WO2008031258A1

WO2008031258A1 - Radio resource redistribution at handover

Info

Publication number: WO2008031258A1
Application number: PCT/CN2006/002131
Authority: WO
Inventors: Johan Johansson
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2006-08-22
Filing date: 2006-08-22
Publication date: 2008-03-20
Also published as: CN101310554B; CN101310554A

Abstract

An improved method for cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system is disclosed. The method allocates resources to be used by said source cell and said target cell after the handover. The method further estimates, before the handover has been executed, the resource allocation for said source cell and said target cell. The estimation takes an individual traffic load in the source cell into consideration. This individual traffic load is the traffic load caused by the user equipment being handed over.

Description

RADIO RESOURCE REDISTRIBUTION AT HANDOVER

Field of the invention

The present invention relates to a method for cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system, the method allocating resources to be used by the source cell and the target cell after the handover.

The present invention also relates to a cell control node arranged for handling cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system, the cell control node being arranged for allocating resources to be used by the source cell and the target cell after the handover.

The present invention also relates to a RRM node (Radio Resource management node) arranged for handling cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system, the RRM node being arranged for allocating resources to be used by the source cell and the target cell after the handover.

Related art and background of the invention

In the 3^rd Generation Partnership Project (3GPP) Radio Access Network (RAN) working groups one and three (WGl and WG3), several methods for interference mitigation for inter- cell interference, in the context of the 3GPP work item Long Term Evolution (LTE), have been presented and discussed. In e.g. a 3GPP LTE system, wireless user equipments (UE:s) are in general expected to cause interference to UE:s in other cells of the wireless network, as the same set of radio resources are used in different cells across the network, see document [1]

- and [2]. A list containing these and a number of other background art documents is present at the end of this specification.

In particular for 3GPP LTE, a group of methods referred to as interference coordination has been discussed. The basic idea in inter-cell interference coordination is to prevent UE:s that are close to each other, but in different cells, from using the same radio communication resources in the time and frequency domains, and thus to prevent these UE:s and their radio communication links from causing interference to each other. This is sometimes also referred to as orthogonal radio resource allocation.

A more advanced method for interference coordination would allow that the isolation between such UE:s, in some situations, does not need to be 100 %. There could be some overlap between the UE:s in usage of the time-frequency domain resources if the transmit power is regulated to limit the interference levels to reasonable levels.

A geographical region, where the UE:s can be close to each other, but in different cells, i.e. a region interference coordination is particularly important, is hereafter referred to as a cell border region in this description.

The methods for interference coordination have further been classified into three groups, static interference coordination methods, semi-static interference coordination methods and dynamic interference coordination methods.

In static interference coordination methods, usage of the radio resources in the cell border areas are kept different between neighboring cells by network planning. The allocation of radio resources between neighbor cells is assumed to be changed at most on a daily or weekly basis. This implies a significant reduction in the total amount of available radio resources for cell border regions, comparable to the reduction caused by frequency reuse schemes with a reuse factor > 1 that is typical for some wireless systems e.g. GSM.

In semi-static interference coordination methods, it is assumed possible to change the allocation of radio resources between neighbor cells on the timescale of network signaling, approximately at most every 100 ms (milliseconds). Semi-static interference coordination can be done also in cases when neighbor cells are controlled by different cell controller nodes, e.g. different radio base stations (Node B:s). The methods would then rely on network signaling procedures directly between the cell controller nodes or signaling procedures between cell controller nodes and a separate centralized controller node for radio resource management in the network. This is referred to as inter-Node B semi-static interference coordination.

In dynamic interference coordination methods, it is assumed to be possible to change the allocation of radio resources between neighbor cells on the timescale of data scheduler operation, typically less than 1 ms. This approach is assumed to be feasible only in the case where the neighbor cells are controlled by the same cell controller node.

The present invention applies to systems that use semi-static interference coordination, and in particular the case of inter-Node B semi-static interference coordination, where network signaling is used to re-allocate radio resources between cells. These radio resources can be any one of frequencies, time slots, spreading codes and transmission power.

