帮我写一个基于OFDM的matlab代码，包括绘制随机数据接受前后的波形图和误码率随信噪比变化图

下面是一个基于OFDM的matlab代码，包括绘制随机数据接受前后的波形图和误码率随信噪比变化图。代码中包含了详细的注释，希望能对你有所帮助。

% OFDM matlab code
clc;
clear all;
close all;

% OFDM parameters
N = 64; % number of subcarriers
cp_len = 16; % length of cyclic prefix
num_ofdm_symbols = 1000; % number of OFDM symbols to transmit
M = 4; % modulation order (QPSK)
SNR = 10; % signal-to-noise ratio (dB)

% generate random data
data = randi([0 M-1], N*num_ofdm_symbols, 1);

% QPSK modulation
mod_data = qammod(data, M);

% reshape data into N subcarriers
mod_data = reshape(mod_data, N, num_ofdm_symbols);

% IFFT operation
ifft_data = ifft(mod_data, N);

% add cyclic prefix
tx_data = [ifft_data(N-cp_len+1:N, :); ifft_data];

% serial to parallel conversion
tx_data = tx_data(:);

% add complex white Gaussian noise
rx_data = awgn(tx_data, SNR);

% parallel to serial conversion
rx_data = reshape(rx_data, N+cp_len, num_ofdm_symbols+1);

% remove cyclic prefix
rx_data = rx_data(cp_len+1:end, :);

% FFT operation
fft_data = fft(rx_data, N);

% reshape data into a vector
rx_data = fft_data(:);

% QPSK demodulation
demod_data = qamdemod(rx_data, M);

% calculate bit error rate
[~, ber] = biterr(data, demod_data);

% plot received data before and after demodulation
figure;
subplot(2,1,1);
plot(real(tx_data));
title('Transmitted Data');
subplot(2,1,2);
plot(real(rx_data));
title('Received Data');

% plot bit error rate vs. SNR
snr_range = 0:2:SNR;
ber_vec = zeros(length(snr_range), 1);
for i = 1:length(snr_range)
rx_data = awgn(tx_data, snr_range(i));
rx_data = reshape(rx_data, N+cp_len, num_ofdm_symbols+1);
rx_data = rx_data(cp_len+1:end, :);
fft_data = fft(rx_data, N);
rx_data = fft_data(:);
demod_data = qamdemod(rx_data, M);
[~, ber_vec(i)] = biterr(data, demod_data);
end
figure;
semilogy(snr_range, ber_vec);
title('Bit Error Rate vs. SNR');
xlabel('SNR (dB)');
ylabel('Bit Error Rate');