METHOD AND APPARATUS FOR MITIGATING PILOT POLLUTION IN A WIRELESS NETWORK

• US 20100020771A1
• Filed: 01/26/2009
• Published: 01/28/2010
• Est. Priority Date: 01/30/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Agrawal, Avneesh, Ji, Tingfang, Gorokhov, Alexei Y.
• Granted Patent: US 8,897,269 B2
• Time in Patent Office: Days
• US Class Current: 370/336
• CPC Class Codes: H04L 1/0004 applied to control information
• CPC Class Codes: H04L 1/001 applied to control information
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/005 of common pilots, i.e. pilots destined for multiple users or terminals
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04L 5/0057 Physical resource allocation for CQI
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04L 5/0062 Avoidance of ingress interference, e.g. ham radio channels
• CPC Class Codes: H04W 52/241 taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
• CPC Class Codes: H04W 52/243 taking into account interferences
• CPC Class Codes: H04W 52/325 Power control of control or pilot channels
• CPC Class Codes: H04W 52/343 taking into account loading or congestion level
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Techniques for mitigating pilot pollution in a wireless network are described. In an aspect, pilot pollution may be mitigated by reducing density and/or transmit power of common pilots whenever possible. A cell may send a common pilot at a first density and a first transmit power level during a first time period and may send the common pilot at a second density and a second transmit power level during a second time period. The second density may be lower than the first density and/or the second transmit power level may be lower than the first transmit power level. Lower density may be achieved by sending the common pilot less frequently, on fewer subcarriers, and/or from fewer antennas. The cell may determine whether to reduce the density and/or transmit power of the common pilot based on network loading, SINRs of terminals, etc. In another aspect, pilot pollution may be mitigated by performing pilot cancellation at a terminal.

Claims

1. A method for wireless communication, comprising:

sending a common pilot at a first density and a first transmit power level during a first time period; and

sending the common pilot at a second density and a second transmit power level during a second time period, the second density being lower than the first density, or the second transmit power level being lower than the first transmit power level, or both.

2. The method of claim 1, further comprising:

determining whether to reduce the density or the transmit power of the common pilot based on at least one of network loading, offered loading at a cell, measured pilot pollution by terminals, signal-to-noise-and-interference ratios (SINRs) of terminals, and pilot requirements of terminals.

3. The method of claim 1, further comprising:

determining the first and second time periods based on network loading, the network loading being light during the second time period and not light during the first time period.

4. The method of claim 1, further comprising:

determining the first and second time periods based on signal-to-noise-and-interference ratios (SINRs) of terminals, the SINRs being high during the second time period and not high during the first time period.

5. The method of claim 1, wherein the common pilot is sent at a lower density and at same transmit power level during the second time period as compared to the first time period.

6. The method of claim 1, wherein the common pilot is sent at same density and at a lower transmit power level during the second time period as compared to the first time period.

7. The method of claim 1, wherein the second density is lower than the first density, and wherein the common pilot is sent less frequently, or on fewer subcarriers, or from fewer antennas, or a combination thereof during the second time period as compared to the first time period.

8. The method of claim 1, wherein the common pilot comprises a configurable portion and a non-configurable portion, the non-configurable portion being sent during the first and second time periods, and the configurable portion being sent during the first time period and not sent during the second time period.

9. The method of claim 8, wherein the non-configurable portion is sent from at least one antenna, and wherein the configurable portion is selectively sent from one or more additional antennas.

10. The method of claim 1, further comprising:

sending a second common pilot at a constant transmit power level and lower density than the common pilot.

11. The method of claim 1, further comprising:

selecting a first modulation and coding scheme (MCS) for a terminal during the first time period; and

selecting a second MCS for the terminal during the second time period, wherein the common pilot is used for channel estimation by the terminal, and wherein the second MCS is lower than the first MCS to account for degradation in channel estimation during the second time period.

12. The method of claim 1, wherein the first time period is for control information and the second time period is for data, the method further comprising:

sending control information during the first time period; and

sending data during the second time period.

13. The method of claim 1, further comprising:

sending data near the common pilot during the second time period to improve decoding performance for the data.

14. The method of claim 1, further comprising:

sending information indicative of a format of the common pilot.

15. The method of claim 1, wherein adjacent cells send common pilots in different intervals during the second time period with time division multiplexing (TDM) or on different sets of subcarriers during the second time period with frequency division multiplexing (FDM).

16. The method of claim 1, wherein the common pilot comprises a cell-specific reference signal sent by a cell on the downlink and used for channel estimation by terminals.

17. The method of claim 1, wherein the common pilot comprises a synchronization signal sent by a cell on the downlink and used for cell acquisition by terminals.

18. An apparatus for wireless communication, comprising:

at least one processor configured to send a common pilot at a first density and a first transmit power level during a first time period, and to send the common pilot at a second density and a second transmit power level during a second time period, the second density being lower than the first density, or the second transmit power level being lower than the first transmit power level, or both.

19. The apparatus of claim 18, wherein the at least one processor is configured to determine whether to reduce the density or the transmit power of the common pilot based on at least one network loading, offered loading at a cell, measured pilot pollution by terminals, signal-to-noise-and-interference ratios (SINRs) of terminals, and pilot requirements of terminals.

20. The apparatus of claim 18, wherein the at least one processor is configured to send a second common pilot at a constant transmit power level and lower density than the common pilot.

21. The apparatus of claim 18, wherein the at least one processor is configured to select a first modulation and coding scheme (MCS) for a terminal during the first time period, and to select a second MCS for the terminal during the second time period, wherein the common pilot is used for channel estimation by the terminal, and wherein the second MCS is lower than the first MCS to account for degradation in channel estimation during the second time period.

