WO2012116709A1

WO2012116709A1 - Methods and apparatuses for a handover using reserved temporal resources

Info

Publication number: WO2012116709A1
Application number: PCT/EP2010/068756
Authority: WO
Inventors: Kari Juhani Hooli; Esa Tapani Tiirola; Juha Korhonen
Original assignee: Nokia Corporation
Priority date: 2011-03-03
Filing date: 2011-03-03
Publication date: 2012-09-07

Abstract

The invention relates to apparatuses, methods and a system for performing a handover. Information about a handover need is obtained. Temporal resources for handovers are reserved based on handover need. Information on the reserved temporal handover resources is conveyed. Handovers are carried out by using the reserved temporal handover resources. The temporal resources may be random access channel resources. The reserved temporal handover resources may correspond to physical resources of a physical uplink shared channel and/or a physical uplink control channel.

Description

METHODS AND APPARATUSES FOR A HANDOVER USING RESERVED TEMPORAL RESOURCES

Field

The invention relates to apparatuses, methods, computer programs, computer program products and a computer- readable media.

Background

The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context .

Recently need for more efficient usage of radio resources has brought out an idea of co-existence or sharing of sys^¬ tems meaning that systems share operational resources, for example spectrum in a given region.

Brief description

According to an aspect of the present invention, there is provided an apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one proces^¬ sor, cause the apparatus at least to: obtain information about a handover need; reserve temporal resources for handovers based on the handover need from a physical up^¬ link shared channel; convey information on the reserved temporal handover resources, and carry out handovers by using the reserved temporal handover resources. According to another aspect of the present invention, there is provided a system, comprising: a handover source node and a handover target node, the handover source node being configured to notify the handover target node about a handover burst, and to obtain information from the handover target node, and the handover target node being configured to obtain a notification of the handover burst, reserve temporal resources for handovers based on the notification, initiate an information trans- fer to the handover source node about the reservation, and carry out handovers by using the reserved temporal hand^¬ over resources.

According to another aspect of the present invention, there is provided a method comprising: obtaining in- formation about a handover need; reserving temporal resources for handovers based on the handover need from a physical uplink shared channel; conveying information on the reserved temporal handover resources, and carrying out handovers by using the reserved temporal handover re- sources.

According to yet another aspect of the present in^¬ vention, there is provided an apparatus comprising: appa^¬ ratus comprising: means for obtaining information about a handover need; means for reserving temporal resources for handovers based on the handover need from a physical up^¬ link shared channel; means for conveying information on the reserved temporal handover resources, and means for carrying out handovers by using the reserved temporal handover resources.

According to yet another aspect of the present in^¬ vention, there is provided a computer program embodied on a computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising: obtaining informa^¬ tion about a handover need; reserving temporal resources for handovers based on the handover need from a physical uplink shared channel; conveying information on the reserved temporal handover resources, and carrying out hand^¬ overs by using the reserved temporal handover resources.

According to yet another aspect of the present in- vention, there is provided a computer-readable medium en^¬ coded with instructions that, when executed by a computer, perform: obtaining information about a handover need; reserving temporal resources for handovers based on the handover need from a physical uplink shared channel; con- veying information on the reserved temporal handover resources, and carrying out handovers by using the reserved temporal handover resources.

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 a system;

Figure 2 is a flow chart;

Figure 3 shows an example of resource usage; and

Figure 4 shows an example of an apparatus.

Description of embodiments

The following embodiments are only examples. Although the specification may refer to "an", "one", or "some" embodiment (s) in several locations, this does not necessarily mean that each such reference is to the same embodi^¬ ment (s), or that the feature only applies to a single em- bodiment . Single features of different embodiments may also be combined to provide other embodiments.

Embodiments are applicable to any user device, such as a user terminal, relay node, server, node, corre- sponding component, and/or to any communication system or any combination of different communication systems that support required functionalities. The communication system may be a wireless communication system or a communication system utilizing both fixed networks and wireless net- works. The protocols used, the specifications of communi^¬ cation systems, apparatuses, such as servers and user ter^¬ minals, especially in wireless communication, develop rap^¬ idly. Such development may require extra changes to an em^¬ bodiment. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, embodiments.

In the following, different embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution (LTE) Advanced, LTE-A, that is based on orthogonal frequency multiplexed access (OFDMA) in a downlink and a single-carrier frequency-division multiple access (SC-FDMA) in an uplink, without restricting the embodiments to such an architec- ture, however.

