Cellular telecommunications networks

Abstract

The present invention relates to a method in a cellular telecommunications network having a first central base station unit connected to each of a plurality of distributed base station units, the method comprising the steps of: identifying a cluster of distributed base station units within the plurality of distributed base station units, wherein each member of the cluster has a threshold-satisfying neighbor relationship with another member of the cluster; using a first functional partitioning, wherein a first set of protocol functions are implemented in the first central base station unit and a second set of protocol functions are implemented by each member of the cluster of distributed base station units; identifying a change in membership of the cluster of distributed base station units; and, in response, causing the first central base station unit and each member of the cluster of distributed base station units to implement a second functional partitioning, wherein a third set of protocol functions are implemented in the first central base station unit and a fourth set of protocol functions are implemented by each member of the cluster of distributed base station units.

Description

Technical Field

[0001] The present invention relates to a cellular telecommunication network. In particular, the present invention relates to a cellular telecommunication network implementing a centralized radio access network. Background Art

[0002] Modern cellular networks support a centralized radio access network (C-RAN) architecture, in which base stations can be divided into a central unit and distributed units. The central unit interconnects the core cellular network with multiple distributed units, and the multiple distributed units each communicate with multiple UEs. The various protocol layers of the cellular protocol used are divided between the central unit and the distributed units, so that the distributed unit implements the lowest layer (e.g., the radio frequency layer) and optionally implements one or more higher layers, and all other higher layers are implemented in the central unit. As more protocol layers are implemented in the central unit, the central unit can improve coordination across multiple distributed units, thereby improving the quality of service. However, this protocol division requires a higher capacity link between the central unit and the distributed units, so a balance must be reached when determining which protocol division to use. Summary of the invention

[0003] According to a first aspect of the present invention, there is provided a method in a cellular telecommunications network having a first central base station unit connected to each of a plurality of distributed base station units, the method comprising the steps of: identifying a cluster of distributed base station units within the plurality of distributed base station units, wherein each member of the cluster has a threshold-satisfying neighbour relationship with another member of the cluster; using a first functional partitioning, wherein a first set of protocol functions are implemented in the first central base station unit and a second set of protocol functions are implemented by each member of the cluster of distributed base station units; identifying a change in membership of the cluster of distributed base station units; and, in response, causing the first central base station unit and each member of the cluster of distributed base station units to implement a second functional partitioning, wherein a third set of protocol functions are implemented in the first central base station unit and a fourth set of protocol functions are implemented by each member of the cluster of distributed base station units.

[0004] A change in membership of a cluster of distributed base station units may be the addition of a new distributed base station unit to the cluster, and the method may further comprise the step of initiating a handover of the new distributed base station unit from the second central base station unit to the first central base station unit before the step of determining to use the second functional division.

[0005] Before executing the step of switching the new distributed base station unit, the method may also include the following steps: causing the second central base station unit and the new distributed base station unit to use a first functional division, wherein a first set of protocol functions is further implemented in the second central base station unit, and a second set of protocol functions is further implemented in the new distributed base station unit.

[0006] The method may further include the steps of receiving data relating to membership of the cluster of distributed base units and determining based on the data that the first central base unit and individual members of the cluster of distributed base units should use the second functional division.

[0007] The first central base station unit and the second central base station unit may be implemented on separate virtual machines on the network node.

[0008] According to a second aspect of the invention there is provided a computer program product comprising instructions which, when executed by a computer, cause the computer to perform the method of the first aspect of the invention. The computer program may be stored on a computer readable data carrier.

[0009] According to a third aspect of the invention there is provided a network node for a cellular telecommunications network, the network node comprising a transceiver, a memory and a processor adapted to cooperate to implement the steps of the method of the first aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to better understand the present invention, embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0011] Figure 1 is a schematic diagram of a cellular telecommunication network according to an embodiment of the present invention;

[0012] Figure 2 yes Figure 1 A schematic diagram of a central base station unit and distributed base station units of a cellular network;

[0013] Figure 3a yes Figure 1 Schematic diagram of a cellular telecommunication network at time t1;

[0014] Figure 3b yes Figure 1 A schematic diagram of a cellular telecommunication network at time t2;

[0015] Figure 3c yes Figure 1 A schematic diagram of a cellular telecommunication network at time t3;

[0016] Figure 3d yes Figure 1 A schematic diagram of a cellular telecommunication network at time t4;

[0017] Figure 3e yes Figure 1 a schematic diagram of a cellular telecommunications network of at time t5; and

[0018] Figure 4 is a flow chart illustrating a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] Now refer to Figure 1 and Figure 2 1 is a diagram to describe a first embodiment of a cellular telecommunication network 1. The cellular telecommunication network 1 is based on a centralized radio access network (C-RAN) architecture having a first central unit 10 and first, second and third distributed units ("first / second / third DUs" in the figure) 20, 30, 40. The central unit 10 interconnects each of the first, second and third distributed units 20, 30, 40 with a cellular core network 50, which includes a network management system (NMS) 100. The coverage area of ​​each of the first, second and third distributed units 20, 30, 40 is shown by their respective envelope circles.

