【无线通信】OQPSK

调制

sps = 8;
RolloffFactor = 0.2;
FilterSpanInSymbols = 10;

bits = randi([0, 1], 224*8, 1); % 1792

symbols = bits*2 - 1;   % 1792
re = -symbols(2:2:end); % 896
im = -symbols(1:2:end); % 896


pFilterTx = comm.RaisedCosineTransmitFilter(...
    'Shape', 'Square root', ...
    'RolloffFactor', RolloffFactor, ...
    'FilterSpanInSymbols', FilterSpanInSymbols, ...
    'OutputSamplesPerSymbol', sps, ...
    'Gain', sqrt(sps/2));

filtered   = pFilterTx([re im]);% 896 * sps = 3584
filteredRe = filtered(:, 1);
filteredIm = filtered(:, 2);

% oqpskWaveform       = complex(filteredRe, filteredIm);
% oqpskWaveform       = complex(filteredRe, filteredAligned);
oqpskWaveform       = complex(...
                    [filteredRe ; zeros(sps/2, 1)], ...
                    [zeros(sps/2, 1) ; filteredIm]); %  3586 * 2 

查看TX的中间状态

% 绘制相位图
plot(unwrap(angle(oqpskWaveform)),'o-')
% 绘制IQ图
plot(1:length(oqpskWaveform),real(oqpskWaveform),1:length(oqpskWaveform),imag(oqpskWaveform))
% 频谱图
plot(abs(fftshift(fft(oqpskWaveform))))
% 星座图
scatterplot(oqpskWaveform);

信道

snr = 7;
rxWaveform = awgn(oqpskWaveform,snr);

解调

pFilterRx = comm.RaisedCosineReceiveFilter(...
    'Shape', 'Square root', ...
    'RolloffFactor', RolloffFactor, ...
    'FilterSpanInSymbols', FilterSpanInSymbols, ...
    'InputSamplesPerSymbol', sps, ...
    'DecimationFactor', sps, ...
    'DecimationOffset', sps/2, ...
    'Gain', sqrt(sps/2));

alignedRx = complex(...
    [zeros(sps/2, 1); real(rxWaveform)], ...
    [imag(rxWaveform);zeros(sps/2, 1)]);  %  3588 * 2 

filteredRx = pFilterRx(alignedRx); % 3588/4 = 897

demodulatedRx = qamdemod(filteredRx, 4, [1 3 0 2]); %  897 
outputBits = int2bit(demodulatedRx, 2); % 1792

BER

delay = 2 * FilterSpanInSymbols; % 20
[~, ber] = biterr(bits(1:end-delay), outputBits(delay+1:end-2))