Method for transmitting a signal over a sidelink channel in an unlicensed radio band of a radio access network

Abstract

A method for transmitting a signal from a first radio node to a second radio node via a sidelink channel in an unlicensed radio band of a radio access network, comprising the following: - Performing a channel survey of the sidelink channel by decoding sidelink information of the sidelink channel during a survey period to identify at least one transmission resource of the sidelink channel for transmitting the signal to the second radio node; - Conducting a channel contest of the sidelink channel using a "listen-before-speak" mechanism during a contest period preceding the at least one identified transmission resource, with the capture period and the contest period overlapping at least partially; - based on a positive result of the channel competition, access to the sidelink channel for the duration of a channel occupancy period with at least one identified transmission resource; and - Transmitting the signal from the first radio node to the second radio node using the at least one identified transmission resource of the sidelink channel.

Description

[0001] The invention relates to two associated methods for transmitting a signal via a sidelink channel in an unlicensed radio band of a radio access network and associated radio nodes, a system for radio communication, associated computer program elements and non-transitory computer-readable media. State of the art

[0002] Connected mobility is the subject of a variety of communications standards, such as IEEE 802.11p / bd and 3GPP LTE / NR V2X. Two scenarios are considered for 3GPP LTE / NR V2X: a user equipment (UE) can be within the communication range of a base station (BS), such as an evolved node BS (eNB) or a 5G NR node BS (gNB), or outside the communication range. Another scenario is that a portion of the connected UEs can be connected to the network, while the rest of the connected UEs can be outside the network coverage. This is referred to as partially out of coverage.

[0003] When a UE (e.g., a vehicle-mounted UE) is within coverage, the UE can typically be configured to perform sidelink communication with other UEs within range. In this case, the resource allocation, data control, and communication procedures are controlled by the UE. If a UE is outside of coverage, for example, EUTRA or 5G NR cells, the UE is preconfigured with a mandatory configuration for autonomous communication using the sidelink. In one example, a UE can be preconfigured with multiple out-of-coverage frequencies. As an example, the out-of-coverage frequencies can include Intelligent Transport System (ITS) frequencies. Sidelink communications can operate in licensed or unlicensed radio frequency bands.

[0004] In LTE, licensed assisted access for the downlink was initially introduced using "listen before talk" (LBT) to avoid collision with existing transmissions in the unlicensed bands. Improvements to licensed assisted access (eLAA) introduced LBT on the uplink. 5G New Radio (NR) introduces unlicensed operation for both the uplink (UL) and downlink (DL), either in licensed coverage or unlicensed coverage. In this case, a radio node such as a UE or gNB starts an LBT channel, which scans to detect nearby interference. After acquiring an LBT, either the gNB or the UE initiates a Channel Occupancy Time (COT). A COT depends on many factors, such as the frequency of the LBT, the number of HARQ NACKs, etc. During the COT, the UE or gNB transmits its UL or DL ​​simultaneously.

[0005] 5G NR for unlicensed operation introduces two methods for channel sharing based on supported traffic needs: a load-based event (LBE) COT or a frame-based event (FBE). With LBE, either the UE or the gNB accesses the channel after a successful LBT as soon as there is data to be transmitted in the uplink or downlink. In this case, the radio node can only initiate an LBT immediately before a pre-scheduled UL grant in order to occupy its scheduled time slot. In a not very different occupancy and grant procedure, the FBE performs an LBT in a time-deterministic manner, but a COT is shared with the other devices to send feedback or return traffic.

[0006] COT sharing between uplink and downlink must guarantee a short time gap between traffic direction switching between a first device (initiating the COT) and a second device (sharing the same COT), such as no more than 16 µs. After such a time gap, the second device is assumed to be sharing the COT and sends feedback or return traffic after a short detection interval (LBT-CAT2) or no detection (LBT-CAT1). However, if a short LBT (LBT-CAT2) is ordered, the second device abstains from transmission if the LBT result is negative. Disclosure of the invention

[0007] According to a first aspect, a method is provided for transmitting a signal from a first radio node to a second radio node via a sidelink channel in an unlicensed radio band of a radio access network.

[0008] The method according to the first aspect comprises the following: - performing a channel detection of the sidelink channel by decoding sidelink information of the sidelink channel during a detection period to identify at least one transmission resource of the sidelink channel for transmitting the signal to the second node; - performing channel contention of the sidelink channel using a "listen before speak" mechanism during a contention period preceding the at least one identified transmission resource, wherein the acquisition period and the contention period at least partially overlap; - based on a positive result of the channel contention, accessing the sidelink channel for the duration of a channel occupancy time with the at least one identified transmission resource; and - transmitting the signal from the first radio node to the second radio node using the at least one identified transmission resource of the sidelink channel.

[0009] Channel acquisition of the sidelink channel is performed to identify one or more transmission resources that can be used to transmit the signal over the sidelink channel. To do this, sidelink information is decoded during the acquisition period. The acquisition period can be understood as an acquisition window of a specific or fixed period preceding the sidelink transmission.

[0010] Sidelink information used to identify the at least one transmission resource may include sidelink control information (SCI) or additional sidelink support information, e.g., sidelink reference signal information or sidelink pilot signal information.

[0011] To identify the at least one transmission resource, sidelink information may be decoded taking into account a specified selection window, ie only transmission resources during the selection window are identified as candidates for transmitting the signal.

[0012] Channel contention of the sidelink channel is performed to avoid collisions between transmissions from different radio nodes. A "listen-before-speak" mechanism is used to detect ongoing transmissions from other radio nodes. The "listen-before-speak" mechanism or procedure preferably includes measuring received energy levels of transmissions from other devices. Channel contention is preferably performed immediately before the transmission resource is identified for transmission. The identified transmission resource may be a candidate resource selected by the first radio node or a reserved periodic resource.

[0013] The outcome of channel contention can be either positive (LBT success) or negative (LBT failure). If the measured energy level of transmissions from other devices is lower than a certain specified threshold (LBT success), the first radio node can access the sidelink channel for a period called the channel occupancy time (COT). The channel occupancy time can start immediately if the channel contention ends with a positive result (LBT success).

[0014] If a measured energy level of transmissions from other devices is equal to or higher than the specified threshold (LBT failure), the first radio node cannot access the sidelink channel. Instead, accessing the channel and transmitting the signal preferably requires the first radio node to perform channel contention again.

[0015] The competition period of the channel competition is preferably shorter than the collection period. The competition period preferably starts later than the collection period. The competition period preferably ends at the same time as or later than the collection period.

