WO2015065441A1

WO2015065441A1 - Method of addressing overlapping networks at a region border

Info

Publication number: WO2015065441A1
Application number: PCT/US2013/067817
Authority: WO
Inventors: William M. Shvodian
Original assignee: NII Holdings, Inc.
Priority date: 2013-10-31
Filing date: 2013-10-31
Publication date: 2015-05-07
Also published as: AR098250A1

Abstract

A method is provided of operating a mobile device in a visited network, comprising: receiving a downlink signal from a visited-network base station, the downlink signal including a border indicator indicating that the base station is near a border between a visited region containing the visited network and one or more adjacent regions, and border information identifying the adjacent regions; determining that the base station is near the border between the visited region and the one or more adjacent regions based on the border indicator; determining whether or not the one or more adjacent regions include a home region for the mobile device; searching for a home network if the one or more adjacent regions include the home region for the mobile device; and processing signals in the visited region without searching for the home network if the one or more adjacent regions do not include the home region.

Description

METHOD OF ADDRESSING OVERLAPPING

NETWORKS AT A REGION BORDER

FIELD OF THE INVENTION

[0001] This application relates generally to a method for addressing overlapping network coverage at the border of two regions. More particularly, it relates to a system and method by which a base station on a regional border transmits border information to allow a mobile device within that base stations area of coverage to determine whether or not to look for a home base station.

BACKGROUND OF THE INVENTION

[0002] It's common for conventional mobile telephone networks to designate a home region in which communication is comparatively cheap for user, but also to allow operation in other regions using higher roaming charges. For example, two countries may have different wireless telephone companies running entirely different wireless telephone networks. These two telephone companies will often make agreements to allow users from one country to access the wireless telephone network in the other country, albeit at a higher roaming cost.

[0003] Similarly, a single wireless telephone company may divide its coverage area into separate regions only one of which can be a home region for a given user. Such a user can operate at comparatively smaller rates while in a home region, and can operate at higher roaming rates while in other regions within the telephone company's network.

[0004] A problem can occur, however, when the two regions (i.e., the home region and the other region) border each other. Because wireless communications do not neatly stop at arbitrary borders, it will be possible to use a telephone in one network while technically operating within the area designated for the other network. For example, a Mexican company might operate a telephone network that covers Tijuana, Mexico, while a United States company operates a telephone network that covers San Diego, California. Each telephone company would have base stations that provide coverage up to the national border between Mexico and the United States. But in each case, the coverage area would likely extend into the bordering country as well.

[0005] Thus, it may be possible for a user from San Diego (whose home network was the US network) to operate a mobile telephone in Tijuana using the US network, provided the user was close enough to the border to access a base station in the United States. Likewise, a user from Tijuana (whose home network was the Mexican network) may be able to operate a mobile telephone in San Diego using the Mexican network, provided the user was close enough to the border to access a base station in Mexico. Given the power used by mobile telephone base stations, this distance can be many miles.

[0006] However, once a user moves far enough into the neighboring region, it will no longer be possible to contact the home network because the mobile device will have moved too far from the home network base stations. When this occurs, the mobile device will seek out a new base station in the neighboring network, and if operation in that network is permitted, will connect using roaming rates. In the example above, once the US user moved far enough into Mexico, her mobile telephone would connect up to the Mexican network at roaming rates. Likewise, once the Mexican user moved far enough into the US, his mobile telephone would connect up to the US network, also at roaming rates.

[0007] A problem can occur when a user returns to his home network. If that user remains close to the border, it's possible that his mobile phone will remain connected to the adjacent network, rather than reconnect to his home network. This can result in the user incurring unnecessary roaming charges when he is within a region covered by his home network. Returning to the example above, if the US user, having been connected to the Mexican network, returns to San Diego, her mobile telephone might still be able to contact the Mexican network, and might stay in contact with the Mexican network at roaming rates, despite the fact that the user and the US operator would want it to connect back up to her home network in the United States.

[0008] In particular when 3GPP (3rd Generation Partnership Project) devices roam into other networks, they are supposed to periodically try to connect to the home network or to the highest priority network available. However, to save battery life the mobile devices are not supposed to scan for the home network when they are in a visited (i.e., roaming) network that is in a foreign country (i.e., that has a mobile country code (MCC) different from the mobile country code of the home network). Also, 3 GPP mobile devices do not need to scan for a higher priority network when they are already connected to the highest priority network in a visited country.

[0009] As a result, when a 3 GPP user returns to their home country, his mobile device can still communicate with the visiting country (e.g., the user is close to the border between the home country and the visited country), it will stay connected to the visited network. This is true even if the mobile device is in its home country and within range of its home network. The current 3 GPP specification (23.122) does not allow the mobile device to scan for its home network when it is connected to a visiting network with a mobile country code (MCC) different from that of the home network. Because of this, a mobile device can stay connected to a visited network indefinitely if it stays near the border between the two networks. This can result in significant roaming charges for the user.

[0010] It would therefore be desirable to provide a system and method whereby a mobile device can quickly and easily connect back to its home network when it gets within range of the home network. It would also be desirable to provide a system in which scanning for a home network were limited to circumstances in which the mobile device was likely to be near the home network, in order to maximize battery life in mobile devices while roaming.

SUMMARY OF THE INVENTION

[0011] A method of operating a mobile device in a visited network, comprising: receiving a downlink signal from a visited-network base station, the downlink signal including a border indicator indicating that the visited-network base station is not near a border between a visited region containing the visited network and one or more neighboring regions; extracting the border indicator from the downlink signal; determining that the visited-network base station is not near the border between the visited region and any of the one or more neighboring regions based on the border indicator; and processing signals in the visited network without searching for a home network after the operation of determining that the visited-network base station is not near the border between the visited region and the one or more neighboring regions.

[0012] The received signal may further include border information, and the border information does not identify any of the neighboring regions as being adjacent to the visited- network base station.

[0013] The visited network may be a 3 GPP network.

[0014] A method is provided of operating a mobile device in a visited network, comprising: receiving a downlink signal from a visited-network base station, the downlink signal including a border indicator indicating that the visited-network base station is near a border between a visited region containing the visited network and one or more adjacent regions, and border information identifying the one or more adjacent regions; extracting the border indicator from the downlink signal; determining that the visited-network base station is near the border between the visited region and the one or more adjacent regions based on the border indicator; extracting the border information from the downlink signal; determining whether or not the one or more adjacent regions include a home region for the mobile device; searching for a home network for the mobile device if it is determined that the one or more adjacent regions include the home region for the mobile device; and processing signals in the visited region without searching for the home network if it is determined that the one or more adjacent regions do not include the home region for the mobile device.

