WO2019138155A1

WO2019138155A1 - Controlling autonomous or conditional handover

Info

Publication number: WO2019138155A1
Application number: PCT/FI2018/050985
Authority: WO
Inventors: Mikko SÄILY; Tommi Jokela; Timo Koskela; Ingo Viering
Original assignee: Nokia Technologies Oy
Priority date: 2018-01-11
Filing date: 2018-12-31
Publication date: 2019-07-18

Abstract

A technique includes receiving a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure; receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and performing the autonomous or conditional handover procedure triggered by the handover command, including: detecting a decrease in a radio link condition; carrying out an urgent cell access procedure based on the configuration; and carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

Description

CONTROLLING AUTONOMOUS OR CONDITIONAL HANDOVER

BACKGROUND OF THE INVENTION

This invention relates to communications.

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.

In 5G, a new type of a handover procedure, namely“conditional handover” is designed to be used in high demanding services to cope with sudden signal strength drops expected to occur due to e.g. user mobility and very high frequency band usage in 5G. In this“conditional Handover”, also called a“UE autonomous handover”, a network prepares the handover in a similar fashion as in the Long Term Evolution (LTE) standard. However, a user device does not immediately access a target cell, instead, it decides the exact point in time to access the target cell, potentially based on a condition provided by the network.

BRIEF SUMMARY OF THE INVENTION

According to an aspect, a method includes receiving a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure; receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and performing the autonomous or conditional handover procedure triggered by the handover command, including: detecting a decrease in a radio link condition; carrying out an urgent cell access procedure based on the configuration; and carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

According to another aspect, an apparatus includes 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: receive a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure; receive a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and perform the autonomous or conditional handover procedure triggered by the handover command, including being configured to: detect a decrease in a radio link condition; carry out an urgent cell access procedure based on the configuration; and carry out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

According to another aspect, an apparatus includes means for receiving a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure; means for receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and means for performing the autonomous or conditional handover procedure triggered by the handover command, including: means for detecting a decrease in a radio link condition; means for carrying out an urgent cell access procedure based on the configuration; and means for carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

According to another aspect, a non-transitory computer-readable storage medium includes instructions stored thereon that, when executed by at least one processor, are configured to cause a computing system to at least: receive a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure; receive a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and perform the autonomous or conditional handover procedure triggered by the handover command, including being configured to: detect a decrease in a radio link condition; carry out an urgent cell access procedure based on the configuration; and carry out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

The apparatus may further comprise a radio unit for carrying out communications on a radio path.

According to yet another aspect, there is provided a computer program, comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out: receiving a configuration for being used in case of decrease in a radio link condition during an autonomous or conditional handover procedure; receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; during the autonomous or conditional handover procedure triggered by the handover command, detecting decrease in radio link condition, and carrying out an urgent cell access procedure based on the configuration and carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

Further aspects may include, for example:

The urgent cell access procedure may be controlled by using a third timer which is started when a first timer controlling the cell access with regard to the autonomous or conditional handover procedure has started and when at least one second timer controlling a radio link re-establishment with regard to the radio link failure has started.

The configuration may include a reduced number of cells to be measured compared to a normal configuration for the autonomous handover, conditional handover or a normal handover procedure.

The configuration may include an adapted filter for speeding up a measurement procedure with regard to the urgent cell access procedure.

The method may include ending the autonomous or the conditional handover procedure, wherein the ending comprises informing a handover source node about the completion of the autonomous handover procedure.

The method may include ending the autonomous or the conditional handover procedure, wherein the ending comprises stopping at least one of the following: the first timer and the at least one second timer provided they are running after the carrying out the cell access.

The details of one or more examples of implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings/figures, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 illustrates an example of a system;

FIG. 2 is a flow chart;

FIG. 3 depicts an example; FIG. 4 illustrates an example of an apparatus.

DETAILED DESCRIPTION

In the following, different exemplifying 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 advanced (LTE Advanced, LTE-A) or new radio (NR, 5G), without restricting the embodiments to such an architecture, however. It is obvious for a person skilled in the art that the embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (ETTRAN or E-UTRAN), long term evolution (LTE, the same as E-UTRA), wireless local area network (WLAN or WiFi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (EWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

FIG. 1 depicts examples of simplified system architectures only showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in FIG. 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 FIG. 1.

