CN113196852A - Sidelink retransmission oversubscription - Google Patents

Abstract

A method of overbooking transmission resources for sidelink communication retransmissions. After the first UE has reserved transmission and retransmission resources for sidelink transmissions, the second UE may also reserve retransmission resources for sidelink communication transmissions from the second UE. Such oversubscription may be enabled by system configuration or by RRC configuration messages. The allowed overbooking may vary depending on the number of retransmissions, such that different overbooking is allowed depending on how many retransmissions.

Description

Sidelink retransmission oversubscription

Technical Field

The present disclosure relates to the use of resources for sidelink communications between mobile devices of a cellular communication system, and in particular to oversubscription of such resources.

Background

Wireless communication systems such as third generation (3G) mobile telephone standards and technologies are well known. Such 3G standards and technologies have been developed by the 3 rd generation partnership project (3 GPP). Third generation wireless communications were developed generally to support macrocell mobile telephone communications. Communication systems and networks have evolved towards broadband and mobile systems.

In a cellular wireless communication system, User Equipment (UE) is connected to a Radio Access Network (RAN) over a radio link. The RAN comprises a set of base stations and an interface to a Core Network (CN). The base station provides a radio link to UEs located in the cell covered by the base station. The core network provides overall network control. It is to be understood that the RAN and CN each perform corresponding functions related to the overall network. For convenience, the term cellular network will be used to refer to the combined RAN and CN. And it is to be understood that the term is used to refer to a corresponding system for performing the disclosed function.

The 3 rd generation mobile communication partnership project has developed a so-called Long Term Evolution (LTE) system, i.e., evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN). The Long Term Evolution (LTE) system is used for mobile access networks. In the mobile access network, one or more macro cells are supported by a base station called eNodeB or eNB (evolved NodeB). Recently, LTE has evolved further towards so-called 5G or NR (new radio) systems. In the 5G or NR (new radio) system, one or more cells are supported by a base station called a gNB. NR is proposed to utilize an Orthogonal Frequency Division Multiplexing (OFDM) physical transmission format.

In conventional cellular communication networks, all signaling is between each mobile device and the base station, rather than directly between the mobile devices, even though the mobile devices are within wireless communication range of each other. This may result in inefficient use of radio transmission resources and may increase base station resource utilization. . Sidelink communications allow mobile devices to communicate directly rather than via a base station, potentially improving wireless and base station resource utilization. Sidelink communications are particularly attractive for machine-to-machine communications, particularly vehicle-to-vehicle (V2V) and vehicle-to-everything/anything (V2X) communications.

The following disclosure relates to improvements to cellular wireless communication systems, and in particular to various improvements to sidelink communication in such systems.

Disclosure of Invention

This summary is provided to introduce a selection of concepts in a simplified form. These concepts are described in further detail below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

A method of oversubscribing transmission resources for sidelink communication retransmission (retransmission) is provided. After the first UE has reserved transmission and retransmission resources for sidelink transmissions, the second UE may also reserve retransmission resources for sidelink communication transmissions from the second UE. Such oversubscription may be enabled by system configuration or by RRC configuration messages. Furthermore, SCI messaging may be used for various aspects of the configuration. The allowed overbooking may vary depending on the number of retransmissions, such that different overbooking is allowed depending on the number of retransmissions, or the allowed overbooking may be different for each retransmission resource within the plurality of retransmission reservations.

A UE is also provided. The UE receives an indication of sidelink transmission resource reservation from a second UE, and the UE reserves resources for sidelink transmission. Wherein the reserved resources include resources reserved by the second UE for retransmission.

The non-transitory computer readable medium may include at least one of: hard disks, CD-ROMs, optical storage devices, magnetic storage devices, read-only memories, programmable read-only memories, electrically erasable programmable read-only memories, and flash memories.

Drawings

Further details, aspects and embodiments of the present application will be described, by way of example only, with reference to the accompanying drawings. Elements in the figures have been illustrated for simplicity and clarity and have not been drawn to scale. For ease of understanding, like reference numerals are included in the various drawings.

FIG. 1 shows a schematic diagram of selected components of a cellular communication network;

FIG. 2 shows a flow chart of a method of resource overbooking;

FIGS. 3 and 4 show schematic diagrams of resource availability;

FIG. 5 shows an example of configuration options; and

fig. 6 shows a flow chart of a method of resource sharing.

