Cellular telecommunications network

Abstract

To provide a method of operating a cellular telecommunication network that ensures continuity of service to a UE previously served by a base station.SOLUTION: In a cellular telecommunication network including a base station and user equipment (UE), in which the base station broadcasts a tracking area code, a management node receives, from the UE, a tracking area update request message including the tracking area code broadcast by the base station, determines, on the basis of the tracking area code, that the base station does not provide a circuit-switched voice service when it is determined that the UE requires the circuit-switched voice service, and sends a tracking area update rejection message to the UE.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a cellular telecommunications network.

Background Art

[0002] A cellular telecommunications network includes a base station that provides voice and data services to a plurality of user equipments (UEs) via wireless communication. The base station is (at least partially) located at a cell site, which further includes a support infrastructure (such as power) for operating the base station. In a conventional architecture, the cell site and the base station are owned and operated by a single mobile network operator (MNO), and the base station is connected only to the core network of that MNO. The base station typically includes an antenna support (such as a pole, an antenna frame, or a rooftop fixture), one or more antennas, and one or more controllers (such as a radio network controller (RNC)).

[0003] There are several ways in which MNOs can cooperate to share infrastructure. The most basic example of shared MNO infrastructure is known as site sharing, where a physical cell site is shared among MNOs, but each MNO maintains ownership and control of the base station equipment (such as poles, antennas, and controllers). Base station support equipment (such as power) may or may not be shared among MNOs in a site sharing arrangement. In a further example of shared MNO infrastructure, there is what is known as pole sharing, where the poles (or equivalent antenna supports) of the base station are shared among MNOs, but each MNO maintains ownership and control of the remaining base station equipment (antennas and controllers). Again, base station support equipment (such as power) may or may not be shared among MNOs in a pole sharing arrangement.

[0004] A more extensive form of the MNO infrastructure is known as a Multi-Operator Radio Access Network (MORAN), where cell sites, base station equipment, and base station support equipment are shared among MNOs. The base station equipment must be configured to communicate with UEs of all MNOs, such as by transmitting each operator's Public Land Mobile Network (PLMN) identifier in its respective signal, but must communicate within each MNO's dedicated spectrum range. The base station equipment must also be configured to direct traffic to the appropriate MNO's core network. A similar arrangement is known as a Multi-Operator Core Network (MOCN), where cell sites, base station equipment, and base station support equipment are also shared among MNOs, and a shared spectrum range may also be used to communicate with UEs of different MNOs.

[0005] A further alternative form of the shared infrastructure is one in which cell sites, base stations, and base station support equipment are owned and / or managed by a third party, and one or more MNOs operate on the third party's infrastructure. This is known as a "neutral host".

[0006] An issue for modern cellular telecommunications networks is for MNOs to meet energy efficiency goals. These goals may risk reducing the coverage and maximum capacity that an MNO's base stations can provide. To address this concern, an energy saving mechanism has been introduced that enables base stations to enter an energy saving mode (where most, but not all, operations are suspended). To ensure service continuity to UEs previously served by an energy saving base station, the UEs may be transferred to one or more neighboring base stations. The neighboring base stations may change their coverage areas to provide service. SUMMARY OF THE INVENTION

[0007] According to a first aspect of the present invention, there is provided a method of operating a cellular telecommunications network, the cellular telecommunications network including a first base station for a first mobile network operator, a second base station, and a management node, the management node being configured to determine, based on a tracking area code, whether a base station associated with the tracking area code supports a circuit-switched voice service, the method comprising the steps of determining that at least a part of the first base station should enter an energy saving mode; in response to the determination, identifying an energy saving solution to guarantee the continuity of a first circuit-switched voice service; causing a reconfiguration of the first base station according to the identified energy saving solution such that the first base station uses a first tracking area code indicating that the first base station does not support the first circuit-switched voice service so that the first circuit-switched voice service supported by the first base station enters the energy saving mode; and continuing to support the first circuit-switched voice service by the second base station, wherein the second base station uses a second tracking area code indicating that the second base station supports the first circuit-switched voice service.

[0008] According to a second aspect of the present invention, there is provided a computer program comprising instructions for causing a computer to perform the steps of the first aspect of the present invention when the program is executed by the computer.

[0009] According to a third aspect of the present invention, there is provided a network node having a processor configured to perform the steps of the first aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a better understanding of the present invention, embodiments thereof will be described, by way of example only, with reference to the accompanying drawings.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0011] Next, a first embodiment of the cellular telecommunications network 1 will be described with reference to FIG. 1. FIG. 1 illustrates a cell site 10 including a support column 20 and base station support equipment 30 (shown as a single unit but may include a plurality of components such as a power supply, a cooling unit, etc.). The cell site 10, the support column 20, and the base station support equipment 30 are shared by a first mobile network operator (MNO) and a second MNO. The first MNO deploys a first base station 100 at the cell site such that one or more transceivers are positioned on the support column 20 and any processing equipment is positioned within the cell site 10 (and may utilize the base station support equipment 30). The second MNO also deploys a second base station 200 at the cell site 10 such that one or more transceivers for the second base station 200 are positioned on the support column 20 and any processing equipment is positioned within the cell site 10 (this may also utilize the base station support equipment 30). The processing equipment of the first base station 100 and the second base station 200 may operate on dedicated hardware or may operate in a virtualized environment on a common hardware platform.

