Patent Publication Number: US-2022224443-A1

Title: Method and apparatus for performing retransmission in wireless communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. § 119(e), this application is a continuation of International Application No. PCT/KR2020/013092, with an international filing date of Sep. 25, 2020, which claims the benefit of Korean Patent Application No. 10-2019-0122719, filed on Oct. 3, 2019, the contents of which are hereby incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to performing a retransmission in wireless communications. 
     BACKGROUND 
     3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement. 
     Work has started in international telecommunication union (ITU) and 3GPP to develop requirements and specifications for new radio (NR) systems. 3GPP has to identify and develop the technology components needed for successfully standardizing the new RAT timely satisfying both the urgent market needs, and the more long-term requirements set forth by the ITU radio communication sector (ITU-R) international mobile telecommunications (IMT)-2020 process. Further, the NR should be able to use any spectrum band ranging at least up to 100 GHz that may be made available for wireless communications even in a more distant future. 
     The NR targets a single technical framework addressing all usage scenarios, requirements and deployment scenarios including enhanced mobile broadband (eMBB), massive machine-type-communications (mMTC), ultra-reliable and low latency communications (URLLC), etc. The NR shall be inherently forward compatible. 
     In wireless communications, devices involved in the wireless communications may transmit/receive data with each other. For example, a device may transmit data/control information to another device. If this data/control information is properly received by the other device, the other device may transmit a positive acknowledgement (ACK) to the device, in response. However, the data/control information may not be received properly by the other device due to various reasons. In this case, the other device may transmit a negative acknowledgement (NACK) to the device, and the device may perform a retransmission of the data/control information. 
     SUMMARY 
     1. Technical Problem 
     An aspect of the present disclosure is to provide method and apparatus for performing a retransmission in a wireless communication system. 
     Another aspect of the present disclosure is to provide method and apparatus for performing a retransmission based on a validity of the retransmission in a wireless communication system. 
     Another aspect of the present disclosure is to provide method and apparatus for performing a retransmission if/when there is no grant for the retransmission in a wireless communication system. 
     Another aspect of the present disclosure is to provide method and apparatus for determining a retransmission resource in a wireless communication system. 
     2. Technical Solution 
     According to an embodiment of the present disclosure, a method performed by a first wireless device in a wireless communication system comprises: reserving a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission; creating a data unit based on the first resource and the second resource; performing the initial transmission of the data unit to a second wireless device by using the first resource; determining whether to reserve a resource for the retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; removing the second resource and reserving a third resource as the resource for the retransmission of the data unit; and performing the retransmission of the data unit by using the third resource to the second wireless device. 
     According to an embodiment of the present disclosure, a first wireless device in a wireless communication system comprising: a transceiver; a memory; and at least one processor operatively coupled to the transceiver and the memory, and configured to: reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission, create a data unit based on the first resource and the second resource, control the transceiver to perform the initial transmission of the data unit to a second wireless device by using the first resource, determine whether to reserve a resource for the retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit, remove the second resource and reserve a third resource as the resource for the retransmission of the data unit, and control the transceiver to perform the retransmission of the data unit by using the third resource to the second wireless device. 
     According to an embodiment of the present disclosure, a method performed by a base station (BS) in a wireless communication system, comprises: receiving, from a first wireless device, a sidelink user equipment (UE) information; and transmitting, to the first wireless device, a configuration of a resource pool, wherein the first wireless device is configured to: reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission, based on resources in the resource pool; create a data unit based on the first resource and the second resource; perform the initial transmission of the data unit by using the first resource; determine whether to reserve a resource for a retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; remove the second resource and reserve a third resource as the resource for the retransmission of the data unit; and perform the retransmission of the data unit to the second wireless device by using the third resource. 
     According to an embodiment of the present disclosure, a base station (BS) in a wireless communication system comprising: a transceiver; a memory; and at least one processor operatively coupled to the transceiver and the memory, and configured to control the transceiver to: receive, from a first wireless device, a sidelink user equipment (UE) information, and transmit, to the first wireless device, a configuration of a resource pool, wherein the first wireless device is configured to: reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission, based on resources in the resource pool; create a data unit based on the first resource and the second resource; perform the initial transmission of the data unit by using the first resource; determine whether to reserve a resource for a retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; remove the second resource and reserve a third resource as the resource for the retransmission of the data unit; and perform the retransmission of the data unit to the second wireless device by using the third resource. 
     According to an embodiment of the present disclosure, a processor for a wireless device in a wireless communication system is configured to control the wireless device to perform operations comprising: reserving a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission; creating a data unit based on the first resource and the second resource; performing the initial transmission of the data unit to a second wireless device by using the first resource; determining whether to reserve a resource for the retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; removing the second resource and reserving a third resource as the resource for the retransmission of the data unit; and performing the retransmission of the data unit by using the third resource to the second wireless device. 
     According to an embodiment of the present disclosure, a computer-readable medium having recorded thereon a program for performing each step of a method on a computer is provided. The method comprises: reserving a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission; creating a data unit based on the first resource and the second resource; performing the initial transmission of the data unit to a second wireless device by using the first resource; determining whether to reserve a resource for the retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; removing the second resource and reserving a third resource as the resource for the retransmission of the data unit; and 
     performing the retransmission of the data unit by using the third resource to the second wireless device. 
     3. Advantageous Effects 
     The present disclosure can have various advantageous effects. 
     For example, a UE performing a HARQ transmission of a packet by using radio resources can dynamically and efficiently allocate resources for retransmissions of the packet by considering service characteristics and requirements, in particular when packets from various services are multiplexed into a single data unit. 
     For example, it is beneficial in that the system can provide dynamic and efficient allocation of resources for data retransmissions for a UE performing HARQ transmission. 
     Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and/or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows examples of 5G usage scenarios to which the technical features of the present disclosure can be applied. 
         FIG. 2  shows an example of a wireless communication system to which the technical features of the present disclosure can be applied. 
         FIG. 3  shows an example of a wireless communication system to which the technical features of the present disclosure can be applied. 
         FIG. 4  shows another example of a wireless communication system to which the technical features of the present disclosure can be applied. 
         FIG. 5  shows a block diagram of a user plane protocol stack to which the technical features of the present disclosure can be applied. 
         FIG. 6  shows a block diagram of a control plane protocol stack to which the technical features of the present disclosure can be applied. 
         FIG. 7  illustrates a frame structure in a 3GPP based wireless communication system. 
         FIG. 8  illustrates a data flow example in the 3GPP NR system. 
         FIG. 9  shows an example of communication links to which technical features of the present disclosure can be applied. 
         FIG. 10  shows an example of sidelink connectivity types to which technical features of the present disclosure can be applied. 
         FIG. 11  shows an example of sidelink channel mapping to which technical features of the present disclosure can be applied. 
         FIG. 12  shows an example of a method for performing a retransmission according to an embodiment of the present disclosure. 
         FIG. 13  shows an example of a method for performing data transmission according to an embodiment of the present disclosure. 
         FIG. 14  shows an example of a signal flow for performing a retransmission according to an embodiment of the present disclosure. 
         FIG. 15  shows an example of a sidelink data transmission of a MAC PDU according to an embodiment of the present disclosure. 
         FIG. 16  shows a UE to implement an embodiment of the present disclosure. 
         FIG. 17  shows another example of a wireless communication system to which the technical features of the present disclosure can be applied. 
         FIG. 18  shows an example of an AI device to which the technical features of the present disclosure can be applied. 
         FIG. 19  shows an example of an AI system to which the technical features of the present disclosure can be applied. 
     
    
    
