Method of and apparatus for transmitting and recovering offset QPSK modulated data
US4281412A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 5, 1979 |
| Grant date | Jul 28, 1981 |
| Priority date | — |
| Expiry date | Jul 5, 1999 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L2027/0081
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
Bit timing references are derived at a receiver for a carrier modulated by OQPSK. A carrier is transmitted with a constant reference phase modulation during a first interval. During a subsequent, second interval the carrier is transmitted with rotational phase modulation representing binary bit values so that orthogonal components phase modulate the carrier with a predetermined bit sequence. A receiver responds to the constant phase modulated carrier to lock the frequency and phase of a phase lock loop oscillator of a carrier recovery loop. Synchronization at the receiver is achieved in response to a reception of the rotational phase modulation, while maintaining the frequency and phase lock. A carrier recovery loop of the receiver is activated to a decision directed operation after bit synchronization has been achieved. Decision directed operation is achieved by sampling and comparing components derived in orthogonal channels of the carrier recovery loop while the receiver is responsive to the rotational phase modulation. The bandwidth of a filter used in achieving bit synchronization is reduced after there has been a decay of transients in the carrier tracking loop resulting from…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.