WO2021164703A1

WO2021164703A1 - Method of obtaining uplink transmission timing and related device

Info

Publication number: WO2021164703A1
Application number: PCT/CN2021/076714
Authority: WO
Inventors: Chienchun CHENG; Hungchen CHEN
Original assignee: FG Innovation Company Limited
Priority date: 2020-02-21
Filing date: 2021-02-18
Publication date: 2021-08-26

Abstract

A method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) is provided. The method includes in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure, transmitting, to a serving cell of the NTN, a first message of the RA procedure, receiving, from the serving cell, a first scheduling offset via system information block 1 (SIB1), receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset, and applying the first scheduling offset and the second scheduling offset for a third message transmission of the RA procedure.

Description

METHOD OF OBTAINING UPLINK TRANSMISSION TIMING AND RELATED DEVICE

CROSS-REFERENCE TO RELATED APPLICATION (S)

The present disclosure claims the benefit of and priority to U.S. provisional Patent Application Serial No. 62/980102 filed on 2/21/2020, entitled “Timing relationship enhancements for earth fixed cell deployment in LEO based NTN, ” (hereinafter referred to as “the ‘102 provisional” ) . The disclosure of the ‘102 provisional is hereby incorporated fully by reference into the present disclosure.

FIELD

The present disclosure is generally related to wireless communications, and more specifically, to a method of obtaining an uplink transmission timing and a related device.

BACKGROUND

With the tremendous growth in the number of connected devices and the rapid increase in user/network traffic volume, various efforts have been made to improve different aspects of wireless communication for the next-generation wireless communication system, such as the fifth-generation (5G) New Radio (NR) , by improving data rate, latency, reliability, and mobility.

The 5G NR system is designed to provide flexibility and configurability for optimizing the network services and types, accommodating various use cases such as enhanced Mobile Broadband (eMBB) , massive Machine-Type Communication (mMTC) , and Ultra-Reliable and Low-Latency Communication (URLLC) .

However, as the demand for radio access continues to increase, there is a need for further improvements in wireless communication for the next-generation wireless communication system.

SUMMARY

The present disclosure provides methods of obtaining an uplink transmission timing and a related device.

According to an aspect of the present disclosure, a method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) is provided. The method includes in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure, transmitting, to a serving cell of the NTN, a first message of the RA procedure, receiving, from the serving cell, a first scheduling offset via system information block 1 (SIB1) , receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset, and applying the first scheduling offset and the second scheduling offset for a third message transmission of the RA procedure.

According to another aspect of the present disclosure, a method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) is provided. The method includes in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure, transmitting, to a serving cell of the NTN, a first message of the RA procedure, receiving, from the serving cell, a first scheduling offset via a downlink control information (DCI) format 1_0 with cyclic redundancy check (CRC) scrambled by random access radio network temporary identifier (RA-RNTI) , receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset, and applying the first scheduling offset and the second scheduling offset for a third message transmission of the RA procedure.

According to another aspect of the present disclosure, a method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) is provided. The method includes in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure, transmitting, to a serving cell of the NTN, a first message of the RA procedure, receiving, from the serving cell, a first scheduling offset via a downlink control information (DCI) format 0_0 with cyclic redundancy check (CRC) scrambled by temporary cell radio network temporary identifier (TC-RNTI) , receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset, and applying the first scheduling offset and the second scheduling offset for a third message retransmission of the RA procedure.

According to another aspect of the present disclosure, a UE for performing an RA procedure is provided. The UE includes a processor configured to execute a computer-executable program, and a memory, coupled to the processor and configured to store the computer-executable program, wherein the computer-executable program instructs the processor to perform the method.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed disclosure when read with the accompanying drawings. Various features are not drawn to scale. Dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic diagram illustrating, according to an implementation of the present disclosure.

FIG. 2 is a schematic diagram illustrating maximum propagation delays associated with user equipment (UE) locations, according to an implementation of the present disclosure.

FIG. 3 is a schematic diagram illustrating a comparison of timing advance (TA) values between the Earth moving beam (EMB) and the Earth fixed beam (EFB) deployment, according to an implementation of the present disclosure.

FIG. 4 is a schematic diagram illustrating a comparison of free space loss (FSL) in dB for the EMB and the EFB, according to an implementation of the present disclosure.

FIG. 5 is a schematic diagram illustrating a polarization reuse for a beam deployment, according to an implementation of the present disclosure.

FIG. 6 is a schematic diagram illustrating circular polarized (CP) and linear polarized (LP) antenna panels, according to an implementation of the present disclosure.

FIG. 7 is a schematic diagram illustrating an evaluation of Doppler shift for Low Earth Orbiting (LEO) in S-band, according to an implementation of the present disclosure.

FIG. 8 is a schematic diagram illustrating a pre-compensation of common frequency shift, according to an implementation of the present disclosure.

FIG. 9 is a schematic diagram illustrating Doppler frequency shift components for a uplink (UL) transmission, according to an implementation of the present disclosure.

FIG. 10 is a schematic diagram illustrating UL frequency misalignment without Global Navigation Satellite System (GNSS) assisted Local Oscillator (LO) synchronization, according to an implementation of the present disclosure.

FIG. 11 is a schematic diagram illustrating 4-step random access (RA) procedure, according to an implementation of the present disclosure.

FIG. 12 is a schematic diagram illustrating 2-step RA procedure, according to an implementation of the present disclosure.

FIG. 13 is a schematic diagram illustrating a 2-step RA procedure for initial TA, according to an implementation of the present disclosure.

FIG. 14 is a schematic diagram illustrating a fallback procedure, according to an implementation of the present disclosure.

FIG. 15 is a schematic diagram illustrating a physical uplink shared channel (PUSCH) scheduling operation, according to an implementation of the present disclosure.

FIG. 16 is a schematic diagram illustrating HARQ feedback on a PUCCH, according to an implementation of the present disclosure.

FIG. 17 is a schematic diagram illustrating a Scheduling Request (SR) on a PUCCH, according to an implementation of the present disclosure.

FIG. 18 is a schematic diagram illustrating a periodic Channel State Information (CSI) reporting on a PUCCH, according to an implementation of the present disclosure.

FIG. 19 is a schematic diagram illustrating a SP CSI reporting on a PUCCH, according to an implementation of the present disclosure.

FIG. 20 is a schematic diagram illustrating a AP sounding reference signal (SRS) scheduling operation, according to an implementation of the present disclosure.

FIG. 21 is a schematic diagram illustrating a SP SRS scheduling operation, according to an implementation of the present disclosure.

FIG. 22 is a schematic diagram illustrating a P-SRS scheduling operation, according to an implementation of the present disclosure.

FIG. 23 is a flowchart illustrating a method of obtaining an uplink transmission timing in a non-terrestrial network (NTN) , according to an implementation of the present disclosure.

FIG. 24 is a block diagram illustrating a node for wireless communication, according to an implementation of the present disclosure.

DESCRIPTION

The following disclosure contains specific information pertaining to exemplary implementations in the present disclosure. The drawings and their accompanying detailed disclosure are directed to exemplary implementations. However, the present disclosure is not limited to these exemplary implementations. Other variations and implementations of the present disclosure will occur to those skilled in the art. Unless noted otherwise, like or corresponding elements in the drawings may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations are generally not to scale and are not intended to correspond to actual relative dimensions.

For consistency and ease of understanding, like features are identified (although, in some examples, not shown) by reference designators in the exemplary drawings. However, the features in different implementations may be different in other respects, and therefore shall not be narrowly confined to what is shown in the drawings.

The phrases “in one implementation, ” and “in some implementations, ” may each refer to one or more of the same or different implementations. The term “coupled” is defined as connected, whether directly or indirectly via intervening components, and is not necessarily limited to physical connections. The term “comprising” may mean “including, but not necessarily limited to” and specifically indicate open-ended inclusion or membership in the disclosed combination, group, series, and equivalents.

The term “and/or” herein is only an association relationship for describing associated objects and represents that three relationships may exist, for example, A and/or B may represent that: A exists alone, A and B exist at the same time, and B exists alone. “A and/or B and/or C” may represent that at least one of A, B, and C exists. Besides, the character “/” used herein generally represents that the former and latter associated objects are in an “or” relationship.

Additionally, any two or more of the following paragraphs, (sub) -bullets, points, actions, behaviors, terms, alternatives, examples, or claims in the present disclosure may be combined logically, reasonably, and properly to form a specific method. Any sentence, paragraph, (sub) -bullet, point, action, behaviors, terms, or claims in the present disclosure may be implemented independently and separately to form a specific method. Dependency, e.g., “based on” , “more specifically” , “preferably” , “In one embodiment” , “In one implementation” , “In one alternative” , in the present disclosure may refer to just one possible example that would not restrict the specific method.

For a non-limiting explanation, specific details, such as functional entities, techniques, protocols, standards, and the like, are set forth for providing an understanding of the disclosed technology. In other examples, detailed disclosure of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the present disclosure with unnecessary details.

Persons skilled in the art will recognize that any disclosed network function (s) or algorithm (s) may be implemented by hardware, software, or a combination of software and hardware. Disclosed functions may correspond to modules that may be software, hardware, firmware, or any combination thereof. The software implementation may comprise computer-executable instructions stored on a computer-readable medium such as memory or other types of storage devices. For example, one or more microprocessors or general-purpose computers with communication processing capability may be programmed with corresponding executable instructions and carry out the disclosed network function (s) or algorithm (s) . The microprocessors or general-purpose computers may be formed of Applications Specific Integrated Circuitry (ASIC) , programmable logic arrays, and/or using one or more Digital Signal Processors (DSPs) . Although some of the disclosed implementations are directed to software installed and executing on computer hardware, nevertheless, alternative implementations as firmware or as hardware or combination of hardware and software are well within the scope of the present disclosure.

The computer-readable medium may include but may not be limited to Random Access Memory (RAM) , Read-Only Memory (ROM) , Erasable Programmable Read-Only Memory (EPROM) , Electrically Erasable Programmable Read-Only Memory (EEPROM) , flash memory, Compact Disc (CD) Read-Only Memory (CD-ROM) , magnetic cassettes, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions.

A radio communication network architecture (e.g., a Long Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system, an LTE-Advanced Pro system, or a New Radio (NR) system) may typically include at least one base station (BS) , at least one UE, and one or more optional network elements that provide connection with a network. The UE may communicate with the network (e.g., a Core Network (CN) , an Evolved Packet Core (EPC) network, an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) , a Next-Generation Core (NGC) , a 5G Core (5GC) , or an internet) via a Radio Access Network (RAN) established by one or more BSs.

A UE according to the present disclosure may include, but is not limited to, a mobile station, a mobile terminal or device, a user communication radio terminal. For example, a UE may be a portable radio equipment, that includes, but is not limited to, a mobile phone, a tablet, a wearable device, a sensor, or a Personal Digital Assistant (PDA) with wireless communication capability. The UE may be configured to receive and transmit signals over an air interface to one or more cells in a RAN.

