Patent Description:
Current wireless communication networks, e.g., based on the LTE (Long Term Evolution) or NR technology as specified by 3GPP (<NUM>rd Generation Partnership Project), also support D2D communication modes to enable direct communication between UEs (user equipments), sometimes also referred to as sidelink communication. Such D2D communication modes may for example be used for vehicle communications, e.g., including communication between vehicles, between vehicles and roadside communication infrastructure and, possibly, between vehicles and cellular networks. Due to wide range of different types of devices that might be involved in the communication with the vehicles, vehicle-to-everything (V2X) communication is another term used to refer to this class of communication. Vehicle communications have the potential to increase traffic safety, reduce energy consumption and enable new services related to intelligent transportation systems.

Due to the nature of the basic road safety services, LTE V2X functionalities have been designed for broadcast transmissions, i.e., for transmissions where all receivers within a certain range of a transmitter may receive a message from the transmitter, i.e., may be regarded as intended recipients. In fact, the transmitter may not be aware or otherwise be able to control the group of intended receivers. V2X functionalities for the NR technology are for example described in <NPL>). In the NR technology, also more targeted V2X services are considered, by supporting also groupcast, multicast, or unicast transmissions, in which the intended receiver of a message consists of only a subset of the receivers within a certain range of the transmitter (groupcast) or of a single receiver (unicast). For example, in a platooning service for vehicles there may be certain messages that are only of interest for a member vehicle of the platoon, so that the member vehicles of the platoon can be efficiently targeted by a groupcast transmission. In another example, the see-through functionality, where one vehicle provides video data from a front facing camera to a following vehicle, may involve V2X communication of only a pair of vehicles, for which unicast transmissions may be a preferred choice. Furthermore, NR sidelink communication supports D2D communication of UEs with and without network coverage, with varying degrees of interaction between the UEs and the network, including the possibility of standalone, network-less operation.

For NR sidelink communication, unicast at access stratum is supported for services requiring high reliability. Between the same UE pair, there can be multiple sidelink unicast links and each link can support multiple SL QoS flows/radio bearers, established via a sidelink radio interface, in the NR and LTE technology referred to as "PC5". At the access stratum, each link can be identified by the source and destination Layer <NUM> identity (L2 ID). <FIG> schematically illustrates utilization of multiple sidelink unicast links between two UEs for supporting multiple different services.

The sidelink unicast link can be established by means of a direct discovery procedure. In this procedure, an initiating UE who intends to communicate with a specific UE or another UE supporting a specific service will broadcast a Direct Communication Request message. If a specific target UE is known to the initiating UE, the initiating UE includes a higher layer identifier of the target UE in the Direct Communication Request message. This case is also referred to as "UE oriented Layer-<NUM> link establishment". If the initiating UE would like to discover all UEs in proximity having interest in the same service, the Direct Communication Request message may include a service identifier instead of the identifier of a specific target UE. This is also referred to as "service oriented Layer-<NUM> link establishment". A UE in proximity which receives the Direct Communication Request will respond to the initiating UE only if it is the identified target UE or if it has interest in the identified service. The link is then established after L2 ID exchange and a security setup procedure. <FIG> schematically illustrates an example of a procedure for sidelink unicast link establishment, involving UE oriented Layer-<NUM> link establishment and/or service-oriented Layer-<NUM> link establishment.

A further potential use case of D2D communication is NSPS (National Security and Public Safety). In traditional specific NSPS communication systems such as TETRA (Terrestrial Trunked Radio), data rates are in the order of a few kbit/s at most, which is regarded to be not sufficient to support future NSPS use case scenarios. Moreover, the NSPS use case requires enhanced coverage and high reliability of communication. Some scenarios of the NSPS use case also involve operation without support from infrastructure, e.g., NSPS communication in tunnels, inside certain buildings, or in certain emergency situations where the infrastructure is destroyed or non-operative. Even though in some of these situations, cellular coverage could be provided using mobile base stations, e.g., trucks with a portable base station, basing at least a part of NSPS communication on LTE or NR sidelink communication can provide benefits concerning the achievable data rates, robustness, and reliability of operation without network coverage. In the case of NR sidelink communication, also NSPS group communication scenarios can be efficiently addressed, such as communication among a group of workers in a building or at an emergency site. In some scenarios, also utilization of multi-hop wireless connections formed of multiple sidelink unicast links could help to enable communication between devices which are not capable of establishing a direct sidelink unicast connection. In some public safety scenarios it may occur that a certain message is only valuable to a certain group of UEs located in a certain area. For example, a commander may want to talk to all first responders in a building. Using the existing D2D and sidelink technologies, such targeting of UEs in a certain area can be achieved by addressing the same message by unicast D2D transmissions to each UE which is assumed to be in the area or by groupcast D2D transmissions to groups of UEs which are assumed to be in the area. This typically requires that the same message is transmitted multiple times and also requires information about where the individual UEs or groups are located. Alternatively, the message can be distributed by flooding, i.e., by broadcasting it to all UEs and causing each UE which receives the message to also forward the message to further UEs within the range of the receiving UE. With such flooding, the message is typically also received by UEs belonging to the group of intended recipients, and it may be up to each UE to decide whether and how to use the received message.

However, transmitting the same message multiple times with unicast addressing of individual UEs may result in rather poor resource efficiency. Further, also when using flooding to distribute the message the resource efficiency may be low because it can occur that the message is received or forwarded by an excessive number of UEs not belonging to the group of intended recipients. This may result in excessive duplicated transmissions or in congestion of the network.

Accordingly, there is a need for techniques which allow for efficiently addressing a D2D transmission to multiple target recipients.

Grid-based protocols for routing of messages in an ad-hoc network are described in "<NPL>), in "<NPL>), and in "<NPL>. A routing protocol for vehicular ad-hoc networks is described om "<NPL>).

Further detailed embodiments are defined in the dependent claims.

