Patent Application
20250168711
At least one of the present embodiments generally relates to a method for resource reservation. At least one of the present embodiments also relates to a device configured to implement the method.
In a Vehicle-to-everything (V2X) communication system information may be exchanged between a vehicle and any entity, e.g. another vehicle, a pedestrian, infrastructure entities such as road-side units (RSU). While previous versions of V2X communication designed as LTE C-V2X were built on top of LTE cellular networks, most recent versions of V2X communications designed as NR (acronym of New Radio) V2X in 3rd Generation Partnership Project (3GPP) are built on top of 5G cellular networks. In NR V2X, the transmission can be done through a sidelink (SL) between two user equipments (UE). Two sidelink communication modes are defined. In SL mode 1, a base station (BS) controls the SL transmission. In SL Mode 2, a UE performs sensing and autonomously, i.e. without assistance of a base station, selects a radio resource from a pool of radio resource candidates for its direct communication with another UE over a so-called PC5 interface. A radio resource or more simply a resource is defined by a time-frequency slot. A UE performing radio resource reservation as specified in 3GPPP NR V2X SL mode 2 is configured to perform three steps.
In a first step, the UE tries to hear other UEs in local radio resources in a sensing window [t0; t1] of typically 1 s, where t0 and t1 are time instants. The UE thus obtains a map of the resources reserved by others and of the free resources, i.e. resources not used by any other UE. In a second step, the UE randomly selects radio resources to use for its own transmission among the free resources identified thanks to the sensing. In a third step, the UE uses the selected resources for its transmissions in a so-called reservation window [t1; t2] of typically 1 to 500 ms where t2 is a time instant.
NR V2X SL mode 2 further considers SPS (English acronym of “Semi-Persistent Scheduling”) for periodic traffic. Once one or multiple resources are selected, the UE repeat the resource reservation N times, N being an integer, without repeating neither the resource sensing step nor the resource selection step. In other words, the UE periodically uses the same resources in a reservation window [t1; N*t2] of typically 1 ms to 15 s. Since the SPS reservation may last for several seconds, the sensing made over 1 s before the resource selection is quickly outdated. As the propagation condition evolves, the sensing information used for reservation becomes obsolete and collisions may happen.
In Release 17 of 3GPP NR V2X, a new feature called “InterUE-coordination” is considered for improving reliability of resource reservation by avoiding the problem of hidden node and thus limiting collisions. It makes it possible for a first UE to provide assistance to a second UE which obverses more or less the same channel but at a distant spatial position. More precisely, the first UE is configured to share its sensing results with the second UE such that the second UE takes benefit from an extended sensing. Thanks to this new feature, the second UE may be aware of UE located outside its communication range but inside the communication range of the first UE. This feature provides an extended sensing in space but not in time and thus cannot resolve the problem of outdated sensing.
Besides, given the limited sensing capability in time and space of the UEs, e.g. because of the communication range R and the sensing window [t0; t1], the UEs often encounter the problem of hidden incoming node, e.g. a node is a UE or more generally a terminal. This problem is illustrated by
It is thus desirable to find a resource reservation method that avoids the problems of outdated sensing and hidden incoming node and thus limits the risk of packet collision.
At least one of the present embodiments generally relates to a resource reservation method in a private wireless communication network comprising a set of terminals moving along a path, a set of road-side units located along the path in radio communication with the terminals and with an application server, the application server being connected to a database associating with each configuration of terminals in a given spatial area metrics values representative of how radio resources are used in said given spatial area. The method comprises:
The method disclosed limits the risk of packet collision by providing assistance data to the terminals, said assistance data being used to adapt their radio resource reservation so as to better orthogonalize their radio resource reservations.
In one embodiment, identifying by the application server whether there is a risk of collision between packets to be sent or received by the terminals whose radio communication ranges intersect comprises identifying that there is a risk of collision in the case where said terminals whose radio communication ranges intersect have at least one identical reserved radio resources.
