Optimal Design Method of MIMO Antenna Directivities and Corresponding Current Distributions by Using Spherical Mode Expansion

Abstract

This paper proposes a new methodology to design optimal antennas for MIMO (Multi-Input Multi-Output) communication systems by using spherical mode expansion. Given spatial channel properties of a MIMO channel, such as the angular profile at both sides, the optimal MIMO antennas should provide the largest channel capacity with a constraint of the limited implementation space (volume). In designing a conventional MIMO antenna, first the antenna structure (current distribution) is determined, second antenna directivity is calculated based on the current distribution, and thirdly MIMO channel capacity is calculated by using given angular profiles and obtained antenna directivity. This process is repeated by adjusting the antenna structure until the performance satisfies a predefined threshold. To the contrary, this paper solves the optimization problem analytically and finally gives near optimal antenna structure (current distribution) without any greedy search. In the proposed process, first the optimal directivity of MIMO antennas is derived by applying spherical mode expansion to the angular profiles, and second a far-near field conversion is applied on the derived optimal directivity to achieve near optimal current distributions on a limited surface. The effectiveness of the proposed design methodology is validated via numerical calculation of MIMO channel capacity as in the conventional design method while giving near optimal current distribution with constraint of an antenna structure derived from proposed methodology.

A Study on Optimal Beam Patterns for Single User Massive MIMO Transmissions

“…Additionally, the convergence may be slow when the channels between BS and UE are correlated as shown in Sect. 5.2 of [10]. In such a case, the calculation is finished based on the iteration counts, elapsed time, and so on.…”

“…By using the SU-massive MIMO system model with SME, we obtain the optimal beam patterns of BS and UE. The optimization method described in [10] is expanded in the case of the different antenna volume at BS and UE. Since the beam patterns are determined by the spherical mode coefficients (SMCs) , we introduce the optimization method of SMCs of BS and UE.…”

“…By using Galerkin method, which is one of the methods for solving the integral equation, Eq. ( 29) is represented as a linear equation as shown in [10], given by…”

“…In this paper, we introduce a method using OBPB (Optimal Beam Projection Beamforming) proposed in [10] for designing antenna configuration parameters of the SU massive MIMO. The goal of the study is to maximize channel capacity by increasing the effective number of beams (streams) in a given propagation channel with special beam patterns and shapes of antenna designed by the OBPB.…”

Antenna Optimization for WBAN Based on Spherical Wave Functions De-Embedding

“…Apart from WBAN applications, Arai et. al have recently utilized SWF modeling for antenna optimization to maximize MIMO channel capacities [15].…”