Now showing 1 - 8 of 8
  • Publication
    Dual-loop Model Extraction for Digital Predistortion of Wideband RF Power Amplifiers
    (IEEE, 2011-09) ;
    A dual-loop parameter characterization structure is proposed in order to improve the accuracy of the model extraction in digital predistortion systems. In this concept, a model reference loop is used in conjunction with a model inverse structure for fine tuning the model parameters. This model extraction process does not increase much of the complexity of system implementation but experimental results show that linearization performance can be significantly improved by employing the proposed structure for wideband RF power amplifiers.
      318Scopus© Citations 28
  • Publication
    Gaussian Pulse-Based Two-Threshold Parallel Scaling Tone Reservation for PAPR Reduction of OFDM Signals
    (Hindawi Publishing Corporation, 2011) ;
    Tone Reservation (TR) is a technique proposed to combat the high Peak-to-Average Power Ratio (PAPR) problem of Orthogonal Frequency Division Multiplexing (OFDM) signals. However conventional TR suffers from high computational cost due to the difficulties in finding an effective cancellation signal in the time domain by using only a few tones in the frequency domain. It also suffers from a high cost of hardware implementation and long handling time delay issues due to the need to conduct multiple iterations to cancel multiple high signal peaks. In this paper, we propose an efficient approach, called two-threshold parallel scaling, for implementing a previously proposed Gaussian pulse-based Tone Reservation algorithm. Compared to conventional approaches, this technique significantly reduces the hardware implementation complexity and cost, while also reducing signal processing time delay by using just two iterations. Experimental results show that the proposed technique can effectively reduce the PAPR of OFDM signals with only a very small number of reserved tones and with limited usage of hardware resources. This technique is suitable for any OFDM-based communication systems, especially for Digital Video Broadcasting (DVB) systems employing large IFFT/FFT transforms.
      239Scopus© Citations 4
  • Publication
    Low-Cost FPGA Implementation of Volterra Series-Based Digital Predistorter for RF Power Amplifiers
    (IEEE, 2010-04) ;
    This paper presents a low-complexity and low-cost hardware implementation of a Volterra series-based digital predistorter (DPD). This is achieved by introducing two novel model complexity reduction techniques into the system, namely, lookup table assisted gain indexing and time-division multiplexing for multiplier sharing. Experimental results show that this novel DPD implementation uses much less hardware resources, but still maintains excellent performance compared to conventional approaches.
      420Scopus© Citations 77
  • 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.
      772Scopus© Citations 191
  • Publication
    Optimized Low-Complexity Implementation of Least Squares-Based Model Extraction for Digital Predistortion of RF Power Amplifiers
    (IEEE, 2012-03) ;
    Least squares (LS) estimation is widely used in model extraction of digital predistortion for RF power amplifiers. In order to reduce computational complexity and implementation cost, it is desirable to use a small number of training samples in the model parameter estimation. However, due to strong correlations between data samples in a real transmit signal, the ill-conditioning problem becomes severe in standard LS, which often leads to large errors occurring in model extraction. Using a short training sequence can also cause mismatch between the statistical properties of the training data and the actual signal that the amplifier transmits, which could degrade the linearization performance of the digital predistorter. In this paper, we propose first to use a 1-bit ridge regression algorithm to eliminate the ill-conditioning problem in the LS estimation and then use root-mean-squares based coefficients weighting and averaging approach to reduce the errors caused by the statistical mismatch. Experimental results show that the proposed approach can produce excellent model extraction accuracy with only a very small number of training samples, which dramatically reduces the computational complexity and the system implementation cost.
      665Scopus© Citations 86
  • 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.
      478Scopus© Citations 19
  • Publication
    Green Communications: Digital Predistortion for Wideband RF Power Amplifiers
    (IEEE, 2014-11-12) ;
    The RF PA, as one of the most essential components in any wireless system, suffers from inherent nonlinearities. The output of a PA must comply with the linearity requirement specified by the standards. Due to its satisfactory linearization capability, DPD has been widely accepted as one of the fundamental units in modern and future wideband wireless systems. With the help of this flexible digital technology, the inherent linearity problem of PAs operating in the saturation region can be significantly improved, which enables us, the wireless engineers, to create more suitable RF transceiver architectures to provide wireless access with better user experience (linearity perspective) and less power waste (power efficiency perspective). This moves us one more step towards the ultimate green communications. In this article, we discussed the DPD techniques in the context of linearizing nonlinear RF PAs. As the computing-horsepower and the transistor-density of digital IC increases while the cost per transistor decreases, the concept that uses digital enhancement techniques to eliminate active analog imperfects will gain more attention from both industry and academia.
      740Scopus© Citations 136
  • Publication
    Peak-to-average power ratio reduction of SFBC MIMO-OFDM signals using unused tones
    Multiple input multiple output techniques combined with orthogonal frequency division multiplexing (MIMO-OFDM) provide a promising approach for wireless systems. However, a serious drawback of the OFDM system is the high peak-toaverage power ratio (PAPR), which may severely affect the power efficiency of RF power amplifiers. In this paper, we propose a simple method to reduce the PAPR of MIMO-OFDM signals based on the use of unused subcarriers. Instead of processing the signals at each transmitter separately, a peak cancelling signal is generated at one antenna and is then applied to all the others with only simple modifications. Simulation has shown that a minimum 2 dB reduction in PAPR can be achieved for all transmit signals using this approach. As the signal processing is nearly all done at a single transmitter, repetition of the operations at each transmitter is avoided, and therefore the overall cost of the system can be significantly reduced.
      111Scopus© Citations 3