WO2021227955A1

WO2021227955A1 - Transmission resource allocation for device to device communications

Info

Publication number: WO2021227955A1
Application number: PCT/CN2021/092175
Authority: WO
Inventors: Virgile Garcia; Umer Salim; Mohamed-Achraf Khsiba
Original assignee: Tcl Communication (Ningbo) Co., Ltd.
Priority date: 2020-05-14
Filing date: 2021-05-07
Publication date: 2021-11-18
Also published as: CN115699966A

Abstract

UEs in a cellular communication network share coordination information to guide selection of transmission resources. When selecting transmission resources a UE excluded previously reserved transmission resources, and may also excluded transmission resources occurring at the same time as scheduled transmissions from the intended recipient of a transmission.

Description

Transmission Resource Allocation For Device to Device Communications

Technical Field

The following disclosure relates to a system to allocate transmission resources for device to device transmissions, and specifically to a method for sharing coordination information between devices.

Background

Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP) (RTM) . The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

In cellular wireless communication systems User Equipment (UE) is connected by a wireless link to a Radio Access Network (RAN) . The RAN comprises a set of base stations which provide wireless links to the UEs located in cells covered by the base station, and an interface to a Core Network (CN) which provides overall network control. As will be appreciated the RAN and CN each conduct respective functions in relation to the overall network. For convenience the term cellular network will be used to refer to the combined RAN &CN, and it will be understood that the term is used to refer to the respective system for performing the disclosed function.

The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN) , for a mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB) . More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a gNB. NR is proposed to utilise an Orthogonal Frequency Division Multiplexed (OFDM) physical transmission format.

The NR protocols are intended to offer options for operating in unlicensed radio bands, to be known as NR-U. When operating in an unlicensed radio band the gNB and UE must compete with other devices for physical medium/resource access. For example, Wi-Fi (RTM) , NR-U, and LAA may utilise the same physical resources.

A trend in wireless communications is towards the provision of lower latency and higher reliability services. For example, NR is intended to support Ultra-reliable and low-latency communications (URLLC) and massive Machine-Type Communications (mMTC) are intended to provide low latency and high reliability for small packet sizes (typically 32 bytes) . A user-plane latency of 1ms has been proposed with a reliability of 99.99999%, and at the physical layer a packet loss rate of 10 ^-5 or 10 ^-6has been proposed.

mMTC services are intended to support a large number of devices over a long life-time with highly energy efficient communication channels, where transmission of data to and from each device occurs sporadically and infrequently. For example, a cell may be expected to support many thousands of devices.

The disclosure below relates to various improvements to cellular wireless communications systems.

Summary

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

There is provided a method of selecting transmission resources for a transmission from a first UE to a second UE in a cellular communications network, the method comprising the steps ofmonitoring a transmission channel for signals reserving transmission resources and storing coordination information regarding transmissions scheduled by other UEs; identifying potential transmission resources for a first transmission by excluding unavailable transmission resources based on a first criteria applied to the coordination information; andselecting transmission resources for a transmission from the potential resources according to a second criteria.

The step of monitoring for signals reserving transmission resources may comprise monitoring for SCI transmissions.

The coordination information may comprise information regarding at least one of resource reservations, scheduling of transmissions, RSRP levels, and transmission priorities.

The first criteria may include the RSRP being higher than a threshold.

The first criteria may include whether the second UE has a transmission scheduled at the time of the first transmission.

The first criteria may include whether the transmission resources are a transmission opportunity for the second UE.

Transmission opportunities may be identified based on the resource pool (s) assigned to the second UE.

Transmission opportunities may be identified based on previous transmissions by the second UE.

The first criteria may include whether a transmission is scheduled in the time and frequency of the transmission resources.

The second criteria may be a random selection process.

The second criteria may include different priorities for potential transmission resources.

Transmission resources which are transmission opportunities for the second UE may be assigned a lower priority for selection.

The priority may be dependent on the time until the transmission resources occur.

Transmission resources excluded from selection may be changed to be available if greater than a threshold amount of potential transmission resources were excluded as unavailable.

The first criteria may be dependent on whether the first transmission is an initial transmission or a retransmission.

The second criteria may be dependent on whether the first transmission is an initial transmission or a retransmission.

The first and/or second criteria may be received at the first UE in RRC signalling.