[0012] FIG. 1 also illustrates a neutral host site 40. The neutral host site 40 has a transport connection to the first base station 100 and the second base station 200, a first backhaul connection to the core network of the first MNO, and a second backhaul connection to the core network of the second MNO. These connections are typically optical fiber connections. The neutral host site 40 includes a controller 42 and a router 44. The router 44 is responsible for routing traffic for the first base station 100 to / from the core network of the first MNO and routing traffic for the second base station 200 to / from the core network of the second MNO. The controller 42 is responsible for managing the shared operations at the cell site and implementing embodiments of the method of the present invention (described below).

[0013] The first base station 100 and the second base station 200 are each configured to transmit a tracking area code. In the following embodiments, the first base station 100 transmits the first tracking area code when the first base station 100 provides a circuit-switched voice service to a user of the network of the first MNO, and transmits the second tracking area code when the first base station 100 does not provide a circuit-switched voice service to a user of the network of the first MNO. Similarly, the second base station 100 transmits the third tracking area code when the second base station 100 provides a circuit-switched voice service to a user of the network of the second MNO, and transmits the fourth tracking area code when the second base station 100 does not provide a circuit-switched voice service to a user of the network of the second MNO.

[0014] The core network of the first MNO includes a first mobility management entity (MME). The core network of the second MNO includes a second MME. The first MME stores a database of tracking area codes, and a first set of tracking area codes is associated with base stations that provide a circuit-switched voice service to users of the network of the first MNO, and a second set of tracking area codes is associated with base stations that do not provide a circuit-switched voice service to users of the network of the first MNO. In this embodiment, the first set of tracking area codes stored in the database of the first MME includes the first tracking area code, and the second set of tracking area codes stored in the database of the first MME includes the second tracking area code.

[0015] Similarly, the second MME stores a database of tracking area codes, where a first set of tracking area codes is associated with base stations that provide circuit-switched voice services to users of the second MNO's network, and a second set of tracking area codes is associated with base stations that do not provide circuit-switched voice services 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 a third tracking area code, and the second set of tracking area codes stored in the second MME's database includes a fourth tracking area code.

[0016] Before describing embodiments of the method of the present invention in more detail, an overview of two processes (used in these embodiments) will be described. The first process is an energy-saving trigger mechanism. In a first step S101 of this first process (shown in FIG. 2), the neutral host controller 42 monitors a plurality of metrics for the first base station 100 and the second base station 200. These metrics include · Measures of load, such as radio throughput as a percentage of the radio resources used or the radio capacity, · Measures of energy consumption (which may be converted to equivalent units of measurement of carbon dioxide emissions), · Identifiers of each service offering and commitment.

[0017] In the second step S103, the neutral host controller 42 determines whether one or more of a plurality of metrics for each monitored base station meet at least one criterion for inclusion in an energy saving solution (e.g., to become a compensating base station). These energy saving solutions will be described in more detail in a second process detailed below. The criteria may be, for example, that the base station has a load low enough that it can compensate for another base station that has entered the energy saving mode, or that the load metric indicates that the base station does not have any service offering / commitment that prohibits switching from the normal (active) mode to either the energy saving mode or the compensating mode. Identify all base stations that meet at least one criterion for inclusion in a candidate energy saving solution. If all metrics for a base station do not meet the criteria, do not identify that base station for inclusion in a candidate energy saving solution.

[0018] In step S105, the neutral host controller 42 determines whether one or more of a plurality of metrics for each monitored base station meet at least one energy saving criterion. For example, a measure of load below a threshold indicates a sufficiently low load, and a measure of energy consumption above a threshold indicates that the base station (or MNO) is consuming excessive energy and / or (based on the MNO's energy target) is causing an excessive unit of carbon dioxide emissions and / or that the base station is not implementing a service offering / commitment that prohibits entering the energy saving mode. If one or more of these metrics for a base station meet at least one criterion, the neutral host controller identifies that base station for inclusion as a potential energy saving base station in a second process. If all metrics for a base station do not meet the relevant criteria, that base station is not identified as a potential energy saving base station in the second process. Once all metrics for all base stations have been analyzed and at least one base station has been identified for inclusion as a potential energy saving base station, the second process is triggered.

