Patent Description:
In cellular telecommunications networks, a User Equipment (UE) and base station may communicate using a cellular telecommunications protocol. Voice service is a key component of these protocols to enable voice traffic to be communicated from a UE to another node in the cellular telecommunications network (typically another UE). In many early telecommunications protocols, such as the <NUM>nd Generation (<NUM>) protocol defined by the Global System for Mobile Communication (GSM) and the <NUM>rd Generation (<NUM>) protocol defined by <NUM>rd Generation Partnership Project (3GPP), voice services utilised circuit switched data transmission. In other, typically more recent, cellular telecommunications protocols, such as the <NUM>th Generation (<NUM>) and <NUM>th Generation (<NUM>) protocols defined by 3GPP, voice services utilised packet switched data transmission (e.g. Voice-Over-Internet-Protocol, VOIP).

As new generations of telecommunications protocol are introduced, Mobile Network Operators (MNOs) must upgrade or replace their infrastructure to support users of these new generations. As the number of users of the older telecommunications protocols decreases, it becomes less economically viable to operate the older infrastructure. Nonetheless, there are still reasons to maintain this older infrastructure, such as to provide access to an emergency services network to users that can only access such a network through a circuit switched voice service.

International patent application publication no. <CIT> provides a distributed or centralized multi-RAT (radio access technology) technique to implement ESM on a LTE (Long Term Evolution) or UMTS (Universal Mobile Telecommunications System) primary cell network.

International patent application publication no. <CIT> discloses long term evolution (LTE) tracking area updates (TAUs), and tracking area code (TAC) and public land mobile network identification (PLMN-ID) assisted optimized wireless transmit/receive unit (WTRU) cell reselection.

According to a first aspect of the invention, there is provided a method as claimed in Claim <NUM>.

The management node may store a second set of tracking area codes and each of the second set of tracking area codes may be associated with a base station that does not support a circuit switched voice service, and the step of accepting or rejecting the tracking area request may include rejecting the tracking area request if the received tracking area code is one of the second set of tracking area codes.

The response message may identify the first tracking area code as forbidden.

According to a second aspect of the invention, there is provided a computer program comprising instructions which, when the program is executed by a management node, cause the management node to carry out the steps of the first or second aspect of the invention. The computer program may be stored on a computer readable carrier medium.

According to a third aspect of the invention, there is provided a management node for a cellular telecommunications network having a processor configured to carry out the steps of the second aspect of the invention.

A first embodiment of a cellular telecommunications network <NUM> will now be described with reference to <FIG> illustrates a first base station <NUM> of a first Mobile Network Operator (MNO). The first base station <NUM> connects to a first core network <NUM> of the first MNO, which includes a first Mobility Management Entity (MME) <NUM>. <FIG> also illustrates a second base station <NUM> of a second MNO, which connects to a second core network <NUM> of the second MNO, which includes a second MME <NUM>.

The first base station <NUM> and second base station <NUM> are each configured to transmit a tracking area code. In the following embodiments, the first base station <NUM> is configured to transmit a first tracking area code if the first base station <NUM> provides a circuit switched voice service for users of the first MNO's network and to transmit a second tracking area code if the first base station <NUM> does not provide a circuit switched voice service to users of the first MNO's network. Similarly, the second base station <NUM> is configured to transmit a third tracking area code if the second base station <NUM> provides a circuit switched voice service to users of the second MNO's network and to transmit a fourth tracking area code if the second base station <NUM> does not provide a circuit switched voice service to users of the second MNO's network.

The first MME <NUM> stores a database of tracking area codes in which a first set of tracking area codes are associated with base stations that provide a circuit switched voice service to users of the first MNO's network and a second set of tracking area codes are associated with base stations that do not provide a circuit switched voice service to users of the first MNO's network. In this embodiment, the first set of tracking area codes stored in the first MME's database includes the first tracking area code, and the second set of tracking area codes stored in the first MME's database includes the second tracking area code.