A BS may include, but is not limited to, a node B (NB) as in the Universal Mobile Telecommunication System (UMTS) , an evolved node B (eNB) as in the LTE-A, a Radio Network Controller (RNC) as in the UMTS, a Base Station Controller (BSC) as in the Global System for Mobile communications (GSM) /GSM Enhanced Data rates for GSM Evolution (EDGE) RAN (GERAN) , a next-generation eNB (ng-eNB) as in an Evolved Universal Terrestrial Radio Access (E-UTRA) BS in connection with the 5GC, a next-generation Node B (gNB) as in the 5G-RAN (or in the 5G Access Network (5G-AN) ) , and any other apparatus capable of controlling radio communication and managing radio resources within a cell. The BS may connect to serve the one or more UEs via a radio interface to the network.

A BS may be configured to provide communication services according to at least one of the following Radio Access Technologies (RATs) : Worldwide Interoperability for Microwave Access (WiMAX) , GSM (often referred to as 2G) , GERAN, General Packet Radio Service (GRPS) , UMTS (often referred to as 3G) according to basic Wideband-Code Division Multiple Access (W-CDMA) , High-Speed Packet Access (HSPA) , LTE, LTE-A, enhanced LTE (eLTE) , NR) (often referred to as 5G) , and/or LTE-A Pro. However, the scope of the present disclosure is not limited to these protocols.

The BS may be operable to provide radio coverage to a specific geographical area using a plurality of cells forming the RAN. The BS may support the operations of the cells. Each cell may be operable to provide services to at least one UE within its radio coverage. More specifically, each cell (often referred to as a serving cell) may provide services to serve one or more UEs within its radio coverage, (e.g., each cell schedules the downlink (DL) and optionally UL resources to at least one UE within its radio coverage for DL and optionally UL packet transmissions) . The BS may communicate with one or more UEs in the radio communication system via the plurality of cells.

A cell may allocate Sidelink (SL) resources for supporting Proximity Service (ProSe) , LTE SL services, and LTE/NR Vehicle-to-Everything (V2X) services. Each cell may have overlapped coverage areas with other cells. In Multi-RAT Dual Connectivity (MR-DC) cases, the primary cell of a Master Cell Group (MCG) or a Secondary Cell Group (SCG) may be called as a Special Cell (SpCell) . A Primary Cell (PCell) may refer to the SpCell of an MCG. A Primary SCG Cell (PSCell) may refer to the SpCell of an SCG. MCG may refer to a group of serving cells associated with the Master Node (MN) , comprising the SpCell and optionally one or more Secondary Cells (SCells) . An SCG may refer to a group of serving cells associated with the Secondary Node (SN) , comprising of the SpCell and optionally one or more SCells.

As disclosed previously, the frame structure for NR is to support flexible configurations for accommodating various next-generation (e.g., 5G) communication requirements, such as eMBB, mMTC, and URLLC, while fulfilling high reliability, high data rate, and low latency requirements. The orthogonal frequency-division multiplexing (OFDM) technology, as agreed in the 3rd Generation Partnership Project (3GPP) , may serve as a baseline for an NR waveform. The scalable OFDM numerology, such as the adaptive sub-carrier spacing, the channel bandwidth, and the cyclic prefix (CP) , may also be used. Additionally, two coding schemes are applied for NR: (1) low-density parity-check (LDPC) code and (2) polar code. The coding scheme adaption may be configured based on the channel conditions and/or the service applications.

Moreover, in a transmission time interval of a single NR frame, at least DL transmission data, a guard period, and UL transmission data should be included. The respective portions of the DL transmission data, the guard period, and the UL transmission data should also be configurable, for example, based on the network dynamics of NR. An SL resource may also be provided via an NR frame to support ProSe services or V2X services.

Non-terrestrial networks (NTN) refer to networks, or segments of networks, using a spaceborne vehicle for transmission (e.g., using Low Earth Orbiting (LEO) satellites) .

In 3GPP Release 17 (Rel-17) NTN working item (WI) , a transparent payload-based LEO scenario addressing at least 3GPP class 3 user equipment (UE) with Global Navigation Satellite System (GNSS) capability and with both Earth fixed beam (EFB) and Earth moving beam (EMB) footprint has been prioritized.

A transparent payload-based LEO network (NW) refers to a relay-based NTN. In this case, LEO satellites simply perform amplify-and-forward in space, and the base station (e.g., gNB) is located on the ground connected to a core NW.

3GPP class 3 UE refers to Power Class UE 3. The definition is used for a uplink (UL) transmit (TX) power level set to be 23dBm with a range of plus and minus 2dB. This setting was mainly driven to ensure backward compatibility with prior technologies (e.g., Rel-15 NR/GSM/UMTS) , so that network deployment topologies remain similar.

GNSS refers to a standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. This term includes the GPS, GLONASS, Galileo, Beidou and other regional systems.

EMB refers to footprints of satellite beams on earth are moving with satellite. Cells on the ground are serviced by different beams with the satellite rotation.

EFB refers to footprints of satellite beams on earth are fixed for a long time. The angle of an antenna for each beam is adjusted during the moving of a satellite to provide service to a fixed area on earth for a long time. The major difference to the EMB situation is that a round trip time (RTT) for a statistic device is varying with the elevation angle of beams, and each cell/area has the largest RTT with the minimum or maximum elevation angle.

In this disclosure, the EFB deployment is applied, which simplifies the inter-cell mobility by extending the cell serving time. Moreover, as cells are fixed on the ground, tracking areas are fixed and a update mechanism can be simple.

In addition, a UE with GNSS has the capability of timing and frequency estimation and compensation.

FIG. 1 is a schematic diagram illustrating a EFB deployment, according to an implementation of the present disclosure. FIG. 1 illustrates an example of the EFB deployment for the LEO-600km transparent-payload based NW.

In FIG. 1, the satellite orbit is 600 km, the UE location is 1000 km, and the gNB with a satellite gateway (GW) is located at 0 km. The satellite moves from -1000km to 2000km with a moving speed of 7.56 km/s. Service link refers to a radio link between the UE and the satellite. The minimum elevation angle for the gNB and the UE to maintain the connection is 10 degrees. Feeder link refers to a radio link between the satellite and the gNB. In this case, the minimum elevation angle for the gNB and the satellite is set to 10 degrees. Service period refers to the period of UE being served by the satellite. During the service period, the elevation angles for both the service link and the feeder link may be greater than 10 degrees. Max delay means the max propagation delay between the gNB and the UE during the service. Max delay rate means the max change with time for the gNB-UE propagation delay.

As illustrated in FIG. 1, for a fixed UE with 1000 km far from a serving gNB, under an assumption that the movement of a satellite aligns with a straight line between the UE and the serving gNB on the ground, the EFB deployment may provide a fixed cell connection for at most 354 seconds until either the feeder link or the service link is failed (e.g., out of the minimum elevation angle as 10 degrees) . During the connection, the UE may experience the propagation delay from around 5 milliseconds (ms) to 10 ms with the maximum change rate of time as 0.05 ms per second. Note that even for the change rate of the propagation delay, time-varying is from -0.04 ms per second to 0.04 ms per second.

Based on the evaluations, the propagation delay may not fit a simple linear regression model (it seems to fit a quadratic model better) . However, in the 3GPP TR 38.821, the indication of the delay rate from the NW to the UE, as known as the timing drift rate, has been supported to enable the TA adjustment at UE side. Since the delay rate is time-varying, the NW may need to update this value with time. In addition, whether the update is still valid is considered in the present disclosure. Since the delay holds a quadratic model instead of a linear one, better signaling methods is also applied to reduce signaling overhead.

Several issues affect the delay rate and are disclosed as follows.

Issue 1: timing advance

Timing advance (TA) refers to an timing offset between UL and downlink (DL) frames. The UL frames may be transmitted in advance based on a TA value that is indicated by the NW. This is used to guarantee UL signals from different UEs to be received at the NW side on time without interfering each other. The typical TA value is set to two times the propagation delay. This value matters because the NW needs this information to:

1. perform UL time scheduling (e.g., UL grants and UL slot offsets) .

2. ensure L1 synchronization (e.g., a specific timing advance group (TAG) timer) .

3. enhance mobility (e.g., SSB-based measurement timing configuration (SMTC) measurement gap and the conditional handover (HO) ) .

In the 3GPP TR 38.821, the TA value is calculated by the NW after the 4-step random access (RA) procedure is completed. Regardless of whether the autonomous acquisition of the TA is applied by the UE, the NW obtains the TA value that is used for the UL transmission at the UE side. However, when the UE is in the RRC_CONNECTED mode, the autonomous acquisition mechanism supported by the UE may become a problem since the NW may not know the real TA value used by the UE. For the TA value in an initial access (e.g., a RA procedure) and the subsequent TA maintenance (e.g., in the RRC_CONNECTED mode) , autonomous acquisition mechanism may be based on a UE known location and satellite ephemeris. In this case, the TA value for UL transmission including Physical random access Channel (PRACH) is calculated by the UE. The corresponding adjustment can be realized, either with a UE-specific differential TA value or full TA value (e.g., consisting of the UE specific differential TA value and a common TA vlaue) .

For the TA maintenance, TA value validating may be applied when the autonomous acquisition mechanism is supported by the UE or the NW can calculate the absolute TA value.

Another issue is related to the feeder link delay. a UE location and satellite ephemeris may assist a UE to estimate the delay of the service link. For transparent architecture, the estimation is involved with the delay of the feeder link. For transparent architecture, the estimation is involved as the delay that needs to be estimated between the UE and the gNB interface on the ground. Some options for the delay estimation are disclosed.

Option 1: To broadcast the position of the satellite along with the delay from satellite to a GW where the gNB interface is established.

Option 2: Signal ephemeris along with GW position to the UE.

Option 3: Signal the feeder link delay or to have the gNB to compensate feeder link delay, so that the UE may estimate the service link delay.

The delay of the feeder link is time-varying during the service period in a cell, so a solution related to broadcast or signaling may require updates from time to time.

For option 1, if the delay from satellite to GW is broadcast to UEs, an system information (SI) update is required, which may or may not be an issue based on the maximum varying rate of the feeder link delay.

For option 2, if the ephemeris is pre-programmed in a UMTS Subscriber Identity Module (USIM) or broadcast and updated via SI, signaling the GW positions along with the ephemeris is feasible. The reason is that the GW is fixed on the ground, and no trajectory information is required like the ephemeris. The information for each GW position is less than the ephemeris for a satellite.

For option 3, if the gNB compensates feeder link delay, the NW may need to manage a DL-UL frame timing offset by itself, which is time-varying with a change of the feeder link delay. This requires additional complex at the NW side. On top of that, different transparent satellites may be connected to the same gNB on the ground, as disclosed in TR 38.821. If the feeder link delay is compensated by the NW, the NW may need to manage multiple feeder link delays simultaneously for the connected satellites, which increases additional workload.

To sum up, option 2 is more practical than the rest of the options if only GNSS UEs are supported in the 3GPP Rel-17 NTN WI. Moreover, if the GW locations are simply used for timing and frequency synchronization, low accurate information (e.g., with an error of kilometres) maybe enough for the UE to perform an initial access.

A UE location is one of the parameters, that matters to estimate a service period, a delay, and a delay rate. To complete the evaluation and find the worst-case delay and delay rate, different UE locations are evaluated as an input parameter configured in FIG. 2, where the UE location is changed from -4000 km to 4000 km and the rest of parameters are set to the same values configured in FIG. 1.

