GB2566103A - Cellular telecommunications network - Google Patents

Cellular telecommunications network Download PDF

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Publication number
GB2566103A
GB2566103A GB1714232.4A GB201714232A GB2566103A GB 2566103 A GB2566103 A GB 2566103A GB 201714232 A GB201714232 A GB 201714232A GB 2566103 A GB2566103 A GB 2566103A
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United Kingdom
Prior art keywords
base station
interface
communicating
configuration parameter
cellular
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Granted
Application number
GB1714232.4A
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GB2566103B (en
GB201714232D0 (en
Inventor
Mackenzie Richard
Tukmanov Anvar
fitch Michael
Briggs Keith
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British Telecommunications PLC
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British Telecommunications PLC
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Priority to GB201714232A priority Critical patent/GB2566103B/en
Publication of GB201714232D0 publication Critical patent/GB201714232D0/en
Publication of GB2566103A publication Critical patent/GB2566103A/en
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Publication of GB2566103B publication Critical patent/GB2566103B/en
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H04W36/0061—Transmission or use of information for re-establishing the radio link of neighbour cell information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/15528—Control of operation parameters of a relay station to exploit the physical medium
    • H04B7/15542—Selecting at relay station its transmit and receive resources
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2603—Arrangements for wireless physical layer control
    • H04B7/2606—Arrangements for base station coverage control, e.g. by using relays in tunnels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/16—Performing reselection for specific purposes
    • H04W36/20—Performing reselection for specific purposes for optimising the interference level
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/32—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data
    • H04W36/322—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data by location data
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/005—Moving wireless networks

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Quality & Reliability (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

A first base station, BS 10, in communication with both a first cellular core networking node and a second mobile BS 20 (Relay Node, RN, moving wireless network, e.g. in a train or car), the second BS in communication with the first BS (a donor BS) and with User Equipment, UE, wherein the UE’s user traffic is transmitted via the first and second BS, comprising: determining an identity of a third 30 and fourth 40 BSs, wherein an overlap of the third and fourth BS’ respective coverage areas cover a route of the second BS; determining a time of arrival of the second BS within the overlap; determining a first configuration parameter of the third BS and a second configuration parameter of the fourth BS in advance of the second BS’s time of arrival; based on the determined first configuration parameter of the third BS, initiating a handover of the second BS to the third BS; and configuring a transmission of the second BS based on the determined second configuration parameter of the fourth BS. Configuration parameters selected to optimise second BS’s performance (i.e. to mitigate any negative impact on second BS’s performance; minimise interference with the third BS’s neighbours).

Description

CELLULAR TELECOMMUNICATIONS NETWORK
Field of the Invention
The present invention relates to a mobile base station in a cellular telecommunications network.
Background
Cellular telecommunications networks typically comprise a plurality of base stations which each have a coverage area for communicating with a plurality of User Equipment (UE). Traditionally, a base station is in a fixed geographical location by being installed at a particular site or by being installed on a building. These fixed base stations utilise local (typically wired) power and data communication interfaces to receive electrical power and to connect to a cellular core network (often known as a backhaul).
Modern cellular telecommunications networks also provide mobile base stations. These mobile base stations are of a non-fixed geographical location and may change their location either by self-powered movement or by being installed on a movable vehicle (e.g. a train or car). The mobile base station also has a coverage area for communicating with a plurality of UEs, which is achieved in the same manner as for fixed base stations. The mobile base station’s backhaul may be provided by a wired interface, but in many circumstances such wired interfaces are unsuitable. Accordingly, mobile base stations typically have a wireless communications interface for carrying backhaul traffic. These wireless communications interfaces connect to a “donor” base station, and the donor base station’s backhaul connection to the cellular core network includes both traffic for its own UEs and traffic for the mobile base station’s UEs.