[0015] The visited network may be a 3 GPP network.

[0016] The received signal may further include border information, and the border information may identify one or more adjacent regions, the one or more adjacent regions being adjacent to the visited-network base station.

[0017] The border information may identify the one or more adjacent regions by a region identification code. The region identification code may be a 3 GPP mobile country code.

[0018] The extracting of the border information from the received downlink signal may occur only if it is determined that the visited-network base station is near the border between the visited region and the one or more neighboring regions

[0019] The method may further comprise: processing signals in the visited region if the operation of searching for the home network does not locate the home network; and processing signals in the home region if the operation of searching for the home network locates the home network.

[0020] The method may further comprise: determining a strength of signals from the home network if the operation of searching for the home network locates the home network; determining whether the strength of signals from the home network is greater than a strength threshold; processing signals in the visited region if it is determined that the strength of the signals from the home network is not greater than the strength threshold; and processing signals in the home region if it is determined that the strength of the signals from the home network is greater than the strength threshold.

[0021] The strength threshold may be a fixed threshold, or it may be a set percentage of a strength of signals from the visited network.

[0022] The downlink signal may be one of a broadcast signal and a directed signal addressed to the mobile device.

[0023] A method is provided of operating a base station in a visited network, comprising: beginning transmission of a downlink signal to a mobile device associated with the base station; transmitting a border indicator to the mobile device in the downlink signal, the border indicator indicating whether or not the base station is adjacent to one or more other networks; transmitting border information to the mobile device in the downlink signal, the border information identifying the one or more networks that are adjacent to the base station, if any; and ending transmission of the downlink signal to the mobile device associated with the base station

[0024] The method may further comprise: associating the base station with the mobile device prior to beginning transmission of the downlink signal.

[0025] The downlink signal may be one of a broadcast signal and a directed signal addressed to the mobile device.

[0026] The visited network may be a 3 GPP network.

[0027] The border information may identify the one or more networks that are adjacent to the base station by a region identification code. The region identification code may be a 3 GPP mobile country code. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying figures where like reference numerals refer to identical or functionally similar elements and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate an exemplary embodiment and to explain various principles and advantages in accordance with the present claimed invention.

[0029] FIG. 1 is a diagram of two overlapping wireless networks according to disclosed embodiments;

[0030] FIG. 2 is a block diagram of a regional border identification transmission scheme according to disclosed embodiments;

[0031] FIG. 3 is a diagram of two adjacent networks at a regional border according to disclosed embodiments;

[0032] FIG. 4 is a diagram of three adjacent networks at two different regional borders according to disclosed embodiments;

[0033] FIG. 5 is a flow chart of an operation of a mobile station determining whether to try and locate its home network according to disclosed embodiments; and

[0034] FIG. 6 is a flow chart of an operation of a base station identifying its border status according to disclosed embodiments.

DETAILED DESCRIPTION

[0035] The instant disclosure is provided to further explain in an enabling fashion the best modes of performing one or more embodiments of the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

[0036] It is further understood that the use of relational terms such as first and second, and the like, if any, are used solely to distinguish one from another entity, item, or action without necessarily requiring or implying any actual such relationship or order between such entities, items or actions. It is noted that some embodiments may include a plurality of processes or steps, which can be performed in any order, unless expressly and necessarily limited to a particular order; i.e., processes or steps that are not so limited may be performed in any order.

[0037] Neighboring Networks

[0038] FIG. 1 is a diagram of two overlapping wireless networks 100 and 105 according to disclosed embodiments. As shown in FIG. 1, the first network 100 includes a first network base station 1 10 that wirelessly transmits and receives first signals 120 to/from mobile devices 130A, 130C. Likewise, the second network 105 includes a second network base station 140 that wirelessly transmits and receives second signals 150 to/from mobile devices 130B, 130C. For ease of disclosure, the reference number 130 will sometimes be used to generically designate a mobile device.

[0039] The first network base station 1 10 is a wireless base station operating within the first wireless network 100. For example, in one embodiment it could be a mobile telephone base station (i.e., cell tower). More particularly, it could be a 3GPP mobile telephone base station. The first network base station 110 transmits downlink (DL) signals to the mobile devices 130A, 130C within its downlink range 160. Similarly, it receives uplink (UL) signals from the mobile devices 130A, 130C within its uplink range 165. (These DL and UL signals are generically referred to as first signals 120.) Because the first network base station 1 10 has a more powerful transmitter than do the mobile devices 13 OA, 130C operating within the first network 100, the downlink range 160 is greater than the uplink range 165. This means that when a mobile device 130 is inside the downlink range 160 but outside of the uplink range 165, the mobile device 130 will be able to receive downlink signals from the first network base station 1 10, but the first network base station 110 will not be able to receive uplink signals from the mobile device 130.

[0040] The second network base station 140 is a wireless base station operating within the second wireless network 105. For example, in one embodiment it could be a mobile telephone base station (i.e., cell tower). More particularly, it could be a 3GPP mobile telephone base station. The second network base station 140 transmits downlink (DL) signals to the mobile devices 130B, 130C within its downlink range 170. Similarly, it receives uplink (UL) signals from the mobile devices 130B, 130C within its uplink range 175. (These DL and UL signals are generically referred to as second signals 150.) Because the second network base station 140 has a more powerful transmitter than do the mobile devices 130B, 130C operating within the second network 105, the downlink range 170 is greater than the uplink range 175. This means that when a mobile device 130 is inside the downlink range 170 but outside of the uplink range 175, the mobile device 130 will be able to receive downlink signals from the second network base station 140, but the second network base station 140 will not be able to receive uplink signals from the mobile device 130.

[0041] As can be seen from FIG. 1, mobile devices 130A are only within range of the first network base station 110. These mobile devices 130A can only communicate with the first network base station 110 (i.e., they can only communicate within the first network 100). Similarly, mobile devices 130B are only within range of the second network base station 140. These mobile devices 130B can only communicate with the second network base station 140 (i.e., they can only communicate within the second network 105). However, device 130C is within the range of both the first network base station 110 and the second network base station 120 (i.e., it can communicate with either the first network 100 or the second network 105).