The method may further comprise the step of transmitting coordination information from the first UE.

The coordination information may be transmitted to the second UE.

The coordination information may be transmitted to a base station of the cellular network.

The coordination information may include one or more resource pools allocated to the first UE.

The coordination information may be transmitted using dynamic signalling.

The coordination information may be transmitted using an SCI or DCI message.

The coordination information may be transmitted using RRC signalling.

There is also provided a UE configured to perform the methods described herein.

Examples of the invention are set out in the following detailed description.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

Figure 1 shows a schematic diagram of selected elements of a cellular communication network; and

Figure 2 shows a schematic diagram of selected elements of a sidelink communication system;

Figure 3 shows an example of transmission resources; and

Figure 4 shows a flow chart of an example of resource selection for transmission.

Detailed description of the preferred embodiments

Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

Figure 1 shows a schematic diagram of three base stations (for example, eNB or gNBs depending on the particular cellular standard and terminology) forming a cellular network. Typically, each of the base stations will be deployed by one cellular network operator to provide geographic coverage for UEs in the area. The base stations form a Radio Area Network (RAN) . Each base station provides wireless coverage for UEs in its area or cell. The base stations are interconnected via the X2 interface and are connected to the core network via the S1 interface. As will be appreciated only basic details are shown for the purposes of exemplifying the key features of a cellular network. A PC5 interface is provided between UEs for SideLink (SL) communications. The interface and component names mentioned in relation to Figure 1 are used for example only and different systems, operating to the same principles, may use different nomenclature.

The base stations each comprise hardware and software to implement the RAN’s functionality, including communications with the core network and other base stations, carriage of control and data signals between the core network and UEs, and maintaining wireless communications with UEs associated with each base station. The core network comprises hardware and software to implement the network functionality, such as overall network management and control, and routing of calls and data.

In vehicle-to-vehicle (V2V) applications, the UEs may be incorporated into vehicles such as cars, trucks and buses. These vehicular UEs are capable of communicating with each other in in-coverage mode, where a base station manages and allocates the resources and in out-of-coverage mode, without any base station managing and allocating the resources. In vehicle-to-everything (V2X) applications, the vehicles may be communicating not only with other vehicles, but also with infrastructure, pedestrians, cellular networks and potentially other surrounding devices. V2X use cases include:

1) Vehicles Platooning -this enables the vehicles to dynamically form a platoon travelling together. All the vehicles in the platoon obtain information from the leading vehicle to manage this platoon. This information allows the vehicles to drive closer than normal in a coordinated manner, going to the same direction and travelling together.

2) Extended Sensors -this enables the exchange of raw or processed data gathered through local sensors or live video images among vehicles, road site units, devices of pedestrian and V2X application servers. The vehicles can increase the perception of their environment beyond of what their own sensors can detect and have a more broad and holistic view of the local situation. High data rate is one of the key characteristics.

3) Advanced Driving -this enables semi-automated or full-automated driving. Each vehicle and/or RSU shares its own perception data obtained from its local sensors with vehicles in proximity and that allows vehicles to synchronize and coordinate their trajectories or manoeuvres. Each vehicle shares its driving intention with vehicles in proximity too.

4) Remote Driving -this enables a remote driver or a V2X application to operate a remote vehicle for those passengers who cannot drive by themselves or remote vehicles located in dangerous environments. For a case where variation is limited and routes are predictable, such as public transportation, driving based on cloud computing can be used. High reliability and low latency are the main requirements.

Figure 2 illustrates a base station 102 forming a RAN, and a sidelink transmitter (SL Tx UE) UE 150 and a sidelink receiver (SL Rx UE) UE 152 in the RAN.

UEs

150 and 152 are described as transmitter and receiver only for the purposes of explanation during a particular communication, and their roles may equally be reversed. The base station 102 is arranged to wirelessly communicate over respective connections 154 with each of the SL Tx UE 150 and the SL Rx UE 152. The SL Tx UE 150 and the SL Rx UE 152 are arranged to wirelessly communicate with each other over a sidelink 156.

Sidelink transmissions utilise TDD (half duplex) on either a dedicated carrier, or a shared carrier with conventional Uu transmissions between a base station and UE. Resource pools of transmission resources are utilised to manage resource and allocation and manage interference between potentially concurrent transmissions. A resource pool is a set of time-frequency resources from which resources for a transmission can be selected. UEs can be configured with multiple transmit and receive resource pools.

