A user cooperative beamforming approach to PAPR reduction in MIMO-OFDM uplink

We consider a scheme for PAPR reduction based on user cooperation in a single-cell multi-user MIMO-OFDM uplink system. The idea is to utilize the unused space-frequency resources induced by collaborative beamforming to transmit dummy symbols, resulting in a transmit signal with reduced per-antenna peak powers. Traditionally collaborative beamforming has been used to acquire beamforming gain, i.e., extended cell coverage and improved rates, while our approach also in addition reduces the transmit signal PAPR of individual user antennas. The reduced PAPR enables the users to allocate more power to data transmission, resulting in a higher system sum-rate for a fixed peak transmit power budget while also relaxing the strict linearity requirements of the user equipment RF components. We also account for the power required to exchange data between cooperating users by utilizing a simple AWGN channel model between users. We formulate the PAPR minimization problem as a convex optimization problem that reduces the PAPR of a given time domain transmit signal provided there are subcarriers with no previous bit allocations, which is a valid assumption especially at mid- and low-SNR regimes.