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 D2D communication by wireless communication devices. These wireless communication devices may include various types of UEs or other wireless devices (WDs). As used herein, the term "wireless device" (WD) refers to a device capable, configured, arranged, and/or operable to communicate wirelessly with network nodes and/or other WDs. Unless otherwise noted, the term WD may be used interchangeably herein with UE. Communicating wirelessly may involve transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information through air. In some embodiments, a WD may be configured to transmit and/or receive information without direct human interaction. For instance, a WD may be designed to transmit information to a network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the network. Examples of a WD include, but are not limited to, a smart phone, a mobile phone, a cell phone, a Voice over IP (VoIP) phone, a wireless local loop phone, a desktop computer, a Personal Digital Assistant (PDA), a wireless camera, a gaming console or device, a music storage device, a playback appliance, a wearable terminal device, a wireless endpoint, a mobile station, a tablet, a laptop, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), a smart device, a wireless Customer Premise Equipment (CPE), a vehicle mounted wireless terminal device, a connected vehicle, etc. In some examples, in an Internet of Things (IoT) scenario, a WD may also represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another WD and/or a network node. The WD may in this case be a Machine-to-Machine (M2M) device, which may in a 3GPP context be referred to as a Machine-Type Communication (MTC) device. As one particular example, the WD may be a UE implementing the 3GPP Narrowband loT (NB-loT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, home or personal appliances (e.g., refrigerators, televisions, etc.), or personal wearables (e.g., watches, fitness trackers, etc.). In other scenarios, a WD may represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation. A WD as described above may represent the endpoint of a wireless connection, in which case the device may be referred to as a wireless terminal. Furthermore, a WD as described above may be mobile, in which case it may also be referred to as a mobile device or a mobile terminal. The illustrated concepts particularly concern WDs that support D2D communication, for example by implementing a 3GPP standard for sidelink communication, Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I), Vehicle-to-Everything (V2X). The D2D communication may for example be based on the LTE radio technology or the NR radio technology as specified by 3GPP, e.g., on the PC5 interface of the LTE or NR technology. However, it is noted that the illustrated concepts could also be applied to other radio technologies, e.g., a WLAN (Wireless Local Area Network) technology.

In the illustrated concepts, multiple geographical areas are defined, e.g., by using RRC (Radio Resource Control), broadcasted SI (SI), and/or network operator preconfiguration. These geographical areas are then used as a basis for addressing D2D transmissions by including an area identifier into the D2D transmission to identify the geographical area the D2D transmission is addressed to. Direct (single-hop) or multi-hop D2D transmissions may be used to convey the D2D transmission to one or more UEs in the target geographical area. Accordingly, a D2D transmission may be conveyed via a direct or single-hop D2D path or via a multi-hop D2D path formed of multiple D2D path segments each corresponding to a direct D2D path.

For enabling efficient propagation of the D2D transmission to other geographical areas, certain UEs may be configured as gateway UE. Here, a gateway UE is a UE that provides a direct D2D path between two adjacent geographical areas. This is achieved by the gateway UE being located in a first geographical area and having a direct D2D connection to another UE in the adjacent second geographical area. This other UE may be regarded as being a counterpart gateway UE. From the perspective of the second geographical area, the counterpart gateway UE may act as a gateway UE to the first geographical area. Using the area identifier for addressing the D2D transmission to a target geographical area may also be referred to as "geocasting" of the D2D transmission. The illustrated concepts thus allow for providing a D2D geocasting mechanism. Here, it is noted that the D2D geocasting mechanism may also be combined with other addressing mechanisms suitable for D2D communication, e.g., by using a groupcasting mechanism to identify a subset of the UEs in the target geographical area.

<FIG> illustrates an exemplary scenario involving V2X communications. In particular, <FIG> shows various UEs <NUM>, which may engage in V2X communication or other D2D communication, illustrated by solid arrows. Further, <FIG> shows an access node <NUM> of a wireless communication network, e.g., an eNB of the LTE technology or a gNB of the NR technology, or an access point of a WLAN. At least some of the UEs <NUM> may also be capable of communicating by using DL radio transmissions and/or UL radio transmissions, illustrated by broken arrows.

The UEs illustrated in <FIG> comprise vehicles, a drone, a mobile phone, and a person, 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 the radio transmissions may be performed by a communication module installed in the vehicle, and that in the case of the person the radio transmissions may be performed by a radio device carried or worn by the person, e.g., a wristband device or similar wearable device. Furthermore, it is noted that the UEs shown in <FIG> are merely exemplary and that in the illustrated concepts other types of V2X communication device or D2D communication device could be utilized as well, e.g., RSUs (roadside units) or other infrastructure based V2X communication devices, V2X communication devices based in an aircraft, like an airplane, or helicopter, in a spacecraft, in a train or car of a train, in a ship, in a motorcycles, in a bicycle, in a mobility scooter, or in any other kind of mobility or transportation device.

In the scenario of <FIG>, the UEs <NUM> may be located in various geographical areas. and the D2D geocasting mechanism may be used to efficiently address the V2X communication to the UEs <NUM> located in a certain geographical area.

<FIG> illustrates an exemplary D2D communication scenario. In particular, <FIG> shows multiple UEs <NUM>, which are connected to each other by radio links implementing direct wireless links (illustrated by double-headed arrows). Further, one of the UEs <NUM> is connected by a radio link to an access node <NUM> of a wireless communication network, e.g., to an eNB of the LTE technology, or a gNB of the NR technology. The access node <NUM> is part of a RAN (Radio Access Network) of the wireless communication network, which typically also includes further access nodes to provide a desired coverage of the wireless communication network. Further, <FIG> shows a core network (CN) <NUM> of the wireless communication network. The CN <NUM> may provide connectivity of the UEs <NUM> to other data networks, e.g., through a GW <NUM> provided in the CN <NUM>. Further, the CN <NUM> may also include various nodes for controlling operation of the UEs <NUM>.

The radio links may be used for D2D communication between the UEs <NUM>. Further, the radio link to the wireless communication network may be used for controlling or otherwise assisting the D2D communication. Further, the D2D communication and/or data communication with the wireless communication network may be used for providing various kinds of services to the UEs <NUM>, e.g., a voice service, a multimedia service, a data service, an intelligent transportation system (ITS) or similar vehicular management or coordination service, and/or an NSPS service. Such services may be based on applications which are executed on the UE <NUM> and/or on a device linked to the UE <NUM>. Accordingly, in the illustrated concepts a D2D transmission may convey or correspond to a V2X message, an ITS message, or some other kind of message related to a service. Further, <FIG> illustrates an application service platform <NUM> in the CN <NUM> of the wireless communication network. Further, <FIG> illustrates one or more application servers <NUM> provided outside the wireless communication network. The application(s) executed on the UE <NUM> and/or on one or more other devices linked to the UE <NUM> may use the radio links with one or more other UEs <NUM>, the application service platform <NUM>, and/or the application server(s) <NUM>, thereby enabling the corresponding service(s) on the UE <NUM>. In some scenarios, the services utilized by the UEs <NUM> may thus be hosted on the network side, e.g., on the application service platform <NUM> or on the application server(s) <NUM>. However, some of the services may also network-independent so that they can be utilized without requiring an active data connection to the wireless communication network. This may for example apply to certain V2X or NSPS services. Such services may however still be assisted from the network side while the UE <NUM> is in coverage of the wireless communication network.