[0019] A second process for determining a suitable energy-saving solution is shown in FIG. 3. Briefly, this neutral host controller 42 evaluates a plurality of candidate energy-saving solutions based on the results of the first process. The neutral host controller 42 evaluates all possible variations of the candidate energy-saving solutions in which one or more of the base stations identified as potential energy-saving base stations (in the first process) enter the energy-saving mode, and one or more of the base stations identified to be included as part of the energy-saving solution operate in the energy-saving mode, the normal (active) mode, or the compensation mode. For each candidate, the neutral host controller 42 evaluates a weighted score of the suitability of the base station to enter the energy-saving mode (the "energy-saving score") for each base station entering the energy-saving mode in that candidate solution, and evaluates a weighted score representing the suitability of the base station to operate in the compensation mode (the "compensation score") for each base station entering the compensation mode in that candidate solution, and sums these energy-saving scores and compensation scores to obtain an overall score for that candidate solution.

[0020] For example, the neutral host controller 42 evaluates a first candidate energy-saving solution in which the first base station 100 enters the energy-saving mode and the second base station 200 enters the compensation mode. In a first step S201, the neutral host controller 42 evaluates the energy-saving score of the first base station 100 and the compensation score of the second base station 200. The energy-saving score ES is evaluated as follows.

Number

[0021] Here, ·n is the identifier of the base station being evaluated for entering the energy-saving mode, · i is the identifier of the candidate solution being evaluated (since there can be different ES scores for the same base station if there are several different candidate solutions), · L represents the load of base station n, normalized to a value between 0 and 1, · D represents the desirability of energy savings for base station n (to be explained in more detail below), normalized to a value between 0 and 1, · C represents the cost to the users of base station n and the users of each compensating base station when base station n is compensated by one or more compensating base stations of the candidate solution being evaluated (this will also be explained in more detail below), normalized to a value between 0 and 1.

[0022] Based on the MNO's policy, weighting may be applied to each coefficient L, D, and C.

[0023] The compensation score Comp is evaluated as follows.

Equation

[0024] Here, · n is the identifier of the base station being evaluated for entering the compensation mode, · i is the identifier of the candidate solution being evaluated (since there can be different compensation scores for the same base station if there are several different candidate solutions), · SC represents the spare capacity of base station n, normalized to a value between 0 and 1 (e.g., based on the total capacity of the base station).

[0025] In step S203, the energy saving score and the compensation score are summed to determine the overall score for the first candidate energy saving solution. The second process then loops back to step S201 to evaluate the overall scores for the remaining candidate energy saving solutions. Then, the energy saving solution with the highest overall score is selected as the energy saving solution to be implemented (step S205).

[0026] The desirability factor D is an evaluation of the benefit for base station n to enter the energy saving mode based on the policy of the relevant MNO. To perform this evaluation, the neutral host controller 42 stores in the memory the policy of each MNO for determining the desirability factor and searches for the relevant policy when evaluating the desirability factor for the base station. Each policy may be based on one or more of: · A measure of the energy consumption of the base station relative to the energy consumption target of the base station, and / or · An estimated value of the energy saved by base station n by entering the energy saving mode in combination i, offset only by the additional energy required by one or more base stations entering the compensation mode to compensate base station n for entering the energy saving mode.

[0027] The measure of the energy consumption of the base station may be based on the equivalent of a unit of energy or its unit of carbon dioxide emissions (based on the amount of carbon dioxide emitted per unit of energy) relative to the target of the MNO. The target of the MNO may also be a cumulative target, for example, over one month.

[0028] The cost factor represents any impairment to a user of a base station entering the energy saving mode or a user of one or more compensating base stations. This may be the impairment of service degradation experienced by the user when being served by a compensating base station, or the impairment suffered by one of the compensating base stations to compensate for the energy saving base station (such as the resources required to switch to the MOCN mode when the energy saving base station and the compensating base station belong to different mobile network operators). Also, in order to perform this evaluation, the neutral host controller 42 stores in the memory the policies of each MNO for determining the cost factor and searches for the relevant policies when evaluating the cost factor for a base station. Each policy may be based on one or more of · the service provided by a base station entering the energy saving mode, · the service commitment of a base station entering the energy saving mode, · the ability of a base station entering the compensation mode to compensate for the service offering / commitment of a base station entering the energy saving mode.

[0029] The service offering and commitment may be weighted to correlate with the relative impairment of not providing a particular service. Thus, the service commitment may be given a greater weight than the service offering, as there may be a more severe penalty for not providing the committed service.

[0030] As illustrated in an embodiment of the method of the present invention, a base station entering the energy saving mode can provide (or commit to providing) a circuit-switched voice service. If a base station entering the compensation mode cannot provide a circuit-switched voice service, the impairment of the degraded service is relatively high. Similarly, a base station entering the energy saving mode can provide a tailored service, such as an ultra-low latency, ultra-high reliability service, that cannot be provided by a base station entering the compensation mode. Again, the impairment of the degraded service is relatively high in this case.

