Patent Description:
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 (<NUM>rd Generation Partnership Project), SL radio transmissions are defined in <NPL>). 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 the LTE radio technology, SL radio transmissions are performed using a physical SL control channel (PSCCH) and a physical SL shared channel (PSSCH). The PSCCH carries SL control information (SCI) which may for example indicate scheduling information for a data transmission on the PSSCH. The SCI may indicate radio resources allocated for the data transmission of the PSSCH, a modulation and coding scheme (MCS) to be used for the data transmission of the PSSCH, a retransmission index, an intention to reserve the same radio resources for a future data transmission, and a priority level in terms of a PPPP (ProSe Per-Packet Priority). The PSCCH has a fixed size of two resource blocks (RBs) and is transmitted in the same subframe with the data transmission on the PSSCH.

In the LTE radio technology, a receiver of a SL radio transmission is typically unaware beforehand of the SL radio transmission. That is to say, the receiver cannot know with certainty whether a SL radio transmission is going to take place or not. Moreover, the receiver typically does not know the parameters used by the transmitter of the SL radio transmission. To simplify the receiver design the LTE radio technology requires that transmission of the SCI on the PSCCH can only be performed on certain predetermined radio resources and using predetermined transmission parameters, and that the transmission of the SCI on the PSCCH always uses the same format. The predetermined RBs on which the transmission of the SCI on the PSCCH transmission can take place are typically referred as a search space (SS). Using these assumptions, complexity of the SL receiver can be limited because it is typically only necessary to attempt to decode PSCCH transmissions in the search space, which is also referred to as blind decoding of the PSCCH or SCI. Document <CIT> discloses pre-configured radio parameter(s) held by a relay UE-<NUM> which includes the same or corresponding configuration as that held by a remote UE-<NUM> for sidelink control information exchange. The pre-configured radio parameters are sent to the UE-<NUM> from the eNB or PLMN network.

However, introduction of new services or utilizations of SL radio communications in the LTE radio technology or a <NUM> (<NUM>th Generation) radio technology, may result in a variety of requirements in terms of latency, reliability, data rates, which cannot be met with the above limitations concerning SS, SCI format, and transmission parameters which may in turn lead to a higher complexity and power consumption of the SL receiver.

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

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 receives first SCI from a further radio device. Based on assistance information stored in the radio device and the received first SCI, the radio device determines a configuration for transmission of second SCI. Based on the determined configuration for transmission of the second SCI, the radio device receives the second SCI from the further radio device. Based on the received second SCI, the radio device receives an SL radio transmission from the further radio device.

According to a further embodiment, a method of controlling SL radio transmissions in a wireless communication network is provided. According to the method, a radio device determines first SCI based on assistance information stored in the radio device. The assistance information relates the first SCI to a configuration for transmission of second SCI. The radio device sends the first SCI to a further radio device. Based on the configuration, the radio device further sends the second SCI to the further radio device. Based on the second SCI, the radio device sends an SL radio transmission to the further radio device.

According to a further embodiment, a method of controlling SL radio transmissions in a wireless communication network is provided. According to the method, assistance information is provided to a first radio device. Further, the assistance information is provided to a second radio device. Providing the assistance information to the first and second radio devices may be accomplished by a node of the wireless communication network. The assistance information relates first SCI, transmitted from the first radio device to the second radio device, to a configuration for transmission of second SCI from the first radio device to the second radio device.

According to a further embodiment, a radio device for a wireless communication network is provided. The radio device is configured to receive first SCI from a further radio device. Further, the radio device is configured to determine, based on assistance information stored in the radio device and the received first SCI, a configuration for transmission of second SCI. Further, the radio device is configured to receive, based on the determined configuration for transmission of the second SCI, the second SCI from the further radio device. Further, the radio device is configured to receive an SL radio transmission from the further radio device based on the received second SCI.

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 receive first SCI from a further radio device; to determine, based on assistance information stored in the radio device and the received first SCI, a configuration for transmission of second SCI; to receive, based on the determined configuration for transmission of the second SCI, the second SCI from the further radio device; and to receive an SL radio transmission from the further radio device based on the received second SCI.

According to a further embodiment, a radio device for a wireless communication network is provided. The radio device is configured to determine first SCI based on assistance information stored in the radio device. The assistance information relates the first SCI to a configuration for transmission of second SCI. Further, the radio device is configured to send the first SCI to a further radio device. Further, the radio device is configured to send, based on the configuration, the second SCI to the further radio device. Further, the radio device is configured to send an SL radio transmission to the further radio device based on the second SCI.

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 determine first SCI based on assistance information stored in the radio device. The assistance information relates the first SCI to a configuration for transmission of second SCI. By the instructions the radio device is further operative to send the first SCI to a further radio device; to send, based on the configuration, the second SCI to the further radio device; and to send an SL radio transmission to the further radio device based on the second SCI.

According to a further embodiment, a node for a wireless communication network is provided. The node is configured to provide assistance information to a first radio device. Further, the node is configured to provide the assistance information to a second radio device. The assistance information relates first SCI, transmitted from the first radio device to the second radio device, to a configuration for transmission of second SCI from the first radio device to the second radio device.

According to a further embodiment, a node for a wireless communication network is provided. The node comprises at least one processor and a memory containing instructions executable by said at least one processor, whereby the node is operative to provide assistance information to a first radio device and to a second radio device. The assistance information relates first SCI, transmitted from the first radio device to the second radio device, to a configuration for transmission of second SCI from the first radio device to the second radio device.

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 and the second radio device store assistance information. The first radio device is configured to: based on the assistance information stored in the first radio device, determine first SCI relating the assistance information to a configuration for transmission of second SCI; send the first SCI to the second radio device; based on the configuration, send the second SCI to the second radio device; and based on the second SCI, send an SL radio transmission to the second radio device. The second radio device is configured to: receive the first SCI from the first radio device; based on the assistance information stored in the second radio device and the received first SIC, determine the configuration for transmission of the second SCI; based on the determined configuration for transmission of the second SCI, receive the second SCI from the first radio device; and based on the received second SCI, receive the SL radio transmission from the first radio device. The system may further comprise a node of a wireless communication network which is configured to provide the assistance information to the first radio device and/or to the second radio device.

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 receive first SCI from a further radio device. Further, execution of the program code causes the radio device to determine, based on assistance information stored in the radio device and the received first SCI, a configuration for transmission of second SCI. Further, execution of the program code causes the radio device to receive, based on the determined configuration for transmission of the second SCI, the second SCI from the further radio device. Further, execution of the program code causes the radio device to receive an SL radio transmission from the further radio device based on the received second SCI.

