High speed modem suitable for operating with a switched network

Details High speed modem suitable for operating with a switched network High speed modem suitable for operating with a switched network

H - Electricity

04

J

363/8

H04J 1/02 (2006.01) H04L 27/26 (2006.01) H04L 27/38 (2006.01)

Patent

CA 1155569

- 1 - Abstract: A high speed modem suitable for operating with a switched network and capable of achieving essentially 9600 bit per second information transfer rate through the switched tele- phone network. The high bit rate is achieved notwithstanding the variations in the characteristics of the switched tele- phone network by phase and amplitude modulating a plurality of sub-carriers at a relatively low baud rate. Correlation detection is employed at the receiver to extract or demodulate the information contained in the various sub-carriers. To allow correlation detection with orthogonal signals, each of the sub-carriers is harmonically related to a fundamental which fundamental is, however, slightly higher than the baud rate. This allows the receiver to delay correlation for a "gap" time, which reduces the effect of transients produced by modulation and also provides greater tolerance to inter- symbol distortion. Since the fundamental of all the sub- carriers is higher than the baud rate, the receiver "sees" orthogonal signals during the integration or correlation time which is maintained as the period of the fundamental. In addition to the information sub-carriers, a pair of un- modulated sub-carriers are also transmitted to enable the receiver to maintain the correlation interval in proper syn- chronization with the transmitter, and to correct for phase distortion and frequency offset.

332948

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