Two modes of operation are used for resource allocation for sidelink communication depending on whether the UEs are within coverage of a cellular network. In Mode 1, the V2X communication is operating in-coverage of the base stations (eg eNBs or gNBs) . All the scheduling and the resource assignments may be made by the base stations.

Mode 2 applies when the V2X services operate out-of-coverage of cellular base stations. Here the UEs need to schedule themselves. For fair utilization, sensing-based resource allocation is generally adopted at the UEs. In Mode 2, UEs reserve resources for a transmission by transmitting a Sidelink Control Information (SCI) message indicating the resources to be used. The SCI notifies the recipient (which may be a single UE in unicast, a group of UEs in groupcast, or all reachable UEs in broadcast) of the details of the transmission it can expect.

In Mode 2 transmission resource selection is performed in two steps. In a first step a UE identifies resources that are expected to be available and hence are candidates for transmission, and then in a second step the UE selects transmission resources from the candidates according to an agreed process; for example random selection to mitigate collisions. The first step considers all resources within a selection window and excludes unavailable resources, for example resources that have been reserved by an SCI message detected by the UE whose SL-RSRP measurement is above a threshold. The threshold may be defined based on the priority of the planned transmission and received reservation.

The process described below seeks to improve the selection of transmission resources by sharing coordination information between UEs. Although the following disclosure is given mainly with reference to sidelink communications in an NR cellular system, the principles are applicable to other device to device communication systems.

In order to supplement information which can be determined by sensing activity and reservations UEs may share coordination information which may include details of scheduled transmissions and expected receptions. A first UE wishing to make a transmission to a second UE can thus apply the conventional sensing arrangements, and also utilise the coordination information, in the first step to identify resources which may be available for transmission. In a specific example this approach will allow the first UE to identify resources on which the second UE is expecting to receive a message and hence avoid those resources. In the conventional sensing approach the first UE may not be aware that those resources are to be used and hence a collision may occur. The coordination information may also other aspects relevant to the selection, for example positive and negative preferences for certain resources.

Figure 3 shows an example of utilising coordination information in the selection of transmission resources. In this example a selection window consists of 7 time slots and 5 frequency resources. A UE intending to schedule a transmission to UE0 performs a sensing operation to identify resources reserved by other UEs, and also receives coordination information from other UEs of their scheduled transmission and expected receptions as well as potentially other information on resources which may be available or not, or preferences. The UE identifies four

transmission resources

300, 301, 302, and 303 which are to be used by other UEs and hence those resources are removed from the candidate resources for the transmission. The UE also removes resources 304 –311 as candidates because they occur in the same time slot as a transmission by the intended recipient (UE0) . Due to the duplex protocol of sidelink transmissions a UE cannot receive a transmission in the same time slot as it is making a transmission, and hence use of resources 304 –311 would lead to loss of the transmission, or pre-emption of the UEs transmission. Transmission resources 312 –319 are considered available for transmission because the transmission in those time slots is from UE 1 or UE2 and hence does not affect the ability of UE0 to receive in those time slots on different frequency resources.

In summary, a UE excludes transmission resources which have been reserved by another UE, or which fall in the same time slot as a transmission by the UE to which the transmitting UE wishes to transmit. If the existing reservation does not allow pre-emption (or pre-emption is not desired) , then the slot can be excluded without consideration of further criteria such as RSRP as discussed herein.

If resources are reserved by another UE for a transmission to a first UE, that first UE must listen to the whole band to receive the transmission, hence all resources of that slot are unavailable for the first UE to transmit on. If a UE has both receive and transmission resources planned in a slot, priority of transmission will decide which action to perform in the slot. That is no distinction is made for resources reserved by a UE for its own use.

In an extension of this principle, when selecting resources for a transmission that will not be reserved in advance (e.g. the initial transmission, or a retransmission after reselection) all resources in time slots that are transmission opportunities for the receiver may be removed as candidate resources. The transmission opportunities are identified from the coordination information shared to the UEs, for example by sharing transmission pool slots, reserved slots, and other parameters which define when a UE may transmit. This approach avoids making a transmission during a slot for which the receiver UE may be preparing a transmission and hence a collision is avoided.

