modulation signal

Modulation signal refers to the signal that is used to modulate a carrier signal in order to transmit information. In modulation, the information signal is superimposed onto the carrier signal. The resulting modulated signal contains both the carrier signal and the information signal. The process of modulation enables the transmission of information over long distances by using high frequency carrier signals that can travel longer distances without significant attenuation. Common modulation techniques include amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).

相关问题

clear all; M = 4; N = 100000; TxAntennas = 2; RxAntennas = 1; signal = randi([0, M-1], TxAntennas, N/2); SNR = 0:15; mimo21_BER = zeros(size(SNR)); for i = 1:length(SNR) mimo21_modulation = qammod(signal, M); symbol_energy = 1;%單一功率 signal_power = TxAntennas * symbol_energy;%總功率 noise_power = signal_power / (10^(SNR(i)/10)); noise = sqrt(noise_power/2) * (randn(TxAntennas, length(mimo21_modulation)) + 1i * randn(TxAntennas, length(mimo21_modulation))); noisy_signal = mimo21_modulation + noise; mimo21_demodulation = qamdemod(noisy_signal, M); mimo21_BER(i) = sum(sum(signal ~= mimo21_demodulation))/length(signal); end semilogy(SNR, mimo21_BER, 'r-x');我這樣的matlab模擬有錯誤嗎

在这段Matlab代码中，我看到以下几个问题：

1. 在计算信号功率时，使用了单个符号的能量，但没有进行平均。应该将每个符号的能量除以信号点数，即 `symbol_energy/TxAntennas`。

2. 在添加噪声时，使用了 `mimo21_modulation`，但应使用 `noisy_signal`。

3. 在计算误码率时，除数应该是 `length(signal(:))`，而不是 `length(signal)`。

下面是修改后的代码：

clear all;
M = 4;
N = 100000;
TxAntennas = 2;
RxAntennas = 1;
signal = randi([0, M-1], TxAntennas, N/2);
SNR = 0:15;
mimo21_BER = zeros(size(SNR));
for i = 1:length(SNR)
    mimo21_modulation = qammod(signal, M);
    symbol_energy = 1; %单个符号能量
    signal_power = TxAntennas * symbol_energy / 2; %平均功率，除以2是因为有实部和虚部
    noise_power = signal_power / (10^(SNR(i)/10));
    noise = sqrt(noise_power/2) * (randn(TxAntennas, length(mimo21_modulation)) + 1i * randn(TxAntennas, length(mimo21_modulation)));
    noisy_signal = mimo21_modulation + noise;
    mimo21_demodulation = qamdemod(noisy_signal, M);
    mimo21_BER(i) = sum(sum(signal ~= mimo21_demodulation))/length(signal(:)); %误码率
end
semilogy(SNR, mimo21_BER, 'r-x');

希望对你有所帮助！