Methods for providing resource selection for D2D communication and related communication devices

Abstract

To provide a communication method for supporting sidelink communications and related devices and nodes.SOLUTION: A first communication device (TX UE) selects a resource within a resource selection window for an initial transmission of a first MAC PDU of a plurality of periodic medium access control protocol data units (MAC PDUs) to be transmitted by a first communication device (TX UE) over a D2D (device-to-device) link to a second communication device (RX UE), and selects a period (P) for periodic transmission of the plurality of periodic MAC PDUs so that initial transmissions of all MAC PDUs of the plurality of periodic MAC PDUs other than the first MAC PDU are performed in resources after the resource selection window.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure generally relates to communications, and more particularly to communication methods and related devices and nodes that support wireless communication.

Background Art

[0002] V2X (vehicle-to-anything) communication is described below.

[0003] Cellular intelligent transportation systems (ITS) aim to define a new cellular ecosystem for the delivery of vehicle services and their distribution. Such an ecosystem includes both short-range V2X service transmission and long-range V2X service transmission, as shown in the C-ITS environment of FIG. 1. In particular, short-range communication involves transmission via a D2D (device-to-device) link, which is also defined as a sidelink (SL) or PC5 interface in 3GPP, to other vehicle UEs or roadside units (RSUs). On the other hand, in the case of long-range transmission, transmission via the Uu interface between the user equipment (UE) and the base station is intended, in which case the packets can be distributed to different ITS service providers, which can be, for example, road traffic authorities, road operators, automotive original equipment manufacturers (OEMs), cellular operators, etc.

[0004] Regarding the sidelink interface, the first standardization work in 3GPP dates back to Release 12, targeting public safety use cases. Since then, several extensions have been introduced to expand the use cases that can benefit from D2D technology. In particular, in Long Term Evolution (LTE) Rel-14 and Rel-15, the extensions for D2D (device-to-device) work include support for V2X communication, including any combination of direct communication between vehicles, pedestrians, and / or infrastructure.

[0005] LTE V2X is mainly targeted at traffic safety services, while New Radio (NR) V2X has a much broader scope that targets not only basic safety services but also non-safety use cases such as sensor / data sharing between vehicles for the purpose of enhancing perception of the surrounding environment. Therefore, a new set of use cases (such as platooning, cooperative maneuvers between vehicles, remote / autonomous driving, etc.) can enjoy such an extended sidelink framework.

[0006] In this new context, the expected requirements to meet the desired / required data rate, capacity, reliability, latency, communication range, and / or speed can be more stringent. For example, assuming various services that can be transmitted via sidelink, a robust Quality of Service (QoS) framework that takes into account the different performance requirements of different V2X services can be useful / required. Further, new radio protocols should be designed to handle more robust and / or reliable communication. All of this is currently under investigation by 3GPP in NR Rel.16.

Summary of the Invention

[0007] The inventors have made several findings regarding sidelink communication. These findings include the following. · The UE behavior in case of insufficient resources for the required Hybrid Automatic Repeat reQuest (HARQ) retransmission is unclear. · Without restrictions on resource reservation interval selection, HARQ retransmissions for periodic Medium Access Control Protocol Data Unit (MAC PDU) can collide. · Without sensing, it is useless to have reservations for both initial transmission and retransmission. · Resource reservation in a dedicated and exclusive resource pool for a particular UE is not necessary. · When the service requires extremely low latency, it may be too late to use reserved resources for the initial transmission. · It is unclear whether multiple resource pools can be configured within a single carrier for sidelink (SL) transmission. · To enable HARQ feedback transmission, the selected resource pool must be configured with physical sidelink feedback channel (PSFCH) resources. · To obtain a mode 2 grant, the UE first selects a pool and then applies a resource allocation procedure to the selected pool.

[0008] Various embodiments of the inventive concept address many of these findings.

[0009] According to some embodiments of the inventive concept, a method is provided that includes selecting a resource within a resource selection window for an initial transmission of a first media access control (MAC) protocol data unit (PDU) of a plurality of periodic MAC PDUs to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link. The method further includes selecting a period (P) for the periodic transmission of the plurality of periodic MAC PDUs such that initial transmissions of all MAC PDUs of the plurality of periodic MAC PDUs other than the first MAC PDU are performed in resources after the resource selection window.

[0010] According to another embodiment of the inventive concept, a first communication device (TX / UE) performs an operation adapted to select a resource within a resource selection window for an initial transmission of a first media access control (MAC) protocol data unit (PDU) among a plurality of periodic MAC PDUs to be transmitted to a second communication device (RX UE) via a device-to-device (D2D) link by the first communication device (TX UE). Those operations further include selecting a period (P) for the periodic transmission of the plurality of periodic MAC PDUs such that the initial transmission of all MAC PDUs of the plurality of periodic MAC PDUs other than the first MAC PDU is performed in a resource after the resource selection window.

[0011] According to some other embodiments of the inventive concept, computer program code to be executed by at least one processor of a first communication device (TX / UE), whereby execution of the program code causes the first communication device (TX / UE) to perform operations similar to those of the above method.

[0012] According to a further embodiment of the inventive concept, a method is provided that includes selecting a resource for an initial transmission of a first media access control (MAC) protocol data unit (PDU) among a plurality of periodic MAC PDUs to be transmitted to a second communication device (RX UE) via a device-to-device (D2D) link by a first communication device (TX UE). The method further includes selecting a period for the periodic transmission of the plurality of periodic MAC PDUs such that a resource for an initial transmission of a second MAC PDU among the plurality of periodic MAC PDUs is determined based on the period. The method further includes selecting a plurality of resources for a retransmission of the first MAC PDU such that all retransmissions of the first MAC PDU are performed before a resource for an initial transmission of the second MAC PDU.

[0013] According to yet further embodiments of the inventive concept, a first communication device (TX / UE) is adapted to perform operations including selecting resources for an initial transmission of a first media access control (MAC) protocol data unit (PDU) among a plurality of periodic MAC PDUs to be transmitted to a second communication device (RX UE) via a device-to-device (D2D) link by the first communication device (TX UE). Those operations further include selecting a period for the periodic transmission of the plurality of periodic MAC PDUs such that resources for an initial transmission of a second MAC PDU among the plurality of periodic MAC PDUs are determined based on the period. Those operations further include selecting a plurality of resources for a retransmission of the first MAC PDU such that all retransmissions of the first MAC PDU are made before resources for an initial transmission of the second MAC PDU.

[0014] According to some other embodiments of the inventive concept, computer program code to be executed by at least one processor of a first communication device (TX / UE), whereby execution of the program code causes the first communication device (TX / UE) to perform operations similar to those of the above method.

[0015] The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate some non-limiting embodiments of the inventive concept.

Brief Description of the Drawings

[0016]

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DETAILED DESCRIPTION OF THE INVENTION

[0017] Next, the inventive concept will be described in more detail below with reference to the accompanying drawings showing examples of embodiments of the inventive concept. However, the inventive concept may be embodied in many different forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the inventive concept to those skilled in the art. It should also be noted that these embodiments are not mutually exclusive. Components from one embodiment may be implicitly assumed to be present / used in another embodiment.

[0018] The following description presents various embodiments of the disclosed subject matter. These embodiments are presented as illustrative examples and should not be construed as limiting the scope of the disclosed subject matter. For example, some details of the described embodiments may be modified, omitted, or expanded without departing from the scope of the described subject matter.

[0019] As previously shown, the inventors have made several findings regarding sidelink. These findings include the following. · The UE behavior in case of insufficient resources for required HARQ retransmissions is unclear. · Without restrictions on resource reservation interval selection, HARQ retransmissions for periodic MAC PDUs may collide. · Without detection, it is unnecessary to have reservations for both initial transmission and retransmission. · Resource reservation is not necessary within a dedicated and exclusive resource pool for a specific UE. · When the service requires extremely low latency, it may be too late to use reserved resources for initial transmission. · It is unclear whether multiple resource pools can be configured within a single carrier for SL transmission. · To enable HARQ feedback transmission, the selected resource pool must be configured with PSFCH resources. · To obtain a mode 2 grant, the UE first selects a pool and then applies a resource allocation procedure to the selected pool.

[0020] Two sidelink resource allocation (RA) modes are defined for NR-V2X sidelink communication, namely, mode 1 RA where the base station schedules the (one or more) sidelink resources to be used by the UE, and mode 2 RA where the UE determines the (one or more) sidelink transmission resources within the sidelink resources configured by the base station / network or pre-configured sidelink resources.

[0021] In the 3GPP RAN1#96 meeting, the following related to Mode 2 RA were agreed upon. · Blind retransmission of TB is supported by NR-V2X for SL. ○ Details are for the WI phase. · NR V2X Mode 2 supports reservation of sidelink resources for at least blind retransmission of TB. ○ Whether reservation is supported for the initial transmission of TB will be discussed in the Work Item (WI) phase. ○ Whether reservation is supported for potential retransmission based on HARQ feedback is for the WI phase.

[0022] In the 3GPP RAN1#96bis meeting, the following related to Mode 2 RA were agreed upon. · NR V2X supports initial transmission of TB without reservation based on detection and resource selection procedures · NR V2X supports reservation of sidelink resources for initial transmission of TB based on detection and resource selection procedures, at least by SCI related to different TBs ○ This function can be enabled / disabled by (pre-)configuration ○ Standalone PSCCH transmission for FFS resource reservation is supported in NR V2X.

[0023] Issues not agreed upon include issues related to resource selection for HARQ retransmission. In the context of sidelink resource allocation, the focus is on resource reservation in Mode 2 resource allocation. Furthermore, issues related to multiple resource pool configurations and Mode 2 resource pool selection were also not agreed upon.

[0024] Before describing embodiments of inventive concepts that address some of these problems, a communication device UE that may be used in the inventive concepts is described.

[0025] FIG. 3 is a block diagram showing elements of a communication device UE300 (also referred to as a mobile terminal, mobile communication terminal, wireless device, wireless communication device, wireless terminal, mobile device, wireless communication terminal, user equipment (UE), user equipment node / terminal / device, etc.) configured to provide wireless communication according to an embodiment of the inventive concept. (Communication device 300 may be provided, for example, as described below with respect to wireless device 1510 of FIG. 15.) As shown, communication device UE may include an antenna 307 (corresponding to antenna 1511 of FIG. 15, for example), and a transceiver circuit 301 (also referred to as a transceiver, corresponding to interface 1514 of FIG. 15, for example) configured to provide uplink wireless communication and downlink wireless communication with one or more base stations (corresponding to network node 1560 of FIG. 15, also referred to as a RAN node, for example) of a radio access network. Communication device UE may also include a processing circuit 303 (also referred to as a processor, corresponding to processing circuit 1520 of FIG. 15, for example) coupled to the transceiver circuit, and a memory circuit 305 (also referred to as a memory, corresponding to device-readable medium 1530 of FIG. 15, for example) coupled to the processing circuit. Memory circuit 305 may include computer-readable program code that, when executed by processing circuit 303, causes the processing circuit to perform operations according to the embodiments disclosed herein. According to other embodiments, processing circuit 303 may be defined to include memory such that a separate memory circuit is not required. Communication device UE may also include an interface (such as a user interface) coupled to processing circuit 303, and / or communication device UE may be incorporated into a vehicle.

[0026] As described herein, the operation of the communication device UE may be performed by the processing circuit 303 and / or the transceiver circuit 301. For example, the processing circuit 303 may control the transceiver circuit 301 to transmit communications over the radio interface to a radio access network node (also called a base station) through the transceiver circuit 301, and / or to receive communications from the RAN node over the radio interface through the transceiver circuit 301. Moreover, modules may be stored in the memory circuit 305, and these modules may provide instructions such that when the instructions of the modules are executed by the processing circuit 303, the processing circuit 303 performs respective operations (for example, the operations described below with respect to exemplary embodiments related to wireless communication devices).

[0027] Hybrid automatic repeat request (HARQ) in sidelink is described below.

[0028] In NR, HARQ processes for SL unicast and groupcast are supported. There are two options for HARQ feedback signaling described below, namely, ACK / NACK and NACK only.

[0029] When ACK / NACK is configured, the receiving UE provides the transmitting UE with an ACK or NACK feedback indicating whether the transport block (TB) was correctly received (ACK) or not correctly received (NACK), respectively. If the feedback is NACK, the transmitting UE will retransmit the same TB until an ACK is received or the maximum number of retransmissions is reached.

[0030] Figure 2A is a message diagram showing an example of a sidelink HARQ process using ACK / NACK. In operation 201, a transmitting UE (TX UE) transmits an initial transmission of a first transport block TB#1. When a receiving UE (RX UE) receives a scheduling allocation SA for the transport block TB#1 in operation 201 but fails to successfully decode the transport block TB#1, the receiving UE transmits a NACK in operation 202. In response to receiving the NACK in operation 202, the transmitting UE retransmits the first transport block TB#1 in operation 203. When the receiving UE successfully decodes the transport block TB#1 in operation 203, the receiving UE transmits an ACK in operation 204. Upon receiving the ACK in operation 204, the transmitting UE may transmit a second transport block TB#2 in operation 205. In response to successfully receiving / decoding the second transport block TB#2 in block 205, the receiving UE transmits an ACK in block 206.

[0031] When only NACK is set, the receiving UE (RX UE) is set to send NACK when reception fails, but the receiving UE does not send feedback when reception is successful. That is, if the receiving UE decodes the scheduling allocation (SA) but fails to decode the TB, the receiving UE transmits a NACK. In other cases (i.e., when the receiving UE correctly decodes both the SA and the TB, or when the receiving UE fails to decode the SA), the receiving UE does not transmit anything. If the TX UE does not receive a NACK, the TX UE assumes that reception was successful and thus the TX UE can transmit a new TB. However, in this case, there is no distinction between the case where the receiving UE does not send feedback due to failed control information (SA) decoding and the case where the receiving UE successfully decodes the data but decides not to send feedback.

[0032] Figure 2B is a message diagram showing an example of a sidelink HARQ process using only NACK. In operation 251, the transmitting UE (TX UE) transmits an initial transmission of the first transport block TB#1. The receiving UE (RX UE) receives a scheduling assignment SA for the transport block TB#1 in operation 201. In response to not successfully decoding the transport block TB#1, the receiving UE transmits a NACK in operation 252. In response to receiving the NACK in operation 202, the transmitting UE retransmits the first transport block TB#1 in operation 253. In response to not receiving a NACK corresponding to the second transmission of the first transport block TB#1 in operation 253, the transmitting UE transmits the second transport block TB#2 in operation 254. After not receiving a NACK after operation 253, the transmitting UE thus assumes that the first transport block TB#1 was successfully received / decoded by the receiving UE in operation 253. However, it is possible that the receiving UE did not receive the scheduling assignment SA of operation 253, and thus the receiving UE did not receive the second transmission of the first transport block and did not send a NACK.

[0033] Mode 2 resource allocation is described below.

[0034] In NR SL, the UE can autonomously select resources for transmission based on randomness and / or sensing (i.e., Mode 2). More specifically, within a scheduling window determined by a (pre-)configured resource pool and other parameters (e.g., T1 and T2), the UE Medium Access Control (MAC) entity can randomly select a set of resources to generate and transmit one or more MAC protocol data units (PDUs). In another case, the UE can also read side link control information (SCI) from other UEs to understand which resources are reserved / occupied and select only the resources available for generating and transmitting one or more MAC PDUs.