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 necessary properties.

The example of FIG. 1 shows a part of an exemplifying radio access network.

FIG. 1 shows user devices 100 and 102 configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB) 104 providing the cell. The physical link from a user device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the user device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point, etc. entity suitable for such a usage. A communications system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signalling purposes. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as 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/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to core network 1 10 (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of user devices (UEs) to external packet data networks, or mobile management entity (MME), etc.

The user device (also called EGE, user equipment, user terminal, terminal device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self- backhauling relay) towards the base station.

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), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, and multimedia device. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may also be a device having capability to operate in Internet of Things (IoT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to -human or human-to-computer interaction. The user device may also utilise cloud. In some applications, a user device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The user device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equipment functionalities. 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.

Various techniques described herein may also be applied to a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals.

Additionally, although the apparatuses have been depicted as single entities, different units, processors and/or memory units (not all shown in FIG. 1) may be implemented.

5G enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. 5G mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine -type communications (mMTC), including vehicular safety, different sensors and real time control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integrable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet 1 12, or utilise services provided by them. The communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in FIG. 1 by“cloud” 114). The communication system may also comprise a central control entity, or a like, providing facilities for networks of different operators to cooperate for example in spectrum sharing.

Edge cloud may be brought into radio access network (RAN) by utilizing network function virtualization (NVF) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU 104) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU 108).

It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent. Some other technology advancements probably to be used are Big Data and all-IP, which may change the way networks are being constructed and managed. 5G (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or nodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well. 5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine -to -machine (M2M) or Internet of Things (IoT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilise geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 106 in the mega-constellation may cover several satellite-enabled network entities that create on-ground cells. The on-ground cells may be created through an on ground relay node 104 or by a gNB located on-ground or in a satellite.

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)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 (e/g)NodeBs or may be a Home(e/g)nodeB. Additionally, in a geographical 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 kilometers, or smaller cells such as micro-, femto- or picocells. The (e/g)NodeBs of FIG. 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 access node provides one kind of a cell or cells, and thus a plurality of (e/g)NodeBs are required to provide such a network structure.

For fulfilling the need for improving the deployment and performance of communication systems, the concept of“plug-and-play” (e/g)NodeBs has been introduced. Typically, a network which is able to use “plug-and-play” (e/g)NodeBs, includes, in addition to Home (e/g)NodeBs (H(e/g)nodeBs), a home node B gateway, or HNB-GW (not shown in FIG. 1). A HNB Gateway (HNB-GW), which is typically installed within an operator’s network may aggregate traffic from a large number of HNBs back to a core network.

In 5G, a new type of a handover procedure, namely“conditional handover” is designed to be used in high demanding services to cope with sudden signal strength drops expected to occur due to e.g. user mobility and very high frequency band usage in 5G. In this“conditional Handover”, also called a“EGE autonomous handover”, a network prepares the handover in a similar fashion as in the Long Term Evolution (LTE) standard. However, a user device does not immediately access the target cell, instead, it decides the exact point in time to access the target cell, potentially based on a condition provided by the network.

Once such a condition is fulfilled (or a UE internal condition) and configured event expires for one of the pre-configured targets, the UE will access this target without any further instruction from the network. Optionally, the UE can indicate to the source cell A that it will leave it. On one hand, this would obviously be helpful since the source cell can stop transmission and initiate the packet forwarding. On the other hand, this indication may not reach the source cell in the case of significant mobility or in the case the uplink quality of source cell is not sufficient. If such an indication is not used, or does not reach the source cell, the target cell, right after identifying the random access channel (RACH) message, will send a similar indication to start packet forwarding.

In the following, LTE terminology is used for the sake of simplicity and it should not be taken as limiting to the implementation of embodiments.

A typical example for such a condition (to perform a conditional handover to a preconfigured target cell) could be an event similar to A3 measurement reporting event in the LTE:

MT + CIOcHO > Ms + offcHO ( 1 )

where MT is the measurement of the preconfigured target, Ms is the measurement of the serving cell, offcHO is an offset value (also called HO hysteresis or HO margin), and CIO_CHO is a cell individual offset.

