WO2009088346A1

WO2009088346A1 - Method and arrangement in a communication network

Info

Publication number: WO2009088346A1
Application number: PCT/SE2008/051466
Authority: WO
Inventors: Joakim Langlet; Niilo Musikka; Tomas Åke BRÄNNLUND
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-01-08
Filing date: 2008-12-16
Publication date: 2009-07-16
Also published as: TW200939838A

Abstract

Method and arrangement in a node in a radio access network for use in improving a success ratio for hard handover of a downlink connection to a user equipment (110) between cells (132, 121) in the radio access network (110). The user equipment and the radio access (110) network are capable of engaging in diversity handover for uplink communications. The method comprises the steps of transmuting to the user equipment (110) information authorising the user equipment (116) Io take a decision on whether to initiate the downlink handover procedure, receiving from the user equipment information establishing a point in time for performing the downlink handover, initiating an activation of a source cell (121) and a target cell (132) in preparation for the downlink handover prior to the established point in time and performing the downlink handover in the radio access network (110) at the established point in time. Also, a method and arrangement in a user equipment (110) is presented.

Description

METHOD AND ARRANGEMENT IN A COMMUNICATION NETWORK

TECHNICAL FIELD

The disclosed subject matter relates to various embodiments of a method and an arrangement in a network node and a method and an arrangement in a user equipment More particularly, the present invention relates to a mechanism for performing a handover in a radio access network.

BACKGROUND Functionality to handle user mobility is a fundamental component in cellular networks. From a service quality perspective, such functionality must ensure that service continuity is maintained as user equipments move from one cell to another during an active session, and that each new session is established in a sufficiently good radio environment From a spectral efficiency perspective, such functionality should ensure that an active user is always served by the most appropriate base station or base stations, which typically means the closest base station/s in a radio sense.

In a handover scenario in e.g. High-Speed Downlink Packet Access (HSDPA), the Radio Network Controller (RNC) may send the High-Speed cell change command over the HS- DSCH (downlink) channel from the source cell, the message must be sent white the signal received by the user equipment from the source cell is still strong enough. The HS-DSCH downlink channel is shared between user equipments using channel-dependent scheduling to make the best use of available radio conditions.

The source cell is the cell which the user equipment at the moment is camping on. The target cell is the cell into which the handover is to be performed as the user equipment is moving into the geographical area covered by that cell.

The High-Speed cell change command, which may be sent using e.g. the Physical Channel Reconfiguration or Radio Bearer Reconfiguration messages, meaning that the user equipments should start listen to the target cell rather than the source cell.

Assuming this message is properly received by the user equipment, it will obey the order from the RNC and typically the change of the downlink High-Speed channel, from source to target cell, will be executed after some time, defined by a parameter received in the High-Speed cell change command.

Occasionally, the user equipment is not able to receive the High-Speed cell change command, as it is sent over the air and the user equipment is situated at the border region of the source cell, or even out of the source cell, in such case the user equipment will continue listen to the source ceil rather than to the target ceil and as the user equipment advances deeper into the target ceil, the call is most likely lost, which of course is most annoying to the user.

The drop rate problem becomes even bigger in cases where the user equipment moves at a high velocity, e.g. when calling from a car driving on a free speed high way. An increased drop rate is also expected in certain coverage scenarios, where the separation between the source cell and the target ceil coverage is sharp and well defined. This can be road side ceils in rural areas and where down tilted antennas are used and where the surroundings provide little mυlti path, e.g. few reflections of emitted radio waves.

Thus, known handover methods are not as robust as one could wish. Handover drops thus may occur according to existing methods.

SUMMARY

It is the object to obviate at least some of the above disadvantages and provide an improved performance in a radio access network.

The object is achieved by a method in a node in a radio access network for use in improving a success ratio for hard handover of a downlink connection to a user equipment between cells in the radio access network. The user equipment and the radio access network are capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications. The method comprises the step of transmitting information to the user equipment, authorising the user equipment to take a decision on whether to initiate the downlink handover procedure. The method further comprises the step of receiving information from the user equipment, which information establishes a point in time for performing the downlink handover. Still further, the method comprises the step of initiating an activation of a source cell and a target cell in preparation for the downlink handover prior to the established point in time. In addition, the method comprises the step of performing the downlink handover in the radio access network at the established point in time.

The object is also achieved by an arrangement in a node in a radio access network for use in improving a success ratio for hard handover of a downlink connection to a user equipment between ceils in the radio access network. The user equipment and the radio access network are capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications. The arrangement comprises a transmitter. The transmitter is adapted to transmit information authorising the υser equipment to take a decision on whether to initiate the downlink handover procedure, to the user equipment. Further, the arrangement comprises a receiver. The receiver is adapted to receive information from the user equipment, which information establishes a point in time for performing the downlink handover. Also, the arrangement comprises a computing unit The computing unit is adapted to initiate the activation of a source cell and a target ceil. The activation is initiated in preparation for the downlink handover prior to the established point in time in order to perform the downlink handover in the radio access network at the established point in time.

The object is also achieved by a method in a user equipment for use in improving a success ratio of hard handover of a downlink connection to the user equipment between ceils in a radio access network. The user equipment and the radio access network are capable of engaging in diversity handover, such as soft and/or softer handover, for uplink Communications. The method comprises the step of receiving information from the radio access network authorising the user equipment, to take a decision on whether to initiate the downlink handover procedure. Also, the method comprises deciding to perform the downlink handover from a source cell to a target cell in accordance with the authorisation. Further, the method comprises the step of calculating a point in time for performing the downlink handover. Further yet, the method comprises the step of initiating the downlink handover at the calculated point in time.

The object is also achieved by an arrangement in a user equipment for use in improving a success ratio of hard handover of a downlink connection to the user equipment between cells in a radio access network. The user equipment and the radio access network are capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications. The arrangement comprises a receiver. The receiver is adapted to receive information from the radio access network authorising the user equipment to take a decision on whether to initiate the downlink handover procedure. Further, the arrangement comprises a deciding unit. The deciding unit is adapted to decide to perform the downlink handover from a source cell to a target cell In accordance with the authorisation. Additionally, the arrangement comprises a calculating unit. The calculating unit is adapted to calculate a point in time for performing the downlink handover and for initiating downlink handover at the calculated point in time.