[0035] Moreover, NR SL supports resource allocation for a single MAC PDU or for periodic transmission of multiple MAC PDUs. In either case, the UE can simultaneously select and reserve up to two HARQ retransmission opportunities for each MAC PDU. The number of HARQ retransmissions and the transmission duration are determined by the MAC entity prior to resource allocation.

[0036] When the UE MAC entity selects resources for transmission and retransmission of a single MAC PDU, the following operations are performed, and Figure 3A shows the resource selection for a single MAC PDU transmission. · The MAC entity first selects resources for the initial transmission within the scheduling window. · If there are resources available within the scheduling window, the MAC entity further selects resources for one or more HARQ retransmissions. · Resource reservation information will be transmitted in the side link control information (SCI).

[0037] When the MAC entity selects resources for the periodic transmission of multiple MAC PDUs and related retransmissions, the following operations are performed. Figure 3B shows the resource selection for the periodic transmission of multiple MAC PDUs. · The MAC entity first selects resources for the initial transmission of the first MAC PDU within the scheduling window. · Then, the MAC entity uses the period value to use the selected resources for the initial transmission of the first MAC PDU to reserve resources for future second, third,... MAC PDUs. For example, if the initial transmission of the first MAC PDU is scheduled in slot T, the initial transmissions of the second, third,... MAC PDUs will be at T+P, T+2*P,.... · If there are resources available within the scheduling window, the MAC entity further selects resources for the retransmission of the first MAC PDU. · Then, the MAC entity uses the period value to use the selected resources for the retransmission of the first MAC PDU to reserve resources for future second, third,... MAC PDU retransmissions. For example, if the retransmission of the first MAC PDU is scheduled in slot T, the retransmissions of the second, third,... MAC PDUs will be at T+P, T+2*P,....

[0038] The approval operation is indicated by the single underline in the following text (related to 3GPP TS38.321, active CR). 5.x.1.1: When the MAC entity is configured by the RRC to transmit using (one or more) pools of resources in the carrier as shown in 3GPP TS38.331 or 3GPP TS36.331 based on sensing or random selection, the MAC entity shall perform the following for each sidelink process. 1> The MAC entity selects to create a configured sidelink grant corresponding to the transmission of a plurality of MAC PDUs, and if the SL data is available in the logical channel, 2> Perform a TX resource (re)selection check as specified in Section 5.x.1.2, 2> If the TX resource (re)selection is triggered as a result of the TX resource (re)selection check, 3> Select one of the allowed values set by RRC within reservationPeriodAllowed and set the resource reservation interval with the selected value. 3> With equal probability, randomly select an integer value within the interval [5,15] for a resource reservation interval higher than or equal to 100 ms and set SL_RESOURCE_RESELECTION_COUNTER to the selected value. ... 3> According to the amount of frequency resources selected and the remaining PDB of the SL data available in the (one or more) logical channels allowed on the carrier, randomly select the time and frequency resources for one transmission opportunity from the resources indicated by the physical layer according to Section 8.1.4 of TS38.214. 3> Use the randomly selected resources to select a set of periodic resources separated by the resource reservation interval for the transmission of PSCCH and PSSCH corresponding to the number of transmission opportunities of the MAC PDU determined in TS38.214. 3> If one or more HARQ retransmissions are selected, 4> If there are available resources left in the resources indicated by the physical layer according to Section 8.1.4 of TS38.214 for more transmission opportunities, ... 5> Consider the set of new transmission opportunities and retransmission opportunities as the selected sidelink grant. 3> In other cases, 4> Consider that set as the selected sidelink grant. 3>Using the selected sidelink grant to determine a set of PSCCH durations and a set of PSSCH durations according to 3GPP TS38.214 3>Consider the selected sidelink grant as the configured sidelink grant.

[0039] The following issues have been identified according to the MAC procedures standardized for sidelink. · In both the single MAC PDU transmission scenario and the periodic multiple MAC PDU transmission scenario, especially when multiple retransmissions are required, if the resources available for retransmission are insufficient, the UE behavior is not clear (i.e., the text of the procedure is missing). In other words, if the resources available for the required number of HARQ retransmissions are not sufficient, it is not clear what will happen. For example, N HARQ retransmissions are selected for one MAC PDU, but the available resources can only support N - 1 HARQ retransmissions. The simplest solution is not to perform HARQ retransmissions. Another alternative is to only perform the number of HARQ retransmissions that can be supported and forget about the rest. · In the scenario of periodic multiple MAC PDU transmissions, it may happen that the resources selected for the retransmission of one MAC PDU collide with the resources reserved for the retransmission of future MAC PDUs. An example of a resource reservation collision for periodic multiple MAC PDU transmissions is shown in Figure 4. For example, ○ In Figure 4, the UE selects slots 10 and 20 for the retransmission of the first MAC PDU. ○ Assuming a period of 10 slots, the retransmission of the second MAC PDU will be performed in slots 20 and 30. ○ In this situation, the second retransmission of the first MAC PDU will collide with the first retransmission of the second MAC PDU.

[0040] FIG. 4 shows a resource reservation collision for a plurality of periodic MAC PDU transmissions.

[0041] Finding 1 The UE behavior in the case of insufficient resources for the required HARQ retransmissions is unclear.

[0042] Therefore, when selecting resources for periodic MAC PDUs, the UE first selects resources for the initial transmission and the required HARQ retransmissions for the first MAC PDU, and then expands the selected set of resources for future MAC PDUs by basing on the selected reservation intervals highlighted by the double underline in the above text. For example, as shown in FIG. 4, the initial transmission and HARQ retransmissions of MAC PDU #1 are selected within a scheduling window bounded by T1 and T2, and then the initial transmission of MAC PDU #2 will occur after the P slot (i.e., its period) of the initial transmission of MAC PDU #1, and the same is true for HARQ retransmissions. However, there is a possibility that the resources selected for the retransmission of MAC PDU #1 may collide with the resources reserved for the retransmission of MAC PDU #2. For example, if the first retransmission and the second retransmission of MAC PDU #1 are scheduled in slot 10 and slot 20, assuming a period of 10 slots, the first retransmission of MAC PDU #2 will occur in slot 20, which collides with the second retransmission of MAC PDU #1.

[0043] According to some embodiments of the inventive concept, improved / suitable resource reservation for SL MAC PDU retransmissions can be provided. The UE provides / guarantees no / lower collisions between resource reservations for retransmissions of different MAC PDUs. Further, operations for handling the case where the resources available to support all required retransmissions are insufficient can be provided, and the UE actions for handling this case are made clear by reducing / avoiding unexpected behavior.

[0044] According to some embodiments of the inventive concept, problems related to resource reservation for retransmission in NR SL can be addressed, and some embodiments can be applied to other D2D wireless access technologies.

[0045] According to some embodiments, when selecting resources for retransmission of one or more MAC PDUs, the UE provides that no / lower reduced collisions occur between resource reservations for retransmission of different MAC PDUs. Further, operations for handling cases where the resources available to support all requested retransmissions are insufficient may be provided.

[0046] A method for providing reduced resource reservation collision / no resource reservation collision is described below.

[0047] According to some embodiments, for periodic multiple MAC PDU transmissions, when determining the transmission period, the UE considers the boundaries of the scheduling window indicated by the physical layer and selects only values from the set of candidates that satisfy any of the following. · The selected period is equal to or greater than the duration of the scheduling window, i.e., T2 - T1, as shown in FIG. 5. · The selected period is equal to or greater than the scheduling window upper limit, i.e., T2.

[0048] Thus, in some embodiments of the inventive concept, to solve this problem, when selecting the resource reservation interval from reservationPeriodAllowed, the duration of the selection window (i.e., T2 - T1) must be taken into account. In particular, the resource reservation interval must be greater than the selection window duration (i.e., T2 - T1) such that the initial transmission of the next MAC PDU will be scheduled after the HARQ retransmission of the current MAC PDU.

[0049] As shown in FIG. 5, a plurality of periodic MAC PDUs can be transmitted over a period greater than the scheduling window duration.

[0050] According to some other embodiments, for the transmission of a plurality of periodic MAC PDUs, when selecting resources for the retransmission of one MAC PDU, as shown in FIG. 6, only the resources before the initial transmission of the next MAC PDU are selected. Here, the resources for the initial transmission of the plurality of MAC PDUs are selected before the retransmission opportunity. According to such embodiments, there is no restriction on determining the transmission period.

[0051] As shown in FIG. 6, a transmission of a plurality of periodic MAC PDUs can be provided, where a retransmission opportunity for each MAC PDU is provided before the initial transmission of the next MAC PDU.

[0052] In yet other embodiments, for the transmission of a plurality of periodic MAC PDUs, resource reservation for MAC PDU retransmission is performed in a per-retransmission manner. Note that in the legacy procedure, resources (e.g., the two requested retransmissions for the first MAC PDU) are selected at once and extended for future MAC PDU retransmissions. More specifically, assuming that two retransmissions are requested, · Operation 1: The UE first selects resources for the initial transmission of the first MAC PDU, e.g., in slot T. · Operation 2: Then, the UE reserves resources for the initial transmission of future MAC PDUs, e.g., in slots T+P, T+2*P,.... · Operation 3: If there are available resources, the UE selects resources for the first retransmission of the first MAC PDU, e.g., in slot Ta. · Operation 4: Then, the UE reserves resources for the first retransmission of future MAC PDUs, e.g., in slots Ta+P, Ta+2*P,.... · Action 5: The UE loops through Steps 3 and 4 for the next retransmission of the first MAC PDU.

[0053] A method for handling insufficient resources for all requested HARQ retransmissions of a MAC PDU is described below.

[0054] According to some embodiments, if the available resources within the scheduling window are insufficient for all the requested retransmissions, the UE will not perform the retransmissions. For example, if the available resources can support only N - 1 retransmissions but N retransmissions are required, the UE will not perform any retransmissions for this MAC PDU.

[0055] According to some other embodiments, the UE will perform only the number of retransmissions that can be supported within the scheduling window and will ignore the remaining requested retransmissions. For example, if the available resources can support only N - 1 retransmissions but N retransmissions are required, the UE will perform only N - 1 retransmissions and will ignore the remaining retransmissions.

[0056] According to yet other embodiments, the UE will first perform the number of retransmissions that can be supported within the scheduling window. The UE will further select resources for the remaining requested retransmissions when the scheduling window shifts and new available resources appear. Information regarding the resource reservation for the remaining requested retransmissions will be transmitted in the next SCI after the resource reservation is made. For example, if the available resources can support only N - 5 retransmissions but N retransmissions are required, the corresponding actions are described below. · Action 1: The UE continues to perform N - 5 retransmissions as scheduled within the scheduling window. · Action 2: When the scheduling window shifts and new available resources appear, the UE further selects resources for the remaining five retransmissions and will send them in the next SCI regarding the new reservation.

[0057] Finding 2 Without restrictions on resource reservation interval selection, HARQ retransmissions for periodic MAC PDUs can collide.

[0058] Therefore, when a reservation is activated, the physical shared control channel (PSCCH) for resource reservation is transmitted in the resources considered to be idle. When a surrounding UE wishes to transmit, the UE first detects and decodes the PSCCH for resource reservation and avoids selecting the resources indicated in the PSCCH for its own transmission so as to avoid collisions. Detection can be seen to be the basis for making the reservation actually useful. When the UE selects resources for its own transmission, the UE will ignore whether the resources are reserved or not, so without detection, it is useless to have reservations for both the initial transmission and retransmissions.

[0059] Finding 3 Without detection, it is useless to have reservations for both the initial transmission and retransmissions.

[0060] On the other hand, in some cases, the detection function is not available. For example, in an exceptional resource pool, only random resource selection is supported, and in the resource pool used for V2X communication, it can be set such that only random resource selection is possible. Therefore, resource reservations for pools where detection is not supported or not enabled should be deactivated.

[0061] For a connected UE that adopts either Mode 1 RA or Mode 2 RA, the NW can set up a dedicated and exclusive Tx resource pool for that UE. In this case, and in the case of Mode 2 RA, the UE knows which resources in the resource pool are available and can select a collision-free resource for (re)transmission without detection. Of course, in this case as well, no reservation is required.

[0062] Finding 4 Resource reservation is not required in a dedicated and exclusive resource pool for a specific UE.

[0063] Another aspect worth discussing is whether / how to support resource reservation for initial transmission. In R1-1908913, "Resource allocation for Mode-2 transmissions", Ericsson, 3GPP Ran1#98 meeting, Prague, October 2019, a method for enabling reservation for initial transmission has been proposed. On the other hand, when the service requires extremely low latency, it may be too late to use reserved resources. In fact, the reservation for initial transmission will add delay to the transmission of the TB. However, in the case of latency-critical, the delay of the TB transmission must be minimized. Considering this, for services with a required latency below a certain level, the resource reservation for initial transmission can be disabled.

[0064] Finding 5 When the service requires extremely low latency, it may be too late to use reserved resources for initial transmission.

[0065] In the 3GPP RAN2#106 meeting, it was confirmed that only a single carrier is assumed for SL transmission in Release 16. However, whether one carrier can be set up in a single resource pool or in multiple resource pools remains unresolved. Agreement on RAN2#106 / LCP: 1: In Release 16, since only a single carrier is used for SL transmission, RAN2 assumes that the mapping restriction between SCS and sidelink LCH in the SL LCP procedure should not be considered.

[0066] Finding 6 It is unclear whether multiple resource pools can be configured within a single carrier for SL transmission.

[0067] In another aspect, NR SL supports different HARQ configurations, and the transmitted TB may require ACK / NACK feedback, NACK-only feedback, or no feedback at all. Sending HARQ feedback must use the PSFCH resources configured in the same resource pool as agreed in the 3GPP RAN1#96bis meeting presented below. Therefore, the selection of the resource pool must consider whether the resource pool can support the required HARQ procedure. RAN1#96bis meeting / agreement: · It is supported that within a resource pool, within the slots related to the resource pool, the PSFCH resources can be periodically (pre-)configured for a period of N slots. ○ N can be set to the following values · 1 · At least one other value > 1 · FFS details ○ The configuration should also include the possibility of no resources for PSFCH. In this case, HARQ feedback for all transmissions in the resource pool is disabled.

[0068] HARQ feedback for transmissions in a resource pool can only be sent on the PSFCH in the same resource pool.

[0069] To enable the 7 HARQ feedback transmission, the selected resource pool shall be configured with PSFCH resources.

[0070] In mode 1, when the gNB allocates an SL grant to the UE, the resource pool selection is implicitly considered, and it is indicated in the DCI whether a given SL grant expects HARQ feedback, as proposed in R2-1915272, Support on HARQ procedure over sidelink, 3GPP TSG RAN2 meeting #108, November 2019.

[0071] In mode 2, the UE shall autonomously select resources for transmission, which can be configured among multiple transmission pools. As described above, the transmission pool may or may not be configured with feedback PHY resources (i.e., PSFCH resources). Therefore, the UE shall first select a pool. The pool selection may be restricted by at least the HARQ mode required for transmission. Once the pool is selected, the resource allocation procedure determines the resources to be used for transmission. In this way, by appropriately selecting the pool and the resources within that pool, the resulting grant is suitable for requesting SL HARQ feedback if necessary. Exemplary restrictions may be as follows. · For SL transmissions triggered by data requiring HARQ feedback, a resource pool with PSFCH resources is selected. · For SL transmissions triggered by data not requiring HARQ feedback, any resource pool may be selected.

