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Precoding is a technique which exploits transmit diversity by weighting information stream, i.e. the transmitter send the coded information to the receiver in order to the pre-knowledge of the channel. The receiver is a simple detector, such as matched filter, and does not have to know the channel side information. This technique will reduce the corrupted effect of communication channel.
For example you are sending information, s
and it will pass through the channel, h
and Gaussian noise, n
The received signal at receiver front-end will be, r=sh+n;
The receiver will have to know the information about h and n. It will supress the effect of n by increasing SNR but what about h? It need information about the channel, h and this will increase the complexity. The receiver, mobile units, have to be simple for many reasons like cost, size of mobile unit. So, the transmitter, base station, will do the hard work and predicts the channel.
Let call the predicted channel, h_est
and for a system with precoder the information will be coded, s/h_est
and the received signal will be, r=(h/h_est)s+n
if your prediction is perfect, h_est=h, and r=s+n, and it turns out to be the detection problem in Gaussian channels which is simple.
It is a preprocessing technique that performs transmit diversity and it is similar to equalization but the main difference is you have to optimize precoder with a decoder. Channel equalization aims to minimize channel errors, but precoder aims to minimize the error in the receiver output.
By using pilot-assisted techniques, transmitter will have ability to predict the channel without feedback. It is called forward error control, and precoding is a technique of forward error control.
Hi, I am a third year undergraduate student of electrical engineering. I have been assigned a summer project to to design,simulate and analyze a multi-antenna precoder for broadcasting data from a satellite to many ground terminals.
I am supposed to do some background reading on this topic before joining the team. However, I have no knowledge of precoding as such...can you help me as to how should I go about reading on this subject? I mean right from scratch?
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