Through the present methods and arrangements, a handover with reduced drop rate is achieved by exploiting the fact that the uplink connection in a handover scenario often is better than the downlink connection, instead of waiting for a command to perform the handover from the network, the user equipment initiates the handover and sends a time value comprising a point in time when the handover is to be performed. Thereby the risk of loosing a connection is reduced, as the user equipment does not necessarily have to wait for receiving a command from the network over the downlink, to perform the handover. Thus an improved performance in a radio access network is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present methods and arrangements will now be described more in detail in relation to the enclosed drawings, in which:

Figure 1 is a schematic block diagram illustrating a radio access network according to some embodiments.

Figure 2A is a schematic block diagram illustrating a first phase of a mobility scenario.

Figure 2B is a schematic block diagram illustrating a second phase of a mobility scenario.

Figure 3A is a schematic block diagram illustrating exemplary components of a user equipment according to some embodiments.

Figure 3B is a schematic block diagram illustrating a user equipment according to some embodiments where the user equipment is embodied as a cellular telephone. Figure 4 is a schematic block diagram illustrating method steps according to some embodiments.

Figure 5 is a schematic block diagram illustrating method steps according to some embodiments.

Figure 6 is a schematic block diagram illustrating method steps according to some embodiments.

Figure 7 is a schematic block diagram illustrating a activation process according to some embodiments.

Figure 8 is a schematic block diagram illustrating a structure of a network node. according to some embodiments.

Figure 9 is a schematic block diagram illustrating a measurement report reception process.

Figure 10 is a schematic block diagram illustrating a delegated cell change process.

Figure 11 is a schematic block diagram illustrating a method in a network node, according to some embodiments.

Figure 12 is a schematic block diagram illustrating an arrangement in a network node, according to some embodiments.

Figure 13 is a schematic block diagram illustrating a method in a user equipment, according to some embodiments.

Figure 14 is a schematic block diagram illustrating an arrangement in a user equipment, according to some embodiments.

DETAILED DESCRIPTION

The disclosed subject matter relates to various embodiments of a method and an arrangement in a radio access network and a method and an arrangement in a user equipment which may be put into practice in the embodiments described below. The disclosed subject matter may, however, be embodied in many different forms and should not be constructed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present methods and arrangements, it should be understood that there is no intent to limit the present method and arrangement in a radio access network and method and arrangement in a user equipment to any of the particular forms disclosed, but on the contrary, the present methods and arrangements is to cover all modifications, equivalents, and alternatives falling within the scope of the methods and arrangements as defined by the claims.

Still other objects and features of the present methods and arrangements will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

Figure 1 is a schematic illustration over a radio access network 100. A user situated in a vehicle 105 is managing a user equipment 110, within the wireless communication system 100. Further, the radio access network 100 may comprise a first base station 120, in a source cell 121 and a second base station 130, in a target cell 132. The source ceil 121 and the target cell 132 are separated by a cell border 150.

Although two base stations 120.130 are shown in Figure 1, it is to be understood that another configuration of base station transceivers may be connected through, for example, a mobile switching centre and other network nodes, to define the radio access network 100. Further, the base stations 120, 130 may be referred to as e.g. a Remote Radio Unit (RRU), an access point, a Node B, an evolved Node B (eNode B) and/or a base transceiver station, Access Point Base Station, base station router, etc depending e.g. of the radio access technology and terminology used.

In some embodiments, the user equipment (UE) 110 may be represented by a wireless communication device, a wireless communication terminal, a mobile cellular telephone, a Personal Communications Systems terminal, a Personal Digital Assistant (PDA), a laptop, a computer or any other kind of device capable of managing radio resources.

The radio access network 100 may be based on technologies such as e.g. Global System for Mobile Telecommunications (GSM), Code division multiple access (CDMA), Wideband Code Division Multiple Access (WCDMA), CDMA 2000. High Speed Downlink Packet Data Access (HSDPA), High Speed Uplink Packet Data Access (HSUPA), High Data Rate (HDR) etc, just to mention some none limiting examples.

Further, as used herein, radio access network 100 may refer to various radio access technologies in the traditional sense, a wireless local area network (LAN) or a wireless personal area network without departing from the teachings of the present invention. These networks may comprise, for example, radio access technologies, such as Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), High Speed Packet Data Access (HSPA), Universal Mobile Telecommunications System (UMTS) and/or Wireless Local Area Networks (WLAN), such as Wireless Fidelity (WiFi) and Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth or according to any other wireless communication technology.

It is to be noted however, that the invention is not in any way limited to be performed exclusively in the radio access network 100, but may be performed in the radio access network 100 wherein some nodes are wirelessly connected and some nodes have a wired connection.

The radio access network 100 may further according to some embodiments comprise a control node 140. The control node 140 may be e.g. a Radio Network Controller (RNC). The Radio Network Controller 140 is a governing element in the radio access network 100, responsible for control of base stations 120, 130, which are connected to the Radio Network Controller 140. The Radio Network Controller 140 may further for example carry out radio resource management; some of the mobility management functions and may be the point where encryption may be done before user data is sent to and from the user equipment 110.

The user equipment 110 may communicate with other user equipments, or network nodes not shown in Figure 1, via any, some or all of the base stations 120, 130 comprised within the radio access network 100. Figure 1 further illustrates the user equipment 110 as It moves from the source cell 121 towards the target cell 132. The various points along the dotted arrow in Figure 1 are important points in the process of this mobility traffic case. Worth noting is that the traffic case comprises two procedures, an active set update procedure and a High Speed ceil change procedure. The active set update procedure adds cell/s 121, 132 to the active set so that there are at least two cells 121, 132 In the active set, which in turn means that the uplink transmission from the user equipment 110 can be received by several base stations

120, 130. The High Speed cell change procedure changes the downlink transmission from the source cell 121 to the target cell 132.

At point A in Figure 1, the downlink of the target cell 132 is detectable and can be measured by the user equipment 110.

At point B in Figure 1, the signal strength exceeds the threshold where the target cell 132 may be added to the active set. The user equipment 110 then may send a Measurement Report (event 1a) indicating to the control node 140 that the target cell 132 can be added to the active set The control node 140 may then transmit an Active Set Update message to the user equipment 110 comprising information about the target cell 132. The addition of the target cell 132 in the active set means that an additional uplink connection is added.

