can anyone help me model my channel to follow a Rayleigh channel so that my BER curve will be a linear one not exponential

%Transmitting End of MISO system

clear

%close all

clc

%% System Parameters

M = 8 ;% modulation order

N = 5e4;%number of message samples

nTx = 2; % number of transmitting antennas

nRx = 1;

noise_power_db = -30;

SNR_dB = -20:5:15; %result oriented

SNR_ln = 10.^(SNR_dB./10);%code oriented

phase_shift = 0;

bit_errors = zeros(1,length(SNR_dB));

%% Transmitter

message = randi([0 M-1],nTx,N);

bits = de2bi(message,log2(M)); %Converting the message to bits

x = pskmod(message,M,phase_shift); % modulating the message (PSK)

%x = qammod(message,M);

x_hat = zeros(nTx,N);

constellation = pskmod(0:M-1,M,phase_shift);

%constellation = qammod(0:M-1,M);

scatterplot(constellation);

combinations = nchoosek(repmat(constellation,1,nTx),nTx);

combined_symbols = unique(combinations,'rows').';

%% building the Channnel // The channel(random variable) follows a Raleigh distribution

for kk = 1:length(SNR_dB)

for ii = 1:N

H = (randn(nRx,nTx)+1i*randn(nRx,nTx))/sqrt(2);

% Receiving End of MISO System

% Noise will surely be experienced at te receiving end

Es = mean2(abs(combined_symbols).^2);

sigma = (Es*nRx)./(log2(M)*SNR_ln(kk));

n = sqrt (sigma/2).*(randn(nRx,1)+ 1i*randn(nRx,1));

% Received Output

y = H*x(:,ii) + n;

%% Receiver

distances = [];

for tt = 1:length(combined_symbols)

ref = H*combined_symbols(:,tt);

distances(:,tt) = norm(y - ref); % Compute Euclidean distance

end

[x_value,x_index] = sort(distances);

detected_symbols = combined_symbols(:,x_index(1));

x_hat(:,ii) = detected_symbols;

end

% Calculate bit error rate (BER)

predicted_message = pskdemod(x_hat,M,phase_shift);

%predicted_message = qamdemod(x_hat,M);

predicted_bits = de2bi(predicted_message,log2(M));

bit_errors(kk) = mean2(predicted_bits ~= bits);

end

%Plot BER curves

figure(2);

hold on;

plot(SNR_dB, bit_errors,'-bh',LineWidth=1.5);

set(gca, 'YScale', 'log');

xlabel('SNR(dB)');

ylabel('Bit Error Rate (BER)');

title('BER Curve for MISO System');

grid on;