FIG. 2 is a schematic diagram illustrating maximum propagation delays associated with UE locations, according to an implementation of the present disclosure. Based on evaluations illustrated in FIG. 2, the max service period and the max delay rate occur when the UE and the GW are co-located (e.g., the UE location is 0 km) . In this case, the max service period is 486 s, the max delay rate is 0.047923 ms/s, and the max TA rate is 0.09584 ms/s. The max delay occurs when a UE enters or leaves the coverage of the GW (e.g., for entering UE location is at -3672 km and for leaving UE location is at 3672 km) . In this case, the max delay is 12.886 ms, and the max TA value is 25.772 ms.

In NR, there are two possible ways for a gNB to provide a TA value to a UE: 1) an initial TA during a RA procedure; and 2) a TA refinement in the RRC_CONNECTED mode.

For the initial TA, the gNB derives a TA value by measuring the received RA preamble and transmits the TA value to the UE via the Timing Advance Command field in a Medium Access Control (MAC) Random Access Response (RAR) . The maximum timing advance compensation during an initial access for different sub-carrier spacing (SCS) is listed in Table 1.

Table 1

For SCS = 15 kHz, the UE may pre-compensate 23.772 ms in the worst scenario, which is 92%of the max TA value of 25.772 ms. In this case, the NW does not control the TA value but notifies the UE of whether its pre-compensation is more than 92%precise. It is worse for higher SCS values. For SCS = 30 kHz, the UE may be 96%precise on its pre-compensation to ensure the NW can correct the timing error within 1ms.

Another issue is that, if the UE over-compensates (e.g., using 25.8 ms) for the TA value of 25.772 ms, there are no negative values in NR for the NW to pull it back. In this case, even though the pre-compensation error is only 0.028 ms as 99.99%precise. The NW may recognize the received preamble from the previous PRACH Occasion (PO) instead of the correct PO. As a result, the NW may fail to compensate the TA due to out of the control range of 2 ms and calculate a wrong random access radio network temporary identifier (RA-RNTI) due to an usage of previous PRACH PO.

For the TA refinement, the gNB derives a TA value by measuring the UL transmission and refines the TA value via a Timing Advance Command MAC control element (CE) . The maximum TA value that is adjusted via a Timing Advance Command is listed in Table 2.

Table 2

For SCS = 15 kHz, the NW may update the TA value every 0.177 second or 5.638 times per second via a TA command. This is used to track the max TA value rate of 0.09584 ms/s. Like the case of the initial TA mentioned above, for higher SCS values, the NW may update the TA value more often as every 0.08347 second or 11.98 times per second. This may be applied for each UE in a serving cell, and for at the most connected time of 486 seconds that may require 2740 TA commands via dynamic or semi-persistent DL scheduling. Comparing to the EMB deployment with 6s connected time, signaling reduction for the EFB (e.g., 2740 TA commands) is more meaningful, to enhance signaling methods.

Issue 2: timing relationships

The NR timing involving DL-UL timing interaction (e.g., an offset between a UL hybrid automatic repeat request (HARQ) feedback and a DL physical downlink shared channel (PDSCH) by K1, and an offset between UL physical uplink shared channel (PUSCH) and a DL downlink control information (DCI) by K2) , may not be appliable since a large offset in the DL and UL timing at the UE side in a NTN occurs.

In the 3GPP TR 38.821, a new offset K_offset is applied to modify the timing relationships. A value of K_offset can be configured per beam or per-cell, which is derived from broadcast information or is signaled by higher layers. The possibility of extending the range K1 and/or K2 may be applied. It is noted that to avoid scheduling disorder (e.g., a scheduled UL transmission is earlier than its scheduling DCI) , the value of K_offset may be equal to or great than the TA value by ignoring the impact of K1 or K2.

However, the connected time of the EMB and the EFB makes a difference on a K_offset configuration. For example, for the EFB, K_offset may be updated with time, but for the EMB, it may not be necessary.

FIG. 3 is a schematic diagram illustrating a comparison of TA values between the EMB and the EFB deployment, according to an implementation of the present disclosure. In FIG. 3, the UE location is set to 1000 km, the GW location is set to 0 km, and the size of a serving cell is set to a diameter of 50 km. In this example, the TA variation within the serving cell is only 0.55 ms for the EMB, but it is up to 9.33 ms for the EFB. It is noted that the value of K_offset may be equal to and greater than the TA values.

Based on the evaluation illustrated in FIG. 3, some options are disclosed.

Option 1: set K_offset as a fixed value (e.g., the max propagation delay of 19.75 ms) .

Option 2: associate K_offset with TA (e.g., a valid TA value + 1 slot) .

Option 3: NW updates K_offset and the updated frequency is based on the NW implementation.

For the EFB, option 2 or option 3 may have better scheduling latency and flexibility than option 1 because the TA value varies 9 ms during the service time of 354 s. In a word, the fixed K_offset may lose 9 ms flexibility. In addition, if K_offset update is needed, a signaling mechanism should be provided.

Another issue is that in the 3GPP Rel-15 NR, a PUSCH transmission may be dynamically scheduled by a UL grant in a DCI, or the transmission may correspond to a configured grant (CG) Type 1 or Type 2. However, only DCI based PUSCH transmission has been disclosed in the 3GPP TR, the CG based PUSCH transmission is not considered yet.

Issue 3: uplink power control

Due to 1) the large free space loss (FSL) ; 2) limited effective isotropically-radiated power (EIRP) ; and 3) limited battery power available at the UE, power margin is limited for mobile terminals. For the max connected period of 486 s in a serving cell, the variation of the free space path loss is from 154 dB to 164 dB with a max rate of 0.055 dB/s. This level of variation can be supported by the 3GPP Rel-15 NR.

FIG. 4 is a schematic diagram illustrating a comparison of FSL in dB for the EMB and the EFB, according to an implementation of the present disclosure. In the 3GPP Rel-15 NR, a closed-loop power control can support a good range of variation (e.g., a mapping of Transmit Power Control (TPC) command in DCIs is listed in Table 3) . Table 3 illustrates a mapping of the TPC command field in DCIs. Based on the evaluations illustrated in FIG. 4, for both EFB and EMB, there is no need for further enhancement on the power control in NTN.

Table 3

Issue 4: Adaptive Modulation and Coding (AMC) and delayed channel state information (CSI) feedback

As to FSL illustrated in FIG. 4, the max loss rate is less than 0.06 dB per second. This can be handled by L1-RSRP reporting. For L1-RSRP reporting, if the higher layer parameter “nrofReportedRS” in “CSI-ReportConfig” is configured to be one, the reported L1-RSRP value is defined by a 7-bit value in the range [-140, -44] dBm with 1dB step size. Based on the evaluation illustrated in FIG. 4, for both EFB and EMB, there is no need for further enhancement on the CSI framework.

Issue 5: beam management and polarization support

For beam management, the service period in a cell can be certain minutes (e.g., up to 486 seconds) . Beam management (L1-mobility) may not be needed for the EFB. Also, the deployment of multiple beams per cell may have no use case for the EFB.

For polarization support, circular polarization is needed for satellite communication. This is because Faraday rotation (e.g., the rotation of the plane of polarization) is proportional to the intensity of the component of the magnetic field in the direction of the beam of light. Linear polarization may not hold the orthogonality when a radio signal passes through the earth magnetic field.

Right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) are commonly supported in satellite communication. However, they are not supported in the 3GPP Rel-15 NR. As a result, a 3-dB reference signal received power (RSRP) loss due to a polarization mismatch has been reported in the TR.

In the 3GPP Rel-15 NR, a UE can differentiate linear polarization (e.g., vertical and horizontal polarized) , via different antenna ports. The antenna port is meant to be that a device can assume that two transmitted signals have experienced the same radio channel if and only if they are transmitted from the same antenna port.

FIG. 5 is a schematic diagram illustrating a polarization reuse for a beam deployment, according to an implementation of the present disclosure. In NTN, if different circular polarizations (e.g., RHCP and LHCP) are applied for frequency reuse, and if a UE can differentiate the RHCP and the LHCP, the CSI framework in the 3GPP Rel-15 NR may need to be enhanced. Specifically, if a UE can differentiate the RHCP and LHCP signals, the antenna ports may be redefined to accommodate the RHCP and LHCP, respectively. Moreover, since the circularly polarized signal may interfere with the linear polarized signal, simultaneous reception on the same panel may not be possible. There is no single PATCH antenna that can support Linear, LHCP, and RHCP simultaneously, so each type of polarization may require an independent antenna element.

Based on the observations, several design guidelines are disclosed as follows.

1. a UE may equip multiple antenna panels, where at least one is for circular polarized (CP) antennal panel and one for LP antenna panel, but only one type of polarization can be active at a time.

2. antenna panel switching for different polarization may be triggered by the NW, to prevent the 3dB polarization mismatch loss.

3. support of circular polarization may be based on a UE capability report.

4. antenna port mapping may follow the 3GPP Rel-15 NR where a different polarization may be treated as a different antenna port.

FIG. 6 is a schematic diagram illustrating CP and linear polarized (LP) antenna panels, according to an implementation of the present disclosure. As illustrated in FIG. 6, the CP and the LP antenna panels (e.g., CP port #1-CP port #4 and LP Port #1-LP Port #4) are visualized. Both panels include four antenna ports made by four independent antenna elements (e.g., RHCP, LHCP, vertical linear polarized (VLP) , and horizontal linear polarized (HLP) antenna elements) . The mapping of the antenna port may be needed for MIMO features.

Issue 6: impact of feeder link switch

As a satellite moves, the feeder link may need to change to a new gNB on the ground. For both EMB and EFB, the feeder link switch is based on the inter-gNB handover procedure, no matter categorized by HARD and SOFT. For the SOFT switch, the satellite is always connected with one or two feeder links.

For the HARD switch, the satellite may lose the feeder link for a moment, depending on the satellite constellation deployment. However, the HO in the 3GPP Rel-15 NR is still doable if the disconnection period ends before the T304 timer expires, which is up to 10 seconds configured by the NW.

Issue 7: DL synchronization

In NR, a UE detects a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) . Those synchronization signals allow time and frequency correction, and cell identity detection. The UE may get good one-shot detection probability with less than 1%false alarm rate with robustness against initial frequency offset up to 5 ppm (e.g., 10 kHz for S-band (2 GHz) ) .

FIG. 7 is a schematic diagram illustrating an evaluation of Doppler shift for LEO in S-band. FIG. 7 illustrates a case of 2 GHz signal at 600 km on DL and UL for a fixed UE and a UE in motion. It shows up to 48 kHz Doppler shift in DL for the whole satellite coverage, which is not covered in a coverage defined in the 3GPP Rel-15 NR. Another issue is the Doppler variation during the service period. For EFB, the connected period is around 6 minutes (mn) , and the UE may experience the max and the min Doppler shift from +48 kHz to -48 kHz. However, for EMB, the connected period is nearly 6 seconds, and the Doppler shift variation can be ignored compared to 10 kHz.

A pre-compensation at the satellite side with beam specific pre-compensation of common frequency shift (e.g., conducted for the spot beam centre at the NW side) is disclosed. FIG. 8 is a schematic diagram illustrating a pre-compensation of common frequency shift, according to an implementation of the present disclosure. For each beam centre, the Doppler frequency shift is 0 ppm for both UL (this is called post-compensation at the satellite side) and DL. The maximum residual Doppler shift happens for a UE at the beam edge.

