Selective modification of antenna directivity pattern to adaptively cancel co-channel interference in TDMA cellular communication system

• US 6,411,612 B1
• Filed: 05/19/1998
• Issued: 06/25/2002
• Est. Priority Date: 05/19/1998
• Status: Expired due to Term

• Current Assignee: North South Holdings Incorporated (Spherix Incorporated)
• Original Assignee: Harris Global Communications, Inc. (L3Harris Technologies, Inc.)
• Inventors: Halford, Karen W., Martin, Gayle Patrick, Willingham, Julian Bartow, Webster, Mark A., Sinclair, Gregory S.
• Primary Examiner(s): Jung, Min
• Application Number:
  US09/081,287
• Time in Patent Office: 1,498 Days
• Field of Search: 370/336, 370/337, 370/345, 370/347, 370/350, 370/328, 455/561, 455/562, 455/278.1, 342/378
• US Class Current: 370/347
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 7/0617 for beam forming
• 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: H04W 84/042 Public Land Mobile systems, e.g. cellular systems
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A base station signal processing mechanism for a time division multiple access (TDMA) cellular communication system adaptively controls weighting coefficients of the base station'"'"'s phased array antenna in a manner that forms a directivity pattern whose gain and/or nulls maximize the signal to noise ratio in the presence of co-channel users whose communication time slots overlap a communication time slot of a desired user. The signal processing mechanism performs correlation processing of synchronization patterns contained in signals transmitted by co-channel users to identify times of transitions between successive co-channel users'"'"' communication time slots relative to a time of transition of the desired user'"'"'s communication time slot, and deriving weighting coefficients in accordance with the times of transitions.

Claims

1. For use with a time division multiple access (TDMA) cellular communication system having a plurality of cells, that are dispersed relative to a cell in which a desired user conducts communications with a base station in said cell, and wherein said dispersed cells contain users which may transmit during time slots that overlap a user time slot used for communications between said user and said base station, a method of reducing interference, as a result of transmissions from said users in said dispersed cells during said time slots, with communications between said user and said base station, said method comprising, at said base station, the steps of:

(a) communicating with said user by way of an antenna having a directivity pattern the gain of which may be selectively reduced in directions of said users in said dispersed cells;

(b) receiving transmissions from said users in said dispersed cells and processing contents of received transmissions to determine offsets of said time slots relative to said user time slot; and

(c) adjusting said directivity pattern in accordance with said relative offsets determined in step (b), so as to selectively reduce the gain of said directivity pattern in said directions of said users in said dispersed cells during said users'"'"' time slots.

2. A method according to claim 1, wherein said antenna comprises a multi-element phased array antenna.

3. A method according to claim 2, wherein said multi-element phased array antenna comprises a two-dimensional arrangement of antenna elements.

4. A method according to claim 2, wherein said multi-element phased array antenna has a variable spacing between adjacent antenna elements.

5. A method according to claim 2, wherein said multi-element phased array antenna comprises a generally circular array of antenna elements.

6. A method according to claim 5, wherein spacings between successive antenna elements of said generally circular array vary such that, for any point on a radial line in the plane of said circular array and passing through an element of said circular array, the vector distance to any two antenna elements is unequal and uniformly distributed modulo 2π

.

7. A method according to claim 6, wherein the angular separation between successive antenna elements varies in accordance with an Nth root of two, wherein N is the number of antenna elements of said circular array.

8. A method according to claim 6, wherein the angular separation between successive ones of the N antenna elements of the array is such that, for one element located at any arbitrary location along the array, the angular spacing α

₁ of a second element relative to the first element is defined by α

₁=2π

*(2^1/N−

1), and wherein the angular spacing α

_j of each additional element relative to the first element is defined by α

_j=α

<sub>j−

1</sub>*2^1/N, where j varies from 2 to N.

9. A method according to claim 1, wherein said contents of said transmissions processed in step (b) comprise synchronization patterns contained in said transmissions, and wherein step (b) comprises correlating with synchronization patterns contained in said transmissions to identify correlation peaks associated with times of transitions between successive ones of said users'"'"' time slots relative to a time of transition of said user time slot.

10. A method according to claim 2, wherein said multi-element phased array antenna has a plurality of amplitude and phase weight control elements associated with said elements of said antenna, and wherein step (c) comprises adjusting said weight control elements in accordance with said offsets of time slots determined in step (b), so that said directivity pattern has reduced gain in said directions of said users in said dispersed cells during said users, time slots.

