Multicode spread spectrum communications system

• US 6,320,897 B1
• Filed: 09/03/1999
• Issued: 11/20/2001
• Est. Priority Date: 10/03/1996
• Status: Expired due to Term

• Current Assignee: Quarterhill Inc. (f/k/a Wi-LAN Inc.)
• Original Assignee: Wi-LAN Inc.
• Inventors: Zaghloul, Hatim, Snell, David L., Fattouche, Michel T., Milligan, Paul R.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Tran, Khai
• Application Number:
  US09/389,394
• Time in Patent Office: 809 Days
• Field of Search: 375/130, 375/140, 375/139, 375/146, 375/147, 375/150
• US Class Current: 375/130
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04J 13/0077 Multicode, e.g. multiple codes assigned to one user
• CPC Class Codes: H04J 13/10 Code generation

Abstract

MultiCode Spread Spectrum (MCSS) is a modulation scheme that assigns a number N of Spread Spectrum (SS) codes to an individual user where the number of chips per SS code is M. When viewed as Direct Sequence Spread Spectrum, MCSS requires up to N correlators (or equivalently up to N Matched Filters) at the receiver with a complexity of the order of NM operations. In addition, a non ideal communication channel can cause InterCode Interference (ICI), i.e. interference between the N SS codes. In this patent, we introduce three new types of MCSS. MCSS Type I allows the information in a MCSS signal to be detected using a sequence of partial corrrelations with a combined complexity of the order of M operations. MCSS Type II allows the information in a MCSS signal to be detected in a sequence of low complexity parallel operations which reduce the ICI. MCSS Type III allows the information in a MCSS signal to be detected using a filter suitable for ASIC implementation or on Digital Signal Processor, which reduces the effect of multipath. In addition to low complexity detection and reduced ICI, MCSS has the added advantage that it is spectrally efficient.

Claims

1. A transceiver for transmitting a first stream of data symbols, the transceiver comprising:

a first converter for converting the first stream of data symbols into plural sets of B data symbols each;

a channel encoder/modulator for encoding the plural sets of B data symbols into plural sets of J modulated symbols;

a spreader for spreading the plural sets of J modulated symbols into plural sets of N spread spectrum symbols of length M chips each;

M combiners for combining each set of the plural sets of N spread spectrum symbols into M multicoded SS symbols; and

a second converter for converting the plural sets of M multicoded SS symbols into a first stream of multicoded SS symbols for transmission.

2. The transceiver if claim 1 in which the spreader includes:

a third converter for converting each one of the plural sets of J modulated symbols into N subsets of modulated symbols; and

a set of N computing means for operating on each one of the N subsets of modulated symbols to produce the N spread spectrum symbols whereby an ith set of computing means operates on an ith subset of modulated symbols to produce an ith spread spectrum symbol.

3. The transceiver of claim 2 in which the ith computing means includes:

a source of available spread spectrum codes; and

a modulator to choose for each ith subset of modulated symbols one spread spectrum code from the source of available spread spectrum codes to become the spread spectrum code representing the ith subset of modulated symbols, thereby spreading each subset of modulated symbols over a separate spread spectrum code.

4. The transceiver of claim 3 in which the spread spectrum codes are generated by operation of a non-trivial transform on a sequence of input signals.

5. The transceiver of claim 4 in which the non-trivial transform consists of either a Walsh transform or a Fourier transform followed by a randomizing transform.

6. The transceiver of claim 3 further including:

means for receiving a sequence of multicoded SS symbols, the multicoded SS symbols having been generated by spreading a second stream of data symbols;

a third converter for converting the received stream of multicoded SS symbols into plural sets of M multicoded SS symbols each;

a despreader for despreading plural sets of M multicoded SS symbols to produce plural sets of J despread symbols;

a channel decoder/demodulator for decoding plural sets of J despread symbols into plural sets of B estimated data symbols of the second stream of data symbols; and

a fourth converter for converting the plural sets of the B estimated data symbols into a stream of estimated data symbols of the second stream of data symbols.

7. The transceiver of claim 6 in which the despreader includes:

a set of N computing means to operate on the set of M multicoded SS symbols, from the received sequence of multicoded SS symbols, to generate a set of N computed values; and

a detector for operating on the set of N computed values to generate a set of J despread symbols.

8. The transceiver of claim 7 in which the ith computing means includes:

a set of partial correlators for partially correlating the set of M multicoded SS symbol with corresponding parts of each spread spectrum code from the ith source of available spread spectrum codes to generate partially correlated values; and

a sub-detector for operating on the partially correlated values to produce the ith computed value.