[0016] The channel occupancy time may at least partially overlap with the selection window for identifying the transmission resource. The channel occupancy time may extend beyond the selection window.

[0017] Transmitting the signal preferably comprises transmitting a physical sidelink control channel for transmitting sidelink control information, followed by transmitting a physical shared sidelink channel for transmitting payload data.

[0018] According to a second aspect, a method is provided for transmitting a signal from a second radio node to a first radio node and / or a third radio node via a sidelink channel in an unlicensed radio band of a radio access network.

[0019] The method according to the second aspect comprises the following: - receiving a signal transmitted from the first radio node to the second radio node via the sidelink channel in the unlicensed radio band during a channel occupancy time of the first radio node, the received signal comprising information regarding the channel occupancy time of the first radio node; - Accessing the sidelink channel during the channel occupancy time of the first radio node; and - transmitting the signal from the second radio node to the first radio node and / or to the third radio node via the sidelink channel, wherein the signal is transmitted by sharing the channel occupancy time of the first radio node.

[0020] Sharing the channel occupancy time of the first radio node can be understood as accessing the channel and transmitting a signal by the second radio node during the channel occupancy time of the first radio node, in particular without performing 3GPP Category 4 channel contention. Sharing the channel occupancy time means that once the first radio node initiates the channel occupancy time and transmits at least one signal, the second radio node can transmit a signal in response to the received signal from the first radio node without performing channel contention using a 3GPP Category 4 "listen before talk" mechanism.

[0021] According to a third aspect, a first radio node is provided. The first radio node comprises a radio modem, non-transitory computer-readable media with machine-readable instructions, and a processor configured to load and execute the machine-readable instructions to cause the first radio node to perform the method according to the first aspect or its embodiments and consequently transmit a signal from the first radio node to a second radio node via a sidelink channel in an unlicensed radio band of a radio access network.

[0022] According to a fourth aspect, a second radio node is provided. The second radio node comprises a radio modem, non-transitory computer-readable media with machine-readable instructions, and a processor configured to load and execute the machine-readable instructions to cause the second radio node to perform the method according to the second aspect or its embodiments and consequently transmit a signal from the second radio node to a first radio node and / or a third radio node via a sidelink channel in an unlicensed radio band of a radio access network.

[0023] According to a fifth aspect, a system for radio communication comprising a first radio node as defined by the third aspect and a second radio node as defined by the fourth aspect is provided.

[0024] According to a sixth aspect, a computer program element is provided comprising machine-readable instructions which, when loaded and executed by a processor, cause the processor to perform the method according to the first aspect and / or the method according to the second aspect.

[0025] According to a seventh aspect, a non-transitory computer-readable medium comprising the machine-readable instructions of the sixth aspect is provided.

[0026] The introduced methods for transmitting a signal over a sidelink channel in an unlicensed radio band of a radio access network enable the coexistence of different radio access technologies in an unlicensed radio band. The methods make it possible to reduce collisions within the system between transmissions from different radio nodes by avoiding interference. Furthermore, the methods are advantageous due to improved efficiency in the use of transmission resources and reduced response times in sidelink communications. Transmitting the signal from the second radio node to the first and / or third radio node by sharing the channel occupancy time of the first radio node makes it possible to reduce the additional delay introduced by conducting channel contention and improve the efficiency of sidelink channel utilization.

[0027] This allows the many regulatory requirements necessary to access the unlicensed spectrum to be preserved (such as a nominal bandwidth and contiguous nominal carrier aggregation by the same device). The technique detailed here is flexible and can be applied to different nominal bandwidths and different nominal aggregate bands, as defined between different domains. For example, the ETSI BRAN regulations mandate a nominal frequency of 20 MHz and 4, 8, 16, etc. aggregate bands in the 5 GHz and 6 GHz frequency bands, although the technique discussed here can be generalized to other domains.

[0028] In other words, the first problem addressed is that sidelink communication is limited to dedicated (ITS) and licensed bands. In this case, unlicensed bands can be used to supplement the ITS / sidelink bands.

[0029] The second issue addressed is that it has not been specified how to perform sidelink operation with all communication cast types for unlicensed carriers. In this case, an unlicensed FBE can be used.

[0030] The third problem addressed is that of initiating a channel occupancy time (COT) and sharing a channel occupancy time (COT). In this application text, when a radio node schedules a sidelink transmission, it uses its channel occupancy time to send sidelink transmissions with other radio nodes. The other radio nodes use the transmission opportunity with a short time gap to avoid losing the channel contention. The short time gap is a switching symbol at the end of each sidelink slot. If the first radio node fails the channel contention, a second radio node fails to detect the first radio node's sidelink control information and performs a CAT-4 LBT.

[0031] The present application therefore proposes a technique for accessing unlicensed frequency bands for sidelink communications. The scheme focuses on assisted access to a dedicated unlicensed carrier that can regulate ISM bands for fair sharing among multiple technologies, such as 3GPP and Wi-Fi. The dedicated carrier is also used to transmit broadcast, groupcast, and / or unicast information; it can also be used to guarantee synchronization among other wireless nodes.

[0032] According to an embodiment of the first aspect, performing the channel detection comprises - performing a first channel acquisition of the sidelink channel by decoding sidelink information of the sidelink channel during a first acquisition period, and - Performing a second channel acquisition of the sidelink channel by decoding sidelink information of the sidelink channel during a second acquisition period, wherein the second acquisition period and the competition period at least partially overlap. Preferably, the first acquisition period precedes the competition period. In particular, the first acquisition period and the competition period may not overlap.

[0033] In other words, the acquisition period may consist of a first acquisition period / window and a second acquisition period / window. The first acquisition period preferably precedes the second acquisition period. The first acquisition period and the second acquisition window may or may not be adjacent in time. The first acquisition period is preferably longer than the second acquisition period. The first acquisition period enables the decoding of possible resource reservations from other radio nodes and the identification of possible resource candidates for transmitting the signal within the selection window. The second acquisition period enables the decoding of possible more recent resource reservations from other radio nodes that are not detected during the first acquisition period.

[0034] According to an embodiment of the first aspect, transmitting the signal comprises transmitting information regarding the channel occupancy time, ie, the channel occupancy time of the first radio node. The information may include the channel occupancy time, a length of the channel occupancy time, an end of the channel occupancy time, and / or how the channel occupancy time is to be shared with other radio nodes.

[0035] The information regarding the channel occupancy time can be transmitted explicitly or implicitly to the second and / or a third radio node. An implicit transmission can include an index, an indicator, and / or a specific choice of transmission format based on which the information regarding the channel occupancy time can be derived or encoded.

