GB2627727A

GB2627727A - Dedicated random access channel allocation

Info

Publication number: GB2627727A
Application number: GB2218821.3A
Authority: GB
Inventors: Hathiramani Navin; Frederiksen Frank
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2022-12-14
Filing date: 2022-12-14
Publication date: 2024-09-04
Also published as: CN120359780A; GB202218821D0; WO2024125988A1

Abstract

Apparatus which receives an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus which is to be applied by the apparatus in relation to transmissions on a RACH using the dedicated RACH preamble identifier (ID). Also disclosed is an apparatus which determines that a monitoring window associated with a dedicated RACH preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period. The apparatus allocates a monitoring window to a candidate user equipment (UE) to use with the dedicated RACH preamble identifier and provides an indication of the preamble identifier and the timing offset associated with the monitoring window allocated to the candidate UE. Arrangements provide a framework to increase the number of available dedicated random-access preambles in a cell by overbooking the dedicated RACH preamble IDs assigned to the UEs.

Description

Intellectual Property Office Application No G132218821 1 RTM Date:9 June 2023 The following terms are registered trade marks and should be read as such wherever they occur in this document: 3 GP P Intellectual Property Office is an operating name of the Patent Office www.gov.uk /ipo

DEDICATED RANDOM ACCESS CHANNEL ALLOCATION

TECHNOLOGICAL FIELD

Various example embodiments relate to methods for allocating dedicated random access channel use to user equipment in a wireless communication network, and apparatus configured to perform those methods.

BACKGROUND

Wireless communications systems are subject to ongoing development and evolution.

Some adaptations to wireless communication devices, infrastructure and signalling may be required to support mobility as wireless communications systems develop and evolve.

Fifth Generation Technology Standards (5G) for broadband cellular networks set out specifications which have been created to address a wide range of use cases. Such use cases include options which move networks away from being voice or data dedicated networks of past generations. The variety of use cases supported by 5G compliant networks can lead to a diverse ecosystem of devices to be supported by a network. Each type of device may have a different capability.

To be able to efficiently handle all use cases and a diverse range of devices, it has been suggested that it could be helpful for a the 5G standards to support arrangements in which it may be possible to identify a reason and/or a type of device trying to access a network as early as possible.

The Random Access Channel (RACH) is an uplink (UL) physical channel employed, as one of its primary uses, by user equipment (UE) to initiate access to a network. During an initial stage of access to a network, the network is unaware of the type of UE trying to access the network. The types of UE which may be trying to access the network include, for example, an energy harvesting device, an Internet of Things (loT) device, a vehicular device, a fixed access device, a reduced capability device, and similar). Furthermore, during the initial stage of access the reason for which a UE is accessing the network may also be opaque to the network. Reasons for accessing a network may include, for example, a request from a UE to access a specific slice. Standards define various triggers that enable a UE to initiate access a base station. Such triggers are defined in section 9.2.6 of TS 38.300. The triggers set out are generally associated with either: a UE having a need to access communication toward a gNB or a gNB indicating to a UE a request to perform a random access procedure, for instance, via paging the UE or via a Physical Downlink Control Channel (PDCCH) order.

Whilst the random access procedure offers an opportunity to exchange information between a UE and a network as early as possible in a connection process, RACH resources are limited and the diversity of options relating to: UE type, capability and reason to access the network are many.

Early knowledge of UE capability may lead to reduced network overheads and higher spectral efficiency.

It is desired to provide methodologies which may support early knowledge of UE capability in a 5G communications network.

BRIEF SUMMARY

The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

According to various, but not necessarily all, example embodiments there is provided an apparatus, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the apparatus at least to: receive an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

In some embodiments, the allocated timing offset is allocated on an a per apparatus basis.

In some embodiments, the allocated timing offset allocated to the apparatus differs from an allocated timing offset allocated to another apparatus for use in relation to the dedicated random access channel preamble identifier.

In some embodiments, the apparatus is configured to: determine one or more condition associated with use of the timing offset allocated to the apparatus to be applied by the apparatus in relation to the dedicated random access channel preamble identifier; and assess whether the one or more condition is met before using the timing offset allocated to the apparatus to be applied by the apparatus in relation to the dedicated random access channel preamble identifier.

In some embodiments, the one or more condition comprises: an assessment by the apparatus of its location in a cell of a wireless communication network.

In some embodiments, the location in a cell comprises an indication of a distance between the apparatus and a serving cell network node.

In some embodiments, the one or more condition comprises: a comparison between the allocated timing offset and an indication of radio propagation delay between the apparatus and a transmitting network node to which the apparatus would transmit the dedicated random access channel preamble identifier.

In some embodiments, if the apparatus is determined to fail to meet at least one of the one or more conditions, the apparatus is configured to avoid use of the dedicated random access preamble identifier for transmission on the random access channel.

