Patent ID: 8559413

Claim:
A method of providing frame synchronization for Global Positioning System (GPS) signals, the method comprising: performing coherent bit extraction on GPS bits, including: finding a first preamble of a first telemetry (TLM) word of a first GPS subframe, parity bits of the first TLM word and a first hand over word (HOW) word, a first time of week (TOW) of the first HOW word, and first subframe ID bits of the first HOW word, and finding a second preamble of a second TLM word of a second GPS subframe, parity bits of the second TLM word and a second HOW word of the second GPS subframe, a second TOW of the second HOW word, and second subframe ID bits of the second HOW word; performing coherent frame boundary detection based on bits of the coherent bit extraction, including: checking validity of the first TLM word using the parity bits of the first TLM word, checking validity of the first HOW word using the parity bits of the first HOW word, declaring a TOW synchronization when a valid first HOW word follows a valid first TLM word, checking validity of the second TLM word using the parity bits of the second TLM word, checking validity of the second HOW word using the parity bits of the second HOW word, and declaring a detected frame boundary when (1) a valid second HOW word follows a valid second TLM word, (2) the second TOW is equal to the first TOW +1, and (3) when the second subframe ID bits equal the first subframe ID bits +1; performing differential bit extraction on the GPS bits; performing differential frame boundary detection based on bits of the differential bit extraction, wherein said performing the differential frame boundary detection and said performing the coherent frame boundary detection are done concurrently; and providing the frame synchronization, wherein whichever of the coherent frame boundary detection and the differential frame boundary detection first finds a frame boundary, that frame boundary is used for the frame synchronization.