[0042] Which network the mobile device 130C will connect to depends upon the rules of operation of the mobile device 130C, whether the first network 100 or the second network 105 is a home network, and how the mobile device 130C has previously been operated.

[0043] If the first network 100 and second network 105 are 3 GPP networks, the mobile device 130C will remain connected to the network base station 110, 140 it was last connected to, unless its network protocol hands it off to another base station within the same network, forces it to search for a higher priority base station within the same network, forces it to search for a new network, or forces it to search for a home network.

[0044] Under the current 3 GPP protocol, in order to save battery life in mobile devices 130, if the mobile device 130 is connected to a network 100, 105 in a region with a different mobile country code (MCC) than the home region of the mobile device 130, then the mobile device 130 is not allowed to scan for its home network. The reasoning behind this restriction is that when the mobile device 130 is in a foreign country, it will likely not be near the home network, and so it would be a waste of power to look for the home network.

[0045] However, this assumption is not true if the visited region is a neighboring region to the home network's home region. Consider a situation in which the first network 100 is in Canada (i.e., the MCC for the first network 100 is 302), and the second network 105 is Verizon's 4G LTE Network in the United States (i.e., the MCC for the second network 105 is 31 1). If the user is from Canada, and the user's home network is the first network 100, then the MCC for the user's home network will be 302. If the user then visits the United States and connects to the second network 105, then the MCC for the user's visited network will be 311. Since these two MCCs are not the same, the user's mobile device 130C will not be allowed to scan for the first network 100 (i.e., the home network of the mobile device 130), as long as it was still connected to the second network 105 (i.e., the visited network).

[0046] This could be a problem if the user lives close to the border between the United States and Canada. For example, the user might live in Windsor, Canada, and be connected to the first network 100 there. But then the user might visit Chicago, Illinois, causing the user's mobile device 130 to connect to the second network 105 as a visited network (thus incurring roaming charges for the user). Upon his return to Windsor, the user's mobile device 130C might still be in range of a base station for the second network 105 located in Detroit, Michigan. As a result, the user's mobile device 130 would remain connected to the second network 105, despite the fact that the user had returned to his home in Windsor, Canada, and was both within range of a first network base station 1 10, and within the area of official coverage of the first network 100.

[0047] Furthermore, even if the user turned his mobile device 130 off and then on again, the problem would remain. This is because the current 3 GPP protocol has a default mode whereby upon power up, a mobile device 130 must first look for the most recent network to which it was connected. As a result, if the user turned his mobile device 130 off and then on again while he was still within range of a the first network base station 110 (i.e., in a network with an MCC different from the MCC of the second network base station 140), his mobile device 130 would rejoin the second network 105, and would again be forbidden from searching for the first network 100.

[0048] Border Base Stations Broadcast Border Information

[0049] One way to allow a mobile device 130 to rejoin its home network more efficiently, would be to have each base station 1 10, 140 that was located at the border between two regions broadcast border data that a mobile device 130 could use as a trigger to start searching for its home network. [0050] This border data could include a border indicator, which indicates whether or not the base station 1 10, 140 is located at a regional border (e.g., a national border), and border information, which indicates what regions the base station 1 10, 140 borders. A mobile device 130 could look for this border data, and only search for its home network when it was connected to a base station 1 10, 140 located at a regional border, and when that border was with the region whose MCC includes the user's home network.

[0051] The passing of the border data could be accomplished in many ways. For example, a border indicator bit could be included in a control channel used by the base station 1 10, 140. This control channel could be a broadcast control channel sent to every mobile device 130 within the downlink range 160, 170 of the base station 110, 140, or it could be a targeted control channel directed only to a given mobile device 130.

[0052] FIG. 2 is a block diagram of a network border identification transmission scheme according to disclosed embodiments. In FIG. 2, the size of an element is not related to that element's duration. As shown in FIG. 2, a wireless transmission 120, 150 from a base station 110, 140 is divided into a plurality of subframes 210. Periodically, a subframe 210 will include a downlink control channel 220, along with some other information 230. A downlink control channel 220 can include a border indicator 240, border information 250, and other control information 260.

[0053] The plurality of subframes 210 represent a plurality of consecutive, time- differentiated transmission periods. In various embodiments they could be called subframes, frames, timeslots, or any similar titles.

[0054] The downlink control channel 220 is a transmission sent from a base station 110, 140 to a mobile device 130 providing network and control information. This can be a broadcast downlink control channel that is broadcast to every mobile device 130 within the downlink range 160, 170 of the base station 1 10, 140, or it can be a targeted downlink control channel that is transmitted to a single mobile device 130 within the downlink range 160, 170 of the base station 110, 140. The downlink control channel 220 is transmitted periodically from the base station 1 10, 140 to the mobile device 130, at a period determined by the network protocol.

[0055] In an embodiment in which the first and second network 100, 105 are 3 GPP networks, the downlink control channel 220 can be a master information block (MIB) sent over a broadcast channel (BCH), a system information block (SIB) sent over a downlink shared channel (DL-SCH), an information block specifically dedicated to border data, or any suitable block of data that is sent from a base station 110, 140 to a mobile device 130.

[0056] The other information 230 can include any other relevant information contained within the downlink control channel, e.g., network information, operational instructions, transmitted data, uplink channels, etc. in some embodiments, the download control channel 220 can take up the entire subframe 210, in which case there would be no other information 230. In the case where there is other information 230, this other information 230 could be located before or after the downlink control channel 220.

[0057] The border indicator 240 indicates whether or not the transmitting base station 1 10, 140 is located adjacent to a base station 1 10, 140 for a network having an MCC value that is different from the MCC value of the transmitting base station. Typically this will occur at national borders, although in some circumstances it may occur within the boundaries of a single country.

[0058] Because this is a Boolean indicator, the border indicator 240 may be implemented in a single bit, e.g., a single bit in an MIB or an SIB, or a single bit elsewhere in the downlink control channel 220, specifically designated to provide a border indication. However, in alternate embodiments a more robust border indicator 240 can be used, e.g. a symbol, a code word, etc. [0059] The border information 250 includes data that indicates what regions the transmitting base station 1 10, 140 is adjacent to. In some embodiments, this can simply be a list of the different MCC values for any adjacent network or networks; in other embodiments it can include more detailed identification of the adjacent networks. If a transmitting base station 110, 140 is not adjacent to any border (i.e., if the border indicator 240 indicates that it is not a border base station), the border information 250 is not used. It can be left random, or it can be set to a particular value, as desired in various embodiments.