In some embodiments, if the apparatus is determined to fail to meet at least one of the one or more conditions, the apparatus is configured to initiate transmission on the random access channel using a contention based random access preamble identifier.

In some embodiments, the apparatus is configured to measure received signal strength received at the apparatus from a source cell and a neighbour cell; and determine a timing difference at the apparatus between the source cell and the neighbour cell.

In some embodiments, the apparatus is configured to report the measured received signal strength received at the apparatus from a source cell and a neighbour cell and the determined timing difference to the source cell.

In some embodiments, the apparatus is configured to implement use of a dedicated random access channel preamble identifier by applying the timing offset allocated to the apparatus.

In some embodiments, the apparatus is configured to transmit the dedicated random access channel preamble identifier with the provided offset. The transmission may be received by the source cell, a neighbour cell or a target neighbour cell.

In some embodiments, the apparatus is configured to: implement use of a dedicated random access channel preamble identifier by applying a timing offset calculated as a sum of: the timing offset allocated to the apparatus by a cell to which the dedicated random access channel preamble identifier is to be transmitted, a determined timing difference at the apparatus between the source cell and the cell to which the dedicated random access channel preamble identifier is to be transmitted; and a timing advance applied by the apparatus its source cell.

In some embodiments, the apparatus is configured to: receive a response to a transmission made using the dedicated random access channel preamble identifier, the response comprising a relative additional timing offset to be applied by the apparatus.

In some embodiments, the apparatus is configured such that in response to the relative additional timing offset received, it can establish a timing offset for the cell from which the response is received based on: a sum of the timing offset employed in the transmission of the dedicated random access channel preamble identifier and the relative additional timing offset.

According to some embodiments, the apparatus comprises user equipment of a wireless communication network.

According to various, but not necessarily all, example embodiments there is provided computer implemented method comprising: receiving an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

In some embodiments, the allocated timing offset allocated to an apparatus differs from an allocated timing offset allocated to another apparatus for use in relation to the dedicated random access channel preamble identifier.

In some embodiments, the method comprises: determining one or more condition associated with use of the timing offset allocated to an apparatus to be applied by the apparatus in relation to the dedicated random access channel preamble identifier; and assessing whether the one or more condition is met before using the timing offset allocated to the apparatus to be applied by the apparatus in relation to the dedicated random access channel preamble identifier.

In some embodiments, if it is determined that at least one of the one or more conditions is not met, the method comprises avoiding use of the dedicated random access preamble identifier for transmission on the random access channel.

In some embodiments, if it is determined that at least one of the one or more conditions is not met, the method comprises initiating transmission on the random access channel using a contention based random access preamble identifier.

In some embodiments, the method comprises measuring received signal strength received at the apparatus from a source cell and a neighbour cell; and determine a timing difference at the apparatus between the source cell and the neighbour cell.

In some embodiments, the method comprises reporting the measured received signal strength received at the apparatus from a source cell and a neighbour cell and the determined timing difference to the source cell.

In some embodiments, the method comprises implementing use of a dedicated random access channel preamble identifier by applying the timing offset allocated to the apparatus.

In some embodiments, the method comprises transmitting the dedicated random access channel preamble identifier with the provided offset. The transmission may be received by the source cell, a neighbour cell or a target neighbour cell.

In some embodiments, the method comprises: implementing use of a dedicated random access channel preamble identifier by applying a timing offset calculated as a sum of: the timing offset allocated to an apparatus by a cell to which the dedicated random access channel preamble identifier is to be transmitted, a determined timing difference at the apparatus between the source cell and the cell to which the dedicated random access channel preamble identifier is to be transmitted; and a timing advance applied by the apparatus its source cell.

In some embodiments, the method comprises: receiving a response to a transmission made using the dedicated random access channel preamble identifier, the response comprising a relative additional timing offset to be applied by the apparatus.

In some embodiments, in response to the relative additional timing offset received, the method may comprise establishing a timing offset for the cell from which the response is received based on: a sum of the timing offset employed in the transmission of the dedicated random access channel preamble identifier and the relative additional timing offset.

According to some embodiments, the method is performed by user equipment of a wireless communication network.

According to various, but not necessarily all, example embodiments there is provided a computer program product, operable when executed on a computer to perform the steps of: receiving an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

According to some embodiments, the computer program product further causes the computer to perform the steps of: applying the timing offset in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

According to various, but not necessarily all, example embodiments, there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: receiving an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

According to some embodiments, the instructions further cause a step of applying the timing offset in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

According to various, but not necessarily all, example embodiments there is provided an apparatus, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the apparatus at least to: determine that a monitoring window associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; allocate a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and provide an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring window allocated to the candidate user equipment.

In some embodiments, the apparatus is configured to: receive an indication of a radio propagation time between the apparatus and the candidate user equipment, and determine, based upon the received indication of radio propagation time, whether the candidate user equipment can use the dedicated random access channel preamble identifier with a monitoring period which has been split into a plurality of monitoring windows.

