Method and system for interference reduction

• US 20070010203A1
• Filed: 05/18/2006
• Published: 01/11/2007
• Est. Priority Date: 05/23/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Navini Networks, Inc. (Cisco Systems, Inc.)
• Inventors: Yang, Weidong, Wee, Daniel, Li, Hang, Xu, Guanghan
• Granted Patent: US 7,885,604 B2
• Time in Patent Office: Days
• US Class Current: 455/63.100
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04J 11/005 of intercell interference
• CPC Class Codes: H04J 13/16 Code allocation
• CPC Class Codes: H04W 16/10 Dynamic resource partitioning
• CPC Class Codes: H04W 16/18 Network planning tools
• CPC Class Codes: H04W 28/18 Negotiating wireless communication parameters
• CPC Class Codes: H04W 72/00 Local resource management
• CPC Class Codes: H04W 72/54 based on quality criteria
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: H04W 88/12 Access point controller devices

Abstract

A method and system for interference reduction for telecommunication systems are disclosed. The system comprises a base station control device (BCD) for configuring one or more parameters for operating one or more base stations (BSs), a first BS covering a first cell having one or more mobile terminals therein, a second BS covering a second cell neighboring to the first cell and sharing a predetermined frequency band with the first cell, wherein one or more radio frames constructed for communications between the first BS and any mobile terminal of the first cell and one or more radio frames constructed for communications between the second BS and any mobile terminal of the second cell are distinguishable by defining different channel configuration sets having one or more operation parameters, wherein the parameters includes a training sequence, a spreading code, and a channel observation window position.

Claims

1. A telecommunication system comprising:

a base station control device (BCD) for configuring one or more parameters for operating one or more base stations (BSs);

a first BS covering a first cell having one or more mobile terminals therein;

a second BS covering a second cell neighboring to the first cell and sharing a predetermined frequency band with the first cell,

wherein one or more radio frames constructed for communications between the first BS and any mobile terminal of the first cell and one or more radio frames constructed for communications between the second BS and any mobile terminal of the second cell are distinguishable by defining different channel configuration sets having one or more operation parameters, wherein the parameters includes a training sequence, a spreading code, and a channel observation window position.

2. The system of claim 1 wherein the BCD stores one or more channel configuration sets for each base station.

3. The system of claim 1 wherein the BS, upon receiving commands from the BCD, configures transmit and receive radio frames according to at least one channel configuration set.

4. The system of claim 1 wherein each mobile terminal synchronizes with the first or second BS when entering its coverage and determines the BS specific channel configuration set.

5. The system of claim 4 wherein the mobile terminal uses one or more spreading codes from a total number of spreading codes provided by the BCD for the first or second BS.

6. The system of claim 1 wherein the spreading code is a pseudo-random sequence that is used to spread at least traffic messages, control messages, random access messages, and probing messages.

7. The system of claim 1 wherein the channel observation window is a time-frequency slot in which either no signal is sent from intra-cell communications or a known signal is transmitted from intra-cell communications.

8. The system of claim 1 wherein the basic training sequence is a pseudo-random complex value sequence, of which periodic auto-correlation has a cyclic shift orthogonal property.

9. The system of claim 1 wherein the mobile terminal determines a channel observation window position by detecting power levels thereof after decoding one or more downlink access symbols and comparing a total power level of each possible window position with an average power level of rest positions.

10. The system of claim 9 wherein the channel observation window position is determined by performing channel observation window search using one or more candidate downlink preambles.

11. The system of claim 1 wherein the BS further comprises a first pseudo-random sequence generator that generates a first set of spreading codes, and a second pseudo-random sequence generator which generates a second set of sequences, wherein both generators use the channel observation window position as a seed.

12. The system of claim 11, wherein an inverse discrete Fourier transform of the second set of sequences provides a set of basic training sequences.

13. The system of claim 11 wherein the first and second pseudo-random sequence generators use the same structure and primitive polynomial.

14. The system of claim 1 wherein the radio frames for the second cell is offset from the radio frames for the first cell.

15. The system of claim 1 wherein the channel configuration set further comprises a base station specific probing channel.

16. The system of claim 16 wherein the probing channel comprises probing training sequence and probing information symbols.

