Abstract
This paper considers the problem of massive multiple-input-multiple-output (MIMO) wireless communication systems with quasi-orthogonal space-time block code (QOSTBC) transmission in the presence of spatial correlation effect (SCE) and mutual coupling effect (MCE). Conventional MIMO channels with QOSTBC transmission suffer from several drawbacks. The number of transmit antennas is restricted to a few in order to achieve full transmission rate. Therefore, it is difficult to make a quasi-orthogonal space time block coded massive MIMO system to achieve full transmission rate. Moreover, MIMO channel with QOSTBC transmission is usually considered for the case where the number of user equipments (UEs) is one. We present a joint beamforming and spatial precoding method to deal with the above drawbacks. The proposed method incorporates a beamforming scheme and spatial precoding to formulate an appropriate optimization process to effectively alleviate the considered problems. The resulting optimization problem will be solved by using a cooperative coevolutionary particle swarm optimization algorithm under two proposed fitness functions. During the optimization process, the proposed method finds the optimal beamforming coefficients of the precoding matrix, the optimal normalized positions of transmit and receive antenna elements for the case of using linear antenna arrays, and the optimal angle differences of transmit and receive antenna elements for the case of using circular arrays. Based on the proposed method, we are able to cure the performance degradation of a quasi-orthogonal space time block coded massive MIMO system due to the SCE and MCE. Moreover, the proposed method makes QOSTBC MIMO communications with full transmission rate for any number of transmit antennas achievable. Several simulation examples are presented to show the superior bit error rate (BER) performances of QOSTBC wireless MIMO scenarios with linear as well as circular antenna arrays by using the proposed method as compared to the existing methods.
Highlights
Achieving higher transmission rates and increasing number of users have become the essential requirements of modern wireless MIMO communications
The main contributions of this paper are summarized as follows: (I) We develop a robust joint beamforming and spatial precoding method to effectively deal with quasi-orthogonal space-time block code (QOSTBC) MIMO communication systems in the presence of mutual coupling and spatial correlation effects due to using massive antennas
3.2.2 Fitness function for the second-step cooperative coevolutionary particle swarm optimization (CCPSO) For the second-step optimization process, we develop an appropriate fitness function based on the bit error rate (BER) performance for implementing the CCPSO to search the optimal spatial precoding matrix and the power constraints for downlink communication in massive MIMO channels
Summary
Achieving higher transmission rates and increasing number of users have become the essential requirements of modern wireless MIMO communications. There are practically no papers concerning the design problem of beamforming and spatial precoding for the massive MIMO systems with QOSTBC transmission and proposing effective approaches to mitigate the SCE and MCE simultaneously. The robust method proposed in this paper explores the joint design of beamforming and precoding for QOSTBC massive MIMO systems with any number of transmit antennas and receive antennas to deal with the SCE and MCE. (II) The proposed joint beamforming and spatial precoding method can preserve the advantage of reducing the overheads for downlink training and feedback of channel state information between the base station (BS) and user equipments (UEs) for the frequency-division duplex (FDD) mode of downlink transmission in MIMO systems. The Frobenius norm of a matrix S is denoted by ||S||
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