[0060] The other control information 260 can include any other operational information that needs to be passed from a base station 110, 140 to the mobile device 130, e.g., network information, operational instructions, etc. this other control information 260 can be formed before the border indicator 240 and the border information 250, after the border indicator 240 and the border information 250, between the border indicator 240 and the border information 250, or any combination of these three options.

[0061] When a mobile device 130 receives a downlink control channel from the base station 110, 140 that it is associated with, it checks the border indicator 240 and the border information 250 to determine whether it is associated with a base station 1 10, 140 that borders its home region. If the mobile device 130 determines that it is not associated with a base station 1 10, 140 that borders its home region, then it does not look for its home region. However, if the mobile device 130 determines that it is associated with a base station 1 10, 140 that borders its home region, it will begin a search for its home region. This search may continue, subject to the number and frequency of retries allowed by the protocol used by the mobile device 130, until either the mobile device 130 finds the home region, and connects to it, or becomes associated with a base station 1 10, 140 that does not border its home region.

[0062] For example, in a 3 GPP network, a value T can be set between 6 minutes and 8 hours. The value for T indicates how frequently the mobile device 130 will look for a network having a higher priority than the network is currently in, if it is permitted to look for such a network. If the border indicator 240 and the border information 250 cause the mobile device 130 in a 3GPP network to search for its home network, this search can occur with a frequency indicated by the value of T.

[0063] First Example of Operation

[0064] FIG. 3 is a diagram of two adjacent networks at a regional border according to disclosed embodiments. As shown in FIG. 3, a home network 301 is located in a home region that is adjacent to a visited region that contains a visited network 302. A plurality of home base stations 311, 312, 313, 314, 315 are located in the home network 301. Each home base station 31 1-315 has an associated area of coverage 321, 322, 323, 324, 325 (i.e., area of transmission). First, second, and third home base stations 31 1, 312, 313 are located adjacent to a border 330 between the home region and the visited region. In highly populated areas, the plurality of home base stations 31 1-315 are generally arranged in an overlapping fashion such that they cover the entirety of the populated area.

[0065] Similarly, a plurality of visited base stations 341, 342, 343, 344, 345 are located in the visited network 302. Each visited base station 341-345 has an associated area of coverage 351, 352, 353, 354, 355 (i.e., area of transmission). First, second, and third visited base stations 341, 342, 343 are located adjacent to the border 330 between the home region 301 and the visited region 302. In highly populated areas, the plurality of visited base stations 341, 342, V343, 344, 345 are generally arranged in an overlapping fashion such that they cover the entirety of the populated area.

[0066] Although, as noted in FIG. 1, each base station 311-315, 341-345 will actually have a different downlink coverage area and uplink coverage area, a single coverage area 321-325, 351-355 is shown for each base station 31 1-315, 341-345 for the sake of simplicity. [0067] The home region and the visited region can represent different countries, or different regions within the same country. In one embodiment in which the home and visited regions are in a 3 GPP network, the home region and the visited region are regions that are identified by different mobile country code (MCC) values. This means that the home network 301 is assigned a home MCC value that is different from a visited MCC value assigned to the visited network 302.

[0068] Because the first, second, and third home base stations 31 1, 312, 313 are located adjacent to the border 330, each of these bordering home base stations 31 1-313 transmits at least partially over the regional border 330 into the visited region (i.e., the area covered by the visited network 302). Similarly, because the first, second, and third visited base stations 341, 342, 343 are located adjacent to the border 330, each of these visited base stations 341- 345 transmits at least partially over the regional border 330 into the home region (i.e., the area covered by the home network 301).

[0069] An example of the operation of the disclosed protocol will be described with respect to FIG. 3. In this example, a user has a mobile device 130 whose home network 301 is associated with the home region. The user travels from point A to point E in the visited region. Then, on a return trip, the user travels from point E in the visited region to point J in the home region.

[0070] At point A, the user's mobile device 130 begins being associated with the home network 301, allowing the user to pay the comparatively inexpensive home rates for mobile device service. In particular, the mobile device 130 is associated with a fourth home base station 314. Since the fourth home base station 314 is not located adjacent to the regional border 330, the fourth home base station 314 broadcasts a downlink control channel 220 having a border indicator 240 that indicates it is not a border base station. The mobile device 130 does not search for the home network 301 because it is already associated with home network 301.

[0071] As the user moves from point A to point B, the mobile device 130 passes from the fourth home coverage area 324 into the first home coverage area 321, requiring a handoff from the fourth home base station 314 to the first home base station 31 1. This is

accomplished using the normal handoff protocol used within the home network 301. Since the first home base station 311 is located adjacent to the regional border 330, the first home base station 311 broadcasts a downlink control channel 220 including a border indicator 240 that indicates it is a border base station, as well as border information 250 identifying the visited region as an adjacent region. However, despite being in a border region, the mobile device 130 does not search for the home network 301 because it is already associated with home network 301.

[0072] When the user reaches point B, she reaches the overlap region between the first home coverage area 321 and the first visited coverage area 351. Again, the first home base station 31 1 broadcasts a downlink control channel 220 including a border indicator 240 that indicates it is a border base station, and a border information 250 that identifies the visited region as an adjacent region. Likewise, the first visited base station 341 broadcasts a downlink control channel 220 having a border indicator 240 that indicates it is a border base station, as well as border information 250 identifying the home region as an adjacent region. But again, despite being in two border regions, the mobile device 130 does not search for the home network 301 because it is already associated with home network 301. In fact, at this point, the mobile device 130 may not even be aware that it has entered the first visited coverage area 351, because it is not looking for another base station or another network.

[0073] As the user moves from point B to point C, she crosses the border 330 and passes from the home region to the visited region. But this transition is unimportant to the home network 301, the visited network 302, and the mobile device 130, since none of these three elements has any way to recognize the border 330. As a result, nothing changes with respect to the mobile device 130 when the user crosses the border 330. The mobile device 130 remains connected to the first home base station 31 1 in the home network 301, and does not look for either the home network or another network.

