There are different antenna gain-combining methods. They are as follows.
1. Equal gain combining (EGC)
2. Maximum ratio combining (MRC)
3. Selective combining (SC)
4. Root mean square gain combining (RMSGC)
1. Equal gain combining method
We add the correlated data streams from different antennas in the equal gain combining method. Then we multiply the resultant data with (1/(number of antennas))
For example, for two antenna gain-combining
If the received symbols are y1 and y2, then
Equal combing gain,
y_egc = 0.5 * (y1 + y2)
2. Maximum ratio combining method
We multiply the individual data streams with weights in the maximum ratio combining method. More weightage is multiplied by those data streams with maximum {|h|^2}, where h denotes the channel impulse response. And less weightage is multiplied by those data streams with corresponding small value of {|h|^2}. Then we sum the data streams to improve SNR.
In the case of Maximum Ratio Combining, if y1 and y2 are received symbols, then.
y_mrc = a1 * y1 + a2*y2
Where a1 = magnitude of the channel impulse response of y1 and a2 is the magnitude of the channel impulse response of another channel.
3. Selective combining method
In the selective combing method, we select a few data streamwise with higher SNR values than others. Then we combine them.