9. The transceiver of claim 1 in which the spreader is based on Wi-LAN codes Type I.

26. The transceiver of claim 1, or claim 10, or claim 20 in which the spreader is wideband.

10. A transceiver for transmitting a first stream of data symbols, the transceiver comprising:

a first converter for converting the first stream of data symbols into plural sets of B data symbols each;

a channel encoder/modulator for encoding plural sets of B data symbols into plural sets of J modulated symbols;

a spreader for spreading plural sets of J modulated symbols into plural sets of M multicoded SS symbols; and

a second converter for converting the plural sets of M multicoded SS symbols into a first stream of multicoded SS symbols for transmission.

11. The transceiver of claim 10 in which the spreader includes:

a third converter for converting each one of the plural sets of J modulated symbols into M subsets of modulated symbols; and

a transformer for operating on the M subsets of modulated symbols to generate M multicoded SS symbols as output, the M multicoded SS symbols corresponding to spreading each subset of modulated symbol over a separate spread spectrum symbol and combining the M spread spectrum symbols.

12. The transceiver of claim 11 in which the transformer effectively applies a first transform corresponding to a randomizing transform of the M data symbols.

13. The transceiver of claim 12 in which the first transform is followed by a second transform corresponding to a Fourier transform.

14. The transceiver of claim 10 in which the channel encoder/modulator includes a Reed-Solomon encoder.

15. The transceiver of claim 10 in which the J modulated symbols contain a number of pilot symbols.

16. The transceiver of claim 10 in which plural sets of M multicoded SS symbols correspond to plural sets of M pilot symbols.

17. The transceiver of claim 12 in which the first transform is followed by a second transform corresponding to a circular finite impulse response filter.

18. The transceiver of claim 11 further including:

means for receiving a sequence of multicoded SS symbols, the multicoded SS symbols having been generated by spreading a second stream of data symbols;

a third converter for converting the received stream of multicoded SS symbols into plural sets of M multicoded SS symbols each;

a despreader for despreading plural sets of M multicoded SS symbols to produce plural sets of J despread symbols;

a channel decoder/demodulator for decoding plural sets of J despread symbols into plural sets of B estimated data symbols of the second stream of data symbols; and

a fourth converter for converting the plural sets of the B estimated data symbols into a stream of estimated data symbols of the second stream of data symbols.

19. The transceiver of claim 10 in which the spreader is based on Wi-LAN codes Type II.

20. A transceiver for transmitting a first stream of data symbols, the transceiver comprising:

a channel encoder/modulator for encoding the first stream of data symbols into a modulated stream; and

a spreader for spreading the modulated stream into a multicoded SS stream corresponding to an invertible randomized spreading of the modulated stream.

21. The transceiver of claim 20 further including means to ramp the multicoded SS stream using a linearly ramping carrier frequency, thereby generating a stream of ramped multicoded SS symbols.

22. The transceiver of claim 20 in which the spreader comprises:

a randomizer for randomizing the modulated stream into a randomized modulated stream; and

a filter for spreading the randomized modulated stream into a multicoded SS stream.

23. The transceiver of claim 22 in which the filter has a finite impulse response and the coefficients of the impulse response are chosen from a set of spread spectrum codes.

24. The transceiver of claim 23 in which the set of spread spectrum codes is the class of polyphase codes.

25. The transceiver of claim 23 in which the set of spread spectrum codes is the class of codes that represent a binary approximation of the polyphase codes.

27. The transceiver of claim 20 further including:

means for receiving a stream of multicoded SS symbols, the multicoded SS symbols having been generated by encoding and invertible randomized spreading of a second stream of data symbols;

a despreader for despreading the received stream of multicoded SS symbols into a detected stream; and

a channel decoder/demodulator for decoding the detected stream to produce an estimate of the second stream of data symbols.

28. The transceiver of claim 20 in which the spreader is based on Wi-LAN codes Type III.

29. A method of exchanging data streams between a plurality of transceivers, the method comprising the steps of:

converting a first stream of data symbols into plural sets of B data symbols each;

channel encoding plural sets of B data symbols into plural sets of J modulated symbols;

spreading plural sets of J modulated symbols into plural sets of N spread spectrum symbols of length M chips each;

combining each set of the plural sets of the N spread spectrum symbols into M multicoded SS symbols;

converting the plural sets of M multicoded SS symbols into a first stream of multicoded SS symbols for transmission; and

transmitting the multicoded SS symbols from a first transceiver at a time when no other of the plurality of transceivers is transmitting.

30. The method of claim 29 in which spreading of plural sets of J modulated symbols into plural sets of N spread spectrum symbols includes the step of:

converting each one of the plural sets of J data symbols into N subsets of data symbols.

