  Interference rejection combiners (IRCs) are very popular in 4G/5G systems. In
particular, they are often times used in co-ordinated multi-point (CoMP)
networks where the antennas of a neighboring cell's base station (BS) are used
in an IRC receiver, in conjunction with the antennas of the BS of a cell-edge
UE's own cell, to improve the IRC-SINR of a cell-edge user. But does the
IRC-SINR always increase with an increase in the number of antennas? In this
paper, we attempt to answer the question theoretically. We give a theoretical
derivation that quantifies the improvement in the IRC-SINR when the number of
antennas increases by unity. We show that this improvement in IRC-SINR is
always greater than or equal to zero. Thus we prove that increasing the number
of antennas even by unity will always improve the IRC-SINR. Selecting the extra
antennas of the neighbouring cell can be viewed as a special case of antenna
selection described in [1]. We also present the IRC-SINR improvement in an
uplink CoMP scenario by simulations and verify that it indeed matches with the
theoretical gains derived in this paper.