Also in the scenario of <FIG>, the UEs <NUM> may be located in various geographical areas, and the D2D geocasting mechanism of the illustrated concepts may be used to efficiently address the D2D communication to the UEs <NUM> located in a certain geographical area. In this way, it is for example possible to utilize support the service(s) on the UEs <NUM> by geocasting based D2D communication.

In the example of <FIG>, the UEs <NUM> are assumed to be a mobile phone and vehicles or vehicle-based communication devices, e.g., a vehicle-mounted or vehicle-integrated communication module, or a smartphone or other user device linked to vehicle systems. However, it is noted that other types of UE could be used as well, e.g., a device carried by a pedestrian, or an infrastructure-based device, such as a roadside unit, like for example illustrated in <FIG>.

<FIG> schematically illustrates an NSPS communication scenario. In particular, <FIG> shows multiple UEs <NUM>, which may exchange NSPS messages associated with one or more NSPS services using D2D communication, e.g., based on the LTE sidelink communication or NR sidelink communication. As further illustrated, the NSPS services may be assisted from the network, by exchanging NSPS messages via access node <NUM>. The NSPS services may for example include group communication of rescue vehicles, rescue personnel or other equipment or personnel of public safety related organizations. Such communication may also involve utilizing the illustrated D2D geocasting mechanism to address an NSPS message by including an area identifier to identify a target geographical area. As a result, the NSPS message may be efficiently conveyed to all UEs or to a subset of the UEs in the target geographical area.

<FIG> shows an example for further illustrating the D2D geocasting mechanism of the illustrated concepts. For this purpose, <FIG> illustrates a plurality of geographical areas, denoted as area #<NUM>, area #<NUM>, area #<NUM>, area #<NUM>, area #<NUM>, area #<NUM>, area #<NUM>, area #<NUM>, and area #<NUM>. An area identifier is assigned to each of the geographical areas and may be used to uniquely identify the geographical area. The area identifier may correspond to a numerical value. For example, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, area #<NUM> may be identified by numerical value <NUM>, and area #<NUM> may be identified by numerical value <NUM>. As further illustrated, a plurality of UEs may be located in the different geographical areas. In the illustrated example, a first UE (UE0), a second UE (UE1), and a third UE (UE2) are located in area #<NUM>. A fourth UE (UE3) and a fifth UE (UE4) are located in area #<NUM>. A sixth UE (UE5), a seventh UE (UE6), and an eight UE (UE7) are located in area #<NUM>. A ninth UE (UE8) and a tenth UE (UE9) are located in area #<NUM>. An eleventh UE (UE10) is located in area #<NUM>. A twelfth UE (UE11) and a thirteenth UE (UE12) are located in area #<NUM>. An fourteenth UE (UE13) is located in area #<NUM>. An fifteenth UE (UE14) is located in area #<NUM>. In the illustrated example, area #<NUM> includes no UE.

In the illustrated concepts, the geographical areas may be defined on the basis of a zone configuration as also utilized for controlling radio resource pools for sidelink transmissions. For example, in the case of sidelink transmission as specified by 3GPP for the LTE technology or the NR technology, a zone configuration may be provided to the UE per RRC (Radio Resource Control) configuration, by SI (System Information) configuration, and/or per network operator pre-configuration. The zone configuration may define multiple zones defined in terms of one or more of the following elements: zone length, zone width, total number of zones configured with respect to longitude, and total number of zones configured with respect to latitude. The UE may determine an identity of the zone where it is located, denoted as Zone_id, using the following relations: <MAT> <MAT> <MAT>.

In these relations L denotes a value of the zone length, W denotes a value of the zone width, Nx denotes the total number of zones configured with respect to longitude, Ny denotes the total number of zones configured with respect to latitude, x denotes the geodesic distance in longitude between UE's current location and geographical coordinates (<NUM>, <NUM>) according to the WGS84 model, y denotes the geodesic distance in latitude between UE's current location and geographical coordinates (<NUM>, <NUM>) according to the WGS84 model. The geographical areas utilized in the illustrated concepts may correspond to these zones or may be defined on the basis of these zones, e.g., by defining each of the geographical areas in terms of a combination of multiple zones.

In the example of <FIG>, it is assumed that UE0, located in area #<NUM>, sends a D2D transmission which is addressed to area #<NUM>. Because area #<NUM> is not adjacent to area #<NUM>, UE0 first selects area #<NUM> and area #<NUM> as candidates which can be expected to provide a D2D path to the target geographical area, i.e., to area #<NUM>. For example, this can be based on the information that each of area #<NUM> and area #<NUM> is adjacent to both area #<NUM> and to area #<NUM>. In a first hop, UE0 first sends the D2D transmission to UE1, which acts as a gateway UE to area #<NUM>, and to UE2, which acts as a gateway to area #<NUM>. In area #<NUM> the first hop D2D transmission is received by UE3. In area #<NUM> the first hop D2D transmission is received by UE10. In a second hop, UE3 sends the D2D transmission to UE4, which acts as a gateway to area #<NUM>. In area #<NUM>, i.e., in the target area, the second hop D2D transmission is received by UE5. In a third hop, UE5 sends the D2D transmission to the other UEs in the target area, i.e., to UE6 and UE7. Concerning area #<NUM>, the illustrated example assumes that the D2D transmission cannot be further propagated to area #<NUM>, because area #<NUM> includes no UE acting as a gateway to area #<NUM>.

The D2D geocasting mechanism may thus operate as follows: Without limitation, it can be assumed that all UEs are capable of relaying a D2D transmission from the previous hop to the next hop. Further, it can be assumed that all UEs have established connection with the other UEs within its communication range. These other UEs may be in the same geographical area or in an adjacent geographical area.

For supporting the D2D geocasting, each UE may maintain a routing table. The routing tables may be managed on the basis of mutual information exchange between the UEs, e.g., as part of the D2D communication. Accordingly, each UE may learn its routing table from received D2D transmissions. However, it is noted that in some cases management of the routing tables could also be supported from the network side, e.g., based on information provided by one or more nodes of the wireless communication network. Such information could be provided in broadcasted SI or by RRC signaling.

