Method and apparatus for steering idle mobile stations

Related Application This application is related to US Patent Application No. 11 / 010,564 by the same applicant with the title "Methods and Devices for Steering Idle Mobile Stations" (Agent Docket No. 2380- 855), the contents of which are incorporated herein by reference.

Technical Fields The present invention relates to mobile communications and, in more detail, to an idle mobile station to another geographical service area, such as a cell, location area (LA), or routing area (RA). Regarding inducing.

Background and Overview Current mobile stations (sometimes referred to as mobile terminals (MTs) or user devices (UEs)) can often connect to and communicate with two or more different types of radio access networks. .. Examples include second generation (2G) radio access networks such as the Pan-European Digital Mobile Phone System (GSM), Digital Advanced Mobile Phone System (D-AMPS), or Personal Digital Cellular System (PDC), and, for example, Universal Mobile. There are dual-mode mobile terminals that can connect to 3rd generation (3G) radio access networks such as the Telecommunication System (UMTS) Terrestrial Radio Access Network (UTRAN). Other radio technologies such as Bluetooth® or 802.11 may be used. An environment that allows access to two or more wireless access technologies (RATs) is called a multi-access environment.

In GSM / GPRS and WCDMA systems, mobility management is related to the state of the mobile station. Generally, when a mobile station is "attached" to a network, the mobile station is either in an idle / ready state or in a connected / active mode. In the idle / ready state, the mobile station is not engaged in an active connection (eg, communicating with other subscribers). In connect / active mode, the mobile station is engaged in an active connection (eg, communicating with other subscribers) and is serviced by the network. The state of the mobile station may have a different name (label) for each system, but the term "idle" mobile station means that the mobile station is powered on but actively participates in communication. Used to cover mobile stations in all states that are not. Mobile subscriber (mobile) In order to receive service when a subscriber) wishes or a call to a mobile subscriber occurs, the mobile station selects a cell while idle and registers in that cell to "camp on". (Camp on) "can be done. Camping is a mode adopted by a mobile station after it has been registered in the cell. Non-limiting examples of idle mobile stations that have selected cells to receive service include idle, ready, standby, CELL_FACH, CELL_PCH, and URA_PCH states.

The mobile station is broadcast by various cells in the idle state, including currently located or registered cells, and adjacent cells to determine whether to select another cell in the service area. Read (all or part of) the system information. If an idle mobile station decides to select another cell in the area, the process may be called cell re-selection. When cell reselection occurs, the network receives a location update message from the mobile terminal and updates the stored location information (eg, cell, location area, routing area, etc.). Location information can be used to page a mobile station.

Ideally, network operators divide subscribers into different service categories, for example, "gold / silver" contracts, when directing or directing mobile subscribers between networks that use different wireless access technologies. You may prefer to have overall flexibility, such as. This would mean that some mobile stations will be in UMTS-based cells as long as they are in the UMTS coverage area while idle. On the other hand, the idle mobile station of the low priority subscriber is guided to be in the GSM / GPRS cell. Even these low-priority subscribers may move to UMTS cells when requesting certain services.

It is important to balance the load of the entire network among the various cells in the network in order to provide satisfactory services to mobile subscribers and maximize the capabilities of the mobile communication network. It is desirable to direct or steer the mobile terminal from the current cell to a neighboring or overlapping cell with a lower load when the load in the current cell exceeds a certain threshold. Let's go. Moving an active mobile station with an active connection between cells is particularly about moving (switching) from one wireless access technology system cell to another wireless access technology system cell (eg WCDMA to GSM). ) Is done, it requires a lot of signaling. Moving an active subscriber ensures that the promised quality of service is maintained with respect to that active connection, so that the connection between the mobile terminal and the network is performing a switch between systems. It also requires that it be maintained at all times. This consumes a lot of resources in both the core network and the wireless network.

