WO2017005321A1

WO2017005321A1 - Method of configuring a radio access network and a radio access network controller

Info

Publication number: WO2017005321A1
Application number: PCT/EP2015/065611
Authority: WO
Inventors: Paola Iovanna; Filippo Ponzini
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2015-07-08
Filing date: 2015-07-08
Publication date: 2017-01-12
Anticipated expiration: 2018-01-08

Abstract

A method (10) of configuring a radio access network comprising a plurality of digital units, DUs, for processing digital baseband signals, and a plurality of radio cells, each configured to handle respective traffic and comprising a remote radio unit. The radio cells are arranged in a plurality of clusters; the radio cells within a cluster are configured for radio coordination. At least one of the DUs is assigned to at least one of the clusters. The method comprises steps: a. selecting at least one of the clusters to be moved from the assigned DU to a different DU (12); b. selecting a respective target DU for each selected cluster (14); c. moving each selected cluster by (16): i. transferring handling of new traffic from each radio cell to at least one respective temporary host radio cell (20), being one of said radio cells that does not comprise a part of the selected cluster, and disabling each radio cell in the selected cluster (22); ii. assigning the target DU to the selected cluster (24); and iii. enabling each radio cell in the selected cluster (26) and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster (28); and d. disabling any of the DUs that are not assigned to any of the clusters (18).

Description

METHOD OF CONFIGURING A RADIO ACCESS NETWORK AND A RADIO ACCESS NETWORK CONTROLLER

Technical Field

The invention relates to a method of configuring a radio access network, a radio access network controller and a radio access network.

Background

A radio base station, RBS, of a radio access network, RAN, can be functionally separated into a digital unit, DU, which generates and processes a digitized baseband radio frequency, RF, signal, and a radio unit, RU, which creates the analogue RF signal from the baseband signal and provides it to a radio antenna for transmission, and digitizes received RF signals. In conventional base stations, both DU and RU units are integrated into a single network element serving one or more radio cells of a radio access network. In a distributed RBS architecture a remote RU, RRU, is connected to a centralized pool of DUs by means of Common Public Radio Interface, CPRI , links across a geographical area. Separating the DU and RRU creates opportunities for network optimization.

The evolution of mobile networks is presenting an increased demand to coordinate radio base stations'! 0, as discussed in V. Jungnickel et al, "The role of small cells, coordinated multipoint, and massive MIMO in 5G", IEEE Communications Magazine, May 2014, pages 44-51 . For example, indoor coverage problems and an increasing demand for data in both indoor and outdoor locations are two of the biggest issues related to current mobile network planning, especially with the migration to 4G; its higher frequency bands cause even more path and penetration losses and shorten coverage range. In this case small cells are used by operators to expand capacity and fill coverage holes in their networks cost- effectively. Small cells should be deployed close to known traffic hot spots in order to provide good data rates and provide for data offload from macro cells. Indoor small cells can be installed in large numbers thanks to their small size and flexible backhaul solutions, providing good indoor data rates and coverage. Outdoor small cells are particularly effective in offloading both indoor and outdoor users in dense urban environments.

Deploying small cells on the same frequency as the macro cell will cause inter-cell interference. There are several known techniques which address this issue, including radio coordination, such as downlink joint transmission, dynamic point blanking, coordinated scheduling, and interference mitigation mechanisms such as Coordinated Multipoint, CoMP, and enhanced Inter-Cell Interference Coordination, elCIC. The requirements on synchronization accuracy and latency depend on the type of radio features that are planned to be used to manage inter-cell interference. In particular some of the radio coordination techniques put very stringent requirements both in terms of latency and in terms of timing accuracy meaning that they are currently intended to be limited to pure centralized baseband scenarios.

A number of macro cells and small cells which need to be radio coordinated can be grouped to form a cluster. Each cluster should be entirely processed by a common DU or by a set of DUs able to work on a joint radio band, for example co-located DUs connected by interface definition language, IDL, interfaces. Conventional RAN deployments, based on dedicated DU co-located with radio units, require an overprovision of baseband processing. This is done to allow for future upgrade of radio base stations to increase the radio bandwidth or to improve radio access technology or to allow small-cells to be added to a "parent" macro cell to operate users and traffic offload and then to increase the network capacity. As the RAN architecture evolves towards the coordinated RAN scenario, when all the processing of a geographical area is centralized, DU resources are provided in a pool and they can be dynamically allocated to RRUs. Summary

It is an object to provide an improved method of configuring a radio access network. It is a further object to provide an improved radio access network controller. It is a further object to provide an improved radio access network.

A first aspect of the invention provides a method of configuring a radio access network comprising a plurality of digital units for processing digital baseband signals and a plurality of radio cells. Each radio cell is configured to handle respective traffic and each radio cell comprises a remote radio unit. The radio cells are arranged in a plurality of clusters and the radio cells within a cluster are configured for radio coordination. At least one of the digital units is assigned to at least one of the cluster. The method comprises steps a. to d . Step a. comprises selecting at least one of the clusters to be moved from the respective assigned digital unit to a respective different one of the digital units. Step b. comprises selecting from the plurality of digital units a respective target digital unit for each selected cluster. Step c. comprises moving each selected cluster by steps i. to iii. Step c. i. comprises transferring handling of new traffic from each radio cell in the selected cluster to at least one respective temporary host radio cell and disabling each radio cell in the selected cluster. Each temporary host radio cell is one of the plurality of radio cells that does not comprise a part of the selected cluster. Step c. ii. comprises assigning the target digital unit to the selected cluster. Step c. iii. comprises enabling each radio cell in the selected cluster and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster. Step d . comprises disabling any of the plurality of digital units that are not assigned to any of the clusters.

