Abstract-In this paper, we present a low-complexity, near maximum-likelihood (ML) performance achieving detector for large MIMO systems having tens of transmit and receive antennas. Such large MIMO systems are of interest because of the high spectral efficiencies possible in such systems. The proposed detection algorithm, termed as multistage likelihood-ascent search (M-LAS) algorithm, is rooted in Hopfield neural networks, and is shown to possess excellent performance as well as complexity attributes. In terms of performance, in a 64 × 64 V-BLAST system with 4-QAM, the proposed algorithm achieves an uncoded BER of 10 −3 at an SNR of just about 1 dB away from AWGN-only SISO performance given by Q( √ SNR). In terms of coded BER, with a rate-3/4 turbo code at a spectral efficiency of 96 bps/Hz the algorithm performs close to within about 4.5 dB from theoretical capacity, which is remarkable in terms of both high spectral efficiency as well as nearness to theoretical capacity. Our simulation results show that the above performance is achieved with a complexity of just O(NtNr) per symbol, where Nt and Nr denote the number of transmit and receive antennas.
I. INTRODUCTIONMIMO techniques have become popular in realizing spatial diversity and high data rates through the use of multiple transmit antennas [1]. We consider large MIMO systems with tens of transmit and receive antennas, which are of interest due to the high spectral efficiencies possible in such systems. The key issues in realizing large MIMO systems include lowcomplexity detection, channel estimation, and communication terminal size to accommodate large number of antennas. We address the issue of low-complexity detection in large MIMO systems here. More recent approaches to lowcomplexity multiuser detection and MIMO detection involve application of techniques from belief propagation [2], neural networks [3],[4], Markov chain Monte-Carlo methods [5], probabilistic data association [6], etc. Detectors based on these techniques have been shown to achieve an average perbit complexity linear in number of users, while achieving near-optimal performance in large multiuser CDMA system settings. These powerful techniques are increasingly being adopted in MIMO detection. In [4], we presented a Hopfield neural network based likelihood ascent search (LAS) algorithm for large MIMO detection; we showed that the LAS detector achieves near-AWGN SISO performance in a large MIMO setting with hundreds of antennas, while performing close to within 4.6 dB from theoretical capacity.