Abstract:
A communication apparatus and method are provided for predicting effects of changes in at least one radio network parameter on a cellular network which comprises a processor which is adapted to: (a) select a source cell in a cellular network; (b) select from among a first plurality of cells being neighbors of that source cell, a second plurality of neighboring cells and define a reference cluster that includes the source cell and the second plurality of cells; and (c) use the reference cluster to predict the effects of carrying out one or more changes in at least one radio network parameter on at least one network performance indicator of the reference cluster, and based on that prediction, establishing an expected impact of the one or more changes in the at least one radio network parameter on a cellular network performance.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a system and a method for managing wireless networks, and in particularly to a system and a method for predicting and optimizing a performance of a cellular communication network. 
       BACKGROUND 
       [0002]    One of the major challenges which any cellular network operator faces is to ensure that the network is operating to its maximum efficiency. As a result, cellular network optimization is a major feature of many modern cellular networks. 
         [0003]    In order to provide the best possible performance to the cellular network subscribers, the network is periodically optimized so that its resources can be more effectively utilized within the core network and/or the Radio Access Network (“RAN”). 
         [0004]    Typically, network optimization is affected by manually modifying network parameters in the Radio and Core Networks based on information that relates to network performance. Such information is retrieved periodically and analyzed by the Operations and Support System (OSS) to derive Key Performance Indicators (KPIs) therefrom. The state of the art KPIs include typical system level (e.g. related to user or cell throughputs) and link level (e.g. various transmission error rates) metrics. 
         [0005]    Traditional optimization methods are slow, operate with a high degree of granularity, and have a long turnaround time. Optimization of a communication network using presently available tools basically entails changing one static parameter setup to another followed by several iterations of a cumbersome verification stage. 
         [0006]    In order to support rapidly changing network needs, it would be highly beneficial to have a fully integrated automated load balancing application with a built in feedback mechanism, thereby freeing the operators from their tedious roles of manual optimization to software applications and focus on defining network policies, performance goals and network plans. 
         [0007]    Several solutions have been proposed in the art for analyzing a wired/wireless communication network to optimize its performance. 
         [0008]    US 2005064820 describes continuously collecting data from all elements constituting the communication network and analyzing the data to find an element of which performance and/or efficiency deteriorates. 
         [0009]    US 2004085909 discloses scheduling transmissions in a wireless communication system using historical information and usage patterns of remote users in the system. Usage patterns for users within a system are stored and analyzed to optimize transmissions and resources in the system. 
         [0010]    US 2010029282 describes collecting various wireless performance metrics by respective network access points as an aggregate measure of the wireless network performance. Aggregated data can be utilized to generate a performance model for the network and for individual access points. Changes to the data are updated to the model to provide a steady-state characterization of network performance. Wireless resources are generated for respective access points in a manner that optimizes wireless performance. Additionally, resource assignments can be updated at various intervals to re-optimize for existing wireless conditions, whether event driven or based on performance metrics. Accordingly, a robust and dynamic optimization is provided for wireless network resource provisioning that can accommodate heterogeneous access point networks in a changing topology. 
         [0011]    US 20060068712 relates to a method of correlating probed data captured from various interfaces to create a combined picture at a call level. Thus, the method described allows real time distributed analysis and troubleshooting of the data on the interfaces of N radio network controllers from a single location. 
         [0012]    US 20080139197 discloses providing a probe application by a network server for downloading by a mobile device. The probe application monitors a level of performance for various use applications provided by the network for the mobile device, and reports the monitored level of performance for at least one of the applications to the network server. The network server collates the performance data from the plurality of communication devices and provides resource allocation instructions to the mobile in order to optimize a level of performance for the use applications for the communication device. 
         [0013]    Our co-pending application U.S. Ser. No. 13/680,779 filed Nov. 19, 2012 describes a computing platform for optimizing operation of a cellular network by: (a) probing for information exchanged between a mobile access network and a core network; (b) retrieving statistical KPIs generated by a plurality of network elements; (c) predicting a trend characterizing future performance of cells; and (d) triggering changes in the operation of the cellular network based on the predicted trend. 
         [0014]    However, there is still a need for a solution that provides further optimization capabilities for operating cellular networks, such that can take into account traffic load effects by using a pre-selected cluster of cells and using parameter settings derived from such considerations, thereby enabling further optimization of the performance of a network under near real time conditions. 
       SUMMARY OF THE DISCLOSURE 
       [0015]    The present invention addresses the shortcomings of the presently known methods by providing an automated solution for near real time optimization of wireless communication networks such as cellular networks as well as providing a solution for management of data bandwidth allocation. 
         [0016]    Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Methods, devices and systems similar or equivalent to those described herein can be used in the implementation or testing of the present invention. 
         [0017]    Implementation of the method, apparatus and system of the present invention involves performing or completing selected tasks or steps manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of the method and system of the present invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions. 
         [0018]    The disclosure may be summarized by referring to the appended claims. 
         [0019]    It is an object of the present invention to provide a method and apparatus to enable managing traffic load in a cellular network by diverting traffic between adjacent wireless cells. 
         [0020]    It is another object of the present invention to provide a method and apparatus to enable predicting the impact of off loading mobile users from one cell to another, upon the performance of the cellular network. 
         [0021]    It is still another object of the present invention to provide a method and apparatus to enable diverting data traffic of mobile stations between wireless cells that belong to a pre-determined cluster of cells. 
         [0022]    It is yet another object of the present invention to provide a method and apparatus to enable diverting traffic of mobile stations between wireless cells that belong to a cluster of cells, based on analysis that was carried for a different cluster of cells. 
         [0023]    Other objects of the present invention will become apparent from the following description. 
         [0024]    According to a first aspect, there is provided a communication apparatus operative to predict effects of changes in at least one radio network parameter on a cellular network which comprises one or more processors adapted to: 
         [0000]    (a) select a first cell (a.k.a. a source/main cell) in a cellular network;
 
(b) select from among a first plurality of cells being neighbors of said first cell, a second plurality of specific neighboring cells (preferably being communication-dependent on the first cell) and defining a reference cluster that includes the first cell and the second plurality of cells; and
 
(c) use the reference cluster to predict effects of carrying out one or more changes in at least one radio network parameter on at least one network performance indicator of said cluster, and based on that prediction, establish an expected impact of the one or more changes in the at least one radio network parameter on a cellular network performance.
 
