WO2019233563A1

WO2019233563A1 - Progressive multi-criteria based sidelink resource allocation

Info

Publication number: WO2019233563A1
Application number: PCT/EP2018/064754
Authority: WO
Inventors: Ricardo BLASCO SERRANO; Shehzad Ali ASHRAF; Marco BELLESCHI; Liang Hu
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2018-06-05
Filing date: 2018-06-05
Publication date: 2019-12-12

Abstract

A radio device (20) monitors a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices (30, 40). The radio device (20) selects a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices (30, 40). Further, the radio device (20) selects a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set by the selected subset and the radio resources estimated to be used. The radio device (20) sends a first sidelink radio transmission (206) on the first subset. The first sidelink radio transmission (206) indicates a reservation of the second subset. Further, the radio device (20) sends a second sidelink radio transmission (208) on the second subset.

Description

Progressive multi-criteria based sidelink resource allocation

Technical Field

The present invention relates to methods for controlling radio transmissions and to corresponding radio devices, systems, and computer programs.

In a wireless communication network a transmission direction from the wireless communication network to a UE (user equipment) is typically referred to as“downlink” (DL) direction, while a transmission direction from the UE to the wireless communication network is typically referred to as“uplink” (UL) direction. In addition to DL radio transmissions and UL radio transmissions, it is known to support direct radio transmissions between UEs. These direct radio transmissions may be referred to as“sidelink” (SL) radio transmissions. For example, in the case of the LTE (Long Term Evolution) radio technology specified by 3GPP (3^rd Generation Partnership Project), SL radio transmissions are defined in 3GPP TS 36.201 V14.1.0 (2017- 03). The SL radio transmissions may for example be used for V2X (vehicle-to-anything) communications, which may for example include: V2V (vehicle-to-vehicle) communications between vehicles; V2P (vehicle-to-pedestrian) communications between a vehicle and a device carried by an individual, e.g., a handheld terminal carried by a pedestrian, cyclist, driver, or passenger; V2I (vehicle-to-infrastructure) communications between a vehicle and a roadside unit (RSU) of traffic infrastructure, e.g., an entity transmitting speed limit notifications, and V2N (vehicle-to-network) communications between a vehicle and a node of the wireless communication network. As a general rule, V2X communications may utilize network infrastructure when available. However, at least basic V2X communication functionalities should also be possible without network infrastructure, e.g., outside network coverage.

In 3GPP TS 36.213 V15.0.0 specifies a mode of operation for SL radio transmissions, referred to as“mode 4”. In mode 4, the UE selects the radio resources to be used for a SL radio transmission from a large set of radio resources configured by the network or preconfigured in the UE. The resource allocation in mode 4 makes combined use of two features: semi- persistent and sensing-based resource allocation. The semi-persistent allocation aspect utilizes the fact that typical safety V2X traffic is more or less periodic, which means that data to be transmitted is typically are generated at regular intervals. This regular character of data transmissions allows a transmitting UE to notify other UEs about its intention to use certain radio resources for future transmissions, by making a reservation of such time-frequency resources. The sensing-based allocation aspect involves monitoring the set of radio resources to learn about the presence of semi-persistent transmissions by other UEs. In this way, the transmitting UE can select the radio resources for its own SL radio transmissions in such a way that collisions with SL radio transmissions by other UEs are avoided.

In mode 4 each UE selects resources for its own SL radio transmission based on locally available information, e.g., sensing measurements and reservations indicated by other UEs. Since both the available information and the decision are local, the combination of choices by different UEs may result in a highly fragmented distribution of the utilized radio resources, which is undesirable from a system point of view. The fragmented distribution can have the effect that although sufficient unutilized radio resources would in principle be present, a collision free allocation of radio resources for a SL radio transmission is not possible due to a lack of sufficiently large contiguous resource space.

Accordingly, there is a need for techniques which allow for efficiently allocating radio resources for SL radio communications.

Summary

According to an embodiment, a method of controlling SL radio transmissions in a wireless communication network is provided. According to the method, a radio device monitors a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices. The radio device selects a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices. Further, the radio device selects a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set by the selected subset and the radio resources estimated to be used. The radio device sends a first SL radio transmission on the first subset. The first SL radio transmission indicates a reservation of the second subset. Further, the radio device sends a second SL radio transmission on the second subset.

According to a further embodiment, a radio device for a wireless communication network is provided. The radio device is configured to monitor a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices. Further, the radio device is configured to select a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices. Further, the radio device is configured to select a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set of radio resources by the selected subset and the radio resources estimated to be used. Further, the radio device is configured to send a first SL radio transmission on the first subset, the first SL radio transmission indicating a reservation of the second subset. Further, the radio device is configured to send a second SL radio transmission on the second subset.

According to a further embodiment, a radio device for a wireless communication network is provided. The radio device comprises at least one processor and a memory containing instructions executable by said at least one processor, whereby the radio device is operative to monitor a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices; to select a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices; to select a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set of radio resources by the selected subset and the radio resources estimated to be used; to send a first SL radio transmission on the first subset, the first SL radio transmission indicating a reservation of the second subset; and to send a second SL radio transmission on the second subset.

According to a further embodiment, a system is provided. The system comprises a first radio device and a second radio device. The first radio device is configured to monitor a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices. Further, the first radio device is configured to select a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices. Further, the first radio device is configured to select a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set of radio resources by the selected subset and the radio resources estimated to be used. Further, the first radio device is configured to send a first SL radio transmission on the first subset, the first SL radio transmission indicating a reservation of the second subset. Further, the first radio device is configured to send a second SL radio transmission on the second subset. The second radio device is configured to receive the first SL radio transmission and the second SL radio transmission. According to a further embodiment of the invention, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of a radio device for a wireless communication network. Execution of the program code causes the radio device to monitor a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices. Further, execution of the program code causes the radio device to select a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices. Further, execution of the program code causes the radio device to select a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set of radio resources by the selected subset and the radio resources estimated to be used. Further execution of the program code causes the radio device to send a first SL radio transmission on the first subset, the first SL radio transmission indicating a reservation of the second subset. Further, execution of the program code causes the radio device to send a second SL radio transmission on the second subset.

Details of such embodiments and further embodiments will be apparent from the following detailed description of embodiments.

Brief Description of the Drawings

Fig. 1 shows an exemplary scenario for illustrating radio transmissions in a wireless communication network according to an embodiment of the invention.

Fig. 2 illustrates an example of processes in which radio resources for SL radio transmissions are allocated according to an embodiment of the invention.

Fig. 3 illustrates an exemplary timing of SL radio transmissions according to an embodiment of the invention.

Figs. 4A, 4B and 4C illustrate examples of radio resource allocations according to an embodiments of the invention. Fig. 5 shows a flowchart for schematically illustrating a method according to an embodiment of the invention.

Fig. 6 shows a block diagram for illustrating functionalities of a radio device according to an embodiment of the invention.

Fig. 7 schematically illustrates structures of a radio device according to an embodiment of the invention.

Detailed Description of Embodiments

In the following, concepts in accordance with exemplary embodiments of the invention will be explained in more detail and with reference to the accompanying drawings. The illustrated embodiments relate to controlling of SL radio transmissions in a wireless communication network. In the illustrated examples, it is assumed that the wireless communication network is assumed to be based on the LTE radio technology. However, it is noted that other radio technologies supporting SL radio transmissions could be used as well, e.g., a 5G radio technology like the NR (New Radio) technology currently developed by 3GPP. As used herein, the term“transmission” is used to cover both aspects of sending and receiving.

In the illustrated concepts, the radio device sending an SL radio transmission is also responsible for selecting the radio resources for the SL radio transmissions. The radio device selects the radio resources from one or more contiguous set of radio resources. Such contiguous set of radio resources may for example correspond to a contiguous group of frequency channels or resource blocks. In the following the contiguous set(s) of radio resources may also be referred to as a resource pool(s). The resource pool(s) may be preconfigured, e.g., based on a standard, or signaled by the network, e.g., using system information or higher layer signaling, e.g., RRC signaling.

