本博文给出了4qam、16qam、64qam、256qam理论仿真曲线，画出了EbN0 vs BER的曲线图，可以作为大家学习的一个参考。
仿真结果:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Theoretical ber curves of different orders of QAM modulation
% Author: 苏大axing
% Version: 1.2
% Date: 2022/4/3
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
close all;
clear all;
clc%% Parameters
EbN0_dB = -5:20;
bits_per_symbol_for_4qam = 2;
bits_per_symbol_for_16qam = 4;
bits_per_symbol_for_64qam = 6;
bits_per_symbol_for_256qam = 8;
Nsym = 2^18;
SNR_for_4qam = EbN0_dB+10*log10(bits_per_symbol_for_4qam);
SNR_for_16qam = EbN0_dB+10*log10(bits_per_symbol_for_16qam);
SNR_for_64qam = EbN0_dB+10*log10(bits_per_symbol_for_64qam);
SNR_for_256qam = EbN0_dB+10*log10(bits_per_symbol_for_256qam);disp(' ');disp(' ');
disp('***********************************');
disp('generating binary bits');
disp('***********************************');
% Generating seeds
randn('state',12013)
rand('state',3693)
binary_bits_forqpsk = randsrc(1,Nsym*bits_per_symbol_for_4qam,[0 1]);
binary_bits_for16qam = randsrc(1,Nsym*bits_per_symbol_for_16qam,[0 1]);
binary_bits_for64qam = randsrc(1,Nsym*bits_per_symbol_for_64qam,[0 1]);
binary_bits_for256qam = randsrc(1,Nsym*bits_per_symbol_for_256qam,[0 1]);% generating MQAM signals
disp(' ');disp(' ');
disp('***********************************');
disp('generating MQAM signal');
disp('***********************************');%%%%%%%%%% 4QAM
paraller_for_4qam = reshape(binary_bits_forqpsk,bits_per_symbol_for_4qam,Nsym);
k_4qam = 2^bits_per_symbol_for_4qam;
[Output] = BitsToInteger(paraller_for_4qam);
qam4_signal = qammod(Output,k_4qam,'gray','UnitAveragePower', true);% figure(1)
% subplot(2,2,1);
% plot(qam4_signal,'.');
% title('4QAM signal');%%%%%%%%%% 16QAM
paraller_for_16qam = reshape(binary_bits_for16qam,bits_per_symbol_for_16qam,Nsym);
k_16qam = 2^bits_per_symbol_for_16qam;
[Output] = BitsToInteger(paraller_for_16qam);
qam16_signal = qammod(Output,k_16qam,'gray','UnitAveragePower', true);% figure(1)
% subplot(2,2,2);
% plot(qam16_signal,'.');
% title('16QAM signal');%%%%%%%%%% 64QAM
paraller_for_64qam = reshape(binary_bits_for64qam,bits_per_symbol_for_64qam,Nsym);
k_64qam = 2^bits_per_symbol_for_64qam;
[Output] = BitsToInteger(paraller_for_64qam);
qam64_signal = qammod(Output,k_64qam,'gray','UnitAveragePower', true);% figure(1)
% subplot(2,2,3);
% plot(qam64_signal,'.');
% title('64QAM signal');%%%%%%%%%% 256QAM
paraller_for_256qam = reshape(binary_bits_for256qam,bits_per_symbol_for_256qam,Nsym);
k_256qam = 2^bits_per_symbol_for_256qam;
[Output] = BitsToInteger(paraller_for_256qam);
qam256_signal = qammod(Output,k_256qam,'gray','UnitAveragePower', true);% figure(1)
% subplot(2,2,4);
% plot(qam256_signal,'.');
% title('256QAM signal');for i=1:length(EbN0_dB)
received_qam4 = awgn(qam4_signal,SNR_for_4qam(i),'measured');
received_qam16 = awgn(qam16_signal,SNR_for_16qam(i),'measured');
received_qam64 = awgn(qam64_signal,SNR_for_64qam(i),'measured');
received_qam256 = awgn(qam256_signal,SNR_for_256qam(i),'measured');%% demodulation
%%%%%%%%%% 4QAM
demod_signal_for_4qam = qamdemod(received_qam4,k_4qam,'gray','UnitAveragePower', true);