The method may enable the number of active DUs in a RAN to be reduced while preserving the radio coordination features by switching entire clusters. The method may mitigate over-provisioning of DU processing resources, since DU processing resources may be dynamically allocated to each cluster to cope with traffic changes over time and in different areas. The method may therefore enable the use of digital units in RBS deployments having centralized processing and radio coordination to be optimized. The method may enable dynamic association between remote radio units and digital units. By temporarily putting the radio cells in clusters that are to be moved off-line, the dynamic association between remote radio units and digital units may be managed without service interruption . Disabling unused DUs may reduce power consumption with the RAN. The method may be applied to any centralized RAN in which it is possible to dynamically allocate DUs to RRUs.

In an embodiment, step a. comprises, for each of the clusters, checking whether each radio cell within the cluster has at least one respective temporary host radio cell available to temporarily handle the respective traffic of said radio cell. If the check is positive, the cluster is selected to be moved and each radio cell within the cluster has at least one said respective temporary host radio cell assigned to it. This may enable clusters to be moved to new DUs while maintaining service continuity.

In an embodiment, step a. further comprises, for each selected cluster, checking whether a radio cell within the selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster. A said selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster is moved according to step c. before said other selected cluster is moved according to step c. This may enable clusters having this relationship to be moved to new DUs without causing any loss of service.

In an embodiment, step b. comprises steps i. to iii. Step b.i. comprises, for each digital unit, obtaining an indication of an available amount of processing resources. Step b.ii. comprises, for each selected cluster, obtaining an indication of a required amount of processing resources. Step b.iii. comprises, for each selected cluster, selecting the digital unit having the smallest available amount of processing resources that is at least equal to the required amount of processing resources of the selected cluster. This may enable the use of

DU processing resources to be fully optimized.

In an embodiment, the available amount of processing resources of a said digital unit is a percentage of a total amount of processing resources of the digital unit that is available to be assigned to a said cluster. This may enable the use of DU processing resources to be fully optimized.

In an embodiment, step b. iii. is performed for each selected cluster in increasing order of the required amount of processing resources. This may enable the use of DU processing resources to be fully optimized.

In an embodiment, step b. ii. additionally comprises arranging the indications of the required amount of processing resources in a list in increasing order of required amount of processing resources and step b. iii. is performed for each selected cluster in the order of the list. This may enable the use of DU processing resources to be fully optimized. In an embodiment, step b. i. additionally comprises assigning a weight to each digital unit based on the available amount of processing resources of the digital unit. Step b. iii. comprises, for each selected cluster, selecting the digital unit having the minimum weight that has an amount of available processing resources that is at least equal to the required amount of processing resources of the selected cluster and assigning said digital unit to the selected cluster. Step b. iii. additionally comprises updating the weight of said digital unit to reflect a current available amount of processing resources. This may enable the use of DU processing resources to be fully optimized.

In an embodiment, a said selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster is positioned earlier in the list than said other selected cluster. This may enable clusters having this relationship to be moved to new DUs without causing any loss of service.

In an embodiment, in step c. i. disabling each radio cell comprises configuring each radio cell not to accept traffic for handling and handing over traffic handling of existing traffic to the respective temporary host radio cell. The method may be operated without service disruption by temporary coverage from adjacent or overlapping cells and by disabling each radio cell using a procedure similar to an intra-RAT soft handover, which is referred to herein as a "soft-lock" procedure.

In an embodiment, handing over traffic handling to the respective temporary host radio cell is performed using one of an inter-radio access technologies, inter-RAT, handover and an intra-radio access technologies, intra-RAT, handover. This may enable clusters to be moved to new DUs without causing any loss of service.

In an embodiment, handing over traffic handling to the respective temporary host radio cell is performed using an intra-RAT soft handover. This may enable clusters to be moved to new DUs without causing any loss of service.

In an embodiment, in step c. i. disabling a said radio cell further comprises one of switching off a said radio cell and configuring a said radio cell into a reduced power mode. In step c. iii. enabling a said radio cell comprises configuring a said radio cell into a normal power mode. This may enable RAN power consumption to be reduced. Disabling a radio cell by configuring the radio cell into a reduced power mode, which may be referred to as a "sleep mode", may enable RAN power consumption to be reduced while ensuring that the radio cell may be returned to full, "online", operation in a short time.

In an embodiment, in step d . disabling a said digital unit comprises one of switching off a said digital unit and configuring a said digital unit into a reduced power mode. This may enable RAN power consumption to be reduced. Disabling a DU by configuring the DU into a reduced power mode, which may be referred to as a "sleep mode", may enable RAN power consumption to be reduced while ensuring that the DU may be returned to full, "online", operation in a short time. In an embodiment, the plurality of radio cells comprises a plurality of macro cells and a plurality of small cells. The method may be applied to heterogeneous networks in which small cells are deployed in support of a "parent" macro cell.

In an embodiment, each cluster comprises a macro cell and at least one small cell. In an embodiment, each temporary host radio cell is adjacent to the respective radio cell or each temporary host radio cell is at least partially overlapping with the respective radio cell. This may enable clusters to be moved to new DUs while maintaining service continuity.

In an embodiment, the method further comprises steps e. and f. In step e. the radio access network is changed by at least one of: adding at least one radio cell to at least one of the clusters or removing at least one radio cell from at least one of the clusters; and enabling at least one digital unit that is not assigned to any of the clusters. In step f. steps a. to d. are repeated. The method may therefore be run during normal network operation any time a cluster changes, for example when one or more small-cells are switched on or switched off to follow traffic changes over time. The method may optimize the use of DU processing resources when additional small-cells are switched-on, for example to cope with a traffic increase, or if new macro-cells are deployed. The method may enable additional clusters to be served by allocating new DUs and applying the method to re-optimize the use of DU processing resources and to switch-off any unused DUs.

