Adaptation of transmit subchannel gains in a system with interference cancellation

• US 20060142041A1
• Filed: 07/29/2005
• Published: 06/29/2006
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tomasin, Stefano, Smee, John Edward, Hou, Jilei, Pfister, Henry David
• Granted Patent: US 8,099,123 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04W 52/146 Uplink power control

Abstract

A method and system for interference cancellation (IC). One aspect relates to traffic interference cancellation. Another aspect relates to joint IC for pilot, overhead and data. Another aspect relates to improved channel estimation. Another aspect relates to adaptation of transmit subchannel gains.

Claims

1. A method comprising:

receiving samples of signals transmitted from a plurality of access terminals, the samples comprising pilot channel data, overhead channel data and traffic channel data;

reconstructing at least one of the pilot channel data, overhead channel data and traffic channel data;

canceling at least a portion of the reconstructed at least one of the pilot channel data, overhead channel data and traffic channel data in the samples;

processing the samples to obtain traffic data sent by a first access terminal;

measuring at least one of a traffic packet error rate (PER), a pilot signal-to-interference-and-noise ratio (SINR) and a total power of the signals; and

controlling at least one of a power and a gain of at least one of the pilot, overhead and traffic channels according to the measured at least one traffic packet error rate, pilot SINR, and total power.

2. The method of claim 1, wherein the signals comprise Code Division Multiple Access (CDMA) signals.

3. The method of claim 1, further comprising:

storing the received samples in a buffer; and

canceling at least one of the reconstructed pilot channel data, overhead channel data and traffic channel data from the stored, received samples.

4. The method of claim 1, wherein the overhead channel comprises at least one of a Reverse Rate Indicator (RRI) channel, an auxiliary pilot channel, a Data Request Control (DRC) channel, a Data Source Control (DSC) channel and an Acknowledge (ACK) channel.

5. The method of claim 1, wherein the overhead channel comprises at least one of a dedicated physical control channel (DPCCH), an enhanced dedicated physical control channel (E-DPCCH), and a high-speed dedicated physical control channel (HS-DPCCH).

6. The method of claim 1, wherein the overhead channel comprises an auxiliary pilot channel, the method further comprising reconstructing the auxiliary pilot channel based on a channel estimate.

7. The method of claim 1, wherein canceling reconstructed pilot channel data comprises:

determining channel estimates for the plurality of access terminals;

using the channel estimates to reconstruct pilot channel data; and

canceling the reconstructed pilot channel data in the samples from all access terminals.

8. The method of claim 1, wherein canceling reconstructed overhead channel data comprises:

determining channel estimates for the plurality of access terminals;

using the channel estimates to reconstruct overhead channel data; and

canceling the reconstructed overhead channel data in the samples from all access terminals.

9. The method of claim 1, wherein canceling reconstructed data channel data comprises:

determining channel estimates for the plurality of access terminals;

using the channel estimates to reconstruct data channel data; and

canceling the reconstructed data channel data in the samples from all access terminals.

10. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

increasing overhead channel gain when traffic channel data is canceled.

11. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

reducing a traffic-to-pilot (T2P) ratio of at least one access terminal.

12. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

controlling a rise-over-thermal (ROT) value with respect to a threshold value.

13. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

using a closed loop pilot channel power control mechanism with an inner loop and an outer loop.

14. The method of claim 13, wherein the outer loop compares the measured traffic packet error rate with a target traffic packet error rate.

15. The method of claim 13, wherein the outer loop compares a measured erasure rate of an overhead channel with a target erasure rate of the overhead channel.

16. The method of claim 15, wherein the overhead channel is a data rate control (DRC) channel.

17. The method of claim 15, wherein the overhead channel comprises an enhanced dedicated physical control channel (E-DPCCH).

18. The method of claim 15, wherein the overhead channel comprises a dedicated physical control channel (DPCCH).

19. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

measuring signal power after canceling at least one of the pilot, overhead and traffic data channels; and

using a closed loop gain control to adapt a change in a traffic-to-pilot (T2P) ratio based on measured signal power after cancellation.

20. The method of claim 19, further comprising sending a message with the adapted change in a traffic-to-pilot (T2P) ratio to at least one access terminal periodically.

21. The method of claim 19, wherein the change in the T2P ratio is adapted through an acknowledgement (ACK) forward channel.

22. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

measuring an effective rise-over-thermal (ROT) value with an averaging window whose length is at least twice as long as a power control update period.

23. The method of claim 1, wherein controlling at least one of the power and the gain comprises:

an open loop gain control of a traffic-to-pilot (T2P) ratio and a closed loop pilot power control.

24. The method of claim 23, wherein the closed loop power control comprises an inner loop that adjusts the pilot power according to a threshold value.

25. The method of claim 24, further comprising:

increasing the threshold value when a data rate control (DRC) erasure rate exceeds a second threshold; and

decreasing the threshold value when the DRC erasure rate is below the second threshold.

26. The method of claim 1, further comprising:

increasing a change in a traffic-to-pilot (T2P) ratio when the measured traffic packet error rate exceeds a threshold; and

decreasing the change in a traffic-to-pilot (T2P) ratio when the measured traffic packet error rate is lower than the threshold.

27. The method of claim 1, further comprising:

adapting overhead channel gains according to the measured at least one traffic packet error rate, pilot signal-to-interference-and-noise ratio (SINR), and total power of the signals.

28. The method of claim 27, wherein adapting overhead channel gains comprises comparing a measured rise-over-thermal value with a target rise-over-thermal value.

29. The method of claim 27, wherein adapting overhead channel gains comprises comparing a measured data rate control (DRC) erasure rate with a target data rate control (DRC) erasure rate.

30. The method of claim 1, further comprising:

transmitting a plurality of commands from a plurality of sectors to an access terminal, each request requesting the access terminal to reduce a traffic-to-pilot (T2P) ratio;

identifying a request among a plurality of requests from fully loaded sectors with a lowest reduction in traffic-to-pilot (T2P) ratio.

31. The method of claim 30, further comprising identifying fully loaded sectors.

32. The method of claim 1, further comprising:

transmitting a plurality of requests from a plurality of sectors to an access terminal, each request requesting the access terminal to reduce a traffic-to-pilot (T2P) ratio;

identifying a request among a plurality of requests from a serving sector associated with the access terminal.

33. The method of claim 1, wherein controlling at least one of a power and a gain comprises:

controlling gain of the overhead and traffic channels.

34. A base station comprising:

a memory configured to store data samples of signals received from a plurality of access terminals, the samples comprising pilot channel data, overhead channel data and traffic channel data;

a demodulator configured to demodulate overhead channel data and traffic channel data for one or more access terminals;

a decoder configured to decode demodulated overhead channel data and traffic channel data and determine which overhead channel data and traffic channel data decoded correctly;

a reconstruction unit configured to reconstruct overhead channel data and traffic channel data for the correctly decoded overhead channel data and traffic channel data, the reconstruction unit being further configured to reconstruct pilot channel data using the channel estimates;

a subtractor configured to subtract reconstructed pilot channel data, reconstructed overhead channel data, and reconstructed traffic channel data from the samples stored in the memory;

a power control unit configured to control a pilot channel power of at least one access terminal after the reconstructed pilot channel data, reconstructed overhead channel data, and reconstructed traffic channel data are subtracted from the samples stored in the memory; and

a gain control unit configured to control a change in a traffic-to-pilot (T2P) ratio based on the measured interference canceled.