In an orthogonal frequency division multiplexing (OFDM) system, the available spectrum is divided into mul^¬ tiple orthogonal sub-carriers. In OFDM systems, available bandwidth is divided into narrower sub-carriers and data is transmitted in parallel streams. Each OFDM symbol is a linear combination of signals on each of the subcarriers . Further, each OFDM symbol is preceded by a cyclic prefix (CP), which is used to decrease Inter-Symbol Interference. Unlike in OFDM, SC-FDMA subcarriers are not independently modulated .

Typically, a (e)NodeB needs to know channel qual- ity of each user device and/or the preferred precoding ma^¬ trices (and/or other multiple input-multiple output (MIMO) specific feedback information, such as channel quantiza^¬ tion) over the allocated sub-bands to schedule transmis^¬ sions to user devices. Required information is usually signalled to the (e)NodeB.

Figure 1 is an example of a simplified system ar^¬ chitecture only showing some elements and functional enti^¬ ties, 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 system typically comprises also other functions and structures than those shown in Figure 1.

Figure 1 shows a part of a radio access network of E-UTRA, LTE or LTE-Advanced (LTE-A) or LTE/SAE (SAE = system architecture evolution, SAE is enhancement of packet switched technology to cope with faster data rates and growth of Internet protocol traffic) . E-UTRA is an air in^¬ terface of Release 8 (UTRA= UMTS terrestrial radio access, UMTS= universal mobile telecommunications system) . Some advantages obtainable by LTE (or E-UTRA) are a possibility to use plug and play devices, and Frequency Division Du^¬ plex (FDD) and Time Division Duplex (TDD) in the same platform.

The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with the necessary properties. Some examples of other op^¬ tions for suitable systems are the universal mobile tele^¬ communications system (UMTS) radio access network (UTRAN or E-UTRAN) , long term evolution (LTE, the same as E- UTRA) , wireless local area network (WLAN or WiFi) , world^¬ wide interoperability for microwave access (WiMAX) , Blue^¬ tooth®, personal communications services (PCS) , wideband code division multiple access (WCDMA) , code division mul^¬ tiple access (CDMA) , groupe special mobile or global sys- tern for mobile communications (GSM) , enhanced data rates for GSM evolution (GSM EDGE or GERAN) , systems using ultra-wideband (UWB) technology and different mesh networks. The embodiments are especially suitable for co-existence networks of two or more systems or layers of one or more systems. In the example of Figure 1, a multilayer sharing or resources is expected and the system producing the layer capable to use a spectrum hole is depicted.

Figure 1 shows user devices 100 and 102 configured to be in a wireless connection on one or more communica- tion channels 104, 106 in a cell with a (e)NodeB 108 pro^¬ viding the cell. The physical link from a user device to a (e)NodeB is called uplink or reverse link and the physical link from the NodeB to the user device is called downlink or forward link.

The NodeB, or advanced evolved node B (eNodeB, eNB) in LTE-Advanced, is a computing device configured to control the radio resources of communication system it is coupled to. The (e) NodeB may also be referred to a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e)NodeB includes transceivers, for instance. From the transceivers of the (e)NodeB, a connection is provided to an antenna unit that establishes bi^¬ directional radio links to user devices. The (e)NodeB is further connected to a core network 110 (CN) . Depending on the system, the counterpart on the CN side can be a serv^¬ ing system architecture evolution (SAE) gateway (routing and forwarding user data packets) , packet data network gateway (PDN GW) , for providing connectivity to user de- vices (UEs) to external packet data networks, or mobile management entity (MME) , etc.

The communication system is also able to communicate with other networks, such as a public switched telephone net^¬ work or the Internet.

The user device illustrates one type of an appara^¬ tus to which resources on the air interface may be allo^¬ cated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal or user equipment (UE) just to mention but a few names or apparatuses.

The user device typically refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM) , including, but not limited to, the following types of devices: a mobile station (mobile phone), smart- phone, personal digital assistant (PDA) , handset, laptop computer, game console, notebook, and multimedia device.

It should be understood that, in Figure 1, user devices are depicted to include 2 antennas only for the sake of clarity. The number of reception and/or transmis- sion antennas may naturally vary according to a current implementation .

Further, although the apparatuses have been de^¬ picted as single entities, different units, processors and/or memory units (not all shown in Figure 1) may be im^¬ plemented .

It is obvious for a person skilled in the art that the de^¬ picted system is only an example of a part of a radio ac^¬ cess system and in practise, the system may comprise a plurality of (e)NodeBs, the user device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the NodeBs or eNodeBs may be a Home (e) nodeB . Additionally, in a geo- graphical area of a radio communication system a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilometres, or smaller cells such as micro-, femto- or picocells. The (e)NodeB 108 of Figure 1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. Typically, in multilayer networks, one node B provides one kind of a cell or cells, and thus a plurality of node Bs are re^¬ quired to provide such a network structure.