If the pre-compensation mechanism is applied at the satellite side, the max Doppler shift and the max Doppler rate is configured in Table 4. Except for the extreme case (e.g., the beam diameter of 1000 km) , the robust performance can be provided by the PSS and SSS in the 3GPP Rel-15 NR. Table 4 illustrates max Doppler shift and rate when the pre/post compensation mechanism is applied.

Table 4

Based on the evaluations illustrated in FIG. 8 and Table 4, beam specific pre-compensation of common frequency shift is essential. Moreover, except for the case of beam diameter 1000 km, no enhancement is needed for DL synchronization. For EFB, the pre-compensated value may be adjusted with time since the radial velocity between the satellite and the beam centre is consistently changing. In simulation calibrations, the Doppler shift for the feeder link may be ignored. The pre-compensation of the common frequency shift may be transparent to UEs.

Based on the observations mentioned above, for the extreme case of diameter 1000 km, some investigation for DL synchronization is needed. The pre-compensation of the common frequency shift and the DL Doppler shift caused by the feeder link may be up to the NW implementation.

Issue 8: random access

A pre-compensation of timing and frequency offset at the UE side for a UL transmission is applied, PRACH formats and preamble sequences in the 3GPP Rel-15 NR can be reused.

However, for the transparent scenario, the UE may have difficulty to estimate the Doppler shift for the feeder link. A simple solution is that NW assistant information may be needed. On the other hand, the Doppler shift due to the feeder link may be ignored during the evaluation for the system-level simulation. This concept may be implemented as the Doppler frequency shift of the feeder link is perfectly compensated by the satellite, such that the UE only needs to pre-compensate the service link.

Another issue is that if the beam specific post-compensation of the common frequency offset is applied at the NW side, the UE may need to calculate the residual UL frequency. The residual UL frequency refers to the Doppler shift difference between the common UL Doppler shift and the UE-specific Doppler shift, for sending a PRACH preamble. It is noted that even if the UE can estimate the UE-specific Doppler shift including the impacts from both the service and the feeder link, the UE may still have difficulty to estimate the residual UL frequency without knowing the common frequency offset used at the NW side. In this case, NW assistant information may be needed.

FIG. 9 is a schematic diagram illustrating Doppler frequency shift components for a UL transmission, according to an implementation of the present disclosure. As illustrated in FIG. 9, the Doppler frequency shift components for the PRACH transmission is visualized. For the PRACH, the UE experiences the full Doppler frequency shift (F_full) caused by the feeder link (f1) and the service link (f2) . The value of F_full can be taken apart into the cell-specific common part (F_com) and the UE-specific differential part (F_ue) (e.g., F_full = F_com + F_ue) , where for the common part (F_com) , the UE composes the impact of the feeder link (f1) and the service link to the beam centre (f3) , i.e., F_com = f1 + f3. For the differential part (F_ue) , a gap between the Doppler frequency shift of the service link (f2) and that of the service link to the beam centre (f3) (e.g., F_ue = f2 -f3) is present.

The UE may need to pre-compensate F_full if the post-compensation is applied at the NW side, or F_ue if there is no post-compensation for the PRACH transmission. However, only f2 can be estimated by the UE with GNSS and ephemeris. Therefore, the NW may provide additional information for f1 and f3.

Some observations are disclosed.

1. for PRACH transmission, no difference between EFB and EMB.

2. different from TA, the NW has no need to know the absolute Doppler shift for scheduling.

3. if UL frequency and timing can be pre-compensated by the UE, no new PRACH format is needed.

4. A UE may have difficulty to estimate the Doppler shift for the feeder link. NW assistant information may be needed (e.g., signaling the GW locations or the Doppler shift value) .

4. if the Doppler shift of the feeder link can be perfectly compensated by the satellite, a UE may only need to pre-compensate the Doppler shift of the service link.

5. if the beam specific post-compensation of common frequency offset at the NW side is applied and if the doppler frequency shift of the feeder link is perfectly compensated. In this case, the UE may still need to have some NW assistant information to calculate the residual UL frequency for sending preamble on PRACH.

6. for the EFB, if the NW assistant information refers to the common post-compensation of common frequency offset, the NW assistant information may be broadcasted per cell and to be updated with time.

Based on the observations mentioned above, the UE may calculate the residual UL frequency according to the NW assistant information.

Moreover, if the UE can estimate the Doppler shift of the service link, some options for estimation of the residual UL frequency are disclosed as follows.

1. the beam specific post-compensation of common frequency offset value of the service link;

2. the geometric location of the beam centre (e.g., a reference point) on the ground;

3. the GW location and the location of the reference point;

4. the GW location and the beam specific post-compensation of the common frequency offset value used at the NW side.

Issue 9: maintenance for UL frequency synchronization

After the RACH procedure in the RRC_CONNECTED mode, the NW may need to maintain the UE-specific UL frequency synchronization. In the 3GPP TR 38.821, two options are disclosed.

For the UL frequency compensation, at least for LEO system, the following solutions are identified with consideration on the beam specific post-compensation of common frequency offset at the NW side:

Option 1: both the estimation and pre-compensation of UE-specific frequency offset are conducted at the UE side. The acquisition of this value can be done by utilizing DL reference signals, UE location and satellite ephemeris.

Option 2: the required frequency offset for UL frequency compensation at least in LEO systems is indicated by the network to UE. The acquisition for this value can be done at the NW side with detection of UL signals (e.g., preamble) .

It is noted that an indication of compensated frequency offset values from the network is also supported in a case that compensation of the frequency offset is conducted by the NW in the UL and/or DL respectively. However, an indication of Doppler drift rate is not necessary.

In the RRC_CONNECTED mode, only the case for the post-compensation at the NW has been considered. The case of no post-compensation is not considered. Both cases have been applied for the PRACH transmission.

However, pre-compensation and post-compensation cannot be decoupled, because when the NW enables the pre-compensation for sending Synchronization Signal Block (SSB) , the UE cannot estimate the absolute Doppler shift for the PRACH transmission. The absolute Doppler shift may be estimated via GNSS and ephemeris. However, the DL signal may be useless for frequency tracking. This forces the NW to apply the post-compensation for receiving the PRACH preambles. As mentioned in the DL synchronization section, the pre-compensation is essential for the robust DL synchronization. Hence, the post-compensation at the NW side for at least the PRACH transmission is unavoidable.

Another observation is that the compensation mechanism may be aligned for PRACH transmission, and maintenance (e.g., PUSCH, sounding reference signal (SRS) , or physical uplink control channel (PUCCH) transmission) . This is because if the post-compensation is only applied for the initial access but not for the maintenance, the PRACH preamble from one UE may interfere with UL transmission from another UE in the same serving cell. Hence, the post-compensation at the NW side for both the PRACH transmission and the maintenance is unavoidable.

Evaluations for the following options are disclosed.

Option 1 requires almost no specification change and it seems feasible considering the residual DL Doppler frequency shift is less than 1.88 ppm for the case of 90 km of serving diameter (Set 2 -S-band) . Note that this is true only if the extreme case of 1000 km diameter is ignored. However, the estimation may be very different depending on whether GNSS assisted Local Oscillator (LO) synchronization is supported. If the GNSS assisted LO sync is not supported, the UE may apply the residual DL Doppler frequency shift during the LO adjustment as misalignment with the NW. This LO error matters because the adjusted LO may be used for pre-compensation generation and the misalignment may be accumulative to the UL TX frequency. Since the pre-compensation also results in errors, the LO error may not be corrected in the RRC_CONNECTED mode if there is no UL frequency indication from the NW. Another issue is that not all UL TX frequency generated by the adjusted LO can be compensated or to be shifted to the desired frequency location (e.g., the desired frequency location is out of the transmission capacity) .

Option 2 needs significant specification change by introducing a TA-like closed-loop frequency control. However, for beam deployments with smaller diameters (e.g., with 20 km beam diameter) , the maximum residual Doppler shift is only 0.94 ppm. Even without GNSS assisted LO synchronization, the UL frequency shift is simply less than 2 ppm. In this case, the indication of the frequency offset for UL frequency compensation may not be efficient in bandwidth use. UL frequency interference may be avoided if additional frequency guards are applied or using less efficient resource management.

FIG. 10 is a schematic diagram illustrating UL frequency misalignment without GNSS assisted LO synchronization, according to an implementation of the present disclosure. FIG. 10 illustrates the GNSS assisted LO synchronization and the DL residual Doppler frequency shift for the UL TX frequency.

During the initial cell-search procedure, the UE detects the SSB and estimates the frequency offset between the DL RX central frequency generated by LO and the experienced DL RX central frequency. The frequency offset is mainly due to the residual DL Doppler shift. This offset estimation is then used to readjust the UE oscillator frequency.

The adjusted LO is used to generate UL TX frequency at the UE side. At the NW side, the UL RX frequency misalignment is defined by a frequency gap between the UL RX experienced frequency and the UL RX frequency after post-compensation. This misalignment comes from many factors such as the LO errors at UE, on satellite, and at gNB, the residual DL Doppler frequency, the LO adjustment, and the UL TX pre-compensation for the residual UL Doppler frequency. Among these factors, the residual DL Doppler frequency may be the largest contributor.

Some observations are disclosed as follows.

1. for UL frequency maintenance, no difference between EFB and EMB.

2. for option 1, the pre-compensation may be very different based on the UE capability of using GNSS. For example, without the GNSS assisted LO synchronization, the UL RX frequency misalignment by the gNB may be nearly the sum of the residual DL RX frequency and the pre-compensation error for the residual UL TX frequency at the UE side. On the other hand, with the GNSS assisted LO synchronization, the UL RX frequency misalignment by the gNB may be around the pre-compensation error for the residual UL TX frequency at the UE side.

3. for option 1, some limitation may be considered for the value of pre-compensation to prevent the target frequency is out of UE capacity either restricted by hardware or legal regulations.

4. for option 2, performance gain for adding the closed-loop frequency control may be questionable when the pre-compensation and the post-compensation have been deployed at the NW.

Based on the observations mentioned above, some proposals are disclosed.

1. the post-compensation at the NW side for both PRACH and the maintenance may be supported.

2. the pre-compensation at the UE side based on option 1 or option 2 may not be essential if the pre-compensation and the post-compensation are used at the NW side.

3. if the pre-compensation at the UE side is used, the target UL frequency after pre-compensation may not be out of UE capacity regarding hardware limitations and legal regulations.

4. if the pre-compensation at the UE side is used, the support of GNSS assisted LO synchronization may be reported to the NW via UE capability reporting.

Issue 10: disabling of HARQ feedback

The disabling of UL HARQ feedback has been disclosed in the 3GPP TR 38.281. However, when the UL HARQ feedback is disabled, some issues may occur. For example, a MAC CE and a RRC signaling are not received by UE, or DL packets are not correctly received by UE for a long period of time without gNB knowing it.

Issue 11: HARQ optimization

Due to long propagation delay, peak data rates may drop without increasing the HARQ number. However, simply disabling of HARQ feedback may increase the peak data rates. Therefore, there is no special issue and difference between the EMB and the EFB deployment.