[0020] Figure 2 The central unit 10 and the first distributed unit 20 are illustrated in more detail. As shown, the central unit 10 has a first transceiver 11, a processor 13, a memory 15, and a second transceiver 17, all of which are connected via a bus 19. The first transceiver 11 is a wired communication interface so that the central unit 10 can communicate with one or more cellular core network nodes (e.g., NMS 100). In this embodiment, the second transceiver 17 is a wired communication interface so that the central unit 10 can communicate with each of the first, second, and third distributed units 20, 30, 40. The transceivers, processors, and memories are configured to cooperate to define a software defined network (SDN) operating environment, allowing the central unit 10 to be reconfigured as needed.

[0021] In addition, the first distributed unit 20 also includes a first transceiver 21 for wired communication with the central unit 10, a processor 23, a memory 25, and a second transceiver 27 for wireless communication with one or more user equipments (UEs), all of which are connected via a bus 29. Similarly, the transceiver, processor, and memory are configured to cooperate to define a software defined network (SDN) operating environment, allowing the first distributed unit 20 to be reconfigured as needed.

[0022] Figure 2The processors of the central unit 10 and the first distributed unit 20 that implement different functions of their operating protocol (in this embodiment, the operating protocol is the Long Term Evolution (LTE) protocol) are also illustrated. The various functions of the LTE protocol are divided between the respective processors 13, 23 of the central unit 10 and the first distributed unit 20, so that the first distributed unit 20 implements the physical (PHY) function and the medium access control (MAC) function, and the central unit 10 implements the radio link control (RLC) function and the packet data convergence control (PDCP) function. In doing so, the central unit 10 can coordinate the transmission of several distributed units to improve the quality of service (QoS) in the cellular network 1.

[0023] The processors of the central unit 10 and the first distributed unit 20 can be reconfigured (when they operate the SDN environment) to implement different functional divisions, for example:

[0024] A) First distributed unit 20: lower PHY, central unit 10, higher PHY, MAC, RLC, PDCP;

[0025] B) First distributed unit 20: PHY, central unit 10: MAC, RLC, PDCP;

[0026] C) First distributed unit 20: PHY, MAC, central unit 10: RLC, PDCP (as shown in the figure);

[0027] D) First distributed unit 20: PHY, MAC, RLC, central unit 10: PDCP;

[0028] E) First distributed unit 20: PHY, MAC, RLC, PDCP, central unit 10: N / A;

[0029] Furthermore, the central unit 10 and the first distributed units 20 may implement other functions (in which case other functional divisions are also possible).

[0030] In this embodiment, the second and third distributed units 30 , 40 are similar to the first distributed unit 20 .

[0031] Now refer to Figures 3a to 3e and Figure 4 The first embodiment of the method of the present invention is described with reference to a flowchart of FIG. Figure 3aA cellular telecommunication network 1 at time t1 is illustrated, wherein a central unit 10 interconnects first, second and third distributed units 20, 30, 40 with a core network 50 and implements a functional division D (as described above), such that the first central unit 10 implements PDCP functionality and the first, second and third distributed units 20, 30, 40 implement PHY, MAC and RLC functionality.

[0032] Figure 3a A fourth distributed unit 60 is also illustrated. The fourth distributed unit 60 is similar to the first, second and third distributed units 20, 30, 40, but is mobile by being mounted on a train (not shown). Furthermore, the fourth distributed unit 60 is connected to a second central unit 70, which is similar to the first central unit 10 and has a forward connection to the cellular core network 50 (and thus to the NMS 100). The second central unit 70 and the fourth distributed unit 60 implement a functional partitioning E (as described above), such that the fourth distributed unit 60 implements all functions of the protocol stack. Figure 3a In FIG. 6 , the fourth distributed unit 60 is located at position p1.

[0033] In such Figure 3a In this illustrated starting scenario, the NMS 100 stores a cluster database identifying various clusters of distributed units and their membership. The definition of a cluster will become clear by reading the following embodiments, but it should be noted that in this starting scenario, the first, second and third distributed units 20, 30, 40 are all members of the first cluster, but the fourth distributed unit 60 is not part of the first cluster (or any other cluster). Therefore, the fourth distributed unit 60 is a "standalone" distributed unit.

