Highly bandwidth-efficient communications

• US 7,106,781 B2
• Filed: 08/03/2001
• Issued: 09/12/2006
• Est. Priority Date: 02/24/1997
• Status: Expired due to Fees

• Current Assignee: AT&T Mobility II LLC (AT&T, Inc.)
• Original Assignee: Cingular Wireless II LLC (AT&T, Inc.)
• Inventors: Ho, Minnie, Stephenson, David, Hoole, Elliott, Agee, Brian G., Gibbons, David, Jesse, Mary, Gerlach, Derek, Mechaley, Robert G. Jr., Ryan, David James, Maxwell, Robert Lee, Bromberg, Matthew, Naish, Robert Ray, Nix, David J., Golden, James Timothy
• Primary Examiner(s): Tran, Khai
• Application Number:
  US09/920,903
• Publication Number:
  US 20020122465A1
• Time in Patent Office: 1,866 Days
• Field of Search: 373/141, 373/150, 373/143, 373/347, 373/267, 373/135, 373/136, 370/519, 370/206, 370/337, 370/341, 370/442, 370/342
• US Class Current: 375/141
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04B 1/692 Hybrid techniques using combinations of two or more spread spectrum techniques
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/03019 adaptive, i.e. capable of adjustment during data reception
• CPC Class Codes: H04L 27/186 in which the information is carried by both the individual signal points and the subset to which the individual signal points belong, e.g. coset coding or related schemes
• CPC Class Codes: H04L 27/3416 in which the information is carried by both the individual signal points and the subset to which the individual points belong, e.g. using coset coding, lattice coding, or related schemes
• CPC Class Codes: H04L 5/0021 in which codes are applied as a frequency-domain sequences, e.g. MC-CDMA
• CPC Class Codes: H04L 5/0026 Division using four or more dimensions
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/026 using code division
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A discrete multitone stacked-carrier spread spectrum communication method is based on frequency domain spreading including multiplication of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading involves energizing the bins of a large Fast Fourier transform (FFT). This provides a considerable savings in computational complexity for moderate output FFT sizes. Point-to-multipoint and multipoint-to-multipoint (nodeless) network topologies are possible. A code-nulling method is included for interference cancellation and enhanced signal separation by exploiting the spectral diversity of the various sources. The basic method may be extended to include multielement antenna array nulling methods for interference cancellation and enhanced signal separation using spatial separation. Such methods permit directive and retrodirective transmission systems that adapt or can be adapted to the radio environment. Such systems are compatible with bandwidth-on-demand and higher-order modulation formats and use advanced adaptation algorithms. In a specific embodiment the spectral and spatial components of the adaptive weights are calculated in a unified operation based on the mathematical analogy between the spectral and spatial descriptions of the airlink.

Claims

1. A highly bandwidth-efficient communications method, comprising:

a) receiving at a base station having a multi-element antenna array, during a first time period, a first spread signal comprising a first data signal redundantly spread over a plurality of discrete tones in accordance with a first spreading code;

b) despreading the first spread signal received at the base station, using despreading codes that are determined adaptively based on at least one characteristic of the first spread signal received at least two of the antenna elements of the array;

c) spreading a second data signal at the base station, using second spreading codes derived from the despreading codes, the second spreading codes redundantly spreading the second data signal over a plurality of discrete tones and over at least two of the antenna elements of the array, to form a second spread signal that is thereby both spectrally and spatially spread; and

d) transmitting the second spread signal during a second time period.

2. The highly bandwidth-efficient communications method of claim 1, wherein both the first and the second spread signals have the spectral form of a discrete multitone signal transmitted on multiple antennas in the array.

3. The highly bandwidth-efficient communications method of claim 1, wherein the despreading step comprises multiplication of a complex number representation of the despreading codes times a complex number representation of the first spread signal.

4. The highly bandwidth-efficient communications method of claim 1, wherein the spreading step comprises multiplication of a complex number representation of the second spreading codes times a complex number representation of the second data signal.