According to some embodiments, the indication of radio propagation time comprises: an indication of a timing advance applied by the candidate user equipment in its source cell, and an indication of a source to target cell timing difference.

According to some embodiments, the indication of source to target cell timing difference comprises a measurement made by the candidate user equipment.

According to some embodiments, the apparatus is configured to allocate the same dedicated random access channel preamble identifier to more than one candidate user equipment, each candidate user equipment having a different timing offset.

According to some embodiments, the apparatus is configured to allocate the same dedicated random access channel preamble identifier to more than one candidate user equipment, each candidate user equipment having a different timing offset, each having a different monitoring window of the monitoring period.

According to some embodiments, the apparatus comprises a network node of a wireless communication network.

According to various, but not necessarily all, example embodiments there is provided a computer implemented method, comprising: determining that a monitoring period associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; allocating a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and providing an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring slot allocated to the candidate user equipment.

In some embodiments, the method comprises: receiving an indication of a radio propagation time between the apparatus and the candidate user equipment, and determining, based upon the received indication of radio propagation time, whether the candidate user equipment can use the dedicated random access channel preamble identifier with a monitoring period which has been split into a plurality of monitoring windows.

According to some embodiments, the indication of source to target cell timing difference 25 comprises a measurement made by the candidate user equipment.

According to some embodiments, the method comprises: allocating the same dedicated random access channel preamble identifier to more than one candidate user equipment, each candidate user equipment having a different timing offset.

According to some embodiments, the method comprises allocating the same dedicated random access channel preamble identifier to more than one candidate user equipment, each candidate user equipment having a different timing offset, each having a different monitoring window of the monitoring period.

According to some embodiments, the method is performed by a network node of a wireless communication network. According to some embodiments, the network node supports a source cell. According to some embodiments, the network node supports a target cell. According to various, but not necessarily all, example embodiments there is provided a computer program product, operable when executed on a computer to perform the steps of: determining that a monitoring period associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; allocating a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and providing an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring slot allocated to the candidate user equipment.

According to various, but not necessarily all, example embodiments, there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: determining that a monitoring period associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; allocating a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and providing an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring slot allocated to the candidate user equipment.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION

Some example embodiments will now be described with reference to the accompanying drawings in which: FIG. 1 illustrates schematically an exemplary procedure for RACH overbooking of a contention free preamble; FIG. 2 illustrates schematically a framework according to which RACH overbooking can be performed; FIG. 3 illustrates schematically a flow chart for implementing a RACH overbooking in accordance with the framework discussed from a UE point of view; FIG. 4 is a signalling diagram illustrating main signalling steps according to one implementation of the framework; FIG. 5 is a graphical representation of gain achievable according to some implementations of the framework; FIG. 6 shows apparatus in a communication system according to an example embodiment; and FIG. 7 shows a flow diagram illustrating steps in methods performed at network nodes according to some example embodiments.

DETAILED DESCRIPTION

Before discussing the example embodiments in any more detail, first a general framework of a wireless communication network is described, in which context an overview of arrangements will be provided.

The concepts described may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. Various aspects are described generally with reference to a wireless communication system. Such a wireless communication system typically includes three interacting domains: a core network, a radio access network (RAN), and user equipment (UE).

The RAN may be configured to implement any suitable wireless communication technology (or combination of technologies) to provide radio access to UE. According to one example, the RAN may be configured to operate according to the 3rd Generation Partnership Project (3GPP) New Radio (NR) specifications, typically referred to as 5G.

As user equipment (UE) moves through a wireless communication system, it may move through regions of radio coverage (cells) supported by one or more radio access network node. The operational characteristics of cells supported by network access nodes within a wireless communication network may differ. The wireless communication system may comprise various Transmission and Reception Points (TRPs). A UE and network are generally configured such that they can continue to communicate effectively as a UE moves through regions of radio coverage.

As set out above, Fifth Generation Technology Standards (5G) for broadband cellular networks set out specifications which have been created to address a wide range of use cases. Such use cases include options which move networks away from being voice or data dedicated networks of past generations. The variety of use cases supported by 5G compliant networks can lead to a diverse ecosystem of devices to be supported by a network. Each type of device may have a different capability.

To be able to efficiently handle all use cases and a diverse range of devices, it has been suggested that it could be helpful for a the 5G standards to support arrangements in which it may be possible to identify a reason and/or a type of device trying to access a network as early as possible. It is believed that early knowledge of UE capability may lead to reduced network overheads and higher spectral efficiency.

The Random Access Channel (RACH) is an uplink (UL) physical channel employed, as one of its primary uses, by user equipment (UE) to initiate access to a network. During an initial stage of access to a network, the network is typically unaware of the type of UE trying to access the network and the reason that the UE may be trying to access the network.

