A New Family of Low-Complexity Decodable STBCs for Four Transmit Antennas

TL;DR

This paper introduces a new family of low-complexity, high-rate space-time block codes for four transmit antennas, optimizing decoding complexity and coding gain through novel construction and constellation stretching.

Contribution

It presents a new construction method for rate-1 FGD STBCs with minimal decoding complexity, and develops rate-2 and rate-3/2 codes with optimized performance and complexity trade-offs.

Findings

Lowest worst-case decoding complexity among comparable STBCs

Constant coding gain regardless of QAM constellation

Lower average decoding complexity in simulations

Abstract

In this paper we propose a new construction method for rate-1 Fast-Group-Decodable (FGD) Space-Time-Block Codes (STBC)s for 2^a transmit antennas. We focus on the case of a=2 and we show that the new FGD rate-1 code has the lowest worst-case decoding complexity among existing comparable STBCs. The coding gain of the new rate-1 code is then optimized through constellation stretching and proved to be constant irrespective of the underlying QAM constellation prior to normalization. In a second step, we propose a new rate-2 STBC that multiplexes two of our rate-1 codes by the means of a unitary matrix. A compromise between rate and complexity is then obtained through puncturing our rate-2 code giving rise to a new rate-3/2 code. The proposed codes are compared to existing codes in the literature and simulation results show that our rate-3/2 code has a lower average decoding complexity while our rate-2 code maintains its lower average decoding complexity in the low SNR region at the expense of a small performance loss.