WO2013135293A1

WO2013135293A1 - Apparatus and method for handover between different carrier networks

Info

Publication number: WO2013135293A1
Application number: PCT/EP2012/054581
Authority: WO
Inventors: Jani Matti Johannes Moilanen; Antti Anton Toskala
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-03-15
Filing date: 2012-03-15
Publication date: 2013-09-19
Also published as: EP2826301A1; EP2826301B1

Abstract

Apparatus and method for communication are provided. The solution comprises controlling (202) a first transceiver of a first communication system and a second transceiver of a second communication system to transmit data to user equipment; estimating (206) available throughput of connections with the first and second transceiver; determining (208) on the basis of differences between the estimated throughputs whether it would be beneficial to use only the second transceiver to transmit data to the user equipment.

Description

APPARATUS AND METHOD FOR HANDOVER BETWEEN DIFFERENT CARRIER NETWORKS

Field

The exemplary and non-limiting embodiments of the invention relate generally to wireless communication networks. Embodiments of the invention relate especially to an apparatus and a method in communication networks where carrier aggregation is utilised.

Background

In carrier aggregation, user equipment communicates with a communication system using more than one carrier. This method of communication is typically used when large bandwidth is needed. The carriers need not belong to a single communication system. For example, carrier aggregation is proposed between LTE (Long Term Evolution) and HSPA (High Speed Packet Access) systems. When carrier aggregation is utilised, user equipment is able to receive data simultaneously from HSPA and LTE cells. Con- trolling handovers during carrier aggregation is a difficult task since two different systems are involved. The handover procedure should be as smooth as possible.

Summary According to an aspect of the present invention, there is provided an apparatus in a first communication system, comprising : at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform : control a first transceiver of a first communication system and a second transceiver of a second communication system to transmit data to user equipment; estimate available throughput of connections with the first and second transceiver; determine on the basis of differences between the estimated throughputs whether it would be beneficial to use only the second trans- ceiver to transmit data to the user equipment.

According to an aspect of the present invention, there is provided an apparatus in a communication system, comprising : at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform : control a transceiver to receive data from another communication system and transmit data to user equipment control the reception of a handover request from the other communication system, the request comprising information on data throughput and user equipment identification; determine available capacity; and determine whether the handover can be supported.

According to another aspect of the present invention, there is provided a method, comprising : controlling a first transceiver of a first communication system and a second transceiver of a second communication system to transmit data to user equipment; estimating available throughput of connections with the first and second transceiver; determining on the basis of differences between the estimated throughputs whether it would be beneficial to use only the second transceiver to transmit data to the user equipment.

According to another aspect of the present invention, there is provided a method, comprising : controlling a transceiver to receive data from another communication system and transmit data to user equipment; controlling the reception of a handover request from the other communication system, the request comprising information on channel quality information, data throughput and user equipment identification; determining available capacity; and determining whether the handover can be supported.

List of drawings

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which

Figure 1 illustrates an example of carrier aggregation;

Figures 2 and 3 are flowcharts illustrating embodiments of the invention;

Figure 4 illustrates an example of signal flows between network elements; and

Figure 5 illustrates examples of apparatuses applying embodiments. Description of some embodiments

Embodiments are applicable to any base station, network element, user equipment (UE), server, corresponding component, and/or to any commu- nication system or any combination of different communication systems that support required functionality.

The protocols used, the specifications of communication systems, servers and user terminals, especially in wireless communication, develop rapidly. Such development may require extra changes to an embodiment. There- fore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, embodiments. Many different radio protocols to be used in communications systems exist. Some examples of different communication systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), HSPA (High Speed Packet Access), long term evolution (LTE, known also as E-UTRA), long term evolution advanced (LTE-A), Wireless Local Area Network (WLAN) based on I EEE 802.11stardard, worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS) and systems using ultra-wideband (UWB) technology. IEEE refers to the Institute of Electrical and Electronics Engineers. LTE and LTE-A are developed by the Third Generation Partnership Project 3GPP.

Figure 1 illustrates a simplified view of a communication environment where carrier aggregation is utilised between two communication systems. The figure shows an eNodeB 102 of LTE system and a NodeB 104 of an HSPA system . The eNodeB comprises following logical layers : Layer 1 (LTE LI), Medium Access Control (LTE MAC), Radio Link Control (LTE RLC) and Packet Data Convergence Protocol (LTE PDCP) . The NodeB comprises layers Layer 1 (HSDPA LI) and Medium Access Control (HSDPA MAC), where HSDPA denotes High Speed Downlink Packet Access.

