Abstract:
Apparatus having corresponding methods and computer programs comprise: a plurality of antennas located in a first cellular telephone cell; an interference module to identify wireless cellular telephone signals received by the plurality of antennas from one or more cellular telephones located in one or more second cellular telephone cells; and a cell module to identify the one or more second cellular telephone cells based on the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/969,026, filed on Aug. 30, 2007, the disclosure thereof incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to cellular telephone communications. More particularly, the present disclosure relates to overload coordination for cellular telephone intercell interference. 
     In the uplink of a cellular telephone system, cellular telephones within a cellular telephone cell transmit wireless cellular telephone signals to the base station serving the cell. However, the base station serving a cell receives wireless cellular telephone signals not only from cellular telephones within the cell, but also from cellular telephones in neighboring cells. The signals received from neighboring cells appear as interference, referred to as “intercell interference,” which severely limits the coverage and throughput of a network.  FIG. 1  shows an example of intercell interference. 
     Referring to  FIG. 1 , a cellular telephone  108  located in one cell  104 B transmits wireless cellular telephone signals  106 , which are received by the base station  102 B serving that cell  104 B. However, wireless cellular telephone signals  106  are also received by a base station  102 A serving a neighboring cell  104 A. Signals  106  constitute intercell interference for base station  102 A. 
     One way to mitigate intercell interference is to force neighboring cells to use different sections of the frequency spectrum. Although this helps to alleviate intercell interference, another problem remains that cannot be addressed by simple frequency domain separation. When cellular telephones at the edge of a cell transmit wireless cellular telephone signals at high power, they can cause the signal level received at a base station in a neighboring cell to be extremely high. This can cause the analog front end of the neighboring base station to be overloaded, leading to degradation of signal quality and loss of service in the neighboring cell. 
     One way to mitigate this type of base station overload is to use an overload indicator.  FIG. 2  shows an example of the conventional use of an overload indicator to mitigate intercell interference. Referring to  FIG. 2 , when base station  102 A becomes overloaded, base station  102 A transmits overload indicators  110 B-G to all neighboring base stations, including base station  102 B. In response, the neighboring base stations instruct the cellular telephones within their cells to reduce transmit power. For example, base station  102 B transmits an instruction  112  to all cellular telephones  108  in cell  104 B. In response to instruction  112 , cellular telephones  108  reduce their transmit power, thereby reducing intercell interference received by base station  102 A. 
     One disadvantage of the conventional overload indicator approach is that a base station does not determine which cell is responsible for causing the intercell interference, and so sends the overload indicator indiscriminately to all neighboring cells. Therefore, even cells that are not causing significant intercell interference are forced to reduce their transmit power unnecessarily, leading to a decrease in throughput in those cells while providing no benefit to the overloaded cell. 
     SUMMARY 
     In general, in one aspect, an embodiment features an apparatus comprising: a plurality of antennas located in a first cellular telephone cell; an interference module to identify wireless cellular telephone signals received by the plurality of antennas from one or more cellular telephones located in one or more second cellular telephone cells; and a cell module to identify the one or more second cellular telephone cells based on the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells. 
     Embodiments of the apparatus can include one or more of the following features. Some embodiments comprise an overload indicator module to send an overload indicator only to base stations serving the one or more second cellular telephone cells. In some embodiments, the cell module comprises: a direction module to determine directions of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells based on a geometry of the plurality of antennas and relative phase delays of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells; wherein the cell module identifies the one or more second cellular telephone cells based on the directions of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells. In some embodiments, the interference module identifies the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells based on wireless cellular telephone signals received by the plurality of antennas when no cellular telephones located in the first cellular telephone cell are transmitting. In some embodiments, the interference module identifies the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the second cellular telephone cell based on a difference between all wireless cellular telephone signals received by the plurality of antennas and wireless cellular telephone signals received by the plurality of antennas from cellular telephones located in the first cellular telephone cell. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the second cellular telephone cell comply with one or more of: the IEEE 802.16 standards; the 3GPP standards; and the 3GPP2 standards. 
     In general, in one aspect, an embodiment features a method comprising: identifying wireless cellular telephone signals received by a plurality of antennas located in a first cellular telephone cell from one or more cellular telephones located in one or more second cellular telephone cells; and identifying the one or more second cellular telephone cells based on the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells. 
     Embodiments of the method can include one or more of the following features. Some embodiments comprise sending an overload indicator only to base stations serving the one or more second cellular telephone cells. Some embodiments comprise determining a direction of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells based on a geometry of the plurality of antennas and relative phase delays of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells; wherein the one or more second cellular telephone cells are identified based on directions of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells are identified based on wireless cellular telephone signals received by the plurality of antennas when no cellular telephones located in the first cellular telephone cell are transmitting. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells are identified based on a difference between all wireless cellular telephone signals received by the plurality of antennas and wireless cellular telephone signals received by the plurality of antennas from cellular telephones located in the first cellular telephone cell. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells comply with one or more of: the IEEE 802.16 standards; the 3GPP standards; and the 3GPP2 standards. 
