System and method used in a mobile telecommunications network for load balancing ongoing calls between different base station controllers

[0002] This application is related to two U.S. applications filed on Mar. 6, 1998 in the name of Pontus Wallentin entitled “Telecommunications Inter-Exchange Measurement Transfer” Ser. No. 09/035,827 and “Telecommunications Inter-Exchange Congestion Control” Ser. No. 09/035,788; both of which are hereby incorporated by reference herein.

[0003] 1. Technical Field of the Invention

[0004] The present invention generally relates to a mobile telecommunications network and, in particular, to a system and method used in a mobile telecommunications network for load balancing ongoing calls between different base station controllers.

[0005] 2. Description of Related Art

[0006] A mobile telecommunications network having an architecture according to the Global System for Mobile Communications (GSM) specification includes a multitude of cells. The cells effectively divide an arbitrary geographic area into a plurality of contiguous radio coverage areas; each of which is served by a base transceiver station (BTS). The BTS serves each cell by utilizing a limited number of traffic channels that are controlled by a base station controller (BSC). The BSC is generally used to supervise and control a group of the BTSs.

[0007] The BSC may have a feature known as “Cell Load Sharing” to increase the capacity and operating performance of the network by effectively balancing the ongoing call loads between the cells that are adjacent to one another. For example, at any time a particular cell may have a high ongoing call load, while adjacent cells have low ongoing call loads, thus triggering the “Cell Load Sharing” feature of the base station controller to balance the various call loads between the different cells. The BSC balances the various call loads by transferring some of the ongoing calls from the cell having the high ongoing call load to the adjacent cell(s) having the low ongoing call load. Of course, the ongoing call load for any cell is constantly changing due mainly to origination of new calls and handovers of calls from traveling mobile terminals.

[0008] However, the “Cell Load Sharing” feature currently used will operate only with respect to the cells or base transceiver stations that are controlled by one base station controller. Thus, if a cell associated with a different base station controller is adjacent to the cell controlled by another base station controller, then no balancing of the ongoing calls can be completed, because the required information is not communicated between the different base station controllers.

[0009] Accordingly, there is a need for a method and system used in a mobile telecommunications network for load balancing ongoing calls between adjacent cells controlled by different base station controllers. There is also a need for a system and method for transmitting load indication messages between different base station controllers. These and other needs are satisfied by the system and method of the present invention.

[0010] The present invention is a method and system for load balancing used in a mobile telecommunications network. The load balancing system includes a mobile services switching center and a first base station controller coupled to the mobile services switching center for managing a first plurality of cells. The load balancing system further includes a second base station controller coupled to the mobile services switching center for managing a second plurality of cells, where one cell of the first plurality of cells is adjacent to one cell of the second plurality of cells. The second base station controller includes a processor responsive to receiving a first load indication message from the first base station controller in order to determine whether to handover at least one ongoing call from the one cell of the second base station controller to the one cell of the first base station controller.

[0011] In accordance with the present invention, a system and method are provided for balancing an ongoing call load across a boundary between adjacent cells that are controlled by different base station controllers.

[0012] Also in accordance with the present invention, a system and method are provided that have a base station controller generating a load indication message whenever the number of available traffic channels within a cell changes so as to exceed or fall below a predetermined threshold.

[0013] Further in accordance with the present invention, a method and system are provided for utilizing a load indication message in a different and more advantageous manner than was intended by the GSM specification.

[0014] A more complete understanding of the method and apparatus of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:

[0015] FIG. 1 is a block diagram of a mobile telecommunications network incorporating a load balancing system, in accordance with the present invention;

[0016] FIG. 2 is a block diagram illustrating in greater detail the load balancing system shown in FIG. 1; and

[0017] FIG. 3 is a simplified flow diagram of an operation of the load balancing system shown in FIG. 1.

[0018] Referring to the Drawings, wherein like numerals represent like parts throughout FIGS. 1-3, there is disclosed an exemplary load balancing system 50, which can be used to implement a preferred embodiment of the present invention.

[0019] Although a mobile telecommunications network 100 embodying the load balancing system 50 of the present invention will be discussed based on the Global System for Mobile Communications (GSM) specification, those skilled in the art will appreciate that the GSM specification is only one of many specifications and standards that may utilize the principles of the present invention. Accordingly, the load balancing system 50 described should not be construed in such a limiting manner.

[0020] Referring to FIG. 1, there is illustrated a block diagram of the mobile telecommunications network 100 incorporating the exemplary load balancing system 50. Excluding the load balancing system 50, the general architecture of the mobile telecommunication network 100 is based substantially on the GSM specification.

