Averaged and Cluster DPDs for Beamforming Applications

This paper addresses the problem of beam angle dependence of the Digital Predistortion (DPD) algorithm in the case of beamforming 5G transmitters. While a beam dependent DPD solution based on characterizing the system for each beam angle can offer good linearity performance, its implementation in practice requires continuous and fast adaptation of the DPD coefficients given that the beam forming vector is set to change every few milliseconds. This work proposes two alternative DPD solutions, the averaged DPD (A-DPD) and the cluster DPD (C-DPD), that trade-off signal quality for reduced dependence on the beamforming angle. Experimental results using a developed MIMO/beamforming test bed using 16 element phased array antenna operating at 2.35 GHz, demonstrates that the proposed C-DPD method is able to maintain an ACPR level within 5 dB of best-case scenario obtained by beam-dependent DPD, while using only a set of 3 DPDs over 90 degrees beam angle range.