     DETAILED DESCRIPTION 
     The technical features described below may be used by a communication standard by the 3rd generation partnership project (3GPP) standardization organization, a communication standard by the institute of electrical and electronics engineers (IEEE), etc. For example, the communication standards by the 3GPP standardization organization include long-term evolution (LTE) and/or evolution of LTE systems. The evolution of LTE systems includes LTE-advanced (LTE-A), LTE-A Pro, and/or 5G new radio (NR). The communication standard by the IEEE standardization organization includes a wireless local area network (WLAN) system such as IEEE 802.11a/b/g/n/ac/ax. The above system uses various multiple access technologies such as orthogonal frequency division multiple access (OFDMA) and/or single carrier frequency division multiple access (SC-FDMA) for downlink (DL) and/or uplink (UL). For example, only OFDMA may be used for DL and only SC-FDMA may be used for UL. Alternatively, OFDMA and SC-FDMA may be used for DL and/or UL. 
     Here, the radio communication technologies implemented in the wireless devices in the present disclosure may include narrowband internet-of-things (NB-IoT) technology for low-power communication as well as LTE, NR and 6G. For example, NB-IoT technology may be an example of low power wide area network (LPWAN) technology, may be implemented in specifications such as LTE Cat NB1 and/or LTE Cat NB2, and may not be limited to the above-mentioned names. Additionally and/or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may communicate based on LTE-M technology. For example, LTE-M technology may be an example of LPWAN technology and be called by various names such as enhanced machine type communication (eMTC). For example, LTE-M technology may be implemented in at least one of the various specifications, such as 1) LTE Cat 0, 2) LTE Cat M1, 3) LTE Cat M2, 4) LTE non-bandwidth limited (non-BL), 5) LTE-MTC, 6) LTE Machine Type Communication, and/or 7) LTE M, and may not be limited to the above-mentioned names. Additionally and/or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may include at least one of ZigBee, Bluetooth, and/or LPWAN which take into account low-power communication, and may not be limited to the above-mentioned names. For example, ZigBee technology may generate personal area networks (PANs) associated with small/low-power digital communication based on various specifications such as IEEE 802.15.4 and may be called various names. 
     In the present disclosure, “A or B” may mean “only A”, “only B”, or “both A and B”. In other words, “A or B” in the present disclosure may be interpreted as “A and/or B”. For example, “A, B or C” in the present disclosure may mean “only A”, “only B”, “only C”, or “any combination of A, B and C”. 
     In the present disclosure, slash (/) or comma (,) may mean “and/or”. For example, “A/B” may mean “A and/or B”. Accordingly, “A/B” may mean “only A”, “only B”, or “both A and B”. For example, “A, B, C” may mean “A, B or C”. 
     In the present disclosure, “at least one of A and B” may mean “only A”, “only B” or “both A and B”. In addition, the expression “at least one of A or B” or “at least one of A and/or B” in the present disclosure may be interpreted as same as “at least one of A and B”. 
     In addition, in the present disclosure, “at least one of A, B and C” may mean “only A”, “only B”, “only C”, or “any combination of A, B and C”. In addition, “at least one of A, B or C” or “at least one of A, B and/or C” may mean “at least one of A, B and C”. 
     Also, parentheses used in the present disclosure may mean “for example”. In detail, when it is shown as “control information (PDCCH)”, “PDCCH” may be proposed as an example of “control information”. In other words, “control information” in the present disclosure is not limited to “PDCCH”, and “PDDCH” may be proposed as an example of “control information”. In addition, even when shown as “control information (i.e., PDCCH)”, “PDCCH” may be proposed as an example of “control information”. 
     Technical features that are separately described in one drawing in the present disclosure may be implemented separately or simultaneously. 
     The terms used throughout the disclosure can be defined as the followings: 
     ‘Sidelink grant’ refers to a resource allocated to be used for performing a sidelink transmission/reception via sidelink. 
     ‘Grant’ refers to a resource allocated to be used for performing a transmission/reception. 
     ‘Configured grant’ refers to a set of periodic resources configured by a network. The set of periodic resources may have an offset with respect to system frame number (SFN)=0 in time domain. The configured grant may comprise 1) a configured grant type 1 where a grant is provided by RRC, and stored as configured grant; and/or 2) a configured grant type 2 where a grant is provided by PDCCH, and stored or cleared as configured grant based on L1 signalling indicating configured grant activation or deactivation. For configured grant type 1, a period and an offset for the set of periodic resources may be configured by RRC. For configured grant type 2, a period for the set of periodic resources may be configured by RRC, and an offset for the set of periodic resources may be determined based on the L1 signalling indicating configured grant activation or deactivation. If the grant/configured grant is related to uplink the grant/configured grant may be called ‘uplink grant/configured uplink grant’. If the grant/configured grant is related to sidelink, the grant/configured grant may be called ‘sidelink grant/configured sidelink grant’. 
     Throughout the disclosure, the terms ‘radio access network (RAN) node’, ‘base station’, ‘eNB’, ‘gNB’ and ‘cell’ may be used interchangeably. Further, a UE may be a kind of a wireless device, and throughout the disclosure, the terms ‘UE’ and ‘wireless device’ may be used interchangeably. 
     The following drawings are created to explain specific embodiments of the present disclosure. The names of the specific devices or the names of the specific signals/messages/fields shown in the drawings are provided by way of example, and thus the technical features of the present disclosure are not limited to the specific names used in the following drawings. 
       FIG. 1  shows examples of 5G usage scenarios to which the technical features of the present disclosure can be applied. 
     The 5G usage scenarios shown in  FIG. 1  are only exemplary, and the technical features of the present disclosure can be applied to other 5G usage scenarios which are not shown in  FIG. 1 . 
     Referring to  FIG. 1 , the three main requirements areas of 5G include (1) enhanced mobile broadband (eMBB) domain, (2) massive machine type communication (mMTC) area, and (3) ultra-reliable and low latency communications (URLLC) area. Some use cases may require multiple areas for optimization and, other use cases may only focus on only one key performance indicator (KPI). 5G is to support these various use cases in a flexible and reliable way. 
     eMBB focuses on across-the-board enhancements to the data rate, latency, user density, capacity and coverage of mobile broadband access. The eMBB aims ˜10 Gbps of throughput. eMBB far surpasses basic mobile Internet access and covers rich interactive work and media and entertainment applications in cloud and/or augmented reality. Data is one of the key drivers of 5G and may not be able to see dedicated voice services for the first time in the 5G era. In 5G, the voice is expected to be processed as an application simply using the data connection provided by the communication system. The main reason for the increased volume of traffic is an increase in the size of the content and an increase in the number of applications requiring high data rates. Streaming services (audio and video), interactive video and mobile Internet connectivity will become more common as more devices connect to the Internet. Many of these applications require always-on connectivity to push real-time information and notifications to the user. Cloud storage and applications are growing rapidly in mobile communication platforms, which can be applied to both work and entertainment. Cloud storage is a special use case that drives growth of uplink data rate. 5G is also used for remote tasks on the cloud and requires much lower end-to-end delay to maintain a good user experience when the tactile interface is used. In entertainment, for example, cloud games and video streaming are another key factor that increases the demand for mobile broadband capabilities. Entertainment is essential in smartphones and tablets anywhere, including high mobility environments such as trains, cars and airplanes. Another use case is augmented reality and information retrieval for entertainment. Here, augmented reality requires very low latency and instantaneous data amount. 
     mMTC is designed to enable communication between devices that are low-cost, massive in number and battery-driven, intended to support applications such as smart metering, logistics, and field and body sensors. mMTC aims ˜10 years on battery and/or ˜1 million devices/km2. mMTC allows seamless integration of embedded sensors in all areas and is one of the most widely used 5G applications. Potentially by 2020, internet-of-things (IoT) devices are expected to reach 20.4 billion. Industrial IoT is one of the areas where 5G plays a key role in enabling smart cities, asset tracking, smart utilities, agriculture and security infrastructures. 
     URLLC will make it possible for devices and machines to communicate with ultra-reliability, very low latency and high availability, making it ideal for vehicular communication, industrial control, factory automation, remote surgery, smart grids and public safety applications. URLLC aims ˜1 ms of latency. URLLC includes new services that will change the industry through links with ultra-reliability/low latency, such as remote control of key infrastructure and self-driving vehicles. The level of reliability and latency is essential for smart grid control, industrial automation, robotics, drones control and coordination. 
     Next, a plurality of use cases included in the triangle of  FIG. 1  will be described in more detail. 
     5G can complement fiber-to-the-home (FTTH) and cable-based broadband (or DOCSIS) as a means of delivering streams rated from hundreds of megabits per second to gigabits per second. This high speed can be required to deliver TVs with resolutions of 4K or more (6K, 8K and above) as well as virtual reality (VR) and augmented reality (AR). VR and AR applications include mostly immersive sporting events. Certain applications may require special network settings. For example, in the case of a VR game, a game company may need to integrate a core server with an edge network server of a network operator to minimize delay. 
     Automotive is expected to become an important new driver for 5G, with many use cases for mobile communications to vehicles. For example, entertainment for passengers demands high capacity and high mobile broadband at the same time. This is because future users will continue to expect high-quality connections regardless of their location and speed. Another use case in the automotive sector is an augmented reality dashboard. The driver can identify an object in the dark on top of what is being viewed through the front window through the augmented reality dashboard. The augmented reality dashboard displays information that will inform the driver about the object&#39;s distance and movement. In the future, the wireless module enables communication between vehicles, information exchange between the vehicle and the supporting infrastructure, and information exchange between the vehicle and other connected devices (e.g. devices accompanied by a pedestrian). The safety system allows the driver to guide the alternative course of action so that he can drive more safely, thereby reducing the risk of accidents. The next step will be a remotely controlled vehicle or self-driving vehicle. This requires a very reliable and very fast communication between different self-driving vehicles and between vehicles and infrastructure. In the future, a self-driving vehicle will perform all driving activities, and the driver will focus only on traffic that the vehicle itself cannot identify. The technical requirements of self-driving vehicles require ultra-low latency and high-speed reliability to increase traffic safety to a level not achievable by humans. 
     Smart cities and smart homes, which are referred to as smart societies, will be embedded in high density wireless sensor networks. The distributed network of intelligent sensors will identify conditions for cost and energy-efficient maintenance of a city or house. A similar setting can be performed for each home. Temperature sensors, windows and heating controllers, burglar alarms and appliances are all wirelessly connected. Many of these sensors typically require low data rate, low power and low cost. However, for example, real-time high-definition (HD) video may be required for certain types of devices for monitoring. 
     The consumption and distribution of energy, including heat or gas, is highly dispersed, requiring automated control of distributed sensor networks. The smart grid interconnects these sensors using digital information and communication technologies to collect and act on information. This information can include supplier and consumer behavior, allowing the smart grid to improve the distribution of fuel, such as electricity, in terms of efficiency, reliability, economy, production sustainability, and automated methods. The smart grid can be viewed as another sensor network with low latency. 
     The health sector has many applications that can benefit from mobile communications. Communication systems can support telemedicine to provide clinical care in remote locations. This can help to reduce barriers to distance and improve access to health services that are not continuously available in distant rural areas. It is also used to save lives in critical care and emergency situations. Mobile communication based wireless sensor networks can provide remote monitoring and sensors for parameters such as heart rate and blood pressure. 
     Wireless and mobile communications are becoming increasingly important in industrial applications. Wiring costs are high for installation and maintenance. Thus, the possibility of replacing a cable with a wireless link that can be reconfigured is an attractive opportunity in many industries. However, achieving this requires that wireless connections operate with similar delay, reliability, and capacity as cables and that their management is simplified. Low latency and very low error probabilities are new requirements that need to be connected to 5G. 
     Logistics and freight tracking are important use cases of mobile communications that enable tracking of inventory and packages anywhere using location based information systems. Use cases of logistics and freight tracking typically require low data rates, but require a large range and reliable location information. 
     NR supports multiple numerology (or, subcarrier spacing (SCS)) to support various 5G services. For example, when the SCS is 15 kHz, wide area in traditional cellular bands may be supported. When the SCS is 30 kHz/60 kHz, dense-urban, lower latency and wider carrier bandwidth may be supported. When the SCS is 60 kHz or higher, a bandwidth greater than 24.25 GHz may be supported to overcome phase noise. 
     The NR frequency band may be defined as two types of frequency range, i.e., FR1 and FR2. The numerical value of the frequency range may be changed. For example, the frequency ranges of the two types (FR1 and FR2) may be as shown in Table 1 below. For ease of explanation, in the frequency ranges used in the NR system, FR1 may mean “sub 6 GHz range”, FR2 may mean “above 6 GHz range,” and may be referred to as millimeter wave (mmW). 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Frequency Range 
                 Corresponding 
                   
               
               
                 designation 
                 frequency range 
                 Subcarrier Spacing 
               
               
                   
               
             
            
               
                 FR1 
                  450 MHz-6000 MHz 
                  15, 30, 60 kHz 
               
               
                 FR2 
                 24250 MHz-52600 MHz 
                 60, 120, 240 kHz 
               
               
                   
               
            
           
         
       
     
     As mentioned above, the numerical value of the frequency range of the NR system may be changed. For example, FR1 may include a frequency band of 410 MHz to 7125 MHz as shown in Table 2 below. That is, FR1 may include a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more. For example, a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more included in FR1 may include an unlicensed band. Unlicensed bands may be used for a variety of purposes, for example for communication for vehicles (e.g., autonomous driving). 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Frequency Range 
                 Corresponding 
                   
               
               
                 designation 
                 frequency range 
                 Subcarrier Spacing 
               
               
                   
               
             
            
               
                 FR1 
                  410 MHz-7125 MHz 
                  15, 30, 60 kHz 
               
               
                 FR2 
                 24250 MHz-52600 MHz 
                 60, 120, 240 kHz 
               
               
                   
               
            
           
         
       
     
