Methods and apparatus for partial interference reduction within wireless networks

• US 20100080323A1
• Filed: 09/30/2008
• Published: 04/01/2010
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Schmidt, Andreas, Bienas, Maik, Mueck, Markus
• Granted Patent: US 8,295,395 B2
• Time in Patent Office: Days
• US Class Current: 375/296
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04B 2215/062 by inhibiting burst transmission
• CPC Class Codes: H04J 11/0033 by pre-cancellation of known interference, e.g. using a matched filter, dirty paper coder or Thomlinson-Harashima precoder correlative coding in synchronous or start-stop systems H04L25/497
• CPC Class Codes: H04L 25/4975 Correlative coding using Tomlinson precoding, Harashima precoding, Trellis precoding or GPRS
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0016 Time-frequency-code
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 72/1263 Mapping of traffic onto schedule, e.g. scheduled allocation or multiplexing of flows
• CPC Class Codes: H04W 72/54 based on quality criteria
• CPC Class Codes: H04W 72/541 using the level of interference

Abstract

Methods and apparatus that enable one or more wireless networks to minimize inter-cellular interference (ICI) at a receiver. In one embodiment, the network comprises an OFDM-based cellular network, and the method comprises utilizing a priori knowledge of non-data portions of signals from multiple base stations in order to schedule transmissions. In one variant, these non-data portions comprise pilot tones; the pilot tones can be scheduled onto various time-frequency resources of the network so as to minimize ICI. The mobility context of the receiver can also be used as a basis for dynamically adjusting the pilot tone density. In another variant, precoding (e.g., Tomlinson-Harashima preceding) can be applied to “shape” the non-data portions of the transmitted signals so as to mitigate ICI. In yet other variants, frame preambles and learning sequences are used as the basis for invoking selective transmission time shifts across the potentially interfering base stations so as to minimize ICI.

Claims

1. A method of operating a wireless transmitter, said method comprising applying partial interference reduction in said transmitter, said partial interference reduction being based at least in part on a priori information received from at least one other transmitter, said information relating to signals to be transmitted at a future time.

2. The method of claim 1, wherein said at least one other transmitter comprises a plurality of cellular base stations geographically proximate to said transmitter.

3. The method of claim 1, wherein said signals comprise non-data signals selected from the group consisting of:

(i) pilot tones;

(ii) learning sequences; and

(iii) frame or packet preambles or mid-ambles.

4. The method of claim 1, wherein said wireless transmitter comprises a base station within a wireless network employing an orthogonal frequency division multiple access (OFDMA) access scheme.

5. The method of claim 4, wherein said wireless network comprises a UMTS-based long term evolution (LTE) network, and said information received at said wireless transmitter comprises information received over an X2 communications link.

6. The method of claim 4, wherein said wireless network comprises a WiMAX IEEE-Std. 802.16m-compliant network, and said information received at said wireless transmitter comprises information received over a broadband communications link.

7. The method of claim 4, wherein said wireless network comprises a network compliant with an IEEE 802.11 standard.

8. The method of claim 1, wherein said signals comprise pilot tones, and said method further comprises:

determining a context of a mobile receiver to which said signals will be transmitted; and

based at least in part on said determining, selecting a pilot tone density.

9. The method of claim 8, wherein said determining a context comprises determining if said mobile receiver has a mobility greater than or less than a threshold value.

10. The method of claim 1, wherein said wireless transmitter and said at least one other transmitter comprise neighboring macrocell base stations within a cellular network.

11. The method of claim 1, wherein said a priori information received from at least one other transmitter comprises scheduling information relating to at least one future transmission schedule for pilot tones.

12. A method of mitigating inter-cell interference within a multi-cell wireless network, the method comprising:

selectively distributing individual ones of a plurality of pilot tones over individual ones of a plurality of time-frequency resources of said network; and

aligning at least one data frame sent by one cell of said network with respect to a data frame sent by another cell of said network;

wherein said acts of distributing and aligning cooperate to substantially mitigate said interference occurring at a receiver of said network.

