Abstract
New perspectives for wireless communications have brought new techniques, such as a very large number of antennas at a base station (BS) serving multiple user terminals (UTs) with a single antenna each, known as massive MIMO (M-MIMO). M-MIMO linear detectors, such as maximal-ratio combining (MRC), zero-forcing (ZF) or minimum-mean-square error (MMSE) can achieve excellent performance with low complexity due to the channel hardening property. However, imperfect channel estimation produces a penalty in the performance. An average bit error rate (BER) performance analysis over time-invariant channel is presented for M-MIMO systems under imperfect channel estimation in contrast with most of M-MIMO literature that uses the ergodic capacity approach. Closed-form expressions and bounds to evaluate the average BER are derived for MRC, ZF and MMSE detectors in a unicellular environment considering M-QAM modulation. Furthermore, an expression to evaluate the normalized signal-to-noise ratio (E b /N 0 ) penalty due to the imperfect channel estimation is presented. Montecarlo numerical simulations are used to verify the tightness of the derived equations which are a function of the number of BS antennas, number of users, coherence time interval, number of pilot symbols and the E b /N 0 of pilot and data symbols used for channel estimation and data detection.
Highlights
The technological transition to fifth generatio (5G) systems is expected to increase a thousand-fold higher throughput [1]–[3]
Massive MIMO (M-MIMO) has emerged as one of the most promising technologies towards this direction, because massive MIMO (M-MIMO) includes a very large number of antennas at the base station (BS) serving a reduced number of user terminals (UTs) which are tipically equipped with one antenna
NUMERICAL RESULTS simulation and numerical results are presented for M-MIMO in a unicellular scenario
Summary
The technological transition to fifth generatio (5G) systems is expected to increase a thousand-fold higher throughput [1]–[3]. In [30], an approximated expression is derived to evaluate the average BER of the MRC detector with ICSI, with this aim the MMSE channel estimator is employed considering the minimum number of pilot symbols in a relay network with M-MIMO. In the literature, there is a lack of studies of linear detectors for M-MIMO systems at bit-level, evaluating studying the BER for M-QAM modulation, under the effects of ICSI using the MMSE channel estimator for different number of pilot symbols. The average BER for the uplink of unicellular M-MIMO systems using MRC, ZF and MMSE detectors under ICSI for flat fading time-invariant channel is presented. Simple and exact expressions are derived for each detector in order to evaluate the average BER For this purpose, M-QAM modulation, N antennas at the BS and K UTs are considered. E {·} or x denotes expectation, Var {·} variance and Cov {·} covariance operators of its argument
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