In a modification of this extension, a transmitting UE may categorise slots that are a TX opportunity of the receiver UE as lower priority resources, rather than excluding them completely as candidates. This reduces the probability of using the resources but makes the resources available if no other higher priority resources are available. The priority applied may be dependent on various factors, for example the proximity of the resources in time. Resources closer in time will be given a lower priority (less preferred) than resources further in the future. Resources farther in the future give the receiver UE more time to perform a reselection, hence the higher priority applied to them compared to proximal resources prior to which there may be no time for a reselection.

The categorisation of potential transmission opportunities of the receiver UE may be performed by marking the resources as virtually reserved with a selected priority and RSRP. This enables conventional resource selection procedures to be applied to these resources even though they haven’t been actually reserved for a transmission. The application of a priority level allows prioritisation of resources and hence protection of some resources to a required extent without completely blocking the resources (for example they may be used for high priority transmissions, or if the channel is very busy and other resources are not available) . The system can thus trade-off the need for access to resources against the risk of a possible collision.

A multi-step process may be applied for the potential transmission resources. In a first iteration the resources may be excluded, but if the available candidate resources are below a threshold (for example 20%of all resources) the resources may be considered available. Further refinement can be made, for example by adding in the resources from the most in the future backwards in time until a large enough set of candidate resources is identified.

Groupcast communications are transmissions destined for more than one receiver and hence the resources to be removed as candidates may be the aggregate of those unavailable for each receiver, including all resources in each slot in which one of the group is scheduled to make a transmission. This relies on the transmitter UE knowing the members of the receiving group of UEs, for example as occurs when the UE is in groupcast connected mode.

As will be apparent the principles discussed herein are applicable to both periodic and aperiodic resource reservations and coordination information.

Resources may be reserved for both the initial transmission of a TB and also any required retransmissions. The principles and criterion for resource selection may be applied in the same way to all such reservations, or different methods/criterion may be utilised for the initial transmission compared to retransmissions. Similarly, different methods/criterion may be used for each individual resource reservation. For example, an iterative method may be applied to each transmission and retransmission with each iteration applying to specific criteria for excluding resources as candidates and selecting resources for transmission.

As an example of varying criteria the threshold for considering resources as reserved, and hence excluded, may be different for the initial transmission and retransmissions. As discussed above, the criteria for excluding resources may be based on the number of resources available within the selection window, which may vary between the initial transmission and each retransmission.

Furthermore, at the step of selecting resources for transmission from the candidates different algorithms may be applied for the initial transmission and retransmissions. For example, a random selection may be used for one and a weighted prioritisation selection used for the other, furthermore the selection window size may be varied. Such approaches may help improve latency or distribution of selected resources within the selection windows.

The criteria to apply for identifying candidates and selecting resources may be signalled to the UEs in RRC signalling. Sets of parameters may be included for each iteration to apply to types of transmissions (initial transmissions, retransmissions, and/or reserved/unannounced transmissions) .

For example, upon resource selection for a transmission: -

a. Perform resource identification for the initial transmission (or an unannounced transmission) , with dedicated criterion/rules, for example exclude all intended destinations’ TX opportunities.

b. Perform resource selection for the initial transmission (or an unannounced transmission) , with dedicated criterion/rules. For example, select the earliest available resource in time, or one of the T earliest (preconfigured parameter) .

c. Perform resource identification for a (or several) retransmission (or an transmission to be reserved) for example with relaxed criterion for selection/final number of resources available

d. Perform, resource selection for a retransmission (or an transmission to be reserved) also with specific criterions/rules, for example, spacing between selected resources constrained by HARQ feedback

As will be apparent from the above discussion a transmitter UE requires knowledge of the transmission opportunities of the intended receiver in order to be able to select appropriate resources. This information may be obtained based on a sensing process as well as shared coordination information. For example, the transmitter UE may be aware of the transmission pool (s) configuration of the intended receiver. The transmission pool (s) configuration identifies slots that the UE can use for transmission, and hence the transmitter UE can determine which slots the receiver UE has as transmission opportunities. The transmitter UE may also infer which slots the receiver has as transmission opportunities based on prior reservations. The prior reservations may be used to infer the transmission pool (s) configured for the receiver UE and hence the transmitter UE can infer which future resources may be transmission opportunities.

