;
y3=0;

% per simulare l'infinito ho inserito 100 somme, valore fittizio 
for s=1:100
  for b=s-1:s
    y2=y2+(LaDsb*(Lsr^s)*(Lbrsb^b))/Dsb;
  end
end

for b=1:100
  for s=b-1:b
    y3=y3+(LaDbs*(Lsr^s)*(Lbrbs^b))/Dbs;
  end
end

%riempio le posizioni relative al cammino diretto

for t=1:ncampioni
y(t)=y1;
end

% riempio le posizioni in ritardo di tausb

for t=ncampioni+1:length(y)-tausb1
y(t+tausb1)=y2;
end

% riempio le posizioni in ritardo di tausb

for t=ncampioni+1:length(y)-taubs1
y(t+taubs1)=y(t+taubs1)+y3;
end

end