Effects of Co-Channel Interference on the Performance of IRS-Assisted Communications

This paper considers intelligent reflecting surface (IRS)-assisted communication systems in the presence of arbitrary interfering signals. The IRS reflects both the desired and interference signals through the same fading channels towards the user equipment. In this scenario, the signal-to-interference-plus-noise ratio might become a ratio of correlated random variables. Therefore, this paper aims to identify practical scenarios in which it is acceptable to disregard or necessary to consider the correlation between the desired and interference signals sharing the same fading channels. Furthermore, in the presence of correlated desired and interference signals, the analytical expressions presented in the existing literature are inadequate for evaluating the system performance. To address this limitation, new accurate expressions for the ergodic capacity, outage probability, and bit error rate are derived, which are applicable to both correlated and uncorrelated scenarios. The accuracy of the newly derived expressions is then validated by Monte-Carlo simulations. In contrast to the existing literature, it is revealed that when interferers have line-of-sight (LOS) components, the desired and interference signals are always correlated. It is also revealed that, in the presence of LOS interference, for a very large number of reflecting elements, the system performance reaches a limit, which cannot be improved by increasing the number of reflecting elements.