[0031] As described above, multiple candidate energy-saving solutions are available for any given arrangement. In the most basic scenario, having a first and a second base station, both being potential energy-saving base stations, at least two candidate energy-saving solutions are available: either the first base station enters the energy-saving mode and the second base station enters the compensation mode, or the second base station enters the energy-saving mode and the first base station enters the compensation mode. However, there may be more options to be evaluated when there is a third base station being evaluated for switching to the energy-saving mode or the compensation mode, and / or when each base station provides services to users according to multiple protocols and these services may be switched independently to the energy-saving mode or the compensation mode, and / or when each base station uses multiple spectrum ranges (multiple "carriers") for communication with the UE and each carrier may be switched independently to the energy-saving mode or the compensation mode. In a scenario where the base station provides multiple access options (e.g., via different protocols or different carriers), the first and second processes may perform their analysis for each of the multiple access options. That is, the first process may analyze metrics for each access option to determine whether to mark each access option for inclusion in the candidate energy-saving solution and whether to mark each access option to enter the energy-saving mode, and the second process may analyze multiple candidate energy-saving solutions in which each access option operates in either the energy-saving mode, the normal (active) mode, or the compensation mode.

[0032] Some embodiments of the method of the present invention will be described. In each embodiment, the first and second base stations 100, 200 are such that the first base station 100 provides "4G" services (i.e., based on one or more of Releases 8 to 14 of the 3rd Generation Partnership Project (3GPP (registered trademark))) and "5G" services (i.e., based on one or more of Release 15 and any subsequent releases of 3GPP regarded as 5G services), and the second base station 200 is configured to provide 4G and 5G services, and further in an initial configuration configured to provide "2G" services (i.e., based on one or more of the specifications of the Global System for Mobile Communications (GSM (registered trademark)) for mobile communications of the European Telecommunications Standards Institute (ETSI)). Thus, the first base station 100 provides voice services via Voice of Internet Protocol (VoIP) technology, and the second base station 200 provides voice services to any 4G and 5G users via VoIP or to 2G users via circuit-switched voice services (since 2G voice services are used for all voice services and 4G / 5G can be used for data services, the VoIP 4G / 5G services are optional).

[0033] In this initial configuration, the first base station 100 broadcasts a second tracking area code (indicating that it does not provide circuit-switched voice services to users of the network of the first MNO), and the second base station 200 broadcasts a third tracking area code (indicating that it provides circuit-switched voice services to users of the network of the second MNO).

[0034] Next, with reference to FIGS. 4 to 6, a first embodiment of the method of the present invention will be described. As described above, FIG. 4 represents the initial configuration of a cellular telecommunications network. In the first step (step S301) of this embodiment, as shown in the flowchart of FIG. 6, the neutral host controller 42 executes a first process (as described above in connection with FIG. 2) and determines that the energy saving threshold has been met. This triggers the second step (step S303) of this embodiment, and the neutral host controller 42 executes a second process (as described above in connection with FIG. 3) to (for all variations of base stations operating in either the energy saving mode, the normal (active) mode, or the compensation mode, where base stations entering the energy saving mode include those identified as potential energy saving base stations in the first process) evaluate the overall score for each candidate energy saving solution (based on the energy saving score and the compensation score). In this embodiment, the energy saving options include: 1. The first base station 100 enters the energy saving mode for all services (i.e., its 4G and 5G services), and the second base station 200 enters the compensation mode for the 4G and 5G services of the first base station; 2. The second base station 200 enters the energy saving mode for all services (i.e., its 2G, 4G, and 5G services), and the first base station 100 enters the compensation mode only for the 4G and 5G services of the second base station; 3. The second base station 200 enters the energy saving mode for its 2G and 4G services (thus maintaining its 5G service), the first base station 100 enables the 2G service, and enters the compensation mode for the 2G and 4G services of the second base station.

[0035] The overall score evaluated for each candidate energy-saving solution indicates that the most appropriate energy-saving solution is Option 3. The overall score for the first candidate energy-saving solution is positively affected by the impairment factor (since the second base station can provide all services of the first base station 100), but is negatively affected by one or more of the load factor (e.g., the first base station 100 has a proportionally high load based on the policy of the first MNO), the desirability factor of the first base station (e.g., the first base station 100 has low energy consumption based on the energy-saving target of the first MNO's policy, and / or the first base station 100 does not save much energy by entering the energy-saving mode, and / or the second base station 100 consumes a significant amount of additional energy to compensate for the first base station 100), and / or the reserve capacity factor (e.g., the second base station 200 has limited reserve capacity). Furthermore, when the second base station 200 enters the energy-saving mode, the first base station 100 cannot compensate for the 2G service, which has a significant negative impact on the overall score for the second candidate energy-saving solution regarding the impairment factor. However, the third energy-saving option involves enabling the first base station 100 to provide the 2G service so that it can compensate for the 2G service previously provided by the second base station 200. Therefore, the impairment factor of the third candidate energy-saving solution does not have the same negative impact as that of the second candidate energy-saving solution, and thus the third candidate energy-saving solution has a higher overall score than the second candidate energy-saving solution.

