Time reversal with post-equalization for OFDM without CP in massive MIMO

Abstract

Abstract-This paper studies the possibility of eliminating the redundant cyclic prefix (CP) of orthogonal frequency division multiplexing (OFDM) in massive multiple-input multiple-output systems. The absence of CP increases the bandwidth efficiency in expense of intersymbol interference (ISI) and intercarrier interference (ICI). It is known that in massive MIMO, different types of interference fade away as the number of base station (BS) antennas tends to infinity. In this paper, we investigate if the channel distortions in the absence of CP are averaged out in the large antenna regime. To this end, we analytically study the performance of the conventional maximum ratio combining (MRC) and realize that there always remains some residual interference leading to saturation of signal to interference (SIR). This saturation of SIR is quantified through mathematical equations. Moreover, to resolve the saturation problem, we propose a technique based on time-reversal MRC with zero forcing multiuser detection (TR-ZF). Thus, the SIR of our proposed TR-ZF does not saturate and is a linear function of the number of BS antennas. We also show that TR-ZF only needs one OFDM demodulator per user irrespective of the number of BS antennas; reducing the BS signal processing complexity significantly. Finally, we corroborate our claims as well as analytical results through simulations.

OFDM Without CP in Massive MIMO

“…In the case of ZF post-equalization, the first two terms given in Table II account for the calculation of the equivalent channel responses g kj (ℓ) given in (15) using fast-convolution 1 . The third term, i.e., 1 2 K 2 N log 2 N , is arising from the calculation of the coefficients G (i,i) kj,pp according to (22). The fourth term is due to the matrix inversion G (i,i) pp −1 .…”

“…In the massive MIMO context, orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) is particularly attractive because it enables the conversion of the frequency-selective channels between each mobile terminal (MT) antenna and the BS antennas into a set of flat-fading channels over each subcarrier band. Therefore, the MT data Parts of the concepts based on which the contents of this paper are built have been presented in [1].…”

Artificial Intelligence-Aided Receiver for a CP-Free OFDM System: Design, Simulation, and Experimental Test

“…The BER performance with 16-QAM is similar to that with 64-QAM. The difference from 64-QAM is that the LMMSE+OAMP and CE-NET+OAMP have more severe amplitude fluctuation and bigger performance degradation when the SNR is more than 25 dB because the damping exploded and the actual noise does not match the estimated noise owing to the greater noise introduced by the first term of (7). Clearly, the OAMP-NET is superior to the OAMP algorithm as the former needs no hand-crafted damping parameters but can prevent damping exploration.…”

“…The OAMP-based detector [30] can be summarized as Algorithm 1. In (7), l indicates the index of the iteration times. According to [13], the optimal matrix P l is given by…”

“…The impact of removing the CP in OFDM in massive multiple-input multiple-output (MIMO) systems has been investigated in [7]- [9]. In addition to signal detection, channel estimation is another challenging issue because the received pilot signals are influenced by CP removal.…”