The selection of the radio resources is based on monitoring the resource pool(s) to determine radio resources which are estimated to be used by one or more other radio devices, in the following also referred to as radio resources estimated to be occupied. Further, the selection of the radio resources is based on applying at least two different criteria: a first criterion which aims at mitigating overlap of the selected radio resources with the radio resources estimated to be occupied, and a second criterion which aims at mitigating fragmentation of the resource pool(s). The first criterion may help to avoid collisions of the SL radio transmissions with other SL radio transmissions in the resource pool. The second criterion may help to improve efficiency of utilizing the resource pool. Here it is noted that the second criterion may also aim at mitigating overlap of the selected radio resources with the radio resources estimated to be occupied, but with a lower priority than the first criterion. By configuring the second criterion to put less emphasis on avoiding overlap with the radio resources estimated to be occupied, avoidance of fragmentation is facilitated.

In the illustrated concepts, the above-mentioned first criterion and second criterion are applied in a progressive manner by using two selection processes which relate to different SL radio transmissions: In a first selection process, the first criterion is applied for selecting a first subset of radio resources from the resource pool(s), and in a second selection process the second criterion is applied for selecting a second subset of radio resources from the resource pool(s). On the first subset, the radio device sends a first SL radio transmission which includes a reservation for the second subset. Accordingly, the resource allocation process operates in a progressive manner by using the first SL radio transmission to assist in controlling the second SL radio transmission. On the second subset, the radio device then sends a second SL radio transmission. The reservation of the second subset may compensate that the second criterion, which was used to select the second subset, may put less emphasis on mitigating overlap with radio resources used by other radio devices, in favor of mitigating fragmentation of the resource pool(s).The reservation may refer to the scheduling of the second SL transmission, e.g., if the second SL radio transmission is used for conveying data which is already present at a transmit buffer. Further, the reservation may also refer an intention of to transmit the second SL radio transmission, e.g., when assuming that the second SL radio transmission will be needed for conveying data that has not yet arrived at the transmit buffer. In other words, the reservation may be applied for an SL radio transmission which is already being scheduled or which is expected to be needed for conveying data in the future.

Fig. 1 illustrates an exemplary scenario involving SL radio transmissions. More specifically, Fig. 1 shows an access node 100 of the wireless communication network, in the LTE radio technology referred to as eNB, and various entities 1 1 , 12, 13, 14, 15 which may communicate by using DL radio transmissions and/or UL radio transmissions, illustrated by solid arrows, and SL radio transmissions, illustrated by broken arrows. A service area, or cell, of the access node is schematically illustrated by 101 . The service area 101 may be defined by a radio coverage area in which DL radio transmissions from the access node 100 and UL radio transmissions to the access node 100 are possible. Here, it is noted that the wireless communication network may comprise further access nodes, each having a corresponding service area which may be overlapping or non-overlapping with the coverage area 101 of the access node 100. The entities illustrated in Fig. 1 comprise vehicles 1 1 , 12, 13, a mobile phone 14, and a person 15, e.g., a pedestrian, a cyclist, a driver of a vehicle, or a passenger of a vehicle. Here, it is noted that in the case of the vehicles 1 1 , 12, 13 the radio transmissions may be performed by a communication module installed in the vehicle, and that in the case of the person 15 the radio transmissions may be performed by a radio device carried or worn by the person 15, e.g., a wristband device or similar wearable device. Those devices and modules may be also referred as UEs. The SL radio transmissions may be enabled by the DL radio transmissions and/or UL radio transmissions, e.g., by using DL radio transmissions from the access node 100 to control or otherwise manage the SL radio transmissions. As further explained below this may involve providing the above-mentioned assistance information to the radio devices and/or modules of the entities. Furthermore, it is noted that the entities shown in Fig. 1 are merely exemplary. The SL radio transmissions may be used for implementing various kinds of V2X communication, including V2V communication, V2P communication and/or V2I communication. Accordingly, the SL radio transmissions may carry various types of V2X messages, e.g., a cooperative awareness message (CAM) or a decentralized environmental notification message (DENM). However, other kinds of SL radio communication could be supported as well.

In accordance with assumed utilization of the LTE radio technology, the SL radio transmissions may be based on the PC5 interface as specified 3GPP TS 23.303 V14.1 .0 (2016-12). The DL radio transmissions and the UL radio transmissions may be based on the LTE Uu interface as specified in 3GPP TS 23.401 V14.6.0 (2017-12). The SL radio transmissions may involve a data transmission on a PSSCH (Physical Sidelink Shared Channel) and a transmission of SCI (Sidelink Control Information) on a PSCCH (Physical Sidelink Control Channel). The SCI may for example be used to indicate the subset of radio resources which was selected to be used for the SL radio transmission.

In the illustrated examples, the allocation of radio resources for a SL radio transmission is performed in a distributed or autonomous manner, similar to the“mode 4” operation defined in 3GPP TS 36.213 V15.0.0, however using the above-mentioned different criteria for selection the radio resources. Specifically, the sending radio device performs channel sensing and uses the results of channel sensing to autonomously determines which radio resources to use for its SL radio transmissions. The channel sensing, herein also referred to as monitoring of radio resources, is used to estimate which radio resources are used by other radio devices. As mentioned above, the selection is based on two different types of criteria: a first criterion aiming at selecting resources which do not overlap with the radio resources estimated to occupied, and a second criterion aiming at avoiding fragmentation of the resource pool(s). The first criterion may be similar to the selection of radio resources as described in 3GPP TS 36.213 V15.0, section 14.1 .1.6, where the radio resources estimated to be occupied are identified by detecting resources where monitoring indicated a received signal power above a threshold. The second criterion may have a similar configuration, but prioritize the selection of subsets of radio resources which are adjacent to the radio resources which are estimated to be occupied or to subsets of radio resources which are adjacent to an edge of the resource pool.

Fig. 2 shows an example of processes in which a SL radio transmission is controlled based on the principles as outlined above. The processes of Fig. 2 involve a first UE 20 (UE1 ), a second UE 30 (UE2), and a third UE 40 (UE3). With respect to the concepts as outlined above, the first UE 20 acts as the sending radio device. The second UE 30 and the third UE 40 act as receiving radio devices. Here, it is noted that the UEs 20, 40, 40 could correspond to any of the entities 1 1 , 12, 13, 14, 15 as illustrated in Fig. 1.

In the example of Fig. 2, the first UE 20 starts monitoring the resource pool(s) at block 201 . This monitoring may continue in the further course of the illustrated processes. The monitoring of the resource pool(s) may for example involve detecting resources in which a received signal strength is above a threshold, indicating that the resources are used for radio transmissions by other radio devices. In the example of Fig. 2, the third UE 40 sends an SL radio transmission 202, which is received by the second UE 30, and the second UE 30 sends an SL radio transmission, which is received by the third UE 40. Further, the second UE 30 sends an SL radio transmission 204 which is received by the third UE 40 and also by the first UE 20. In the case of the SL radio transmissions 202 and 203, the first UE 20 may detect that in certain radio resources the received signal power is above the threshold and thus estimate that these radio resources are also occupied in the future. Also in the case of the SL radio transmission 204, which was received also by the first UE 20, the first UE 20 can estimate that the radio resources used for the SL radio transmission 204 will also be used in the future for SL radio transmissions by the second UE 30 and thus occupied. The monitoring and estimation of occupied radio resources may continue throughout the further course of the illustrated processes and also while the first UE 20 itself is transmitting.

