Evaluation of Cover and Reflector in Receiver Antennas for SM-MIMO Wireless Communications

Spatial multiplexing multiple-input multiple-output (SM-MIMO) is effective in increasing communication throughput. However, performance degradation occurs in poor multipath and line-of-sight (LOS) channels due to the high spatial correlation. This paper presents the evaluation of cover and reflector in receiver antennas to overcome the performance degradation in MIMO LOS channels. We measured the characteristics of packet error rate (PER), signal-to-noise ratio (SNR), spatial correlation coefficient, and received power ratio in farm, groove, passage, and corner environments. The farm environment degraded communication performance due to the high spatial correlation coefficient. Following the measurement results, we fabricated cover and reflector in receiver antennas to decrease the high spatial correlation and confirmed the improvement of communication performance. 1. Introduction A multiple-input multiple-output (MIMO) [1] technique can improve communication reliability or increase data throughput and attracts a great deal of attention in current wireless communications. Spatial multiplexing (SM) enables independent and parallel data transmission in spatial domain; however, its communication performance strongly depends on MIMO channel conditions. For poor multipath and line-of-sight (LOS) conditions, the high spatial correlation induces performance degradation. In our previous work, we have reported outdoor evaluation of MIMO-OFDM communication in farm and passage (between buildings) environments [2, 3]. The farm condition showed the worst communication performance due to the high spatial correlation. To overcome the performance degradation of SM-MIMO, antenna polarization [4] and transmit-array that lies between transmitter and receiver [5, 6] and simulation analysis of near-field MIMO communication with back reflector [7] have been presented. However, antenna polarization is affected by cross-polarization discrimination depending on propagation environments. Their transmission characteristics might be degraded by weather or obstacles. The transmit-array restricts the locations because the transmit-array should be placed away from the transmit and receive antennas. Our approach is use of cover and reflector in MIMO receiver antennas, which does not rely on polarization and transmit-array and is suitable for long-distance communication. First, we evaluated communication characteristics of farm, groove, passage, and corner environments corresponding to rich/poor multipath and LOS/non-LOS (NLOS) conditions. The parameters of signal-to-noise ratio (SNR),