Forward Modeling Assisted Digital Predistortion Method for Hybrid Beamforming Transmitters with a Single PA Feedback

Li, Hongmin; Li, Gang; Zhang, Yikang; Qiao, Wen; Liu, Falin

doi:10.1109/apccas.2018.8605680

Cited by 9 publications

(3 citation statements)

References 5 publications

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“…Compared to simply backing off the PA input power, a much more efficient approach to control the PA-induced emissions while still operating close to saturation is to utilize digital predistortion (DPD) [29], [30]. DPD has been recently studied in the context of large antenna arrays in [31]- [40]. In [31], [32], fully digital beamforming based system was investigated.…”

Section: A Nonlinear Distortion and State-of-the-artmentioning

confidence: 99%

“…Since the PA units are in practice mutually different, this is essentially an under-determined problem and generally yields reduced linearization performance, when compared to linearizing each PA individually. In [33], the DPD learning is based on observing only a single PA output, within each subarray, while the works in [34], [40] consider the multiuser case but adopt a simplifying assumption that all the PAs are mutually identical. As a result, both approaches lead to reduced linearization performance in practice, due to the mutual differences between real PA units and their exact nonlinear distortion characteristics.…”

Section: A Nonlinear Distortion and State-of-the-artmentioning

confidence: 99%

“…Such DPD processing results in minimizing the OOB emissions in the direction of the intended receiver [36]. The works in [32]- [40] either assume single-user transmission or adopt some other simplifying assumptions such as all PAs being identical, pure LOS propagation or narrowband fading. Thus, DPD techniques for true multi-user hybrid MIMO systems under mutually different PA units and broadband channels do not exist in the current literature.…”

Section: A Nonlinear Distortion and State-of-the-artmentioning

confidence: 99%

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Digital Predistortion for Multiuser Hybrid MIMO at mmWaves

Brihuega,

Anttila,

Abdelaziz

et al. 2019

Preprint

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Efficient mitigation of power amplifier (PA) nonlinear distortion in hybrid precoding based broadband mmWave systems is an open research problem. In this article, we first carry out detailed signal and distortion modeling in broadband multi-user hybrid MIMO systems with a bank of nonlinear PAs in each subarray. Building on the derived models, we then propose a novel digital predistortion (DPD) solution that requires only a single DPD unit per transmit chain or subarray. The proposed DPD system makes use of a closed-loop learning architecture and combined feedback observation receivers that merge the individual PA output signals within each subarray for DPD parameter learning purposes. Such combined feedback signals reflect the true received signals at the intended users, from the nonlinear distortion point of view. We show that, under spatially correlated multipath propagation, each DPD unit can provide linearization towards every intended user, or more generally, towards all spatial directions where coherent propagation is taking place. In the directions with less coherent combining, the joint effect of DPD and beamforming keeps the nonlinear distortion at a sufficiently low level. Extensive numerical results are provided, demonstrating and verifying the excellent linearization performance of the proposed DPD system in different evaluation scenarios.

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