Design of Optimal High-Rank Line-of-Sight MIMO Channels

Abstract

This paper describes a technique for realizing a high-rank channel matrix in a line-of-sight (LOS) multiple-input multiple-output (MIMO) transmission scenario. This is beneficial for systems which are unable to make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading subchannels. The technique is based on optimization of antenna placement in uniform linear arrays with respect to mutual information (MI). By introducing a new and more general 3-D geometrical model than that applied in earlier work, additional insight into the optimal design parameters is gained. We also perform a novel analysis of the sensitivity of the optimal design parameters, and derive analytical expressions for the eigenvalues of the pure LOS channel matrix which are valid also when allowing for non-optimal design. Furthermore, we investigate the approximations introduced in the derivations, in order to reveal when the results are applicable. The LOS matrix is employed in a Ricean fading channel model, and performance is evaluated with respect to the average MI and the MI cumulative distribution function. Our results show that even with some deviation from the optimal design, the LOS MIMO case outperforms the i.i.d. Rayleigh case in terms of MI.

Modelling for vehicle to vehicle applications

“…Examining the situation for larger displacements, capacities in excess of 8 bits/s/Hz can still be achieved at a separation of 50 m. In the region where the separation distance is less than 20 m, the achievable capacity is in excess of the Rayleigh capacity of 11.4 bits/s/Hz for the same SNR. This observation is consistent with results in [12] where different optimised architectures are proposed for near-field LoS propagation. component of the propagation.…”

“…As indicated, the results for the VTR situation, indicating that higher K factors result in capacity increases, are in line with results presented in [3,4,11,12]. However, as the mobile separation increases between communicating vehicles, the capacity falls below that of the Rayleigh case as the channels become more correlated.…”

Indoor Millimeter Wave MIMO: Feasibility and Performance

“…Our interest here is in antennas with larger antenna spacing (feasible because the wavelength is so small), where purely LOS channels can indeed offer multiple degrees of freedom. The capacity of LOS MIMO channels was previously studied by several authors [11], [12], [13], [14], with a view to identifying the optimal antenna array geometries that maximize the LOS channel capacity. In this paper, we show that such geometries are indeed near-optimal in terms of degrees of freedom maximization, given a constraint on the node form factor.…”

“…We refer to a pair of arrays satisfying (5) as optimally spaced ULAs. This orthogonality condition was originally derived in [11], and equivalent conditions have since been derived for broadside aligned uniform rectangular arrays (URAs) [13], as well as arbitrarily aligned ULAs [14] and URAs [19]. Now, if the lengths of the transmit and receive arrays are constrained and is arbitrary, we can determine from (5) the maximum number of antennas that can be supported while preserving the orthogonality condition.…”

Design of a Practical and Compact mm-Wave MIMO System with Optimized Capacity and Phased Arrays

“…In order to get spatial multiplexing at lower frequencies, rich multipath is needed. The main advantage of using MIMO at mm-wave bands is that by having a proper inter-element spacing in both transmitting and receiving antennas, multiple independent streams, and thus high capacity, can be obtained, even in LOS [5]. Different LOS MIMO systems have been proposed and tested indoor [6] and outdoor [7,8].…”