5. The highly bandwidth-efficient communications method of claim 1, wherein the despreading step comprises determination of complex despreading code values which are then multiplied with a complex number representation of the received signals, resulting in an estimate of the first data signal.

6. The highly bandwidth-efficient communications method of claim 1, the despreading step further comprising:

despreading the first spread signal with an, adaptive despreading code that is based on the characteristics of the received signals, where a given element of the spreading code corresponds to the combination of a given one of the antenna elements and a given one of the discrete tones;

whereby the despreading step determines spatial and spectral elements of the first spread signal in the same mathematical operation.

7. The highly bandwidth-efficient communications method of claim 6, wherein the despreading step adaptively positions the spatial direction of receive sensitivity towards a desired signal source and diminishes receive sensitivity from interfering sources.

8. The highly bandwidth-efficient communications method of claim 1, wherein the spreading step adaptively positions transmitted signal energy of the second spread signal towards a source of the first spread signal and adaptively diminishes transmitted signal energy towards interferers.

9. The highly bandwidth-efficient communications method of claim 1, wherein the first period and the second period comprise a time division duplex period.

10. The highly bandwidth-efficient communications method of claim 1, wherein the base station receives interference signals from interfering signal sources along with the first spread signal, the despreading step further comprising:

adaptively reducing the interference signals by adaptively adjusting the despreading codes to improve a signal quality characteristic of the received signal.

11. A highly bandwidth-efficient communications method, comprising:

a) receiving at a base station having a multi-element antenna array, during a first time period, a first spread signal comprising a first data signal redundantly spread over a plurality of discrete tones in accordance with a first spreading code;

b) despreading the first spread signal received at the base station, using despreading codes that are determined adaptively based on at least one characteristic off the first spread signal received at least two of the antenna elements of the array, where a given component of the spreading code is associated with the combination of a given one of the antenna elements and a given one of the discrete tones;

c) spreading a second data signal at the base station, with second spreading codes derived from the despreading codes, the second spreading codes redundantly spreading the second data signal over a plurality of discrete tones and over at least two of the antenna elements of the array, to form a second spread signal that is thereby both spectrally and spatially spread; and

d) transmitting the second spread signal during a second time period.

12. The highly bandwidth-efficient communications method of claim 11, wherein both the first and the second spread signals have the spectral form of a discrete multitone signal transmitted on multiple antennas in the array.

13. The highly bandwidth-efficient communications method of claim 11, wherein the despreading step comprises multiplication of a complex number representation of the despreading codes times a complex number representation of the first spread signal.

14. The highly bandwidth-efficient communications method of claim 11, wherein the spreading step comprises multiplication of a complex number representation of the second spreading codes times a complex number representation of the second data signal.

15. The highly bandwidth-efficient communications method of claim 11, wherein the despreading step determines values of complex despreading codes which are then multiplied with a complex number representation of the received signals, resulting in an estimate of the first data signal.

16. The highly bandwidth-efficient communications method of claim 11, wherein the despreading step adaptively positions the spatial direction of receive sensitivity towards a desired signal source and diminishes receive sensitivity from interfering sources.

17. The highly bandwidth-efficient communications method of claim 11, wherein the spreading step adaptively positions transmitted signal energy of the second spread signal towards a source of the first spread signal.

18. The highly bandwidth-efficient communications method of claim 11, wherein the despreading step comprises treating spatial and spectral components of the first spread signal independent of their spatial or spectral characteristics.

19. The highly bandwidth-efficient communications method of claim 11, wherein the first period and the second period comprise a time division duplex period.

20. The highly bandwidth-efficient communications method of claim 11, wherein the base station receives interference signals from interfering signal sources along with the first spread signal, the despreading step further comprising:

adaptively reducing the interference signals by adaptively adjusting the despreading codes to maximize the signal quality of the received signal.

