Effects of Mutual Coupling and Doppler Spectrum on the Performance of 2 × 2 MIMO E-SDM Systems

To satisfy the dramatically growing wireless mobile communication demands, using multiple antennas at both a base station and a mobile terminal, referred as a multiple-input multiple-output (MIMO) system, is a promising major breakthrough. Without additional power and spectrum compared with conventional single-input single-output (SISO) systems, channel capacity of MIMO systems can increase proportionally to the number of antennas in independent and identically distributed (i.i.d.) Rayleigh fading environments [1]. The performance of MIMO systems can be improved more by applying eigenbeam-space division multiplexing (E-SDM) technique when channel state information is available at a transmitter [2]. In actual communications, line-of-sight (LOS) waves may exist between the transmitter (TX) and the receiver (RX), and correlations between channels appear unlike i.i.d. fading environments. Also, mutual coupling between antenna elements, which affects the MIMO system performance, could not be ignored. In addition, due to the processing delay at the TX and the RX, a channel change during the delay may degrade the performance of MIMO E-SDM systems. Therefore, more investigations into the systems in realistic cases are necessary. Doppler Spectrum is a useful measure to evaluate mobile communication applications [3]. There may be a relation between Doppler spectrum and the performance of MIMO E-SDM systems in timevarying fading environments. Besides, due to various scatterers’ distribution, LOS wave existance, and multual coupling effect between antennas, Doppler spectrum of MIMO channels in actual environments may be different from the theoretical analyses. To the best of our knowledge, such work has rarely been considered. In addition, although measurement campaigns for time-varying fading environments are important, unfortunately, just a few MIMO measurement campaigns have been conducted in the environments until now [4]. We conducted MIMO measurement campaigns in indoor environments. Based on the measured channel data, in this paper we first examine average received power and Doppler spectrum in a case where the RX is moving while the TX and scatterers are fixed. Then, we evaluate the bit error rate (BER) performance of 2 × 2 MIMO E-SDM system in time-varying fading environments.