<p> A better solution for satisfying subscriber preferences and network operator preferences, providing subscription services, and achieving network management type features such as load redistribution. To dynamically distribute or "guide" an idle mobile station to a particular cell or area. For example, an idle mobile station may be directed to a lighter load monitoring area (eg, cell, location area, etc.) in the same or different network.</p><p> In a non-limiting example, it is provided by one or both of the first broadcast signal in a cell in the first load monitoring area and the second broadcast signal in a cell in the second load monitoring area1 Based on the above parameters, when the mobile station is in the state of selecting the cell to be serviced, the mobile station is distributed among the load monitoring areas. The load on the first area where one or more mobile stations are currently located is determined. In order to reduce the load on the first area (eg, the load monitoring area where the load is too high or otherwise exceeds the threshold), some mobile stations are replaced with a second (preferably lower load). ) One or more parameter adjustments in one or both broadcast messages are initiated to direct the user to be in the load monitoring area.</p><p> The first and second load monitoring areas may be cells, location areas, routing areas, or service areas. This coordination can be initiated based on load information from the core network node, radio access network node, or central server. In a preferred, non-limiting example application, the first load monitoring area is associated with a first mobile communication network that provides a first set of services, and the second load monitoring area is It is associated with a second mobile communication network that provides a second set of services. Of course, this methodology is extensible to third and higher (additional) communication networks, especially if the contracted service is available from the additional network.</p><p> The first mobile communication network can adopt the first wireless access technology, and the second mobile communication network can adopt the second wireless access technology. For example, the first mobile communication network may be a second generation based network and the second communication network may be a third generation based network. The first and second service sets may be different or the same.</p><p> Coordination instructions are based on the exchange of load information between the first radio access network node in the first mobile communication network and the second radio access network node in the second mobile communication network. May be good. Alternatively, the adjustment instruction may be based on the load information from the core network node or the load information from the central server.</p><p> As an implementation example of adjusting broadcast parameters, offsets can be applied to broadcast parameters. Offset parameters can be added or subtracted from the signal measured by the mobile station for cell selection or cell reselection procedures. The frequency of changes in which the broadcast parameters are changed can be controlled to avoid unnecessary battery consumption in the idle mobile terminal.</p>

Detailed Description The following description describes, for example, specific details such as specific embodiments, procedures, techniques, etc., but this is for illustration purposes only and not for limitation purposes. Those skilled in the art will appreciate that other embodiments that depart from these particular details are also available. For example, the following description is given using a non-limiting example of GSM / GPRS / UMTS, but wireless access technologies other than GSM / GPRS / UMTS can also be used. In addition, the principles described can be adopted in communication systems that use only one type of wireless access technology, or in communication systems that combine a number of different wireless access technologies.

In some examples, detailed descriptions of well-known methods, interfaces, circuits, and signaling are omitted, which avoids obscuring the description with unnecessary details. In addition, individual blocks are shown in the figure. For those skilled in the art, the functionality of these blocks can be implemented using separate hardware circuits or by using software programs and data with a well-programmed digital microprocessor or general purpose computer. You can see that it can be implemented using application specific integrated circuits (ASICs), and it can also be implemented using one or more digital signal processors (DSPs).

FIG. 1 is a diagram showing a communication system 10 including one or more core networks 12 coupled to two radio access networks (RANs) 14 and 16 labeled RAN1 and RAN2. In this example, the radio access network 1 uses the radio access technology 1 (RAT1) and the radio access network 2 uses the radio access technology 2 (RAT2). RAT1 and RAT2 may support the same wireless access technology or may support different wireless access technologies. RAN1 supports several cells 20, labeled cells A, B, and C as examples. Similarly, the radio access network 16 supports several cells 22 labeled, for example, cells 1, 2, and 3. Each network can support a routing area (RA) containing one or more cells, and can also include one or more location areas (LA) containing one or more routing areas. UMTS also allows core network nodes to monitor load in the service area (SA). Balancing the load is desired based on cell broadcast, cell reselection, mobility management, and other features that exist for air interfaces, cell level, location area level, routing level, or any other. It can be improved by using idle mobile station guidance at the geographic service / coverage level. For the sake of brevity, any such area is referred to as the load monitoring area.

Each cell produces a broadcast message. For the sake of brevity, one multimode radio station 24 is shown to receive and detect broadcast messages from cells B, C, and 1. The multimode radio station 24 can communicate with any radio access network and receive services from it, even if the radio access technology of each radio access network is different. The multimode wireless terminal 24 is in an idle state. That is, it is in a state where it is possible to register and select a cell in the service area. For example, the mobile radio station 24 can determine to be in the cell with the broadcast message with the highest received signal strength. Any other measure of the current radio status in the cell can also be used.