One minor difference is that for the EFB deployment UE may experience low elevation angles for a longer time compared to the EMB. Lower elevation means lower light of sight (LOS) probability, as illustrated in Table 5.

Table 5

For elevation angles lower than 20 degrees, the LOS probability is less than 40 %for the Urban scenario and less than 90 %for Suburban and Rural scenarios. Poor channel quality due to the low LOS probability is not a preferred scenario for the disabling of HARQ feedback. The reason is that the retransmission from Radio Link Control (RLC) is just simple repetition. Comparing to the HARQ in the physical layer, no combination gain (e.g., soft combination via redundancy version (RV) ) can be achieved, which may highly degrade the throughput and latency performance in the low SINR region or the low LOS probability region.

Based on the 3GPP TR 38.821, the configuration of K_offset may be: 1) cell-specific; and 2) applied for RRC Connection Request (e.g., a Msg3 of a RA procedure) , PUSCH, PUCCH and SRS. To fulfill all these requirements, especially for a Msg3, SI (e.g., system information block 1 (SIB1) ) is used to configure K_offset.

It is noted that SI updates should be considered when a UE in the RRC_CONNECTED mode. The reason is that based on the 3GPP TR 38.331, the UE may obtain the SIB1 in the RRC_CONNECTED mode only if one of the following conditions is met.

1. an indication associated with a change of SI is received;

2. T311 timer is running for a RRC connection re-establishment procedure.

For the obtained SIB, the validity may last for hours in the 3GPP Rel-15 NR. For example, in the 3GPP TS 38.331, a UE deletes any stored version of the SIB after 3 hours from the moment it was successfully confirmed as valid. Note that, the UE in the RRC_CONNECTED mode is required to acquire broadcasted SIB1 only if the UE can acquire it without disrupting unicast data reception (e.g., the broadcast and unicast beams are quasi co-located) . This leads to an uncertainty for PUSCH, PUCCH and SRS scheduling if the validity of K_offset is based on SI updates.

In the 3GPP Rel-15 NR, an additional slot delay is only applied to a Msg3 initial transmission scheduled by a MAC RAR, where additional Layer 2 processing time is required. However, for Msg3 retransmission scheduled by DCI, there is no additional slot delay.

In a NTN, if a UE performs a TA pre-compensation operation, since the NW schedules a Msg3 without knowing the absolute TA value, the NW may use the max TA (e.g., 25ms) of a cell to schedule the UE. On the other hand, for Msg3 retransmission, the NW may use another offset (e.g., 4 ms) in accommodating the max TA variation with time of the cell if the time gap between the Msg3 initial transmission and the Msg3 retransmission is 45 ms. Also, a shorter scheduling offset may increase a few more chances for the Msg3 retransmission based on the configuration at the NW.

It is noted that the Msg3 initial transmission and the Msg3retransmission may need different scheduling offsets. As a result, at least two scheduling offsets may be required. In a word, a scheduling offset (e.g., K_offset) for the initial Msg3 scheduled by a MAC RAR may be different from a scheduling offset (e.g., K_offset) for the Msg3 retransmission scheduled by the DCI format 0_0 with cyclic redundancy check (CRC) scrambled by temporary cell radio network temporary identifier (TC-RNTI) .

Due to lack of the absolute TA value during initial access, several scheduling mechanisms for the Msg3 initial transmission and the Msg3 retransmission are provided in this disclosure. In addition, a scheduling mechanism for the Msg3 initial transmission and retransmission may be different from a scheduling mechanism for PUSCH, PUCCH and SRS transmission.

Msg3 initial transmission and retransmission

FIG. 11 is a schematic diagram illustrating a Msg3 transmission and retransmission, according to an implementation of the present disclosure. FIG. 11 illustrates a 4-step RA procedure for the UE in RRC_INACTIVE mode or RRC_IDLE mode. As illustrated in FIG. 11, the UE reads DL SSB to acquire Master Information Block (MIB) and SIB1 (e.g., actions 1102-1104) to perform the 4-step RA procedure for initial access. The 4-step RA procedure includes Msg1-Msg4 transmission between the UE and the NW, where the Msg1 refers to a PRACH preamble transmission (e.g., action 1106) from the UE to the NW, Msg2 refers to a RAR (e.g., action 1110) that is scheduled by the NW via the DCI format 1_0 (e.g., action 1108) , Msg3 may include a Msg3 initial transmission (e.g., action 1112) and Msg3 retransmission (e.g., action 1116) that is scheduled by the NW via DCI format 0_0 (e.g., action 1114) , and Msg4 refers to a contention resolution (e.g., action 1118) .

In NTN scenario, a scheduling offset (e.g., K_offset) is required to schedule the Msg3 initial transmission. K_offset is provide by the NW with one of the following options.

Option 1: via MIB (periodically broadcast on a broadcast channel (BCH) )

Option 2: via SIB1 (periodically broadcast on DL Shared Channel (SCH) )

Option 3: via DCI format 1_0 with CRC scrambled by RA-RNTI (unicast on PDCCH)

Option 4: via MAC RAR (or MAC payload) (unicast on PDSCH)

Option 5: predefined in specification (e.g., not configurable)

Option 1: MIB includes parameters that are needed to acquire SIB1 from a cell, which is a very small amount of information carried by SSB with specific coding structures (e.g., only 55 bits in the 3GPP Rel-15 NR for higher-frequency bands (FR2) ) .

Option 2: SIB1 contains offset-related information required at least for initial access. For example, as introduced in the 3GPP TR 38.331, the physical layer may impose a limit to the maximum size of 2976 bits in which a SIB can take, which is feasible to carry the offset-related information for initial access. For example, the K_offset range (e.g., from the min to the max TA) is from 8 ms to 26 ms. With a quantization step of 2 ms, that needs 4 bits. These 4 bits may be carried by PUSCH-ConfigCommon information element (IE) used to configure cell-specific PUSCH parameters or the RACH-ConfigCommon IE used to specify the cell-specific RA parameters.

Option 2-1: RACH-ConfigCommon

A UE may obtain a configuration of K_offset by decoding the following IEs in order: SIB1 > ServingCellConfigCommonSIB > UplinkConfigCommonSIB > BWP-UplinkCommon >RACH-ConfigCommon.

The IE contains most of the parameters for Msg1, but also one parameter for Msg3 in the 3GPP Rel-15 NR. If K_offset is configured only for Msg3, it may be the best option.

Option 2-2: PUSCH-ConfigCommon

A UE may acquire a configuration of K_offset by decoding the following IEs in order: SIB1 > ServingCellConfigCommonSIB > UplinkConfigCommonSIB > BWP-UplinkCommon >PUSCH-ConfigCommon.

The IE contains a list of time-domain allocation for UL timing scheduling (e.g., a list of configurable values K2, and a power offset for Msg3) . Note that the IE is also used for all PUSCH transmission in the RRC_CONNECTED mode. If K_offset is only configured for Msg3, a different IE may be needed (e.g., a new IE as msg3-K_offset, to differentiate with K_offset used for PUSCH, PUCCH, and SRS in the RRC_CONNECTED mode.

Option 3: DCI format 1_0 with CRC scrambled by RA-RNTI refers to a UE-specific signaling. The DCI format 1_0 with CRC scrambled by RA-RNTI has 16 reserved bits, which is the highest reserved bits among different RNTIs and DCI formats. Adding a new field of K_offset (e.g., with a 4-bit length or a configurable x-bit length) in the DCI format 1_0 may be feasible.

Option 4: MAC RAR refers to a UE-specific signaling. There is only one reserved bit left and adding 4 bits needs a new octal digit. In some implementations, a UL grant field may indicate the corresponding K_offset to apply. In some implementations, an offset field may be included in a MAC RAR to indicate the corresponding K_offset to apply for the UL grant. In some implementations, a bit (e.g., a reserved bit) in a MAC RAR may be used to indicate whether a UL grant field includes the corresponding K_offset. For example, if the bit is set to 0, the UL grant field does not include the corresponding K_offset. If the bit is set to 1, the UL grant field includes the corresponding K_offset. In some implementations, a bit (e.g., a reserved bit) may be used to indicate whether an offset field is included. For example, if the bit is set to 0, the offset field is not included in the MAC RAR. If the bit is set to 1, the offset field is included in the MAC RAR.

Option 5: predefined in specification. In the 3GPP Rel-15 NR, the Msg3 initial transmission has an additional slot delay (e.g., delta that is defined in the 3GPP TS 38.214) . The delta that is specific to the PUSCH subcarrier spacing is applied in addition to the K2. The same concept may be applied for K_offset, so that the K_offset specific to the PUSCH subcarrier spacing is applied in addition to the K2 and the delta. Thus, the UE may apply the K_offset, based on NW assistant information (e.g., satellite ephemeris, types, and subcarrier spacing) .

In one implementation, as to slots for a PUSCH transmission (e.g., Msg3 initial transmission) scheduled by a UL grant in a RAR message, if the UE receives a PDSCH with the RAR message ending in slot n for a corresponding PRACH transmission from the UE, the UE transmits the PUSCH in the slot n + K2 + delta + K_offset, where K2 and delta are defined in the 3GPP TS 38.214.

It is noted that option 2-1 may be the best solution with a balance of scheduling flexibility and minimum signaling overhead. On the other hand, option 5 may be the simplest one by sacrificing scheduling flexibility for no overhead.

To schedule the Msg3 retransmission with a scheduling offset (e.g., K_offset) , the NW may provide K_offset with one of the following options.

Option 1: via SIB1 (e.g., PUSCH-ConfigCommon)

Option 2: via DCI format 0_0 with CRC scrambled by TC-RNTI (unicast on PDCCH)

Option 3: using the same scheduling mechanism as to PUSCH, PUCCH and SRS transmission

Option 1: PUSCH-ConfigCommon may contain a value of K_offset that is cell-specific for PUSCH transmission for Msg3 retransmission and in the RRC_CONNECTED mode. To distinguish with the Msg3 initial transmission, the PUSCH-ConfigCommon IE may contain a new K-offset IE for both the Msg3 retransmission and PUSCH transmission in the RRC_CONNECTED mode, meanwhile, another new msg3-K-offset IE is only used for the initial Msg3 transmission.

Option 2: DCI format 0_0 includes 5 reserved bits from the fields of a new data indicator (e.g., 1 bit) and HARQ process number (e.g., 4 bits) . There may be one additional bit reserved if no supplementary uplink (SUL) is present. In this case, a new field of a scheduling offset (e.g., K-offset-indicator with 4 bits) is included in DCI format 0_0 for TA variation.

Option 3: using the same scheduling mechanism as to PUSCH, PUCCH and SRS transmission. In the 3GPP Rel-15 NR, Msg3 retransmission has the same scheduling mechanism as a PUSCH scheduling in the RRC_CONNECTED mode, except using TC-RNTI instead of C-RNTI.

It is noted that option 3 may be the simplest one by providing an integrated solution for all UL scheduling except the initial Msg3 transmission. Option 2 may provide the best scheduling flexibility with the cost of running out all the reserved bits for DCI format 0_0 with TC-RNTI.