The transmission pool (s) configuration is an RRC configuration which indicates which slots a UE can utilised for transmission. Each UE may have multiple configurations, and it is possible for transmission and receive pools to overlap. The pools may be configured based on expected transmissions, for example ongoing traffic (data in a queue or periodic traffic or anticipated queue) , traffic requirements (QoS) , and user capabilities etc.

UEs may share their transmission pool configurations with connected UEs such that, as noted above, the transmission opportunities can be determined by the transmitter UE. Each UE is aware of its configured dedicated resource pools from RRC (re) configuration. Each UE can aggregate the available transmission opportunities from the configuration and notify connected UEs such that each UE is aware of its paired UE’s transmission opportunities. The other UE can utilise the appropriate transmission opportunities depending on the active resource pool for the connection.

Knowledge of a paired UE’s transmission pools only indicates when a connected pair of UEs may transmit to each other, but does not provide any information when connections with other UEs may have transmission opportunities. A UE may therefore also transmit the transmission pools configured for connections to all (or a set of) other UEs to which the UE is connected. Each UE therefore has greater awareness of transmission resources that may be utilised by the receiver UE.

The UEs may transmit the transmission pool configuration by transmitting each transmission pool configuration separately (for example by transmitting the actual configuration, or an index if configurations are shared by the UEs such that the other UE is aware of the details of a specific configuration) . Alternatively, an aggregate of the transmission pools may be sent, indicating the slots of all transmission opportunities for a UE. The indication could also be sent using a bitmap to indicate the transmission opportunity slots. The bitmap may represent a periodic configuration of one frame (10 slots) .

Transmitting the coordination using SCI/DCI dynamic signalling may lead to a large overhead, particularly where there are a large number of transmission opportunities. To avoid this overhead the information may be transmitted using higher-layer signalling, for example RRC, during connection setup or a connection configuration update. The higher layer signalling provides a more appropriate signalling platform for the semi-static configuration information which does not change frequently. Alternatively, a PSSCH payload can be used for conveying higher-layer information, which may be particularly appropriate where the information is sent in response to a trigger; for example due to an unexpected change or transmitter/receiver changes.

A drawback with utilising semi-static/higher layer signalling is that a UE cannot share dynamic information about its actual scheduling of transmissions with other UEs. To address this, while avoiding dynamic transmissions, UEs communicating (two UEs for unicast or a group of UEs for groupcast) can agree a split of resources which they will use for all of their transmissions. This may be shared via the higher-layer signalling, and may be semi-static to avoid frequent updates. For example, in a unicast pair of UE-A and UE-B it may be agreed that UE-A will only transmit on even-numbered slots, and UE-B will only transmit on odd-numbered slots. This arrangement may generalised by stating that the UEs agree a duplex configuration for the timing of transmissions between the UEs.

This applies to all transmissions by those UEs, not only transmissions to the other UE of the pair. This arrangement can be shared between the two UEs using higher-layer signalling (e.g. RRC) and allows each UE to know which resources the other UE may schedule a transmission on and can hence avoid those resources when selecting a transmission. This information may be used in either step 1 of the resource selection process to mark resources as unavailable, or in step 2 such that a selection is only made from resources on which the other UE is not scheduled to transmit. Other utilisation patterns may be agreed to share the resources in a predictable manner.

The information on sharing resources (duplex configuration) may be sent with a specified periodicity such that the pattern repeats itself, which avoids the need to retransmit the information periodically. The sequence length can be fixed in the standard or based on configuration (e.g. resource pool or RRC configuration) . The starting position for the sequence may be indicated or defined as a standard (e.g. starting from the next new frame, starting from slot N+x, x defined as well, e.g. 2 or 4 slots) . Also, the repeated pattern may vary on each repeat, for example using a shifting or hopping pattern to provide shuffling of resources periodically.

The configuration of the UEs to share resources (duplex configuration) can also be configured as part of the resource pool configuration. Certain UEs may be defined with additional responsibilities, for example as a group or platoon leader, or a scheduling UE, in which case the UEs may be utilised to define and share the relevant parameters.