[0072] Observation 8 To obtain a mode 2 grant, the UE shall first select a pool and then apply the resource allocation procedure to the selected pool.

[0073] RAN2 discusses the mode 2 pool selection restrictions, at least for the HARQ mode required for transmission. a. In SL transmission triggered by data that requires HARQ feedback, a resource pool with PSFCH resources is selected. b. In SL transmission triggered by data that does not require HARQ feedback, any resource pool can be selected.

[0074] The following findings were made in the above discussion. · Finding 1 The UE behavior in the case of insufficient resources for the required HARQ retransmission is unclear. · Finding 2 Without restrictions on resource reservation interval selection, HARQ retransmissions for periodic MAC PDUs can collide. · Finding 3 Without detection, it is unnecessary to have reservations for both initial transmission and retransmission. · Finding 4 Resource reservation in a dedicated and exclusive resource pool for a specific UE is not necessary. · Finding 5 When the service requires extremely low latency, it may be too late to use reserved resources for the initial transmission. · Finding 6 It is unclear whether multiple resource pools can be set in a single carrier for SL transmission. · Finding 7 To enable HARQ feedback transmission, the selected resource pool must be set with PSFCH resources. · Finding 8 To obtain a mode 2 grant, the UE first selects a pool and then applies the resource allocation procedure to the selected pool.

[0075] Based on the description in this specification and the above findings, the inventors proposed the following invention concepts. · Proposal 1 RAN2 discusses the UE behavior in the case of insufficient resources for the required number of HARQ retransmissions, considering the following alternatives. a. Do not select resources for HARQ retransmission b. Select as many resources as possible for HARQ retransmission · Proposal 2 The selected resource reservation interval is larger than the selection window duration, i.e., T2 - T1. · Proposal 3 Resource reservation for the pool where detection is not used, i.e., the exceptional pool, should be invalidated. · Proposal 4 For services that require low latency, resource reservation for the initial transmission can be invalidated. · Proposal 5 RAN2 should discuss at least the mode 2 pool selection restrictions according to the HARQ mode required for transmission. a. In SL transmission triggered by data that requires HARQ feedback, a resource pool with PSFCH resources is selected. b. In SL transmission triggered by data that does not require HARQ feedback, any resource pool can be selected.

[0076] Next, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) is described with reference to the flowchart of FIG. 8 according to some embodiments of the inventive concept. For example, modules can be stored in the memory 305 of FIG. 7, and these modules can provide instructions such that when the instructions of the modules are executed by their respective communication device processing circuits 303, the processing circuit 303 performs each operation of the flowchart.

[0077] In block 8011, the processing circuit 303 selects a resource (e.g., a slot) within a resource selection window (also called a scheduling window) for the initial transmission of a first medium access control (MAC) protocol data unit (PDU) among a plurality of periodic MAC PDUs to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (e.g., a sidelink SL). According to some embodiments of FIG. 8, the resource selection window is indicated from the physical protocol layer of the first communication device.

[0078] In block 8031, the processing circuit 303 selects a period (P) for the periodic transmission of the plurality of periodic MAC PDUs such that the initial transmission of all MAC PDUs of the plurality of periodic MAC PDUs other than the first MAC PDU is performed in a resource after the resource selection window.

[0079] According to some embodiments of FIG. 8, the period (P) is at least as long as the duration of the resource selection window. According to some other embodiments of FIG. 8, the resource selection window is defined by a first slot having a first slot number (T1) and a second slot having a second slot number (T2) greater than the first slot number, and the period (P) is defined by the number of slots greater than the difference (T2 - T1) between the second slot number and the first slot number. According to still other embodiments of FIG. 8, the resource selection window is defined by a first slot having a first slot number (T1) and a second slot having a second slot number (T2) greater than the first slot number, and the period (P) is defined by the number of slots at least as large as the second slot number (T2).

[0080] Next, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) will be described with reference to the flowchart of FIG. 9 according to some embodiments of the inventive concept. For example, modules may be stored in the memory 305 of FIG. 7, and these modules may provide instructions such that when the instructions of the modules are executed by their respective communication device processing circuits 303, the processing circuit 303 performs each operation of the flowchart.

[0081] In block 9011, the processing circuit 303 selects a resource (e.g., a slot) for the initial transmission of a first media access control (MAC) protocol data unit (PDU) among a plurality of periodic MAC protocol data units (PDUs) to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (e.g., a sidelink SL).

[0082] In block 9031, the processing circuit 303 selects a period for the periodic transmission of a plurality of periodic MAC PDUs such that a resource (e.g., a slot) for the initial transmission of a second MAC PDU among the plurality of periodic MAC PDUs is determined based on the period.

[0083] In block 9051, the processing circuit 303 selects a plurality of resources (e.g., slots) for the retransmission of the first MAC PDU such that all retransmissions of the first MAC PDU are performed before the resource for the initial transmission of the second MAC PDU.

[0084] According to some embodiments of FIG. 9, the resource for the initial transmission of the first MAC PDU and the resource for the initial transmission of the second MAC PDU are included in the same resource selection window (also referred to as a scheduling window) indicated from the physical protocol layer of the first communication device.

[0085] Next, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) will be described with reference to the flowchart of FIG. 10 according to some embodiments of the inventive concept. For example, modules may be stored in the memory 305 of FIG. 7, and these modules may provide instructions such that when the instructions of the modules are executed by their respective communication device processing circuits 303, the processing circuit 303 performs each operation of the flowchart.

[0086] In block 10011, the processing circuit 303 selects respective resources (e.g., slots) for the initial transmission of a plurality of MAC PDUs to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a D2D (device-to-device) link (e.g., sidelink SL).

[0087] In block 10031, after the processing circuit 303 selects respective resources for the initial transmission of the plurality of MAC PDUs, it determines whether sufficient resources are available for the first retransmission of the first MAC PDU among the plurality of MAC PDUs.

[0088] In block 10051, in response to determining that sufficient resources are available for the first retransmission of the first MAC PDU, the processing circuit 303 selects respective resources (e.g., slots) for the first retransmission of the plurality of MAC PDUs.

[0089] According to some embodiments of FIG. 10, selecting respective resources for the initial transmission of a plurality of MAC PDUs may include selecting resources (e.g., slots) within a scheduling window for the initial transmission of the first MAC PDU, and determining whether sufficient resources are available for the first retransmission of the first MAC PDU may include determining whether sufficient resources within a scheduling window for the first retransmission of the first MAC PDU are available.

[0090] According to some embodiments of FIG. 10, the plurality of MAC PDUs can be a plurality of periodic MAC PDUs, and selecting each resource can include selecting each resource based on the transmission period for the plurality of periodic MAC PDUs.

[0091] Next, with reference to the flowchart of FIG. 11 according to some embodiments of the inventive concept, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) is described. For example, modules can be stored in the memory 305 of FIG. 7, and these modules can provide instructions such that when the instructions of the modules are executed by the respective communication device processing circuits 303, the processing circuit 303 performs each operation of the flowchart.

[0092] In block 11011, the processing circuit 303 selects a resource (e.g., a slot) within a resource selection window (also referred to as a scheduling window) for the initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (e.g., a sidelink SL). Moreover, the first communication device is set to provide up to N retransmissions for the MAC PDU, where N is greater than 0. According to some embodiments of FIG. 11, the resource selection window can be indicated from the physical protocol layer of the first communication device.

[0093] In block 11031, after the processing circuit 303 selects a resource within the resource selection window for the initial transmission of the MAC PDU, it determines whether sufficient resources are available for N retransmissions of the MAC PDU within the resource selection window.

[0094] In block 11051, in response to determining that there are not enough resources available for N retransmissions of the MAC PDU in the resource selection window, the processing circuit 303 blocks all retransmissions of the MAC PDU.

[0095] Next, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) will be described with reference to the flowchart of FIG. 12, according to some embodiments of the inventive concept. For example, modules may be stored in the memory 305 of FIG. 7, and these modules may provide instructions such that when the instructions of the modules are executed by their respective communication device processing circuits 303, the processing circuit 303 performs each operation of the flowchart.

[0096] In block 12011, the processing circuit 303 selects resources (e.g., slots) within a resource selection window (also referred to as a scheduling window) for an initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (e.g., a sidelink SL), where the first communication device is configured to provide up to N retransmissions for the MAC PDU, and where N is greater than 0.

[0097] In block 12031, after selecting resources within the resource selection window for the initial transmission of the MAC PDU, the processing circuit 303 determines that there are resources available for only M retransmissions of the MAC PDU in the resource selection window, where M is less than N and M is greater than 0.

[0098] In block 12051, in response to determining that there are resources available for only M retransmissions of the MAC PDU in the resource selection window, the processing circuit 303 limits the retransmissions of the MAC PDU to M retransmissions.

[0099] According to some embodiments of FIG. 12, a resource selection window is indicated from the physical protocol layer of the first communication device.

[0100] Next, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) is described with reference to the flowchart of FIG. 13 according to some embodiments of the inventive concept. For example, modules may be stored in the memory 305 of FIG. 7, and these modules may provide instructions such that when the instructions of the modules are executed by their respective communication device processing circuits 303, the processing circuit 303 performs each operation of the flowchart.

[0101] In block 13011, the processing circuit 303 selects a resource (e.g., a slot) within a resource selection window (also referred to as a scheduling window) for the initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a D2D (device-to-device) link (e.g., a sidelink SL). The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0. According to some embodiments of FIG. 13, a resource selection window is indicated from the physical protocol layer of the first communication device.

[0102] In block 13021, after the processing circuit 303 selects a resource within the resource selection window for the initial transmission of the MAC PDU, it determines that resources are available only for M retransmissions of the MAC PDU within the resource selection window, where M is less than N and M is greater than 0.

[0103] In block 13031, in response to determining that resources are available for only M retransmissions of the MAC PDU in the resource selection window, the processing circuit 303 selects M resources (e.g., slots) of the resource selection window for retransmission of the MAC PDU.

[0104] In block 13041, the processing circuit 303 transmits each retransmission of the MAC PDU within each of the M slots of the resource selection window.

[0105] In block 13051, the processing circuit 303 selects N - M resources (e.g., slots) after the resource selection window for retransmission of the MAC PDU.

[0106] In block 13061, the processing circuit 303 transmits a retransmission of the MAC PDU in at least one of the N - M resources after the resource selection window.

[0107] According to some embodiments of FIG. 13, each retransmission of the MAC PDU may be transmitted within each of the M resources of the resource selection window in response to each NACK received from the second communication device, and the retransmission of the MAC PDU may be retransmitted in at least one of the N - M resources in response to each NACK received from the second communication device after transmitting each retransmission of the MAC PDU within each of the M resources.

[0108] Next, the operation of the communication device 300 (implemented using the block diagram structure of FIG. 7) will be described with reference to the flowchart of FIG. 14 according to some embodiments of the inventive concept. For example, modules may be stored in the memory 305 of FIG. 7, and these modules may provide instructions such that when the instructions of the modules are executed by the respective communication device processing circuit 303, the processing circuit 303 performs each operation of the flowchart.

[0109] In block 14011, the processing circuit 303 selects a resource (e.g., a slot) within a resource selection window (also referred to as a scheduling window) for the initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (e.g., a sidelink SL). The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0. According to some embodiments of FIG. 14, the resource selection window is indicated from the physical protocol layer of the first communication device.

[0110] In block 14021, after the processing circuit 303 selects a resource within the resource selection window for the initial transmission of the MAC PDU, it determines that resources are available only for M retransmissions of the MAC PDU within the resource selection window, where M is less than N and M is greater than 0.

[0111] In block 14031, in response to determining that resources are available only for M retransmissions of the MAC PDU within the resource selection window, the processing circuit 303 selects M resources (e.g., slots) of the resource selection window for retransmission of the MAC PDU.

[0112] According to some embodiments of this specification, a resource may include one slot or multiple slots, and / or a MAC PDU may be a transport block.

