function?[dalfaNNpf0alfa0SCD]?=?SCD_FAM（IfsdfM）
%?輸入
%?I：信號實部
%?fs:信號采樣率
%?df：頻率分辨率
%?M?：不確定量

%?輸出
%?dalfa：循環頻率分辨率
%?N?：觀測時間內離散取樣總數
%?Np：第一個FFT的點數N‘是靠近且大于fs/df的2的冪次方
%?f0：頻率軸
%?alfa0：循環頻率軸
%?SCD：循環譜
dalfa?=?df/M;???????????????????????%?循環頻率分辨率
x?=?I;??????????????????????????????%?實信號序列
Np?=?pow2（nextpow2（fs/df））;?????????%?第一個FFT的點數N‘是靠近且大于fs/df的2的冪次方？???????????????????????????????????
L?=?Np/4;???????????????????????????%?滑動因子，為了避免估計中的混疊現象和循環泄漏應該小于等于四分之一的時間窗口Np。???????????????????????????????????
P?=?pow2（nextpow2（fs/dalfa/L））;?????%?用一個P點FFT的傅里葉變換取代計算復解調序列乘積的平均
N?=?P*L;????????????????????????????%?觀測時間內離散取樣總數

if?length（x）????x（N）?=?0;
elseif?length?（x）>N
????x?=?x（1:N）;????????????????????%觀測時間內離散取樣的總數
end

NN?=?（P-1）*L+Np;
xx?=?x;
xx（NN）?=?0;
xx?=?xx（:）;
X?=?zeros（NpP）;
for?k?=?0:P-1
????X（:k+1）?=?xx（k*L+1:k*L+Np）;????%將數據按時域滑動L點保存大小為窗口的大小Np
end

a?=?hamming?（Np）;
XW?=?diag（a）*X;?%數據削度

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%?復解調的計算——第一次Np點FFT的計算

XF1?=?fft（XW）;????????????????????????%滑動Np點FFT
XF1?=?fftshift（XF1）;??????????????????%將fft的主值區間變換至[-pipi]
XF1?=?[XF1（:P/2+1:P）?XF1（:1:P/2）];??%第9列-16列和第1列-8列交換——f

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E?=?zeros（NpP）;
for?k?=?-Np/2:Np/2-1?????????????????????????????%分別左右搬移循環頻率的一半
????for?m?=?0:P-1
????????E（k+Np/2+1?m+1）?=?exp（-i*2*pi*k*m*L/Np）;%頻移量
????end
end
XD?=?XF1.*E;?????????????????????????????????????%對Np點FFT的輸出進行頻移
XD?=?conj（XD‘）;??????????????????????????????????%計算每一小段譜的共軛

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