         [0025]    It should be noted however, that the number of cells included in the first plurality of cells may be equal to or greater than the number of cells included in the second plurality of cells. 
         [0026]    In accordance with another embodiment, the cells which are selected from among the first plurality of cells to belong to the second plurality of cells, if: 
         [0027]    (i) a number of handovers carried out from the first cell to each of the selected second plurality of cells within a pre-defined period of time, divided by a total number of handovers carried out from the first cell to all of its neighboring cells belonging to the first plurality of cells within that pre-defined period of time exceeds a pre-defined threshold; and/or 
         [0028]    (ii) a geographical distance extending between said first cell and each of the selected second plurality of cells is equal to or less than a predetermined value. 
         [0029]    By yet another embodiment, the at least one radio network parameter being changed is offloading of communication traffic from the first cell to at least one cell from among the second plurality of cells. 
         [0030]    According to still another embodiment, the at least one radio network parameter is a member of the group that consists of: antenna tilt, pilot power usage and/or handover hysteresis offset between the first cell and the second plurality of cells. 
         [0031]    In accordance with another embodiment, the first cell is characterized by having radio resource utilization which exceeds a predetermined threshold. 
         [0032]    By still another embodiment, the one or more processor are adapted to repeat (c) until the expected impact on the cellular network performance, of the one or more changes in the at least one radio network parameter, is maximized. 
         [0033]    According to another embodiment, the at least one radio network parameter change leading to maximization of impact on the cellular network performance, is applied for optimizing cellular network performance associated with a second cluster. 
         [0034]    By yet another embodiment, the communication apparatus is adapted for use in a process of balancing a traffic load of the cellular network, wherein the one or more processors are further adapted to: 
         [0035]    (I) use the reference cluster to determine an effect of carrying out one or more changes in at least one radio network parameter on at least one network performance indicator of the reference cluster, and based on that determination, derive traffic load optimization rules for the cellular network; and 
         [0036]    (II) obtain at least one network performance indicator which is associated with the cellular network and optimize load performance of the cellular network according to the at least one network performance indicator and the load optimization rules. 
         [0037]    According to another aspect, a method is provided for predicting effects of changes in at least one radio network parameter on a cellular network, wherein the method comprises the steps of: 
         [0000]    (a) selecting a first (source) cell in a cellular network;
 
(b) selecting from among a first plurality of cells being neighbors of the first cell, a second plurality of specific neighboring cells being communication-dependent on said first cell and establishing a reference cluster that includes the first cell and the second plurality of cells; and
 
(c) using the reference cluster established to predict effects of carrying out one or more changes in at least one radio network parameter on at least one network performance indicator of the reference cluster, and based on that prediction, establishing an expected impact of the one or more changes in the at least one radio network parameter on a cellular network performance.
 
         [0038]    According to another embodiment of this aspect, the method provided is used in a process of balancing traffic loads in the cellular network, and wherein the method further comprising the steps of: 
         [0039]    (I) using the reference cluster to determine an effect of carrying out one or more changes in at least one radio network parameter on at least one network performance indicator of the reference cluster, and based on that determination, derive traffic load optimization rules for the cellular network; and 
         [0040]    (II) obtaining at least one network performance indicator which is associated with the cellular network and optimize load performance of the cellular network according to the at least one network performance indicator and the load optimization rules. 
         [0041]    By yet another embodiment, the method is used in managing data radio resources of a cellular network, wherein the method further comprising: 
         [0000]    (a) retrieving information that relates to: 
         [0042]    (i) radio resource load conditions of a cell; and 
         [0043]    (ii) radio conditions for each user of that cell; 
         [0000]    (b) identifying data-overloaded cells and correlating their associated information with that retrieved in (a); and
 
(c) ranking users of these cells according to their impact on radio load of the cell.
 
