Abstract:
Technologies for load balancing among neighboring cells of a mobile wireless communication network can reduce traffic congestion and improve network system capacity. Load balancing can be accomplished by adjusting various radio access network parameters. Such adjustments may be made at the cell level or at the neighboring cell level. The adjustments can be applied iteratively in response to various collected operational statistics. The adjustments can adapt cell size and cell shape as well as adapt handover to maximize system resource and hardware utilization. An iterative process of optimization can periodically collect performance statistics and network configuration from a mobile wireless network. The collected information can be periodically analyzed to determine parameter adjustments. Configuring additional capacity from the communication network can prevent or substantially delay the acquisition of additional hardware resources to mitigate system capacity issues.

Description:
BACKGROUND 
     Wireless communication networks, such as those supporting mobile telephone and data services, naturally have operational limitations. These limitations may be physical limitations, such as equipment limitations, frequency allocations, power limits, base station placement, antenna configurations, noise, environmental factors, or otherwise. Limitations may also be introduced by suboptimal system configurations. One manifestation of wireless system limitation is a ceiling on capacity. Capacity can be considered in terms of a number of mobile radios supported, a data rate supported, a number of calls supported, or some other measure of wireless system capacity. 
     Vendors of mobile communication infrastructure equipment sometimes offer radio resource management (RRM) features. While these RRM features can be leveraged to relieve brief, periodic congestion problems, the solutions offered are generally locally oriented over a limited physical domain. Moreover, such techniques are generally based on reducing user resources. For example, degrading call or data quality, blocking calls, forcing handovers, and call preemption are some traditional RRM techniques. Such capacity overload mitigation techniques may be suitable for brief periods of congestion. For example, on the scale of seconds or tens of minutes. However, such approaches do not typically support persistent capacity improvement. Furthermore, these approaches generally do not guarantee call quality or support increased long-term traffic trends. 
     Traditionally long-term solutions to capacity problems in wireless communication networks involve acquiring additional resources. For example, purchasing and installing additional base station equipment is a typical approach to increasing the capacity of a mobile communication system. Unfortunately, such an approach can have considerable lead-time delays as well as considerable costs in both capital expenditure and operating expenses. Furthermore, adding physical resources is generally a locally isolated solution with little flexibility for reallocating increased capacity within the network. 
     It is with respect to these considerations and others that the disclosure made herein is presented. 
     SUMMARY 
     Technologies are described herein for load balancing among neighboring cells of a mobile wireless communication network. Such load balancing can reduce traffic congestion and improve network system capacity. Load balancing can be accomplished by adjusting various radio access network (RAN) parameters. Such adjustments may be made at the cell level or at the neighboring cell level. The adjustments can be applied iteratively in response to various collected operational statistics. The adjustments can adapt cell size and cell shape as well as adapt handover to maximize system resource and hardware utilization. An iterative process of optimization can periodically collect performance statistics and network configuration from a mobile wireless network. The collected information can be periodically analyzed to determine parameter adjustments. Extracting additional capacity from the communication network can prevent or substantially delay acquisition of additional hardware resources to address capacity concerns. 
     According to one embodiment, cell size and cell shape can be adjusted. The bounds between a cell and a neighboring cell can be adjusted to balance the offered traffic among multiple sets of base station resources. The adjustments can be made by adjusting handover parameters, power levels, antenna tilt, and various other system characteristics. 
     According to another embodiment, load balancing can allocate traffic to maximize the hardware utilization. Loaded cells or operating frequencies can have associated load reallocated to underutilized frequencies, cells, or network systems. 
     According to yet another embodiment, an iterative process of optimization can periodically collect performance statistics and network configuration. The iterative process can use the collected information to adjust various operating parameters in the system to achieve a desired load balancing goal. 
