Constellation multiplexed inband secondary channel for voiceband modem
US4891806A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 18, 1987 |
| Grant date | Jan 2, 1990 |
| Priority date | — |
| Expiry date | Sep 18, 2007 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/3472
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A method of providing an inband secondary channel for a data modem includes encoding the main channel data using a convolutional encoder so that main channel data symbols are selected from a first constellation. The secondary channel data are encoded using a differential encoder and secondary channel data symbols are selected from a second constellation. The transmission of the main channel symbols takes place during 48 frames of a 49 frame master frame. The differentially encoded secondary channel data symbols are transmitted during the remaining frame. The symbols of the secondary channel constellation are selected to have a higher average energy than those of the main channel data so that the secondary channel is easily detected and may be used to obtain frame synchronization for the modem after brief dropouts without having to retrain the modem.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.