Interference rejection combining - Rx diversity series (2）

As mentioned earlier, while using Rx diversity, multiple received signals need to be combined in order to maximize the Rx signal's quality.

The combination is just a matter of choosing different weight to each receiving taps.

Selective combining (SC) assigns weight 1 to the strongest signal, assign weight 0 to all the others;

Equal gain combining (EGC) assigns all signal the same weight, i.e. the decoded signal is the sum of all signals after phase adjustion;

Maximum ratio combining (MRC) assigns weight according to each Rx signal's SINR, i.e. the signals are equalized based on each channel before being summed up. The output SNR is, therefore, the sum of the SNR at each element.

The MRC technique assumed that the fading signal at each element is independent of the signal at other elements. Interference rejection combining (IRC) on the other hand, not only estimate each channel independently, but also calculates the Covariance matrix. After knowing the coherence between each channel, interference from other channels can be removed.

one good website on this topic:

http://www.dsplog.com/

MIMO in LTE (2) - Rx Diversity receiver combining techniques (1)

As mentioned in an earlier post about MIMO, in Rx diveristy, the receiver needs to combine multiple streams from different antenna into a single stream. The challenge here is how to use "effectively" the information from allmthe antennas. In fact, it is a just a matter of choose the appropriate weight for each received signals (see figure below). There are multiple ways:

Selective Combining (SC):
The receiver selects the antenna with the highest received signal power and ignore observations from the other antennas. w=[1,0,0,0...].

On flat-fading Rayleigh channel, if the channels from each receiving antenna is independent, then:
- with two receive antenna the effective big energy to noise ratio is 1.5 times Eb/N0
- with three receive antennas the effective bit energy to noise ratio is 1.833 times Eb/N0

- with four receive antennas, the effective bit energy to noise ratio is 2 times Eb/N0