[0113] Exemplary embodiments are described below. 1. A method of operating a first communication device (TX UE), the method comprising: Selecting a resource within a resource selection window for an initial transmission of a first Medium Access Control (MAC) protocol data unit (PDU) among a plurality of periodic MAC PDUs to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (8011); Selecting a period (P) for the periodic transmission of the plurality of periodic MAC PDUs such that initial transmissions of all MAC PDUs of the plurality of periodic MAC PDUs other than the first MAC PDU are made in resources after the resource selection window (8031); A method comprising the above. 2. The method according to Embodiment 1, wherein the resource comprises at least one slot. 3. The method according to Embodiment 1 or 2, wherein the period (P) is at least as long as the duration of the resource selection window. 4. The method according to Embodiment 1 or 2, wherein the resource selection window is defined by a first slot having a first slot number (T1) and a second slot having a second slot number (T2) greater than the first slot number, and the period (P) is defined by the number of slots greater than the difference (T2 - T1) between the second slot number and the first slot number. 5. The method according to Embodiment 1 or 2, wherein the resource selection window is defined by a first slot having a first slot number (T1) and a second slot having a second slot number (T2) greater than the first slot number, and the period (P) is defined by the number of slots at least as large as the second slot number (T2). 6. Transmitting an initial transmission of the first MAC PDU to the second communication device via the D2D link using the resource selected within the resource selection window The method according to any one of Embodiments 1 to 5, further comprising the above. 7. Transmitting sidelink control information (SCI) indicating an initial transmission of a first MAC PDU to a second communication device via a D2D link, wherein the SCI indicates use of a resource selected within a resource selection window The method according to any one of Embodiments 1 to 6, further comprising. 8. Selecting a resource after a resource selection window for an initial transmission of a second MAC PDU among a plurality of periodic MAC PDUs, wherein the resource after the resource selection window is selected based on a period Using the resource after the resource selection window to transmit an initial transmission of a second MAC PDU among a plurality of periodic MAC PDUs via a D2D link The method according to any one of Embodiments 1 to 7, further comprising. 9. Selecting a plurality of resources for a retransmission of a first MAC PDU within a resource selection window Using a first resource among the plurality of resources for retransmission to transmit a retransmission of the first MAC PDU to a second communication device via a D2D link The method according to any one of Embodiments 1 to 8, further comprising. 10. Receiving a NACK from a second communication device, wherein the NACK corresponds to an initial transmission of a first MAC PDU In response to receiving the NACK, selecting a resource for a retransmission of the first MAC PDU within a resource selection window Using the resource selected for a retransmission of the first MAC PDU within the resource selection window to transmit a retransmission of the MAC PDU to a second communication device via a D2D link The method according to any one of Embodiments 1 to 8, further comprising. 11. The method according to any one of embodiments 6 to 10, wherein all resources for retransmission of the first MAC PDU are restricted to a resource selection window. 12. The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0, and the method comprises: after selecting a resource within a resource selection window for an initial transmission of the first MAC PDU, determining whether sufficient resources are available for N retransmissions of the first MAC PDU within the resource selection window; in response to determining that sufficient resources are not available for N retransmissions of the first MAC PDU within the resource selection window, blocking all retransmissions of the first MAC PDU The method according to any one of embodiments 1 to 8, further comprising. 13. The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0, and the method comprises: after selecting a resource within a resource selection window for an initial transmission of the first MAC PDU, determining that resources are available only for M retransmissions of the first MAC PDU within the resource selection window, where M is less than N and M is greater than 0; in response to determining that resources are available only for M retransmissions of the first MAC PDU within the resource selection window, limiting the retransmissions of the first MAC PDU to M retransmissions The method according to any one of embodiments 1 to 8, further comprising. 14. The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0, and the method comprises: After selecting a resource within a resource selection window for an initial transmission of a first MAC PDU, determining that resources are available only for M retransmissions of the first MAC PDU in the resource selection window, where M is less than N and M is greater than 0, In response to determining that resources are available only for M retransmissions of the first MAC PDU in the resource selection window, selecting M resources of the resource selection window for retransmission of the first MAC PDU The method according to any one of Embodiments 1 to 8, further comprising 15. Transmitting at least one retransmission of the first MAC PDU in at least one of the M resources of the resource selection window The method according to Embodiment 14, further comprising 16. The method according to Embodiment 15, wherein at least one retransmission of the first MAC PDU is transmitted in response to a NACK received from a second communication device. 17. Transmitting each retransmission of the first MAC PDU in each of the M resources of the resource selection window, Selecting N - M resources that occur after the resource selection window for retransmission of the first MAC PDU, Transmitting a retransmission of the first MAC PDU in at least one of the N - M resources after the resource selection window The method according to Embodiment 14, further comprising 18. The method according to Embodiment 17, wherein the N - M resources are selected after transmitting each retransmission of the first MAC PDU in each of the M resources of the resource selection window. 19. The method according to Embodiment 17 or 18, wherein the N - M resources are selected after selecting the M resources. 20. Each retransmission of the first MAC PDU is transmitted in each of M resources in response to each NACK received from the second communication device, and after transmitting each retransmission of the first MAC PDU in each of the M slots, each retransmission of the first MAC PDU is transmitted in at least one of the N-M resources in response to each NACK received from the second communication device, the method according to any one of embodiments 17 to 19. 21. The method according to any one of embodiments 1 to 20, wherein the resource selection window is indicated by the physical protocol layer of the first communication device. 22. The method according to any one of embodiments 1 to 21, wherein the D2D link is a sidelink (SL). 23. A method of operating a first communication device (TX UE), the method comprising: selecting (9011) a resource for an initial transmission of a first media access control (MAC) protocol data unit (PDU) among a plurality of periodic MAC PDUs to be transmitted by the first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link; selecting (9031) a period for periodic transmission of the plurality of periodic MAC PDUs such that a resource for an initial transmission of a second MAC PDU among the plurality of periodic MAC PDUs is determined based on the period; selecting (9051) a plurality of resources for retransmission of the first MAC PDU such that all retransmissions of the first MAC PDU are performed before a resource for an initial transmission of the second MAC PDU; and the method comprising. 24. The method according to embodiment 23, wherein the resource comprises at least one slot. 25. transmitting an initial transmission of the first MAC PDU to the second communication device via the D2D link using the resource selected for the initial transmission of the first MAC PDU The method according to embodiment 23 or 24, further comprising. 26. Transmitting sidelink control information (SCI) indicating an initial transmission of a first MAC PDU to a second communication device via a D2D link, wherein the SCI indicates use of a resource selected for the initial transmission of the first MAC PDU The method according to any one of embodiments 23 to 25, further comprising 27. The method is Transmitting an initial transmission of a second MAC PDU among a plurality of periodic MAC PDUs via a D2D link using a resource for the initial transmission of the second MAC PDU The method according to any one of embodiments 23 to 26, further comprising 28. The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0, and the method is After selecting a resource for an initial transmission of a first MAC PDU, determining whether sufficient resources are available for N retransmissions of the first MAC PDU before a resource for an initial transmission of a second MAC PDU Blocking all retransmissions of the first MAC PDU in response to determining that sufficient resources are not available for N retransmissions of the first MAC PDU before a resource for an initial transmission of a second MAC PDU The method according to any one of embodiments 23 to 27, further comprising 29. The first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0, and the method is After selecting a resource for an initial transmission of a first MAC PDU, determining that resources are available only for M retransmissions of the first MAC PDU before a resource for an initial transmission of a second MAC PDU In response to determining that resources are available only for M retransmissions of a first MAC PDU before resources for an initial transmission of a second MAC PDU, limiting retransmissions of the first MAC PDU to M retransmissions The method according to any one of Embodiments 23 to 27, further comprising. 30. A first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, where N is greater than 0, and the method comprises: After selecting resources for an initial transmission of a first MAC PDU, determining that resources are available only for M retransmissions of the first MAC PDU before resources for an initial transmission of a second MAC PDU, where M is less than N and M is greater than 0; In response to determining that resources are available only for M retransmissions of the first MAC PDU before resources for an initial transmission of the second MAC PDU, selecting M resources before the resources for the initial transmission of the second MAC PDU for retransmission of the first MAC PDU The method according to any one of Embodiments 23 to 27, further comprising. 31. In response to receiving a NACK from a second communication device, transmitting a retransmission of the first MAC PDU to the second communication device via a D2D link using a first resource among a plurality of resources for retransmission The method according to any one of Embodiments 23 to 30, further comprising. 32. The method according to any one of Embodiments 23 to 31, wherein resources for an initial transmission of a first MAC PDU and resources for an initial transmission of a second MAC PDU are included in the same resource selection window. 33. The method according to Embodiment 32, wherein the resource selection window is indicated by a physical protocol layer of the first communication device. 34. The method according to any one of Embodiments 23 to 33, wherein the D2D link is a sidelink (SL). 35. A method for operating a first communication device (TX UE), the method comprising: selecting (10011) respective resources for an initial transmission of a plurality of MAC PDUs to be transmitted by the first communication device (TX UE) to a second communication device (RX UE) via a D2D (device-to-device) link; after selecting respective resources for an initial transmission of the plurality of MAC PDUs, determining (10031) whether sufficient resources are available for a first retransmission of a first MAC PDU among the plurality of MAC PDUs; in response to determining that sufficient resources are available for a first retransmission of the first MAC PDU, selecting (10051) respective resources for a first retransmission of the plurality of MAC PDUs; and a method as described above. 36. The method according to embodiment 35, wherein each of the respective resources comprises at least one slot. 37. after selecting respective resources for a first retransmission of the plurality of MAC PDUs, determining whether sufficient resources are available for a second retransmission of a first MAC PDU among the plurality of MAC PDUs; and in response to determining that sufficient resources are not available for a second retransmission of the first MAC PDU, limiting retransmissions for the plurality of MAC PDUs to only one retransmission; and The method according to embodiment 35 or 36, further comprising the above steps. 38. after selecting respective resources for a first retransmission of the plurality of MAC PDUs, determining whether sufficient resources are available for a second retransmission of a first MAC PDU among the plurality of MAC PDUs; and in response to determining that sufficient resources are not available for a second retransmission of the first MAC PDU, blocking all retransmissions for the plurality of MAC PDUs; and The method according to embodiment 35 or 36, further comprising 39. Selecting respective resources for initial transmission of a plurality of MAC PDUs includes selecting resources within a scheduling window for initial transmission of a first MAC PDU, and determining whether sufficient resources are available for a first retransmission of the first MAC PDU includes determining whether sufficient resources within a scheduling window for the first retransmission of the first MAC PDU are available, and determining whether sufficient resources are available for a second retransmission of the first MAC PDU includes determining whether sufficient resources within a scheduling window for the second retransmission of the first MAC PDU are available. The method according to embodiment 37 or 38. 40. Selecting respective resources for initial transmission of a plurality of MAC PDUs includes selecting resources within a scheduling window for initial transmission of a first MAC PDU, and determining whether sufficient resources are available for a first retransmission of the first MAC PDU includes determining whether sufficient resources within a scheduling window for the first retransmission of the first MAC PDU are available. The method according to any one of embodiments 35 to 38. 41. The method according to any one of embodiments 35 to 40, wherein a first communication device is configured to provide up to N retransmissions for each of a plurality of MAC PDUs, and N is greater than 1. 42. Transmitting an initial transmission of a first MAC PDU to a second communication device via a D2D link using each resource selected for the first MAC PDU among a plurality of MAC PDUs The method according to any one of embodiments 35 to 41, further comprising 43. In response to receiving a NACK from the second communication device after the initial transmission of the first MAC PDU, transmitting a first retransmission of the first MAC PDU using respective resources for the first retransmission of the first MAC PDU among a plurality of MAC PDUs The method according to embodiment 42, further comprising. 44. In response to receiving a NACK from the second communication device after the first retransmission of the first MAC PDU, omitting further retransmissions of the first MAC PDU based on limiting the retransmission to only one retransmission The method according to embodiment 43, further comprising. 45. Transmitting sidelink control information (SCI) indicating an initial transmission of a first MAC PDU to a second communication device via a D2D link, the SCI indicating use of selected resources, transmitting sidelink control information (SCI) The method according to any one of embodiments 35 to 44, further comprising. 46. The method according to any one of embodiments 35 to 45, wherein the D2D link is a sidelink (SL). 47. The method according to any one of embodiments 35 to 46, wherein the plurality of MAC PDUs are a plurality of periodic MAC PDUs, and selecting respective resources includes selecting respective resources based on a transmission period for the plurality of periodic MAC PDUs. 48. A method of operating a first communication device (TX UE), the method comprising: Selecting (11011) a resource within a resource selection window for an initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by the first communication device (TX UE) to a second communication device (RX UE) via a D2D (device-to-device) link, the first communication device being configured to provide up to N retransmissions for the MAC PDU, where N is greater than 0, selecting (11011) a resource within the resource selection window; After selecting a resource within a resource selection window for an initial transmission of a MAC PDU, determining (11031) whether sufficient resources are available for N retransmissions of the MAC PDU within the resource selection window, and in response to determining that sufficient resources are not available for N retransmissions of the MAC PDU within the resource selection window, blocking all retransmissions of the MAC PDU (11051) and A method comprising. 49. The method according to embodiment 48, wherein the resource comprises at least one slot. 50. Transmitting an initial transmission of the MAC PDU to a second communication device via a D2D link using the resource selected within the resource selection window The method according to embodiment 48 or 49, further comprising. 51. Transmitting sidelink control information (SCI) indicating an initial transmission of the MAC PDU to a second communication device via a D2D link, the SCI indicating the use of the resource selected within the resource selection window, transmitting sidelink control information (SCI) The method according to any one of embodiments 48 to 50, further comprising. 52. The method according to any one of embodiments 48 to 51, wherein the resource selection window is indicated by a physical protocol layer of the first communication device. 53. The method according to any one of embodiments 48 to 52, wherein the D2D link is a sidelink (SL). 54. A method of operating a first communication device (TX UE), the method comprising Selecting a resource within a resource selection window for an initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by a first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link (12011), wherein the first communication device is configured to provide up to N retransmissions for the MAC PDU, and N is greater than 0, selecting a resource within the resource selection window (12011) After selecting a resource within the resource selection window for an initial transmission of a MAC PDU, determining that resources are available only for M retransmissions of the MAC PDU in the resource selection window (12031), wherein M is less than N and M is greater than 0, determining that resources are available (12031) In response to determining that resources are available only for M retransmissions of the MAC PDU in the resource selection window, limiting retransmissions of the MAC PDU to M retransmissions (12051) A method comprising the above. 55. The method according to embodiment 54, wherein the resource comprises at least one slot. 56. Transmitting an initial transmission of a MAC PDU to a second communication device via a D2D link using the resource selected within the resource selection window The method according to embodiment 54 or 55, further comprising the above. 57. Transmitting sidelink control information (SCI) indicating an initial transmission of a MAC PDU to a second communication device via a D2D link, wherein the SCI indicates the use of the resource selected within the resource selection window, transmitting sidelink control information (SCI) The method according to any one of embodiments 54 to 56, further comprising the above. 58. The method according to any one of embodiments 54 to 57, wherein the resource selection window is indicated by a physical protocol layer of the first communication device. 59. The method according to any one of embodiments 54 to 58, wherein the D2D link is a sidelink (SL). 60. A method of operating a first communication device (TX UE), the method comprising: selecting (13011) a resource within a resource selection window for an initial transmission of a media access control (MAC) protocol data unit (PDU) to be transmitted by the first communication device (TX UE) to a second communication device (RX UE) via a device-to-device (D2D) link, wherein the first communication device is configured to provide up to N retransmissions for each of a plurality of periodic MAC PDUs, and N is greater than 0; after selecting a resource within the resource selection window for an initial transmission of a MAC PDU, determining (13021) that resources are available only for M retransmissions of the MAC PDU in the resource selection window, where M is less than N and M is greater than 0; in response to determining that resources are available only for M retransmissions of the MAC PDU in the resource selection window, selecting (13031) M resources of the resource selection window for retransmission of the MAC PDU; and the method. 61. The method according to embodiment 60, wherein the resource comprises at least one slot, and each of the M resources comprises at least one slot. 62. transmitting at least one retransmission of the MAC PDU in at least one of the M resources of the resource selection window; The method according to embodiment 60 or 61, further comprising: 63. The method according to embodiment 62, wherein at least one retransmission of the MAC PDU is transmitted in response to a NACK received from the second communication device. 64. Transmitting each retransmission of the MAC PDU among each of the M resources of the resource selection window (13041); Selecting N - M resources after the resource selection window for retransmission of the MAC PDU (13051); Transmitting a retransmission of the MAC PDU in at least one of the N - M resources after the resource selection window (13061); The method according to embodiment 60 or 61, further comprising: 65. Each retransmission of the MAC PDU is transmitted in each of the M resources of the resource selection window in response to each NACK received from the second communication device, and after transmitting each retransmission of the MAC PDU in each of the M resources, each retransmission is transmitted in at least one of the N - M resources in response to each NACK received from the second communication device. The method according to embodiment 64. 66. The method according to embodiment 64 or 65, wherein the N - M resources are selected after transmitting each retransmission of the MAC PDU in each of the M resources of the resource selection window. 67. The method according to any one of embodiments 64 to 66, wherein the N - M resources are selected after selecting the M resources. 68. Transmitting an initial transmission of the MAC PDU to the second communication device via a D2D link using the resources selected within the resource selection window The method according to any one of embodiments 60 to 67, further comprising: 69. Transmitting sidelink control information (SCI) indicating an initial transmission of the MAC PDU to the second communication device via a D2D link, wherein the SCI indicates the use of the resources selected within the resource selection window. The method according to any one of embodiments 60 to 68, further comprising: 70. A method according to any one of embodiments 60 to 69, wherein the resource selection window is indicated from the physical protocol layer of the first communication device. 71. A method according to any one of embodiments 60 to 70, wherein the D2D link is a sidelink (SL). 72. A first communication device (300), comprising: a processor (303); a memory (305) coupled to the processor; wherein the memory includes instructions that, when executed by the processor, cause the first communication device to perform the operations according to any one of embodiments 1 to 71. The first communication device (300). 73. A communication device (300) adapted to perform according to any one of embodiments 1 to 71. 74. A computer program comprising program code to be executed by at least one processor (303) of a communication device (300), whereby execution of the program code causes the communication device (300) to perform the operations according to any one of embodiments 1 to 71. 75. A computer program product comprising a non-transitory storage medium including program code to be executed by at least one processor (303) of a communication device (300), whereby execution of the program code causes the communication device (300) to perform the operations according to any one of embodiments 1 to 71.