Moreover, it can be assumed that each UE is aware of the geographical area where it is located. For example, each UE may derive its geographical position using the GPS (Global Positioning System) or other satellite positioning system, and/or using a network based positioning mechanism. The geographical position of the UE may then be compared to the definitions of the geographical areas to determine the geographical area where the UE is located. This may for example be accomplished using the above-mentioned relations to derive the Zone_id.

For better illustrating the D2D geocasting mechanism, the following explanations will distinguish between four UE types depending on the role of the UE with respect to the delivery or forwarding of D2D transmission. It is however noted that the assignment of these roles is not fixed and that each UE could also combine the functionalities of two or more of these UE types. These UE types include: An "initial UE" which initially generates a D2D transmission, i.e., is the source of the D2D transmission. An "intermediate UE" which receive a D2D transmission from a previous hop and forwards the D2D transmission to the next hop. A "gateway UE" which keeps a D2D connection to one or more UEs in another geographical area. A "target UE" which is located in the target geographical area and constitutes an intended recipient of the D2D transmission. As mentioned above, the roles may overlap. For example, for a given geocasted D2D transmission, the initial UE could also be a gateway UE. Further, an intermediate UE could also be a gateway UE. Still further, a target UE could also be an intermediate UE and/or a gateway UE.

When an initial UE wants to send a D2D transmission to the UEs in a certain target geographical area, it associates the D2D transmission with an address of the target geographical area. This address will in the following be referred to as area identifier. It may for example correspond to a numerical value, e.g., like the above-mentioned zone identifiers. Associating the D2D transmission with the address is accomplished by incorporating the area identifier into the D2D transmission, e.g., into a packet header or frame header. The initial UE then sends the D2D transmission with the area identifier to a gateway UE which is expected to enable delivery of the D2D transmission to the target geographical area. Sending the D2D transmission to the gateway UE may also be accomplished via one or more intermediate UEs. The D2D transmission is then further relayed by the intermediate and/or gateway UEs until it reaches the target UEs in the target geographical area.

In order to efficiently and reliably enable delivery of the D2D transmission to the target geographical area, the gateway UE provides one or more direct D2D connections to one or more UEs in one or more neighboring geographical areas. The gateway UE may thus facilitate delivery of the D2D transmission towards the target geographical area. Depending on the D2D connections available at a given UE, it can be determined whether this UE should be regarded as a gateway UE: If a UE has a D2D connection to another UE in a different geographical area, it can be regarded as gateway UEs to this geographical area. Information about the context of such gateway UE may be made available to the other UEs in the same geographical area and to the respective counterpart gateway UE(s) in the other geographical area(s). The context of the gateway UE may indicate to which of the geographical areas the gateway UE provides a D2D connection, a channel quality of the D2D connection to the other geographical area, the UE type of the counterpart gateway UEs, the number of counterpart gateway UEs, or the like. In some scenarios, D2D transmissions to and/or from a gateway UE may be assigned a higher priority than other D2D transmissions. This prioritization may for example be provided on access stratum level.

In order to reduce the needed number of transmissions and provide efficient resource utilization, a UE relaying or otherwise transmitting the D2D transmission to other UEs within the same geographical area may use a unicast transmission mode, a groupcast transmission mode, a broadcast transmission mode, or a combination of two or more of these transmission modes.

As mentioned above, each UE may maintain a routing table. The routing table of a given UE may include the following information:.

Accordingly, if a UE wants to relay or otherwise send a D2D transmission to a different geographical area, it may first select one or more gateway UEs in its own geographical area, which are expected to enable reaching the target geographical area. The UE may then first send the D2D transmission to the identified gateway UE(s). This may be accomplished through a direct D2D connection to the gateway UE. If no such direct D2D connection to the gateway UE is available, sending the D2D transmission to the identified gateway UE may also be accomplished through one or more intermediate UEs. In the example of <FIG>, UE0 is the initial UE and selects UE1 and UE2 as gateway UEs. UE3 then selects UE4 as a further gateway UE which allows for reaching the target geographical area, i.e., area #<NUM>. In some scenarios, the UE may first try to find a gateway UE that has direct D2D connection to the target geographical area. If this is not possible, the UE may try to find gateway UEs that can reach a neighbor geographical area of the target geographical area. For example, in the scenario illustrated in <FIG>, the target geographical area is area#<NUM>. However, for UE0 no gateway UE is available in area #<NUM> that has a direct D2D connection to area#<NUM>. Nonetheless, UE0 may determine from its routing table and/or from the configuration information defining the geographical areas that area#<NUM> and area#<NUM> are neighbor geographical areas of area#<NUM>. For the latter geographical areas, gateway UEs are available in area #<NUM>, namely UE1 and UE2. Accordingly, in the example of <FIG>, UE0 selects UE1 and UE2 as gateway UEs and first sends its D2D transmission to these gateway UEs. In such situations where multiple gateway UEs are available, the UE may also select among these multiple gateway UEs. For example, the UE may select the gateway UE which provides the shortest path to the target geographical area. This may for example consider an expected number of D2D hops from the gateway UE to the target geographical area and/or an expected number of hops from the UE to the gateway UE.

In some scenarios where multiple gateway UEs are associated with the same neighbor geographical area, only one gateway UE among them may be selected. This selection may be based on channel quality, e.g., measured in terms of RSRP (Reference Signal Received Power) or RSRQ (Reference Signal Received Quality), between the gateway UE and the initial UE. Additionally or alternatively also the channel quality, e.g., measured in terms of RSRP or RSRQ, of at least some or even all other hops to the gateway UE may be considered in the selection. Further, the selection may be based on the length of the D2D path to the target geographical area, e.g., by considering an expected number of D2D hops from the gateway UE to the target geographical area and/or an expected number of hops from the UE to the gateway UE.

In order to deliver the D2D transmission to the selected gateway UE(s), the UE can add an address of the selected gateway UE(s) to the D2D transmission, e.g., by including it in a packet header or frame header. The address may for example correspond to a device identifier. As a result, the D2D transmission may then include the area identifier of the target geographical area and the device identifier of the selected gateway UE(s). The UE may then check its routing table to identify a next hop intermediate UE which allows to reach the selected gateway UE(s). Next, the UE may then send the D2D transmission to the selected next hop intermediate UE.