In this example, user equipment 100 receives data simultaneously from eNodeB 102 of LTE system and NodeB 104 of HSPA system . This LTE-HSPA carrier aggregation (L-H CA) provides fast load balancing between the two systems. In addition, it allows combining the peak data rates and cell edge data rates of both radio systems and ensures highest possible spectrum utilization when both LTE and HSPA systems are deployed .

In the example of Figure 1, the eNodeB 102 of LTE acts as a master node. The UE 100 receives downlink transmissions 106, 108 from both the eNodeB 102 and NodeB 104. However, all uplink traffic is handled by the eNodeB. Thus, the UE transmit also the HSDPA uplink feedback 110 using LTE uplink. The feedback may comprise hybrid automatic repeat request

(Hybrid ARQ or HARQ) acknowledgements and channel quality indication (CQI) messages.

Figure 1 is only showing some elements and functional entities, all being logical units whose implementation may differ from what is shown . The connections shown in Figure 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the systems also comprise other functions and structures. It should be appreciated that the functions, structures, elements and the protocols used in or for communication are irrelevant to the actual invention . Therefore, they need not to be discussed in more detail here.

The inter-system measurements between LTE and HSPA are currently based on the Radio Resource Control (RRC) layer signalling message that is created once a specific triggering conditions are fulfilled, which may cause delay for the actual handover event. The regular measurement report from HSPA cells contains only Common Pilot Channel CPICH Received Signal Code Power/ Received Signal Strength Indicator RSCP/RSSI (Ec/No) information that is not directly related to the expected data rates to be achieved if moving from LTE to HSPA. Thus a faster trigger for handover is desirable.

The embodiments of the invention are not limited to the above example scenario of Figure 1. For example, the NodeB/Radio Network Controller of HSPA could be the master node and the uplink traffic could be handled by the NodeB.

Figure 2 is a flowchart illustrating an embodiment of the invention . The flowchart describes an example of the operation of a master node, i .e. eNodeB in Figure 1. The embodiment starts at step 200.

In step 202, a first transceiver of a first communication system and a second transceiver of a second communication system are controlled to transmit data to user equipment.

In an embodiment, the first transceiver is controlled to receive data and control information from the user equipment in step 204, the control in- formation comprising channel quality information related to the transmission of data to the user equipment by the first and second transceivers.

In step 206, available throughput of connections with the first and second transceiver is estimated .

In step 208, it is determined on the basis of differences between the esti- mated throughputs whether it would be beneficial to use only the second transceiver to transmit data to the user equipment.

In an embodiment, it is determined on the basis of the channel quality information and/or observed data throughput based on flow control information whether it would be beneficial to use only the second transceiver to transmit data to the user equipment. The motivation for such decision could be e.g . improved uplink throughput, more efficient network resource utilization, or reduced UE power consumption if the current primary link is not contributing enough to the throughput.

The process ends in step 210.

Step 204 above is not present in all embodiments. For example, in cases where UE transmits uplink to both first and second transceiver, the first transceiver does not receive CQI information regarding the second transceiver connection . Figure 3 is a flowchart illustrating an embodiment of the invention . The flowchart describes an example of the operation of NodeB in Figure 1. The embodiment starts at step 300.

In step 302, a transceiver is controlled to receive data from another com- munication system and transmit data to user equipment.

In an embodiment, the transceiver is controlled to receive control information comprising channel quality information in step 304 from the other communication system, the information being related to the transmission of data to the user equipment.

In step 306 a handover request is received from the other communication system . The request comprises information on data throughput and user equipment identification . In an embodiment, the request comprises information on channel quality information .

In step 308, available capacity is determined .

In step 310, it is determined whether the requested handover can be supported .

The process ends in step 312.

Step 304 above is not present in all embodiments. For example, in cases where UE transmits uplink to both to the transceiver and the other com- munication system second transceiver, the second transceiver does not receive CQI information from the other communication system .

