Synchronous coherent orthogonal frequency division multiplexing system, method, software and device

• US 5,867,478 A
• Filed: 06/20/1997
• Issued: 02/02/1999
• Est. Priority Date: 06/20/1997
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Baum, Kevin Lynn, Nadgauda, Nikhil Shashank
• Primary Examiner(s): MARCELO, MELVIN C
• Application Number:
  US08/879,403
• Time in Patent Office: 592 Days
• Field of Search: 370/203, 370/208, 370/210, 370/343, 370/480
• US Class Current: 370/203
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, system, method, software and device include a plurality of SC-OFDM transmitters and a plurality of SC-OFDM receivers. Each of the plurality of SC-OFDM transmitters is synchronized to a reference where the reference is derived from a common source, for transmitting SC-OFDM signals. The plurality of SC-OFDM receivers is arranged to receive the SC-OFDM signals from at least one of the plurality of SC-OFDM transmitters. The SC-OFDM signals each have a cyclic extension, and the SC-OFDM signals from each SC-OFDM transmitter include at least one pilot code in accordance with a predetermined pilot code scheme.

Claims

1. A synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, system that includes a plurality of SC-OFDM transmitters and a plurality of SC-OFDM receivers, comprising:

A) the plurality of SC-OFDM transmitters, wherein each SC-OFDM transmitter is synchronized to a reference where the reference is derived from a common source, for transmitting SC-OFDM signals; and

B) the plurality of SC-OFDM receivers, arranged to receive the SC-OFDM signals from at least one of the plurality of SC-OFDM transmitters;

wherein, in A and B, the SC-OFDM signals each have a cyclic extension, and the SC-OFDM signals from each SC-OFDM transmitter include at least one pilot code in accordance with a predetermined pilot code scheme.

2. The SC-OFDM system of claim 1 wherein the cyclic extension has a duration based at least in part on inter-SC-OFDM transmitter propagation delay.

3. The SC-OFDM system of claim 1 wherein the at least one pilot code is comprised of a sequence from a set of sequences with minimal/zero/known cross-correlation and the predetermined pilot code scheme places each pilot code in a predetermined set of symbol locations.

4. The SC-OFDM system of claim 3 wherein, where a number of SC-OFDM transmitters exceeds a number of sequences in the set of sequences, a same pilot code is utilized by at least two SC-OFDM transmitters.

5. The SC-OFDM system of claim 1 wherein each SC-OFDM transmitter is in a base unit and each SC-OFDM receiver is in a subscriber unit.

6. The SC-OFDM system of claim 1 wherein each SC-OFDM transmitter is in a subscriber unit and each SC-OFDM receiver is in a base unit.

7. The SC-OFDM system of claim 6 wherein the base unit further includes a transmitter, the subscriber unit further includes a receiver, and the reference derived from the common source is based on a closed loop timing adjustment scheme.

8. The SC-OFDM system of claim 1 wherein the cyclic extension is further based on a duration of a channel impulse response.

9. The SC-OFDM system of claim 1 where the common source is one of:

A) a global positioning system; and

B) a wireline network clock.

10. The SC-OFDM system of claim 1 wherein plurality of SC-OFDM transmitters are co-located.

11. The SC-OFDM system of claim 1 wherein the SC-OFDM transmitters and SC-OFDM receivers include one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

67. The method of claim 6 wherein the steps are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code;

E) a combination of at least two of A-D.

12. A base unit having an SC-OFDM transmitter synchronized to a reference where the reference is derived from a common source, for transmitting SC-OFDM signals, the SC-OFDM transmitter comprising:

A) a modulator, coupled to receive predetermined pilot codes and data, for providing at least one OFDM signal in accordance with a predetermined pilot code scheme;

B) a cyclic extension unit, coupled to the modulator, for extending the at least one OFDM signal using a cyclic extension, and

C) a synchronizing unit, coupled to the cyclic extension unit and to receive a time reference signal, for deriving a local reference signal from the time reference signal and synchronizing transmission of an at least one SC-OFDM signal of the SC-OFDM transmitter in accordance with the local reference signal,

wherein, each SC-OFDM signal has a cyclic extension and each SC-OFDM signal from the SC-OFDM transmitter includes at least one pilot code in accordance with the predetermined pilot code scheme.

13. The base unit of claim 12 wherein the cyclic extension has a duration based at least in part on inter-SC-OFDM transmitter propagation delay.