13. The method of claim 12, wherein said one cell and said another cell of said network comprise neighboring fixed base stations within a UMTS-based cellular network.

14. The method of claim 12, wherein said aligning comprises at least partly overlapping at least one of a learning sequence and a frame preamble of said data frame sent by said one cell with a data portion of said data frame sent by said another cell.

15. The method of claim 14, wherein said at least partly overlapping comprises maximizing an overlap of both said learning sequence and said preamble with said data portion.

16. The method of claim 14, wherein said at least partly overlapping comprises aligning at least one frame portion boundaries of said data frame sent by said one cell with frame portion boundary of said data frame sent by said another cell.

17. The method of claim 12, wherein said method further comprises transferring information relating to said pilot tones between at least to cells of said multi-cell network, said transferred information facilitating said act of selectively distributing said pilot tones.

18. The method of claim 17, further comprising applying a precoding process to signals sent from at least one of said cells, said precoding based at least in part on said transferred information relating to said pilot tones.

19. The method of claim 18, wherein said precoding comprises Tomlinson-Harashima precoding (THP).

20. Base station apparatus, comprising:

a digital processor;

a wireless interface in data communication with said processor;

a network interface in data communication with said processor; and

a storage device in data communication with said processor, said storage device comprising instructions that, when executed by said digital processor;

receive information of a first future non-data signal from said network interface; and

modify operation of said wireless interface;

wherein said modification of said operation reduces interference caused by said first non-data signal at a receiving device.

21. The method of claim 20, wherein said modification of said operation comprises a precoding of the first future non-data signal according to a Tomlinson-Harashima Precoding (THP) technique.

22. The method of claim 20, wherein said modification of said operation comprises a change to the transmit scheduling of the wireless interface.

23. The method of claim 22, wherein said transmit scheduling comprises increments of time according to a regular time interval.

24. The method of claim 23, wherein said regular time interval comprises a transmission time interval for an OFDM symbol.

25. The method of claim 22, wherein said transmit scheduling comprises transmission times in one or more irregular increments.

26. The method of claim 25, wherein said one or more irregular increments shift the transmission to a time offset from one or more other base station data signals.

27. The method of claim 20, wherein said storage device further comprises instructions that when executed by said digital processor transmit information relating to a second non-data signal via said network interface, said information being adapted to modify the operation of one or more neighboring base stations to improve interference reduction caused by said second non-data signal at said receiving device.

28. A method of operating a wireless transmitter, said transmitter being part of a network having a plurality of transmitters, said method comprising preceding only non-data portions of signals sent by at least said transmitter, said precoding being based at least in part on data received from other ones of said transmitters regarding their future transmissions of corresponding non-data portions of their signals.

29. The method of claim 28, wherein said precoding comprises Tomlinson-Harashima precoding (THP).

30. The method of claim 28, wherein said precoding comprises signal processing adapted to selectively alter at least one of the amplitude and phase of at least portions of a waveform sent by said transmitter corresponding to said non-data portions.

31. Receiver apparatus, comprising:

a digital processor;

a wireless interface in data communication with said digital processor; and

a storage device in data communication with said processor, said storage device comprising at least one computer program which, when run on said processor;

receives data relating to an at least partly corrupted symbol received over said wireless interface;

suppresses at least one first signal from an interfering source, said at least one first signal having been processed for partial interference reduction;

suppresses at least one second signal from an interfering source, said at least one second signal not having been processed for partial interference reduction; and

decodes said received symbol to extract useful data.

32. The apparatus of claim 31, wherein said processing for partial interference reduction comprises processing only with respect to non-data portions of said at least one first signal.

33. The apparatus of claim 32, wherein said processing comprises Tomlinson-Harashima preceding.

34. The apparatus of claim 31, wherein said suppressing comprises:

estimating at least one interfering signal on carriers for which said partial interference reduction processing was performed;

decoding said estimated signal;

re-encoding said estimate signal; and

subtracting said re-encoded signal from the received symbol.