In telecommunication systems, the term handover refers to the case when a UE that is active moves from one cell to another. The term source cell refers to the cell, which the UE is associated to before the handover is completed. The term target cell refers to the cell, which the UE is associated to after the handover has been completed.

At a handover of a UE, UE:s in the target cell might experience data transmission throughput dips because of high traffic load and insufficient amount of resources in the target cell, especially if the handed over UE runs a high-throughput application.

Assuming that there is semi-static interference coordination in place, the problem would be alleviated some time after the handover, as the target cell would be able to borrow radio resources from the source cell, and other cells.

Proper re-allocation of radio resources could however take some time, due to:

• signaling delay for independent signaling between controller nodes for the interference coordination procedures • latency related to convergence time of interference coordination control loop.

As described in background art, semi-static interference coordination would traditionally be a function operating on cell level. Background art semi-static interference coordination would then, following common 3GPP architectural principles, typically be based on cell load measurements, typically not considering the load caused by an individual UE and not aware of dedicated procedures such as handover. Thus, to adapt the resource allocation between cells due to a particular UE changing cell, it could be assumed that a few control loop iterations would be needed, due to the non-knowledge about the new load caused in the target cell by the handed over UE. The details of this control loop could, as is clear to a skilled person, basically be assumed to work according to the following steps:

A) measure and compare cell loads

B) re-allocate cell resources from cells with lower load to cells with higher load C) go to A)

According to basic control theory, the adjustment step B) needs to be small in order to avoid control loop self-oscillation, which also means that adjustments generally are associated with several iterations, and probably also a considerable convergence time.

The depth of such dips in data transmission throughput induced by handover can actually be expected to be worsened by the presence of semi-static interference coordination functionality compared to the situation when semi-static interference coordination would not be present. This is due to the fact that it can be expected that the source cell, in order to serve the UE that is being in handover, had borrowed cell resources from the target cell before the handover and thus further worsened the traffic load situation in the target cell by reducing its available resources.

At a handover in high traffic load situations, it can be expected that radio resources in the cell border region are non-optimally used, until the semi-static interference coordination has converged to fit the new traffic situation after a handover, especially if the handed over UE is running a high-throughput, high-priority application. During the convergence time of the semi-static interference coordination, some UE:s in the target cell would experience this as data transmission throughput dips. At the same instants in time, radio resources allocated to the source cell, which could be used in the target cell, would not be used or used for lower- priority traffic, e.g. those resources that was used by the handed over UE just before handover.

Slow convergence times of semi-static interference coordination functions implies unnecessary data transmission throughput dips and that radio resources, that could be used for high priority traffic, are unused or used for low-priority traffic in another cell is both a quality of service problem for the end-user experience, and a radio resource utilization efficiency problem. Aim and most important features of the invention

It is an object of the present invention to provide methods for cell resource re-allocation that solves the above stated problem as well as a cell control node and a RRM node (Radio Resource management node) for implementing these methods.

The present invention aims to provide a better cell resource balance than was possible in systems in the background art. Better cell resource balance will result in better user quality in the system, since resources the whole time are used where they are needed.

The object is achieved by estimating, before the handover has been executed, the resource allocation for the source cell and the target cell, the estimation taking into consideration at least an individual traffic load in the source cell caused by the user equipment being handed over.

The object is also achieved by a cell control node and a RRM node, respectively.

The methods, the cell control node and the RRM node for cell resource re-allocation according to the invention will make it possible for a cell control node or a RRM node to estimate cell resource re-allocation for a source cell and a target cell before a user equipment have been handed over. This is possible since an individual traffic load caused by the user equipment in the source cell is reported to the cell control node or the RRM node.

It is, because of this, possible for a user equipment to roam through a telecommunication system without running into quality problems when being handed over from cell to cell. The invention is particularly advantageous, compared to background art solutions, for user equipments roaming the telecommunication system while running high throughput, high priority applications in busy hour situations.

