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 estimate 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 one 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 channels fading are considered to evaluate system performance with different channel taps. Their performances are compared in terms of Bit Error Rate (BER). Moreover, to enhance linear detectors performance nonlinear detectors are used. The requirement of pilot sequence and the increased receive diversity provide a lower BER for the nonlinear detector.
Key words: Massive MIMO, OFDM, flat and frequency selective fading, OSIC, Rician channel and Rayleigh channel
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