14. The base unit of claim 12 wherein the cyclic extension is further based on a duration of a channel impulse response.

15. The base unit of claim 12 where the common source for the SC-OFDM transmitter is one of:

A) a global positioning system; and

B) a wireline network clock.

16. The base unit of claim 12 wherein the at least one pilot code is comprised of a sequence from a set of sequences with minimal/zero/known cross-correlation and the predetermined pilot code scheme places each pilot code in a predetermined set of symbol locations.

17. The base unit of claim 16 wherein the predetermined set of symbol locations are the same as a predetermined set of symbol locations for another base unit containing another SC-OFDM transmitter.

18. The base unit of claim 12 further having a plurality of SC-OFDM transmitters arranged to be coupled to a directional antenna system.

19. The base station of claim 18 wherein the plurality of SC-OFDM transmitters each use a different pilot code.

20. The base unit of claim 12 wherein the SC-OFDM transmitter transmits at least one of:

synchronization signals and identification signals.

21. The base unit of claim 20 wherein at least one of:

the synchronization signals and the identification signals are one of;

A) non-interfering with a synchronization/identification signal from another SC-OFDM transmitter; and

B) separable from a synchronization/identification signal from another SC-OFDM transmitter.

22. The base unit of claim 20 wherein the SC-OFDM transmitter transmits at least one of the synchronization signal and the identification signal at a different time/frequency/code than the synchronization/identification signal transmitted by another SC-OFDM transmitter.

23. The base unit of claim 12 wherein the predetermined pilot codes and data are spread across a frequency band in a set of predetermined frequency locations and modulated to form the at least one SC-OFDM signal.

24. The base unit of claim 23 wherein the predetermined pilot codes and data are moved from the set of predetermined frequency locations to another set of predetermined frequency locations according to a predetermined frequency hopping method.

25. The base unit of claim 12 wherein the modulator/cyclic extension unit/synchronizing unit is implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

26. A base unit having a synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, receiver arranged to receive at least one composite SC-OFDM signal demodulated and parsed into a plurality of composite SC-OFDM symbols and at least one composite SC-OFDM pilot code, the SC-OFDM receiver comprising:

A) a multi-channel channel response measurement unit, arranged to receive the at least one composite SC-OFDM pilot code, for computing channel response measurements for a plurality of components of the composite SC-OFDM signal based on a plurality of associated pilot codes, and

B) a detector, coupled to the multi-channel channel response measurement unit and to receive at least one of the plurality of composite SC-OFDM symbols, for detecting at least one symbol component from the at least one composite SC-OFDM symbol based on the channel response measurement/measurements and the at least one composite SC-OFDM symbol.

27. The base unit of claim 26 further including a transmitter for providing a common source based on a closed loop timing adjustment scheme.

28. The base unit of claim 26 wherein the detector provides the at least one symbol component as a soft decision.

29. The base unit of claim 26 wherein the multi-channel channel response measurement unit/detector is implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

30. A base unit having a synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, receiver unit having a plurality of diversity antennas arranged to receive a plurality of composite SC-OFDM signals demodulated and parsed into a plurality of composite SC-OFDM symbols and a plurality of composite SC-OFDM pilot codes, the SC-OFDM receiver unit comprising:

A) a plurality of multi-channel channel response measurement units, each arranged to receive at least one composite SC-OFDM pilot code and a plurality of composite SC-OFDM symbols, for computing channel response measurements for a plurality of components for each of the plurality of composite SC-OFDM signals based on a plurality of associated pilot codes, and

B) a diversity detector, coupled to the plurality of multi-channel channel response measurement units and to receive at least two of the plurality of composite SC-OFDM symbols, for detecting at least one symbol component from the composite SC-OFDM symbols based on the channel response measurements and the composite SC-OFDM symbols.

31. The base unit of claim 30 wherein the diversity detector provides the at least one symbol component as a soft decision.

32. The base unit system of claim 30 wherein the multichannel channel response measurement unit/diversity detector is implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

33. A subscriber unit having a synchronous, coherent, orthogonal frequency division multiplexing, SC-OFDM, transmitter synchronized to a reference where the reference is derived from a common source, for transmitting SC-OFDM signals, the SC-OFDM transmitter comprising:

A) a modulator, coupled to receive predetermined pilot codes and data, for providing at least one OFDM signal in accordance with a predetermined pilot code scheme;

B) a cyclic extension unit, coupled to the modulator, for extending the OFDM signal using a cyclic extension, and

C) a synchronizing unit, coupled to the cyclic extension unit and to receive a time reference signal, for deriving a local reference signal from the time reference signal and synchronizing transmission of an SC-OFDM signal of the SC-OFDM transmitter in accordance with the local reference signal,

wherein, the SC-OFDM signals each have a cyclic extension and the SC-OFDM signals from the SC-OFDM transmitter include at least one pilot code in accordance with a predetermined pilot code scheme.

