Providing wireless communication services

Abstract

A network node (104) receiving a location update request from a mobile device (112) via a base station (102) located in a region of marginal or no cellular coverage by a home network (110) of the mobi

Description

The present invention relates to the provision of wireless communications services in regions of marginal or no cellular coverage from a public land mobile network (PLMN). Background Mobile network operators aim to provide cellular coverage over defined regions, for example entire countries or states. However, the distribution of cell sites required to provide high quality cellular coverage over the entirety of a large region can be impracticable or financially unviable. The issue of incomplete coverage may be exacerbated by the fact that mobile network operators may not allow their subscribers to access services of competitor networks. It may nevertheless be desirable to provide cellular services in particular regions of interest where a home network has marginal or no cellular coverage (“not spots”), for example in the vicinity of a premises or facility in a remote location. Mobile network operators typically enable roaming in which subscribers can connect to other networks when out of range of their home network. The network operator may implement various safeguards to prevent a mobile device from unnecessarily connecting to another network, for example at a border region between the home network and the other network. Summary According to a first aspect of the present invention, there is provided a system. The system includes a base station apparatus located in a region of marginal or no cellular coverage by a home network of a mobile communication device, and a network node communicatively coupled to the base station apparatus and to a roaming partner network. The network node is arranged to perform operations including receiving a location update request from the mobile communication device via the base station apparatus, authenticating the mobile communication device with the home network of the mobile communication device, and upon successful completion of the authenticating, transmitting a location update accept response to the mobile communications device via the base station apparatus, and enabling the mobile communication device to access a packet data connection via a packet data network (PDN) that is independent from the roaming partner network. The operations further include, while the mobile communication device is enabled to access the packet data connection, sending an update location message to a home network of the mobile communication device, and receiving a response to the update location message from the home network of the mobile communication device. The response to the update location message indicates whether the home network of the mobile communication device permits the network node to provide telephony services to the mobile communications device via the roaming partner network. By enabling the packet data connection before the location update procedure is complete, the network node can provide data services to the user almost immediately (conditional on successful authentication of the device), even in the event that the location update fails or takes a significant period of time, for example because the home network has implemented measures to prevent unnecessary or unauthorized roaming. The authentication and the location update may be performed in accordance with a different wireless communication standards. In particular, the network node may include a mobile management entity (MME) and a mobile switching centre (MSC) connected to the MME via an SGs interface. The authentication of the mobile device may be performed using the Diameter protocol to enable the packet data connection according to the 4G or 5G standard, whereas the messages exchanged with the home network to complete the location update may be in accordance with the Mobile Application Part (MAP) protocol. The SGs interface may enable circuit switched fall back whereby an incoming call is routed to 2G or 3G, which may thwart Diameterbased methods that could reveal the network node as not being a true node of the roaming partner network and cause the incoming call to fail. In the event that the response to the update location message is a reject response, the operations may include sending one or more further update location messages to the home network of the mobile communication device, wherein the or each further update location message is delayed according to a schedule. In some cases, the home network may be configured to deny the location update request a certain number of times, or for a certain period of time, to prevent unwanted roaming at border regions between the home network and a visitor network. By sending further, delayed, attempts according to a schedule, the method may eventually be able to provide telephony services to the device, all the while providing the data service. In the event that the or each further update location message is rejected, the operations may include transmitting a message to the mobile communication device indicating that a data-only service is available to the mobile communication device. In the event that the response to the update location message is an accept response, the operations may include receiving subscriber data from the home network of the mobile communication device, and using the subscriber data to provide telephony services to the mobile communications device via the roaming partner network. This can enable the device to originate and terminate voice calls, for example circuit switched calls or voice over LTE (VoLTE) calls, and to send and receive SMS messages. The method may involve modifying the subscriber data. For example, the subscriber data may indicate that the mobile communication device is barred from telephony services, and the operations may include modifying the subscriber data to no longer indicate that the mobile communication device is barred from telephony services. When telephony services are provided to the mobile communications device via the roaming partner network, the operations may include receiving a short message service (SMS) message for the mobile communication device from the home network of the mobile communication device, and upon determining that the SMS message is at least part of a welcome message, acknowledging acceptance of the SMS message on behalf of the roaming partner network and refraining from transmitting the SMS message to the mobile communication device. Mobile network providers often send welcome messages to their subscribers when they enter an area covered by a visited network other than the home network, for example to inform them that they have entered a region not covered by the home network and of any billing implications. To the home network may treat, the device may appear as