A critical analysis of receiver diversity with multiple antennas with spatially coloured noise

Receive diversity with multiple antennas is a very well-known technique to improve receiver performance in fading environments. The concept is particularly simple in OFDM systems, where the channel effect on each subcarrier amounts to a complex multiplication of the transmitted symbol. It is also well known that, provided the antenna noise covariance matrix is known by the receiver, interference rejection combining (IRC) is the optimal linear combining solution. However, estimation of this matrix is usually unfeasible, in which case suboptimum combining techniques such as antenna selection, equal gain combining (EGC) and maximum ratio combining (MRC) are employed. MRC is commonly employed, because it is the optimum technique for uncorrelated noise. However, we will see in this contribution that when interference is taken into account, sub-optimum MRC or EGC may be a better choice.