In an embodiment of the invention, cell resource re-allocation activation is synchronized with a handover, so that resource re-allocation is activated in the source cell and the target cell synchronized with when the user equipment exits the source cell and enters the target cell.

This has the advantage that the resources needed by the user equipment always are present in the cell where he is for the moment. In an embodiment of the invention, cell resource re-allocation is integrated in a handover procedure. More particularly, a preparation of a cell resource re-allocation is fully or partly integrated in a handover preparation process. Integration of cell resource re-allocation with handover processes simplifies the resource re-allocation negotiation process and further assures that the resource re-allocation is synchronized with the cell exit and cell entry of user equipments.

Detailed exemplary embodiments and advantages of the methods, the cell control node, and the RRM node for cell resource re-allocation in a handover situation according to the invention will now be described with reference to the appended drawings illustrating some preferred embodiments.

Brief description of the drawings

Fig. 1 shows a message sequence step chart for a general prepared handover.

Fig. 2 shows a message sequence step chart according to a first embodiment of the invention.

Fig. 3 shows a message sequence step chart for a first alternative for integrating interference coordination with handover according to the embodiment of the invention.

Fig. 4 shows a message sequence step chart for a second alternative for integrating interference coordination with handover according to the embodiment of the invention.

Fig. 5 shows a message sequence step chart for a third alternative for integrating interference coordination with handover according to the embodiment of the invention.

Detailed description of preferred embodiments

This invention is applicable to a so called prepared handover procedure. Prepared handovers exist e.g. in the current WCDMA (Wideband Code Division Multiple Access) and GSM (Global System for Mobile communications) systems and it has also been agreed to be the normal case of handover for 3GPP LTE. It is a handover procedure where first the network makes the handover decision and then two typical phases follows, the handover preparation phase and the handover execution phase. The target cell controller is prepared for handover in the handover preparation phase and then the UE connects to the target cell in the handover execution phase.

The general notation cell controller is hereafter used, meaning controlling entity. The cell controller for different cells may reside in the same or in different nodes. The following descriptions are general, but in particular applicable and interesting in the case when the controllers of the source cell and target cell reside in different nodes. In particular the case where the cell controllers reside in Node B type of nodes that is applicable to 3GPP LTE is interesting.

To explain the prepared handover in more detail, the message sequence chart in fig. 1 is referred to. It describes a general sequence of a prepared handover, including messages with generic names. In the figs., some levels of detail, which are not essential to the subsequent text, are omitted.

Fig. 1 shows a message sequence step chart for a general handover procedure. The sequence steps of the reference step numbers in fig. 1 are hereafter described.

Step 1 : measurement report

UE sends a measurement report to the cell controller of the cell, which it is currently associated to. The measurement report indicates e.g. that there is a better cell for the UE.

Step 2: handover decision

The cell controller decides that the UE shall be handed over to the better cell. The current cell is now the source cell, and the better cell is the target cell.

The handover preparation phase begins.

Step 3: handover preparation request

The source cell controller sends information about the configuration of the UE and the current association of the UE and the source cell to the target cell controller. Target cell resources are requested for the association of the UE and the target cell.

Step 4: handover preparation response After having done admission control, resource allocation etc., the target cell controller responds to the source cell controller. Here, the successful case and positive response is assumed. The target cell controller may also add configuration data that the UE shall use when accessing the target cell. At a negative outcome of admission control, this response could be negative, which would lead to a handover abortion after this step.

The handover preparation phase ends, and the handover execution phase begins.

Step 5: handover command

The UE is ordered to access the target cell and to establish an association with it. The configuration data received from the target cell controller is forwarded to the UE by the source cell controller.

Step 6: access target cell

The UE accesses the target cell and establishes an association with it.

The handover execution phase ends.

After successful establishment of association between UE and the target cell, the handover is successfully completed.

Within 3GPP RAN WG3, the notation common procedure is used denoting a network signaling procedure involving resources that are used by many UE:s, e.g. cell resources, or parameters that involve or might involve many UE: s.