having connected to the roaming partner network, even though the base station apparatus may not be located in a region usually associated with the roaming partner network. Any welcome message transmitted to the device may therefore be perceived by a user of the device as nonsensical or confusing. The SMS message may be a first SMS message, and the operations may include storing a flag set to a first value in association with the subscriber data, receiving a second SMS message for the mobile communication device from the home network of the mobile communication device, acknowledging acceptance of the second SMS message on behalf of the roaming partner network and refraining from transmitting the second SMS message to the mobile communication device upon determining that the second SMS message is an over the air (OTA) update message and that the flag is set to the first value, and setting the flag to a second value upon determining that an entirety of the welcome message has been received from the roaming partner network. The OTA update message may prompt a subscriber identity module (SIM) of the device to rescan for the home network. If the entirety of the welcome message has not been received, then the device will find the welcome message, or parts of the welcome message, upon rescanning for networks, resulting in confusion for the user. Alternatively, OTA update messages may be suppressed indefinitely, irrespective of when and whether any welcome message is received. The operations may include caching the second SMS message, and transmitting the second SMS message to the mobile communication device when the flag has been set to the second value. In this way, transmission of nonsensical welcome messages can be avoided while minimising any obstruction to the operation of the home network. The refraining from transmitting the second SMS message to the mobile communication device may be dependent on the MSC not having caused telephony services to be provided to the mobile communication device via the roaming partner network for at least a threshold period of time. The home network may be configured not to send a welcome message in the event of a device leaving a visited network and returning after less than a given amount of time (e.g., 48 hours), so it may be possible to avoid supressing OTA update messages in such cases without any undesirable welcome messages (or parts of welcome messages) being received by the device. The welcome message may be a first welcome message and may refer to a location associated with the roaming partner network, and the operations may include transmitting a second welcome message not referring to the location associated with the roaming partner network to the mobile communication device. Some networks may send “welcome back” messages when a device returns from a visited network. Such a message may be confusing in the absence of any prior welcome message being transmitted to the device. The operations may include associating a temporary or dummy telephone number to the mobile communication device prior to receiving the subscriber data. The temporary telephone number may not be used for any telephony functionality, but this is not a problem as it is replaced by the real telephone number when the home network has accepted the update location message from the network node. The operations may include, responsive to receiving the location update request, iteratively: transmitting an error message comprising instructions to retry after a given period of time to the mobile communication device, and incrementing an access control counter. The transmitting of the location update accept response may be responsive to the access control counter reaching a threshold value. By intentionally refraining from performing the location update a threshold number of times, the system may avoid appropriating the device from the home network when the device is located in a region of marginal cellular coverage, which may otherwise unnecessarily frustrate the operation of the device on the home network. The operations may include receiving an emergency call request from the mobile communication device, and connecting the mobile communication device to a public safety answering point (PSAP). This may include providing information indicative of a location of the base station apparatus to the PSAP. In this way, the system may enable emergency calls in regions of no cellular coverage by any other networks. Enabling the mobile communication device to access the packet data connection may include receiving a packet data protocol (PDP) context request from the mobile communications device via the base station apparatus, and transmitting a PDP context response to the mobile communication device via the base station apparatus. The location update request may include a temporary mobile subscriber identity (TMSI) and a location area index (LAI) associated with a last visited MSC, and the operations may include, while the mobile communication device is enabled to access the packet data connection: identifying the last visited MSC using the LAI, and retrieving an international mobile subscriber identity (IMSI) of the mobile communication device from the MSC using the TMSI. The update location message may include the retrieved IMSI. According to further aspects, there are provided a computer-implemented method, a computer program product (such as one or more non-transient storage media) comprising instructions for carrying out the method, and a data processing system comprising means to carry out the method (for example at least one processor and at least one memory storing instructions which, when executed by the at least one processor, cause the at least one processor to carry out the method). The method includes receiving a location update request from a mobile communication device via a base station apparatus located in a region of marginal or no cellular coverage by a home network of the mobile communication device, transmitting a location update accept response to the mobile communications device via the base station apparatus, and enabling the mobile communication device to access a packet data connection via a PDN that is independent from the roaming partner network. The operations further include, while the mobile communication device is enabled to access the packet data connection, sending an update location message to the home network of the mobile communication device, and receiving a response to the update location message from the home network of the mobile communication device. The response to the update location message indicates whether the home network of the mobile communication device permits the network node to provide telephony services to the mobile communications device via the roaming partner network. Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings. Brief Description of the Drawings Fig. 1 shows schematically an example of a system for providing wireless communication services in accordance with the present disclosure. Figs. 2A-C is a flow diagram representing an example of a method of providing wireless communication services in accordance with the present disclosure. Fig. 3 is a flow diagram representing an example of a method that may be performed in a region of marginal cellular coverage by a home network of a mobile communication device. Detailed Description Details of systems and methods according to examples will become apparent from the following description with reference to the figures. In this description, for the purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to ‘an example’ or similar language means that a feature, structure, or characteristic described in connection with the example is included in at least that one example but not necessarily in other examples. It should be further noted that certain examples are described schematically with certain features omitted and / or necessarily simplified for the ease of explanation and understanding of the concepts underlying the examples. Embodiments of the present disclosure relate to provision of wireless communication services to a user of a mobile device in a region of marginal or no cellular coverage by a home network of the mobile device. In particular, embodiments described herein address challenges caused by measures implemented by home networks to prevent unauthorized roaming and / or to inform users when roaming is taking place. In the present disclosure, roaming may refer to a process by which a mobile device access services via a visited network that is different from their home network. The provision of wireless communication services may be implemented by means of a system comprising a base station apparatus and a network node. The network node may include one or more computing devices and may provide the functionality of an MME and an MSC. The MME and the MSC functionalities may be connected via the SGs interface. The network node may be interconnected to a roaming partner network that is different from the home network of the mobile device. The roaming partner network may include a packet data network (PDN) component and a circuit-switched network component. The operator of the system, for example Wave Mobile Ltd (TM), may have an interconnect agreement with an operator of the roaming partner network, and may have obtained one or more global titles associated with the roaming partner network. In some examples, the roaming partner network may have a zero tariff roaming agreement with the home network provider. As an illustrative example, the home network may be a public land mobile network (PLMN) based in the UK, and the roaming partner network may be a PLMN based in one of the Channel Islands, such as Jersey or Guernsey. In another example, the home network may be a PLMN based in one state in the USA, and the roaming partner network may be a PLMN based in another state in the USA, such as a neighbouring state. Fig. 1 shows an example of a system 100 comprising a base station subsystem (BSS) 102 and a network node 104, which includes the functionality of an MME and an MSC. In this example, the network node 104 is connected to a single BSS, but in other examples an MSC may be connected to multiple BSS’s. The BSS 102 includes a base transceiver station (BTS) 106 and a base station controller (BSC) 108. The BTS 106 in this example is located in a region of marginal or no cellular coverage by a home network 110 of a mobile communication device or mobile station (MS) 112. The BTS 106 may be a microcell BTS with a power of less than 1W (for example, 0.25W) and a range in the order of tens or hundreds of metres. The system 100 also includes a packet data network (PDN) 113 connected to the BSC 108. In this example, the PDN 113 is a locally-provided PDN that is co-sited with the other components of the system 100. The PDN 113 includes both a gateway GPRS support node (GGSN) / packet data gateway (PGW) and a serving GPRS support node (SGSN), which together can provide a connection to the internet 115 using the GPRS tunnelling protocol (GTN). In other examples, one or more components or nodes of the PDN 113 may be sited elsewhere. The network node 104 has an associated visitor location register (VLR) 114, which is a database configured to store information about subscribers currently roaming in a location area of the network node 104. The information stored in the VLR 114 for a given subscriber may include an international mobile subscriber identity (IMSI), a mobile subscriber integrated services digital network (MSISDN), information on the services allowed for a particular IMSI / MSISDN pair, and authentication data. The system 100 is interconnected to a roaming partner network 116, which enables the MS 112 to access communication services via the base station apparatus 102 and the roaming partner network 116, including circuit-switch telephony services (represented by the solid arrows in Fig. 1) and packet data services (represented by the dashed arrows in Fig. 1). The interconnection may for example be by means of a physical wired interconnect or a satellite-based interconnect using Starlink (RTM). The network node 104 is arranged to exchange messages with components of the home network 110, for example using the MAP protocol and / or the Diameter protocol, to facilitate the provision of wireless communication services to a user of the mobile device 116 when the mobile device 116 is in range of the BTS 106. Relevant components of the home network 110 for the present disclosure include the HLR 118 of the home network 110, and an MSC 120 (with associated VLR 122) most recently visited by the MS 112. It is to be noted that the PDN 113 is independent from the roaming partner network 116, so a connection to the PDN 113 can be accessed via the BSS 102 even if a connection to the roaming partner network 116 cannot be established or has not yet been established. Figs. 2A-2D show an example of a method to provide wireless communication services to an MS. The method may for example be carried out by the system 100 to provide wireless communication services to the MS 112 of Fig. 1. More specifically, the method be carried out by the network node 104, or by another network component or computer system in communication with the network node 104 and / or the VLR 114. Prior to the method being carried out, the MS 112 may leave a region of cellular coverage by the home network 110. Upon determining that there is no cellular coverage by the home network 110, the MS 112 may enter a cold start mode in which the MS 112 scans for any non-forbidden network. Meanwhile, the BTS 106 may continually broadcast a signal containing a location area identity (LAI) that is different from the LAI of any nearby location areas associated with the home network 110. When scanning for any non-forbidden network, the MS 112 may