Method and apparatus for mitigating pilot pollution in a wireless network

• US 8,897,269 B2
• Filed: 01/26/2009
• Issued: 11/25/2014
• Est. Priority Date: 01/30/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Ji, Tingfang, Agrawal, Avneesh, Gorokhov, Alexei Y.
• Primary Examiner(s): ADHAMI, MOHAMMAD SAJID
• Application Number:
  US12/359,992
• Publication Number:
  US 20100020771A1
• Time in Patent Office: 2,129 Days
• Field of Search: None
• 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;

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;

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

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; and

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.

2. The method of claim 1, wherein said determining is further based on at least one of offered loading at a cell, measured pilot pollution by terminals, and pilot requirements of terminals.

3. The method of claim 1, further comprising:

determining the first and second time periods further 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, 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.

5. 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.

6. 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.

7. 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.

8. The method of claim 7, 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.

9. 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.

10. 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.

11. 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.

12. The method of claim 1, further comprising:

sending information indicative of a format of the common pilot.

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

14. 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.

15. 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.

16. An apparatus for wireless communication, comprising:

a transmitter 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; and

at least one processor 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;

the at least one processor further configured to determine 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.

17. The apparatus of claim 16, wherein said determining is further based on at least one of offered loading at a cell, measured pilot pollution by terminals, and pilot requirements of terminals.

18. The apparatus of claim 16, 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.

19. 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;

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;

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

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; and

means for 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.

20. The apparatus of claim 19, wherein the determining is further based on at least one of offered loading at a cell, measured pilot pollution by terminals, and pilot requirements of terminals.

21. The apparatus of claim 19, further comprising:

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

22. A computer program product, comprising:

a non-transitory 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;

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;

code for causing the at least one computer 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; and

code for causing the at least one computer to determine 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.