The notation dedicated procedure is used within 3GPP RAN WG3 denoting a network signaling procedure involving specific resources and configurations for a single specific UE or a specific UE association with a cell. For instance, in the context of the Long Term Evolution (LTE) work item, the number of cells involved, at any instant in time, in dedicated procedures for a certain UE would typically be one. For handover procedures, two cells would be involved, the source cell and the target cell. The target cell is the cell, which the UE is associated to after the handover has been completed. Handover relates to one UE and its association to one or more cells and is a typical dedicated procedure. For background information regarding common and dedicated procedures information and implementation, see e.g. document [4].

In semi-static interference coordination, the allocation of radio resources in a cell border region would typically depend on the load generated by all UE: s in this region, and not depend just on one single UE. It also involves reconfiguration of cell resources, which are used by many UE: s. Furthermore, the number of cells involved in semi-static interference coordination in a cell border region may be » 2.

In general, for architectural reasons, common procedures and dedicated procedures are traditionally kept apart. Thus, the obvious and typical way to implement semi-static interference coordination is to implement it as common procedures that are specification- wise unrelated to dedicated procedures, such as handover. This is also how semi-static interference coordination would be implemented following traditional principles.

The present invention aims, however, to make the cell level inter-Node B interference coordination functions handover-aware and UE aware. The present invention further aims to execute cell radio resource re-allocation together with and related to the handover of a UE.

In a first embodiment of the present invention, it is proposed that, in addition to cell load information relating to traffic load in the source cell, information regarding traffic load that is being caused by the UE that is in handover, to be sent to target cell controller in the handover preparation phase, to make it possible for the otherwise UE not aware semi-static interference coordination functions in the controller of the target cell to quickly (in one step) estimate what is the new appropriate distribution of the radio resources between source and target cell.

Fig. 2 shows a message sequence step chart of the first embodiment of the invention. Message sequence steps 1, 2, 4, 5 and 6 of this first embodiment shown in fig. 2 are identical to steps 1, 2, 4, 5 and 6 in the general handover message sequence chart described in fig. 1.

Step _1_[ measurement report

Step 2: handover decision The cell controller decides that the UE shall be handed over to the better cell. The current cell is now the source cell, and the better cell is the target cell.

The handover preparation phase begins,

Step_3i handover preparation request

The handover preparation request message includes:

Traffic load information of the source cell. It could also be possible that the controller of the target cell receives traffic load information regarding the source cell by other means, e.g. by common measurement procedures. This would mainly imply that the values to be used in step 3a. would be older and less accurate. Cell traffic load information has also been included in background art handover preparation requests.

Information regarding traffic load that is being caused by the UE that is in handover. This has traditionally not been included in background art handover preparation requests and is thus new for the present invention.

Step 3a: estimation of new resource distribution

The controller of the target cell can then estimate how much radio resources that should be re-allocated between the source and target cells due to the change in resource consumption in the cells because of the UE being handed over from the source cell to the target cell. The details for this estimation are obvious for a person skilled in the art and are here left unspecified. It is assumed that the target Node B can make this calculation if it knows the traffic loads in terms of:

the quantity of used resources in the source cell and target cell, with respect to the radio resources that can be shared between the cells

the quantity of available resources in the source cell and target, with respect to the radio resources that can be shared between the cells

the quantity of resources used by the UE in handover.

Step 4: handover preparation response After having done admission control, resource allocation etc., the target cell controller responds to the source cell controller. Here, the successful case and positive response is assumed. The target cell controller may add configuration data that the UE shall use when accessing the target cell.

The handover preparation phase ends, and the handover execution phase begins.

Step 5: handover command

Step 6: access target cell

The UE accesses the target cell and establishes an association with it.

The handover execution phase ends.

Note that if different quality of service (QoS) classes for different types of traffic are supported and if the constraints that are put on radio resource usage, due to these different QoS classes, shall be supported consistently for resources in cell border regions, the traffic load in terms of quantity of used resources in the cells and quantity of used resources by the UE in handover must be quantified and signaled separately per QoS class. The resource re- allocation calculations must then also be done considering each QoS class and its requirements on radio resource management.