Similarly, the second MME <NUM> stores a database of tracking area codes in which a first set of tracking area codes are associated with base stations that provide a circuit switched voice service to users of the second MNO's network and a second set of tracking area codes are associated with base stations that do not provide a circuit switched voice service to users of the second MNO's network. In this embodiment, the first set of tracking area codes stored in the second MME's database includes the third tracking area code, and the second set of tracking area codes stored in the second MME's database includes the fourth tracking area code.

A first embodiment of a method of the present invention will now be described with reference to <FIG>. As shown in <FIG>, the first and second base stations <NUM>, <NUM> are in an initial configuration in which the first base station <NUM> is configured to provide a "<NUM>" service (i.e. based on one or more of Release <NUM> to Release <NUM> of the <NUM>rd Generation Partnership Project (3GPP)), and a "<NUM>" service (i.e. based on one or more of Release <NUM> and any subsequent Release of 3GPP considered as a <NUM> service), and the second base station <NUM> is configured to provide <NUM> and <NUM> services and is further configured to provide a "<NUM>" service (i.e. based on one or more of the Global System for Mobile Communications (GSM) specifications). The first base station <NUM> therefore provides packet switched voice services via Voice of Internet Protocol (VoIP) technology, and the second base station <NUM> provides packet switched voice services via VoIP for any <NUM> and <NUM> users or via a circuit switched voice service for <NUM> users (the VoIP <NUM>/<NUM> service is optional, as the <NUM> voice service may be used for all voice services and <NUM>/<NUM> used for data services).

In this initial configuration, the first base station <NUM> broadcasts the second tracking area code (indicating that it does not provide a circuit switched voice service to users of the first MNO's network) and the second base station <NUM> broadcasts the third tracking area code (indicating that it does provide a circuit switched voice service to users of the second MNO's network).

In a first step of this embodiment (step S101), as shown in the flow diagram of <FIG>, the second base station <NUM> determines that an energy saving trigger condition has been satisfied. In step S103, it is determined (e.g. by negotiation between the first and second base stations <NUM>, <NUM>) that the second base station <NUM> should enter energy saving mode for its <NUM> and <NUM> services (thus maintaining its <NUM> service), and the first base station <NUM> should enable a <NUM> service and enter compensation mode for the second base station's <NUM> and <NUM> services.

In step S105, the first base station <NUM> enables a <NUM> service. The first base station <NUM> may enable the <NUM> service by activating a <NUM> radio function and utilising the first MNO's <NUM> licensed spectrum (that previously wasn't being used by the first base station <NUM>). In other implementations, the first base station <NUM> may reassign spectrum ("refarm") from other protocols (e.g. the first MNO's <NUM> and/or <NUM> spectrum) to be used for <NUM> services, use some of second MNO's licensed spectrum (either the <NUM> spectrum or refarmed <NUM> spectrum) for <NUM> services (e.g. under a spectrum sharing agreement), use shared licenced spectrum (e.g. Licensed Shared Access), or unlicensed spectrum.

In step S107, the first base station <NUM> reconfigures to compensate for the second base station <NUM>. This includes a switch from a Multi-Operator Radio Access Network (MORAN) configuration to a Multi-Operator Core Network (MOCN) configuration, in which the first base station <NUM> begins transmitting both the first MNO's Public Land Mobile Network (PLMN) identifier and the second MNO's PLMN identifier, and accepts handovers and redirections of all users being served by the second base station <NUM>. As part of this reconfiguration, the first base station <NUM> connects to both the first MME <NUM> of the first MNO's core network and the second MME <NUM> of the second MNO's core network. As the first base station <NUM> is enabling a <NUM> service for at least users of the second MNO's network, the first base station <NUM> retrieves, from the second MME <NUM>, the third tracking area code indicating that it provides a circuit switched voice service to users of the second MNO's network. The first base station <NUM> then broadcasts this third tracking area code.

Additionally, in a scenario where the newly-enabled <NUM> service of the first base station <NUM> may also be used by users of the first MNO's network, then the first base station <NUM> switches from broadcasting the second tracking area code to broadcasting the first tracking area code (indicating that it also provides a circuit switched voice service to users of the first MNO's network) in addition to broadcasting the third tracking area code.

