m序列解扩后的信号时域和频域波形

clear all; close all; clc; A = 0; B = 0; C = 1; m = 350; %重复50遍的7位单极性m序列 for iii = 1:m C_ = C; B_ = B; A_ = A; C = B_; B = A_; A = xor(C_,A_); m_seq(iii) = A_; end for iii = 1:m bipolar_seq(iii) = 1-2*m_seq(iii); %将单极性m序列变为双极性m序列 end figure(1) %%绘制m序列图 subplot(3,1,1) stairs(0:length(bipolar_seq)-1,bipolar_seq,'r','LineWidth',1.5); axis([0,7,-1,1]); xlabel('序号'); ylabel('m序列'); ylim([-1.2 1.2]) title('双极性7位m序列') ; %%绘制双极性m序列频谱 subplot(3,1,2) spectrum = fft(bipolar_seq,4096); magm = abs(spectrum); freq = (1:2048)*200/2048; plot(freq,magm(1:2048)*2/4096,'g','LineWidth',1.5); title('双极性7位M序列的频谱') axis([90,140,0,0.1]); %%求双极性m序列自相关函数 [speadsig_fft,tau] = xcorr(bipolar_seq,'unbiased'); subplot(3,1,3) plot(tau,speadsig_fft,'b','LineWidth',1.5); axis([-20,20,-0.5,1.2]); xlabel('\tau') title('双极性m序列的自相关函数'); saveas(gcf,'发送序列的基本特性.png') %% bit_num = 50; id = 0; bit_gen = rand(1,bit_num); %产生50个0与1之间随机数 for iii = 1:bit_num if bit_gen(iii) >= 0.5 %大于等于0.5的取1，小于0.5的取0 trans_bits(iii) = 1; id = id+1; else trans_bits(iii) = 0; end end time = 0:bit_num-1; figure(2) %%绘制发送比特流 subplot(2,1,1) stairs(time,trans_bits,'r','LineWidth',1.5); xlabel('序列'); ylabel('幅度'); ylim([-0.1 1.1]); title('扩频前的发送比特流'); subplot(2,1,2) bits_stream = zeros(1,7*bit_num); for iii = 1:bit_num jj = 7*iii-6; bits_stream(jj) = trans_bits(iii); jj = jj+1;bits_stream(jj) = trans_bits(iii); jj = jj+1;bits_stream(jj) = trans_bits(iii); jj = jj+1;bits_stream(jj) = trans_bits(iii); jj = jj+1;bits_stream(jj) = trans_bits(iii); jj = jj+1;bits_stream(jj) = trans_bits(iii); jj = jj+1;bits_stream(jj) = trans_bits(iii); end spread_data = zeros(1,7*bit_num); for iii = 1:350 %扩频后，码率变为100/7*7 = 100Hz spread_data(iii) = xor(m_seq(iii),bits_stream(iii)); end tt = 0:7*bit_num-1; stem(tt,spread_data,'.'); axis([0,350,-0.1,1.1]); xlabel('序列'); ylabel('幅度'); title('扩频后的发送比特流'); saveas(gcf,'扩频前后发送比特流比较.png') %% fc_ = 2000; fs = 100000; %%采样频率为100kHz ts = 0:1/fs:3.5-1/fs; figure(3) subplot(2,1,1) data_shaped2 = rectpulse(trans_bits,7000); nospread_sig = (1-2.*data_shaped2).*cos(2*pi*fc_*ts);%无扩频信号BPSK调制时域波形 plot(ts,nospread_sig,'r'); xlabel('时间/s');ylabel('幅度') axis([0.035,0.095,-1.2,1.2]); title('未扩频BPSK调制信号时域波形') subplot(2,1,2) data_shaped = rectpulse(spread_data,1000); %将矩形信号成型滤波 spread_sig = (1-2.*data_shaped).*cos(2*pi*fc_*ts);%扩频后信号BPSK调制时域波形 plot(ts,spread_sig); xlabel('时间/s');ylabel('幅度') axis([0.035,0.095,-1.2,1.2]) title('扩频BPSK调制信号时域波形'); saveas(gcf,'扩频与否BPSK调制信号时域波形比较.png') %% figure(4) bit_num = 400000; spectrum_ = fft(nospread_sig,bit_num); %无扩频信号BPSK调制频谱 magb = abs(spectrum_); freq = (1:bit_num/2)*100000/bit_num; subplot(2,1,1) plot(freq,magb(1:bit_num/2)*2/bit_num,'r'); axis([1800,2200,0,0.4]); title('无扩频BPSK调制信号频谱'); xlabel('频率/Hz'); ylabel('幅度'); grid on; subplot(2,1,2) spectrum__ = fft(spread_sig,bit_num); %扩频信号BPSK调制频谱 speadsig_fft = abs(spectrum__); freq = (1:bit_num/2)*100000/bit_num; plot(freq,speadsig_fft(1:bit_num/2)*2/bit_num); axis([1800,2200,0,0.4]); title('扩频BPSK调制信号频谱'); xlabel('频率/Hz'); ylabel('幅度') grid on; %% SNR = 5; %信噪比 dB figure(5) subplot(2,1,1) recv_sig_nospread = awgn(nospread_sig,SNR,'measured');%经过信道加高斯白噪,信噪比为3dbw plot(ts,recv_sig_nospread,'r',ts,nospread_sig,'b','LineWidth',1.5); axis([0,0.005,-1.5,1.5]); legend('加噪声后','加噪声前') xlabel('时间/s'); ylabel('幅度') title('未扩频信号加噪声前后对比'); subplot(2,1,2) recv_sig_spread = awgn(spread_sig,SNR,'measured'); plot(ts,recv_sig_spread,'r',ts,spread_sig,'b','LineWidth',1.5); title('扩频信号加噪声前后对比'); legend('加噪声后','加噪声前') xlabel('时间/s'); ylabel('幅度') axis([0.0575,0.0625,-1.5,1.5]); saveas(gcf,'接收信号的频域波形.png') figure(6) subplot(2,1,1) spectrum_ = fft(recv_sig_nospread,bit_num); %无扩频调制信号经信道后频谱分析 magba = abs(spectrum_); plot(freq,magba(1:bit_num/2)*2/bit_num); title('未扩频信号加噪后信号频谱'); axis([1800,2200,0,0.4]); xlabel('频率/Hz'); ylabel('幅度') subplot(2,1,2) spectrum__ = fft(recv_sig_spread,bit_num); %扩频调制信号经信道后频谱分析 maga = abs(spectrum__); freq = (1:bit_num/2)*100000/bit_num; plot(freq,maga(1:bit_num/2)*2/bit_num,'r'); axis([1800,2200,0,0.4]); xlabel('频率/Hz'); ylabel('幅度') title('扩频后经信道调制信号频谱'); saveas(gcf,'接收信号的时域波形.png') %% figure(7) subplot(2,1,1) recv_data = recv_sig_nospread.*cos(2*pi*fc_*ts); %无扩频系统接收信号乘以本地恢复载波信号 plot(ts,recv_data); axis([0.065,0.095,-1.5,1.5]); xlabel('时间/s'); ylabel('幅度') title('接收未扩频BPSK信号去载波调制'); subplot(2,1,2) recv_data_ = recv_sig_spread.*cos(2*pi*fc_*ts); %扩频系统接收信号乘以本地恢复载波信号 plot(ts,recv_data_,'r'); axis([0.065,0.095,-1.5,1.5]); xlabel('时间/s'); ylabel('幅度') title('接收扩频BPSK信号去载波调制'); saveas(gcf,'接收扩频BPSK信号去载波调制.png') %% figure(8) subplot(2,1,1) recv_data_fft = fft(recv_data,bit_num); mag_rmv_carri = abs(recv_data_fft); freq = (1:bit_num/2)*100000/bit_num; plot(freq,mag_rmv_carri(1:bit_num/2)*2/bit_num);grid on; axis([0,5000,0,0.15]); xlabel('频率/Hz'); ylabel('幅度') title('未扩频信号去载波调制后的信号频谱'); subplot(2,1,2) recv_data_fft_ = fft(recv_data_,bit_num); mag_rmv_carri_ = abs(recv_data_fft_); plot(freq,mag_rmv_carri_(1:bit_num/2)*2/bit_num,'r');grid on; title('扩频信号去载波调制后的信号频谱'); axis([0,5000,0,0.15]); xlabel('频率/Hz'); ylabel('幅度') saveas(gcf,'扩频信号去载波调制后的信号频谱.png') %% figure(9) subplot(2,1,1) fp_ = 100; fc_ = 200; as_ = 100;%衰减100dB fsw_ = 22000; wp_ = 2*fp_/fsw_; wc_ = 2*fc_/fsw_; Nw_ = ceil((as_-7.95)/(14.36*(wc_-wp_)/2))+1; %求凯萨尔窗低通滤波器阶数 beta = 0.1102*(as_-8.7); wind = kaiser(Nw_+1,beta); tau = fir1(Nw_,wc_,wind); bs = abs(freqz(tau,1,400000,fsw_))'; % plot(bs) lowpass_mag_nospread = bs.*mag_rmv_carri; %频谱与低通滤波器相乘 plot(freq,lowpass_mag_nospread(1:bit_num/2)*2/bit_num); axis([0,200/7,0,0.2]); title('未扩频信号经过凯萨尔窗函数低通滤波'); xlabel('频率/Hz'); ylabel('幅度') subplot(2,1,2) lowpass_mag_spread = bs.*mag_rmv_carri_; plot(freq,lowpass_mag_spread(1:bit_num/2)*2/bit_num,'r'); title('扩频信号经过凯萨尔窗函数低通滤波'); axis([0,200,0,0.2]); xlabel('频率/Hz'); ylabel('幅度') saveas(gcf,'扩频信号经过凯萨尔窗函数低通滤波.png') %% figure(10) subplot(2,1,1) lowpass_sig = real(ifft(bs.*recv_data_fft,400000)); %对未扩频系统频谱做ifft变换 tm = (1:bit_num)/bit_num*4; plot(tm,lowpass_sig); xlabel('时间/s'); ylabel('幅度') title('未扩频信号经凯萨尔窗函数滤波后时域波形'); subplot(2,1,2) lowpass_sig_ = real(ifft(bs.*recv_data_fft_,400000)); %对扩频系统频谱做ifft变换 plot(tm,lowpass_sig_); xlabel('时间/s'); title('扩频信号经凯萨尔窗函数滤波后时域波形'); saveas(gcf,'扩频信号经凯萨尔窗函数滤波后时域波形.png') %% figure(11) subplot(2,1,1) mseq_ = rectpulse(bipolar_seq,1000); %扩频信号乘以解扩序列 data_despread = mseq_.*lowpass_sig_(1:350000); plot(ts(1:350000),data_despread); xlabel('时间/s'); ylabel('幅度'); grid on; axis([0,3,-0.5,0.5]); title('m序列解扩后的信号时域波形'); subplot(2,1,2) data_despread_fft = fft(data_despread,bit_num); data_despread_mag = abs(data_despread_fft); plot(freq,data_despread_mag(1:bit_num/2)*2/bit_num,'r'); axis([0,500,0,0.15]); title('m序列解扩后的信号频域波形'); xlabel('频率/Hz'); ylabel('幅度'); grid on; saveas(gcf,'m序列解扩后的信号时域和频域波形.png') %% figure(12) title('解扩前后信号频带宽度