     In general, in one aspect, an embodiment features a computer program comprising: instructions for identifying wireless cellular telephone signals received by a plurality of antennas located in a first cellular telephone cell from one or more cellular telephones located in one or more second cellular telephone cells; and instructions for identifying the one or more second cellular telephone cells based on the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells. 
     Embodiments of the computer program can include one or more of the following features. Some embodiments comprise instructions for sending an overload indicator only to base stations serving the one or more second cellular telephone cells. Some embodiments comprise instructions for determining a direction of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells based on a geometry of the plurality of antennas and relative phase delays of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells; wherein the one or more second cellular telephone cells are identified based on directions of the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells are identified based on wireless cellular telephone signals received by the plurality of antennas when no cellular telephones located in the first cellular telephone cell are transmitting. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells are identified based on a difference between all wireless cellular telephone signals received by the plurality of antennas and wireless cellular telephone signals received by the plurality of antennas from cellular telephones located in the first cellular telephone cell. In some embodiments, the wireless cellular telephone signals received by the plurality of antennas from the one or more cellular telephones located in the one or more second cellular telephone cells comply with one or more of: the IEEE 802.16 standards; the 3GPP standards; and the 3GPP2 standards. 
     In general, in one aspect, an embodiment features an apparatus comprising: a plurality of antenna means for receiving wireless signals, wherein the plurality of antenna means is located in a first cellular telephone cell; interference means for identifying wireless cellular telephone signals received by the plurality of antenna means from one or more cellular telephones located in one or more second cellular telephone cells; and cell means for identifying the one or more second cellular telephone cells based on the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the one or more second cellular telephone cells. 
     Embodiments of the apparatus can include one or more of the following features. Some embodiments comprise overload indicator means for sending an overload indicator only to base stations serving the one or more second cellular telephone cells. In some embodiments, the cell means comprises: direction means for determining directions of the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the one or more second cellular telephone cells based on a geometry of the plurality of antenna means and relative phase delays of the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the one or more second cellular telephone cells; wherein the cell means identifies the one or more second cellular telephone cells based on the directions of the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the one or more second cellular telephone cells. In some embodiments, the interference means identifies the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the one or more second cellular telephone cells based on wireless cellular telephone signals received by the plurality of antenna means when no cellular telephones located in the first cellular telephone cell are transmitting. In some embodiments, the interference means identifies the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the second cellular telephone cell based on a difference between all wireless cellular telephone signals received by the plurality of antenna means and wireless cellular telephone signals received by the plurality of antenna means from cellular telephones located in the first cellular telephone cell. In some embodiments, the wireless cellular telephone signals received by the plurality of antenna means from the one or more cellular telephones located in the second cellular telephone cell comply with one or more of: the IEEE 802.16 standards; the 3GPP standards; and the 3GPP2 standards. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an example of intercell interference. 
         FIG. 2  shows an example of the conventional use of an overload indicator to mitigate intercell interference. 
         FIG. 3  shows a cellular telephone system featuring directional coordination for intercell interference according to one embodiment. 
         FIG. 4  shows an intercell interference mitigation process for the local base station of  FIG. 3  according to one embodiment. 
     
    
    
     The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
     DETAILED DESCRIPTION 
     Modern base stations employ multiple receive antennas to increase service reliability through the use of receive diversity, to increase throughput through the use of spatial multiplexing, and the like. Embodiments of the present invention employ these multiple receive antennas to determine the direction of intercell interference by, for example, measuring the spatial correlation of the interference across the antenna array at the base station. The cell(s) responsible for the intercell interference are identified based on the direction of the intercell interference. In one embodiment, an overload indicator is sent only to the identified cell(s). By targeting the overload indicator only to the base station(s) responsible for the intercell interference, the unnecessary reduction of cellular telephone transmit power in cells not responsible for intercell interference is avoided. One benefit of this approach compared to the conventional approach is a relative increase in overall network throughput. 
       FIG. 3  shows a cellular telephone system  300  featuring directional coordination for intercell interference according to one embodiment. Referring to  FIG. 3 , cellular telephone system  300  includes a cellular telephone base station  302 A serving a cell  304 A and a neighboring cellular telephone base station  302 B serving a neighboring cell  304 B. Cellular telephone base station  302 A is implemented according to an embodiment of the present invention, as described in detail below. Neighboring cellular telephone base station  302 B can be implemented as a conventional cellular telephone base station or according to embodiments of the present invention. Embodiments of the present invention can operate with multiple neighboring cells. However, for clarity, only one neighboring cell  304 B is shown. 