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 determine first SCI based on assistance information stored in the radio device. The first SCI relates the assistance information to a configuration for transmission of second SCI. Further, execution of the program code causes the radio device to send the first SCI to a further radio device. Further, execution of the program code causes the radio device to send, based on the configuration, the second SCI to the further radio device. Further, execution of the program code causes the radio device to send an SL radio transmission to the further radio device based on the second SCI.

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 node for a wireless communication network. Execution of the program code causes the node to provide assistance information to a first radio device. Further, execution of the program code causes the node to provide the assistance information to a second radio device. The assistance information relates first SCI, transmitted from the first radio device to the second radio device, to a configuration for transmission of second SCI from the first radio device to the second radio device.

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 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 <NUM> 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 examples, SCI for the SL radio transmissions between two radio devices, in the following referred to as UEs, is organized in a multi-stage way: first SCI, in the following also referred to as first stage SCI, and second SCI, in the following also referred to as second stage SCI. The first SCI and the second SCI may be sent in a dynamic manner for each SL radio transmission. The first SCI is used in connection with assistance information stored by the radio devices. The assistance information relates the first SCI to a configuration for transmission of the second SCI. The assistance information may be preconfigured in the UEs, e.g., based on a standard, may be signaled from the network to the UEs, e.g., as part of system information and/or using higher layer signaling like RRC (Radio Resource Control), or may be transferred from a first UE to a second UE, for example when the second UE enters a radio coverage area of the first UE.

Accordingly, a first UE which intends to send an SL radio transmission to a second UE may first select a suitable configuration for transmission of the second SCI. This selection may be use case dependent. For example, the selection may depend on whether the SL radio transmission is a unicast transmission or a broadcast transmission. Further, the selection may depend on a transmission mode of the SL radio transmission. For example, the selection may depend on whether the SL radio transmission uses a SISO (Single Input / Single Output) mode or a MIMO (Multiple Input / Multiple Output) mode. Further, the selection may depend on QoS (Quality of Service) requirements of the SL radio transmission, e.g., in terms of latency, data rate, reliability, or transmission range. Using the assistance information, the first UE may determine the first SCI which is related to the selected configuration and send the first SCI to the second UE. Based on the first SCI received from the first UE and the stored assistance information the second UE can determine the configuration for transmission of the second SCI. Accordingly, the first UE can then use the selected configuration for sending the second SCI to the second UE, and the second UE can use the selected configuration for receiving the second SCI from the first UE. Based on the second SCI, the first UE may then send the SL radio transmission to the second UE, and the second UE may receive the SL radio transmission. Accordingly, the assistance information and the first SCI allow for a high variability of the second SCI, enabling to support various use cases and requirements while limiting the blind decoding effort needed for the second SCI at the second UE.

<FIG> illustrates an exemplary scenario involving SL radio transmissions. More specifically, <FIG> shows an access node <NUM> of the wireless communication network, in the LTE radio technology referred to as eNB, and various entities <NUM>, <NUM>, <NUM>, <NUM>, <NUM> 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 <NUM>. The service area <NUM> may be defined by a radio coverage area in which DL radio transmissions from the access node <NUM> and UL radio transmissions to the access node <NUM> 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 <NUM> of the access node <NUM>.

The entities illustrated in <FIG> comprise vehicles <NUM>, <NUM>, <NUM>, a mobile phone <NUM>, and a person <NUM>, 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 <NUM>, <NUM>, <NUM> the radio transmissions may be performed by a communication module installed in the vehicle, and that in the case of the person <NUM> the radio transmissions may be performed by a radio device carried or worn by the person <NUM>, 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 <NUM> 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> 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 <NPL>). The DL radio transmissions and the UL radio transmissions may be based on the LTE Uu interface as specified in <NPL>). The SL radio transmissions may involve a data transmission on the PSSCH, and the first SCI and the second SCI may be transmitted on the PSCCH. Each data transmission on the PSSCH may be scheduled by first SCI and second SCI transmitted on the PSCCH. Transmission parameters of the SL radio transmissions, such as the number of utilized RBs, number of retransmissions, and/or the MCS can be adapted based on a priority level, e.g., defined in terms of a PPPP, congestion level of the utilized carrier, and movement speed of the transmitting radio device. As for example specified in 3GPP TS <NUM> V14. <NUM>, the PPPP is set on an application layer for each message transmitted over the PC5 interface.

The allocation of radio resources for a SL radio transmission may be performed in a centralized manner, using DL control information (DCI) which the access node <NUM> transmits to the radio device sending and/or receiving the SL radio transmission. In particular, for a certain SL radio transmission, the access node <NUM> may send DCI indicating allocated radio resources of the PSCCH to be used for transmission of the first SCI and the second SCI, and allocated radio resources of the PSSCH to be used for sending the actual data transmission.

Further, the allocation of radio resources for a SL radio transmission may be performed in a distributed or autonomous manner. In this case the sending radio device uses a specified algorithm to autonomously determine which radio resources to use for the SL radio transmission, for both the PSCCH and the PSSCH. The allocation of the radio resources may also be based on channel sensing performed by the sending radio device, e.g., in order to avoid collisions or other conflicts arising from multiple radio devices attempting to use the dame radio resources. The autonomously allocated radio resources may be selected from one or more resource pools. 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 sensing-based autonomous allocation of the radio resources may for example be performed in accordance with "Mode <NUM>" of SL radio transmission as specified in <NPL>). In Mode <NUM>, autonomous resource allocation makes combined use of two features: semi-persistent resource allocation and sensing-based resource allocation. The semi-persistent resource allocation involves allocation of the radio resources over an extended time interval, so that they can be re-used in a more or less regular manner. The sensing based allocation involves monitoring the radio channel to detect the presence of such regular transmissions by other devices. In this way, the UE can avoid collisions when selecting autonomously selecting the radio resources from a resource pool shared by multiple radio devices.

<FIG> shows an example of processes in which a SL radio transmission is controlled based on the principles as outlined above. The processes of <FIG> involve the access node (AN) <NUM>, a sending UE (SL TX) <NUM>, and a receiving UE (SL RX) <NUM>. Here, it is noted that the sending UE <NUM> and the receiving UE <NUM> could correspond to any pair of the entities <NUM>, <NUM>, <NUM>, <NUM>, <NUM> illustrated in <FIG>.