[0114] Explanations of various abbreviations / acronyms used in the present disclosure are provided below. Abbreviation Explanation 3GPP Third Generation Partnership Project 5G Fifth Generation ACK Acknowledgment ARQ Automatic Repeat reQuest CDMA Code Division Multiple Access C-ITS Cellular ITS (Intelligent Transport System) DCI Downlink Control Information D2D Device-to-Device eNB E-UTRAN Node B E-UTRAN Evolved UTRAN FFS Further Feasibility Study gNB gNode B in NR GSM Global System for Mobile Communications HARQ Hybrid Automatic Repeat reQuest IP Internet Protocol ITS Intelligent Transport System LCH Logical Channel Group LCP Link Control Protocol LTE Long Term Evolution MAC Media Access Control MDT Minimization of Drive Tests MSC Mobile Switching Center NACK Negative ACKnowledgement NR New Radio NW Network O&M Operation and Maintenance OEM Original Equipment Manufacturer PDB Packet Delay Budget PDU Packet Data Unit QoS Quality of Service RA Resource Allocation PSFCH Physical Sidelink Feedback Channel PSCCH Physical Sidelink Control Channel PSSCH Physical Sidelink Shared Channel PUSCH Physical Uplink Shared Channel PUCCH Physical Uplink Control Channel PHY Physical RA Resource Allocation RAN Radio Access Network RAT Radio Access Technology RNC Radio Network Controller RRC Radio Resource Control SA Scheduling Assignment SCI Sidelink Control Information SCS Subcarrier Spacing SL Sidelink TB Transport Block UE User Equipment UMTS Universal Mobile Telecommunication System UTRAN Universal Terrestrial Radio Access Network WCDMA Wideband CDMA WI Work Item WLAN Wireless Local Area Network V2X Vehicle-to-Everything

[0115] References are identified as follows. [1]TS 36.331,V15.5.1, “Radio Resource Control (RRC); Protocol specification (Release 15)” [2]R1-1908913, Resource allocation for Mode-2 transmissions, Ericsson, 3GPP RAN1#98 meeting, Prague, October 2019. [3]R2-1906495, Summary of 105bis#31 NR V2X Resource pool configuration and selection (ZTE) [4]R2-1915272, Support on HARQ procedure over sidelink, 3GPP TSG RAN2 Meeting #108, November 2019

[0116] Additional explanations are provided below.

[0117] Generally, all terms used in this specification should be interpreted according to their ordinary meanings in the relevant technical field, unless different meanings are clearly given and / or implied from the context in which the terms are used. All references to an element, apparatus, component, means, step, etc. should be construed openly as referring to at least one instance of that element, apparatus, component, means, step, etc., unless otherwise expressly stated. None of the steps of any method disclosed herein need to be performed in the exact order disclosed, unless the step is expressly described as following or preceding another step and / or it is implicit that the step must follow or precede another step. Any feature of any of the embodiments disclosed herein may, where appropriate, be applied to any other embodiment. Similarly, any advantage of any of the embodiments may be applied to any other embodiment, and vice versa. Other objects, features, and advantages of the enclosed embodiments will become apparent from the following description.

[0118] Next, some of the embodiments contemplated herein are described more fully with reference to the accompanying drawings. However, other embodiments are included within the scope of the subject matter disclosed herein, and the disclosed subject matter should not be construed as limited to only the embodiments described herein. Rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0119] FIG. 15 shows a wireless network according to some embodiments.

[0120] The subject matter described in this specification can be implemented in any suitable type of system using any suitable components, but the embodiments disclosed herein are described with respect to wireless networks such as the exemplary wireless network shown in FIG. 15. For simplicity, the wireless network of FIG. 15 only shows network 1506, network nodes 1560 and 1560b, and WDs (also called mobile terminals) 1510, 1510b, and 1510c. In practice, the wireless network can further include any additional elements suitable for supporting communication between wireless devices or between a wireless device and another communication device such as a landline phone, a service provider, or any other network node or end device. Among the components shown, network node 1560 and wireless device (WD) 1510 are illustrated with additional details. The wireless network can provide communication and other types of services to one or more wireless devices to facilitate access of the wireless devices to the wireless network and / or use of services provided by or via the wireless network.

[0121] A wireless network may comprise any type of communication, telecommunication, data, cellular, and / or wireless network, or other similar types of systems, and / or interface with them. In some embodiments, the wireless network may be configured to operate according to a particular standard or other type of predefined rules or procedures. Thus, particular embodiments of a wireless network may implement communication standards such as the pan-European digital cellular system (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, or 5G standards, wireless local area network (WLAN) standards such as IEEE 802.11 standards, and / or any other appropriate wireless communication standards such as Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, and / or ZigBee standards.

[0122] Network 1506 may comprise one or more backhaul networks, core networks, IP networks, public switched telephone networks (PSTN), packet data networks, optical networks, wide area networks (WAN), local area networks (LAN), wireless local area networks (WLAN), wired networks, wireless networks, metropolitan area networks, and other networks for enabling communication between devices.

[0123] Network nodes 1560 and WD 1510 include various components that are described in more detail below. These components cooperate to provide network node and / or wireless device functionality, such as providing a wireless connection in a wireless network. In different embodiments, the wireless network may include any number of wired or wireless networks, network nodes, base stations, controllers, wireless devices, relays, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals, whether via a wired connection or a wireless connection.

[0124] As used herein, a network node refers to a device that is configured, constructed, and / or operable to communicate directly or indirectly with a wireless device and / or with other network nodes or devices in a wireless network to enable and / or provide wireless access to the wireless device and / or to perform other functions (e.g., administration) in the wireless network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., wireless access points), base stations (BSs) (e.g., wireless base stations, Node B, evolved Node B (eNB), and NR Node B (gNB)). Base stations can be categorized based on the amount of coverage provided by the base station (or, alternatively, the transmission power level of the base station), in which case they may also be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station can be a relay node or a relay donor node that controls relays. A network node can also include one or more (or all) parts of a distributed radio base station, such as a centralized digital unit and / or a remote radio unit (RRU), sometimes referred to as a remote radio head (RRH). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may sometimes be referred to as nodes in a distributed antenna system (DAS). Further examples of network nodes include MSR devices such as multi-standard radio (MSR) BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multi-cast coordination entities (MCEs), core network nodes (e.g., MSC, MME), O&M nodes, OSS nodes, SON nodes, positioning nodes (e.g., E-SMLC), and / or MDT. As another example, a network node can be a virtual network node, as described in more detail below.However, more generally, a network node can represent any suitable device (or group of devices) that is configured, constructed, and / or operable to enable access to a wireless network and / or provide it to a wireless device, or provide some service to a wireless device that has accessed the wireless network.

[0125] In FIG. 15, network node 1560 includes a processing circuit 1570, a device-readable medium 1580, an interface 1590, auxiliary equipment 1584, a power source 1586, a power circuit 1587, and an antenna 1562. Network node 1560, shown in the exemplary wireless network of FIG. 15, can represent a device that includes the shown combination of hardware components, although other embodiments can include network nodes with different combinations of components. It should be understood that a network node can comprise any suitable combination of hardware and / or software required to implement the tasks, features, functions, and methods disclosed herein. Moreover, the components of network node 1560 are shown as a single box located within a larger box or as a single box nested within multiple boxes, but in reality, a network node can comprise multiple different physical components that make up a single shown component (e.g., device-readable medium 1580 can comprise multiple separate hard drives as well as multiple RAM modules).

[0126] Similarly, network node 1560 can be assembled from a plurality of physically distinct components (e.g., a Node B component and an RNC component, or a BTS component and a BSC component, etc.), each of which can have its own respective components. In some scenarios where network node 1560 comprises a plurality of distinct components (e.g., a BTS component and a BSC component), one or more of the distinct components can be shared among several network nodes. For example, a single RNC can control a plurality of Node Bs. In such scenarios, each unique pair of Node B and RNC can, in some cases, be regarded as a single distinct network node. In some embodiments, network node 1560 can be configured to support a plurality of radio access technologies (RATs). In such embodiments, some components can be replicated (e.g., separate device-readable media 1580 for different RATs), and some components can be reused (e.g., the same antenna 1562 can be shared by RATs). Network node 1560 can also include a plurality of sets of various illustrated components for different radio technologies, such as, for example, GSM, WCDMA, LTE, NR, WiFi, or Bluetooth radio technologies, integrated into network node 1560. These radio technologies can be integrated into the same or different chips or sets of chips, and other components within network node 1560.

[0127] The processing circuit 1570 is configured to perform any decision-making operation, computing operation, or similar operation (e.g., some acquisition operations) described herein as provided by the network node. These operations performed by the processing circuit 1570 may include processing the information obtained by the processing circuit 1570, for example, by converting the obtained information into other information, comparing the obtained information or the converted information with the information stored in the network node, and / or performing one or more operations based on the obtained information or the converted information and as a result of the decision made by the said processing.

[0128] The processing circuit 1570 can comprise a microprocessor, a controller, a microcontroller, a central processing unit, a digital signal processor, an application-specific integrated circuit, a field programmable gate array, or any other suitable computing device, one or more combinations of resources, or a combination of hardware, software and / or encoded logic, operable to provide the network node 1560 function either alone or in conjunction with other network node 1560 components such as the device-readable medium 1580. For example, the processing circuit 1570 can execute instructions stored in the device-readable medium 1580 or instructions stored in the memory within the processing circuit 1570. Such functions may include providing any of the various wireless features, functions, or benefits described herein. In some embodiments, the processing circuit 1570 may include a system-on-chip (SOC).

[0129] In some embodiments, processing circuit 1570 may include one or more of radio frequency (RF) transceiver circuit 1572 and baseband processing circuit 1574. In some embodiments, radio frequency (RF) transceiver circuit 1572 and baseband processing circuit 1574 may be on separate chips (or sets of chips), boards, or units such as a radio unit and a digital unit. In alternative embodiments, some or all of RF transceiver circuit 1572 and baseband processing circuit 1574 may be on the same chip or set of chips, board, or unit.

[0130] In some embodiments, some or all of the functions described herein as provided by a network node, base station, eNB or other such network device may be implemented by processing circuit 1570 executing instructions stored in device-readable medium 1580, or in the memory within processing circuit 1570. In alternative embodiments, some or all of the functions may be provided by processing circuit 1570 without executing instructions stored in a separate or discrete device-readable medium, such as in a hardwired manner. In any of those embodiments, whether or not executing instructions stored in a device-readable storage medium, processing circuit 1570 may be configured to implement the described functions. The benefits provided by such functions are not limited to processing circuit 1570 alone, or to other components of network node 1560, but are enjoyed generally by network node 1560 as a whole, and / or by end users and the wireless network.

[0131] Device-readable medium 1580 may include, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (e.g., hard disk), removable storage media (e.g., flash drive, compact disc (CD) or digital video disc (DVD)), any form of volatile or non-volatile computer-readable memory, and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory device that can store information, data, and / or instructions used by processing circuit 1570. Device-readable medium 1580 may store any suitable instructions, data or information, including an application that includes one or more of a computer program, software, logic, rules, code, tables, etc., and / or other instructions that can be executed by processing circuit 1570 and utilized by network node 1560. Device-readable medium 1580 may be used to store calculations performed by processing circuit 1570 and / or data received via interface 1590. In some embodiments, processing circuit 1570 and device-readable medium 1580 may be considered integrated.

[0132] Interface 1590 is used for wired or wireless communication of signaling and / or data between the network node 1560, network 1506, and / or WD 1510. As shown, interface 1590 includes (one or more) ports / (one or more) terminals 1594 for sending and receiving data to and from network 1506, for example, over a wired connection. Interface 1590 also includes a radio front-end circuit 1592 that is coupled to antenna 1562 or, in some embodiments, can be part of antenna 1562. The radio front-end circuit 1592 includes a filter 1598 and an amplifier 1596. The radio front-end circuit 1592 can be connected to antenna 1562 and processing circuit 1570. The radio front-end circuit can be configured to condition signals communicated between antenna 1562 and processing circuit 1570. The radio front-end circuit 1592 can receive digital data to be sent to other network nodes or WDs via a wireless connection. The radio front-end circuit 1592 can convert the digital data into a wireless signal having appropriate channel and bandwidth parameters using a combination of filter 1598 and / or amplifier 1596. The wireless signal can then be transmitted via antenna 1562. Similarly, when receiving data, antenna 1562 can collect the wireless signal, which is then converted into digital data by radio front-end circuit 1592. The digital data can be passed to processing circuit 1570. In other embodiments, the interface can comprise different components and / or different combinations of components.

[0133] In some alternative embodiments, network node 1560 may not include a separate radio front-end circuit 1592. Instead, processing circuit 1570 may comprise a radio front-end circuit and may be connected to antenna 1562 without a separate radio front-end circuit 1592. Similarly, in some embodiments, all or part of RF transceiver circuit 1572 may be regarded as part of interface 1590. In still other embodiments, interface 1590 may include one or more ports or terminals 1594, radio front-end circuit 1592, and RF transceiver circuit 1572 as part of a wireless unit (not shown), and interface 1590 may communicate with baseband processing circuit 1574, which is part of a digital unit (not shown).

[0134] Antenna 1562 may include one or more antennas or antenna arrays configured to transmit and / or receive wireless signals. Antenna 1562 may be coupled to radio front-end circuit 1592 and may be any type of antenna capable of wirelessly transmitting and receiving data and / or signals. In some embodiments, antenna 1562 may comprise one or more omnidirectional, sector, or panel antennas operable to transmit / receive wireless signals, for example, between 2 GHz and 66 GHz. Omnidirectional antennas may be used to transmit / receive wireless signals in any direction, sector antennas may be used to transmit / receive wireless signals from devices within a particular area, and panel antennas may be line-of-sight antennas used to transmit / receive wireless signals in a relatively straight line. In some cases, the use of two or more antennas may be referred to as MIMO. In some embodiments, antenna 1562 may be separate from network node 1560 and may be connectable to network node 1560 through an interface or port.

[0135] Antenna 1562, interface 1590, and / or processing circuit 1570 may be configured to perform any receiving operations and / or some acquisition operations described herein as being performed by a network node. Any information, data, and / or signals may be received from a wireless device, another network node, and / or any other network equipment. Similarly, antenna 1562, interface 1590, and / or processing circuit 1570 may be configured to perform any transmitting operations described herein as being performed by a network node. Any information, data, and / or signals may be transmitted to a wireless device, another network node, and / or any other network equipment.

[0136] Power circuit 1587 may comprise a power management circuit or be coupled to a power management circuit and is configured to supply power for implementing the functions described herein to the components of network node 1560. Power circuit 1587 may receive power from power source 1586. Power source 1586 and / or power circuit 1587 may be configured to provide power to the various components of network node 1560 in a form suitable for each respective component (e.g., at the voltage and current levels required for each respective component). Power source 1586 may be either included within power circuit 1587 and / or network node 1560 or external to power circuit 1587 and / or network node 1560. For example, network node 1560 may be connectable to an external power source (e.g., an electrical outlet) via an input circuit or interface such as an electrical cable, whereby the external power source supplies power to power circuit 1587. As a further example, power source 1586 may comprise a power source in the form of a battery or battery pack connected to or integrated within power circuit 1587. The battery may provide backup power in the event of a loss of external power. Other types of power sources, such as photovoltaic devices, may also be used.

