Now showing 1 - 10 of 15
  • Publication
    A Single Envelope Modulator-Based Envelope-Tracking Structure for Multiple-Input and Multiple-Output Wireless Transmitters
    (IEEE, 2012-10) ;
    A single envelope modulator-based envelope tracking (ET) power amplifier (PA) structure with a related digital predistortion (DPD) technique for multiple-input and multiple-output (MIMO) wireless transmitters is presented in this paper. By generating a common tracking envelope, only one envelope modulator is employed for controlling supply voltage of the RF PAs in all branches in the system, which dramatically reduces the system implementation cost. Due to the structurechange, additional distortion is introduced, and it is difficult to directly compensate by using the conventional DPD because the tracking envelope is no longer the same as the RF envelope and thus the MIMO ET PA becomes a two-input and one-output system. To resolve this problem, in this paper we propose a novel DPD technique in which the PA input and output data are reconstructed into multiple data subsets according to variations of the tracking envelope. It converts the 2-to-1 mapping into multiple 1-to-1 ones, where the conventional DPD can be employed again. Experimental results demonstrated that the distortion, including static nonlinearities, memory effects and additional distortion caused by the structure change, can be effectively compensated by using the proposed DPD technique. Compared to the conventional ET, the overall efficiency of the system is only slightly decreased, but the system cost is much lower because only one envelope modulator is required in the whole system.
      310Scopus© Citations 23
  • Publication
    Digital Compensation for Transmitter Leakage in Non-Contiguous Carrier Aggregation Applications With FPGA Implementation
    In this paper, a generalized dual-basis envelope-dependent sideband (GDES) distortion model structure is proposed to compensate the distortion induced by transmitter leakage in concurrent multi-band transceivers with non-contiguous carrier aggregation. This model has a generalized structure that is constructed via first generating a nonlinear basis function that maps the inputs to the target frequency band where the distortion is to be cancelled, and then multiplying with a second basis function that generates envelope-dependent nonlinearities. By combining these two bases, the model keeps in a relatively compact form that can be flexibly implemented in digital circuits such as field programmable gate array (FPGA). Experimental results demonstrated that excellent suppression performance can be achieved with very low implementation complexity by employing the proposed model.
      495Scopus© Citations 14
  • Publication
    High-performance digital predistortion test platform development for wideband RF power amplifiers
    (Cambridge University Press, 2013-04) ; ; ;
    In this paper, a complete design procedure, together with robust system validation approaches, is presented for implementing a high-performance re-configurable digital predistortion (DPD) test platform for compensating for nonlinear distortion and memory effects induced by radio frequency (RF) power amplifiers (PAs) in the transmitters of modern wireless communication systems. This hardware and software co-operated test system not only enables effective validation for DPD algorithm development, but also provides a high-performance and reliable hardware-based linearization test platform. The experimental test was applied on a medium power Doherty amplifier, which was designed for 3 G/4 G wireless communication base stations. By applying our DPD algorithms on the proposed platform, more than 30 dB improvements in adjacent channel power ratio can be achieved for Universal Mobile Telecommunications System and long-term evolution signal excitations.
      471Scopus© Citations 19
  • Publication
    Highly Isolated Compact Tri-Band MIMO Antenna with Trapezoidal Defected Ground Plane for 5G Communication Devices
    In this paper a compact tri-band MIMO antenna has been proposed for 5G wireless communication devices. The isolation of -20 dB has been obtained between the two input ports using meander line structures and five vias incorporating at different places of the structure. Two rectangular slots have been etched on the radiating patch to further improve antenna performance. The designed antenna provides multiband characteristic in S, C and X frequency bands. Different characteristic parameters such as Envelope Correlation Coefficient, diversity gain, electric field distribution and radiation pattern are also presented and discussed . The overall antenna volumetric size is 42×34×1mm 3 .
      136Scopus© Citations 4
  • Publication
    Simplified online coefficients updating for digital predistortion of wideband/multi-band RF power amplifiers
    (IEEE, 2015-12-09) ; ;
    In this paper, a simplified online coefficients updating technique is proposed to realize real-time timing of digital predistortion (DPD) for RF power amplifiers (PAs), particularly focusing on wideband and concurrent multi-band scenarios. It is achieved by equally weighting the memory terms in conventional DPD models that leads to a significant reduction of numerical calculation complexity in the coefficients updating process and thus saves time and power during real system operation. To validate the proposed method, both wideband LTE- A (100 MHz) and concurrent dual-band (20 MHz + 20 MHz) cases have been tested. Experimental results show that the proposed method can achieve excellent performance with significant reduction of system complexity compared to the conventional approaches.