In the example of <FIG>, it is assumed that the access node <NUM> first provides at least a part of the assistance information to the UEs <NUM>, <NUM>, as illustrated by messages <NUM> and <NUM>. The assistance information is stored by the UEs <NUM>, <NUM>. The messages <NUM>, <NUM> could for example be part of signaled system information and/or RRC messages. Another part of the assistance information could be preconfigured in the UEs <NUM>, <NUM>, e.g., based on a standard. In an alternative scenario, the assistance information could be completely preconfigured in the UEs <NUM>, <NUM>. It is noted that in the illustrated concepts it may also be possible that the assistance information stored by the UE <NUM> varies from the assistance information stored by the UE <NUM>, e.g., because the UEs <NUM>, <NUM> differ in UE type and/or supported functionalities. However, typically at least a part of the assistance information is common for the two UEs <NUM>, <NUM>, and this common part will be used for controlling the SL radio transmission as further explained below. As further explained below, the assistance information may for example be provided in terms of a configuration table.

As illustrated by block <NUM>, the sending UE <NUM> then selects a configuration for transmission of the first stage SCI and the second stage SCI. The configuration for transmission of the first stage SCI may be preconfigured and be the same for all UEs in the wireless communication system. The configuration for transmission of the first stage SCI may define a search space for transmission of the first stage SCI, e.g., in terms of position in the time and frequency domain, an MCS for transmission of the first stage SCI, an aggregation level for transmission of the first stage SCI, and/or an SCI format of the first stage SCI. The aggregation level may be regarded as representing a number of control channel elements (CCEs), or amount of control channel radio resources, which is required for transmission of the SCI.

The determination of the second stage SCI involves a larger variability and may be based on a use case underlying the intended SL radio transmission or a type of the intended SL radio transmission, e.g., on the PPPP set by the application layer, on whether the intended SL radio transmission is a unicast transmission or a broadcast transmission, and/or on whether the SL radio transmission is intended to be performed in a SISO mode or in an MIMO mode. The configuration for transmission of the second stage SCI may define one or more search spaces for transmission of the second stage SCI, e.g., in terms of position in the time and frequency domain, one or more MCSs for transmission of the second stage SCI, one or more aggregation levels for transmission of the second stage SCI, and/or SCI format of the second stage SCI. The configuration for transmission of the second stage SCI can be selected from multiple possible candidate configurations and is typically different from the configuration for transmission of the first stage SCI. For example, the configuration for transmission of the second stage SCI may define other and larger search spaces, different aggregation levels and/or a more complex SCI format than the configuration for transmission of the first stage SCI. Further, the configuration for transmission of the second stage SCI may be set individually for each UE and/or for each SL radio transmission.

The sending UE <NUM> uses the stored assistance information to determine the first stage SCI which is related to the selected configuration. The first stage SCI could for example include an index pointing to the selected configuration. Further, the first stage SCI could include one or more transmission parameters which are associated with the selected configuration, e.g., the PPPP, an indicator whether the intended SL radio transmission is a unicast transmission or a broadcast transmission, and/or an indicator whether the SL radio transmission is intended to be performed in a SISO mode or in an MIMO mode. The first stage SCI may be limited to information which enables identification of the selected configuration, thereby allowing to transmit the first stage SCI with low complexity. As illustrated by message <NUM>, the sending UE <NUM> then sends the first stage SCI to the receiving UE <NUM>. As illustrated by message <NUM>, the sending UE <NUM> also sends the second stage SCI to the receiving UE <NUM>, which is accomplished on the basis of the configuration selected at block <NUM>.

Having received the first stage SCI, the receiving UE <NUM> uses the assistance information to identify the configuration related to the first stage SCI. Based on the identified configuration, the receiving UE <NUM> receives the second SCI. By being able to identify the configuration used for transmission of the second stage SCI, complexity of receiving the second stage SCI can be reduced in a significant manner, e.g., by narrowing down the possible search space(s), possible MCSs, possible SCI formats, and/or possible aggregation levels. In some scenarios, the first stage SCI in combination with the assistance information may identify a search space and a set of candidate SCI formats for transmission of the second stage SCI. The receiving UE <NUM> may then perform blind decoding in the identified search space using the different candidate SCI formats. In some scenarios the first stage SCI in combination with the assistance information may also define the configuration for transmission of the second stage SCI to an extent that enables the receiving UE <NUM> to decode the second stage SCI without requiring any blind decoding. For example, the configuration could indicate the exact radio resources, MCS, SCI format, and aggregation level which are used for transmission of the second stage SCI.

As further illustrated in <FIG>, the sending UE <NUM> further sends the SL radio transmission to the receiving UE <NUM>. This may involve sending SL data <NUM> on the PUSSCH. Further, this may involve sending one or more reference symbols (RS) <NUM>. The SL radio transmission is performed on the basis of information indicated in the second stage SCI. For example, the second stage SCI could indicate radio resources allocated for the SL radio transmission, an MCS of the SL radio transmission, and/or a priority level of the SL radio transmission, e.g., in terms of the PPPP. Further, the second stage SCI may indicate retransmission parameters of the SL radio transmission, e.g., whether the SL radio transmission includes an initial transmission of data or a retransmission of data or the number of retransmission attempts, and/or a redundancy version of retransmitted data. Further, the second stage SCI could also indicate whether there is a reservation of radio resources for a subsequent SL radio transmission from the sending UE <NUM> to the receiving UE <NUM>.

As mentioned above, the sending UE <NUM> may send one or more reference symbols <NUM>. The sending of the reference symbols <NUM> may be controlled by the second stage SCI, thereby allowing usage of different configurations of reference symbols, while at the same time allowing for efficient monitoring of the reference symbols by the receiving UE <NUM>. The reference symbols <NUM> may for example be used as a basis for performing sensing based scheduling of SL radio transmissions.

It is noted that while <FIG> illustrates the transmission of the first stage SCI to occur before the transmission of the second stage SCI, and the transmission of the second stage SCI to occur before the SL radio transmission, this does not need to be the case. For example, the first stage SCI, the second stage SCI, and the SL radio transmission could be transmitted substantially at the same time, e.g., on different RBs in the same subframe. The receiving UE <NUM> may monitor all possible RBs of the subframe and use the first stage SCI to reduce complexity of blind decoding of the second stage SCI. The decoded second stage SCI may then be used for decoding the SL data <NUM> and/or for monitoring the reference symbols <NUM>. That is to say, while the second stage SCI can be transmitted using a configuration selected from a wide range of candidate configurations, the first stage SCI in combination with the assistance information allows for narrowing down the blind decoding performed by the receiving UE <NUM> to a single configuration or at least a limited subset of the candidate configurations.

<FIG> shows an example of processes which may be used to provide the sending UE <NUM> and the receiving UE <NUM> with the assistance information. In the processes of <FIG>, it is assumed that the sending UE <NUM> enters the service area <NUM> of the access node <NUM>, as indicated by block <NUM>. The receiving UE <NUM> may be outside the service area <NUM> of the access node <NUM>, or may have previously entered the coverage area <NUM> of the access node <NUM>.