The types of UE which may be trying to access the network include, for example, an energy harvesting device, an Internet of Things (loT) device, a vehicular device, a fixed access device a reduced capability device. Reasons for accessing a network may include, for example, a request from a UE to access a specific slice.

Standards define various triggers that enable a UE to initiate access a base station. Such triggers are defined in section 9.2.6 of TS 38.300. The triggers set out are generally associated with either: a UE having a need to access communication toward a gNB or a gNB indicating to a UE a request to perform a random access procedure, for instance, via paging the UE or via a Physical Downlink Control Channel (PDCCH) order.

Using procedures to exchange additional information between UE and a network may have associated problems. For example, for cases where a UE is establishing a link for only a short connection, the exchange of UE capabilities or UE features may further delay the time until a network can fully leverage the UE capabilities. Early knowledge of capabilities of a UE can allow a connection to be established which can lead to reduced overheads and higher spectral efficiency.

It is possible to obtain UE feature capabilities from a central entity (for example, via the Access and Mobility Management Function AMF) but such a route may not always provide required information with an appropriately short delay, for example, such information may not be provided in time to support intelligent decisions in relation to how to handle transmission of messages related to initial RRC connection setup.

It is possible to provide or allocate separate RACH resource(s) allowing for differential treatment for each type of UE or use case, but such differential allocation results in a reduction of pooling gain in, for example, the typical available 64 random access preambles. By pre-allocating random access preambles to particular UE use or capability, it leads to higher RACH collision probability.

It is possible to add additional RACH occasions in time/frequency domain, but such an addition incurs additional overheads which need to be semi-statically configured.

Arrangements described address ways to increase RACH capacity in a manner which may support provision of "more" random access preambles to offer a mechanism to provide a network with an early indication of UE capability and/or a UE request without incurring excessive overhead or RACH channel performance degradation.

Before discussing the example embodiments in any more detail, first an overview will be provided.

A framework may provide, an apparatus, for example, user equipment, comprising: means to receive an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

The framework may further provide an apparatus, for example a network node supporting a source or target cell, comprising: means to determine that a monitoring window associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; means to allocate a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and means provide an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring window allocated to the candidate user equipment.

The framework may provide that the means comprise circuitry or logic configured to perform the function set out herein.

It will be appreciated that there are two types of random access: contention-based random access and non-contention based (dedicated) random access.

When a UE transmits a random access preamble, it transmits with a specific pattern and this specific pattern is called a signature. In each cell there are typically a total of 64 random access preamble signatures available.

According to a dedicated random access procedure, a network is configured to inform a UE, usually via RRC signalling, or via physical layer signalling, for example, downlink control information (DCI),according to which a UE is provided with a random access preamble index indicating when and which random access preamble signature to use. According to such a case, a network operates to allocate dedicated preamble signature so that they do not collide.

Arrangements provide a framework to increase the number of available dedicated random access preambles in a cell by "overbooking" the dedicated random access preamble IDs assigned to UEs. By using such a framework to overbook dedicated random access preambles, a cell could, for example, be operable to configure fewer dedicated preambles and allow for more contention-based preambles. Either way, the framework supports a mechanism by which RACH capacity can be increased.

According to the overbooking framework, the network, for example, a source cell, or a target cell, may be configured to indicate an offset to be applied by a UE when performing a random access procedure towards that cell.

FIG. 2 illustrates schematically a framework according to which random access channel preamble overbooking can be performed.

FIG. 2 illustrates, on the left hand side, a typical random access procedure according to which one dedicated random access preamble ID 10 belongs, fits or is expected, in one cyclic shift (CS) correlation zone 20. Accordingly, a receiving node in a network, for example at a base station supporting a cell, can interpret such a random access preamble ID 10 if it is received. A dedicated random access preamble is transmitted by the UE at a known timing instance. To ensure that a cell receiver can receive transmissions made by a UE as expected, each UE has an associated timing advance, which takes into account radio propagation delay, resulting from distance between the UE and the source receiver. The further away, a UE and a cell receiver, the greater the timing advance (TA) which is applied by the UE.

The timing advance in relation to a random access procedure (which may help set the TA for a UE in the first instance) is illustrated as period 5.

FIG. 2 illustrates, on the right hand side, an example of RACH preamble "overbooking" in accordance with the framework described herein. In the example shown in Figure 2, two UEs are configured to share a dedicated RACH preamble ID 10a, 10b and can use the same cyclic shift (CS) correlation zone 20a as illustrated. In other words, a traditional single cyclic shift space is split into multiple (in this case, two) monitoring windows 60a, 60b. The sampling period 70a, 70b of each monitoring window is separated from an adjacent sampling period of a monitoring window by taking into account likely delay spread 30 and allowing also for guard samples 40. Each UE can have a different determinable timing advance 5a, 5b.