In one implementation, the UE may transmit the PUSCH (e.g., Msg3 retransmission) in the slot that is determined by K2 + K_offset as

where n is the slot with the scheduling DCI with CRC scrambled by TC-RNTI, K2 is based on the numerology of PUSCH, and μ _PUSCH and μ _PDCCH are the subcarrier spacing configurations for PUSCH and PDCCH, respectively.

FIG. 12 is a schematic diagram illustrating a 2-step RA procedure, according to an implementation of the present disclosure. It is noted that the UE may perform a 2-step RA procedure instead of 4-step RA procedure for initial access. In a case that when the 2-step RA procedure (e.g., Type-2 L1 RA procedure) performed by the UE fails, the UE may switch back to the 4-step RA procedure (e.g., Type-1 L1 RA procedure) .

From the physical layer perspective, the Type-1 L1 RA procedure includes the transmission of a RA preamble in a PRACH (e.g., Msg1 as illustrated in FIG. 11) , a RAR message with a PDCCH/PDSCH (e.g., Msg2 as illustrated in FIG. 11) , the transmission of a PUSCH (e.g., Msg3 as illustrated in FIG. 11) scheduled by a RAR UL grant, and a PDSCH for contention resolution (e.g., Msg4 as illustrated in FIG. 11) .

From the physical layer perspective, the Type-2 L1 RA procedure includes the transmission of a RA preamble and a PUSCH payload (e.g., MsgA as illustrated in FIG. 12) and the reception of a RAR message (e.g., MsgB as illustrated in FIG. 12) .

FIG. 13 is a schematic diagram illustrating a 2-step RA procedure for an initial TA, according to an implementation of the present disclosure. In the 2-step RA procedure, the UE includes the initial TA in assistance information in the PUSCH payload (e.g., MsgA) (e.g., actions 1302-1304) , so that the NW obtains the value of the initial TA applied by the UE via the assistance information (e.g., action 1306) . In detail, the UE estimates and applies the initial TA before the transmission of MsgA (e.g., action 1302) . The UE includes the assistance information in MsgA for the NW to know the initial TA. If a contention resolution is successful, the NW transmits MsgB to the UE (e.g., action 1308) , so that the UE applies a correction for a TA value in MsgB (e.g., action 1310) . In this case, both the UE and the NW are aware of the final correction TA.

However, if MsgA fails, the UE may perform a fallback procedure. FIG. 14 is a schematic diagram illustrating a fallback procedure, according to an implementation of the present disclosure. The fallback from 2-step to 4-step RA is like the legacy contention-based (CBRA) 4-step RA procedure as illustrated in FIG. 14, except that Msg1 is replaced by MsgA. It is noted that Msg2 of FIG. 14 may carry a fallback indication or is used as a fallback indication. Thus, when the UE receives Msg2, the UE switches to the 4-step RA procedure, and may perform Msg3 and Msg4 transmissions.

As illustrated in FIG. 14, the NW obtains the initial TA applied at the UE side via MsgA, which makes a better scheduling for the Msg3 transmission. The scheduling offset (e.g., K_offset) additional to the initial TA for the Msg3 initial transmission may be indicated via:

Option 1: MIB (periodically broadcast on BCH)

Option 2: SIB1 (periodically broadcast on DL-SCH)

Option 3: DCI format 1_0 with CRC scrambled by RA-RNTI (unicast on PDCCH)

Option 4: MAC RAR (or MAC payload) (unicast on PDSCH)

Moreover, scheduling mechanisms for PUSCH, PUCCH and SRS transmission for the UE in the RRC_CONNECTED mode are disclosed.

PUSCH transmission

FIG. 15 is a schematic diagram illustrating a PUSCH scheduling operation, according to an implementation of the present disclosure. For a PUSCH transmission in the RRC_CONNECTED mode, the slot offset K2 is determined by 1) whether pusch-Config is present; 2) whether TB is present; 3) whether an pusch-TimeDomainAllocationList IE is present.

The NW may schedule the PUSCH transmission with K_offset additional to K2 in a NTN scenario via the following options.

Option 1: via pusch-ConfigCommon (e.g., cell-specific) in SIB1

Option 2: via pusch-Config (e.g., UE-specific)

Option 3: via DCI format 0_0, DCI format 0_1, or new DCI formats

Option 4: predefined in specification (e.g., not configurable or associated with other parameters)

Option 1: pusch-ConfigCommon is carried in SIB1 (e.g., action 1502) , which may has lower scheduling flexibility than other options. To differentiate the PUSCH scheduling from the Msg3 scheduling, a new IE (e.g., pusch-K-offset) isconfigured in SIB1, to accommodate TA variations of served UEs. To obtain K_offset configured in SIB1, the UE may start a SI-window for receiving a PDCCH containing a SI-RNTI, and if K_offset is not received by the end of the SI- window, the UE may repeat a reception at the next SI-window occasion for receiving K_offset in SIB1.

In one implementation, the UE applies the new K_offset in N+2 modification period (e.g., the UE receives a SI change indication in Modification period N, updates SI in Modification period N+1, and applies the latest K_offset in Modification period N+2) .

Option 2: pusch-Config IE is indicated by a UE-specific RRC message (e.g., action 1504) , which overwrites pusch-ConfigCommon IE when a UE is configured pusch-TimeDomainAllocationList in both IEs. If option 1 is supported, option 2 may provide a way to update K_offset with a UE-specific manner. The benefit is that a UE-specific RRC message is not regulated by the SI-window, so it has better scheduling flexibility.

Option 3: DCIs provide dynamic scheduling with a UE-specific manner (e.g., action 1506) . The DCIs may include DCI formats 0_0 or 0_1. In the case that the current DCI formats cannot fit the requirement, a new DCI format 0_3 may be used for scheduling the PUSCH transmission.

Option 3-1: DCI format 0_0 has no reserved bits with CRC scrambled by C-RNTI or CS-RNTI or MCS-C-RNTI. To introduce a new DCI field (e.g., a 4-bit DCI field) for K_offset, a new RNTI (e.g., NTN-RNTI) may be used, to redefine the bit fields of the DCI format 0_0.

Option 3-2: DCI format 0_1 is used to configure all the bit fields with CRC scrambled by C-RNTI or CS-RNTI or SP-CSI-RNTI or MCS-C-RNTI. It is feasible to add a new bit field without impact.

Option 3-3: DCI format 0_3 is used to provide group-based K_offset indication or UE-specific K_offset indication. This new DCI format 0_3 may be only used for NTN scenarios.

After the UE obtains K_offset via the options 1-3 mentioned above, the UE performs PUSCH transmission (e.g., including TB) according to the configured K_offset (e.g., action 1508) .

Option 4: predefined in specification. The value of K_offset may be determined based on a configured SCS value.

Option 4-1: K_offset may be associated with the absolute TA value. The UE may determine K_offset by applying a ceiling function to the TA value, if it is valid, in slots based on a configured SCS. The ceiling function may be used for mapping x to the least integer greater than or equal to x, denoted as ceil (x) . For example, if a TA value is configured with 2.4, the ceil (2.4) =3.

Option 4-2: K_offset may be associated with NW assistance information (e.g., a common TA value that is the same as the TA value based on the min propagation delay for all served UEs in a serving cell) or the max propagation delay in a serving cell. This assistance information from the NW to the UEs is broadcast in the cell.

However, if K_offset is associated with other parameters, the parameters may be synchronized between the UEs and the NW.

Option 4-1 may provide no signaling overhead but the scheduling flexibility is limited by K2, meanwhile option 3-3 may provide the best scheduling flexibility with a cost of a new DCI format.

PUSCH transmission (s) (e.g., including CSI) can be dynamically scheduled by an UL grant in DCI (e.g., action 1510) , or the transmission can correspond to a configured grant Type 1 or Type 2. After the UE obtains K_offset via the DCI (e.g., DCI format 0_0 or 0_1) , the UE performs PUSCH transmission according to the configured K_offset in the DCI (e.g., action 1512) .

The configured grant Type 1 PUSCH transmission is semi-statically configured when a higher layer parameter of configuredGrantConfig including rrc-ConfiguredUplinkGrant without an UL grant in DCI is received.

The configured grant Type 2 PUSCH transmission is semi-persistently scheduled by an UL grant in DCI when a higher layer parameter of configuredGrantConfig not including rrc-ConfiguredUplinkGrant is received.

For Type 2 PUSCH transmission, the scheduling mechanism is similar to the dynamic one. However, for the Type 1 PUSCH transmission, a new UE behavior may be used for adapting the long propagation delay. Thus, the UE may perform one of the following options.

Option 1: if a UE is configured with K_offset or if the UE determines that, for a Type 1 PUSCH transmission, after the TA value is applied by the UE, the timing for the PUSCH transmission in a slot is earlier than a slot where the valid and up to date RRC message of configuredGrantConfig is applied by the UE, the UE does not transmit the PUSCH in the slot.

Option 2: a UE may start the first Type 1 PUSCH transmission in a slot n + K_offset, where n is a slot that the configuredGrantConfig IE is applied by the UE after the RRCSetupComplete or RRCReconfigurationComplete is transmitted.

In one implementation, the UE may transmit the PUSCH in a slot that is determined by k2 + K_offset as

where n is the slot with the scheduling DCI with CRC scrambled by C-RNTI, K2 is based on the numerology of PUSCH, and μ _PUSCH and μ _PDCCH are the subcarrier spacing configurations for PUSCH and PDCCH, respectively.

PUCCH transmission

For PUCCH transmission in RRC_CONNECTED mode, the PUCCH transmission is used for UCI reporting that includes HARQ feedback (e.g., HARQ-ACK) , Scheduling Request (SR) , and Channel State Information (CSI) transmission.

1. HARQ feedback

In one implementation, K1 + K_offset is a number of slots for a PUCCH transmission with HARQ-ACK for the PDSCH reception, where K1 is indicated by the PDSCH-to-HARQ_feedback timing indicator field in the DCI format that schedules the PDSCH reception.

The slot offset K1 between a PUCCH and a PDSCH is indicated by:

1. fallback DCI with the PDSCH-to-HARQ_feedback timing indicator field mapping to a list of K1 = {1, 2, 3, 4, 5, 6, 7, 8} ; or

2. non-fallback DCI with the same field mapping to a configurable list provided by dl-DataToUL-ACK from the UE specific IE of PUCCH-Config.

To schedule HARQ-ACK on a PUCCH with K_offset additional to K1, the NW may provide K_offset by the options listed below:

Option 1: via PUCCH-ConfigCommon (cell-specific) or SIB1

Option 2: via PUCCH-Config (UE-specific)

Option 3: via DCI format 1_0, DCI format 1_1, or new DCI formats

FIG. 16 is a schematic diagram illustrating HARQ feedback on a PUCCH, according to an implementation of the present disclosure. FIG. 16 illustrates a scheduling operation for HARQ-ACK.

Option 1: PUCCH-ConfigCommon is carried by SIB1 (e.g., action 1602) , which has a lower scheduling flexibility than other options.

Option 2: PUCCH-Config indicated by a UE-specific RRC message (e.g., action 1604) may overwrite PUCCH-ConfigCommon when both IE are configured. If option 1 is supported, option 2 may provide a way to update K_offset in a UE-specific manner.