The duplex configuration may be shared using a bitmap to define the duplexing pattern. The pattern may be derived from a formula or template, for example using a periodic or pseudo-random based formula. The pattern and its definition may also be dependent on the UE identity. Using a periodic transmit opportunity template/formula, the signalling may be limited to the periodicity chosen, and an offset for the start of that periodic transmission. The periodicity chosen may be based on higher layer parameters and traffic requirements. Using pseudo-random schemes, the seeds or initial conditions are to be sent as sequence parameters. The density (probability of occurrence of a transmission) of the scheme can also be tuned to take into account traffic requirement and given sent as parameter. A further alternative is to use an index-based table with predefined sets of duplexing schemes. The duplexing scheme could reuse or be based on the TDD duplexing scheme tables.

As noted briefly above, a UE may infer transmission opportunities of another UE based on their previous transmissions and reservations which may have been received at the UE as part its sensing process. The UE may reconstruct the transmission opportunities of other UEs from the detected information, and hence infer when future transmission opportunities may occur (which can then be removed as candidates for transmissions) .

A UE can determine scheduling information by decoding the source of the transmission and reserved resources from a received second-stage SCI. The UE can thus determine that the UE has a transmission slot in the slot the SCI is received in and slots indicated for retransmissions. If the source of the SCI is a UE with which the monitoring UE is paired it can store and track all transmission slots of that UE and assume they belong to the UE’s transmission pools. This approach allows a UE to determine the transmission slots of the other UE for other UEs without having to update RRC configuration. The latest received SCI information represents the latest version of ongoing configurations and can be used to overwrite previous configurations that do not match the new information. A validity duration may be applied to transmission opportunity information and the information deemed invalid after that duration to avoid information becoming inaccurate if other UE’s change configuration.

UEs may also share coordination information in the form of direct indications of available or excluded resources or resource sets. The UEs receiving such information may then be able to identify a good transmission opportunity at a specific time and frequency. The first phase resource identification is expected to identify 20%of resources as available. This approach may be restricted as there are limitations how many resources can be indicated, for example if a transmitter and receiver do not have commonly available resources, or do not have sufficient common resources to ensure a large enough resource selection set. This restriction may be particularly acute for groupcast communications where several users need to be scheduled on a common resource.

A UE may transmit an indication of resources that another UE should avoid when transmitting to the UE. For example, resources which have strong interference at the receiver, where there are scheduled reception resources/slots, or where the UE has its own scheduled transmissions or opportunities. These types of exclusions can be signalled with a common “busy” or “excluded” indication, or information may be provided on why they are not available. For example, knowing resources are not suitable for transmission (as opposed to being already scheduled) may assist a UE to locate other suitable resources.

Available, or excluded, resources are likely to change on a dynamic basis and hence signalling should utilise an appropriate format. For example, dynamic configuration messages may be most appropriate, including PSCCH or PSSCH. The information may be broadcast to specific UEs for a certain connection (e.g. using unicast to the other UE of a unicast link, using groupcast to other members of a groupcast connection, or unicast to one or a subset of members of a groupcast connection) , or may be broadcast to all UEs which can receive it. Utilising transmission to specific UEs may be more adaptive (e.g. if based on an on-demand procedure) , and the transmission may minimise resource and power utilisation. However, the information may also be beneficial to other UEs and hence the additional resources for a broadcast transmission may be worthwhile. The type of transmission to use can be specified in the configuration, for example by resource pool. The configuration may specify a threshold such that if the number of unicast links and users in groupcast links are below the threshold unicast or groupcast is used, whereas above that threshold broadcast is used.

The coordination information may be transmitted on a periodic basis, or in response to a trigger or event. Specific examples of triggers or events include: -

- Connection establishment or updates. The shared information can be included in the RRC connection or configuration messages.

- Last known information expired; user can send a new coordination information.

○ When the expiration date is passed (e.g. for repeated sequences) .

○ When no expiration is set but the explicit sequence sent is finished.

- Group member composition changed

○ In groupcast, when the group composition changes, to collect coordination information from other members (e.g. new member added) .

- Traffic requirement updates

○ If a user traffic requirement changed (e.g. need for more or less transmission opportunities) , even before a potential expiration, it can share new coordination information to others.

- Jointly transmitted with CSI reports

For unicast and groupcast operation, the traffic flow directions may be known and different varieties of situations may exist. There may be a user or a subset of users, who may be holding the role of the transmitters through most of the session, thus the uniform per member configurations may not be relevant in such situations. To accommodate such situations, on demand coordination requests triggering the transmission of coordination information may be made. Information of coordination can also be transmitted on-demand, where a node willing to transmit data to a receiving node (or group) requests the receiving node (or group) to transmit the coordination information. The request can specify a limited set of resource to consider, in time or frequency domain, to limit the sensing/processing required or because non-requested resources are not available at the transmitter side. The time or frequency to consider can be specified with a range whose start and end are specified in the request. These limitations will then override (pre-) configured limitations if any. The on-demand requests can also be triggered by similar events as described in the previous paragraph.

