NULL PILOTS FOR INTERFERENCE ESTIMATION IN A WIRELESS COMMUNICATION NETWORK

• US 20100099428A1
• Filed: 04/16/2009
• Published: 04/22/2010
• Est. Priority Date: 04/22/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Bhushan, Naga, Agrawal, Avneesh, Ji, Tingfang, Khandekar, Aamod D., Borran, Mohammad J., Gorokhov, Alexei Y.
• Granted Patent: US 8,559,879 B2
• Time in Patent Office: Days
• US Class Current: 455/452.1
• CPC Class Codes: H04J 11/0059 Out-of-cell user aspects
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0035 Resource allocation in a cooperative multipoint environment
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic
• CPC Class Codes: H04W 72/541 using the level of interference

Abstract

Techniques for transmitting null pilots to support interference estimation in a wireless network are described. A null pilot is non-transmission on designated time-frequency resources by a cell or a cluster of cells supporting cooperative transmission to a UE. The received power of the null pilot from the cell or cluster of cells may be indicative of interference from other cells. In one design, a cell in the cluster may determine resources for sending a null pilot by the cell. The cell may transmit the null pilot (i.e., send no transmissions) on the resources to allow UEs to estimate out-of-cluster interference. Some or all cells in the cluster may transmit null pilots on the same resources. The cell may receive interference and channel information from the UE and may send data transmission to the UE based on the interference and/or channel information. Remaining cells in the cluster may reduce interference to the UE.

Claims

1. A method of supporting interference estimation in a wireless communication network, comprising:

determining resources for sending a null pilot by a cell in a cluster of cells; and

transmitting the null pilot on the resources by the cell to allow user equipments (UEs) to estimate out-of-cluster interference comprising interference from cells not in the cluster.

2. The method of claim 1, wherein each cell in the cluster is assigned different resources for sending null pilot.

3. The method of claim 1, wherein all cells in the cluster use same resources for sending null pilots, and wherein different clusters are assigned different resources for sending null pilots.

4. The method of claim 1, wherein the determining the resources for sending the null pilot comprises determining the resources for sending the null pilot based on a function of an identity (ID) of the cell or the cluster.

5. The method of claim 1, wherein the transmitting the null pilot comprises sending no transmissions on the resources for sending the null pilot by puncturing symbols mapped to the resources.

6. The method of claim 1, wherein the transmitting the null pilot comprises sending no transmissions on the resources for sending the null pilot by determining symbols mapped to the resources and remapping the symbols to other resources.

7. The method of claim 1, further comprising:

receiving interference information indicative of out-of-cluster interference observed by a UE; and

sending a data transmission to the UE based on the interference information.

8. The method of claim 7, further comprising:

estimating received signal quality at the UE based on the interference information from the UE; and

determining a rate based on the estimated received signal quality, and wherein the data transmission is sent at the determined rate to the UE.

9. The method of claim 1, further comprising:

receiving channel information for the cell from the UE;

determining a precoding matrix based on the channel information; and

sending a data transmission with the precoding matrix to the UE, wherein each remaining cell in the cluster reduces interference to the UE.

10. The method of claim 1, further comprising:

receiving interference information indicative of out-of-cluster interference observed by a UE;

receiving channel information for at least one cell in the cluster from the UE; and

determining whether to schedule the UE for data transmission based on the interference information and the channel information.

11. An apparatus for wireless communication, comprising:

means for determining resources for sending a null pilot by a cell in a cluster of cells; and

means for transmitting the null pilot on the resources by the cell to allow user equipments (UEs) to estimate out-of-cluster interference comprising interference from cells not in the cluster.

12. The apparatus of claim 11, wherein each cell in the cluster is assigned different resources for sending null pilot.

13. The apparatus of claim 11, wherein all cells in the cluster use same resources for sending null pilots, and wherein different clusters are assigned different resources for sending null pilots.

14. The apparatus of claim 11, further comprising:

means for receiving interference information indicative of out-of-cluster interference observed by a UE; and

means for sending a data transmission to the UE based on the interference information.