To indicate an appropriate TA to each UE, account may need to be taken of the overbooking framework which has effectively split the zero correlation zone into a plurality of monitoring slots. In effect, an explicit timing advance has to be indicated to the UEs which are to be "overbooked" into the zero correlation zone, each explicit timing advance comprising a multiple of the new monitoring window period.

In a numerical example, assume RACH Format 0 is configured with 24 dedicated random access preambles reserved.

The parameter Zero Correlation Zone (ZCZ) (represented by 20, 20a) is chosen to enable a RACH Cell range of 10 km the NCS Configuration value = 10, leading to: * 76 samples per cyclic shift (NCS) * 839/76 =11 orthogonal signatures per root sequence.

Assuming a delay spread (30) of 5 ps and 2.25 "Guard" samples to form a guard period (40), and if it can be assumed that, based on cell topology and deployment scenario, the UE compensated error in timing difference between the source cell and target cell and mobility since the measurement report sent by the UE is no larger than 2 km (13ps) then: * Considering 2km = 13.98 samples, delay spread = 4.96 samples, then according to the overbooking framework, it is possible to have: Floor (76/(13.98+4.96+2.25)) = 3 UEs per ZCZ (ie per dedicated RACH preamble).

For 1 km as max relative difference, the framework allows for an increase to 5 UEs per dedicated RACH preamble * This means that instead of resource allocating 24 of an available 48 possible RACH preambles to dedicated preambles, it is possible to reserve 1/3 (in the case of 2km) or 1/5 (in the case of 1km) fewer and that saved RACH preamble capacity could instead be used for 15 contention-based RACH access to a network.

Available Gain Assuming 24 dedicated RACH preambles are made available, with an overbooking factor of 5, it is possible to increase by close to 50% the number of contention-based RACH preambles available to a cell. By applying an overbooking factor of 2, it is possible to achieve an almost 30% gain. Figure 5 illustrates graphically gain available in contention-based RACH preambles, as a factor of RACH overbooking factor applied.

It will be appreciated that the time to prepare and execute a handover is relatively fast (smaller than 1 second). As a result, if a UE is considered to be able to shift 2 km in the period between its last Measurement Report as sent to the source cell and when it initiates a RACH procedure, that would mean that the UE would be moving at a speed of 7200 km/h (which would only be experienced for deployments like non terrestrial networks (NTN) where there are typically other means in place to control the initial access timing). As a result, in practice RACH can be "overbooked" even more than the numerical examples set out above and that the main factor(s) to account for, in the context of whether to apply RACH preamble overbooking techniques according to the framework, will be: Timing Advance (TA) timing drifts of the source cell, TA accuracy and timing errors.

Example Implementation: Network Controlled Approach According to one example implementation of the framework, a network may be configured to decide, based on various conditions being met, whether an overbooked RACH preamble should be employed by a UE in its use of a RACH to connect to a cell.

An exemplary procedure for RACH overbooking of a contention free random access preamble is illustrated schematically in FIG. 1.

The scenario mapped in FIG. 1 is one in which a UE may be the subject of a handover between a source cell 100 and a target cell 200.

According to the illustrated example of the framework the source cell 100 may be configured to perform the following steps: S10: The source cell configures the UE to perform measurements for one or more neighbour cell. The measurements may include, for example: at least Reference Signal Received Power (RSRP) and timing difference measurements.

S20: Upon receiving a Measurement Report from the UE, the source cell 100 may decide to trigger a handover in relation to that UE.

S30: The source cell 100 initiates a handover (HO) preparation request procedure with target cell 200. The source cell is configured to include additional information, for example, the UE measured timing difference between the source cell and target cell, and the UEs current Timing Advance (TA) value at the source cell.

S40: After successful completion of the handover preparation procedure to the target cell, the source cell is configured to forward a handover command to the UE.

According to the illustrated example of the framework the target cell 200 may be configured to perform the following steps: T10: The target cell 200 is configured to receive a Handover Preparation Request and initiate an appropriate procedure. The handover preparation request includes the UE measured timing difference between the source cell 100 and target cell 200 and the timing advance (TA) value of the UE as applied in the source cell 100.

T20: The target cell 200 is configured to determine whether RACH overbooking in accordance with the framework can be employed for this UE.

The determination at the target cell may depend upon: the measured timing difference between the source and target cells, the timing advance applied by the UE in the source cell, and may additionally account for other possible parameters of relevance, for example, UE speed, which may, for example, be determined, based on Handover Preparation information shared with the target cell 200 by the source cell 100. The target cell is configured to decide whether to assign a UE an "overbooked" preamble contention free based on a configured Zero Correlation Zone parameter of the cell and potential UE timing errors related to, for example, the subcarrier spacing of the target cell. More details on the determination process are provided below.

T30: If the target cell 200 decides, on the basis of the determination referred to above, to employ an overbooked RACH preamble ID for the UE handover procedure, in accordance with the RACH overbooking framework, it provides the UE with the ID of the allocated preamble together with an Explicit Timing Advance (TA) offset which the UE is to employ for the RACH procedure.