The event expires if the condition above is fulfilled for a certain time to trigger TTT_CHO. A similar condition (as depicted in Equation (1)) may be used for reporting potential candidate cells to a network (the network decides on whether to preconfigure reported cell for the conditional handover). Alternative events, such as A4 (when a cell becomes better than an absolute threshold), may also be considered.

The switching condition must still be reliable and the erroneous condition expiry must be avoided, i.e. the measurements have to be valid and thus shall use conservative L3 filtering, TTT_cHO and offset/ C/O. An erroneous expiry will lead to a lot of unnecessary signaling. It may also lead to ping-pong handovers and even to failures, if the selected cell has no stable radio conditions. A user device may detect a radio link failure, when one or more targets have already been configured and before the switching condition expires. This can happen for example in significant mobility / heavy shadowing, i.e. the channel degrades fast compared with the used filter coefficients and time to triggers, when radio link failure (RLF) timer T310 (in the LTE, corresponding timer may have been named differently in other standards, T310 should be only taken as a clarifying example) may have been started before the cells were pre-configured, and/or at higher frequencies, where the communication between a user device (UE) and network may be done using narrow high gain beams, the link quality can change rapidly due to changes in the radio environment e.g. beam blockage. Other examples are T310 being very short in the case of a time to trigger being long and/or filtering with regard to a switching event, or a trigger offset being non-optimal.

A radio link failure leads to a radio resource control (RRC) connection re-establishment attempt. Such a re-establishment would comprise cell identification, system information reading, and a contention based RACH (random access) procedure. This approach introduces loss of already available information and in case re-establishment procedure fails, will lead state transition to RRC IDLE and loss of connection.

It should be understood that transmission was already poor or even impossible during the runtime of the RLF timer T310. It is not possible to connect to a new cell because the user device waits until the T310 expires, although one of the preconfigured targets is a suitable cell and good for communication.

Additionally, typically, a measurement event triggers only a measurement report for a configured measurement object (e.g., carrier) and it is up to a network to decide on further actions. This introduces additional latency via processing delay at radio access network (RAN) node and via further signaling steps, which also are in the risk of failing due to already poor radio conditions.

In the following, embodiments enabling an autonomous or conditional handover with improved reliability are explained.

One embodiment starts in block 200 of FIG. 2. This embodiment is suitable for being carried out by a user device or as a service in cloud reachable by a user device, for instance.

As used or described herein, the terms receiving, transmitting, conveying, etc., may mean or include one or more of a physical activity, carried out for example over the radio interface, preparation of a message for transmission, or detecting a received message, etc., depending on the implementation.

In block 202, a configuration (typically from a serving/handover source access node, but it is possible that there might be co-operation between access nodes and then this configuration may be received from some other access node) is received for being used in case of decrease in radio link condition during an autonomous or conditional handover procedure.

In one embodiment, the configuration may comprise a condition or a trigger to be used when a radio link failure (RLF) is detected, or when RLF timer T310 has been started after detecting a decrease in a radio link condition (radio link problem). The detection may be based on comparing a measured value to a preconfigured threshold. No result measurement report(s) from a user device to a source cell are triggered, but instead the user device starts autonomous handover to the target cell. Thus, the event can be considered as an emergency trigger or urgent handover trigger causing a cell access (a contention free access) towards the already prepared target cell.

Thus, a user device may receive a handover command from an access node pre-configuring at least one target cell, comprising two switching event configurations:

The first event may be a conventional trigger event, e.g. an“A3-like” condition with conservative parameters as described in prior-art.

The second event may be a trigger event or condition valid only for prepared target cells for conditional handover. The event may be triggered when one of the pre-configured targets exceeds a certain threshold T_CHO for a certain (short) time to trigger TTTaio_, short, i.e., M_T> T_CHO, including also the case of TTTcHO, short = 0 with immediate triggering. The second event may only be evaluated, if a decrease in a radio link condition (radio link problem) has been detected, e.g. RLF timer T310 is already running.