15. The apparatus of claim 11, further comprising:

means for receiving channel information for the cell from the UE;

means for determining a precoding matrix based on the channel information; and

means for sending a data transmission with the precoding matrix to the UE, wherein each remaining cell in the cluster reduces interference to the UE.

16. A method of estimating interference in a wireless communication network, comprising:

receiving null pilots from multiple cells in a cluster of cells; and

estimating out-of-cluster interference observed by a user equipment (UE) based on the null pilots from the multiple cells, the out-of-cluster interference comprising interference from cells not in the cluster.

17. The method of claim 16, further comprising:

determining resources used to send the null pilots by the multiple cells in the cluster, wherein each cell in the cluster is assigned different resources for sending null pilot.

18. The method of claim 16, further comprising:

determining resources used to send the null pilots by the multiple cells in the cluster, wherein all cells in the cluster use same resources for sending null pilots, and wherein different clusters are assigned different resources for sending null pilots.

19. The method of claim 17, wherein the estimating the out-of-cluster interference comprises

determining received power of a null pilot from each cell in the cluster,

determining total received power at the UE, and

estimating the out-of-cluster interference based on received powers of the null pilots from all cells in the cluster and the total received power at the UE.

20. The method of claim 19, wherein the estimating the out-of-cluster interference further comprises

limiting the out-of-cluster interference based on a minimum or an average of the received powers of the null pilots from the multiple cells in the cluster.

21. The method of claim 17, wherein the estimating the out-of-cluster interference comprises

determining received power of each cell in the cluster,

determining received power of a null pilot from each of at least one cell in the cluster, and

estimating the out-of-cluster interference based on the received power of each cell in the cluster and the received power of the null pilot from each of the at least one cell in the cluster.

22. The method of claim 18, wherein the estimating the out-of-cluster interference comprises

determining received power of the null pilots from all cells in the cluster, and

estimating the out-of-cluster interference based on the received power of the null pilots from all cells in the cluster.

23. The method of claim 17, further comprising:

determining total received power at the UE;

determining received power of a null pilot from a cell in the cluster; and

determining received power of the cell based on the total received power at the UE and the received power of the null pilot from the cell.

24. The method of claim 16, wherein the UE is equipped with multiple receive antennas, and wherein the estimating the out-of-cluster interference comprises determining a covariance matrix of the out-of-cluster interference.

25. The method of claim 16, further comprising:

determining a spatial filter matrix based on the out-of-cluster interference; and

applying the spatial filter matrix to the out-of-cluster interference to obtain post-processed out-of-cluster interference.

26. The method of claim 16, further comprising:

determining interference information indicative of the out-of-cluster interference; and

sending the interference information to at least one designated cell in the cluster.

27. The method of claim 26, wherein the interference information comprises at least one of out-of-cluster interference power at the UE, a covariance matrix of the out-of-cluster interference, received out-of-cluster interference prior to receiver spatial processing at the UE, and post-processed out-of-cluster interference after receiver spatial processing at the UE.

28. The method of claim 16, further comprising:

determining channel information for at least one potential serving cell in the cluster; and

sending the channel information to at least one designated cell in the cluster.

29. The method of claim 28, wherein the channel information for each potential serving cell comprises a channel matrix for the cell or a composite channel matrix for the cell with receiver spatial processing at the UE.

30. The method of claim 16, further comprising:

receiving a data transmission from at least one cell in the cluster, wherein each remaining cell in the cluster reduces interference to the UE.

31. An apparatus for wireless communication, comprising:

means for receiving null pilots from multiple cells in a cluster of cells; and

means for estimating out-of-cluster interference observed by a user equipment (UE) based on the null pilots from the multiple cells, the out-of-cluster interference comprising interference from cells not in the cluster.

32. The apparatus of claim 31, further comprising:

means for determining resources used to send the null pilots by the multiple cells in the cluster, wherein each cell or each cluster of cells is assigned different resources for sending null pilot.

33. The apparatus of claim 31, wherein the means for estimating the out-of-cluster interference comprises

means for determining received power of a null pilot from each of at least one cell in the cluster, and

means for estimating the out-of-cluster interference based on the received power of the null pilot from each of the at least one cell in the cluster.