T40: Upon detection of the assigned dedicated Preamble ID, the target cell 200 is configured to transmit to the UE a Random-Access Response message including a relative TA value to apply; T50: The target cell may then be configured to proceed and set an absolute TA value for the UE. The absolute TA value may be based upon: the UE-measured timing difference, the latest TA of the source cell and the relative TA value sent via the Random Access Request (RAR).

T60: If it is determined at T20 that it is not possible to employ RACH overbooking, the UE may be provided with a non-overbooked dedicated RACH preamble or be asked to implement contention based network access in accordance with standard 3GPP RACH procedures.

According to the framework, an assessment or determination of whether an overbooked preamble can be assigned to a UE can be based on a variety of factors. Depending upon implementation, those factors may include, as set out above, in the case where a UE is moving from primary connection with one cell to a primary connection with another cell: the timing difference measured by the UE between a source cell and a target cell, a timing advance. The factors of relevance to the overbooking framework also include: * Target cell Zero Correlation Zone (ZCZ): This parameter sets the number of cyclic shifts per root sequence and the length in samples of each cyclic shift. The cell range of the RACH can be determined via the ZCZ setting, since any detected preamble has to fall within its determined samples of one cyclic shift.

* Although the framework assumes that the network cells are synchronized, there can be an up to 3ps timing alignment error between cells as per 3GPP specifications. In addition, other factors such as UE timing error, UE TA adjustment accuracy and UE mobility during the handover procedure can be considered.

* It will be appreciated that a UE is likely to not be able to perfectly determine the TA for a target cell based on measurements made and the TA applied in the source cell. However, if the error involved in determining the TA of the target cell is less than the RACH cell range of target cell (based on its ZCZ) there is a possibility of using the framework to overbook a RACH preamble ID.

A flow chart for implementing a RACH overbooking in accordance with the framework discussed from a UE point of view is shown schematically in FIG. 3.

In particular, a UE 300 as shown in FIG. 3 is in communication with a source cell 100 and eventually performs a handover to a target cell 200. The source cell 100 and target cell 200 are configured to perform steps in accordance with the flowcharts of FIG. 1. The UE 300 is configured, according to one implementation, to perform the following steps: U10: The UE is configured to perform neighbour cell measurements. The measurement configuration includes at least reference signal received power (RSRP) and timing difference between the source cell and a measured cell.

U20: The UE is configured to send a Measurement Report relating to a neighbour cell, that measurement report includes the neighbour cell RSRP and timing difference, and potentially indicates that the UE is a candidate for the handover to the neighbour cell.

U30: The UE is configured to receive a Handover Command from source cell 100. The Handover Command includes an instruction to handover to a target cell 200 which may correspond to the neighbour cell on which the UE reported in step U20. The Handover Command, in accordance with RACH overbooking framework, may include an Explicit timing advance (TA) offset to be applied by the UE together with a dedicated RACH preamble ID.

U50: The UE is configured to estimate an appropriate TA to apply in relation to the target cell 200, based on the measured timing cell difference and the TA value of the source cell. Note that in some embodiments, the UE may not need to estimate an appropriate TA, as the network may provide an absolute offset to be employed within the Explicit TA.

U60: The UE is configured to apply the Explicit TA offset provided in the Handover 30 Command.

U70: The UE is configured to initiate a RACH procedure using the provided dedicated RACH preamble ID and the TA value determined in U50 and U60.

U80:' Upon reception of the Random-Access Response (RAR) Message from target cell 200, the UE is configured to determine or receive an indication of a new absolute TA.

According to one implementation, the target cell 200 provides a relative TA in RAR (TA_RAR) and the UE may be configured to derive the absolute TA based on: TA_compensated+TA_RAR.

FIG. 4 is a signalling diagram showing signalling, in accordance with a RACH overbooking framework, between a UE 300, source cell 100 and target cell 200 in support of a handover event such as that described on an entity by entity basis in relation to FIG. 1 and FIG. 3.

A process applied between the source node 100, UE 300 and target node 200 according to one implementation may comprise the following steps: C10: The source node 100 is configured to transmit a measurement configuration to UE 300. C20: The UE is configured to perform the measurements as requested by the source node and transmit a measurement report, including, for example a measured timing offset to potential target cells), to the source cell 100.

C30: If a handover parameter is met at the UE in relation to a target cell, the source node 100 transmits a handover preparation request to a target node 200. The handover preparation request can include a timing difference measurement and a current timing advance applied in the source cell by the UE.

C40: The target node determines, based on information provided to it, whether the UE is a candidate for use of an "overbooked" dedicated RACH.