Option 3: DCIs provide dynamic scheduling in a UE-specific manner. The DCIs may include DCI formats 1_0 and 1_1 (e.g., action 1606 and 1610) scheduling HARQ-ACK on a PUCCH. In this case, the UE applies K_offset for transmitting HARQ-ACK on the PUCCH (e.g., actions 1608 and 1612) . It is noted that if the DCI formats cannot fit the requirement, a new DCI format 1_3 may be used for indicating K_offset.

Option 3-1: DCI format 1_0 has no reserved bits with CRC scrambled by C-RNTI or CS-RNTI or MCS-C-RNTI. To introduce a new DCI field (e.g., a 4-bit DCI field) for K_offset, a new RNTI, (e.g., NTN-RNTI) may be required, to redefine the bit fields of the DCI format 1_0.

Option 3-2: DCI format 1_1 is used to configure all the bit fields with CRC scrambled by C-RNTI or CS-RNTI or SP-CSI-RNTI or MCS-C-RNTI. It is feasible to add a new bit field without impact.

Option 3-3: DCI format 1_3 is used to provide group-based K_offset indication or UE-specific K_offset indication. This new DCI format may be only used for NTN scenarios.

Option 4-1: K_offset may be associated with the absolute TA value. The UE may determine K_offset by applying a ceiling function to the TA value, if it is valid, in slots based on a configured SCS.

Option 4-2: K_offset may be associated with NW assistance information (e.g., a common TA value that is the same as TA value based on the min propagation delay for all served UEs in a serving cell) or the max propagation delay in a serving cell. This assistance information from the NW to the UEs is broadcast in the cell.

Option 4-1 may provide no signaling overhead but the scheduling flexibility is limited by K1, meanwhile, option 3-3 may provide the best scheduling flexibility with the cost of a new DCI format.

2. SR

The SR is used for requesting UL-SCH resources for a new transmission.

To schedule a SR on a PUCCH with K_offset, the K_offset is indicated by the NW via one of the following options:

Option 1: PUCCH-ConfigCommon (cell-specific) or SIB1

Option 2: PUCCH-Config (UE-specific)

Option 3: DCI format 1_0, DCI format 1_1, or new DCI formats

FIG. 17 is a schematic diagram illustrating a SR scheduling operation on a PUCCH, according to an implementation of the present disclosure. In this case, K_offset is provided by the NW via PUCCH-Config IE (e.g., action 1700) . After the UE receives a SR configuration (e.g., SchdulingRequestResourceConfig IE for indicating a physical layer resource on the PUCCH) from the NW (e.g., action 1702) , a SR periodicity and the configured scheduling offset indicated by the periodicityAndOffset IE (e.g., action 1704) is received from NW. Thus, the UE applies K_offset for transmitting the SR on the PUSCCH with the SR periodicity (e.g., actions 1706-1708) .

In one implementation, the UE may start a SR transmission in a slot n + K_offset, where n is a slot that SR configuration is applied by the UE after the UE transmits RRCSetupComplete or RRCReconfigurationComplete message.

In some implementations, if the UE determines that, for an SR transmission occasion in a PUCCH, after a TA value is applied by the UE, the timing for the PUCCH transmission in a slot is earlier than a slot that the valid and up to date RRC message of the SchedulingRequestResoutceConfig IE is applied by the UE, the UE does not transmit the PUCCH in the slot.

3. CSI

For CSI on a PUCCH, there are two types of CSI reporting is transmitted on a PUCCH:

1. periodic CSI reporting; and

2. semi-persistent (SP) CSI reporting.

For periodic CSI reporting on a PUCCH with K_offset, K_offset may be indicated by the NW via one of the following options:

Option 1: via PUCCH-ConfigCommon (cell-specific) or SIB1

Option 2: via PUCCH-Config (UE-specific)

Option 3: via DCI format 1_0, DCI format 1_1, or new DCI formats

FIG. 18 is a schematic diagram illustrating a periodic CSI reporting on a PUCCH, according to an implementation of the present disclosure. FIG. 18 illustrates a scheduling operation for the periodic CSI reporting. The UE receives a RRC message including CSI-ReportConfig IE from the NW (e.g., action 1800) , where CSI-ReportConfig IE is used to configure the periodic or semi-persistent report sent on the PUCCH, and CSI-ReportPeriodicityAndOffset IE is used for indicating a CSI periodicity. Thus, the UE applies K_offset for transmitting the periodic CSI on the PUCCH with the CSI periodicity (e.g., actions 1802-1804) .

Moreover, the UE may perform one of the following options.

Option 1: if the UE is configured with K_offset (e.g., via one of the above mentioned options 1-4 for the NW to indicate K_offset to the UE) or if the UE determines that, for a periodic CSI reporting transmission occasion in a PUCCH, after the TA value is applied by the UE, the timing for the PUCCH transmission in a slot is earlier than a slot where the valid and up to date RRC message of the CSI-ReportConfig IE is applied by the UE, the UE does not transmit the PUCCH in the slot.

Option 2: the UE may start the first periodic CSI reporting transmission in a slot n +k_offset, where n is a slot that the CSI-ReportConfig IE is applied by UE after the UE transmits RRCSetupComplete or RRCReconfigurationComplete.

For SP CSI reporting on a PUCCH with K_offset, K_offset may be indicated by the NW via one of the following options:

Option 1: via MAC CE (e.g., SP CSI Activation/Deactivation) or a new MAC CE

Option 2: via PUCCH-ConfigCommon (cell-specific) or SIB1 (e.g., servingCellConfigCommon)

Option 3: via PUCCH-Config (UE-specific)

Option 4: via DCI format 1_0, DCI format 1_1, or a new DCI format

Option 5: predefined in specification (e.g., not configurable or associated with other parameters)

Option 1: a MAC CE for activation or deactivation of a SP CSI reporting is used for indicating K_offset, or a new MAC CE identified by a new MAC subheader with a logical channel identity (LCID) is used for indicating K_offset.

FIG. 19 is a schematic diagram illustrating a SP CSI reporting on a PUCCH, according to an implementation of the present disclosure. FIG. 19 illustrates a scheduling operation for the SP CSI reporting. The UE receives RRC message for a configuration of the SP CSI reporting from the NW (e.g., action 1900) . In addition, the UE receives, from the NW, the MAC CE for activation of the SP CSI reporting, which indicates K_offset (e.g., action 1902) or a new signaling (e.g., MAC CE identified by a new MAC subheader with LCID) for indicating K_offset (e.g., action 1904) . Thus, the UE applies K_offset for transmitting the SP CSI on the PUCCH with CSI periodicity of the CSI-ReportPeriodicityAndOffset IE (e.g., actions 1906-1908) .

Moreover, the UE may perform one of the following options.

Option 1: if a UE is configured K_offset or if the UE determines that, for an SP CSI reporting transmission occasion in a PUCCH, after the timing advance value is applied by the UE, the timing for the PUCCH transmission in a slot is earlier than a slot n + x, where n is the slot that the UE transmits a PUCCH with HARQ-ACK and x is related to MAC CE parsing time related to SCS for the PUCCH, the UE does not transmit the PUCCH in the slot.

Option 2: if the UE is configured or indicated a value of K_offset, the UE may perform SP CSI reporting on the PUCCH applied to start from the first slot that is after slot n + x + K_offset.

For option 2 of the UE behavior, a signaling from the NW is used to indicate the value of K_offset.

SRS

For SRS in the RRC_CONNECTED mode, there are three types of SRS.

1. Aperiodic SRS (AP-SRS)

2. Semi-persistent SRS (SP-SRS)

3. Periodic SRS (P-SRS)

The NW may signal or configure K_offset to the UE via one of the following options.

Option 1: via RRC message SIB1 (cell-specific) (e.g., servingCellConfigCommon)

Option 2: via RRC message SRS-Config (UE-specific) (e.g., SRS-ResourceSet, slotOffset)

Option 3: via DL DCI format 1_1, group common DCI format 2_3, or UL DCI format 0_1

Option 4: a new signaling from the NW

Option 3: for DL DCI format 1_1 and group common DCI format 2-3, K_offset may be configured with a new RRC parameter or with CRC scrambled by a new RNTI to carry a value of K_offset. For UL DCI format 0_1, it may be implemented with CRC scrambled by a new RNTI to carry a value of K_offset.

Option 4: a new signaling from the NW may include the following method.

1. via DCI: a new DL DCI format, group common DCI format, and UL DCI format with CRC scrambled by the existing RNTIs or a new RNTI.

2. via a MAC CE: a new MAC CE command identified by a new LCID.

3. via a RRC message: a new RRC IE configured in a cell-specific or a UE-specific manner.

FIG. 20 is a schematic diagram illustrating an AP SRS scheduling operation, according to an implementation of the present disclosure. In one example, the UE receives RRC message including SRS-Config IE for indicating K_offset from the NW (e.g., action 2000) . In another example, the UE may receive SRS request (e.g., via DL DCI format 1_1, group common DCI format 2_3, or UL DCI format 0_1) for indicating K_offset from the NW (e.g.,

actions

2002, 2004 or 2006) . In other examples, the UE may receive a new signaling for indicating K_offset from the NW (e.g., action 2008) . Thus, the UE applies K_offset for transmitting the AP SRS to the NW (e.g., action 2010) .

Moreover, the UE may perform one of the following options.

Option 1: if the UE is configured or indicated a value of K_offset, the UE transmits AP-SRS in each of the triggered SRS resource set (s) in slot

where k is configured via higher layer parameter slotOffset for each triggered SRS resources set and is based on the subcarrier spacing of the triggered SRS transmission, μSRS and μPDCCH are the subcarrier spacing configurations for triggered SRS and PDCCH carrying the triggering command (e.g., DL DCI format 1_1, group common DCI format 2_3, or UL DCI format 0_1 that triggers one or more SRS resources set (s) ) respectively.

For scheduling SP-SRS, the NW may signal or configure K_offset to the UE via one of the following options.

Option 1: via RRC message SIB1 (cell-specific) (e.g., servingCellConfigCommon)

Option 2: via RRC message SRS-Config (UE-specific) (e.g., SRS-Resource, periodicityAndOffset-sp)

Option 3: via a MAC CE (e.g., SP SRS Activation/Deactivation)

Option 4: via a new signaling from the NW, which may include the following methods:

1. DCI: new DL DCI format, group common DCI format, and UL DCI format with CRC scrambled by the existing RNTIs or a new RNTI.

2. MAC CE: new MAC-CE command identified by a new LCID.

3. RRC: a new RRC IE configured in a cell-specific or a UE-specific manner.

FIG. 21 is a schematic diagram illustrating a SP SRS scheduling operation, according to an implementation of the present disclosure. In one example, the UE receives RRC message including SRS-Config IE for indicating K_offset from the NW (e.g., action 2100) . In another example, the UE may receive a MAC CE for activation/deactivation of SP SRS for indicating K_offset from the NW (e.g., action 2102) . In other examples, the UE may recevie a new signaling for indicating K_offset from the NW (e.g., action 2104) . Thus, the UE applies K_offset for transmitting the SP SRS to the NW with SRS periodicity of periodicityAndyOFfset-sp IE (e.g., actions 2106-2108) .

Moreover, the UE may perform one of the following options.