As the mobile base station may move relative to the fixed base stations, such that it may move out of a coverage area of its “serving” donor base station, cellular networking protocols define a handover process such that the mobile base station may disconnect from its serving donor base station and connect to a target donor base station with minimal disruption. This process mirrors the corresponding process for UE handover between a serving and target base station, and the mobile base station therefore includes a subset of UE functionality to support this process.
Summary of the Invention
According to a first aspect of the invention, there is provided a method in a cellular telecommunications network, the cellular telecommunications network including a first and second base station, the first base station having a first interface for communicating with a first cellular core networking node and a second interface for wirelessly communicating with the second base station, the second base station being mobile and having a first interface for wirelessly communicating with the first base station and a second interface for communicating with a User Equipment, UE, wherein the UE’s user traffic is transmitted between the first cellular core networking node and the UE via the first and second base stations, the method comprising the steps of: determining a first identity of a third base station and a second identity of a fourth base station, wherein an overlap of the third and fourth base stations’ respective coverage areas cover a route of the second base station; determining a time of arrival of the second base station within the overlap; determining a first configuration parameter of the third base station and a second configuration parameter of the fourth base station in advance of the second base station’s time of arrival; based on the determined first configuration parameter of the third base station, initiating a handover of the second base station to the third base station; and configuring a transmission of the second base station based on the determined second configuration parameter of the fourth base station.
Embodiments of the present invention provide the advantage that a mobile base station may configure its transmissions in advance of its arrival at a target donor base station by taking into account the configuration parameters of its future neighbouring base stations. This ensures that any UE connected to the mobile base station continues to experience the same or similar Quality of Service (QoS) as the mobile base station is handed over to the target donor base station.
The method may further comprise the step of sending a message to the third base station, in advance of the second base station’s time of arrival, requesting a resource. Thus, if it is determined, before the mobile base station’s arrival at the target donor base station, that further resources are required to ensure continuity of QoS for a UE of the mobile base station, these resources can be reserved in advance.
The moving base station’s second interface for communicating with the UE may be a
Wireless Local Area Network (WLAN) interface or a cellular networking interface.
The cellular telecommunications network may further include a fifth base station having a first interface for communicating with a second cellular core networking node and a second interface for wirelessly communicating with the second base station, and the second base station’s first interface may have: a first wireless connection to the first base station for transmission of the UE’s user traffic between the first cellular core networking node and the UE via the first base station, and a second wireless connection to the fifth base station for transmission of the UE’s user traffic between the second cellular core networking node and the UE via the fifth base station, the method may further comprise the steps of: based on the determined configuration parameter of the third base station, determining whether to initiate the handover of the first wireless connection to the third base station.
The mobile base station may therefore maintain a plurality of donor connections (to donor base stations), and the method of the present invention may apply to one or more of these donor connections.
According to a second aspect of the invention, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the first aspect of the invention. The computer program may be stored on a computer-readable data carrier.
According to a third aspect of the invention, there is provided a network node for a cellular telecommunications network, the cellular telecommunications network including a first and second base station, the first base station having a first interface for communicating with a first cellular core networking node and a second interface for wirelessly communicating with the second base station, the second base station being mobile and having a first interface for wirelessly communicating with the first base station and a second interface for communicating with a User Equipment, UE, wherein the UE’s user traffic is transmitted between the first cellular core networking node and the UE via the first and second base stations; the network node comprising: a transceiver and a processor configured to cooperate to: determine a first identity of a third base station and a second identity of a fourth base station, wherein an overlap of the third and fourth base stations’ respective coverage areas cover a route of the second base station; determine a time of arrival of the second base station within the overlap; determine a first configuration parameter of the third base station and a second configuration parameter of the fourth base station in advance of the second base station’s time of arrival; based on the determined first configuration parameter of the third base station, initiate a handover of the second base station to the third base station; and configure a transmission of the second base station’s first and/or second communications interface based on the determined second configuration parameter of the fourth base station.
The transceiver may be further configured to send a message to the third base station, in advance of the second base station’s time of arrival, requesting a resource.