In an embodiment, step b. comprises selecting from the plurality of digital units a plurality of respective target digital units for at least one said selected cluster. Said plurality of digital units are configured to provide combined processing resources to said selected cluster. The method may be operated where a set of DUs configured to operate on a shared radio band are used to provide processing resources to one or more clusters.

In an embodiment, step b. further comprises, for each radio cell within the selected cluster, specifying a path within the radio access network from the respective remote radio unit to the target digital unit.

In an embodiment, step b. further comprises moving the cluster to the target digital unit and setting up the respective paths from the remote radio units to the target digital unit.

A second aspect of the invention provides a radio access network controller for a radio access network. The radio access network comprises a plurality of digital units for processing digital baseband signals and a plurality of radio cells each configured to handle respective traffic and each comprising a remote radio unit. The radio cells are arranged in a plurality of clusters and the radio cells within a cluster are configured for radio coordination. At least one of the digital units is assigned to at least one of the clusters. The radio access network controller is configured to select at least one of the clusters to be moved from the respective assigned digital unit to a respective different one of the digital units. The radio access network controller is configured to select from the plurality of digital units a respective target digital unit for each selected cluster. The radio access network controller is configured to move each selected cluster by: transferring traffic handling from each radio cell in the selected cluster to at least one respective temporary host radio cell, being one of the plurality of radio cells that does not comprise a part of the selected cluster, and disabling each radio cell in the selected cluster; assigning the target digital unit to the selected cluster; and enabling each radio cell in the selected cluster and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster. The radio access network controller is configured to generate at least one control signal comprising instructions to disable any of the plurality of digital units that are not assigned to any of the clusters.

The RAN controller may enable the number of active DUs in a RAN to be reduced while preserving the radio coordination features by switching entire clusters. The controller may mitigate over-provisioning of DU processing resources, since DU processing resources may be dynamically allocated to each cluster to cope with traffic changes over time and in different areas. The controller may therefore enable the use of digital units in RBS deployments having centralized processing and radio coordination to be optimized . The controller may enable dynamic association between remote radio units and digital units. By temporarily putting the radio cells in clusters that are to be moved off-line, the dynamic association between remote radio units and digital units may be managed without service interruption. Disabling unused DUs may reduce power consumption with the RAN . The RAN controller may be used in any centralized RAN in which it is possible to dynamically allocate DUs to RRUs.

In an embodiment, the radio access network controller is configured to select at least one of the clusters to be moved by, for each of the clusters, checking whether each radio cell within the cluster has at least one respective temporary host radio cell available to temporarily handle the respective traffic of said radio cell. The radio access network controller is configured to, if the check is positive, select the cluster to be moved and to assign to each radio cell within the cluster at least one said respective temporary host radio cell. This may enable the RAN controller to move clusters to new DUs while maintaining service continuity.

In an embodiment, the radio access network controller is configured to, for each selected cluster, check whether a radio cell within the selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster. The radio access network controller is configured to move a said selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster before moving said other selected cluster. This may enable the RAN controller to move clusters having this relationship to new DUs without causing any loss of service.

In an embodiment, the radio access network controller is configured to select a respective target digital unit for each selected cluster by: for each digital unit, obtaining an indication of an available amount of processing resources; for each selected cluster, obtaining an indication of a required amount of processing resources; and for each selected cluster, selecting the digital unit having the smallest available amount of processing resources that is at least equal to the required amount of processing resources of the selected cluster. This may enable the RAN controller to fully optimize the use of DU processing resources.

In an embodiment, the radio access network controller is configured to select a said digital unit for each selected cluster in increasing order of the required amount of processing resources. This may enable the RAN controller to fully optimize the use of DU processing resources.

In an embodiment, the radio access network controller is further configured to arrange the indications of the required amount of processing resources in a list in increasing order of required amount of processing resources and to select a digital unit for each selected cluster in the order of the list. This may enable the RAN controller to fully optimize the use of DU processing resources.

In an embodiment, the radio access network controller is further configured to assign a weight to each digital unit based on the available amount of processing resources of the digital unit. The radio access network controller is configured to, for each selected cluster, select the digital unit having the minimum weight that has an amount of available processing resources that is at least equal to the required amount of processing resources of the selected cluster and assign said digital unit to the selected cluster. The radio access network controller is further configured to update the weight of said digital unit to reflect a current available amount of processing resources. This may enable the RAN controller to fully optimize the use of DU processing resources.

In an embodiment, the radio access network controller is configured to position a said selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster earlier in the list than said other selected cluster. This may enable the RAN controller to move clusters having this relationship to new DUs without causing any loss of service.

In an embodiment, the radio access network controller is configured to disable each radio cell by configuring each radio cell not to accept traffic for handling and handing over traffic handling of existing traffic to the respective temporary host radio cell. Temporary coverage from adjacent or overlapping cells and disabling each radio cell using a procedure similar to an intra-RAT soft handover, which is referred to herein as a "soft-lock" procedure, may enable the RAN controller to move clusters without causing service disruption .

In an embodiment, handing over traffic handling to the respective temporary host radio cell is performed using one of an inter-radio access technologies, inter-RAT, handover and an intra-radio access technologies, intra-RAT, handover. This may enable the RAN controller to move clusters to new DUs without causing any loss of service.

In an embodiment, handing over traffic handling to the respective temporary host radio cell is performed using an intra-RAT soft handover. This may enable the RAN controller to move clusters to new DUs without causing any loss of service. In an embodiment, the radio access network controller is configured to disable a said radio cell by one of switching off a said radio cell and configuring a said radio cell into a reduced power mode. The radio access network controller is configured to enable a said radio cell by configuring a said radio cell into a normal power mode. This may enable RAN power consumption to be reduced. Disabling a radio cell by configuring the radio cell into a reduced power mode, which may be referred to as a "sleep mode", may enable RAN power consumption to be reduced while ensuring that the radio cell may be returned to full, "online", operation in a short time.