In Figure 1, node (e) odeB 114 may be a Home (e) ode or pico or femto node. It is operably coupled 120 to the (e) NodeB 108 which may provide a macro cell or a primary communication system cell. User device 116 depicts a user device communicating with the (e) NodeB via a radio link 118. The (e)NodeB may be coupled to the core network 110 directly 122 or indirectly via another network node.

Recently for fulfilling the need for improving the deploy^¬ ment and performance of communication systems, concept of "plug-and-play" node (e)Bs has been introduced. Typically, a network which is able to use "plug-and-play" node (e)Bs, includes, in addition to Home node (e)Bs (Home (e) nodeBs) , a home node B gateway, or HNB-GW (not shown in Figure 1) . A HNB Gateway (HNB-GW) , which is typically installed within an operator's network aggregates traffic from a large number of HNBs back to a core network through Iu-cs and Iu-ps interfaces.

With increasing number of personal, local and wireless communication systems operating in a same geographical area, the questions of co-existence and inter-networking are raised. Cognitive and re-configurable radios may be a key for obtaining a heterogeneous communication environment where mitigation techniques and cognitive signalling are used for sharing the spectrum and routing information. Cognitive radios are designed to efficient spectrum use deploying so-called smart wireless devices being capable to sense and detect the environment and adapt to it thus being suitable for opportunistic spectrum usage, in which also the frequency bands not being used by their primary (usually licensed) users may be utilized by secondary us^¬ ers. For this purpose cognitive radios are designed to de^¬ tect unused spectrum, such as spectrum holes.

The heterogeneous networks may also create new interfer^¬ ence challenges due to the deployment of different wire- less nodes such as macro/micro eNBs, pico eNBs, and Home eNBs creating a multi-layer network using the same spectrum resource. In the following, some embodiments of a method for secondary spectrum use are explained in further detail by means of Figures 2 and 3. The embodiments are especially suitable for enabling system operation for a primary sys- tern when one or more secondary systems are allowed to op^¬ erate on the same physical resources in the situation of co-existence/sharing of systems. Co-existence/spectrum sharing is one of major challenges in open spectrum usage.

Another exemplary use case is network energy saving in which one or more LTE cells (that is to say carriers) may be switched on and off in a way which is advantageous in the energy saving point of view. The LTE cells may be switched off when traffic has decreased to such an amount that a reduced number of carriers may deal with the re- maining traffic.

Yet another exemplary use case is a communication service provider having multiple networks using different radio access technologies and, possibly, also multiple carriers or frequency layers with network operation and maintenance, wherein a radio resource management unit or some other corresponding network elements providing control functionalities are used commonly or in a coordinate manner. In such a case, a network element may decide to switch on or off one or more LTE cells.

Typically, in a geographical area, a system which is a licensed user has a primary user status and possible ad-hoc users or opportunistic users which are ready to use spectrum holes or corresponding resources are called sec^¬ ondary users. Secondary users are typically not allowed to cause too much interference to primary users.

If a need for transferring many or even all users from a cell exists, a handover burst is in many cases go- ing to take place, since especially in urban areas, cells are typically densely occupied. A burst of handovers may take place especially in the case, when a cell is switch on or off. Then a lot of traffic is transferred from cur- rently used resources to new ones. One example of such a situation is when LTE and legacy (in this application for example, GSM) cells coexist in a same, shared frequency layer. On the shared layer, the legacy and LTE cells are not at least completely co-located but separated by a va- cant buffer zone. Other layers may be reserved solely for the legacy system and/or LTE. LTE cells on the shared layer are switched on when GSM traffic is low and LTE traffic approaches the capacity of LTE layer or, in the absence of an LTE-specific layer, sufficient amount of LTE-capable user devices are detected. The LTE cells are switched off when more GSM capacity is needed based on a traffic load.

In this example, when an LTE cell is switched on and, in particular, switched off, user devices in the LTE cell currently using the resources to be switched off need to be handed over to other radio cells in that location. If no LTE cells are provided on other frequency layers in that location, a need for inter radio access technology (RAT) handovers exist. If LTE cells on other layers have an overlapping coverage, inter-frequency handovers within LTE system cells may be carried out. Typically, an assump^¬ tion can be made that a significant number of user devices are handed over to a same target cell.

Switching the LTE cells off will thus cause a burst of handovers with considerable amount of radio re^¬ source control signaling both in source and target cells as well as random accesses to the target cell. Further- more, motivation to minimize signaling delays regarding to these handovers exist.