[0036] The transmission of information regarding the channel occupancy time enables the second and / or the third radio node to share the channel occupancy time of the first radio node.

[0037] According to an embodiment of the first aspect, the method according to the first aspect comprises the following: Receiving a signal transmitted from the second radio node to the first radio node in the unlicensed band of the radio access network, wherein the received signal is transmitted by the second radio node by sharing the channel occupancy time of the first radio node. Sharing the channel occupancy time of the first radio node makes it possible to reduce the additional delay introduced when channel contention is performed and to improve the efficiency of sidelink channel utilization.

[0038] According to an embodiment of the first aspect, the method according to the first aspect comprises the following: Responding to the received signal by transmitting another signal to the second radio node and / or to the third radio node in the unlicensed band of the radio access network, whereby the further signal is transmitted during the channel occupancy time of the first radio node.

[0039] The further signal can be transmitted using one or the last transmission resource of the channel occupancy time of the first radio node.

[0040] According to an embodiment of the first aspect, a category of the "listen-before-speak" mechanism used to perform channel contention is one of the following 3GPP categories: Category 4, Category 2, Category 1. Here, a Category 1 "listen-before-speak" mechanism may be understood as not using a "listen-before-speak" mechanism. Other suitable "listen-before-speak" mechanisms known to those skilled in the art may be used as an alternative.

[0041] For an initial transmission by the first radio node, a Category 4 "listen before talk" mechanism is preferably used. For a further transmission by the first radio node within the channel occupancy time, a Category 2 or Category 1 "listen before talk" mechanism can be used by the first radio node. Here, the category of the "listen before talk" mechanism can be selected depending on a gap period between a previous transmission in the sidelink channel during the channel occupancy time and the transmission of the further signal transmitted by the first radio node. The gap period can be understood as the period during which a measured energy level of transmissions from other devices is lower than a certain specified threshold.

[0042] According to an embodiment of the first aspect and / or an embodiment of the second aspect, the transmission resource used to transmit the signal by the first radio node and / or a transmission resource used to transmit the signal by the second radio node are part of an interleaving structure of multiple transmission resources of the sidelink channel. The interleaving structure can be understood as a structured allocation of the unlicensed radio band to the multiple transmission resources. Here, the unlicensed radio band can be divided, distributed, or assigned to the multiple transmission resources such that the multiple transmission resources are interleaved over a frequency range of the unlicensed radio band. In other words, the interleaving structure consists of multiple interleaved interleaving patterns, each of which represents a transmission resource.

[0043] Each radio node can select a different transmission resource or interleaving pattern to transmit a signal in the unlicensed radio band. Transmissions from multiple radios can be multiplexed on the same unlicensed radio band, thus avoiding collisions between simultaneous transmissions from different radio nodes.

[0044] Advantageously, a predetermined section of the unlicensed radio band can be divided into a plurality of consecutive subsections using the plurality of transmission resources, wherein each of the transmission resources comprises at least two non-consecutive subsections of the unlicensed radio band, such that the plurality of transmission resources form the interleaving structure of the sidelink channel over the predetermined section of the unlicensed radio band.

[0045] The specified section of the unlicensed radio band may comprise the entire unlicensed radio band or only a portion, e.g., 80%, of the unlicensed radio band. The subsections may be of the same frequency length. Subsections contained by or assigned to the same transmission resource are non-consecutive or non-adjacent in frequency and may also be equally spaced in frequency.

[0046] By forming the interleaving structure of the sidelink channel over the specified section of the unlicensed radio band, each of the multiple transmission resources enables individual transmissions to be distributed over the frequency range of the specified section.

[0047] According to a first advantageous alternative two consecutive subsections represent resource blocks from different sidelink subchannels of the sidelink channel, Each of the sidelink subchannels comprises several non-consecutive resource blocks and each of the transmission resources includes all resource blocks belonging to the same sidelink subchannel.

[0048] As an example, the given section of the unlicensed radio band can be divided into N = S*M consecutive subsections, where S denotes the number of different subchannels. Here, S consecutive subsections can each represent resource blocks of the S different sidelink subchannels, which are preferably arranged in the same order across the given section of the unlicensed radio band. Consequently, the subchannels themselves are interleaved across the frequency range of the unlicensed radio band.

[0049] According to a second advantageous alternative each of the subsections represents a different sidelink subchannel of the sidelink channel, and each of the transmission resources comprises at least two non-consecutive sidelink subchannels.

[0050] In other words, the subchannels consist of a single resource block or comprise only consecutive resource blocks. By combining at least two non-consecutive subchannels into one transmission resource, the multiple transmission resources are interleaved across the frequency range of the unlicensed radio band.

[0051] For transmission over a sidelink channel of an unlicensed radio band, the interleaving structure is therefore configured to guarantee operation at the minimum nominal bandwidth.

[0052] According to an embodiment of the first aspect and / or an embodiment of the second aspect, performing the channel contention comprises performing the channel contention of a plurality of subbands of the sidelink channel, wherein a bandwidth portion of the sidelink channel is adjusted based on the result of the channel contention of the plurality of subbands.

[0053] According to an embodiment of the first aspect and / or an embodiment of the second aspect, the adjusted bandwidth portion may comprise subbands of the sidelink channel for which a result of the channel contention is positive. As an example, the channel may comprise multiple subbands, wherein for at least one subband the result of the channel contention is positive and for at least one other subband the result of the channel contention is negative. The adjusted bandwidth portion preferably comprises only the at least one subband for which the channel contention is positive. In other words, the bandwidth portion of the sidelink channel is adjusted by eliminating the at least one subband for which the result of the channel contention is negative. The subbands of the adjusted bandwidth portion may be (non-)consecutive or (non-)adjacent in terms of frequency.

[0054] This embodiment addresses the problem of designing the bandwidth portion (BWP) for broadband operation. In the case of unlicensed bands, broadband operation depends on the successful "listen before talk" mechanism in each subband. Therefore, the BWP design does not perfectly apply to the sidelink issue 16. This embodiment provides flexible bandwidth operation for broadband operation on a "listen before talk" basis.

[0055] According to an embodiment of the second aspect, the method further comprises: Before accessing the sidelink channel, conducting a channel competition of the sidelink channel using a “listen before speaking” mechanism.

[0056] Preferably, the channel contention is performed by the second radio node after the signal transmitted from the first radio node is received by the second radio node. Based on a positive result of the channel contention, the sidelink channel can be accessed by the second radio node during the channel occupancy time of the first radio node.

