Abstract
This article presents the performance analysis of multiple-input/multiple-output (MIMO) systems with quadrature amplitude modulation (QAM) transmission in the presence of cochannel interference (CCI) in nonfading and flat Rayleigh fading environments. The use of optimum transmission (OT) and maximum ratio transmission (MRT) is considered and compared. In addition to determining precise results for the performance of QAM in the presence of CCI, it is our another aim in this article to examine the validity of the Gaussian interference model in the MRT-based systems. Nyquist pulse shaping and the effects of cross-channel intersymbol interference produced by CCI due to random symbol of the interfering signals are considered in the precise interference model. The error probability for each fading channel is estimated fast and accurately using Gauss quadrature rules which can approximate the probability density function (pdf) of the output residual interference. The results of this article indicate that Gaussian interference model may overestimate the effects of interference, particularly, for high-order MRT-based MIMO systems over fading channels. In addition, OT cannot always outperform MRT due to the significant noise enhancement when OT intends to cancel CCI, depending on the combination of the antennas at the transmitter and the receiver, number of interference and the statistical characteristics of the channel.
Highlights
The most adverse effect mobile radio systems suffer from is mainly multipath fading and cochannel interference (CCI), which limit the quality of service offered to the users
We find that optimum transmission (OT) with two receiver antennas is unable to show the superiority over maximum ratio transmission (MRT) for higher value of SIR (e.g., SIR > 7 dB) for the case with (T, R) = (1, 2); interference cancellation can compensate for noise enhancement effect for low value of SIR
Unlike the results of equal gain combining (EGC) presented in [10], we show that the Gaussian interference approach always overestimates the effect of interference with the MRTbased MIMO system in nonfading and fading cases
Summary
The performance of OC was studied for both nonfading [1] and fading [2,3,4,5,6,7,8,9,10,11,12] communication systems in the presence of a single or multiple cochannel interferers. This article studies the average BER of quadrature amplitude modulation (QAM) with OT and provides the comparison with MRT using the precise CCI model when the desired signal and interferers are subject to nonfading and Rayleigh fading for Nyquist pulse shaping. K=1 i=1 n where the random variable τi is uniformly distributed in [0, Ts] and it represents a possible symbol timing offset between the desired signal and the ith interferer; pulse response g(t) having the raised-cosine spectrum is the combined transmitter filter gt(t) and receiver filter gr (t) which have the same response; the filtered noise is vm(t) = nm(t) ⊗ gr(t) and the power is calculated as σv2 = N0 where ⊗ denotes the convolution operation.
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