      278Scopus© Citations 2
  • Publication
    OTA-Based Data Acquisition and Signal Separation for Digital Predistortion of Multi-User MIMO Transmitters in 5G
    In this paper, a non-interruptive over-the-air (OTA) data acquisition method is presented to characterize system nonlinearity and calibrate digital predistortion (DPD) in multi-user (MU) multiple-input multiple-output (MIMO) transmitters with low hardware complexity. Based on a unified system model for fully-digital and hybrid MU-MIMO transmitters, the requirements and difficulties of data acquisition for MU-MIMO DPD are outlined first. A versatile OTA data acquisition technique, featuring a multi-observation forward modelling procedure, is thereby developed to obtain power amplifier (PA) output without interrupting the operation of the MIMO transmitters. By using this method, the output of each PA can be reconstructed instead of directly measuring each PA's output, even when the output signals of PAs are correlated. DPD can therefore be effectively constructed to mitigate the distortion. Experimental results demonstrate that the proposed approach can accurately estimate each PA output and linearize all PAs in the array.
      189Scopus© Citations 4
  • Publication
    A channelized sideband distortion model for suppressing unwanted emission of Q-band millimeter wave transmitters
    In this paper, a channelized sideband distortion model is proposed to suppress the unwanted emission of Q-band millimeter wave (mmWave) transmitters in wideband contiguous carrier aggregation scenarios. By employing this model, the compensating bandwidth or center frequency can be agilely controlled. Experiments were conducted on a 40 GHz mmWave power amplifier to validate this idea. The satisfactory performance proved that the proposed model is a promising candidate for future 5G applications.
      117Scopus© Citations 6
  • Publication
    Pattern Sensing Based Digital Predistortion of RF Power Amplifiers under Dynamical Signal Transmission
    In this paper, a pattern sensing based digital predistortion (DPD) technique for radio frequency (RF) power amplifiers (PAs) under dynamical signal transmission is proposed. Unlike conventional methods where real time re-calibration is required, this approach utilizes a low resolution amplitude-modulation to amplitude-modulation (AM/AM) pattern to sense PA characteristics and then quickly select proper DPD coefficients to linearize the PA. Experimental results show that the proposed method can provide an efficient a nd effective w ay to deal with complex dynamic signal transmission scenarios and maintain very good linearization performance, which is very suitable for future 5G applications.
      114Scopus© Citations 2
  • Publication
    Band-Limited Volterra Series-Based Digital Predistortion for Wideband RF Power Amplifiers
    The continuously increasing demand for wide bandwidth creates great difficulties in employing digital predistortion (DPD) for radio frequency (RF) power amplifiers (PAs) in future ultra-wideband systems because the existing DPD system requires multiple times the input signal bandwidth in the transmitter and receiver chain, which is sometimes almost impossible to implement in practice. In this paper, we present a novel band-limited digital predistortion technique in which a band-limiting function is inserted into the general Volterra operators in the DPD model to control the signal bandwidth under modeling, which logically transforms the general Volterra series-based model into a band-limited version. This new approach eliminates the system bandwidth constraints of the conventional DPD techniques, and it allows users to arbitrarily choose the bandwidth to be linearized in the PA output according to the system requirement without sacrificing performance, which makes the DPD system design much more flexible and feasible. In order to validate this idea, a high-power LDMOS Doherty PA excited by various wideband signals, including 100-MHz long-term evolution advanced signals, was tested. Experimental results showed that excellent linearization performance can be obtained by employing the proposed approach. Furthermore, this technique can be applied to other linear-in-parameter models. In future ultra-wideband systems, this new technique can significantly improve system performance and reduce DPD implementation cost.
      729Scopus© Citations 188
  • Publication
    Data-Clustering-Assisted Digital Predistortion for 5G Millimeter-Wave Beamforming Transmitters With Multiple Dynamic Configurations
    Motivated by data science, in this article, a data-clustering-assisted digital predistortion (DPD) is proposed to linearize millimeter-wave (mmWave) beamforming transmitters with multiple dynamic configurations. Based on the data analysis, similar transmitter states with different configurations can be clustered, resulting in a significant reduction of linearization states. Model complexity within the cluster can be further reduced by utilizing a penalty factor method. To validate the proposed concept, experiments were carried out on a 16-channel mmWave beamforming transmitter with configurable beam angle, operating frequency, and input power. Total 216 transmitter states can be reduced to 8, 20, and 40 states with unequal optimal model parameters for each state, without losing much performance. The proposed method can be extended to the scenario where a large scale of dynamic states can occur in complex transmitter structures in future wireless systems.
      260Scopus© Citations 7