[0057] According to an embodiment of the second aspect, a category of the "listen-before-speak" mechanism used to perform channel contention is one of the following 3GPP categories: Category 4, Category 2, Category 1. Here, a Category 1 "listen-before-speak" mechanism may be understood as not using a "listen-before-speak" mechanism. Other suitable "listen-before-speak" mechanisms known to those skilled in the art may be used as an alternative.

[0058] According to an embodiment of the second aspect, the category of the "listen before speak" mechanism is selected depending on a gap period between a previous transmission during the channel occupancy time and a transmission of the signal transmitted by the second radio node. In other words, both the previous signal and the signal transmitted by the second radio node are transmitted during the channel occupancy time of the first radio node.

[0059] As an example, the sidelink channel may be accessed and shared by the second radio node using a Category 1 "listen before talk" mechanism if there is a gap between the first radio node's transmission and the second radio node's transmission of less than 16 microseconds within the channel occupancy time. The sidelink channel may be accessed and shared by the second radio node using a Category 2 "listen before talk" mechanism if there is a gap between the first radio node's transmission and the second radio node's transmission of more than 16 microseconds and less than 25 microseconds within the channel occupancy time.If there is no gap between the transmission of the first radio node and the transmission of the second radio node of more than 25 microseconds, the sidelink channel can only be accessed by the second radio node if a Category 4 "listen before speak" mechanism is used.

[0060] According to an embodiment of the second aspect, the transmission of the signal comprises transmitting information regarding the channel occupancy time of the first radio node, preferably regarding the remaining channel occupancy time of the first radio node. Here, the signal transmitted by the second radio node by sharing the channel occupancy time of the first radio node may comprise information regarding the channel occupancy time of the first radio node.

[0061] The information regarding the channel occupancy time can be transmitted explicitly or implicitly to the first and / or a third radio node. An implicit transmission can include an index, an indicator, and / or a specific choice of transmission format based on which the information regarding the channel occupancy time can be derived or encoded.

[0062] Transmitting information regarding the channel occupancy time enables the other radio nodes to share the channel occupancy time of the first radio node.

[0063] According to an embodiment of the first aspect or the second aspect - the signal is transmitted via a physical shared sidelink channel (PSSCH), a physical sidelink control channel (PSCCH) and / or a physical sidelink broadcast channel (PSBCH) and - the channel occupancy time information is transmitted via a physical sidelink control channel (PSCCH) or alternative means for transmitting sidelink control information.

[0064] Alternative means for transmitting sidelink control information may include variants of sidelink control information or indicators, indices, and selection of a format representing sidelink control information. Consequently, information regarding channel occupancy time may be transmitted in sidelink control information.

[0065] According to an embodiment of the first aspect and / or the second aspect, if at least one of the signals transmitted during the channel occupancy time is transmitted over several subbands of the sidelink channel, preferably using a wideband operation, at least part of the sidelink control information is transmitted in the physical sidelink control channel (PSCCH), wherein the physical sidelink control channel (PSCCH) - in at least one subband of the sidelink channel or - is transmitted to all sub-bands for which the result of the channel competition is positive.

[0066] The one subband in which the PSCCH is transmitted can be the first subband. The portion of the sidelink control information can be copied to all subbands for which the channel contention result is positive.

[0067] According to an embodiment of the first aspect or the second aspect, the first radio node and / or the second radio node operate either in frame-based device mode (FBE mode) or in load-based device mode (LBE mode).

[0068] In LBE mode, the radio node can access the sidelink channel based on a positive result of channel contention, which is performed as soon as the radio node has data to transmit over the sidelink channel. In FBE mode, channel contention is only performed at synchronized frame boundaries. In FBE mode, the transmitted information regarding channel occupancy time may include information about the periodicity of transmissions.

[0069] According to one embodiment, the unlicensed radio band may be included within at least one of the following ranges: 410-7125 MHz; 24.25-52.6 GHz; 28-60 GHz; > 60 GHz.

[0070] In particular, the unlicensed radio band may be contained within at least one of the following ranges: 5150-5925 MHz; 5150-5350 MHz (WAS / RLAN); 5470-5725 MHz (WAS / RLAN); 5725-5855 MHz (FWA); 5855-5875 MHz; 5875-5925 MHz (ITS), 5150-5250 (U-NII-1), 5250-5350 (U-NII-2A), 5350-5470 (U-NII-2B), 5470-5725 (U-NII-2C), 5725-5850 (U-NII-3), or 5850-5925 (U-NII-4).

[0071] In particular, the unlicensed radio band may be contained within at least one of the following ranges: 5925-7125 MHz (e.g. in the US) or 5925-6425 MHz (e.g. in the EU).

[0072] According to one embodiment, at least the first and second radio nodes are members of a 5G NR radio network. The first and / or second radio node may be a user device. The first and / or second radio node may comprise an input interface configured to receive input data, e.g., commands from a higher layer, to perform sidelink communication. The first and / or second radio node may comprise a power supply and / or an antenna coupled to the radio modem of the respective radio node. The first and / or second radio node may support device-to-device, Internet of Things, and / or V2X communications. Description of the characters

[0073] Exemplary embodiments of the present invention are illustrated in the figures, which are not to be construed as limiting the claims and are explained in more detail below; they show: Fig. 1A-C schematically show three possible options of the “listen before speaking” mechanism; Fig. 2 schematically shows an example of channel time sharing between two radio nodes operating in frame-based device mode; Fig. 3 schematically shows another example of sharing channel occupancy time between two radio nodes; Fig. 4A, B schematically show two alternative entanglement structures of several transmission resources of a sidelink channel; Fig. 5A-D schematically show various bandwidth sharing options for broadband operations. Fig. 6 schematically shows an example of a signaling protocol for sharing channel occupancy time on an unlicensed radio band; and Fig. 7A, B schematically show methods according to the first and second aspects.

[0074] The invention proposes a standalone, self-organized channel access for sidelink transmission on an unlicensed carrier. The unlicensed carrier can be used for sidelink communication (sending data, control, and feedback).

[0075] In this case, stations can also synchronize on Carrier 2 when transmitting broadcast and synchronization information. The synchronization procedure can include any possible 3GPP synchronization option, e.g., synchronization with a synchronization master / GNSS, synchronization with a gNB (broadcasting a synchronization signal in either licensed or unlicensed bands), synchronization of a synchronization source UE, etc.