     It should be appreciated that the above-described subject matter may also be implemented as a computer-controlled apparatus, a computer process, a computing system, or as an article of manufacture such as a computer-readable medium. These and various other features will be apparent from a reading of the following Detailed Description and a review of the associated drawings. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a network architecture diagram illustrating aspects of a GSM and UMTS mobile wireless communication system according to one exemplary embodiment; 
         FIG. 2  is a mobile radio cell diagram illustrating cell reshaping for load balancing between neighboring cells according to one exemplary embodiment; 
         FIG. 3  is a mobile traffic allocation diagram illustrating load balancing among three types of neighbors to rebalance traffic away from a congested cell according to one exemplary embodiment; 
         FIG. 4  is a logical flow diagram illustrating a process load balancing in a mobile wireless network according to one exemplary embodiment; and 
         FIG. 5  is a computer architecture diagram illustrating computing system hardware capable of traffic load balancing within a mobile wireless radio network according to one exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is directed to technologies for load balancing within a mobile wireless radio network. Through the use of the embodiments presented herein, system capacity can be improved within a wireless radio network by iteratively adjusting cell size and shape while also adjusting system resource utilization by updating handover parameters. Network capacity problems can be related to traffic congestion or pre-congestion, such as excessive resource utilization. A capacity issue can be detected by collecting metrics associated with key performance indicators (KPI). For example, statistics can be collected that are associated with transmitter power utilization, code allocation utilization, aggregation link utilization, channel elements, call processor load, and various other system characteristics. Network statistics can be retrieved from the operation and support system (OSS) or any intermediate system element. 
     While the subject matter described herein is presented in the general context of program modules that execute in conjunction with the execution of an operating system and application programs on a computer system or embedded processor system, those skilled in the art will recognize that other implementations may be performed in combination with other types of program modules. Generally, program modules include routines, programs, components, data structures, and other types of structures that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the subject matter described herein may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like. 
     In the following detailed description, references are made to the accompanying drawings that form a part hereof, and which are shown by way of illustration specific embodiments or examples. Referring now to the drawings, in which like numerals represent like elements through the several figures, aspects of a computing system and methodology for improving system capacity within a mobile wireless radio network using load balancing. 
     Turning now to  FIG. 1 , details will be provided regarding an illustrative operating environment for the implementations presented herein, as well as aspects of several software components that provide the functionality described herein for load balancing within a mobile wireless radio network. In particular,  FIG. 1  is a network architecture diagram illustrating aspects of a Global System for Mobile (GSM) and Universal Mobile Telecommunications System (UMTS) mobile wireless communication system  100  according to one exemplary embodiment. 
     A GSM radio access network (GSM RAN)  110  can service multiple mobile subscribers such as a mobile station  104 . A base station subsystem (BSS) can handle traffic and signaling between a mobile station  104  and the telephone switching network. The BSS can include a base transceiver station (BTS)  112  providing multiple transceivers, antennas, and other radio equipment to support transmitting and receiving radio signals with the mobile stations  104  being serviced. A “Um” link, or air interface, can be established between each mobile station  104  and the BTS  112 . 
     A base station controller (BSC)  114  associated with the BTS  112  can provide control intelligence for the GSM RAN  110 . A BSC  114  can have multiple BTS systems  112  under its control. The BSC  114  can allocate radio channels, receive measurements from mobile stations  104 , and control handovers from one BTS  112  to another. The interface between a BTS  112  and a BSC  114  can be an “Abis” link. The BSC  114  can act as a concentrator where many Abis links can be aggregated and relayed to the network core. 
     A UMTS radio access network (UMTS RAN)  120  can provide another example of a base station subsystem (BSS). UMTS is an example of a third generation (3G) mobile communications technology. The UMTS RAN  120  can service mobile units, such as user equipment  108 . The air interface in a UMTS RAN  120  can be referred to as a “Uu” link. A UMTS base station subsystem can include a Node-B  122  and a radio network controller (RNC)  124 . A Node-B  122  and a RNC  124  can be interconnected by an “Iub” link. 
     An RNC  124  or BSC  114  can generally support as many as hundreds of Node-B  122  or BTS  112  respectively. A Node-B  122  or BTS  112  can generally support three or six cells, although other numbers may be used. Multiple GSM RAN  110  base stations or UTMS RAN  120  base stations can connect to either or both of a circuit switched core network  130  or a packet switched core network  150 . 
     A BSC  114  within a GSM RAN  110  can connect to a MSC/VLR  132  within a circuit switched core network  130  over an “A” Link. An “A” link can carry traffic channels and SS7 control signaling. Similarly, a BSC  114  within a GSM RAN  110  can connect to a serving GPRS support node (SGSN)  152  within a packet switched core network  150  over a “Gb” link. 
     An RNC  124  within a UMTS RAN  120  can connect to a MSC/VLR  132  within a circuit switched core network  130  over an “Iu-CS” link. Similarly, an RNC  124  within a UMTS RAN  120  can connect to a serving GPRS support node (SGSN)  152  within a packet switched core network  150  over an “Iu-PS” link. 