[0137] An alternative embodiment of network node 1560 may be responsible for providing some aspects of the functionality of a network node, including any of the functions described herein and / or any of the functions necessary to support the subject matter described herein, and may include additional components other than those shown in FIG. 15. For example, network node 1560 may include user interface equipment for enabling input of information to network node 1560 and for enabling output of information from network node 1560. This may enable a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1560.

[0138] As used herein, a wireless device (WD) refers to a device that is configured, arranged, and / or operable to communicate wirelessly with a network node and / or another wireless device. Unless otherwise specified, the term WD may be used interchangeably with user equipment (UE) herein. Communicating wirelessly may involve transmitting and / or receiving a wireless signal using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information over the air. In some embodiments, a WD may be configured to transmit and / or receive information without direct human interaction. For example, a WD may be designed to transmit information to a network at a predetermined schedule when triggered by an internal or external event or in response to a request from the network. Examples of WDs include, but are not limited to, smartphones, mobile phones, cell phones, voice over IP (VoIP) phones, wireless local loop phones, desktop computers, personal digital assistants (PDAs), wireless cameras, gaming consoles or devices, music storage devices, playback appliances, wearable terminal devices, wireless endpoints, mobile stations, tablets, laptop computers, laptop embedded equipment (LEE), laptop-mounted equipment (LME), smart devices, wireless customer premise equipment (CPE), in-vehicle wireless terminal devices, etc. A WD may support device-to-device (D2D) communication, for example, by implementing 3GPP standards for sidelink communication, vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-everything (V2X), in which case it may be referred to as a D2D communication device. As another specific example, in an Internet of Things (IoT) scenario, a WD may represent a machine or other device that performs monitoring and / or measurement and transmits the results of such monitoring and / or measurement to another WD and / or a network node. In this case, the WD may be a machine-to-machine (M2M) device, and M2M devices may sometimes be referred to as machine type communication (MTC) devices in the 3GPP context.As one specific example, the WD can be a UE implementing the 3GPP narrowband Internet of Things (NB-IoT) standard. Specific examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or household or personal electrical appliances (such as refrigerators, televisions, etc.), personal wearables (such as watches, fitness trackers, etc.). In other scenarios, the WD can represent a vehicle or other equipment, and the vehicle or other equipment can monitor its operating status and / or report on its operating status, or other functions related to its operation are possible. The WD described above can represent an endpoint of a wireless connection, in which case the device may be called a wireless terminal. Further, the WD described above can be mobile, in which case the device may also be called a mobile device or a mobile terminal.

[0139] As shown, the wireless device 1510 includes an antenna 1511, an interface 1514, a processing circuit 1520, a device-readable medium 1530, a user interface device 1532, an auxiliary device 1534, a power supply 1536, and a power circuit 1537. The WD 1510 can include one or more sets of the shown components for different wireless technologies supported by the WD 1510, such as, by way of example only, GSM, WCDMA, LTE, NR, WiFi, WiMAX, or Bluetooth wireless technologies. These wireless technologies can be integrated into the same or different chips or sets of chips as other components within the WD 1510.

[0140] Antenna 1511 may include one or more antennas or antenna arrays configured to transmit and / or receive wireless signals and is connected to interface 1514. In some alternative embodiments, antenna 1511 is separate from WD 1510 and may be connectable to WD 1510 through an interface or port. Antenna 1511, interface 1514, and / or processing circuit 1520 may be configured to perform any of the receive operations or transmit operations described herein as being performed by the WD. Any information, data, and / or signals may be received from network nodes and / or another WD. In some embodiments, the radio front-end circuitry and / or antenna 1511 may be regarded as an interface.

[0141] As shown, interface 1514 includes a radio front-end circuit 1512 and an antenna 1511. The radio front-end circuit 1512 includes one or more filters 1518 and an amplifier 1516. The radio front-end circuit 1512 is connected to the antenna 1511 and the processing circuit 1520 and is configured to condition signals communicated between the antenna 1511 and the processing circuit 1520. The radio front-end circuit 1512 may be coupled to the antenna 1511 or may be part of the antenna 1511. In some embodiments, WD 1510 may not include a separate radio front-end circuit 1512. Instead, the processing circuit 1520 may include a radio front-end circuit and may be connected to the antenna 1511. Similarly, in some embodiments, some or all of the RF transceiver circuit 1522 may be considered part of the interface 1514. The radio front-end circuit 1512 may receive digital data to be sent to other network nodes or WDs via a wireless connection. The radio front-end circuit 1512 may convert the digital data into a wireless signal having appropriate channel and bandwidth parameters using a combination of filters 1518 and / or amplifier 1516. The wireless signal may then be transmitted via the antenna 1511. Similarly, when receiving data, the antenna 1511 may collect a wireless signal, which is then converted into digital data by the radio front-end circuit 1512. The digital data may be passed to the processing circuit 1520. In other embodiments, the interface may include different components and / or different combinations of components.

[0142] The processing circuit 1520 can be a microprocessor, a controller, a microcontroller, a central processing unit, a digital signal processor, an application specific integrated circuit, a field programmable gate array, or any other suitable computing device, resource, or a combination of one or more of them, or a combination of hardware, software, and / or encoded logic, which can operate alone or in combination with other WD1510 components such as the device-readable medium 1530 to provide the WD1510 functionality. Such functionality can include providing any of the various wireless features or benefits described herein. For example, the processing circuit 1520 can execute instructions stored in the device-readable medium 1530 or instructions stored in the memory within the processing circuit 1520 to provide the functionality disclosed herein.

[0143] As shown, processing circuit 1520 includes one or more of RF transceiver circuit 1522, baseband processing circuit 1524, and application processing circuit 1526. In other embodiments, the processing circuit may comprise different components and / or different combinations of components. In some embodiments, the processing circuit 1520 of WD 1510 may comprise a system-on-a-chip (SOC). In some embodiments, RF transceiver circuit 1522, baseband processing circuit 1524, and application processing circuit 1526 may be on separate chips or a set of chips. In an alternative embodiment, some or all of baseband processing circuit 1524 and application processing circuit 1526 may be combined to form one chip or a set of chips, and RF transceiver circuit 1522 may be on a separate chip or a set of chips. In yet another alternative embodiment, some or all of RF transceiver circuit 1522 and baseband processing circuit 1524 may be on the same chip or a set of chips, and application processing circuit 1526 may be on a separate chip or a set of chips. In still other alternative embodiments, some or all of RF transceiver circuit 1522, baseband processing circuit 1524, and application processing circuit 1526 may be combined within the same chip or a set of chips. In some embodiments, RF transceiver circuit 1522 may be part of interface 1514. RF transceiver circuit 1522 may condition RF signals for processing circuit 1520.

[0144] In some embodiments, some or all of the functions described herein as being performed by the WD may be provided by a processing circuit 1520 that executes instructions stored on a device-readable medium 1530, which in some embodiments may be a computer-readable storage medium. In alternative embodiments, some or all of the functions may be provided by the processing circuit 1520 without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hardwired fashion. In any of those particular embodiments, whether or not executing instructions stored on a device-readable storage medium, the processing circuit 1520 may be configured to perform the described functions. The benefits provided by such functions are enjoyed not limited to the processing circuit 1520 alone or other components of the WD1510, but rather by the WD1510 as a whole, and / or generally by the end user and the wireless network.

[0145] The processing circuit 1520 may be configured to perform any decision-making operation, computational operation, or similar operation (e.g., some acquisition operations) described herein as being performed by the WD. These operations as performed by the processing circuit 1520 may include processing the information acquired by the processing circuit 1520, e.g., by converting the acquired information into other information, comparing the acquired information or the converted information with information stored by the WD1510, and / or performing one or more operations based on the acquired information or the converted information and as a result of the processing having made a decision.

[0146] The device-readable medium 1530 can be operative to store an application that includes one or more of a computer program, software, logic, rules, code, tables, etc., and / or other instructions that can be executed by the processing circuit 1520. The device-readable medium 1530 can include a computer memory (e.g., random access memory (RAM) or read-only memory (ROM)), a mass storage medium (e.g., a hard disk), a removable storage medium (e.g., a compact disc (CD) or digital video disc (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory device that can store information, data, and / or instructions used by the processing circuit 1520. In some embodiments, the processing circuit 1520 and the device-readable medium 1530 can be considered to be integrated.

[0147] The user interface device 1532 may provide components that enable a human user to interact with the WD1510. Such interactions can be in many forms, such as visual, auditory, tactile, etc. The user interface device 1532 may be operable to produce output to the user and to enable the user to provide input to the WD1510. The type of interaction may vary depending on the type of user interface device 1532 installed on the WD1510. For example, if the WD1510 is a smartphone, the interaction may be via a touch screen, and if the WD1510 is a smart meter, the interaction may be through a screen that provides usage (e.g., the number of gallons used) or a speaker that provides an audible alarm (e.g., if smoke is detected). The user interface device 1532 may include an input interface, devices and circuits, as well as an output interface, devices and circuits. The user interface device 1532 is configured to enable the input of information to the WD1510 and is connected to the processing circuit 1520 to enable the processing circuit 1520 to process the input information. The user interface device 1532 may include, for example, a microphone, a proximity or other sensor, keys / buttons, a touch display, one or more cameras, a USB port, or other input circuits. The user interface device 1532 is also configured to enable the output of information from the WD1510 and to enable the processing circuit 1520 to output information from the WD1510. The user interface device 1532 may include, for example, a speaker, a display, a vibration circuit, a USB port, a headphone interface, or other output circuits. Using one or more input and output interfaces, devices, and circuits of the user interface device 1532, the WD1510 may communicate with an end user and / or a wireless network, enabling the end user and / or the wireless network to benefit from the functions described herein.

[0148] Auxiliary device 1534 is operable to provide more specific functions that may not generally be performed by the WD. This may include special sensors for performing measurements for various purposes, interfaces for additional types of communication such as wired communication, etc. The inclusion and type of components of the auxiliary device 1534 may vary depending on the embodiment and / or scenario.

[0149] Power source 1536 may, in some embodiments, be in the form of a battery or battery pack. Other types of power sources may also be used, such as an external power source (e.g., an electrical outlet), a photovoltaic device, or a battery. The WD 1510 may further include a power circuit 1537 for distributing power from the power source 1536 to various parts of the WD 1510 that require power to perform any of the functions described or indicated herein. The power circuit 1537 may, in some embodiments, include a power management circuit. The power circuit 1537 may alternatively or additionally be operable to receive power from an external power source, in which case the WD 1510 may be connectable to an external power source (such as an electrical outlet) via an input circuit or interface such as a power cable. The power circuit 1537 may also, in some embodiments, be operable to distribute power from an external power source to the power source 1536. This may be, for example, for charging the power source 1536. The power circuit 1537 may perform any formatting, conversion, or other modification on the power from the power source 1536 to make it suitable for each component of the WD 1510 to which the power is supplied.

[0150] FIG. 16 shows a user device according to some embodiments.

[0151] FIG. 16 shows an embodiment of a UE according to various aspects described herein. The user equipment or UE used herein does not necessarily have a user in the sense of a human user who owns and / or operates the associated device. Instead, the UE may represent a device (e.g., a smart sprinkler controller) that is intended for sale to or operation by a human user but may not be associated with a particular human user or may not initially be associated with a particular human user. Alternatively, the UE may represent a device (e.g., a smart power meter) that is not intended for sale to or operation by an end user but may be associated with a user or operated for the benefit of a user. UE16200 can be any UE identified by the Third Generation Partnership Project (3GPP), including an NB-IoT UE, a machine type communication (MTC) UE, and / or an extended MTC (eMTC) UE. The UE1600 shown in FIG. 16 is an example of a WD configured for communication according to one or more communication standards published by 3GPP, such as the GSM, UMTS, LTE, and / or 5G standards of the Third Generation Partnership Project (3GPP). As described above, the terms WD and UE may be used interchangeably. Thus, FIG. 16 shows a UE, but the components described herein are equally applicable to a WD and vice versa.

[0152] In FIG. 16, UE 1600 includes a processing circuit 1601 operatively coupled to an input / output interface 1605, a radio frequency (RF) interface 1609, a network connection interface 1611, a memory 1615 including a random access memory (RAM) 1617, a read-only memory (ROM) 1619, a storage medium 1621, etc., a communication subsystem 1631, a power supply 1613, and / or other components, or any combination thereof. The storage medium 1621 includes an operating system 1623, an application program 1625, and data 1627. In other embodiments, the storage medium 1621 may include other similar types of information. Some UEs may utilize all of the components shown in FIG. 16 or only a subset of those components. The level of integration between components may vary from UE to UE. Further, some UEs may include multiple instances of components such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0153] In FIG. 16, the processing circuit 1601 may be configured to process computer instructions and data. The processing circuit 1601 may be any sequential state machine operable to execute machine instructions stored in memory as a machine-readable computer program, such as one or more hardware-implemented state machines (e.g., in discrete logic, FPGA, ASIC, etc.), programmable logic together with appropriate firmware, a microprocessor or digital signal processor (DSP) together with appropriate software, one or more program embedded general-purpose processors, or any combination of the above. For example, the processing circuit 1601 may include two central processing units (CPUs). Data may be information in a form suitable for use by a computer.

[0154] In the illustrated embodiment, the input / output interface 1605 can be configured to provide a communication interface to an input device, an output device, or an input / output device. The UE 1600 can be configured to use an output device via the input / output interface 1605. The output device can use the same type of interface port as the input device. For example, a USB port can be used to provide input to and output from the UE 1600. The output device can be a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smart card, another output device, or any combination thereof. The UE 1600 can be configured to use an input device via the input / output interface 1605 to enable a user to capture information to the UE 1600. The input device can include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smart card, etc. The presence-sensitive display can include a capacitive or resistive touch sensor for detecting input from a user. The sensor can be, for example, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, another similar sensor, or any combination thereof. For example, the input device can be an accelerometer, a magnetometer, a digital camera, a microphone, and an optical sensor.

[0155] In FIG. 16, the RF interface 1609 can be configured to provide a communication interface to RF components such as a transmitter, a receiver, and an antenna. The network connection interface 1611 can be configured to provide a communication interface to the network 1643a. The network 1643a can include wired and / or wireless networks such as a local area network (LAN), a wide area network (WAN), a computer network, a wireless network, a communication network, another similar network, or any combination thereof. For example, the network 1643a can comprise a Wi-Fi network. The network connection interface 1611 can be configured to include a receiver and a transmitter interface used to communicate with one or more other devices on the communication network according to one or more communication protocols such as Ethernet, TCP / IP, SONET, ATM, etc. The network connection interface 1611 can implement receiver and transmitter functions suitable for a communication network link (e.g., optical, electrical, etc.). The transmitter and receiver functions can share circuit components, software, or firmware, or alternatively, can be implemented separately.

