Method and apparatus for interference rejection with different beams, polarizations, and phase references

• US 6,081,566 A
• Filed: 04/19/1996
• Issued: 06/27/2000
• Est. Priority Date: 08/02/1994
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Ostman, Thomas, Molnar, Karl James, Bottomley, Gregory Edward
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): WEBSTER, BRYAN E
• Application Number:
  US08/634,719
• Time in Patent Office: 1,530 Days
• Field of Search: 375/262, 375/265, 375/267, 375/341, 375/346, 375/347, 375/348, 375/349, 375/229, 375/230, 375/232, 375/235, 375/343, 375/316, 375/259, 455/132, 455/133, 329/304, 342/374, 342/81, 342/154, 342/354, 342/457, 342/373
• US Class Current: 375/347
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 25/03331 Arrangements for the joint estimation of multiple sequences
• CPC Class Codes: H04W 16/28 using beam steering

Abstract

A digital radio communication system includes processing to jointly mitigate the deleterious effects of fading, time dispersion and interference using interference rejection and diversity combining. The system employs a selection processor for preliminarily reducing the number of signals for interference rejection and diversity combining based on one or more criterion. The system accommodates signals from dual polarized antennas. In one particular embodiment, the system performs interference rejection and diversity combining by separating a received signal into its in-phase and quadrature components.

Claims

1. A method for reducing the effects of signal fading, time dispersion, and interference in a radio communications system, comprising the steps of:

(a) receiving a radio signal on at least one antenna element representing a transmitted symbol sequence;

(b) processing said radio signal to produce received signal samples for said at least one antenna;

(c) estimating a channel tap for said at least one antenna to a produce a channel tap estimate;

(d) estimating scalar impairment correlation properties among the received signal samples to produce an estimate of scalar impairment correlation properties;

(e) forming scalar branch metrics in a scalar branch metric processor using said received signal samples, said channel tap estimate, and said scalar estimate of impairment correlation properties; and

(f) employing said scalar branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence.

2. A method according to claim 1, in which said forming step (e) comprises:

(g) generating hypothetical symbol sequences;

(h) filtering said hypothetical signal sequences with said channel tap estimate to produce hypothesized received signal samples for said at least one antenna;

(i) subtracting said hypothesized received signal samples from the received signal samples to produce complex error signals; and

(j) processing said complex error signals with said scalar estimate of impairment correlation properties to produce branch metrics.

3. A method according to claim 2, in which said forming step (j) further comprises:

(k) extracting an in-phase phase component from said complex error signal, and extracting a quadrature component from said complex error signal;

(l) processing said in-phase component and said quadrature component to produce said branch metrics.

4. A method according to claim 1, in which said estimating step (d) comprises:

(g) generating tentative detected symbol sequences;

(h) filtering said tentative detected symbol sequences with said scalar channel tap estimate to produce estimated received signal samples for said at least one antenna;

(i) subtracting said estimated received signal samples from the received signal samples to produce impairment signal samples; and

(j) processing said impairment signal samples with said estimate of scalar impairment correlation properties to produce an updated estimate of said scalar impairment correlation properties.

5. A method according to claim 4, in which said forming step (j) further comprises:

(k) extracting an in-phase phase component from said impairment signal samples, and extracting a quadrature component of said impairment signal samples;

(l) processing said in-phase component and said quadrature component to produce said updated estimate of said scalar correlation properties.

6. An apparatus for reducing the effects of signal fading, time dispersion, and interference in a radio communications system, comprising:

means for receiving a radio signal on at least one antenna element representing a transmitted symbol sequence;

means for processing said radio signal to produce received signal samples for said at least one antenna;

means for estimating a channel tap for said at least one antenna to a produce a channel tap estimate;

means for estimating scalar impairment correlation properties among said radio signal samples to produce an estimate of scalar impairment correlation properties;

means for forming scalar branch metrics in a scalar branch metric processor using said received signal samples, said channel tap estimates, and said scalar estimate of impairment correlation properties; and

means for employing said scalar branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence.

7. An apparatus according to claim 6, in which said means for forming scalar branch matrices comprises:

means for generating hypothetical symbol sequences;

means for filtering said hypothetical signal sequences with said channel tap estimate to produce hypothesized received signal samples for said at least one antenna;

means for subtracting said hypothesized received signal samples from the received signal samples to produce complex error signals; and

means for processing said complex error signals with said scalar estimate of impairment correlation properties to produce branch metrics.