When a user device performs a handover, its first transmission in a handover target cell takes place at a physical random access channel (PRACH) where random access preambles are transmitted. The user device usually re^¬ ceives parameters for the preamble transmission through a source cell. These parameters may define time and fre^¬ quency resources of PRACH and the available preamble se- quences. Additionally, a dedicated preamble sequence may be given for a non-contention based random access. A dedicated preamble sequence may be in the use of one user de^¬ vice at a time. Thus, the preamble collisions may be avoided and the user device may be identified in the tar- get cell by the preamble sequence that makes a non- contention based random access more reliable and faster than a contention based random access.

In LTE Rel. 8-10, non-contention based and contention based physical random access channel preambles are transmitted on same physical resources. The physical re^¬ sources are communicated in broadcasted system informa^¬ tion. The system information also communicates which one or ones of the totally 64 preambles are reserved for non- contention based use and cannot thus be selected by user devices for contention based access.

A random access channel (RACH) load may become substantially high during a handover burst, and a method of temporarily increasing the RACH capacity is hence needed. One option is to increase physical resources re- served for PRACH and the number of preambles reserved for non-contention based access for the duration of a handover burst. This requires changing or modifying system informa- tion and notifying user devices in the target cell about this change or modification.

User devices in a handover target cell should re^¬ ceive updated system information before extended amount of preambles for non-contention based access are used for a handover. Otherwise a risk exists that a same preamble is simultaneously used for both a handover related non- contention based random access and for a normal contention based random access. This may lead to erroneous timing measurements as well as loosing a contention based random access attempt.

When system information is changed or modified, a system information modification indicator is sent to a user device during a first broadcast control channel (BCCH) modification period and only after that transmission of updated system information is started. Additionally, the start of aBCCH modification period is restricted to particular radio frames (SFN mod modification period = 0) . Thus average delay from a (e)NodeB decision of system information change or modification to the start of updated system information transmission depends on configured modification period. Thus the increase of PRACH preambles for non-contention based access via changing or modifying system information may be seen as a slow solution causing delay to handovers. Further, the share of PRACH preambles reserved for non-contention based random access is dimensioned for typical needs in each cell and is thus usually insufficient for burst of handovers.

If a need for transferring many or even all users from a cell exists, a handover burst is in many cases go^¬ ing to take place, since especially in urban areas, cells are typically densely occupied. Embodiments provide an im- proved method for dealing with a handover burst. A shorter delay time in dealing with a handover burst is provided .

An embodiment starts in block 200 of Figure 2.

In block 202, information about a handover need is obtained. Typically, a handover source cell notifies a handover target cell about a handover need, such as a burst of handovers. Notifying may be carried out by trans^¬ mitting a handover request which then is received by the target cell.

In block 204, temporal resources for handovers are reserved based on the handover need.

In an embodiment, reserved temporal handover re^¬ sources may correspond to physical resources of a physical uplink shared channel and/or a physical uplink control channel .

For example, the handover target cell reserves from a physical uplink shared channel (PUSCH) temporal PRACH resources solely for the use of user devices to be handed over from the source cell. It should be appreciated that these temporal RACH resources are at least partially different form normal PRACH resources which are signaled as a part of normal system information in a system information block.

In block 206, information on the reserved temporal resources for handovers is conveyed. This may be carried out by signaling between a node reserving the resources and the node which needs a handover burst to be carried out. Conveyance may mean preparing a message including this information.

Typically, the target cell informs the source cell about its readiness to receive the offered new users. The information may for instance be a handover grant message that includes information about temporal PRACH resources and dedicated preambles.

The source cell is typically informed about a tem- poral RACH resource configuration. Typically, data regard^¬ ing to a handover burst, such as handover preambles, is conveyed using at least partially different physical re^¬ sources than for "normal" handover signaling. In the following, a clarifying example for the LTE-system is ex- plained in further detail:

In the LTE-system, a part of a handover command, MobilityControlInfo information element, may be transmit^¬ ted by a target cell node and is transparently forwarded to a user terminal by a source cell node. The command may contain rach-ConfigDedicated and radioResourceConfigCommon information elements, wherein the rach-ConfigDedicated in^¬ formation element defines at least one subframe and pream^¬ ble to be used by the user device in a handover, and wherein the radioResourceConfigCommon contains two infor- mation elements: rach-ConfigCommon and prach-Config that provide cell-specific PRACH parameters in the target cell. In particular, rach-ConfigCommon information element defines the number of non-dedicated preambles in a subframe used for contention based random access (RA) with num- berOfRA-Preambles , and the prach-Config information ele^¬ ments defines subframes containing PRACH with prach- Configlndex and the frequency offset of PRACH with prach- FreqOffset .

Further, in the same example, for temporal PRACH resource configuration: prach-Configlndex in prach-Config may be set to a different value than prach-Configlndex in prach-ConfigSIB, which is broadcasted as target system in- formation in order that handover PRACH burst is to be transmitted in subframes that are at least partially dif^¬ ferent from subframes used for a normal PRACH burst ac^¬ cording to the broadcasted system information.