As further illustrated, in response to entering the service area <NUM> of the access node <NUM>, the sending UE <NUM> sends a request <NUM> to the access node <NUM>. The request <NUM> could for example be send in a message of a procedure used for setting up a connection between the sending UE <NUM> and the access node <NUM>. In response to the request <NUM>, the access node <NUM> sends assistance information <NUM> to the sending UE <NUM>. The sending UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the sending UE <NUM>, the sending UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

As further illustrated, the sending UE <NUM> may also send assistance information <NUM> to the receiving UE <NUM>. The assistance information <NUM> may correspond to at least a part of the assistance information <NUM> received by the sending UE <NUM>, which is forwarded to the receiving UE <NUM>. Further, the sending UE <NUM> could also forward at least a part of assistance information previously stored by the sending UE <NUM> to the receiving UE <NUM>. The sending of the assistance information <NUM> could for example be part of an SL discovery procedure, e.g., a ProSe discovery procedure as specified in 3GPP TS <NUM> V14. The receiving UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the receiving UE <NUM>, the receiving UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

<FIG> shows a further example of processes which may be used to provide the sending UE <NUM> and the receiving UE <NUM> with the assistance information. In the processes of <FIG>, it is assumed that the receiving UE <NUM> enters the service area <NUM> of the access node <NUM>, as indicated by block <NUM>. The sending UE <NUM> may be outside the service area <NUM> of the access node <NUM>, or may have previously entered the coverage area <NUM> of the access node <NUM>.

As further illustrated, in response to entering the service area <NUM> of the access node <NUM>, the receiving UE <NUM> sends a request <NUM> to the access node <NUM>. The request <NUM> could for example be send in a message of a procedure used for setting up a connection between the receiving UE <NUM> and the access node <NUM>. In response to the request <NUM>, the access node <NUM> sends assistance information <NUM> to the receiving UE <NUM>. The receiving UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the receiving UE <NUM>, the receiving UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

As further illustrated, the receiving UE <NUM> may also send assistance information <NUM> to the sending UE <NUM>. The assistance information <NUM> may correspond to at least a part of the assistance information <NUM> received by the receiving UE <NUM>, which is forwarded to the sending UE <NUM>. Further, the receiving UE <NUM> could also forward at least a part of assistance information previously stored by the receiving UE <NUM> to the sending UE <NUM>. The sending of the assistance information <NUM> could for example be part of an SL discovery procedure, e.g., a ProSe discovery procedure as specified in 3GPP TS <NUM> V14. The sending UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the sending UE <NUM>, the sending UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

<FIG> shows a further example of processes which may be used to provide the sending UE <NUM> and the receiving UE <NUM> with the assistance information. In the processes of <FIG>, the access node <NUM> first sends assistance information <NUM> to the sending UE <NUM>. The sending UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the sending UE <NUM>, the sending UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

In the processes of <FIG>, it is further assumed that the receiving UE <NUM> then enters a radio coverage area of the sending UE <NUM>, as indicated by block <NUM>. At that point, the receiving UE <NUM> may be outside the service area <NUM> of the access node <NUM>, so that obtaining assistance information directly from the access node <NUM> is not possible.

As further illustrated, in response to entering the radio coverage area of the sending UE <NUM>, the receiving UE <NUM> sends a request <NUM> to the sending UE <NUM>. The request <NUM> could for example be part of an SL discovery procedure, e.g., a ProSe discovery procedure as specified in 3GPP TS <NUM> V14. In response to the request <NUM>, the sending UE <NUM> sends assistance information <NUM> to the receiving UE <NUM>. The assistance information <NUM> may correspond to at least a part of the assistance information <NUM> received by the sending UE <NUM>, which is forwarded to the receiving UE <NUM>. Further, the sending UE <NUM> could also forward at least a part of assistance information previously stored by the sending UE <NUM> to the receiving UE <NUM>. The receiving UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the receiving UE <NUM>, the receiving UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

<FIG> shows a further example of processes which may be used to provide the sending UE <NUM> and the receiving UE <NUM> with the assistance information. In the processes of <FIG>, it is assumed that the sending UE <NUM> enters the service area <NUM> of the access node <NUM>. As indicated by block <NUM>, the access node <NUM> may detect that the sending UE <NUM> entered the service area <NUM> of the access node <NUM>, e.g., based on the sending UE <NUM> setting up a connection to the access node <NUM>.

As further illustrated, in response to the sending UE <NUM> entering the service area <NUM> of the access node <NUM>, the, the access node <NUM> sends assistance information <NUM> to the sending UE <NUM>. The sending UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the sending UE <NUM>, the sending UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

In the processes of <FIG>, it further assumed that at some point the receiving UE <NUM> enters the service area <NUM> of the access node <NUM>. As indicated by block <NUM>, the access node <NUM> may detect that the receiving UE <NUM> entered the service area <NUM> of the access node <NUM>, e.g., based on the receiving UE <NUM> setting up a connection to the access node <NUM>.

As further illustrated, in response to the receiving UE <NUM> entering the service area <NUM> of the access node <NUM>, the, the access node <NUM> sends assistance information <NUM> to the sending UE <NUM>. The receiving UE <NUM> stores the received assistance information <NUM>. If previously stored assistance information is available in the receiving UE <NUM>, the sending UE <NUM> may use the received assistance information <NUM> for replacing or updating the previously stored assistance information.

As can be seen, in the example of <FIG> no explicit request from the sending UE <NUM> or the receiving UE <NUM> is needed for triggering the sending of the assistance information <NUM>, <NUM> by the access node <NUM>. Furthermore, it is also noted that in some scenarios the detection of the sending UE <NUM> or the receiving UE <NUM> entering the service area <NUM> and one of the access node <NUM> could also be omitted. For example, the access node <NUM> could broadcast the assistance information <NUM>, <NUM>, e.g., as part of system information, so that the assistance information <NUM>, <NUM>.

It is noted that the processes of <FIG>, <FIG> are merely exemplary and could be modified and/all combined in various ways in order to provide the assistance information to the sending UE <NUM> and to the receiving UE <NUM>. For example, similar to the processes of <FIG>, the sending UE <NUM> could request the assistance information from the receiving UE <NUM> in response to the sending UE <NUM> entering a radio coverage area of the receiving UE <NUM>.