Since the cell load should be taken into account during cell selection or cell reselection, information about the load level in each cell (or associated with each cell) can be determined by one or more of the following: .. That is, at least one of a node or entity in the core network 12, a node or entity in one or both of the radio access networks 14 and 16, and an optional (optional) central radio resource server 18. is there. The load information communicated between the various entities is shown by the dashed line in FIG.

With reference to the flowchart of FIG. 2, the current load of the first cell is determined (step S1). Assuming the example of FIG. 1, one or more mobile wireless terminals 24 are in the cell C. Since there are usually a large number of mobile radio terminals in a cell, the mobile terminals are guided as a whole rather than individually. By changing the broadcast parameters in a particular cell, all mobile terminals in that particular cell are affected by the change and "rank" potential candidate cells in various ways. Will be. Since the radio state is unique to the individual mobile terminal, these particular states affect whether changing the broadcast parameters triggers the mobile terminal to select another cell. Will give. Therefore, the induction of broadcast parameters can be seen as a "statistical" induction or as an "average" mobile terminal induction. The current load in other adjacent cells is also determined. A decision is made as to whether it is desirable to reduce the load in the first (cell C) (step S2). If not desired, the process of determining load continues. If the load needs to be reduced, one or more parameters in one or more broadcast messages to guide one or more mobile terminals 24 to occupy a second cell, which is probably relatively uncrowded. A step to adjust occurs (step S3).

Consider an example scenario from Figure 1. It may be desirable to keep the idle mobile station 24 within the same radio access network 14. In that case, it would be appropriate to adjust the parameters of the broadcast message so that the idle mobile terminal 24 is directed to cell B in RAN1. Here, it is assumed that the load of cell B is not as high as that of cell C or cell A. Such cell reselection would be particularly seamless if all cells in the radio access network 14 could provide the same service. In any case, this cell reselection within the network does not require messaging of cell reselection between networks.

Load determination and broadcast parameter adjustment can be performed or initiated by any suitable node or entity, including, for example, those listed below. That is, one or more core network nodes, one or more radio access network nodes in one or more radio access networks, a central radio resource server 18 (which is optional and implementation dependent), and so on. The method by which the broadcast parameters are actually adjusted can be performed in any suitable way. It may also be desirable to control the frequency or rate of changes that the mobile station may be directed to new cells to avoid unnecessary cell changes and associated signaling loads. Measurement results may be exchanged between various entities and nodes, but this is of course arbitrary and the load and parameter adjustment determinations may be made within one node or entity. The actual coordination may be performed by the base station or node B.

In the context of communication system 100 shown in FIG. 3, other more detailed but also non-limiting examples are referred to. The system 100 has two different radio access technologies used in two radio access networks. The GSM / GPRS radio access network 104 uses TDMA type RAT, and the UMTS radio access network 106 uses CDMA or WCDMA based RAT. Both radio access networks are coupled to core network nodes 102 associated with these types of radio access networks. The core network node 102 includes a home location register (HLR), a mobile communication exchange (MSC), a regional GPRS support node (SGSN), a barrier GPRS support node (GGSN), and the like. GSM / GPRS The RAN104 includes one or more base station controllers (BSCs), but for simplicity, only one BSC110 is shown. BSC110s are coupled to one or more base stations (BTS) 112, and each base station 112 is associated with a particular cell 118. Three cells, A, B, and C, are illustrated. The UMTS radio access network 106 includes one or more radio network controllers (RNCs), but for simplicity, only one RNC114 is shown. Each RNC114 is attached to one or more nodes B116. Each node B is associated with one or more cells. For simplicity, the three nodes B shown are related to only one cell 1, 2, and 3, respectively. Each cell produces a broadcast or reception by a mobile terminal. FIG. 3 includes a dual-mode radio station 122 capable of communicating using the RAT of the GSM / GPRS network 104 and the RAT of the UMTS radio access network 106.

