Power Scalable Beam-Oriented Digital Predistortion for Compact Hybrid Massive MIMO Transmitters

This article proposes a power scalable beam-oriented digital predistortion (PSBO-DPD) architecture suitable for linearizing PAs in compact hybrid massive multiple-input multiple-output (MIMO) transmitters, without the need to implement a dedicated observation path for each PA. Based on an assumption that all PAs are similar, the feedback configuration for only one PA is sufficient to acquire the nonlinear information of PAs in a given subarray, which are driven at different power levels due to amplitude beamforming. Therefore, the PSBO-DPD resolves the deficiency of current DPD techniques in hybrid beamforming array by estimating the output signal of each PA from the only captured output signal from one PA to construct the main beam signal of the subarray. The predistorter is identified based on the estimated main beam signal and the input signal driving the subarray. To estimate the outputs of each PA efficiently, a power scalable cascade PA model is proposed to reduce the computational complexity and associated overhead in terms of cost and energy consumption. Measurements on a 4-element antenna array with up to 100 MHz bandwidth signal are carried out to validate and bench mark the proposed PSBO-DPD against the existing DPD technique in hybrid massive MIMO transmitters.