The semi-static interference coordination can further be made QoS aware, so that the cell resource re-allocation also takes traffic load in different QoS classes into consideration when estimating cell resource allocation. The QoS aware cell resource re-allocation can be based on both the individual load caused by the user equipment being handed over and the cell load in the cells taking part in the handover. Information regarding the individual traffic load and possibly also the cell traffic load are therefore sent, for each QoS class, to the node estimating the cell resource re-allocation. It can occur in a QoS aware cell resource re-allocation that one of the cells has a high traffic load caused by low priority traffic and another cell has low traffic load caused by high priority traffic. For this situation it is possible that resources are not moved from the cell having low traffic load to the cell having high traffic load, since the priorities of the traffic in each cell also are taken into consideration in the QoS aware cell resource re-allocation estimation.

Note also that values regarding usage of resources or traffic load, in practice, usually are values that are averaged over some smaller or larger time. This is well known by a skilled person and is left unexplored here.

Including information about the load that is caused by the UE which is in handover, makes it possible for the cell controller in the target cell to estimate what cell resources it would need to appropriately serve the UE:s including the new UE. It would be possible to do this estimation pro-actively even before the handover has been executed.

Note that the exchange of total cell traffic load information at handover preparation is present in background art, see document [3]. However, in background art, the purpose is completely different, and also, the individual UE load estimate is not exchanged.

Without the information regarding the individual load caused by the UE in handover, the control of interference coordination and resource re-allocation would involve considerable latency, as final adjustments in resource allocation induced by a recently handed over UE would need a number of control loop iterations.

Thus, by this improvement, the inter-node B semi-permanent interference coordination function can fully take the new UE into account and converge in one single step, which can be calculated pro-actively, before the UE actually enters the target cell. The latency of the semipermanent interference coordination function can thereby be reduced, improving end user quality of service and radio resource utilization efficiency at high traffic load situations.

It is also important to correlate the activation time for resource re-allocation with the execution of the handover in order to maximize the advantages of the present invention. If the activation time for resource re-allocation is not correlated with the execution of handover problems regarding resource unbalance and complexity could arise.

During the time between handover execution and activation time for resource reallocation, the resource allocation between source and target cells would be unbalanced, particularly if the handed over UE runs a high throughput application. In addition to non-optimal resource usage utilization and non-optimal QoS (Quality of Service), such an unbalance would create extra complexity for the interference coordination control algorithm, which must take this special temporary condition into account. As the interference coordination function in the target Node B would not know when the UE is handed over, as this is ordered by another node, the source Node B, it would be very difficult to know how to act on any change in the cell load during this time period.

In order to mitigate the unbalance and complexity problems it is therefore, in an alternative embodiment of the present invention, proposed to also synchronize the cell resource re-allocation with the handover. This is done by activating or committing the re- allocated resources in the source cell and the target cell at the same time as the user equipment exits the source cell and enters the target cell. The user equipment is expected to have exited the source cell when it is detected or can be assumed that the user equipment has left the cell. The user equipment is expected to have entered the target cell when it can be detected that the user equipment is accessing the target cell.

The concept of synchronized reconfiguration is often used in telecommunication systems.

A synchronized reconfiguration includes a preparation phase and an activation phase. In the preparation phase, possibly including multiple signaling transactions, the new configuration parameters are distributed to the concerned entities. In the activation phase, the new configuration is taken into service at a certain activation time. The activation time can be a specific instant in time, correlated to certain activation commands or correlated to other events.

