Method and system for interference reduction

• US 7,885,604 B2
• Filed: 05/18/2006
• Issued: 02/08/2011
• Est. Priority Date: 05/23/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Yang, Weidong, Wee, Daniel, Li, Hang, Xu, Guanghan
• Primary Examiner(s): Nguyen; Duc
• Assistant Examiner(s): AYOTUNDE, AYODEJI O
• Application Number:
  US11/437,998
• Publication Number:
  US 20070010203A1
• Time in Patent Office: 1,727 Days
• Field of Search: None
• US Class Current: 455/63.1
• 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 system comprising:

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

a first BS configured to cover a first cell having one or more mobile terminals therein, wherein the first BS is configured to communicate with the BCD;

a second BS configured to cover a second cell neighboring the first cell having one or more mobile terminals therein and sharing a predetermined frequency band with the first cell, wherein the second BS is configured to communicate with the BCD;

wherein the BCD generates and transmits to the first BS and second BS parameters that the first BS and second BS use to construct downlink radio frames for communications with any mobile terminal in their respective first and second cells, wherein the BCD generates the parameters for the first BS and second BS such that downlink radio frames used for communication in the first and second cells are distinguishable from each other according to different channel configuration sets, each channel configuration set comprising one or more training sequences having a pseudo random complex value sequence, spreading codes used to spread traffic messages and control messages, and channel observation window positions in downlink radio frames communicated in the first and second cells, respectively;

wherein the BCD generates the channel configuration sets such that the downlink radio frames that the second BS transmits in the second cell are offset in time from the downlink radio frames that the first BS transmits in the first cell with respect to global position signal information in order to isolate the downlink radio frames that the second BS transmits in the second cell from the downlink radio frames that the first BS transmits in the first cell;

wherein a mobile terminal in the first cell or second cell generates random access packets and traffic data packets in accordance with the spreading code and training sequence depending from which of the first and second BSs a downlink radio frame is received; and

wherein the first BS and the second BS, upon receiving commands from the BCD, which commands comprise the channel configuration set assigned to the first BS and the channel configuration set assigned to the second BS, respectively, configures downlink radio frames accordingly.

2. The system of claim 1, wherein the BCD is configured to generate a first channel configuration set for the first cell, wherein the first channel configuration set defines a first training sequence, a first spreading code and a first channel observation window position, and is configured to generate a second channel configuration set for the second cell, wherein the second channel configuration set defines a second training sequence, a second spreading code and a second channel observation window position, wherein the first channel configuration set and the second channel configuration set enables detection of interference between downlink radio frames transmitted by the first BS and downlink radio frames transmitted by the second BS.

3. The system of claim 1, wherein the first BS and the second BS are configured to transmit downlink radio frames that are configured to allow a mobile terminal to synchronize with the first or second BS when entering the first cell or the second cell, respectively, and to thereby determine the channel configuration set in use for that cell based on reception of the downlink radio frames and for use in communicating with the first BS or second BS, respectively.

4. The system of claim 2, wherein the first BS and the second BS are configured to generate and transmit downlink radio frames in the first and second cells, respectively, each downlink radio frame comprising a preamble slot, a training slot, a channel observation window slot whose position is determined by the channel observation window position defined in the corresponding channel configuration set and one or more traffic or control slots in which traffic or control information is sent, and wherein the BCD is configured to assign the first and second cells with a frequency band that is shared by one or more neighboring cells having predetermined channel configuration sets.

5. The system of claim 2, wherein the BCD is configured to generate the channel configuration set for the first cell and for the second cell so as to define the first channel observation window position in downlink radio frames transmitted by the first BS in the first cell and the second channel observation window position in downlink radio frames transmitted by the second BS in the second cell, wherein each channel observation window position is a time frequency slot in a downlink radio frame in which either no intra-cell communications are sent or in which a known signal is transmitted for intra-cell communications.

6. The system of claim 1, wherein the first BS and the second BS are configured to generate a training sequence from a basic training sequence that is a pseudo-random complex value sequence having a periodic auto-correlation cyclic shift orthogonal property.

7. The system of claim 3, and further comprising one or more mobile terminals each configured to determine a channel observation window position by detecting power levels associated with one or more symbols contained in the one or more traffic or control slots of a received downlink radio frame, computing a ratio of an average power associated with the one or more symbols excluding power of symbols associated with the channel observation window with an average power level of symbols associated with the channel observation window, comparing the ratio with a threshold, and when the ratio satisfies the threshold, determining the channel observation window position based on positions of the one or more symbols in the one or more traffic or control slots.

