Pulse or digital communications – Spread spectrum – Direct sequence
Patent
1986-10-15
1989-10-31
Jennings, Derek S.
Pulse or digital communications
Spread spectrum
Direct sequence
370 321, 3408252, H04L 704, H04L 514
Patent
active
048782327
ABSTRACT:
In a data transmission system data is sent, after suitable conversion, as a ternary analogue type signal. Using two-wire twisted pairs and hybrids, echo cancellation and feedback equalization are needed. Synchronization between the two ends, e.g. of a 144 Kb/sec. subscriber's loop, is maintained by a low amplitude pilot tone sent with the data, which is detected at the same time as the data is detected. Detection and elimination of this pilot tone use coefficient generation circuitry similar to those used in the equalizer and echo canceller. To reduce the effect of time phase steps on the system performance, in addition to the transmission of a specific zero valued frame synchronization word which immediately precedes the phase step, the incoming synchronization word is also aligned to this time so that the value of a symbol as received can be predicted, as for a synchronization word, the predicted value is given preference if there is a difference between that symbol's value as received and its predicted value. In addition, the location of the high-pass filters used in the system are specified, alternative methods of bit timing control are specified and advantageous realizations of the canceller and equalizer using tap interpolation are disclosed.
REFERENCES:
patent: 3390232 (1968-06-01), Jager et al.
patent: 4766589 (1988-08-01), Fisher
Jennings Derek S.
STC PLC
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