Spread spectrum modem
US4481640A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 23, 1982 |
| Grant date | Nov 6, 1984 |
| Priority date | — |
| Expiry date | Sep 23, 2002 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/2331
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A MODEM for a high frequency radio data link which substantially enhances the recovery of data transmitted via the link in the face of multipath distortion and fading. A serial digital input signal for transmission is split into odd bit and even bit data streams, having synchronous bit timing. Each pair of bits, referred to as a symbol, is phase shifted by .pi./4 which encodes its timing, for later clock recovery. The resulting signal is then twice differentially phase encoded which facilitates the recovery, when demodulated, of the original symbols overcoming the effect of Doppler shift and/or transmitted oscillator center frequency offset. The resulting signal then phase modulates a subcarrier signal having a frequency much higher than the symbol rate, and the phase modulated subcarrier is converted to a spread spectrum signal for transmission. This digital signal is provided to a high frequency analog transmitter for transmission with the signal spread over a particular HF channel, to a receive point. The spread spectrum signal thus substantially reduces or eliminates the effect of multipath fading, the double differential coding of the symbols substantially reduces or eliminate…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.