34. The apparatus of claim 31, wherein the means for estimating the out-of-cluster interference comprises

means for determining received power of the null pilots from all cells in the cluster, and

means for estimating the out-of-cluster interference based on the received power of the null pilots from all cells in the cluster.

35. The apparatus of claim 31, further comprising:

means for determining interference information indicative of the out-of-cluster interference;

means for determining channel information for at least one potential serving cell in the cluster;

means for sending the interference information and the channel information to at least one designated cell in the cluster; and

means for receiving a data transmission sent by at least one serving cell in the cluster based on the interference information and the channel information, wherein each remaining cell in the cluster reduces interference to the UE.

36. An apparatus for wireless communication, comprising:

at least one processor configured to receive null pilots from multiple cells in a cluster of cells, and to estimate out-of-cluster interference observed by a user equipment (UE) based on the null pilots from the multiple cells, the out-of-cluster interference comprising interference from cells not in the cluster.

37. The apparatus of claim 36, wherein the at least one processor is configured to determine resources used to send the null pilots by the multiple cells in the cluster, and wherein each cell or each cluster of cells is assigned different resources for sending null pilot.

38. The apparatus of claim 36, wherein the at least one processor is configured to determine received power of a null pilot from each of at least one cell in the cluster, and to estimate the out-of-cluster interference based on the received power of the null pilot from each of the at least one cell in the cluster.

39. The apparatus of claim 36, wherein the at least one processor is configured to determine received power of the null pilots from all cells in the cluster, and to estimate the out-of-cluster interference based on the received power of the null pilots from all cells in the cluster.

40. The apparatus of claim 36, wherein the at least one processor is configured to determine interference information indicative of the out-of-cluster interference, to determine channel information for at least one potential serving cell in the cluster, to send the interference information and the channel information to at least one designated cell in the cluster, and to receive a data transmission sent by at least one serving cell in the cluster based on the interference information and the channel information, and wherein each remaining cell in the cluster reduces interference to the UE.

41. A computer program product, comprising:

a computer-readable medium comprising;

code for causing at least one computer to receive null pilots from multiple cells in a cluster of cells, and

code for causing the at least one computer to estimate out-of-cluster interference observed by a user equipment (UE) based on the null pilots from the multiple cells, the out-of-cluster interference comprising interference from cells not in the cluster.

42. A method of supporting interference estimation in a wireless communication network, comprising:

determining resources reserved for null pilots for a cell; and

transmitting a null pilot on the reserved resources by a user equipment (UE) to allow the cell to estimate interference from UEs.

43. The method of claim 42, further comprising:

receiving an interference indicator from the cell, and wherein the null pilot is transmitted by the UE honoring the interference indicator to allow the cell to estimate uncontrolled interference from UEs not honoring the interference indicator.

44. The method of claim 42, further comprising:

receiving an interference indicator from the cell, and wherein the null pilot is transmitted by the UE not honoring the interference indicator to allow the cell to estimate controlled interference from UEs honoring the interference indicator.

45. The method of claim 42, wherein the reserved resources are for null pilots for cells of a particular power class, and wherein the null pilot is transmitted by the UE served by the cell of the particular power class to allow the cell to estimate interference due to UEs served by cells of other power classes.

46. A method of estimating interference in a wireless communication network, comprising:

determining resources reserved for null pilots for a cell;

receiving null pilots from first user equipments (UEs) at the cell; and

estimating interference observed by the cell from second UEs based on the null pilots from the first UEs.

47. The method of claim 46, further comprising:

sending an interference indicator from the cell, and wherein null pilots are transmitted by the first UEs honoring the interference indicator to allow the cell to estimate uncontrolled interference from the second UEs not honoring the interference indicator.

48. The method of claim 46, further comprising:

sending an interference indicator from the cell, and wherein null pilots are transmitted by the first UEs not honoring the interference indicator to allow the cell to estimate controlled interference from the second UEs honoring the interference indicator.

49. The method of claim 46, wherein the reserved resources are for null pilots for cells of a particular power class, and wherein the null pilots are transmitted by the first UEs served by the cell of the particular power class to allow the cell to estimate interference due to the second UEs served by cells of other power classes.