function r=rice_doppler(fm,M,dt,N,Kdb)
T=N*dt-dt;
K=10^(Kdb/10); 
const=1/(2*(K+1));
t=0:dt:T;
c=sqrt(2/M);w=2*pi*fm;x=0;y=0;
for n=1:M 
alpha=(2*pi*n-pi+(2*pi*rand-pi))/(4*M);
ph1=2*pi*rand-pi;
ph2=2*pi*rand-pi;
x=x+c*cos(w*t*cos(alpha)+ph1);
y=y+c*cos(w*t*sin(alpha)+ph2);
end
r=sqrt(const*((x+sqrt(2*K)).^2+y.^2));
rice_RdB=20*log10(r);
plot(t,rice_RdB)