detect the signal broadcasted by the BTS 106 and therefore determine that it has entered a new location area. When the MS 112 determines that it has entered a new location area, the MS 112 may initiate a location update procedure as described in 3GPP TS 23.012 version 8.2.0. As shown in Fig. 2A, the method proceeds with receiving, at 202, a location update request from the MS 112 via the BSS 102. The location update request may be received on a dedicated channel established between the BSS 102 and the MS 112. The location update request may include an IMSI or TMSI of the MS 112 and an LAI corresponding to a location area most recently visited by the MS 112. The method continues with authenticating, at 204, the MS 112 with the home network 110 in response to receiving the location update request. The authentication may advantageously be performed in accordance with the Diameter protocol, though it will be appreciated that other protocols such as MAP or RADIUS may be used in certain circumstances. In the event of the authentication being unsuccessful, the network node 104 may reject, at 206, the location update request and the method may terminate. In the event of the authentication being completed successfully, the method may continue with transmitting, at 206, a location update accept response to the MS 112 via the BSS 102. The method may then continue with enabling, at 208, a packet data connection to the MS 112 via the PDN 113. Enabling the packet data connection may include receiving, at 206, a packet data protocol (PDP) context request from the MS 112 via the BSS 102, and transmitting, at 208, a PDP context response to the MS 112 via the BSS 102. The PDP context response may define a PDP context, which is a logical association between the MS 112 and the PDN 113 for use in a data session. The PDP context response may include information to enable the MS 112 to access the packet data connection via the PDN 113. If the authentication at 204 is performed using the Diameter protocol, then the packet data connection may be a 4G or 5G data connection. The PDP context response may include routing information defining a route that data packets should take for a data session, a quality of service (QoS) parameter specifying the level of service required for a data session, security parameters to facilitate integrity and confidentiality of the data packets, and billing information for a data session if applicable. The method may additionally include allocating a temporary or dummy MSISDN to the MS 112 to enable the connection and circumvent errors resulting from the real MSISDN not having yet been obtained. Having received the PDP context response, the MS 112 is enabled to access a data packet connection via the PDN 113 (though not any services that require the MSISDN, such as Voice over LTE (VoLTE)). Because the PDN 113 is independent from the roaming partner network 116, the packet data connection can be provided without needing an Gn / Gp link, which would otherwise be needed to access a data connection via the roaming partner network 116, and under normal circumstances is established only when the location update procedure has taken place. Therefore, by providing the packet data connection via the PDN 113, the system 100 enables the MS 112 to connect to the internet 115 before the location update procedure is complete. During a standard location area update, a PDP context response would not be transmitted until after the home network 110 has approved the location update, which may take several attempts or may not happen at all. One reason for this is that the home network 110 may implement so-called steering of roaming measures to direct the MS 112 to preferred partner networks, which may include rejecting the location area update a given number of times, or for a given amount of time. By contrast, according to the present method the PDP context response may be transmitted almost immediately, or after authentication of the MS 112, meaning that the user of the MS 112 can enjoy data services soon after entering the coverage area of the BSS 102. While the MS 112 is enabled to access the data packet connection, the method continues with sending, at 210, an update location message to the HLR 118, and receiving, at 212, a response to the update location message. The update location message includes the IMSI of the MS 112. If the location update request received at 202 included a TMSI, the method may include additional steps (not shown) of identifying the MSC 120 most recently visited by the MS 112 using the LAI specified in the update location request, and retrieving the IMSI of the MS 112 from the VLR 122 associated with the MSC 120. The response to the update location message may be sent by the HLR 118 or a routing node of the home network 110 which may reject the update location message and decline from forwarding the update location message to the HLR 118. The response may indicate whether the home network 110 of permits the network node 104 to provide telephony services to the MS 112 via the roaming partner network 116. Telephony services may include communication services that are not enabled by the packet data connection enabled at 208, such as services requiring the MSISDN of the MS 112. Telephony services may include originating and / or terminating telephone calls (including VoLTE calls), sending or receiving faxes, and sending or receiving SMS messages. According to GSM Official Document IR.73 - Steering of Roaming Implementation, the home network 110 may reject a location update request a given number of times or for a given amount of time, for example by sending an error message indicating “roaming not allowed”, “data missing”, unexpected data value”, system failure”, or another reason. The intention of this may be to steer the MS 112 to a different network that is preferred by the provider of the home network 110, because according to 3GPP TS 24.008, the MS 112 will try to select another network in the event of a given number of rejections (depending on the reason for the rejection). In the event that the response is a reject response (node A in Figs. 2A and 2B) the method may continue with waiting, at 214, according to a schedule. The schedule may specify a sequence of delays between successive attempts to perform a location update, or a sequence of delays after receiving successive rejections from the home network 110. The schedule may include a finite sequence of delays, which may be equal to one another or may vary in a specified manner. The delays may for example increase with successive attempts. In this way, the shortest delays may be at the start of the schedule which may increase the likelihood of successfully completing the location update in a short amount of time, with longer delays being specified later in the schedule so that the method continues to attempt for a suitably long period of time without creating unnecessarily high