[0034] In a first step (step S1) of this embodiment, each distributed unit 20, 30, 40, 60 monitors its radio environment (directly or indirectly) to identify one or more neighbor relations with other distributed units in the cellular telecommunication network 1. In this embodiment, this step is periodically triggered when a) a measurement report is received from a UE connected to the respective distributed unit 20, 30, 40, 60, and / or when b) the respective distributed unit 20, 30, 40, 60 has a network listening function. In response, each distributed unit 20, 30, 40, 60 may cooperate with its corresponding central unit 10, 70 to process the data (i.e., using the processing functions implemented in the central unit). Then, each distributed unit 20, 30, 40, 60 updates a neighbor relation table (NRT), which identifies each neighboring distributed unit and further identifies the signal strength (e.g., reference signal received power, RSRP) from each neighboring distributed unit. After this step, the NRT of each distributed unit is:

[0035] Base Station Identifier (eCGI) RSRP(dBm) Second distributed unit >X The third distributed unit >X

[0036] Table 1: NRT of the first distributed unit 20 at time t1

[0037] Base Station Identifier (eCGI) RSRP(dBm) First distributed unit >X The third distributed unit >X

[0038] Table 2: NRT of the second distributed unit 30 at time t1

[0039] Base Station Identifier (eCGI) RSRP(dBm) First distributed unit >X Second distributed unit >X Fourth distributed unit <X

[0040] Table 3: NRT of the third distributed unit 40 at time t1

[0041] Base Station Identifier (eCGI) RSRP(dBm) Second distributed unit <X

[0042] Table 4: NRT of the fourth distributed unit 60 at time t1

[0043] Although the value of threshold X may vary in any particular cellular network, in this embodiment, the value is -100 dBm. The threshold may also be in the range of -120 dBm to -90 dBm.

[0044] In step S3, each distributed unit 20, 30, 40, 66 reports these NRTs to the NMS 100 via their respective central units 10, 70. In doing so, the NMS 100 records the central unit associated with each distributed unit that reports its NRT. In step S5, the NMS 100 identifies a cluster of one or more distributed units based on the data. In this embodiment, a cluster is a subset of distributed units where each member of the cluster receives a reference signal from at least one other member of the cluster with a strength above X dBm. Based on the above data, the first, second and third distributed units 20, 30, 40 are all in the cluster (because they all measure an RSRP value of another member of the cluster that is above X dBm), but the fourth distributed unit 60 is not in the cluster (because it does not measure an RSRP value of a member of the cluster that is above X dBm).

[0045] In step S7, the NMS 100 determines whether there is a change in membership of any cluster of distributed units based on a comparison of the data in the cluster database with the clusters identified in step S5. As described above, the initial scenario of the cellular network 1 is that there is a first cluster including the first, second and third distributed units 20, 30, 40. After step S5, the latest NRT indicates that the first cluster still includes the first, second and third distributed units 20, 30, 40. Therefore, there is no change in membership of the first cluster. Therefore, the first iteration of the method ends.

[0046] The method then loops back to step S1 for a second iteration. The starting point of the second iteration is at time t2, such as Figure 3b As shown, the fourth distributed unit 60 moves to a new position (p2) with a larger overlapping coverage area with the third distributed unit 40. In the second iteration of step S1, the first, second, third and fourth distributed units 20, 30, 40, 60 update their respective NRTs based on the new measurements, such that:

[0047] Base Station Identifier (eCGI) RSRP(dBm) Second distributed unit >X The third distributed unit >X

[0048] Table 5: NRT of the first distributed unit 20 at time t2

[0049] Base Station Identifier (eCGI) RSRP(dBm) First distributed unit >X The third distributed unit >X

[0050] Table 6: NRT of the second distributed unit 30 at time t2

[0051] Base Station Identifier (eCGI) RSRP(dBm) First distributed unit >X Second distributed unit >X Fourth distributed unit >X

[0052] Table 7: NRT of the third distributed unit 40 at time t2

[0053] Base Station Identifier (eCGI) RSRP(dBm) Second distributed unit >X

[0054] Table 8: NRT of the fourth distributed unit 60 at time t2

[0055] Therefore, the fourth distributed unit 60 has moved to a position where the RSRP of the signal of the fourth distributed unit 60 measured by the third distributed unit 40 has risen above X dBm and the RSRP of the signal of the third distributed unit measured by the fourth distributed unit 60 has also risen above X dBm.