[0036] Furthermore, in this example, the third candidate energy saving solution has a higher overall score than the first candidate energy saving solution. (Due to consuming more energy when the first base station 100 is currently providing 2G services), there may be a greater negative impact from the desirability factor, but there is more positive impact from one or more of the load factor, another factor of the desirability factor of the first base station (e.g., the energy saved by the second base station 200 entering the energy saving mode), and / or the spare capacity factor. As a result, the overall score of the third candidate energy saving solution is higher than that of the first candidate energy saving solution. Therefore, the neutral host controller 42 selects the third energy saving solution.

[0037] In step S305, the neutral host controller 42 sends a command message to the first base station 100 to enable the 2G service for the first base station 100. In response, in step S307, the first base station 100 enables the 2G radio function and enables the 2G service by utilizing the 2G licensed spectrum of the first MNO (which was not previously used by the first base station 100). In other implementations, the first base station 100 may reallocate ( "refarm") spectrum from other protocols (e.g., the 4G and / or 5G spectrum of the first MNO to be used for 2G services), or use some of the licensed spectrum of the second MNO for 2G services (e.g., under a spectrum sharing agreement), or use shared licensed spectrum (e.g., licensed shared access) or unlicensed spectrum.

[0038] In step S309, the neutral host controller further sends an instruction message to the first base station 100, causing the first base station 100 to be reconfigured to compensate the second base station 200. This includes switching from the MORAN configuration to the MOCN configuration. The first base station 100 starts transmitting both the public land mobile network (PLMN) identifier of the first MNO and the PLMN identifier of the second MNO, and accepts handover and redirection of all users served by the second base station 200. As part of this reconfiguration, the first base station 100 connects to both the first MME of the core network of the first MNO and the second MME of the core network of the second MNO. Since the first base station 100 enables 2G services for at least the users of the second MNO's network, the first base station 100 extracts a third tracking area code indicating that circuit-switched voice services are provided to the users of the second MNO's network from the second MME. Then, the first base station 100 broadcasts this third tracking area code.

[0039] In addition, in the scenario where the newly enabled 2G service of the first base station 100 may also be used by the users of the first MNO's network, in addition to broadcasting the third tracking area code, the first base station 100 switches to broadcasting the first tracking area code (indicating that circuit-switched voice services are also provided to the users of the first MNO's network) from broadcasting the second tracking area code.

[0040] In step S311, the neutral host controller 42 reconfigures the neutral host router so that any 2G and / or 4G traffic for the users of the second MNO currently served by the first base station 100 is routed between the first base station 100 and the core network of the second MNO.

[0041] In step S313, the neutral host controller 42 sends an instruction message to the second base station 200, causing the second base station to enter an energy-saving mode for its 2G and 4G services. As part of this reconfiguration, since the second base station 200 broadcasts a third tracking area code, it switches to broadcasting a fourth tracking area code (indicating that circuit-switched voice services are not provided to users of the second MNO's network). The final state of the network is illustrated in FIG. 5.

[0042] Therefore, this first embodiment provides an energy-saving solution considering circuit-switched services (2G services), and as a result, the circuit-switched services are maintained following the implementation of the energy-saving solution. Such a solution may not provide the maximum amount of energy savings, but users can still maintain their circuit-switched services. Furthermore, by adjusting the weighting of various factors in the energy-saving score and compensation score, the MNO can adjust the network's response to favor either energy savings or service maintenance.

[0043] This first embodiment also provides an additional benefit in ensuring that a user equipment (UE) that requires a circuit-switched voice service (e.g., a UE not configured for voice services of 4G and 5G cellular telecommunication protocols) does not connect to a base station that no longer provides a circuit-switched voice service. This process is illustrated by the flowchart of FIG. 10. When a UE that requires a circuit-switched voice service and is not connected to the second base station 200 receives the fourth tracking area code broadcast by the second base station 200, the UE can initiate a tracking area code update process. As part of this process, the UE sends a tracking area update request including the fourth tracking area code (received at the second MME in step S601) to the second MME via the second base station 200. Upon receiving the tracking area update request, in step S603, the second MME determines whether the UE requires a circuit-switched voice service based on the UE's capabilities. These capabilities may already be known to the second MME (from previous capability signaling procedures), or may be obtained upon receipt of the tracking area update request (e.g., by obtaining its subscription status from the home subscriber server (HSS)). In this example, the second MME determines that the UE requires a circuit-switched voice service, and the process proceeds to step S605, where the second MME determines whether the second base station 200 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 using that database of tracking area codes (each marked as either for a base station that provides a circuit-switched voice service to users of the second MNO's network or for a base station that does not provide a circuit-switched voice service to users of the second MNO's network) to determine whether the fourth tracking area code is associated with a base station that provides a circuit-switched voice service to users of the second MNO's network. In this example, the second MME determines from this lookup operation that the second base station 200 does not provide a circuit-switched voice service to users of the second MNO's network.Therefore, in step S607, the second MME sends a Tracking Area Update Reject message to the UE. This prevents the UE from connecting to the second base station 200 when the second base station 200 does not provide circuit-switched voice service.