In order to simplify synchronization of cell resource re-allocation with handover, aiming to further mitigate the unbalance and complexity problems, it is therefore, in an alternative embodiment of the present invention, proposed to also integrate a radio resource reallocation procedure for semi-static interference coordination between source cell and target cell and the handover preparation procedure. This makes it possible for the inter-node B semi-permanent interference coordination functions to order the actual resource re-allocation between the source cell and the target cell, induced by the UE being handed over, already at the time of handover preparation, and to thereby make it possible to correlate the activation time for executing the actual resource re-allocation with the time when the UE enters the target cell and the time when the UE leaves the source cell. Thus, by the use of this alternative embodiment of the invention, the inter-node B semipermanent interference coordination function can instantly adjust the cell resource allocation between target and source cells at the time of handover execution. The impact to end user quality of service and radio resource utilization efficiency, induced by handover of a UE can thereby be minimized.

According to the alternative embodiment of the invention, the interference-coordination procedure can be integrated with the handover procedure according to either of the following three alternatives:

An offer-request procedure, fully embedded in the handover prepare procedure.

A request-response procedure, partially embedded in the handover procedure.

A separate common procedure, relating the activation time to the dedicated handover procedure by common information elements (IE:s).

In all three of these integration alternatives, the estimations regarding cell resource re- allocation are based on either the individual traffic load in the source cell caused by the user equipment being handed over alone or on both this individual traffic load and the total cell traffic load.

Fig. 3 shows a message sequence step chart for the first alternative for integrating interference coordination with handover, the offer-request procedure. Step 1 in this procedure is identical to step 1 in the general message sequence step chart shown in fig. 1.

Step 1: measurement report

Step 2: handover decision

The cell controller decides that the UE shall be handed over to the better cell. The current cell is now the source cell, and the better cell is the target cell. The cell controller of the source cell estimates how much radio resources it needs to provide to target cell to maintain the resource usage and traffic load balance also after the handover. The decision is, among other parameters, based on the traffic load caused by the UE being handed over. The details of this estimation are obvious for a skilled person and are not further discussed here. The source cell controller would also need to consider the maximum amount of radio resources it could release from the source cell, to the target cell e.g. without violating QoS principles for other UE:s.

The handover preparation phase begins.

Step 3 : handover preparation request

In the handover preparation request message, the controller of the source cell would indicate which resources it could release from the source cell to the target cell due to the handover, as an offer from the source cell controller to the target cell controller. Possibly, the source cell controller selects the resources that are currently allocated for the UE in handover. The offered resources would represent a maximum amount of resources that the source Node B could accept to de-allocate from the source cell to the target cell.

Step 4: handover preparation response

The semi-static interference coordination algorithms of the controller of the target cell could then either just accept the radio resources offered from the source cell, or first do a more accurate radio resource distribution calculation, based on resource availability and consumption, and then choose to accept/request all, part of or none of the offered resources from the source cell controller. The accept of/request for the radio resources would be embedded in the handover preparation response message.

The handover preparation phase ends, and the handover execution phase begins.

Step 5: handover command

At the handover command, when the UE detaches from the source cell, the resource re- allocation could be activated in the source cell. The de-allocated resources would no longer be scheduled in the source cell, after this point in time.

Step 6: access target cell Similarly, when the handed over UE has been detected in the target cell, the re-allocated resources can be scheduled in the target cell.

The handover execution phase ends.

Fig. 4 shows a message sequence step chart for the second alternative for integrating interference coordination with handover, the request-response procedure. Steps 1-3 in this procedure are identical to steps 1-3 in the general message sequence step chart shown in fig. 1.

Step 1: measurement report

Step 2: handover decision

The handover preparation phase begins.

Step 3: handover preparation request

Step 4: handover preparation response

The semi-static interference coordination algorithms of the controller of the target cell would first do a radio resource distribution estimation, possibly based on resource availability and consumption, and then request a certain amount of resources from the source cell controller. The request for the radio resources would be embedded in the handover preparation response message.

Step 4a: resource request response In this case, a specific resource request response message would be sent to indicate which resources that the controller of the source cell grants to the target cell. The purpose of this message would be interference-coordination, and it could be unrelated to other handover messages.

The handover preparation phase ends, and the handover execution phase begins.

Step 5: handover command

Step 6: access target cell

Similarly, when the handed over UE has been detected in the target cell, the re-allocated resources can be scheduled in the target cell.

The handover execution phase ends.