Detailed Description

Those skilled in the art will recognize and appreciate that the specifics of the described examples are merely illustrative of some embodiments and that the teachings set forth in this application are applicable in a variety of alternative settings.

Fig. 1 shows three base stations (which are enbs or gnbs, depending on the particular cellular standard and terminology) forming a cellular network. Typically, each base station will be deployed by one cellular network operator, providing geographic coverage for UEs in the area. The base stations form a Radio Area Network (RAN). Each base station provides radio coverage for UEs in its area or cell. The base stations are interconnected by an X2 interface and connected to the core network by an S1 interface. The reader will understand that only the basic details are shown in order to illustrate key features of the cellular network. In the proposed NR protocol, the Uu interface is between the base station and the UE. A PC5 interface for Sidelink (SL) communications is provided between UEs. The interface and component names mentioned with respect to fig. 1 are for exemplary purposes only, and different systems operating according to the same principles may use different nomenclature.

Each base station includes hardware and software for implementing RAN functions. These RAN functions include communicating with the core network and other base stations, controlling the transmission of signals and data signals between the core network and the UEs, and maintaining wireless communication with the UEs associated with each base station. The core network includes hardware and software for implementing network functions, such as overall network management and control and routing of calls and data.

Resources for SL communication are discussed in TR 38.885. Particularly relevant for the present disclosure are: -

(A)5.1.1 physical layer Structure

In this section, the design of the Physical SL Control Channel (PSCCH), physical SL shared channel (PSCCH), Physical SL Feedback Channel (PSFCH), and other matters related to the physical layer structure are studied. In addition to what is discussed in the TR, at least aspects related to modulation, scrambling (scrambling), RE mapping and rate matching will be included in the normative work. For the design of the Physical SL Broadcast Channel (PSBCH), refer to section 5.2.

The waveform supported in this study is CP-OFDM.

[…]

(1)5.1.1.3SL Bandwidth portion and resource pool

BWP is defined for SL and the same SL BWP is used for transmission and reception. In the specification terminology, in the licensed carrier, SL BWP will be defined separately and have configuration signaling separate from Uu BWP. One SL BWP is (pre) configured for RRC IDLE and out-of-coverage in carrier NR V2X UEs. For a UE in RRC _ CONNECTED mode, one SLBWP in a carrier is activated. No signaling is exchanged over the SL for activation or deactivation of SL BWP.

In a carrier, only one SL BWP is configured for a UE, and it is not desirable for the UE to simultaneously use a different number (numerology) in the SL BWP than the activated UL BWP.

A resource pool is a collection of time-frequency resources that may be used for SL transmission and/or reception. From the UE perspective, the resource pool is within the UE's bandwidth, within the SL BWP, and has a single encoding. The time domain resources in the resource pool may be non-contiguous. Multiple resource pools in a carrier may be preconfigured for one UE.

(2)5.1.1.4 resource arrangement

NR V2X may be deployed in a carrier dedicated to ITS services or in a carrier shared with cellular services. Thus, resource arrangements are supported in which all symbols in one slot are available for SL, and resource arrangements are supported in which only a subset of consecutive symbols in one slot (which are not dynamically indicated) are available for SL. The latter case is not intended for use in the ITS spectrum if the normative specification work does not find forward compatibility issues.

The resource allocation for the psch is based on the concept of a subchannel in the frequency domain, and the UE performs transmission (transmission) or reception in a slot on a carrier.

[…]

Two modes of resource allocation for SL communication are defined. In the first mode (mode 1), the base station schedules SL resources (the term UE will be used as a convenient descriptor for any mobile device) to be used by the UE for SL communications. In a second mode (mode 2), the base station allocates resources that can be used for SL communication, and the UE selects which resources to use for each SL transmission. In this second mode, the UE operates autonomously to select resources for transmission. Resource selection is based on sensing available resources and then reserving the appropriate available resources. To enable this procedure, the UEs reserve their resources by transmitting Sidelink Control Information (SCI) messages. This message may be sensed by other UEs so that they know which resources have been reserved. In the second mode, the UE may also utilize measurements to determine which resources are available.

HARQ transmission protocols for SL communication are proposed, which means that in case of transmission failure, the transport block is retransmitted. Thus, transmission resources are required for the initial transmission and any potential retransmissions. The resources for retransmission may be reserved in advance, e.g. in case of initial transmission, or on demand if retransmission is needed. The disadvantage of the reservation-ahead approach is that if the initial transmission is successful, resources can be reserved but not used and are therefore wasted (retransmissions are typically expected to occur in 10% of the transmissions), but the reservation-on-demand approach introduces additional delay for any retransmissions. For many proposed SL applications, the extra delay is too high, and therefore the on-demand reservation method cannot be utilized.