messaging traffic. The delays may be of the order of one or more minutes - an example of a schedule specifies delays between attempts of one minute, one minute, two minutes, two minutes, three minutes, three minutes, three minutes. In this example, the schedule is therefore completed after 15 minutes. The schedule may be implemented by means of a counter to track how many attempts have been made and a timer that is dependent on the value of the counter to enforce the delays between attempts. After waiting, the method continues with sending, at 216, a further update location message to the HLR 118, and receiving, at 218, a response to the further update location message. If the response is another reject response and if the schedule is incomplete, the method may return to 214 to wait for the next interval specified in the schedule before further sending another update location message to the HLR 118. If the response is another reject response and the schedule is complete, this may indicate that the home network 110 will not allow roaming on the roaming partner network, in which case the method may conclude with transmitting, at 220, an SMS message to the MS 112 to be displayed to the user of the MS 112 indicating that only data services are available. The message may take the form of a welcome message, for example indicating, “Welcome to Wave Mobile, this is a data only service”, or words to a similar effect. In the event that the MS 112 receives an accept response to an update location message (node B in Figs. 2A, 2B and 2C), the method may continue with receiving, at 222, subscriber data from the HLR 118. The subscriber data may include information used by the network node 104 to provide telephony services to the MS 112 via the roaming partner network 116, including an MSISDN or telephone number of the MS 112. The MSC 112 may store the MSISDN in the VLR 114, for example replacing a previously allocated temporary MSISDN. Having received and stored the subscriber data, the network node 104 may then provide, at 224, telephony services to the MS 112 via the roaming partner network 116. In other words, the MS 112 has been successfully roamed. Once the MS 112 has been roamed, the home network 110 may optionally send either or both of two different SMS messages to be forwarded to the MS 112. The first SMS message is a welcome message to be displayed to the user. The second SMS message is an OTA update message implementing an update to the SIM of the MS 112, triggering the MS 112 to rescan for the home network 110. The respective platforms and / or network components (e.g., servers) used to send the welcome message and the OTA message may be different, and as a result either of the two SMS messages may be received first by the MS 112. The order in which the two SMS messages are received may affect how the method proceeds, as explained hereafter. The method may include receiving, at 226, a first SMS message from the home network 110. The first SMS message may be received in several parts, for example two, three, five or more parts. The method may continue with identifying, at 228, the first SMS messages (or each part of the first SMS message) as a welcome message. This may be done for example by looking for certain data in the header and / or body of the message, such as a carrier ID in the header and / or the words “Welcome” and a location associated with roaming partner network in the body. When the entire welcome message has been received, the method continues with acknowledging, at 230, acceptance of the welcome message on behalf of the roaming partner network 116, to prevent the home network 110 from resending the welcome message. However, the method may refrain indefinitely from transmitting the welcome message to the MS 112 as the welcome message may indicate a location that is inconsistent with the actual location of the MS 112. For example, in the case of a home network 110 based in the UK, the roaming partner network 116 be an offshore network based in one of the Channel Islands such as Jersey, so the welcome message may say “Welcome to Jersey”, along with optionally other information such as setting out applicable charges. The BSS 102, on the other hand, may be set up in a remote part of the mainland UK, so such a welcome message may be surprising and nonsensical to the user of the MS 112. The welcome message may therefore have a detrimental effect on user experience. The method may continue with setting, at 232, a flag to indicate that the entirety of the welcome message has been received. For example, an additional field may be included in a database such as the VLR 114 in association with the subscriber information such as the IMSI, IMEI, and MSISDN of the MS 112, and setting the flag may involve changing the value in the additional field from a first value (e.g., 0 or “false”) to a second value (e.g., 1 or “true”). The method may include receiving, at 234, a second SMS message from the home network 110. As explained above, the second SMS message may be received before or after the first message, and therefore step 234 and any or all of the subsequently-listed steps (234-240) may take place before steps 226-232. The method continues with identifying, at 236, the second SMS message as an OTA update message. This may again be done by looking for certain data in the header and / or body of the second SMS message. As mentioned above, the OTA message may trigger the MS 112 to rescan for the home network. A potential problem with receiving the OTA update message before receiving the entirety of the welcome message is that after rescanning for the home network 110 and reconnecting to the roaming partner network 116, the MS 112 may start to receive parts of the welcome message, which may then be displayed to the user. To prevent this undesirable behaviour, in the event that the flag has not been set, indicating that at least part of the welcome message has not yet been received, the method may refrain, at 238, from forwarding the OTA message to the MS 112. In some examples, the OTA message may instead be forwarded if it is determined that the MS 112 is returning to the location area of the BSS 102 after having left for less than a given amount of time. This is because the home network 110 will not typically send multiple welcome message in a predetermined amount of time, for example 48 hours. Therefore, if the MS 112 has returned to the location area having already been in the location area less than this predetermined amount of time ago, then there will be no welcome message from the home network 110 and the OTA message can be forwarded without risk of the MS 112 receiving parts of a welcome message. In the event that the flag has already been set, indicating that the entirety of the welcome message has been received, then the method may continue with forwarding, at 238, the OTA message to the MS 112. Although this may result in the MS 112 losing