C50: If the target node determines that RACH overbooking can be applied, the target node transmits a handover preparation response towards the UE via the source node. The handover preparation response includes a handover command for the UE including an explicit timing advance offset to be applied and a dedicated RACH preamble ID. C60: The source cell passes a handover command to the UE. The Handover command includes an explicit TA offset and the selected dedicated preamble ID.

C70: The UE compensates for the timing of the target node and applies the provided explicit TA offset. Note that in some embodiments, the UE may not need to perform this compensation, as the network may provide an absolute offset to be employed with the dedicated preamble.

C80: The UE transmits the dedicated RACH preamble.

C90: The target node transmits a random access response to the UE which includes a relative timing offset.

C100: The UE sets its TA based upon the relative timing offset, the measured timing difference between source and target cells and the TA applied by the source node.

Example Implementation: UE Controlled Approach According to one example implementation of the framework, a network may be configured to decide, based on various conditions being met, whether an overbooked RACH preamble should be employed by a UE.

In a second example implementation of the framework, a network could be configured to provide the UE with an explicit timing advance (TA) offset and a dedicated RACH preamble ID, and the UE could be configured to autonomously decide, based on fulfilment of one or more certain conditions, whether to employ the dedicated "overbooked" RACH preamble assigned or to use a contention based RACH preamble when contacting the network. In this case, the determination or assessment of whether the UE should use the allocated "overbooked" RACH resource or use contention-based RACH may be based on one or more factor which is known, or derivable, to the UE. Such factors may include: knowledge of UE location; location of the source and/or target cell(s); propagation delay and/or timing difference between the source and target cells.

Whether the overbooking framework falls into the network implemented or UE implemented category may depend upon the nature of event supported by the dedicated RACH preamble ID. Those dedicated RACH preamble IDs allocated for use in cell change events may be natural candidates for use of the overbooking framework as described above in a network-implemented scenario. Those dedicated RACH preamble IDs allocated for use by the UE whilst remaining under nominal control of a single cell, for example, radio link failure, Physical Downlink control Channel order, or similar, may be natural candidates for use of the overbooking framework as described above in a UE-implemented scenario.

Arrangements in accordance with a framework as described may provide for an increased number of preambles for a single RACH occasion, whilst generally preserving legacy RACH configuration and with a minimal impact to standard UE RACH procedure.

Whilst particular implementations of the framework have been described in detail, it will be appreciated that it is possible to remain within the framework described, whilst adjusting various implementation details.

For example, as described above, an offset may be of relevance to a UE and be utilised in relation to use of a dedicated RACH preamble. The offset may be applicable to a UE in a conditional manner, for example, the UE may be configured to measure and report a timing difference between a source and target cell and an appropriate network node (that is, either the source or the target cell) may decide whether overbooking in accordance with the framework could or should be applied based on potential RACH timing offset differences.

According to the framework, a UE may be configured to perform a RACH procedure with RACH timing adjusted in a manner which considers: source cell timing advance (TA); source to target cell timing difference; and an explicit timing advance (TA) offset provided to the UE by a source cell.

According to the framework, a target cell may be configured to provide a relative Timing Advance Command (TAG) as a response to a received RACH preamble from a UE.

According to the framework, a source or target cell may be configured to assign the same dedicated RACH preamble ID simultaneously to a plurality of UE, each having a different explicit offset. The source or target cell may be configured to assign the same dedicated RACH preamble ID to such a plurality of UE without the need to change the overarching RACH configuration (for example, the Zero Correlation Zone).

According to the framework, during a Handover preparation procedure, a source cell may be configured to share a UE's current TA value and UE measured source-target cell timing difference with a target cell. According to some implementations, rather than sharing the independent TA value and timing difference, a combined value is shared.

According to the framework, the source cell may be configured to indicate an offset to be applied by the UE when performing RACH, that offset to be applied in a conditional manner, for example, the UE may be configured to make one or more measurements and make an autonomous determination of, for example, its location in a cell. That measurement may be representative of a timing offset to its serving cell (or a neighbour cell(s)), and the UE may be configured to determine whether the offset, and hence overbooking, can be applied based on potential RACH timing offset differences.

FIG. 6 shows apparatus in a communication system according to an example embodiment; and FIG. 7 shows a flow diagram illustrating steps in methods performed at network nodes 30 according to some example embodiments.

In particular, FIG. 6 illustrates a wireless communication network in which a transmitting node 6000 is configured to communicate with user equipment 6100. The transmitting node may comprise a base station, for example, a gNB, and may support a source cell to which the UE 6100 is connected.

A UE 6100 in accordance with one example embodiment may comprise circuitry 6110 configured to receive an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the UE in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

The transmitting node 6000 in accordance with one embodiment may comprise: circuitry 6010 configured to determine that a monitoring window associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; circuitry 6020 configured to allocate a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and circuitry 6030 configured to provide an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring window allocated to the candidate user equipment.

