扩频通信直接序列扩频系统的matlab仿真实现

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % 课程作业-直接序列扩频信号的产生与捕获模拟 % 调用GoldGenerator.m生成GOLD伪码 % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% fPN = 1023; % 伪码速率 fCarrier = fPN*30; % 载波频率 > 伪码速率 fSample = fCarrier * 4; % 载波的采样点频率 %chip = 31; % 伪码长度，普通码31位 chip = 1023; % 伪码长度，GOLD码1023位 dataLength = 10; % 待发送数据位数 % 初始化随机数，每次不同 rand('twister', sum(100*clock)); %产生均匀分布的随机变量 randn('state', sum(100*clock)); %产生高斯分布的随机变量 % 待发送数据 sourceData = randsrc(1, dataLength, [0 1]); % 0,1的数据源 sourceData sendDataLength = dataLength * chip; % 准备调制发送时的数据长度，目前一样，没有在数据前面加噪音 figure(1); stem(sourceData); title('数据源'); % 生成GOLD码 pnSequence = GoldGenerator(); % GOLD码1024位 figure(2); stem(pnSequence(1:50)); title('1023位gold码'); % 扩频 spreadData = zeros(1, dataLength*chip); temp = ones(1, chip); for i = 1:dataLength temp = ones(1, chip)*sourceData(i); % 相加模2，异或 spreadData(((i-1)*chip+1):i*chip) = xor(temp, pnSequence); end figure(3); stem(spreadData(1:50)); title('扩频后的数据'); % 调制输出 %[sendedMData,t] = modulate(h, spreadData); %h = modem.pskmod(); %sendedMData = modulate(h, spreadData); [sendedMData,t] = dmod(spreadData, fCarrier, fPN, fSample, 'psk', 2); sendedMDataLength = length(sendedMData); figure(4); plot(t(1:50),sendedMData(1:50)); title('经BPSK调制后的数据'); % 附加白噪声 recvMData = awgn(sendedMData, -20, 'measured', 'dB'); %recvMData = sendedMData; figure(5); plot(recvMData(1:50)); title('附加白噪声后的数据'); % 解调成数字信号 recvDData = ddemod(recvMData, fCarrier, fPN, fSample, 'psk', 2); recvDDataLen = length(recvDData); % 捕获到的数据长度 figure(6); stem(recvDData(1:50)); title('解调后的信号'); % 接收数据有效码捕获的阈值 thresholdUp = 0.2; thresholdDn = 0.8; % 每次取5个码字长度的数据进行捕获测试 testVCodes = 5; % 解调数据末尾追加4倍chip的0，防止在捕获时数据溢出 recvDData = [recvDData zeros(1, chip*(testVCodes-1))]; despreadData = zeros(1, dataLength); % 存放解扩后的数据 % 判断阈值的依据 power = zeros(1, chip*testVCodes); for i=1:chip*testVCodes power(i) = sum(xor(pnSequence, recvDData(i:i+chip-1)))/chip; % 计算能量 end figure(8); plot(power); title('能量对比'); % TAG111 % 采用串行方法捕获 m = 1; i = 1; while(m <= (recvDDataLen-chip+1)) % 查看是否是码字的起始位置 % 取连续5个码字长度的数据,一起作为判断依据 toVerf = recvDData(m: m+chip*testVCodes-1); totalVCodes = 0; % 此次检测站，总检测的码字数 yesVCodes = 0; % 超过阈值，认为是码字的数目 noVCodes = 0; % 不认为是的数目 while (totalVCodes < testVCodes) if (totalVCodes*chip+m > recvDDataLen) % 后面的已经不需要再计算了，没有数据 break; end power = sum(xor(pnSequence, toVerf((totalVCodes*chip+1):(totalVCodes+1)*chip)))/chip; % 计算能量 if((power >= thresholdUp) || (power <= thresholdDn)) yesVCodes = yesVCodes + 1; end totalVCodes = totalVCodes + 1; end % 阈值判断是否是有效码字, 0.7 if(yesVCodes < totalVCodes*0.7) m = m+1; continue; end % 是有效码字 % 对码块数据与伪码进行加1模2，恢复原数据 % M/N判别 if sum(xor(pnSequence, recvDData(m:m+chip-1))) > chip*thresholdUp despreadData(i) = 1; else despreadData(i) = 0; end m = m + chip; i = i + 1; end % 判断正确数据的个数 correct = 0; for i = 1:dataLength if despreadData(i) == sourceData(i) correct = correct + 1; end end despreadData figure(7); stem(despreadData); title('恢复后的数据'); correct/dataLength