8. The system of claim 4, wherein the first BS and second BS are configured, based on their respective channel configuration set, to transmit preamble sequences in their respective preamble slots of downlink radio frames using different spreading codes, and further comprising one or more mobile terminals each configured to detect a channel observation window position in a received downlink radio frame by detecting the preamble sequence contained in the received downlink radio frame and determining therefrom positions of the training slot and channel observation window slot in the received downlink radio frame.

9. The system of claim 1, wherein each of the first BS and second BS further comprises a first pseudo-random sequence generator that is configured to generate a first set of spreading codes, and a second pseudo-random sequence generator configured to generate a second set of sequences, wherein the first and second pseudo-random sequence generators use the channel observation window position as a seed.

10. The system of claim 9, wherein each of the first BS and second BS is configured to apply an inverse discrete Fourier transform of the second set of sequences in order to generate a set of basic training sequences.

11. The system of claim 2, wherein each of the first BS and second BS is configured to, based on the first channel configuration set and second channel configuration set, respectively, generate positions for the first and second channel observation windows at a symbol boundary in an associated downlink radio frame and such that the first and second channel observation windows have a length of multiple symbols and symbols in the first and second channel observation windows are at power levels lower than that of symbols in traffic or control slots.

25. The system of claim 1, wherein the radio frames used for communication in the first and second cells contains a traffic channel and a control channel, wherein the control channel operates as a downlink access channel, and wherein the BCD assigns a spreading code to the access channel.

26. The system of claim 25, wherein the BCD verifies the channel configuration sets by performing symbol detection, error correction, and error detection using signals on the access channel.

27. The system of claim 1, wherein the mobile terminal uses a rotational error correction code to identify a channel observation window position.

28. The system of claim 27, wherein the mobile terminal identifies the channel observation window position based on a known spreading code.

31. The method of claim 2, wherein the BCD is further configured to use a channel observation window index to generate seeds for a pseudo random number and to truncate the pseudo random number into segments in order to generate the training sequence for the channel configuration sets for the first BS and second BS.

32. The method of claim 1, wherein the first BS and the second BS reallocate channel observation window based carriers for the mobile terminal when the first BS and the second BS determine that the carriers are interfered by cells of other base stations.

12. A method comprising:

providing a first base station (BS) configured to service one or more mobile terminals in a first cell;

providing a second BS configured to service one or more mobile terminals in a second cell that is adjacent to the first cell, and wherein the first BS and the second BS share a predetermined frequency band for communication with mobile terminals in their respective cells;

at a base station control device, generating a first channel configuration set for the first BS that contains parameters for a first training sequence having a first pseudo random complex value sequence, a first spreading code used to spread traffic messages and control messages in the first cell and a first channel observation window position from which the first BS uses to generate downlink radio frames in the first cell and a second channel configuration set for the second BS that contains parameters for a second training sequence having a second pseudo random complex value sequence, a second spreading code used to spread traffic messages and control messages in the second cell and a second channel observation window position that the second BS uses to generate downlink radio frames in the second cell such that the downlink radio frames transmitted by the first BS in the first cell are distinguishable from the downlink radio frames transmitted by the second BS in the second cell;

communicating the first channel configuration set from the base station control device to the first BS and communicating the second channel configuration set from the base station control device to the second BS;

generating the first channel configuration set and the second channel configuration set such that the downlink radio frames that the second BS transmits in the second cell are offset in time from the downlink radio frames that the first BS transmits in the first cell with respect to global position signal information in order to isolate the downlink radio frames that the second BS transmits in the second cell from the downlink radio frames that the first BS transmits in the first cell;

at the mobile terminals, generating random access packets and traffic data packets in accordance with the first and the second spreading code and the first and the second training sequence depending from which of the first and second BSs a downlink radio frame is received; and

the first BS and second BS, upon receiving the first and second channel configuration sets, respectively, from the base station control device, configuring downlink radio frames according to the first channel configuration set and the second channel configuration set, respectively.

13. The method of claim 12, wherein the first channel observation window position is a time frequency slot in downlink radio frames transmitted by the first BS in which either no intra-cell communications are sent or in which a known signal is transmitted for intra-cell communications and the second channel observation window position is a time frequency slot in downlink radio frames transmitted by the second BS in which no intra-cell communications are sent or in which a known signal is transmitted for intra-cell communications.

14. The method of claim 12, wherein configuring comprises the first BS and second BS generating the first training sequence and second training sequence from a basic training sequence that is a pseudo-random complex value sequence having a periodic auto-correlation cyclic shift orthogonal property.