     Within the circuit switched core network  130 , the MSC/VLR  132  can interface to an equipment identity register  136 , a home location register  138 , and an authentication center  139 . The MSC/VLR  132  can also interface to a gateway mobile switching center  134  to access external circuit switched networks  140 . External circuit switched networks  140  may include Integrated Services Digital Network (ISDN) systems, Public Switched Telephone Network (PSTN) systems, and various other circuit switched technologies. 
     Within the packet switched core network  150 , the SGSN  152  can interface with a gateway GPRS support node (GGSN)  154  to access external packet switched networks  160 . External packet switched networks  160  can include the Internet, intranets, extranets, and various other packet data network technologies. 
     Referring now to  FIG. 2 , a mobile radio cell diagram illustrates cell reshaping for traffic balancing between neighboring cells according to one exemplary embodiment. A mechanism for load balancing can reshape neighboring cells to reallocate traffic from a highly loaded cell to a neighboring cell with spare capacity. For example, an initial cell structure  210  can be reshaped to a modified cell structure  220 . In the illustrated example, a reduction in the size and shape of CELL A and an increase in the size and shape of neighboring CELL C can provide a reallocation of traffic from CELL A to neighboring CELL C. 
     Cell coverage adjustment can be accomplished using pilot power adjustment. Pilot power can be adjusted between neighboring cells so as to displace the center point between the two cells. Shifting the center between the two cells closer to the overloaded cell can effectively reduce the size of the overloaded cell and thus reallocate traffic from that cell to the neighboring cell. 
     Cell coverage adjustment can be accomplished using antenna tilt. A remote electrical antenna tilt (RET) mechanism can provide a downward tilt to an antenna in an overloaded cell. Applying a downward tilt can reduce the propagation horizon of the antenna and effectively reduce the size of the overloaded cell. Such a reduction can support a reallocation of traffic from the overloaded cell to a neighboring cell. 
     Intra-frequency (IAF) neighbors, or those on the same carrier frequency, can be considered for neighboring load balancing. Inter-frequency (IEF) neighbors, or those on different carrier frequencies, can also be considered for neighboring load balancing techniques. 
     Coverage checks can be performed while adjusting cell coverage. When reducing pilot power or increasing antenna tilt for load balancing, there can be a reduction in cell coverage area and thus a risk of coverage loss in the network system. Likewise, when increasing the pilot power or reducing the antennae tilt, coverage area can be increased thus risking over-shots or excessive interference to neighboring cells. 
     A coverage check against reduced coverage or coverage loss can use any statistic that counts events triggered by call drop conditions falling below a certain poor quality threshold. For example, excessive inter-system handovers may indicate coverage loss. In such conditions, cell coverage reduction for load balancing can be avoided. 
     A coverage check against excess coverage or over-shoot can use propagation delay counters. When propagation delay is higher than a specified threshold a cell may be suffering from over-shoot. Also high up-link block error rate (UL BLER) or high mobile device transmit power can indicate that a cell may be suffering from over-shoot. When the cell suffers from overshooting or excessive overlapping, cell coverage increase for load balancing may cease. 
     Referring now to  FIG. 3 , a mobile traffic allocation diagram illustrates load balancing among three types of neighbors to rebalance traffic away from a congested cell according to one exemplary embodiment. A mechanism for load balancing can modify handover and reselection parameters after considering various handover and reselection thresholds. Such considerations can occur at the cell level or at the level of neighboring cells. The consideration can also occur at three different neighbor levels: intra-frequency (IAF) neighbors using the same carrier, inter-frequency (IEF) neighbors using different carriers, and inter-system (IS) neighbors in different radio access networks (RAN). Additional details related to interlayer handovers are disclosed in co-pending U.S. patent application Ser. No. 11/847,172, filed on Aug. 29, 2007, entitled “Optimization of Interlayer Handovers in Multilayer Wireless Communication Networks,” which is assigned to the assignee of the instant patent application and is expressly incorporated herein by reference in its entirety. 
