%定义参数 M = 2; %定义为M元调制 Rs = 1000; % 定义波特率 Rb = Rs*log2(M); %计算比特率 Ts = 1/Rs; %计算符号发送间隔 sample_rate = 100*Rs; % 采样率 EbN0 =0:15;%传送每个比特所用能量平均值/噪声单边功率谱密度（单位：dB） % 生成随机比特序列 num_bits = 100000;% 比特数 bit_sequence = randi([0, 1], 1, num_bits); bit_sequence_dou = bit_sequence*2-1; t_origin = (0:num_bits-1)*Ts; %显示时间（按发送间隔） % ber = zeros(1,length(EbN0)); % ber_dou =zeros(1,length(EbN0)); %设置矩形脉冲NRZ发送滤波器 % 脉冲的幅度 A = 1; % 生成时间向量 t_sendfilter = 0:1/sample_rate:Ts-1/sample_rate; % 生成矩形脉冲滤波器 rect_pulse_filter = [A * ones(1, length(t_sendfilter))]; % 上采样发送序列（每个数据后添0） upsampled_bits = zeros(1, length(bit_sequence)*sample_rate*Ts); upsampled_bits(1:sample_rate*Ts:end) = bit_sequence; t_upsampled = 0:1/sample_rate:(length(upsampled_bits)-1)/sample_rate; %Double upsampled_bits_dou = zeros(1, length(bit_sequence_dou)*sample_rate*Ts); upsampled_bits_dou(1:sample_rate*Ts:end) = bit_sequence_dou; % 将上采样的发送序列通过滤波器 s_rz = conv(upsampled_bits, rect_pulse_filter, 'full'); s_rz = s_rz(1:sample_rate/Rs*num_bits); % 将上采样的发送序列通过滤波器 Double s_rz_dou = conv(upsampled_bits_dou, rect_pulse_filter, 'full'); s_rz_dou = s_rz_dou(1:sample_rate/Rs*num_bits); % 生成时间向量 t_send = (0:length(s_rz)-1) / sample_rate; % %求s_rz的功率谱 % [P_srz, f_srz] = periodogram(s_rz,[],[],sample_rate); for indx=1:length(EbN0) %加噪声 s_rz_noise=awgn(s_rz,EbN0(indx)+10*log10(2*Rb/sample_rate),'measured'); s_rz_noise_dou = awgn(s_rz_dou,EbN0(indx)+10*log10(2*Rb/sample_rate),'measured'); %LPF % d = designfilt('lowpassfir', 'FilterOrder', 50, 'CutoffFrequency', 2*Rs, 'SampleRate', sample_rate); % y_first = filter(d, s_rz_noise); % % y_first = conv(s_rz_noise, b); % 通过滤波器 % y = y_first(n/2+1:end-n/2); % 移除滤波器产生的过渡带 d = designfilt('lowpassfir', 'FilterOrder', 80, 'CutoffFrequency', 2*Rs, 'SampleRate', sample_rate); y = filter(d, s_rz_noise); % 验证基带信号带宽B % passband = [0 2*Rs]; % 通带频率范围 % original_signal = s_rz_noise; % fs = sample_rate; % % 使用傅里叶变换将modulated_signal转换为频域表示 与前面画频谱的时候是一样的操作 但是不在乎复杂度 hhh % original_signal_spectrum = fftshift(fft(original_signal)); % % 确定要保留的频率范围，将其他频率分量置零 % f1 = (-fs/2 : fs/length(original_signal) : fs/2 - fs/length(original_signal)); % original_signal_spectrum(abs(f1) < passband(1) | abs(f1) > passband(2)) = 0; % filtered_signal_spectrum = original_signal_spectrum; % % 使用逆傅里叶变换将修改后的频域信号转换回时域表示 % filtered_original_signal = ifft(ifftshift(filtered_signal_spectrum)); % y = filtered_original_signal; %采点 rn = y(Ts*sample_rate/2:Ts*sample_rate:num_bits*Ts*sample_rate); % 生成时间向量2 t_rev = (0:length(y)-1) / sample_rate; %判决 %计算门限值 threshold = 0.5; rev_bit_sequences = zeros(1, length(rn)); % 预分配决策向量的空间 for i = 1:length(rn) if rn(i) > threshold rev_bit_sequences(i) = 1; else rev_bit_sequences(i) = 0; end end % original_signal_dou = s_rz_noise_dou; % original_signal_spectrum_dou = fftshift(fft(original_signal_dou)); % % 确定要保留的频率范围，将其他频率分量置零 % f1_dou = (-fs/2 : fs/length(original_signal_dou) : fs/2 - fs/length(original_signal_dou)); % original_signal_spectrum_dou(abs(f1_dou) < passband(1) | abs(f1_dou) > passband(2)) = 0; % filtered_signal_spectrum_dou = original_signal_spectrum_dou; % % 使用逆傅里叶变换将修改后的频域信号转换回时域表示 % filtered_original_signal_dou = ifft(ifftshift(filtered_signal_spectrum_dou)); % y_dou = filtered_original_signal_dou; %采点 d = designfilt('lowpassfir', 'FilterOrder', 80, 'CutoffFrequency', 2*Rs, 'SampleRate', sample_rate); y = filter(d, s_rz_noise_dou); rn_dou = y_dou(Ts*sample_rate/2:Ts*sample_rate:num_bits*Ts*sample_rate); rev_bit_sequences_dou = zeros(1, length(rn_dou)); % 预分配决策向量的空间 for i = 1:length(rn) if rn_dou(i) > 0 rev_bit_sequences_dou(i) = 1; else rev_bit_sequences_dou(i) = -1; end end %计算误比特率 [numErrors, ber80(indx)] = biterr(bit_sequence, rev_bit_sequences); error_count80(indx) = ; ber_dou80(indx) = error_count80(indx) / length(bit_sequence); bit_error_theory80(indx) =qfunc(sqrt((10.^(EbN0(indx)/10))/2)); bit_error_dou80(indx)=qfunc(sqrt((10.^(EbN0(indx)/10)))); end %以下绘图 figure; plot(EbN0, ber, '-r*', EbN0, ber_dou, '-k*', EbN0, bit_error_theory, '-ro',EbN0, bit_error_dou, '-ko'); title('2-PAM信号在AWGN信道下的性能(线性坐标)') xlabel('Eb/N0(dB)');ylabel('误符号率') legend('单极性误比特率','双极性误比特率','单极性理论误比特率','双极性理论误比特率') grid on figure; semilogy(EbN0,bit_error_theory,'-ro',EbN0,ber,'-co',EbN0,ber200,'-r*',EbN0,ber80,'-k^',EbN0,ber70,'-g*',EbN0,ber60,'-c*',EbN0,ber1,'-k*',EbN0,ber40,'-m*',EbN0,ber30,'-b*',EbN0,ber20,'-y*'); title('2-PAM信号在AWGN信道下的性能(对数坐标)') xlabel('Eb/N0(dB)');ylabel('误符号率') legend('理论误比特率','误比特率-理想LPF','误比特率-200阶','误比特率-80阶','误比特率-70阶','误比特率-60阶','误比特率-50阶','误比特率-40阶','误比特率-30阶','误比特率-20阶') grid on
关于实现低通滤波器 一定要考虑延时 收、发节拍一定要猜准