The second base station’s second communications interface may be a Wireless Local Area Network (WLAN) interface or a cellular networking interface for communicating with the UE.
The cellular telecommunications network may further include a fifth base station having a first interface for communicating with a second core networking node, and the second base station’s first communications interface may have: a first wireless connection to the first base station for transmission of the UE’s user traffic between the first cellular core networking node and the UE via the first and second base stations, and a second wireless connection to the fifth base station for transmission of the UE’s user traffic between the second cellular core networking node and the UE via the second and fifth base station, the transceiver and the processor may be further configured to cooperate to: based on the determined configuration parameter of the third base station, determining whether to initiate the handover of the first wireless connection to the third base station.
The network node may be the second base station.
Brief Description of the Figures
In order that the present invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic diagram of a first embodiment of a cellular telecommunications network of the present invention;
Figure 2 is a schematic diagram of the first base station of Figure 1;
Figure 3 is a flow diagram of a first process of a first embodiment of a method of the present invention;
Figure 4 is a flow diagram of a second process of the first embodiment of the method of the present invention;
Figure 5 is a flow diagram of a third process of the first embodiment of the method of the present invention;
Figure 6 is a schematic diagram of a second embodiment of a cellular telecommunications network of the present invention;
Figure 7 is a flow diagram of a first process of a second embodiment of a method of the present invention; and
Figure 8 is a flow diagram of a second process of the second embodiment of the method of the present invention.
Detailed Description of Embodiments
A first embodiment of a cellular telecommunications network 1 will now be described with reference to Figures 1 to 2. The cellular telecommunications network 1 includes a first, second, third and fourth base station 10, 20, 30, 40, wherein the first base station 10 is a macro base station and the second, third and fourth base stations are femto base stations. The macro base station therefore has a relatively large coverage area compared to those of the second, third and fourth base stations. The first, third and fourth base stations 10, 30, 40 are of fixed geographical locations whereas the second base station 20 is affixed to a movable train. The second base station’s route is shown in Figure 1, and passes through an overlapping portion of the respective coverage areas of the first, third and fourth base stations 10, 30, 40.
In this embodiment, the cellular network 1 further includes a network resource server 100, which stores the identity (e.g. the enhanced Cell Global Identifier, eCGI), location and coverage area of each base station in the cellular network 1.
Figure 1 illustrates the cellular network 1 at a first point in time when the second base station 20 has a wireless connection to the first base station 10 (such that the first base station 10 is the second base station’s serving “donor” base station). This form of connection, between the mobile base station and its serving donor base station, will hereinafter be known as the “donor connection”. The first base station 10 has a wired connection to the core network (not shown) which carries traffic for the User Equipment (UE) of the first base station 10 and, in this scenario, for the UEs of the second base station 20. This form of connection, between the base station and the core network, will hereinafter be known as the “core connection”.
A schematic diagram of the first base station 10 is illustrated in Figure 2. The first base station 10 includes a first transceiver 11, a processor 13, memory 15 and a second transceiver 17, all connected via bus 19. The first transceiver 11 is an antenna configured for 1) communication with a plurality of User Equipment (UE) via the Long Term Evolution (LTE) protocol, and 2) forming the donor connection with the second base station 20. The second transceiver 17 is an optical fibre connection, which is used for communicating with one or more cellular core networking entities (including the network resource server 100) via the core connection and/or for communicating with one or more neighbouring base stations (e.g. using an X2 message).
The second, third and fourth base stations 20, 30, 40 are similar to the first base station 10, although their components may be adapted for shorter range communications. As noted above, the second base station 20 is a mobile base station (i.e. of a non-fixed geographical location) and therefore further differs from the first base station 10 in that the second transceiver is an antenna for wireless communication (via the donor connection) with a donor base station. In this embodiment, each base station 10, 20, 30, 40 may also communicate (directly or indirectly) with the network resource server 100 via their second transceivers.
