Minimum mean square error interference rejection combining (MMSE-IRC) equalizer is used at the base station (BS) receiver (Rx) in cellular systems to mitigate inter and intra cell interference. However, it has a complexity of the order O(N^3), where N is the number of Rx antennas at the BS. As a result, it will become impractical to implement MMSE-IRC in the context of extreme massive MIMO (extreme-mMIMO) where the number of antennas at the BS may range from 256 to 4096. To this end, this paper proposes a low complexity equalizer called Diagonal-Interference Rejection combining (D-IRC). It uses diagonal loading of the noise and interference covariance matrix. It is shown that the proposed D-IRC equalizer has a computational complexity of order O(N^2) which is significantly less than the conventional MMSE-IRC equalizer with similar bit error rate (BER) performance. Further, the implementation of the proposed D-IRC in the centralized/cloud radio access networks is demonstrated in this paper.

https://ieeexplore.ieee.org/abstract/document/10570661