Figure 4 illustrates an embodiment of the invention . Figure illustrates an example of the signal flows between LTE and HSPA network elements and user equipment. The figure shows user equipment 400 which is capable of carrier aggregation between LTE and HSPA systems. From the LTE communication system eNodeB 402 and core network 404 are illustrated . From the HSPA system Radio Network Controller RNC 406 and NodeB 408 are illustrated .

The eNodeBs (Enhanced node Bs) of an LTE communication system may host the functions for Radio Resource Management: Radio Bearer Control,

Radio Admission Control, Connection Mobility Control, Dynamic Resource Allocation (scheduling) . The core network 404 may comprise several components and it is responsible for the overall UE control in mobility, session/call and state management with assistance of the eNodeBs through which the UEs connect to the network. In addition, it acts as a gateway between the network and other parts of communication network such as the Internet for example. Radio Network Controller of an HSPA system controls the radio resources of NodeBs connected to it. RNC is the service access point for UEs of the HSPA system . RNC controls NodeBs through IuB interface.

User equipment UE refers to a portable computing device. Such computing devices include wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices : mobile phone, smartphone, personal digital assistant (PDA), tablet computer, laptop computer.

In an embodiment, the LTE eNodeB 402 receives 410 from the core net- work 404 data to be transmitted to the UE 400. The eNodeB transmits 412 part of the data directly to the UE and part is forwarded 414 to NodeB 408, which transmits 416 the data to the UE using HSPA channels.

The UE 400 is configured to transmit 418 uplink data only to the LTE eNodeB. In addition, UE transmits CQI feedback to the eNodeB. The CQI feedback is related to the transmissions of the eNodeB and NodeB. The eNodeB is configured to forward 414 the CQI related to the NodeB transmission to the NodeB.

In an embodiment, the LTE eNodeB 402 is configured to monitor the throughput of the LTE data 412. The eNodeB may determine on the basis of LTE data throughput and CQI received from the UE if the throughput or CQI in LTE side is below a predetermined threshold or if achievable throughout on the HSPA side would be better. As the eNodeB is aware of the HSPA side throughput is may also be taken into account. Furthermore, as the HSPDA uplink feedback (HARQ acknowledgements and CQIs) are transmitted in LTE uplink 418 the eNodeB is aware of CQI results of the

HSPA side and can utilize them in the process.

For example, the situation may be that the on LTE side the data rate is low and expectation based on HSPA CQI (or monitored throughput) is that on the HSPA side the throughput could be clearly better.

In an embodiment, there are other factors in addition to the throughput which may support a handover. These may be, for example, improved uplink throughput, more efficient network resource utilization, or reduced UE power consumption if the current primary link is not contributing enough to the throughput.

If the eNodeB determines that transferring the LTE side data transmission of the carrier aggregation to HSPA side would lead to better throughput it is configured to signal 420 to the RNC 406 in HSPA side the desire for an inter-system handover with the measurement report containing CQI information . The signalling may comprise observed HSPA side throughput based on flow control information between eNodeB and NodeB and indication of the particular UE using LTE/HSPA carrier aggregation in a particular cell . The eNodeB 402 may transmit the signaling 420 via the core network 404 or via a direct interface between the eNodeB and the RNC.

When the RNC receives the request from the eNodeB, it is configured to determine if the available capacity of the HSPA system support the hand- over and whether an optimized handover process is to be used. As the UE is in connection with both the LTE side and the HSPA side, it has information on the cell parameters of both sides. In an embodiment, if the UE were instructed to perform a handover from LTE to HSPA, it may utilise existing cell parameters of HSPA stored in the UE. This may reduce the handover related signalling . However, if RNC is aware that the cell parameters are in process of changing, it may decide that the handover should be made as a regular handover without reduced signalling .

The RNC is configured to send a response 422 to the handover request to the eNodeB. The response may comprise indication whether the handover may be realized utilizing existing cell information stored in user equipment. If the response was positive the eNodeB sends a handover command to the UE. If the RNC indicated that reduced signalling may be used, the command may instruct the UE to adopt the same HSPA cell parameters it has been using during the cell aggregation reception . If the RNC indicated that reduced signalling cannot be used, the UE is configured to obtain HSPA cell parameters from system information block (SI B) messages transmitted by the NodeB.