[0156] RAM 1617 can be configured to interface with the processing circuit 1601 via the bus 1602 to provide storage or caching of data or computer instructions during the execution of software programs such as an operating system, application programs, and device drivers. ROM 1619 can be configured to provide computer instructions or data to the processing circuit 1601. For example, ROM 1619 can be configured to store invariant low-level system code or data for basic system functions such as basic input / output (I / O), startup, or reception of keystrokes from a keyboard, which is stored in non-volatile memory. The storage medium 1621 can be configured to include memory such as RAM, ROM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk, optical disk, floppy disk, hard disk, removable cartridge, or flash drive. In one example, the storage medium 1621 can be configured to include an operating system 1623, an application program 1625 such as a web browser application, widget or gadget engine, or another application, and a data file 1627. The storage medium 1621 can store any of a variety of operating systems or combinations of operating systems for use by the UE 1600.

[0157] The memory medium 1621 can be configured to include several physical drive units, such as a redundant array of independent disks (RAID), a floppy disk drive, a flash memory, a USB flash drive, an external hard disk drive, a thumb drive, a pen drive, a key drive, a high-definition digital versatile disc (HD-DVD) optical disc drive, an internal hard disk drive, a Blu-Ray optical disc drive, a holographic digital data storage (HDDS) optical disc drive, an external mini dual in-line memory module (DIMM), a synchronous dynamic random access memory (SDRAM), an external micro DIMM SDRAM, a subscriber identity module or a removable user identity information (SIM / RUIM) module such as a smart card memory, other memories, or any combination thereof. The memory medium 1621 can enable the UE 1600 to access computer-executable instructions, application programs, etc. stored in a temporary or non-temporary memory medium, offload data, or upload data. A manufactured product such as a manufactured product using a communication system can be tangibly embodied in the memory medium 1621, and the memory medium 1621 can comprise a device-readable medium.

[0158] In FIG. 16, the processing circuit 1601 can be configured to communicate with the network 1643b using the communication subsystem 1631. The network 1643a and the network 1643b can be the same one or more networks or different one or more networks. The communication subsystem 1631 can be configured to include one or more transceivers used to communicate with the network 1643b. For example, the communication subsystem 1631 can be configured to include one or more transceivers for communicating with one or more remote transceivers of another WD, UE, or base station capable of wireless communication, such as another device in a radio access network (RAN) according to one or more communication protocols, such as IEEE802.11, CDMA, WCDMA, GSM, LTE, UTRAN, WiMax, etc. Each transceiver can include a transmitter 1633 and / or a receiver 1635 for implementing a transmitter function or a receiver function suitable for a RAN link (e.g., frequency allocation, etc.), respectively. Further, the transmitter 1633 and the receiver 1635 of each transceiver can share circuit components, software, or firmware, or alternatively, can be implemented separately.

[0159] In the illustrated embodiment, the communication functions of the communication subsystem 1631 can include data communication, voice communication, multimedia communication, short-range communication such as Bluetooth, near-field communication, location-based communication such as the use of the Global Positioning System (GPS) for determining location, other similar communication functions, or any combination thereof. For example, the communication subsystem 1631 can include cellular communication, Wi-Fi communication, Bluetooth communication, and GPS communication. The network 1643b can include wired and / or wireless networks such as a local area network (LAN), a wide area network (WAN), a computer network, a wireless network, a communication network, other similar networks, or any combination thereof. For example, the network 1643b can be a cellular network, a Wi-Fi network, and / or a near-field network. The power supply 1613 can be configured to provide alternating current (AC) or direct current (DC) power to the components of the UE 1600.

[0160] The features, benefits, and / or functions described herein can be implemented in one of the components of the UE 1600 or can be divided across multiple components of the UE 1600. Further, the features, benefits, and / or functions described herein can be implemented in any combination of hardware, software, or firmware. In one example, the communication subsystem 1631 can be configured to include any of the components described herein. Further, the processing circuitry 1601 can be configured to communicate with any of such components over the bus 1602. In another example, any of such components can be represented by program instructions stored in a memory that, when executed by the processing circuitry 1601, implement the corresponding functions described herein. In another example, the functions of any of such components can be divided between the processing circuitry 1601 and the communication subsystem 1631. In another example, the non-computation-intensive functions of any of such components can be implemented in software or firmware, and the computation-intensive functions can be implemented in hardware.

[0161] FIG. 17 shows a virtualized environment according to some embodiments.

[0162] FIG. 17 is a schematic block diagram showing a virtualized environment 1700 in which functions implemented according to some embodiments can be virtualized. In this context, virtualizing means creating a virtual version of a device or apparatus, which may include virtualizing a hardware platform, memory device, and networking resources. As used herein, virtualization can be applied to a node (e.g., a virtualized base station or a virtualized radio access node), or to a device (e.g., a UE, a wireless device, or any other type of communication device) or a component of that device, and at least a portion of the function is implemented as one or more virtual components (e.g., via one or more applications, components, functions, virtual machines, or containers running on one or more physical processing nodes in one or more networks).

[0163] In some embodiments, some or all of the functions described herein can be implemented as virtual components executed by one or more virtual machines hosted in one or more virtual environments 1700 hosted by one or more of the hardware nodes 1730. Further, in embodiments where the virtual node is not a radio access node or does not require wireless connectivity (e.g., a core network node), the network node can be fully virtualized.

[0164] The functionality may be implemented by one or more applications 1720 (alternatively, sometimes referred to as software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) that are operable to implement some of the features, functionality, and / or benefits of some of the embodiments disclosed herein. The application 1720 is operated in a virtualized environment 1700 that provides hardware 1730 comprising a processing circuit 1760 and a memory 1790. The memory 1790 includes instructions 1795 executable by the processing circuit 1760, whereby the application 1720 is operable to provide one or more of the features, benefits, and / or functionality disclosed herein.

[0165] The virtualized environment 1700 comprises a general-purpose or special-purpose network hardware device 1730 comprising a set of one or more processors or processing circuitry 1760, the set of one or more processors or processing circuitry 1760 being a commercially-off-the-shelf (COTS) processor, a dedicated application-specific integrated circuit (ASIC), or any other type of processing circuitry including digital or analog hardware components or dedicated processors. Each hardware device may comprise a memory 1790-1, the memory 1790-1 being a non-persistent memory for temporarily storing instructions 1795 or software executed by the processing circuitry 1760. Each hardware device may comprise one or more network interface controllers (NICs) 1770, also known as network interface cards, the network interface controller (NIC) 1770 including a physical network interface 1780. Each hardware device may also include a non-transitory, persistent, machine-readable storage medium 1790-2 storing software 1795 and / or instructions executable by the processing circuitry 1760. The software 1795 may include any type of software including software for instantiating one or more virtualization layers (also called hypervisors) 1750, software for executing virtual machines 1740, and software enabling it to perform the functions, features, and / or benefits described in relation to some of the embodiments described herein.

[0166] The virtual machine 1740 comprises virtual processing, virtual memory, virtual networking or interfaces, and virtual storage, and may be operated by a corresponding virtualization layer 1750 or hypervisor. Different embodiments of instances of the virtual appliance 1720 may be implemented on one or more of the virtual machines 1740, and the implementation may be done in different ways.

[0167] During operation, the processing circuit 1760 executes software 1795 to instantiate a hypervisor or virtualization layer 1750, which may sometimes be referred to as a virtual machine monitor (VMM). The virtualization layer 1750 may present a virtual operating platform to the virtual machines 1740 that appears as networking hardware.

[0168] As shown in FIG. 17, the hardware 1730 can be a stand-alone network node with general or specific components. The hardware 1730 can include an antenna 17225 and can implement some functions via virtualization. Alternatively, the hardware 1730 can be part of a larger class of hardware (such as in the case of a data center or customer premise equipment (CPE)) that is managed via a management and orchestration (MANO) 17100 where multiple hardware nodes cooperate and in particular oversee the lifecycle management of the application 1720.

[0169] The virtualization of hardware is, in some contexts, referred to as network function virtualization (NFV). NFV can be used to consolidate many network equipment types onto industry-standard high-volume server hardware, physical switches, and physical storage that can be located within data centers and customer premise equipment.

[0170] In the context of NFV, the virtual machines 1740 can be software implementations of physical machines on which programs operate as if they were running on a non-virtualized physical machine. Each of the virtual machines 1740 forms a separate virtual network element (VNE) with that part of the hardware 1730 that executes it, whether that hardware is dedicated to that virtual machine and / or shared by other virtual machines among the virtual machines 1740.

[0171] Furthermore, in the context of NFV, a virtual network function (VNF) is responsible for handling a specific network function running on one or more virtual machines 1740 on a hardware networking infrastructure 1730, corresponding to the application 1720 in FIG. 17.

[0172] In some embodiments, one or more radio units 17200, each including one or more transmitters 17220 and one or more receivers 17210, may be coupled to one or more antennas 17225. The radio unit 17200 may communicate directly with the hardware node 1730 via one or more suitable network interfaces and may be used in combination with virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station.

[0173] In some embodiments, some signaling may be implemented using a control system 17230 that may alternatively be used for communication between the hardware node 1730 and the radio unit 17200.

[0174] FIG. QQ4 shows a communication network connected to a host computer via an intermediate network according to some embodiments.

[0175] Referring to FIG. QQ4, according to one embodiment, a communication network 1810, such as a 3GPP type cellular network, includes an access network 1811, such as a radio access network, and a core network 1814. The access network 1811 includes a plurality of base stations 1812a, 1812b, 1812c, such as NB, eNB, gNB, or other types of radio access points, each defining a corresponding coverage area 1813a, 1813b, 1813c. Each base station 1812a, 1812b, 1812c can be connected to the core network 1814 over a wired or wireless connection 1815. A first UE 1891 located in the coverage area 1813c is configured to wirelessly connect to the corresponding base station 1812c or be paged by the corresponding base station 1812c. A second UE 1892 in the coverage area 1813a can wirelessly connect to the corresponding base station 1812a. Although a plurality of UEs 1891, 1892 are shown in this example, the disclosed embodiments are equally applicable to situations where only one UE is in the coverage area or only one UE is connected to the corresponding base station 1812.

[0176] The communication network 1810 is itself connected to a host computer 1830, which can be embodied in the hardware and / or software of a stand-alone server, a cloud-implemented server, a distributed server, or as processing resources in a server farm. The host computer 1830 can be under the ownership or control of a service provider, or can be operated by or on behalf of a service provider. The connections 1821 and 1822 between the communication network 1810 and the host computer 1830 can extend directly from the core network 1814 to the host computer 1830, or can proceed via an optional intermediate network 1820. The intermediate network 1820 can be one of a public network, a private network, or a hosted network, or a combination of two or more of them, and the intermediate network 1820 can be, if any, a backbone network or the Internet, and in particular, the intermediate network 1820 can comprise two or more sub-networks (not shown).

[0177] The communication system of FIG. 18 enables connectivity between the connected UEs 1891, 1892 and the host computer 1830. The connectivity can be described as an over-the-top (OTT) connection 1850. The host computer 1830 and the connected UEs 1891, 1892 are configured to communicate data and / or signaling via the OTT connection 1850, mediated by the access network 1811, the core network 1814, any intermediate network 1820, and any additional infrastructure (not shown). The OTT connection 1850 can be transparent in the sense that the participating communication devices through which the OTT connection 1850 passes are unaware of the routing of the uplink and downlink communications. For example, the base station 1812 may not be informed or need to be informed about the past routing of the incoming downlink communication with data generated from the host computer 1830 that is to be forwarded (e.g., handed over) to the connected UE 1891. Similarly, the base station 1812 does not need to be aware of the future routing of the outgoing uplink communication originating from the UE 1891 and destined for the host computer 1830.

[0178] FIG. 19 shows a host computer communicating with a user equipment via a base station over a partial wireless connection, according to some embodiments.

[0179] Next, an exemplary implementation of the UE, base station, and host computer described in the previous paragraph according to one embodiment will be described with reference to FIG. 19. In communication system 1900, host computer 1910 comprises hardware 1915 including a communication interface 1916 configured to set up and maintain a wired or wireless connection with an interface of different communication devices of communication system 1900. Host computer 1910 further comprises a processing circuit 1918 which may have storage and / or processing capabilities. In particular, processing circuit 1918 may comprise one or more programmable processors, application specific integrated circuits, field programmable gate arrays, or combinations thereof (not shown) adapted to execute instructions. Host computer 1910 further comprises software 1911 stored on or accessible by host computer 1910 and executable by processing circuit 1918. Software 1911 includes host application 1912. Host application 1912 may be operable to provide services to a remote user such as UE 1930 which is connected via an OTT connection 1950 terminating at UE 1930 and host computer 1910. When providing services to a remote user, host application 1912 may provide user data transmitted using OTT connection 1950.

[0180] The communication system 1900 further includes a base station 1920 provided in the communication system, and the base station 1920 comprises hardware 1925 that enables the base station 1920 to communicate with the host computer 1910 and the UE 1930. The hardware 1925 includes a communication interface 1926 for setting up and maintaining a wired or wireless connection with an interface of different communication devices of the communication system 1900, and a wireless interface 1927 for setting up and maintaining at least a wireless connection 1970 with the UE 1930 located in a coverage area (not shown in FIG. 19) served by the base station 1920. The communication interface 1926 may be configured to facilitate the connection 1960 to the host computer 1910. The connection 1960 may be direct, or the connection 1960 may pass through a core network (not shown in FIG. 19) of the communication system and / or one or more intermediate networks external to the communication system. In the illustrated embodiment, the hardware 1925 of the base station 1920 further includes a processing circuit 1928, and the processing circuit 1928 may comprise one or more programmable processors, application specific integrated circuits, field programmable gate arrays, or combinations thereof (not shown) adapted to execute instructions. The base station 1920 further has software 1921 stored internally or accessible via an external connection.

[0181] Communication system 1900 further includes the UE 1930 already mentioned. The hardware 1935 of the UE 1930 may include a radio interface 1937 configured to set up and maintain a radio connection 1970 with a base station serving the coverage area where the UE 1930 is currently located. The hardware 1935 of the UE 1930 further includes a processing circuit 1938, which may comprise one or more programmable processors, application specific integrated circuits, field programmable gate arrays, or combinations thereof (not shown) adapted to execute instructions. The UE 1930 further comprises software 1931 stored in or accessible by the UE 1930 and executable by the processing circuit 1938. The software 1931 includes a client application 1932. The client application 1932 may be operable to provide services to a human or non - human user via the UE 1930 under the support of the host computer 1910. In the host computer 1910, the running host application 1912 may communicate with the running client application 1932 via an OTT connection 1950 that terminates at the UE 1930 and the host computer 1910. When providing services to the user, the client application 1932 may receive request data from the host application 1912 and provide user data in response to the request data. The OTT connection 1950 may transfer both the request data and the user data. The client application 1932 may interact with the user to generate the user data provided by the client application 1932.

[0182] Note that the host computer 1910, base station 1920, and UE 1930 shown in FIG. 19 can be the same as or equivalent to one of the host computer 1830, base stations 1812a, 1812b, 1812c in FIG. 18, and one of UEs 1891, 1892, respectively. That is, the operation inside these entities can be as shown in FIG. 19, and separately, the surrounding network topology can be the same as that in FIG. 18.