[0076] Regarding resource allocation, if a gNB exists, configuration and control signaling can be transmitted via a Uu bearer, e.g., for a Mode 1 resource allocation scheme, where the Uu bearer is a network operating carrier. However, if only an unlicensed band is available and no other synchronization source(s) are available, synchronization between UEs can be performed by configuring a Mode 2 resource pool (but in the unlicensed bands) and exchanging a synchronization sequence. Sidelink for the load-based device (LBE) in the unlicensed band

[0077] With this technique, sidelink communication can be transmitted in a load-based device (LBE) manner, i.e., transmitting data on demand. This means that a UE (or group of UEs) can perform the LBT (simultaneously). The UE (or multiple UEs) that finds the channel free acquires the LBT. Furthermore, the acquiring UE (or group of UEs) can select resources based on their acquisition history of other sidelink transmission and reservation signals. In this case, the UE (or group of UEs) with the acquiring LBT can allocate 1 of N interleaving patterns in frequency, where the interleaving pattern can be randomly selected. The selected pattern in time and frequency (after a successful LBT) is used to transmit its control and shared data.Other UEs in the network can either receive a control and / or data transmission or attempt to acquire the channel (based on LBT and sidelink transmission window acquisition) to send their sidelink transmission. Sidelink for frame-based device (FBE) in the unlicensed band

[0078] Another option would be to allow sharing of the channel occupancy time (COT) of any urgently needed UE to transmit its frame-based equipment (FBE). The initial procedure: An initial UE (or a group of asynchronous UEs) should acquire the channel with an initial LBT (e.g., the longest with CCA, LBT-4) and perform a sliding-window acquisition for sidelink communication. Based on the success of the LBT (for other radio access technology (RAT)) and a longer window-based acquisition (for an equivalent sidelink acquisition), the initial UE (or a group of asynchronous UEs) should randomly select one of N interleaving patterns and perform the control and data transmission.

[0079] Any other station (or group of stations) that can detect the network and decode possible control information that may contain a specific COT duration may share the COT initiated by UE1. Another UE (or some "other" UEs) that share the COT may transmit its sidelink transmission following an interleaving pattern. The other UE (or group of UEs) may share the initiated initial COT, provided the COT is sufficient to transmit more sidelink transmission.

[0080] Furthermore, the initial UE 1 (or UE group 1) may transmit on the last transmission opportunity of its initiated COT. In the case of an FBE, the initiated COT may send some information about the periodicity of grants configured for the sidelink transmission, i.e., the initial procedure is repeated before each of the declared periods, see Fig. 2.

[0081] Channel access using window-based sensing followed by LBT

[0082] According to one embodiment, a first transmission TR1 of a first radio node, e.g., a first user equipment UE1, must be transmitted on an unlicensed carrier used for sidelink communication. For this purpose, the UE1 is configured to perform both channel acquisition and channel contention. A "listen-before-speak" mechanism is used for channel contention.

[0083] The UE1 is configured to perform a sidelink channel acquisition (normal length or short) to extract and decode an existing (similar) sidelink transmission from foreign UEs (other UEs). Here, the UE1 may be configured to perform a sidelink acquisition with sidelink control channel decoding, e.g., as in Rel-16 (decoding possible sidelink control information (SCI) from other devices with sidelink reservation to select free candidate resources).

[0084] Preferably, the UE1 is configured to perform window-based (or sliding window-based) channel acquisition with two acquisition windows of preferably different sizes, in particular a long acquisition window of size W1 and a short acquisition window of size W2.

[0085] In sidelink communication, a long sensing window can be used to decode all possible reservations from other UEs to select a possible candidate resource within a selection window Sw. In addition, UE1 can start a short sensing window immediately before the selected resources. The main role of the short sensing window is to avoid any recent reservations from other UEs that are not detected during the normal (long) sensing window.

[0086] The UE1 may be configured to conduct channel contention using a "listen-before-speak" mechanism to detect existing / competing radio access technologies, e.g., Wi-Fi, within the unlicensed band. The "listen-before-speak" mechanism is used within or near the end of the short detection window, or starting near the end of the short detection window.

[0087] If the short acquisition window is not configured, the UE1 shall be requested to perform a channel contention using the "listen before speak" mechanism immediately before the selected candidate resources (all candidate resources or performing the acquisition one after the other, sequentially in time).

[0088] Fig. Figure 1 schematically illustrates three possible options of the “listen before speaking” mechanism that can be used for channel competition. In the example of Fig. 1, the channel acquisition of the sidelink channel is performed by a first radio node UE1. The acquisition period comprises a first acquisition window W1 and a second acquisition window W2. Here, the first acquisition window W1 precedes the second acquisition window W2 and is longer in duration than the second acquisition window W2. Performing the channel acquisition enables the first radio node UE1 to identify at least one candidate transmission resource within a selection window for transmitting a signal.

[0089] During the second acquisition window W2, channel contention is conducted using a "listen before talk" (LBT) mechanism. If the "listen before talk" mechanism ends with a positive result (LBT success), the UE1 is configured to access the sidelink channel, initiating a Channel Occupancy Time (COT).

[0090] Fig. Figure 1A illustrates a first option of the "listen-before-speak" mechanism, assuming either an LBE (load-based device) or FBE (frame-based device) with a long transmission gap (larger than a permissible short gap, e.g., 16 microseconds). Then, the UE1 is configured to perform channel contention using a long "listen-before-speak" mechanism, e.g., based on CAT-4 LBT, during (and / or extending) the short sidelink acquisition window W2. As an example, the UE1 may be configured to perform the option according to Fig. 1A before initiating a COT.

[0091] Fig. Figure 1B illustrates a second option of the "listen-before-speak" mechanism assuming FBE with a short transmission gap (between a transmission of UE1 initiating the COT and a subsequent transmission of another EU sharing the COT). Then, UE2 is configured to perform channel contention using a short "listen-before-speak" mechanism.

[0092] Fig. Figure 1C illustrates a third option of the "listen before talk" mechanism, assuming FBE with an extremely short transmission gap (shorter than a predefined threshold). Then, no "listen before talk" mechanism is performed by the UE2, i.e., the UE2 is configured to transmit without any LBT mechanism by sharing the COT initiated by the UE1. The third option also applies to a subsequent transmission by the UE1 following a previous transmission by the UE1 within the same COT.

[0093] Fig. Figure 2 schematically illustrates an example of channel time sharing between two radio nodes UE1, UE2 operating in frame-based device mode.