Above an example where LTE eNodeB controls the carrier aggregation between LTS and HSPA is described. However, in some embodiments of the invention the controlling network can be HSPA. In such cases, RNC and NodeB of HSPA system control the carrier aggregation . Thus, the UE transmit uplink data and control information including CQI to the NodeB which forwards LTE related CQI to the eNodeB. The eNodeB transmits only downlink data to the UE. The NodeB would be configured to monitor CQI/throughput and trigger handover by sending a local handover indication to eNodeB.

The above example of Figure 4 illustrates an embodiment where UE transmits uplink only to the first transceiver. Embodiments of the invention may also be applied in arrangements where the UE transmits uplink to both first and second transceivers. In such a case the first transceiver controlling the arrangement does not receive CQI information regarding the second transceiver connection . In these cases the handover determination may be based on flow control information, for example.

Let us study a simplified example of a device in which embodiments of the invention may be applied wit reference to Figure 5. In some embodiments, the device may a master node controlling the carrier aggregation between two systems or radio access technologies. It should be understood that the apparatus is depicted herein as an example illustrating some embodiments. It is apparent to a person skilled in the art that the device may also comprise other functions and/or structures and not all described functions and structures are required. Although the device has been depicted as one entity, different modules and memory may be implemented in one or more physical or logical entities.

The device of the example includes a control circuitry 500 configured to control at least part of the operation of the device.

The device may comprise a memory 502 for storing data. Furthermore the memory may store software 504 executable by the control circuitry 500. The memory may be integrated in the control circuitry.

The device may further comprise one or more interfaces 508 operationally connected to the control circuitry 500. The control circuitry is configured to communicate with other network elements through the one or more inter- faces 508. For example, if the device is eNodeB or a part of an eNodeB it may communicate with core network, radio network controller and NodeB of HSPA network and other eNodeBs of LTE network. If the device is an RNC or a part of an RNC, it may communicate with core network, other radio network controllers and NodeBs of USPA network and eNodeBs of LTE network. If the device is an RNC or a part of an RNC it may control the transceiver of a NodeB connected to the RNC.

In an embodiment, the device comprises a transceiver 506. The transceiver is operationally connected to the control circuitry 500. It may be connected to an antenna arrangement (not shown).

The control circuitry 500 is configured to execute one or more applications. The applications may be stored in the memory 502. The control circuitry 500 may control a first transceiver of a first communication system and a second transceiver of a second communication system to transmit data to UE and control the first transceiver to receive data and control information from the user equipment, the control information comprising channel quality information related to the transmission of data to the user equipment by the first and second transceivers.

The control circuitry 500 may determine on the basis of the channel quality information and data throughput whether data throughput would be better if only the second transceiver were used to transmit data to the user equipment.

In an embodiment, if the device is an eNodeB or a part of an eNodeB, the first communication system is LTE and the second communication system is HSPA. The first transceiver is a transceiver of the eNodeB and the sec- ond transceiver is a transceiver of a NodeB of HSPA. In an embodiment, if the device is an RNC or a part of an RNC, the first communication system is HSPA and the second communication system is LTE. The first transceiver is a transceiver of a NodeB and the second transceiver is a transceiver of an eNodeB of LTE.

Let us study another simplified example of a device in which embodiments of the invention may be applied wit reference to Figure 5. In some embodiments, the device may a non-master node of a carrier aggregation between two systems or radio access technologies.

It should be understood that the apparatus is depicted herein as an exam- pie illustrating some embodiments. It is apparent to a person skilled in the art that the device may also comprise other functions and/or structures and not all described functions and structures are required. Although the device has been depicted as one entity, different modules and memory may be implemented in one or more physical or logical entities.

The device may further comprise one or more interfaces 508 operationally connected to the control circuitry 500. The control circuitry is configured to communicate with other network elements through the one or more interfaces 508. For example, if the device is eNodeB or a part of en eNodeB it may communicate with core network, radio network controller and NodeB of USPA network and other eNodeBs of LTE network. If the device is an

RNC or a part of an RNC, it may communicate with core network, other radio network controllers and NodeBs of USPA network and eNodeBs of LTE network. If the device is an RNC or a part of an RNC it may control the transceiver of a NodeB connected to the RNC.

The control circuitry 500 is configured to execute one or more applications. The applications may be stored in the memory 502. The control circuitry 500 may control a transceiver to receive data from another communication system and transmit data to user equipment, control a transceiver to receive control information comprising channel quality information from the other communication system, the information being related to the transmission of data to the user equipment. The control circuitry may control the reception of a handover request from the other communication system, the request comprising information on channel quality information, data throughput and user equipment identification, determine available capacity; and determine whether the handover can be supported.