       FIG. 2  shows an example of a wireless communication system to which the technical features of the present disclosure can be applied. Referring to  FIG. 2 , the wireless communication system may include a first device  210  and a second device  220 . 
     The first device  210  includes a base station, a network node, a transmitting UE, a receiving UE, a wireless device, a wireless communication device, a vehicle, a vehicle equipped with an autonomous driving function, a connected car, a drone, an unmanned aerial vehicle (UAV), an artificial intelligence (AI) module, a robot, an AR device, a VR device, a mixed reality (MR) device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a fin-tech device (or, a financial device), a security device, a climate/environmental device, a device related to 5G services, or a device related to the fourth industrial revolution. 
     The second device  220  includes a base station, a network node, a transmitting UE, a receiving UE, a wireless device, a wireless communication device, a vehicle, a vehicle equipped with an autonomous driving function, a connected car, a drone, a UAV, an AI module, a robot, an AR device, a VR device, an MR device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a fin-tech device (or, a financial device), a security device, a climate/environmental device, a device related to 5G services, or a device related to the fourth industrial revolution. 
     For example, the UE may include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation device, a slate personal computer (PC), a tablet PC, an ultrabook, a wearable device (e.g. a smartwatch, a smart glass, a head mounted display (HMD)). For example, the HMD may be a display device worn on the head. For example, the HMD may be used to implement AR, VR and/or MR. 
     For example, the drone may be a flying object that is flying by a radio control signal without a person boarding it. For example, the VR device may include a device that implements an object or background in the virtual world. For example, the AR device may include a device that implements connection of an object and/or a background of a virtual world to an object and/or a background of the real world. For example, the MR device may include a device that implements fusion of an object and/or a background of a virtual world to an object and/or a background of the real world. For example, the hologram device may include a device that implements a 360-degree stereoscopic image by recording and playing stereoscopic information by utilizing a phenomenon of interference of light generated by the two laser lights meeting with each other, called holography. For example, the public safety device may include a video relay device or a video device that can be worn by the user&#39;s body. For example, the MTC device and the IoT device may be a device that do not require direct human intervention or manipulation. For example, the MTC device and the IoT device may include a smart meter, a vending machine, a thermometer, a smart bulb, a door lock and/or various sensors. For example, the medical device may be a device used for the purpose of diagnosing, treating, alleviating, handling, or preventing a disease. For example, the medical device may be a device used for the purpose of diagnosing, treating, alleviating, or correcting an injury or disorder. For example, the medical device may be a device used for the purpose of inspecting, replacing or modifying a structure or function. For example, the medical device may be a device used for the purpose of controlling pregnancy. For example, the medical device may include a treatment device, a surgical device, an (in vitro) diagnostic device, a hearing aid and/or a procedural device, etc. For example, a security device may be a device installed to prevent the risk that may occur and to maintain safety. For example, the security device may include a camera, a closed-circuit TV (CCTV), a recorder, or a black box. For example, the fin-tech device may be a device capable of providing financial services such as mobile payment. For example, the fin-tech device may include a payment device or a point of sales (POS). For example, the climate/environmental device may include a device for monitoring or predicting the climate/environment. 
     The first device  210  may include at least one or more processors, such as a processor  211 , at least one memory, such as a memory  212 , and at least one transceiver, such as a transceiver  213 . The processor  211  may perform the functions, procedures, and/or methods of the first device described throughout the disclosure. The processor  211  may perform one or more protocols. For example, the processor  211  may perform one or more layers of the air interface protocol. The memory  212  is connected to the processor  211  and may store various types of information and/or instructions. The transceiver  213  is connected to the processor  211  and may be controlled by the processor  211  to transmit and receive wireless signals. 
     The second device  220  may include at least one or more processors, such as a processor  221 , at least one memory, such as a memory  222 , and at least one transceiver, such as a transceiver  223 . The processor  221  may perform the functions, procedures, and/or methods of the second device  220  described throughout the disclosure. The processor  221  may perform one or more protocols. For example, the processor  221  may perform one or more layers of the air interface protocol. The memory  222  is connected to the processor  221  and may store various types of information and/or instructions. The transceiver  223  is connected to the processor  221  and may be controlled by the processor  221  to transmit and receive wireless signals. 
     The memory  212 ,  222  may be connected internally or externally to the processor  211 ,  212 , or may be connected to other processors via a variety of technologies such as wired or wireless connections. 
     The first device  210  and/or the second device  220  may have more than one antenna. For example, antenna  214  and/or antenna  224  may be configured to transmit and receive wireless signals. 
       FIG. 3  shows an example of a wireless communication system to which the technical features of the present disclosure can be applied. 
     Specifically,  FIG. 3  shows a system architecture based on an evolved-UMTS terrestrial radio access network (E-UTRAN). The aforementioned LTE is a part of an evolved-UTMS (e-UMTS) using the E-UTRAN. 
     Referring to  FIG. 3 , the wireless communication system includes one or more user equipment (UE)  310 , an E-UTRAN and an evolved packet core (EPC). The UE  310  refers to a communication equipment carried by a user. The UE  310  may be fixed or mobile. The UE  310  may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc. 
     The E-UTRAN consists of one or more evolved NodeB (eNB)  320 . The eNB  320  provides the E-UTRA user plane and control plane protocol terminations towards the UE  10 . The eNB  320  is generally a fixed station that communicates with the UE  310 . The eNB  320  hosts the functions, such as inter-cell radio resource management (RRM), radio bearer (RB) control, connection mobility control, radio admission control, measurement configuration/provision, dynamic resource allocation (scheduler), etc. The eNB  320  may be referred to as another terminology, such as a base station (BS), a base transceiver system (BTS), an access point (AP), etc. 
     A downlink (DL) denotes communication from the eNB  320  to the UE  310 . An uplink (UL) denotes communication from the UE  310  to the eNB  320 . A sidelink (SL) denotes communication between the UEs  310 . In the DL, a transmitter may be a part of the eNB  320 , and a receiver may be a part of the UE  310 . In the UL, the transmitter may be a part of the UE  310 , and the receiver may be a part of the eNB  320 . In the SL, the transmitter and receiver may be a part of the UE  310 . 
     The EPC includes a mobility management entity (MME), a serving gateway (S-GW) and a packet data network (PDN) gateway (P-GW). The MME hosts the functions, such as non-access stratum (NAS) security, idle state mobility handling, evolved packet system (EPS) bearer control, etc. The S-GW hosts the functions, such as mobility anchoring, etc. The S-GW is a gateway having an E-UTRAN as an endpoint. For convenience, MME/S-GW  330  will be referred to herein simply as a “gateway,” but it is understood that this entity includes both the MME and S-GW. The P-GW hosts the functions, such as UE Internet protocol (IP) address allocation, packet filtering, etc. The P-GW is a gateway having a PDN as an endpoint. The P-GW is connected to an external network. 
     The UE  310  is connected to the eNB  320  by means of the Uu interface. The UEs  310  are interconnected with each other by means of the PC5 interface. The eNBs  320  are interconnected with each other by means of the X2 interface. The eNBs  320  are also connected by means of the S1 interface to the EPC, more specifically to the MME by means of the S1-MME interface and to the S-GW by means of the S1-U interface. The S1 interface supports a many-to-many relation between MMEs/S-GWs and eNBs. 
       FIG. 4  shows another example of a wireless communication system to which the technical features of the present disclosure can be applied. 
     Specifically,  FIG. 4  shows a system architecture based on a 5G NR. The entity used in the 5G NR (hereinafter, simply referred to as “NW”) may absorb some or all of the functions of the entities introduced in  FIG. 3  (e.g. eNB, MME, S-GW). The entity used in the NR may be identified by the name “NG” for distinction from the LTE/LTE-A. 
     Referring to  FIG. 4 , the wireless communication system includes one or more UE  410 , a next-generation RAN (NG-RAN) and a 5th generation core network (5GC). The NG-RAN consists of at least one NG-RAN node. The NG-RAN node is an entity corresponding to the eNB  320  shown in  FIG. 3 . The NG-RAN node consists of at least one gNB  421  and/or at least one ng-eNB  422 . The gNB  421  provides NR user plane and control plane protocol terminations towards the UE  410 . The ng-eNB  422  provides E-UTRA user plane and control plane protocol terminations towards the UE  410 . 
     The 5GC includes an access and mobility management function (AMF), a user plane function (UPF) and a session management function (SMF). The AMF hosts the functions, such as NAS security, idle state mobility handling, etc. The AMF is an entity including the functions of the conventional MME. The UPF hosts the functions, such as mobility anchoring, protocol data unit (PDU) handling. The UPF an entity including the functions of the conventional S-GW. The SMF hosts the functions, such as UE IP address allocation, PDU session control. 
     The gNBs  421  and ng-eNBs  422  are interconnected with each other by means of the Xn interface. The gNBs  421  and ng-eNBs  422  are also connected by means of the NG interfaces to the 5GC, more specifically to the AMF by means of the NG-C interface and to the UPF by means of the NG-U interface. 
     A protocol structure between network entities described above is described. On the system of  FIG. 3  and/or  FIG. 4 , layers of a radio interface protocol between the UE and the network (e.g. NG-RAN and/or E-UTRAN) may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the open system interconnection (OSI) model that is well-known in the communication system. 
       FIG. 5  shows a block diagram of a user plane protocol stack to which the technical features of the present disclosure can be applied.  FIG. 6  shows a block diagram of a control plane protocol stack to which the technical features of the present disclosure can be applied. 
     The user/control plane protocol stacks shown in  FIG. 5  and  FIG. 6  are used in NR. However, user/control plane protocol stacks shown in  FIG. 5  and  FIG. 6  may be used in LTE/LTE-A without loss of generality, by replacing gNB/AMF with eNB/MME. 
     Referring to  FIG. 5  and  FIG. 6 , a physical (PHY) layer belonging to L1. The PHY layer offers information transfer services to media access control (MAC) sublayer and higher layers. The PHY layer offers to the MAC sublayer transport channels. Data between the MAC sublayer and the PHY layer is transferred via the transport channels. Between different PHY layers, i.e., between a PHY layer of a transmission side and a PHY layer of a reception side, data is transferred via the physical channels. 
     The MAC sublayer belongs to L2. The main services and functions of the MAC sublayer include mapping between logical channels and transport channels, multiplexing/de-multiplexing of MAC service data units (SDUs) belonging to one or different logical channels into/from transport blocks (TB) delivered to/from the physical layer on transport channels, scheduling information reporting, error correction through hybrid automatic repeat request (HARQ), priority handling between UEs by means of dynamic scheduling, priority handling between logical channels of one UE by means of logical channel prioritization (LCP), etc. The MAC sublayer offers to the radio link control (RLC) sublayer logical channels. 
     The RLC sublayer belong to L2. The RLC sublayer supports three transmission modes, i.e. transparent mode (TM), unacknowledged mode (UM), and acknowledged mode (AM), in order to guarantee various quality of services (QoS) required by radio bearers. The main services and functions of the RLC sublayer depend on the transmission mode. For example, the RLC sublayer provides transfer of upper layer PDUs for all three modes, but provides error correction through ARQ for AM only. In LTE/LTE-A, the RLC sublayer provides concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer) and re-segmentation of RLC data PDUs (only for AM data transfer). In NR, the RLC sublayer provides segmentation (only for AM and UM) and re-segmentation (only for AM) of RLC SDUs and reassembly of SDU (only for AM and UM). That is, the NR does not support concatenation of RLC SDUs. The RLC sublayer offers to the packet data convergence protocol (PDCP) sublayer RLC channels. 
     The PDCP sublayer belong to L2. The main services and functions of the PDCP sublayer for the user plane include header compression and decompression, transfer of user data, duplicate detection, PDCP PDU routing, retransmission of PDCP SDUs, ciphering and deciphering, etc. The main services and functions of the PDCP sublayer for the control plane include ciphering and integrity protection, transfer of control plane data, etc. 
     The service data adaptation protocol (SDAP) sublayer belong to L2. The SDAP sublayer is only defined in the user plane. The SDAP sublayer is only defined for NR. The main services and functions of SDAP include, mapping between a QoS flow and a data radio bearer (DRB), and marking QoS flow ID (QFI) in both DL and UL packets. The SDAP sublayer offers to 5GC QoS flows. 
     A radio resource control (RRC) layer belongs to L3. The RRC layer is only defined in the control plane. The RRC layer controls radio resources between the UE and the network. To this end, the RRC layer exchanges RRC messages between the UE and the BS. The main services and functions of the RRC layer include broadcast of system information related to AS and NAS, paging, establishment, maintenance and release of an RRC connection between the UE and the network, security functions including key management, establishment, configuration, maintenance and release of radio bearers, mobility functions, QoS management functions, UE measurement reporting and control of the reporting, NAS message transfer to/from NAS from/to UE. 
     In other words, the RRC layer controls logical channels, transport channels, and physical channels in relation to the configuration, reconfiguration, and release of radio bearers. A radio bearer refers to a logical path provided by L1 (PHY layer) and L2 (MAC/RLC/PDCP/SDAP sublayer) for data transmission between a UE and a network. Setting the radio bearer means defining the characteristics of the radio protocol layer and the channel for providing a specific service, and setting each specific parameter and operation method. Radio bearer may be divided into signaling RB (SRB) and data RB (DRB). The SRB is used as a path for transmitting RRC messages in the control plane, and the DRB is used as a path for transmitting user data in the user plane. 
     An RRC state indicates whether an RRC layer of the UE is logically connected to an RRC layer of the E-UTRAN. In LTE/LTE-A, when the RRC connection is established between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in the RRC connected state (RRC_CONNECTED). Otherwise, the UE is in the RRC idle state (RRC_IDLE). In NR, the RRC inactive state (RRC_INACTIVE) is additionally introduced. RRC_INACTIVE may be used for various purposes. For example, the massive machine type communications (MMTC) UEs can be efficiently managed in RRC_INACTIVE. When a specific condition is satisfied, transition is made from one of the above three states to the other. 
     A predetermined operation may be performed according to the RRC state. In RRC_IDLE, public land mobile network (PLMN) selection, broadcast of system information (SI), cell re-selection mobility, core network (CN) paging and discontinuous reception (DRX) configured by NAS may be performed. The UE shall have been allocated an identifier (ID) which uniquely identifies the UE in a tracking area. No RRC context stored in the BS. 
     In RRC_CONNECTED, the UE has an RRC connection with the network (i.e. E-UTRAN/NG-RAN). Network-CN connection (both C/U-planes) is also established for UE. The UE AS context is stored in the network and the UE. The RAN knows the cell which the UE belongs to. The network can transmit and/or receive data to/from UE. Network controlled mobility including measurement is also performed. 
     Most of operations performed in RRC_IDLE may be performed in RRC_INACTIVE. But, instead of CN paging in RRC_IDLE, RAN paging is performed in RRC_INACTIVE. In other words, in RRC_IDLE, paging for mobile terminated (MT) data is initiated by core network and paging area is managed by core network. In RRC_INACTIVE, paging is initiated by NG-RAN, and RAN-based notification area (RNA) is managed by NG-RAN. Further, instead of DRX for CN paging configured by NAS in RRC_IDLE, DRX for RAN paging is configured by NG-RAN in RRC_INACTIVE. Meanwhile, in RRC_INACTIVE, 5GC-NG-RAN connection (both C/U-planes) is established for UE, and the UE AS context is stored in NG-RAN and the UE. NG-RAN knows the RNA which the UE belongs to. 
     NAS layer is located at the top of the RRC layer. The NAS control protocol performs the functions, such as authentication, mobility management, security control. 
     The physical channels may be modulated according to OFDM processing and utilizes time and frequency as radio resources. The physical channels consist of a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain and a plurality of subcarriers in frequency domain. One subframe consists of a plurality of OFDM symbols in the time domain. A resource block is a resource allocation unit, and consists of a plurality of OFDM symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific OFDM symbols (e.g. first OFDM symbol) of the corresponding subframe for a physical downlink control channel (PDCCH), i.e. L1/L2 control channel. A transmission time interval (TTI) is a basic unit of time used by a scheduler for resource allocation. The TTI may be defined in units of one or a plurality of slots, or may be defined in units of mini-slots. 
     The transport channels are classified according to how and with what characteristics data are transferred over the radio interface. DL transport channels include a broadcast channel (BCH) used for transmitting system information, a downlink shared channel (DL-SCH) used for transmitting user traffic or control signals, and a paging channel (PCH) used for paging a UE. UL transport channels include an uplink shared channel (UL-SCH) for transmitting user traffic or control signals and a random access channel (RACH) normally used for initial access to a cell. 
     Different kinds of data transfer services are offered by MAC sublayer. Each logical channel type is defined by what type of information is transferred. Logical channels are classified into two groups: control channels and traffic channels. 
     Control channels are used for the transfer of control plane information only. The control channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH) and a dedicated control channel (DCCH). The BCCH is a DL channel for broadcasting system control information. The PCCH is DL channel that transfers paging information, system information change notifications. The CCCH is a channel for transmitting control information between UEs and network. This channel is used for UEs having no RRC connection with the network. The DCCH is a point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is used by UEs having an RRC connection. 
     Traffic channels are used for the transfer of user plane information only. The traffic channels include a dedicated traffic channel (DTCH). The DTCH is a point-to-point channel, dedicated to one UE, for the transfer of user information. The DTCH can exist in both UL and DL. 
     Regarding mapping between the logical channels and transport channels, in DL, BCCH can be mapped to BCH, BCCH can be mapped to DL-SCH, PCCH can be mapped to PCH, CCCH can be mapped to DL-SCH, DCCH can be mapped to DL-SCH, and DTCH can be mapped to DL-SCH. In UL, CCCH can be mapped to UL-SCH, DCCH can be mapped to UL-SCH, and DTCH can be mapped to UL-SCH. 
       FIG. 7  illustrates a frame structure in a 3GPP based wireless communication system. 
     The frame structure illustrated in  FIG. 7  is purely exemplary and the number of subframes, the number of slots, and/or the number of symbols in a frame may be variously changed. In the 3GPP based wireless communication system, an OFDM numerology (e.g., subcarrier spacing (SCS), transmission time interval (TTI) duration) may be differently configured between a plurality of cells aggregated for one UE. For example, if a UE is configured with different SCSs for cells aggregated for the cell, an (absolute time) duration of a time resource (e.g. a subframe, a slot, or a TTI) including the same number of symbols may be different among the aggregated cells. Herein, symbols may include OFDM symbols (or CP-OFDM symbols), SC-FDMA symbols (or discrete Fourier transform-spread-OFDM (DFT-s-OFDM) symbols). 
     Referring to  FIG. 7 , downlink and uplink transmissions are organized into frames. Each frame has Tf=10 ms duration. Each frame is divided into two half-frames, where each of the half-frames has 5 ms duration. Each half-frame consists of 5 subframes, where the duration Tsf per subframe is 1 ms. Each subframe is divided into slots and the number of slots in a subframe depends on a subcarrier spacing. Each slot includes 14 or 12 OFDM symbols based on a cyclic prefix (CP). In a normal CP, each slot includes 14 OFDM symbols and, in an extended CP, each slot includes 12 OFDM symbols. The numerology is based on exponentially scalable subcarrier spacing Δf=2 u*15 kHz. The following table shows the number of OFDM symbols per slot, the number of slots per frame, and the number of slots per for the normal CP, according to the subcarrier spacing Δf=2 u*15 kHz. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 u 
                 Nslotsymb 
                 Nframe, uslot 
                 Nsubframe, uslot 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 0 
                 14 
                 10 
                 1 
               
