Communication Networks and Services Research, Annual Conference on (2004)
Fredericton, N.B., Canada
May 19, 2004 to May 21, 2004
Tong Wang , Dalhousie University
Jacek Ilow , Dalhousie University
<p>High-level linear modulation schemes utilized in modern digital communication systems to achieve high bandwidth efficiency exhibit large peak-to-average power ratios (PAPRs), and the performance of the communication transceivers is very sensitive to nonlinear distortions, which arise mainly from the high power amplifier (HPA). In addition, the wideband characteristics of the transmitted signals cause the nonlinear distortions to be frequency-dependent. This paper proposes an algebraic solution to compensate at the transmitter for nonlinearity of the HPA with memory effects, where the HPA behaviorial model is represented by the Hammerstein structure, a cascade of a memoryless nonlinear block followed by a linear filter. In particular, a frequency domain parameter identification methodology is developed that first estimates the parameters of the unknown nonlinearity, which is modelled through a polynomial expansion. The frequency response of the unknown filter is then calculated, in order to capture the memory effects in the system. Using the identified nonlinear system parameters, an inverse Wiener structure, consisting of a cascade of the inverse filter and the inverse memoryless nonlinearity, is constructed preceding the HPA, in order to predistort the input signals so as to achieve overall linear transmitter characteristics.</p> <p>The performance of the proposed scheme is examined through computer simulations for quadrature amplitude modulations (QAM). Specifically, improvements in the reduction of the bit error rate (BER) and out-of-band spectrum regrowth are demonstrated for the travelling wave tube (TWT) HPA model. The results show that the proposed method is effective in compensating for amplitude-to-amplitude (AM/AM) distortions with memory using a relatively small number of data points in the identification stage.</p>
J. Ilow and T. Wang, "Compensation of Nonlinear Distortions with Memory Effects in Digital Transmitters," Communication Networks and Services Research, Annual Conference on(CNSR), Fredericton, N.B., Canada, 2004, pp. 3-9.