A Simplified Adaptive Decision Feedback Equalization Technique for π/4-DQPSK Signals

We present a simplified equalization technique for a π/4 differential quadrature phase shift keying ( π/4 -DQPSK) modulated signal in a multipath fading environment. The proposed equalizer is realized as a fractionally spaced adaptive decision feedback equalizer (FS-ADFE), employing exponential step-size least mean square (LMS) algorithm as the adaptation technique. The main advantage of the scheme stems from the usage of exponential step-size LMS algorithm in the equalizer, which achieves similar convergence behavior as that of a recursive least squares (RLS) algorithm with significantly reduced computational complexity. To investigate the finite-precision performance of the proposed equalizer along with the π/4 -DQPSK modem, the entire system is evaluated on a 16-bit fixed point digital signal processor (DSP) environment. The proposed scheme is found to be attractive even for those cases where equalization is to be performed within a restricted number of training samples.

Authors:

• V. Prapulla
• A. Mitra
• R. Bhattacharjee
• S. Nandi

Keywords:

• Adaptive decision feedback equalizer
• Fractionally spaced equalizer
• π/4 DQPSK signal
• Digital signal processor.

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