[0094] For a first frame, a channel contention using a "listen before talk" (LBT) mechanism performed by the first radio node UE1 fails (LBT failure). A channel contention using a "listen before talk" (LBT) mechanism performed by the second radio node UE2 succeeds (LBT success). Consequently, the second radio node UE2 initiates a channel occupancy time (COT) and transmits control data with its COT over a sidelink control channel and further data over a physical shared sidelink channel. The COT of the second radio node UE2 ends without being shared by the first radio node UE1.

[0095] For a second frame, channel contention using a listen-before-talk (LBT) mechanism performed by the first radio node UE1 is successful (LBT success). Consequently, the first radio node UE1 initiates a channel occupancy time (COT) and transmits control data with its COT over a sidelink control channel and further data over a physical shared sidelink channel. The COT of the first radio node UE1 is shared by the second radio node UE2, i.e., the UE2 is configured to transmit a signal without performing channel contention or only using a short listen-before-talk mechanism, e.g., 3GPP Category 2, within a specified short gap after the transmission of the first radio node UE1.

[0096] In other words, the UE1 may be configured to convey information regarding the initiated COT (e.g., start and duration of the COT) in its control information. As mentioned above, the LBT mechanism is performed before one or more possible selected candidate resources or before one or more possible reserved periodic resources. The LBT mechanism may also be performed on candidate resources (one after the other) in a sequence (i.e., close to the time the LBT is first).

[0097] According to one embodiment, channel access can be shared by a first radio node UE1 with a second or further radio node (“groupcast”). To this end, the first radio node UE1 initiates a channel occupancy time (COT), transmits a signal, and shares its COT with the other UE(s), preferably in a dedicated sidelink control field. Consequently, for each other UE that can share its initial COT through UE1 (e.g., in group communication), its individual UE control and UE data can be transmitted within the COT of the first radio node UE1 after a short or no LBT.

[0098] Therefore, the control information of the initial transmission of the first radio node UE1 can transmit the COT information to all other UEs in the network (including those in a group). Subsequently, for each group member sharing this COT, the respective transmitted control information can transmit the remaining COT to other group members.

[0099] For the remaining COT initiated by the first radio node UE1, another UE (e.g., the second radio node UE2) or other UEs can share the COT in an organized manner. To organize the transmission of other UEs sharing the remaining COT, the following may apply: - The coordination of the transmission of the UEs sharing the COT with the first radio node UE1 can be performed via the first radio node UE1, e.g. at least for replying to the message of the first radio node UE1. - The coordination of the transmission of the UEs sharing the COT with the first radio node UE1 can be performed via the first radio node UE1, e.g. at least for groupcast communication. - The coordination of the transmission of the UEs sharing the COT with the first radio node UE1 can be performed via the first radio node UE1, e.g. at least for acknowledging the message of the first radio node UE1 with either ACK or NACK.

[0100] For the remaining COT initiated by the first radio node UE1, after the transmission of all UEs sharing the COT, the first radio node UE1 can answer the transmission of the other UEs in the last transmission opportunities in its initiated COT.

[0101] Fig. Figure 3 schematically illustrates another example of channel occupancy time sharing between two radio nodes. Here, first, after performing a successful channel acquisition (not shown) and second, a successful channel contention using a "listen-before-speak" mechanism, sidelink control information with the COT of the first radio node UE1 and further data are transmitted to at least the second radio node UE2. The COT of the first radio node UE1 is shared by the second radio node UE2. A response signal answering the signal of the second radio node UE2 is transmitted by the first radio node UE1 using the last transmission opportunities within the COT initiated by the first radio node UE1.

[0102] Fig. 4A, B schematically represent two alternative entanglement structures of multiple transmission resources of a sidelink channel.

[0103] The sidelink transmission can follow an interleaving structure, where the interleaving structure should cover at least a specified portion, e.g., a certain percentage such as 80%, of the unlicensed radio band. The sidelink interleaving structure for a group of UEs sharing the same slot (e.g., a UE Group-X is just a set of UEs that multiplex their sidelink transmission over the specified portion of the nominal frequency (between 18 and 20 MHz)).

[0104] If all UEs in the above set (UE-Group-X) transmit their sidelink transmission, the entire band is interleaved with the corresponding sidelink resource blocks. Otherwise, only successful UEs (with a winning LBT) in the UE-Group-X set can share the sidelink slot band with the interleaved frequency structure, as shown in Fig. 4 shown.

[0105] Therefore, in unlicensed access, the sidelink control and sidelink data can be interleaved in an interleaved structure to meet the required bandwidth span, allowing only successful LBT or COT-sharing UEs to interleave their sidelink transmission.

[0106] Fig. Figure 4A illustrates a resource pool configuration and subchannel design of a first alternative. Here, the resource pool is configured with multiple sidelink subchannels, where each individual subchannel is not frequency continuous but interleaved across the nominal frequency. The interleaving width and length of the subchannels are configurable.

[0107] A single radio node can transmit a signal over one of the subchannels. Multiple radio nodes can transmit signals simultaneously using different subchannels, thus multiplexing their sidelink transmissions.

[0108] Fig. Figure 4B illustrates a resource pool configuration and subchannel design of a second alternative. Here, the resource pool is configured with multiple adjacent sidelink subchannels, where the subchannels have continuous resources in terms of frequency. The interleaving width can be configurable, but the channel length can depend on each time allocation.

[0109] A single radio node can transmit a signal using a subchannel interleaving pattern distributed across the nominal bandwidth, i.e., with, for example, three non-adjacent or non-consecutive subchannels. Multiple radio nodes can transmit signals simultaneously using different interleaving patterns, thus multiplexing their sidelink transmissions.

[0110] Fig. Figure 5 schematically illustrates various bandwidth sub-options (BWP options) for broadband operations depending on the outcome of the “listen before speak” mechanism for the respective sub-bands of an unlicensed radio band. The radio band according to Fig. 5 comprises 5 subbands. Channel contention is conducted for each subband using a "listen-before-speak" mechanism.

[0111] In unlicensed access, the sidelink BWP is scaled by the LBT subbands for which the result of the LBT mechanism is positive, i.e., the free or inactive subbands. In this case, the BWP part is configured to have a maximum width and a minimum width. The BWP is scaled to one or more or all subbands depending on which of the subbands the results of the LBT mechanism are positive. Preferably, the following applies: The bandwidth part can start from the first subband for which the result of the LBT mechanism is positive and ends after the last consecutive subband for which the result of the LBT mechanism is positive.

[0112] The subchannel transmission should start from the first subband for which the result of the LBT mechanism is positive to the last one for which the result of the LBT mechanism is positive, or vice versa.

