(Received: 2-May-2020, Revised: 2-Jul.-2020 and 2-Aug.-2020 , Accepted: 28-Aug.-2020)
In this paper, the least-squares channel estimation (LSCE) is investigated for Massive-Multiple-Input Multiple- Output (Ma-MIMO) OFDM systems based on pilot tones. The uplink (UL) transmission is considered, in which a channel estimation approach is proposed by forming a matrix equation with all the unknown channel parameters (UCPs) in one vector and estimating that vector by the least-square (LS). The mean square error (MSE) of the LSCE is computed. Flat fading and frequency-selective fading are evaluated for single and multiple OFDM symbols, concerning this MSE. The requirement of the pilot sequence is investigated in flat fading and frequency- selective fading. Besides, it is shown that the number of pilots exhibits desirable trade-offs between the base station (BS) antenna and channel taps. Rayleigh and Rician channel fading is considered to evaluate the system performance with different channel taps. Performances are compared in terms of Bit Error Rate (BER). Moreover, to enhance linear detector performance, nonlinear detectors are used. The requirement of pilot sequence and the increased receive diversity provide a lower BER for the nonlinear detector.

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