Somewhere between point B and C in Figure 1. the target cell 132 becomes the best cell. At that point in time, it may be decided to initiate a handover from the source cell 121 to the target ceil 132. Such decision also must be agreed upon between the user equipment 110 and the control node 140. A new Measurement Report (event 1d) may be sent from the user equipment 110 to the control node 140. indicating that the target ceil 132 has become the new best cell, according to some embodiments.

The control node 140 may then order the user equipment 110 to do a High Speed ceil change, using e.g. the Physical Channel Reconfiguration or Radio Bearer Reconfiguration messages, meaning that the user equipment 110 may start to listen to the target ceil 132 rather than the source cell 121, assumed to be sent to the user equipment 110 at point O.

Assuming this message is properly received by the user equipment 110, it will obey the order from the control node 140 and typically the change of the downlink High Speed channel, from source cell 121 to target cell 132, may be executed after some time, defined by a parameter received in the High Speed cell change command.

The source cell 121 and the target cell 132 may be controlled by different control nodes 140, which control nodes 140 may communicate with each other.

Figure 2A is a combined signalling and flowchart that depicts the transmission of signals between the user equipment 110, the first base station 120. the second base station 130, and a control node 140, according to some embodiments, when performing a handover.

The user equipment 110 continuously perform measurements, which measurements may result in an Radio Resource Control Layer (RRC) Measurement Report message at point B in Figure 1, when a new potential target cell 132 exceeds the set threshold.

210

The user equipment 110 sends an RRC Measurement Report to the control node 140.

220

As a result the control node 140 may set up a Radio Link (RL) in the target cell 132 and send an RRC Active Set Update to the user equipment 110, adding the target cell 132 to the active set

230

New information may be added to this message that comprises a preparation for a High Speed cell change, sometimes also referred to as target cell preconfiguratioα This information corresponds to what is sent in an RRC Physical Channel Reconfiguration, or RRC Radio Bearer Reconfiguration, also comprising a cell change trigger level criteria.

The new information elements used may be optional for the network node 140 but mandatory for the user equipment 110.

240

The user equipment 110 may respond with an RRC Active Set Update Complete message which in this case also tells the network that the trigger for a High Speed cell change is armed. Figure 2B is a combined signalling and flowchart that depicts the transmission of signals between the user equipment 110, the first base station 120, the second base station 130, and a control node 140, according to some embodiments, when performing a handover.

250

When the cell change trigger level criteria is fulfilled, typically somewhere between point B and C in Rgυre 1, the user equipment 110 will indicate to the radio access network 100 to go ahead with the High Speed cell change by sending a new message, here called RRC Cell Change Indication, comprising information describing the current Connection Frame Number (CFN) in the user equipment 110 at the time of trigger. The trigger may unleash the handover when the measurement continuously performed by the user equipment 110 shows that the new cell 132 fulfils the criteria to be regarded as the best cell. The sum of the activation time, conveyed from the network in an earlier message to the user equipment 110, and the Connection Frame Number may be the time when the user equipment 110 start to listen to the (down link) High Speed channel from the new cell 132. The Connection Frame Number sent to the network 100 may be based on the Connection Frame Number at the time of the decision.

260, 270, 280. 290 In a number of steps 260, 270. 280, 280. while the set activation time is running, the first base station 120 and the second base station 130 are prepared for performing the handover.

The activation time may correspond to the minimum time needed to reconfigure the radio links and to change the Medium Access Control MAOd flow to the target cell 132 and may typically be sent to the user equipment 110 as a part of the RRC Active Set Update.

The user equipment 110 will use the activation time to know when to start listen to the target cell 132 and the network 100 will use the Connection Frame Number + activation time as activation time for the radio link reconfigurations.

295

The MAC-d flow is changed to the target ceil 132, i.e. the handover is accomplished. The MAC-d flow is a flow of MAOd Protocol Data Units (PDU) which belongs to logical channels which are MAOd multiplexed. There may be as many triggers as there can be members in the active set of the user equipment 110.

If new ceils 121, 132 are added to the active set and others are excluded from the active set, the triggers corresponding to the removed cells may also removed.

Figure 3A illustrates the user equipment 110 consistent with exemplary embodiments. The user equipment 110 may comprise e.g. a transceiver 305, a processing unit 310. a memory 315, an input device 320, an output device 325, a bus 330 and a control system 335.

The transceiver 305 may comprise transceiver circuitry for transmitting and/or receiving symbol sequences using radio frequency signals via one or more antennas.

The processing unit 310 may comprise a Central Processing Unit (CPU), processor, microprocessor, or processing logic that may interpret and execute instructions. The processing unit 310 may perform all data processing functions for inputting, outputting, and processing of data including data buffering and device control functions, such as call processing control, user interface control, or the like.

The memory 315 may provide permanent, semi-permanent, or temporary working storage of data and instructions for use by processing unit 310 in performing device processing functions. The memory 315 may include ROM, RAM, large-capacity storage devices, such as a magnetic and/or optical recording medium and its corresponding drive, and/or other types of memory devices. The input device 320 may comprise mechanisms for entry of data into the user equipment 110. As a non limiting example only, the input device 320 may comprise a key pad. The key pad may permit manual user entry of data into the user equipment 110. The input device 320 may further, according to some embodiments, comprise a microphone. The microphone may in turn comprise mechanisms for converting auditory input into electrical signals. According to some embodiments, a touch screen functionality is comprised within or associated with the input device 320.

The output device 325 may comprise mechanisms for outputting data in audio, video and/or hard copy format. For example, the output device 325 may comprise a speaker that comprises mechanisms for converting electrical signals into auditory output. The output device 325 may further comprise a display unit that displays output data to the user. For example, the display unit may provide a graphical user interface that displays output data to the user. The bus 330 may interconnect the various internal components of the user equipment 110 to permit the components to communicate with one another.

The user equipment 110 has various processes to control the connection to the radio network infrastructure 100. Embodiments of the present methods and arrangements propose a modification to the method for High Speed cell change and for the purpose of the description of these embodiments, the control system 335 that maintains the radio connection towards the network infrastructure 100 may be referred to as the Radio Link Control System. It may be part of the overall control system 335 placed in software in a processor in the user equipment 110.

The Radio Link Control System in the user equipment 110 has a process that monitors the neighbour cells and reports when the signal strength of a neighbour cell reaches above a certain threshold level or when the signal strength of a cell which is already part of the active set gets below another defined threshold. These measurements are reported to the control node 140 in order for the control node 140 to be able to order changes to the active set.