The switching may comprise a contention free access to at least one pre-configured target cell, where system information is available via a handover command.

Additionally, the configuration may comprise a reduced number of cells to be measured compared to a normal configuration for the autonomous handover, conditional handover or a normal handover procedure and/or an adapted filter (with decreased number of coefficients) for speeding up a measurement procedure with regard to the urgent cell selection procedure. The selection of cells to be measured as well as the filter adaptation may be based on the measurements the user device reported to the access node triggering transmission of the handover command for the autonomous or conditional handover procedure. The cells to be measured may be those found the most strongest ones that may fulfill additional conditions as well, such as the load information, size compared to the mobility of the user device (to avoid ping-pong) and/or services available, etc. For instance, stationary IoT/mMTC devices have likely only few candidates. In filter adaptation, normal methods for configuring filter coefficients may be used. However, because the cells to be measured are known to be able to provide adequate radio links, the filters may be shortened without a remarkable deterioration is detection.

The autonomous or conditional handover is typically controlled by a timer or a time-offset.

In block 204, a handover command comprising parameters for a contention-free access with regard to the autonomous or conditional handover procedure from a handover source node is received.

The parameters may be normal access parameters needed for a contention-free access with regard to a handover.

It should be understood that messages described in blocks 202 and 204 can also be combined in one message. In other words, the configuration of block 202 can be sent in advance in a separate message or in the same message with the parameters for a contention-free random access procedure of block 204. Some latency benefits may be obtained with transmitting only one message, on the other hand, configuration may be sent in advance, for example for enabling the user device to carry out additional measurements for the handover based on the configuration. It is also possible that the configuration is sent from some other node than the handover source node based on collaboration between nodes (especially in small cell network configurations, for example the configuration is transmitted from a macro cell while the serving ccll/handovcr source node is a small cell node).

In block 206, a decrease in radio link condition (in a handover source cell) is detected during the autonomous or conditional handover procedure triggered by the handover command.

For a radio link failure detection, a user device monitors a radio link as configured. The user device may detect the risk of a radio link failure (RLF) based on finding that the measured reference signal received power (RSRP) is too low (under a certain limit or threshold), measured signal-to-noise-ratio is too low (under a certain limit or threshold), hypothetical physical downlink control channel (PDCCH) block error rate (BLER) is above a threshold value, it failed to decode a PDCCH signal due to low power or signal quality and/or it failed to decode a physical downlink shared channel (PDSCH) signal due to low power or signal quality.

The radio link failure is typically controlled by a timer. In LTE, it is based on the expiry of timer T310 (this timer is started when physical layer problems are detected, i.e., upon receiving a pre defined number of consecutive out-of-sync indications from lower layers), for instance.

It should be understood that the user device has not yet carried out a handover, since it can itself decide on the timing of the autonomous or conditional handover(based on a network configured trigger, see block 202).

In block 208, an urgent cell access procedure based on the configuration and a cell access to a cell selected in the urgent cell access procedure are carried out based on the parameters.

The cell access procedure may be triggered in response to the detection of the risk of a radio link failure. In an example implementation, no additional measurement report(s) are transmitted to a source cell.

The parameters (for a cell access with regard to the autonomous or conditional handover procedure) may be normal access parameters needed for a cell access with regard to a handover. The cell access in relation to an autonomous or conditional handover may be a contention-free access as in the LTE or any corresponding access procedure to a handover target cell. In a contention free-based random access procedure, specific access resources are allocated to user devices. A user device is in a connect state (having a radio connection) when carrying out a handover. A handover may be seen as a radio connection reconfiguration.

The urgent cell access procedure may be controlled by using a special (third) timer which is started when the (first) timer controlling a cell access (to a pre-configured target cell) with regard to the autonomous or conditional handover procedure has started and when the at least one (second) timer controlling a radio link re-establishment with regard to the radio link failure has started (the radio link failure as well as the re-establishment procedure are typically controlled by timers). Radio resource control (RRC) re-establishment is a mechanism to perform a radio link recovery after a radio link failure has occurred. The urgent cell access procedure may be carried out as a normal target cell access with regard to a handover. “Urgent” depicts herein the handover procedure being speeded up compared to a conventional procedure for enabling a more reliable handover procedure and minimizing data interruption due to a connection outage.