In some scenarios, the UE may also directly send the D2D transmission to the selected gateway UE(s), i.e., if a direct D2D connection to the selected gateway UE is available. If multiple gateway UEs are selected, the D2D transmission may be replicated to be sent separately to each of the multiple gateway UEs.

If an intermediate UE receives a D2D transmission from the previous hop, it may check the indicated address of gateway UE(s) and check its routing table to identify a next hop intermediate UE which allows to reach the selected gateway UE(s). The intermediate UE may then relay the D2D transmission to the selected next hop intermediate UE. In some scenarios, the intermediate UE may also directly send the D2D transmission to the selected gateway UE(s), i.e., if a direct D2D connection to the selected gateway UE is available.

In some scenarios, the above operations of sending or relaying a D2D transmission to one or more selected gateway UEs may involve that the UE generates a MAC PDU (Medium Access Control Packet Data Unit) which includes the address of the selected gateway UE and the address of the selected next hop intermediate UE in its packet header. The UE may then send this MAC PDU to the selected next hop intermediate UE. In some scenarios, the UE may also directly send the MAC PDU to the selected gateway UE(s), i.e., if a direct D2D connection to the selected gateway UE is available. In this case, the packet header of the MAC PDU would not include an address of a next hop intermediate UE. If multiple gateway UEs are selected, the same data may be sent to each of the multiple gateway UEs in separate MAC PDUs.

If the gateway UE receives the D2D transmission, it may select one or more counterpart gateway UEs in its neighbor geographical area. Specifically, it may select those counterpart gateway UEs which are expected to allow reaching the target geographical area. The gateway UE may then send the D2D transmission to the selected counterpart gateway UE(s). In some scenarios, if multiple counterpart gateway UEs are selected, the gateway UE may replicate the D2D transmission to be sent separately to each of the multiple counterpart gateway UEs, e.g., as separate MAC PDUs.

In some scenarios, it may occur that the counterpart gateway UE receives the D2D transmission from the neighboring geographical area and finds that the D2D transmission is to be delivered to yet another geographical area, i.e., that the target geographical area is different from the geographical area where the counterpart UE is located. The counterpart gateway UE may then operate in a similar manner as described above for selecting one or more further gateway UEs which are expected to allow reaching the target geographical area. For example, in the scenario of <FIG>, when UE1 receives the D2D transmission from UE0, UE1 is a gateway UE to area #<NUM> and relays the D2D transmission to UE3, which is a counterpart gateway UE in area #<NUM>. Next, UE3 then proceeds by identifying a further gateway UE which allows for reaching the target area, i.e., area #<NUM>, and selects UE4 that has a direct D2D connection to area #<NUM>. UE3 then relays the D2D transmission to UE4.

Once the D2D transmission arrives at the target geographical area, the D2D transmission is delivered to the target UEs within the target geographical area. This may involve distributing the D2D transmission to all UEs in the target geographical area. Alternatively, the D2D transmission could be delivered to only a subset of the UEs in the target geographical area, i.e., the target UEs may be only a subset of the UEs in the target geographical area. Here, it is to be noted that in some scenarios the D2D transmission will arrive at a gateway UE of the target geographical area, from a neighboring geographical area. In other scenarios, the initial UE could already be located in the target geographical area. In this case, arrival of the D2D transmission at the target geographical area would already occur when the initial UE generates the D2D transmission.

Within the target geographical area, delivering the D2D transmission to the target UEs may involve that the gateway UE floods the D2D transmission into a sub-network consisting of all the target UEs within the target geographical area. Similarly, if the initial UE is already located in the target geographical area, the initial UE could flood the D2D transmission into a sub-network consisting of all the target UEs within the target geographical area.

Alternatively or in addition, the gateway UE or initial UE could check its routing table and replicate the D2D transmission to be sent separately to each of the target UEs, e.g., as separate MAC PDUs. This may involve adding a respective device address of the target UE to the D2D transmission. In some scenarios, this may also involve replacing the area identifier of the target geographical area with the respective device address.

Alternatively or in addition, the gateway UE or initial UE could check its routing table and groupcast the D2D transmission to at least some of the target UEs. This may involve adding a respective group address assigned to some of the target UEs to the D2D transmission. In this case, the same MAC PDU could be decoded by the target UEs of the group addressed by the groupcast transmission. In some scenarios, this may also involve replacing the area identifier of the target geographical area with the respective group address.

In some scenarios, a target UE may receive the D2D transmission and resend the received D2D transmission to ensure that the D2D transmission can reach all target UEs within the target geographical area, including those UEs which are not within communication range of the gateway UE or initial UE at which the D2D transmission arrives in the target geographical area. The target UE may resend the packet using unicast transmission mode, using a groupcast transmission mode, using in a broadcast transmission mode, or using a combination of two or more of these transmission modes. The target UE may resend the D2D transmission in response to at least one of the following conditions being met:.

<FIG> shows an example of delivering the D2D transmission in the target geographical area. In the example of <FIG>, UE-A sends a D2D transmission in a groupcast transmission mode, with the D2D transmission being addresses to UE-B, UE-C, UE-D, and UE-E. The communication range from UE-A is illustrated by a broken line. As can be seen, the transmission from UE-A can directly reach UE-B and UE-C, but cannot directly reach UE-D and UE-E. By measuring the RSRP from UE-A, UE-C can determine that it is located at the edge of UE-A's communication range. Further, based on RSRP measurements with respect to UE-D and UE-E, UE-C can estimate that these UEs can be reached from UE-C, but not from UE-A. UE-C can thus decide to resend the D2D transmission received from UE-A towards UE-D and UE-E. This can be accomplished in a unicast transmission mode, which targets UE-D and UE-E by two separate D2D transmissions, or in a groupcast transmission mode which targets UE-D and UE-E by a single D2D transmission which decodable by both UEs.

<FIG> shows a flowchart for illustrating a method, which may be utilized for implementing the illustrated concepts. The method of <FIG> may be used for implementing the illustrated concepts in a wireless communication device, e.g., corresponding to any of the above-mentioned UEs. In some scenarios, the wireless communication device may be a vehicle or vehicle-mounted device, but other types of WD, e.g., as mentioned above, could be used as well.

If a processor-based implementation of the wireless communication device is used, at least some of the steps of the method of <FIG> may be performed and/or controlled by one or more processors of the wireless communication device. Such wireless communication 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>.

