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

Hindawi Publishing Corporation Journal of Electrical and Computer Engineering Volume 2013, Article ID 123827, 8 pages http://dx.doi.org/10.1155/2013/123827 Research Article Evaluation of Cover and Reflector in Receiver Antennas for SM-MIMO Wireless Communications Shingo Yoshizawa1 and Yoshikazu Miyanaga2 1 Department of Electrical and Electronic Engineering, Kitami Institute of Technology, 165, Koen-cho, Kitami, Hokkaido 090-8507, Japan 2 Graduate School of Information Science and Technology, Hokkaido University, Kita-14 Nishi-9, Kita-ku, Sapporo, Hokkaido 060-0814, Japan Correspondence should be addressed to Shingo Yoshizawa; Received 22 August 2013; Revised 28 October 2013; Accepted 1 November 2013 Academic Editor: George Tsoulos Copyright © 2013 S. Yoshizawa and Y. Miyanaga. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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 2 × 2 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 transmitarray 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 transmitarray 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), spatial correlation coefficient, and received power ratio were important to prospect communication performance. Following the measurements, we fabricated cover and reflector to coordinate the parameters of spatial correlation coefficient and received power ratio. By using the cover and reflector, we confirmed the improvement of communication performance in the farm environment. The paper is organized as follows. Section 2 reports the outdoor experiment in basic antenna. Section 3 describes 2 Journal of Electrical and Computer Engineering Table 1: Experimental conditions. RF band Signal bandwidth Number of subcarriers Max. trans. power TX antenna (directional) Figure 1: Photograph of experimental platform. RX antenna (omnidirectional) 2 × 2 MIMO Transmission Antenna height Distance (TX-RX) MIMO detection Coding rate Modulation RF (TX) FPGA board RF (RX) FPGA board PCI bus PCI bus CPU board Embedded PC1 (TX) CPU board Embedded PC2 (RX) Figure 2: Structure of experimental platform for 2 × 2 MIMOOFDM communication. the fabrication of cover and reflector in MIMO receiver antennas. The evaluation of the proposed cover and reflector is presented in Section 4. Section 5 summarizes the paper. 2. Outdoor Experiment for Basic Antenna 2.1. Experimental Platform. The experimental platform that was developed in our previous work [2] is depicted in Figure 1. The platform structure for 2 × 2 MIMO-OFDM communication is illustrated in Figure 2. Open-loop spatial multiplexing (OLSM) that does not share channel state information (CSI) in transmitter and receiver is adopted in the MIMO-OFDM communication. The platform consists of the baseband units with the CPU and FPGA boards and the RF units. The CPU board generates transmit data, records received data on software processing, and evaluates the packet error rate (PER), signal-to-noise ratio (SNR), and MIMO propagation channel. The FPGA board provides MIMO-OFDM modulation/demodulation on hardware processing. The baseband signal bandwidth of OFDM is about 80 MHz according to the similar specifications of IEEE 802.11ac WLAN [8]. The RF unit is designed by superheterodyne architecture modulating 374 and 5,200 MHz in IF and 5150–5250 MHz 79.68 MHz 512 357 mW NATEC PAT509S-4953 Gain 9 dBi Half-power angle E-plane 58 deg/H-plane 76 deg SANSEI ELECTRIC ANTDP-010A0 Gain 0 dBi E-plane 360 deg/H-plane 360 deg 1m 40 m MMSE 1/2 16 QAM RF bands, respectively. Figure 3 shows a block diagram of 2 × 2 MIMO-OFDM transmitter and receiver. The functions in the transmitter and receiver blocks are the same as those of IEEE802.11n PHY. The MIMO detection block recovers data symbols from spatially multiplexed data streams for SMMIMO. The linear detection based on a minimum meansquare-error (MMSE) criterion is adopted in the MIMO detection block. 2.2. Experimental Conditions. Table 1 shows the experimental conditions for 2 × 2 MIMO-OFDM communication. The transmitter antenna has a directional characteristic where the half-power angles are 58 and 76 degrees in E- and H-planes, respectively. The receiver antenna has an omnidirectional characteristic with 360 degrees in both E- and H-planes. The experimental place is illustrated in Figure 4. We evaluate communication characteristics in passage (between buildings), corner (of building), farm, and groove environments. Their photographs are shown in Figur (...truncated)