It should be appreciated that the cell selection may be based on measuring pre-configured cells announced in the configuration message of block 202. The use device already has a priori information on the pre-configured cells for measurements. In dense deployments, usually, several candidate cells are provided. Carrying out measurements is beneficial especially in the case some time passes between the handover command the actual access to a handover target cell, since the radio channel may have been changed in between. However, it is also possible that the user device only picks up, for example, the first cell in the list of candidates when in urgency. If the handover does not succeed, the user device may pick up a second cell, etc.

After the autonomous or conditional handover has been carried out, the procedure may be stopped by signaling and/or by stopping non-extended timers. The signaling may comprise informing the source node about the completion of the autonomous handover procedure and/or stopping the (first) timer controlling the autonomous or conditional handover procedure and/or the at least one (second) timer controlling a radio link re-establishment with regard to the radio link failure provided they are running after the carrying out the cell access to the new cell. The stopping the timers may save resources. Additionally, the timers are then ready for controlling new procedures without a delay involved.

The embodiment ends in block 210. The embodiment is repeatable.

In the following, some timing examples with regard to FIG. 2 are explained by means of FIG. 3. Timers of the LTE are used as examples for clarification purposes, but they are not limiting to the implementation of the embodiments.

In FIG. 3, arrow 300 depicts the time axis. Dotted line 302 shows when a command for an autonomous or conditional handover is received by a user device. The command comprises information on pre-configured target cells and on two contention-free switching procedures (TTT (A3) and T310 conditioned TTT (A4) in this example). Dotted line 304 shows when TTT (A3) starts, i.e. the A3 condition is fulfilled. Dotted line 306 depicts the time when T310 is started because of a radio link problem (in the LTE, for example, N310 consecutive out of sync messages are received from lower layers) which may predict a radio link failure. In the case T310 has started, the T310 conditioned A4 event is evaluated. If the A4 condition expires (dotted line 308), timer TTT (A4) is started for enabling a shorter delay in proceeding to a handover to a new cell. Without timer TTT (A4) no actions are taken until TTT (A3) expires. With timer TTT (A4) a contention-free switching is started after a shorter delay as shown by dotted line 310.

T312 can be configured to trigger a contention-based re-establishment. Without T312 re establishment is triggered when T310 expires and with T312 the re-establishment is triggered when T312 expires (dotted line 314) (and T310 is stopped, shown by dotted line 316). T312 is started when TTT (A3) expires which is shown by dotted line 312. With autonomous or conditional handover TTT (A3) triggers a contention-free switching procedure to a handover target cell (dotted line 312). In the situation in Fig. 3 this would happen before the radio link failure has taken place, but still much later than necessary. In other situations, when TTT(A3) is started later, e.g. when T310 is already running, a radio link failure may have taken place before a handover has been carried out.

According to this example, a user device evaluates the contention-free switching procedure condition with shorter or more aggressive timing, when the user device is in a risk of a radio link failure (RLF), e.g., T310 is started. When the (short) TTT of this switching event expires, the user device switches to the handover target cell.

It should be appreciated that TTT (A3) condition is evaluated when a radio link failure risk is not detected that is to say when T310 is not running. It may or may not be evaluated in parallel with TTT (A4), however.

If either of the 2 conditions expires while T310 is running, T310 is stopped and the user device accesses the handover target cell.

It should be understood that T312 mechanism is only needed for cells which have not been pre configured. For pre-configured cells identified in the handover command for an autonomous or conditional handover (see description of FIG. 2), a user device carries out a contention-free switching procedure before T312 would be started and thus it is obsolete in the case the handover succeeds (re-establishment is not needed). FIG. 4 illustrates a simplified block diagram of an apparatus according to an embodiment in relation to FIG. 2.

As an example of an apparatus according to an embodiment, it is shown apparatus 400, such as a user device, including facilities in control unit or circuit/circuitry 404 (including one or more processors, for example) to carry out functions of embodiments according to FIG. 2. The facilities may be software, hardware or combinations thereof as described in further detail below.

