Multipath receiver (Urgent Help needed)

[ayousu]

Hello,

I have BPSK/QPSK data with a raised cosine pulse going through a multipath channel. On the receiver side, I have trouble coming up with a scheme that will separate the multipaths. I have looked into Rake receivers, but they tend to be for CDMA and require a spreading sequence, which I don't have.

Any help would be greatly appreciated, as I have been stuck on this problem for a while and have no idea how to proceed.

Thanks in advance.
A.

 

[mahdithdn]

Hi,

If you are going to compensate the effect of multipath distortion use equalizer. However, if you want to identify multipath coefficient use channel identification algorithm.

 

[drizzd]

The Rake receiver is simply a filter matched to the channel impulse response and as such it does not require spreading. But a matched filter does not work very well, so without spreading gain the performance may not be good enough.

 

[ayousu]

Thanks for your response, mahdithdn

But with equalizer I won't be able to make use of multipath diversity, right?

As for multipath coefficient, you mean the channel coef? I can assume that the receiver has perfect knowledge of the channel and access to channel coefficients.

 

[mahdithdn]

You are working in classic communication regime, so forget about what happens in spread spectrum communication. your system suffers from ISI that is intrinsically trivial in spread spectrum communication.

We also want to use multipath diversity in classic communication regime, which means, we want to collect all the signal energy that is dispersed in time. There are two approach for this problem.
Signal extraction
Channel equalization

Note that we can not use some strategies like rake receiver, because we have no spreading code and consequently not such a synchronization system like spread spectrum systems. In other hand, ISI is a very restrictive distortion.

There are two major methods for equalization
Pilot based channel equalization: Transmitter sends a pilot sequence periodically that is known for the receiver. Receiver use this sequence to Adaptively or in a One shot manner estimate the equalizer coefficient.
Blind channel equalization: Receiver uses some statistics of data to estimate the channel or equalizer coefficient without knowledge of the data.

regards

 

[ayousu]

Thanks for the response.

I have implemented the system with equalizer. But I have another question about array weights.

I have perfect channel knowledge at the receiver. Knowing that how would I get the array weights to minimize channel effects?

Thanks for your responses.

Best,
A.