A first embodiment of a method of the present invention will now be described with reference to Figures 1 to 5. In Figure 1, as noted above, the second base station 20 is affixed to a moving train and is initially in a first position and is served by the first base station 10. Figure 1 also illustrates the route of the moving train and the coverage areas of each base station, thus showing the overlapping coverage areas of the third and fourth base stations 30, 40 which further cover a part of the moving train’s future route.
In a first process of this embodiment (step S1 of Figure 3), the second base station 20 sends a request message to the network resource server 100, including data on its future route and a request for data of one or more base stations having coverage areas which cover the future route. In this embodiment, the second base station 20 creates the data on its future route by estimating its location (in Global Positioning System (GPS) coordinates) upon expiry of a plurality of time intervals (e.g. ten successive one-minute time intervals). The data therefore includes the second base station’s estimated GPS coordinates in one-minute’s time, the second base station’s estimated GPS coordinates in two minutes’ time, etc., for the next ten minutes. These locations, and the second base station’s time of arrival, tn, at each location, are illustrated in Figure 1.
The network resource server 100 receives this message and, in step S3, determines the identity of each base station having a coverage area including the second base station’s location for each time interval. In this example, for time intervals ti to t4, it is determined that the first base station 10 has a coverage area including the second base station’s location at those times; for time intervals t5 and t6, it is determined that the first, third and fourth base stations have coverage areas including the second base station’s location at those times; for time intervals t7 to t9, it is determined that the first and third base station have coverage areas including the second base station’s location at those times; and for time interval tw, it is determined that the first base station has a coverage area including the second base station’s location at that time.
In step S5, the network resource manager 100 sends a response message to the second base station 20 identifying each base station (by its eCGI) that has a coverage area including its location at each time interval, and including data on the coverage areas of each identified base station.
The second base station 20 receives this data and stores it in memory (step S7), and the process loops back to step S1 (via a delay timer), such that a new request message is sent to the network resource server 100. The second base station 20 therefore updates its data for its expected locations for the next ten minutes. This iterative loop will therefore address any changes to the second base station’s location or any changes in the identified base station’s location and/or coverage area.
A second process of this embodiment will now be described with reference to Figure 4, in which the second base station 20 utilises the data it receives in the first process. In step S10, the second base station 20 determines its next location at which point it would be covered by at least two base stations other than its serving donor base station (the first base station 10). In this embodiment, that is at time t5 when it its location will be covered by the first, third and fourth base stations 10, 30, 40.
In step S12, the second base station 20 then determines which of the third and fourth base stations 30, 40 (hereinafter, third and fourth “target” donor base stations) would be its preferred target donor base station if a handover is to occur. This is achieved by the second base station 20 setting up an X2 connection with each of the identified target donor base stations, and sending a request for data on their operating parameters (e.g. its Radio Access Technologies (RATs) used for the donor connection (e.g. LTE, microwave P2P, WiFi), and PCI value) and performance indicators (e.g. its capacity and load information). The target donor base stations respond with this data (which, where appropriate, include current, average and forecast values), and the second base station 20 analyses each target donor base station’s data to determine which would be a more suitable donor connection and is therefore its “preferred” target donor base station. In this embodiment, this analysis is based one or more of the following non-exhaustive list:
• Which target donor base station has/will have the greatest capacity;
• Which target donor base station has/will have the smallest load;
• The target donor base stations’ current/forecast energy saving statuses; and • The interference techniques the second base station must implement for each target base station.
The second base station 20 then determines which of the third and fourth base stations 30, 40 is its preferred target donor base station based on this data. In this example, the third base station 30 is selected as the preferred target donor base station. In step S14, the second base station 20 sends an information message (e.g. within an RNReconfiguration message) to its serving donor base station (the first base station 10) identifying the third base station 30 as its preferred target donor base station, its estimated time of arrival in the coverage area of that target donor base station, and data regarding its resource requirements (i.e. capacity). On receipt of this information message, the first base station 10 stores this data in memory 15.