Although the apparatuses have been depicted as one entity in FIG. 4, different modules and memory may be implemented in one or more physical or logical entities. Apparatus 400 may, for instance, be divided into functions carried out by a simple user device comprising radio modem/unit 406 and possibly also memory unit 402 (or part of it, in which case an external memory unit may exist in cloud providing more storage capacity) and a processor or other type of calculation capacity locating in cloud available to the user device via the radio unit. Also this type of a user device normally has a display which provides a user interface (user interface operations are not, however, relevant with regard to embodiments).

In FIG. 4, block 406 includes parts/units/modules needed for reception and transmission, usually called a radio front end, RF-parts, radio parts, remote radio head, etc. The parts/units/modules needed for reception and transmission may be comprised in the apparatus or they may be located outside the apparatus the apparatus being operationally coupled to them. The apparatus may also include or be coupled to one or more internal or external memory units. As stated above, the apparatus may also be able to use cloud via radio parts in which case computation and/or control functions may be carried out in the cloud at least partially. The at least one external memory unit may also locate in the cloud. The apparatus may be a combination of a radio modem or radio parts in a portable device and one or more algorithms executed in the cloud, for example.

Another example of apparatus 400 may include at least one processor 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 processor, cause the apparatus at least to: receive a configuration for being used in case of decrease in radio link condition during an autonomous or conditional handover procedure, receive a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node, during the autonomous or conditional handover procedure triggered by the handover command, detect decrease in radio link condition, and carry out an urgent cell access procedure based on the configuration and carry out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

It should be understood that the apparatus may include or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. This is depicted in FIG. 4 as optional block 406. The apparatus may also include or be coupled to a user interface which could comprise a display, for example.

Yet another example of an apparatus comprises means for carrying out the embodiments described by means of FIG. 2 (and 3). The apparatus comprises means (404, 404, 406) for receiving a configuration for being used in case of decrease in radio link condition during an autonomous or conditional handover procedure, means (402, 404, 406) for receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node, means (404, 406) for, during the autonomous or conditional handover procedure triggered by the handover command, detecting decrease in radio link condition, and means (402, 404, 406) for carrying out an urgent cell access procedure based on the configuration and carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure. The apparatus comprises means for ending the autonomous or the conditional handover procedure, wherein the ending comprises informing a handover source node about the completion of the autonomous handover procedure. The urgent cell access procedure may be controlled by using a third timer which is started when a first timer controlling the autonomous or conditional handover procedure has started and when at least one second timer controlling a radio link re-establishment with regard to the radio link failure has started. In this case the apparatus may comprise means for ending the autonomous or the conditional handover procedure, wherein the ending comprises stopping at least one of the following: the first timer and the at least one second timer provided they are running after the carrying out the cell access.

An apparatus may in general include at least one processor, controller, unit, module or (electronic) circuitry designed for carrying out functions of embodiments operationally coupled to at least one memory unit (or service) and to typically various interfaces. A circuitry may refer to hardware -only circuit implementations, such as implementations in only analog and/or digital circuitry, combinations of circuits and software (and/or firmware), such as different kind of processors of portions of them, software and/or circuit components, such as a microprocessor(s) or a portion of a microprocessor(s). Further, the memory units 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 described above in relation to FIG. 2 (and 3). 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 memory may be of any type suitable for the current technical environment and it may be implemented using any suitable data storage technology, such as semiconductor-based technology, flash memory, magnetic and/or optical memory devices. The memory may be fixed or removable.

The apparatus may comprise an electronic circuit or a system of electronic circuits performing a particular function in an electronic device or a in distributed system with one or more computer program code or portions thereof. The electronic circuit may comprise at least one processor and additionally at least one internal or external memory. It should be understood that the term circuit/circuitry or electronic circuit may refer to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of circuit/circuitry applies to all uses of this term in this application.

The apparatus may be, include or be associated with at least one software application, module, unit or entity configured as arithmetic operation, or as a program (including an added or updated software routine), executed by at least one operation processor. Programs, also called program products or computer programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and they include program instructions to perform particular tasks. The data storage medium may be a non-transitory medium. The computer program or computer program product may also be downloaded to the apparatus. A computer program product may comprise one or more computer-executable components which, when the program is run, for example by one or more processors possibly also utilizing an internal or external memory, are configured to carry out any of the embodiments or combinations thereof described above by means of FIG. 2 (and 3). The one or more computer-executable components may be at least one software code or portions thereof. Computer programs may be coded by a programming language or a low-level programming language.

