Haoyu Wang

Bio: Haoyu Wang is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Predistortion & RF power amplifier. The author has an hindex of 4, co-authored 11 publications receiving 60 citations. Previous affiliations of Haoyu Wang include Chinese Academy of Sciences.

1-bit Observation for Direct-Learning-Based Digital Predistortion of RF Power Amplifiers

Abstract: In this paper, we propose a low-cost data-acquisition approach for model extraction of digital predistortion (DPD) of RF power amplifiers. The proposed approach utilizes only 1-bit-resolution analog-to-digital converters (ADCs) in the observation path to digitize the error signal between the input and output signals. The DPD coefficients are then estimated based on the direct learning architecture using the measured signs of the error signal. The proposed solution is proved feasible in theory, and the experimental results show that the proposed algorithm achieves the performance equivalent to that using the conventional method. Replacing high-resolution ADCs with 1-bit comparators in the feedback path can dramatically reduce the power consumption and cost of the DPD system. The 1-bit solution also makes DPD become practically implementable in future broadband systems since it is relatively straightforward to achieve an ultrahigh sampling speed in data conversion using only simple comparators.

2D orthogonal polynomials for concurrent dual-band digital predistortion

Abstract: In order to alleviate the ill-conditioning problem when using the 2D memory polynomial (MP) model for concurrent dual-band digital predistortion (DPD), 2D orthogonal polynomials are proposed in this paper. Closed form expressions for 2D orthogonal polynomials are derived for uniform amplitude distribution. Experimental results show that 2D orthogonal polynomials yield better linearization performance than conventional polynomials in finite precision processing.

A random demodulation based reduced sampling rate method for wideband digital predistortion

Abstract: The linearization performance of the traditional wideband digital predistortion (DPD) is seriously limited by the analog-to-digital converter (ADC) sampling rate in the feedback path. In this paper, a random demodulation based reduced sampling rate (RDRS) method is proposed to model and linearize the broadband power amplifiers (PAs). Compared with the existing spectrum extrapolation method, the proposed method can further reduce the sampling rate, but still maintain good performances. The simulation results demonstrate that the proposed method is well suitable for the ultra wideband digital predistortion.

One-step extraction of optimal normalisation gain for digital predistortion linearisation

Abstract: It has been proved that the choice of normalisation gain, which is used to synthesise the predistortion function, has significant influence on the linearity performance of linearised power amplifiers. A one-step method is proposed to extract the optimal normalisation gain. The proposed method is directly derived from physical logics to keep the gain of predistortion function unity. Thus, it has much lower complexity compared to the scanning strategy in the conventional method and has easy implementation. A experimental test shows that the linearity performance of the proposed method is comparable to the optimal normalisation gain and also outperforms other published ones.

One-step model extraction method for direct learning digital predistortion

Abstract: A one-step model extraction method is proposed for direct learning (DL) digital predistortion (DPD) system. The expected predistortion signal of the training sequence is first derived by iterative injection of the baseband distortion components, which enables one-step model extraction of the DPD model by least squares estimation afterwards. Compared with the conventional model extraction method for DL DPD, the proposed method yields comparable linearisation performance but has much lower computational complexity.

Concurrent Linearization: The State of the Art for Modeling and Linearization of Multiband Power Amplifiers

Abstract: With the explosive growth of the smartphone and tablet markets, wide bandwidth voice and data communication have become ubiquitous. Users expect to use their wireless portable phone/computing devices at any place and at any time. Furthermore, with the today's economy of scale, yesterday's high-performance devices are today's entry-model devices.

Baseband Equivalent Volterra Series for Digital Predistortion of Dual-Band Power Amplifiers

Abstract: This paper proposes a new dual-band baseband equivalent (BBE) Volterra model devised to predict the behavior of dual-band power amplifiers (PAs) and/or to linearize their response. A series of derivations were applied to the original continuous passband Volterra-series expression to uncover a simple formulation that related the BBE envelopes of the output signals in each band to those at the input in the discrete domain. This yielded an inherently low-complexity dual-band Volterra-series model that does not require the empirical pruning commonly applied to the low-pass equivalent Volterra series. The proposed model was successfully applied to digitally predistort and linearize a dual-band 45-W class-AB GaN PA driven with different dual-band dual-standard test signals. For each band, the model necessitated less than 25 coefficients to reduce the adjacent channel leakage power ratio ACLR by up to 25 dB.

FPGA Implementation of Orthogonal 2D Digital Predistortion System for Concurrent Dual-Band Power Amplifiers Based on Time-Division Multiplexing

Abstract: A concurrent dual-band digital predistortion (DPD) system is presented to compensate for the nonlinearity of the radio-frequency power amplifiers (PAs) driven by a concurrent dual-band signal. Recently, a closed-form orthogonal polynomial basis has been introduced showing stability improvement compared with the conventional polynomial. An experimental test bed employing a field-programmable gate array (FPGA) linked to two mixed-signal system boards has also been presented. Based on the FPGA, this paper focuses on the hardware implementation of the new concurrent dual-band orthogonal DPD forward path using time-division multiplexing. Performances are evaluated with an experimental test setup cascading 1-10 W peak PAs and a dual-band signal center frequency spaced by 310 MHz. The lower side band (LSB) and upper side band (USB) are centered at 1890 and at 2200 MHz, respectively. Two signal scenarios are presented combining alternatively 1-carrier wide-band code-division multiple access (WCDMA) and 10-MHz long-term evolution (LTE) signals to a 5-carrier WCDMA signal. Experimental results show that the proposed time-division-multiplexing implementation approach gives similar performance compared with the software implementation with half of the resources. Adjacent channel power ratios (ACPRs) are reduced below -50 dBc and normalized mean-square error (NMSE) close to -40 dB.

Concurrent Dual-Band Digital Predistortion With a Single Feedback Loop

Abstract: This paper proposes a compact and low-cost architecture with only a single feedback loop to implement concurrent dual-band digital predistortion (DPD) of power amplifiers (PAs). This technique is based on a new approach, down-converted carrier co-location $({\rm DC}^{3})$ , in conjunction with a 2-D carrier co-located memory polynomial model in PA forward modeling. The concurrent dual-band DPD models for each band can then be extracted successfully according to the forward modeling results. Experimental tests have been performed for a commercial Mini Circuits amplifier and a 120-W peak power GaN base-station PA. Different signal combinations have been tested for both balanced and unbalanced output power operations in the dual bands. The results validate that the proposed method is able to achieve linearization performances comparable to those of the conventional two parallel feedback loops based technique. Even when a nonideal feedback loop with nonflat frequency responses in the two bands is used, the new method performs well when the feedback loop is calibrated in advance. This single feedback loop based concurrent dual-band DPD architecture is a strong candidate for future broadband dual-band transmitting systems.

Single-Model Single-Feedback Digital Predistortion for Concurrent Multi-Band Wireless Transmitters

Abstract: In this paper, a novel single-model single-feedback digital predistortion (DPD) technique is proposed to linearize concurrent multi-band wireless transmitters. By employing carrier relocation and band-limiting functions in digital signal processing, DPD model complexity is significantly reduced and only one narrowband feedback loop is required for data acquisition. In the new system, the linearization bandwidth can be arbitrarily reconfigured, which provides considerable flexibility for DPD system design in wideband concurrent operations. Experimental tests were conducted to validate various cases including a concurrent quad-band scenario that is reported for the first time to date. Excellent performance demonstrates that the proposed approach provides an effective solution for reducing DPD system implementation complexity and cost in both digital and analog domains for future wideband concurrent multi-band transmitters.