Synchronizing circuit for modems in a data communications network
US3955141A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 18, 1974 |
| Grant date | May 4, 1976 |
| Priority date | — |
| Expiry date | Oct 18, 1994 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/3477
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A modem with transmitter and reciever sections. Incoming digital data signals produce successive coordinate signals to define successive transmission points representing a given digital value and to modulate quadrature carrier signals. The coordinate signals have unit values of 0, 1, 2.707, 3 and 5 and together control the amplitude and phase of the modulated carrier signals. The receiver section uses received coordinate signals, after they are properly conditioned, to select a decision region which corresponds to a transmission point to produce the digital data signals. The decision regions have rectilinear boundaries on a Cartesian coordinate system at unit values 0, 1.25, 2 and 4 and each region is either rectangular or non-rectangular. Digital synchronism between separate modems is maintained by transmitting coordinate signals corresponding to a framing point which is separate from the transmission points, but which has the same digital value as a transmission point. Certain decision regions defined by the receiver use the receipt of the modulated carrier signals corresponding to a framing point to initiate a synchronizing operation.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.