Rake receivers in Fading Channels

[saeddawoud]

Fading Channels

Hello,

In a multipath fading channel, we know that the transmitted signal travels over different paths subjected to different attenuation and delay factors. The receiver combine all these signals together as a superposition. The question is: why the receiver has to wait until all replicas are recieved, or wait a specific amount of time before performing detection. Why not detect the signal directly from the first signal received?

Thanks in advance

 

[er.rakeshjain]

Re: Fading Channels

Receiver has to wait for specific time so that it gets best of the received signal. The first received signal may get too much faded that it may not be able to recover the orignal data frm it, so it is needed to wait for some time to get good reception of the original data.

 

[Joatt]

Re: Fading Channels

A wireless signal will be subject to many phenomena during transmission, such as reflection, scattering, etc. This leads to the decomposition of the signal into several copies, each with different power level, noting that the sum of the powers of those signals is equal to the power of the original signal. Anyway, several copies of this signal will arrived at the receiver but with different phase delays (thus in some cases the copies of the signal may cancel each other). Therefore a rake receiver is used for two purposes: the first to accumulate the power of these copies into one signal; and the second is to make all the received copies so they can be added together. For that purpose, the receiver waits a period of time to collect the delayed multi-copies of the signal.

Regards

 

[saeddawoud]

Re: Fading Channels

Ok, I see. So, the receiver has to wait to collect the original power and get the best received signal as possible, eventhough, the superposition of these replicas may added to zero (deep fading).

Thanks