how to simulate multipath fading?
@MohammedFatehy If you put up -exactly- what you currently know and have, we can help you more. 

Generally speaking, let us say you have a signal x[n]. And lets say your sampling rate is 1 Hz. So you take one sample every second. 

Now you want to construct a channel for multipath. Right off the bat, your multipath channel is going to be an FIR filter btw. Let us say someone tells you, "your first echo is going to be 5 seconds away, and attenuates the amplitude by 50%. The second echo is going to be 8 seconds away, and attenuates the amplitude by 70%". 

Now, your channel is going to be simply a vector, (call it channel), such that: channel =  [1 0 0 0 0 0.5 0 0 0.3]. (You have the 1 in the beginning, because that is the 'line of sight' co-efficient. That is, the signal without any echos). 

Now, you simply filter your signal x[n] with channel, and you have a multipath response. Does that make sense?