function [] = cyclic_spectrum(x, N, fs, M)
%%%%% 參量說明 %%%%%
% x -- 信號(hào)
% N -- 循環(huán)譜檢測采樣長度，必須小于等于信號(hào)序列長度
% fs -- 采樣頻率, 檢測帶寬為-fs/2至fs/2
% M -- 平滑點(diǎn)數(shù), 時(shí)間分辨率*頻率分辨率=M
%%%%%%%%%%%%%%%%%%%

%%% 參數(shù) %%% 
win = 'hamming'; % 平滑窗類型

d_alpha = fs/N; % 1/時(shí)間分辨率=循環(huán)頻率分辨率
alpha = 0:d_alpha:fs; % 循環(huán)頻率, 分辨率=1/時(shí)間分辨率
a_len = length(alpha); % 循環(huán)頻率取樣個(gè)數(shù)

f_len = floor(N/M-1)+1; % 最大平滑窗個(gè)數(shù), 即頻率采樣個(gè)數(shù)
f = -(fs/2-d_alpha*floor(M/2)) + d_alpha*M*(0:f_len-1); % 頻率采樣點(diǎn)位置

S = zeros(a_len, f_len); % 初始相關(guān)功率譜
i = 1; 

%%% 信號(hào)fft變換 %%%
X = fftshift(fft(x(1:N))); 
X = X';

%%% 遍歷循環(huán)頻率取值 %%%
for alfa = alpha

    interval_f_N = round(alfa/d_alpha); % 循環(huán)頻率所對應(yīng)的頻譜序列序號(hào)
    f_N = floor((N-interval_f_N-M)/M)+1; % 平滑窗的個(gè)數(shù)
    
    %%% 生成平滑窗函數(shù) %%%
    g = feval(win, M); 
    window_M = g(:, ones(f_N,1));
    
    %%% 頻域序列平滑模板 %%%
    t = 1:M*f_N;
    t = reshape(t, M, f_N);
    
    %%% 計(jì)算X1,X2 %%%
    X1 = X(t).*window_M;
    X2 = X(t+interval_f_N).*window_M; 

    %%% 計(jì)算譜相關(guān) %%%
    St = conj(X1).*X2;
    St = mean(St, 1); % 平滑平均
    S(i, floor((f_len-f_N)/2)+(1:f_N)) = St/N; % 將結(jié)果平移至序列中央以便作圖
    i = i+1;
    
end
%%% 遍歷循環(huán)頻率取值結(jié)束 %%%
 
%%% 循環(huán)功率譜作圖 %%%
mesh(f, alpha, abs(S)); 
axis tight;
%title('BPSK-OFDM');
xlabel('f'); ylabel('a');