Method and apparatus for reducing co-channel interference in a frame-synchronized wireless communication system

Abstract

The present invention is a method and apparatus for reducing co-channel interference. The present invention includes a powerful means for eliminating co-channel interference from base stations in a wireless communication system. The present co-channel interference reducing method and apparatus utilizes frame synchronization between selected time frames (e.g., odd and even time frames) to reduce co-channel interference. Advantageously, the present invention reduces co-channel interference and, thus, allows robust modulation schemes to operate even at worst case line-of-sight (LoS) interference scenarios of 100%. The present invention can also use an uplink/downlink ratio formula to further improve system capacity (i.e., reduce co-channel interference) in ATDD systems. The present inventive method and apparatus can be used in any type of frame based and frame synchronized communication system.

1. A method of reducing co-channel interference in a frame-based broadband wireless communication system, wherein the communication system comprises a plurality of base stations and a plurality of terminal stations, wherein each terminal station is associated with at least one base station, and wherein each base station has an associated and corresponding cell, wherein each cell includes a plurality of associated and corresponding sectors, and wherein the plurality of base stations use frame-synchronized communication, and wherein the communication system comprises an uplink and a downlink, and wherein the uplink comprises an uplink signal divided into a plurality of time frames, and wherein each time frame has an associated and corresponding frame number, the method comprising the steps of:
 a) determining a set of terminal stations that may potentially interfere with a selected base station;  
 b) determining a geographically diagonal subset of the set of terminal stations, wherein the diagonal subset communicates with a first set of associated and corresponding base stations that are approximately diagonal to the selected base station;  
 c) determining a geographically non-diagonal subset of the set of terminal stations, wherein the non-diagonal subset communicates with a second set of associated and corresponding base stations that are not approximately diagonal to the selected base station;  
 d) allocating a first set of time frames for the first set of base stations;  
 e) allocating a second set of time frames for the second set of base stations;  
 f) transmitting uplink information from terminal stations associated with the first set of base stations during the first set of time frames; and  
 g) transmitting up link information from terminal stations associated with the second set of base stations during the second set of time frames.  
 
     
     
       2. The method of reducing co-channel interference in a frame-based broadband wireless communication system of  claim 1 , wherein the communication system is a half-duplex frequency-division duplexed (FDD) system. 
     
     
       3. The method of reducing co-channel interference in a frame-based broadband wireless communication system of  claim 1 , wherein the communication system is a time-division duplexed (TDD) system. 
     
     
       4. The method of reducing co-channel interference in a frame-based broadband wireless communication system of  claim 1 , wherein the first set of time frames comprises odd-numbered time frames. 
     
     
       5. The method of reducing co-channel interference in a frame-based broadband wireless communication system of  claim 1 , wherein the second set of time frames comprises even-numbered time frames. 
     
     
       6. The method of reducing co-channel interference as set forth in  claim 1 , wherein a net uplink/downlink ratio comprises a 1/N ratio, wherein N is a positive number. 
     
     
       7. The method of reducing co-channel interference as set forth in  claim 6 , wherein the net uplink/downlink ratio is determined from a downlink average spectrum efficiency and an uplink average spectrum efficiency. 
     
     
       8. The method of reducing co-channel interference as set forth in  claim 6 , wherein the net uplink/downlink ratio is determined from an R d  value and an R u  value, and wherein the R d  value comprises a first fractional part of a time frame that is dedicated for the downlink and the R u  value comprises a second fractional part of a time frame that is dedicated for the uplink. 
     
     
       9. The method of reducing co-channel interference as set forth in  claim 8 , wherein the R d  value is calculated in accordance with the following formula:
   R d =1/[(S d /S u )/(T d /T u )+1],  
 
       and wherein, S d =a spectrum efficiency for the downlink;
 S u =a spectrum efficiency for the uplink;  
 T d =time slots allocated by the system on the downlink; and  
 T u =time slots allocated by the system on the uplink.  
 
     
     
       10. The method of reducing co-channel interference as set forth in  claim 9 , wherein the R u  value is calculated in accordance with the following formula:
   R u = 1− R d .  
 
     
     
       11. The method of reducing co-channel interference as set forth in  claim 8 , wherein the R d  value is calculated in accordance with the following formula:
   R d =1/[(S d /S u )/(T d /T u /2)+1],  
 
       and wherein, S d =a spectrum efficiency for the downlink;
 S u =a spectrum efficiency for the uplink;  
 T d =time slots allocated by the system on the downlink; and  
 T u =time slots allocated by the system on the uplink.  
 
     
     
       12. The method of reducing co-channel interference as set forth in  claim 1 , wherein the communication system comprises an Adaptive Time Division Duplexing (ATDD) communication system. 
     
