Method and apparatus for generating a synchronization sequence in a spread spectrum communications transceiver
A novel and useful acquisition and synchronization mechanism for spread spectrum communication systems whereby a synchronization sequence comprising a plurality of known symbols spaced apart by predefined time delay intervals is transmitted as the start of packet signal. At the transmitter, a synchronization sequence is transmitted at the beginning of each packet. A synchronization sequence is generated which includes a plurality of symbols with predefined time gaps between each of the symbols. Multiple synchronization sequences may be generated wherein each sequence comprises a unique set of time delays or gaps between each of the symbols. Each set of unique time delays or gaps between symbols of a sequence is stored as a synchronization sequence gap template in memory. When required to generate a synchronization sequence, the sequence generator outputs the plurality of synchronization symbols and inserts a specific time delay between each of the symbols in accordance with the contents of the gap template for the particular synchronization sequence.
1. A method of generating a start of packet synchronization sequence for use in a transmitter, said method comprising the steps of:
generating a plurality of N symbols to be transmitted in said synchronization sequence, wherein N is a positive integer;
generating N−1 predetermined signals, chosen to maximize autocorrelation properties of said synchronization sequence, wherein said N−1 predetermined signals convey packet type information to a receiver;
inserting one of said N−1 predetermined signals after each of the first N−1 symbols in said synchronization sequence;
encoding said synchronization sequence; and
transmitting said encoded synchronization sequence into a channel.
2. The method according to claim 1 , wherein said predetermined signals comprise time delays or transmitting gaps.
3. The method according to claim 1 , wherein N equals seven.
4. The method according to claim 1 , further comprising generating a plurality of synchronization sequences wherein each synchronization sequence corresponds to a unique set of N−1 predetermined signals comprising time delays, each set of N−1 time delays chosen so as to minimize cross correlation between synchronization sequences.
5. The method according to claim 1 , further comprising generating a plurality of synchronization sequences wherein each synchronization sequence corresponds to a different packet type.
6. The method according to claim 1 , wherein said each symbol comprises a zero shifted code shift keying modulated symbol.
7. A method of generating a start of packet synchronization sequence for use in a code shift keying (CSK) based transmitter, said method comprising the steps of:
generating a plurality of symbols of known shift rotation to be transmitted in said synchronization sequence;
inserting a respective predetermined time delay between each of said symbols;
encoding said synchronization sequence;
transmitting said encoded synchronization sequence onto a channel; and
wherein said respective predetermined time delays inserted between said symbols are adapted to convey packet type information to a receiver.
8. The method according to claim 7 , wherein said predetermined time delays are chosen to yield a synchronization sequence having relatively high auto correlation properties.
9. A transmitter for use in a spread spectrum communications system, comprising:
a synchronization sequence generator adapted to generate a synchronization sequence, said synchronization sequence representing a plurality of synchronization symbols with predetermined time delays inserted therebetween;
an encoder adapted to determine shift indices to be applied to spreading waveforms, said shift indices determined based on said synchronization sequence;
a spreading waveform generator adapted to generate spreading waveform signals in accordance with said shift indices; and
wherein delays between spreading waveform signals are determined by said predetermined time delays in said synchronization sequence.
10. The transmitter according to claim 9 , further comprising a synchronization sequence gap memory adapted to store a plurality of synchronization sequences, each synchronization sequence comprising a set of symbols with predefined time delays between each of said symbols.
11. The transmitter according to claim 9 , implemented in an Application Specific Integrated Circuit (ASIC).
12. The transmitter according to claim 9 , implemented in a Field Programmable Gate Array (FPGA).
13. A method of generating a start of packet synchronization sequence, said method comprising the steps of:
generating a plurality of symbols to be transmitted in said synchronization sequence;
inserting specific time delays between said plurality of symbols in said synchronization sequence, wherein said synchronization sequence selected to be substantially orthogonal to other synchronization sequences;
transmitting said synchronization sequence onto a channel; and
wherein said specific time delays are adapted to convey information.
14. The method according to claim 13 , wherein said information comprises packet type information.
15. The method according to claim 13 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
16. The method according to claim 13 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
17. The method according to claim 13 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
18. The method according to claim 13 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
19. The method according to claim 13 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
20. A method of generating a start of packet synchronization sequence, said method comprising the steps of:
generating a plurality of symbols to be transmitted in said synchronization sequence;
inserting specific time delays between said plurality of symbols in said synchronization sequence, said time delays chosen to yield both a high autocorrelation function for a respective synchronization sequence and a low cross-correlation function for each pair of synchronization sequences; and
transmitting said synchronization sequence onto a channel.
21. The method according to claim 20 , wherein said specific time delays are adapted to convey information.
22. The method according to claim 20 , wherein said specific time delays are adapted to convey packet type.
23. The method according to claim 20 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
24. The method according to claim 20 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
25. The method according to claim 20 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
26. The method according to claim 20 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.
27. The method according to claim 20 , wherein said synchronization sequence comprises seven symbols having respective time delays of therebetween.