Peak Cancellation Signal-Based Parallel PAPR Reduction Method Using Low-Dimensional Null Space in Massive MIMO-OFDM

We investigate the peak-to-average power ratio (PAPR) reduction method in downlink massive multi-user multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) transmission. In this paper, we develop a new complexity-reduced PAPR reduction method based on peak cancellation (PC) signals using the null space in a MIMO channel for MIMO-OFDM signals. The proposed method divides the transmitter antennas jointly considered in the PAPR reduction process and utilizes the low-dimensional null space in the MIMO channel to reduce the computational complexity in the PAPR reduction process. Besides, it can execute PAPR reduction based on PC signals in parallel, suppressing the degradation of PAPR reduction capability due to the reduction of the dimension of the null space in the MIMO channel. Computer simulation results show that the proposed method significantly reduces computational complexity while keeping a sufficient PAPR reduction capability.

I. Introduction

In future wireless communications systems such as 6G, an extremely high data rate will be demanded. As one of the promising technologies, terahertz (THz) communications have been much gained attention since wide bandwidth is available. Meanwhile, the signal in THz communications suffers from very high path loss [1]. Hence, downlink orthogonal frequency division multiplexing (OFDM)-based multi-user (MU) massive multiple-input multiple-output (MIMO) [2], [3] transmission with beamforming (BF) is essential to extend the range of mobile broadband. However, peak-to-average power ratio (PAPR) of the OFDM signals is usually very high, which is further enhanced because of the difference in the levels of transmission power among the transmitter antennas caused by the BF process in massive MIMO. In a massive MIMO environment, the cost and size of power amplifier for each transmission antenna are desired to be low. Therefore, the PAPR reduction is essential to realize massive MIMO-OFDM transmission with BF.