In the proposed solution, a handover process may be triggered quickly as there is no need to wait for the inter-systems measurements to take place (event or trigger initiated) which are using Radio Resource Control RRC signaling.

Assuming LTE eNodeB is the master node of the Carrier Aggregation situation, the LTE eNodeB has more information to determine the expected UE specific Quality of Service when moving to HSPA side only operation.

There is more reliable information available in the RNC to understand the expected throughput (compared to the Common Pilot Channel CPICH measurements only). The RNC can send data with existing understanding what is the expected achievable data rate in the NodeB side (since the CQI is now known that takes lot more into account that only the CPICH power.

The existing HSDPA downlink allows also to take specific actions to shorten the actual HSPA connection set-up (degree depends on the detailed

LTE/HSDPA Carrier aggregation solution, including if HSPA side uplink would be present or not). No need to wait for specific SIBs to be received for the access.

Above remarks naturally apply also in other situations, such as when the roles of the eNodeB and RNC are reversed. In general, the proposed solu- tion results to faster handover time and shorter break in the data stream with better prediction on Common Pilot Channel after handover.

The steps and related functions described in the above and attached figures are in no absolute chronological order, and some of the steps may be performed simultaneously or in an order differing from the given one. Other functions can also be executed between the steps or within the steps. Some of the steps can also be left out or replaced with a corresponding step.

The apparatuses or controllers able to perform the above-described steps may be implemented as an electronic digital computer, or a circuitry which may comprise a working memory (RAM), a central processing unit (CPU), and a system clock. The CPU may comprise a set of registers, an arithmetic logic unit, and a controller. The controller or the circuitry is controlled by a sequence of program instructions transferred to the CPU from the RAM . The controller may contain a number of microinstructions for basic operations. The implementation of microinstructions may vary depending on the CPU design. The program instructions may be coded by a program- ming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system services to a computer program written with the program instructions.

As used in this application, the term 'circuitry' refers to all of the following : (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firmware), such as (as applicable) : (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a mi- croprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term 'circuitry' would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term 'circuitry' would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

An embodiment provides a computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, are configured to control the apparatus to execute the embodiments described above.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program . Such carriers include a record medium, computer memory, read-only memory, and a software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

The apparatus may also be implemented as one or more integrated circuits, such as application-specific integrated circuits ASIC. Other hardware embodiments are also feasible, such as a circuit built of separate logic components. A hybrid of these different implementations is also feasible.

When selecting the method of implementation, a person skilled in the art will consider the requirements set for the size and power consumption of the apparatus, the necessary processing capacity, production costs, and production volumes, for example.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. An apparatus in a first communication system, comprising :

at least one processor; and

at least one memory including computer program code,

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform : control a first transceiver of a first communication system and a second transceiver of a second communication system to transmit data to user equipment;

estimate available throughput of connections with the first and second transceiver;

determine on the basis of differences between the estimated throughputs whether it would be beneficial to use only the second transceiver to trans- mit data to the user equipment.

2. The apparatus of claim 1, the apparatus being configured to

control the first transceiver to receive data and control information from the user equipment, the control information comprising channel quality information related to the transmission of data to the user equipment by the first and second transceivers;

estimate the achievable throughput based on channel quality information related to the transmission of data to the user equipment by the first and second transceivers.

3. The apparatus of claim 1 or 2, the apparatus being configured to estimate the achievable throughput based on flow control information between the first and second communication system.

4. The apparatus of any preceding claim, the apparatus being configured to send the second communication system a request to transfer all data transmission to the user equipment under the second communication system.

5. The apparatus of claim 4, the apparatus being configured to send a request comprising information on the channel quality information, data throughput and user equipment identification .

6. The apparatus of claim 4 or 5, the apparatus being configured to receive acknowledgement from the second communication system and initiate the transmission of a handover command to the user equipment .

7. The apparatus of claim 6, the apparatus being configured to detect that the acknowledgement comprises permission to perform a handover utilizing existing cell information stored in the user equipment;

and command the user equipment in the handover command to utilise existing cell information .

8. The apparatus of any preceding claim 4 to 7, wherein the apparatus is configured to send the request through a core network, the core network being common to both communication systems.

