PC-Signal-Based PAPR Reduction Using Null Space in MIMO Channel for MIMO-OFDM Signals in Frequency-Selective Fading Channel

In this paper, we propose an extension to a previously reported complexity-efficient algorithm for adaptive peak-to-average power ratio (PAPR) reduction using the null space in a multiple-input multiple-output (MIMO) channel for MIMO-orthogonal frequency division multiplexing (OFDM) signals in a frequency-selective fading channel. We show that the effect of the adaptive PAPR reduction method using the null space in a MIMO channel is enhanced in a frequency-selective fading channel. We extend a previously reported peak cancellation (PC) signal-based algorithm (PCCNC) to accommodate the frequency-selective fading channel. In the newly proposed PCCNC, the PC signal vector is generated by multiplying basic time-domain pulse signal whose transmission band is limited to the respective frequency blocks with a beamforming (BF) vector directed at the null space of the MIMO channel in each frequency block. By adding the average PC signals of each frequency block to the transmitted signal vector in the time domain, PAPR reduction is achieved. We observe no interference imparted from the PC signal to the data streams on the receiver side when implementing a constraint limiting the transmission of the PC signal to only the null space in the MIMO channel using BF. We show that the throughput-vs.-PAPR performance of the proposed method is improved as the frequency-selectivity of the channel is increased and the proposed PCCNC successfully reduces the computational complexity compared to the conventional clipping and filtering (CF)-based algorithm.