In step S16, the second base station 20 analyses the data received from each target donor base station to determine one or more transmission configuration parameters for when it arrives at the location, at time t5. These configuration parameters are selected so as to optimise the second base station’s performance, and therefore take into account the operating parameters of its preferred target donor base station (the third base station 30) so as to select complimentary parameters for the second base station 20, and further take into account the operating parameters of any other base station which has a coverage area including the second base station’s location at that time (i.e. the first and fourth base stations 10, 40) so as to mitigate any negative impact on the second base station’s performance. The analysis may result in one or more of the following example configuration parameters:
Data Analysis Configuration Parameter
Second base station 20 has PCI conflict with fourth base station 40 Non-conflicting PCI
Second base station 20 is co-channel with strong overlap with the fourth base station 40 Use soft frequency reuse with orthogonal high power resources
Second base station 20 is co-channel with strong overlap with fourth base station 40, but only for short amount of time Adapt idle and connected mode mobility parameters to minimise unnecessary ping pong (as overlap is too short term)
First base station 10 broadcasts Almost Bblank Subframes (ABS). Second base station 20 and fourth base station 40 will use ABS Coordinate so that ABS are used effectively
The second base station then stores the identity of its preferred target donor base station, the timestamp corresponding to its expected time of arrival in the coverage area of the preferred target donor base station, and its configuration parameters if it is handed over to the preferred target donor base station, in memory.
In this embodiment, in step S17, the second base station 20 sends a message to the third base station 30 specifying its time of arrival within the coverage area of the third base station 30, specifying what resources the second base station 20 requires if it uses the third base station 30 as a donor base station, and specifying the transmission parameters determined in step S16. The third base station 30 may react to this message by making suitable reconfigurations to accommodate (e.g. by initialising a further radio to increase capacity, or making changes to its own transmission parameters such that they are complimentary to those of the second base station 20).
In step S18, the second base station 20 determines if there are any further locations at which point it would be covered by at least two base stations other than its serving base station. In this example, there are no further locations which satisfy this criterion. However, if this determination was positive, then the second base station 20 would loop back to step S12 in order to select its preferred target donor base station at that location, to reserve resources at its determined preferred target donor base station when it arrives at that location, and to determine what transmission configuration parameters it should use at that location. Once the second base station determines that there are no further locations at which point it would be covered by at least two base stations other than its serving base station, then the process loops back to step S10, via a delay timer. The second base station 20 therefore iteratively updates its serving donor base station with the identity of (and time of arrival at) its preferred target donor base station at its next location (and, if applicable, any further future locations) where it will be covered by at least two other base stations. This, again, accounts for any changes in the target donor base station’s operational parameters or performance indicators.
A third process of this embodiment will now be described with reference to Figure 5. In a first step (step S20) of this third process, the second base station 20 monitors its radio environment to determine, for example, the Reference Signal Received Power (RSRP) for all base stations for which it can receive a signal. The second base station 20 then determines whether this data satisfies a trigger condition to initiate a handover from its serving donor base station to a target donor base station (e.g. a target donor base station having a greater RSRP than the serving donor base station). If this condition is not met, then the process loops back (via a delay timer) to be repeated at a later time. However, in this example at time t5, the trigger condition is met and the second base station 20 sends a measurement report (step S22) to its serving donor base station (the first base station 10). The measurement report identifies both the third and fourth base stations 30, 40 as potential target donor base stations.
In response, the first base station 10 initiates a handover process. In step S24, the first base station 10 determines the identity of the preferred target donor base station. In this example, the preferred target donor base station is the third base station 30.
Accordingly, the first base station 10 identifies the third base station 30 as the target of the handover, and sends an X2 Handover Request message to the third base station 30.
Once the first and third base stations 10, 30 have successfully negotiated the handover, the first base station 10 sends (in step S26) an instruction message to the second base station 20 to cause it to disconnect from the first base station 10 and connect to the second base station 20. In response, the second base station 20 reconfigures its transmissions based on the stored configuration parameters in memory, and completes the handover to the third base station 30. Accordingly, the second base station 20 is handed over from the first base station 10 to the third base station 30 with its transmissions configured in advance of its arrival to minimise interference with the third base station’s neighbours (i.e. the first and fourth base stations 10, 40).