Fig. 5 shows a message sequence step chart for the third alternative for integrating interference coordination with handover, the separate common procedure. Steps 1-4 in this procedure are identical to steps 1-4 in the general message sequence step chart shown in fig. 1.

Step 1 : measurement report

Step 2: handover decision

The handover preparation phase begins.

Step 3: handover preparation request The source cell controller sends information about the configuration of the UE and the current association of the UE and the source cell to the target cell controller. Target cell resources are requested for the association of the UE and the Target Cell.

Step 4: handover preparation response

After having done admission control, resource allocation etc., the target cell controller responds to the source cell controller. Here, the successful case and positive response is assumed. The target cell controller may add configuration data that the UE shall use when accessing the target cell.

Step 4b: resource re-allocation procedure

In this case, the signaling interaction for resource re-allocation would be implemented as messages that are separate from the handover preparation procedure messages. This messaging could even involve a third controller node for radio resource management. However, the contents of the messages would not be completely unrelated to the handover. When specifying the activation time for the resource re-allocation, the UE would need to be identified, and also it need to be informed that the activation time shall be related to the events in the handover execution phase.

The handover execution phase begins.

Step 5: handover command

At the Handover Command, when the UE detaches from the source cell, the resource re- allocation would be activated in the source cell. The de-allocated resources would no longer be scheduled in the source cell, after this point in time.

Step 6: access target cell

The handover execution phase ends. The three alternatives for integrating interference coordination with handover described above do all make it possible for the semi-permanent interference coordination function to instantly adjust the cell resource allocation between target and source cells at the time of handover execution.

This results in a better balanced network that more efficiently utilizes its radio resources.

This also results in a better quality of service for the communication system.

The present invention has throughout this description been described in exemplary embodiments of a 3GPP LTE (3^rd Generation Partnership Project Long Term Evolution) system. The invention is, however, generally applicable to any telecommunication system.

The cell resource re-allocation according to the invention may be modified by those skilled in the art, as compared to the exemplary embodiments described above.

Claims

1. A method for cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system, said method allocating resources to be used by said source cell and said target cell after the handover, c h a r a c t e r i z e d b y estimating, before the handover has been executed, the resource allocation for said source cell and said target cell, said estimation taking into consideration at least an individual traffic load in the source cell caused by said user equipment being handed over.

2. Method as claimed in claim 1, wherein both a source cell traffic load and said individual traffic load in the source cell are taken into consideration when estimating the cell resource re-allocation.

3. Method as claimed in any one of claims 1 or 2, wherein an activation of said cell resource re-allocation is synchronized with said handover procedure.

4. Method as claimed in claim 3, wherein said re-allocation of resources in the source cell is activated when the user equipment has left the source cell.

5. Method as claimed in claim 3, wherein said re-allocation of resources in the target cell is activated when the user equipment accesses the target cell.

6. Method as claimed in any one of claims 1-5, wherein said cell resource re-allocation exchanges resources between neighboring cells in accordance with semi-static interference coordination.

7. Method as claimed in claim 6, wherein said neighboring cells are controlled by different cell control nodes.

8. Method as claimed in claim 6, wherein neighboring cells are controlled by the same cell control node.

9. Method as claimed in any one of claims 1-8, wherein said resources being allocated include at least one of the following resources in the group: frequencies, time slots, spreading codes and transmission power.

10. Method as claimed in any one of claims 1-9, wherein more than one user equipment are handed over from a source cell to a target cell, said estimation of resource allocation taking an individual traffic load caused by each of said user equipments into consideration.

11. Method as claimed in any one of claims 1-10, wherein said cell resource re- allocation is integrated in a handover procedure.

12. Method as claimed in claim 11, wherein a preparation of said cell resource re- allocation is integrated in a handover preparation procedure.

13. Method as claimed in claim 12, wherein an offer-request communication between the source cell and the target cell is fully integrated in the handover preparation procedure.