     In the illustrated example, an initial traffic pattern  310  has eight mobile radios  305  in a central cell using the frequency F 1 . Other neighbors using the same frequency F 1  and intra-frequency (IAF) neighbors  320 A and have no mobile radio traffic. Neighbors using a difference carrier F 2  are inter-frequency (IEF) neighbors  330 A and also have no mobile radio traffic. Neighbors using other GSM systems are inter-system (IS) neighbors  340 A and also have no mobile radio traffic. 
     After a load balancing procedure, a load balanced traffic pattern  350  illustrates the same eight mobile radios  305  that have been handed over to neighbors to balance the traffic load. The load balanced IAF neighbors  320 B have three of the mobiles  305  allocated one each to each of three neighbors. The central neighbor among the IEF neighbors  330 B using F 2  has four of the mobiles  305 . Also, the nearest GSM neighbor of the other GSM IS neighbors  340 B has one of the mobiles  305 . 
     During the load balancing, cells can be collapsed or expanded to trigger handovers earlier or later than the original configuration. Handover and reselection parameters can be changed accordingly. This can maintain a match cell borders and reduce the volume of early handovers. Overloaded cells can be collapsed while low or medium loaded cells can be expanded. 
     IAF, IEF and IS neighbors may be treated differently by applying different threshold ranges. Neighbor level parameters can bias some neighbors against others and finely redirect traffic loads to less loaded neighbors. Cell level parameters can be used when neighbor level parameters are not available or when the neighbor level parameter adjustment is less inefficient in mitigating a given capacity problem. Neighbor parameters can be applied as offsets that are added to measured values for neighboring cells. Application of the offset can bias the cell using a positive or negative value. The cell border can be redefined unequally depending on the overlapping areas between neighbors. 
     Turning now to  FIG. 4 , additional details will be provided regarding the embodiments presented herein for improving system capacity within a mobile wireless radio network using load balancing. In particular,  FIG. 4  is a flow diagram showing a routine  400  that illustrates aspects of a process for load balancing in a mobile wireless network according to one exemplary embodiment. It should be appreciated that the logical operations described herein are implemented (1) as a sequence of computer implemented acts or program modules running on a computing system and/or (2) as interconnected machine logic circuits or circuit modules within the computing system. The implementation is a matter of choice dependent on the performance and other requirements of the computing system. Accordingly, the logical operations described herein are referred to variously as operations, structural devices, acts, or modules. These operations, structural devices, acts and modules may be implemented in software, in firmware, in special purpose digital logic, and any combination thereof. It should also be appreciated that more or fewer operations may be performed than shown in the figures and described herein. These operations may also be performed in parallel, or in a different order than those described herein. 
     The routine  400  can begin with operation  410  where performance parameters and configuration information is collected from the wireless network. The configuration and performance items may be retrieved, in whole or in part, from the operation and support system (OSS). Key performance indicators (KPI) can be collected to determine the need for system adjustments. Load balancing can be triggered by traffic congestion or over-utilization of neighboring cells. 
     A neighbor capacity KPI can be defined in two different ways. A first definition for the neighbor capacity KPI can apply the same capacity KPI used for the reference cell in the neighbor cell. A second definition for neighbor capacity KPI can be the average of each cell capacity KPI defined in the reference cell neighbor list weighted by the number of outgoing handovers to each neighbor. 
     At operation  420 , cell size and shape can be adjusted to balance traffic load between neighboring cells. Reshaping neighboring cells can reallocate traffic from a highly loaded cell to a neighboring cell with spare capacity. Cell coverage adjustment can be accomplished using pilot power adjustment. Pilot power can be adjusted between neighboring cells so as to displace the center point between the two cells to shift the center between the two cells closer to the overloaded cell and effectively reduce the size of the overloaded cell. Cell coverage adjustment can be also accomplished using remote electrical antenna tilt (RET) to provide downward tilt to an antenna in an overloaded cell. Applying a downward tilt can reduce the propagation horizon of the antenna and effectively reduce the size of the overloaded cell. 
     At operation  430 , handover and reselection can be adjusted to balance traffic load between neighboring cells after considering specified handover and reselection thresholds. The threshold comparisons and adjustments can occur at the level of a particular cell or at the level of a set of neighboring cells. Traffic reallocation can occur at three different neighbor levels: intra-frequency (IAF) neighbors using the same carrier, inter-frequency (IEF) neighbors using different carriers, and inter-system (IS) neighbors in different radio access networks (RAN). 