In one embodiment, each configuration of terminals in the database being associated with a tag indicating whether said configuration is associated with difficult radio conditions, identifying by the application server whether there is a risk of collision between packets to be sent or received by the terminals whose radio communication ranges intersect comprises:
In one embodiment, generating by the application server assistance data in the form of non-preferred radio resources comprises:
In one embodiment, determining the set of preferred and/or non-preferred radio resources from the collision rate comprises determining a radio resource as a non-preferred radio resource in the case where said collision rate of is above a threshold value and as a preferred resource otherwise.
In one embodiment, generating by the application server assistance data in the form of preferred and/or non-preferred radio resources comprises:
In one embodiment, determining the set of preferred and/or non-preferred radio resources from the probabilities of interference comprises determining a radio resource as a non-preferred radio resource in the case where said probability of interference is above a threshold value and as a preferred resource otherwise.
In one embodiment, generating by the application server assistance data in the form of preferred and/or non-preferred radio resources comprises:
In one embodiment, determining the set of preferred and/or non-preferred radio resources from values of degradation in transmission performance comprises determining a radio resource as a non-preferred radio resource in the case where said values of degradation in transmission performance is above a threshold value and as a preferred resource otherwise.
In one embodiment, using, by said least one terminal, the generated assistance data transmitted by the application server for adapting radio resource reservation comprises selecting, for a final pool of radio resource candidates, radio resources identified as preferred resources in both an initial pool of radio resource candidates and the assistance data.
In one embodiment, using, by said least one terminal, the generated assistance data transmitted by the application server for adapting radio resource reservation comprises removing, from an initial pool of radio resource candidates, the radio resources identified as non-preferred resources in the assistance data.
A private wireless communication network is also disclosed. The private wireless network comprises a set of terminals moving along a path, a set of road-side units located along the path in radio communication the terminals and with an application server, the application server being connected to a database associating with each configuration of terminals in a given spatial area metrics values representative of how radio resources are used in said given spatial area. The application server and the terminals are configured to implement the resource reservation method according to anyone of the embodiments disclosed.
A computer program product is disclosed that comprises program code instructions that can be loaded in a programmable device, the program code instructions causing implementation of the resource reservation method according to anyone of the embodiments disclosed when the program code instructions are run by the programmable device.
A storage medium is disclosed that stores a computer program comprising program code instructions, the program code instructions causing implementation of the resource reservation method according to anyone of the embodiments disclosed 1 when the program code instructions are read from the storage medium and run by a programmable device.
The characteristics of the invention will emerge more clearly from a reading of the following description of at least one example of embodiment, said description being produced with reference to the accompanying drawings.
The RSU 110, 111 offer services of the wireless communication network to UEs. The train 130 that receives/sends data regarding its trajectory's control or a terminal 131 located in the train 130 are examples of such UEs. The terminal 131 is for instance a mobile terminal or a relay station allowing mobile terminals located in the train to access the services of the wireless communication network via the RSU. Each RSU being a fixed radio terminal is able to transmit/receive control and data information with neighboring equipment, e.g. another RSU or one vehicle (e.g. one train). Each RSU is provided with some application layer features, such as encapsulation and decapsulation to read (to send respectively) data from/to an access layer to/from application layer, to be able to exchange information with any application server SRV.
