Linearization for Hybrid Beamforming Array Utilizing Embedded Over-the-Air Diversity Feedbacks

Liu, Xin; Chen, Wenhua; Chen, Long; Ghannouchi, Fadhel M.; Feng, Zhenghe

doi:10.1109/tmtt.2019.2944821

Cited by 47 publications

(38 citation statements)

References 33 publications

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“…Coupling antennas in near-field are used in [13], but those can effectively only collect paths connected to the adjacent antenna elements without significant attenuation and require breaking the uniform array geometry. The conductive FB architectures contain a single power amplifier (PA) FB [10], switchable FB [4], [5], [7] and combined anti-beamforming or phased FB [6], [11].…”

Section: A State-of-the-art Array Feedback Rx Architecturesmentioning

confidence: 99%

“…2(a). The DPD trained with such a feedback is presented for example in [3], [8], [12], [13], [15], [16]. Use of reference antennas does not add post-PA losses from e.g., couplers and switches that would decrease the overall power efficiency.…”

Section: A Over-the-air Feedbackmentioning

confidence: 99%

“…The reference antenna is only placed in a certain steering angle, and the antenna may interfere with the actual beam formed by the array towards the end user. The feedback antenna or a probe can be also placed to the nearfield as in [13], where the authors use a coupling antenna surrounded by the actual Tx elements to sample individual PA outputs. From the RF implementation perspective, this offers a possibility to integrate the measurement Rx as a part of the actual array in a compact form factor.…”

Section: A Over-the-air Feedbackmentioning

confidence: 99%

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Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Far-Field Calibration

Tervo¹,

Khan²,

Kursu³

et al. 2021

IEEE Trans. Microwave Theory Techn.

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Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). In this paper, we propose a FB concept for DPD in a time-division-duplex (TDD) phased arrays. We use a single FB line to collect the waveform samples from the parallel transmit paths to the FB Rx. The TDD switches are used to enable and disable individual transmit paths. The feedback is calibrated by comparing the FB outputs from individual PAs to over-the-air (OTA) measurement reference performed with a frequency modulated continuous wave (FMCW) signal. The individual PA measurements are post-equalized before the DPD training to model the far-field signal. Three alternative strategies are considered for training the DPD through the calibrated FB line and compared with the OTA DPD. The performance is verified by OTA measurements of a 28 GHz phased array transmitter and with fifth generation New Radio waveform in terms of total radiated (TR) adjacent channel power ratio (ACPR), cumulative absolute ACP (CACP), and main lobe error vector magnitude (EVM). The best EVM and ACPR performance is achieved by the strategy where the individual PA responses are treated independently. The methods were comparable to the OTA DPD performance, achieving all < 37 dB TRACPR, −29 dBm/MHz CACP, and ≤ 7 % EVM.

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Section: A State-of-the-art Array Feedback Rx Architecturesmentioning

confidence: 99%

Section: A Over-the-air Feedbackmentioning

confidence: 99%

Section: A Over-the-air Feedbackmentioning

confidence: 99%

See 1 more Smart Citation

Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Far-Field Calibration

Tervo¹,

Khan²,

Kursu³

et al. 2021

IEEE Trans. Microwave Theory Techn.

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“…In practice, this can be implemented as part of the receiver section of the same device (i.e. diversity receiver) which has been presented by [17]. This kind of adaptive on-line OTA-DPD based on the diversity feedback uses an iterative procedure to eliminate the uncorrelated components from the feedback signal for accurate DPD.…”

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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“…Authors of [1] used uncorrelated signals in each RF chain, which eases DPD model extraction but the system cannot achieve beamforming. DPD for MU-MIMO transmitters sending each user's data via a seperate subarray in hybrid MIMO transmitters was proposed in [2], [3]. Since each subarray can process only one user's signals and signals in different subarrays must be uncorrelated, these solutions are not compatible with common precoding schemes and greatly reduce the flexibility in system design.…”

Section: Introductionmentioning

confidence: 99%

OTA-Based Data Acquisition and Signal Separation for Digital Predistortion of Multi-User MIMO Transmitters in 5G

Wang

et al. 2020

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

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In this paper, a non-interruptive over-the-air (OTA) data acquisition method is presented to characterize system nonlinearity and calibrate digital predistortion (DPD) in multiuser (MU) multiple-input multiple-output (MIMO) transmitters with low hardware complexity. Based on a unified system model for fully-digital and hybrid MU-MIMO transmitters, the requirements and difficulties of data acquisition for MU-MIMO DPD are outlined first. A versatile OTA data acquisition technique, featuring a multi-observation forward modelling procedure, is thereby developed to obtain power amplifier (PA) output without interrupting the operation of the MIMO transmitters. By using this method, the output of each PA can be reconstructed instead of directly measuring each PA's output, even when the output signals of PAs are correlated. DPD can therefore be effectively constructed to mitigate the distortion. Experimental results demonstrate that the proposed approach can accurately estimate each PA output and linearize all PAs in the array.

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Linearization for Hybrid Beamforming Array Utilizing Embedded Over-the-Air Diversity Feedbacks

Cited by 47 publications

References 33 publications

Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Far-Field Calibration

Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Far-Field Calibration

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

OTA-Based Data Acquisition and Signal Separation for Digital Predistortion of Multi-User MIMO Transmitters in 5G

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