               
                   
                 1 
                 14 
                 20 
                 2 
               
               
                   
                 2 
                 14 
                 40 
                 4 
               
               
                   
                 3 
                 14 
                 80 
                 8 
               
               
                   
                 4 
                 14 
                 160 
                 16 
               
               
                   
                   
               
            
           
         
       
     
     The following table shows the number of OFDM symbols per slot, the number of slots per frame, and the number of slots per for the extended CP, according to the subcarrier spacing Δf=2 u*15 kHz. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 u 
                 Nslotsymb 
                 Nframe, uslot 
                 Nsubframe, uslot 
               
               
                   
                   
               
             
            
               
                   
                 2 
                 12 
                 40 
                 4 
               
               
                   
                   
               
            
           
         
       
     
     A slot includes plural symbols (e.g., 14 or 12 symbols) in the time domain. For each numerology (e.g. subcarrier spacing) and carrier, a resource grid of Nsize,ugrid,x*NRBsc subcarriers and Nsubframe,usymb OFDM symbols is defined, starting at common resource block (CRB) Nstart,ugrid indicated by higher-layer signaling (e.g. radio resource control (RRC) signaling), where Nsize,ugrid,x is the number of resource blocks (RBs) in the resource grid and the subscript x is DL for downlink and UL for uplink. NRBsc is the number of subcarriers per RB. In the 3GPP based wireless communication system, NRBsc is 12 generally. There is one resource grid for a given antenna port p, subcarrier spacing configuration u, and transmission direction (DL or UL). The carrier bandwidth Nsize,ugrid for subcarrier spacing configuration u is given by the higher-layer parameter (e.g. RRC parameter). Each element in the resource grid for the antenna port p and the subcarrier spacing configuration u is referred to as a resource element (RE) and one complex symbol may be mapped to each RE. Each RE in the resource grid is uniquely identified by an index k in the frequency domain and an index 1 representing a symbol location relative to a reference point in the time domain. In the 3GPP based wireless communication system, an RB is defined by 12 consecutive subcarriers in the frequency domain. In the 3GPP NR system, RBs are classified into CRBs and physical resource blocks (PRBs). CRBs are numbered from 0 and upwards in the frequency domain for subcarrier spacing configuration u. The center of subcarrier 0 of CRB 0 for subcarrier spacing configuration u coincides with ‘point A’ which serves as a common reference point for resource block grids. In the 3GPP NR system, PRBs are defined within a bandwidth part (BWP) and numbered from 0 to NsizeBWP,i-1, where i is the number of the bandwidth part. The relation between the physical resource block nPRB in the bandwidth part i and the common resource block nCRB is as follows: nPRB=nCRB+NsizeBWP,i, where NsizeBWP,i is the common resource block where bandwidth part starts relative to CRB 0. The BWP includes a plurality of consecutive RBs. A carrier may include a maximum of N (e.g., 5) BWPs. A UE may be configured with one or more BWPs on a given component carrier. Only one BWP among BWPs configured to the UE can active at a time. The active BWP defines the UE&#39;s operating bandwidth within the cell&#39;s operating bandwidth. 
     In the present disclosure, the term “cell” may refer to a geographic area to which one or more nodes provide a communication system, or refer to radio resources. A “cell” of a geographic area may be understood as coverage within which a node can provide service using a carrier and a “cell” as radio resources (e.g. time-frequency resources) is associated with bandwidth (BW) which is a frequency range configured by the carrier. The “cell” associated with the radio resources is defined by a combination of downlink resources and uplink resources, for example, a combination of a downlink (DL) component carrier (CC) and a uplink (UL) CC. The cell may be configured by downlink resources only, or may be configured by downlink resources and uplink resources. Since DL coverage, which is a range within which the node is capable of transmitting a valid signal, and UL coverage, which is a range within which the node is capable of receiving the valid signal from the UE, depends upon a carrier carrying the signal, the coverage of the node may be associated with coverage of the “cell” of radio resources used by the node. Accordingly, the term “cell” may be used to represent service coverage of the node sometimes, radio resources at other times, or a range that signals using the radio resources can reach with valid strength at other times. 
     In carrier aggregation (CA), two or more CCs are aggregated. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. CA is supported for both contiguous and non-contiguous CCs. When CA is configured the UE only has one radio resource control (RRC) connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the non-access stratum (NAS) mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as the Primary Cell (PCell). The PCell is a cell, operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure. Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. An SCell is a cell providing additional radio resources on top of Special Cell. The configured set of serving cells for a UE therefore always consists of one PCell and one or more SCells. For dual connectivity operation, the term Special Cell (SpCell) refers to the PCell of the master cell group (MCG) or the PSCell of the secondary cell group (SCG). An SpCell supports PUCCH transmission and contention-based random access, and is always activated. The MCG is a group of serving cells associated with a master node, comprising of the SpCell (PCell) and optionally one or more SCells. The SCG is the subset of serving cells associated with a secondary node, comprising of the PSCell and zero or more SCells, for a UE configured with dual connectivity (DC). For a UE in RRC_CONNECTED not configured with CA/DC there is only one serving cell comprising of the PCell. For a UE in RRC_CONNECTED configured with CA/DC the term “serving cells” is used to denote the set of cells comprising of the SpCell(s) and all SCells. In DC, two MAC entities are configured in a UE: one for the MCG and one for the SCG. 
       FIG. 8  illustrates a data flow example in the 3GPP NR system. 
     In  FIG. 8 , “RB” denotes a radio bearer, and “H” denotes a header. Radio bearers are categorized into two groups: data radio bearers (DRB) for user plane data and signalling radio bearers (SRB) for control plane data. The MAC PDU is transmitted/received using radio resources through the PHY layer to/from an external device. The MAC PDU arrives to the PHY layer in the form of a transport block. 
     In the PHY layer, the uplink transport channels UL-SCH and RACH are mapped to their physical channels PUSCH and PRACH, respectively, and the downlink transport channels DL-SCH, BCH and PCH are mapped to PDSCH, PBCH and PDSCH, respectively. In the PHY layer, uplink control information (UCI) is mapped to PUCCH, and downlink control information (DCI) is mapped to PDCCH. A MAC PDU related to UL-SCH is transmitted by a UE via a PUSCH based on an UL grant, and a MAC PDU related to DL-SCH is transmitted by a BS via a PDSCH based on a DL assignment. 
     Data unit(s) (e.g. PDCP SDU, PDCP PDU, RLC SDU, RLC PDU, RLC SDU, MAC SDU, MAC CE, MAC PDU) in the present disclosure is(are) transmitted/received on a physical channel (e.g. PDSCH, PUSCH) based on resource allocation (e.g. UL grant, DL assignment). In the present disclosure, uplink resource allocation is also referred to as uplink grant, and downlink resource allocation is also referred to as downlink assignment. The resource allocation includes time domain resource allocation and frequency domain resource allocation. In the present disclosure, an uplink grant is either received by the UE dynamically on PDCCH, in a Random Access Response, or configured to the UE semi-persistently by RRC. In the present disclosure, downlink assignment is either received by the UE dynamically on the PDCCH, or configured to the UE semi-persistently by RRC signalling from the BS. 
       FIG. 9  shows an example of communication links to which technical features of the present disclosure can be applied. 
     Referring to  FIG. 9 , the communication links comprise uplink, downlink, and sidelink. The uplink is a communication interface from a UE (e.g., UE  920 ) to a base station (e.g., base station  910 , such as eNB and/or gNB). The downlink is a communication interface from a base station (e.g., base station  910 ) to a UE (e.g., UE  920 ). 
     The sidelink is UE to UE interface for sidelink communication, sidelink discovery and/or V2X (vehicle to everything) communication. For example, the sidelink may correspond to a PC5 interface for sidelink communication, sidelink discovery and/or V2X sidelink communication. 
     A UE may perform a communication via network infrastructure. For example, as shown in  FIG. 9 , the UE 1   920  may perform an uplink transmission and/or receive a downlink transmission, via the base station  910 . 
     Also, a UE may perform a communication directly with a peer UE without using the network infrastructure. For example, as shown in  FIG. 9 , the UE 1   920  may perform a direct communication with the UE 2   930  via sidelink, without a support of the network infrastructure such as base station  910 . 
     In the direct communication via sidelink, a UE which performs a transmission to another UE via sidelink may be referred to as a transmission (TX) UE, and a UE which receives the transmission from another UE via sidelink may be referred to as a reception (RX) UE. For example, if the UE 1   920  performs a transmission to the UE 2   930  via sidelink, the UE 1   920  may be TX UE, and the UE 2   930  may be RX UE. For another example, if the UE 2   930  performs a transmission to the UE 1   920  via sidelink, the UE 1   920  may be RX UE, and the UE 2   930  may be TX UE. 
     According to various embodiments, upper layers configure the UE to receive or transmit sidelink communication on a specific frequency, to monitor or transmit non-public safety (PS) related sidelink discovery announcements on one or more frequencies or to monitor or transmit PS related sidelink discovery announcements on a specific frequency, but only if the UE is authorized to perform these particular proximity service (ProSe) related sidelink activities. 
     Sidelink communication comprises one-to-many and one-to-one sidelink communication. One-to-many sidelink communication comprises relay related and non-relay related one-to-many sidelink communication. One-to-one sidelink communication comprises relay related and non-relay related one-to-one sidelink communication. In relay related one-to-one sidelink communication the communicating parties comprise one sidelink relay UE and one sidelink remote UE. 
     Sidelink discovery comprises public safety related (PS related) and non-PS related sidelink discovery. PS related sidelink discovery comprises relay related and non-relay related PS related sidelink discovery. Upper layers indicate to RRC whether a particular sidelink announcement is PS related or non-PS related. 
     According to various embodiments, upper layers indicate to radio resource control (RRC) whether a particular sidelink procedure is V2X related or not. 
     According to various embodiments, the UE shall perform V2X sidelink communication operation if at least one of the following conditions 1)-3) is met: 
     Condition 1) if the UE&#39;s serving cell is suitable (RRC_IDLE or RRC_CONNECTED); and if either the selected cell on the frequency used for V2X sidelink communication operation belongs to the registered or equivalent public land mobile network (PLMN) as specified in 3GPP TS 24.334 or the UE is out of coverage on the frequency used for V2X sidelink communication operation as defined in 3GPP TS36.304; 
     Condition 2) if the UE&#39;s serving cell (for RRC_IDLE or RRC_CONNECTED) fulfils the conditions to support V2X sidelink communication in limited service state as specified in 3GPP TS 23.285; and if either the serving cell is on the frequency used for V2X sidelink communication operation or the UE is out of coverage on the frequency used for V2X sidelink communication operation as defined in 3GPP TS 36.304; or 
     Condition 3) if the UE has no serving cell (RRC_IDLE). 
       FIG. 10  shows an example of sidelink connectivity types to which technical features of the present disclosure can be applied. 
     Referring to  FIG. 10 , a sidelink connectivity between UE  1011  and UE  1013  may be “in-coverage”, where the two UEs UE  1011  and UE  1013  are under a coverage of a network (e.g., base station  1010 ). Also, the sidelink connectivity between the UE  1011  and the UE  1013  may be in-coverage of intra-cell type, as the UE  1011  receiving a sidelink transmission is within a same cell as the UE  1013  transmitting the sidelink transmission. 
     A sidelink connectivity between UE  1017  and UE  1021  may be also in-coverage, as the two UEs  1017  and  1021  are under a coverage of a network. However, unlike the case of the UE  1011  and the UE  1013 , the sidelink connectivity between the UE  1017  and the UE  1021  may be in-coverage of inter-cell type, as the UE  1021  receiving a sidelink transmission is within a cell coverage of a base station  1020  while the UE  1017  transmitting the sidelink transmission is within a cell coverage of a base station  1010 . 
     A sidelink connectivity between UE  1015  and UE  1031  may be “partial-coverage”, where one of the two UEs (e.g., UE  1015 ) is under a coverage of a network while the other UE (e.g., UE  1031 ) is outside the coverage of the network. 
     A sidelink connectivity between UE  1033  and UE  1035  may be “out-of-coverage”, where the two UEs UE  1033  and UE  1035  are outside a coverage of a network. 
       FIG. 11  shows an example of sidelink channel mapping to which technical features of the present disclosure can be applied. 
     Referring to  FIG. 11 , sidelink logical channels may comprise sidelink traffic channel (STCH) and sidelink broadcast control channel (SBCCH). Sidelink transport channels may comprise sidelink shared channel (SL-SCH), sidelink discovery channel (SL-DCH), and sidelink broadcast channel (SL-BCH). Sidelink physical channels and/or signals may comprise physical sidelink shared channel (PSSCH), physical sidelink control channel (PSCCH), physical sidelink discovery channel (PSDCH), sidelink synchronization signal (SLSS), and physical sidelink broadcast channel (PSBCH). 
     The STCH carries user data for sidelink communication. The STCH is mapped to the SL-SCH which, in turn, is mapped to the PSSCH. 
     The PSCCH carries sidelink control information (SCI). The SCI contains sidelink scheduling information such as resource block assignment, modulation and coding scheme, and/or group destination ID. 
