Fast-Decodable Space-Time Codes for the $N$-Relay and Multiple-Access MIMO Channel

TL;DR

This paper introduces new fast-decodable space-time codes for NAF MIMO relay and multiple-access channels, significantly reducing decoding complexity while maintaining full diversity and optimal tradeoffs.

Contribution

It presents the first general constructions of (conditionally) g-group decodable codes for NAF MIMO relay channels and extends techniques to K-user MIMO MAC channels.

Findings

Decoding complexity reduced by up to 75%.

Codes achieve full diversity and nonvanishing determinants.

Applicable to both relay and multiple-access MIMO channels.

Abstract

In this article, the first general constructions of fast-decodable, more specifically (conditionally) $g$-group decodable, space-time block codes for the Nonorthogonal Amplify and Forward (NAF) Multiple-Input Multiple-Output (MIMO) relay channel under the half-duplex constraint are proposed. In this scenario, the source and the intermediate relays used for data amplification are allowed to employ multiple antennas for data transmission and reception. The worst-case decoding complexity of the obtained codes is reduced by up to $75%$. In addition to being fast-decodable, the proposed codes achieve full-diversity and have nonvanishing determinants, which has been shown to be useful for achieving the optimal Diversity-Multiplexing Tradeoff (DMT) of the NAF channel. Further, it is shown that the same techniques as in the cooperative scenario can be utilized to achieve fast-decodability for $K$-user MIMO Multiple-Access Channel (MAC) space-time block codes. The resulting codes in addition exhibit the conditional nonvanishing determinant property which, for its part, has been shown to be useful for achieving the optimal MAC-DMT.