         [0044]    According to still another embodiment, the method further comprising: 
         [0000]    (d) limiting data provisioning to specific users of the cell based on step (c) and subscriber information associated with these specific users. 
         [0045]    It should be noted however, that even in case where no change in performed in any of the cells of the reference cluster, still, the invention should be understood to cover affecting changes at the source cell and impact the usage and loading pattern of cells in the area, in order to balance the load between the cells located in that area. This may in fact be regarded as being intra carrier spatial load balancing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    For a more complete understanding of the present invention, reference is now made to the following detailed description taken in conjunction with the accompanying drawings wherein: 
           [0047]      FIG. 1  illustrates a system that comprises a reference cells&#39; cluster including a source cell and its cluster-specific neighboring cells and the radio network and optimization network (cSON) servers; 
           [0048]      FIG. 2  is a flowchart outlining steps in the process of generating a reference cluster (A) and the use of specific rules in load balancing of traffic applied to a specific cluster (B); 
           [0049]      FIGS. 3-4  illustrate typical prior art architecture of PCRF/PCEF in an IMS framework; 
           [0050]      FIG. 5  illustrates one configuration according to an embodiment of the present invention which enables communication between the PCRF node and the cSON server of the present invention; 
           [0051]      FIG. 6  illustrates results of user&#39;s radio quality sampled over 3 minutes and their distribution per cells in the radio network. 
           [0052]      FIG. 7-10  illustrate the effect of load balancing as practiced using the solution of the present invention on radio resource load and relevant KPI trends. 
           [0053]      FIG. 11  illustrates daily hardware load patterns for a specific source cell of a cluster showing the effect of activating the load balancing (LB) algorithm in the last four days of monitoring (arrows). 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    According to one embodiment, the present invention relates to a system which utilizes predefined rules for near real time optimization of a cellular network performance. Specifically, this embodiment of the present invention can be used to automate the task of network performance optimization and provide in near real time network performance gains in cells that are characterized by suboptimal performance as indicated by relevant KPIs. 
         [0055]    The principles and implementation of the present invention may be better understood with reference to the drawings and accompanying descriptions. 
         [0056]    In this disclosure, the term “comprising” is intended to have an open-ended meaning so that when a first element is stated as comprising a second element, the first element may also include one or more other elements that are not necessarily identified or described herein, or recited in the claims. 
         [0057]    In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a better understanding of the present invention by way of examples. It should be apparent, however, that the present invention may be practiced without these specific details. 
         [0058]    Operators of cellular networks are facing nowadays an avalanche of demand, driven by the mobile data crunch—fast penetration of smartphones and mobile broadband. In order for them to support this increase in traffic, it requires to introduce proportional increase in resources, causing a linear increase in under-utilized resources. 
         [0059]    Cellular networks have dynamic RF traffic patterns that change throughout the week, and over the course of a day. Such dynamic patterns result from changes in voice and data communication loads, geographical changes in the position of the user equipment (UE) and the like. Unexpected load imbalances due to massive gatherings, cell malfunction or introduction of new cells in an area all effect the load distribution, and have to be dealt with as soon as they occur. 
         [0060]    In static networks with no time-sharing of resources, costly resources (e.g. cells) which can be used to support peak traffic are obviously often under-utilized. Although dimensioning rules dictate adding new cells or resources when peak capacity approaches saturation, the load in unbalanced networks is uneven, and hence dimensioning rules are not applicable. 
         [0061]    On the other hand, leaving the cellular network in unbalanced status without expansion, will limit the data/voice capacity that can be made available to subscribers at peak times, and consequently lower subscribers&#39; satisfaction leading to a possible loss of revenue. 
         [0062]    Existing optimization solutions are affected through large time cycles. It might take days or even weeks to optimize a network. By their very nature, such solutions are suitable for long term or predicted load issues and not for dealing with immediate load imbalances. 
         [0063]    Using decision-supporting software to perform the optimization calculations such as required expansions, RF parameter changes, and the predicted impact on performance, gives the radio engineers more optimization choices than using manual input. However, these tools provide reports—not actions, and are prone to error due to the high degree of sensitivity to initial conditions. The radio engineers are still left with the tasks of verifying the resulting recommendations, updating the cells configurations, and checking the results. This is an open-loop solution, where the entire end-to-end process still requires manual stages in order to complete it. 
         [0064]    Some equipment vendors offer solutions of inter-frequency load balancing. These solutions can balance loads between carriers—generally co-sectors on the same pole. 
         [0065]    These solutions, while efficient in resolving localized load imbalance cases, do not provide a solution for a load in a specific group of cells, require installation of infrastructure of multiple carriers, do not solve problems near the cells&#39; edges and do not optimize the utilization of a single carrier layer. 
         [0066]    For local areas with consistent capacity problems, operators can elect to offload the data portion to another layer such as Wi-Fi, LTE or small cells. However, in order to extract value from Wi-Fi offload mobile operators will require carrier-grade Wi-Fi networks that are tightly integrated into the operator&#39;s network and back office environments. In any case, such a solution can only add capacity to a fixed location, but does not provide a solution to congestion situations that change over time and place. 
         [0067]    The above described solutions are not designed to be compatible with the degree and extent of usage variations, typically encountered in present day cellular networks and have practical limitations such as required handset support or multi vendor functional complexities. 