     The SL-DCH is used for discovery announcements. The SL-DCH is mapped to the PSDCH. 
     The SLSS is a physical signal, which is used to synchronize a sidelink communication between UE and peer UE. The SLSS is associated with a specific sidelink identity (SLI). 
     The SBCCH is mapped to the SL-BCH which, in turn, is mapped to the PSBCH. These channels are also used for sidelink synchronization, and comprise sidelink related system information. For example, the sidelink related system information may be referred to as sidelink master information block (SL-MIB). 
     Although not illustrated in  FIG. 11 , there might be other channel(s) such as sidelink feedback channel (SL-FCH) and/or physical sidelink feedback channel (PSFCH). These channels are used to carry sidelink feedback control information (SFCI) from a device receiving a sidelink transmission. 
     Hereinafter, sidelink HARQ operation is described. 
     The MAC entity may be configured by upper layers to transmit using pool(s) of resources on one or multiple carriers. For each carrier, there may be one sidelink HARQ entity at the MAC entity for transmission on SL-SCH, which maintains a number of parallel sidelink processes. 
     For sidelink communication, the number of transmitting sidelink processes associated with the sidelink HARQ entity may be 8 if the UE supports multiple transmissions of sidelink communication to different destinations in one sidelink control (SC) period. 
     For V2X sidelink communication, the maximum number of transmitting sidelink processes associated with each sidelink HARQ entity may be 8. A sidelink process may be configured for transmissions of multiple MAC PDUs. For transmissions of multiple MAC PDUs, the maximum number of transmitting sidelink processes associated with each sidelink HARQ entity may be 2. 
     A delivered and configured sidelink grant and HARQ information associated with the sidelink grant may be associated with a sidelink process. 
     For each subframe of the SL-SCH and each sidelink process, the sidelink HARQ Entity shall: 
     1&gt; if a sidelink grant corresponding to a new transmission opportunity has been indicated for this sidelink process and there is SL data, for sidelink logical channels of proximity service (ProSe) destination associated with this sidelink grant, available for transmission: 
     2&gt; obtain the MAC PDU from the “Multiplexing and assembly” entity; 
     2&gt; deliver the MAC PDU and the sidelink grant and the HARQ information to this sidelink process; 
     2&gt; instruct this Sidelink process to trigger a new transmission. 
     1&gt; else, if this subframe corresponds to retransmission opportunity for this Sidelink process: 
     2&gt; instruct this sidelink process to trigger a retransmission. 
     Hereinafter, sidelink process is described. 
     The Sidelink process may be associated with a HARQ buffer. 
     The sequence of redundancy versions may be 0, 2, 3, 1. The variable CURRENT IRV may be an index into the sequence of redundancy versions. This variable may be updated modulo 4. 
     New transmissions and retransmissions either for a given SC period in sidelink communication or in V2X sidelink communication may be performed on the resource indicated in the sidelink grant and with the proper MCS. 
     If the sidelink process is configured to perform transmissions of multiple MAC PDUs for V2X sidelink communication, the sidelink process may maintain a counter SL_RESOURCE_RESELECTION_COUNTER. For other configurations of the sidelink process, this counter may not be available. 
     If the sidelink HARQ entity requests a new transmission, the sidelink process shall: set CURRENT_IRV_to 0; store the MAC PDU in the associated HARQ buffer; store the sidelink grant received from the Sidelink HARQ Entity; and generate a transmission as described below. 
     If the sidelink HARQ entity requests a retransmission, the sidelink process shall: generate a transmission as described below. 
     To generate a transmission, the sidelink process shall: 
     1&gt; if there is no uplink transmission; or if the MAC entity is able to perform uplink transmissions and transmissions on SL-SCH simultaneously at the time of the transmission; or if there is a MAC PDU to be transmitted in this TTI in uplink, except a MAC PDU obtained from the Msg3 buffer and transmission of V2X sidelink communication is prioritized over uplink transmission; and 
     1&gt; if there is no sidelink discovery gap for transmission or no transmission on PSDCH at the time of the transmission; or, in case of transmissions of V2X sidelink communication, if the MAC entity is able to perform transmissions on SL-SCH and transmissions on PSDCH simultaneously at the time of the transmission: 
     2&gt; instruct the physical layer to generate a transmission according to the stored sidelink grant with the redundancy version corresponding to the CURRENT_IRV_value. 
     1&gt; increment CURRENT_IRV_by 1; 
     1&gt; if this transmission corresponds to the last transmission of the MAC PDU: 
     2&gt; decrement SL_RESOURCE_RESELECTION_COUNTER by 1, if available. 
     The transmission of the MAC PDU for V2X sidelink communication may be prioritized over uplink transmissions if the following conditions 1˜3 are met: 
     Condition 1) if the MAC entity is not able to perform all uplink transmissions and all transmissions of V2X sidelink communication simultaneously at the time of the transmission; and 
     Condition 2) if uplink transmission is not prioritized by upper layer; and 
     Condition 3) if the value of the highest priority of the sidelink logical channel(s) in the MAC PDU is lower than thresSL-TxPrioritization if thresSL-TxPrioritization is configured. 
     For sidelink transmission, TX UE may transmit HARQ (re-)transmissions of a MAC PDU. Then, RX UE can send positive or negative HARQ feedback to TX UE. When TX UE receives, from RX UE, a negative feedback (i.e., NACK) for a (re-)transmission of a MAC PDU, TX UE can perform a retransmission of the MAC PDU. However, in some cases, TX UE may not have resource(s) for retransmission of the MAC PDU. 
     In particular, when TX UE has no retransmission resource for sidelink retransmission, TX UE can request sidelink resource(s) to a base station (e.g. gNB/NG-RAN). Then, when TX UE receives a sidelink grant for the retransmission, TX UE will perform retransmission of the MAC PDU based on the received sidelink grant for the retransmission. However, it may take some time in steps of requesting the resources and receiving the sidelink grant for the retransmission. Thus, the steps of requesting the resources and receiving the sidelink grant for the retransmission may not need delay requirement. 
     Therefore, various embodiments of the present disclosure provide a method and apparatus for reserving retransmission resources based on at least one of a congestion level and/or a priority of a data unit. 
       FIG. 12  shows an example of a method for performing a retransmission according to an embodiment of the present disclosure. Steps illustrated in  FIG. 12  may be performed by a first wireless device and/or a UE. 
     Referring to  FIG. 12 , in step S 1201 , the first wireless device may reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission. For example, to reserve the set of resources, the first wireless device may randomly select time and frequency resources from resources in a resource pool. The resource pool may be configured by a network. Then, the first wireless device may select a set of periodic resources spaced by a resource reservation interval based on the time and frequency resources. Among the set of periodic resources, the first wireless device may determine the set of resources comprising a first subset of resources for the initial transmission and a second subset of resources for the retransmission. The first subset of resources may comprise the first resource, and the second subset of resources may comprise the second resource. 
     In step S 1203 , the first wireless device may create a data unit based on the first resource and the second resource. The data unit may comprise a MAC PDU. 
     In step S 1205 , the first wireless device may perform the initial transmission of the data unit by using the first resource. 
     In step S 1207 , the first wireless device may determine whether to reserve a resource for a retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit. How the first wireless device can determine to reserve a resource for a retransmission of a data unit or determine not to reserve a resource for a retransmission of a data unit will be described below. 
     In step S 1209 , the first wireless device may remove/release the second resource and reserve a third resource as the resource for the retransmission of the data unit. The first wireless device may remove the second resource and reserve a third resource as the resource for the retransmission of the data unit, based on i) a determination to reserve the resource for the retransmission of the data unit, and/or ii) a determination that the retransmission of the data unit is still valid but there is no grant valid for the retransmission of the data unit. On the other hand, rather than removing the second resource and reserving the third resource, the first wireless device may perform the retransmission of the data unit by using the second resource to the second wireless device, based on i) a determination not to reserve the resource for the retransmission of the data unit, and/or ii) a determination that the retransmission of the data unit is still valid and there is a grant valid for the retransmission of the data unit. 
     In step S 1211 , the first wireless device may perform the retransmission of the data unit to the second wireless device by using the third resource. 
     According to various embodiments, the set of resource may be related to/correspond to one or more sidelink grants. 
     According to various embodiments, the first wireless device may determine to newly reserve the resource for the retransmission of the data unit if/when a CBR on resources comprising the second resource is above a CBR threshold. The CBR threshold may be configured or signalled by a network to the first wireless device via at least one of downlink control information (DCI), a media access control (MAC) control element (MAC CE), or a radio resource control (RRC) signalling. The CBR threshold may be related to the priority of the data unit. 
     According to various embodiments, the first wireless device may determine whether to newly reserve the resource for the retransmission of the data unit based on a QoS requirement. The QoS requirement may comprise at least one of a required delay, a required error rate, or a required communication range. 
     According to various embodiments, the first wireless device may determine to newly reserve the resource for the retransmission of the data unit if/when a NACK for a most recent transmission of the data unit is received after a tolerance period from a start time of the initial transmission of the data unit. The tolerance period may be the required delay minus a delay threshold. The delay threshold may be configured or signalled by a network to the first wireless device via at least one of downlink control information (DCI), a media access control (MAC) control element (MAC CE), or a radio resource control (RRC) signalling. 
     According to various embodiments, the first wireless device may determine to newly reserve the resource for the retransmission of the data unit if/when a physical uplink control channel (PUCCH) resource for a scheduling request (SR) is unavailable within a tolerance period from a start time of the initial transmission of the data unit. The tolerance period may be the required delay minus a delay threshold. The delay threshold may be configured or signalled by a network to the first wireless device via at least one of downlink control information (DCI), a media access control (MAC) control element (MAC CE), or a radio resource control (RRC) signalling. 
     According to various embodiments, the first wireless device may determine to newly reserve the resource for the retransmission of the data unit if/when a distance between the first wireless device and the second wireless device is longer than the required communication range. 
     According to various embodiments, the first wireless device may determine to newly reserve the resource for the retransmission of the data unit if/when the QoS requirement for the data unit is not satisfied on the second resource. 
     According to various embodiments, the first wireless device may determine not to newly reserve the resource for the retransmission of the data unit if/when a channel busy ratio (CBR) on the second resource is lower than the CBR threshold. 
     According to various embodiments, the first wireless device may determine not to newly reserve the resource for the retransmission of the data unit if/when a NACK for a most recent transmission of the data unit is received within the tolerance period from a start time of the initial transmission of the data unit. 
     According to various embodiments, the first wireless device may determine not to newly reserve the resource for the retransmission of the data unit if/when a PUCCH resource for a scheduling request (SR) is available within the tolerance period from the start time of the initial transmission of the data unit. 
     According to various embodiments, the first wireless device may determine not to newly reserve the resource for the retransmission of the data unit if/when a distance between the first wireless device and the second wireless device is shorter than or equal to the required communication range. 
       FIG. 13  shows an example of a method for performing data transmission according to an embodiment of the present disclosure. The steps illustrated in  FIG. 13  may be performed by a wireless device and/or a UE. 
     Referring to  FIG. 13 , in step S 1301 , the UE may reserve resources for transmission for a data unit. When data is available for transmission in a UE buffer, the UE may reserve one or more resources for transmission of a data unit and/or multiple resources for transmission of multiple data units. The reserved resources may be considered as one or more grants. The data unit may comprise a MAC PDU. 
     Alternatively, the UE may request one or more resources to the network and receive one or more grants on PDCCH from the network. The grant may comprise at least one of a sidelink dynamic grant or a configured sidelink grant type 1 or 2. 
     In step S 1303 , the UE may select one of the grants for a new transmission and create a data unit based on the selected grant. 
     In step S 1305 , the UE may perform a new transmission of the data unit to a receiving node by using the grant. The UE may provide the data unit and the selected grant to a HARQ process, and then perform a new transmission of the data unit from the HARQ process towards a receiving node by using the grant. The receiving node may comprise at least one of another UE or a base station (e.g., gNB and/or eNB). If the receiving node is another UE, the transmission may be performed in sidelink. If the receiving node is a base station, the transmission may be performed in uplink. The grants may be associated with a HARQ process ID of the HARQ process. 
