On the sphere decoding complexity of high-rate multigroup decodable STBCs in asymmetric MIMO systems

Natarajan, Lakshmi Prasad and Srinath, Pavan K and Rajan, Sundar B (2013) On the sphere decoding complexity of high-rate multigroup decodable STBCs in asymmetric MIMO systems. In: IEEE: Transactions on Information Theory, 59 (9). pp. 5959-5965.

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Abstract

A space-time block code (STBC) is said to be multigroup decodable if the information symbols encoded by it can be partitioned into two or more groups such that each group of symbols can be maximum-likelihood (ML) decoded independently of the other symbol groups. In this paper, we show that the upper triangular matrix encountered during the sphere decoding of a linear dispersion STBC can be rank-deficient even when the rate of the code is less than the minimum of the number of transmit and receive antennas. We then show that all known families of high-rate (rate greater than 1) multigroup decodable codes have rank-deficient matrix even when the rate is less than the number of transmit and receive antennas, and this rank-deficiency problem arises only in asymmetric MIMO systems when the number of receive antennas is strictly less than the number of transmit antennas. Unlike the codes with full-rank matrix, the complexity of the sphere decoding-based ML decoder for STBCs with rank-deficient matrix is polynomial in the constellation size, and hence is high. We derive the ML sphere decoding complexity of most of the known high-rate multigroup decodable codes, and show that for each code, the complexity is a decreasing function of the number of receive antennas.

Item Type:	Journal Article
Publication:	IEEE: Transactions on Information Theory
Publisher:	IEEE-Institute of Electrical and Electronics Engineers
Additional Information:	Copyright of this article belongs to IEEE-Institute of Electrical and Electronics Engineers.
Keywords:	Maximum-Likelihood (ML); MIMO; Multigroup Decodable Codes; Space-Time Block Codes (STBCs); Sphere Decoder
Department/Centre:	Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited:	23 Sep 2013 09:53
Last Modified:	23 Sep 2013 09:53
URI:	http://eprints.iisc.ac.in/id/eprint/47388

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