US 5,309,476 A · Automode signal detection in full duplex modems

Abstract

Method and apparatus for determining occurrence of an S1 modem identification sequence is disclosed. An S1 sequence is found to exist when the sum of conjugate complex multiplication of signal sample amplitudes taken at an interval T/2 result in a negative scalar value for an arbitrary number of sequential occurrences. Complex samples taken from incoming baseband waveform at twice the modulation rate are interleaved in pairs of two with two even numbered samples and two odd numbered samples being considered separately by first performing complex multiplication followed by scalar multiplication of an output of the complex multiplication and an output of the previous complex multiplication delayed by one modulation interval T. The separate results from the sets of pairs of signal samples are summed to form a scalar whose value when consistently less than 0 indicates the presence of an S1 modem identification sequence in accordance with the CCITT S1 recommendation.

Claims6

Dependent claims

In a currently receiving modem a method of detecting a received Consultative Committee of Internal Telephone and Telegraph (CCITT) S1 standard modem identification signal sequence being sent by a currently sending modem, comprising steps of:

Complex sampling of amplitude of received baseband signals at a rate of twice a carrier modulation rate to yield four consecutive samples x.sub.2n-0, x.sub.2n-1, x.sub.2n-2, and x.sub.2n-3 of the form:
##EQU3## where .tau. and .phi. may be an arbitrary value of a sampling phase and carrier phase, respectively, n is an integer, k is an integer having range from 0 to n and T is a modulation interval;
Forming a sum u.sub.n in accordance with u.sub.n =.nu..sub.cos,n .nu..sub.cos,n-1 +.nu..sub.sin,n .nu..sub.sin,n-1 where v.sub.cos,n is ##EQU4## Counting an arbitrary number of consecutive occurrences of a value of said sum being less than 0 as indicative of reception of said signal sequence;
and
Establishing full duplex communications with said currently sending modem by sending one or more start-up sequences.

2 more elements

Dependencies are inferred from the claim text.

Automode signal detection in full duplex modems

Life of this patent

Automode signal detection in full duplex modems

Life of this patent

Abstract

Claims6