[0044] Furthermore, in this embodiment, the Tracking Area Update Reject message includes a cause code that causes the UE to update the list of prohibited 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 prohibited tracking area codes is stored in the UE until it is reset.

[0045] Following the rejected tracking area update request, the UE can connect to a base station that provides circuit-switched voice service, such as the first base station 100 that has enabled circuit-switched voice service. That is, following the above process of FIG. 10, when the UE receives the third tracking area code broadcast by the first base station 100 and sends a tracking area update request to the first base station 100, the first base station 100 forwards the tracking area update request message to the second MME (using the connection established to the second MNO's core network as part of the switch to the MOCN mode). The second MME determines that the third tracking area code broadcast by the first base station 100 indicates that the first base station 100 provides 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 that permits the UE to connect to the first base station 100 (step S609).

[0046] Referring to FIGS. 7 to 9, a second embodiment of the method of the present invention will be described. FIG. 7 illustrates a network in an initial state including first, second, and third base stations 100, 200, 300 at a cell site. The first and second base stations 100, 200 are the same as those described in the above first embodiment, and the third base station 300 is further deployed on the same pillar 20 of the cell site 10. The third base station 300 is operated by a third MNO, and the neutral host is responsible for managing the third base station 300 (via the controller 42) and routing traffic between the third base station 300 and the core network of the third MNO (via the router 24). The core network of the third MNO also includes a third MME, and the third MME includes a database of tracking area codes, where the first set of tracking area codes is for base stations that provide circuit-switched voice services to users of the third MNO's network, and the second set of tracking area codes is for base stations that do not provide circuit-switched voice services to users of the third MNO's network. In this embodiment, the first set of tracking area codes in the database of the third MME includes a fifth tracking area code, and the second set of tracking area codes in the database of the third MME includes a sixth tracking area code.

[0047] The third base station 300 is configured to provide 2G services, 4G services, and 5G services to its users.

[0048] In this initial configuration, the first base station 100 broadcasts a second tracking area code (indicating that it does not provide circuit-switched voice services to users of the first MNO's network), the second base station 200 broadcasts a third tracking area code (indicating that it provides circuit-switched voice services to users of the second MNO's network), and the third base station 300 broadcasts a fifth tracking area code (indicating that it provides circuit-switched voice services to users of the third MNO's network).

[0049] In the first step (S501) of this second embodiment, as shown in the flowchart of FIG. 9, the neutral host controller 42 executes the first process (as described above in connection with FIG. 2) and determines that the energy saving threshold for at least one base station is satisfied. This triggers the second step (step S503) of this embodiment, and the neutral host controller 42 executes the second process (as described above in connection with FIG. 3) to evaluate the overall score for each candidate energy saving solution (based on the energy saving score and the compensation score). Since there are three base stations each having multiple protocols, there are many different candidate energy saving solutions available (not all of which are identified in this description). In this embodiment, all options involving the first base station 100 entering the energy saving mode generate a relatively low overall score (e.g., due to the negative impact of one or more of the load factor, desirability factor, and / or impairment factor). Further, all options that do not guarantee the continuity of the 2G service (i.e., when one or both of the second base station 200 and the third base station 300 enter the energy saving mode with respect to at least their 2G services and the compensation for the 2G service is not provided by another base station) all have a very low overall score (e.g., due to the negative impact of the impairment factor). In this second embodiment, the candidate energy saving solution with the maximum overall score is for the second base station 200 to enter the energy saving mode for its 2G and 4G services (thus maintaining its 5G service), the first base station 100 to compensate for its 4G service, and the third base station 300 to compensate for its 2G service.

[0050] In step S505, the neutral host controller 42 sends a command message to the first base station 100, causing the first base station 100 to be reconfigured to compensate for the 4G services of the second base station 200. This includes a switch from the MORAN configuration to the MOCN configuration, in which the first base station 100 starts transmitting both the public land mobile network (PLMN) identifier of the first MNO and the PLMN identifier of the second MNO for 4G transmission, and accepts handover and redirection of all 4G users served by the second base station 200.

[0051] In step S507, the neutral host controller 42 sends a command message to the third base station 300, causing the third base station 300 to be reconfigured to compensate for the 2G services of the second base station 200. This also includes a switch from the MORAN configuration to the MOCN configuration, in which the third base station 300 starts transmitting both the PLMN identifier of the second MNO and the PLMN identifier of the third MNO for 2G transmission, and accepts handover and redirection of all 2G users served by the second base station 200. The third base station 300 also extracts the third tracking area code indicating that circuit-switched voice services are provided to users of the second MNO's network (in addition to broadcasting the fifth tracking area code indicating that circuit-switched voice services are provided to users of the third MNO's network) from the second MME, and then broadcasts the third tracking area code.