11. A method according to claim 10, wherein step (c) comprises updating values of said weight control elements of said antenna, in response to a transition between successive ones of said users'"'"' time slots, and maintaining said values of said weight control elements of said antenna until a further transition between successive ones of said users'"'"' time slots.

12. A method according to claim 10, wherein step (c) comprises, for a respective set of said users having time slots that overlap said user time slot, generating a respective set of values of said weight control elements of said antenna that are effective to reduce the gain of said directivity pattern in the direction of each of said users of said respective set of users for the duration of their overlap with said user time slot, and adjusting said directivity in accordance with said respective set of values of said weight control elements, so as to selectively reduce the gain of said directivity pattern in the direction of each of said users of said respective set of users and, in response to another respective set of said users having time slots that overlap said user time slot, generating another set of values of said weight control elements of said antenna that are effective to reduce the gain of said directivity in directions of each of the users of said another set of users for the duration of their overlap of said user time slot, and adjusting said directivity pattern in accordance with said another respective set of values of said weight control elements, so as to selectively reduce the gain of said directivity pattern in the direction of each of the users of said another respective set of users.

13. A method according to claim 12, wherein step (c) comprises, for each respective set of said users having time slots that overlap said user time slot, storing an associated set of values of said weight control elements of said antenna that are effective to reduce the gain of said directivity pattern in the direction of each of said users of said each respective set of users, until the next occurrence of time slots of said each respective set of said users overlapping said user time slot and, in response to said next occurrence, updating said respective set of values of said weight control elements of said antenna that are effective to reduce the gain of said directivity pattern in the direction of each of said users of said respective set of users.

14. A method according to claim 1, wherein step (b) comprises receiving transmissions from said users in said dispersed cells exclusive of a transmission from said user in said cell, and processing contents of said transmissions from said users to determine relative offsets between said users'"'"' time slots and said user time slot.

15. For use with a time division multiple access (TDMA) cellular communication system, a method of preventing co-channel interference from users in cells adjacent to a cell containing a desired user comprising the

steps of:

(a) providing a base station in said cell with a phased array antenna; and

(b) adaptively modifying the directivity pattern of said base station'"'"'s phased array antenna, in a manner that forms a beam whose gain and/or nulls maximize the signal to noise ratio in the presence of co-channel users whose communication time slots overlap a communication time slot of said desired user.

16. A method according to claim 15, wherein said phased array antenna comprises a circular array of antenna elements, and wherein spacings between successive antenna elements of said generally circular array vary such that, for any point on a radial line in the plane of said circular array and passing through an element of said circular array, the vector distance to any two antenna elements is unequal and uniformly distributed modulo 2π

.

17. A method according to claim 16, wherein the angular separation between successive antenna elements varies in accordance with an Nth root of two, wherein N is the number of antenna elements of said circular array.

18. A method according to claim 16, wherein the angular separation between successive ones of the N antenna elements of the array is such that, for one element located at any arbitrary location along the array, the angular spacing α

₁ of a second element relative to the first element is defined by α

₁32 2π

*(2^1/N−

1), and wherein the angular spacing α

_j of each additional element relative to the first element is defined by α

_j=α

<sub>j−

1</sub>*2^1/N, where j varies from 2 to N.

19. A method according to claim 15, wherein said antenna elements of said base station'"'"'s phased array are driven by a set of weighting coefficients, and wherein step (b) comprises, during an unused time slot, deriving values of said set of weighting coefficients that are effective to form a beam whose gain and/or nulls maximize the signal to noise ratio in the presence of co-channel users whose communication time slots overlap a communication time slot of said desired user.

20. A method according to claim 15, wherein step (b) comprises correlating with synchronization patterns contained in transmissions from said users to identify times of transitions between successive ones of said users'"'"' time slots relative to a time of transition of said desired user'"'"'s time slot, and deriving said set of weighting coefficients in accordance with said times of transitions.

21. A method according to claim 20, wherein step (b) further comprises said weighting coefficients, in response to a transition between successive ones of said users'"'"' time slots, and maintaining said values of said weighting coefficients until a further transition between successive ones of said users'"'"' time slots.