Correspondingly, prach_FreqOffset may be set to a different value than prach_FreqOffset in prach-ConfigSIB that is broadcasted in target cell system information in order that handover PRACH burst is to be transmitted at a frequency different from a frequency used for normal PRACH burst according to the broadcasted system information.

Data field numberOfRA-Preambles may be set on tem^¬ poral PRACH resources into lower value than the num^¬ berOfRA-Preambles broadcasted by a target cell. Some preambles on temporal PRACH resources may be reserved for contention-based RA as a need may exists that some user devices making a handover carry out a random access after they have completed their handover, but before they have acquired a broadcasted configuration for the normal PRACH resources in the cell. A different numberOfRA-Preambles value on temporal and normal PRACH resources is possible even in the case of temporal and normal PRACH resources being partially overlapping, since data field rach- ConfigDedicated controls both the preamble and subframe to be used in non-contention based random access (RA) .

In block 208, handovers are carried out by using the reserved temporal handover resources. The handovers may otherwise be carried out by using a "normal" handover procedure of the current radio protocol, but the resources used for this purpose are at least partly the reserved temporal resources.

It should be understood that starting from the be^¬ ginning of a handover burst a target cell may avoid unnec- essary interference on the temporal PRACH by not schedul^¬ ing PUSCH resources corresponding to temporal PRACH resources .

Typically, after a handover, temporal PRACH re- sources are released to their normal use. Thus, temporal RACH resources may be returned to a normal PUSCH use by rescheduling. The user device is required to acquire broadcasted system information, and overwrite any stored system information. Thus, the user device begins to use normal PRACH resources after it has acquired Systemlnfor- mationBlockType2-information which carries a radioResour- ceConfigCommon data field.

Thus, the target cell may re-schedule PUSCH used as temporal PRACH resources after the handovers are com- pleted and sufficient time for devices to acquire Sys- temlnformationBlockType2 information has passed.

An example is illustrated in Figure 3. The example is only used for clarification purposes and is non- limiting of a nature. The example illustrates how a hand- over burst may be started earlier than using conventional handover methods, as temporal PRACH 302 resources may sim^¬ ply be created by PUSCH scheduling instead of system information change or modification. The delay from the moment when a source cell indicates a need for a handover burst to the beginning of the handover burst is only caused by signaling between a target cell and source cell and radio resource controlling signaling between a source cell and user device. This delay is similar to a "normal" handover signaling even if a large number of handovers is taken care o in the case of a handover burst. Furthermore, the temporal PRACH resources for dedicated preambles may be released earlier as the delay after the handover burst is caused by system information blocks SIB1 and SIB2 acquisition and application by the user device, not by broadcast control channel (BCCH) modification involving modification periods 306 (arrows with two heads illustrate the periods) . The conventional BCCH modification typically causes a delay (i.e. 1½ modification periods with uniform time distribution for (e)NB decision) that as an average ranges from 480 ms to over 30 seconds in other extreme.

In Figure 3, normal PRACH resources are depicted as 300, the temporal PRACH resources as 302 and timing of a handover burst as 310. Block 304 shows when a source cell indicates the need for a handover burst to a target cell. Part of temporal PRACH resources marked as 308 de^¬ picts the time needed for user devices carrying out hand- overs to acquire and apply SIB1 and SIB2 via BCCH.

The example described above is also suitable for devices supporting earlier LTE generations back to Release 8 as long as the temporal RACH handover resources are not overlapping in time with normal RACH resources. However, if handover preambles are transmitted by using same sub frames, devices supporting these earlier standards may not allow a target cell to send separate responses for hand^¬ over preambles and for preambles that have been sent on a regular PRACH. A message of preamble responses may be ad- dressed by using an identity that is a so called random access radio network temporary identifier (RA-RNTI) that according to earlier LTE specifications is obtained by a fixed mapping from the PRACH resource index. For instance, if one regular PRACH resource per a subframe of an FDD system is provided, RA-RNTI values from 1 to 10 are in use. Thus, if a user device transmits a preamble in sub- frame n (n can have a value from 0 to 9) , it typically searches a response addressed with RA-RNTI value n+1 irre^¬ spective of prach-FreqOffset value. One possibility to en^¬ able the separation of responses to handover preambles from responses to "normal" preambles is defining different mappings from PRACH resources to random access radio net^¬ work temporary identifier (RA-RNTI) for the temporal and/or "normal" RACH resources. The difference may be an offset defined in a standard or given by a handover target cell. Such an offset would even make possible code divi- sion multiplexing of temporal and regular PRACH by reusing time and frequency resources and defining a different pre^¬ amble set for handovers .

