High rate space-time codes for millimeter-wave systems with reconfigurable antennas

Abstract

In this paper, we propose a high-rate space-time block code (STBC) for millimeter-wave wireless communica- tion systems that are equipped with reconfigurable multiple- input multiple-output (MIMO) antennas. We assume that each reconfigurable antenna element has the capability of forming its beam and can independently change the characteristics of its radiation pattern 1 . We exploit this feature of the antenna elements to construct the proposed space-time block code where each coded symbol is sent over independent beams. As a result, the received coded symbols at different receive antennas will have different power levels, a desired property that can be used in data detection. We show that the proposed code achieves a coding rate of two and requires a low-complexity maximum likelihood (ML) detector. We carry out computer simulations that demonstrate the performance of the proposed code and shows its superiority in compared to previous rate-2 STBC counterparts. We also comment on the generalization of the proposed STBC for higher MIMO dimensions. Index Terms—Multiple-input multiple-output (MIMO), recon- figurable antennas, space-time block coding. From the physical layer perspective, if reconfigurable an- tennas are used in mmWave systems, new signal processing algorithms need to be designed to benefit from the antennas capabilities. Essentially, the previous microwave-band signal processing algorithms which are developed based on the assumption of omni-directional signal propagation and rich scatterer environment may not remain optimal for mmWave systems (12). This can be attributed to the propagation charac- teristics of the signal that are particular to the mmWave band, which are quite different than those encountered in the mi- crowave band (13). At the mmWave frequencies, multipath is insignificant, while attenuation from atmospheric precipitation is more important (14). The space-time block codes (STBCs) is one of the key building blocks of wireless communication systems that their performance will be impacted by signal propagation behavior in mmWave systems. The STBCs have been designed based on the well accepted notion that the transceiver is equipped with omni-directional antennas, while in the mmWave systems, the radiation pattern of the antennas need to be directive to compensate for the large path loss at mmWave frequencies. Therefore, the STBCs designed for conventional MIMO sys- tems ignore the antenna gain and directivity in the mmWave systems. Naturally, a more effective STBC design approach should exploit the directive radiation pattern of the antennas utilized in mmWave systems. In this paper, we propose a high-rate space-time block code for a 2×2 MIMO system equipped with reconfigurable antenna elements. The proposed code uses the properties of the recon- figurable antennas to enhance the coding rate, while reducing the computation complexity of the receiver. In particular, we design a STBC code based on the rotated quasi-orthogonal coding principles (15)-(18). At each time slot, the system transmits multiple rotated symbols each intended for a partic- ular desired direction and receive antenna. The deployment of reconfigurable antennas at the transmitter enables the system to amplify the transmitted signal towards the desired receive antenna, while placing nulls towards the remaining directions (19). By using this mechanism, the system suppresses the interference from the undesired beams at the receiver. This is feasible if the antenna elements at the transmitter and