<FIG> shows an example of organizing the assistance information in terms of a configuration table <NUM>. The configuration table <NUM> includes a plurality of rows, each corresponding to a different candidate configuration for the transmission of the second stage SCI. As indicated by the left column of the configuration table <NUM>, each candidate configuration may be identified by an index. In the illustrated example a first candidate configuration is identified by index <NUM>, a second candidate configuration is identified by index <NUM>, a third candidate configuration is identified by index <NUM>, a fourth candidate configuration is identified by index <NUM>, a fifth candidate configuration is identified by index <NUM>, and a sixth candidate configuration is identified by index <NUM>. However, it is noted that the illustrated number of candidate configurations is merely exemplary and that the assistance information could also define a higher or lower number of candidate configurations.

As illustrated by the middle column of the configuration table <NUM>, each of the different candidate configurations may be associated with a certain use case. The use cases may differ with respect to reliability requirements, e.g., represented by different PPPPs assigned to the SL radio transmissions. For example, a safety related use case may involve transmission of emergency messages or hazard warnings and may involve assigning a high priority level to the SL radio transmissions. On the other hand, use case which is not safety related may involve transmission of traffic information messages and may involve assigning a lower priority level to the SL radio transmissions. In the example of <FIG>, the different priority levels are represented by different PPPPs. As further illustrated by the middle column of the configuration table <NUM>, the use cases may also differ with respect to a transmission scenario, e.g., depending on whether the SL radio transmissions are unicast transmissions or broadcast transmissions. As further illustrated by the middle column of the configuration table <NUM>, the use cases may also differ with respect to a transmission mode, e.g., depending on whether the SL radio transmissions are performed in a SISO mode or in a MIMO mode.

The right column of the configuration table indicates the parameters of the configuration for transmission of the second stage SCI. As illustrated, these parameters may indicate one or more search spaces for transmission of the second stage SCI, e.g., defined in terms of RBs and/or subframe(s), one or more MCSs for transmission of the second stage SCI, one or more aggregation levels for transmission of the second stage SCI, and/or SCI format of the second stage SCI. Further, the parameters may indicate a reference symbol (RS) configuration, or a sensing based scheduling (SBS) configuration.

By having the use case dependent configurations, it is for example possible to define a configuration for a use-case requiring high reliability, e.g., transmission of emergency messages or hazard warnings, which involves using a small-sized SCI format for the second stage SCI and/or a higher aggregation level, thereby ensuring reliable transmission of the second stage SCI, which increases reliability of the SL radio transmission itself. On the other hand, if a use case requires less reliability, e.g., transmission of traffic information, a configuration can be defined which involves using larger size SCI format and/or lower aggregation level. Similarly, one SCI format may be used for transmissions in SISO mode while another SCI format may be used transmissions in MIMO mode.

It is noted that while the parameters of the configuration as shown in <FIG> typically differ between the different configurations, there may also be an overlap of the parameters. For example, two or more of the SCI formats (SCI format <NUM>, SCI format <NUM>, SCI format <NUM>, SCI format <NUM>, SCI format <NUM>, SCI format <NUM>) could be the same. Further, they could also be a partial or full overlap of two or more of the different search spaces (Search Space <NUM>, Search Space <NUM>, Search Space <NUM>, Search Space <NUM>, Search Space <NUM>, Search Space <NUM>, Search Space <NUM>, Search Space <NUM>, Search Space <NUM>).

As further illustrated, at least some of the configurations may also include sub-configurations. For example, such sub-configurations could correspond to the configuration defining multiple candidate search spaces, like shown for the fifth configuration and the sixth configuration of the example of <FIG>. Further, such sub-configurations could correspond to the configuration defining multiple candidate aggregation levels, like shown for the first to fifth configuration of the example of <FIG>. Further, such sub-configurations could correspond to the configuration defining multiple candidate SCI formats, like shown for the third configuration of the example of <FIG>.

As further illustrated, if a configuration defines sub-configurations, the configuration may also define a priority order of the sub-configurations. For example, in the case of the fifth and sixth configuration, which define sub-configurations corresponding to different candidate search spaces, the configuration also defines a search space priority (SS priority). In the case of the fifth configuration, Search Space <NUM> is defined to have the highest priority, followed by Search Space <NUM>, and then by Search Space <NUM>. Accordingly, the receiving UE <NUM> will first perform blind decoding in Search Space <NUM>, and if sufficient blind decoding capacity remains in Search Space <NUM>, and if there is still sufficient remaining blind decoding capacity in Search Space <NUM>. In the case of the sixth configuration, Search Space <NUM> is defined to have the highest priority, followed by Search Space <NUM>. Accordingly, the receiving UE <NUM> will perform blind decoding in Search Space <NUM>, and if sufficient blind decoding capacity remains in Search Space <NUM>. In some scenarios, the decision whether to attempt blind decoding in a certain search space may also depend on the speed of the receiving UE <NUM>. For example, the receiving UE <NUM> could decide to refrain from attempting blind decoding in one of the lower priority search spaces if the receiving UE <NUM> moves at high speed, resulting in a degradation of transmission performance in the lower priority search space.

In some scenarios, the configurations may also define different search spaces, aggregation levels, and/or SCI formats for the transmission of different types of SCI. By way of example, the wireless communication system could supporting the following functionalities: (A) scheduling, involving transmission of SCI of a first type that is necessary to decode a data transmission; (B) resource booking, involving transmission of SCI of a second type that notifies the intention of the sending UE <NUM> to use certain radio resources at a later point in time; (C) resource unbooking, involving transmission of SCI of a third type that notifies the intention of the sending UE <NUM> to release previously booked radio resources, and (D) resource pre-emption involving, transmission of SCI of a fourth type that notifies the receiving UE <NUM> that it should refrain from using previously booked radio resources. For each of the above-mentioned types of SCI, a different configuration for transmission of the second stage SCI may be defined, e.g., differing with respect to search space(s), aggregation level(s), and/or SCI format. For example, in the case of the first type of SCI and the second type of SCI, the configuration for transmission of the second stage SCI may define using a first search space, e.g., corresponding to the first OFDM (Orthogonal Frequency Division Multiplexing) symbols in a group of OFDM symbols or slot), whereas the in the case of the third type of SCI and the fourth type of SCI, the configuration for transmission of the second stage SCI may define using in a second search space, e.g., corresponding to using later OFDM symbols in the group or slot. On the side of the receiving UE <NUM>, the functionalities may be supported to different extent. For example, the receiving UE <NUM> could support only the scheduling and the resource booking. In this case, the receiving UE <NUM> could attempt decoding the second stage SCI only in the first search space. On the other hand, if the receiving UE <NUM> supports the above-mentioned functionalities (A) to (D) to full extent, it could attempt decoding the second stage SCI in both the first search space and the second search space.

It is noted that the above-mentioned different functionalities are merely an example and that similar different types of SCI may also be defined with respect to other functionalities.

