Behavioral modeling and digital pre-distortion techniques for RF PAs in a 3 × 3 MIMO system

Abstract

Modern telecommunications are moving towards (massive) multi-input multi-output (MIMO) systems in 5th generation (5G) technology, increasing the dimensionality of the systems dramatically. In this paper, the impairments of radio frequency (RF) power amplifiers (PAs) in a 3 × 3 MIMO system are compensated in both the time and the frequency domains. A three-dimensional (3D) time-domain memory polynomial-type model is proposed as an extension of conventional 2D models. Furthermore, a 3D frequency-domain technique is formulated based on the proposed time-domain model to reduce the dimensionality of the model, while preserving the performance in terms of model errors. In the 3D frequency-domain technique, the bandwidth of the system is split into several narrow sub-bands, and the parameters of the model are estimated for each sub-band. This approach requires less computational complexity, and also the procedure of the parameters estimation for each sub-band can be implemented independently. The device-under-test consists of three RF PAs including input and output cross-talk channels. The proposed techniques are evaluated in both behavioral modeling and digital pre-distortion (DPD) perspectives. The experimental results show that the proposed DPD technique can compensate the errors of non-linearity and memory effects in the both time and frequency domains.

Adaptive digital predistortion based on Feedback–Wiener Model for aeronautical applications

“…Therefore, complex mathematical functions are implemented to describe its gain/phase inverse characteristics and memory effects. In the literature, various models are used as a predistorter, such as the Volterra series and their variations like Hammerstein or Wiener models [23][24][25][26][27], the Memory Polynomial (MP) model [28,29], the Generalized Memory Polynomial (GMP) model [30][31][32], or the cascaded models [33,34]. In these models, a large number of coefficients is required to achieve good accuracy, but this has the consequence of making their implementation complex and slowing down the estimation process, especially when considering the real-time linearization.…”

Highly non‐linear and wide‐band mmWave active array OTA linearisation using neural network

“…Several solutions using a SISO model and modified DPD algorithms for linearisation have been proposed to combat the above challenges [2–6]. A SISO modelling where the entire transmitter is considered as a two‐port system has been presented in [7–10] using an observation receiver in far‐field together with using an MPM‐based DPD technique for linearisation of the antenna array in the presence of crosstalk.…”

“…The traditional linearisation techniques like digital pre-distortion (DPD) that are mainly based on the memory polynomial model (MPM) are facing new challenges [1] such as the following.� Highly integrated front-ends and a large number of PA's do not allow placement of feedback circuits for each branch so a single-input single-output (SISO) over-the-air (OTA) model is needed.� mmWave frequencies and wide-band linearisation must be handled. � The increasing desire for high power efficiency requires linearisation of power-efficient but highly non-linear APAs.Several solutions using a SISO model and modified DPD algorithms for linearisation have been proposed to combat the above challenges [2][3][4][5][6]. A SISO modelling where the entire transmitter is considered as a two-port system has been presented in [7-10] using an observation receiver in far-field together with using an MPM-based DPD technique for linearisation of the antenna array in the presence of crosstalk.…”

Linearization Trade-Offs in a 5G mmWave Active Phased Array OTA Setup

“…4) Using multiple transmitters and multiple antennas introduces crosstalk at PA's inputs and outputs. For mitigating the impact of these crosstalks the complexity of the algorithm is expected to increase [5] and avoiding a complexity explosion of the algorithm is another challenge. In this paper insight into the linearization mechanisms in a 5G millimeter wave (mmWave) active phased array (APA) over the air (OTA) setup is provided through measurements.…”