In an embodiment, the radio access network controller is configured to disable a digital unit by one of switching off a said digital unit and configuring a said digital unit into a reduced power mode. This may enable RAN power consumption to be reduced. Disabling a DU by configuring the DU into a reduced power mode, which may be referred to as a "sleep mode", may enable RAN power consumption to be reduced while ensuring that the DU may be returned to full, "online", operation in a short time.

In an embodiment, the plurality of radio cells comprises a plurality of macro cells and a plurality of small cells. The RAN controller may be used in heterogeneous networks in which small cells are deployed in support of a "parent" macro cell.

In an embodiment, each cluster comprises a macro cell and at least one small cell.

In an embodiment, each temporary host radio cell is adjacent to the respective radio cell or each temporary host radio cell is at least partially overlapping with the respective radio cell. This may enable the RAN controller to move clusters to new DUs without causing any loss of service.

In an embodiment the controller is implemented as one or more processors, hardware, processing hardware or circuitry.

References to processors, hardware, processing hardware or circuitry can encompass any kind of logic or analog circuitry, integrated to any degree, and not limited to general purpose processors, digital signal processors, ASICs, FPGAs, discrete components or logic and so on . References to a processor are intended to encompass implementations using multiple processors which may be integrated together, or co-located in the same node or distributed at different locations for example.

A third aspect of the invention provides a radio access network comprising a radio access network controller, a plurality of digital units for processing digital baseband signals, and a plurality of radio cells. The radio access network controller is configured to select at least one of the clusters to be moved from the respective assigned digital unit to a respective different one of the digital units. The radio access network controller is configured to select from the plurality of digital units a respective target digital unit for each selected cluster. The radio access network controller is configured to move each selected cluster by: transferring traffic handling from each radio cell in the selected cluster to at least one respective temporary host radio cell, being one of the plurality of radio cells that does not comprise a part of the selected cluster, and disabling each radio cell in the selected cluster; assigning the target digital unit to the selected cluster; and enabling each radio cell in the selected cluster and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster. The radio access network controller is configured to generate at least one control signal comprising instructions to disable any of the plurality of digital units that are not assigned to any of the clusters. Each radio cell is configured to handle respective traffic and each radio cell comprising a remote radio unit. The radio cells are arranged in a plurality of clusters and the radio cells within a cluster are configured for radio coordination. At least one of the digital units is assigned to at least one of the clusters.

The RAN controller may enable the number of active DUs in the RAN to be reduced while preserving the radio coordination features by switching entire clusters. The controller may mitigate over-provisioning of DU processing resources within the RAN , since DU processing resources may be dynamically allocated to each cluster to cope with traffic changes over time and in different areas. The controller may therefore enable the use of digital units in RBS deployments having centralized processing and radio coordination to be optimized. The controller may enable dynamic association between remote radio units and digital units. By temporarily putting the radio cells in clusters that are to be moved off-line, the dynamic association between remote radio units and digital units may be managed without service interruption. Disabling unused DUs may reduce power consumption with the RAN. The RAN may be any centralized RAN in which it is possible to dynamically allocate DUs to RRUs.

In an embodiment, the radio access network controller is configured to disable each radio cell by configuring each radio cell not to accept traffic for handling and handing over traffic handling of existing traffic to the respective temporary host radio cell. Temporary coverage from adjacent or overlapping cells and disabling each radio cell using a procedure similar to an intra-RAT soft handover, which is referred to herein as a "soft-lock" procedure, may enable the RAN controller to move clusters without causing service disruption.

References to processors, hardware, processing hardware or circuitry can encompass any kind of logic or analog circuitry, integrated to any degree, and not limited to general purpose processors, digital signal processors, ASICs, FPGAs, discrete components or logic and so on. References to a processor are intended to encompass implementations using multiple processors which may be integrated together, or co-located in the same node or distributed at different locations for example.

A fourth aspect of the invention provides a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out any of the steps of the above method of configuring a radio access network.

A fifth aspect provides a carrier containing the computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out any of the steps of the above method of configuring a radio access network. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

Brief Description of the drawings

Figure 1 shows the steps of a method according to a first embodiment of the invention of configuring a radio access network;

Figure 2 shows the detail of one of the steps of the method of Figure 1 ;

Figure 3 shows the steps of a method according to a second embodiment of the invention of configuring a radio access network;

Figure 4 shows the steps of a method according to a third embodiment of the invention of configuring a radio access network;

Figure 5 shows the steps of a method according to a fourth embodiment of the invention of configuring a radio access network;

Figure 6 shows the detail of one of the steps a method according to a fifth embodiment of the invention of configuring a radio access network;

Figure 7 shows the steps of a method according to a sixth embodiment of the invention of configuring a radio access network;

Figure 8 shows the steps of a method according to a seventh embodiment of the invention of configuring a radio access network;

Figure 9 shows the detail of the first step of the method of Figure 8;

Figure 10 illustrates clusters to which the method of Figure 8 is applied;

Figure 1 1 illustrates the first step of the method of Figure 8;

Figure 12 shows the detail of the second step of the method of Figure 8; and

Figure 13 is a schematic illustration of a radio access network according to an eighth embodiment of the invention.

Detailed description

The same reference numbers will used for corresponding features in different embodiments.

Referring to Figures 1 and 2, a first embodiment of the invention provides a method

10 of configuring a radio access network, RAN , comprising a plurality of digital units, DUs, for processing digital baseband signals and a plurality of radio cells each configured to handle respective traffic. Each radio cell comprises a remote radio unit, RRU , and the radio cells are arranged in a plurality of clusters; the radio cells within a cluster are configured for radio coordination. At least one of the digital units is assigned to at least one of the clusters.