34. The subscriber unit of claim 33 wherein the at least one pilot code is comprised of a sequence from a set of sequences with minimal/zero/known cross-correlation and the predetermined pilot code scheme places each pilot code in a predetermined set of symbol locations.

35. The subscriber unit of claim 33 wherein the cyclic extension has a duration based at least in part on inter-SC-OFDM transmitter propagation delay.

36. The subscriber unit of claim 33 wherein the cyclic extension is further based on a duration of a channel impulse response.

37. The subscriber unit of claim 33 where the common source for the SC-OFDM transmitter is one of:

A) a global positioning system; and

B) a wireline network clock.

38. The subscriber unit of claim 33 further including a receiver, and wherein the reference derived from the common source is based on a closed loop timing adjustment scheme.

39. The subscriber unit of claim 33 wherein the modulator/the cyclic extension unit/synchronizing unit is implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

40. A subscriber unit having a synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, receiver arranged to receive at least one composite SC-OFDM signal demodulated and parsed into a plurality of composite SC-OFDM symbols and at least one composite SC-OFDM pilot code, the SC-OFDM receiver comprising:

A) a multi-channel channel response measurement unit, arranged to receive the at least one composite SC-OFDM pilot code, for computing channel response measurements for a plurality of components of the composite SC-OFDM signal based on a plurality of associated pilot codes, and

B) a detector, coupled to the multi-channel channel response measurement unit and to receive at least one of the plurality of composite SC-OFDM symbols, for detecting at least one symbol component from the at least one composite SC-OFDM symbol based on the channel response measurement/measurements and the at least one composite SC-OFDM symbol.

41. The subscriber unit of claim 40 wherein the detector provides the at least one symbol component as a soft decision.

42. The subscriber unit of claim 40 wherein a number of channel response measurements is greater than a number of the at least one composite SC-OFDM pilot code.

43. The subscriber unit of claim 40 wherein at least two composite SC-OFDM pilot codes are received and the multichannel channel response measurement unit further computes filtered channel response measurements for at least one component of the composite SC-OFDM signal by interpolation filtering the channel response measurements for the at least one component according to a predetermined interpolation filtering scheme.

44. The subscriber unit of claim 40 Wherein the multichannel channel response measurement unit further computes an average phase difference between at least one of:

a number of the plurality of composite SC-OFDM symbols; and

a number of the at least one composite SC-OFDM pilot code.

45. The subscriber unit of claim 44 wherein the multichannel channel response measurement unit further adjusts for the average phase difference by multiplying the at least one of

the number of the plurality of composite SC-OFDM symbols;

and

the number of the at least one composite SC-OFDM pilot code by at least one phase adjustment factor.

46. The subscriber unit of claim 44 wherein the multichannel channel response measurement unit further adjusts for the average phase difference by adjusting the predetermined interpolation filtering scheme.

47. The subscriber unit of claim 40 wherein the detector jointly detects a plurality of symbol components from the at least one composite SC-OFDM symbol in accordance with a predetermined joint detection scheme.

48. The subscriber unit of claim 40 wherein the multichannel response measurement unit/detector is implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

49. A subscriber unit having a synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, receiver unit having a plurality of diversity antennas arranged to receive a plurality of composite SC-OFDM signals demodulated and parsed into a plurality of composite SC-OFDM symbols and a plurality of composite SC-OFDM pilot codes, the SC-OFDM receiver unit comprising:

A) a plurality of multi-channel channel response measurement units, each arranged to receive at least one composite SC-OFDM pilot code, for computing channel response measurements for a plurality of components for each of the plurality of composite SC-OFDM signals based on a plurality of associated pilot codes, and

B) a diversity detector, coupled to the plurality of multi-channel channel response measurement units and to receive at least two of the plurality of composite SC-OFDM symbols, for detecting at least one symbol component from the composite SC-OFDM symbols based on the channel response measurements and the composite SC-OFDM symbols.

50. The subscriber unit of claim 49 wherein the diversity detector provides the at least one symbol component as a soft decision.