The configuration of components of the user equipment 110 illustrated in Figure 3A is for illustrative purposes only. Other configurations comprising more, fewer, or a different arrangement of components may be implemented.

Figure 3B illustrates an exemplary implementation of the user equipment 110 in which the user equipment 110 comprises a cellular radiotelephone. As shown in Figure 3B, the user equipment 110 may comprise a microphone 355, e.g. of input device 320 for entering audio information into the user equipment 110, a speaker 340, e.g. of output device 325 for providing an audio output from the radiotelephone, a keypad 345, e.g. of input device

320 for manual entry of data or selection of telephone functions, and a display 350, e.g. of input device 320 or output device 325 that may visually display data to the user and/or which may provide a user interface that the user may use to enter data or to select telephone functions, in conjunction with the keypad 345.

The display unit 350 may comprise a screen display that may provide a user interface, e.g., a graphical user interface that can be used by a user for selecting device functions. The display unit 350 may be a touch screen, adapted to register inputs from a user of the user equipment 110, according to some embodiments.

The screen display of the display unit 350 may comprise any type of visual display, such as, for example, a Liquid Crystal Display (LCD), a plasma screen display, a Light-Emitting Diode (LED) display, a Cathode Ray Tube (CRT) display, an Organic Light-Emitting Diode (OLED) display, etc.

Figure 4 illustrates the process of the continuous monitoring of neighbour cells.

The Radio Link Control System 335 may use the radio parts and the Baseband Processing parts to monitor the neighbour cells as depicted by steps 410, 420 and 430.

In a first step 410, the neighbour cells are measured. In a next step 420, a ceil may be added to, or removed from, the active set

In step 430. an RRC Measurement Report message may be sent to indicate changes in the list of cells that may be part of the active set

The monitoring process described in Figure 4 may continue as long as the user equipment 110 is in CELL-DCH state.

The Radio Link Control System 335 may expect RRC Active Set Update messages from the control node 140 as a result of measurement reports sent.

Figure 5 depicts a process waiting for an RRC Active Set Update message. According to some embodiments, it is suggested to extend the contents and meaning of the RRC Active Set Update message.

In step 510 in Figure 5, the process waits for an RRC Active Set Update message. This message may order the user equipment 110 to add, remove or replace a cell to/from the active set. In step 520. the radio links may be added and/or removed from the active set as indicated from the control node 140.

In addition to adding an uplink radio link to the new cell, the user equipment 110 is, via the RRC Active Set Update message from the control node 140, optionally presented with all the necessary information to perform the High Speed cell change, when the new cell becomes the best ceil according to cell change trigger level criteria set up by the control node 140. The optional added High Speed cell change behaviour is called Delegated Cell Change. In step 570. a new message, here called RRC Cell Change Indication, may be prepared in order to be ready for a change of best cell within the active set.

Absence of Delegated Cell Change content in the RRC Active Set Update message may result in maintaining the legacy 3GPP behaviour, which means that an RRC Measurement Report may be sent when a new best cell is discovered as noted by step 560 in Figure 5.

Step 540 of Figure 5 shows that when a cell is removed from the active set, the corresponding High Speed cell change preparation information, received at the time when that the cell was added to the active set, is removed.

Figure 6 is illustrating the process of monitoring an active set This process may be active as soon as there are two or more cells in the active set.

In step 610 of Figure 6. the signal strength of the cells 121 , 132 in the active set are measured and monitored. If a cell 121, 132 within the active set, which is not the High

Speed serving cell, fulfils the criteria for being the best cell, the process checks the

'delegated cell change" status of the cell 121, 132 in step 630. If the cell 121, 132 is marked for "delegated cell change", the Connection Frame Number (CFN) is set in the prepared RRC Cell Change Indication in step 650 and the message is sent to the control node 140 to indicate that the user equipment 110 will perform a High Speed cell change at the time given by the connection frame number plus the activation timer, which may typically be received in the RRC Active Set Update message from the control node 140.

This message, indicating that the user equipment 110 will execute the High Speed ceil change, is sent uplink to the control node 140. Since the uplink uses multiple radio links, ^'which may be referred to as macro diversity, where one of the links is the new High

Speed serving cell, the probability of successful completion of the High Speed cell change is much higher than in the legacy 3GPP solution.

In step 670 in Figure 6. the process starts an activation timer for the cell change, and the corresponding process. Figure 7 below shows the activation process that is used to wait for the exact right moment to change to the target cell 132 in the downlink. The downlink transmission on the High Speed channel will be changed from the source cell 121 to the target cell 132 at the same time in the control node 140 thanks to the signalled connection frame number. The control node 140 will be described more in detail in connection with Figure 8.

On expiry of the activation timer in step 701 of Figure 7, the process reconfigures the Base Band parts to receive the downlink data from the target cell 132. The process is then stopped and the High Speed cell change procedure has been completed.

The control node 140 has various processes to control the connections to all the user equipments 110.

Here, the control node 140 is for the purpose of illustration shown as a separate entity from the base stations 120, 130. The 3GPP standards, however, allows implementations where the function of the control node 140 is combined with the base stations 120, 130. The described invention is independent on whether the network nodes 120, 130, 140 are co-located or not.

This embodiment proposes a modification of the method for High Speed cell change. In this embodiment, by way of example, the control system that maintains the radio connection between the user equipment 110 and the network infrastructure has been named the control node Mobility/Handover control, it is part of the overall control system placed in software in a processor in the control node 140.

Figure 8 shows the location of the Mobility/Handover control in a schematic system structure of a control node 140.

The Mobility/Handover control unit has a process that receives measurement event messages from the user equipment 110 that it controls. This process expects RRC Measurement Report messages from any user equipment 110 in connected mode.

The messages of interest for this embodiment are the notifications about cells to be added or removed from the active set, or when a cell 121, 132 has become the best cell in the active set. for connections that use HSDPA in the downlink. The process described in Figure 9 below is a part of the RNC Mobility/Handover control. In Step 910 of Figure 9, the process waits for an RRC Measurement Report message to be received from the user equipment 110.