         [0068]    To traverse these limitations of prior art optimization approaches, the present invention devised an automatic optimization solution (referred to herein as a self optimized network—SON) which can respond to demand patterns as they form and change. 
         [0069]    The present invention relates among others to a method (e.g. carried out as an algorithm, referred to hereinafter as LB algorithm) which comprises the following steps: 
         [0070]    (i) selecting a specific cell (typically a resource loaded cell) being a first cell and several of its neighbors (from among all its neighbors) and forming a cluster of cells where that specific cell is the main cell of the cluster; 
         [0071]    (ii) changing radio network parameters of the cluster; 
         [0072]    (iii) monitoring the effect of such changes on KPIs of the main (source) cell or cluster; 
         [0073]    (iv) repeating steps (ii) and (iii) until resource loading of the main cell (or cluster) is decreased. 
         [0074]    The results gained by following such a process can be applied to optimize performance of the same cluster following the cluster formation and at different time points (e.g. Example 3), as well as to optimize performance of an identical or similar cluster (or a main cell thereof). 
         [0075]    As further described in the Examples section which follows, use of the SON system of the present invention can lead to dramatic improvement in overall network resources&#39; utilization, reduction in the number of loaded cells and noticeable improvement in the end user QoE (Quality of Experience). 
         [0076]    Thus, according to one embodiment of the present invention there is provided a system for monitoring the effect of changes in radio network parameter(s) on manageable resources of a communication network such as a cellular network (which can include WI-FI, 802.11a/b/g/n, GSM, UMTS, EVDO, LTE, LTE-A, WiMax 802.16e and others). 
         [0077]    As used herein the terms “manageable resources” or “resources” refer to utilization (or over-utilization) of various network resources, including available transmission power of the base station power amplifier, baseband processing capacity available in the baseband hardware cards installed in the base station, available codes in the OVSF code tree in UMTS/CDMA technology, or available PRBs (Physical Resource Blocks) in LTE technology, or the accumulated uplink noise correlated to the carried traffic by the cell. Additional resources which can be affected and managed by the present invention include transmission (or backhaul) link to the base stations, RNC (Radio Network Controller) resources such as MP (Main Processor) load etc. 
         [0078]    As used herein the terms “Radio Network Parameters” and “radio parameters” interchangeably refer to various parameters which can have an effect on the consumption and performance efficiency of the cellular network resources. Such parameters include both software and/or hardware radio parameters, e.g. CPICH power settings, vertical tilt angle settings, handover threshold settings, handover offsets between different cells, and the like. 
         [0079]    Such radio parameters changes affect the network performance e.g. its ability to support voice and data communication with UEs, its power consumption, and all other network resources described above such as power usage, code usage, etc. 
         [0080]    The system according to an embodiment of the present invention includes a computing platform (e.g. hardware running a dedicated software application, for example a standard HP Proliant G7 server running the software application) which is in communication with the OSS (Operation and Support System) of the network. 
         [0081]    The computing platform is in communication with individual cells of the cellular network by direct connection to the network elements or through a mediation layer such as an OSS server connection and is capable of selecting a specific cell of a cellular network to be the first cell (a.k.a. source cell, main cell) according to one or more of the following criteria: 
         [0082]    (i) Power usage of the cell exceeds a pre-defined threshold; 
         [0083]    (ii) Code tree usage of the cell exceeds a pre-defined threshold; 
         [0084]    (iii) Baseband hardware resources of the cell exceed a pre-defined threshold; 
         [0085]    (iv) Transmission resources consumed by the cell exceed a pre-defined threshold; 
         [0086]    (v) Number of CS and/or PS links supported by the cell exceeds a pre-defined threshold; 
         [0087]    (vi) Number of HS (High Speed) links served by the cell exceeds a pre-defined threshold; 
         [0088]    (vii) Number/Percent of rejected PS/CS/HS establishment attempts which are rejected by the Admission Control mechanism implemented by the RNC or by the cell itself, exceeds a pre-defined threshold. 
         [0089]    (viii) Data Traffic payload to Voice traffic Erlang carried by the cell exceeds a pre-defined threshold. 
         [0090]    Once such a source cell is selected, the computing platform selects from a list of its neighbors (i.e. a first plurality of cells), a number of specific neighbor cells (being a second plurality of cells selected from the first plurality of cells) that are dependent on that source cell in as far as communication capabilities, i.e. neighbor cells that are RF related to the source cell. The selected neighbor cells are preferably cells that are highly coupled from RF perspective to the source cell. In other words, they have substantial overlapping with the source cell. This may be expressed by the relative number of handover attempts between any destination cell to the source cell. 
         [0091]    Selecting such specific neighbor cells may be done according to one or more of the following criteria: 
         [0092]    (i) Cells that are defined as intra frequency neighbor cells to the source cell either in the management system or by the cell itself (for example in the case of LTE ANR mechanism); and/or 
         [0093]    (ii) A weighting function is implemented for the neighbor cells and certain neighbors are selected according to a weighting ranking algorithm. A possible weighting function may be the relative number of HO attempts (or successes) between any relation to the overall number of HO attempts (or successes) measured for the cell. Another possible weighting function may be for example the relative number of measurement reports from UEs under the domain of the source cell that report the specific neighbor cell as present in the Active Set (for CDMA technology) or as exceeding a certain signal strength threshold (for any type of technology). Once the source cell and the specific neighbors are selected, the computing platform establishes a monitored cluster (also referred to herein as reference cluster) which comprises one or more of the following combinations: 
         [0094]    (i) the source cell and the specific neighbor cells; 
         [0095]    (ii) the source cell and all of the cells being a first degree neighbors of the source cell; and 
         [0096]    (iii) the source cell and a combination of cells that comprises first and second degree neighbors, or Nth degree neighbor of the cell according to their calculated weight, such that the final weight calculated for any specific neighbor is above a predetermined threshold. 