22. An apparatus for wireless communication, comprising:

means for sending a common pilot at a first density and a first transmit power level during a first time period; and

means for sending the common pilot at a second density and a second transmit power level during a second time period, the second density being lower than the first density, or the second transmit power level being lower than the first transmit power level, or both.

23. The apparatus of claim 22, further comprising:

means for determining whether to reduce the density or the transmit power of the common pilot based on at least one of network loading, offered loading at a cell, measured pilot pollution by terminals, signal-to-noise-and-interference ratios (SINRs) of terminals, and pilot requirements of terminals.

24. The apparatus of claim 22, further comprising:

means for sending a second common pilot at a constant transmit power level and lower density than the common pilot.

25. The apparatus of claim 22, further comprising:

means for selecting a first modulation and coding scheme (MCS) for a terminal during the first time period; and

means for selecting a second MCS for the terminal during the second time period, wherein the common pilot is used for channel estimation by the terminal, and wherein the second MCS is lower than the first MCS to account for degradation in channel estimation during the second time period.

26. A computer program product, comprising:

a computer-readable medium comprising;

code for causing at least one computer to send a common pilot at a first density and a first transmit power level during a first time period, and

code for causing the at least one computer to send the common pilot at a second density and a second transmit power level during a second time period, the second density being lower than the first density, or the second transmit power level being lower than the first transmit power level, or both.

27. A method for wireless communication, comprising:

receiving a common pilot sent by a cell at a first density and a first transmit power level during a first time period; and

receiving the common pilot sent by the cell at a second density and a second transmit power level during a second time period, the second density being lower than the first density, or the second transmit power level being lower than the first transmit power level, or both.

28. The method of claim 27, further comprising:

receiving a second common pilot sent by the cell at a constant transmit power level and lower density than the common pilot; and

using at least one of the common pilot and the second common pilot to select a serving cell.

29. The method of claim 27, further comprising:

performing channel estimation based on the common pilot;

receiving data sent by the cell in accordance with a first modulation and coding scheme (MCS) during the first time period; and

receiving data sent by the cell in accordance with a second MCS during the second time period, the second MCS being lower than the first MCS to account for degradation in channel estimation during the second time period.

30. An apparatus for wireless communication, comprising:

at least one processor configured to receive a common pilot sent by a cell at a first density and a first transmit power level during a first time period, and to receive the common pilot sent by the cell at a second density and a second transmit power level during a second time period, the second density being lower than the first density, or the second transmit power level being lower than the first transmit power level, or both.

31. The apparatus of claim 30, wherein the at least one processor is configured to receive a second common pilot sent by the cell at a constant transmit power level and lower density than the common pilot, and to use at least one of the common pilot and the second common pilot to select a serving cell.

32. The apparatus of claim 30, wherein the at least one processor is configured to perform channel estimation based on the common pilot, to receive data sent by the cell in accordance with a first modulation and coding scheme (MCS) during the first time period, and to receive data sent by the cell in accordance with a second MCS during the second time period, the second MCS being lower than the first MCS to account for degradation in channel estimation during the second time period.

33. A method for wireless communication, comprising:

determining whether to perform pilot cancellation for a neighbor cell; and

if a determination is made to perform pilot cancellation,

canceling a common pilot from the neighbor cell at a terminal,

determining received signal quality of a serving cell at the terminal after canceling the common pilot,

determining channel quality indicator (CQI) information based on the received signal quality, and

sending the CQI information to the serving cell.

34. The method of claim 33, wherein the determining whether to perform pilot cancellation comprises deciding to perform pilot cancellation if the neighbor cell is one of M strongest neighbor cells or if received signal strength for the neighbor cell exceeds a threshold, where M is one or greater.

35. The method of claim 33, wherein the determining whether to perform pilot cancellation comprises determining whether to perform pilot cancellation based on network loading, or a required signal-to-noise-and-interference ratio (SINR) of the terminal, or both.

36. The method of claim 33, wherein the determining whether to perform pilot cancellation comprises determining whether to perform pilot cancellation based on information received from a serving cell, the information identifying at least one neighbor cell to perform pilot cancellation, or at least one common pilot to perform pilot cancellation, or both.

37. The method of claim 33, wherein the canceling the common pilot comprises

obtaining a channel estimate for the neighbor cell based on a received signal at the terminal,

estimating interference due to the common pilot from the neighbor cell based on a locally generated common pilot for the neighbor cell and the channel estimate, and

subtracting the estimated interference from the received signal to obtain an interference-canceled signal.

38. An apparatus for wireless communication, comprising:

at least one processor configured to determine whether to perform pilot cancellation for a neighbor cell and, if a determination is made to perform pilot cancellation, to cancel a common pilot from the neighbor cell at a terminal, to determine received signal quality of a serving cell at the terminal after canceling the common pilot, to determine channel quality indicator (CQI) information based on the received signal quality, and to send the CQI information to the serving cell.

39. The apparatus of claim 38, wherein the at least one processor is configured to decide to perform pilot cancellation if the neighbor cell is one of M strongest neighbor cells or if received signal strength for the neighbor cell exceeds a threshold, where M is one or greater.

40. The apparatus of claim 38, wherein the at least one processor is configured to obtain a channel estimate for the neighbor cell based on a received signal at the terminal, to estimate interference due to the common pilot from the neighbor cell based on a locally generated common pilot for the neighbor cell and the channel estimate, and to subtract the estimated interference from the received signal to obtain an interference-canceled signal.