Following these reconfigurations, any <NUM> and/or <NUM> traffic for the second MNO's users now being served by the first base station <NUM> is routed between the first base station <NUM> and the second MNO's core network.

In step S109, the second base station <NUM> enters energy saving mode for its <NUM> and <NUM> services. As part of this reconfiguration, the second base station <NUM> switches from broadcasting the third tracking area code to broadcasting the fourth tracking area code (indicating that it does not provide a circuit switched voice service to users of the second MNO's network). The final state of the network is illustrated in <FIG>.

This first embodiment ensures a User Equipment (UE) that requires a circuit switched voice service (for example, a UE that is not configured for voice services of the <NUM> and <NUM> cellular telecommunications protocols) does not connect to a base station that no longer provides a circuit switched voice service. This process is illustrated by the flow diagram of <FIG>. When a UE that requires a circuit switched voice service, that is not connected to the second base station <NUM>, receives the fourth tracking area code broadcast by the second base station <NUM>, it may initiate a tracking area code update process. As part of this process, the UE sends a tracking area update request to the second MME <NUM>, via the second base station <NUM>, which includes the fourth tracking area code (received at the second MME <NUM> in step S201). On receipt of the tracking area update request, in step S203, the second MME <NUM> determines whether the UE requires a circuit switched voice service based on the capabilities of the UE. These capabilities may already be known to the second MME <NUM> (from an earlier capability signalling procedure) or retrieved on receipt of the tracking area update request (e.g. by retrieving its subscription status from the Home Subscriber Server (HSS)). In this example, the second MME <NUM> determines that the UE requires a circuit switched voice service and the process continues to step S205 in which the second MME <NUM> determines whether or not the second base station <NUM> provides a circuit switched voice service to users of the second MNO's network. This is achieved, in this embodiment, by performing a lookup operation with its database of tracking area codes (which are each marked as being for base stations that either provide circuit switched voice service to users of the second MNO's network or do not provide circuit switched voice service to users of the second MNO's network) to determine whether or not the fourth tracking area code is associated with base stations that provide a circuit switched voice service to users of the second MNO's network. In this example, the second MME <NUM> determines from this lookup operation that the second base station <NUM> does not provide a circuit switched voice service to users of the second MNO's network. Accordingly, in step S207, the second MME sends a tracking area update reject message to the UE. This prevents the UE from connecting to the second base station <NUM> when the second base station <NUM> does not provide a circuit switched voice service.

Furthermore, in this embodiment, the tracking area update reject message includes a cause code that causes the UE to update a list of forbidden tracking area codes with the fourth tracking area code. This will prevent the UE from connecting to any base station that transmits the fourth tracking area code without having to perform the tracking area update/reject process outlined above. This list of forbidden tracking area codes is stored in the UE until it is reset.

Following the rejected tracking area update request, the UE may connect to a base station that provides a circuit switched voice service, such as the first base station <NUM> that has enabled a circuit switched voice service. That is, following the above process of <FIG>, when the UE receives the third tracking area code broadcast by the first base station <NUM> and sends a tracking area update request to the first base station <NUM>, the first base station <NUM> forwards the tracking area update request message to the second MME <NUM> (using the connection established to the second MNO's core network as part of the switch to MOCN mode). The second MME <NUM> determines that the third tracking area code broadcast by the first base station <NUM> indicates that the first base station <NUM> does provide a circuit switched voice service to users of the second MNO's network and, in response, sends a tracking area update accept message to the UE (step S209) permitting the UE to connect to the first base station <NUM>.

The skilled person will understand that it is non-essential that the first and second base stations are operated by distinct operators. That is, in a single operator implementation of the first embodiment, the first and second base stations would transmit a first tracking area code if they provided a circuit switched voice service and a second tracking area code if they did not provide a circuit switched voice service, and a single MME would store these first and second tracking area codes in a database.