In some scenarios, the SCI format(s) used in the second stage SCI may also be designed to facilitate backwards compatibility. This may be achieved by defining one or more information fields which are common to all SCI formats and to define future SCI formats by supplementing one or more additional information fields. The common information field(s) may be arranged in the first bits of the SCI format, and the additional information field(s) may be arranged in later bits of the SCI format. The common information fields indicate information like allocated radio resources, resource reservation, priority level. The receiving UE <NUM> may utilize the information indicated by the common information fields for controlling selection of radio resources for a presently received SL radio transmission and/or a subsequent SL radio transmission, e.g., in terms of allocation of radio resources, reservation of radio resources, reselection of radio resources, or pre-emption of radio resources.

Accordingly, in some scenarios the multi-stage SCI of the illustrated concepts may also be used for facilitating backwards compatibility. For example, legacy UEs and more advanced UEs could coexist in the wireless communication network. In this case, the first stage SCI may utilize in SCI format which is supported by both the legacy UEs and the more advanced UEs.

Similarly, also the second stage SCI may utilize one or more SCI formats which are supported by both the legacy UEs and the more advanced UEs. However, the second stage SCI could also utilize one or more SCI formats which are not fully supported by the legacy UEs. These SCI formats may define one or more common information fields which are supported by the legacy UEs, and one or more additional information fields, which are only supported by the more advanced UEs. The common information fields thus support all functionalities of the legacy UEs and ensure backwards compatibility. The additional information fields may be introduced to support enhanced functionalities of the more advanced UEs. If the sending UE <NUM> corresponds to a more advanced UE, it can send the second stage SCI with the common information field(s) and the additional information field(s). If the receiving UE <NUM> in turn corresponds to a legacy UE, it can receive the common information field(s) of the second stage SCI and ignore the additional information field(s) of the second stage SCI.

As mentioned above, the second stage SCI may indicate information concerning allocation of radio resources for an SL radio transmission. The radio resources may be scheduled in a centralized manner, i.e., the selected on the basis of scheduling information in DCI from the access node <NUM>. However, in other scenarios the radio resources for the SL radio transmission may also be allocated in an autonomous manner by the sending UE <NUM>. This may involve channel sensing by the sending UE <NUM>, i.e., be based on a sensing-based scheduling mechanism. Accordingly, the second stage SCI could also indicate information for performing the sensing-based scheduling. However, in some cases all information needed for performing the sensing-based scheduling. e.g., allocated radio resources and/or priority level, could also be included in the first stage SCI.

The SCI used in the illustrated concepts may be protected by an error detection code, e.g., a CRC (cyclic redundancy check) code or similar redundancy check code for verifying integrity of the transmitted SCI. In this case, it is possible to protect the first stage SCI with a first error detection code and to protect the second stage SCI with a second error detection code, e.g., to use a separate error detection code for each stage of the SCI. However, in view of resource efficiency, also a common error detection code for both the first stage SCI and the second stage SCI could be used. In this case, the common error detection code could be carried by the first stage SCI, by the second stage SCI, or by both the first stage SCI and the second stage SCI. If the common error detection code is transmitted by both the first stage SCI and the second stage SCI, a first part of the error detection code could be transmitted in the first stage SCI, and a second part of the error detection code could be transmitted in the second stage SCI, and the first part and the second part of the error detection code could be concatenated by the receiving UE <NUM>.

<FIG> shows a flowchart for illustrating a method of controlling SL radio transmissions, which may be utilized for implementing the illustrated concepts. The method of <FIG> may be used for implementing the illustrated concepts in a radio device which receives an SL radio transmission from a further radio device. For example, the radio device could correspond to the above-mentioned receiving UE <NUM>, and the further radio device could correspond to the above-mentioned sending UE <NUM>. The SL radio transmission may include a transmission on a data channel, such as the above-mentioned transmission of SL data <NUM>. Alternatively or in addition, the SL radio transmission may include a transmission of one or more reference signals, such as the above-mentioned transmission of reference symbols <NUM>.

If a processor-based implementation of the radio 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 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>.

At step <NUM>, the radio device may receive assistance information. The radio device may receive at least a part of the assistance information from a node of the wireless communication network, such as the above-mentioned access node <NUM>. This may for example be accomplished in response to the radio device entering a service area of the node, such as explained in connection with the processes of <FIG>. Alternatively or in addition, the radio device may receive at least a part of the assistance information from the further radio device, such as explained in connection with the processes of <FIG> or <FIG>. In the latter case, the radio device may receive the at least part of the assistance information in response to the radio device entering a radio coverage area of the further radio device, such as explained in connection with the processes of <FIG>. The radio device may request the assistance information from the node and/or the further radio device. That is to say, the radio device may receive the at least part of the assistance information in response to a request from the radio device, such as explained in connection with the processes of <FIG>. The radio device may then store the received assistance information for later usage.

At step <NUM>, the radio device receives first SCI from the further radio device, such as the above-mentioned first stage SCI <NUM>. In some scenarios, the first SCI may also include information for sensing-based allocation of radio resources for the SL radio transmission, e.g., information defining a resource pool from which the radio resources can be located by the sensing-based allocation mechanism and/or information defining one or more radio channels to be monitored by the sensing-based allocation mechanism.

At step <NUM>, the radio device determines a configuration for transmission of second SCI, such as the above-mentioned second stage SCI <NUM>. This determination is accomplished based on assistance information stored in the radio device. This assistance information may at least in part correspond to the assistance information received at step <NUM>. Further, the determination of step <NUM> is based on the first SCI received at step <NUM>.

In some scenarios, a first part of the configuration for transmission of the second SCI information may be defined by the first SCI and a second part of the configuration for transmission of the second SCI may be defined by the assistance information. For example, the assistance information may include one or more parameters defining the configuration, which in turn allow for implicitly deriving further parameters of the configuration. Examples of such parameters are the above-mentioned PPPP, the above-mentioned indicator whether the intended SL radio transmission is a unicast transmission or a broadcast transmission, and/or the above-mentioned indicator whether the SL radio transmission is intended to be performed in a SISO mode or in an MIMO mode, e.g., parameters as for example shown in the middle column of the configuration table of <FIG>.

The assistance information may define multiple candidate configurations for transmission of the second SCI. In this case the first SCI may identify the configuration for transmission of the second SCI among the candidate configurations. For example, the first SCI could include an index identifying the configuration for transmission of the second SCI among the candidate configurations, such as the configuration index explained in connection with <FIG>. However, it is noted that the first SCI could also include other information which may be used for implicitly identifying the configuration, such as the PPPP, an indicator whether the intended SL radio transmission is a unicast transmission or a broadcast transmission, and/or an indicator whether the SL radio transmission is intended to be performed in a SISO mode or in an MIMO mode, e.g., parameters as for example shown in the middle column of the configuration table of <FIG>.