8. An apparatus according to claim 7, in which said forming means for processing said complex error signals further comprises:

means for extracting an in-phase phase component from said complex error signal, and extracting a quadrature component from said complex error signal;

means for processing said in-phase component and said quadrature component to produce said branch metrics.

9. An apparatus according to claim 6, in which said means for estimating scalar impairment correlation properties comprises:

means for generating tentative detected symbol sequences;

means for filtering said tentative detected symbol sequences with said scalar channel tap estimate to produce estimated received signal samples for said at least one antenna;

means for subtracting said estimated received signal samples from the received signal samples to produce impairment signal samples; and

means for processing said impairment signal samples with said estimate of scalar impairment correlation properties to produce an updated estimate of said scalar impairment correlation properties.

10. An apparatus according to claim 9, in which said means for processing said impairment signal samples further comprises:

means for extracting an in-phase phase component from said impairment signal samples, and extracting a quadrature component from said impairment signal samples;

means for processing said in-phase component and said quadrature component to produce said updated estimate of said scalar correlation properties.

11. A method for reducing degradation in a transmitted signal sequence comprising the step of:

(a) providing a number of radio signals representing said transmitted signal sequence;

(b) selecting a second number of signals from said number of radio signals using a selection processor on the basis of one or more selection criterion, where said second number is less than said first number;

(c) processing said second number of signals to generate an estimate of said transmitted signal sequence;

wherein said step (c) further comprises the steps of;

(d) receiving said second number of signals from said selection processor;

(e) processing said second number of signals to produce received signal samples;

(f) estimating channel taps for said signals to produce channel tap estimates;

(g) estimating impairment correlation properties among said received signals to produce an estimate of impairment correlation properties;

(h) forming branch metrics in a branch metric processor using said received signal samples, said channel tap estimates, and said estimate of impairment correlation properties; and

(i) employing said scalar branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence.

12. The method of claim 11, wherein step (a) further comprises:

(d) receiving radio signals from a plurality of co-phased antenna elements;

(e) processing said radio signals received from said antenna elements using a fixed beamforming processor to produce said first number of radio signals.

13. The method of claim 12, wherein said antenna elements include at least one element from each of two orthogonal polarizations.

14. The method of claim 11, wherein step (a) further comprises:

(d) receiving radio signals from a plurality of antenna elements, wherein said antenna elements form a plurality of groupings of antenna elements;

(e) processing said radio signals received from said antenna elements using a plurality of beamforming processors, wherein each beamforming processor is associated with one of said groupings of antenna elements, to produce said first number of radio signals.

15. The method of claim 14, wherein a collection of antenna elements having a first polarization form a first grouping, and a collection of antenna elements having a second polarization form a second grouping, further wherein said first polarization is orthogonal to said second polarization.

16. The method of claim 14, wherein a first collection of spatially associated antenna elements form a first grouping, and a second collection of spatially associated antenna elements form a second grouping.

17. The method of claim 11, wherein step (a) further comprises:

(d) receiving radio signals from at least one sector antenna.

18. The method of claim 11, wherein said criterion is one or more criterion from the following group of criteria:

instantaneous power of a signal;

average power of a signal;

beam center direction relative to a desired signal direction; and

signal quality as measured from a sync word.

19. The method of claim 11, wherein said step (b) is constrained to select at least one signal having a first polarization, and at least one signal having a second polarization, wherein the first polarization is orthogonal to said second polarization.

20. The method of claim 11, wherein:

step (h) comprises estimating scalar impairment correlation properties among said received signals to produce an estimate of scalar impairment correlation properties;

step (h) comprises forming scalar branch metrics in a scalar branch metric processor using said received signal samples, said channel tap estimates, and said estimate of scalar impairment correlation properties; and

step (i) comprises employing said scalar branch metrics in said sequence estimation algorithm to estimate said transmitted symbol sequence.

31. The method of claim 11, wherein:

step (a) comprises receiving said first number of signals representing said transmitted signal sequence from a corresponding first number of antenna elements, wherein said first number of antenna elements include at least one element having a first polarization, and at least one other antenna element having a second polarization.

32. The method of claim 31, wherein said first and second polarizations are orthogonal to each other.

33. The method of claim 32, wherein said orthogonal first and second polarizations are:

i) horizontal and vertical polarizations, respectively;

ii) plus and minus 45 degree polarizations, respectively;

or iii) right and left circular polarizations, respectively.

