Browsing by Author "Hsu, Chen-Jui"

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A New Self-Calibration Method for Transmitter and Receiver Radio Impairments in Direct-Conversion Architecture
(2010)
Hsu, Chen-Jui
;
Sheen, Wern-Ho
;
電機工程學系
;
Department of Electrical and Computer Engineering
Direct-conversion radio architecture is a low-cost, small-size design for the analog front-end subsystem in a wireless communication transceiver. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that incur severe degradation in communication performance. In this paper, a new time-domain method is proposed to self-calibrate simultaneously the transmitter and receiver impairments without a dedicated analog circuit in the feedback loop. Thanks to the time-domain approach, the method is applicable to all types of systems and is able to calibrate jointly the frequency-independent I-Q imbalance, frequency-dependent I-Q imbalance, and dc offset. In addition, training sequence design is investigated to optimize the performance of calibration. Analytical and simulation results confirm the effectiveness of the proposed method.
Digital Predistortion for Concurrent Dual-band Transmitter Using a 2D LUT Based Method
(2015)
Cheng, Sheng-Lung
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Wu, Wen-Rang
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Peng, Chun-Hsien
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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.
Joint Calibration of Transmitter and Receiver Impairments in Direct-Conversion Radio Architecture
(2012-02-01)
Hsu, Chen-Jui
;
Sheen, Wern-Ho
;
電機工程學系
;
Department of Electrical and Computer Engineering
Direct-conversion radio architecture is a low-cost, low-power and small-size design that has been widely employed in today's wireless devices. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that may incur severe degradation in communication performance if left uncompensated. In this paper, a new method is proposed to calibrate simultaneously a transceiver's own transmitter and receiver radio impairments with no dedicated analog circuit in the feedback loop. Based on a unified time-domain approach, the proposed method is able to calibrate jointly the frequency-independent I-Q imbalance, frequency-dependent I-Q imbalance and dc offset and is applicable to any type of communication systems (single-carrier, multiple-carrier, etc.). The existing methods in the literature either need a dedicated analog circuit in the feedback loop and/or are applicable only to a particular type of systems with some radio impairments present. The issue of training sequence design is also investigated to optimize the calibration performance, and analytical and simulation results show that the performance loss due to radio impairments can be recovered by the proposed method.