     In step S 1307 , the UE may determine to reserve a retransmission resource based on at least one of a QoS requirement, a congestion level and/or a priority of the data unit. For example, if no positive acknowledgment for the transmission of the data unit has been received and if there is no grant for a retransmission for the HARQ process, the UE may determine whether to reserve a retransmission resource based on at least one of a QoS requirement, a congestion level and/or a priority of the data unit. 
     The QoS requirement may comprise at least one of a requirement on delay, an error rate, and/or a communication range. The congestion level may comprise a channel busy ratio (CBR). 
     In step S 1309 , the UE may trigger a TX resource reselection (or, TX carrier reselection) to clear the currently reserved resources and resource one or more new grants for the retransmission of the data unit. That is, if the UE determines to reserve retransmission resources and if there is no grant valid for the retransmission of the data unit, the UE may trigger a TX resource reselection (or, TX carrier reselection) to clear the currently reserved resources and reserve one or more new grants for the retransmission of the data unit. 
     The number of retransmissions and/or the number of grants used for the retransmissions may be determined based on at least one of a QoS requirement, a congestion level and/or a priority of the data unit. 
     Alternatively, the UE may select to create a configured sidelink grant corresponding to transmissions of the data unit and reserve one or more new grants for retransmissions of the data unit from the HARQ process on a carrier in parallel with the currently reserved resources. The currently reserved resources and the new grants may be on the same carrier or different carriers. 
     In step S 1311 , the UE may perform one or more retransmissions of the data unit from the HARQ process towards the receiving node by using the one or more new grants that are reserved for the retransmissions of the data unit. Upon reserving one or more grants, the UE may select one of the reserved grant(s) and provide the selected grant(s) to the HARQ process and then perform one or more retransmissions of the data unit from the HARQ process towards the receiving node by using the grant(s). The grants may be associated with the HARQ process ID of the HARQ process. 
       FIG. 14  shows an example of a signal flow for performing a retransmission according to an embodiment of the present disclosure. Steps illustrated in  FIG. 14  may be performed by a base station (BS), a first wireless device and/or a second wireless device. 
     Referring to  FIG. 14 , in step S 1401 , the BS may receive, from the first wireless device, a sidelink UE information. 
     In step S 1403 , the BS may transmit, to the first wireless device, a configuration of a resource pool for configuring with the first wireless device with the resource pool. 
     In step S 1405 , the first wireless device may reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission, based on resources in the resource pool. 
     In step S 1407 , the first wireless device may create a data unit based on the first resource and the second resource. The data unit may comprise a MAC PDU. 
     In step S 1409 , the first wireless device may perform the initial transmission of the data unit by using the first resource. 
     In step S 1411 , the first wireless device may determine whether to reserve a resource for a retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit. 
     In step S 1413 , the first wireless device may remove/release the second resource and reserve a third resource as the resource for the retransmission of the data unit. 
     In step S 1415 , the first wireless device may perform the retransmission of the data unit to the second wireless device by using the third resource. 
     The BS in  FIG. 14  may be an example of a second device  220  in  FIG. 2 , and therefore, steps of the BS as illustrated in  FIG. 14  may be implemented by the second device  220 . For example, the processor  221  may be configured to control the transceiver  223  to receive, from a first wireless device, a sidelink UE information. The processor may be configured to control the transceiver  223  to transmit, to the first wireless device, a configuration of a resource pool for configuration with the first wireless device with the resource pool. The first wireless device may reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission, based on resources in the resource pool. The first wireless device may create a data unit based on the first resource and the second resource. The first wireless device may perform the initial transmission of the data unit by using the first resource. The first wireless device may determine whether to reserve a resource for a retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit. The first wireless device may remove/release the second resource and reserve a third resource as the resource for the retransmission of the data unit. The first wireless device may perform the retransmission of the data unit to the second wireless device by using the third resource. 
       FIG. 15  shows an example of a sidelink data transmission of a MAC PDU according to an embodiment of the present disclosure.  FIG. 15  describes an embodiment regarding the sidelink data transmission, but the embodiment and/or various embodiments of the present disclosure can also be applied to uplink data transmission as well. 
     Referring to  FIG. 15 , in step S 1501 , the TX UE may reserve one or more resources for transmission and/or retransmission of a data unit. The data unit may comprise a MAC PDU. For example, the TX UE may transmit a sidelink UE information to a network and/or a base station, and receive a resource pool configuration. After/upon receiving the resource pool configuration, the TX UE may be configured with a resource pool. The resource pool may refer to a set of physical resources (e.g., subframes and/or resource blocks), available to a UE and/or a wireless device for sidelink transmissions. When data is available for transmission in a UE buffer, the TX UE may reserve one or more resources for transmissions of a data unit and/or multiple resources for transmissions of multiple data unit, based on resources in the resource pool. The reserved resources may be considered as one or more grants. 
     For one or more HARQ retransmission, the TX UE may reserve one or more resources based on resources in the resource pool, as the followings steps 1) to 4): 
     Step 1) The TX UE may randomly select time and frequency resources for one or more transmission opportunities from resources in the resource pool. The resources in the resource pool may comprise the entire resources in the resource pool, or a part of the entire resources in the resource pool. 
     Step 2) The TX UE may use the randomly selected resources to select a set of periodic resources spaced by the resource reservation interval. 
     Step 3) Among the selected set of periodic resources, the TX UE may consider a first subset of resources as resources for new transmission(s), and a second subset of resources as resources for retransmission(s). 
     Step 4) The TX UE may consider the first subset of resources for new transmission(s) and the second subset of resources for retransmission(s) as a sidelink grant. 
     Therefore, a sidelink grant may be a set of resources comprising one or more resources for a new/initial transmission, and one or more resources for a retransmission. 
     Alternatively, the TX UE may request one or more resources to the network and receive one or more grants on PDCCH from the network. The grant may comprise a sidelink dynamic grant or a configured sidelink grant type 1 or 2. 
     The TX UE may select one of the grants for new transmission and/or retransmission, and create a data unit based on the selected grant. 
     In step S 1503 , the TX UE may provide the data unit and the selected grant to a HARQ process and then perform a new/initial transmission of the data unit (e.g., MAC PDU #1) from the HARQ process towards a receiving node by using the grant. The receiving node may comprise another UE, and the transmission may be performed in sidelink. The grants may be associated with a HARQ process ID of the HARQ process. 
     The TX UE may monitor physical sidelink feedback channel (PSFCH) providing acknowledgement information for the HARQ (re-)transmission. Upon receiving a negative acknowledgement (NACK), no acknowledgment, and/or a grant for a retransmission of the data unit, the TX UE may perform a retransmission of the data unit. 
     If no positive acknowledgement for the transmission of the data unit has been received yet and if there is no grant for retransmission for the HARQ process, the TX UE may determine whether a retransmission of the data unit is still valid or not (and/or whether to reserve a retransmission resource) based on at least one of a QoS requirement, congestion level and/or a priority of the data unit. 
     The QoS requirement may include at least one of a required delay, a required error rate, and/or a required communication range. 
     The congestion level may include a channel busy ratio (CBR). 
     For example, if the required delay of the data unit is 100 ms, and if acknowledgement information (e.g., NACK) for the most recent (re-)transmission of the data unit is received within {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine that a retransmission of the data unit is still valid. But, if acknowledgement information for the most recent (re-)transmission of the data unit is received after {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine that a retransmission of the data unit is not valid. The threshold may be configured by the network or pre-configured. 
     For example, if the required delay of the data unit is 100 ms, and if there is a valid PUCCH resource for scheduling request within {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine that a retransmission of the data unit is still valid. But, if there is no valid PUCCH resource for scheduling request within {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine that a retransmission of the data unit is not valid. The threshold may be configured by the network or pre-configured. 
     For example, if the required communication range is 200 m, and if the distance between the TX UE and the receiving node is shorter than or equal to 200 ms, the TX UE may determine that a retransmission of the data unit is still valid. But, if the distance between the TX UE and the receiving node is longer than 200 ms, the TX UE may determine that a retransmission of the data unit is not valid. 
     For example, the TX UE may measure a channel busy ratio (CBR) on sidelink resources. If the CBR is below or equal to a threshold related to the priority of the data unit, UE may determine that a retransmission of the data unit is still valid. But, if the CBR is above a threshold related to the priority of the data unit, UE may determine that a retransmission of the data unit is not valid. 
     For example, if the required delay of the data unit is 100 ms, and if acknowledgement information (e.g., NACK) for the most recent (re-)transmission of the data unit is received within {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine not to reserve a retransmission resource for the data unit. But, if acknowledgement information for the most recent (re-)transmission of the data unit is received after {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine to reserve a retransmission resource for the data unit. The threshold may be configured by the network or pre-configured. 
     For example, if the required delay of the data unit is 100 ms, and if there is a valid PUCCH resource for scheduling request within {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine not to reserve a retransmission resource for the data unit. But, if there is no valid PUCCH resource for scheduling request within {100 ms—a threshold} from the start of the first/initial transmission of the data unit, the TX UE may determine to reserve a retransmission resource for the data unit. The threshold may be configured by the network or pre-configured. 
     The threshold may be configured by the network or pre-configured. 
     For example, if the required communication range is 200 m, and if the distance between the TX UE and the receiving node is shorter than or equal to 200 ms, the TX UE may determine not to reserve a retransmission resource for the data unit. But, if the distance between the TX UE and the receiving node is longer than 200 ms, the TX UE may determine to reserve a retransmission resource for the data unit. The threshold may be configured by the network or pre-configured. 
     For example, the TX UE may measure a channel busy ratio (CBR) on sidelink resources. If the CBR is below or equal to a threshold related to the priority of the data unit, UE may determine not to reserve a retransmission resource for the data unit. But, if the CBR is above a threshold related to the priority of the data unit, UE may determine to reserve a retransmission resource for the data unit. The threshold may be configured by the network or pre-configured. 
     In step S 1505 , if the TX UE determines that a retransmission of the data unit is still valid (and/or a reservation of retransmission resource(s) and/or if there is no grant valid for a retransmission of the data unit, the TX UE may trigger a TX resource reselection (or TX carrier reselection) to clear the currently reserved resource(s) and reserve one or more new grants for the retransmission(s) of the data unit. 
     The number of retransmissions and the number of grants used for the retransmissions may be determined based on at least one of the QoS requirement, congestion level and/or the priority of the data unit. 
     For example, if the TX UE had already performed  5  (re-)transmissions of the MAC PDU on a carrier, if 3 more retransmissions are still valid for the MAC PDU, and if the currently reserved resources cannot meet QoS requirement of the MAC PDU and/or no resources valid for retransmissions of the MAC PDU are reserved, the TX UE may trigger the TX resource reselection in which the TX UE clears the currently reserved grant(s) and reserves one or more new grants on the carrier for new transmissions and retransmissions of one or more MAC PDUs. 
     For example, if the TX UE had already performed  5  (re-)transmissions of the MAC PDU on a carrier, if 3 more retransmissions are still valid for the MAC PDU, and if the currently reserved resources cannot meet QoS requirement of the MAC PDU and/or no resources valid for retransmissions of the MAC PDU are reserved, the TX UE may trigger the TX carrier reselection in which the TX UE clears the currently reserved grant(s) on the carrier, reselects to a new carrier or the same carrier, and reserves one or more new grants on the reselected carrier for new transmissions and retransmissions of one or more MAC PDUs. 
     When a new grant is reserved for a retransmission of the data unit, a PSFCH resource may also be reserved for a transmission of acknowledgement information to the retransmission. 
     Alternatively, the TX UE may select to create a configured sidelink grant corresponding to transmission(s) of the data unit and reserve one or more new grants for retransmission(s) of the data unit from the HARQ process on a carrier in parallel with the currently reserved resources. 