As noted, coordination information may also be transmitted periodically, for example jointly with SL-SSB or other broadcast information. Such broadcast information has very limited resources and so it is preferable to minimise adding additional content. Paragraphs may therefore be reused (for example, node ID, slot timing, etc) and the coordination information derived using a known mapping. For example, for the duplex pattern, the node ID may be used as an offset for period transmissions or the initial condition for a pseudo-random sequence.

As noted above, a validity or expiration time for coordination may be defined. This may be set generally, or for each connection, or resource pool by configuration or standard. Furthermore, the validity or expiration time may be transmitted with the coordination information if it is not configured, or to override the configuration.

The sharing of coordination information may be activated or deactivated by configuration, according to resource pool or link (using RRC configuration) . The activation and deactivation may be triggered by a range of parameters and situations. For example, the utilisation level of resources. For example, utilisation may be defined by the Channel Busy Ratio and a threshold applied. Sharing of coordination information may be activated if the CBR is above the threshold and deactivated if the CBR is below the threshold. The sharing of coordination information between UEs may also be dependent on the capability of the UEs, since legacy UEs may not support the functionality.

The quantity of resources to be indicated in the coordination information may be configured, for example by resource pool or for each link. This may set the length of the bitmap for the duplexing scheme coordination, or the number of resources indicated. The resource considered for coordination can also be restricted to a certain set of sub-channels or slots, and the relevant set (or start/stop index) may be configured by higher layer configuration. These limitations can be based on the UE/network desired limitation (e.g. power saving mode, traffic requirement) or to consider the scheduling that it has already done.

A UE may also transmit the coordination information to a base station to which it is connected in order to enable the information to be used by the base station for scheduling in Mode 1 mode, if both Mode 1 and Mode 2 are used simultaneously in a resource pool. The information may be transmitted using MAC CE (i.e. carried as data in the PUSCH) . This can be sent as a stand-alone information or carried jointly with other MAC relevant information such as a Buffer Status Report to jointly signal an updated buffer status with the corresponding resource information. This can be done joint or separately from the rest of the information sharing between users in Mode 2.

For groupcast transmissions resources which are suitable for all UEs in the group must be selected and hence information from all UEs may be useful. When a UE receives coordination information from a member of the group it may aggregate the information with its own information and transmit it to other members of the group. The set of information can be simply stacked together or can be aggregated/merged into a single combined information to reduce the content and remove redundancy. The ID of the UE which accumulates the information may also be passed together with the aggregated information. In the case of duplexing scheme, the merged information can be to indicate transmission when either of the UEs are in transmission mode. In the case of resource indication, the aggregation can be restricted to the commonly available (or cumulate the non-available) resources.

There is therefore a method of sharing resource coordination information to improve selection of transmission resources for device to device transmissions. In an example a UE may determine future transmission opportunities for a UE to which it intends to transmit and may exclude all resources in the slots in which the other UE may transmit. The UEs may also exchange information to agree a subset of resources which each UE may utilise for transmissions. That is, the UEs may agree a duplex configuration for transmissions in each direction between the UEs. The coordination information may be shared by dynamic signalling or via higher layer signalling.

Figure 4 shows a flow chart of an example method of selecting resources for transmissions from a first UE to a second UE using the principles discussed herein. At step 400 a first UE monitors the transmission channel for signals reserving resources and other transmission such as RRC configuration updates. At step 401 the UE stores information regarding other UE’s planned transmission scheduling, for example as received in SCI messages from other UEs. This information may be termed coordination information and may include resource reservations, timing of scheduling, RSRP levels, packet priorities, and other data relevant to utilisation of transmission resources by other UEs.