As described in detail below, the present disclosure allows for over-reservation of resources for retransmission. That is, more than one UE may schedule retransmissions on the same resources. It can be expected that the initial transmission will be very reliable and therefore the probability that more than one UE utilizes the over-subscribed resource is low. A target of 10% failure rate for the first transmission has been proposed, which if met means that both UEs will only make the first retransmission (and thus collision) in 1% of the cases. Collisions between transmissions result in interference between signals, which may degrade the error rate of one or both transmissions and may result in failure of one or both transmissions.

Overbooking thus allows for improved resource utilization (since less resources are allocated for a group of UEs in total) while having less risk of retransmission failure due to collisions.

Fig. 2 shows a flow chart of a method for overbooking resources for SL communication. The term overbooking is used herein to indicate that the same resources are reserved for more than one potential transmission. For example, two different UEs may reserve the same resources for transmission.

At step 200, the cellular network configures the UE to enable SL resource overbooking. As set forth in more detail below, this configuration may be performed in any suitable manner, such as with a default configuration or RRC communication. A series of options for overbooking configuration are set forth below.

At step 201, a first UE, UE a, has SL transmission to form and reserve resources for initial transmission and any retransmissions. The reservation may be indicated by transmission of a SCI message. At step 202, the second UE, UE B, receives and decodes the SCI message of UE a to determine which resources have been reserved. At step 203, UE B is to make SL transmission and therefore selects and reserves resources. When selecting its resources, UE B may select the resources that have been reserved by UE a for its retransmission according to the configuration at step 200. That is, the resources reserved by UE B for its retransmission may be overbooked. At step 204, UEs a and B make their transmissions and any required retransmissions on the reserved resources. If both UEs need to retransmit, a collision may occur.

The method of fig. 2 thus allows the same resources to be reserved by UEs a and B for retransmission of their SL transmissions. Resource utilization is thus reduced, but there is a risk of collisions between retransmissions that utilize the same resources.

The resources reserved by UE a for initial transmission cannot be reserved also by UE B, since it is unambiguously determined which resources will be utilized by UE a. That is, in general, resources reserved by one UE for initial transmission are no longer available and cannot be oversubscribed. However, the resources reserved for retransmission may be reserved by another UE for initial transmission. However, the resources reserved for retransmissions may be considered to have a lower selection priority. This is because the certainty that the initial transmission will be made results in a higher likelihood of collision and the resource may be only one of the reserved resources that may not be utilized.

Figure 3 shows a graphical representation of the process of figure 2. UE a transmits SCI message 300, SCI message 300 falling within the sensing period of UE B for detecting which resources are available to UE B for SL transmission. UE a reserves resource 301 for the initial transmission and resources 302, 303, 304 are reserved for three potential retransmissions. Based on UE a receiving SCI message 300, UE B may update the resources it considers available for SL transmission, as shown in graph 305. Resource 301 is unavailable because it is used by UE a for initial transmission. But resources 302, 303, 304 may be reserved by UE B because they are reserved for retransmissions. And thus the resources 302, 303, 304 may be overbooked if the active configuration allows.

To balance between resources saved from overbooking and increased risk of collisions, the details of how overbooking occurs may be configured and adjusted for specific situations. In the basic approach, oversubscription is a binary (binary) configuration and is enabled or disabled for all retransmission resources. Where all retransmission resources are treated equally. The activation of the oversubscription may be indicated in a suitable control signal, e.g. in an RRC signal, using a specific true/false indication.

Alternatively, retransmissions may be treated differently, involving oversubscription. For example, each retransmission opportunity is less likely to be utilized than the previous retransmission opportunity. Thus, a greater overbooking may be allowed for later retransmissions because the probability of collisions is lower. For example, overbooking may only be allowed for the last N transmissions, where N is defined by the system between a range from 0 (no overbooking) to a maximum number of retransmissions (which would indicate that all retransmission resources may be overbooked). A value of 1 would indicate that only the last retransmission can be oversubscribed. This may be configured by a control message (e.g., RRC) indicating the value of N.