In the illustrated processes, the resources estimated to be occupied are used as a basis for resource selection processes by the first UE 20. At block 205, the first UE 20 applies the first criterion to select a first subset of radio resources (SS1 ) for a first SL radio transmission 206. This selection is based on the currently available results of monitoring and estimation of occupied radio resources. As mentioned above, the first criterion may aim at mitigating overlap of the selected first subset with the radio resources estimated to be occupied at the time of the first SL radio transmission 206. For example, the first criterion may prioritize selecting radio resources which are spaced apart from the radio resources estimated to be occupied. Accordingly, the first criterion may reduce the probability that the first UE 20 selects the first subset in such a way that it overlaps with the radio resources selected for another SL radio transmission by the second UE 30 or by the third UE 40. It is noted that in some scenarios the selection process of block 205 could also be used for selecting multiple subsets based on the first criterion, e.g., the first subset to be used for the first SL radio transmission 206 and one or more further subsets to be used for an additional SL radio transmission and/or one more further subsets to be used for a retransmission of the first SL radio transmission 206 or another retransmission.

Further, at block 205 the first UE 20 also applies the second criterion to select a second subset of radio resources (SS2) for a second SL radio transmission 208. Like in the case of the first subset, this selection is based on the currently available results of monitoring and estimation of occupied radio resources. The selection of the second subset may be performed after the selection of the first subset, and thus also on updated results of monitoring and estimation of occupied radio resources. It is noted that in some scenarios the selection process of block 205 could also be used for selecting multiple subsets based on the second criterion, e.g., the second subset to be used for the second SL radio transmission 208 and one or more further subsets to be used for an additional SL radio transmission and/or one more further subsets to be used for a retransmission of the second SL radio transmission 208 or another retransmission.

As mentioned above, the second criterion may aim at mitigating fragmentation of the resource pool(s) from which the second subset is selected. For example, the second criterion may prioritize selecting radio resources which are adjacent to the radio resources estimated to be occupied or radio resources which are adjacent to an edge of the resource pool(s). Accordingly, the second criterion may avoid fragmentation of the resource pool(s) be the selected second subset and by the radio resources estimated to be occupied.

Having selected the first subset and the second subset, the first UE 20 sends the first SL radio transmission 206 on the first subset. The first SL radio transmission 206 indicates a reservation of the second subset and optionally also for other subsets selected at block 205. In addition to the reservation, the first SL radio transmission 206 may also indicate SCI for the second SL radio transmission 208, e.g., an indication of an MCS (Modulation and Coding Scheme), data priority, or the like. Before sending the second SL radio transmission 208, the first UE 20 may further apply the second criterion to select a third set of radio resources for a third SL radio transmission 210, as illustrated by block 207. The selection at block 207 is based on the currently available results of monitoring and estimation of occupied radio resources. Since the selection of the third subset is performed after the selection of the first subset and second subset, updated results of monitoring and estimation of occupied radio resources may be available for the selection of the third subset at block 207. It is noted that in some scenarios the selection process of block 207 could also be used for selecting multiple subsets based on the second criterion, e.g., the third subset to be used for the third SL radio transmission 210 and one or more further subsets to be used for an additional SL radio transmission and/or one more further subsets to be used for a retransmission of the third SL radio transmission 210 or another retransmission.

The first UE 20 then sends the second SL radio transmission 208 on the second subset. The second SL radio transmission 208 may indicate a reservation of the third subset and optionally also for other subsets selected at block 207. In addition to the reservation, the second SL radio transmission 208 may also indicate SCI for the second SL radio transmission 210, e.g., an indication of an MCS, data priority, or the like.

Before sending the third SL radio transmission 210, the first UE 20 may further apply the second criterion to select a fourth set of radio resources for a fourth SL radio transmission, as illustrated by block 209. The selection at block 209 is based on the currently available results of monitoring and estimation of occupied radio resources. Since the selection of the fourth subset is performed after the selection of the first subset, second subset, and third subset, updated results of monitoring and estimation of occupied radio resources may be available for the selection of the fourth subset at block 209. It is noted that in some scenarios the selection process of block 209 could also be used for selecting multiple subsets based on the second criterion, e.g., the fourth subset to be used for the fourth SL radio transmission and one or more further subsets to be used for an additional SL radio transmission and/or one more further subsets to be used for a retransmission of the fourth SL radio transmission or another retransmission.

The first UE 20 then sends the third SL radio transmission 210 on the third subset. The third SL radio transmission 210 may indicate a reservation of the fourth subset and optionally also for other subsets selected at block 209. In addition to the reservation, the third SL radio transmission 210 may also indicate SCI for the second SL radio transmission, e.g., an indication of an MCS, data priority, or the like. As can be seen, the second criterion may be repeatedly applied before performing an SL radio transmission, in order to efficiently for select radio resources for a further SL radio transmission. The upcoming SL radio transmission may then be used for making a reservation of the selected radio resources, thereby allowing to avoid collisions on the selected radio resources even though the second criterion involves a higher risk of overlap with radio resources which could be used by other radio devices.

Fig. 3 illustrates an exemplary timing when controlling SL radio transmissions as explained above. In the example of Fig. 3, the sending radio device, e.g., the first UE 20, continuously estimates occupied radio resources by monitoring the resource pool(s). At time t=TsEu , the sending radio device applies the first criterion to select a first subset in a first target time interval [Tsi , TEI] from the resource pool. This occurs before start of the target time interval, i.e., TSELI <TSI < TEI . By varying the position and/or duration of the target time interval [Tsi , TEI], it is possible to manage the risk that the selected first subset overlaps with a selection made by another radio device. In Fig. 3, the start time of selected first subset is denoted by Ttci. As can be seen, the selection of the first subset occurs before the start time of the first subset, i.e.,

TSEL^TTXI .

At time t=Ts_Ei_2, the sending radio device applies the second criterion to select a second subset in a second target time interval [Ts2, TE2] from the resource pool. This occurs before the start time of the first subset, i.e., TSEL2<TTXI . Further, the selection of the second subset occurs before start of the second target time interval, i.e., T_SEL2<T_S2<TE2. The start time of selected second subset is denoted by Ttc2. As can be seen, the selection of the second subset occurs before the start time of the second subset, i.e., T_SEL2<TTX2. For the selection of the second subset, the sending radio device may utilize the results of monitoring and estimation of the occupied radio resources as available until T_SEL2. At time t= Ttci, the sending radio device starts a first SL radio transmission on the selected first subset. The first SL radio transmission indicates a reservation of the second subset, i.e., informs other radio devices receiving the first SL radio transmission that the sending radio device intends to use the second subset for a second SL radio transmission. Based on this indication, the other radio devices may avoid selecting radio resources from the second subset for performing an SL radio transmission, so that a risk of collisions can be reduced. Further, the risk the risk that the selected first subset overlaps with a selection made by another radio device can also be managed by varying the position and/or duration of the target time interval [Ts2, TE2]. At time t=Tix2, the sending radio device then starts a second SL radio transmission on the selected second subset. In some scenarios, there may be a minimum time gap T_g between the first SL radio transmission and the second SL radio transmission, i.e., Ttc2³Ttci+T₉, with T_g>0. This may help to ensures that other radio devices can read the control information, an in particular the indication of the reservation, which is included in the first SL transmission and can react accordingly, e.g., by adapting their own selection of radio resources from the resource pool(s) accordingly. In some scenarios, the time gap T_g may be sufficiently large that the first SL radio transmission ends before the start of the second SL radio transmission, and in particular that the start of the second SL radio transmission is outside the first target time interval [Tsi, TEI]. In this way, the risk of collisions can be further reduced by increasing the number of radio resources which are available for selection by other radio devices. In some scenarios, the subsets may be selected according to a periodic pattern. For example, when selecting the first subset at time t=Trxi, the first subset could also be selected an reserved for future time slots corresponding to times t=Tixi+kAT, where k=1 , 2, 3, .... and DT indicates the period of the periodic pattern.