The wireless communication network PNW further comprises at least one application server SRV configured to get information, e.g. the local channel environment, from each RSU. The server SRV may be an independent physical entity or an extended software entity distributed in all the RSUs. The SRV is further configured to compute radio-based metrics, e.g. Channel Busy Ratio (CBR) or Channel occupancy Ratio (CR). In addition, the SRV knows all the terminals in the private network, namely it knows their physical deployment and mobility, e.g. their spatial position, velocity, trajectory. These latter data may be known by the SRV with a certain granularity in time, e.g. every second in which case the SRV is able to interpolate between the sampled data to extrapolate a continuous prediction of the terminal's trajectory. The SRV is further able to associate a position in space and duration in time with any identified application packet attached to a terminal. SRV represents the application layer group of all RSUs. The RSUs are distinct physical entities but given their connection with the SRV, any terminal in the PNW targets the best RSU to reach the SRV and the SRV targets the best RSU to reach any terminal in the PNW. The best RSU is for example the RSU for which the channel is the most reliable or the RSU that is physically the closest to the terminal. The wireless communication network PNW further comprises a database DB. Database assistance is routinely used in navigation and radio communication services. The DB-assisted services usually rely on statistical data related to the users' experience in space and time. The DB is thus filled, e.g. during one week, with several metrics by considering numerous terminals crossing a given spatial area at various time instants. The metrics are representative of a radio situation from the point of view of the terminals indicating how the radio resources are used in the given spatial area. Therefore, the metrics can be computed from the sensing of the RSU and/or from the sensing of the terminals. During this timeframe, for each terminals' configuration (TC) a specific radio situation is thus stored. The metrics may correspond to a model of the wireless communication channel such as a channel power delay profile, to a fading level in different radiofrequency resources, to an interference level in different radiofrequency resources, to a power level in different radiofrequency resources, to a CBR, to one or more previous estimates of the instantaneous wireless communication. More generally, the metrics may correspond to any type of data related to a wireless communication channel experienced in the given spatial area that may be useful for a terminal to adjust its communication settings in the area.
A terminals' configuration TC is defined as a spatial organization of a set of terminals (defined by spatial position of each terminal) with a certain velocity in the given spatial area. An example of Nb, e.g. Nb=10, such terminal configurations is depicted on
In order to limit the number of TC, an average processing may be performed such that for similar TC, the DB gets an average radio situation. Consequently, in the DB, for each registered TC an average radio situation is stored.
In a variant, no average is made. The DB only keeps the last measured metric values. This is a particular case where only one time instant is considered. The radio situation is thus recent but not representative of the past.
In another variant, the DB is a collection over time and space of instantaneous situations in which a specific TC implies a specific radio situation.
From the stored configurations in association with metrics representative of a radio situation, one is able to predict the radio situation of a current configuration TCcurr by selecting as a prediction the metric values associated in the DB with the TC that is the closest to TCcurr.
In a step S300, the physical trajectory, velocity and radio communication range of each terminal are obtained by the SRV. For example, the SRV gets the trajectories, velocities and communication ranges from a memory where they are stored.
In a step S302, the SRV identifies from the trajectories, the terminals' velocities determined at S300 and further from the communication ranges which are known by the SRV whether there is a space area [si; sf] and consequently a corresponding time interval [ti; tf]>t0 wherein the respective radio communication ranges of at least two terminals UE1 and UE2 are going to intersect. In the case where there is no such intersection, i.e. no space area [si; sf], the method ends for the at least two terminals UE1 and UE2.
In a step S304, it is detected whether there is a risk of collision between the packets to be sent/received by the at least two terminals UE1 and UE2 in [ti; tf]. More precisely, in the case where the respective radio communication ranges of the at least two terminals intersect, it is determined that there is a risk of collision in the case where some of their reserved radio resources are identical. In the case where a risk of collision is detected then the method continues at S306. In the case where no risk of collision is detected, e.g. because their resource reservation are disjointed, then the method ends.
It may be determined that the radio communication ranges intersect but that there is no risk of collision because the reserved radio resources are orthogonal. In one embodiment, a risk of radio collision in [ti; tf] is detected from the reserved radio resources determined at time to and the periodicity of the SPS. Indeed, as soon as a terminal uses the resources that it selected, it transmits, in a part of the packet, the Sidelink Control Information (SCI) that indicates reservation details, e.g. the time-frequency position of its next reservation(s) and the periodicity of these reservations, if any.
In a second embodiment, the RSUs gather radio measurements, e.g. sensing reports, from the neighbouring terminals. The SRV aggregates information from the RSUs, comprising each RSU internal data such as the terminals' sensing but also the associated terminals' positions, velocity, density, etc. Through a learning process, the SRV is then able to construct a space-time map of radio resource used to associate with any terminals' configuration (TC) a status of interference as a function of space and time. Consequently, knowing the status of interference as a function of space and time, the TC associated with difficult radio conditions may be tagged as such in the database. In S304, the SRV identifies what TC the terminals belong to, or identifies the closest TC they belong to. If the said TC is associated with difficult radio conditions, a risk of collision is thus detected and the method continue to S306.
