Background and Objects of the Present Invention Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.

With reference now to FIGURE 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) (terminal) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 12 is divided into a number of cells 22.

Mobile Station (MS) 20 is the physical equipment, e. g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.

The MS 20 may also include a Subscriber Identity Module (SIM) card 13, or other

memory, which provides storage of subscriber related information, such as a subscriber authentication key, temporary network data, and service related data (e. g. language preference).

The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several base transceiver stations 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.

With further reference to FIGURE 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e. g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIGURE 1.

The VLR 16 is a database containing information about all of the Mobile Stations 20 currently located within the MSC/VLR area 12. If a MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that Mobile Station 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.

When a subscriber is roaming outside of the subscribers home PLMN, the subscriber often has a choice of several other cellular networks. Currently, the selection of the network for use by the MS 20 is based on a list of PLMNs available to the subscriber, stored, for example, within the SIM card 13, or other programmable memory, within the MS 20. Once this list is created, the first PLMN on the list is

selected whenever possible. In many situations, the subscriber may also select the PLMN manually.

However, at present, only the network name (identity) is displayed to the subscriber prior to the subscriber making a manual selection of the desired cellular network. Therefore, in either of the above situations, the chosen cellular network may not provide the lowest rates to the roaming subscriber.

It is therefore an object of the invention to allow a subscriber to select a cellular network, while roaming, based on both the identity of the cellular network and the charging information associated therewith.

SUMMARY OF THE INVENTION The present invention is directed to telecommunications systems and methods for allowing a subscriber to select a cellular network (PLMN), while roaming outside of the subscribers home cellular network, based on charging information received by the subscribers mobile terminal for each cellular network available to the subscriber.

This can be accomplished by allowing PLMNs within the geographical area of the mobile terminal to broadcast the charging information applicable to roaming subscribers from other networks. This information can be broadcast, for example, on a Broadcast Control Channel (BCCH), for GSM-based systems. The identity of each PLMN within the geographical area of the MS is received by the MS and compared with a list of allowable PLMNs stored in the SIM card to determine which PLMNs are available to the subscriber. Thereafter, if more than one PLMN is available to the subscriber, charging information associated with each available PLMN is received by the MS/SIM, which can then select the least cost PLMN. For manual PLMN selection, the identity of each available PLMN and associated charging information is received by the MS/SIM and displayed to the subscriber, to allow the subscriber to select the desired (least cost) PLMN

BRIEF DESCRIPTION OF THE DRAWINGS The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein: FIGURE 1 is a block diagram of a conventional terrestrially-based wireless telecommunications system; FIGURE 2 illustrates a choice of cellular networks available to a mobile terminal while roaming; and FIGURE 3 describes steps in a sample cellular network selection process based on charging information, in accordance with preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS The numerous innovative teachings of the present application will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others.

With reference now to FIGURE 2 of the drawings, a Mobile Station (MS) 200, which has roamed outside of its home Public Land Mobile Network (PLMN), often has a choice of PLMN's (PLMN1 240 and PLMN2 250) within a geographic area 230.

Each PLMN (240 and 250) within that geographic area 230 broadcasts information related to that PLMN (240 and 250, respectively). For example, each PLMN (240 and 250) can broadcast the respective network code (PLMN identity information) and synchronization information. The MS 200 has the capability to receive messages from each PLMN (240 and 250) at the same time, while roaming in the geographic area 230 designated to these PLMNs (240 and 250). In order for the MS 200 to determine which PLMN (240 or 250) to use, each PLMN (240 and 250) can also broadcast the

charging information associated therewith, which is applicable to all roaming MSs 200 within that geographical area 230. This information can be broadcast, for example, on separate Broadcast Control Channels (BCCH) (245 and 255) for each PLMN (240 and 250, respectively), for GSM-based systems.

As described in FIGURE 3 of the drawings, for the purpose of PLMN selection based on roaming charges, the charging information for each PLMN (240 and 250) is entered into a charging application (247 and 257, respectively) within a Base Station Controller (BSC) (246 and 256, respectively) associated with each PLMN (240 and 250) (step 300). Alternatively, the charging application (247 and 257) can be located within a Mobile Switching Center (248 and 258, respectively) connected to the BSC (246 and 256, respectively). The charging information can be updated in the BSC (246 and 256) or MSC (248 and 258) by various methods, such as by manual commands.

This charging information and the PLMN identity information is then sent to the Base Transceiver Station (242 and 252) to be broadcast on the BCCH (245 and 255, respectively) (step 310).

Thereafter, the charging information and PLMN identity information can be received by a Subscriber Identity Module 210, or other programmable memory, within the MS 200 (step 320). A list 215 containing the PLMNs allowed to the subscriber is stored in the SIM card 210. Not all PLMNs (240 and 250) within a geographical area 230 are allowed to a roaming subscriber. The allowability of a PLMN (240 or 250) depends upon the agreement between the subscribers home PLMN (not shown) and the PLMNs (240 and 250) within the geographical area 230 the MS 200 is in. This list of allowable PLMNs 215 within the SIM card 210 can then be compared with the received PLMN identity information (step 330) to determine which PLMNs within the geographical area 230 are available to the subscriber. If there is only one received PLMN identity on the list 215, for example, PLMN 1 240, the MS 200 registers with that PLMN 240 (step 340).

However, if the mobile subscriber has several available PLMNs (240 and 250), the MS 200 then collects the roaming charge information received on the BCCH channels (245 and 255, respectively) by the MS 200 for all of the available PLMNs (240 and 250) (step 350). After collecting the charging information (step 350), a

PLMN charge-based selection application 220 within the SIM card 210 compares the received charging information for each available PLMN (240 and 250) (step 360) and registers,, by performing a location update, as is well known in the art, with the PLMN (240 or 250) having the lowest charging rate (step 370).

For manual PLMN selection, the roaming charges can be displayed to the subscriber on a display 205, along with the received PLMN identities that are on the list 215 (available PLMNs 240 and 250). The subscriber can then have the option of selecting the least cost PLMN, or another PLMN, using, for example, existing function keys 202 on the keypad 208 of the MS 200.

As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed.