Secondary channel for digital modems using spread spectrum subliminal induced modulation
US4811357A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 4, 1988 |
| Grant date | Mar 7, 1989 |
| Priority date | — |
| Expiry date | Jan 4, 2008 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L1/0059
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A system and method are provided for use of a secondary channel in high speed (greater than 2400 bits per second) wire line modems to provide low speed (around 110 bits per second) non-interfering communications for control or monitoring functions. The secondary channel is used to monitor, configure and test the modems in the network using commands sent over the secondary channel. Secondary channels are also used in low duty cycle applications such as in alarms or teletype data transmission. The invention provides a spread spectrum secondary channel which occupies the same bandwidth as the primary data channel and is immune to jamming tones that would interfere with conventional frequency shift keying secondary channels. The spectrum spreading is achieved through use of the primary channel's trellis encoder. Phase shifts of 0.degree., 90.degree., 180.degree. or 270.degree. are induced depending upon the trellis state. This rotation simplifies decoding which as a result can be done in the reference system of the decoded primary trellis signals instead of the baseband equalizer reference system. The primary trellis decoder automatically resolves the 90.degree. references. There is no…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.