At step <NUM>, the wireless communication device obtains configuration information defining multiple geographical areas. The wireless communication device may receive at least a part of the configuration information by RRC signaling while the wireless communication device is connected to a wireless communication network. Alternatively or in addition, the wireless communication device may receive at least a part of the configuration information by broadcasted system information while the wireless communication device is in coverage of a wireless communication network. Alternatively or in addition, the wireless communication device may receive at least a part of the configuration information by operator preconfiguration. The geographical areas may for example be defined in terms of longitude, latitude, width along the latitude direction, and/or length along the longitude direction. In some scenarios the geographical areas may be defined based on zones as also used for resource assignment for D2D transmissions, e.g., as used for allocating resource pools in the sidelink mode of the LTE or NR technology.

At step <NUM>, the wireless communication device may store first information. The first information may be part of the above-mentioned routing tables. In particular, for each of one or more second geographical areas which are adjacent to a first geographical area where the wireless communication device is located, the wireless communication device may store first information indicating one or more wireless communication devices located in the first geographical area and providing a direct D2D path to the second geographical area. The wireless communication device may store the first information based on one or more incoming D2D transmissions received from other wireless communication devices in the first geographical area. Accordingly, the wireless communication device may learn the first information from received D2D transmissions.

At step <NUM>, the wireless communication device may store second information. The second information may be part of the above-mentioned routing tables. The second information may overlap with the first information stored at step <NUM>. The second information may indicate one or more other wireless communication devices connected by a direct D2D path to the wireless communication device. These wireless communication devices may include wireless communication devices located in the same geographical area as the wireless communication device and wireless communication devices located in one or more adjacent geographical areas. The wireless communication device may store the second information based on one or more incoming D2D transmissions received from other wireless communication devices. Accordingly, the wireless communication device may learn the second information from received D2D transmissions.

In some scenarios, the second information may include a device identifier of each of the one or more other wireless communication devices. Further, the second information may include, for each of the one or more other wireless communication devices, an area identifier of the geographical area where the other wireless communication device is located. Further, the second information may indicate, for each of the one or more other wireless communication devices, further wireless communication devices connected by a D2D path to the wireless communication device. The second information may thus indicate multi-hop information which allows for determining which other wireless communication devices could be reached through the other wireless communication device. Further, the second information may indicate, for each of the one or more other wireless communication devices, whether the other wireless communication device provides a direct D2D path between a first geographical area, where the other wireless communication device is located, and at least one second geographical area which is adjacent to the first geographical area, i.e., whether the other wireless communication device is a gateway.

At step <NUM>, the wireless communication device may receive an incoming D2D transmission. The incoming D2D transmission may include an area identifier to identify one of the geographical areas as target geographical area of the incoming D2D transmission and to address the incoming D2D transmission to one or more wireless communication devices in the identified target geographical area of the incoming D2D transmission. The wireless communication device may receive the incoming D2D transmission via one or more multi-hop D2D paths each formed by one or more intermediate wireless communication devices forwarding the D2D transmission from one D2D path segment to a next D2D path segment. Each of these one or more multi-hop D2D paths may include one of the one or more wireless communication devices providing a direct D2D path between two geographical areas, i.e., gateways.

In some scenarios, the incoming D2D transmission may include multiple area identifiers to identify two or more of the geographical areas as target geographical areas of the incoming D2D transmission and to address the incoming D2D transmission to one or more wireless communication devices in the identified target geographical areas of the incoming D2D transmission.

Based on the geographical area where the wireless communication device is located and the identified target geographical area of the received incoming D2D transmission, the wireless communication device may then determine whether it is a target recipient of the received incoming D2D transmission. For this purpose, the wireless communication device may also determine its own geographical position, e.g., based on satellite positioning measurements, network based positioning measurements, and/or other positioning mechanisms.

In some scenarios, the incoming D2D transmission may also include additional address information to address the incoming D2D transmission to a subset of the wireless communication devices in the target geographical area of the incoming D2D transmission. In such cases, the wireless communication device may further consider the additional address information when determining whether it is a target recipient of the D2D transmission.

At step <NUM>, in response to the wireless communication device being located in a first one of the geographical areas and the target geographical area of the outgoing D2D transmission being different from the first geographical area, the wireless communication device determines one or more gateways, i.e., wireless communication devices located in the first geographical area and providing a direct D2D path to at least one second geographical area, which is adjacent to the first geographical area and is expected to provide a D2D path to the target geographical area. The wireless communication device may determine the one or more gateways based on the first information stored at step <NUM>.

In response to determining multiple gateways to the at least one second geographical area, the wireless communication device may select at least one of the multiple gateways. For example, for each of the multiple gateways, the wireless device may determine a respective number of D2D path segments to a target geographical area of an outgoing D2D transmission and select the at least of the multiple gateways based on the determined numbers of D2D path segments to the target geographical area of the outgoing D2D transmission. For example, the wireless communication device may select the gateway providing the lowest number of path segments, to thereby keep the resulting multi-hop D2D path as short as possible. Further, for each of the multiple gateways to the at least one second geographical area, the wireless device may determine a respective number of D2D path segments from the wireless communication device to the gateway and select the at least one of the gateways based on the determined numbers of D2D path segments from the wireless device to the gateway. For example, the wireless communication device may select the gateway providing the lowest number of path segments, to thereby keep the resulting multi-hop D2D path as short as possible. Further, for each of the multiple gateways, the wireless device may determine a respective channel quality of at least one D2D path segment between the wireless communication device and the gateway, e.g., in terms of an RSRP or RSRQ, and select the at least of the multiple gateways based on the determined channel qualities. For example, the wireless communication device may select the gateway providing higher channel qualities, to thereby overall channel quality of the resulting multi-hop D2D path as high as possible. In some scenarios, the selection may also be based on the channel qualities of all D2D path segments between the wireless communication device and the gateway. In some scenarios the wireless communication device may also select at least two of the multiple gateways.

At step <NUM>, the wireless communication device sends an outgoing D2D transmission comprising an area identifier to identify one of the geographical areas as target geographical area of the outgoing D2D transmission and to address the outgoing D2D transmission to one or more wireless communication devices in the identified target geographical area of the outgoing D2D transmission.

The wireless communication device may send the outgoing D2D transmission via one or more multi-hop D2D paths each formed by one or more intermediate wireless communication devices forwarding the D2D transmission from one D2D path segment to a next D2D path segment. Each of these one or more multi-hop D2D paths may include one of the one or more wireless communication devices providing a direct D2D path to at least one second geographical area, i.e., gateways, as determined or selected at step <NUM>. In some scenarios, each of the one or more multi-hop D2D paths may include a further wireless communication device located in the at least one second geographical area and providing a direct D2D path to the first geographical area, i.e., a counterpart gateway in the second geographical area.

