University of Minnesota

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Mitigating Nonlinear Power Amplifier Effects in Communication Systems

The increasing need for bandwidth and power efficiency in terrestrial and satellite digital wireless communications dictates operation of nonlinear high power amplifiers (HPA) in their saturation region. Mitigation of the resulting nonlinear distortions becomes particularly important with non-constant modulus transmission schemes having large dynamic range. This is the case with multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) and Discrete Multi-Tone (DMT), that exhibit high peak-to-average ratio (PAR) in their transmit-power profile.

We explore pre-equalizers and redundant precoders for mitigating such HPA nonlinearities at the transmitter in both single- and multi-user scenarios. So far, an all-digital zero-forcing (ZF) predistorter based on modulo arithmetic has been developed to equalize nonlinear Volterra channels whose estimates are assumed to be available at the transmitter. Relative to existing analog predistorting approaches, the novel all-digital pre-equalizer guarantees the ZF property and does not require oversampling, while relative to digital post-distorting approaches it offers low noise sensitivity. Our modulo pre-equalizer remains operational even with severely nonlinear channels and amplifiers operating at very low backoff.

More details and our preliminary results can be found in:

  1. A. Kambanellas and G. B. Giannakis, "All-Digital Modulo Pre-Equalization of Nonlinear Communication Channels," IEEE Transactions on Communications, January 1999 (submitted).
  2. A. Kambanellas and G. B. Giannakis, "Modulo pre-equalization of nonlinear communication channels," in Proc. of IEEE-SP Workshop on Signal Proc. Advances in Wireless Comm. (SPAWC'99), Annapolis, MD, May 9-12, 1999.

 

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