         [0097]    The cluster described above is monitored to identify effects of changes in the network parameter(s) on the operating performance within the cells belonging to the cluster being monitored or with the main cell of that cluster itself. The source cell/cluster performance can be measured either by retrieving values of KPIs collected from the OSS system, or by any other near real time means such as probe based calculated KPIs, to identify the impact of changes induced in the network parameter(s) on the cellular network. The relationship between the changes of the parameter(s) and KPIs may be used to establish a set of optimization rules which are applied to the cluster in a continuous fashion until a performance thereof or of its source cell is optimized. 
         [0098]    Such optimization rules may include, but are not limited to, the following: 
         [0099]    (i) change of CPICH (Common Pilot Channel) by −Δ 1 dB for the source cell, and +Δ 2  dB for the selected neighbor cells; 
         [0100]    (ii) change HO offset for the source cell by −Δ 1 dB, and +Δ 2  dB for the selected neighbor cells; and/or (iii) change tilt by −Δ 1 ° for the source cell and by −Δ 2 ° for the selected neighbor cells. 
         [0101]    Some or all of the above optimization steps can be repeated in a predefined order, until the cause of source cell over-utilization (loading), e.g. power load, falls below a threshold, or until performance degradation occurs. Once performance degradation is detected, the system reverts to the last change prior to that degradation. This is implemented using a feedback function which constantly monitors the reference cluster performances in terms of for example drop call rate, number of voice and data calls, HS payload and throughput. In addition, under-layer cells to the reference cluster cells may also be monitored, such as cells associated with another layer (e.g. GSM or another UMTS carrier) to confirm that no change in the KPI pattern has occurred in those under-layer cells. 
         [0102]    A system for modeling and optimizing a communication network, which is referred to herein as system  10  is illustrated in  FIG. 1 . 
         [0103]    System  10  includes a cluster of cells  12  which includes a source cell  14  and several (typically, between 4-6) neighbors&#39; cells  16 . The neighbors can have the same frequency as the source cell (referred to herein as “Intra cluster”) or a different frequency (referred to herein as “Inter cluster”), or there may be cases where different technologies is implemented in one or more of the neighbor cells from that of the source cell (referred to herein as “iRAT cluster”). 
         [0104]    Each of cells  14  and  16  is in communication with the radio network controller  18  (RNC) or another equivalent mobility control entity, or OSS, or cSON server, in other technologies, which is in turn connected to the core network servers  20  and the OSS servers  22  which include an OSS database  24 . 
         [0105]    For a cSON server, all the coordination is carried out internally, since the cSON server is operative to control directly control all the cells in the network, and can have a centralized view of the KPI effect to any change in performance resulting from radio parameters&#39; changes. In a non centralized configuration of SON, a communicating and coordinating function between SON functions which control subset of the network may be used, to allow site specific load balancing activities, and performance monitoring. 
         [0106]    A flow chart illustrating a cluster setup is shown in  FIG. 2  (steps  1 - 5 ). The present system (referred to as system  50 —further described hereinbelow) is synchronized every several minutes (e.g. 3-10 minutes) with OSS  24  in order to obtain KPIs of the network (step  1 ). In step  2 , the system monitors all cells of a network for load metrics (monitoring is implemented by applying specific load balancing (LB) algorithms which are executed by cSON server  52 ), thereafter congested cell (or cells) are identified by cSON  52  (step  3 ) based on load metrics. Such a congested cell will be determined to be the source cell. If no source cell is identified, system  50  reverts to step (step  4 ). The LB algorithm of the present invention then identifies the relevant offloading neighbor cells to the source cell and determines their loading status (step  5 ); the source cell and its offloading neighbors and then defined as the cluster to be monitored. 
         [0107]    As mentioned hereinabove, such a cluster can be used for optimizing the performance of the source cell and/or of the cluster and/or a source cell belonging to an identical or similar cluster. 
         [0108]    Thus, according to another aspect of the present invention there is provided a system for optimizing network performance in a cellular network. 
         [0109]    System  50  illustrated in  FIG. 1  includes an optimization server (cSON)  52  and database  54  communicating with OSS servers  22 . 
         [0110]    Load balancing optimization is based on constant KPI monitoring. Therefore, system  50  continuously extracts KPI values from the network (from the performance management database of OSS  20 ) and provides these KPI values to the SON application for analysis. A load balancing application executed by server  52  checks a list of load and admission control statistics (which are stored at cSON DB  54 ), and compares them to thresholds configured by cSON users (e.g. optimization engineers running the cSON system on a routine basis). When any of these thresholds are exceeded in any cell of the network, this cell is determined as a “source cell”, cells (selected neighbor cells of the source cell) are added to a work list, and the application initiates re-balancing of network resources&#39; consumption of users by means of RF shaping of the loaded cell and the surrounding cells. By fine tuning the settings of these thresholds, the operator can deal with load conditions even before the load can actually be felt by subscribers. The performance of the re-balancing process highly depends on the accuracy of the neighbor relation lists and on the configured time constants of the application. 
         [0111]    System  50  provides a near-real time response (typically minutes) to the rapidly changing and unpredictable load demands imposed on the network. The Load Balancing application of server  52  modifies the RF footprint of the loaded and surrounding cells to fit the current usage demand and match the subscriber distribution to the available resources. Using RF shaping increases the efficiency of the network, and increases the utilization of existing resources. 
         [0112]    The Load balancing application of server  52  determines the RF parameters for the loaded cell and its neighboring cells based on the KPI and PM data collected from the OSS. 
         [0113]    In order to ensure that RF shaping may indeed be carried out without damaging the quality of service for cell edge users, namely—loose coverage, the solution provided by the present invention enables utilizing a metric of cells&#39; overlap which has to exceed a threshold before a load balancing procedure may be initiated. In a UMTS (Universal Mobile Telecommunications System) for example, this metric is calculated as the Soft Handover Factor of the source cell and is used to indicate the influence of soft handover exerted on NodeB CE and to evaluate the subscriber resource utilization. If this Soft Handover factor is high enough, e.g. &gt;1.6, then the load balancing procedure may be executed when this cell becomes congested. 