Furthermore, the skilled person will understand that it is not essential for the second base station to perform the above process, but they could instead be calculated by a centralised server (having communication interfaces with base stations in the network, such as the network resource manager).
A second embodiment of the present invention will now be described with reference to Figures 6, 7 and 8. The network of the second embodiment is substantially similar to that of the first embodiment, but only includes a first, second, and third base station 110, 120, 130, in which the first base station is a fixed macro base station, the second base station is a mobile femto base station, and the third base station is a fixed femto base station. The locations and coverage areas of each base station are illustrated in Figure
6. In this embodiment, the second base station does not predetermine and reserve resources in advance of its arrival within the coverage area of its future donor base stations. Instead, this second embodiment illustrates an alternative technique in which the donor base stations broadcast their backhaul capabilities and the mobile base station receives and reacts to this broadcast in its preferred donor base station selection process. A first process of this embodiment will now be described with reference to Figure 7.
In a first step, S40, the second base station 20 uses a Network Listen (NL) function, implemented by its processor and first transceiver, to monitor its radio environment. In particular, the second base station 20 monitors frequency bands and RATs that could be used for a donor connection (which may have been identified by its serving donor base station).
In step S42, the second base station 20 enters the coverage area of the third base station
30. The NL function identifies the third base station 30 (e.g. by its eCGI) and performs various measurements to prepare a measurement report (e.g. by measuring the Reference Signal Received Power, RSRP). The second base station 20 also decodes the System Information Block (SIB), which, in this embodiment, includes one or more of the following information on the third base station’s donor connection capabilities from the following non-exhaustive list:
• Its supported RATs and frequency bands;
• Its current capacity and loading;
• Information on its core connection;
• Donor connection preference indicators (e.g. charge related information);
• Coverage information (so the second base station 20 can predict how long the third base station 30 may act as a donor base station); and • Contact/ldentifying information (e.g. SSID of WLAN RAT).
In step S44, the second base station 20 stores this information in its Neighbour Relations Table (NRT) in memory. The process then loops back round to step S40, via a delay timer, such that the second base station 20 periodically performs a new NL function and updates its NRT.
In a second process, as illustrated in Figure 8, will now be described. In step S50, the second base station 20 determines whether any candidate target donor base station in its NRT is a more preferable donor to its serving donor base station (the first base station 10). The second base station 20 bases this decision, at least in part, on the donor connection information from the SIB message, such as the supported RATs, and capacity and loading information. In this example, the second base station 20 determines that the third base station 30 would provide a better donor connection than the first base station 10.
In this embodiment, in step S51, the second base station 20 sends a request message to the third base station 30 specifying what resources the second base station 20 requires. In this embodiment, the second base station 20 sends a request message by establishing a communication channel with the third base station 30 over a WLAN communication interface (e.g. as defined in any one of the 802.11 family of standards, commonly known as “Wi-Fi”), for example by using the SSID in the broadcast information. However, in alternative arrangements, the communication channel may be established via the first base station (e.g. using an X2 message).
The third base station 30 may react to this message by making suitable reconfigurations to accommodate (e.g. by initialising a further radio to increase capacity).
In step S52, the second base station 20 informs the first base station 10 of the identity of the target donor base station offering the preferable donor connection (again using the RNReconfiguration message). In this embodiment, in step S53, the first base station 10 is configured to react to receipt of an RNReconfiguration message by initiating a handover of the second base station 20 to the identified target donor base station. The first base station 10 sends an X2 Handover Request message to the third base station 30 and, once the handover is successfully negotiated, the first base station 10 sends an instruction message to the second base station 20 causing it to disconnect from the first base station 10 and connect to the third base station 30.