A handover burst typically takes place in the situation when at least one cell is going to be switched off as described above. After the handover burst, a source cell may stop transmitting common channels and a common reference signal in the downlink. After that the source cell is considered to be switched off.

Some other signaling may be used as well to en- hance camping of idle user devices in a target cell: up^¬ dating inter-frequency neighbouring cell list on neighbouring cells, changing frequency layer priorities and/or frequency layer-specific reselection parameters for transferring camping idle user devices to other cells, and/or configuring a cell to be barred.

It is also possible to prevent new user devices entering a source cell (that is the cell to be switched off) : updating inter-frequency neighbouring cell list on neighboring cells, refusing handover requests, and/or not responding to PRACH after the last handover of the burst is completed. Embodiments may be used for some other purposes as well. For example for energy saving: handing over a considerable amount of user devices from one cell to another one in a short period of time enable a shorter switch-off time for the cell to be emptied.

The embodiment ends in block 210. The embodiment is repeatable and one option for repetition is shown with arrow 212. Other options are naturally also possible.

It should be appreciated that reception formats typically corresponds to transmission formats.

The steps/points, signaling messages and related functions described above in Figures 2 and 3 are in no absolute chronological order, and some of the steps/points may be performed simultaneously or in an order differing from the given one. Other functions can also be executed between the steps/points or within the steps/points and other sig^¬ naling messages sent between the illustrated messages.

Some of the steps/points or part of the steps/points can also be left out or replaced by a corresponding step/point or part of the step/point.

It should be understood that transmitting and/or receiving may herein mean preparing a transmission and/or reception, preparing a message to be transmitted and/or received, or physical transmission and/or reception itself, etc on a case by case basis. In an embodiment, a server, node or host may convey information on reserved temporal handover resources. This conveyance may or may not include trans^¬ mission and/or reception.

In the following an example of a system where embodiments may be applied to is explained in further detail by means of Figure 1. The system includes at least two nodes of which two are depicted .

In this example, (e)NodeB 108 is a source cell node and node 114 is a target cell node. The node 114 may be an (e)NodeB or a base station or any suitable network element generating a radio cell. The rest of the network which the node 114 belongs to, is not shown, since the structure of the network is not relevant in this context. In Figure 1, only one user device 116 having a radio connection 118 with the node 114 is shown for the sake of clarity. It is obvious for a skilled person that typically, a plurality of user devices exists in the cell, some of them having a radio resource connection to the serving node and some of them being in an idle mode. The (e)NodeB 108 and the node 114 are operably coupled to each other which is depicted by arrow 120.

If a need for transferring many or even all users from a cell exists, a handover burst is in many cases going to take place, since especially in urban areas, cells are typically densely occupied. Then, in an embodiment, a source cell notifies a target cell about a large handover burst. The target cell reserves temporal resources for handovers from a physical uplink shared channel based on the handover burst information and initiates an informa- tion transfer about the reservation to the source cell. The source cell obtains the information and the target cell carries out handovers by using the reserved temporal handover resources. Further details and non-limiting examples of embodiments are described above in relation to Figures 2 and 3.

An embodiment provides an apparatus which may be any node, host, server or any other suitable apparatus able to carry out processes described above in relation to Figures 2 and 3.

Figure 4 illustrates a simplified block diagram of an ap^¬ paratus according to an embodiment. It should be appreci- ated that the apparatus may also include other units or parts than those depicted in Figure 4. Although the appa^¬ ratus has been depicted as one entity, different modules and memory (one or more) may be implemented in one or more physical or logical entities.

The apparatus 400 may in general include at least one processor, controller or a unit designed for carrying out control functions operably coupled to at least one memory unit and to various interfaces. Further, a memory unit may include volatile and/or non-volatile memory. The memory unit may store computer program code and/or operating systems, information, data, content or the like for the processor to perform operations according to embodiments. Each of the memory units may be a random access memory, hard drive, etc. The memory units may be at least partly removable and/or detachably operationally coupled to the apparatus .

The apparatus may be a software application, or a module, or a unit configured as arithmetic operation, or as a program (including an added or updated software rou- tine), executed by an operation processor. Programs, also called program products or computer programs, including software routines, applets and macros, can be stored in any apparatus-readable data storage medium and they in^¬ clude program instructions to perform particular tasks. Computer programs may be coded by a programming language, which may be a high-level programming language, such as objective-C, C, C++, Java, etc., or a low-level program- ming language, such as a machine language, or an assem^¬ bler .