After event discrimination in step 920, an event 1a occurrence is forwarded to step 930. where the process could check a system parameter or evaluation procedure if the reported cell should be using the legacy High Speed cell change method or the new delegated cell change method. It should be noted that the principles of measurement reporting described in the 3GPP standards allow for the use of other events and can be extended with new events to accomplish the same result as described in this embodiment. This description makes reference to event 1a only as a useful implementation example.

in steps 940 and 950, respectively, RRC Active Set Update messages are prepared for the two methods. The delegated cell change method requires additional parameters in the RRC Active Set Update message. The additional parameters convey information needed for the High Speed cell change, which are sent using an RRC Radio Bearer Reconfiguration or an RRC Physical Channel Reconfiguration in the legacy High Speed cell change procedure.

In step 960 of Figure 9. the RRC Active Set Update is sent to the user equipment 110. For the delegated cell change alternative introduced by this embodiment, the user equipment 110 will be asked to prepare itself for a delegated cell change decision based on the information in this message.

The Mobility/Handover control in the control node 140 may also use a process that waits for an RRC Active Set Update Complete message from the user equipment 110. This process in the control node 140 is similar to legacy behaviour and is therefore not shown here.

Figure 10 shows the delegated cell change process of the Mobility/Handover control in the control node 140. In step 1010, the process waits for an RRC Ceil Change Indication message, indicating that a delegated cell change has commenced. This message contains information about the CFN, which reveals when the user equipment 110 triggered the delegated cell change. This is used as a time reference to accomplish a synchronized High Speed cell change. An NBAP Radio Link Reconfiguration Prepare is sent to the base station 120 of the source ceil 121 and the base station 130 of the target ceil 132. This is shown in step 1020. This is similar to a legacy High Speed ceil change procedure.

Using the CFN received from the user equipment 110 and adding the activation time, which is defined by the control node 140 as the basis for when the base stations 120, 130 should do the switch, an NBAP Radio Link Reconfiguration Commit, with the relevant time information, is sent to the base stations 120. 130 in step 1030.

The control node 140 will then wait for the activation time in step 1040 and change the user plane connection to the target cell 132 in step 1050.

Exemplary embodiments are based on the principle that the processing delay in the handover decision may be minimized and that the uplink is in soft/softer handover state and provides a more reliable link than the downlink at the cell borders 150. When the

Signalling Radio Bearer is mapped on to a HS-DSCH transport channel there may be a risk of losing the connection at High Speed cell change. Embodiments of the invention therefore reduce this risk by using the upiink to signal the cell change decision. Since the uplink supports soft handover, multiple radio links are used comprising a link through the new best cell. This will make the probability of a successful cell change considerably higher than in the legacy scenario. The network may. in exemplary embodiments, prepare the user equipment 110 for a High Speed cell change, but may allow the final decision to execute the order, to the user equipment 110. Exemplary embodiments thus may minimize the processing delay between the measurement and the execution of the High

Speed cell change and use the uplink to notify the network of the intention to switch to the target ceil 132, which belongs to the active set.

Figure 11 is a flow chart illustrating a method in a node 120, 130, 140 in a radio access network 100 for use in improving a success ratio for hard handover of a downlink connection to a user equipment 110 between cells 121, 132 in the radio access network

100. The user equipment 110 and the radio access network 100 being capable of engaging in diversity handover, such as e.g. soft and/or softer handover, for uplink communications. The node 120, 130. 140 within the radio access network 100 may be e.g. a control node 140 such as a RNC. According to some embodiments, the node 120,

130, 140 may be a base station 120, 130. According to still some optional embodiments, the method may be performed partially in the base station 120. 130 and partially in the control node 140.

To appropriately improving the success ratio for hard handover, the method may comprise a number of steps 1101-1105. It is to be noted that It is however to be noted that the method steps 1101-1105 may be performed in another chronological order than the enumeration indicates and that some of them, e.g. step 1103 and step 1104, or even all steps may be performed simultaneously or in an altered, arbitrarily rearranged. decomposed or even completely reversed chronological order. It is further to be noted that some of the presented method steps, e.g. step 1102 are optional and may only be performed within some embodiments. The method may comprise the following steps:

Step 1101

The user equipment 110 transmits information, authorising the user equipment 110 to take a decision on whether to initiate the downlink handover procedure.

The authorisation of the user equipment 110 may according to some embodiments relate to one or more selected cells 121, 132. According to some embodiments however, the authorisation may relate to at least one cell 121, 132 in an active set of the user equipment 110.

The information transmitted to the user equipment 110 may comprise e.g. handover trigger criteria, such as target ceil preconfiguration, to be used by the user equipment 110 when taking the decision on whether to initiate the downlink handover procedure.

Step 1102

This method step is optional and may only be performed within some embodiments.

An activation time value may be transmitted to the user equipment 110. The activation time value may establish a time span that may be sufficient for an activation of a source cell 121 and a target cell 132 in preparation for the downlink handover.

The activation time value indicates the point in time when the hand over is to be performed, counted from a certain starting point Thus the transmitted activation time value may be used e.g. as starting value in a count down timers, which count down timers may run simultaneously on the user equipment 110 and the control node 140. Step 1103

Information for establishing a point in time for performing the downlink handover is received from the user equipment 110.

The information received from the user equipment 110 may according to some embodiments comprise information indicating that the user equipment 110 has taken a decision on to initiate the downlink handover procedure and identifying the target cell 132 for the downlink handover.

Step 1104

An activation of a source cell 121 and a target cell 132 is initiated in preparation for the downlink handover prior to the established point in time.

Step 1105

The downlink handover in the radio access network 100 is performed at the established point in time.

When the established point in time is reached, the hand over is performed from the source cell 121 to the target cell 132. Optionally, a signal confirming the performance of the hand over at the established point in time may be sent to the user equipment 110, according to some embodiments.

Figure 12 schematically depicts an embodiment of an arrangement 1200 in a node 120. 130, 140 in a radio access network 100, adapted to perform at least some of the above described method steps 1101-1105. The arrangement 1200 in the user equipment 110 is thus adapted to improve a success ratio for hard handover of a downlink connection to a user equipment 110 between cells 121, 132 in the radio access network 100. The user equipment 110 and the radio access network 100 being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications.