Overbooking may also be allowed only for transmission resources used for Redundancy Versions (RVs) that are not self-decodable (i.e., not used for RV0 and RV 3). This may be configured in conjunction with other options discussed herein.

In another configuration option, the amount of oversubscription between two specific pairs of devices (a pair of devices being a transmitter and an intended destination device for data sent by the transmitter (which may be a single UE in a unicast transmission, or a group for multicast)) may be limited. This may avoid successive collisions. Consecutive collisions may generate duplicate NACKs on both sides (at the receiver of the corresponding SCI transmission). One option used as an example is that only a subset M of the overbookable retransmission resources may be overbooked by two pairs of devices.

The number of times each reserved resource can be overbooked may be defined in the configuration. To achieve this, the UE must listen for reservations (SCI messages) and accumulate the reservations made. The total reservation can then be utilized to indicate which resources can be reserved for retransmission. If the value is set to 0, no overbooking of those resources is allowed.

The overbooking number may be formed according to an index of retransmission (or RV index), a retransmission coding scheme, and/or a total number of retransmissions. For example, this value may be set to 0 on self-decodable RVs (RV 0 and RV3 in the 4-transmission example) and may be set to a value greater than 0 (e.g., 8) for other retransmissions. Further, the value may vary with the retransmission sequence. Since the probability of utilizing a subsequent retransmission is low, as discussed above. Assuming a 10% error rate target, the first retransmission has a 10% chance of being used, the second retransmission has a 1% chance of being used, and the third retransmission has a 0.1% chance of being used. In one example, the number of overbooking may be set to 4 for the first transmission. For the second transmission, the oversubscription number may be set to 8. For the third transmission, the overbooking number may be set to 16, etc. The UE may utilize the available (or remaining) overbooking number when selecting resources to be reserved. For example, resources with a higher available overbooking number may be selected.

Fig. 4 illustrates another example of resource reservation according to principles described herein, and also illustrates an extension to a third UE. As described with reference to fig. 3, UE a transmits the SCI message. The SCI message is received by UE B. UE B updates its available resources but includes the number of available overbooking on each resource. Thus, resource 400 has 4 overbooking available, resource 401 has 8 overbooking available, and resource 402 has 16 overbooking available.

UE B selects resources for its retransmission and transmits the SCI at 403 for reserving resources 404 and 405. Resource 404 is used for initial transmission by UE B. Resource 405 is for one retransmission. UE C receives the SCIs of both UE a and UE B and updates its available resources appropriately. Thus, resources 406 and 407 are not available (previously used for initial transmission), while resources 400 and 401 still have 4 and 8 overbooking available, but resource 408 now has only 15 overbooking available.

Thus, UE C determines which resources to reserve for its SL transmission based on the accumulated reservations from UE a and UE B and the previously configured available oversubscription.

The principles described with respect to fig. 4 may be extended to any number of UEs and any mode and number of resource overbooking.

Any suitable configuration method may be utilized to configure the UE with overbooking of resources. RRC configuration may be preferred because it allows semi-static configuration but has the flexibility to adjust the configuration depending on the circumstances. SCI messaging may be used for configuration, which may provide a more dynamic configuration process. A predefined set of configurations may be defined to reduce RRC signaling overhead. For example, an integer of 3 bits (bits) would allow a configuration to be selected from 8 options.

The SCI message reserving resources may also include specific oversubscription information for the indicated reservation to override or supplement the currently active configuration. The UE receiving the SCI may update its configuration appropriately. For example, SCI may be used for coverage configuration if the UE has high reliability and/or low latency data packets to be communicated. The UE may disable oversubscription or reduce the amount of oversubscription for certain resources reserved for transmission to avoid the possibility of collisions and help ensure that reliability and/or delay targets are met. For example, a flag may be included in the SCI to disable over-subscription of resources. In another example, if the initial transmission is successful and no retransmission resources are needed, the system may allow the same UE to reuse the reserved retransmission resources for other TBs. If the UE has data in its buffer, the UE knows that the retransmission resources (TBS for retransmission or pending) will be used, and can therefore disable oversubscription.

The SCI information may include the remaining overbooked number or the original available number (each UE may update this information based on the received SCI). Alternatively, the cumulative number of overbooking may be indicated. Wherein the UE calculates the remaining number based on the configuration. If all retransmissions are treated identically, a single value may be sent. Or a set/array of values may be sent if the available overbooking varies with resources/retransmissions. The parameters may suitably be transmitted as binary or integer values, giving a direct indication of the value or giving a reference to a set of predefined values.