At step 402 the UE wishes to schedule a transmission and thus implements the (re) selection process to identify resources. At step 403 the UE excludes unavailable transmission resources from the selection window. Unavailable resources are determined based on the coordination information, for example reservations for a resource with an RSRP that is higher than a threshold. Other criteria may also be applied as discussed herein, for example all resources in a slot in which the destination UE has a transmission scheduled may be excluded. At step 404, after excluding the unavailable resources the UE chooses resources for the transmission from the remaining resources, for example using a random selection, potentially with constraints as defined by standard or configuration. The UE then proceeds with the transmission on the selected resources at step 405.

At step 403 the UE may mark resources with further information such as the relevant priority or RSRP values This may enable the UE to make use of those resources if other resources are not available and relevant thresholds for priority and RSRP are. For example, a high priority transmission may pre-empt the previously scheduled transmission. When applying the criteria at step 403 the UE may exclude all resources in a slot in which the UE is scheduled to receive a transmission. Similarly, all resources in the slot may be marked with the relevant RSRP and/or priority to guide pre-emption if appropriate.

Although not shown in detail any of the devices or apparatus that form part of the network may include at least a processor, a storage unit and a communications interface, wherein the processor unit, storage unit, and communications interface are configured to perform the method of any aspect of the present invention. Further options and choices are described below.

The signal processing functionality of the embodiments of the invention especially the gNB and the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc. ) , mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) (RTM) read or write drive (R or RW) , or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card) , a communications port (such as for example, a universal serial bus (USB) port) , a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms ‘computer program product’ , ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally 45 referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings) , when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory. In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code) , when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP) , or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices.

Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’ , ‘an’ , ‘first’ , ‘second’ , etc. do not preclude a plurality.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims

A method of selecting transmission resources for a transmission from a first UE to a second UE in a cellular communications network, the method comprising the steps of

monitoring a transmission channel for signals reserving transmission resources and storing coordination information regarding transmissions scheduled by other UEs;

identifying potential transmission resources for a first transmission by excluding unavailable transmission resources based on a first criteria applied to the coordination information; and

selecting transmission resources for a transmission from the potential resources according to a second criteria.
A method according to claim 1, wherein the step of monitoring for signals reserving transmission resources comprises monitoring for SCI transmissions.
A method according to claim 1, wherein the coordination information comprises information regarding at least one of resource reservations, scheduling of transmissions, RSRP levels, and transmission priorities.
A method according to any preceding claim, wherein the first criteria includes the RSRP being higher than a threshold.
A method according to any preceding claim, wherein the first criteria includes whether the second UE has a transmission scheduled at the time of the first transmission.
A method according to any preceding claim, wherein the first criteria includes whether the transmission resources are a transmission opportunity for the second UE.
A method according claim 6, wherein transmission opportunities are identified based on the resource pool (s) assigned to the second UE.
A method according to claim 7, wherein transmission opportunities are identified based on previous transmissions by the second UE.
A method according to any preceding claim, wherein the first criteria include whether a transmission is scheduled in the time and frequency of the transmission resources.
A method according to any preceding claim, wherein the second criteria is a random selection process.
A method according to any preceding claim, wherein the second criteria include different priorities for potential transmission resources.
A method according to claim 11, wherein transmission resources which are transmission opportunities for the second UE are assigned a lower priority for selection.
A method according to claim 11, wherein the priority is dependent on the time until the transmission resources occur.
A method according to any preceding claim, wherein transmission resources excluded from selection are changed to be available if greater than a threshold amount of potential transmission resources were excluded as unavailable.
A method according to any preceding claim, wherein the first criteria are dependent on whether the first transmission is an initial transmission or a retransmission.
A method according to any preceding claim, wherein the second criteria are dependent on whether the first transmission is an initial transmission or a retransmission.
A method according to any preceding claim, wherein the first and/or second criteria are received at the first UE in RRC signalling.
A method according to any preceding claim, further comprising the step of transmitting coordination information from the first UE.
A method according to claim 18, wherein the coordination information is transmitted to the second UE.
A method according to claim 18, wherein the coordination information is transmitted to a base station of the cellular network.
A method according to any of claims 18 to 20, wherein the coordination information includes one or more resource pools allocated to the first UE.
A method according to any of claims 18 to 21, wherein the coordination information is transmitted using dynamic signalling.
A method according to any of claims 18 to 22, wherein the coordination information is transmitted using an SCI or DCI message.
A method according to any of claims 18 to 21, wherein the coordination information is transmitted using RRC signalling.
A UE configured to perform the method of any preceding claim.