[0074] It is only when the user reaches point D that additional network connection action takes place. At point D, the mobile device 130 leaves the coverage area 321 of the first home base station 31 1, and does not enter a coverage area for any other base station in the home network 301. Since the mobile device can no longer communicate with the first home base station 31 1, and has not been handed off to another base station in the first network 301, it begins looking for a new network. This search should cause it to contact the visited network 302 through a signal received from the first visited base station 341.

[0075] Once the mobile device 130 is associated with the first visited base station 341 in the visited network 302, the user will begin to pay the relatively higher roaming rates for using the mobile device 130. In addition, the mobile device 130 will begin receiving a downlink control channel 220 from the first visited base station 341. This downlink control channel 220 will include a border indicator 240 indicating that the first visited base station 341 is a border base station, and border information 250 identifying the home region as an adjacent region. The mobile device 130 remains associated with the first visited base station 341, but commences searching for the home network 301. This is because the border indicator 240 and the border information 250 indicate that the mobile device 130 is associated with a base station that is adjacent to the home region. However, since the user is outside all of the areas of transmission 321-325 of the first network 301, the mobile device 130 does not connect up to the home network 301. [0076] When the user reaches point E, she has left the first visited coverage area 351, and has entered the fourth visited coverage area 354. Somewhere in the overlap between these two areas, the visited network 302 will have handed off the mobile device 130 from the first visited base station 341 to the fourth visited base station 344 using a standard handoff procedure. By point E, the mobile device 130 is receiving a downlink control channel 220 from the fourth visited base station 344. This downlink control channel 220 will include a border indicator 240 indicating that the fourth visited base station 344 is not a border base station. The mobile device 130 stops searching for the home network 301 because it is no longer associated with a border base station located next to the home region.

[0077] As the user moves from point E to point F, the mobile device 130 moves from the fourth visited coverage area 354 to the fifth visited coverage area 355, necessitating an internetwork handoff between the fourth visited base station 344 and the fifth visited base station 345, again using a standard handoff procedure. Since the fifth visited base station 345 is also not located near the border 330, the downlink control channel 220 that it transmits will include a border indicator 240 indicating that the fifth visited base station 345 is not a border base station. The mobile device 130 still not search for the home network 301 because it is not associated with a border base station located next to the home region.

[0078] When the user reaches point F, she has left the fifth visited coverage area 355, and has entered the third visited coverage area 353. Somewhere in the overlap between these two areas, the visited network 302 will have handed off the mobile device 130 from the fifth visited base station 345 to the third visited base station 343, again by a standard handoff procedure. By point F, the mobile device 130 is receiving a downlink control channel 220 from the third visited base station 343. This downlink control channel 220 will include a border indicator 240 indicating that the third visited base station 343 is a border base station, and border information 250 indicating that the home region is an adjacent region. The mobile device 130 will begin searching for the home network 301, because the mobile device 130 is now associated with a border base station located adjacent to the home region. However, because it is not in a coverage area of any base station in the home network 301 the mobile device 130 will remain associated with the visited network 302.

[0079] As the user moves from point F to point G, the mobile device 130 will remain associated with the visited network 301 via the third visited base station 343. However, because it is receiving a downlink control channel 220 that indicates the local visited base station 343 is adjacent to the home network 301, the mobile device 130 will continue to look for the home network 301 according to its own network protocol.

[0080] Once the user reaches point G, however, the mobile device 130 will be within the third home coverage area 323. At this point, the mobile device 130 will be able to communicate with the third home base station 313 and can rejoin the home network 301. At this point, the user will stop paying roaming rates, and will go back to paying the comparatively smaller home rates. The third home base station 313 broadcasts a downlink control channel 220 including a border indicator 240 that indicates it is a border base station, and border information 250 that identifies the visited region as an adjacent region. The third visited base station 343 continues to broadcast a downlink control channel 220 having a border indicator 240 that indicates it is a border base station, as well as border information 250 identifying the home region as an adjacent region. However, despite being in two border regions, the mobile device 130 does not search for the home network 301 because it is already associated with home network 301.

[0081] As with the first crossing of the border 330, when the user passes from the visited region back to the home region, there is no effect. This transition is unimportant to the home network 301, the visited network 302, and the mobile device 130, since none of these three elements has any way to recognize the border 330. As a result, nothing changes with respect to the mobile device 130 when the user crosses the border 330. The mobile device 130 remains connected to the third home base station 313 in the home network 301, and does not look for either the home network or another network.

[0082] When the user reaches point I, the mobile device 130 is out of the third visited coverage area of the third visited base station 343, placing it completely outside the visited network 302. The third home base station 313 continues to broadcast a downlink control channel 220 including a border indicator 240 that indicates it is a border base station, and border information 250 that identifies the visited region as an adjacent region. However, all of this is unimportant to the mobile device 130, since it is not looking for another network, since it is already connected to the home network 301.

[0083] Finally, when the user reaches point J, the mobile device 130 has been handed off by the first network 301 from the third home base station 313 to the fifth home base station 315 using a standard handoff protocol. Since the fifth home base station 315 is not located adjacent to the regional border 330, the fifth home base station 315 broadcasts a downlink control channel 220 having a border indicator 240 that indicates it is not a border base station. But this is irrelevant to the mobile device 130, since it does not search for the home network 301 because it is already associated with home network 301.

[0084] In this way, a user who travels from her home region to an adjacent region (i.e., a visited region) can effectively rejoin her home network, even when she is still within the coverage area of the visited network. This can save the user a great deal of money in unnecessary roaming costs.

[0085] Second Example of Operation

[0086] FIG. 4 is a diagram of three adjacent regions at two different regional borders according to disclosed embodiments. As shown in FIG. 4, a home network 401 is located in a home region that is adjacent to a visited region that contains a visited network 402. The visited region is further adjacent to a neighboring region that includes a neighboring network 403. The neighboring region is not adjacent to the home region.

[0087] A home base station 41 1 is located in the home network 401, and has an associated area of coverage 421 (i.e., coverage area). The home base station 41 1 is located adjacent to a first border 404 between the home region and the visited region.

