Xiao Li

Bio: Xiao Li is an academic researcher from Portland State University. The author has contributed to research in topics: Amplifier & RF power amplifier. The author has an hindex of 5, co-authored 17 publications receiving 70 citations.

Obtaining polynomial coefficients from intercept points of RF power amplifiers

Abstract: The RF power amplifier is a critical component in 4G wireless communication systems. One of the main concerns of RF power amplifier design is its nonlinearity, which is more severe in OFDM modulation widely used in LTE and WiMAX systems. Nonlinearity is typically described in terms of the intercept points. It is very useful for the design to obtain coefficients of the memoryless polynomial of the power amplifier model from those intercept points. Previously, the expression of the fifth-order coefficient from the fifth intercept point IP5 was derived. This expression is low generalised to arbitrarily high order. A downlink LTE advanced signal is used for experimental verification. This result could be used for the design of power amplifiers or predistorters.

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.

Spectrum modelling and regrowth for 4G wireless signals

Abstract: Long term evolution (LTE) and WiMAX are the two emerging technologies dominating for the fourth generation (4G) of mobile networks. The in-band and out-of-band emission limits are specified in these two systems, however these relatively new standards still lack mathematical descriptions on spectrum regrowth. Previously, the authors analysed and predicted the spectrum regrowth caused by the nonlinearity of RF power amplifiers related to their intermodulation parameters for two OFDM based signals: Wi-Fi and digital broadcasting. In this reported work, this technology is advanced further to LTE and WiMAX signals and verified by the validity of the theoretical result derived by real experiments. This provides insight for designing power amplifier and digital predistortion in terms of out-band spectrum regrowth.

Nonlinearity Analysis and Predistortion of 4G Wireless Communication Systems

Abstract: ............................................................................................................................... i Acknowledgements ............................................................................................................ iii List of Tables .................................................................................................................... vii List of Figures .................................................................................................................. viii Chapter

Digital and analog communication systems

Abstract: Add this article to private library Remove from private library Submit corrections to this record View record in the new ADS The book presents an introductory treatment of digital and analog communication systems with emphasis on digital systems. Attention is given to the following topics: systems and signal analysis, random signal theory, information and channel capacity, baseband data transmission, analog signal transmission, noise in analog communication systems, digital carrier modulation schemes, error control coding, and the digital transmission of analog signals. Bibtex entry for this abstract Preferred format for this abstract

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.

In-Band Emission in LTE-A D2D: Impact and Addressing Schemes

Abstract: In recent years, the device-to-device (D2D) proximity services in the long term evolution advanced (LTE-A) system drew much attention and is now being investigated and standardized in LTE Release-12. Device discovery is a fundamental aspect of D2D proximity services, allowing discovery user to advertise its presence and/or discover others in its neighborhood. Due to the essential nature of D2D networks, the in- band emission emerges as a critical issue that impacts the in-band coexistence of D2D and cellular systems. This paper systematically studies the in-band emission issue, including its modeling, the impact on cellular system and the potential schemes to address this issue, which is further evaluated by system simulations. It is shown that the impact of the in-band emission could be addressed with the resource grouping method and/or the power control method.