[0183] In FIG. 19, the OTT connection 1950 is abstractly depicted to show the communication between the host computer 1910 and the UE 1930 via the base station 1920 without explicit mention of the intermediary device and the exact routing of messages through these devices. The network infrastructure can determine the routing, and the network infrastructure can be configured to hide the routing from the UE 1930, from the service provider operating the host computer 1910, or from both. While the OTT connection 1950 is active, the network infrastructure can further make a determination to dynamically change the routing (e.g., based on network load distribution considerations or reconfiguration).

[0184] The radio connection 1970 between the UE 1930 and the base station 1920 follows the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments can use the OTT connection 1950 of which the radio connection 1970 forms the last segment to improve the performance of the OTT service provided to the UE 1930. More precisely, the teachings of these embodiments can improve the random access speed and / or reduce the random access failure rate, thereby providing benefits such as faster and / or more reliable random access.

[0185] Measurement procedures may be provided for the purpose of monitoring data rate, latency, and other factors that one or more embodiments improve. There may further be optional network functions for reconfiguring the OTT connection 1950 between the host computer 1910 and the UE 1930 in response to variations in the measurement results. The measurement procedures and / or the network functions for reconfiguring the OTT connection 1950 may be implemented in the software 1911 and hardware 1915 of the host computer 1910 or in the software 1931 and hardware 1935 of the UE 1930, or both. In an embodiment, sensors (not shown) may be deployed in or in relation to the communication device through which the OTT connection 1950 passes, and the sensors may participate in the measurement procedures by supplying values of the monitored quantities exemplified above or by supplying values of other physical quantities that the software 1911, 1931 may calculate or estimate the monitored quantities. The reconfiguration of the OTT connection 1950 may include message format, retransmission settings, preferred routing, etc., and the reconfiguration need not affect the base station 1920 and may be unknown or imperceptible to the base station 1920. Such procedures and functions are known and practicable in the art. In some embodiments, the measurement may involve proprietary UE signaling that facilitates measurement of the host computer 1910, such as throughput, propagation time, latency, etc. The measurement may be implemented in that the software 1911 and 1931 cause messages, particularly empty or "dummy" messages, to be transmitted using the OTT connection 1950 while the software 1911 and 1931 monitor propagation time, errors, etc.

[0186] FIG. 20 shows a method implemented in a communication system including a host computer, a base station, and a user equipment, according to some embodiments.

[0187] Figure 20 is a flowchart showing a method implemented in a communication system according to an embodiment. The communication system may include a host computer, a base station, and a UE, as described with reference to FIGS. 18 and 19. For simplicity of the present disclosure, only the drawing reference to FIG. 20 is included in this section. In step 2010, the host computer provides user data. In an optional sub-step 2011 of step 2010, the host computer provides user data by executing a host application. In step 2020, the host computer initiates a transmission that conveys the user data to the UE. In an optional step 2030, the base station transmits the user data conveyed in the transmission initiated by the host computer to the UE according to the teachings of the embodiments described throughout the present disclosure. In an also optional step 2040, the UE executes a client application related to the host application executed by the host computer.

[0188] FIG. 21 shows a method implemented in a communication system including a host computer, a base station, and a user equipment according to some embodiments.

[0189] Figure 21 is a flowchart showing a method implemented in a communication system according to an embodiment. The communication system may include a host computer, a base station, and a UE, as described with reference to FIGS. 18 and 19. For simplicity of the present disclosure, only the drawing reference to FIG. 21 is included in this section. In step 2110 of the method, the host computer provides user data. In an optional sub-step (not shown), the host computer provides user data by executing a host application. In step 2120, the host computer initiates a transmission that conveys the user data to the UE. The transmission may proceed via the base station according to the teachings of the embodiments described throughout the present disclosure. In an optional step 2130, the UE receives the user data conveyed in the transmission.

[0190] Figure 22 shows a method implemented in a communication system including a host computer, a base station, and a user equipment according to some embodiments.

[0191] Figure 22 is a flowchart showing a method implemented in a communication system according to one embodiment. The communication system may include a host computer, a base station, and a UE as described with reference to FIGS. 18 and 19. For simplicity of the present disclosure, only the drawing reference to FIG. 22 is included in this section. Optionally, in step 2210, the UE receives input data provided by the host computer. Additionally or alternatively, in step 2220, the UE provides user data. In an optional sub-step 2221 of step 2220, the UE provides user data by executing a client application. In an optional sub-step 2211 of step 2210, the UE executes a client application that provides user data in response to the received input data provided by the host computer. When providing user data, the executed client application may further consider user input received from the user. Regardless of the particular manner in which the user data is provided, the UE starts transmitting the user data to the host computer in an optional sub-step 2230. In step 2240 of the method, the host computer receives the user data transmitted from the UE according to the teachings of the embodiments described throughout the present disclosure.

[0192] Figure 23 shows a method implemented in a communication system including a host computer, a base station, and a user equipment according to some embodiments.

[0193] FIG. 23 is a flowchart showing a method implemented in a communication system according to an embodiment. The communication system may include a host computer, a base station, and a UE, which may be the ones described with reference to FIGS. 18 and 19. For the sake of simplicity of the present disclosure, only the drawing reference to FIG. 23 is included in this section. In optional step 2310, according to the teachings of the embodiments described throughout the present disclosure, the base station receives user data from the UE. In optional step 2320, the base station initiates transmission of the received user data to the host computer. In optional step 2330, the host computer receives the user data carried in the transmission initiated by the base station.

[0194] Any suitable steps, methods, features, functions, or benefits disclosed herein may be implemented through one or more functional units or modules of one or more virtual devices. Each virtual device may comprise several of these functional units. These functional units may be implemented via a processing circuit that may include one or more microprocessors or microcontrollers, as well as other digital hardware that may include a digital signal processor (DSP), dedicated digital logic, etc. The processing circuit may be configured to execute program code stored in a memory, which may include one or several types of memory such as read-only memory (ROM), random access memory (RAM), cache memory, flash memory devices, optical storage devices, etc. The program code stored in the memory includes program instructions for executing one or more communication and / or data communication protocols, as well as instructions for performing one or more of the techniques described herein. In some implementations, the processing circuit may be used to cause each functional unit to perform the corresponding function according to one or more embodiments of the present disclosure.

[0195] The term "unit" may have its ordinary meaning in the field of electronics, electrical devices, and / or electronic devices, and may include, for example, electrical and / or electronic circuits, devices, modules, processors, memories, logic solids and / or individual devices, computer programs or instructions, etc. for performing each task, procedure, calculation, output, and / or display function, such as those described herein.

[0196] Further provisions and embodiments are described below.

[0197] In the above description of various embodiments of the present inventive concept, it should be understood that the technical terms used herein are only for describing specific embodiments and do not limit the present inventive concept. Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by those skilled in the art to which the present inventive concept pertains. Terms such as those defined in commonly used dictionaries shall be construed to have a meaning consistent with their meaning in the context of this specification and the related art, and should not be construed in an ideal or overly formal sense unless expressly so defined herein.

[0198] When an element is said to be "connected to", "coupled to", "responsive to", or a variation thereof, with respect to another element, the element can be directly connected to, coupled to, or responsive to the other element, or intervening elements may be present. In contrast, when an element is said to be "directly connected to", "directly coupled to", "directly responsive to", or a variation thereof, with respect to another element, no intervening elements are present. Like numbers refer to like elements throughout. Further, as used herein, "coupled to", "connected to", "responsive to", or variations thereof can include wirelessly coupled, wirelessly connected, or wirelessly responsive. As used herein, the singular forms "a", "an" and "the" are to be construed to include the plural forms as well, unless the context clearly dictates otherwise. For brevity and / or clarity, well-known functions or constructions may not be described in detail. The term "and / or" (abbreviated " / ") includes any and all combinations of one or more of the associated listed items.

[0199] To describe various elements / acts, terms such as first, second, third, etc. may be used herein, but it should be understood that these elements / acts should not be limited by these terms. These terms are only used to distinguish one element / act from another. Thus, without departing from the teachings of the inventive concept, a first element / act in some embodiments may be referred to as a second element / act in other embodiments. The same reference numbers or the same reference signs indicate the same or similar elements throughout this specification.

[0200] As used herein, the terms "comprise", "comprising", "comprises", "include", "including", "includes", "have", "has", "having", or variations thereof are open-ended and include one or more recited features, integers, elements, steps, components or functions but do not preclude the presence or addition of one or more other features, integers, elements, steps, components, functions or groups thereof. Further, as used herein, the common abbreviation "e.g." derived from the Latin phrase "exempli gratia" may be used to introduce or specifically enumerate one or more general examples of the foregoing items and is not limiting thereof. The common abbreviation "i.e." derived from the Latin phrase "id est" may be used to specifically enumerate a particular item from a more general recitation.

[0201] Exemplary embodiments are described herein with reference to block diagrams and / or flowchart illustrations of a computer-implemented method, apparatus (system and / or device) and / or computer program product. It will be understood that the blocks of the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, can be implemented by computer program instructions executed by one or more computer circuits. These computer program instructions may be provided to the processor circuits of a general purpose computer circuit, a special purpose computer circuit, and / or other programmable data processing circuits for creating machines, and thus the instructions executed via the processor of a computer and / or other programmable data processing apparatus serve to implement the functions / acts specified in one or more blocks of the block diagrams and / or flowchart, and thereby create means (functions) and / or structures for implementing the functions / acts specified in (one or more of) the blocks of the block diagrams and / or flowchart, to transform and control transistors, values stored in memory locations, and other hardware components within such circuits.

[0202] These computer program instructions may also be stored in a tangible computer-readable medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, and thus the instructions stored in the computer-readable medium produce a manufactured article including instructions for implementing the functions / acts specified in one or more blocks of the block diagrams and / or flowchart. Accordingly, embodiments of the inventive concept may be implemented in hardware and / or software (including firmware, resident software, microcode, etc.) running on a processor, such as a digital signal processor, sometimes collectively referred to as a "circuit", "module" or variations thereof.

[0203] Also, note that in some alternative implementations, the functions / acts recited in a block may occur out of the order recited in the flowchart. For example, depending on the functions / acts involved, two blocks shown in succession may in fact be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order. Additionally, the functionality of a given block in a flowchart and / or block diagram may be split into multiple blocks, and / or the functionality of two or more blocks in a flowchart and / or block diagram may be at least partially integrated. Finally, other blocks may be added / inserted between the blocks shown, and / or blocks / acts may be omitted without departing from the scope of the inventive concept. Additionally, although some of the figures include arrows on communication paths to indicate a primary direction of communication, it should be understood that communication may occur in a direction opposite to that shown by the arrows.

[0204] Many variations and modifications can be made to the embodiments without substantially departing from the principles of the inventive concept. All such variations and modifications are intended to be included herein within the scope of the inventive concept. Accordingly, the subject matter disclosed above should be regarded as illustrative and not restrictive, and the examples of embodiments are intended to cover all such modifications, extensions, and other embodiments that fall within the spirit and scope of the inventive concept. Accordingly, to the maximum extent permitted by law, the scope of the inventive concept should be determined by the broadest permissible interpretation of this disclosure, including examples of embodiments and their equivalents, and should not be limited or restricted by the foregoing detailed description.

Claims

1. A method for operating a first communication device (TX UE), the method comprising: selecting a resource within a resource selection window for an initial transmission of a first medium access control (MAC) protocol data unit (PDU) among a plurality of MAC protocol data units (PDUs) for periodic transmission to a second communication device (RX UE) via a device-to-device (D2D) link by the first communication device (TX UE) (8011); selecting a resource reservation interval, which is a period of resources reserved for periodic transmission of the plurality of MAC PDUs, such that initial transmissions of all MAC PDUs of the plurality of MAC PDUs other than the first MAC PDU are performed in resources after the resource selection window (8031); A method comprising.

2. The method according to claim 1, wherein the resource comprises at least one slot.

3. The method according to claim 1 or 2, wherein the resource reservation interval is at least as long as the duration of the resource selection window.

4. The method according to claim 3, wherein the duration of the resource selection window is T2 - T1, and the resource selection window is defined by a first slot having a first slot number (T1) and a second slot having a second slot number (T2) greater than the first slot number.

5. Further comprising transmitting the initial transmission of the first MAC PDU to the second communication device via the D2D link using the resource selected within the resource selection window. The method according to any one of claims 1 to 4.

6. Transmitting sidelink control information (SCI) indicating the initial transmission of the first MAC PDU to the second communication device via the D2D link, the SCI indicating the use of the resource selected within the resource selection window. The method according to any one of claims 1 to 5.

7. Selecting a resource after the resource selection window for the initial transmission of the second MAC PDU among the plurality of MAC PDUs, wherein the resource after the resource selection window is selected based on the resource reservation interval; Transmitting the initial transmission of the second MAC PDU among the plurality of MAC PDUs via the D2D link using the resource after the resource selection window; The method according to any one of claims 1 to 6, further comprising.

8. Selecting one or more resources for retransmission of the first MAC PDU within the resource selection window; Transmitting a retransmission of the first MAC PDU to the second communication device via the D2D link using a first resource among the one or more resources for retransmission; The method according to any one of claims 1 to 7, further comprising.

9. The method according to any one of claims 1 to 8, wherein all resources for retransmission of the first MAC PDU are limited to the resource selection window.

10. The first communication device is configured to provide up to N retransmissions for each of the plurality of MAC PDUs, N is greater than 0, and the method comprises: After selecting the resource within the resource selection window for the initial transmission of the first MAC PDU, determining whether sufficient resources are available for N retransmissions of the first MAC PDU in the resource selection window; Blocking all retransmissions of the first MAC PDU in response to determining that sufficient resources are not available for N retransmissions of the first MAC PDU in the resource selection window; The method according to any one of claims 1 to 7, further comprising.

11. The first communication device is configured to provide up to N retransmissions for each of the plurality of MAC PDUs, N is greater than 0, and the method comprises: After selecting the resource within the resource selection window for the initial transmission of the first MAC PDU, determining that resources are available only for M retransmissions of the first MAC PDU in the resource selection window, where M is less than N and M is greater than 0, and In response to determining that resources are available only for M retransmissions of the first MAC PDU in the resource selection window, - Limiting the retransmission of the first MAC PDU to M retransmissions, and - Selecting M resources of the resource selection window for the retransmission of the first MAC PDU Performing one or more of the above The method according to any one of claims 1 to 7, further comprising.

12. A first communication device (TX UE) (300), Selecting a resource within a resource selection window for an initial transmission of a first MAC protocol data unit (PDU) among a plurality of media access control (MAC) protocol data units (PDUs) for periodic transmission to a second communication device (RX UE) via a D2D (device-to-device) link by the first communication device (TX UE) (300) (8011); Selecting a resource reservation interval, which is a period of resources reserved for the periodic transmission of the plurality of MAC PDUs, such that initial transmissions of all MAC PDUs of the plurality of MAC PDUs other than the first MAC PDU are performed in resources after the resource selection window (8031) A first communication device (TX UE) (300) adapted to perform operations including.

13. The first communication device (TX UE) (300) according to claim 12, wherein the first communication device (TX UE) (300) is adapted to perform according to any one of claims 2 to 11.

14. A computer program comprising program code to be executed by at least one processor (303) of a first communication device (TX UE) (300), whereby execution of the program code causes the first communication device (TX UE) (300) to perform the operations according to any one of claims 1 to 11.

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