Data Detection in Single User Massive MIMO Using Re-Transmissions

Abstract

Single user massive multiple input multiple output (MIMO) can be used to increase the spectral efficiency, since the data is transmitted simultaneously from a large number of antennas located at both the base station and mobile. It is feasible to have a large number of antennas in the mobile, in the millimeter wave frequencies. However, the major drawback of single user massive MIMO is the high complexity of data recovery at the receiver. In this work, we propose a low complexity method of data detection with the help of re-transmissions. A turbo code is used to improve the bit-error-rate (BER). Simulation results indicate significant improvement in BER with just two re-transmissions as compared to the single transmission case. We also show that the minimum average SNR per bit required for error free propagation over a massive MIMO channel with re-transmissions is identical to that of the additive white Gaussian noise (AWGN) channel, which is equal to −1.6 dB. Index TermsChannel capacity, massive MIMO, turbo codesThe authors are with the

Coherent Receiver for Turbo Coded Single-User Massive MIMO-OFDM with Retransmissions

“…A question might arise: how does N ¼ 4, 8 correspond to a massive MIMO system, whereas in [34] N was as large as 512? The answer is in [34], an ideal massive MIMO was considered, wherein the channel, timing, and carrier frequency offset were assumed to be known, whereas in this work, the channel, timing, and carrier frequency offset are estimated. The estimation complexity and memory requirement increase as N 2 , for an N Â N MIMO system.…”

“…The forward (α) backward (β) recursions for decoder 1 of the turbo code is given by Eqs. (28) and (31) in [34]. The term γ 1, i, m, n in Eq.…”

“…Data detection in single-user massive MIMO systems using retransmissions, having a complexity of N rt  N 3 , where N rt is the number of retransmissions, has been proposed [34], where it was assumed thatH is known at the receiver. In this work, which is an extension of [34], we present a coherent receiver for massive MIMO systems, where not onlyH but also the carrier frequency offset and timing are estimated. Moreover, the signal model in Eq.…”

“…and it is assumed that each receive antenna gets 1= 2N rt ðÞ bits of information in each transmission [34]. We impose the constraint that…”

“…The extrinsic information from decoder 1 to decoder 2 is computed using Eqs. (32) and (33) of [34], with γ 1, i, n, ρ þ n ðÞ replaced by γ 1, i, n, ρ þ n ðÞ , n t .Theequationsfor decoder 2 are similar, except that γ 2, i, m, n in Eq. 34of [34] should be replaced by…”