[0052] In step S509, the neutral host controller 42 reconfigures the neutral host router 44 such that any traffic for 4G users of the second MNO currently served by the first base station 100 is routed between the first base station 100 and the core network of the second MNO, and any traffic for 2G users of the second MNO currently served by the third base station 300 is routed between the third base station 300 and the core network of the second MNO.

[0053] In step S511, the neutral host controller 42 sends a command message to the second base station 200 to cause the second base station to enter an energy saving mode for its 2G and 4G services. Following this reconfiguration, the second base station 200 switches from broadcasting the third tracking area code to broadcasting a fourth tracking area code (indicating that the second MNO's network does not provide circuit switched voice services) since the second base station 200 broadcasts the third tracking area code. The final state of the network is illustrated in FIG. 8.

[0054] After the process illustrated in FIG. 10, a second embodiment may follow to ensure that UEs of the second MNO's network that require circuit switched voice services do not connect to base stations that do not provide circuit switched voice services.

[0055] In the above embodiment, the base stations are in a MORAN scenario such that the MNOs share the same cell site, poles, and support equipment for each base station. However, this is not essential, and any form of shared arrangement between the MNOs may exist as long as the base stations are configured to serve users of another MNO. Further, since the base stations may be reconfigured according to a sharing contract, it is not essential for the base stations to switch from a MORAN to a MOCN arrangement.

[0056] In the above-described second embodiment, the third base station 300 is deployed at the same cell site. However, the third base station may be located at a different cell site and can provide services to users of the base station that enters the energy-saving mode (this may be due to a change in the coverage area of the third base station), so this is not essential. Further, the third base station 300 may be owned by the same network operator as the base station that enters the energy-saving mode, in which case (since the PLMN is the same), the third base station 300 does not need to reconfigure its transmission.

[0057] Furthermore, those skilled in the art will understand that the trigger for the energy-saving switch (in the first process shown in FIG. 2) does not necessarily have to be based on one or more base stations that enter the energy-saving mode or the compensation mode. That is, it can be based on adjacent base stations. Further, the first process may be implemented at each base station, and a message may be sent to the neutral host controller after the trigger condition is satisfied (the base station may also execute its own energy-saving solution, such as entering the energy-saving mode for one of its services, before notifying the neutral host of the network-scale response).

[0058] In the above embodiment, the circuit-switched voice service is a GSM 2G service. However, this is not essential, and those skilled in the art will understand that the above embodiment may be applied to a circuit-switched voice service of any protocol, such as a 3G voice service (standardized by 3GPP).

[0059] Those skilled in the art will also understand that the second process detailed above (as shown in FIG. 3) is exemplary, and other processes may be implemented where the maintenance of the circuit-switched voice service is a consideration in the energy-saving solution.

[0060] In all of the embodiments detailed above, there may be subsequent decisions for the base station to end the energy saving mode and switch back to the active mode. This may be based on the same trigger used in the first process or on an independent trigger. When the base station returns to the active mode, the user may be transferred back to the active mode base station, and the compensation mode base station may return to the active mode. The neutral host controller and router may also be reconfigured to route user traffic through the user's serving base station.

[0061] Furthermore, the above embodiments may be executed repeatedly, whereby a new energy saving solution may be determined as the most suitable one, and the neutral host controller may instruct the relevant base station to switch to this new energy saving solution.

[0062] Those skilled in the art will also understand that it is not essential for the various processes described above to be executed on the neutral host controller. That is, any entity within the cellular telecommunications network can implement the above processes, typically being supported by a shared arrangement between operators.

[0063] In the above embodiment, the base station may require reconfiguration. Typically, the reconfiguration requires the base station to reboot, and as a result, the user loses service. Therefore, in the enhancement, by using a multi-carrier base station, such service interruption can be avoided. For example, users of a multi-carrier base station may be transferred between carriers such that one carrier becomes an unused carrier, and this unused carrier may be reconfigured to the MOCN mode, thereby providing service to users of both its own operator and the operator of the base station being reconfigured. Then, users of the base station being reconfigured may be transferred to the unused carrier of the multi-carrier base station, and as a result, the base station being reconfigured can be reconfigured without service interruption to the users it previously served or the users of the multi-carrier base station. Further, in the above embodiment where there are multiple candidate solutions, the adverse impact on users during the transition from the current state of the network to its final state may be analyzed as part of the selection process.

[0064] In the above embodiment, the tracking area code transmitted by each base station indicates whether the base station provides or does not provide a circuit-switched voice service. However, the tracking area code can more generally indicate whether the base station supports or does not support a circuit-switched voice service. That is, a base station can support a circuit-switched voice service if it provides the circuit-switched voice service itself or, if it does not provide the circuit-switched voice service but facilitates fallback to the circuit-switched voice service. Conversely, a base station cannot support a circuit-switched voice service if it does not provide the circuit-switched voice service and does not facilitate fallback to the circuit-switched voice service. For example, in a modification to the first embodiment, after reconfiguring the first and second base stations (such that the first base station 100 enables a 2G service and the second base station 200 enters an energy-saving mode for that 2G service), the second base station 200 can still support a circuit-switched voice service to users of the second MNO's network if it facilitates circuit-switched fallback to the newly enabled 2G service of the first base station. In such a scenario, the second base station 200 may also broadcast a third tracking area code so that a user (who requires a circuit-switched voice service) is permitted to connect to the second base station 200.

