October 2013, 20(5): 51–56 www.sciencedirect.com/science/journal/10058885 http://jcupt.xsw.bupt.cn The Journal of China Universities of Posts and Telecommunications Mutual information assessment of LOS MIMO systems with reconfigurable antenna arrays GAO Jun-jun 1 (), ZHANG Jian-hua 2,3 , TAO Xiao-feng 2,3 1. Science and Technology on Information Systems Engineering Laboratory, Beijing 100038, China 2. Wireless Technology Innovation Institute, Beijing University of Posts and Telecommunications, Beijing 100876, China 3. Key Laboratory of Universal Wireless Communication, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing 100876, China Abstract In presence of line-of-sight (LOS) propagation, multiple-input multiple-output (MIMO) systems can achieve maximum capacity over the whole signal-to-noise ratio (SNR) region by deploying reconfigurable antenna arrays. In this paper, the moment generating function (MGF) formulas of the mutual information (MI) is obtained for LOS MIMO systems with reconfigurable arrays. Then the exact expression of the mean MI is derived in an easily evaluated form. The results show an excellent match between the theoretical curves and the Monte-Carlo simulations. Keywords multiple-input multiple-output, line-of-sight, mutual information, reconfigurable antenna array, Wishart 1 Introduction MIMO systems have aroused a lot of academia and industry interest due to the promising channel capacity without the spending of additional bandwidth and transmit power [1]. Assuming independent and identically distributed (i.i.d.) Rayleigh fading channel, the capacity will linearly increase with the minimum amount of the transmit and receive antennas in theory. The existence of dominated line-of-sight (LOS) propagation is often unavoidable in practice, and the channel between each antenna pair can be commonly modeled as Ricean distribution. Due to the high spatial correlation of the received signal between different antenna pairs, LOS propagation is usually a great limitation to MIMO technique, which results in rank-deficient channel matrix. An attractive scheme, known as the optimized LOS MIMO systems, is proposed in Ref. [2] to break through the LOS propagation limitation. The idea is that full-rank LOS channel is constructed by smart configuration of the Received date: 07-01-2013 Corresponding author: GAO Jun-jun, E-mail: gaojunjun1986@gmail.com DOI: 10.1016/S1005-8885(13)60089-8 transmit and receive antenna arrays, which will lead to LOS rays orthogonality. The performance of the optimized LOS MIMO system and its sensitivity to array displacement and orientation were experimentally evaluated through channel measurements [3]. Exact and high signal-to-noise ratio (SNR) asymptotic expressions for the mutual information (MI) statistics of the optimized LOS MIMO system were derived in [4]. Other approaches such as using reflectarray [5] and repeaters [6] to improve LOS MIMO channel capacity have appeared recently. However, the optimized LOS MIMO systems only exhibit optimal performance in the high SNR region. To achieve maximum capacity at any given operating SNR, the reconfigurable antenna array scheme is proposed [7] that adaptively adjusting the transmit and receive array configuration as a function of the SNR. The MI statistics are crucial for MIMO performance assessment [8]. In this paper, the joint ordered eigenvalue probability density function (p.d.f.) is first derived for LOS MIMO systems with reconfigurable arrays based on the Wishart random matrix theory. Then the exact expression for the MI MGF is obtained. Based on the moment generating function (MGF),