tailieunhanh - Digital predistortion for Hybrid MIMO transmitters

This article investigates digital predistortion (DPD) linearization of hybrid beamforming large-scale antenna transmitters. We propose a novel DPD processing and learning technique for an antenna sub-array, which utilizes a combined signal of the individual power amplifier (PA) outputs in conjunction with a decorrelation-based learning rule. In effect, the proposed approach results in minimizing the nonlinear distortions in the direction of the intended receiver. This feature is highly desirable, since emissions in other directions are naturally weak due to beamforming. The proposed parameter learning technique requires only a single observation receiver, and therefore supports simple hardware implementation. | 1 Digital Predistortion for Hybrid MIMO Transmitters Mahmoud Abdelaziz Member IEEE Lauri Anttila Member IEEE Alberto Brihuega Student Member IEEE Fredrik Tufvesson Fellow IEEE Mikko Valkama Senior Member IEEE arXiv 6 Apr 2018 Abstract This article investigates digital predistortion DPD linearization of hybrid beamforming large-scale antenna transmitters. We propose a novel DPD processing and learning technique for an antenna sub-array which utilizes a combined signal of the individual power amplifier PA outputs in conjunction with a decorrelation-based learning rule. In effect the proposed approach results in minimizing the nonlinear distortions in the direction of the intended receiver. This feature is highly desirable since emissions in other directions are naturally weak due to beamforming. The proposed parameter learning technique requires only a single observation receiver and therefore supports simple hardware implementation. It is also shown to clearly outperform the current state-of-the-art technique which utilizes only a single PA for learning. Analysis of the feedback network amplitude and phase imbalances reveals that the technique is robust even to high levels of such imbalances. Finally we also show that the array system out-of-band emissions are wellbehaving in all spatial directions and essentially below those of the corresponding single-antenna transmitter due to the combined effects of the DPD and beamforming. Index Terms 5G digital predistortion large-array transmitters hybrid beamforming power amplifiers out-of-band emissions. I. INTRODUCTION LARGE-scale antenna systems are expected to be one of the key enablers of enhanced spectral and energy efficiency in future wireless communication systems 1 2 . Utilizing fully-digital beamforming at the transmitter as most works assume would mean that each antenna should have a dedicated transmit chain as depicted in Fig. 1 a . To relieve the large hardware costs of such implementations