The oversubscription rule to be applied by the UE may be traffic/QoS/priority dependent. Several rule sets may be predefined (configured as a standard in a static setting or via RRC) and then select which rule to apply to a given transmission or retransmission based on the data transmitted for that transmission or retransmission (e.g., (re-) using some QoS information, traffic class information, priority information typically included in the SCI). Activation of overbooking may also depend on system load, such that below a certain threshold, overbooking is not utilized (thereby avoiding a collision risk), but above the threshold overbooking is activated to reduce resource utilization. For example, the Channel Busy Ratio (CBR) may be used as an indicator of system load.

Fig. 5 shows an example of a hierarchy of configurations. A range of possible options is provided by enabling oversubscription at the system level, and the RRC configuration may then define a subset of those options that are available. SCI messaging may then specify more details from the RRC configuration set.

Examples of parameters for configuring oversubscription configurations include:

enabling: yes/no/load based

Type: system, priority based

A limitation: maximum value of overbooked number

Mode: last N, last N-1, last N-2, non-self-decodable

Fig. 6 illustrates an exemplary method. In the method, a UE with overbooked resources may indicate whether to utilize the resource using feedback from other UEs sharing the resource. At step 600, UE B schedules resources for retransmission in the same resources as another UE a has already scheduled retransmissions on. At step 601, UE B identifies a previous retransmission or initial transmission from UE a for oversubscription of resources and a corresponding feedback channel.

At step 602, UE B listens to the identified feedback channel and decodes the transmitted feedback. If the feedback is a NACK at step 602, this indicates that UE A will be retransmitting using the shared resource. At step 603, UE B may therefore not make its transmissions to avoid collisions. If no feedback or positive feedback is detected at step 602, this indicates that UE a will not use the shared resource. And UE B may utilize the resources for retransmission at step 604, if needed. If no retransmission is made at step 603, UE B may transmit an indication of this, e.g., by flushing the HARQ buffer, corruption indication (corruption indication), or another retransmission reservation.

The method of fig. 6 thus allows for overbooking of resources as described above, but may also allow for collision avoidance. In a conflict, more than one UE needs to use the overbooked resources.

Although not shown in detail, any device or apparatus forming part of a network may include at least one processor, a memory unit, and a communication interface. Wherein the processor unit, the memory unit and the communication interface are configured to perform the method of any aspect of the present application. Further options and choices are described below.

The signal processing functions of the embodiments of the present application (particularly the gNB and the UE) may be implemented using computing systems or architectures known to those skilled in the art. Computing systems such as desktop, laptop or notebook computers, handheld computing devices (PDAs, cell phones, palmtops, etc.), mainframes, servers, clients, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system may include one or more processors. The processor may be implemented using a general-purpose or special-purpose processing engine. Such as a microprocessor, microcontroller or other control module.

The computing system may also include a main memory (e.g., Random Access Memory (RAM) or other dynamic memory) to store information and instructions to be executed by the processor. The main memory may also be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may also include a Read Only Memory (ROM) or other static storage device for storing static information and instructions for the processor.

The computing system may also include an information storage system. The information storage system may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a Compact Disc (CD) or Digital Video Drive (DVD), a read-write drive (R or RW), or other removable or fixed media drive. The storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that can be read by and written to by a media drive. The storage media may include a computer-readable storage medium having stored therein particular computer software or data.

In alternative embodiments, the information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computer system. Such components may include, for example, removable storage units and interfaces, such as program cartridges and cartridge interfaces, removable memory (e.g., flash memory or other removable memory modules) and memory slots, and other removable storage units and interfaces. The interface allows software and data to be transferred from the removable storage unit to the computing system.

The computing system may also include a communications interface. Such communication interfaces can be used to allow software and data to be transferred between the computing system and external devices. Examples of communication interfaces may include modems, network interfaces (e.g., ethernet or other NIC cards), communication ports (e.g., Universal Serial Bus (USB) ports), PCMCIA slots and cards, and the like. Software and data transferred via the communication interface are in the form of signals. The signal can be an electronic signal, an electromagnetic signal, an optical signal, or other signal capable of being received by the communication interface medium.