[0021] The mobile telecommunications network 100 includes a plurality of cells 110a-110hthat effectively divide an arbitrary geographic area into a plurality of contiguous radio coverage areas. A single base transceiver station (BTS) 125a-125hconsisting of transmitter and receiver antenna(s) (not shown) is positioned within each cell 110a-110h.

[0022] Different groups of neighboring cells (e.g., cells 110a-110c) are then associated with a particular base station controller (e.g., BSC-1 150). A number of BSCs (e.g., BSC-1 150 and BSC-2 155) may, in turn, be associated with a mobile services switching center/visitor location register (e.g., MSC/VLR 130). As an illustration, the BSC-1 150 provides mobile service for cells 110a-110c, while the BSC-2 155 provides mobile service for cells 110d-110h.The BSC-1 150 and BSC-2 155 are in turn coupled to the MSC/VLR 130, which generally functions as an interface between the mobile telecommunications network 100 and, for example, a public switched telephone network (PSTN) (not shown). The load balancing system 50 preferably includes the BSCs (e.g., BSC-1 150 and BSC-2 155) and the MSC/VLR 130, which are discussed in greater detail with reference to FIGS. 2-3.

[0023] Referring to FIG. 2, there is illustrated a block diagram of the exemplary load balancing system 50. The load balancing system 50 generally includes the MSC/VLR 130 coupled to the BSC-1 150 and the BSC-2 155 for balancing an ongoing call load in opposite directions across a boundary 202 between the adjacent cells 110band 110f.The adjacent cells 110band 110fare controlled by the BSC-1 150 and the BSC-2 155, respectively. For clarity, the description of the load balancing system 50 will include only two BSCs (e.g., BSC-1 150 and BSC-2 155) each having adjacent cells (e.g., cells 110band 110f); however, the system may include any number of BSCs.

[0024] The BSC-1 150 includes a processor-1 210 for determining whether or not to handover at least one ongoing call from the cell 110bto the cell 110f, in view of the number of ongoing calls within the two cells. Likewise, the BSC-2 155 includes a processor-2 230 responsible for determining whether or not to handover at least one ongoing call from the cell 110fto the cell 110b. The BSC-1 150 and BSC-2 155 can further include conventional components, such as a regional processor, group switch and signaling terminal central, etc.

[0025] The reason for ordering a handover associated with load balancing is not to be confused with the traditional handover associated with a moving mobile terminal 245. For example, the traditional handover would be completed when the mobile terminal 245 travels from the cell 110bto the cell 110f,and the ongoing call is transferred to the cell 110fas the mobile terminal enters the cell 110f. Notably, the load balancing handover of the present invention may be completed for load balancing purposes to transfer the ongoing call from the cell 110bto the cell 110feven though the mobile terminal 245 remains within the cell 110b.

[0026] The processors 210 and 230 each include a load monitor 234 for continuously or periodically updating the number of traffic channels that are currently active and can not accept a new call or an ongoing call via a traditional handover procedure. The load monitor 234 may also periodically or continuously calculate a percentage of the active traffic channels with respect to a total number of traffic channels assigned to any one of the cells. The number of active traffic channels or the percentage described above may be referred to as a resource utilization number (RUN).

[0027] A comparator-1 236 incorporated within the processor-1 210 compares a predetermined threshold (described below) to the RUN associated with the cell 110bto determine if a load indication message-1 238 must be generated and transmitted via the MSC/VLR 130 to the BSC-2 155. The load indication message-1 238 is generated whenever the RUN (e.g., the number of active traffic channels) within the cell 110bchanges so as to exceed or fall below a predetermined threshold. It should be noted that the load indication message-1 238 of the present invention is thus used in a different, more advantageous manner than was originally intended by the GSM standard.

[0028] For example, the load indication message-1 238 will not be generated if a prior RUN was below/above the predetermined threshold and the current resource utilization number is below/above the predetermined threshold, respectively. However, the load indication message-1 238 will be generated and transmitted to the BSC-2 155 whenever the prior RUN was below/above the predetermined threshold and the current RUN is above/below (e.g., opposite sides) the predetermined threshold, respectively.

[0029] Alternatively, the load indication message-1 238 may be periodically generated and transmitted to the BSC-2 155 during predetermined intervals of time without comparing the RUN associated with the cell 110bto the predetermined threshold. In such a case, the load indication message-1 238 would be comparable to the resource utilization number.