[0113] The PSCCH should start from the first subchannel in the BWP that consumes one or more subchannels (filling towards the last subchannel) or vice versa (from the last towards the first).

[0114] Fig. Figure 5A represents a BWP option where the result of the LBT mechanism is positive for all subbands. Consequently, the bandwidth portion starts from the first subband and ends with the fourth subband.

[0115] Fig. Figure 5B illustrates a BWP option, where the result of the LBT mechanism is negative for the first subband and positive for the last three subbands. Consequently, the bandwidth portion starts from the second subband and ends with the fourth subband.

[0116] Fig. Figure 5C represents a BWP option, where the result of the LBT mechanism is positive for the first three subbands and negative for the fourth subband. Consequently, the bandwidth portion starts from the first subband and ends with the third subband.

[0117] Fig. Figure 5D represents a BWP option, where the result of the LBT mechanism is negative for the first and fourth subbands and positive for the second and third subbands. Consequently, the bandwidth portion starts from the second subband and ends with the third subband.

[0118] Fig. Figure 6 schematically illustrates an example of a signaling protocol for sharing channel occupancy time on an unlicensed radio band.

[0119] In the example of Fig. 10, a first radio node UE1, a second radio node UE2, and a third radio node UE3 communicate via a sidelink channel in an unlicensed radio band F1 of a radio access network. Initially, a resource pool in the unlicensed band F1 is configured either via a preconfiguration received from a UE or a gNB or is a previously stored configuration.

[0120] The first radio node UE1 establishes channel contention using a "listen-before-talk" (LBT) mechanism and, if successful, transmits a short control to configure subsequent signaling and a first signal to at least the second radio node UE2 and optionally the third radio node UE3 (the third radio node UE3 may passively receive all signals transmitted by the first radio node UE2). The first signal includes information regarding the channel occupancy time (COT) of the first radio node UE1 and additional data.

[0121] The second radio node UE2 transmits its signal with a permissible gap without channel contention, thus sharing the channel occupancy time of the first radio node UE1. The first radio node UE1 and optionally the third radio node UE3 receive the signal transmitted by the second radio node UE2.

[0122] If an amount of time greater than the permitted gap elapses, a third radio node UE3 must perform a new channel contention operation to access the unlicensed band. Upon completion of the channel contention, the third radio node UE3 transmits a short control to configure subsequent signaling and another signal to at least the second radio node UE2 and optionally to the first radio node UE3.

[0123] Fig. 7A schematically illustrates a method according to the first aspect. According to a first aspect, a method 100 is provided for transmitting a signal from a first radio node to a second radio node via a sidelink channel in an unlicensed radio band of a radio access network.

[0124] The method 100 according to the first aspect comprises the following: - performing 110 a channel detection of the sidelink channel by decoding sidelink information of the sidelink channel during a detection period to identify at least one transmission resource of the sidelink channel for transmitting the signal to the second radio node; - performing 120 a channel contention of the sidelink channel using a "listen before speak" mechanism during a contention period preceding the at least one identified transmission resource, wherein the acquisition period and the contention period at least partially overlap; - Based on a positive result of the channel contention, accessing 130 the sidelink channel for the duration of a channel occupancy time with the at least one identified transmission resource; and - Transmitting 140 the signal from the first radio node to the second radio node using the at least one identified transmission resource of the sidelink channel.

[0125] Fig. 7B schematically illustrates a method according to the second aspect. According to a second aspect, a method 200 is provided for transmitting a signal from a second radio node to a first radio and / or third radio node via a sidelink channel in an unlicensed radio band of a radio access network.

[0126] The method 200 according to the second aspect comprises the following: - receiving 210 a signal transmitted from the first radio node to the second radio node via the sidelink channel in the unlicensed radio band during a channel occupancy time of the first radio node, the received signal comprising information regarding the channel occupancy time of the first radio node; - Optionally, conducting 220 a channel contention of the sidelink channel using a “listen before speak” mechanism and based on a positive outcome of the channel contention; - Accessing 230 the sidelink channel during the channel occupancy time of the first radio node; and - transmitting 240 the signal from the second radio node to the first radio node and / or to the third radio node via the sidelink channel, wherein the signal is transmitted by sharing the channel occupancy time of the first radio node.

[0127] The examples provided in the drawings and described in the preceding written description are intended to provide an understanding of the principles of this application. No limitation on the scope of the appended claims is intended thereby. This application describes variations and modifications to the illustrated examples. Only the preferred examples have been illustrated, and it is intended that all variations, modifications, and further applications thereof be protected within the scope of the application.