[Output] = IntegerToBits(demod_signal_for_4qam,bits_per_symbol_for_4qam);
received_Bits_for_4qam = reshape(Output,1,Nsym*bits_per_symbol_for_4qam);
ErrorNumber_for_4qam = size(find(received_Bits_for_4qam-binary_bits_forqpsk),2);
BER_for_4qam(i) = ErrorNumber_for_4qam/(Nsym*bits_per_symbol_for_4qam)%%%%%%%%%% 16QAM
demod_signal_for_16qam = qamdemod(received_qam16,k_16qam,'gray','UnitAveragePower', true);
[Output] = IntegerToBits(demod_signal_for_16qam,bits_per_symbol_for_16qam);
received_Bits_for_16qam = reshape(Output,1,Nsym*bits_per_symbol_for_16qam);
ErrorNumber_for_16qam = size(find(received_Bits_for_16qam-binary_bits_for16qam),2);
BER_for_16qam(i) = ErrorNumber_for_16qam/(Nsym*bits_per_symbol_for_16qam)%%%%%%%%%% 64QAM
demod_signal_for_64qam = qamdemod(received_qam64,k_64qam,'gray','UnitAveragePower', true);
[Output] = IntegerToBits(demod_signal_for_64qam,bits_per_symbol_for_64qam);
received_Bits_for_64qam = reshape(Output,1,Nsym*bits_per_symbol_for_64qam);
ErrorNumber_for_64qam = size(find(received_Bits_for_64qam-binary_bits_for64qam),2);
BER_for_64qam(i) = ErrorNumber_for_64qam/(Nsym*bits_per_symbol_for_64qam)%%%%%%%%%% 256QAM
demod_signal_for_256qam = qamdemod(received_qam256,k_256qam,'gray','UnitAveragePower', true);
[Output] = IntegerToBits(demod_signal_for_256qam,bits_per_symbol_for_256qam);
received_Bits_for_256qam = reshape(Output,1,Nsym*bits_per_symbol_for_256qam);
ErrorNumber_for_256qam = size(find(received_Bits_for_256qam-binary_bits_for256qam),2);
BER_for_256qam(i) = ErrorNumber_for_256qam/(Nsym*bits_per_symbol_for_256qam)
endfigure(2)
semilogy(EbN0_dB,BER_for_4qam,'g-<','MarkerFaceColor','g','LineWidth',1);hold on;
semilogy(EbN0_dB,BER_for_16qam,'m->','MarkerFaceColor','m','LineWidth',1);hold on;
semilogy(EbN0_dB,BER_for_64qam,'b-^','MarkerFaceColor','b','LineWidth',1);hold on;
semilogy(EbN0_dB,BER_for_256qam,'r-<','MarkerFaceColor','r','LineWidth',1);hold on;
axis([-5 20 1e-5 1]);
plot([-5 20],[3.8e-3,3.8e-3],'r','LineWidth',1);hold on;
grid on;
xlabel('E_{b}N_{0}(dB)');ylabel('BER');
legend('4qam','16qam','64qam ','256qam',...'FEC(3.8x10^-^3)','Location','SouthWest');function [Output] = BitsToInteger(input)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Convert Bits to Integer
% Author: Zhongxing Tian
% Version: 1.1
% Date: 2022/2/18
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[M,N] = size(input);Value = zeros(1,N);for i = 2:MValue = Value+input(i,:).*2^(i-1); % 阶数从上到下（第一行最小
endValue = Value+input(1,:);Output = Value;
endfunction [Output] = IntegerToBits(input,bits_per_symbol)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Convert Integer to Bits
% Author: Zhongxing Tian
% Version: 1.1
% Date: 2022/2/18
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[~,N] = size(input);Value = zeros(bits_per_symbol,N);for i = 1:Nk = 2^bits_per_symbol;for j = 1:bits_per_symbolif input(1,i)<k/2Value(bits_per_symbol-j+1,i) = 0;% 阶数从上到下（第一行最小）k = k-2^(bits_per_symbol-j); elseValue(bits_per_symbol-j+1,i) = 1;k = k+2^(bits_per_symbol-j);endend
endOutput = Value;
end