its connection to the roaming partner network 116, the operator of the home network 110 may consider it deliberately obstructive to block the OTA message without justification. Nevertheless, in other examples the method may refrain from forwarding the OTA message to the MS 112 indefinitely, for example in cases where the location of the BSS 102 is so remote that rescanning for the home network 110 will inevitably fail. In this way, disruption of the connection between the MS 112 and the roaming partner network 116 may be avoided. In further examples still, the method may include storing or caching the OTA message until the flag is set, at which point the OTA may be sent to the MS 112, thereby minimizing obstruction to the home network 110 whilst avoiding erroneous welcome message effects. In some examples, the home network 110 may be configured to send a “welcome home” message when the MS 112 returns to the home network 110, which may be surprising to the user if the user has not previously received a welcome message informing them that the MS 112 is connected to a different network to the home network 110. The method may therefore optionally include sending an alternative welcome message in place of the welcome message sent by the home network, for example saying, “Welcome to Wave Mobile”, and optionally referring to the genuine location of the MS 112. The method described above may seamlessly provide the user of the MS 112 with communication services in a region of zero or no coverage by the home network 110, with minimal disruption to operation of the home network 110, particularly in situations where the area of coverage of the BSS 102 has little or no overlap with the coverage area of any base station of the home network 110. In other situations the method may be augmented or modified to mitigate disruption to the operation home network 110, for example when a region of marginal coverage by the home network coincides with the coverage area of the BSS 102. Fig. 3 shows an example of modified initial steps for the method. Similarly to the method of Fig. 2A, the method of Fig. 3 proceeds with receiving, at 302, a first location update request from the MS 112 via the BSS 102. Upon receiving the first location update request, the method may optionally initialise an access control counter in association with the MS 112 (for example, in association with the TMSI or IMSI of the MS 112). Initialising the access control counter may include setting the access control counter to a predetermined value, such as 0 or 1. The method continues with determining, at 304, whether the access control counter has reached a threshold value, which may be referred to as an access control limit. If the access control counter has not reached the threshold value (or has not yet been initialised), then the method may proceed with transmitting, at 306, an error message to the MS 112, such as a “network failure” message indicating that the MS 112 should retry after a given amount of time, for example after one minute or after five minutes. The error message may be sent for example using the SI interface, the next-generation application protocol (NGAP), or using a virtual private network (VPN) such as WireGuard over 2G, 4G or 5G. Having send the error message, the method continues with incrementing, at 308, the access control counter associated with the MS 112, or initialising an access control counter if this was not done when the first location update request was received. The method may then return to 302 where a further location update request may be received from the MS 112. If the access control counter has reached the threshold value, then the method may continue with transmitting, at 310, a location update response to the MS 112. Step 310 may correspond substantially to step 204 of Fig. 2A, and may optionally be dependent on authenticating the MS 112 with the home network as described in relation to step 204. The method of Fig. 3 may continue in the same way as the method of Fig. 2A. The method of Fig. 3 intentionally rejects the MS 112 a number of times, preventing one-off connections between the MS 112 and the roaming partner network 116 that may result from the MS 112 temporarily losing signal from the home network 110 in a region of marginal coverage by the home network 110. The access control limit may be set in dependence on the level of coverage by the home network 110 in the vicinity of the BSS 102. For marginal coverage, a relatively high access control limit may be used, whereas for little or no coverage, a relatively low access control limit may be used, or the access control counter may be dispensed with entirely. Aside from improving the effective cellular coverage for a subscriber of the home network 110, the systems and methods described herein may bring additional benefits, for example providing the ability to handle emergency calls in a region where no existing PLMN has coverage. In the event of receiving an emergency call request from the MS 112 when connected to the roaming partner network via the BSS 102, the system 100 may connect the MS 112 to a PSAP and provide the PSAP with an accurate and precise location of the BSS 102. The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, although the description above uses a modified location area update in accordance with the GSM standard, those skilled in the art will appreciate that the techniques may equally be applied for other Radio Access Technologies (RATs), for example as a modified tracking area update in LTE or 5G. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A system comprising:a base station apparatus located in a region of marginal or no cellular coverage by a home network of a mobile communication device; anda network node communicatively coupled to the base station apparatus and to a roaming partner network, wherein the network node is arranged to perform operations comprising:receiving, from the mobile communication device via the base station apparatus, a location update request;authenticating the mobile communication device with the home network of the mobile communication device;upon successful completion of the authenticating:transmitting a location update accept response to the mobile communications device via the base station apparatus; andenabling the mobile communication device to access a packet data connection via a packet data network (PDN) that is independent from the roaming partner network; andwhile the mobile communication device is enabled to access the packet data connection:sending an update location message to the home network of the mobile communication device; andreceiving a response to the update location message,wherein the response to the update location message indicates whether the home network of the mobile communication device permits the network node to provide telephony services to the mobile communications device via the roaming partner network.