The method comprises steps a. to d., as follows:

a. selecting at least one of the clusters to be moved from the respective assigned DU to a respective different one of the DUs 12; b. selecting from the plurality of DUs a respective target DU for each selected cluster 14;

c. moving each selected cluster by 16:

i. transferring handling of new traffic from each radio cell in the selected cluster to at least one respective temporary host radio cell 20, being one of the plurality of radio cells that does not comprise a part of the selected cluster, and disabling each radio cell in the selected cluster 22; ii. assigning the target DU to the selected cluster 24; and iii. enabling each radio cell in the selected cluster 26 and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster 28; and

d. disabling any of the plurality of DUs that are not assigned to any of the clusters 18.

Radio coordination includes downlink joint transmission, dynamic point blanking, coordinated scheduling, and interference mitigation mechanisms such as Coordinated

Multipoint, CoMP, and enhanced Inter-Cell Interference Coordination, elCIC.

In downlink joint transmission data is sent to a user from more than one RRU, transmission point, simultaneously. The data to be transmitted needs to be available at all coordinated points simultaneously, implying the use of a common data buffer and scheduler. For most practical realizations this requirement has limited the use of this technique to the common baseband architecture. Downlink joint transmission requires latency in the order of

0.5ms and time accuracy of about 1 .5μ5.

Dynamic Point Blanking, or Coordinated Scheduling, is used to improve radio cell edge bit rates by coordinating when to schedule users in different radio cells. The best possible performance gain from using this technique is achieved when dynamic blanking can be executed on a per-TTI , Transmission Time Interval, level, for example every ms. Due to the very short time available for scheduling decisions, this typically requires the technique to be implemented in the common baseband architecture. It is also possible to coordinate the scheduling on a slower time-scale over the X2 interface, but performance gains are typically lower in these scenarios since the X2 delay usually exceeds the one ms timeframe of the radio interface scheduler. The nodes being coordinated in a distributed base station scenario need to be time aligned, with 1 .5 με typically being required.

Enhanced Inter Cell Interference Coordination, elCIC, is an interference coordination technique that targets small cell deployment specifically, by expanding the range of small cells. elCIC is typically implemented in the distributed base station architecture, but there are no specific requirements on the X2 delay. However, in order to avoid interference overlap between macro cells and small cells, they have to be time aligned to about 1 μ5.

A cluster of radio cells configured for radio coordination may be referred to as a

"coordination cluster". A digital unit, DU, is also known as a baseband unit, BBU, and a radio cell is also known as a radio node in Long Term Evolution, LTE, networks.

Disabling a DU here means turning the power off or configuring the DU into a reduced power mode, which may be referred to as a "sleep mode", in which the DU power consumption is reduced as compared to its normal, or "full power", mode.

Figure 3 shows the steps of a method 30 according to a second embodiment of the invention of configuring a RAN. In this embodiment, step a. comprises, for each of the clusters, checking whether each radio cell within the cluster has at least one respective temporary host radio cell available to temporarily handle the respective traffic of the radio cell 32. If the check is positive, i.e. if there is a respective temporary host radio cell available to temporarily handle the traffic of each radio cell within the cluster, the cluster is selected to be moved. Each radio cell within the cluster then has at least one of the respective available temporary host radio cells assigned to it 34.

Figure 4 shows the steps of a method 40 according to a third embodiment of the invention of configuring a RAN . The method 40 of this embodiment is similar to the method of the previous embodiment, with the following addition to step a.

For each selected cluster, step a. additionally comprises checking whether a radio cell within the selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster 42. A selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster is moved according to step c. before said other selected cluster is moved according to step c. 44. Consider for example a first selected cluster and a second selected cluster. Step a. checks whether a radio cell within the first selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster. Here the check is positive for the second selected cluster; that is to say, a radio cell within the first selected cluster is assigned as a temporary host radio cell to a radio cell within the second selected cluster. The first selected cluster is therefore moved according to step c. before the second selected cluster is moved according to step c. This ensures that no service interruption occurs while moving the second selected cluster.

Figure 5 shows the steps of a method 50 according to a fourth embodiment of the invention of configuring a RAN . The method 50 of this embodiment is similar to the method of the first embodiment, with the following modifications.

In this embodiment, step b. comprises steps i. to iii. In step b.i. , an indication of an available amount of processing resources is obtained for each digital unit 52. In step b.ii. , an indication of a required amount of processing resources is obtained for each selected cluster 54. In step b.iii., for each selected cluster, the digital unit is selected that has the smallest available amount of processing resources that is at least equal to the required amount of processing resources of the selected cluster 56. Step b.iii. is performed serially for each of the selected clusters. Step b.iii. may be performed for each selected cluster in increasing order of the required amount of processing resources.

Figure 6 shows the steps of a method 60 according to a fifth embodiment of the invention of configuring a RAN . The method 60 of this embodiment is similar to the method of the first embodiment, with the following modifications.

In this embodiment, step c.i. of disabling each radio cell in a selected cluster that is being moved comprises configuring each radio cell within the selected cluster not to accept traffic for handling 60 and then handing over traffic handling of existing traffic to the respective temporary host radio cell 62. It will be appreciated that these steps may be reversed , with the handing over of traffic handling of existing traffic being performed before configuring each radio cell within the selected cluster not to accept traffic for handling.

Each temporary host radio cell is either adjacent to the respective radio cell or at least partially overlapping with the respective radio cell.

Figure 7 shows the steps of a method 70 according to a sixth embodiment of the invention of configuring a RAN . The method 70 of this embodiment is similar to the method of the first embodiment, with the following additions.

The method 70 of this embodiment includes step e. of changing the RAN 72. The change may comprise any one or more of:

adding at least one radio cell to at least one of the clusters;

removing at least one radio cell from at least one of the clusters; and

enabling at least one DU that is not assigned to any of the clusters.

Steps a. to d. are then repeated.