[0065] In the above embodiment, the MME stored a first set of tracking area codes that identify base stations that support or provide circuit-switched voice services, and a second set of tracking area codes that identify base stations that do not support or provide circuit-switched voice services. This is not essential, and those skilled in the art will understand that other implementations are possible. For example, the MME could store a single list of tracking area codes that identify base stations that support or provide circuit-switched voice services, and then the MME would only permit access to the base station if the tracking area update request included a tracking area code on that list. In another example, the MME could store a single list of tracking area codes that identify base stations that do not support or provide circuit-switched voice services, and then the MME would only permit access to the base station if the tracking area update request that includes the tracking area code is not on that list.

[0066] Those skilled in the art will understand that any combination of features is possible within the scope of the invention as claimed. The matters described in the claims of the original application are appended as they are below. [C1] A method for operating a cellular telecommunications network, wherein the cellular telecommunications network includes a first base station for a first mobile network operator, a second base station, and a management node, and the management node is configured to determine, based on a tracking area code, whether a base station associated with the tracking area code supports a circuit-switched voice service, and the method includes: determining that at least a part of the first base station should enter an energy-saving mode; identifying an energy-saving solution to ensure the continuity of a first circuit-switched voice service in response to the determination; causing the first base station to enter the energy-saving mode for the first circuit-switched voice service supported by the first base station; causing the first base station to use a first tracking area code indicating that the first base station does not support the first circuit-switched voice service; causing reconfiguration of the first base station according to the identified energy-saving solution; continuing to support the first circuit-switched voice service by the second base station, wherein the second base station uses a second tracking area code indicating that the second base station supports the first circuit-switched voice service. [C2] The method according to C1, wherein the step of continuing to provide the first circuit-switched voice service includes enabling the second base station to use a second circuit-switched voice service. [C3] The second base station is for a second mobile network operator, and the method according to C2 further includes: causing reconfiguration of the second base station so that the second base station is configured to communicate with users of the first mobile network operator. [C4] The cellular telecommunications network further includes a third base station, the first base station also provides a second service, and the step of causing the reconfiguration of the first base station includes the first base station entering an energy saving mode for the first circuit switched voice service and the second service, and the method further includes the third base station continuing to provide the second service, the method according to C2 or 3. [C5] The third base station is for a second or third mobile network operator, and the method The method according to C4, further including the step of causing the reconfiguration of the third base station such that the third base station is configured to communicate with users of the first mobile network operator. [C6] The method according to any one of C1 to 5, wherein the step of determining includes evaluating a plurality of candidate energy saving solutions. [C7] The evaluation is based on one or more of a measure of the load of the first base station and / or the second base station, a measure of the capacity of the first base station and / or the second base station, a measure of the desirability of the first base station and / or the second base station entering the energy saving mode based on the policies of the respective mobile network operators, a measure of the damage of the degraded service for the first base station to compensate the second base station based on the policy of the second mobile network operator, a measure of the energy saved by the second base station entering the energy saving mode, and a measure of the additional energy consumed for the first base station to compensate the second base station, the method according to C6. [C8] The method according to any one of C1 to 7, implemented on a neutral host controller. [C9] The method according to any one of C1 to 8, further including an initial step in which the cellular telecommunications network meets at least one condition for triggering an energy saving solution. [C10] The method according to C9, wherein the at least one condition includes a measure of the load in the first base station and / or the second base station, and / or a measure of the energy consumption of the first base station and / or the second base station. [C11] A computer program including instructions, which when the program is executed by a computer, causes the computer to perform the steps according to any one of C1 to 10. [C12] A computer-readable carrier medium comprising the computer program according to C11. [C13] A network node having a processor configured to execute the steps according to any one of C1 to C10.

Claims

1. 1. A method of operating a management node in a cellular telecommunications network, the cellular telecommunications network comprising base stations and user equipment, UE, wherein the base stations broadcast tracking area codes, the method comprising the steps of: receiving a tracking area update request message from the UE, the tracking area update request message including the tracking area code broadcast by the base station; determining that the UE requires circuit switched voice service; determining, based on the tracking area code, that the base station does not provide circuit switched voice service; sending a tracking area update reject message to the UE based on these determinations; A method comprising:

2. A computer program comprising instructions, which when executed by a computer, cause the computer to carry out the steps of claim 1.

3. A computer readable storage medium comprising the computer program of claim 2.

4. 2. A management node having a processor configured to perform the steps of claim 1.

Images