Furthermore, it is non-essential that the compensating base station enables a circuit switched voice service in order to compensate for the circuit switched voice service that is entering energy saving mode. That is, the compensating base station may already provide a circuit switched voice service (although there may be a requirement for reconfiguring this service to make it available to users of another network). This situation may arise where the energy saving base station is a femtocell and the compensating base station is a macrocell.

A second embodiment of a cellular telecommunications network <NUM> of the present invention will now be described with reference to <FIG>. This second embodiment includes a first base station <NUM>, a second base station <NUM>, a core network <NUM>, and an MME <NUM>. The first and second base stations <NUM>, <NUM> are both connected to the core network <NUM> and MME <NUM>.

<FIG> further illustrates a building defining an interior space. The second base station <NUM> is positioned in the building and provides a <NUM> service throughout the interior space of the building. The first base station <NUM> is positioned outside the building and provides a circuit switched voice service according to the <NUM> cellular telecommunications protocol. The first base station <NUM> is configured to provide circuit switched voice service to the second base station's users by circuit switched fallback. In other words, the second base station <NUM> supports a circuit switched voice service via fallback to the first base station <NUM>.

In this embodiment, the first base station <NUM> is configured to manage its load (as defined by utilisation of the first base station's resources, such as radio resources or processing resources) by varying its coverage area. For example, if the first base station's load satisfies a threshold indicating that it is operating at a relatively high load, then in response the first base station <NUM> decreases its coverage area (by reducing its transmission power) so that users at the edge of the first base station's coverage area are encouraged to transfer to another base station. This reduces the number of served users for the first base station <NUM>, thus reducing its load. Conversely, if the first base station's load satisfies a threshold indicating that it is operating at a relatively low load, then in response the first base station <NUM> increases its coverage area (by increasing its transmission power) so that more users are transferred to the first base station <NUM>. This increases the number of served users for the first base station <NUM>, thus increasing its load. This operation is known as "cell-breathing".

As the first base station's transmission power is variable, the coverage area of the first base station <NUM> may or may not cover the interior space of the building depending on whether the first base station's transmission power meets a transmission power threshold. This transmission power threshold therefore represents the minimum transmission power required for the first base station's coverage area to cover the interior space of the building. This transmission power threshold may be determined by the second base station <NUM>, by the second base station's users and/or by operator measurements of the first base station's signal strength (e.g. Signal-to-Interference-plus-Noise Ratio (SINR)) in the interior space of the building at various transmission powers so as to determine the minimum transmission power required for a UE to receive service from the first base station <NUM> in the interior space. Alternatively, the threshold may be calculated using a propagation model. The transmission power threshold is stored in the second base station's memory.

In this embodiment, the second base station <NUM> is configured to transmit a first tracking area code if the second base station <NUM> supports a circuit switched voice service (that is, when the first base station's transmission power is above the transmission power threshold), and the second base station <NUM> is configured to transmit a second tracking area code if the second base station <NUM> does not support a circuit switched voice service (that is, when the transmission power of the first base station <NUM> is below the transmission power threshold). The MME <NUM> stores a database of tracking area codes in which a first set of tracking area codes are associated with base stations that support a circuit switched voice service to users in the interior space of the building and a second set of tracking area codes are associated with base stations that do not support a circuit switched voice service to the interior space of the building. In this embodiment, the first set of tracking area codes stored in the MME's database includes the first tracking area code, and the second set of tracking area codes stored in the MME's database includes the second tracking area code.

A second embodiment of a method of the present invention will now be described with reference to <FIG>. In a first step of this second embodiment (step S301), the second base station <NUM> obtains data indicating a change in the transmission power of the first base station <NUM>. This data may be obtained as an update message from another network entity (e.g. the first base station <NUM> via X2 messaging), from measurements by the second base station <NUM>, or from measurements by the second base station's users.

This data indicates that a change has occurred and further indicates a new transmission power for the first base station <NUM> (either explicitly, or indicates data from which the new transmission power can be derived). In step S303, the second base station <NUM> determines whether the new transmission power satisfies the transmission power threshold. If the new transmission power is greater than the transmission power threshold, then (in step S305) the second base station <NUM> is configured to use the first tracking area code (indicating that it supports a circuit switched voice service to users in the interior space of the building). If the new transmission power is less than the transmission power threshold then (in step S307) the second base station <NUM> is configured to use the second tracking area code (indicating that it does not support a circuit switched voice service to users in the interior space of the building).

