时间选择性衰落和频率选择性衰落

我知道时间选择性是由多普勒频移引起的，频率选择性是由时延扩展引起的
以下的matlab代码我由结果可看出是时间和频率选择性的，是一篇文献作者给出的，但他的仿真好像没考虑时延扩展。看到其他文献中仿真一般会给出时延扩展来。就是不知道在这段代码里是在哪体现的或是可在那修改阿？还请高人指点。
%Rayleigh六径
userNum=2;
sampleNum=200;
fm=30;
Ts=1e-3;
N=200; %number of input waves
n=[0:N-1];
cita=2*pi*n/N; %input angles
for user=1:userNum
alfa1=randn(1,N); %magnitudes of input waves, tap 1
alfanormed(1,:)=alfa1/sqrt(sum(alfa1.^2)); %normalized magnitude, tap 1
alfa2=randn(1,N); %magnitudes of input waves, tap 2
alfanormed(2,:)=alfa2/sqrt(sum(alfa2.^2)); %normalized magnitude, tap 2
alfa3=randn(1,N); %magnitudes of input waves, tap 3
alfanormed(3,:)=alfa3/sqrt(sum(alfa3.^2)); %normalized magnitude, tap 3
alfa4=randn(1,N); %magnitudes of input waves, tap 4
alfanormed(4,:)=alfa4/sqrt(sum(alfa4.^2)); %normalized magnitude, tap 4
alfa5=randn(1,N); %magnitudes of input waves, tap 5
alfanormed(5,:)=alfa5/sqrt(sum(alfa5.^2)); %normalized magnitude, tap 5
alfa6=randn(1,N); %magnitudes of input waves, tap 6
alfanormed(6,:)=alfa6/sqrt(sum(alfa6.^2)); %normalized magnitude, tap 6
phaseinit1=randn(1,N);
phaseinit(1,:)=phaseinit1*2*pi/max(phaseinit1); %initial phases, tap 1
phaseinit2=randn(1,N);
phaseinit(2,:)=phaseinit2*2*pi/max(phaseinit2); %initial phases, tap 2
phaseinit3=randn(1,N);
phaseinit(3,:)=phaseinit3*2*pi/max(phaseinit3); %initial phases, tap 3
phaseinit4=randn(1,N);
phaseinit(4,:)=phaseinit4*2*pi/max(phaseinit4); %initial phases, tap 4
phaseinit5=randn(1,N);
phaseinit(5,:)=phaseinit5*2*pi/max(phaseinit5); %initial phases, tap 5
phaseinit6=randn(1,N);
phaseinit(6,:)=phaseinit6*2*pi/max(phaseinit6); %initial phases, tap 6
%using one-sided exponential profile
to=1*Ts;
tt=[0:5]*Ts;
g=exp(-tt/to);%relative engery for the 6 taps
    for j=1:6
        for i=0:sampleNum-1
            t=i*Ts;
            is=g(j)*sum(alfanormed(j,:)cos(2*pi*fm*t*cos(cita)+phaseinit(j,:)));  %每条径的相对幅度g(j)
            qs=g(j)*sum(alfanormed(j,:)sin(2*pi*fm*t*cos(cita)+phaseinit(j,:)));
            I(user,j,i+1)=is;
            Q(user,j,i+1)=qs;
            envs=sqrt(qs^2+is^2);
            env(user,j,i+1)=envs;%对于用户user，在第j条径，第i个采样点的值
        end
    end
end
for diffsamp=1:sampleNum
for j=1:userNum
            user=I(j,:,diffsamp)+sqrt(-1)*Q(j,:,diffsamp);
            ch(:,j)=abs(fft(user,N));%用户j的频率选择性信道
        end
end

大约瞅了瞅，I Q 分别是高斯，然后合起来幅度瑞利，
这行代码：tt=[0:5]*Ts; g=exp(-tt/to);%relative engery for the 6 taps
就是表示多径时延，时间上从0到5，总共6径，power profile--其实这里是幅度 服从exp
不过一般有0径的话……exp()=1 挺大了

最经典的信道建模。
参考mobile fading channel，一本很老的书。