Now showing 1 - 10 of 15
  • 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.
      387Scopus© Citations 4
  • 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.
      1073Scopus© Citations 211
  • 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.
      509Scopus© Citations 14
  • 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.
      373Scopus© Citations 2
  • 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.
      249Scopus© Citations 2
  • 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.
      261Scopus© Citations 6
  • Publication
    Power Adaptive Digital Predistortion for Wideband RF Power Amplifiers With Dynamic Power Transmission
    (IEEE, 2015-10-05) ; ;
    To reduce power consumption of wireless transmitters, the transmission power level of RF power amplifiers (PAs) may dynamically change according to real-time data traffic. This leads that the existing digital predistortion (DPD) techniques cannot be directly employed because they are mainly suitable for eliminating distortion induced by the PAs operated at a relatively stable condition, e.g., at a constant average power level. To resolve this problem, a power adaptive DPD is proposed in this paper. By accurately modeling the behavior change pattern of the PA with the input power adjustments and embedding it into the DPD model, the proposed DPD system is able to adjust its coefficients to adapt to the behavior variation of the PA induced by the power adjustments without real-time recalibration. A low-complexity online coefficients updating method is also proposed to track the behavior change of the PA caused by other factors, such as bias shifting or temperature variation, during real-time operation. Measurements with a high power LDMOS Doherty PA have been used to validate the proposed approach. Results show that the proposed DPD and its coefficients updating approach can produce excellent performance with very low complexity compared to the conventional approaches.
      506Scopus© Citations 45
  • 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 .
      263Scopus© Citations 5
  • 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.
    Scopus© Citations 19  829
  • Publication
    Single-Model Single-Feedback Digital Predistortion for Concurrent Multi-band Wireless Transmitters
    In this paper, a novel single-model single-feedback digital predistortion (DPD) technique is proposed to linearize concurrent multi-band wireless transmitters. By employing carrier relocation and band-limiting functions in digital signal processing, DPD model complexity is significantly reduced and only one narrowband feedback loop is required for data acquisition. In the new system, the linearization bandwidth can be arbitrarily reconfigured, which provides considerable flexibility for DPD system design in wideband concurrent operations. Experimental tests were conducted to validate various cases including a concurrent quad-band scenario that is reported for the first time to date. Excellent performance demonstrates that the proposed approach provides an effective solution for reducing DPD system implementation complexity and cost in both digital and analog domains for future wideband concurrent multi-band transmitters.
      532Scopus© Citations 15