15. The method of claim 12, and further comprising a mobile terminal synchronizing with the first BS or the second BS when entering the first cell or second cell, respectively, and determining the channel configuration set for communication with the first BS or the second BS, accordingly.

16. The method of claim 15, wherein synchronizing comprises determining a channel observation window position by detecting power levels associated with one or more symbols contained in the one or more traffic or control slots of a received downlink radio frame, computing a ratio of an average power associated with the one or more symbols excluding power of symbols associated with the channel observation window with an average power level of symbols associated with the channel observation window, comparing the ratio with a threshold, and when the ratio satisfies the threshold, determining the channel observation window position based on positions of the one or more symbols in the one or more traffic or control slots.

17. The method of claim 15, and further comprising the first BS and the second BS transmitting preamble sequences in preamble slots of their respective downlink radio frames using the first and second spreading codes, respectively, and further comprising a mobile terminal determining a channel observation window position in a received downlink radio frame by detecting the preamble sequence contained in the received downlink radio frame and determining therefrom positions of the training slot and channel observation window slot in the received downlink radio frame.

18. The method of claim 12, and further comprising the first BS generating a first set of spreading codes and a second set of sequences using the first channel observation window position as a seed and the second BS generating a first set of spreading codes and a second set of sequences using the second channel observation window position as a seed.

19. The method of claim 18, and further comprising the first BS generating a set of basic training sequences by an inverse discrete Fourier transform of the second set of sequences generated from the first channel observation window position and the second BS generating a set of basic training sequences by an inverse discrete Fourier transform of the second set of sequences generated from the second channel observation window position, wherein the first channel configuration set and the second channel configuration set enables detection of interference between downlink radio frames transmitted by the first BS and downlink radio frames transmitted by the second BS.

20. The method of claim 12, and further comprising the first BS transmitting downlink radio frames in the first cell and the second BS transmitting downlink radio frames in the second cell with a timing offset with respect to the downlink radio frames transmitted by the first BS in the first cell.

21. The method of claim 12, wherein configuring comprises the first BS, based on the first channel configuration set, generating the first channel observation window position at a symbol boundary in a downlink radio frame and such that the first channel observation window has a length of multiple symbols and symbols of the first channel observation window are transmitted at power levels lower than that of symbols in traffic or control slots, and the second BS, based on the second channel configuration set, generating the second channel observation window position at a symbol boundary in a downlink radio frame and such that the second channel observation window has a length of multiple symbols and symbols of the second channel observation window are transmitted at power levels lower than that of symbols in traffic or control slots.

29. The method of claim 12, further comprising, at the mobile terminal, using a rotational error correction code to identify a channel observation window position.

30. The method of claim 29, further comprising, at the mobile terminal, identifying a channel observation window position based on a known spreading code.

22. A method comprising:

at a base station control device, generating multiple channel configuration sets each for a corresponding base station assigned to serve multiple terminals in a corresponding cell, wherein base stations associated with adjacent cells operate in the same radio frequency channel, wherein generating comprises generating a channel configuration set comprising a training sequence having a pseudo random complex value sequence, a spreading code used to spread traffic messages and control messages and a channel observation window position for downlink radio frames transmitted by the base station in its corresponding cell such that downlink radio frames transmitted by base stations for adjacent cells are distinguishable from each other;

generating the channel configuration sets such that the downlink radio frames transmitted by different base stations are offset in time with respect to global position signal information in order to isolate the downlink radio frames transmitted by the base stations;

at the terminals, generating random access packets and traffic data packets in accordance with the spreading code and the training sequence depending from which base station a downlink radio frame is received; and

communicating the channel configuration sets from the base station control device to corresponding base stations.

23. The method of claim 22, and further comprising each base station generating a position for the channel observation window in downlink radio frames transmitted in its cell at a symbol boundary in the downlink radio frame and such that the channel observation window has a length of multiple symbols and symbols of the channel observation window are at power levels lower than that of symbols in traffic or control slots in an associated downlink radio frame.

24. The method of claim 23, and further comprising a mobile terminal determining a channel observation window position in a received downlink radio frame by detecting power levels associated with one or more symbols contained in the one or more traffic or control slots of a received downlink radio frame, computing a ratio of an average power associated with the one or more symbols excluding power of symbols associated with the channel observation window with an average power level of symbols associated with the channel observation window, comparing the ratio with a threshold, and when the ratio satisfies the threshold, determining the channel observation window position based on positions of the one or more symbols in the one or more traffic or control slots.