Time-Varying Space-Only Codes for Coded MIMO

TL;DR

This paper introduces a novel space-only, time-varying precoder for MIMO systems, achieving full diversity and maximal multiplexing gain with reduced detection complexity, validated through theoretical proofs and numerical simulations.

Contribution

It proposes the EMI code, a new coded modulation paradigm that simplifies MIMO decoding while maintaining optimal diversity and multiplexing performance.

Findings

Achieves full diversity in MIMO channels.

Maintains maximal multiplexing gain.

Reduces detection complexity compared to traditional codes.

Abstract

Multiple antenna (MIMO) devices are widely used to increase reliability and information bit rate. Optimal error rate performance (full diversity and large coding gain), for unknown channel state information at the transmitter and for maximal rate, can be achieved by approximately universal space-time codes, but comes at a price of large detection complexity, infeasible for most practical systems. We propose a new coded modulation paradigm: error-correction outer code with space-only but time-varying precoder (as inner code). We refer to the latter as Ergodic Mutual Information (EMI) code. The EMI code achieves the maximal multiplexing gain and full diversity is proved in terms of the outage probability. Contrary to most of the literature, our work is not based on the elegant but difficult classical algebraic MIMO theory. Instead, the relation between MIMO and parallel channels is exploited. The theoretical proof of full diversity is corroborated by means of numerical simulations for many MIMO scenarios, in terms of outage probability and word error rate of LDPC coded systems. The full-diversity and full-rate at low detection complexity comes at a price of a small coding gain loss for outer coding rates close to one, but this loss vanishes with decreasing coding rate.