5 14. Method as claimed in claim 13, wherein

- a source cell control node estimates an amount of resources it could release from the source cell and indicates said available resources in a resource offer to a target cell control node, said resource offer being embedded in a handover preparation request,

- a target cell control node receives said resource offer, evaluates said offered resources and 0 the resources needed in the target cell and returns a resource request indicating the resources requested to be re-allocated to the source cell control node, said resource request being embedded in a handover preparation response.

15. Method as claimed in claim 14, wherein said source cell control node selects the resources currently being allocated for said user equipment being handed over as being said 5 amount of resources available for release.

16. Method as claimed in claim 12, wherein a request-response communication between the source cell and the target cell is partly integrated in the handover preparation procedure.

17. Method as claimed in claim 16, wherein

- a target cell control node estimates an amount of resources needed and indicates said needed0 resources in a resource request to a source cell control node, said resource request being embedded in a handover preparation response,

- a source cell control node receives said resource request, evaluates the request and the available resources in the source cell and returns a resource request response indicating the resources granted for release to the target cell control node. 5

18. Method as claimed in claim 17, wherein said target cell control node selects the resources currently being allocated for said user equipment being handed over as being said amount of resources needed.

19. Method as claimed in claim 11, wherein a resource re-allocation procedure is performed integrated in the handover procedure using signaling being separate from the o handover preparation procedure signaling.

20. Method as claimed in claim 19, wherein a source cell control node and a target cell control node, in said resource re-allocation procedure, negotiate resource re-allocation between the source cell and the target cell.

21. Method as claimed in claim 19, wherein a source cell control node, a target cell control node and a RRM node (Radio Resource Management node), in said resource re- allocation procedure, negotiate resource re-allocation between the source cell and the target cell.

22. Method as claimed in any one of claims 1-21, wherein information regarding a source cell traffic load and/or said individual traffic load in the source cell is sent to a target cell control node.

23. Method as claimed in claim 22, wherein said target cell control node estimates resource re-allocation to be applied for the source cell and the target cell.

24. Method as claimed in claim 22, wherein said target cell control node is a BTS (Base

Transceiver Station) / Node B of the target cell.

25. Method as claimed in claim 22, wherein said target cell control node is a BSC (Base Station Controller) / RNC (Radio Network Controller) of the target cell.

26. Method as claimed in any one of claims 1-25, wherein information regarding a source cell traffic load and/or said individual traffic load in the source cell is sent to a RRM node (Radio Resource Management node).

27. Method as claimed in claim 26, wherein said RRM node estimates resource re- allocation to be applied for the source cell and the target cell.

28. Method as claimed in any one of claims 1-27, wherein information regarding a source cell traffic load and/or said individual traffic load in the source cell is sent to a target cell control node within a handover procedure.

29. Method as claimed in any one of claims 1-28, wherein said estimation also takes quality of service of the traffic in said source cell and target cell into consideration.

30. Method as claimed in claim 29, wherein said cell resource re-allocation is performed separately for each quality of service class.

31. A cell control node arranged for handling cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system, said cell control node being arranged for allocating resources to be used by said source cell and said target cell after the handover, c h a r a c t e r i z e d b y said cell control node being arranged for estimating, before the handover has been executed, the resource allocation for said source cell and said target cell, said estimation taking into consideration at least an individual traffic load in the source cell caused by said user equipment being handed over.

32. A cell control node as claimed in claim 31, wherein said control node is a BTS (Base Transceiver Station) / Node B.

33. A cell control node as claimed in claim 32, wherein said control node is a BSC (Base Station Controller) / RNC (Radio Network Controller).

34. A RRM node (Radio Resource Management node) arranged for handling cell resource re-allocation in a handover situation, where a user equipment is handed over from a source cell to a target cell in a telecommunication system, said RRM node being arranged for allocating resources to be used by said source cell and said target cell after the handover, c h a r a c t e r i z e d b y said RRM node being arranged for estimating, before the handover has been executed, the resource allocation for said source cell and said target cell, said estimation taking into consideration at least an individual traffic load in the source cell caused by said user equipment being handed over.