In this document, the terms "computer program product," "computer-readable medium," and the like may be used generally to refer to tangible media, such as memory, storage devices, or storage units. These and other forms of computer-readable media may store one or more instructions for use by a processor, including a computer system, to cause the processor to perform specified operations. These instructions, which are generally referred to as "computer program code" (which may be grouped in the form of computer programs or otherwise), when executed, enable the computing system to perform the functions of embodiments of the present application. Note that the code may directly cause the processor to perform specified operations, be compiled to cause the processor to perform specified operations, and/or be combined with other software, hardware, or firmware elements (e.g., libraries for performing standard functions) to cause the processor to perform specified operations.

The non-transitory computer readable medium may include at least one of: hard disks, CD-ROMs, optical storage devices, magnetic storage devices, read-only memories, programmable read-only memories, electrically erasable programmable read-only memories, and flash memories. In embodiments in which the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into the computing system using, for example, a removable storage drive. When executed by a processor in a computer system, the control module (in this example, software instructions or executable computer program code) causes the processor to perform the functions of the present application as described herein.

Furthermore, the concepts of the present application can be applied to any circuit that performs a signal processing function within a network element. For example, it is also contemplated that a semiconductor manufacturer may employ the concepts of the present application in the design of a stand-alone device (e.g., a microcontroller of a Digital Signal Processor (DSP)) or an Application Specific Integrated Circuit (ASIC) and/or any other subsystem element.

It should be appreciated that the above description, for clarity, describes embodiments of the application with reference to single processing logic. However, the inventive concept may equally be implemented by a plurality of different functional units and processors to provide the signal processing functionality. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, and not indicative of a strict logical or physical structure or organization.

Aspects of the present application may be implemented in any suitable form including hardware, software, firmware or any combination of these. The present application may optionally be implemented at least in part as computer software. The computer software may be run on one or more data processors and/or digital signal processors or configurable modular components such as FPGA devices.

Thus, the elements and components of an embodiment of the application may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the present application has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. The scope of the application is limited only by the claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the application. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Likewise, the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate.

Furthermore, the order of features in the claims does not imply that the features must be performed in any particular order. Especially the order of individual steps in the method claims does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. Furthermore, singular references do not exclude a plurality. Thus, references to "a", "an", "first", "second", etc., do not preclude a plurality.

Although the present application has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. The scope of the application is limited only by the claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the application. In the claims, the term "comprising" or "comprises" does not exclude the presence of other elements.

Claims (12)

1. A method for reserving transmission resources for sidelink communication between UEs in a cellular communication network, the method comprising the steps of:

transmitting, at a first UE, a message reserving first transmission resources for a first sidelink transmission, the first transmission resources including a first initial transmission resource and a first retransmission resource;

receiving, at a second UE, the message and decoding at least the first transmission resource that is reserved; and

selecting, at the second UE, a second transmission resource for a second sidelink transmission, wherein the second transmission resource comprises at least a portion of the first retransmission resource.

2. The method of claim 1, wherein the second transmission resource comprises a second initial transmission resource and a second retransmission resource, and wherein the second retransmission resource comprises at least a portion of the first retransmission resource.

3. The method according to claim 1 or 2, characterized in that during the selection of the second transmission resource the first retransmission resource is given a lower priority than the unreserved transmission resources.

4. Method according to any of the preceding claims, wherein said message is a SCI message.

5. The method according to any one of the preceding claims, further comprising the step of: receiving, at the second UE, a configuration message that allows the UE to select resources previously reserved by another UE.

6. The method of claim 5 wherein the configuration message is an RRC message or a SCI message.

7. The method of claim 5, wherein the configuration message indicates that the UE can select only a subset of resources reserved for retransmission by another UE.

8. The method of claim 5, wherein the configuration message indicates that the second UE can only select retransmission resources reserved for non-self-decodable redundancy versions.

9. The method of claim 5, wherein the configuration message indicates how many UEs can select the retransmission resources reserved by the first UE.

10. The method of claim 5, wherein the configuration message indicates that the second UE is allowed to select resources previously reserved by the other UE according to a priority of messages to be transmitted by the first UE or the second UE.

11. The method according to any one of the preceding claims, further comprising the step of:

at the second, a feedback message related to the transmission on the first initial transmission resource is received, and

if the feedback message is an ACK, utilizing at least a portion of the first retransmission resources selected by the second UE when needed by the second UE, and if the feedback message is a NACK, not utilizing at least a portion of the first retransmission resources selected by the second UE.

12. A UE configured to perform the method of any of claims 1 to 11.

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