Browsing by Author "Peng, Chun-Hsien"

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Digital Predistortion for Concurrent Dual-band Transmitter Using a 2D LUT Based Method
(2015)
Cheng, Sheng-Lung
;
Wu, Wen-Rang
;
Peng, Chun-Hsien
;
Hsu, Chen-Jui
;
Liang, Paul
The digital predistortion (DPD) technique has been utilized in radio-frequency power amplifier linearization for its low cost and good performance. However, the conventional singleband OPO design is not applicable to the concurrent dual-band transmitters since the cross modulations are induced. The twodimensional (20) polynomial based OPO has been proposed as a remedy. Despite its good performance, the main drawbacks are the high computational complexity for the identification of the DPD coefficients and the high implementation complexity. It is known that the look-up-table (LUT) based method, which has been applied in conventional single-band transmitters, can effectively overcome the problems. In this paper, we consider a 20 LUT based DPD for the concurrent dual-band transmitters. First, we formulate a cost function from which the elements of the tables can be obtained through the optimization. Then, we propose an adaptive algorithm using the gradient-descent (GO) method to conduct the search. Moreover, we propose a practical method to implement the GO method which can significantly reduce the computational and implementation complexities. Finally, some measurement results are presented to demonstrate that the proposed algorithm has the satisfactory performance.
Digital predistortion for concurrent dual-band transmitter using a 2D-LUT based Hammerstein architecture
(2017-01)
Cheng, Sheng-Lung
;
Wu, Wen-Rong
;
Peng, Chun-Hsien
;
Liu, Jen-Yang
;
Hsu, Chen-Jui
Digital predistortion has been proved to be an effective remedy for the nonlinear distortion in radio-frequency power amplifier. Unfortunately, conventional digital predistorters (DPDs) developed for single-band transmitters can not be directly applied to concurrent dual-band. To solve the problem, DPDs with two dimensional memory polynomials were then proposed. Although they can provide good performance, its computational complexity is high for the estimation of polynomial coefficients. Look-up-table (LUT) based DPDs, developed for single-band transmitters, can effectively solve the problem. However, there are limited studies about LUT based DPDs for concurrent dual-band transmitters. In this paper, we propose a two-dimensional LUT based Hammerstein DPD to solve the problem. Analyzing the signals on both bands, we propose a new adaptive algorithm with the gradient-descent and recursive-least-squares (RLS) methods to train the DPD iteratively. With the proposed method, the computational complexity in the identification of the DPDs can be significantly reduced. Finally, simulations and experiments are conducted to demonstrate that the performance of the proposed DPD is comparable to that of the polynomial based DPD.