Modifications and configurations required for im^¬ plementing functionality of an embodiment may be performed as routines, which may be implemented as added or updated software routines, application circuits (ASIC) and/or pro^¬ grammable circuits. Further, software routines may be downloaded into an apparatus. The apparatus, such as a node device, or a corresponding component, may be config- ured as a computer or a microprocessor, such as a single- chip computer element, or as a chipset, including at least a memory for providing storage capacity used for arithme^¬ tic operation and an operation processor for executing the arithmetic operation.

As an example of an apparatus according to an em^¬ bodiment, it is shown an apparatus, such as a node device, including facilities in a control unit 404 (including one or more processors, for example) to carry out functions of embodiments according to Figures 2 and 3. This is depicted in Figure 4.

The apparatus may also include at least one proc^¬ essor 404 and at least one memory 402 including a computer program code, the at least one memory and the computer program code configured to, with the at least one proces- sor, cause the apparatus at least to: obtain information about a handover need, reserve temporal resources for handovers based on the handover need from a physical up^¬ link shared channel, convey information on the reserved temporal handover resources and carry out handovers by us- ing the reserved temporal handover resources.

Another example of an apparatus comprises means 404 for obtaining information about a handover need, means 404 for reserving temporal resources for handovers based on the handover need from a physical uplink shared channel, means 404 (406) for conveying information on the reserved temporal handover resources and means 404 for car- rying out handovers by using the reserved temporal hand^¬ over resources.

Yet another example of an apparatus comprises an informa^¬ tion unit configured to obtain information about a hand^¬ over need, a reserving unit configured to reserve temporal resources for handovers based on the handover need from a physical uplink shared channel, a conveyance unit config^¬ ured to convey information on the reserved temporal hand^¬ over resources, and a handover unit configured to carry out handovers by using the reserved temporal handover re- sources.

Embodiments of Figures 2 and 3 may be carried out in proc^¬ essor or control unit 404 possibly with aid of memory 402 as well as a transmitter and/or receiver 406.

It should be appreciated that different units may be implemented as one module, unit, processor, etc, or as a combination of several modules, units, processor, etc.

It should be understood that the apparatuses may include other units or modules etc. used in or for trans^¬ mission. However, they are irrelevant to the embodiments and therefore they need not to be discussed in more detail herein. Transmitting may herein mean transmitting via antennas to a radio path, carrying out preparations for physical transmissions or transmission control depending on the implementation, etc. The apparatus may utilize a transmitter and/or receiver which are not included in the apparatus itself, such as a processor, but are available to it, being operably coupled to the apparatus. This is depicted as an option in Figure 4 as a transceiver 406. Embodiments provide computer programs embodied on a dis^¬ tribution medium, comprising program instructions which, when loaded into electronic apparatuses, constitute the apparatuses as explained above.

Other embodiments provide computer programs embodied on a computer readable medium, configured to control a proces^¬ sor to perform embodiments of the methods 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, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers in- elude a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and 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 techniques described herein may be implemented by various means. For example, these techniques may be imple^¬ mented in hardware (one or more devices) , firmware (one or more devices) , software (one or more modules) , or combina- tions thereof. For a hardware implementation, the appara^¬ tus may be implemented within one or more application spe^¬ cific integrated circuits (ASICs) , digital signal proces^¬ sors (DSPs) , digital signal processing devices (DSPDs) , programmable logic devices (PLDs) , field programmable gate arrays (FPGAs) , processors, controllers, micro^¬ controllers, microprocessors, other electronic units de^¬ signed to perform the functions described herein, or a combination thereof. For firmware or software, the imple^¬ mentation can be carried out through modules of at least one chip set (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the compo- nents of systems described herein may be rearranged and/or complimented by additional components in order to facili^¬ tate achieving the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept may be imple^¬ mented 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 comprising:

at least one processor and at least one memory including a 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:

obtain information about a handover need;

reserve temporal resources for handovers based on the handover need;

convey information on the reserved temporal handover re^¬ sources, and

carry out handovers by using the reserved temporal hand^¬ over resources.

2. The apparatus of claim 1, wherein the temporal re^¬ sources are random access channel resources.

3. The apparatus of any of preceding claim, wherein the reserved temporal handover resources correspond to physi- cal resources of at least one of the following uplink channel: a physical uplink shared channel and physical up^¬ link control channel.

4. The apparatus of any preceding claim, wherein the temporal resources are physical random access resources and information element prach-Configlndex in prach-Config is set to a different value than information element prach-Configlndex in prach-ConfigSIB for handover physical random access data to be conveyed in sub frames that are at least partially different from sub frames used for nor^¬ mal physical random access data.

5. The apparatus of any preceding claim, wherein the temporal resources are physical random access resources and information element prach_FreqOffset is set to a dif^¬ ferent value than information element prach_FreqOffset in prach-ConfigSIB for handover physical random access data to be conveyed at a frequency different from frequency used for normal physical random access data.

