Digital discriminator for pulse shaped .pi./4 shifted differenti

Details Digital discriminator for pulse shaped .pi./4 shifted differenti Digital discriminator for pulse shaped .pi./4 shifted differenti

1991-05-21

1993-04-13

Chin, Stephen

Pulse or digital communications

Repeaters

Testing

329304, 455 60, H04L 2722

Patent

active

052029018

ABSTRACT:
A digital radio receiver for synchronization of radiowave transmissions for digital and analog FM signals in TDMA systems such as cellular telephones uses a tangent type discriminator that minimizes the bit error rate. The digital discriminator employs A/D converter circuit that samples a received intermediate frequency (IF) signal, a sorter circuit that produces a predetermined number of samples to be used in the decoding, a sample and phase adjustment circuit that allows for a carrier phase adjustment and sample timing adjustment, a divider circuit that eliminates the need for a conventional limiter by causing a ratio of amplitudes to be processed instead of absolute signal amplitudes, an inverse tangent circuit that creates a decoded phase angle from the ratio, a delay circuit and a summer circuit that create a differential signal, a modulo-2.pi. correction circuit that corrects for wrap-around errors about the real axis, an integrate and dump filter for summing up all phase angles pertaining to a single symbol, and a four-phase decoder circuit to decode the signal into a pair of bits. An adjustment circuit minimizes phase error between a reference sequence of symbols and the decoded symbols by simultaneously adjusting the sample timing and carrier phase adjustments. The digital discriminator also can decode conventional analog FM radio broadcasts by deactivating the IDF, the adjustment circuit, and SPA circuit, and bypassing the four-phase decoder.

REFERENCES:
patent: 4379266 (1983-04-01), Rubin
patent: 4570126 (1986-02-01), Demmer et al.
patent: 4773083 (1988-09-01), Baumbach et al.
patent: 4814719 (1989-03-01), Guyer
T. S. Rappaport, S. Y. Seidel and R. Singh. "900 MHZ Multipath Propagation Measurements for U.S. Digital Cellular Radiotelephone." IEEE Globecom Conference Record, Nov. 1989, Dallas, Tex. vol. 1, pp. 3.2.1-3.2.6.
Motorola, Inc., Arlington Heights, Ill. "Discussion of Pi/4 Shift DQPSK." Submitted to the TIA Technical Subcommittee, TR-45.3 WG III Modulation Task Force, Washington, D.C. pp. 1-13.
G. J. Saulnier; C. McD. Puckette, IV; R. C. Gaus, Jr.; R. J. Dunki-Jacobs and T. E. Thiel. "A VLSI Demodulator for Digital RF Network Applications: Theory and Results." IEEE Journal on Selected Areas in Communications, Oct. 1990. vol. 8, No. 8, pp. 1500-1511.

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