51. The subscriber unit of claim 49 wherein the diversity detector uses:

the channel response measurements; and

the composite SC-OFDM symbols

to form at least one weighted sum of the at least two of the plurality of composite SC-OFDM symbols in accordance with a minimum mean squared error combining scheme and then detects the at least one symbol component based on the at least one weighted sum.

52. The subscriber unit of claim 51 wherein the minimum mean squared error combining scheme calls for the computation of a signal covariance matrix and steering vector based on at least one of:

the channel response measurements; and

the composite SC-OFDM symbols.

53. The subscriber unit of claim 49 wherein the diversity detector uses the channel response measurements and the composite SC-OFDM symbols to form at least one weighted sum of the at least two of the plurality of composite SC-OFDM symbols in accordance with a diversity with signal quality weighting combining scheme and then detects the at least one symbol component from the at least one weighted sum.

54. The subscriber unit of claim 49 wherein the diversity detector uses the channel response measurements and the composite SC-OFDM symbols to form at least one weighted sum of the at least two of the plurality of composite SC-OFDM symbols in accordance with a maximal ratio combining scheme and then detects the at least one symbol component from the at least one weighted sum.

55. The subscriber unit of claim 49 wherein at least two composite SC-OFDM pilot codes are received on each diversity antenna and each of the plurality of multi-channel channel response measurement units further compute filtered channel response measurements for at least one component of each of the composite SC-OFDM signals by interpolation filtering the channel response measurements for the at least one component of each of the composite SC-OFDM signals according to a predetermined interpolation filtering scheme.

56. The subscriber unit of claim 49 wherein the detector jointly detects a plurality of symbol components from the at least two composite SC-OFDM symbols in accordance with a predetermined joint detection scheme.

57. The subscriber unit of claim 49 wherein the multichannel channel response measurement units/diversity detector is implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

58. A method for implementing synchronous coherent orthogonal frequency division multiplexing utilizing a plurality of SC-OFDM transmitters and a plurality of SC-OFDM receivers, comprising the steps of:

A) utilizing the plurality of SC-OFDM transmitters, wherein each SC-OFDM transmitter is synchronized to a reference where the reference is derived from a common source, for transmitting SC-OFDM signals, wherein the SC-OFDM signals each have a cyclic extension, and the SC-OFDM signals include at least one pilot code in accordance with a predetermined pilot code scheme; and

B) utilizing the plurality of SC-OFDM receivers, arranged for receiving the SC-OFDM signals from at least one of the plurality of SC-OFDM transmitters, for detecting information transmitted by at least one of the plurality of the SC-OFDM transmitters.

59. The method of claim 58 wherein the cyclic extension has a duration based at least in part on inter-SC-OFDM transmitter propagation delay.

60. The method of claim 58 wherein the cyclic extension is further based on a duration of a channel impulse response.

61. The method of claim 58 where the common source is one of:

A) a global positioning system; and

B) a wireline network clock.

62. The method of claim 58 wherein the reference derived from the common source is based on a closed loop timing adjustment scheme.

63. The method of claim 58 wherein the steps are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

64. A method for implementing synchronous coherent orthogonal frequency division multiplexing transmission utilizing a plurality of OFDM transmitters, comprising the steps of:

A) synchronizing transmission times of OFDM signals for each of the plurality of OFDM transmitters;

B) transmitting pilot codes and data from each of the plurality of OFDM transmitters according to a predetermined pilot code scheme where the pilot codes are transmitted on a same plurality of predetermined subcarriers for each OFDM transmitter.

65. The method of claim 64 wherein the steps are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

66. A method for implementing synchronous coherent orthogonal frequency division multiplexing reception utilizing an OFDM receiver arranged to receive SC-OFDM signals, comprising the steps of:

A) demodulating and parsing the SC-OFDM signals into received pilot codes and received symbols;

B) measuring a channel response based on at least one of the received pilot codes and a stored pilot code;

C) recovering an estimate of transmitted information in the SC-OFDM signals based on a channel response measurement and the received symbols.

68. A method for providing efficient orthogonal frequency division multiplexing reception upon receiving at least one orthogonal frequency division multiplexing signal, where a receiver uses at least frequency demultiplexed signals from a plurality of subcarriers to provide a detected signal, the method comprising the steps of:

A) measuring an average adjacent-subcarriers phase difference based on at least frequency demultiplexed signals from a plurality of subcarriers to provide a measured adjacent-subcarriers phase difference; and

B) compensating for the measured average adjacent-subcarriers phase difference in the formation of the detected signal.

