Pulse or digital communications – Repeaters – Testing
Patent
1979-09-14
1981-08-18
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
333 18, 364724, 375 39, H04B 314
Patent
active
042850614
ABSTRACT:
In a multipoint data communication system using quadrature-amplitude modulation, a master modem (20) and a plurality of tributary modems (11a, 11b . . . 11n) are interconnected via respective transmission channels (13a, 13b . . . 13n, 16). Adaptive equalizer circuitry (55, 56) in the master modem equalizes the channel from a particular tributaryly multiplying samples of signals received from the tributary by an ensemble of tap coefficients associated with the tributary. The tap coefficient ensembles for each tributary are stored in a memory (91) from which they are retrieved at the start of transmission from that tributary. Timing-acquisition circuitry (29) within the master modem adjusts the phase of the letter's sampling circuitry (23, 27) at the start of transmission from a given tributary so that the received signals are sampled at the correct time points. In particular, a timing acquisition signal having spectral components only within the non-rolloff region of the equalized baseband-equivalent transfer function is transmitted by the tributary. The master samples and equalizes the received timing acquisition signal to form a succession of timing acquisition equalizer outputs. The time by which the operation of the sampling circuitry is to be advanced or retarded is determined as a trigonometric function of two successive ones of the timing acquisition equalizer outputs. The timing acquisition signal is illustratively a double-dotting pattern having a four-symbol-interval period. That period is integrally related to the carrier frequency. This allows the samples needed in order to begin forming the timing acquisition equalizer outputs to be generated by replicating the samples taken over only four symbol intervals.
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patent: 3935535 (1976-01-01), Motley et al.
patent: 3962637 (1976-06-01), Motley et al.
patent: 4025719 (1977-05-01), Nussbaumer
patent: 4061978 (1977-12-01), Motley et al.
Bell Telephone Laboratories Incorporated
Safourek Benedict V.
Slusky Ronald D.
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