circconv.m

matlab应用实例。如：FIR、IIR数字滤波器设计等。

function [y,n]=circconv(x1,x2,N)
% implement circle convolution of x1 and x2
% x1 and x2 are input sequences of n1,n2<=N
% y is output sequence 
% N is size of circle buffer 
% Method:y(n)=sum(x1(m)*x2((n-m) mod N))
% check for length of x1

if (length(x1)>N)|(length(x2)>N)
   error('序列长度超过了圆周卷积长度')
end
x1=[x1 zeros(1,N-length(x1))];
x2=[x2 zeros(1,N-length(x2))];
m=[0:1:N-1];x2=x2(mod(-m,N)+1);		%x2圆周反转
H=zeros(N,N);					    %圆周卷积矩阵
for n=1:1:N
   H(n,:)=circshift(x2,n-1,N);	    %圆周移位
end
y=x1*H';							%实现圆周卷积