The method 70 of this embodiment enables new radio cells to be added to a cluster or to the RAN, which may result in creating a new cluster; existing deployed radio cells may be enabled (by switching on or powering up from a reduced power mode) or new radio cells may be physically added to the RAN. The method also enables radio cells to be removed from a cluster or from the RAN; the radio cells may be disabled (by switching off or configuring into a reduced power mode) or may be physically removed. Existing DUs may be enabled by powering up from a reduced power mode or new DUs may be physically added to the RAN.

A seventh embodiment of the invention provides a method 80 of configuring a RAN, as illustrated in Figures 8 to 12.

The method 80 of this embodiment, based on interworking between radio management and fronthaul RAN control, is able to optimize the number of active DUs in a centralized, and radio coordinated , RAN. In addition the method 80 is able to preserve all the radio coordination features, as decided by the radio management, and to avoid any "out of service" when the radio cells to be moved are put off-line before starting the migration from a current DU to a new DU. The main steps of the method 80 are illustrated in Figure 8 and comprise processing steps 90, 100, 1 12 and execution steps 1 14, 1 16, 1 1 8. In the processing steps, movable clusters are identified 90, together with DUs candidate to "receive" the selected "moveable" clusters 100. In addition, the availability of physical resources of the fronthaul network, including paths and switch ports to be configured , to be used during the migration are checked. In the execution steps, the radio cells of each selected cluster go off-line while ensuring service continuity, the selected clusters are assigned to the target DUs and finally the radio cells of each selected cluster are put back online.

The radio cells are put off-line using a procedure similar to an inter-RAT soft handover, here referred to as a "soft lock" procedure, in which a radio cell is put off-line so that it will no longer accept traffic, all the existing traffic that is being handled by the radio cell is moved away from cell, and the radio cell is then disabled.

The process of selecting movable clusters 90 is shown in more detail in Figure 9. During the creation of the list of all the 'movable' clusters, the presence of adjacent or overlapping radio cells able to temporarily accept the traffic of the clusters selected to be moved is verified 92 and each radio cell of each selected, 'movable', cluster has a respective temporary host radio cell or cells assigned to it 94. The list of the selected, 'moveable', clusters is then sorted 96 according to the required DU processing resources of each selected cluster, to fully optimize the use of DUs at the end of the process; in this embodiment the list is sorted in increasing order of required DU processing resources. A further check 98 is then performed to avoid service disruption while moving any of the selected clusters; in the case where a radio cell (or more than one radio cell) in a selected cluster is also a temporary host radio cell for a radio cell in another selected cluster, the selected cluster containing the temporary host radio cell is moved before the selected cluster containing the radio cell that it is a temporary host radio cell for.

The first step 90a illustrated in Figure 9 comprises group all the radio cells into clusters and assigning DU processing resources to each cluster according to its radio coordination requirements. This step is shown in dashed outline to indicate that it is not an essential step of the method 80; this step 90a may have been performed before the method 80 is applied , or this step 90a may be performed following a change to the RAN as described above with reference to Figure 7.

The method 80 of this embodiment is applied to a RAN comprising macro radio cells (known as "macro cells") and small radio cells (known as "small cells"). A macro cell will be understood by the skilled person to refer to a radio cell in a RAN that provides the main radio coverage and the RRUs for macrocells are generally mounted on ground-based masts, rooftops and other existing structures, at a height that provides a clear view over the surrounding buildings and terrain, and may have a range of a few tens of kilometres; a macro cell is referred to as a macro node in LTE networks. Macro cells are generally deployed outdoors. A small cell is a low-powered RAN node that has a range of 10 meters to 1 or 2 kilometres. Small cells are "small" compared to a macro cell and are generally added to a RAN to provide additional capacity to take load off a macro cell according to traffic demand. Small cells are generally 'underlaid' at lower height than macro cells, have lower power and often use same spectrum as the macro cell. The term small cell encompasses microcell, picocell, and femtocell. Small cells are often deployed indoors but can also be deployed outdoors, for example to fill holes in a RAN between macro cells. As will be known by the skilled person, a network formed of both macro cells and small cells may be referred to as a heterogeneous network.

Figure 10 illustrates three example clusters. Cluster A is formed of a macro cell, macro A, and two small cells, SC, SC A and SC B, and has a first DU, DU 1 , assigned to it. Cluster C is formed of two macro cells, macro B and macro C, and has a second DU, DU 2, assigned to it. Cluster DE is formed of two macro cells, macro D and macro E, and has a third DU, DU 3, assigned to it.

Figure 1 1 illustrates the step of checking for the presence of adjacent or overlapping radio cells able to temporarily accept the traffic of the clusters selected to be moved 92. An LTE macro cell 92a is in a cluster that is being considered for moving to a new DU . The LTE macro cell 92a is overlapped by a radio cell 92b of a high speed packet access, HSPA, network. The HSPA cell 92b is able to temporarily accept traffic from the LTE cell 92a through an inter-RAT handover. The cluster containing the LTE cell is therefore movable, so long as each other radio cell in the cluster similarly has an overlapping or adjacent cell or cells able to act as a temporary host radio cell.

Figure 12 illustrates the step of appending to the list of selected, 'movable', clusters suitable target DUs 100. This commences by assigning to each DU a weight based on the percentage of its processing resources that are available 102. For each cluster in the list, starting at the first cluster in the list, i=1 , the DU that can process the moveable cluster with the minimum weight is selected and assigned to the selected cluster currently being considered 106. The weight of the DU that was assigned to the selected cluster currently being considered is then updated 108 to take into account the amount of its previously available processing resources that have just been allocated to that selected cluster. The next selected cluster in the list is then considered, and the process repeated until the end of the list is reached. If the list is empty no process of assignment of DUs is performed 104.