[0088] First and second visited base stations 431 and 451 are located in the visited region 402. Each visited base station has an associated area of coverage 441, 461 (i.e. coverage area). The first visited base station 431 is located adjacent to the first border 404 between the home region and the visited region; and the second visited base station 451 is located adjacent to a second border 408 between the visited region and the neighboring region. The first and second visited base stations 431, 451 are arranged such that the first and second areas of coverage 441, 461 at least partially overlap.

[0089] A neighboring base station 471 is located in the neighboring network 403, and has an associated area of coverage 481 (i.e., coverage area). The neighboring base station 471 is located adjacent to the second border 408 between the visited region and the neighboring region.

[0090] Although as noted in FIG. 1, each base station 411, 431, 351, and 471 will actually have a different downlink coverage area and uplink coverage area, a single coverage area 421 , 441 , 461 , 481 is shown for each base station 411 , 431 , 351 , and 471 for the sake of simplicity.

[0091] In addition, although the first, second, and third networks 401, 402, 403 would have many more base stations, these four base stations are shown by way of example.

[0092] The home region, the visited region, and the neighboring region can represent different countries, different regions within the same country, or a combination of these two. In one embodiment in which the home, visited, and neighboring regions are in a 3 GPP network, the home region, the visited region, and the neighboring region are regions that are identified by different mobile country code (MCC) values. This means that the home network 401, the visited network 402, and the neighboring network 403 will each be assigned mutually exclusive MCC values.

[0093] Because the base stations 41 1, 431, 351, and 471 are all located adjacent to the one of the two borders 404, 408, each of these base stations 411, 431, 351, and 471 transmits at least partially over a regional border 404, 408. The home base station 41 1 transmits at least partially over the first border 404 into the visited region; the first visited base station 431 transmits at least partially over the first border 404 into the home region; the second visited base station 451 transmits at least partially over the second border 408 into the neighboring region; and the neighboring base station 471 transmits at least partially over the second border 308 into the visited region.

[0094] An example of the operation of the disclosed protocol will be described with respect to FIG. 4. In this example, a user has a mobile device 130 whose home network 401 is associated with the home region. The user travels from point K, through the visited region, to point P in the neighboring region.

[0095] At point K, the user's mobile device 130 begins being associated with the home network 401, allowing the user to pay the comparatively cheap home rates for mobile device service. In particular, the mobile device 130 is associated with a home base station 41 1. Since the home base station 41 1 is adjacent to the first border 404, the home base station 411 broadcasts a downlink control channel 220 having a border indicator 240 that indicates it is a border base station, and border information 250 identifying the visiting region as an adjacent region. The mobile device 130 does not search for the home network 401 because it is already associated with home network 401. [0096] As the user moves from point K to point L, she enters the first visited coverage area 441 of the first visited base station 431 in the visited network 402, and crosses the border 404, passing from the home region to the visited region. But both of these transitions are unimportant to the mobile device 130. When the user enters the first visited coverage area 441, the mobile device 130 is still connected to the home network 401, and so has no need to search for another network. Furthermore, none of the home network 401, the visited network 402, and the mobile device 130, has any way to recognize the first border 304.

[0097] In this overlap area between the home network 401 and the visited network 402, the home base station 41 1 transmits a downlink control channel 220 that includes a border indicator 240 indicating that the home base station 411 is a border station, and border information 250 identifying the visited region as an adjacent region. Similarly, the first visited base station 431 transmits a downlink control channel 220 that includes a border indicator 240 indicating that the visited base station 431 is a border station, and border information 250 identifying the home region as an adjacent region. Regardless, the mobile device 130 remains connected to the home base station 41 1 in the home network 401, and does not look for either the home network 401 or another network.

[0098] It is only when the user reaches point M that additional network connection action takes place. At point M, the mobile device 130 leaves the coverage area 421 of the home base station 41 1, and does not enter a coverage area for any other base station in the home network 401. Since the mobile device can no longer communicate with the home base station 411, and has not been handed off to another base station in the home network 401, it begins looking for a new network. This search should cause it to contact the visited network 402 through a signal received from the first visited base station 431.

[0099] Once the mobile device 130 is associated with the first visited base station 431 in the visited network 402, the user will begin to pay the comparatively larger roaming rates for using the mobile device 130. In addition, the mobile device 130 will begin receiving a downlink control channel 220 from the first visited base station 431. This downlink control channel 220 will include a border indicator 240 indicating that the first visited base station 431 is a border base station, and border information 250 identifying the home region as an adjacent region. The mobile device 130 remains associated with the visited network 402 through the first visited base station 431, but commences searching for the home network 401 because the border indicator 240 and the border information 250 indicate that the mobile device 130 is associated with a base station that is adjacent to the home region. The mobile device 130 does not rejoin the home network 401 because it is not within the coverage area of any of the base stations in the home network 401.

[00100] When the user reaches point N, she has left the first visited coverage area 441, and has entered the second visited coverage area 461. Somewhere in the overlap between these two areas, the visited network 402 will have handed off the mobile device 130 from the first visited base station 431 to the second visited base station 451 using a standard handoff procedure. By point N, the mobile device 130 is receiving a downlink control channel 220 from the second visited base station 451. This downlink control channel 220 will include a border indicator 240 indicating that the second visited base station 451 is a border base station, and border information 250 identifying the neighboring region as an adjacent region. The mobile device 130 stops searching for the home network 301, because although it is associated with a border base station, that border base station does not border the home region.

[00101] Once the user reaches point O, the mobile device 130 will be within the third home coverage area 481. At this point, the mobile device 130 will be able to communicate with the neighboring base station 471, though it will have no need to do so since it is still associated with the visiting network 402. The second visited base station 451 continues to transmit a downlink control channel 220 that includes a border indicator 240 indicating that the second visited base station 451 is a border base station, and border information 250 identifying the neighboring region as an adjacent region. Similarly, the neighboring base station 471 transmits a downlink control channel 220 that includes a border indicator 240 indicating that the neighboring base station 471 is a border base station, and border information 250 identifying the visited region as an adjacent region.

[00102] When the user approaches point P, the mobile device 130 will leave the second visited coverage area 461 of the second visited base station 451, and will not enter a coverage area for any other base station in the visited network 402. Since the mobile device can no longer communicate with the second visited base station 451, and has not been handed off to another base station in the visited network 402, it begins looking for a new network. This search should cause it to associate itself with the neighboring network 403 through a signal received from the neighboring base station 471. At this point, the user continues paying the relatively higher roaming rates because she is still not connected to her home network 401.