The process then loops back to step S50, via a delay timer, and the second base station 20 determines if there are any other candidate target donor base stations in its NRT (which may have been updated following subsequent iterations of the first process, outlined in steps S40 to S44, as the second base station 20 moves along its route).
In the above embodiments, the handover of the second base station is triggered either by a measurement report satisfying a particular condition, or by the serving donor base station being configured to react to a particular message sent by the second base station when a condition is met. The skilled person will understand that both options are applicable to each embodiment. Furthermore, the second base station may complete a handover to its preferred donor base station in other ways, such as by forming a donor connection with the preferred donor base station before disconnecting from its current serving base station (known as a “make-before-break” handover).
Furthermore, the above embodiments include the step of the second base station monitoring its radio environment (either to determine when a trigger condition has been met or to decode a particular broadcast message). In an enhancement to either embodiment, the second base station may increase the rate at which it performs such monitoring as its connection with the serving base station degrades. For example, the second base station may have a plurality of signal strength thresholds, and the rate of performing each monitoring function may increase when each signal strength threshold is met.
In the above second embodiment, the donor base stations broadcast their donor connection information in a SIB message. This is advantageous as the second base station may determine this information relatively quickly (than the first embodiment in which an X2 connection is set up before the second base station arrives in the target donor base station’s coverage area) and the second base station may directly determine particular measurements (e.g. RSRP) rather than determining an estimate. Furthermore, broadcast messages are often relatively robust and easy to decode (e.g. by using standard defined portions of the frame and by using simple modulation schemes), such that base stations can readily decode these messages with minimal processing cost. Nonetheless, the skilled person will understand that any other broadcast message, or a bespoke broadcast message, may be used. Other broadcast messages that may be suitable include the Multimedia Broadcast Multicast Service (MBMS) in LTE and the beacon frame in WiFi.
In both of the above embodiments, the second base station may have a plurality of donor connections (that is, a plurality of donor connections to one donor base station, or a plurality of donor connections to a plurality of donor base stations). Both embodiments of the invention may be applied to one or a subset of these donor connections. Accordingly, if a first donor connection is for Voice of Internet Protocol (VoIP) traffic and a second donor connection is for file downloads, then a first target donor base station may be selected for the first donor connection (e.g. if its donor connection capabilities indicate suitably low latency) and a second target donor base station may be selected for the second donor connection (e.g. if it has suitably high capacity). One of these donor connections may remain with the second base station’s current serving base station if it has the most suitable characteristics.
In the above embodiments, the second base station configures its transmissions in response to data it receives on several target donor base stations. These may be transmissions both on the first transceiver (i.e. with a UE) and/or on the second transceiver (i.e. with the donor base station).
The skilled person will also understand that it is not essential for the other first, third and fourth base stations to be fixed, as they too could be mobile. The first embodiment above may address issues with data for the target donor mobile base stations becoming inaccurate (e.g. due to the target donor mobile base station having a changeable coverage area) by having a Time-To-Live limit for any associated data.
In the first embodiment above, the second base station sends a request to the network resource manager for data on candidate target donor base stations that cover its future route, and the network resource manager responds with a message identifying each candidate target donor base station and the coverage area of each candidate. In one implementation, the coverage area may be indicated by the GPS coordinates of the candidate target donor base station and a radius measurement of its coverage area. However, more complex network resource maps may be used instead. Furthermore, the skilled person will understand that it is not essential for the network resource manager to respond with data regarding the coverage areas, as the second base station may establish an X2 connection with the candidate target base station (using the identifier from the network resource manager) and request this information from the candidate.
The skilled person will understand that any combination of features is possible within the scope of the invention, as claimed.