17. A method for interference reducing in a wireless communications system, the method comprising:

estimating a vector channel impulse response for at least one mobile terminal using a training sequence assigned thereto;

estimating a spatial signature derived based on the training sequence for the mobile terminal;

estimating an interference covariance matrix using data from a channel observation window;

generating one or more uplink nulling weights for the mobile terminal using the estimated spatial signature and the interference covariance matrix;

performing a nulling operation based on the vector channel impulse response derived from uplink signals with the uplink nulling weights to derive a scalar channel impulse response;

detecting one or more uplink symbols using the scalar channel impulse response;

generating one or more downlink nulling weights from the uplink nulling weights; and

beamforming downlink transmissions with the downlink nulling weights.

18. The method of claim 17 further comprising performing at the mobile terminal a downlink symbol detection using the scalar channel.

19. The method of claim 17 wherein estimating the spatial signature further includes computing the spatial signature using the vector channel impulse response.

20. The method of claim 17 wherein estimating for the spatial signature further comprises computing the spatial signature using a training sequence in a probing channel sent by the mobile terminal.

21. The method of claim 20 wherein communications through the probing channel is scheduled in a predetermined manner by using predetermined hash operations based on at least one broadcasted frame number and at least one terminal specific equipment identification number to reduce a frequency reuse, and therefore, an inter-cell interference.

22. The method of claim 20 wherein communications through the probing channel are scheduled by adding random delays to transmission timing thereof to reduce intracell interference.

23. The method of claim 17 wherein the detected symbols are symbols either in a traffic or control portion of a frame, or in an information portion of the probing channel.

24. The method of claim 17 further comprising:

computing a residual interference intensity after the nulling operation using the uplink nulling weights; and

determining whether to issue a carrier switch command to the mobile terminal based on the residual interference intensity.

25. The method of claim 24 further comprising:

determining at the mobile terminal a residual interference intensity; and

determining whether to send a carrier switch request to the base station based on the residual interference intensity.

26. The method of claim 25 wherein the mobile terminal sends the carrier switch request using an uplink control channel.

27. The method of claim 25 wherein the mobile terminal sends the carrier switch request using a probing channel.

28. An interference reduction method for a telecommunication system, the system having a base station control device (BCD) for configuring one or more parameters for operating one or more base stations (BSs), a first BS covering a first cell having one or more mobile terminals therein, a second BS covering a second cell neighboring to the first cell and sharing a predetermined frequency band with the first cell, the method comprising:

defining a first channel configuration set of operation parameters for constructing one or more radio frames used for communications between the first BS and any mobile terminal of the first cell; and

defining a second channel configuration set of operation parameters for constructing one or more radio frames used for communications between the second BS and any mobile terminal of the second cell,

wherein the first and second sets each includes a training sequence, a spreading code, and a channel observation window position, and the first and second sets are distinguishable having differences in at least one operation parameter.

29. The method of claim 28 wherein the spreading code is a pseudo-random sequence that is used to spread at least traffic messages, control messages, random access messages, and probing messages.

30. The method of claim 28 wherein the channel observation window is a time-frequency slot in which either no signal is sent from intra-cell communications or a known signal is transmitted from intra-cell communications.

31. The method of claim 28 wherein the basic training sequence is a pseudo-random complex value sequence, of which periodic auto-correlation has a cyclic shift orthogonal property.

32. The method of claim 28 further comprising synchronizing each mobile terminal with the first or second BS when entering respective cells and determines the BS specific channel configuration set for communication therewith.

33. The method of claim 32 wherein the synchronizing further includes determining a channel observation window position by detecting the position based on a power level based on one or more demodulated downlink access symbols.

34. The method of claim 33 wherein the determining a channel observation window position further includes performing channel observation window search using one or more candidate downlink preambles.

35. The method of claim 28 further comprising generating a first set of spreading codes, and generating a second set of sequences, both using the channel observation window position as a seed.

36. The method of claim 35 further comprising generating a set of basic training sequences by an inverse discrete Fourier transform of the second set of sequences.

37. The method of claim 28 wherein the frames for the second cell is offset from the frames for the first cell.

38. The method of claim 28 wherein the channel configuration set further comprises an operation parameter for a base station specific probing channel.

39. The method of claim 38 wherein the probing channel comprises probing training sequence and probing information symbols.