[00103] Once the mobile device 130 is associated with the neighboring base station 471 in the neighboring network 403, it will begin receiving a downlink control channel 220 from the neighboring base station 471. This downlink control channel 220 will include a border indicator 240 indicating that the neighboring base station 471 is a border base station, and border information 250 identifying the visited region as an adjacent region. The mobile device 130 will not search for the home network 401 at this time, because while the border indicator 240 indicates that the neighboring base station 471 is a border base station, the border information 250 does not indicate that the neighboring base station 471 is adjacent to the home region.

[00104] This example shows how it is possible to be in a border area, but not search for a home region. This is because two things are required before the mobile device 130 will search for the home region: (1) the border indicator 240 indicates that the currently associated base station is a border base station; and (2) the border information 250 indicates that the home region is an adjacent region.

[00105] Method of Operating a Mobile Device

[00106] FIG. 5 is a flow chart of an operation 500 of a mobile device 130 in determining whether or not to try and locate its home network according to disclosed embodiments. As shown in FIG. 5, the operation begins with the mobile device 130 associating itself with a visited region (i.e., a region that is not the home region of the mobile device 130). (505)

[00107] The mobile device 130 then processes signals in the visited region. (510) This can involve passing data signals back and forth, or any suitable processing for the mobile device 130.

[00108] At some point, the mobile device 130 receives control signals from a base station 110, 140 to which it is associated. (515) These control signals can be downlink control signals in a downlink control channel, or any other downlink transmission used to pass control data or information from the base station 110, 140 to the mobile device 130. As noted above, by way of example, in a 3 GPP system, the control signals can be a master information block (MIB) sent over a broadcast channel (BCH), a system information block (SIB) sent over a downlink shared channel (DL-SCH), an information block specifically dedicated to transmit border data, or any suitable block of data that is sent from a base station 110, 140 to a mobile device 130.

[00109] Once it receives the control signal from the base station 110, 140, the mobile device 130 extracts the border indicator data, which indicates whether or not the base station is a border base station located adjacent to a border between two regions (e.g., a national border). (520) As noted above, this border indicator could be a bit, a symbol, a code word, or any other desirable format for passing this information. [00110] The mobile device 130 then determines whether or not the transmitting base station 110, 140 is located near a border by examining the border indicator. (525)

[00111] If the transmitting base station is not near a border, then the mobile device 130 maintains its current network (530), and returns to processing signals in the visited region. (510)

[00112] If, however, the border indicator indicates that the base station is near a border, the mobile device extracts the border information from the control signal received from the base station. (535) Although the extraction of the border information (535) is shown as being separate from extracting the border indicator data (520), these two operations can be performed at the same time.

[00113] The mobile device 130 then determines whether the border information indicates that a region adjacent to the transmitting base station is the home region for the mobile device 130. (540)

[00114] If the transmitting base station is not adjacent to the home region, then the mobile device 130 maintains its current network (530), and returns to processing signals in the visited region. (510)

[00115] If, however, the border information indicates that the transmitting base station is adjacent to the home region, then the mobile device 130 searches for its home network (545), to determine whether it can find its home network. (550) This searching can be performed periodically for as long as the mobile device 130 is associated with a base station that indicates it is adjacent to the home region of the mobile device 130, subject to the limitations in the duration of the attempt before timing out, the allowable time between retry attempts, and the allowable number of retry attempts set forth by the protocol used by the mobile device 130. [00116] If, for example, the mobile device 130 is a 3GPP device, then a value of T is set between 6 minutes and 8 hours. This value for T indicates how frequently a search attempt will be made for the home network. There is no limit on the number of retries under this protocol.

[00117] If the mobile device 130 cannot find the home network within the time period allotted by the protocol for the attempt, then it maintains its current network (530), and returns to processing signals in the visited region. (510)

[00118] If, however, the mobile device 130 finds the home network, then it determines the strength of the transmissions from the home network. (555)

[00119] The mobile device 130 then compares the strength of the transmissions from the home network against a threshold value. (560) This threshold value can be an absolute value indicative of a minimum level of acceptable strength, or it can be a variable value varying based on any suitable parameter (e.g., it could be set to be equal to the strength of the signals from the visited network, some percentage of the strength of the signals from the visited network, or any desirable strength formula).

[00120] If the mobile device 130 determines that the strength of the home network transmissions are below the threshold of acceptability, then it maintains its current network (530), and returns to processing signals in the visited region. (510)

[00121] If, however, the mobile device 130 determines that the strength of the home network is above the minimum threshold, then it connects to the home network (565) and proceeds with processing in the home network. (570)

[00122] In this way, the mobile device 130 will be able to know when it would be reasonable to look for the home network (i.e. when there is a comparatively high likelihood of finding the home network), and when it would be unreasonable to do so (i.e., when there is a comparatively low likelihood of finding the home network). Under this system, it is considered reasonable to look for the home network when the mobile device 130 is associated with a base station 110, 140 that is adjacent to the home region that the home network is in. It is considered unreasonable to look for the home network when the mobile device 130 is associated with a base station 110, 140 that is not adjacent to the home region.

[00123] As a result, this method allows the mobile device 130 to look for the home network in an efficient manner. In other words, the mobile device 130 will not waste its battery life searching for the home network in situations where the home network could not be found (e.g., when the mobile device 130 was associated with a base station 110, 140 that was not even adjacent to the home region), but will only attempt to find the home network when there's a possibility it might be found (e.g., when the mobile device 130 was associated with the base station 110, 140 that was adjacent to the home region). Furthermore, by checking signal strength, the mobile device 130 will not flip-flop act and forth between the home network and the visited network if it is located at the very edge of the coverage area of a base station in the home network.

[00124] In alternate embodiments, the operations of determining the strength of the home network (555) and determining whether the strength of the network is above a threshold strength (560) can be omitted.

[00125] Method of Operating a Base Station

[00126] FIG. 6 is a flow chart of an operation 600 of a base station 110, 140 identifying its border status according to disclosed embodiments. As shown in FIG. 6, the base station begins with the base station 1 10, 140 associating with a mobile device 130. (610)

[00127] In some embodiments this association operation is not required. For example, if border data is transmitted in a broadcast command, then there is no need for the base station 110, 140 to be associated with any particular mobile device 130. If, however, the border data is transmitted in a control signal directed to a particular mobile device 130, then it will be necessary to associate with that device 130 before the border data can be sent.