Referring to Figure 13, an eighth embodiment of the invention provides a RAN controller 200 for a RAN 300 comprising a plurality of DUs 202 for processing digital baseband signals and a plurality of radio cells 204. Each radio cell is configured to handle respective traffic and comprises a RRU 206. The radio cells are arranged in a plurality of clusters 208; the radio cells within a cluster are configured for radio coordination . At least one of the DUs is assigned to at least one of the clusters.

The RAN controller 200 is configured to: select at least one of the clusters 208 to be moved from the respective assigned DU 202 to a respective different one of the DUs;

select from the plurality of DUs a respective target DU for each selected cluster; move each selected cluster by:

· transferring traffic handling from each radio cell in the selected cluster to at least one respective temporary host radio cell, being one of the radio cells that does not comprise a part of the selected cluster, and disabling each radio cell within the selected cluster;

• assigning the target DU to the selected cluster; and

· enabling each radio cell within the selected cluster and transferring traffic handling from each temporary host radio cell back to the respective radio cell in the selected cluster; and

generate at least one control signal comprising instructions to disable any of the DUs that are not assigned to any of the clusters.

In a ninth embodiment, the RAN controller 200 is configured to select at least one of the clusters to be moved by, for each of the clusters, checking whether each radio cell 204 within the cluster has at least one respective temporary host radio cell available to temporarily handle the respective traffic of the radio cell. If the check is positive, i.e. if there is a respective temporary host radio cell available to temporarily handle the traffic of each radio cell within the cluster, the cluster is selected to be moved. The RAN controller is configured to assign to each radio cell within the cluster at least one of its available temporary host radio cells.

In a tenth embodiment, the RAN controller 200 is additionally configured to, for each selected cluster 204, check whether a radio cell within the selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster. The RAN controller is configured to move a selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster before moving the other selected cluster. Consider for example a first selected cluster 208a and a second selected cluster 208b. The RAN controller 200 checks whether a radio cell within the first selected cluster 208a is assigned as a temporary host radio cell to a radio cell within an other selected cluster. Here the check is positive for the second selected cluster 208b; that is to say, a radio cell within the first selected cluster is assigned as a temporary host radio cell to a radio cell within the second selected cluster. The RAN controller therefore moves the first selected cluster 208a before it moves the second selected cluster 208b. This ensures that no service interruption occurs while moving the second selected cluster.

In an eleventh embodiment, the RAN controller 200 is configured to select a respective target DU for each selected cluster 208 by:

for each DU, obtaining an indication of an available amount of processing resources; for each selected cluster, obtaining an indication of a required amount of processing resources; and for each selected cluster, selecting the DU having the smallest available amount of processing resources that is at least equal to the required amount of processing resources of the selected cluster.

The RAN controller 200 may be configured to select a DU for each selected cluster in increasing order of the required amount of processing resources of the selected clusters.

In a twelfth embodiment, the RAN controller 200 is configured to disable each radio cell 204 by configuring each radio cell not to accept traffic for handling and handing over traffic handling of existing traffic to the respective temporary host radio cell. It will be appreciated that the RAN controller 200 may be configured to perform these steps in the opposite order, handing over of traffic handling of existing traffic before configuring each radio cell within the selected cluster not to accept traffic for handling.

The RAN controller 200 is configured to select as a temporary host radio cell a radio cell that is adjacent to the respective radio cell or that at least partially overlaps the respective radio cell.

In a thirteenth embodiment, the RAN controller 200 is configured to perform the above described process of selecting at least one cluster to be moved, selecting a target DU for each selected cluster 208 and moving each selected cluster in response to a change in the RAN network. For example, in response to any one or more of:

at least one radio cell being added to at least one of the clusters;

at least one radio cell being removed from at least one of the clusters; and at least one DU that is not assigned to any of the clusters being enabled.

New radio cells may be added to a cluster or to the RAN , which may result in creating a new cluster, as a result of existing deployed radio cells being enabled (by switching on or powering up from a reduced power mode) or new radio cells being physically added to the RAN. Radio cells may be removed from a cluster or from the RAN as a result of being disabled (by switching off or configuring into a reduced power mode) or may be physically removed. Existing DUs may be enabled by powering up from a reduced power mode or new DUs may be physically added to the RAN.

In a fourteenth embodiment, the RAN controller 200 is configured to perform the steps of the method 80 of configuring a RAN network as described above with reference to Figures 8 to 12.

As will be readily understood by the person skilled in the art, in any one of the above described embodiments the RAN controller 200 may be implemented as one or more processors, hardware, processing hardware or circuitry.

Referring to Figure 13, a fifteenth embodiment of the invention provides a RAN 300 comprising a RAN controller 200, a plurality of DUs 202 for processing digital baseband signals and a plurality of radio cells 204. Each radio cell is configured to handle respective traffic and each radio cell comprise a RRU 206. The radio cells are arranged in a plurality of clusters 208; the radio cells within a cluster are configured for radio coordination. At least one of the digital units is assigned to at least one of the clusters.

The RAN controller 200 is as described above in any one of the eighth to fourteenth embodiments of the invention.

In this embodiment, the RAN 300 comprises a DWDM ring, comprising three remote switches 216, a central office 210 where the DUs 202 are located, and a CPRI over WDM fronthaul link 214 connecting the DWDM ring to a CPRI and wavelength switch 212 at the central office, configured to convert the CPRI over WDM signals into electrical CPRI signals for distribution to the DUs. The DUs 202 are connected to the backhaul of a core network, which is shown for completeness but which does not form part of the RAN of this embodiment.

A sixteenth embodiment of the invention provides a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out any of the above described steps of the method 10, 30, 40, 50, 70, 80 of configuring a RAN.

