Xianzhen Yang

Bio: Xianzhen Yang is an academic researcher from Portland State University. The author has contributed to research in topics: Amplifier & Intermodulation. The author has an hindex of 3, co-authored 12 publications receiving 29 citations.

Spectrum Modeling of Cross-Modulation for Concurrent Dual-Band RF Power Amplifiers in OFDM Modulation

Abstract: In this paper, the nonlinear effects of amplified dual-band orthogonal frequency-division multiplexing (OFDM) signals are analyzed. Furthermore, a spectrum model of the intermodulation and cross-modulation for dual-band OFDM signals in terms of third-order intercept points ( ${IP}_{3}$ ) is derived. The experimental measurements match the analytical predictions, which is useful to the design and test of concurrent dual-band RF transmitters for RF engineers.

A Unified Spectrum Formulation for OFDM, FBMC, and F-OFDM

Abstract: Although orthogonal frequency division multiplexing (OFDM) has been standardized for 5G, filter bank multi-carrier (FBMC) and filtered orthogonal frequency division multiplexing (F-OFDM) remain competitive as candidates for future generations of wireless technologies beyond 5G, due to their reduced spectrum leakage and thus enhanced spectrum efficiency. In this article, we developed a unified spectrum expression for OFDM, FBMC, and F-OFDM, which provides comparative insights into those techniques. A representative sideband quantification is included at the end of this article.

Saleh Model and Digital Predistortion for Power Amplifiers in Wireless Communications Using the Third-Order Intercept Point

Abstract: This paper presents a novel approach for estimating the Saleh model’s parameters using the gain and third-order intercept point (IP3) of a power amplifier. The IP3 is a widely used technical parameter for describing the nonlinearity of the power amplifier in wireless communications. The proposed approach minimizes an objective function of error between the third-order Taylor series and the Saleh Amplitude-to-Amplitude (AM/AM) model. This approach of the parameters estimation is also used for identifying the Digital Predistortion (DPD) to compensate for the memoryless AM/AM nonlinear distortion of power amplifiers in wireless communications. Finally, the Saleh model accuracy and DPD linearization are validated based on the WCDMA measurement signal.

On Dual-Band Amplifications Using Dual Two-Tones: Clarifications and Discussion

Abstract: A significant development of recent research in nonlinear distortion is the expansion of the conventional two-tone test for power amplifiers to the concurrent dual-band transmitters, by Amin et al . A general framework using dual two-tones is developed, which shows that the output signal is affected not only by intermodulation (IM) products but also by cross-modulation (CM) products. In this paper, we will make a number of clarifications to Amin et al. ’s paper. The effects of IM and CM in passband will be discussed, IM represents a reduction for compressive devices, and CM reflects an interference caused by the signal from the other band, and followed by the analysis of out-of-band IM. It was concluded that out-of-band IM needs to be taken into consideration for the design of power amplifiers when two bands are very close.

Improved estimation for Saleh model and predistortion of power amplifiers using 1-dB compression point

Abstract: This paper proposes an improved estimation approach for modelling RF power amplifiers (PAs) using the Saleh behavioural model. The proposed approach is appropriate for solid-state PA technologies. The 1-dB compression point of the PA is included in the estimation approach to improve the estimation of the Saleh coefficients. Thus, expressions are derived to describe the relationship between the parameters of the Saleh model and the manufacturing specifications of PAs: gain ( G ), third-order intercept point (IP 3 ) and 1-dB compression point ( P 1dB ). This method is a simple estimation of a memoryless amplitude-to-amplitude (AM/AM) nonlinearity to benefit RF designers evaluating the PA distortion using the PA parameters: P 1dB , G , and IP 3 , before conducting experimental validation. The linearisation method using digital predistortion (DPD) is derived as a function of G , IP 3 , and P 1dB , for mitigating the AM/AM nonlinear distortion. Finally, the modelling and DPD techniques are both evaluated using the experimental results of the GaAs PA.

Single-Tap Precoders and Decoders for Multi-User MIMO FBMC-OQAM under Strong Channel Frequency Selectivity

Abstract: The design of linear precoders or decoders for multiuser multiple-input multiple-output filterbank multicarrier (FBMC) modulations in the case of a strong channel frequency selectivity is presented. The users and the base station (BS) communicate using space division multiple access. The low complexity proposed solution is based on a single tap per-subcarrier precoding/decoding matrix at the BS in the downlink/uplink. As opposed to classical approaches that assume flat channel frequency selectivity at the subcarrier level, the BS does not make this assumption and takes into account the distortion caused by channel frequency selectivity. The expression of the FBMC asymptotic mean squared error (MSE) in the case of strong channel selectivity derived in earlier works is developed and extended. The linear precoders and decoders are found by optimizing the MSE formula under two design criteria, namely zero forcing or minimum MSE. Finally, simulation results demonstrate the performance of the optimized design. As long as the number of BS antennas is larger than the number of users, it is shown that those extra degrees of freedom can be used to compensate for the channel frequency selectivity.

A generalized Isserlis theorem for location mixtures of Gaussian random vectors

Abstract: In a recent paper, Michalowicz et al. provide an extension of Isserlis theorem to the case of a Bernoulli location mixture of a Gaussian vector. We extend here this result to the case of any location mixture of Gaussian vector; we also provide an example of the Isserlis theorem for a "scale location" mixture of Gaussian, namely the d-dimensional generalized hyperbolic distribution.

Low-Cost RF in –RF out Predistorter Linearizer for High-Power Amplifiers and Ultra-Wideband Signals

Abstract: The 5G and beyond systems require the highly efficient linear power amplifier (PA) at the base station to deliver promised data rate in a power efficient manner. To facilitate higher data rates in future 5G communication, the demands for the wideband signals are continuously increasing, which creates adversity in employing digital predistortion (DPD) for the linearization of RF PA in ultra-wideband systems. System bandwidth constraint of the conventional DPD does not provide sufficient linearization of wideband signals. In this paper, we present two types of predistorter, first is RFin–RFout analog predistorter, in which linearization is performed by RF components in the analog domain, and the second is hybrid RF predistorter which takes the advantage of advanced DSP platform for improving the performance of RFin–RFout analog predistorter. The proposed predistorters eliminate the constraint on the system bandwidth of the conventional DPD. The requirements of data converters and reconstruction filters are relaxed in the analog predistorter (APD) architecture, whereas hybrid digitally controlled (HDC) APD eliminates the need of analog components by compensating the delay digitally. In order to validate this concept, a ZX60V-63+ PA from minicircuits is tested with 160-MHz eight-component carrier-long term evolution signal. The proposed APD architecture is able to deliver an adjacent channel power ratio (ACPR) of −46.4 dBc with an ACPR improvement of 13.4 dB at 1-dB back-off. Furthermore, with digital intervention, modified model, HDC-APD further provides a significant improvement in the linearization performance and delivers an ACPR of −53.5 dBc with an ACPR improvement of 20.5 dB.

Rf Power Amplifier Behavioral Modeling

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Spectrum Modeling of Cross-Modulation for Concurrent Dual-Band RF Power Amplifiers in OFDM Modulation

Abstract: In this paper, the nonlinear effects of amplified dual-band orthogonal frequency-division multiplexing (OFDM) signals are analyzed. Furthermore, a spectrum model of the intermodulation and cross-modulation for dual-band OFDM signals in terms of third-order intercept points ( ${IP}_{3}$ ) is derived. The experimental measurements match the analytical predictions, which is useful to the design and test of concurrent dual-band RF transmitters for RF engineers.