For the sake of clarity and in order not to render unnecessary complications for the reader to understand the functionality and advantages of the present method and arrangement 1200 within the node 120, 130. 140, any internal electronics of the node 120, 130. 140, not completely necessary for performing the present method according to steps 1101- 1105 has been omitted from Figure 12. The arrangement 1200 comprises a transmitter 1210. The transmitter 1210 is adapted to transmit information authorising the user equipment 110 to take a decision on whether to initiate the downlink handover procedure, to the user equipment 110. The arrangement 1200 also comprises a receiver 1230. The receiver 1230 is adapted to receive information from the user equipment 110. which information establishes a point in time for performing the downlink handover. Further, the arrangement 1200 comprises a computing unit 1240. The computing unit 1240 is adapted to initiate the activation of a source cell 121 and a target cell 132 in preparation for the downlink handover prior to the established point in time and to perform the downlink handover in the radio access network 100 at the established point in time.

Optionally, the arrangement 1200 also may comprise a timer or other time measuring means, in order to count the time that has passed since the information for establishing a point in time for performing the downlink handover has been received from the user equipment 110 in step 1103.

Further, the arrangement 1200 in the node 120. 130, 140 may according to some embodiments also comprise a Central Processing Unit (CPU), a microprocessor, a Peripheral interface Controller (PIC) microcontroller or any other appropriate device which may be adapted to interpret computer program instructions and processes data.

It is to be noted that the described units 1210-1240 comprised within the arrangement 1200 in the node 120. 130, 140 are to be regarded as separate logical entities but not with necessity separate physical entities.

Any, some or all of the units 1210-1240 may be comprised or co-arranged within the same physical unit However, in order to facilitate the understanding of the functionality of the arrangement 1200 in the node 120. 130, 140. the comprised units 1210-1240 are illustrated as separate physical units in Figure 12.

As a non limiting example only, the transmitting unit 1210 and the receiving unit 1230 may according to some embodiments be comprised within one physical unit, a transceiver, which may comprise a transmitter circuit and a receiver circuit, which respectively transmits outgoing radio frequency signals and receives incoming radio frequency signals, such as e.g. voice call and/or data signals, via an antenna. The antenna may be an embedded antenna, a retractable antenna or any antenna known to those having skill in the art without departing from the scope of the present invention. The radio frequency signals transmitted between the user equipment 110 and the node 120, 130, 140 may comprise both traffic and control signals e.g., paging signals/messages for incoming calls, which are used to establish and maintain a voice call communication with another party or to transmit and/or receive data, such as SMS, e-mail or MMS messages, with other nodes 120. 130, 140.

Figure 13 is a flow chart illustrating a method in the user equipment 110 for use in improving a success ratio for hard handover of a downlink connection to the user equipment 110 between cells 121, 132 in the radio access network 100. The user equipment 110 and the radio access network 100 are capable of engaging in diversity handover, such as e.g. soft and/or softer handover, for uplink communications. The user equipment 110 may be e.g. a mobile radio telephone.

To appropriately improving the success ratio for hard handover, the method may comprise a number of steps 1301-1307. It is to be noted that It is however to be noted that the method steps 1301-1307 may be performed in another chronological order than the enumeration indicates and that some of them, e.g. step 1301 and step 1302, or even all steps may be performed simultaneously or in an altered, arbitrarily rearranged, decomposed or even completely reversed chronological order. It is further to be noted that some of the presented method steps, e.g. step 1301 are optional and may only be performed within some embodiments. The method may comprise the following steps:

Step 1301

Receive an activation time value. The activation time value is received from a node 120, 130, 140 within the radio access network 100. The activation time value establishing a time span that is sufficient for an activation such as radio link reconfiguration and change of a MAC-d flow, of the source cell 121 and the target cell 132 in preparation for the downlink handover.

Step 1302

Information is received from the radio access network 100, authorising the user equipment 110 to take a decision on whether to initiate the downlink handover procedure. The received authorisation may according to some embodiments relate to one or more selected cells 121. 132. However may the authorisation according to some embodiments relate to at least one cell 121 , 132 in an active set of the user equipment 110.

The information received from the radio access network 100 may optionally comprise handover trigger criteria, such as target cell preconfigυration. to be used by the user equipment 110 when taking the decision on whether to perform the downlink handover.

Step 1303 It is decided to perform the downlink handover from a source cell 121 to a target cell 132 in accordance with the authorisation.

Step 1304

A current time value such as a current connection frame number is registered for the user equipment 110 in response to taking the decision to perform the downlink handover, the current time value indicating when the decision to perform the downlink handover was taken.

Step 1305 A point in time for performing the downlink handover is calculated. According to some embodiments, the calculation may be based on the registered current time value and the activation time value.

Step 1306 Timing information is transmitted to the radio access network 100, which timing information comprises information for establishing the calculated point in time.

The timing information may according to some optional embodiments comprise the calculated point in time. However, according to some embodiments the timing information may comprise the registered current time value such as a current connection frame number.

Step 1307

The downlink handover is initiated at the calculated point in time. Figure 14 schematically depicts an embodiment of an arrangement 1400 in a user equipment 110 for use in improving a success ratio of hard handover of a downlink connection to the user equipment 110 between ceils 121. 132 in a radio access network 100. The user equipment 110 and the radio access network 100 are capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications. The user equipment 110 may be represented by a portable communication device such as e.g. a mobile cellular telephone.

For the sake of clarity and in order not to render unnecessary complications for the reader to understand the functionality and advantages of the present method and arrangement 1400 within the user equipment 110, any internal electronics of the user equipment 110, not completely necessary for performing the present method according to steps 1301- 1307 has been omitted from Figure 14.

The arrangement 1400 comprises a receiver 1420. The receiver 1420 is adapted to receive information from the radio access network 100, authorising the user equipment 110 to take a decision on whether to initiate the downlink handover procedure.

The arrangement 1400 further comprises a deciding unit 1430. The deciding unit 1430 is adapted to decide to perform the downlink handover from a source cell 121 to a target cell 132 in accordance with the received authorisation.

Further, the arrangement 1400 comprises a calculating unit 1450. The calculating unit 1450 is adapted to calculate a point in time for performing the downlink handover and initiating downlink handover at the calculated point in time. The calculating unit 1450 may comprise a Central Processing Unit (CPU), a microprocessor, a Peripheral Interface Controller (PIC) microcontroller or any other appropriate device which may be adapted to interpret computer program instructions and processes data.