2. The system of any preceding claim, wherein:the network node comprises:a mobile management entity (MME); anda mobile switching centre (MSC) connected to the MME via an SGs interface;the authenticating of the mobile communication device is performed by the MME using the Diameter protocol; andthe sending of the or each location update message, and the receiving of the or each response, is performed by the MSC using the Mobile Application Part (MAP) protocol.

3. The system of claim 2, wherein:the mobile communication device is a first mobile communication device; and the operations comprise:receiving an incoming call from a second mobile communication device; performing, using the MME and the MSC, a circuit switched fall back to route the incoming call through a circuit-switched network component of the roaming partner network.

4. The system of any of claims 1 to 3, wherein:the response to the update location message is a reject response;the operations comprise sending one or more further update location messages to the home network of the mobile communication device; andthe or each further update location message is delayed according to a schedule.

5. The system of claim 4, wherein the operations comprise, in the event that the or each further update location message is rejected, transmitting a message to the mobile communication device indicating that a data-only service is available to the mobile communication device.

6. The system of any of claims 1 to 3, wherein:the response to the update location message is an accept response; andthe operations comprise:receiving subscriber data from the home network of the mobile communication device; andproviding, using the subscriber data, telephony services to the mobile communications device via the roaming partner network.

7. The system of claim 6, wherein the operations comprise:receiving, from the home network of the mobile communication device, a short message service (SMS) message for the mobile communication device; andupon determining that the SMS message is at least part of a welcome message, acknowledging acceptance of the SMS message on behalf of the roaming partner network and refraining from transmitting the SMS message to the mobile communication device.

8. The system of claim 7, wherein the SMS message is a first SMS message, the operations comprising:storing a flag in association with the subscriber data, the flag being set to a first value;receiving, from the home network of the mobile communication device, a second SMS message for the mobile communication device;upon determining that the second SMS message is an over the air (OTA) update message and that the flag is set to the first value, acknowledging acceptance of the second SMS message on behalf of the roaming partner network and refraining from transmitting the second SMS message to the mobile communication device; andupon determining that an entirety of the welcome message has been received from the roaming partner network, setting the flag to a second value.

9. The system of claim 8, wherein the operations comprise:caching the second SMS message; andtransmitting the second SMS message to the mobile communication device when the flag has been set to the second value.

