Digital predistortion of amplitude varying phased array utilising over-the-air combining

Abstract

Abstract-In this paper, we propose a simple polynomial linearisation technique for nonlinear phased arrays including amplitude control. Due to the large number of antennas and thus power amplifiers in the array, it is inefficient to linearise each power amplifier individually. Therefore, it is demonstrated that the array can be linearised over-the-air using single polynomial. The simulations show that the linearisation is achieved by first linearising the higher driven PAs at the precompression region and then cancelling the compression by the heavily expanding lower driven PAs. The proposed approach offers an alternative way of re-thinking the concept of array linearisation over multiple PAs.Index Terms-digital predistortion, hybrid beamforming, polynomial model, power amplifiers, 5G.

Analyzing the Effects of PA Variations on the Performance of Phased Array Digital Predistortion

“…Hence, the nonlinearity of an array may depend on the direction of observation. This has been further discussed in [3] where the authors show that these differences can be actually utilized to compensate each other in the array far field. Hence, the standard figures of merit describing the nonlinear distortion of an array should be revised to have a right meaning from the system perspective [10].…”

“…Two main strategies has been proposed to linearize a phased array [3] with a single DPD. One can either try to linearize the individual PAs e.g.…”

“…By using the combined feedback, standard DPD techniques can be used to linearize the whole array with single DPD. Other feedback methods proposed in the literature are single PA feedback [7], reference antenna [5] or timely-shared feedback [3], [6]. The channel-emulating phased feedback proposed in this paper enables fast DPD process and utilization of direction dependency of the nonlinear array response.…”

“…Utilization of a single DPD for the complete array has been studied e.g. in [3]- [7]. However, the significance of large variations over parallel PA operation points have not been discussed in detail in the mentioned references.…”

“…However, the significance of large variations over parallel PA operation points have not been discussed in detail in the mentioned references. For example in [3], the effects of the parametric variations of individual PAs were limited to a fixed tapering scheme, which was used to reduce the sidelobes of the beam pattern. In this paper we highlight that any amplitude and phase variations can be utilized to enhance the EVM by allowing them to cancel each other in the desired direction.…”