Optionally, the arrangement 1400 also may comprise a registration unit 1440. The optional registration unit 1440, which is comprised in some embodiments, may be configured to register a current time value. The current time value may be a current connection frame number for the user equipment 110. The registration may be made in response to taking the decision to perform the downlink handover. The registered current time value indicates when the decision to perform the downlink handover was taken. Further, the arrangement 1400 optionally may comprise a transmitter 1460. The transmitter 1460 may be adapted to transmit timing information to the radio access network 100, for establishing the calculated point in time. Thus the receiver of the transmitted timing information, such as e.g. the node 120, 130. 140 may establish the point in time when to perform the hand over.

In addition, the arrangement 1400 optionally may comprise a timer unit 1470, The timer unit 1470 may be adapted to measure or count the passed time.

It is to be noted that the described units 1420-1470 comprised within the arrangement 1400 in the node 110 are to be regarded as separate logical entities but not with necessity separate physical entities.

Any, some or all of the units 1420-1470 may be comprised or co-arranged within the same physical unit. However, in order to facilitate the understanding of the functionality of the arrangement 1400 in the user equipment 110. the comprised units 1420-1470 are illustrated as separate physical units in Figure 14.

As a non limiting example only, the transmitting unit 1460 and the receiving unit 1420 may according to some embodiments be comprised within one physical unit, a transceiver, which may comprise a transmitter circuit and a receiver circuit, which respectively transmits outgoing radio frequency signals and receives incoming radio frequency signals, such as e.g. voice call and/or data signals, via an antenna. The antenna may be an embedded antenna, a retractable antenna or any antenna known to those having skill in the art without departing from the scope of the present invention. The radio frequency signals transmitted between the user equipment 110 and the node 120, 130, 140 may comprise both traffic and control signals e.g., paging signals/messages for incoming calls, which are used to establish and maintain a voice call communication with another party or to transmit and/or receive data, such as SMS. e-mail or MMS messages, with other nodes 120. 130, 140.

The present methods for improving the success ratio for hard handover of a downlink connection may be implemented through one or more processors 1240 in the network node 120, 130, 140 and through one or more processors 1450 in the user equipment 110, together with computer program code for performing the functions of the methods. The program code mentioned above may also be provided as a computer program product for instance in the form of a data carrier carrying computer program code for performing the methods according to the present solution when being loaded into the processor unit. The data carrier may be a CD ROM disc, a memory stick, or any other appropriate medium such as a disk or tape that can hold machine readable data. The computer program code may furthermore be provided as pure program code on a server and downloaded to the network node 120, 130. 140 and/or user equipment 110 remotely.

Thus a computer readable medium encoded with a computer program for improving the success ratio for hard handover of a downlink connection may perform the method steps according to steps 1101 -1105.

Further, a computer readable medium is provided, encoded with a computer program for improving the success ratio for hard handover of a downlink connection to a user equipment 110 between cells 121, 132 in the radio access network 100. The user equipment 110 and the radio access network 100 being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications.

The computer program comprises computer program code configured to make a processor 1240, comprised within the network node 120, 130, 140 perform the step of transmitting to the user equipment 110 information authorising the user equipment 110 to take a decision on whether to initiate the downlink handover procedure. Also, the computer program code is configured to make the processor 1240 perform the step of receiving from the user equipment 110 information establishing a point in time for performing the downlink handover. Further, the computer program code is configured to make the processor 1240 perform the step of initiating an activation of a source cell 121 and a target cell 132 in preparation for the downlink handover prior to the established point in time. In addition, the computer program code is configured to make the processor 1240 perform the downlink handover in the radio access network 100 at the established point in time.

Thus also a computer readable medium encoded with a computer program for improving the success ratio for hard handover of a downlink connection may perform the method steps according to steps 1301-1307.

Further, a computer readable medium is provided, encoded with a computer program for improving a success ratio of hard handover of a downlink connection to the user equipment 110 between ceils 121, 132 in a radio access network 100. The user equipment 110 and the radio access network 100 being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications.

The computer program comprises computer program code configured to make a processor 1450, comprised within the user equipment 110 perform the step of receiving information from the radio access network 100 authorising the user equipment 110 to take a decision on whether to initiate the downlink handover procedure. Also, the computer program comprises computer program code configured to make a processor 1450, comprised within the user equipment 110 perform the step of deciding to perform the downlink handover from a source cell 121 to a target cell 132 In accordance with the authorisation. Further, the computer program comprises computer program code configured to make a processor 1450, comprised within the user equipment 110 perform the step of calculating a point in time for performing the downlink handover. In addition, the computer program comprises computer program code configured to make a processor 1460, comprised within the user equipment 110 perform the step of initiating downlink handover at the calculated point in time. The enumerated steps are performed when the computer program code is loaded into the processor 1450.

The present invention may be embodied as an arrangement 1200 in a network node 120, 130. 140, an arrangement 1400 in a user equipment 110, a method in a network node 120. 130, 140 a method in a user equipment 110 or computer program products. Accordingly, the present invention may take the form of an entirety hardware embodiment, a software embodiment or an embodiment combining software and hardware aspects alt generally referred to herein as a "circuit" or "module." Furthermore, the present invention may take the form of a computer program product on a compυter-usabiβ storage medium having computer-usable program code embodied in the medium. Any suitable computer readable medium may be utilized including hard disks, CD-ROMs, optical storage devices, a transmission media such as those supporting the Internet or an intranet, or magnetic storage devices.

Computer program code for carrying out operations of the present methods may be written in any arbitrary programming language such as Java®, Smalltalk or C++. However, the computer program code for carrying out the steps of the present method may also be written in any conventional procedural programming languages, such as the "C programming language and/or a lower level assembler language. The program code may execute entirely on the node 120, 130, 140, partly on the node 120, 130, 140, as a stand-alone software package, partly on the node 120. 130, 140 and partly on a remote computing device or entirely on the remote computing device. In the latter scenario, the remote computing device may be connected to the node 120, 130, 140 through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer, for example, through the Internet using an Internet Service Provider.