A sensing window used for monitoring of the resource pool(s) may be chosen and dynamically or semi-statically adapted based on various criteria. Such criteria may for example be based on mobility of the sending radio device and/or on a type of services configured on the sending radio device. For example, if the sending radio device has high mobility, e.g., because it moves with high velocity, it may apply a longer sensing window in order to obtain more stable monitoring results. Further, if the sending radio device is configured with a service requiring high reliability of the SL radio transmissions, it may apply a longer sensing window in order to obtain more stable monitoring results and thus a higher accuracy of the determination of radio resources estimated to be occupied. In each case, the longer sensing window may allow for further reducing a risk of collisions. Further, the sensing window can be adapted based on stability of resource allocations. For example, in scenarios with rapidly changing resource allocation, as for example indicated by changes of the radio resources estimated to be occupied, a longer sensing window may be used to get a broader basis of monitoring results and thus a higher accuracy of the determination of radio resources estimated to be occupied.

In some embodiments, validity of the monitoring results on a particular resource could also depend on mobility of the sending radio device and/or on a type of services configured on the sending radio device. For instance, if the sending radio device has high mobility, e.g., because it moves with high velocity, the size of the target time interval of selecting the subset(s) may be reduced to ensure that the monitoring results are still valid at the start time of the selected subset. Further, the end time of the target time interval could be set depending on a maximum allowed latency imposed by a service on the SL radio transmissions. Here, setting a lower end time allows for reducing the latency. On the other hand, lowering the end time reduces the width of the target time interval and may thus result in an increased risk of collisions on the selected subset.

Figs. 4A, 4B, and 4C illustrate examples of resources allocations for SL radio transmission as made on the basis of the above concepts. In Figs. 4A, 4B, and 4C, the radio resources which are estimated to be occupied are illustrated by a light dotted shading. In the example of Figs. 4A, 4B, and 4C, it is assumed that the radio resources to be used for SL radio transmissions are selected from a resource pool defined by frequency subchannels contiguously arranged within a system bandwidth (system BW) of the underlying radio technology. The radio resources which are selected according to the first criterion are illustrated by a diagonal hatch, the radio resources which are selected according to the second criterion are illustrated by a dark dotted shading. Reservations are illustrated by solid arrows. Reservations which are later modified are illustrated by broken arrows.

In the example of Fig. 4A, a first SL radio transmission is denoted by SLTX1 , a second SL radio transmission is denoted by SLTX2, and a third SL radio transmission is denoted by SLTX3. For the first SL radio transmission, the sending radio device applies the first criterion to select a first subset of radio resources from the resource pool. The first subset is illustrated by diagonal hatching. The selection of the first subset may for example be based on randomly selecting the first subset from the resource pool, excluding those radio resources which are estimated to be occupied. In the illustrated example, it can be seen that the selection of the first subset is not optimal from a resource fragmentation point of view. In particular, the selected first subset fragments and the radio resources estimated to be occupied fragments the remaining part of the resource pool into two small fragments that can only be used for transmission of small messages. On the other hand, the selected first subset has some distance from the resources estimated to be occupied, which means that overlap with radio resources selected and used by other radio devices is likely avoided, even if the estimation of occupied radio resources turns out to be inaccurate.

For the second SL radio transmission and the third SL radio transmission, the sending radio device applies the second criterion to select a second subset and a third subset of radio resources from the resource pool. The second subset and the third subset are illustrated by dark shading. As can be seen, the second subset and the third subset are arranged adjacent to the radio resources estimated to be occupied, thereby avoiding fragmentation of the resource pool. Here, it is noted that in the illustrated example fragmentation could also be avoided by selecting the second subset and the third subset to be adjacent to the high- frequency edge of the resource pool. As compared to the first criterion, the second criterion narrows down the degree of freedom of selecting the subset from the resource pool. Accordingly, there is a higher risk of overlapping selections by multiple radio devices applying the second criterion. In accordance with the above-described principles, the increased risk is compensated for by indicating a reservation for the second subset in the first SL radio transmission, as indicated by a solid arrow pointing from the first SL radio transmission to the second SL radio transmission, and by indicating a reservation for the third subset in the second SL radio transmission, as indicated by a solid arrow pointing from the second SL radio transmission to the third SL radio transmission.

In some scenarios, a selection of radio resources can also be made for more than one time slot. This may for example allow for efficiently considering a more or less periodic need to transmit data by a SL radio transmission, like often the case if the SL radio transmissions are used to transmit V2X messages. In this case, a SL radio transmission may indicate a reservation of a subset of radio resources for multiple time slots. Figs. 4A and 4B illustrate corresponding examples.

In the example of Fig. 4B, a first SL radio transmission is denoted by SLTX1 , a second SL radio transmission is denoted by SLTX2, a third SL radio transmission is denoted by SLTX3, and a fourth SL radio transmission is denoted by SLTX4. For the first SL radio transmission, the sending radio device applies the first criterion to select a first subset of radio resources from the resource pool. The first subset is illustrated by diagonal hatching. The selection of the first subset may for example be based on randomly selecting the first subset from the resource pool, excluding those radio resources which are estimated to be occupied. Again, it can be seen that the selection of the first subset is not optimal from a resource fragmentation point of view. In particular, the selected first subset fragments and the radio resources estimated to be occupied fragments the remaining part of the resource pool into two small fragments that can only be used for transmission of small messages. On the other hand, the selected first subset has some distance from the resources estimated to be occupied, which means that overlap with radio resources selected and used by other radio devices is likely avoided, even if the estimation of occupied radio resources turns out to be inaccurate.

Further, the sending radio device applies the second criterion to select a second subset of radio resources from the resource pool. The second subset is illustrated by dark shading. As can be seen, the second subset is arranged adjacent to the radio resources estimated to be occupied, thereby avoiding fragmentation of the resource pool. Here, it is noted that in the illustrated example fragmentation could also be avoided by selecting the second subset to be adjacent to the high-frequency edge of the resource pool.

In the example of Fig. 4B, it is assumed that the sending radio device needs to send SL radio transmissions in a periodic manner, e.g., in order to transmit one or more V2X messages. Accordingly, the sending radio device uses the first SL radio transmission to indicate a reservation of the first subset and the second subset in one or more future time slots. Furthermore, after sending the first SL radio transmission, but before sending the second SL radio transmission, the sending radio device reselects the first subset according to the second criterion. The second SL radio transmission is then used to indicate a modification of the reservation of the first subset. This may involve indicating a new reservation of the reselected first subset, as illustrated by a solid arrow starting from the second SL radio transmission. Further, this may involve indicating a cancellation of the existing reservation of the first subset, as indicated by the broken arrow starting from the first SL radio transmission. The reselected first subset, illustrated by dark shading, is then used sending the third SL radio transmission. The second subset as reserved in the future time slot is used for sending the fourth SL radio transmission. In the example of Fig. 4B, application of the second criterion for reselecting the first subset results in the reselected first subset being arranged adjacent to the radio resources estimated to be occupied, thereby avoiding fragmentation of the resource pool. Here, it is noted that in the illustrated example fragmentation could also be avoided by reselecting the first subset to be adjacent to the high-frequency edge of the resource pool.

In the example of Fig. 4B, the first subset which was initially selected based on the first criterion, is subsequently reselected based on the second criterion, thereby allowing to reduce fragmentation of the resource pool in the future time slot(s). However, in some scenarios a reselection can also be made for a subset which was already selected based on the second criterion. In this case, the reselection may be used to take into account updates concerning the radio resources estimated to be occupied. Fig. 4C illustrates a corresponding example.

In the example of Fig. 4C, a first SL radio transmission is denoted by SLTX1 , a second SL radio transmission is denoted by SLTX2, a third SL radio transmission is denoted by SLTX3, and a fourth SL radio transmission is denoted by SLTX4. For the first SL radio transmission, the sending radio device applies the first criterion to select a first subset of radio resources from the resource pool. The first subset is illustrated by diagonal hatching. The selection of the first subset may for example be based on randomly selecting the first subset from the resource pool, excluding those radio resources which are estimated to be occupied. Again, the selection of the first subset is not optimal from a resource fragmentation point of view. In particular, the selected first subset fragments and the radio resources estimated to be occupied fragments the remaining part of the resource pool into two small fragments that can only be used for transmission of small messages. On the other hand, the selected first subset has some distance from the resources estimated to be occupied, which means that overlap with radio resources selected and used by other radio devices is likely avoided, even if the estimation of occupied radio resources turns out to be inaccurate.

