Digital Predistortion of Millimeter-Wave RF Beamforming Arrays Using Low Number of Steering Angle-Dependent Coefficient Sets

Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). This paper proposes a simplified FB architecture to be used for phased array DPD. A single FB line collects the waveform samples from the parallel paths to the FB Rx. The gain and phase of the common FB line is obtained by comparing the FB outputs to over-the-air (OTA) measurements. The overall DPD training is done by collecting the PA outputs with the common FB line, post-equalizing them to model the main lobe waveform and combining them to create the object used for array DPD. The DPD performance was verified by OTA measurements with 5GNR waveform and 28 GHz 8-path phased array transmitter. The DPD trained through the local FB line with the proposed calibration method achieved <-45dB ACPR which was close to OTA DPD performance.

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“…In general, they can be divided into conductive (e.g. [4]- [9], [10]- [11]), and over-the-air (OTA) (e.g. [3], [8], [12]- [14]) FB methods.…”

Section: Panmentioning

confidence: 99%

“…For achieving good EVM, the main target of the DPD is in the beamforming direction. Directive DPD has been proposed for example in [4]- [9].…”

Section: Introductionmentioning

confidence: 99%

Digital Predistortion of Millimeter-Wave Phased Array Transmitter With Over-the-air Calibrated Simplified Conductive Feedback Architecture

Tervo

Khan

Kursu

et al. 2020

2020 IEEE/MTT-S International Microwave Symposium (IMS)

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“…Content may change prior to final publication. receiver in order to analyse the impact of load modulation due to crosstalk is an important topic for the linearization approach and has been investigated in [18].…”

Section: Active Array Linearization Topologies State-of-the-art mentioning

confidence: 99%

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

et al. 2020

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The new generation of 5G mobile communication systems is using millimeter wave (mmWave) active phased arrays (APA) which have up to hundreds of individual analog transmitter and receiver chains and antennas. For these highly integrated systems linearization of each analog path is very challenging. Therefore a single input single output (SISO) system in combination with over the air (OTA) measurement is considered as an efficient approach for linearization. However, the knowledge about the dependency of the total SISO nonlinearity on the contributions from different blocks in the antenna array, as well as the linearization trade-offs is still missing. In this paper, an overview of the possible linearization trade-offs in an OTA setup with a mmWave APA is provided. The linearization technique is applied to a 4x4 active phased array containing up-conversion of a sub 6 GHz LTE10 signal to an RF frequency of 28 GHz. Through measurements, the effects on adjacent channel power ratio (ACPR) and error vector magnitude (EVM) have been investigated for the following scenarios: i. impact from the up-converter, ii. impact of the steering angle due to antenna crosstalk and iii. a linearity comparison between a linearized and a backed-off system. INDEX TERMS active phased array (APA), single input single output (SISO), over the air (OTA), power amplifier (PA), millimeter wave (mmWave), digital pre-distortion (DPD).

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“…Recently, [9] proposed tuning boxes for each PA, but this structure still needs at least one digital tuning component for each PA. The other way to solve this problem is to optimize the linearity of the primary beam signal, which means bad linearity in each channel but excellent linearity in the primary direction beam after signal combination in space [10]- [14]. The tricky point of this method is the estimation of the primary beam signal, which can be performed by algorithm or hardware [15].…”

Section: Introductionmentioning

confidence: 99%

Analog Predistorter Averaged Digital Predistortion for Power Amplifiers in Hybrid Beam-Forming Multi-Input Multi-Output Transmitter

You

et al. 2020

IEEE Access

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For higher data throughput, the Massive Multi-input Multi-output (MIMO) system has been widely used in modern communication systems. Due to the circuit size and power consumption, it is difficult to integrate one Radio Frequency (RF) chain for each power amplifier (PA). As a result, MIMO transmitters with hybrid beam-forming don't have enough RF chains, and this demands the digital predistortion (DPD) block to deal with several power amplifiers (PA) simultaneously, which causes a shared DPD problem. This paper presents an Analog Predistorter Averaged DPD (A 2-DPD) for hybrid beam-forming massive MIMO transmitters. To linearize more than one PAs with one shared digital predistortion unit, continuously tunable Analog Predistortion (APD) modules are employed to uniform the nonlinear behavior of PAs in each channel. Based on iterative learning control (ILC) technique, crossed normalized mean square error (CNMSE) is derived to judge the uniformity of PAs. By comparing the CNMSE of each PAs, the best similarity state of PAs can be found. The nonlinear behavior of PAs can be adjusted to a similar state by tuning the APD control voltage. The adjustment makes PAs easier to be linearized by a shared DPD. Furthermore, an averaged DPD algorithm is proposed to improve the total linearity performance for each PA. Simulations are performed to study the relationship between CNMSE and PA uniformity and further simulations show the ability of A 2-DPD to deal with a multi-PA scenario. In the end, to verify the feasibility of the proposed A 2-DPD, two class-AB PAs with operating frequency at 3.5 GHz with the same type transistor and similar design are tested. Experimental results show the proposed A 2-DPD can significantly improve the uniformity of PAs and the Adjacent Channel Power Ratio (ACPR) can be improved by 8 dB compared with using the DPD parameter of the other PA.

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Digital Predistortion of Millimeter-Wave RF Beamforming Arrays Using Low Number of Steering Angle-Dependent Coefficient Sets

Cited by 47 publications

References 17 publications

Digital Predistortion of Millimeter-Wave Phased Array Transmitter With Over-the-air Calibrated Simplified Conductive Feedback Architecture

Digital Predistortion of Millimeter-Wave Phased Array Transmitter With Over-the-air Calibrated Simplified Conductive Feedback Architecture

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

Analog Predistorter Averaged Digital Predistortion for Power Amplifiers in Hybrid Beam-Forming Multi-Input Multi-Output Transmitter

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