     At operation  440 , updated system configuration parameters can be generated according to adjustments determined in operation  420  and operation  430 . System parameters can be adjusted on two different levels. Firstly, parameters can be adjusted at the cell level. Secondly, neighbor level parameters can be adjusted. These neighbor parameters can be considered per adjacency relationship. 
     Generally, the step applied in updating configuration parameters can be small with respect to the range allowed for each parameter. Such a small step refinement can support slow convergence within the configuration update algorithm. A slow parameter convergence can minimize second order effects within the control system. 
     At operation  450 , the updated system configuration parameters as determined in operation  440  can be applied to the various configurable subsystems within the wireless radio network. Operation  460  can comprise a delay or wait cycle for the beginning of the next iteration period. The iteration period can determine the timing of the iterative process that collections system parameters and updates configuration parameters based on a periodic cycle. The period can be determined by a counter, timer, clock, real-time clock, interrupt, or other source of periodic scheduling or timing. 
     The performance parameters and KPI data can be collected for a predefined measurement period. Generally, a longer collection period can provide improved stability and reliability of the statistics. However, the increased collection period can provide a control system that is less reactive to changes. After operation  460 , the routine  400  can loop back to operation  410  to collect the next set of performance parameters. 
     Turning now to  FIG. 5 , an illustrative computer architecture  500  can execute software components described herein for improving system capacity within a mobile wireless radio network using load balancing. The computer architecture shown in  FIG. 5  illustrates an embedded control computer, a conventional desktop, a laptop, or a server computer and may be utilized to execute aspects of the software components presented herein. It should be appreciated however, that the described software components can also be executed on other example computing environments, such as mobile devices, television, set-top boxes, kiosks, vehicular information systems, mobile telephones, embedded systems, or otherwise. 
     The computer architecture illustrated in  FIG. 5  can include a central processing unit  10  (CPU), a system memory  13 , including a random access memory  14  (RAM) and a read-only memory  16  (ROM), and a system bus  11  that can couple the system memory  13  to the CPU  10 . A basic input/output system containing the basic routines that help to transfer information between elements within the computer  500 , such as during startup, can be stored in the ROM  16 . The computer  500  may further include a mass storage device  15  for storing an operating system  18 , software, data, and various program modules, such as those associated with the load balancing system  510 . 
     The mass storage device  15  can be connected to the CPU  10  through a mass storage controller (not illustrated) connected to the bus  11 . The mass storage device  15  and its associated computer-readable media can provide non-volatile storage for the computer  500 . Although the description of computer-readable media contained herein refers to a mass storage device, such as a hard disk or CD-ROM drive, it should be appreciated by those skilled in the art that computer-readable media can be any available computer storage media that can be accessed by the computer  500 . 
     By way of example, and not limitation, computer-readable media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. For example, computer-readable media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, digital versatile disks (DVD), HD-DVD, BLU-RAY, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer  500 . 
     According to various embodiments, the computer  500  may operate in a networked environment using logical connections to remote computers through a network such as the network  20 . The computer  500  may connect to the network  20  through a network interface unit  19  connected to the bus  11 . It should be appreciated that the network interface unit  19  may also be utilized to connect to other types of networks and remote computer systems. The computer  500  may also include an input/output controller  12  for receiving and processing input from a number of other devices, including a keyboard, mouse, or electronic stylus (not illustrated). Similarly, an input/output controller  12  may provide output to a video display, a printer, or other type of output device (also not illustrated). 
     As mentioned briefly above, a number of program modules and data files may be stored in the mass storage device  15  and RAM  14  of the computer  500 , including an operating system  18  suitable for controlling the operation of a networked desktop, laptop, server computer, or other computing environment. The mass storage device  15 , ROM  16 , and RAM  14  may also store one or more program modules. In particular, the mass storage device  15 , the ROM  16 , and the RAM  14  may store the natural language engine  130  for execution by the CPU  10 . The load balancing system  510  can include software components for implementing portions of the processes discussed in detail with respect to  FIGS. 1-4 . The mass storage device  15 , the ROM  16 , and the RAM  14  may also store other types of program modules. 
     Based on the foregoing, it should be appreciated that technologies for improving system capacity within a mobile wireless radio network using load balancing are presented herein. Although the subject matter presented herein has been described in language specific to computer structural features, methodological acts, and computer readable media, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features, acts, or media described herein. Rather, the specific features, acts and mediums are disclosed as example forms of implementing the claims. 
     The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.