Modifications and configurations required for implementing functionality of an embodiment may be performed as routines, which may be implemented as added or updated software routines, application circuits (ASIC) and/or programmable circuits. Further, software routines may be downloaded into an apparatus. The apparatus, such as a user device, or a corresponding component, may be configured as a computer or a microprocessor, such as single-chip computer element, or as a chipset, including at least a memory for providing storage capacity used for arithmetic operation and an operation processor for executing the arithmetic operation.

Embodiments provide computer programs embodied on a distribution medium, comprising program instructions which, when loaded into electronic apparatuses, constitute the apparatuses as explained above. The distribution medium may be a non-transitory medium.

Embodiments provide computer programs comprising instructions which, when the program is executed by a computer, cause an apparatus to carry out embodiments described by means of FIG. 2 (and 3).

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 include a record medium, computer memory, read-only memory, photoelectrical and/or 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 computer readable medium or computer readable storage medium may be a non-transitory medium.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, digitally enhanced circuits, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation may 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 may be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of systems described herein may be rearranged and/or complimented by additional components in order to facilitate 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 implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method comprising:

receiving a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure;

receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and

performing the autonomous or conditional handover procedure triggered by the handover command, including:

detecting a decrease in a radio link condition;

carrying out an urgent cell access procedure based on the configuration; and carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

2. The method of claim 1 and further comprising:

controlling the urgent cell access procedure by using a third timer which is started when a first timer controlling the cell access with regard to the autonomous or conditional handover procedure has started and when at least one second timer controlling a radio link re establishment with regard to the radio link failure has started.

3. The method of any of claims 1-2, wherein the configuration comprises a reduced number of cells to be measured compared to a normal configuration for the autonomous handover, conditional handover or a normal handover procedure.

4. The method of any of claims 1-3, wherein the configuration comprises a reduced number of cells to be measured compared to a normal configuration for the autonomous handover, conditional handover or a normal handover procedure.

5. The method of any of claims 1-4, wherein the configuration comprises an adapted filter for speeding up a measurement procedure with regard to the urgent cell access procedure.

6. The method of any of claims 1 -5 and further comprising:

ending the autonomous or the conditional handover procedure, wherein the ending comprises informing a handover source node about the completion of the autonomous handover procedure.

7. The method of any of claims 1 -6 and further comprising:

ending the autonomous or the conditional handover procedure, wherein the ending comprises stopping at least one of the following: the first timer and the at least one second timer provided they are running after the carrying out the cell access.

8. An apparatus comprising means for performing a method of any of claims 1-7.

9. An apparatus comprising at least one processor and at least one memory including computer instructions that, when executed by the at least one processor, cause the apparatus to perform a method of any of claims 1-7.

10. An apparatus comprising a computer program product including a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method of any of claims 1 -7.

11. 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:

receive a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure;

receive a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and

perform the autonomous or conditional handover procedure triggered by the handover command, including being configured to:

detect a decrease in a radio link condition;

carry out an urgent cell access procedure based on the configuration; and carry out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

12. The apparatus of claim 11 and further comprising:

a radio unit for carrying out communications on a radio path.

13. An apparatus comprising:

means for receiving a configuration for being used in case of a decrease in a radio link condition during an autonomous or conditional handover procedure; means for receiving a handover command comprising parameters for a cell access with regard to the autonomous or conditional handover procedure from a handover source node; and means for performing the autonomous or conditional handover procedure triggered by the handover command, including:

means for detecting a decrease in a radio link condition;

means for carrying out an urgent cell access procedure based on the configuration; and

means for carrying out, based on the received parameters, a cell access to a cell selected in the urgent cell access procedure.

14. A non-transitory computer-readable storage medium comprising instructions stored thereon that, when executed by at least one processor, are configured to cause a computing system to at least:

detect a decrease in a radio link condition;