Claims

[1] A method (100) for transmitting a signal from a first radio node (UE1) to a second radio node (UE2) via a sidelink channel in an unlicensed radio band of a radio access network, comprising: - performing (110) a channel detection of the sidelink channel by decoding sidelink information of the sidelink channel during a detection period to identify at least one transmission resource of the sidelink channel for transmitting the signal to the second radio node (UE2); - performing (120) a channel contention of the sidelink channel using a listen-before-talk (LBT) mechanism during a contention period preceding the at least one identified transmission resource, wherein the acquisition period and the contention period at least partially overlap; - based on a positive result of the channel contention, accessing (130) the sidelink channel for the duration of a channel occupancy time (COT) with the at least one identified transmission resource; and - transmitting (140) the signal from the first radio node (UE1) to the second radio node (UE2) using the at least one identified transmission resource of the sidelink channel. [2] Method (100) according to claim 1, wherein performing (110) the channel detection comprises - performing a first channel acquisition of the sidelink channel by decoding sidelink information of the sidelink channel during a first acquisition period, and - performing a second channel acquisition of the sidelink channel by decoding sidelink information of the sidelink channel during a second acquisition period, whereby the second collection period and the competition period at least partially overlap. [3] The method (100) of claim 1 or 2, wherein transmitting (140) the signal comprises transmitting information regarding the channel occupancy time (COT). [4] The method (100) of any preceding claim, further comprising: Receiving a signal transmitted from the second radio node (UE2) to the first radio node (UE1) in the unlicensed band of the radio access network, wherein the received signal is transmitted by the second radio node (UE2) by sharing the channel occupancy time (COT) of the first radio node (UE1). [5] The method (100) of claim 4, further comprising: Responding to the received signal by transmitting a further signal to the second radio node (UE2) and / or to a third radio node in the unlicensed band of the radio access network, wherein the further signal is transmitted during the channel occupancy time (COT) of the first radio node (UE1). [6] The method (100) of any preceding claim, wherein a category of the listen-before-talk (LBT) mechanism used to perform (120) the channel contention is one of the following 3GPP categories: Category 4, Category 2, Category 1. [7] Method (100) according to one of the preceding claims, wherein the transmission resource used to transmit the signal is part of an interleaving structure of a plurality of transmission resources of the sidelink channel. [8] Method (100) according to claim 7, wherein - a given section of the unlicensed radio band with the multiple transmission resources is divided into several consecutive sub-sections, and - each of the transmission resources comprises at least two non-consecutive sub-sections of the unlicensed radio band, so that the plurality of transmission resources form the interleaving structure of the sidelink channel over the predetermined section of the unlicensed radio band. [9] Method (100) according to claim 8, wherein - two consecutive subsections represent resource blocks from different sidelink subchannels of the sidelink channel, - each of the sidelink subchannels comprises several non-consecutive resource blocks, and - each of the transmission resources includes all resource blocks belonging to the same sidelink subchannel. [10] Method (100) according to claim 8, wherein - each of the subsections represents a different sidelink subchannel of the sidelink channel, and - each of the transmission resources comprises at least two non-consecutive sidelink subchannels. [11] The method (100) of any preceding claim, wherein performing (120) the channel contention comprises performing a channel contention of a plurality of subbands of the sidelink channel, wherein a bandwidth portion of the sidelink channel is adjusted based on the result of the channel contention of the plurality of subbands. [12] The method (100) of claim 11, wherein the adjusted bandwidth portion comprises subbands of the sidelink channel for which a result of the channel contention is positive. [13] A method (200) for transmitting a signal from a second radio node (UE2) to a first radio node (UE1) and / or third radio node via a sidelink channel in an unlicensed radio band of a radio access network, comprising: - receiving (210) a signal transmitted from the first radio node (UE1) to the second radio node (UE2) via the sidelink channel in the unlicensed radio band during a channel occupancy time (COT) of the first radio node (UE1), the received signal comprising information regarding the channel occupancy time (COT) of the first radio node (UE1); - accessing (230) the sidelink channel during the channel occupancy time (COT) of the first radio node (UE1); and - transmitting (240) the signal from the second radio node (UE2) to the first radio node (UE1) and / or third radio node via the sidelink channel, wherein the signal is transmitted by sharing the channel occupancy time (COT) of the first radio node (UE1). [14] The method (200) of claim 13, further comprising: before accessing (230) the sidelink channel, performing (220) a channel contention of the sidelink channel using a listen-before-talk (LBT) mechanism. [15] The method (200) of claim 14, wherein a category of the listen-before-talk (LBT) mechanism used to perform (220) the channel contention is one of the following 3GPP categories: Category 4, Category 2, Category 1. [16] The method (200) of claim 15, wherein the category of the listen-before-talk (LBT) mechanism is selected depending on a gap period between a previous transmission during the channel occupancy time (COT) and a transmission of the signal transmitted by the second radio node (UE2). [17] Method (200) according to one of claims 13 to 16, wherein transmitting (240) the signal comprises transmitting information regarding the channel occupancy time (COT) of the first radio node (UE1), preferably regarding the remaining channel occupancy time (COT) of the first radio node (UE1). [18] The method (200) of any one of claims 13 to 17, wherein a transmission resource used to transmit the signal is part of an interleaving structure of a plurality of transmission resources of the sidelink channel. [19] Method (200) according to claim 18, wherein - a given section of the unlicensed radio band with the multiple transmission resources is divided into several consecutive sub-sections, and - each of the transmission resources comprises at least two non-consecutive sub-sections of the unlicensed radio band, so that the plurality of transmission resources form the interleaving structure of the sidelink channel over the predetermined section of the unlicensed radio band. [20] Method (200) according to claim 19, wherein - two consecutive subsections represent resource blocks from different sidelink subchannels of the sidelink channel, - each of the sidelink subchannels comprises several non-consecutive resource blocks, and - each of the transmission resources includes all resource blocks belonging to the same sidelink subchannel. [21] Method (200) according to claim 19, wherein - each of the subsections represents a different sidelink subchannel of the sidelink channel, and - each of the transmission resources comprises at least two non-consecutive sidelink subchannels. [22] The method (200) of any one of claims 13 to 21, wherein performing (220) the channel contention comprises performing the channel contention of a plurality of subbands of the sidelink channel, and wherein a bandwidth portion of the sidelink channel is adjusted based on the result of the channel contention of the plurality of subbands. [23] The method (200) of claim 22, wherein the adjusted bandwidth portion comprises subbands for which a channel contention result is positive. [24] Method (100, 200) according to one of claims 1 to 12 and / or according to one of claims 13 to 23, wherein - the signal is transmitted via a physical shared sidelink channel (PSSCH), a physical sidelink control channel (PSCCH) and / or a physical sidelink broadcast channel (PSBCH), and - the channel occupancy time (COT) information is transmitted via a physical sidelink control channel (PSCCH) or alternative means for transmitting sidelink control information. [25] Method (100, 200) according to one of claims 1 to 12 and / or according to one of claims 13 to 24, wherein, if at least one of the signals transmitted during the channel occupancy time (COT) is transmitted over several subbands of the sidelink channel, preferably using a wideband operation, at least part of the sidelink control information is transmitted in the physical sidelink control channel (PSCCH), wherein the physical sidelink control channel (PSCCH) is in - at least one subband of the sidelink channel, or - is transmitted to all sub-bands for which the result of the channel competition is positive. [26] Method (100, 200) according to one of claims 1 to 12 and / or according to one of claims 13 to 25, wherein the first radio node (UE1) and / or the second radio node (UE2) operate either in frame-based device mode or in load-based device mode. [27] First radio node (UE1), comprising - a radio modem; - non-transitory computer-readable media containing machine-readable instructions; - a processor configured to load and execute the machine-readable instructions to cause the second radio device to perform the method (100) of any one of claims 1 to 12. [28] Second radio node (UE2), comprising: - a radio modem; - non-transitory computer-readable media containing machine-readable instructions; - a processor configured to load and execute the machine-readable instructions to cause the second radio device to perform the method (200) of any one of claims 13 to 26. [29] Radio communication system comprising: - a first radio node (UE1) as defined by claim 27; and - a second radio node (UE2) as defined by claim 28. [30] Computer program element containing machine-readable instructions which, when loaded and executed by a processor, - cause the processor to carry out the method (100) according to one of claims 1 to 12, and / or - cause the processor to perform the method (200) according to any one of claims 13 to 26. [31] A non-transitory computer-readable medium containing the machine-readable instructions defined by claim 30.

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