[0030] A comparator-2 240 is incorporated within the processor-2 230 to compare a predetermined threshold and the RUN associated with the cell 110fto determine if a load indication message-2 242 will be generated and transmitted via the MSC/VLR 130 to the BSC-1 150. The load indication message-2 242 is generated whenever the RUN within the cell 110hchanges so as to exceed or fall below the predetermined threshold. As mentioned above, the load indication message-2 242 may be periodically generated and transmitted to the BSC-1 150 during predetermined intervals of time without comparing the RUN of the cell 110fto the predetermined threshold. Also, some of the load indication information could be included in messages transmitted using the traditional handover procedures.

[0031] Upon receiving the load indication message-2 242, the BSC-1 150 (and more specifically the processor-1 210) will determine whether to attempt transfer of at least one of the ongoing calls within the cell 110bto the cell 110f.The processor-1 210 will transfer or handover at least one of the ongoing calls when the RUN of the cell 110bis greater than a predetermined threshold and the BSC-2 155 can accept the ongoing call(s). The BSC-2 155 can accept the ongoing call(s) from the BSC-1 150 when the RUN of the cell 110fis below the predetermined threshold, otherwise, the BSC-2 may not accept the at least one ongoing call.

[0032] Similarly, the BSC-2 155 and the processor-2 230 upon receiving the load indication message-1 238 will determine whether to attempt a transfer of at least one of the ongoing calls within the cell 110fto the cell 110bassociated with the BSC-1 150. The processor-2 230 will transfer or handover at least one of the ongoing calls when the RUN the cell 110fis greater than a predetermined threshold and the BSC-1 150 can accept the ongoing call(s). The BSC-1 150 can accept at least one of the ongoing calls from the BSC-2 155 when the RUN of the cell 110bis below the predetermined threshold; otherwise, the BSC-1 will not accept the ongoing call(s) from cell 110f.

[0033] The predetermined threshold is generally the same level for each of the BSCs 150 and 155, and may be submitted to the processors 210 and 230 via an operation and support system (OSS) 250. The OSS 250 may also change the levels of the predetermined threshold so that there is a different level for each cell 110band 110f. Also, the predetermined threshold level may include an upper threshold and lower threshold to help assure that the RUN is stable above or below the respective threshold before generating the load indication message.

[0034] Referring to FIG. 3, there is illustrated a simplified flow diagram of a method of operation for the exemplary load balancing system 50. As discussed earlier, the operation of the load balancing system 50 may be performed within the mobile telecommunications network 100 based on the GSM specification. However, other specifications or standards may be used such as, for example, the Advanced Mobile Phone System (AMPS), the Digital Advanced Mobile Phone System (DAMPS) and the Personal Digital Cellular (PDC) System.

[0035] Beginning at step 302 of the preferred method, the OSS 250 establishes the predetermined threshold and distributes the predetermined threshold to the BSC-1 150 and the BSC-2 155 (FIG. 2). The predetermined threshold is generally the same level within each of the BSCs 150 and 155.

[0036] At step 304, the load indication messages (e.g., load indication message-1 238) are generated and updated within the respective BSCs (e.g., BSC-1 150) whenever the RUN within the corresponding cell (e.g., cell 110b) changes so as to exceed or fall below the predetermined threshold. Alternatively, the load indication messages (e.g., load indication message-1 238) may be periodically updated and generated during predetermined intervals of time, without comparing the RUN associated with the cells (e.g., cell 110b) to the predetermined threshold.

[0037] At step 306, each of the generated load indication messages (e.g., load indication message-1 238) are transmitted to the other BSCs (e.g, BSC-2 155). Then at step 308, each processor (e.g., processor-2 230) compares the received load indication messages (e.g., load indication message-1 238) to the predetermined threshold.

[0038] At step 310, a determination is made by each processor (e.g. processor-2 230) upon receiving the load indication message (e.g., load indication message-1 238) about whether to attempt a handover of at least one of the ongoing calls from one BSC (e.g., BSC-2 155) to the other BSC (e.g., BSC-1 150). The processor (e.g., processor-2 230), at step 312, will handover at least one of the ongoing calls when the RUN of the cell (e.g., cell 110f) is greater than a predetermined threshold, and the other BSC (e.g., BSC-1 150) can accept that ongoing call. Otherwise at step 314, the ongoing calls within the particular cell (e.g., cell 110f) will remain within that cell.

[0039] From the foregoing, it can be readily appreciated by those skilled in the art that the present invention provides a load balancing system and method for use in a mobile telecommunications network for distributing ongoing calls between adjacent cells controlled by different base station controllers. Also, the load balancing system as disclosed may be used to transmit load indication messages between different base station controllers.

[0040] Although one embodiment of the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.