         [0114]    Optimization of a cluster is described by steps  6 - 10  of the flow chart of  FIG. 2 . Using the cluster generated in steps  1 - 5 , the LB algorithm then changes the radio parameters of the cluster to implement traffic offloading from the source cell to its less loaded neighbor(s) (step  6 ). Source cell and/or cluster performance is then monitored (step  7 ) and a determination is made (based on a performance threshold) whether to implement further changes to enable further offloading, to remain at last state, or to revert to the previous state (by canceling the parameter change). Steps  6 - 7  are then repeated until a performance threshold is achieved as determined by the rate of successful call initiations or any other applicable measure (step  8 ). If degradation in the quality of service occurs, system  50  reverts to the initial radio parameter settings (step  9 ). If the system cannot obtain KPIs for a predetermined time period, the status is reset and the cluster is reverted to its initial radio parameter settings (step  10 ). 
         [0115]    The above description relates to optimization procedure of a generated cluster, by conducting several iterative steps of parameters&#39; changes and KPI monitoring. However, it should be noted that the results obtained from optimizing such a cluster (termed herein as a reference cluster) can be applied to optimizing network performance of other loaded cells that can form a cluster similar to or identical to the currently optimized cluster. 
         [0116]    For example, clusters in which the user radio map and radio resource utilization of the cells are substantially identical to that of the reference cluster can be generated (as described in steps  1 - 5 ) and then be optimized by simply applying the radio parameter changes that lead to successful optimization of the reference cluster. This negates the need for the time consuming iterative process described in steps  6 - 8  of  FIG. 2 . The user radio map and radio resource utilization of substantially identical clusters can be determined by comparing the overall distribution of quality metric such as Ec/Io and signal strength indicator such as RSCP. 
         [0117]    In another example, in cases where the load balancing procedure is triggered repeatedly every day at same cell ( FIG. 11 ), the parameter change information can be used to drive coverage and capacity optimization (CCO) in order to plan and implement (automatically) a constant change to the RF footprint of the source cell and of some of its neighbor cells by using a single step. In such cases, predetermined radio parameter changes can be applied to specific clusters at specific times of the day, or days of the week, without having to go through the iterative optimization steps as depicted in  FIG. 2 . 
         [0118]    According to an embodiment of the present invention, the system provided can identify different cluster types and store information that relates to such clusters along with information on optimization and various radio parameters (e.g. user radio map and radio resource utilization) at a database. 
         [0119]    The clusters can then be categorized according to one or more of the following: 
         [0120]    (i) voice and data traffic being conveyed within the cluster; 
         [0121]    (ii) traffic distribution between the cells that belong to the cluster; 
         [0122]    (iii) radio conditions of each cell comprised the cluster and of the cluster in overall; 
         [0123]    (iv) handover statistics and soft handover (SHO) factor between the cells that belong to the cluster; 
         [0124]    (v) radio resources configuration of the cells included within the cluster; 
         [0125]    (vi) radio hardware configuration of the cells included within the cluster; and 
         [0126]    (vii) radio software parameter settings of the cells included within the cluster. 
         [0127]    Once a specific cluster category is generated, it can be used later on e.g. in other SON applications. 
         [0128]    The database may also be used to store details associated with the SON activity (for example, LB procedures activated per cell in the cluster) for each cluster configuration as well as performance metrics (KPIs) for each cluster. The system can also generate and store KPI performance trends for each cluster type, and create a predictive function that will enable predicting the KPI behavior of any cluster based on similar cluster types stored in the DB. 
         [0129]    It will be appreciated by those skilled in the art that although load balancing according to the present invention can be applied to substantially enhance the performance of the network and thus to better accommodate the subscribers&#39; demands, mobile operators today are facing an avalanche of demand which is driven in part by heavy mobile data demand. Thus, to further support this increase in data traffic, the solution provided by the present invention also offers a novel approach for enhancing policy control and resource management in cellular networks. 
         [0130]    At present, operators utilize a node or nodes for policy and charging rule function (referred to herein as PCRF) and DPI techniques to restrict and manage data sessions regardless of radio resource consumption. In presently deployed 3G/4G mobile networks, data traffic is streamed from the user through the radio network (UTRAN/E-UTRAN) and packet core (PS-Core/EPC) to the Internet. 
         [0131]    An IP multimedia subsystem (IMS) is a framework defined by 3GPP Standard to provide Internet and data services over cellular networks. Part of the IMS framework is the PCRF/PCEF which relates to two nodes configured to provide a platform for policy and charging rules function (PCRF) and policy and charging enforcement function (PCEF). The PCRF node determines, in real time and according to various considerations, a set of rules governing the way that data user traffic is handled. Such considerations normally include subscriber&#39;s subscription data (from HSS), QoS approved level, network load, operator service policy etc. 
         [0132]    The main purpose of the PCRF is to enable management of the core network resources effectively in order to provide the best suited Quality of Service to users of data services. 
         [0133]    A typical architecture of PCRF/PCEF in IMS framework is illustrated in  FIGS. 3 and 4 . The PCEF node is designated to perform DPI (Deep Packet Inspection) into user traffic and enforce the rules created by the PCRF in real time. The PCRF node interacts with various network elements and uses several types of information, such as user&#39;s subscription records, allowed QoS levels for users and prioritization of services. The PCRF utilizes this information to create rules for enforcing bandwidth consumption limits per user (per PDP context) which are compatible with the user&#39;s contractual terms and with the operator&#39;s services&#39; priorities, e.g. VoIP is prioritized over Streaming etc. 