In a step S306, assistance data are generated by the SRV between t1 and ti from data extracted from the database DB. The assistance data are, for example, in the form of non-preferred and/or preferred radio resources. In an example, the assistance data is provided as a table as depicted on
To this aim, the InterUE-coordination mechanism of 3GPP NR Release 17 may be used. This mechanism makes it possible for a first terminal to share its sensing result with a second terminal which therefore benefits from an extended sensing. To this aim, the first terminal informs the second terminal of its set of preferred and/or non-preferred resources determined based on its sensing results. In an embodiment, the second terminal selects, for its final pool of radio resource candidates, the resources that are identified as preferred resources in both its initial pool of radio resource candidates and in the set of preferred resources transmitted by the first terminal. In another embodiment, the second terminal removes from its initial pool of radio resource candidates the set of non-preferred resources transmitted by the first terminal to obtain its final pool of radio resource candidates.
The same principles are used herein, SRV determines a set of preferred and/or non-preferred radio resource and transmits this set of preferred and/or non-preferred resources to UE1 and/or UE2 as assistance data. In one embodiment, at least one of the two terminals selects, for its final pool of radio resource candidates, the resources that are identified as preferred resources in both its initial pool of resource candidates and the assistance data sent by SRV. In a variant, at least one of the two terminals removes from its initial pool of radio resource candidates the set of non-preferred resources identified as such in the assistance data in order to obtain its final pool of radio resource candidates.
According to the specifications of the standard 3GPP TR 37.985 v17.0.0 (2021-12) “Overall description of Radio Access Network (RAN) aspects for Vehicle-to-everything (V2X) based on LTE and NR (Release 17)”, Section 6.3.2.2, a first terminal provided with its final pool of resource candidates randomly selects a given number Nr of resources from the said pool where Nr depends on the terminal requirements and needs. For example, Nr equals 3 to allow for an initial transmission and two retransmissions of a single packet. The size of the final pool of resource candidates should be greater than or equal x % of the pre-configured resource pool shared by the first terminal and other terminals, wherein x is set, for example, to 20, 35 or 50 depending on the traffic priority of the first terminal. The Nr resources selected by the first terminal are then effectively used by the first terminal according to their time-frequency position for transmission and retransmissions of a packet. A packet transmitted, or retransmitted, on a resource by the first terminal contains, at least, a data and an SCI such that a second terminal is able to sense the said resource used by the first terminal by trying to decode the said SCI and by measuring the associated RSRP. When the said SCI is decoded by the second terminal and when the associated RSRP is above a pre-configured threshold of the second terminal, then the said resource, and potentially the next resources indicated in the said SCI, are said to be occupied or reserved by the first terminal and the second terminal does not include these said resources in its initial pool of resource candidates.
In a step S306-1, the current terminals' configuration (TCcurr) is determined. The TC in the database that is the closest from TCcurr is identified. The radio situation associated with the identified TC is then used as a prediction of the radio situation for the current terminals' configuration. To each space position for one TC close to one single registered TC, the DB gets a radio situation to be used as a prediction of the radio situation associated with TCcurr. This information (TC versus radio situation) may optionally be used in step S303-2.
In a step S306-2, from the sensing reports stored in the DB and associated with the TC identified in S306-1 as the closest to TCcurr, SRV deduces the future status of each resource r, e.g. the number of terminals that may use the resource r which amounts to the number of collisions for r. By dividing this number by the number of resource reservations, SRV obtains a collision rate λr. By comparing the collision rates of all the resources, SRV is able to extract the resources more likely to host a serious collision. In a step S306-3, the collision rate λr is compared with a preconfigured threshold to determine the set of non-preferred and/or preferred resources. In the case where the collision rate λr is greater than a preconfigured threshold λTH then the associated resource is tagged as a non-preferred resource and otherwise as a preferred resource. The set of non-preferred and/or preferred resources is then transmitted to the terminals.