Claims (13)

1. A method in a cellular telecommunications network, the cellular telecommunications network including a first and second base station, the first base station having a first interface for communicating with a first cellular core networking node and a second interface for wirelessly communicating with the second base station, the second base station being mobile and having a first interface for wirelessly communicating with the first base station and a second interface for communicating with a User Equipment, UE, wherein the UE’s user traffic is transmitted between the first cellular core networking node and the UE via the first and second base stations, the method comprising the steps of:
determining a first identity of a third base station and a second identity of a fourth base station, wherein an overlap of the third and fourth base stations’ respective coverage areas cover a route of the second base station;
determining a time of arrival of the second base station within the overlap; determining a first configuration parameter of the third base station and a second configuration parameter of the fourth base station in advance of the second base station’s time of arrival;
based on the determined first configuration parameter of the third base station, initiating a handover of the second base station to the third base station; and configuring a transmission of the second base station based on the determined second configuration parameter of the fourth base station.
2. A method as claimed in Claim 1, further comprising the step of:
sending a message to the third base station, in advance of the second base station’s time of arrival, requesting a resource.
3. A method as claimed in any one of the preceding claims, wherein the moving base station’s second interface for communicating with the UE is a Wireless Local Area Network (WLAN) interface.
4. A method as claimed in any one of Claims 1 to 2, wherein the moving base station’s second interface for communicating with the UE is a cellular networking interface.
5. A method as claimed in any one of the preceding claims, wherein the cellular telecommunications network further includes a fifth base station having a first interface for communicating with a second cellular core networking node and a second interface for wirelessly communicating with the second base station, and the second base station’s first interface has:
a first wireless connection to the first base station for transmission of the UE’s user traffic between the first cellular core networking node and the UE via the first base station, and a second wireless connection to the fifth base station for transmission of the UE’s user traffic between the second cellular core networking node and the UE via the fifth base station, the method further comprising the steps of: based on the determined configuration parameter of the third base station, determining whether to initiate the handover of the first wireless connection to the third base station.
6. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of the preceding claims.
7. A computer-readable data carrier having stored thereon the computer program of Claim 6.
8. A network node for a cellular telecommunications network, the cellular telecommunications network including a first and second base station, the first base station having a first interface for communicating with a first cellular core networking node and a second interface for wirelessly communicating with the second base station, the second base station being mobile and having a first interface for wirelessly communicating with the first base station and a second interface for communicating with a User Equipment, UE, wherein the UE’s user traffic is transmitted between the first cellular core networking node and the UE via the first and second base stations; the network node comprising:
a transceiver and a processor configured to cooperate to:
determine a first identity of a third base station and a second identity of a fourth base station, wherein an overlap of the third and fourth base stations’ respective coverage areas cover a route of the second base station;
determine a time of arrival of the second base station within the overlap; determine a first configuration parameter of the third base station and a second configuration parameter of the fourth base station in advance of the second base station’s time of arrival;
based on the determined first configuration parameter of the third base station, initiate a handover of the second base station to the third base station; and configure a transmission of the second base station’s first and/or second communications interface based on the determined second configuration parameter of the fourth base station.
9. A networking node as claimed in Claim 8, wherein the transceiver is further configured to send a message to the third base station, in advance of the second base station’s time of arrival, requesting a resource.
10. A networking node as claimed in either Claim 8 or Claim 9, wherein the second base station’s second communications interface is a Wireless Local Area Network (WLAN) interface for communicating with the UE.
11. A networking node as claimed in either Claim 8 or Claim 9, wherein the second base station’s second communications interface is a cellular networking interface for communicating with the UE.
12. A networking node as claimed in any one of Claims 8 to 11, wherein the cellular telecommunications network further includes a fifth base station having a first interface for communicating with a second core networking node, and the second base station’s first communications interface has:
a first wireless connection to the first base station for transmission of the UE’s user traffic between the first cellular core networking node and the UE via the first and second base stations, and a second wireless connection to the fifth base station for transmission of the
UE’s user traffic between the second cellular core networking node and the UE via the second and fifth base station, the transceiver and the processor being further configured to cooperate to:
based on the determined configuration parameter of the third base station, determine whether to initiate the handover of the first wireless connection to the third base station.
13. A networking node as claimed in any one of Claims 8 to 12, being the second base station.
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