In the example of Fig. 4C, it is assumed that the sending radio device needs to send SL radio transmissions in a periodic manner, e.g., in order to transmit one or more V2X messages. Accordingly, the sending radio device uses the first SL radio transmission to indicate a reservation of the first subset and the second subset in one or more future time slots. Furthermore, after sending the first SL radio transmission, but before sending the second SL radio transmission, the sending radio device reselects the first subset according to the second criterion. The second SL radio transmission is then used to indicate a modification of the reservation of the first subset. This may involve indicating a new reservation of the reselected first subset, as illustrated by a solid arrow starting from the second SL radio transmission. Further, this may involve indicating a cancellation of the existing reservation of the first subset, as indicated by the broken arrow starting from the first SL radio transmission. The reselected first subset, illustrated by dark shading, is then used sending the third SL radio transmission. In the example of Fig. 4C, application of the second criterion for reselecting the first subset results in the reselected first subset being arranged adjacent to the radio resources estimated to be occupied, thereby avoiding fragmentation of the resource pool. Here, it is noted that in the illustrated example fragmentation could also be avoided by reselecting the first subset to be adjacent to the high-frequency edge of the resource pool.

In the example of Fig. 4C, also the second subset is subjected to a reselection. In particular, before sending the third SL radio transmission on the reselected first subset, the sending radio device also reselects the second subset according to the second criterion, taking into account updated results concerning the radio resources estimated to be occupied. The third SL radio transmission in the reselected first subset is then used to indicate a modification of the reservation of the second subset. This may involve indicating a new reservation of the reselected second subset, as illustrated by a solid arrow starting from the third SL radio transmission. Further, this may involve indicating a cancellation of the existing reservation of the second subset, as indicated by the broken arrow starting from the first SL radio transmission. The reselected second subset, illustrated by dark shading, is then used sending the fourth SL radio transmission.

It is noted that in a similar manner as illustrated in Figs. 4B and 4C, any subset having an existing reservation may be subjected to a reselection, with an upcoming SL radio transmission being used to indicate a modification of the reservation.

When applying the first criterion in the above examples, the radio resources that are estimated to be occupied, i.e., for which a received signal power above a threshold is detected, may excluded from selection or may be assigned a low priority for selection. In some cases, this may be combined with assessing signal strength values. For example, radio resources for which a relatively low signal strength value is detected may assumed to be used by other radio devices which are far away. These radio resources may be treated as radio resources not estimated to be occupied or may be assigned a higher selection priority than radio resources for which a relatively high signal strength value is detected, and which may be assumed to be used by other radio devices which are located nearby. The monitoring may be based on measurements of RSRP (reference signal received power) and/or measurements of RSSI (received signal strength indicator).

In some scenarios, the first criterion may also involve excluding selection of radio resources which avoid fragmentation of the resource pool, i.e., radio resources which meet the second criterion. In this way, the risk can be reduced that a subset selected under the first criterion overlaps with a subset selected by another radio device under the second criterion. As an alternative to excluding selection of radio resources which could be selected under the second criterion, such radio resources could also be assigned a lower selection probability than radio resources which meet the first criterion, but not the second criterion.

As mentioned above, the second criterion aims at selecting radio resources that avoid fragmentation of the resource pool(s). This may for example be accomplished by selecting a subset of radio resources which is adjacent to an edge of the resource pool, selecting a subset of radio resources which is adjacent to the radio resources estimated to be occupied, or selecting a subset of radio resources which minimizes an amount of radio resources remaining between the subset and the radio resources estimated to be occupied. In the latter case, the second criterion may for example be met if the amount of radio resources remaining between the subset and the radio resources estimated to be occupied does not exceed a threshold. The threshold may be configurable. Setting the threshold to zero corresponds to the above requirement of selecting a subset of radio resources which is adjacent to the radio resources estimated to be occupied. In some case, the second criterion may involve assessing multiple candidate subsets in terms of a number of fragments and/or a size of fragments of the remaining radio resources of the resource pool, i.e., of the resource pool without the candidate subset and without the radio resources estimated to be occupied. In this case, the second criterion may involve selecting that subset which results in the lowest number of fragments. If there are multiple candidate subsets resulting in the lowest number of fragments, a further selection may be performed among these candidate subsets to select that candidate subset which results in the lowest size of the fragment(s).

In in some scenarios, the second criterion may involve excluding the selection of radio resources that produce fragmentation of the resource pool(s). Alternatively, to excluding the selection of radio resources that produce fragmentation, such radio resources could also be assigned a lower selection probability than radio resources which avoid fragmentation of the resource pool(s).

If the second criterion involves identifying multiple candidate subsets, further criteria which may additionally or alternatively be used for selecting among the candidate subsets. For example, such further criteria may be based on the size of the candidate subset and involve selecting the candidate subset having the largest size or the candidate subset having the smallest size which still allows for conveying the intended SL radio transmission. In the latter case, the selection among the candidate subsets may optionally also take into account an MCS of the intended SL radio transmission or assume that the intended SL radio transmission is performed with the least efficient MCS. The required size for performing the intended SL radio transmission may for example be considered in terms of a typical message size, e.g., the size of a MAC PDU (Medium Access Control Packet Data Unit). In some scenarios, the selection among the candidate subsets may also be based on an ordering of radio resources. For example, the radio resources could be ordered or indexed in the frequency domain and the second criterion could involve selecting the candidate subset arranged having the lowest or highest frequency position. If the radio resources are indexed, e.g., configured as indexed subchannels, this may involve selecting the subset corresponding to the lowest or highest index values. In some scenarios, application of the second criterion and subsequent reservation may be controlled in a selective manner and selection of radio resources on the basis of the second criterion may be precluded under certain conditions, e.g., if the amount of remaining radio resources after selection of a subset of radio resources based on the second criterion would not be sufficient to convey an SL radio transmission with the most efficient supported MCS. In this way, it can be avoided that the reservation of the subset selected according to the second subset blocks other radio devices from access to the resource pool.

In some embodiments, the first criterion and/or the second criterion may at least in part be configured by the wireless communication network, e.g., by configuration information transmitted by the above mentioned access node 100 or provided by some other node of the wireless communication network. The configuration information may define rules for implementing the first criterion and/or the second criterion. Alternatively or in addition, the configuration information may indicate one or more parameters utilized in the first criterion and/or second criterion, e.g., in terms of one or more threshold values. The configuration information may be provided through unicast signalling or broadcast signalling. The configuration information may also be used to selectively activate or deactivate the application of the second criterion and subsequent reservation of the selected subset of radio resources. For example, in response to detecting that the occupancy level of the resource pool(s) exceed a certain threshold, the access node 100 or some other node of the wireless communication network could activate the application of the second criterion and subsequent reservation of the selected subset of radio resources for one or more radio devices. In a similar manner, the selective activation could be accomplished depending a size or number of the resource pool(s). Accordingly, the if the occupancy level is low, e.g., below a certain threshold, one or more radio devices could be controlled to perform resource allocation for SL radio transmissions on the basis of the first criterion only, while if the occupancy level exceeds the threshold, one or more radio devices may be controlled to also apply the second criterion and subsequent reservation of the selected subset of radio resources, to thereby avoid excessive fragmentation of the resource pool(s).