The wireless communication device may control the sending of the outgoing D2D transmission based on the second information stored at step <NUM>. This may for example involve selecting an output D2D path or selecting a unicast transmission mode, groupcast transmission mode, and/or broadcast transmission mode.

If at step <NUM> the wireless communication device received an incoming D2D transmission, step <NUM> may also involve that the wireless communication device forwards at least a part of the received incoming D2D transmission in the outgoing D2D transmission. In this case, the area identifier of the outgoing D2D transmission may correspond to the area identifier of the received incoming D2D transmission.

In some scenarios, the wireless communication device may decide whether to forward the incoming D2D transmission based on at least one of the following conditions being met:.

If at step <NUM> the wireless communication device received an incoming D2D transmission, step <NUM> may also involve that, in response to the wireless communication device being located in the target geographical area of the incoming D2D transmission, the wireless communication device adds to the outgoing D2D transmission at least one device identifier and/or group identifier assigned to at least one wireless communication device which is located in the target geographical area.

In some scenarios, the outgoing D2D transmission comprises a respective device identifier for each of the one or more gateways determined at step <NUM>.

If at step <NUM> the wireless communication device selected two or more gateways, step <NUM> may involve that the wireless communication device sends the D2D transmission via the multi-hop D2D paths including the selected gateways. In this way, the D2D transmission may be sent in a redundant manner, thereby improving chances of successfully reaching the target geographical area.

In some scenarios, the outgoing D2D transmission may be addressed to all wireless communication devices in the target geographical area of the outgoing D2D transmission. Alternatively, the outgoing D2D may include additional address information to address the outgoing D2D transmission to a subset of the wireless communication devices in the target geographical area of the outgoing D2D transmission.

In response to the wireless communication device providing a direct D2D path between two of the geographical areas, i.e., being a gateway, the wireless communication device may prioritize the outgoing D2D transmission over one or more other D2D transmissions.

In some scenarios, the outgoing D2D transmission may include multiple area identifiers to identify two or more of the geographical areas as target geographical areas of the outgoing D2D transmission and to address the outgoing D2D transmission to one or more wireless communication devices in the identified target geographical areas of the outgoing D2D transmission.

<FIG> shows a block diagram for illustrating functionalities of a wireless communication device <NUM> which operates according to the method of <FIG>. The wireless communication device <NUM> may for example correspond to any of the above-mentioned UEs. As illustrated, the wireless communication device <NUM> may be provided with a module <NUM> configured to obtain configuration information defining geographical areas, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> device may be provided with a module <NUM> configured to store first information, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to store second information, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to receive an incoming D2D transmission, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to determine one or more gateways, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to send an outgoing D2D transmission, such as explained in connection with step <NUM>.

It is noted that the wireless communication device <NUM> may include further modules for implementing other functionalities, such as known functionalities of a UE in the LTE and/or NR radio technology. Further, it is noted that the modules of the wireless communication device <NUM> do not necessarily represent a hardware structure of the wireless communication device <NUM>, but may also correspond to functional elements, e.g., implemented by hardware, software, or a combination thereof.

At step <NUM>, the wireless communication device receives an incoming D2D transmission. The incoming D2D transmission includes an area identifier to identify one of the geographical areas as target geographical area of the incoming D2D transmission and to address the incoming D2D transmission to one or more wireless communication devices in the identified target geographical area of the incoming D2D transmission.

The wireless communication device may receive the incoming D2D transmission via one or more multi-hop D2D paths each formed by one or more intermediate wireless communication devices forwarding the D2D transmission from one D2D path segment to a next D2D path segment. Each of these one or more multi-hop D2D paths may include one of the one or more wireless communication devices providing a direct D2D path between two geographical areas, i.e., gateways.

At step <NUM>, the wireless communication device determines based on the geographical area where the wireless communication device is located and the identified target geographical area of the received incoming D2D transmission, whether the wireless communication device is a target recipient of the received incoming D2D transmission. For this purpose, the wireless communication device may also determine its own geographical position, e.g., based on satellite positioning measurements, network based positioning measurements, and/or other positioning mechanisms.

At step <NUM>, the wireless communication device may send an outgoing D2D transmission. The outgoing D2D transmission may include an area identifier to identify one of the geographical areas as target geographical area of the outgoing D2D transmission and to address the outgoing D2D transmission to one or more wireless communication devices in the identified target geographical area of the outgoing D2D transmission.

The wireless communication device may send the outgoing D2D transmission via one or more multi-hop D2D paths each formed by one or more intermediate wireless communication devices forwarding the D2D transmission from one D2D path segment to a next D2D path segment. Each of these one or more multi-hop D2D paths may include one or more wireless communication devices providing a direct D2D path between two of the geographical areas, i.e., gateways. Such gateways may be determined and selected in a similar manner as explained in connection with step <NUM> of <FIG>.

The wireless communication device may control the sending of the outgoing D2D transmission based on various information stored by the wireless communication device. Controlling sending of the outgoing D2D transmission may for example involve selecting an output D2D path or selecting a unicast transmission mode, groupcast transmission mode, and/or broadcast transmission mode.

The information used for controlling sending of the outgoing D2D transmission may be part of the above-mentioned routing tables. The information may for example indicate one or more other wireless communication devices connected by a direct D2D path to the wireless communication device. These wireless communication devices may include wireless communication devices located in the same geographical area as the wireless communication device and wireless communication devices located in one or more adjacent geographical areas. The wireless communication device may store the second information based on one or more incoming D2D transmissions received from other wireless communication devices.

In some scenarios, the information may include a device identifier of each of the one or more other wireless communication devices. Further, the information may include, for each of the one or more other wireless communication devices, an area identifier of the geographical area where the other wireless communication device is located. Further, the information may indicate, for each of the one or more other wireless communication devices, further wireless communication devices connected by a D2D path to the wireless communication device. The second information may thus indicate multi-hop information which allows for determining which other wireless communication devices could be reached through the other wireless communication device. Further, the second information may indicate, for each of the one or more other wireless communication devices, whether the other wireless communication device provides a direct D2D path between a first geographical area, where the wireless communication device is located, and at least one second geographical area which is adjacent to the first geographical area, i.e., whether the other wireless communication device is a gateway.