A seventeenth embodiment of the invention provides a carrier containing the computer program of the sixteenth embodiment. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Claims

1 . A method of configuring a radio access network comprising a plurality of digital units for processing digital baseband signals and a plurality of radio cells each configured to handle respective traffic and each comprising a remote radio unit, the radio cells being arranged in a plurality of clusters and the radio cells within a cluster being configured for radio coordination, and at least one of the digital units being assigned to at least one of the clusters, the method comprising steps:

a. selecting at least one of the clusters to be moved from the respective assigned digital unit to a respective different one of the digital units;

b. selecting from the plurality of digital units a respective target digital unit for each selected cluster;

c. moving each selected cluster by:

i. transferring handling of new traffic from each radio cell in the selected cluster to at least one respective temporary host radio cell, being one of the plurality of radio cells that does not comprise a part of the selected cluster, and disabling each radio cell;

ii. assigning the target digital unit to the selected cluster; and iii. enabling each radio cell in the selected cluster and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster; and d. disabling any of the plurality of digital units that are not assigned to any of the clusters.

2. A method as claimed in claim 1 , wherein step a. comprises, for each of the clusters, checking whether each radio cell within the cluster has at least one respective temporary host radio cell available to temporarily handle the respective traffic of said radio cell and if the check is positive, selecting the cluster to be moved and assigning to each radio cell within the cluster at least one said respective temporary host radio cell.

3. A method as claimed in claim 2, wherein step a. further comprises, for each selected cluster, checking whether a radio cell within the selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster, and wherein a said selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster is moved according to step c. before said other selected cluster is moved according to step c.

4. A method as claimed in any preceding claim, wherein step b. comprises:

i. for each digital unit, obtaining an indication of an available amount of processing resources; ii. for each selected cluster, obtaining an indication of a required amount of processing resources; and

iii. for each selected cluster, selecting the digital unit having the smallest available amount of processing resources that is at least equal to the required amount of processing resources of the selected cluster.

A method as claimed in claim 4, wherein step b. iii. is performed for each selected cluster in increasing order of the required amount of processing resources.

A method as claimed in any preceding claim, wherein in step c. i. disabling each radio cell comprises configuring each radio cell not to accept traffic for handling and handing over traffic handling of existing traffic to the respective temporary host radio cell.

A method as claimed in any preceding claim, wherein the plurality of radio cells comprises a plurality of macro cells and a plurality of small cells.

A method as claimed in any preceding claim, wherein each temporary host radio cell is one of adjacent and at least partially overlapping with the respective radio cell. A method as claimed in any preceding claim, further comprising:

e. changing the radio access network by at least one of:

i. adding at least one radio cell to at least one of the clusters or removing at least one radio cell from at least one of the clusters; and

ii. enabling at least one digital unit that is not assigned to any of the clusters; and

f. repeating steps a. to d.

A radio access network controller for a radio access network comprising a plurality of digital units for processing digital baseband signals and a plurality of radio cells each configured to handle respective traffic and each comprising a remote radio unit, the radio cells being arranged in a plurality of clusters and the radio cells within a cluster being configured for radio coordination, and at least one of the digital units being assigned to at least one of the clusters, the radio access network controller being configured to:

select at least one of the clusters to be moved from the respective assigned digital unit to a respective different one of the digital units;

select from the plurality of digital units a respective target digital unit for each selected cluster;

move each selected cluster by:

transferring traffic handling from each radio cell in the selected cluster to at least one respective temporary host radio cell, being one of the plurality of radio cells that does not comprise a part of the selected cluster, and disabling each radio cell in the selected cluster;

assigning the target digital unit to the selected cluster; and enabling each radio cell in the selected cluster and transferring traffic handling from each said temporary host radio cell back to the respective radio cell in the selected cluster; and

generate at least one control signal comprising instructions to disable any of the plurality of digital units that are not assigned to any of the clusters.

1 1 . A radio access network controller as claimed in claim 10, configured to select at least one of the clusters to be moved by, for each of the clusters, checking whether each radio cell within the cluster has at least one respective temporary host radio cell available to temporarily handle the respective traffic of said radio cell and if the check is positive, selecting the cluster to be moved and assigning to each radio cell within the cluster at least one said respective temporary host radio cell.

12. A radio access network controller as claimed in claim 1 1 , configured to, for each selected cluster, check whether a radio cell within the selected cluster is assigned as a temporary host radio cell to a radio cell within an other selected cluster, and configured to move a said selected cluster having a radio cell that is assigned as a temporary host radio cell to a radio cell within a said other selected cluster before moving said other selected cluster.

13. A radio access network controller as claimed in any of claims 10 to 12, configured to select a respective target digital unit for each selected cluster by:

for each digital unit, obtaining an indication of an available amount of processing resources;

for each selected cluster, obtaining an indication of a required amount of processing resources; and

for each selected cluster, selecting the digital unit having the smallest available amount of processing resources that is at least equal to the required amount of processing resources of the selected cluster.

14. A radio access network controller as claimed in claim 13, configured to select a said digital unit for each selected cluster in increasing order of the required amount of processing resources.

15. A radio access network controller as claimed in any of claims 10 to 1 1 , configured to disable each radio cell by configuring each radio cell not to accept traffic for handling and handing over traffic handling of existing traffic to the respective temporary host radio cell.

16. A radio access network controller as claimed in any of claims 10 to 15, wherein the plurality of radio cells comprises a plurality of macro cells and a plurality of small cells.

17. A radio access network controller as claimed in any of claims 10 to 16, wherein each temporary host radio cell is one of adjacent and at least partially overlapping with the respective radio cell.

18. A radio access network comprising: a radio access network controller as claimed in any of claims 10 to 17; a plurality of digital units for processing digital baseband signals; and

a plurality of radio cells each configured to handle respective traffic and each radio cell comprising a remote radio unit, wherein the radio cells are arranged in a plurality of clusters and the radio cells within a cluster are configured for radio coordination, and wherein at least one of the digital units is assigned to at least one of the clusters.

19. A computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of claims 1 to 9.

20. A carrier containing the computer program of the previous claim, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.