31. The method of claim 30 in which spreading of plural sets of J modulated symbols into plural sets of N spread spectrum symbols further includes:

choosing for each ith subset of modulated symbols one spread spectrum code from a number of available spread spectrum codes to become the spread spectrum symbol representing the ith subset of modulated symbols, thereby spreading each subset of modulated symbols over a separate spread spectrum code.

32. The method of claim 31 further including the steps of:

receiving, at a transceiver distinct from the first transceiver, the sequence of multicoded SS symbols;

converting the received stream of multicoded SS symbols into plural sets of M multicoded SS symbols each;

despreading plural sets of M multicoded SS symbols to produce plural sets of J despread symbols;

decoding plural sets of J despread symbols into plural sets of B estimated data symbols of the first stream of data symbols; and

converting the plural sets of the B estimated data symbols into a stream of estimated data symbols of the first stream of data symbols.

33. The method of claim 32 in which despreading the received sequence of multicoded SS symbols includes the steps of:

partially correlating each set of M multicoded SS symbols from the received sequence of multicoded SS symbols with corresponding parts of each spread spectrum code from the set of available spread spectrum codes;

operating on the partially correlated values through the use of a set of N sub-detectors to produce a set of N computed values; and

operating on the set of N computed values through the use of a detector to generate a set of J despread symbols.

34. The method of claim 29 in which spreading of plural sets of J modulated symbols into plural sets of N spread spectrum symbols is based on a filter with coefficients equal to Wi-LAN codes Type I.

44. The method of claim 29, or claim 35, or claim 41 in which spreading is wideband.

35. A method of exchanging data streams between a plurality of transceivers, the method comprising the steps of:

converting a first stream of data symbols into plural sets of B data symbols each;

channel encoding plural sets of B data symbols into plural sets of J modulated symbols;

spreading plural sets of J modulated symbols into plural sets of M multicoded SS symbols;

converting the plural sets of M multicoded SS symbols into a first stream of multicoded SS symbols for transmission; and

transmitting the multicoded SS symbols from a first transceiver at a time when no other of the plurality of transceivers is transmitting.

36. The method of claim 35 in which spreading of plural sets of J modulated symbols into plural sets of M multicoded SS symbols further includes:

converting each one of the plural sets of J modulated symbols into M subsets of modulated symbols; and

transforming, by way of a transform, the M subsets of modulated symbols to generate M multicoded SS symbols as output, the M multicoded SS symbols corresponding to spreading each subset of modulated symbol over a separate spread spectrum symbol and combining the M spread spectrum symbols.

37. The method of claim 36 in which transforming the M subsets of modulated symbols includes applying to the M subsets of modulated symbols a randomizing transform and a Fourier transform.

38. The method of claim 36 in which transforming the M subsets of modulated symbols includes applying to the M subsets of modulated symbols a randomizing transform and a circular convolution.

39. The method of claim 36 further including the steps of:

receiving, at a transceiver distinct from the first transceiver, the sequence of multicoded SS symbols;

converting the received stream of multicoded SS symbols into plural sets of M multicoded SS symbols each;

despreading plural sets of M multicoded SS symbols to produce plural sets of J despread symbols;

decoding plural sets of J despread symbols into plural sets of B estimated data symbols of the first stream of data symbols; and

converting the plural sets of the B estimated data symbols into a stream of estimated data symbols of the first stream of data symbols .

40. The method of claim 35 in which spreading of plural sets of J modulated symbols into plural sets of N spread spectrum symbols is based on Wi-LAN codes Type II.

41. A method of exchanging data streams between a plurality of transceivers, the method comprising the steps of:

channel encoding a first stream of data symbols into a stream of modulated symbols; and

spreading the stream of modulated symbols to produce a multicoded SS stream corresponding to an invertible randomized spreading of the first modulated stream.

42. The method of claim 41 further including ramping the multicoded SS stream using a linearly ramping carrier frequency, thereby generating a stream of ramped multicoded SS symbols.

43. The method of claim 42 in which spreading the stream of modulated symbols to produce a multicoded SS stream comprises:

randomizing the modulated symbols, through the use of a randomizer to generate a stream of randomized modulated symbols; and

filtering the randomized modulated symbols, through the use of a filter to generate a stream of multicoded SS symbols.

45. The method of claim 41 further including the steps of:

receiving, at a transceiver distinct from the first transceiver, the stream of multicoded SS symbols;

despreading the received stream of multicoded SS symbols to produce a detected stream; and

decoding the detected stream to produce an estimate of the first stream of data symbols.

46. The method of claim 42 in which spreading the stream of modulated symbols to produce a multicoded SS stream is based on a filter with coefficients equal to Wi-LAN codes Type III.