In a first variant, the collision rate λr per resource r is combined with a power level. Indeed, a resource collision results in interference if the associated signals physically collide implying that the terminals are capable of sensing the others. From the reports stored in the DB and associated with the TC identified in S306-1 as the closest to TCcurr, the SRV computes a number of interferences or a probability of interference regarding the associated power of each terminal. More precisely, the SRV being provided with the transmitted power of each terminal, it is able to predict for each resource, previously mentioned as hosting a collision in the near future, i.e. for which λr>λTH, a SIR (acronym of Signal-to-Interference Ratio). By comparing it to a first preconfigured threshold, the SRV is able to define a probability of interference, e.g. using the relative difference between the first threshold and the predicted SIR. In the case where the probability of interference is greater than a second preconfigured threshold, then the associated resource is tagged as a non-preferred resource in S306-3 and is tagged as a preferred resource otherwise. The set of non-preferred and/or preferred resources are then transmitted to the terminals.
In a second variant, link-level parameters can be associated with each TC in the database. In this case, the link-level parameters associated with the TC identified as the closest to TCcurr in the step S306-1 are used to predict the performance of the transmission, e.g. the Packet Received Ratio (PRR), the Frame Error Rate (FER). Indeed, according to link-level parameters of the terminals, the interference might impact the performance of the transmission, e.g. the Packet Received Ratio (PRR), the Frame Error Rate (FER). Given a noise figure and a previously mentioned SIR, the SRV is able to deduce a SINR (acronym of Signal to Interference and Noise Ratio). The SRV being provided with a modulation and coding scheme to be used by the terminals, it is able to predict a frame error rate and/or a packet received ratio, used as usual performance metrics in such a scenario. In the case where the performance degradation, e.g. the FER, is greater than a preconfigured threshold then the associated resource is tagged as a non-preferred resource in step S306-3 and is tagged as a preferred resource otherwise. The set of non-preferred and/or preferred resources are then transmitted to the terminals.
The transmitted set of non-preferred and/or preferred resources used as assistance data in step S308 by the terminals may also be generated in S306 according to the various embodiments disclosed below.
In a first embodiment, SRV allows one terminal U1 for freely selecting its resource. Then, upon the need for resource selection of U2, U2 is provided the set of non-preferred resources being the resources reserved by U1. Generally, upon the need for resource selection of Un>1, Un is provided the set of non-preferred resources being the resources reserved by {Uk<n} k in E, where E represents the terminals potentially interfering.
In a second embodiment, from the TC identified in S306-1 as the closest to TCcurr, the SRV predicts what resources any terminal would select. According to the TCs, SRV extracts assistance data that lead to good radio situations in the past. Therefore, before any resource reservation, SRV transmits the assistance data to the terminals.
In a third variant, if SRV predicts too much interference in such a way that the distributed approach is too much detrimental to the performance, then SRV decides to schedule the terminals. Imitating a base station, SRV computes the exact set of preferred resources for each terminal in such a way that none set collide with any other set.
The server 10 comprises, connected by a communication bus 106: a processor or CPU (acronym of “Central Processing Unit”) 101; a random access memory RAM 102; a read only memory ROM 103; a storage unit 104 such as a hard disk or such as a storage medium reader, e.g. an SD (acronym of “Secure Digital”) card reader; and at least one set of communication interfaces COM 105 enabling the server 10 to transmit and receive data.
The processor 101 is capable of executing instructions loaded into the RAM 102 from the ROM 103, from an external memory (such as an SD card), from a storage medium (such as the HDD), or from a communication network. When the server 10 is powered up, the processor 101 is capable of reading instructions from the RAM 102 and executing them. These instructions form a computer program causing the implementation, by the processor 101, of the methods described in relation to
The methods described in relation to
| Number | Date | Country | Kind |
|---|---|---|---|
| 22305359.6 | Mar 2022 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/028552 | 7/15/2022 | WO |