FIG. 7 shows a flow diagram illustrating steps in methods performed at network nodes according to some example embodiments as shown in FIG. 6.

In particular, UE 6100 may be configured to: 7110: receive an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the UE in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.

Transmitting network node 6000 may be configured to: 7010: determine that a monitoring window associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; 7020: allocate a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and 7030: configured to provide an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring window allocated to the candidate user equipment.

A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods. The tern non-transitory as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs ROM).

As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

Although example embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. An apparatus, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the apparatus at least to: receive an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.
2. An apparatus according to claim 1, wherein the apparatus is configured to: determine one or more condition associated with use of the timing offset allocated to the apparatus to be applied by the apparatus in relation to the dedicated random access channel preamble identifier; and assess whether the one or more condition is met before using the timing offset allocated to the apparatus to be applied by the apparatus in relation to the dedicated random access channel preamble identifier.
3. An apparatus according to claim 2, wherein the one or more condition comprises: an assessment by the apparatus of its location in a cell of a wireless communication network.
4. An apparatus according to claim 2 or claim 3, wherein the one or more condition comprises: a comparison between the allocated timing offset and an indication of radio propagation delay between the apparatus and a transmitting network node to which the apparatus would transmit the dedicated random access channel preamble identifier.
5. An apparatus according to claim 2, wherein upon failure to meet at least one of the one or more conditions, the apparatus is configured to avoid use of the dedicated random access preamble identifier for transmission on the random access channel.
6. An apparatus according to claim 5, wherein upon failure to meet at least one of the one or more conditions, the apparatus is configured to initiate transmission on the random access channel using a contention based random access preamble identifier.
7. An apparatus according to any preceding claim, wherein the apparatus is configured to measure received signal strength received at the apparatus from a source cell and a neighbour cell; and determine a timing difference at the apparatus between the source cell and the neighbour cell.
8. An apparatus according to claim 7, wherein the apparatus is configured to report the measured received signal strength received at the apparatus from a source cell and a neighbour cell and the determined timing difference to the source cell.
9. An apparatus according to any preceding claim, wherein the apparatus is configured to implement use of a dedicated random access channel preamble identifier by applying the timing offset allocated to the apparatus.
10. An apparatus according to any one of claims 1 to 9, wherein the apparatus is configured to implement use of a dedicated random access channel preamble identifier by applying a timing offset calculated as a sum of: the timing offset allocated to the apparatus by a cell to which the dedicated random access channel preamble identifier is to be transmitted, a determined timing difference at the apparatus between the source cell and the cell to which the dedicated random access channel preamble identifier is to be transmitted; and a timing advance applied by the apparatus its source cell.
11. An apparatus according to any one of claims 1 to 10, wherein the apparatus is configured to receive a response to a transmission made using the dedicated random access channel preamble identifier, the response comprising a relative additional timing offset to be applied by the apparatus.
12. An apparatus according to claim 11, wherein in response to the relative additional timing offset received, the apparatus is configured to establish a timing offset for the cell from which the response is received based on: a sum of the timing offset employed in the transmission of the dedicated random access channel preamble identifier and the relative additional timing offset.
13. A computer implemented method comprising: receiving an indication of a dedicated random access channel preamble identifier and an indication of a timing offset allocated to the apparatus to be applied by the apparatus in relation to transmission on a random access channel using the dedicated random access channel preamble identifier.
14. An apparatus, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the apparatus at least to: determine that a monitoring window associated with a dedicated random access channel preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; allocate a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and provide an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring window allocated to the candidate user 15 equipment.
15. An apparatus according to claim 14, wherein the apparatus is configured to receive an indication of a radio propagation time between the apparatus and the candidate user equipment, and determine, based upon the received indication of radio propagation time, whether the candidate user equipment can use the dedicated random access channel preamble identifier with a monitoring period which has been split into a plurality of monitoring windows.
16. An apparatus according to claim 15, wherein the indication of radio propagation time comprises: an indication of a timing advance applied by the candidate user equipment in its source cell, and an indication of a source to target cell timing difference.
17. An apparatus according to claim 16, wherein the indication of source to target cell timing difference comprises a measurement made by the candidate user equipment.
18. An apparatus according to any one of claims 14 to 17, wherein the apparatus is configured to allocate the same dedicated random access channel preamble identifier to more than one candidate user equipment, each candidate user equipment having a different timing offset.
19. A computer implemented method, comprising: determining that a monitoring period associated with a dedicated random access channel RACH preamble identifier is to be split into a plurality of monitoring windows, the start of a monitoring window being offset in time from the start of the monitoring period; allocating a monitoring window to a candidate user equipment to use in relation to the dedicated random access channel preamble identifier; and providing an indication of the dedicated random access channel preamble identifier and the timing offset associated with the monitoring slot allocated to the candidate user equipment.
20. A computer program product operable, when executed on a computer, to perform the method steps of claim 13 or claim 19.