21. A highly bandwidth-efficient communications method, comprising:

a) receiving at a base station, in a first propagation direction, during a first time period, a first spread signal comprising a first data signal redundantly spread over a plurality of discrete tones in accordance with a first spreading code;

b) despreading the first spread signal received at the base station, using despreading codes that are determined adaptively based on at least one characteristic of the first spread signal received at the base station in the first propagation direction;

c) spreading a second data signal at the base station, with second spreading codes derived from the despreading codes, the second spreading codes based on substantial channel reciprocity between the propagation direction and a reverse propagation direction, the second spreading codes redundantly spreading the second data signal over a plurality of discrete tones, to form a second spread signal; and

d) transmitting the second spread signal in the reverse propagation direction during a second time period.

22. The highly bandwidth-efficient communications method of claim 21, wherein both the first and the second spread signals have the spectral form of a discrete multitone signal.

23. The highly bandwidth-efficient communications method of claim 21, wherein the despreading step comprises multiplication of a complex number representation of the despreading codes times a complex number representation of the first spread signal.

24. The highly bandwidth-efficient communications method of claim 21, wherein the spreading step comprises multiplication of a complex number representation of the second spreading codes times a complex number representation of the second data signal.

25. The highly bandwidth-efficient communications method of claim 21, wherein the despreading step determines values of complex despreading codes which are then multiplied with a complex number representation of the received signals, resulting in an estimate of the first data signal.

26. The highly bandwidth-efficient communications method of claim 21, wherein the base station has a multi-element antenna array receiving the first spread signal, the despreading step further comprising:

despreading the first spread signal with a unitary, adaptive despreading code that is based on the characteristics of the received spread signal, where a given element of the spreading code corresponds to the combination of a given element of the multi-element antenna array and a given one of the discrete tones;

whereby the despreading step determines spatial and spectral components of the first spread signal in a mathematical operation that is independent of the spatial or spectral characteristics of the the components.

27. The highly bandwidth-efficient communications method of claim 26, wherein the despreading step adaptively positions the spatial direction of receive sensitivity towards a desired signal source and diminishes receive sensitivity from interfering sources.

28. The highly bandwidth-efficient communications method of claim 21, wherein the base station has a multi-element antenna array transmitting the second spread signal, and wherein the spreading step adaptively positions transmitted signal energy of the second spread signal towards a source of the first spread signal.

29. The highly bandwidth-efficient communications method of claim 21, wherein the first period and the second period comprise a time division duplex period.

30. The highly bandwidth-efficient communications method of claim 21, wherein the base station receives interference signals from interfering signal sources along with the first spread signal, the despreading step further comprising:

adaptively reducing the interference signals by adaptively adjusting the despreading codes to improve the signal quality of the received signal.

31. A highly bandwidth-efficient communications method, comprising:

a) receiving at a base station having a multi-element antenna array, in a first propagation direction, during a first time period, a first spread signal comprising a first data signal redundantly spread over a plurality of discrete tones in accordance with a first spreading code;

b) despreading the first spread signal received at the base station, using despreading codes that are determined adaptively based on at least one characteristic of the first spread signal received, in the first propagation direction, at least two of the antenna element of the array;

c) spreading a second data signal at the base station, with second spreading codes derived from the despreading codes, the second spreading codes based on substantial channel reciprocity between the first propagation direction and a reverse propagation direction, the second spreading codes redundantly spreading the second data signal over a plurality of discrete tones and over at least two of the antenna elements of the the array, to form a second spread signal that is thereby both spectrally and spatially spread; and

d) transmitting the second spread signal in the reverse propagation direction during a second time period.

32. The highly bandwidth-efficient communications method of claim 31, wherein both the first and the second spread signals have a spectral form of a discrete multitone signal transmitted on multiple antennas in the array.

33. The highly bandwidth-efficient communications method of claim 31, wherein the despreading step is a multiplication of a complex number representation of the despreading codes times a complex number representation of the first spread signal.

34. The highly bandwidth-efficient communications method of claim 31, wherein the spreading step is a multiplication of a complex number representation of the second spreading codes times a complex number representation of the second data signal.