69. The method system of claim 68 wherein the steps are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

70. An orthogonal frequency division multiplexing OFDM receiver for receiving at least one orthogonal frequency division multiplexing signal, frequency demultiplexing the signal into a plurality of demultiplexed signals from a plurality of subcarriers, and for detecting at least one symbol from the demultiplexed signals, comprising:

A) an adjacent-subcarriers phase difference measurement unit, coupled to receive the demultiplexed signals, for measuring an average adjacent-subcarriers phase difference, to provide a measured average adjacent-subcarriers phase difference;

B) an adjacent-subcarriers phase difference compensation unit, coupled to the adjacent-subcarriers phase difference measurement unit and the demultiplexed signals, for compensating the demultiplexed signals for the measured average adjacent-subcarriers phase difference to provide compensated signals; and

C) detector, coupled to the adjacent-subcarriers phase difference compensation unit, for detecting at least one symbol to provide at least one detected symbol, based on at least the compensated signals.

71. The OFDM receiver of claim 70 wherein the adjacent-subcarriers phase difference measurement unit/adjacent-subcarriers phase difference compensation unit/detector are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

72. An orthogonal frequency division multiplexing receiver for receiving at least one orthogonal frequency division multiplexing signal, frequency demultiplexing the signal into a plurality of demultiplexed signals from a plurality of subcarriers, and for detecting at least one symbol from the demultiplexed signals, comprising:

A) an adjacent-subcarriers phase difference measurement unit, coupled to receive the demultiplexed signals, for measuring an average adjacent-subcarriers phase difference to provide a measured average adjacent-subcarriers phase difference; and

B) a detector with phase compensation unit, coupled to the adjacent-subcarriers phase difference measurement unit and the demultiplexed signals, for providing at least one detected symbol based on at least the demultiplexed signals and the measured adjacent-subcarriers phase difference.

73. The OFDM receiver of claim 72 wherein the adjacent-subcarriers phase difference measurement unit/detector with phase compensation unit are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

74. A synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, receiver for receiving at least one composite SC-OFDM signal, frequency demultiplexing the composite SC-OFDM signal into a plurality of composite SC-OFDM symbols from a plurality of subcarriers, and for detecting at least one symbol component from at least one composite SC-OFDM symbol, comprising:

A) an adjacent-subcarriers phase difference measurement unit, coupled to receive the composite synchronous coherent orthogonal frequency division multiplexing symbols, for measuring an average adjacent-subcarriers phase difference, to provide a measured average adjacent-subcarriers phase difference;

B) an adjacent-subcarriers phase difference compensation unit, coupled to the adjacent-subcarriers phase difference measurement unit and the composite SC-OFDM symbols, for compensating the composite SC-OFDM symbols for the measured average adjacent-subcarriers phase difference to provide compensated composite SC-OFDM symbols; and

C) a detector, coupled to the adjacent-subcarriers phase difference compensation unit, for detecting at least one symbol component of at least one composite SC-OFDM symbol to provide at least one detected symbol component based on at least the compensated composite SC-OFDM symbols.

75. The SC-OFDM receiver of claim 74 wherein the adjacent-subcarriers phase difference measurement unit/adjacent-subcarriers phase difference compensation unit/detector are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.

76. A synchronous coherent orthogonal frequency division multiplexing, SC-OFDM, receiver for receiving at least one composite SC-OFDM signal, frequency demultiplexing the composite SC-OFDM signal into a plurality of composite SC-OFDM symbols from a plurality of subcarriers, and for detecting at least one symbol component from at least one composite SC-OFDM symbol, comprising:

A) a multichannel adjacent-subcarriers phase difference measurement unit, coupled to receive the composite SC-OFDM symbols, for measuring an average adjacent-subcarriers phase difference for a plurality of components of the composite SC-OFDM symbols, to provide a plurality of measured average adjacent-subcarriers phase differences; and

B) a detector with multi-channel adjacent-subcarriers phase difference compensation unit, coupled to the multichannel adjacent-subcarriers phase difference measurement unit and the composite SC-OFDM symbols, for detecting at least one symbol component of at least one composite SC-OFDM symbol to provide at least one detected symbol component based on at least the compensated composite SC-OFDM symbols and the plurality of measured average adjacent-subcarriers phase differences.

77. The SC-OFDM receiver of claim 76 wherein the multichannel adjacent-subcarriers phase difference measurement unit/detector with multi-channel adjacent-subcarriers phase difference compensation unit are implemented in one of:

A) an application-specific integrated circuit;

B) a digital signal processor;

C) a processor;

D) code; and

E) a combination of at least two of A-D.