     
       13. The method of reducing co-channel interference as set forth in  claim 1 , wherein the step (a) of determining a set of terminal stations comprises the sub-steps of:
 i) determining an operating property set for a selected sector of the selected base station; and  
 ii) determining a set of terminal stations that comprise the operating property set of the selected sector.  
 
     
     
       14. The method of reducing co-channel interference as set forth in  claim 13 , wherein the operating property set comprises a polarization, a frequency and a base station antenna direction. 
     
     
       15. The method of reducing co-channel interference as set forth in  claim 13 , wherein the set of terminal stations includes terminal stations that are associated with sectors of at least one base station. 
     
     
       16. The method of reducing co-channel interference as set forth in  claim 1 , wherein the step (a) of determining a set of terminal stations comprises the sub-steps of:
 i) determining a polarization and a frequency of a communication signal and determining an antenna direction for a selected sector of the selected base station; and  
 ii) determining a set of terminal stations that include polarizations and frequencies of the communication signal similar to those determined in sub-step (i) and that also include a similar antenna direction for the selected sector as that determined in sub-step (i).  
 
     
     
       17. The method of reducing co-channel interference as set forth in  claim 1 , wherein the communication system includes a communication re-use scheme having a frequency re-use factor of 2, a 2-frequency set and having a 4 sectors-per-cell configuration. 
     
     
       18. The method of reducing co-channel interference as set forth in  claim 1 , wherein the communication system includes a communication re-use scheme having a frequency re-use factor of 2, a 1-frequency set and having a 4 sectors-per-cell configuration. 
     
     
       19. The method of reducing co-channel interference as set forth in  claim 1 , wherein the communication system includes a communication re-use scheme using a frequency re-use factor of 2, a 3-frequency set and having a 6 sectors-per-cell configuration. 
     
     
       20. The method of reducing co-channel interference as set forth in  claim 1 , wherein the communication system includes a communication re-use scheme using a frequency re-use factor of 3/2, a 4-frequency set and having a 6 sectors-per-cell configuration. 
     
     
       21. An apparatus for reducing co-channel interference in a frame-based broadband wireless communication system, wherein the communication system comprises a plurality of base stations and a plurality of terminal stations, wherein each terminal station is associated with at least one base station, and wherein each base station has an associated and corresponding cell, wherein each cell includes a plurality of associated and corresponding sectors, and wherein the plurality of base stations use frame-synchronized communication, and wherein the communication system comprises an uplink and a downlink, and wherein the uplink comprises an uplink signal divided into a plurality of time frames, and wherein each time frame has an associated and corresponding frame number, comprising:
 a) a set determining means for determining a set of terminal stations that may potentially interfere with a selected base station;  
 b) a diagonal subset determining means for determining a geographically diagonal subset of the set of terminal stations, wherein the diagonal subset communicates with a first set of associated and corresponding base stations that are approximately diagonal to the selected base station;  
 c) a non-diagonal subset determining means for determining a geographically non-diagonal subset of the set of terminal stations, wherein the non-diagonal subset communicates with a second set of associated and corresponding base stations that are not approximately diagonal to the selected base station;  
 d) a first allocating means for allocating a first set of time frames for the first set of base stations;  
 e) a second allocating means for allocating a second set of time frames for the second set of base stations;  
 f) a first transmitting means for transmitting uplink information from terminal stations associated with the first set of base stations during the first set of time frames; and a second transmitting means for transmitting uplink information from terminal stations associated with the second set of base stations during the second set of time frames.  
 
     
     
       22. A frame-based broadband wireless communication system for reducing co-channel interference, comprising:
 a) a plurality of base stations for transmitting and receiving communication signals within a cell;  
 b) a base station controller, operatively coupled to the plurality of base stations, for controlling the plurality of base stations;  
 c) a general purpose computer, operatively connected to the base station controller, for: 
 i)determining a set of terminal stations that may potentially interfere with a selected base station;  
 ii) determining a geographically diagonal subset of the set of terminal stations, wherein the diagonal subset communicates with a first set of associated and corresponding base stations that are approximately diagonal to the selected base station;  
 iii) determining a geographically non-diagonal subset of the set of terminal stations, wherein the non-diagonal subset communicates with a second set of associated and corresponding base stations that are not approximately diagonal to the selected base station;  
 iv) allocating a first set of time frames for the first set of base stations;  
 v) allocating a second set of time frames for the second set of base stations; and  
 
 d) a plurality of terminal stations, communicatively coupled to at least one of the plurality of base stations, for transmitting and receiving communication signals within the cell.  
 