     Base station  302 A includes a plurality of antennas  306 A-N, an interference module  308 , a cell module  310 , and an overload indicator module  312 . Cell module  310  includes a direction module  314 . One or more cellular telephones  316 A are located in cell  304 A, and one or more cellular telephones  316 B are located in neighboring cell  304 B. For clarity, in this description cell  304 A is referred to as the “local” cell, while cell  304 B is referred to as a “neighboring” cell. 
     Although in the described embodiments, the elements of base station  302 A are presented in one arrangement, other embodiments may feature other arrangements. For example, the elements of base station  302 A can be implemented in hardware, software, or combinations thereof. 
       FIG. 4  shows an intercell interference mitigation process  400  for local base station  302 A of  FIG. 3  according to one embodiment. Although in the described embodiments, the elements of process  400  are presented in one arrangement, other embodiments may feature other arrangements. For example, in various embodiments, some or all of the steps of process  400  can be executed in a different order, concurrently, and the like. In addition, embodiments of the present invention can mitigate intercell interference from multiple neighboring cells. However, for clarity, only one neighboring cell  304 B is described. 
     Referring to  FIGS. 3 and 4 , antennas  306  receive wireless cellular telephone signals  318 , including not only local wireless cellular telephone signals  318 A from cellular telephones  316 A located in local cell  304 A, but also wireless cellular telephone signals  318 B from cellular telephones  316 B located in neighboring cell  304 B (step  402 ). Wireless cellular telephone signals  318 B present intercell interference to base station  302 A. Wireless cellular telephone signals  318  can comply with the IEEE 802.16 standards; the 3GPP standards, the 3GPP2 standards, and the like. 
     Interference module  308  identifies wireless cellular telephone signals  318 B received from cellular telephones  316 B located in neighboring cell  304 B as intercell interference (step  404 ). That is, interference module  308  distinguishes wireless cellular telephone signals  318 B from wireless cellular telephone signals  318 A. For example, interference module  308  can identify intercell interference as the wireless cellular telephone signals  318  received by antennas  306  when no cellular telephones  316 A located in local cell  304 A are transmitting. As another example, interference module  308  can identify intercell interference as the difference between all of the wireless cellular telephone signals  318  received by antennas  306  and the wireless received from cellular telephones  316 A located in local cell  304 A. Local base station  302 A can identify cellular telephones  316 A located in local cell  304 A by the reference sequences transmitted by cellular telephones  316 A. Other techniques can be used. 
     Direction module  314  determines the direction of the source of the intercell interference (step  406 ). In the example of  FIG. 3 , direction module  314  determines the direction of the wireless cellular telephone signals  318 B identified by interference module  308  as intercell interference. For example, direction module  314  determines the direction of the source of wireless cellular telephone signals  318 B based on the geometry of antennas  306  and the relative phase delays of the wireless cellular telephone signals  318  received by antennas  306 . In the example of  FIG. 3 , the direction is east. Of course, other techniques can be used. 
     Cell module  310  identifies the cellular telephone cell  304  where the source of the intercell interference is located based on the direction of the source of the intercell interference (step  408 ). For example, cell module  310  identifies the cellular telephone cell based on the direction of wireless cellular telephone signals  318  determined by direction module  314 . In the example of  FIG. 3 , the direction is east, and the cell to the east of local cell  304 A is cell  304 B. 
     In one embodiment, overload indicator module  312  sends an overload indicator  320  only to the base station(s) serving the cellular telephone cell(s)  304  identified by cell module  310  (step  410 ). In the example of  FIG. 3 , overload indicator module  312  sends overload indicator  320  to base station  302 B. Overload indicator  320  can be a conventional overload indicator, and can be sent in a conventional manner. In contrast to conventional approaches, overload indicator  320  is sent only to the neighboring base station(s)  302  serving cells  304  that are the source of intercell interference for local base station  302 A. In one embodiment, overload indicator module  312  sends overload indicator  320  also to one or more base stations in cells that are adjacent to identified cell(s). In such an embodiment, a reduction in intercell interference can be maintained in situations where a cellular telephone is at the edge of an identified cell and the cellular telephone transitions to an adjacent cell. In one embodiment, an overload indicator  320  can be sent to an adjacent cell (e.g., a cell to which a cellular telephone moves into) if the cellular telephone in question still generates serious interference in this adjacent cell. The information on which adjacent cell a cellular telephone moves to can be obtained, for example, through a handover message. 
     Each base station  302  that receives an overload indicator  320  sends an instruction  322  to the cellular telephones  316  within the cell  304  served by that base station  302 . In response to instruction  322 , cellular telephones  316  reduce their transmit power, thereby reducing intercell interference for the originator of overload indicator  320 . In the example of  FIG. 3 , neighboring base station  302 B sends instruction  322  to the cellular telephone(s)  316 B located in neighboring cell  304 B, thereby reducing the intercell interference received by local base station  302 A. 
     Various embodiments can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions by operating on input data and generating output. Embodiments can be implemented in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.