Initial synchronization and tracking circuits for spread spectrum receivers
US5365550A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 18, 1991 |
| Grant date | Nov 15, 1994 |
| Priority date | — |
| Expiry date | Jul 18, 2011 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B1/7095
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A direct sequence digital spread spectrum receiver acquires and maintains synchronization in a reliable, yet simple manner, even under severe multipath and interference conditions. A sliding correlator and a voltage controlled crystal oscillator (VCXO) cooperate to acquire initial synchronization, and once synchronization is acquired, the VCXO is linearly frequency modulated (FM) for accurate tracking. The difficult problem of keeping the receiver code clock synchronized to that of the transmitter under severe multipath and interference conditions is solved by virtue of a dual switched bandwidth low pass filter section of the tracking circuit, allowing a wide bandwidth for initial acquisition and tracking but once the clocks are aligned, a narrow loop takes over that follows the transmitter closely. A commercially available intermediate frequency (IF) integrated circuit (IC) is used as an amplitude modulated (AM) detector to achieve the large dynamic range required. The IF IC has an internal received signal strength indicator (RSSI) output which is used to demodulate the amplitude variations generated by the tracking circuit.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.