     The currently reserved resources and the new grants may be on the same carrier or different carriers. 
     For example, if the TX UE had already performed  3  (re-)transmissions of the MAC PDU on a carrier and one more retransmission is still valid for the MAC PDU, the TX UE may reserve one or more new grants on the carrier for retransmissions of the MAC PDU. 
     In step S 1507 , upon reserving one or more grants, the TX UE may select one of the reserved grant(s) and provide the selected grant(s) to the HARQ process and then perform one or more retransmissions of the data unit from the HARQ process towards a receiving node by using the grant(s). 
     The grants may be associated with the HARQ process ID of the HARQ process. 
     Alternatively, upon receiving one or more grants on PDCCH from the network, if one of the grants is valid for a retransmission of the data unit, the TX UE may provide the grant to the HARQ process and perform the retransmission of the data unit from the HARQ process towards a receiving node by using the grant(s). The grants may be received with a HARQ process ID of the HARQ process. 
     When the TX UE determines that a retransmission of the data unit is not valid, the TX UE may discard the data unit from the HARQ process or replace the data unit by a new data unit with the HARQ process. 
     In step S 1509 , the TX UE may receive a positive acknowledgement (i.e., ACK) for the retransmission on PSFCH. 
     In step S 1511 , if the positive acknowledgement for the retransmission (i.e., ACK) is received on PSFCH, the TX UE may (re-)allocate the remaining grant(s) to another data unit (e.g., MAC PDU #2) to the same or a different HARQ process. 
     Alternatively, if the positive acknowledgement for the retransmission (i.e., ACK) is received, the TX UE may skip the remaining grant(s). 
     According to various embodiments, a wireless device may perform the following steps: 
     1&gt; if the MAC entity selects to create a configured sidelink grant corresponding to transmission(s) of a single MAC PDU, and SL data is available in a logical channel or a single MAC PDU stored in a Sidelink process has no sidelink grant valid for retransmission(s) of the MAC PDU: 
     2&gt; perform the TX resource (re-)selection check; 
     2&gt; if the TX resource (re-)selection is triggered as the result of the TX resource (re-) selection check; 
     3&gt; select a set of resources; 
     3&gt; use the selected sidelink grant to determine the set of PSCCH/PSSCH duration(s); 
     3&gt; consider the selected sidelink grant to be a configured sidelink grant. 
     According to various embodiments, a wireless device may perform the following steps: 
     1&gt; if no positive acknowledgement has been received for transmission of a MAC PDU, the number of retransmissions of the MAC PDU has been not reached yet, and there is no sidelink grant which can meet delay requirement of the MAC PDU; 
     2&gt; clear the configured sidelink grant associated to the Sidelink process, if available; 
     2&gt; trigger the TX resource (re-)selection. 
     According to various embodiments, a wireless device may perform the following steps for TX resource (re-)selection check: 
     1&gt; if a resource(s) of the selected sidelink grant is indicated for re-evaluation or pre-emption by the physical layer; or 
     1&gt; if retransmission of a MAC PDU on the selected sidelink grant has been dropped by either sidelink congestion control or de-prioritization: 
     2&gt; remove the resource(s) from the selected sidelink grant associated to the Sidelink process, if the resource(s) of the selected sidelink grant is indicated for re-evaluation or pre-emption by the physical layer; 
     2&gt; randomly select the time and frequency resource from the resources indicated by the physical for either the removed resource or the dropped resource, according to the amount of selected frequency resources, the selected number of HARQ retransmissions and the remaining PDB of either SL data available in the logical channel(s) by ensuring the minimum time gap between any two selected resources of the selected sidelink grant in case that PSFCH is configured for this pool of resources, and that a resource can be indicated by the time resource assignment of a SCI for a retransmission; 
     2&gt; if no resource(s) is selected by ensuring that the resource(s) can be indicated by the time resource assignment of a SCI for one or more retransmissions: 
     3&gt; randomly select the time and frequency resources for one or more transmission opportunities from the available resources, according to the amount of selected frequency resources, the selected number of HARQ retransmissions and the remaining PDB of SL data available in the logical channel(s) allowed on the carrier. 
     2&gt; replace the removed or dropped resource(s) by the selected resource(s) for the selected sidelink grant. 
       FIG. 16  shows a UE to implement an embodiment of the present disclosure. The present disclosure described above for UE side may be applied to this embodiment. The UE in  FIG. 16  may be an example of first device  216  as illustrated in  FIG. 2 . 
     A UE includes a processor  1610  (i.e., processor  211 ), a power management module  1611 , a battery  1612 , a display  1613 , a keypad  1614 , a subscriber identification module (SIM) card  1615 , a memory  1620  (i.e., memory  212 ), a transceiver  1630  (i.e., transceiver  213 ), one or more antennas  1631 , a speaker  1640 , and a microphone  1641 . 
     The processor  1610  may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor  1610 . The processor  1610  may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The processor  1610  may be an application processor (AP). The processor  1610  may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a modem (modulator and demodulator). An example of the processor  1610  may be found in SNAPDRAGON™ series of processors made by Qualcomm®, EXYNOS™ series of processors made by Samsung®, A series of processors made by Apple®, HELIO™ series of processors made by MediaTek®, ATOM™ series of processors made by Intel® or a corresponding next generation processor. 
     The processor  1610  may be configured to, or configured to control the transceiver  1630  to implement steps performed by the UE and/or the wireless device throughout the disclosure. 
     The power management module  1611  manages power for the processor  1610  and/or the transceiver  1630 . The battery  1612  supplies power to the power management module  1611 . The display  1613  outputs results processed by the processor  1610 . The keypad  1614  receives inputs to be used by the processor  1610 . The keypad  1614  may be shown on the display  1613 . The SIM card  1615  is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers). It is also possible to store contact information on many SIM cards. 
     The memory  1620  is operatively coupled with the processor  1610  and stores a variety of information to operate the processor  1610 . The memory  1620  may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the memory  1620  and executed by the processor  1610 . The memory  1620  can be implemented within the processor  1610  or external to the processor  1610  in which case those can be communicatively coupled to the processor  1610  via various means as is known in the art. 
     The transceiver  1630  is operatively coupled with the processor  1610 , and transmits and/or receives a radio signal. The transceiver  1630  includes a transmitter and a receiver. The transceiver  1630  may include baseband circuitry to process radio frequency signals. The transceiver  1630  controls the one or more antennas  1631  to transmit and/or receive a radio signal. 
     The speaker  1640  outputs sound-related results processed by the processor  1610 . The microphone  1641  receives sound-related inputs to be used by the processor  1610 . 
     According to various embodiments, the processor  1610  may be configured to, or configured to control the transceiver  1630  to implement steps performed by the UE and/or the wireless device throughout the disclosure. For example, the processor  1610  may be configured to reserve a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission. The processor  1610  may be configured to create a data unit based on the first resource and the second resource. The processor  1610  may be configured to control the transceiver  1630  to perform the initial transmission of the data unit by using the first resource. The processor  1610  may be configured to determine whether to reserve a resource for a retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit. The processor  1610  may be configured to remove/release the second resource and reserve a third resource as the resource for the retransmission of the data unit. The processor  1610  may be configured to control the transceiver  1630  to perform the retransmission of the data unit to the second wireless device by using the third resource. 
     According to various embodiments, the set of resource may be related to/correspond to one or more sidelink grants. 
     According to various embodiments, the processor  1610  may be configured to determine to newly reserve the resource for the retransmission of the data unit if/when a CBR on resources comprising the second resource is above a CBR threshold. The CBR threshold may be configured or signalled by a network to the first wireless device via at least one of downlink control information (DCI), a media access control (MAC) control element (MAC CE), or a radio resource control (RRC) signalling. The CBR threshold may be related to the priority of the data unit. 
     According to various embodiments, the processor  1610  may be configured to determine whether to newly reserve the resource for the retransmission of the data unit based on a QoS requirement. The QoS requirement may comprise at least one of a required delay, a required error rate, or a required communication range. 
     According to various embodiments, the processor  1610  may be configured to determine to newly reserve the resource for the retransmission of the data unit if/when a NACK for a most recent transmission of the data unit is received after a tolerance period from a start time of the initial transmission of the data unit. The tolerance period may be the required delay minus a delay threshold. The delay threshold may be configured or signalled by a network to the first wireless device via at least one of downlink control information (DCI), a media access control (MAC) control element (MAC CE), or a radio resource control (RRC) signalling. 
     According to various embodiments, the processor  1610  may be configured to determine to newly reserve the resource for the retransmission of the data unit if/when a physical uplink control channel (PUCCH) resource for a scheduling request (SR) is unavailable within a tolerance period from a start time of the initial transmission of the data unit. The tolerance period may be the required delay minus a delay threshold. The delay threshold may be configured or signalled by a network to the first wireless device via at least one of downlink control information (DCI), a media access control (MAC) control element (MAC CE), or a radio resource control (RRC) signalling. 
     According to various embodiments, the processor  1610  may be configured to determine to newly reserve the resource for the retransmission of the data unit if/when a distance between the first wireless device and the second wireless device is longer than the required communication range. 
     According to various embodiments, the processor  1610  may be configured to determine to newly reserve the resource for the retransmission of the data unit if/when the QoS requirement for the data unit is not satisfied on the second resource. 
     According to various embodiments, the processor  1610  may be configured to determine not to newly reserve the resource for the retransmission of the data unit if/when a channel busy ratio (CBR) on the second resource is lower than the CBR threshold. 
     According to various embodiments, the processor  1610  may be configured to determine not to newly reserve the resource for the retransmission of the data unit if/when a NACK for a most recent transmission of the data unit is received within the tolerance period from a start time of the initial transmission of the data unit. 
     According to various embodiments, the processor  1610  may be configured to determine not to newly reserve the resource for the retransmission of the data unit if/when a PUCCH resource for a scheduling request (SR) is available within the tolerance period from the start time of the initial transmission of the data unit. 
     According to various embodiments, the processor  1610  may be configured to determine not to newly reserve the resource for the retransmission of the data unit if/when a distance between the first wireless device and the second wireless device is shorter than or equal to the required communication range. 
       FIG. 17  shows another example of a wireless communication system to which the technical features of the present disclosure can be applied. 
     Referring to  FIG. 17 , the wireless communication system may include a first device  1710  (i.e., first device  210 ) and a second device  1720  (i.e., second device  220 ). 
     The first device  1710  may include at least one transceiver, such as a transceiver  1711 , and at least one processing chip, such as a processing chip  1712 . The processing chip  1712  may include at least one processor, such a processor  1713 , and at least one memory, such as a memory  1714 . The memory may be operably connectable to the processor  1713 . The memory  1714  may store various types of information and/or instructions. The memory  1714  may store a software code  1715  which implements instructions that, when executed by the processor  1713 , perform operations of the first device  910  described throughout the disclosure. For example, the software code  1715  may implement instructions that, when executed by the processor  1713 , perform the functions, procedures, and/or methods of the first device  1710  described throughout the disclosure. For example, the software code  1715  may control the processor  1713  to perform one or more protocols. For example, the software code  1715  may control the processor  1713  to perform one or more layers of the radio interface protocol. 
     The second device  1720  may include at least one transceiver, such as a transceiver  1721 , and at least one processing chip, such as a processing chip  1722 . The processing chip  1722  may include at least one processor, such a processor  1723 , and at least one memory, such as a memory  1724 . The memory may be operably connectable to the processor  1723 . The memory  1724  may store various types of information and/or instructions. The memory  1724  may store a software code  1725  which implements instructions that, when executed by the processor  1723 , perform operations of the second device  1720  described throughout the disclosure. For example, the software code  1725  may implement instructions that, when executed by the processor  1723 , perform the functions, procedures, and/or methods of the second device  1720  described throughout the disclosure. For example, the software code  1725  may control the processor  1723  to perform one or more protocols. For example, the software code  1725  may control the processor  1723  to perform one or more layers of the radio interface protocol. 
