Research Projects:

  • Efficient Digital Predistortion Algorithms and Parallel Designs on Embedded Processors
    Modern radio transceivers are targeting low design costs and high power efficiency, while entailing imperfections of analog RF and digital baseband, such as power amplifier (PA) nonlinearities, imbalance of complex in-phase and quadrature (I/Q) signals, and local oscillator (LO) leakage, which result in intermodulation distortion and spurious spectrum emissions. One obvious solution to decrease the levels of unwanted emissions is to back off the transmit power from its saturation region, which is called maximum power reduction (MPR) in 3GPP LTE context, but it will significantly sacrifice transmit efficiency and distance. Currently, digital predistortion (DPD) technique serves as an alternative solution for suppressing spurious emissions by preprocessing the I/Q samples to enable cancellation effects at baseband before passing through the PA, which also poses challenges on low-complexity algorithm development and flexible and efficient implementation for low transceiver design costs. This project proposes both novel efficient DPD algorithms and high performance implementations using modern embedded parallel processors, such as mobile multi-core CPUs and GPUs, and SoC FPGAs: 
    (1) Full-band Digital Predistortion
    Full-band DPD seeks to linearize the full composite transmit signal. We develop a customized software-defined radio (SDR) platform using WARP V3 radio board and general purpose processors, and experimentally monitor the DPD suppression effect by integrating our embedded parallel DPD implementations on the SDR platform. Above figure shows our experimental setup, see details here.
    Related Publications:
    [J1] Parallel Digital Predistortion Design on Mobile GPU and Embedded Multicore CPU for Mobile Transmitters, JSPS 2017
    [C1] Mobile GPU Accelerated Digital Predistortion on a Software-defined Mobile Transmitter, GlobalSIP 2015
    [C2] A High Performance GPU-based Software-defined Basestation, Asilomar 2014

    (2) Sub-band Digital Predistortion
    Sub-band DPD seeks to suppress the spurious emissions in non-contiguous transmission cases, concentrating the linearization efforts to the most critical intermodulation distortion band, but not the main component carrier bands. We develop novel low-complexity sub-band DPD algorithms and demonstrate the effectiveness on WARP V3 radio board with real-time implementations on its SoC FPGA.
    Related Publications:
    [J2] Low-Complexity Sub-band Digital Predistortion for Spurious Emission Suppression in Noncontiguous Spectrum Access, TMTT 2016
    [C3] Sub-band Digital Predistortion for Noncontiguous Transmissions: Algorithm Development and Real-Time Prototype Implementation, Asilomar 2015

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