There are many different methods that can determine the load information for each cell 118 and 120. For example, an MSC or SGSN in the core network can determine load information in each location area (LA), routing area (RA), service area (SA), or cell. At higher area levels, regardless of which "level" the load is measured, if the current standard only provides broadcast parameters at the cell level to guide idle mobile terminals. The measured load is mapped to the cell level within LA, RA, or SA. Load information is transmitted to at least one of BSC110 and RNC114. Alternatively, the optional central radio resource server 108 may collect load information to determine the load on the cell or other area. Alternatively, at least one of the BSC 110 and the base station 112 may determine the information, and similarly, at least one of the RNC 114 and the node B 116 may determine the information. Information may be exchanged between networks or, if desired, communicated to an optional wireless resource server 108. Any suitable signaling format can be used. For example, when exchanging load information between BSC110 and RNC114, the signaling and load containers described in the 3GPP 25.413 standard (ie, Inter-System Information Transparent Container) may be used. Load calculation in BSC / RNC would be preferred because load information is generally computable by BSC / RNC and does not require additional signaling or configuration. Coordination of broadcast messages may be made by any of these same entities and communicated for implementation at the corresponding base station or node B.

The flowchart shown in FIG. 4 will be referred to. In step S10, load measurements are made on some of cells 118 and 120 shown in FIG. The load can be observed in terms of any one or more resources used in these cells. As an example, resources include bandwidth, power, frequency, time slot, spread code, memory, data processing resources, terrestrial line transfer bandwidth, and the like. The load can be measured in at least one of the downlink direction from the cell to the mobile terminal and the uplink direction from the mobile terminal to the cell. Load measurement results can be combined. The load can be expressed as an absolute value or a relative value. Filtering and averaging (or one of them) of load measurement results can also be adopted. The load measurement results can be exchanged between nodes or entities within the same network or different networks (step S11), but this information exchange is arbitrary depending on the situation. If the load change, or the cumulative load change, exceeds a certain threshold, it may be desirable to just exchange load information. Further, the mobile terminal can be guided to another cell in the same network (for example, the mobile radio station 122 in FIG. 3 can be guided from cell 1 to cell 2 in the UMTS radio access network 106 together). If so, signaling and delays between networks can be avoided.

One or more broadcast parameters are adjusted for one or more cells (step S12). In fact, a new set of parameter values (eg, cell offsets) can be calculated based on the differences between loads in adjacent cells. Offsets can be expressed in decibels or linear units. One or more previously determined load samples are available as inputs, and the new calculated parameter values can be used as adjustments to this previously determined value. Alternatively, a new absolute parameter value may be calculated. Since load values can vary significantly, it may be desirable to perform at least one of filtering, averaging, and thresholding to avoid unnecessary calculations, cell switching, and signaling. .. Limiting the frequency of updates of broadcast parameters to avoid updating broadcast message information too often helps maintain battery life and system stability of mobile terminals. The new offset value is broadcast by at least one of the territorial cell and the neighboring cell.

Examples of parameters that can be adjusted in the broadcast information are signal strength offsets or signal quality offsets (which can potentially be combined with timer values if temporary offsets are desired), cell priorities, cells. Includes level priority, Minimum Quality Threshold, and allowed power level. Specific non-limiting examples of existing parameters that can be used in UMTS cells are Qoffset1 (s, n) for signal strength or Qoffset2 (s, n) for Ec / No measurements, which are cell ranks. Can be used for attachment. These parameters specify the offset between the area (s) cell and the neighboring (n) cell. The relationships between neighboring cells can be set individually. Specific non-limiting examples of GSM are CELL_RESELECT_OFFSET or GPRS_RESELECT_OFFSET, which are used in cell selection / cell reselection evaluations and are potentially used to push the load of GSM cells onto neighboring cells. obtain.

An example of the equation that determines the offset is shown below.

Offset (Source, Neighbor, T_{n + 1}) = Offset (Source, Neighbor, T_n) + C · [Load (Neighbor, T)_n)-Load (Source, T_n)] (1) Offset (Source, Neighbor, T_{n + 1}) = Offset (Source, Neighbor, T_n) + Func [Load (Neighbor, T)_n)-Load (Source, T_n)] (2) Offset (Source, Neighbor, T_{n + 1}) = Const₀+ Const₁ (Load (Neighbor, T)_n)-Load (Source, T_n)] (3)

Examples of offsets are CRO (Cell_Reselect_Offset), GRO (n) (GPRS_Reselect_Offset), and UMTS offset Qoffset1 for signal strength RSCP or signal quality Ec / No._{s, n}Or Qoffset2_{s, n}including. T_nMeans "at the nth event" and may be regular or non-regular. Here, n is an event counter when the calculation is performed. Source indicates an identifier for a cell or area in which the mobile terminal is currently located. Neighbor indicates an identifier for a cell or area adjacent to a source cell or area. Of course, each source cell is usually an adjacent cell to the other cells.

