OFDM系统各种QAM调制阶数在多径信道下的误码性能仿真（暂存版本）

clc;close all;clear

%% Seting parameters
EbN0_list = 20:2:40;
Q_order_list = 2:2:10;
loopNumber = 10000;
fprintf('Qm\t EbN0 \t \t EsN0 \t \t SNR_Cal \t \t ser \t\t ser_theory\t\t\t ber\t\t nloop \t\t \n');
for iQorder = 1 : length(Q_order_list)
for iEbN0 = 1 : length(EbN0_list)

%% Frame structure
N_Frame = 1;
N_Symbol = 1;
N_RB = 106;
N_SC_perRB = 12;
N_SC = N_RB * N_SC_perRB;
N_Ant = 1;
N_fft_order = floor(log2(N_RB * N_SC_perRB));
N_fft = 2^(N_fft_order+1);
N_cp = N_fft/8;
EbN0 = EbN0_list(iEbN0);

%% Modulation
Q_order = Q_order_list(iQorder);
Qm = 2^Q_order;
N_bit = N_Frame * N_Symbol * N_RB * N_SC_perRB * Q_order;

%% Noise Calculation
SNR =  EbN0 + 10 * log10(Q_order);

%% Loop
for iloop = 1 :loopNumber
data_bit_in = randi([0 1], 1, N_bit);
dataSymbolsIn = bi2de(reshape(data_bit_in, Q_order, N_bit/Q_order).', 'left-msb'); 
dataMod = qammod(dataSymbolsIn, Qm,'UnitAveragePower', true); 

%% Show Constellation
%scatterplotme(dataMod)

%% Resource Mapping
RE_Grid = zeros(N_RB * N_SC_perRB,N_Symbol * N_Frame);
dataMod_tmp = reshape(dataMod,N_RB * N_SC_perRB,[]); %only data
Power_Scale = 1;
RE_Grid_all = Power_Scale * dataMod_tmp;

%% IFFT add CP
frame_mod_shift = ifftshift(RE_Grid_all); 
ifft_data = ifft(frame_mod_shift,N_fft)*sqrt(N_fft); 
%ifft_data = ifft(frame_mod_shift)*sqrt(1272); 
Tx_cd = [ifft_data(N_fft-N_cp+1:end,:);ifft_data];
time_signal = reshape(Tx_cd,[],1);

%% Channel
power_RE = sum(sum(abs(RE_Grid_all).^2)) / N_RB / N_SC_perRB / N_Symbol / N_Frame;
power_tp = sum(sum(abs(ifft_data).^2)) / N_RB / N_SC_perRB / N_Symbol / N_Frame;  %IFFT zero padding averages the true RE Power
N0 = power_RE .* 10.^(-SNR / 10);
white_noise_starand = 1/sqrt(2)*(randn(size(time_signal)) + 1j * randn(size(time_signal)));
nTap = 2;
taps = RayleighChanTaps(nTap);
% taps = [0.9,0.1];
time_signal_path = Multipath_channel(time_signal,taps);
TransmittedSignal = time_signal_path + sqrt(N0) * white_noise_starand;

%% Receive and Sys
ReceivedSignal = TransmittedSignal;
hF = fftshift(fft(taps,N_fft));

%% FFT and Frame   
frame_recieved_parallel = reshape(ReceivedSignal, N_fft + N_cp, []);
frame_Received = frame_recieved_parallel(N_cp + 1:end,:);    
frame_Grid_fft = fft(frame_Received,N_fft) / sqrt(N_fft);
RE_Grid_all_fftshift = fftshift(frame_Grid_fft);
RE_Grid_all_fftshift_eq = fftshift(diag(1./hF)*RE_Grid_all_fftshift);
RE_Grid_all_Received = fftshift(RE_Grid_all_fftshift_eq(1:N_SC,:));
% figure(1)
% plot(abs(RE_Grid_all_fftshift(:,1)))
% figure(2)
% plot(abs(RE_Grid_all_fftshift_eq(:,1)))
% figure(3)
% plot(abs(abs(hF)))
% figure(4)
% plot(abs(abs(1./hF)))

%% Demodulation
RE_PreDeMod = reshape(RE_Grid_all_Received,[],1);
dataSymbolsOut = qamdemod(RE_PreDeMod, Qm,'UnitAveragePower', true); 
data_bit_out = reshape((de2bi(dataSymbolsOut, 'left-msb')).',1,[]); 
power_RE_receid = sum(sum(abs(RE_PreDeMod).^2)) / N_RB / N_SC_perRB / N_Symbol / N_Frame;
snr_all(iQorder,iEbN0,iloop) = 10*log10(power_RE/(power_RE_receid - power_RE));

%% Result: Ser and Ber
%Ser
sym_err = length(find(dataSymbolsOut - dataSymbolsIn));
ser_all(iQorder,iEbN0,iloop) = sym_err / length(dataSymbolsOut);
%Ber
bit_error = sum(abs(data_bit_out - data_bit_in));
ber_all(iQorder,iEbN0,iloop) = bit_error / length(data_bit_out);
end
sers = mean(ser_all,3);
snrs = mean(snr_all,3);
bers = mean(ber_all,3);
sers_theory(iQorder,iEbN0) = QAM_SER_Theory(Qm,EbN0);

    fprintf('%dQAM\t%f\t %f\t %f\t %e\t\t%e\t\t%e\t\t%d\t\n', Qm, EbN0, SNR,snrs(iQorder,iEbN0),sers(iQorder,iEbN0),sers_theory(iQorder,iEbN0),bers(iQorder,iEbN0),loopNumber);
    end
end

figure(1)
semilogy(EbN0_list, bers(1,:), 'k--+');
hold on 
grid on
semilogy(EbN0_list, bers(2,:), 'r--o');
semilogy(EbN0_list, bers(3,:), 'b--x');
semilogy(EbN0_list, bers(4,:), 'g--s');
xlabel('Eb/N0,dB');
ylabel('BER');
title('BER VERS SNR');
legend('QPSK','16QAM','256QAM','1024QAM');


figure(2)
semilogy(EbN0_list, sers(1,:), 'k--+');
hold on 
grid on
semilogy(EbN0_list, sers(2,:), 'r--o');
semilogy(EbN0_list, sers(3,:), 'b--x');
semilogy(EbN0_list, sers(4,:), 'g--s');
xlabel('Eb/N0,dB');
ylabel('SER');
title('SER VERS SNR');
%SML =  simulation, THR = theory
legend('QPSK','16QAM','256QAML','1024QAM');

function taps = RayleighChanTaps(nTap)
  taps= 1/sqrt(2)*1/sqrt(nTap)*(randn(nTap,1) + 1j*randn(nTap,1));
  taps = taps./sum(abs(taps));
end

function taps = ExponentialChanTaps(SampRateMHz, delaySprdNsec)
sampTimeNsec = 1000 / SampRateMHz;

if delaySprdNsec == 0
    Kmax = 0;
    vark = 1;
else
    Kmax = ceil(10 * delaySprdNsec/sampTimeNsec);
    var0 = 1 - exp(- sampTimeNsec /delaySprdNsec);
    k = (0:Kmax)';
    vark = var0 * exp( -k *sampTimeNsec/delaySprdNsec);
end
    stdDevReOrIm = sqrt(vark/2);
    taps = stdDevReOrIm .*(randn(Kmax +1,1) + 1j*randn(Kmax+1,1));
end

function yt = Multipath_channel(xt,taps)
    ht = taps;
    xht = conv(ht,xt);
    %yt = xht(end - length(xt)+1:end);
    yt = xht(1:length(xt));
end