10. The system of claim 8 or 9, wherein the refraining from transmitting the second SMS message to the mobile communication device is dependent on the network nodenot having caused telephony services to be provided to the mobile communication device via the roaming partner network for at least a threshold period of time.

11. The system of any of claim 7 to 10, wherein;the welcome message is a first welcome message and refers to a location associated with the roaming partner network; andthe operations comprise transmitting, to the mobile communication device, a second welcome message not referring to the location associated with the roaming partner network.

12. The system of any of claims 6 to 11, wherein:the subscriber data indicates that the mobile communication device is barred from telephony services; andthe operations comprise modifying the subscriber data to no longer indicate that the mobile communication device is barred from telephony services.

13. The system of any of claims 6 to 12, wherein the operations comprise associating a temporary telephone number to the mobile communication device prior to receiving the subscriber data.

14. The system of any preceding claim, wherein the operations comprise, responsive to receiving the location update request, iteratively:transmitting, to the mobile communication device, an error message comprising instructions to retry after a given period of time; andincrementing an access control counter,wherein the transmitting of the location update accept response is responsive to the access control counter reaching a threshold value.

15. The system of any preceding claim, wherein the operations comprise:receiving, from the mobile communication device, an emergency call request;andconnecting the mobile communication device to a public safety answering point (PSAP), including providing, to the PSAP, information indicative of a location of the base station apparatus.

16. The system of any preceding claim, wherein enabling the mobile communication device to access the packet data connection comprises:receiving, from the mobile communications device via the base station apparatus, a packet data protocol (PDP) context request; andtransmitting, to the mobile communication device via the base station apparatus, a PDP context response.

17. The system of any preceding claim, wherein:the location update request comprises a temporary mobile subscriber identity (TMSI) and a location area index (LAI) associated with a last visited mobile switching centre (MSC);the operations comprise, while the mobile communication device is enabled to access the packet data connection:identifying the last visited MSC using the LAI; andretrieving, from the last visited MSC using the TMSI, an international mobile subscriber identity (IMSI) of the mobile communication device; and the update location message includes the retrieved IMSI.

18. The system of any preceding claim, wherein the PDN is a co-sited with the network node.

19. A computer-implemented method comprising:receiving, from a mobile communication device via a base station apparatus located in a region of marginal or no cellular coverage by a home network of the mobile communication device, a location update request;transmitting, to the mobile communications device via the base station apparatus, a location update accept response;receiving, from the mobile communications device via the base station apparatus, a PDP context request;authenticating the mobile communication device against the home network of the mobile communication device;upon successful completion of the authenticating:transmitting a location update accept response to the mobile communications device via the base station apparatus; andenabling the mobile communication device to access a packet data connection via a PDN that is independent from the roaming partner network; andwhile the mobile communication device is enabled to access the packet data connection:sending an update location message to the home network of the mobile communication device; andreceiving a response to the update location message,wherein the response to the update location message indicates whether the home network of the mobile communication device permits telephony services to be provided to the mobile communications device via the roaming partner network.

20. The computer-implemented method of claim 19, wherein:the authenticating of the mobile communication device uses the Diameter protocol; andthe sending of the or each location update message, and the receiving of the or each response, uses the Mobile Application Part (MAP) protocol.

21. The computer-implemented method of claim 19 or claim 20, wherein:the response to the update location message is a reject response;the method comprises sending one or more further update location messages to the home network of the mobile communication device; andthe or each further update location message is delayed according to a schedule.

22. The computer-implemented method of any of claims 19 to 21, wherein:the response to the update location message is an accept response; andthe method comprises:receiving subscriber data from an HLR of the mobile communication device; andproviding, using the subscriber data, telephony services to the mobile communications device via the roaming partner network.

23. The computer-implemented method of claim 22, comprising:storing a flag in association with the subscriber data, the flag being set to a first value;receiving, from the home network of the mobile communication device, a first SMS message for the mobile communication device;upon determining that the first SMS message is at least part of a welcome message, acknowledging acceptance of the first SMS message on behalf of the roaming partner network and refraining from transmitting the first SMS message to the mobile communication device;receiving, from the home network of the mobile communication device, a second SMS message for the mobile communication device;upon determining that the second SMS message is an OTA update message and that the flag is set to the first value, acknowledging acceptance of the second SMS message on behalf of the roaming partner network and refraining from transmitting the second SMS message to the mobile communication device; andupon determining that an entirety of the welcome message has been received from the roaming partner network, setting the flag to a second value.

24. A computer program product comprising instructions for carrying out the method of any of claims 19 to 23.

25. A data processing system comprising means for carrying out the method of any of claims 19 to 23.

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