Decision feedback equalization for digital cellular radio

Pulse or digital communications – Repeaters – Testing

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3647242, H03H 730

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active

052838110

ABSTRACT:
An adaptive Decision Feedback Equalizer (DFE) (40) for a digital cellular mobile radio channel demodulator (30) employs a Complex Fast-Kalman Adaptation algorithm (56) to track channel variations. Sensitivity to sample timing jitter is reduced by providing the DFE with fractionally spaced feed-forward taps (50'). Deficiencies inherent in using a reduced precision implementation are overcome by adding a dither signal to sets of operations in the algorithm, the dither signal comprising an appropriately selected Gaussian random variable. For small delay spreads of approximately one third of a symbol duration or less, a resulting degradation in Bit Error Rate is avoided by switching the DFE out of the circuit or by reducing the number of taps of the DFE. For delay spreads of less than 40 microseconds and greater than approximately 10 microseconds, a (2,3) fractionally spaced DFE provides an adequate compromise between complexity and performance.

REFERENCES:
patent: 4852090 (1989-07-01), Borth
patent: 5068873 (1991-11-01), Murakami
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"Bit Synchronization and Timing Sensitivity in Adaptive Viterbi Equalizers for Narrowband-TDMA Digital Mobile Systems", A. Baier et al., IEEE Vehicular Technology Conference, Philadelphia, Pa., pp. 377-384, 1988.
"Design and Performance of Synchronization Techniques and Viterbi Adaptive Equalizers for Narrowband TDMA Mobile Radio", G. D'Aria et al., 3rd Nordic Seminar on Digital Land Mobile Radio Comm., Copenhagen, Denmark, Sep. 13-15, 1988.
S. Chennakeshu et al., "Decision Feedback Equalization for Digital Cellular Radio", IEEE International Communications Conference, Atlanta, Ga., Apr. 1990, pp. 1492-1496.

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