     
     
       23. A wireless communication system, comprising:
   a plurality of base stations to transmit and/or receive communication signals within cells; and        a base station controller, operatively coupled to said plurality of base stations, to:      determine a set of terminal stations that potentially interfere with reception at a selected base station from a terminal station in a line of sight of a sector associated with the selected base station, wherein one or more of said terminal stations operates on a same frequency as the selected base station, a same polarization as the selected base station and/or comprises an antenna facing the selected base station;        determine a first subset of the set of terminal stations, wherein the first subset communicates with a first set of associated base stations that are approximately located along a ray that substantially intersects the selected base station and that is oblique and/or perpendicular to the line of sight of the sector;        determine a second subset of the set of terminal stations, wherein the second subset communicates with a second set of associated base stations including one or more base stations that are not approximately located along the ray that substantially intersects the selected base station;        determine a first set of time frames for the first subset of the set of terminal stations; and        determine a second set of time frames for the second subset of the set of terminal stations,          wherein the first subset and the second subset of the set of terminal stations respectively transmit uplink information during the first set of time frames and the second set of time frames.     
     
     
       24. The wireless communication system of  claim 23 , further comprising:
   a communication hub to provide one or more communication services to customers; and        a video server to provide a video service to at least one of said customers through said communication hub.     
     
     
       25. The wireless communication system of  claim 24 , further comprising:
   a plurality of customer premises equipment  ( CPE )  stations to deliver said one or more communication services to said customers; and        at least one residential gateway coupled to one of said CPE stations.     
     
     
       26. The wireless communication system of  claim 24 , wherein the communication hub further comprises at least one ATM switch to provide at least one ATM service to one or more of said customers. 
     
     
       27. The wireless communication system of  claim 26 , wherein said at least one ATM service includes at least one of a video service, a voice service and a data service. 
     
     
       28. The wireless communication system of  claim 23 , wherein the selected base station further comprises a sectored active antenna array. 
     
     
       29. A wireless communication system, comprising:
   a plurality of base stations to transmit and/or receive communication signals within cells;        a base station controller to control two or more of said plurality of base stations; and        a general purpose computer, coupled to the base station controller, to:      determine a set of terminal stations that potentially interfere with reception at a selected base station from a terminal station in a line of sight of a sector associated with the selected base station, wherein one or more of said terminal stations operates on a same frequency as the selected base station, a same polarization as the selected base station and/or comprises an antenna facing the selected base station;        determine a first subset of the set of terminal stations, wherein the first subset communicates with a first set of associated base stations that are approximately located along a ray that substantially intersects the selected base station and that is oblique and/or perpendicular to the line of sight of the sector;        determine a second subset of the set of terminal stations, wherein the second subset communicates with a second set of associated and corresponding base stations including one or more base stations that are not approximately located along the ray that substantially intersects the selected base station;        determine a first set of time frames for the first subset of the set of terminal stations; and        determine a second set of time frames for the second subset of the set of terminal stations,          wherein the first subset and the second subset of the set of terminal stations respectively transmit uplink information during the first set of time frames and the second set of time frames.     
     
     
       30. A method, comprising:
   identifying, by a general purpose computer, a set of one or more terminal stations that potentially interfere with reception at a selected base station from a terminal station in a line of sight of a sector associated with the selected base station, wherein the one or more of said terminal stations operates on a same frequency as the selected base station, a same polarization as the selected base station and/or comprises an antenna facing the selected base station;        identifying, by said general purpose computer, a first subset of the set of terminal stations, wherein the first subset communicates with a first set of associated base stations that are approximately located along a ray that substantially intersects the selected base station and that is oblique and/or perpendicular to the line of sight of the sector;        identifying, by said general purpose computer, a second subset of the set of terminal stations, wherein the second subset of terminal stations communicates with a second set of associated base stations including one or more base stations that are not approximately located along the ray that substantially intersects the selected base station;        determining a first set of time frames for the first subset of the set of terminal stations; and        determining a second set of time frames for the second subset of the set of terminal stations,        wherein the first subset and the second subset of the set of terminal stations respectively transmit uplink information during the first set of time frames and the second set of time frames.     
     
     
       31. The method of  claim 30 , wherein said selected base station and said terminal station in the line of sight of the sector associated with the selected base station communicate using a half- duplex frequency - division duplexed  ( FDD )  communication system.   
     
     
       32. The method of  claim 30 , wherein said selected base station and said terminal station in the line of sight of the sector associated with the selected base station communicate using a time- division duplexed  ( TDD )  system.   
     
     
       33. The method of  claim 30 , wherein said selected base station and said terminal station in the line of sight of the sector associated with the selected base station using a frame- synchronized communication system that transmits information in an uplink signal and a downlink signal, said uplink signal being partitioned into sequentially numbered time frames.   
     
     
       34. The method of  claim 30 , wherein said selected base station and said terminal station in the line of sight of the sector associated with the selected base station communicate using an Adaptive Time Division Duplexing ( ATDD )  communication system.