In some scenarios, the second criterion may also depend on a priority of the SL radio transmissions. For example, such priority could be indicated by a PPPP (ProSe Per-Packet Security). As for example specified in 3GPP TS 23.303 V14.1 .0, the PPPP is set on an application layer for each message transmitted over the PC5 interface. For example, in the case of the intended SL radio transmission having a high priority, the second criterion may be configured to more emphasis on avoiding overlap with selections of radio resources by other radio devices, and less emphasis on avoiding fragmentation of the resource pool(s). This may for example be accomplished by adjusting selection priorities or threshold values. Accordingly, for an SL radio transmission having a high priority, the second criterion may allow selection of a subset of radio resources producing some degree of fragmentation, while for an SL radio transmission having a lower priority the second criterion prevents selection of a subset producing the same degree of fragmentation. Accordingly, the first criterion and the second criterion may also differ with respect to the consideration of a priority of the SL radio transmissions.

In some scenarios, the second criterion may also depend on an occupancy level of the resource pool(s). The occupancy level may be measured by metrics such as CR (channel or occupancy ratio) or CBR (channel busy ratio). For example, in the case of occupancy level of the resource pool(s) being low, the second criterion may be configured to more emphasis on avoiding overlap with selections of radio resources by other radio devices, and less emphasis on avoiding fragmentation of the resource pool(s). In the case of occupancy level of the resource pool(s) being high, the second criterion may be configured to less emphasis on avoiding overlap with selections of radio resources by other radio devices, and more emphasis on avoiding fragmentation of the resource pool(s). The occupancy level dependent adaptation of the second criterion may for example be accomplished by adjusting selection priorities or threshold values. Accordingly, in the case of the occupancy level being low, the second criterion may allow selection of a subset of radio resources producing some degree of fragmentation, while in the case of the occupancy level being high the second criterion prevents selection of a subset producing the same degree of fragmentation. Accordingly, the first criterion and the second criterion may also differ with respect to the consideration of a an occupancy level of the resource pool(s).

In some scenarios, the second criterion may also depend on the resource pool(s) available for selection of the subset. For example, a resource pool may be reserved for dedicated services or applications, e.g., for the transmission of safety related messages. If such resource pool is used as a basis for making a selection based on the second criterion, the second criterion may be configured to more emphasis on avoiding overlap with selections of radio resources by other radio devices, and less emphasis on avoiding fragmentation of the resource pool(s) than in cases when another resource pool is used as a basis for making the selection. The resource pool dependent adaptation of the second criterion may for example be accomplished by adjusting selection priorities or threshold values. Accordingly, in the case of making a selection from a first resource pool, the second criterion may allow selection of a subset of radio resources producing some degree of fragmentation, while in the case of making a selection from a second resource pool the second criterion prevents selection of a subset producing the same degree of fragmentation.

Fig. 5 shows a flowchart for illustrating a method of controlling SL radio transmissions in a wireless communication network. The method of Fig. 5 which may be utilized for implementing the illustrated concepts. The method of Fig. 5 may be used for implementing the illustrated concepts in a radio device which sends SL radio transmissions to one or more further radio devices. For example, the radio device could correspond to the above-mentioned first UE 20, and the further radio device(s) could correspond to the above-mentioned second UE 30 and/or third UE 40. The SL radio transmissions may for example be used for conveying V2X messages.

If a processor-based implementation of the radio device is used, at least some of the steps of the method of Fig. 5 may be performed and/or controlled by one or more processors of the radio device. Such radio device may also include a memory storing program code for implementing at least some of the below described functionalities or steps of the method of Fig. 5.

At step 510, the radio device may receive configuration information. The radio device may receive the configuration information from a node of the wireless communication network, such as the above-mentioned access node 100. The configuration information may in particular define at least one criterion to be applied by the radio device for selecting radio resources for SL radio transmissions. At least a part of the configuration information may be received in a unicast transmission dedicated to the radio device, e.g., in RRC signalling. Further, at least a part of the configuration information may be received in a broadcast transmission, e.g., as part of system information. The radio resources may be frequency channels distinguished only in the time domain, e.g., subchannels as defined for the LTE PC5 interface, or resource blocks distinguished both in the frequency domain and the time domain.

At step 520, the radio device monitors a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices.

At step 530, the radio device selects a first subset of radio resources from the contiguous set. The contiguous set may for example correspond to a resource pool. The radio device selects the first subset according to a first criterion. The first criterion is configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices. At least a part of the first criterion may be defined by the selection information received at step 510. The first criterion may for example be based on randomly selecting the first subset from the contiguous set. The random selection may exclude the radio resources estimated to be used by one or more other radio devices. Alternatively, the random selection may assign a lower selection priority to the radio resources estimated to be used by one or more other radio devices than to other radio resources of the contiguous set.

At step 540, the radio device selects a second subset of radio resources from the contiguous set. The radio device selects the second subset according to a second criterion. The second criterion is configured to mitigate fragmentation of the contiguous set by the selected subset and the radio resources estimated to be used. At least a part of the second criterion may be defined by the selection information received at step 510.

In order to mitigate fragmentation of The second criterion may is configured to minimize a distance of the selected subset to the radio resources estimated to be used and/or to an edge of the contiguous set of radio resources. In some scenarios the second criterion may require that the selected subset is arranged adjacent to the radio resources estimated to be used and/or adjacent to an edge of the contiguous set of radio resources. Further, the second criterion is configured to maximize a size of a contiguous part of the contiguous set without the selected subset and the radio resources estimated to be used.

In some scenarios, the second criterion may depend on a priority of data conveyed by the second SL radio transmission. Alternatively or in addition, the second criterion may depend on a type of data conveyed by the second SL radio transmission. Alternatively or in addition, the second criterion may depend on an occupancy value or occupancy level of the contiguous set of radio resources.

At step 550, the radio device sends a first SL radio transmission on the first subset. The first SL radio transmission indicates a reservation of the second subset. In some scenarios, the first SL radio transmission may indicate the reservation of the second subset for multiple time slots, e.g., like explained in connection with the example of Fig. 4B or 4C. In some scenarios, the radio device may also indicate a reservation of the first subset for one or more time slots in the first SL radio transmission, e.g., like explained in connection with the example of Fig. 4B or 4C.

At step 560, the radio device sends a second SL radio transmission on the second subset. As indicated by step 570, the radio device may indicate a modification of the reservation of the second subset in the second SL radio transmission, e.g., like explained in connection with the example of Fig. 4C. The modification of the reservation of the second subset may involve a cancellation of at least a part of the reservation and/or making a new reservation for the second subset. The modification of the reservation of the second subset may be based on the radio device further monitoring the contiguous set of radio resources after sending the first SL radio transmission at step 550 and reselecting the second subset according to the second criterion, e.g., by repeating step 540 based on updated results obtained by the further monitoring of the contiguous set of radio resources.

If the radio device indicated a reservation of the first subset for one or more time slots in the first SL radio transmission, the radio device may also indicate a modification of the reservation of the first subset in the second SL radio transmission, e.g., like explained in connection with the example of Fig. 4B or 4C. The modification of the reservation of the first subset may involve a cancellation of at least a part of the reservation and/or making a new reservation for the first subset. The modification of the reservation of the first subset may be based on the radio device further monitoring the contiguous set of radio resources after sending the first SL radio transmission at step 550 and reselecting the first subset according to the second criterion. This reselection of the first subset may be based on updated results obtained by the further monitoring of the contiguous set of radio resources.

A start of the first SL radio transmission and a start of the second SL radio transmission may be separated by a time gap, e.g., like explained in connection with Fig. 3. In particular, the second SL radio transmission may start after an end of the first SL radio transmission.