In some scenarios, step <NUM> may also involve that the wireless communication device forwards at least a part of the received incoming D2D transmission in the outgoing D2D transmission. In this case, the area identifier of the outgoing D2D transmission may correspond to the area identifier of the received incoming D2D transmission.

In some scenarios, step <NUM> may also involve that, in response to the wireless communication device being located in the target geographical area of the incoming D2D transmission, the wireless communication device adds to the outgoing D2D transmission at least one device identifier and/or group identifier assigned to at least one wireless communication device which is located in the target geographical area.

In some scenarios, the outgoing D2D transmission comprises a respective device identifier for each of the one or more gateways to be used for forwarding the D2D transmission to another geographical area.

<FIG> shows a block diagram for illustrating functionalities of a wireless communication device <NUM> which operates according to the method of <FIG>. The wireless communication device <NUM> may for example correspond to any of the above-mentioned UEs. As illustrated, the wireless communication device <NUM> may be provided with a module <NUM> configured to obtain configuration information defining geographical areas, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> device may be provided with a module <NUM> configured to receive an incoming D2D transmission, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to determine whether it is a target recipient of a received D2D transmission, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to send an outgoing D2D transmission, such as explained in connection with step <NUM>.

The wireless communication device may determine based on the geographical area where the wireless communication device is located and the identified target geographical area of the received incoming D2D transmission, whether the wireless communication device is a target recipient of the received incoming D2D transmission. For this purpose, the wireless communication device may also determine its own geographical position, e.g., based on satellite positioning measurements, network based positioning measurements, and/or other positioning mechanisms.

At step <NUM>, in response to the wireless communication device being located in the target geographical area of the incoming D2D transmission, the wireless communication device replaces the area identifier of the incoming D2D transmission with at least one device identifier and/or group identifier assigned to at least one wireless communication device which is located in the target geographical area.

At step <NUM>, the wireless communication device sends an outgoing D2D transmission which forwards at least a part of the received incoming D2D transmission with the area identifier being replaced by the at least one device identifier and/or the at least one group identifier.

The wireless communication device may send the outgoing D2D transmission via one or more multi-hop D2D paths each formed by one or more intermediate wireless communication devices forwarding the D2D transmission from one D2D path segment to a next D2D path segment.

The information used for controlling sending of the outgoing D2D transmission may be part of the above-mentioned routing tables. The information may for example indicate one or more other wireless communication devices connected by a direct D2D path to the wireless communication device. These wireless communication devices may include wireless communication devices located in the same geographical area as the wireless communication device and wireless communication devices located in one or more adjacent geographical areas. The wireless communication device may store the information based on one or more incoming D2D transmissions received from other wireless communication devices.

<FIG> shows a block diagram for illustrating functionalities of a wireless communication device <NUM> which operates according to the method of <FIG>. The wireless communication device <NUM> may for example correspond to any of the above-mentioned UEs. As illustrated, the wireless communication device <NUM> may be provided with a module <NUM> configured to obtain configuration information defining geographical areas, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> device may be provided with a module <NUM> configured to receive an incoming D2D transmission, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to replace an area identifier of the received incoming D2D transmission, such as explained in connection with step <NUM>. Further, the wireless communication device <NUM> may be provided with a module <NUM> configured to send an outgoing D2D transmission, such as explained in connection with step <NUM>.

It is to be understood that the functionalities as described in connection with <FIG> may also be combined in various ways, e.g., in a system which includes two or more of a wireless communication device operating according to the method of <FIG>, a wireless communication device operating according to the method of <FIG>, and a wireless communication device operating according to the method of <FIG>. For example, a first wireless communication device could operate according to the method of <FIG> to send the outgoing D2D transmission, and a second wireless communication device could operate according to the method of <FIG> or <FIG> to handle this outgoing D2D transmission as the incoming D2D transmission of step <NUM> or of step <NUM>. Further, the same wireless communication device could implement functionalities corresponding to the steps of two or more of the method of <FIG>, the method of <FIG>, and the method of <FIG>.

<FIG> illustrates a processor-based implementation of a wireless communication device <NUM> which may be used for implementing the above-described concepts. For example, the structures as illustrated in <FIG> may be used for implementing the concepts in any of the above-mentioned UEs.

As illustrated, the wireless communication device <NUM> includes one or more radio interfaces <NUM>. The radio interface(s) <NUM> may for example be based on the NR technology or the LTE technology. The radio interface(s) <NUM> may support D2D communication, e.g., using sidelink communication as specified for the NR technology or the LTE technology.

Further, the wireless communication device <NUM> may include one or more processors <NUM> coupled to the radio interface(s) <NUM> and a memory <NUM> coupled to the processor(s) <NUM>. By way of example, the radio interface(s) <NUM>, the processor(s) <NUM>, and the memory <NUM> could be coupled by one or more internal bus systems of the wireless communication device <NUM>. The memory <NUM> 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 <NUM> may include software <NUM> and/or firmware <NUM>. The memory <NUM> may include suitably configured program code to be executed by the processor(s) <NUM> so as to implement the above-described functionalities for controlling D2D communication, such as explained in connection with <FIG>.

It is to be understood that the structures as illustrated in <FIG> are merely schematic and that the wireless communication device <NUM> may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces, such as a dedicated management interface, or further processors. Also, it is to be understood that the memory <NUM> may include further program code for implementing known functionalities of a UE. According to some embodiments, also a computer program may be provided for implementing functionalities of the wireless communication device <NUM>, e.g., in the form of a physical medium storing the program code and/or other data to be stored in the memory <NUM> 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 efficiently addressing D2D transmissions. In particular, the concepts may be used for efficiently targeting a D2D transmission to devices in a certain geographical area. This may be achieved with low signaling overhead and high resource efficiency. Further, the illustrated concepts may allow for efficiently determining a single or multi-hop D2D path to the target geographical area. This may also help to avoid or reduce possible transmission delays.

Claim 1:
A method of controlling device-to-device, D2D, communication, the method comprising:
a wireless communication device (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) obtaining configuration information defining multiple geographical areas; and
via one or more multi-hop D2D paths each formed by one or more intermediate wireless communication devices forwarding the D2D transmission from one D2D path segment to a next D2D path segment, the wireless communication device (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) sending an outgoing D2D transmission comprising an area identifier to identify one of the geographical areas as target geographical area of the outgoing D2D transmission and to address the outgoing D2D transmission to one or more wireless communication devices in the identified target geographical area of the outgoing D2D transmission.