[0056] In a second iteration of steps S3 and S5, each distributed unit 20, 30, 40, 60 reports its NRT to the NMS 100, and the NMS 100 identifies a cluster of one or more distributed units based on the data. Since the third distributed unit 40 now has a neighbor relationship with the fourth distributed unit 60 that is above the first threshold (i.e., RSRP>X dBm), the NMS 100 determines that the first cluster now includes the first, second, third and fourth distributed units. For the sake of completeness, the NRTs of the third and fourth distributed units do not necessarily both indicate that the neighbor relationship is already above the threshold. That is, if one of the NRTs of the third or fourth distributed units 40, 60 indicates that the neighbor relationship is already above the threshold (e.g., the NRT is updated based on a measurement report from a UE connected to one of the third or fourth distributed units), the NMS 100 can determine that the cluster now also includes the fourth distributed unit 60.

[0057] In the second iteration of step S7, the NMS 100 positively determines that the membership of the first cluster has changed. The NMS 100 responds to this determination by reconfiguring the cellular network 1 so that all distributed units are served by the same central unit and have the same functional division. In this embodiment, this is achieved by implementing the following steps.

[0058] In step S9, the NMS 100 determines whether all distributed units in the first cluster are served by the same central unit. If so, the process proceeds to step S21. However, in this embodiment, because the first, second and third distributed units 20, 30, 40 are served by the first central unit 10, but the fourth distributed unit 60 is served by the second central unit 70, the determination is negative. In response, in step S11, the NMS 100 determines which central unit should become the common central unit serving all distributed units of the cluster. The determination can be based on the number of handovers that need to be performed, the quality of the connections between the various central units and the various distributed units, and / or the spare processing capacity of the central units. In this embodiment, the NMS 100 determines that the fourth distributed unit 60 should be handed over to the first central unit 10 and sends an instruction message to the second central unit 70.

[0059] In step S13, the second central unit 70 establishes a connection (e.g., an X2 connection) with the first central unit 10. Once established, the second central unit 70 sends a request message to the first central unit 10 to discover the current functional division implemented by the first central unit 10. The first central unit 10 responds with information related to its functional division (e.g., using an identifier). In step S15, the second central unit 70 determines whether the functional division used between the second central unit 70 and the fourth distributed unit 60 is different from the functional division implemented by the first central unit 10. If not, the process proceeds to step S19. However, in this embodiment, the determination is affirmative and the process proceeds to step S17, where the second central unit 70 and the fourth distributed unit 60 are reconfigured to use the same functional division as used by the first central unit 10. After this reconfiguration, the cellular network 1 is as follows. Figure 3c As shown, the functional division implemented between the first central unit 10 and the first, second and third distributed units 20, 30, 40 matches the functional division implemented between the second central unit 70 and the fourth distributed unit 60.

[0060] In step S19, the second central unit 70 cooperates with the first central unit 10 to complete the handover of the fourth distributed unit 60 to the first central unit 10. After the handover, the cellular network 1 is as follows: Figure 3dAs shown, the first central unit 10 serves the first, second, third and fourth distributed units 20, 30, 40, 60 so that it now serves the updated membership of the first cluster. After completing the handover, the first central unit 10 sends a message to the NMS 100 indicating that the handover is complete.

[0061] In step S21, the NMS 100 determines the functional partitioning between each distributed unit cluster and their respective central unit, and between each individual distributed unit (i.e., not a member of a cluster) and its respective central unit (if applicable). In this embodiment, the NMS 100 compares the signal strength data (from the NRT) with the corresponding thresholds for each functional partitioning, and determines that the functional partitioning B (as described above) is appropriate between the first central unit 10 and the first cluster. In step S23, the NMS 100 sends an instruction message to the first central unit 10 and the first cluster to implement the functional partitioning B. After this reconfiguration, the cellular network 1 is as follows: Figure 3e shown.

[0062] The above embodiments provide the benefit of introducing a trigger for reconfiguring the functional division between the central unit and the cluster of distributed units based on positive identification of a change in membership in the cluster. A cluster may be defined as a subset of distributed units that have a neighbor relationship above a certain threshold, such that the trigger for reconfiguring the functional division is effectively based on a distributed unit increasing or decreasing its neighbor relationship with another distributed unit passing that threshold. This is an interesting point in time to evaluate the functional division, as any new or departing member of the cluster may significantly change the potential interference in the cluster.

[0063] The neighbor relation threshold may be configurable by the operator to reflect when it is appropriate for signals from two neighboring distributed units to significantly interfere with the coordination of the central unit. This may be inferred from, for example, RSRP measurements of the distributed units or their UEs. Furthermore, determining what functional partition to use is not necessarily based on a comparison of RSRP to one or more thresholds (e.g., corresponding thresholds for each functional partition). That is, the functional partition may be selected based on the number of distributed units in the cluster.