35. The highly bandwidth-efficient communications method of claim 31, wherein the despreading step determines values of complex despreading codes which are then multiplied with a complex number representation of the received signals, resulting in an estimate of the first data signal.

36. The highly bandwidth-efficient communications method of claim 31, the despreading step further comprising:

despreading the first spread signal with a unitary, adaptive despreading code that is based on the characteristics of the received signals at the antenna elements of the array, where a given element of the spreading code corresponds to a given one of the antenna elements and a given one of the discrete tones;

whereby the despreading step treats spatial and spectral components of the first spread signal simultaneously.

37. The highly bandwidth-efficient communications method of claim 36, wherein the despreading step adaptively positions the spatial direction of receive sensitivity towards a desired signal source and diminishes receive sensitivity from interfering sources.

38. The highly bandwidth-efficient communications method of claim 31, wherein the spreading step adaptively positions transmitted signal energy of the second spread signal towards a source of the first spread signal and adaptively diminishes transmitted signal energy towards interferers.

39. The highly bandwidth-efficient communications method of claim 31, wherein the first period and the second period are parts of a time division duplex period.

40. The highly bandwidth-efficient communications method of claim 31, wherein the base station receives interference signals from interfering signal sources along with the first spread signal, the despreading step further comprising:

adaptively reducing the interference signals by adaptively adjusting the despreading codes to maximize the signal quality of the received signal.

41. A highly bandwidth-efficient communications method, comprising:

a) receiving at a base station having a multi-element antenna array, in a first propagation direction, during a first time period, a first spread signal comprising a first data signal redundantly spread over a plurality of discrete tones in accordance with a first spreading code;

b) despreading the first spread signal received at the base station, using despreading codes that are determined adaptively based on at least one characteristic of the first spread signal received, in the first propagation direction, at least two of the antenna elements of the array, where a given component of the spreading code is associated with the combination of a given one of the antenna elements and a given one of the discrete tones;

c) spreading a second data signal at the base station, with second spreading codes derived from the despreading codes based on substantial channel reciprocity between the first propagation direction and the a reverse propagation direction, the second spreading codes redundantly spreading the second data signal over a plurality of discrete tones and over at least two of the antenna elements of the array, to form a second spread signal that is spectrally and spatially spread; and

d) transmitting the second spread signal in the reverse propagation direction during a second time period.

42. The highly bandwidth-efficient communications method of claim 41, wherein both the first and the second spread signals have a spectral form of a discrete multitone signal transmitted on multiple antennas in the array.

43. The highly bandwidth-efficient communications method of claim 41, wherein the despreading step is a multiplication of a complex number representation of the despreading codes times a complex number representation of the first spread signal.

44. The highly bandwidth-efficient communications method of claim 41, wherein the spreading step is a multiplication of a complex number representation of the second spreading codes times a complex number representation of the second data signal.

45. The highly bandwidth-efficient communications method of claim 41, wherein the despreading step determines values of complex despreading codes which are then multiplied with a complex number representation of the received signals, resulting in an estimate of the first data signal.

46. The highly bandwidth-efficient communications method of claim 41, wherein the despreading step adaptively positions the spatial direction of receive sensitivity towards a desired signal source and diminishes receive sensitivity from interfering sources.

47. The highly bandwidth-efficient communications method of claim 41, wherein the spreading step adaptively positions transmitted signal energy of the second spread signal towards a source of the first spread signal and adaptively diminishes transmitted signal energy towards interferers.

48. The highly bandwidth-efficient communications method of claim 41, wherein the despreading step treats spatial and spectral components of the first spread signal simultaneously.

49. The highly bandwidth-efficient communications method of claim 41, wherein the first period and the second period are parts of a time division duplex period.

50. The highly bandwidth-efficient communications method of claim 41, wherein the base station receives interference signals from interfering signal sources along with the first spread signal, the dispreading step further comprising:

adaptively reducing the interference signals by adaptively adjusting the dispreading codes to maximize the signal quality of the received signal.