[00128] The base station 110, 140 then begins transmitting a control signal to the mobile device 130. (620) As noted above, this transmission could be via a broadcast command that is not addressed to any particular device, or it could be through a directed command specifically addressed to one or more mobile devices 130.

[00129] In an embodiment in which the network is a 3GPP network, the control signal can be a master information block (MIB) sent over a broadcast channel (BCH), a system information block (SIB) sent over a downlink shared channel (DL-SCH), an information block specifically dedicated to transmit border data, or any suitable block of data that is sent from a base station 1 10, 140 to a mobile device 130.

[00130] Once the base station 1 10, 140 begins transmission of the control signal to the mobile device, it transmits a border indicator to the mobile device 130. (630) This border indicator indicates whether or not the base station 110, 140 is located adjacent to a border between two regions. The precise definition of a region border is left to the transmission protocol. For example, in one embodiment using a 3 GPP network, the border indicator only considers that the base station 110, 140 is adjacent to a region border if its region and the adjacent region are identified by different mobile country code (MCC) values.

[00131] The base station 1 10, 140 then transmits border information to the mobile device 130. This border information indicates which regions the base station 110, 140 is adjacent to (e.g., it could send the MCC values for the adjacent regions). If the base station 110, 140 is not adjacent to any other region, then the content of the border information is unimportant. It can be null data, a set data pattern, left random, etc.

[00132] Additional data may be passed in the control signal. This additional data can be located before the border indicator and the border information, after the border indicator and the border information, between the border indicator and the border information, or any combination of these three options.

[00133] The base station 110, 140 then ends transmission of the control signal to the mobile device 130 (650) and begins passing data to and from the mobile device (660), returning later to begin transmission of another control signal to the mobile device 130. (620) This data can be voice data, image data, text data, other control signals, etc. In addition, this operation may be performed between associating with a mobile device 130 (610) and beginning transmission of the control signal to the mobile device 130 (620).

[00134] In this way, a base station 1 10, 140 can easily provide a mobile device 130 with the information it needs to determine whether it should search for a home network or not. Furthermore, the border data (i.e., border indicator and border information) is a relatively small amount of information, and would not significantly affect the overhead of

transmissions between the base station 110, 140 and mobile devices 130.

[00135] Conclusion

[00136] This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment(s) was chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. The various circuits described above can be implemented in discrete circuits or integrated circuits, as desired by implementation.

Claims

CLAIMS What is claimed is:

1. A method of operating a mobile device in a visited network, comprising: receiving a downlink signal from a visited-network base station, the downlink signal including a border indicator indicating that the visited-network base station is not near a border between a visited region containing the visited network and one or more neighboring regions;

extracting the border indicator from the downlink signal;

determining that the visited-network base station is not near the border between the visited region and any of the one or more neighboring regions based on the border indicator; and

processing signals in the visited network without searching for a home network after the operation of determining that the visited-network base station is not near the border between the visited region and the one or more adjacent regions.

2. The method of claim 1, wherein

the received signal further includes border information, and

the border information does not identify any of the one or more neighboring regions as being adjacent to the visited-network base station.

3. The method of claim 1, wherein the visited network is a 3 GPP network.

4. A method of operating a mobile device in a visited network, comprising: receiving a downlink signal from a visited-network base station, the downlink signal including a border indicator indicating that the visited-network base station is near a border between a visited region containing the visited network and one or more adjacent regions, and border information identifying the one or more adjacent regions;

extracting the border indicator from the downlink signal;

determining that the visited-network base station is near the border between the visited region and the one or more adjacent regions based on the border indicator;

extracting the border information from the downlink signal;

determining whether or not the one or more adjacent regions include a home region for the mobile device;

searching for a home network of the mobile device if it is determined that the one or more adjacent regions include the home region for the mobile device; and

processing signals in the visited region without searching for the home network if it is determined that the one or more adjacent regions do not include the home region for the mobile device.

5. The method of claim 4, wherein the visited network is a 3 GPP network.

6. The method of claim 4, wherein

the received signal further includes border information, and

the border information identifies one or more adjacent regions, the one or more adjacent regions being adjacent to the visited-network base station.

7. The method of claim 6, wherein the border information identifies the one or more adjacent regions by a region identification code.

8. The method of claim 7, wherein the region identification code is a 3 GPP mobile country code.

9. The method of claim 4, wherein the extracting of the border information from the received downlink signal occurs only if it is determined that the visited-network base station is near the border between the visited region and the one or more neighboring regions

10. The method of claim 4, further comprising:

processing signals in the visited region if the operation of searching for the home network does not locate the home network; and

processing signals in the home region if the operation of searching for the home network locates the home network.

11. The method of claim 4, further comprising:

determining a strength of signals from the home network if the operation of searching for the home network locates the home network;

determining whether the strength of signals from the home network is greater than a strength threshold;

processing signals in the visited region if it is determined that the strength of the signals from the home network is not greater than the strength threshold; and

processing signals in the home region if it is determined that the strength of the signals from the home network is greater than the strength threshold.

12. The method of claim 1 1, wherein the strength threshold is fixed threshold.

13. The method of claim 1 1, wherein the strength threshold is set percentage of a strength of signals from the visited network.

14. The method of claim 4, wherein the downlink signal is one of a broadcast signal and a directed signal addressed to the mobile device.

15. A method of operating a base station in a visited network, comprising:

beginning transmission of a downlink signal to a mobile device associated with the base station;

transmitting a border indicator to the mobile device in the downlink signal, the border indicator indicating whether or not the base station is adjacent to one or more other networks; transmitting border information to the mobile device in the downlink signal, the border information identifying the one or more networks that are adjacent to the base station, if any; and

ending transmission of the downlink signal to the mobile device associated with the base station

16. The method of claim 14, further comprising:

associating the base station with the mobile device prior to beginning transmission of the downlink signal.

17. The method of claim 14, wherein the downlink signal is one of a broadcast signal and a directed signal addressed to the mobile device.

The method of claim 14, wherein the visited network is a 3GPP network.

19. The method of claim 14, wherein the border information identifies the one or more networks that are adjacent to the base station by a region identification code.

20. The method of claim 19, wherein the region identification code is a 3GPP mobile country code.