22. For use with a time division multiple access (TDMA) cellular communication system having a plurality of cells, that are dispersed relative to a cell in which a desired user conducts communications with a base station in said cell, and wherein said dispersed cells contain co-channel users which may transmit during time slots that overlap a desired user'"'"'s time slot used for communications between said desired user and said base station, a base station signal processing arrangement for reducing interference of communications between said desired user and said base station, by transmissions from said co-channel users in said dispersed cells during said time slot, comprising:

a phased array antenna; and

a signal processor, coupled to said phased array antenna and being operative to process signals transmitted from said co-channel users, and adaptively modify the directivity pattern of said phased array antenna in a manner that forms a beam whose gain and/or nulls maximize the signal to noise ratio in the presence of co-channel users whose communication time slots overlap a communication time slot of said desired user.

23. A base station signal processing arrangement according to claim 22, wherein said antenna comprises a non-linear array of antenna elements having a variable spacing between adjacent antenna elements.

24. A base station signal processing arrangement according to claim 22, wherein said phased array antenna comprises a generally circular array of antenna elements, and wherein spacings between successive antenna elements of said generally circular array vary such that, for any point on a radial line in the plane of said circular array and passing through an element of said circular array, the vector distance to any two antenna elements is unequal and uniformly distributed modulo 2π

.

25. A base station signal processing arrangement according to claim 24, wherein the angular separation between successive antenna elements varies in accordance with an Nth root of two, wherein N is the number of antenna elements of said circular array.

26. A base station signal processing arrangement according to claim 25, wherein the angular separation between successive ones of the N antenna elements of the array is such that, for one element located at any arbitrary location along the array, the angular spacing α

₁ of a second element relative to the first element is defined by α

₁=2π

*(2^1/N−

1) and wherein the angular spacing α

_j of each additional element relative to the first element is defined by α

_j=α

<sub>j−

1</sub>*2^1/N, where j varies from 2 to N.

27. A base station signal processing arrangement according to claim 22, wherein antenna elements of said base station'"'"'s phased array are driven by a set of weighting coefficients, and wherein said signal processor is operative, during an unused time slot, to derive values of said set of weighting coefficients that are effective to form a beam whose gain and/or nulls maximize the signal to noise ratio in the presence of co-channel users whose communication time slots overlap a communication time slot of said desired user.

28. A base station signal processing arrangement according to claim 27, wherein said signal processor is operative to perform correlation processing of synchronization patterns contained in signals transmitted by said co-channel users to identify times of transitions between successive ones of said users'"'"' communication time slots relative to a time of transition of said desired user'"'"'s communication time slot, and deriving said set of weighting coefficients in accordance with said times of transitions.

29. A base station signal processing arrangement according to claim 28, wherein signal processor is operative to perform correlation processing of said synchronization patterns to identify correlation peaks associated with times of transitions between successive ones of said users'"'"' communication time slots relative to a time of transition of said user communication time slot.

30. A base station signal processing arrangement according to claim 27, wherein said signal processor is operative to update values of said weighting coefficients, in response to a transition between successive ones of said users'"'"' communication time slots, and maintaining said values of said weighting coefficients until a further transition between successive ones of said users'"'"' communication time slots.

31. A base station signal processing arrangement according to claim 28, wherein said signal processor comprises a narrowband tuner, which provides decimated in-phase (I) and quadrature (Q) baseband channels, a finite impulse response (FIR) filter coupled to filter said decimated I and Q baseband channels, and having a transfer characteristic that is matched to the shape of a signal from a co-channel user correlates with said synchronization pattern.

32. A base station signal processing arrangement according to claim 31, wherein said finite impulse response filter comprises a plurality of correlation filters, each of which correlates a decimated baseband signal with a copy of a respectively different synchronization pattern associated with co-channel interferers of said adjacent cells.

33. A base station signal processing arrangement according to claim 31, wherein said signal processor is further operative to derive an output representative of the magnitude of the output of said finite impulse response filter, and a timing selector, which is operative to derive timings of peaks in average sets of correlations of synchronization patterns associated with said co-channel users, said timings of correlation peaks being representative of times of transitions between successive co-channel users'"'"' communication time slots relative to the time of transition of said desired user'"'"'s communication time slot.

34. A base station signal processing arrangement according to claim 33, wherein said signal processor includes a weighting coefficient control operator, which is operative to adjust said set of weighting coefficients, as necessary, to form a directivity pattern whose gain and/or nulls maximize the signal to noise ratio in the presence of co-channel interferer whose whose synchronization pattern correlation peak has been identified by said timing selector.

35. A base station signal processing arrangement according to claim 27, wherein said signal processor is operative to update said weighting coefficients in accordance with participant changes of a plurality of said co-channel users, and to store updated weighting coefficient values, for use in determining weighting coefficients in response to a subsequent transition between successive time slots of any co-channel users in said adjacent cells.