6. The apparatus of claims 4 or 5, wherein mappings from a physical random access channel resource to a random access radio network temporary identifier are different for temporal and normal random access resources.

7. The apparatus of any preceding claim, wherein af- ter the handovers, the temporal resources are physical up^¬ link shared channel resources, and they are returned to a normal physical uplink shared channel use by rescheduling.

8. The apparatus of any preceding claim, the apparatus comprising a server, host or node device.

9. A computer program comprising program instructions which, when loaded into the apparatus, constitute the mod^¬ ules of any preceding claim 1 to 7.

10. A system, comprising:

a handover source node and a handover target node, the handover source node being configured to notify the handover target node about a handover burst, and to obtain information from the handover target node, and the handover target node being configured to obtain a no^¬ tification of the handover burst, reserve temporal re^¬ sources for handovers based on the notification, initiate an information transfer to the handover source node about the reservation, and carry out handovers by using the re^¬ served temporal handover resources.

11. A method comprising:

obtaining information about a handover need;

reserving temporal resources for handovers based on the handover need from a physical uplink shared channel,;; conveying information on the reserved temporal handover resources, and

carrying out handovers by using the reserved temporal handover resources.

12. The method of claim 11, wherein the temporal re^¬ sources are random access channel resources.

13. The method of any preceding claim 11 to 12, wherein the reserved temporal handover resources corre^¬ spond to physical resources of at least one of the follow^¬ ing uplink channel: a physical uplink shared channel and physical uplink control channel.

14. The method of any preceding claim 11 to 13, wherein the temporal resources are physical resources re^¬ served for a physical random access channel and for preairv bles reserved for non-contention based access.

15. The method of any preceding claim 11 to 14, wherein the temporal resources are physical random access resources and information element prach-Configlndex in prach-Config is set to a different value than information element prach-Configlndex in prach-ConfigSIB for handover physical random access data to be conveyed in sub frames that are at least partially different from sub frames used for normal physical random access data.

16. The method of any preceding claim 11 to 15, wherein the temporal resources are physical random access resources and information element prach_FreqOffset is set to a different value than information element

prach_FreqOffset in prach-ConfigSIB for handover physical random access data to be conveyed at a frequency different from frequency used for normal physical random access data .

17. The method of claims 15 or 16, wherein mappings from a physical random access channel resource to a random access radio network temporary identifier are different for temporal and normal random access resources.

18. The method of any preceding claim 11 to 17, wherein after the handovers, the temporal resources are physical uplink shared channel resources, and they are re^¬ turned to a normal physical uplink shared channel use by rescheduling .

19. An apparatus comprising:

means for obtaining information about a handover need; means for reserving temporal resources for handovers based on the handover need from a physical uplink shared chan- nel;

means for conveying information on the reserved temporal handover resources, and

means for carrying out handovers by using the reserved temporal handover resources.

20. A computer program embodied on a computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising:

obtaining information about a handover need; reserving temporal resources for handovers based on the handover need from a physical uplink shared channel;

conveying information on the reserved temporal handover resources, and

carrying out handovers by using the reserved temporal handover resources.

21. The computer program of claim 20, wherein the temporal resources are random access channel resources.

22. The computer program of any preceding claim 20 to

21, wherein the reserved temporal handover resources cor^¬ respond to physical resources of at least one of the fol^¬ lowing uplink channel: a physical uplink shared channel and physical uplink control channel.

23. The computer program of any preceding claim 20 to

22, wherein the temporal resources are physical resources reserved for a physical random access channel and for pre- ambles reserved for non-contention based access.

24. The computer program of any preceding claim 20 to

23, wherein the temporal resources are physical random ac^¬ cess resources and information element prach-Configlndex in prach-Config is set to a different value than informa^¬ tion element prach-Configlndex in prach-ConfigSIB for handover physical random access data to be conveyed in sub frames that are at least partially different from sub frames used for normal physical random access data.

25. The computer program of any preceding claim 20 to

24, wherein the temporal resources are physical random ac^¬ cess resources and information element prach_FreqOffset is set to a different value than information element

26. The computer program of claims 24 or 25, wherein mappings from a physical random access channel resource to a random access radio network temporary identifier are different for temporal and normal random access resources.

27. The computer program of any preceding claim 20 to

26, wherein after the handovers, the temporal resources are physical uplink shared channel resources, and they are returned to a normal physical uplink shared channel use by rescheduling .

28. A computer-readable medium encoded with instruc^¬ tions that, when executed by a computer, perform:

obtaining information about a handover need;

reserving temporal resources for handovers based on the handover need from a physical uplink shared channel;

conveying information on the reserved temporal handover resources, and

carrying out handovers by using the reserved temporal handover resources.