         [0134]    For example, service providers can use PCRF to charge subscribers based on their volume of usage of high-bandwidth applications, charge extra for QoS guarantees, restrict applications&#39; usage while the user is roaming, or lower the bandwidth of wireless subscribers using heavy-bandwidth apps during peak usage times. PCRF can also be used to restrict user data traffic selectively to handle load situations in networks. 
         [0135]    Currently the PCRF and PCEF nodes are not “aware” of cases in which overloaded cells are serving users with low bandwidth needs in low coverage areas. Such users may overload the radio resources of a cell which is designed to limit high bandwidth users that are near the cell. 
         [0136]    The present invention provides a solution to such cases by managing specific data links that consume radio resources in order to reduce traffic loads from cells having high radio-resource utilization. This is achieved by providing the core bandwidth management systems (PCRF and PCEF) with information regarding users in specific radio-overloaded cells (e.g. with very limited remaining-radio resources), allowing such systems to apply specific policies to users who consume radio-resources for reducing the radio-resource loads on such cells. 
         [0137]      FIG. 5  illustrates one approach for enabling communication between the PCRF node and the cSON server of the present invention thus making the PCRF ‘aware’ of users in specific cells that have high radio-load information in the UTRAN. The information communicated from the cSON server to the PCRF node preferably includes cell level details of radio-resource loads for each and every cell, as well as radio resource consumption data for users present in each cell at any given moment. The PCRF node can use this information to selectively restrict specific users consuming high radio resources, to identify users consuming lower priority services, or users having a lower priority SLA (Service Level Agreement) in order to make sure that users of high priority SLAs are provided with the best data service. 
         [0138]    To enable such optimization of data bandwidth provisioning, the cSON server may periodically provide the PCRF node (under near real time conditions) with UTRAN and UEs load information such as: 
         [0139]    (i) list of all cells and their radio resource load conditions (power, channel elements, codes) and backhaul; and/or 
         [0140]    (ii) list of all users identified by IMSI (unique UE identifier). 
         [0141]    For each user the information may include: 
         [0142]    (1) To which cell is the user connected in the sampled time period (in cases where a user was identified in different cells during the sample time period, the identification of the latest cell is provided). Optionally, a “mobility filter” may be applied, by which, if during the sample time the user is active in a number of cells and this number is higher than a threshold, then user will be designated as a “high mobility user”. 
         [0143]    (2) The measured radio conditions for the user in the last serving-cell (average during relevant sample time). 
         [0144]    (iii) cSON Load balancing activity status on all the cells (e.g. is it active at the cell, what action was performed, etc.). 
         [0145]    The PCRF node then assess which cells are overloaded from data backhaul and data usage perspective (may be based also on information retrieved from other sources) and correlates this information with information provided by the cSON (as discussed above). For each loaded cell having also radio resource loaded, the PCRF node uses the provided subscriber potential load information in conjunction with other subscriber related information, to determine to which of the subscribers active in a certain cell, their activity will be restricted in that cell. 
         [0146]    By applying selective restriction on a “per user” basis to the RR loaded cells, the actions taken by the PCRF node are more accurate and will ensure efficient usage of the UTRAN radio resources in compliance with the operator charging, service priorities and user SLAs according to their contracts. 
         [0147]      FIG. 6  illustrates user radio quality sampled over 3 minutes and their distribution per cells in the radio network. The average quality (Avg Quality) indicates the users&#39; potential to consume high radio resources even while using low bit rate applications; the PCRF node will prioritize restriction of the activities of users with low Avg quality. 
         [0148]    Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. 
       EXAMPLES 
       [0149]    Reference is now made to the following examples, which, together with the above description illustrate the invention in a non limiting fashion. 
       Example 1 
     Cluster Setup 
       [0150]    In order to create a reference cluster for a congested cell, the system considers all the neighboring cells of that cell, e.g. cells that are defined by the OSS as being neighbors of this cell. Then, for each one of the neighbors, the system calculates a weighing function. The weighting function represents the intensity of the RF influence on users connected to the source cell, from a respective neighbor cell. For example, if for source cell A the weight of neighbor cell B is 10%, it means that in a given time interval (which is typically the weighing averaging window) 10% of the users which were connected to A, would experience B as the strongest neighbor or one of the top N strongest neighbors [where N depends on the active set size parameter which is defined in the RNC]. According to neighbor weights, the system selects the top weighted M (M=5 typically) neighboring cells, and relates to those cells as being the cluster neighbors for traffic offloading and for performance monitoring. 
       Example 2 
     Load Balancing 
       [0151]    In this example, two clusters (specified in tables 1 and 2) were generated, monitored and optimized using the LB algorithm in accordance with an embodiment of the present invention. 
         [0152]    Main Cell 103417060299 (Table 1) had a power load which exceeded the defined power load threshold. The system identified the top 5 neighbors of this main (source) cell according to their weight (Table 1). Additional filtering of the top 5 neighbors in the reference cluster was performed by selecting neighbors that can be used for offloading traffic from the source cell. Only neighboring cells which were not congested were selected for offloading traffic as shown in Table 1. The system then determined the action needed for each neighbor. The action in this case was to change the CPICH (pilot channel) transmission power from its current value by some offset in dB. 
         [0153]    Once all radio parameter changes were applied by the system to neighbor cells, performance is monitored and a return (to initial settings) cause is logged. The same procedure was applied to the cluster of Table 2. 
         [0154]    Cluster of Table 1 relates to return to initial settings following normal LB timeout (4 h). In the cluster of Table 2, there is an abnormal return as the system had identified missing KPI samples which led to its inability to monitor the performance effect of LB. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Neighbor cell 
                 Neighbor 
                 Selected 
                   