     According to various embodiments, the first device  1710  as illustrated in  FIG. 17  may comprise a wireless device. The wireless device may comprise a transceiver  1711 , a processing chip  1712 . The processing chip  1712  may comprise a processor  1713 , and a memory  1714 . The memory  1714  may be operably connectable to the processor  1713 . The memory  1714  may store various types of information and/or instructions. The memory  1714  may store a software code  1715  which implements instructions that, when executed by the processor  1713 , perform operations comprising: reserving a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission; creating a data unit based on the first resource and the second resource; performing the initial transmission of the data unit to a second wireless device by using the first resource; determining whether to reserve a resource for the retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; removing the second resource and reserving a third resource as the resource for the retransmission of the data unit; and performing the retransmission of the data unit by using the third resource to the second wireless device. 
     According to various embodiments, a computer-readable medium having recorded thereon a program for performing each step of a method on a computer is provided. The method comprises: reserving a set of resources comprising at least a first resource for an initial transmission and a second resource for a retransmission; creating a data unit based on the first resource and the second resource; performing the initial transmission of the data unit to a second wireless device by using the first resource; determining whether to reserve a resource for the retransmission of the data unit based on at least one of a congestion level and/or a priority of the data unit; removing the second resource and reserving a third resource as the resource for the retransmission of the data unit; and performing the retransmission of the data unit by using the third resource to the second wireless device. 
     The present disclosure may be applied to various future technologies, such as AI, robots, autonomous-driving/self-driving vehicles, and/or extended reality (XR). 
     &lt;AI&gt; 
     AI refers to artificial intelligence and/or the field of studying methodology for making it. Machine learning is a field of studying methodologies that define and solve various problems dealt with in AI. Machine learning may be defined as an algorithm that enhances the performance of a task through a steady experience with any task. 
     An artificial neural network (ANN) is a model used in machine learning. It can mean a whole model of problem-solving ability, consisting of artificial neurons (nodes) that form a network of synapses. An ANN can be defined by a connection pattern between neurons in different layers, a learning process for updating model parameters, and/or an activation function for generating an output value. An ANN may include an input layer, an output layer, and optionally one or more hidden layers. Each layer may contain one or more neurons, and an ANN may include a synapse that links neurons to neurons. In an ANN, each neuron can output a summation of the activation function for input signals, weights, and deflections input through the synapse. Model parameters are parameters determined through learning, including deflection of neurons and/or weights of synaptic connections. The hyper-parameter means a parameter to be set in the machine learning algorithm before learning, and includes a learning rate, a repetition number, a mini batch size, an initialization function, etc. The objective of the ANN learning can be seen as determining the model parameters that minimize the loss function. The loss function can be used as an index to determine optimal model parameters in learning process of ANN. 
     Machine learning can be divided into supervised learning, unsupervised learning, and reinforcement learning, depending on the learning method. Supervised learning is a method of learning ANN with labels given to learning data. Labels are the answers (or result values) that ANN must infer when learning data is input to ANN. Unsupervised learning can mean a method of learning ANN without labels given to learning data. Reinforcement learning can mean a learning method in which an agent defined in an environment learns to select a behavior and/or sequence of actions that maximizes cumulative compensation in each state. 
     Machine learning, which is implemented as a deep neural network (DNN) that includes multiple hidden layers among ANN, is also called deep learning. Deep learning is part of machine learning. In the following, machine learning is used to mean deep learning. 
       FIG. 18  shows an example of an AI device to which the technical features of the present disclosure can be applied. 
     The AI device  1800  may be implemented as a stationary device or a mobile device, such as a TV, a projector, a mobile phone, a smartphone, a desktop computer, a notebook, a digital broadcasting terminal, a PDA, a PMP, a navigation device, a tablet PC, a wearable device, a set-top box (STB), a digital multimedia broadcasting (DMB) receiver, a radio, a washing machine, a refrigerator, a digital signage, a robot, a vehicle, etc. 
     Referring to  FIG. 18 , the AI device  1800  may include a communication part  1810 , an input part  1820 , a learning processor  1830 , a sensing part  1840 , an output part  1850 , a memory  1860 , and a processor  1870 . 
     The communication part  1810  can transmit and/or receive data to and/or from external devices such as the AI devices and the AI server using wire and/or wireless communication technology. For example, the communication part  1810  can transmit and/or receive sensor information, a user input, a learning model, and a control signal with external devices. The communication technology used by the communication part  1810  may include a global system for mobile communication (GSM), a code division multiple access (CDMA), an LTE/LTE-A, a 5G, a WLAN, a Wi-Fi, Bluetooth™, radio frequency identification (RFID), infrared data association (IrDA), ZigBee, and/or near field communication (NFC). 
     The input part  1820  can acquire various kinds of data. The input part  1820  may include a camera for inputting a video signal, a microphone for receiving an audio signal, and a user input part for receiving information from a user. A camera and/or a microphone may be treated as a sensor, and a signal obtained from a camera and/or a microphone may be referred to as sensing data and/or sensor information. The input part  1820  can acquire input data to be used when acquiring an output using learning data and a learning model for model learning. The input part  1820  may obtain raw input data, in which case the processor  1870  or the learning processor  1830  may extract input features by preprocessing the input data. 
     The learning processor  1830  may learn a model composed of an ANN using learning data. The learned ANN can be referred to as a learning model. The learning model can be used to infer result values for new input data rather than learning data, and the inferred values can be used as a basis for determining which actions to perform. The learning processor  1830  may perform AI processing together with the learning processor of the AI server. The learning processor  1830  may include a memory integrated and/or implemented in the AI device  1800 . Alternatively, the learning processor  1830  may be implemented using the memory  1860 , an external memory directly coupled to the AI device  1800 , and/or a memory maintained in an external device. 
     The sensing part  1840  may acquire at least one of internal information of the AI device  1800 , environment information of the AI device  1800 , and/or the user information using various sensors. The sensors included in the sensing part  1840  may include a proximity sensor, an illuminance sensor, an acceleration sensor, a magnetic sensor, a gyro sensor, an inertial sensor, an RGB sensor, an IR sensor, a fingerprint recognition sensor, an ultrasonic sensor, an optical sensor, a microphone, a light detection and ranging (LIDAR), and/or a radar. 
     The output part  1850  may generate an output related to visual, auditory, tactile, etc. The output part  1850  may include a display unit for outputting visual information, a speaker for outputting auditory information, and/or a haptic module for outputting tactile information. 
     The memory  1860  may store data that supports various functions of the AI device  1800 . For example, the memory  1860  may store input data acquired by the input part  1820 , learning data, a learning model, a learning history, etc. 
     The processor  1870  may determine at least one executable operation of the AI device  1800  based on information determined and/or generated using a data analysis algorithm and/or a machine learning algorithm. The processor  1870  may then control the components of the AI device  1800  to perform the determined operation. The processor  1870  may request, retrieve, receive, and/or utilize data in the learning processor  1830  and/or the memory  1860 , and may control the components of the AI device  1800  to execute the predicted operation and/or the operation determined to be desirable among the at least one executable operation. The processor  1870  may generate a control signal for controlling the external device, and may transmit the generated control signal to the external device, when the external device needs to be linked to perform the determined operation. The processor  1870  may obtain the intention information for the user input and determine the user&#39;s requirements based on the obtained intention information. The processor  1870  may use at least one of a speech-to-text (STT) engine for converting speech input into a text string and/or a natural language processing (NLP) engine for acquiring intention information of a natural language, to obtain the intention information corresponding to the user input. At least one of the STT engine and/or the NLP engine may be configured as an ANN, at least a part of which is learned according to a machine learning algorithm. At least one of the STT engine and/or the NLP engine may be learned by the learning processor  1830  and/or learned by the learning processor of the AI server, and/or learned by their distributed processing. The processor  1870  may collect history information including the operation contents of the AI device  1800  and/or the user&#39;s feedback on the operation, etc. The processor  1870  may store the collected history information in the memory  1860  and/or the learning processor  1830 , and/or transmit to an external device such as the AI server. The collected history information can be used to update the learning model. The processor  1870  may control at least some of the components of AI device  1800  to drive an application program stored in memory  1860 . Furthermore, the processor  1870  may operate two or more of the components included in the AI device  1800  in combination with each other for driving the application program. 
       FIG. 19  shows an example of an AI system to which the technical features of the present disclosure can be applied. 
     Referring to  FIG. 19 , in the AI system, at least one of an AI server  1920 , a robot  1910   a , an autonomous vehicle  1910   b , an XR device  1910   c , a smartphone  1910   d  and/or a home appliance  1910   e  is connected to a cloud network  1900 . The robot  1910   a , the autonomous vehicle  1910   b , the XR device  1910   c , the smartphone  1910   d , and/or the home appliance  1910   e  to which the AI technology is applied may be referred to as AI devices  1910   a  to  1910   e.    
     The cloud network  1900  may refer to a network that forms part of a cloud computing infrastructure and/or resides in a cloud computing infrastructure. The cloud network  1900  may be configured using a 3G network, a 4G or LTE network, and/or a 5G network. That is, each of the devices  1910   a  to  1910   e  and  1920  consisting the AI system may be connected to each other through the cloud network  1900 . In particular, each of the devices  1910   a  to  1910   e  and  1920  may communicate with each other through a base station, but may directly communicate with each other without using a base station. 
     The AI server  1920  may include a server for performing AI processing and a server for performing operations on big data. The AI server  1920  is connected to at least one or more of AI devices constituting the AI system, i.e. the robot  1910   a , the autonomous vehicle  1910   b , the XR device  1910   c , the smartphone  1910   d  and/or the home appliance  1910   e  through the cloud network  1900 , and may assist at least some AI processing of the connected AI devices  1910   a  to  1910   e . The AI server  1920  can learn the ANN according to the machine learning algorithm on behalf of the AI devices  1910   a  to  1910   e , and can directly store the learning models and/or transmit them to the AI devices  1910   a  to  1910   e . The AI server  1920  may receive the input data from the AI devices  1910   a  to  1910   e , infer the result value with respect to the received input data using the learning model, generate a response and/or a control command based on the inferred result value, and transmit the generated data to the AI devices  1910   a  to  1910   e . Alternatively, the AI devices  1910   a  to  1910   e  may directly infer a result value for the input data using a learning model, and generate a response and/or a control command based on the inferred result value. 
     Various embodiments of the AI devices  1910   a  to  1910   e  to which the technical features of the present disclosure can be applied will be described. The AI devices  1910   a  to  1910   e  shown in  FIG. 19  can be seen as specific embodiments of the AI device  1800  shown in  FIG. 18 . 
     The present disclosure can have various advantageous effects. 
     For example, a UE performing a HARQ transmission of a packet by using radio resources can dynamically and efficiently allocate resources for retransmissions of the packet by considering service characteristics and requirements, in particular when packets from various services are multiplexed into a single data unit. 
     For example, it is beneficial in that the system can provide dynamic and efficient allocation of resources for data retransmissions for a UE performing HARQ transmission. 
     Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and/or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure. 
     In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope of the present disclosure. 
     Claims in the present description can be combined in a various way. For instance, technical features in method claims of the present description can be combined to be implemented or performed in an apparatus, and technical features in apparatus claims can be combined to be implemented or performed in a method. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in an apparatus. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in a method. Other implementations are within the scope of the following claims.