Line of Sight 2 x nr MIMO with Random Antenna Orientations

TL;DR

This paper investigates LoS MIMO channels with random antenna orientations, revealing how array geometry affects error rates and proposing a system design that maintains good performance across orientations.

Contribution

It analyzes the impact of array geometry on error probability in LoS MIMO with random orientations and proposes a robust system design for consistent performance.

Findings

Planar arrays have error decay similar to rank 1 channels.

Tetrahedral arrays achieve exponential error decay in SNR.

A new LoS MIMO system design ensures reliable performance across orientations.

Abstract

Line-of-sight (LoS) multiple-input multiple-output (MIMO) gives full spatial-multiplexing gain when the antenna array geometry and orientation are designed based on the inter-terminal distance. These known design methodologies, that hold for antenna arrays with fixed orientation, do not provide full MIMO gains for arbitrary array orientations. In this paper, we study LoS MIMO channels with random array orientations when the number of transmit antennas used for signalling is 2. We study the impact of common array geometries on error probability, and identify the code design parameter that describes the high signal-to-noise ratio (SNR) error performance of an arbitrary coding scheme. For planar receive arrays, the error rate is shown to decay only as fast as that of a rank 1 channel, and no better than 1/SNR^3 for a class of coding schemes that includes spatial multiplexing. We then show that for the tetrahedral receive array, which uses the smallest number of antennas among non-planar arrays, the error rate decays faster than that of rank 1 channels and is exponential in SNR for every coding scheme. Finally, we design a LoS MIMO system that guarantees a good error performance for all transmit/receive array orientations and over a range of inter-terminal distances.