Furthermore, the present methods were described in part above with reference to flowchart illustrations and/or block diagrams of a network node 120. 130, 140, a user equipment 110, methods, and computer program products according to embodiments of the invention. It will be understood that each block of the various flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, may be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The terminology used in the detailed description of the particular exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the present methods and arrangements. In the drawings, like numbers refer to like elements. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Further, as used herein, the common abbreviation "e.g.", which derives from the Latin phrase "exempli gratia," may be used to introduce or specify a general example or examples of a previously mentioned item, and is not intended to be limiting of such item. If used herein, the common abbreviation "i.e.", which derives from the Latin phrase "id est," maybe used to specify a particular item from a more general recitation. The common abbreviation "etc.". which derives from the Latin expression ^*et cetera" meaning "and other things^* or "and so on" may be used herein to indicate that further features, similar to the ones that have just been enumerated, exist, which features however are well known to the person skilled in the art and for that reason omitted herein to not unnecessarily obscure the less Initiated readers comprehension of the presented subject matter.

Functions or structures which are well known to the person skilled in the art may not be described in detail for brevity and/or clarity.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms "includes," "comprises." "including" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present Furthermore, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The word "information" as used herein is to be understood as meaning not only typographical letters but may also comprise pictures, images, photos, animations, graphics, maps, multimedia, movies, film sequences, sound, engravings, music, spoken words etc. which may be used for presenting a piece of information or a message to a user. Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary ski in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealzed or overly formal sense unless expressly so defined herein.

Claims

1. Method in a node (120. 130. 140) in a radio access network (100) for use in improving a success ratio for hard handover of a downlink connection to a user equipment (110) between cells (121, 132) in the radio access network (100), the user equipment (110) and the radio access network (100) being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications, the method comprises the steps of: transmitting (1101) to the user equipment (110) information authorising the user equipment (110) to take a decision on whether to initiate the downlink handover procedure, receiving (1103) from the user equipment (110) information establishing a point in time for performing the downlink handover, initiating (1104) an activation of a source cell (121) and a target cell (132) in preparation for the downlink handover prior to the established point in time; and performing (1105) the downlink handover in the radio access network (100) at the established point in time.

2. Method according to claim 1, wherein the authorisation relates to one or more selected cells (121, 132).

3. Method according to claim 2. wherein the authorisation relates to at least one cell (121. 132) in an active set of the user equipment (110).

4. Method according to any of the previous claims 1-3, wherein the information transmitted to the user equipment (110) comprises handover trigger criteria, such as target cell preconfigυration, to be used by the user equipment (110) when taking the decision on whether to initiate the downlink handover procedure.

5. Method according to any of the previous claims 1-4, wherein the method further comprises the step of: transmitting (1102) an activation time value to the user equipment (110), the activation time value establishing a time span that is sufficient for an activation of a source cell (121) and a target cell (132) in preparation for the downlink handover.

6. Method according to any of the previous claims 1-5, wherein the information received from the user equipment (110) comprises information indicating that the user equipment (110) has taken a decision on to initiate the downlink handover procedure and identifying the target cell (132) for the downlink handover.

7. Method according to any one of the previous claims 1-6. wherein the method is performed at least partially in a node (120, 130, 140) such as a base station (120, 130) or a radio network controller (140) of the radio access network (100).

8. Arrangement (1200) in a node (120, 130, 140) in a radio access network (100) for use in improving a success ratio for hard handover of a downlink connection to a user equipment (110) between cells (121, 132) in the radio access network (100), the user equipment (110) and the radio access network (100) being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications, the arrangement ( 1200) comprises: a transmitter (1210), adapted to transmit information authorising the user equipment (110) to take a decision on whether to initiate the downlink handover procedure, to the user equipment (110), a receiver (1230), adapted to receive information from the user equipment (110). which information establish a point in time for performing the downlink handover, a computing unit (1240), adapted to initiate the activation of a source cell (121) and a target cell (132) in preparation for the downlink handover prior to the established point in time and to perform the downlink handover in the radio access network (100) at the established point in time.

9. Method in a user equipment (110) for use in improving a success ratio of hard handover of a downlink connection to the user equipment (110) between cells (121, 132) in a radio access network (100). the user equipment (110) and the radio access network (100) being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications, the method comprises the steps of: receiving (1302) information from the radio access network (100) authorising the user equipment (110) to take a decision on whether to initiate the downlink handover procedure, deciding (1303) to perform the downlink handover from a source ceil (121) to a target cell (132) in accordance with the authorisation. calculating (1305) a point in time for performing the downlink handover: and initiating (1307) downlink handover at the calculated point in time.

10. Method according to claim 9, wherein the method further comprises the step of: transmitting (1306) timing information to the radio access network (100), for establishing the calculated point in time.

11. Method according to any of the claims 9 or 10, wherein the authorisation relates to one or more selected cells (121, 132).

12. Method according to any of the claims 9-11. wherein the authorisation relates to at least one cell (121, 132) in an active set of the user equipment (110).

13. Method according to any of the previous claims 9-12, wherein the information received from the radio access network (100) comprises handover trigger criteria, such as target cell preconfiguration, to be used by the user equipment (110) when taking the decision on whether to perform the downlink handover.

14. Method according to any of the previous claims 9-13, comprising the further steps of: receiving (1301) an activation time value from the radio access network (100), the activation time value establishing a time span that is sufficient for an activation such as radio link reconfiguration and change of a MAC-d flow, of the source ceil (121) and the target cell (132) in preparation for the downlink handover, registering (1304) a current time value such as a current connection frame number for the user equipment (110) in response to taking the decision to perform the downlink handover, the current time value indicating when the decision to perform the downlink handover was taken; and wherein the step of calculating (1305) the point in time comprises calculating the point in time based on the registered current time value and the activation time value.

15. Method according to any of the previous claims 9-14, wherein the timing information comprises the calculated point in time.

16. Method according to any of the previous claims 9-15, wherein the timing information comprises the registered current time value such as a current connection frame number.

17. Arrangement (1400) in a user equipment (110) for use in improving a success ratio of hard handover of a downlink connection to the user equipment (110) between cells (121. 132) in a radio access network (100), the user equipment (110) and the radio access network (100) being capable of engaging in diversity handover, such as soft and/or softer handover, for uplink communications, the arrangement (1400) comprises: a receiver (1420). adapted to receive information from the radio access network (100) authorising the user equipment (110) to take a decision on whether to initiate the downlink handover procedure. a deciding unit (1430). adapted to decide to perform the downlink handover from a source ceil (121 ) to a target cell (132) in accordance with the authorisation. a calculating unit (1450), adapted to calculate a point in time for performing the downlink handover and initiating downlink handover at the calculated point in time.