The cellular telecommunications network of this second embodiment may then follow the process described in reference to <FIG> so as to ensure that UE that require a circuit switched voice service only connect to the second base station <NUM> if it supports a circuit switched voice service in a particular region (e.g. the interior space of the building). For example, if the first base station <NUM> configures its transmission power such that it does not cover the interior space of the building such that the second base station <NUM> transmits the second tracking area code, then a UE positioned in the interior space of the building would send a tracking area update request message to the MME on receipt of the second tracking area code transmitted by the second base station <NUM> within the interior space of the building. This results in a tracking area update reject message from the MME, thus ensuring that the UE would not be able to connect to the second base station <NUM>. Conversely, if the first base station <NUM> configures its transmission power such that it does cover the interior space of the building such that the second base station <NUM> transmits the first tracking area code, then a UE positioned in the interior space of the building and requiring a circuit switched voice service would send a tracking area update request message to the MME on receipt of the first tracking area code from the second base station <NUM>. This results in a tracking area update accept message from the MME, such that the UE would be able to connect to the second base station <NUM>. This second embodiment therefore provides the benefit of using tracking area codes to control access based on the relative position of the UE to the base station's circuit switched voice service coverage area.

The skilled person will understand that the above second embodiment applies to other scenarios where a circuit switched voice service has a changeable coverage area. This may apply, for example, where a base station transmits both a <NUM> and <NUM> service, but varies the coverage area of the <NUM> service.

A third embodiment of a cellular telecommunications network <NUM> will now be described with reference to <FIG>. This third embodiment includes a first base station <NUM>, a core network <NUM>, and an MME <NUM>. The first base station <NUM> is connected to the first core network <NUM> and first MME <NUM>.

In this third embodiment, the first base station <NUM> is configured for communications according to a plurality of protocols, in which at least one of these protocols includes circuit switched voice service. In this example, the first base station <NUM> is configured to provide both a <NUM> service and a <NUM> service. The first base station <NUM> is also configured to reassign spectrum between the <NUM> and <NUM> services, such that some or all of the <NUM> spectrum may be reassigned for use by the <NUM> service (and vice-versa).

The first base station <NUM> is further configured to transmit a tracking area code. In this embodiment, the first base station <NUM> is configured to transmit a first tracking area code if the first base station provides a circuit switched voice service (that is, at least some of the <NUM> spectrum is still being used for a <NUM> service) and to transmit a second tracking area code if it does not provide a circuit switched voice service (that is, all of the <NUM> spectrum has been reassigned to the <NUM> service). The MME <NUM> stores a database of tracking area codes in which a first set of tracking area codes are associated with base stations that provide a circuit switched voice service and a second set of tracking area codes are associated with base stations that do not provide a circuit switched voice service. In this embodiment, the first set of tracking area codes stored in the MME's database includes the first tracking area code, and the second set of tracking area codes stored in the MME's database includes the second tracking area code.

A third embodiment of a method of the present invention will now be described with reference to <FIG>. In a first step of this third embodiment (step S401), it is determined that a trigger condition has been satisfied for the first base station <NUM> to change its spectrum assignment of its circuit switched voice service. In step S403, the first base station <NUM> determines its new spectrum assignment for its circuit switched voice service.

In step S405, the third base station <NUM> determines whether the new spectrum assignment is greater than a spectrum assignment threshold required to provide the <NUM> service. This threshold may be <NUM>. If this determination is positive, then, in step S407, the first base station <NUM> transmits the first tracking area code. If this determination is negative, then, in step S409, the first base station <NUM> transmits the second tracking area code.