                   
               
               
                 Main cell id 
                 Load Trigger 
                 id 
                 weight 
                 for LB 
                 Cause/Action 
                 Revert cause 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 103417060299 
                 ‘load_power’ 
                 Main cell - 103417060299 
                 Yes 
                 level 1 
                 Feedback 
               
             
          
           
               
                   
                 103417062599 
                  5.3%; 
                 No 
                 CPICH 298 of neighbor 
                 ended 
               
               
                   
                   
                   
                   
                 is already at its 
                 After 4 hours 
               
               
                   
                   
                   
                   
                 maximum. Can&#39;t 
               
               
                   
                   
                   
                   
                 increase it 
               
               
                   
                 103417063198 
                 14.9%; 
                 No 
                 Discarded neighbors - 
               
               
                   
                   
                   
                   
                 ‘is_active’ 
               
               
                   
                 103417061697 
                 36.4%; 
                 Yes 
                 Changing CPICH of 
               
               
                   
                   
                   
                   
                 neighbor from 240 to 
               
               
                   
                   
                   
                   
                 245 
               
               
                   
                 103417061609 
                  7.9%; 
                 No 
                 CPICH 305 of neighbor 
               
               
                   
                   
                   
                   
                 is already at its 
               
               
                   
                   
                   
                   
                 maximum. Can&#39;t 
               
               
                   
                   
                   
                   
                 increase it 
               
               
                   
                 103417060298 
                 10.40%     
                 No 
                 CPICH 305 of neighbor 
               
               
                   
                   
                   
                   
                 is already at its 
               
               
                   
                   
                   
                   
                 maximum. Can&#39;t 
               
               
                   
                   
                   
                   
                 increase it 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Neighbor cell 
                 Neighbor 
                 Selected 
                   
                   
               
               
                 Main cell id 
                 Load Trigger 
                 id 
                 weight 
                 for LB 
                 Cause/Action 
                 Revert cause 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 103449005187 
                 ‘load_power’ 
                 Main cell - 103449005187 
                 Yes 
                 level 1 + level 2 
                 “Cell had too 
               
             
          
           
               
                   
                 103449033057 
                 6.50% 
                 No 
                 Discarded neighbor - 
                 many missing 
               
               
                   
                   
                   
                   
                 ‘load_power’ 
                 KPIs and will be 
               
               
                   
                 103449032028 
                 5.10% 
                 Yes 
                 Changing CPICH of 
                 reverted” - After 
               
               
                   
                   
                   
                   
                 neighbor from 300 to 
                 50 Min. 
               
               
                   
                   
                   
                   
                 305 
               
               
                   
                 103449002268 
                 5.30% 
                 Yes 
                 Changing CPICH of 
               
               
                   
                   
                   
                   
                 neighbor from 310 to 
               
               
                   
                   
                   
                   
                 312 
               
               
                   
                 103449031459 
                 6.60% 
                 No 
                 CPICH 310 of neighbor 
               
               
                   
                   
                   
                   
                 is already at its 
               
               
                   
                   
                   
                   
                 maximum. Can&#39;t 
               
               
                   
                   
                   
                   
                 increase it 
               
               
                   
                 103449031398 
                 11.80% 
                 Yes 
                 Changing CPICH of 
               
               
                   
                   
                   
                   
                 neighbor from 281 to 
               
               
                   
                   
                   
                   
                 286 
               
               
                   
                 103449032029 
                 16.80% 
                 No 
                 Discarded neighbor - 
               
               
                   
                   
                   
                   
                 ‘load_power’ 
               
               
                   
                 103449005188 
                 16.70% 
                 No 
                 CPICH 316 of neighbor 
               
               
                   
                   
                   
                   
                 is already at its 
               
               
                   
                   
                   
                   
                 maximum. Can&#39;t 
               
               
                   
                   
                   
                   
                 increase it 
               
               
                   
                 103449030707 
                 5.80% 
                 No 
                 Discarded neighbor - 
               
               
                   
                   
                   
                   
                 ‘load_power’, ‘is_active’ 
               
               
                   
                   
               
             
          
         
       
     
         [0155]      FIGS. 7-10  illustrate the effect of load balancing using the system of the present invention solution on KPIs and load metrics (as derived from OSS) of the cells described in Tables 1 and 2 above. Numbers on the right of the Figure note the cell ID which corresponds to the cell ID in the Tables. 
         [0156]      FIG. 7  illustrates the power load of the main cell of the cluster and its neighbors (presented in Table 1). As shown in this Figure, applying the LB algorithm in accordance with the solution provided by the present invention starting at 1:30:00, resulted in a dramatic decrease of traffic load in the main cell of main (source) cell &#39;299, without overloading the neighbor cells. 
         [0157]      FIG. 8  illustrates the power load of the main cell of the cluster and its neighbors (Table 2 without discarded neighbors) showing that application of the LB algorithm of the present invention solution resulted in a load drop. However, due to the fact that KPIs could not be retrieved for the main cell of this cluster following time point 11:15:00, the system stopped the LB application and reverted to its initial settings. 
         [0158]      FIG. 9  illustrates power load vs. RRC_Succ (Accessibility KPIs—indicates rate of successful call initiation) for main cell 187 (Table 2). As illustrated in this Figure, application of the LB algorithm of the present invention resulted in power load decrease and a significant increase in RRC_Succ. As was noted for  FIG. 8 , KPIs for this source cell could not be retrieved beyond time point 11:15:00 and as such the system reverted to its initial settings. 
         [0159]      FIG. 10  illustrates the same monitoring for main cell 299 of Table 1. As illustrated in this Figure, activation of LB algorithm (at time point 1:30:00) resulted in a decrease in power load and increase in RRC_Succ. 
       Example 3 
     Load Balancing-Reduced Hardware Load 
       [0160]      FIG. 11  illustrates the effect of applying the LB algorithm on the same cluster at specific time points during the day, the last 4 peaks in the graph represent days in which the present load balancing algorithm was utilized to reduce load of a main cell. In this case LB action can be permanent, subject to the rules and conditions of the CCO (Coverage and Capacity Optimization) platform. This is due to the fact that LB changes are consistent at a specific time point each day (busy hour) and as such, the same radio parameters can be applied at these time points. 
         [0161]    In the description and claims of the present application, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. 
         [0162]    The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention in any way. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.