21. An apparatus for reducing degradation in a transmitted signal sequence comprising:

(a) means for providing a first number of radio signals representing said transmitted signal sequence;

(b) means for selecting a second number of signals from said first number of radio signals using a selection processor on the basis of one or more selection criterion, where said second number is less than said first number;

(c) means for processing said second number of signals to generate an estimate of said transmitted signal sequences;

wherein said means for processing further comprises;

means for receiving said second number of signals from said selection processor;

means for processing said second number of signals to produce received signal samples;

means for estimating channel taps for said signals to produce channel tap estimates;

means for estimating impairment correlation properties among said received signals to produce an estimate of impairment correlation properties;

means for forming branch metrics in a branch metric processor using said received signal samples, said channel tap estimates, and said estimate of impairment correlation properties; and

means for employing said scalar branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence.

22. The apparatus of claim 21, wherein said means for receiving further comprises:

means for receiving radio signals from a plurality of co-phased antenna elements;

means processing said radio signals from said antenna elements using a fixed beamforming processor to produce said first number of radio signals.

23. The apparatus of claim 22, wherein said antenna elements include at least one element from each of two orthogonal polarizations.

24. The apparatus of claim 21, wherein said means for receiving further comprises:

a plurality of antenna elements for receiving signals, wherein said antenna elements form a plurality of groupings of antenna elements;

a plurality of beamforming processors, each beamforming processor associated with one of said groupings of antenna elements, said beamforming processors producing said first number of signals.

25. The apparatus of claim 24, wherein a collection of antenna elements having a first polarization form a first grouping, and a collection of antenna elements having a second polarization form a second grouping, further wherein said first polarization is orthogonal to said second polarization.

26. The apparatus of claim 24, wherein a first collection of spatially associated antenna elements form a first grouping, and a second collection of spatially associated antenna elements form a second grouping.

27. The apparatus of claim 21, wherein means for receiving further comprises:

means for receiving radio signals from at least one sector antenna.

28. The apparatus of claim 21, wherein said criterion is one or more criterion from the following group of criteria:

instantaneous power of a signal;

average power of a signal;

beam center direction relative to a desired signal direction; and

signal quality as measured from a sync word.

29. The apparatus of claim 21, wherein said means for selecting is constrained to select at least one signal having a first polarization and at least one signal a second polarization, wherein said first polarization is orthogonal to said second polarization.

30. The apparatus of claim 21, wherein:

said means for estimating estimates scalar impairment correlation properties among said received signals to produce an estimate of scalar impairment correlation properties;

said means for forming forms scalar branch metrics in a scalar branch metric processor using said received signal samples, said channel tap estimates, and said estimate of scalar impairment correlation properties; and

said means for employing employs said scalar branch metrics in said sequence estimation algorithm to estimate said transmitted symbol sequence.

34. The apparatus of claim 21, further comprising:

a first number of antenna elements for receiving said first number of radio signals representing said transmitted signal sequence, wherein said first number of antenna elements includes at least one element having a first polarization, and at least one other antenna element having a second polarization.

35. The apparatus of claim 34, wherein said first and second polarizations are orthogonal to each other.

36. The apparatus of claim 35, wherein said orthogonal first and second polarizations are:

i) horizontal and vertical polarizations, respectively;

ii) plus and minus 45 degree polarizations, respectively;

or iii) right and left circular polarizations, respectively.

37. A method for reducing the effects of signal fading, time dispersion, and interference in a radio communications system, comprising the steps of:

(a) receiving a signal representing a transmitted symbol sequence on plural antenna elements;

(b) processing said signal to produce received signal samples for each of said plural antenna elements;

(c) estimating channel taps for said plural antenna elements to a produce channel tap estimates;

(d) estimating impairment correlation properties among said received signals to produce an estimate of impairment correlation properties;

(e) forming branch metrics in a branch metric processor using said received signal samples, said channel tap estimates, and said estimate of impairment correlation properties; and

(f) employing said branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence,

wherein said plural antenna elements include at least a first element producing a first polarization, and a second element producing a second polarization.

38. The method of claim 37, wherein said processing step (b) includes processing said radio signal using at least one fixed beamforming processor.

39. An apparatus for reducing the effects of signal fading, time dispersion, and interference in a radio communications system, comprising:

plural antenna elements for receiving a signal representing a transmitted symbol sequence;

processing logic for processing said signal to produce received signal samples for each said plural antenna elements;

a first estimator for estimating channel taps for said plural antenna elements to a produce channel tap estimates;

a second estimator for estimating impairment correlation properties among said received signals to produce an estimate of impairment correlation properties;

a branch metric processor for forming branch metrics using said received signal samples, said channel tap estimates, and said estimate of impairment correlation properties; and

logic for employing said branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence,

wherein said plural antenna elements include at least a first element producing a first polarization, and a second element producing a second polarization.

40. The apparatus method of claim 39, wherein said processing logic employs at least one fixed beamforming processor.

41. In a digital communications system for transmitting a sequence of digital symbols, a method for reducing the effects of signal fading, time dispersion, and interference in a radio communications system, comprising the steps of:

(a) receiving a number of radio signals;

(b) selecting groups of radio signals using a selection processor;

(c) processing each group of radio signals to produce branch metrics;

(d) adding said branch metrics from different groups to produce combined branch metrics; and

(e) employing said combined branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence.

42. The method according to claim 41, in which processing step (c) is applied to each of said groups of radio signals, and further comprises, for each of said groups, the steps of:

(f) receiving a group of radio signals from said selection processor;

(g) processing said group of signals to produce received signal samples;

(h) estimating channel taps for said group of signals to produce channel tap estimates;

(i) estimating impairment correlation properties among the signals within the group to produce an estimate of impairment correlation properties;

(j) forming branch metrics in a branch metric processor using said received signal samples, said channel tap estimates, and said estimate of impairment correlation properties.

43. An apparatus for reducing the effects of signal fading, time dispersion, and interference in a radio communications system, comprising:

means for receiving a number of radio signals representing a transmitted sequence of symbols;

means for selecting groups of radio signals using a selection processor;

a plurality of processing means, each for processing a respective group of radio signals, to produce branch metrics;

means for adding said branch metrics from different groups to produce combined branch metrics; and

means for employing said combined branch metrics in a sequence estimation algorithm to estimate said transmitted symbol sequence.

44. The apparatus according to claim 43, in which each one of said plurality of processing means comprises:

means for receiving said group of radio signals to produce received signal samples;

means for processing said group of signals to produce received signal samples;

means for estimating channel taps for said group of signals to produce channel tap estimates;

means for estimating impairment correlation properties among the signals within the group to produce an estimate of impairment correlation properties; and

means for forming branch metrics in a branch metrics processor using said received signals samples, said channel tap estimates, and said estimate of impairment correlation properties.

45. A method for reducing degradation in a transmitted signal sequence comprising the step of:

(a) receiving a number of radio signals from a plurality of antenna elements, a first group of said antenna elements using a first polarization and a second group of said antenna elements using a second polarization;

(b) processing said radio signals in at least one beamforming processor to produce a first number of radio signals;

(c) selecting a second number of radio signals from said first number of radio signals using a selection processor on the basis of one or more selection criterion, where said second number is less than said first number, and said second number is greater than 1; and

(d) processing said second number of signals to generate an estimate of said transmitted signal sequence using a sequence estimation algorithm employing branch metrics;

wherein said step (c) is constrained to select at least one signal having a first polarization, and at least one signal having a second polarization, wherein the first polarization is orthogonal to said second polarization.

46. The method of claim 45, wherein said criterion is one or more criterion from the following group of criteria:

instantaneous power of a signal;

average power of a signal;

beam center direction relative to a desired signal direction; and

signal quality as measured from a sync word.

47. An apparatus for reducing degradation in a transmitted signal sequence comprising:

a plurality of antenna elements for receiving a number of radio signals, a first group of said antenna elements using a first polarization and a second group of said antenna elements using a second polarization;

at least one beamformer for processing said radio signals to produce a first number of radio signals;

a selector for selecting a second number of radio signals from said first number of radio signals using a selection processor on the basis of one or more selection criterion, where said second number is less than said first number, and said second number is greater than 1; and

a processor for processing said second number of signals to generate an estimate of said transmitted signal sequence using a sequence estimation algorithm employing branch metrics;

wherein said selector is constrained to select at least one signal having a first polarization, and at least one signal having a second polarization, wherein the first polarization is orthogonal to said second polarization.

48. The apparatus of claim 47, wherein said criterion is one or more criterion from the following group of criteria:

instantaneous power of a signal;

average power of a signal;

beam center direction relative to a desired signal direction; and

signal quality as measured from a sync word.