The cellular telecommunications network of this third embodiment may then follow the process described in reference to <FIG> so as to ensure that UE that require a circuit switched voice service only connect to the first base station <NUM> if it provides its circuit switched voice service. For example, if the first base station <NUM> has no spectrum assigned to its <NUM> service (that is, it has reassigned all <NUM> spectrum to its <NUM> service) and therefore transmits the second tracking area code, then a UE would send a tracking area update request message to the MME on receipt of the second tracking area code. If the UE requires a circuit switched voice service, then the MME would reject this tracking area update message, thus ensuring that the UE would not be able to connect to the first base station <NUM>. Conversely, if the first base station <NUM> has a non-zero spectrum assignment for its <NUM> service and therefore transmits the first tracking area code, then a UE would send a tracking area update request message to the MME on receipt of the first tracking area code. If the UE required a circuit switched voice service, then the MME would accept this tracking area update message and the UE would be able to connect to the first base station <NUM>. This third embodiment therefore provides the benefit of using tracking area codes to control access based on a current spectrum assignment to a circuit switched voice service when the base station implements spectrum refarming.

In the above embodiments, the circuit switched voice service is a GSM <NUM> service. However, this is non-essential and the skilled person would understand that the above embodiments may apply to a circuit switched voice service of any protocol, such as the <NUM> voice service (as standardised by 3GPP).

In the embodiments above, the tracking area codes transmitted by each base station indicate whether that base station either provides or does not provide a circuit switched voice service. However, the tracking area codes may more generally indicate whether that base station either supports or does not support a circuit switched voice service.

That is, a base station may support a circuit switched voice service if it either provides a circuit switched voice service itself, or it does not provide a circuit switched voice service but facilitates fallback to a circuit switched voice service. Conversely, a base station may not support a circuit switched voice service if it does not provide a circuit switched voice service and it does not facilitate fallback to a circuit switched voice service. For example, in a modification to the first embodiment, following the reconfigurations of the first and second base stations (such that the first base station <NUM> enables a <NUM> service and the second base station <NUM> enters energy saving mode for its <NUM> service), the second base station <NUM> may still support circuit switched voice service to users of the second MNO's network if it facilitates circuit switched fallback to the first base station's newly enabled <NUM> service. In such a scenario, the second base station <NUM> may also broadcast the third tracking area code so that users (requiring circuit switched voice service) are permitted to connect to the second base station <NUM>.

In the above embodiments, the MME stored a first set of tracking area codes identifying base stations that support or provide a circuit switched voice service and a second set of tracking area codes identifying base stations that do not support or provide a circuit switched voice service. This is non-essential and the skilled person will understand that other implementations are possible. For example, the MME may store a single list of tracking area codes which identify base stations that support or provide a circuit switched voice service, and the MME would then only permit access to a base station if the tracking area update request included a tracking area code on that list. In another example, the MME may store a single list of tracking area codes which identify base stations that do not support or provide a circuit switched voice service, and the MME would then only permit access to a base station if the tracking area update request included a tracking area code that is not on that list.

Claim 1:
A method performed by a management node (<NUM>, <NUM>, <NUM>, <NUM>) in a cellular telecommunications network, the cellular telecommunications network including a first base station and a User Equipment, UE, wherein the first base station is configured to transmit a first tracking area code and the UE is configured to send a tracking area update request message to the first base station identifying the first tracking area code, the method comprising the steps of:
receiving a request message from the first base station, the request including the first tracking area code identified in the tracking area update request message;
the method characterised by:
the management node (<NUM>, <NUM>, <NUM>, <NUM>) storing a first set of tracking area codes,
comparing the received first tracking area code to the first set of tracking area codes; and
sending a response message to the first base station, the response message accepting or rejecting the tracking area update area request based on the comparison,
wherein:
each of the first set of tracking area codes is associated with a base station that supports a circuit switched voice service, and the step of accepting or rejecting the tracking area update request includes accepting the tracking area update request if the received tracking area code is one of the first set of tracking area codes, or
each of the first set of tracking area codes is associated with a base station that does not support a circuit switched voice service, and the step of accepting or rejecting the tracking area update request includes rejecting the tracking area update request if the receiving tracking area code is one of the first set of tracking area codes.