9. The apparatus of any preceding claim 4 to 8, wherein the apparatus is configured to send the request to an apparatus of the second communication system using an interface between the apparatuses, the apparatus of the second communication system controlling the second transceiver.

10 The apparatus of claim 6, wherein the handover command comprises a command to utilize information on the parameters of the second communication system stored in the user equipment.

11. An apparatus in a communication system, comprising :

at least one processor; and

at least one memory including computer program code,

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform : control a transceiver to receive data from another communication system and transmit data to user equipment; control the reception of a handover request from the other communication system, the request comprising information on data throughput and user equipment identification;

determine available capacity; and

determine whether the handover can be supported .

12. The apparatus of claim 11, the apparatus being configured to send i formation on whether the handover may be supported to the other com munication system .

13. The apparatus of claim 11, the apparatus being configured to receive the request through a core network, the core network being common to both communication systems.

14. The apparatus of claim 11, the apparatus being configured to receive the request from an apparatus of the other communication system through an interface between the apparatuses.

15. The apparatus of claim 11, the apparatus being configured to determine whether a handover may be realized utilizing existing cell information stored in user equipment.

16. The apparatus of claim 11, the apparatus being configured to control a transceiver to receive control information comprising channel quality information from the other communication system, the information being related to the transmission of data to the user equipment.

17. The apparatus of claim 16, the apparatus being configured to control the reception of a handover request from the other communication system, the request comprising information on data throughput and user equipment identification .

18. A method, comprising: controlling a first transceiver of a first communication system and a second transceiver of a second communication system to transmit data to user equipment; estimating available throughput of connections with the first and second transceiver; determining on the basis of differences between the estimated throughputs whether it would be beneficial to use only the second transceiver to trans- mit data to the user equipment.

19. The method of claim 18, further comprising: controlling the first transceiver to receive data and control information from the user equipment, the control information comprising channel qual- ity information related to the transmission of data to the user equipment by the first and second transceivers; and estimating the achievable throughput based on channel quality information related to the transmission of data to the user equipment by the first and second transceivers.

20. The method of claim 18, further comprising: estimating the achievable throughput based on flow control information between the first and second communication system.

21. The method of any preceding claim 18 to 20, further comprising: sending the second communication system a request to transfer all data trans^¬ mission to the user equipment under the second communication system.

22. The method of claim 21, further comprising: sending a request com- prising information on the channel quality information, data throughput and user equipment identification.

23. The method of claim 21, further comprising: receiving acknowledgement from the second communication system and initiating the transmis- sion of a handover command to the user equipment .

24. The method of claim 23, further comprising : detecting that the acknowledgement comprises permission to perform a handover utilizing existing cell information stored in the user equipment;

and commanding the user equipment in the handover command to utilise existing cell information .

25. The method of any preceding claim 21 to 23, further comprising sending the request through a core network, the core network being common to both communication systems.

26. The method of any preceding claim 21 to 24, further comprising sending the request to an apparatus of the second communication system using an interface between the apparatuses, the apparatus of the second com- munication system controlling the second transceiver.

27. The method of claim 23, wherein the handover command comprises a command to utilize information on the parameters of the second communication system stored in the user equipment.

28. A method, comprising :

controlling a transceiver to receive data from another communication system and transmit data to user equipment;

controlling the reception of a handover request from the other communica- tion system, the request comprising information on channel quality information, data throughput and user equipment identification ;

determining available capacity; and

determining whether the handover can be supported .

29. The method of claim 28, further comprising : sending information on whether the handover may be supported to the other communication system .

30. The method of claim 28, further comprising :

receiving the request through a core network, the core network being common to both communication systems.

31. The method of claim 28, further comprising :

receiving the request from an apparatus of the other communication system through an interface between the apparatuses.

32. The method of claim 28, further comprising :

determining whether a handover may be realized utilizing existing cell information stored in user equipment.

33. The method of claim 28, further comprising :

controlling a transceiver to receive control information comprising channel quality information from the other communication system, the information being related to the transmission of data to the user equipment.

34. The method of claim 33, further comprising :

controlling the reception of a handover request from the other communica- tion system, the request comprising information on channel quality information, data throughput and user equipment identification .

35. A computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute the method according to any of claims 16 to 32.