The configuration for transmission of the second SCI may define radio resources forming a search space for transmission of the second SCI. In some scenarios, the configuration for transmission of the second SCI may also define radio resources forming multiple search spaces for transmission of the SCI. In this case, the configuration may also define a priority order of the multiple search spaces.

The configuration for transmission of the second SCI may also define one or more formats for transmission of the second SCI, such as the above-mentioned SCI formats. When defining multiple formats, the configuration may also define a priority order of these multiple formats. In addition or as an alternative, the configuration for transmission of the second SCI may also define one or more one or more aggregation levels for transmission of the second SCI. When defining multiple aggregation levels, the configuration may also define a priority order of these multiple aggregation levels. In addition or as an alternative, the configuration for transmission of the second SCI may also define one or more modulation and/or coding schemes for transmission of the second SCI. When defining multiple modulation and/or coding schemes, the configuration may also define a priority order of these multiple modulation and/or coding schemes.

At step <NUM>, the radio device receives the second SCI from the further radio device. This is accomplished based on the configuration determined at step <NUM>.

The second SCI may include information indicating at least one of: radio resources to be used for the SL radio transmission, an modulation and/or coding scheme to be used for the SL radio transmission, one or more retransmission parameters of the SL radio transmission, and a priority level of the SL radio transmission. The radio resources can be indicated in terms of time/frequency location and/or in terms of a resource reservation.

In some scenarios, at least one of the first SCI and the second SCI includes a common error detection code for checking integrity of both the first SCI and the second SCI. Based on the common error detection code, the radio device may perform a single integrity check to find out whether the first SCI and the second SCI were correctly received by the radio device.

At step <NUM>, the radio device receives the SL radio transmission from the further radio device. This is accomplished based on the second SCI received at step <NUM>.

<FIG> shows a block diagram for illustrating functionalities of a radio device <NUM> which operates according to the method of <FIG>. The radio device <NUM> may for example correspond to the above-mentioned receiving UE <NUM>. As illustrated, the radio device <NUM> may optionally be provided with a module <NUM> configured to receive assistance information, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to receive first SCI, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to determine a configuration for transmission of second SCI, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to receive the second SCI, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to receive the SL radio transmission, such as explained in connection with step <NUM>.

It is noted that the radio device <NUM> 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 <NUM> do not necessarily represent a hardware structure of the radio device <NUM>, but may also correspond to functional elements, e.g., implemented by hardware, software, or a combination thereof.

<FIG> shows a flowchart for illustrating a method of controlling SL radio transmissions, which may be utilized for implementing the illustrated concepts. The method of <FIG> may be used for implementing the illustrated concepts in a radio device which sends an SL radio transmission to a further radio device. For example, the radio device could correspond to the above-mentioned sending UE <NUM>, and the further radio device could correspond to the above-mentioned receiving UE <NUM>. The SL radio transmission may include a transmission on a data channel, such as the above-mentioned transmission of SL data <NUM>. Alternatively or in addition, the SL radio transmission may include a transmission of one or more reference signals, such as the above-mentioned transmission of reference symbols <NUM>.

At step <NUM>, the radio device may receive assistance information. The radio device may receive at least a part of the assistance information from a node of the wireless communication network, such as the above-mentioned access node <NUM>. This may for example be accomplished in response to the radio device entering a service area of the node, such as explained in connection with the processes of <FIG> or <FIG>. Alternatively or in addition, the radio device may receive at least a part of the assistance information from the further radio device, such as explained in connection with the processes of <FIG>. In the latter case, the radio device may receive the at least part of the assistance information in response to the radio device entering a radio coverage area of the further radio device. The radio device may request the assistance information from the node and/or from the further radio device. That is to say, the radio device may receive the at least part of the assistance information in response to a request from the radio device, such as explained in connection with the processes of <FIG>. The radio device may then store the received assistance information for later usage.

At step <NUM>, the radio device determines first SCI, such as the above-mentioned first stage SCI <NUM>. The assistance information relates the first SCI to a configuration for transmission of second SCI. such as the above-mentioned second stage SCI <NUM>. This determination is accomplished based on assistance information stored in the radio device. This assistance information may at least in part correspond to the assistance information received at step <NUM>. The determination of step <NUM> may involve that the radio device first determines the configuration, e.g., depending on a use case involving the transmission of the SL radio transmission or a type of the SL radio transmission. The radio device may then select the second SCI in such a way that it allows for identifying the configuration based on the stored assistance information.

The configuration for transmission of the SCI may define radio resources forming a search space for transmission of the second SCI. In some scenarios, the configuration for transmission of the second SCI may also define radio resources forming multiple search spaces for transmission of the SCI. In this case, the configuration may also define a priority order of the multiple search spaces.

At step <NUM>, the radio device sends the first SCI to the further radio device. In some scenarios, the first SCI may also include information for sensing-based allocation of radio resources for the SL radio transmission, e.g., information defining a resource pool from which the radio resources can be located by the sensing-based allocation mechanism and/or information defining one or more radio channels to be monitored tourer at by the sensing-based allocation mechanism.

At step <NUM>, the radio device sends the second SCI to the further radio device. This is accomplished based on the configuration related to the first SCI determined at step <NUM>.

At step <NUM>, the radio device receives the SL radio transmission to the further radio device. This is accomplished based on the second SCI sent at step <NUM>.

<FIG> shows a block diagram for illustrating functionalities of a radio device <NUM> which operates according to the method of <FIG>. The radio device <NUM> may for example correspond to the above-mentioned sending UE <NUM>. As illustrated, the radio device <NUM> may optionally be provided with a module <NUM> configured to receive assistance information, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to determine first SCI, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to send the first SCI, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to send the second SCI, such as explained in connection with step <NUM>. Further, the radio device <NUM> may be provided with a module <NUM> configured to send the SL radio transmission, such as explained in connection with step <NUM>.

<FIG> shows a flowchart for illustrating a method of controlling SL radio transmissions, which may be utilized for implementing the illustrated concepts. The method of <FIG> may be used for implementing the illustrated concepts in a node of a wireless communication network which controls at least one of a first radio device and a second radio device. Accordingly, at least some steps of the method may be performed by the node. The node could correspond to the above-mentioned access node <NUM>, the first radio device could correspond to the above-mentioned sending UE <NUM>, and the second radio device could correspond to the above-mentioned receiving UE <NUM>. The first radio device may send an SL radio transmission to the second radio device. The SL radio transmission may include a transmission on a data channel, such as the above-mentioned transmission of SL data <NUM>. Alternatively or in addition, the SL radio transmission may include a transmission of one or more reference signals, such as the above-mentioned transmission of reference symbols <NUM>.