In some scenarios, the second criterion may also be applied for selecting radio resources for further SL radio transmissions, as indicated by step 580. For example, this may involve that the radio device selects a third subset of radio resources from the contiguous set according to the second criterion, indicates a reservation of the third subset in the second SL radio transmission transmitted at step 560, and then sends a third SL radio transmission on the third subset. Examples of corresponding processes in which the selection of a subset according to the second criterion and using an upcoming SL radio transmission to indicate a reservation for the selected subset are explained in connection with Fig. 2. The second SL radio transmission may also be used to indicate the reservation of the third subset for multiple time slots, and the radio device may indicate a modification of the reservation of the third subset in the third SL radio transmission. As explained in connection with step 570, the modification of the reservation of the third subset may involve a cancellation of at least a part of the reservation and/or making a new reservation for the third subset. Further, the modification of the reservation may be based on the radio device further monitoring the contiguous set of radio resources after sending the second SL radio transmission and reselecting the third subset according to the second criterion.

In some scenarios, the method of Fig. 5 may also be applied with respect to multiple contiguous sets of radio resources, e.g., multiple resource pools as mentioned above. In such cases, the above-mentioned subsets may each be selected from one of the multiple contiguous sets. However, selection of a subset from two or more different contiguous sets would also be possible. In such cases the selected subset would consist of multiple parts which are each selected from a different contiguous set.

Fig. 6 shows a block diagram for illustrating functionalities of a radio device 600 which operates according to the method of Fig. 5. The radio device 600 may for example correspond to the above-mentioned sending radio device or first UE 20. As illustrated, the radio device 600 may optionally be provided with a module 610 configured to receive configuration information, such as explained in connection with step 510. Further, the radio device 600 may be provided with a module 620 configured to monitor a contiguous set of radio resources, such as explained in connection with step 520. Further, the radio device 600 may be provided with a module 630 configured to select a first subset of radio resources based on a first criterion, such as explained in connection with step 530. Further, the radio device 600 may be provided with a module 640 configured to select a second subset of radio resources based on a second criterion, such as explained in connection with step 540. Further, the radio device 600 may be provided with a module 650 configured to send a first SL radio transmission with a reservation, such as explained in connection with step 550. Further, the radio device 600 may be provided with a module 660 configured to send a second SL radio transmission, such as explained in connection with step 560. Further, the radio device 600 may optionally be provided with a module 670 configured to indicate a new reservation or modification of an existing reservation in the second SL radio transmission, such as explained in connection with step 570. Further, the radio device 600 may optionally be provided with a module 680 configured to send one or more further SL radio transmission(s), such as explained in connection with step 580.

It is noted that the radio device 600 may include further modules for implementing other functionalities, such as known functionalities of a UE supporting V2X or other types of SL communication. Further, it is noted that the modules of the radio device 600 do not necessarily represent a hardware structure of the radio device 600, but may also correspond to functional elements, e.g., implemented by hardware, software, or a combination thereof. Further, it is noted that the method of Figs. 5 could also be implemented in a system which comprises the radio device sending the SL radio transmissions and the at least one further radio device which receives the SL radio transmissions.

Fig. 7 illustrates a processor-based implementation of a radio device 700 which may be used for implementing the above described concepts. For example, the structures as illustrated in Fig. 7 may be used for implementing the concepts in the above-mentioned sending UE 20 or receiving UE 30.

As illustrated, the radio device 700 includes one or more radio interfaces 710. The radio interface(s) 710 may for example support a wireless access technology supporting SL radio transmissions, such as the LTE radio technology or NR radio technology. Furthermore, the radio interface(s) 710 may support DL radio transmissions and UL radio transmissions with a wireless communication network.

Further, the radio device 700 may include one or more processors 750 coupled to the radio interface(s) 710 and a memory 760 coupled to the processor(s) 750. By way of example, the radio interface(s) 1210, the processor(s) 750, and the memory 760 could be coupled by one or more internal bus systems of the radio device 700. The memory 760 may include a Read- Only-Memory (ROM), e.g., a flash ROM, a Random Access Memory (RAM), e.g., a Dynamic RAM (DRAM) or Static RAM (SRAM), a mass storage, e.g., a hard disk or solid state disk, or the like. As illustrated, the memory 760 may include software 770, firmware 1280, and/or control parameters 790. The memory 760 may include suitably configured program code to be executed by the processor(s) 750 so as to implement the above-described functionalities of a radio device or apparatus for controlling radio devices, such as explained in connection with Fig. 5.

It is to be understood that the structures as illustrated in Fig. 7 are merely schematic and that the radio device 700 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces or processors. Also, it is to be understood that the memory 760 may include further program code for implementing known functionalities of a UE supporting SL radio transmissions, e.g., for implementing V2X communication. According to some embodiments, also a computer program may be provided for implementing functionalities of the radio device 700, e.g., in the form of a physical medium storing the program code and/or other data to be stored in the memory 760 or by making the program code available for download or by streaming. As can be seen, the concepts as described above may be used for controlling SL radio transmissions in a highly efficient manner. In particular, excessive fragmentation of one or more resource pool(s) used for autonomous selection of radio resources for SL radio transmissions may be avoided, while at the same time avoiding an excessive risk of colliding SL radio transmissions.

It is to be understood that the examples and embodiments as explained above are merely illustrative and susceptible to various modifications. For example, the illustrated concepts may be applied in connection with various kinds of radio technologies, without limitation to the above-mentioned examples of the LTE radio technology or NR radio technology. Further, it is noted that while the above examples referred to mitigating fragmentation of the radio resources in the frequency domain, the same principles could also be applied to reduce fragmentation in the time domain or in any other domain in which the notion of adjacent resources exists, e.g., in the code domain for code-division multiple access based transmissions, or in the space domain for space-division multiple access transmissions, e.g., based on beamforming or the like. Moreover, it is to be understood that the above concepts may be implemented by using correspondingly designed software to be executed by one or more processors of an existing device or apparatus, or by using dedicated device hardware. Further, it should be noted that the illustrated apparatuses or devices may each be implemented as a single device or as a system of multiple interacting devices or modules.

Claims

1 . A method of controlling sidelink radio transmissions in a wireless communication network, the method comprising:

- a radio device (20; 600; 700) monitoring a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices (30,40);

- the radio device (20; 600; 700) selecting a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices (30,40);

- the radio device (20; 600; 700) selecting a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set by the selected subset and the radio resources estimated to be used;

- the radio device (20; 600; 700) sending a first sidelink radio transmission (206) on the first subset, the first sidelink radio transmission (206) indicating a reservation of the second subset; and

- the radio device (20; 600; 700) sending a second sidelink radio transmission (208) on the second subset.

2. The method according to claim 1 ,

wherein the second criterion is configured to minimize a distance of the selected subset to the radio resources estimated to be used and/or to an edge of the contiguous set of radio resources.

3. The method according to claim 1 or 2,

wherein the second criterion requires that the selected subset is arranged adjacent to the radio resources estimated to be used and/or adjacent to an edge of the contiguous set of radio resources.

4. The method according to any one of the preceding claims,

wherein the second criterion is configured to maximize a size of a contiguous part of the contiguous set without the selected subset and the radio resources estimated to be used.

5. The method according to any one of the preceding claims,

wherein the second criterion depends on a priority of data conveyed by the second sidelink radio transmission (208).

6. The method according to any one of the preceding claims, wherein the second criterion depends on a type of data conveyed by the second sidelink radio transmission (208).

7. The method according to any one of the preceding claims,

wherein the second criterion depends on an occupancy value of the contiguous set of radio resources.

8. The method according to any one of the preceding claims,

wherein the first sidelink radio transmission (206) indicates the reservation of the second subset for multiple time slots.

9. The method according to claim 8, comprising:

- the radio device (20; 600; 700) indicating a modification of the reservation of the second subset in the second sidelink radio transmission (208).

10. The method according to claim 9,

wherein the modification of the reservation of the second subset comprises a cancellation of at least a part of the reservation and/or making a new reservation for the second subset.

1 1 . The method according to claim 9 or 10,

wherein the modification of the reservation is based on the radio device (20; 600; 700) further monitoring the contiguous set of radio resources after sending the first sidelink radio transmission (206) and reselecting the second subset according to the second criterion.