[0064] Furthermore, those skilled in the art will appreciate that it is not necessary to perform the steps of the present invention in the NMS. Instead, another entity (including a central unit) may perform the method.

[0065] In the example above, the fourth distributed unit is mobile so that it becomes part of the cluster when it moves to position p2. However, this is not necessary, and those skilled in the art will appreciate that another distributed unit may always be located in a suitable geographical location to become a member of the cluster, but only be enabled if the neighbor relationship threshold is met (for example) during reconfiguration, after energy saving or when the load becomes heavier.

[0066] Furthermore, it is not necessary that the fourth distributed unit is connected to the second central unit. That is, the fourth distributed unit may be connected to the first central unit but not meet the neighbor relation threshold to be part of the first cluster. In this case, the first central unit may implement different virtual machines to serve the first cluster using the first functional division and to serve the fourth distributed unit using the second functional division.

[0067] In the above embodiment, the fourth distribution unit is switched to the first central unit. This is beneficial because it is easier to achieve a common functional division between all distributed units. However, it is not necessary because the functional division can be coordinated across independent central units (especially if the two central units are implemented by independent virtual machines on the same platform).

[0068] In the above embodiment, the fourth distributed unit is a separate distributed unit before joining the first cluster. However, this is not necessary. The fourth distributed unit can be part of the second cluster. In this case, the fourth distributed unit (and one or more other distributed units of the second cluster) can leave the second cluster and join the first cluster.

[0069] In the above embodiments, the central unit and its respective distributed units implement different proportions of the functionality of the overall set of protocols used (LTE in the above examples, of course any other cellular / wireless communication protocol can be used). Those skilled in the art will appreciate that the entire layer of the protocol can be moved between the central unit and the distributed units, or only a portion thereof (i.e., the functionality) can be moved between them. Thus, the central unit can implement a first set of protocol functions, and the distributed units can implement a second set of protocol functions. The first set of functions can be the lowest functions and include specific functions, and the second set of functions can be all functions above the specific functions. In other words, the first set of functions and the second set of functions can be different.

[0070] Furthermore, the distributed unit may implement only the RF functionality of the protocol, and all other functionality may be implemented in the central unit. Furthermore, the present invention may be implemented across cascaded RANs, where the functionality of the entire group is distributed across, for example, remote radio heads, distributed units and central units.

[0071] It will be understood by a person skilled in the art that any combination of features is possible within the scope of the present invention, as set out in the claims.

Claims

1. A method in a cellular telecommunications network having a first central base station unit connected to each of a plurality of distributed base stations units, the method comprising the steps of: identifying a cluster of distributed base stations within the plurality of distributed base stations, wherein each member of the cluster has a neighbor relationship satisfying a threshold with another member of the cluster; using a first functional division, wherein a first set of protocol functions are implemented in the first central base station unit and a second set of protocol functions are implemented by individual members of the cluster of distributed base station units; identifying a change in membership of the cluster of distributed base units; and, in response, The first central base station unit and each member of the cluster of distributed base station units are caused to implement a second functional division, wherein a third group of protocol functions are implemented in the first central base station unit and a fourth group of protocol functions are implemented by each member of the cluster of distributed base station units.

2. The method according to claim 1, wherein: The change in the membership of the cluster of distributed base station units is the addition of a new distributed base station unit to the cluster, and the method further comprises the steps of: Prior to the step of determining to use the second functional division, a handover of the new distributed base station unit from the second central base station unit to the first central base station unit is initiated.

3. The method according to claim 2, wherein: Prior to the step of performing the switching of the new distributed base station unit, the method further comprises the following steps: The second central base station unit and the new distributed base station unit are caused to use the first functional division, wherein the first set of protocol functions are further implemented in the second central base station unit, and the second set of protocol functions are further implemented in the new distributed base station unit.

4. The method according to any one of claims 1 to 3, further comprising the following steps: receiving data relating to said membership of said cluster of distributed base units; as well as A determination is made based on the data that each member of the cluster of the first central base unit and the distributed base units should use the second functional division.

5. The method according to claim 2, wherein: The first central base station unit and the second central base station unit are implemented on separate virtual machines on a network node.

6. A computer program product comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 5.

7. A computer-readable data carrier having stored thereon a computer program product according to claim 6.

8. A network node for a cellular telecommunications network, the network node comprising a transceiver, a memory and a processor adapted to cooperate to implement the method according to any one of claims 1 to 5.

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