If a processor-based implementation of the node 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 node. 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>.

At step <NUM>, assistance information is provided to the first radio device. For example, the above-mentioned node may send the assistance information in response to the first radio device entering a service area of the node, such as explained in connection with the processes of <FIG> or <FIG>. The node may send the assistance information via the second radio device to the first radio device, such as explained in connection with the processes of <FIG>.

The assistance information relates first SCI, such as the above-mentioned first stage SCI <NUM>, transmitted from the first radio device to the second radio device, to a configuration for transmission of second SCI, such as the above-mentioned second stage SCI <NUM>, from the first radio device to the second radio device.

At step <NUM>, the assistance information is provided to the second radio device. This may for example be accomplished in response to the second radio device entering the service area of the node, such as explained in connection with the processes of <FIG>. The node may send the assistance information via the first radio device to the second radio device, such as explained in connection with the processes of <FIG> and <FIG>.

The first and the second radio device may then store the received assistance information for later usage.

In some scenarios, the first SCI may also include information for sensing-based allocation of radio resources for the SL radio transmission, e.g., information defining a resource pool from which the radio resources can be located by the sensing-based allocation mechanism and/or information defining one or more radio channels to be monitored tourer at by the sensing-based allocation mechanism.

<FIG> shows a block diagram for illustrating functionalities of a node <NUM> which operates according to the method of <FIG>. The node <NUM> may for example correspond to the above-mentioned access node <NUM>. As illustrated, the node <NUM> may be provided with a module <NUM> configured to provide assistance information to a first radio device, such as explained in connection with step <NUM>. Further, the node may be provided with a module <NUM> configured to provide the assistance information to a second radio device, such as explained in connection with step <NUM>.

It is noted that the radio device <NUM> may include further modules for implementing other functionalities, such as known functionalities of an eNB of the LTE radio technology, a gNB of the NR technology, or similar access node.

It is noted that the functionalities as explained in connection with <FIG> and <FIG>, and optionally also <FIG> could also be combined in a system which includes a first radio device operating according to the method of <FIG>, a second radio device operating according to the method of <FIG>, and optionally a network node operating according to the method of <FIG>. In such system, the first radio device may determine the first SCI based on the assistance information stored in the first radio device. The assistance information relates the first SCI to a configuration for transmission of second SCI. Further, the first radio device sends the first SCI to the second radio device. Based on the configuration related to the first SCI, the first radio device also sends the second SCI to the second radio device. Based on the second SCI, the first radio device sends an SL radio transmission to the second radio device. The second radio device receives the first SCI from the first radio device. Further, the second radio device determines, based on the assistance information stored in the second radio device and the received first SCI, the configuration for transmission of the second SCI. Further, the second radio device receives the second SCI based on the determined from the first radio device. Further, the second radio device receives the SL radio transmission based on the received second SCI from the first radio device. The node operating according to the method of <FIG> may provide the assistance information to the first radio device and/or to the second radio device.

Further, it is noted that the methods of <FIG> and <FIG> could also be implemented within the same radio device, which acts both as a receiver and a sender of SL radio transmissions, e.g., when performing bidirectional SL communication with the further radio device.

<FIG> illustrates a processor-based implementation of a radio 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 the above-mentioned sending UE <NUM> or receiving UE <NUM>.

As illustrated, the radio device <NUM> includes one or more radio interfaces <NUM>. The radio interface(s) <NUM> 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) <NUM> may support DL radio transmissions and UL radio transmissions with a wireless communication network.

Further, the radio 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 radio 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>, firmware <NUM>, and/or control parameters <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 of a radio device or apparatus for controlling radio devices, such as explained in connection with <FIG> and/or <NUM>.

It is to be understood that the structures as illustrated in <FIG> are merely schematic and that the radio device <NUM> 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 <NUM> 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 <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.

<FIG> illustrates a processor-based implementation of a network node <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 the above-mentioned sending.

As illustrated, the network node <NUM> includes an access interface <NUM>. The access interface <NUM> may be used for communication with one or more radio devices by DL radio transmissions and UL radio transmissions and for controlling these radio devices. If the network node corresponds to an access node, the access interface <NUM> may be a radio interface. However, in some scenarios the network node <NUM> could also correspond to a more centralized node, e.g., a core network node. In this case, the access interface <NUM> could also correspond to an interface for communication with an access node serving the radio devices. The above-mentioned sending UE <NUM> and receiving UE <NUM> are examples of such radio devices. As further illustrated, the access node may also include a network interface <NUM> which may be used for communication with other network nodes.

Further, the network node <NUM> may include one or more processors <NUM> coupled to the access interface <NUM> and a memory <NUM> coupled to the processor(s) <NUM>. By way of example, the access interface <NUM>, the processor(s) <NUM>, and the memory <NUM> could be coupled by one or more internal bus systems of the network node <NUM>. The memory <NUM> may include a ROM, e.g., a flash ROM, a RAM, e.g., a DRAM or 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>, firmware <NUM>, and/or control parameters <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 of a network node, 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 network node <NUM> 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 <NUM> may include further program code for implementing known functionalities of eNB of the LTE radio technology, a gNB of the NR radio technology, or similar network node. According to some embodiments, also a computer program may be provided for implementing functionalities of the network node <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 controlling SL radio transmissions in a highly efficient manner. In particular, variability of SCI used for controlling the SL radio transmissions may be enhanced without excessively increasing complexity required at a receiver of the SL radio transmissions. In particular, blind decoding by the receiver of the SL radio transmissions can be reduced or even completely avoided. In this way, various use cases having different requirements can be efficiently supported for the SL radio transmissions. Furthermore, the transmission of the SCI can be organized in a manner which facilitates backwards compatibility.

Claim 1:
A method of controlling transmissions on a physical sidelink shared channel in a wireless communication network, the method comprising:
a user equipment (<NUM>) receiving a first stage sidelink control information (<NUM>) from a further user equipment (<NUM>);
based on assistance information stored in the user equipment (<NUM>) and the received first stage sidelink control information (<NUM>), the user equipment (<NUM>) determining a configuration for transmission of second stage sidelink control information (<NUM>);
based on the determined configuration for transmission of the second stage sidelink control information (<NUM>), the user equipment (<NUM>) receiving the second stage sidelink control information (<NUM>) from the further user equipment (<NUM>); and
based on the received second stage sidelink control information (<NUM>), the user equipment (<NUM>) receiving a transmission on the physical sidelink shared channel (<NUM>, <NUM>) from the further user equipment (<NUM>).