12. The method according to any one of the preceding claims, comprising:

- the radio device (20; 600; 700) indicating a reservation of the first subset for one or more time slots in the first sidelink radio transmission (206); and

- the radio device (20; 600; 700) indicating a modification of the reservation of the first subset in the second sidelink radio transmission (208).

13. The method according to claim 12,

wherein the modification of the reservation of the first subset comprises a cancellation of at least a part of the reservation and/or making a new reservation for the first subset.

14. The method according to claim 12 or 13, wherein the modification of the reservation is based on the radio device (20; 600; 700) further monitoring the contiguous set of radio resources after sending the first sidelink radio transmission (206) and reselecting the first subset according to the second criterion.

15. The method according to any one of the preceding claims, comprising:

- the radio device (20; 600; 700) selecting a third subset of radio resources from the contiguous set according to the second criterion;

- the radio device (20; 600; 700) indicating a reservation of the third subset in the second sidelink radio transmission (208); and

- the radio device (20; 600; 700) sending a third sidelink radio transmission (210) on the third subset.

16. The method according to claim 15,

wherein the second sidelink radio transmission (208) indicates the reservation of the third subset for multiple time slots.

17. The method according to claim 16, comprising:

- the radio device (20; 600; 700) indicating a modification of the reservation of the third subset in the third sidelink radio transmission (210).

18. The method according to claim 17,

wherein the modification of the reservation of the third subset comprises a cancellation of at least a part of the reservation and/or making a new reservation for the third subset.

19. The method according to claim 17 or 18,

wherein the modification of the reservation is based on the radio device (20; 600; 700) further monitoring the contiguous set of radio resources after sending the second sidelink radio transmission (208) and reselecting the third subset according to the second criterion.

20. The method according to any one of the preceding claims,

wherein a start of the first sidelink radio transmission (206) and a start of the second sidelink radio transmission (208) are separated by a time gap.

21 . The method according to any one of the preceding claims,

wherein the second sidelink radio transmission (208) starts after an end of the first sidelink radio transmission (206).

22. The method according to any one of the preceding claims, comprising:

- the radio device (20; 600; 700) receiving configuration information defining at least a part of the second criterion from a node (100) of the wireless communication network.

23. The method according to any one of the preceding claims,

wherein the radio resources are frequency channels.

24. A radio device (20; 600; 700) for a wireless communication network, the radio device (20; 600; 700) being configured to:

- monitor a contiguous set of radio resources to determine radio resources estimated to be used by one or more other radio devices (30,40);

- select a first subset of radio resources from the contiguous set according to a first criterion configured to mitigate overlap of the first subset with the radio resources estimated to be used by one or more other radio devices (30,40);

- select a second subset of radio resources from the contiguous set according to a second criterion configured to mitigate fragmentation of the contiguous set of radio resources by the selected subset and the radio resources estimated to be used;

- send a first sidelink radio transmission on the first subset, the first sidelink radio transmission indicating a reservation of the second subset; and

- send a second sidelink radio transmission on the second subset.

25. The radio device (20; 600; 700) according to claim 24,

26. The radio device (20; 600; 700) according to claim 24 or 25,

27. The radio device (20; 600; 700) according to any one of claims 24 to 26,

28. The radio device (20; 600; 700) according to any one of claims 24 to 27, wherein the second criterion depends on a priority of data conveyed by the second sidelink radio transmission.

29. The radio device (20; 600; 700) according to any one of claims 24 to 28,

wherein the second criterion depends on a type of data conveyed by the second sidelink radio transmission.

30. The radio device (20; 600; 700) according to any one of claims 24 to 29,

31. The radio device (20; 600; 700) according to any one of claims 24 to 30,

wherein the first sidelink radio transmission indicates the reservation of the second subset for multiple time slots.

32. The radio device (20; 600; 700) according to claim 31 ,

wherein the radio device (20; 600; 700) is configured to indicate a modification of the reservation of the second subset in the second sidelink radio transmission.

33. The radio device (20; 600; 700) according to claim 32,

34. The radio device (20; 600; 700) according to claim 32 or 33,

wherein the radio device (20; 600; 700) is configured to further monitor the contiguous set of radio resources after sending the first sidelink radio transmission and reselect the second subset according to the second criterion, and

wherein the modification of the reservation is based on the reselected second subset.

35. The radio device (20; 600; 700) according to any one of claims 24 to 34,

wherein the radio device (20; 600; 700) is configured to:

- indicate a reservation of the first subset for one or more time slots in the first sidelink radio transmission; and

- indicate a modification of the reservation of the first subset in the second sidelink radio transmission.

36. The radio device (20; 600; 700) according to claim 35, wherein the modification of the reservation of the first subset comprises a cancellation of at least a part of the reservation and/or making a new reservation for the first subset.

37. The radio device (20; 600; 700) according to claim 35 or 36,

wherein the radio device (20; 600; 700) is configured to further monitor the contiguous set of radio resources after sending the first sidelink radio transmission and reselect the first subset according to the second criterion, and

wherein the modification of the reservation is based on the radio device (20; 600; 700) the reselected first subset.

38. The radio device (20; 600; 700) according to any one of claims 24 to 37,

wherein the radio device (20; 600; 700) is configured to:

- select a third subset of radio resources from the contiguous set according to the second criterion;

- indicate a reservation of the third subset in the second sidelink radio transmission (208); and

- the radio device (20; 600; 700) sending a third sidelink (210) radio transmission on the third subset.

39. The radio device (20; 600; 700) according to claim 38,

wherein the second sidelink radio (208) transmission indicates the reservation of the third subset for multiple time slots.

40. The radio device (20; 600; 700) according to claim 39,

wherein the radio device (20; 600; 700) is configured to indicate a modification of the reservation of the third subset in the third sidelink radio transmission (210).

41. The radio device (20; 600; 700) according to claim 40,

42. The radio device (20; 600; 700) according to claim 40 or 41 ,

wherein the radio device (20; 600; 700) is configured to further monitor the contiguous set of radio resources after sending the second sidelink radio transmission (208) and reselect the third subset according to the second criterion, and

wherein the modification of the reservation is based on the reselected third subset.

43. The radio device (20; 600; 700) according to any one of claims 24 to 42, wherein a start of the first sidelink radio transmission (206) and a start of the second sidelink radio transmission (208) are separated by a time gap.

44. The radio device (20; 600; 700) according to any one of claims 24 to 43,

45. The radio device (20; 600; 700) according to any one of claims 24 to 44,

wherein the radio device (20; 600; 700) is configured to receive configuration information defining at least a part of the second criterion from a node (100) of the wireless communication network.

46. The radio device (20; 600; 700) according to any one of claims 24 to 45,

wherein the radio resources are frequency channels.

47. The radio device (20; 600; 700) according to claim 24,

wherein the radio device (20; 600; 700) is configured to perform the steps of a method according to any one of claims 2 to 23.

48. The radio device (20; 600; 700) according to any one of claims 24 to 47, comprising: at least one processor (750) and a memory (760) containing instructions executable by said at least one processor (750), whereby the radio device (20) is operative to perform a method according to any one of claims 1 to 23.

49. A system, comprising:

a first radio device (20; 600; 700) and at least one second radio device (30, 40),

the first radio device (20; 600; 700) being configured to:

- send a first sidelink radio transmission (206) on the first subset, the first sidelink radio transmission (206) indicating a reservation of the second subset; and - send a second sidelink radio transmission (208) on the second subset,

the second radio device (30, 40) being configured to receive the first sidelink radio transmission

(206) and the second sidelink radio transmission (208). 50. A computer program comprising program code to be executed by at least one processor of a radio device (20; 600; 700), whereby execution of the program code causes the radio device (20; 600; 700) to perform a method according to any one of claims 1 to 23.

51. A computer program product comprising program code to be executed by at least one processor of a radio device (20; 600; 700), whereby execution of the program code causes the radio device (20; 600; 700) to perform a method according to any one of claims 1 to 23.