Therefore, the identifier of the same cell may exist in different "positions". For example, consider the identifiers of two cells A and B. Broadcasting the offset in cell A will use "A" at the source position and "B" at the adjacent position. The offset broadcast in cell B will use "B" at the source position and "A" at the adjacent position. In other words, equations (1)-(3) can be evaluated "simultaneously" with respect to each adjacent cell in all cells. FIG. 5 shows the offsets in two of the three cells A, B, and D, cells A and B.

Parameter C is a selectable constant. For slower and slower adaptation, the value of C should be smaller. Func (X) shows some function for the input variable X that is chosen to be the difference in load between the two cells in this example. A simple example of a function is C * X, which is a reduction of equation (2) into equation (1). A more advanced example is C * X^αIs. Here, α is usually greater than 1. This effect would mean making larger adjustments for larger load differences. Both equations (1)-(2) are adjusted based on the difference in the remaining load between the source cell where the parameter was broadcast and each neighboring cell, based on the previous parameter value (at "time Tn"). Set a new parameter value (at "time Tn + 1") to accompany. Therefore, this is a gradual or gradual parameter adjustment for each "time interval Tn". The direction and size depend on the difference in load. The adjustment may be based solely on the load in the cell itself, but is preferably based on the difference in load. However, as is executed in equation (3), it is also possible to independently calculate a new parameter value for each "time interval Tn" without considering the previous calculation.

To calculate the new broadcast parameter in equation (3), the "next value" is set equal to Const0. This value is set appropriately by summing the product of the other well-selected constants (Const1) and the measured load difference. Equations (1)-(2) will be suitable when adjustments are frequent, and equation (3) will be used when adjustments are infrequent. Equation (3) generally has a relatively long calculation / averaging time similar in length to the parameter update time interval (ie, Tn to Tn + 1).

Of course, there are many more possible ways to calculate the offset parameters. Another example is a general purpose lowpass filter type equation.

Offset (Source, Neighbor, T_{n + 1}) = (1-C) Offset (Source, Neighbor, T_n) + C · [Load (Neighbor, T)_n)-Load (Source, T_n)] (4)

The difference between equations (1) and (4) is that the magnitude of the Offset is limited, even if the load difference persists for a long period of time. This would be a desirable property.

The above example is the Offset parameter (Qoffset1) broadcast on PBCCH in GSM (GRO) and BCH in UTRAN._{s, n}Or Qoffset2_{s, n}) Is assumed to be used. That is, there is one Offset value for each cell. However, "pair-wise" offsets cannot exist in all cells. For example, in a GSM with a traditional broadcast channel (BCCH), each cell has only one Offset parameter (CRO), which is common to all neighboring cells. Therefore, the example equation shown above may need to be modified.

Idle mobile stations are dynamically guided between cells based on load, whether within networks of the same radio access network technology or between networks of different radio access technologies. This brings a number of benefits. That is, it is necessary to perform active connection handover for the purpose of network operator flexibility, optimization of network resources, reduction of overload conditions, guarantee of satisfactory delivery of contracted quality of service, and balance of load. Minimization of sex.

The present invention has been described in the context of one or more examples of embodiments. However, the invention is not limited to any disclosed embodiment, and conversely is intended to cover various modifications and equivalent configurations within the scope of the appended claims. Should be understood.

<figref num="1">It is a figure which shows the communication system including two radio access networks which use different radio access technologies.</figref><figref num="2">It is a flowchart which shows the step for reducing the load in the 1st cell which a mobile station is currently in the area.</figref><figref num="3">It is a figure which shows other communication systems including a GSM / GPRS radio access network and a UMTS radio access network.</figref><figref num="4">It is a flowchart which shows the procedure example which follows one non-limiting example about load distribution.</figref><figref num="5">It is a figure which shows the state of the offset adjustment of a broadcast parameter.</figref>