Option 1: if a UE is configured K_offset or if the UE determines that, for an SP SRS transmission occasion, after the timing advance value is applied by the UE, the timing for the SRS transmission in a slot is earlier than a slot n + x, where n is the slot that the UE would transmit a PUCCH with HARQ-ACK and x is related to MAC CE parsing time related to SCS for the PUCCH, the UE does not transmit the PUCCH in the slot.

Option 2-1: for SP-SRS activation, if the UE is configured or indicated a value of K_offset when a UE receives an activation command for an SRS resource, and when the UE would transmit a PUCCH with HARQ-ACK in slot n corresponding to the PDSCH carrying the activation command is transmitted in slot n, the corresponding actions and the UE assumptions on SRS transmission corresponding to the configured SRS resource set may be applied starting from the first slot that is after slot n + x + K_offset, where x is related to the SCS for the PUCCH.

Option 2-2: for SP-SRS deactivation, if the UE is configured or indicated a value of K_offset when a UE receives a deactivation command for an activated SRS resource set, and when the UE would transmit a PUCCH with HARQ-ACK in slot n corresponding to the PDSCH carrying the deactivation command, the corresponding actions and UE assumption on cessation of SRS transmission corresponding to the deactivated SRS resource set may apply starting from the first slot that is after slot n + x + K_offset, where x is related to the SCS for the PUCCH.

For scheduling P-SRS, the NW may signal or configure K_offset to the UE via one of the following options.

Option 1: via RRC message SIB1 (cell-specific) (e.g., servingCellConfigCommon)

Option 2: via RRC message SRS-Config (UE-specific) (e.g., SRS-Resource, periodicityAndOffset-p)

Option 3: via a MAC CE (e.g., SP SRS Activation/Deactivation)

Option 4: via a new signaling from NW, which may include the following methods:

1. via DCI: new DL DCI format, group common DCI format, and UL DCI format with CRC scrambled by the existing RNTIs or a new RNTI.

2. via MAC-CE: new MAC-CE command identified by a new LCID

3. via RRC: a new RRC IE configured in a cell-specific or a UE-specific manner.

FIG. 22 is a schematic diagram illustrating a P-SRS scheduling operation, according to an implementation of the present disclosure. The UE receives the RRC message including SRS-Config IE for indicating K_offset from the NW (e.g., action 2200) , and thus applies K_offset for transmitting P-SRS to the NW with SRS periodicity of periodicityAnyOffset-p IE (e.g., actions 2202-2204) .

Moreover, the UE may perform one of the following options.

Option 1: if a UE is configured K_offset or if the UE determines that, for a periodic SRS transmission occasion, after the timing advance value is applied by the UE, the timing for the SRS transmission in a slot is earlier than a slot where the valid and up to date RRC message of SRS-Resource is applied by the UE, the UE does not transmit the SRS in the slot.

Option 2: UE may start the first P-SRS in a slot n + k_offset, where n is a slot that SRS-Resource is applied by UE after the UE transmits RRCSetupComplete or RRCReconfigurationComplete message.

FIG. 23 is a flowchart illustrating a method for the UE to obtain an UL transmission timing in a NTN, according to an implementation of the present disclosure. In action 2302, the UE in a radio resource control (RRC) inactive mode or an RRC idle mode initiates a RA procedure for initial access. In action 2304, the UE transmits a first message (e.g., Msg1 or MsgA) of the RA procedure (4-step or 2-step RA) to a serving cell of the NTN. In action 2306, the UE receives a first scheduling offset (e.g., K_offset) via SIB1, DCI format 1_0 with CRC scrambled by RA-RNTI, or DCI format 0_0 with CRC scrambled by TC-RNTI from the serving cell. In action 2308, the UE receives a second message (e.g., Msg2 or MsgB) of the RA procedure, where the second message includes a second scheduling offset (e.g., K2) from the serving cell. In action 2310, the UE applies the first scheduling offset and the second scheduling offset for a third message transmission (e.g., Msg3) of the RA procedure.

In one implementation, after the UE receives the second message of the RA procedure, the UE determines whether the second message includes a fallback indication for indicating the UE to switch an RA type of the RA procedure to a 4-step RA type (e.g., from a 2-step RA to a 4-step RA) . The UE applies the first scheduling offset and the second scheduling offset for the third message transmission or a third message retransmission only if the UE determines the second message includes the fallback indication.

In some implementations, when the UE completes the RA procedure, the UE may enter an RRC connected mode from the RRC inactive mode or the RRC idle mode. Thus, the UE applies the first scheduling offset and the third scheduling offset for a PUSCH transmission when the UE receives, from the serving cell, SI including the third scheduling offset, an RRC message including the third scheduling offset, or a DCI format including the third scheduling offset.

In some implementations, when the UE completes the RA procedure, the UE may enter an RRC connected mode from the RRC inactive mode or the RRC idle mode. Thus, the UE applies the third scheduling offset for a PUCCH transmission when the UE receives, from the serving cell, SI including the third scheduling offset, an RRC message including the third scheduling offset, or a DCI format including the third scheduling offset.

The PUCCH transmission includes at least one of a hybrid automatic repeat request (HARQ) feedback transmission, a scheduling request (SR) transmission and a channel state information (CSI) transmission.

In some implementations, when the UE completes the RA procedure, the UE may enter an RRC connected mode from the RRC inactive mode or the RRC idle mode. Thus, the UE applies the third scheduling offset for a SRS transmission when the UE receives, from the serving cell, SI including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset.

FIG. 24 is a block diagram illustrating a node 2400 for wireless communication, according to an implementation of the present disclosure.

As illustrated in FIG. 24, the node 2400 may include a transceiver 2420, a processor 2426, a memory 2428, one or more presentation components 2434, and at least one antenna 2436. The node 2400 may also include a Radio Frequency (RF) spectrum band module, a BS communications module, a network communications module, and a system communications management module, input/output (I/O) ports, I/O components, and a power supply (not illustrated in FIG. 24) .

Each of these components may be in communication with each other, directly or indirectly, over one or more buses 2440. The node 2400 may be a UE or a BS that performs various disclosed functions illustrated in FIG. 23.

The transceiver 2420 may include a transmitter 2422 (with transmitting circuitry) and a receiver 2424 (with receiving circuitry) and may be configured to transmit and/or receive time and/or frequency resource partitioning information. The transceiver 2420 may be configured to transmit in different types of subframes and slots including, but not limited to, usable, non-usable and flexibly usable subframes and slot formats. The transceiver 2420 may be configured to receive data and control channels.

The node 2400 may include a variety of computer-readable media. Computer-readable media may be any media that can be accessed by the node 2400 and include both volatile (and non-volatile) media, removable (and non-removable) media. Computer-readable media may include computer storage media and communication media. Computer storage media may include both volatile (and/or non-volatile) , as well as removable (and/or non-removable) media implemented according to any method or technology for storage of information such as computer-readable media.

Computer storage media may include RAM, ROM, EPROM, EEPROM, flash memory (or other memory technology) , CD-ROM, Digital Versatile Disks (DVD) (or other optical disk storage) , magnetic cassettes, magnetic tape, magnetic disk storage (or other magnetic storage devices) , etc. Computer storage media do not include a propagated data signal.

Communication media may typically embody computer-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanisms and include any information delivery media. The term “modulated data signal” may mean a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. Communication media may include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the disclosed media should be included within the scope of computer-readable media.

The memory 2428 may include computer-storage media in the form of volatile and/or non-volatile memory. The memory 2428 may be removable, non-removable, or a combination thereof. For example, the memory 2428 may include solid-state memory, hard drives, optical-disc drives, etc. As illustrated in FIG. 24, the memory 2428 may store computer-readable and/or computer-executable instructions 2432 (e.g., software codes) that are configured to, when executed, cause the processor 2426 (e.g., processing circuitry) to perform various disclosed functions. Alternatively, the instructions 2432 may not be directly executable by the processor 2426 but may be configured to cause the node 2400 (e.g., when compiled and executed) to perform various disclosed functions.

The processor 2426 may include an intelligent hardware device, a central processing unit (CPU) , a microcontroller, an ASIC, etc. The processor 2426 may include memory. The processor 2426 may process the data 2430 and the instructions 2432 received from the memory 2428, and information through the transceiver 2420, the baseband communications module, and/or the network communications module. The processor 2426 may also process information to be sent to the transceiver 2420 for transmission via the antenna 2436, to the network communications module for transmission to a CN.

One or more presentation components 2434 may present data to a person or other devices. Presentation components 2434 may include a display device, a speaker, a printing component, a vibrating component, etc.

From the present disclosure, it is evident that various techniques can be utilized for implementing the disclosed concepts without departing from the scope of those concepts. Moreover, while the concepts have been disclosed with specific reference to specific implementations, a person of ordinary skill in the art would recognize that changes can be made in form and detail without departing from the scope of those concepts. As such, the present disclosure is to be considered in all respects as illustrative and not restrictive. It should also be understood that the present disclosure is not limited to the specific disclosed implementations, but that many rearrangements, modifications, and substitutions are possible without departing from the scope of the present disclosure.

Claims

A method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) , the method comprising:

in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure;

transmitting, to a serving cell of the NTN, a first message of the RA procedure;

receiving, from the serving cell, a first scheduling offset via system information block 1 (SIB1) ;

receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset; and

applying the first scheduling offset and the second scheduling offset for a third message transmission of the RA procedure.
The method of claim 1, further comprising:

determining whether the second message includes a fallback indication for indicating the UE to switch an RA type of the RA procedure to a 4-step RA type;

wherein applying the first scheduling offset and the second scheduling offset for the third message transmission comprises applying the first scheduling offset and the second scheduling offset for the third message transmission or a third message retransmission after determining the second message includes the fallback indication.
The method of claim 1, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the first scheduling offset and the third scheduling offset for a physical uplink shared channel (PUSCH) transmission.
The method of claim 1, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the third scheduling offset for a physical uplink control channel (PUCCH) transmission;

wherein the PUCCH transmission includes at least one of a hybrid automatic repeat request (HARQ) feedback transmission, a scheduling request (SR) transmission and a channel state information (CSI) transmission.
The method of claim 1, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the third scheduling offset for a sounding reference signal (SRS) transmission.
A method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) , the method comprising:

in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure;

transmitting, to a serving cell of the NTN, a first message of the RA procedure;

receiving, from the serving cell, a first scheduling offset via a downlink control information (DCI) format 1_0 with cyclic redundancy check (CRC) scrambled by random access radio network temporary identifier (RA-RNTI) ;

receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset; and

applying the first scheduling offset and the second scheduling offset for a third message transmission of the RA procedure.
The method of claim 6, further comprising:

determining whether the second message includes a fallback indication for indicating the UE to switch an RA type of the RA procedure to a 4-step RA type;

wherein applying the first scheduling offset and the second scheduling offset for the third message transmission comprises applying the first scheduling offset and the second scheduling offset for the third message transmission or a third message retransmission after determining the second message includes the fallback indication.
The method of claim 6, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the first scheduling offset and the third scheduling offset for a physical uplink shared channel (PUSCH) transmission.
The method of claim 6, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the third scheduling offset for a physical uplink control channel (PUCCH) transmission;

wherein the PUCCH transmission includes at least one of a hybrid automatic repeat request (HARQ) feedback transmission, a scheduling request (SR) transmission and a channel state information (CSI) transmission.
The method of claim 6, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the third scheduling offset for a sounding reference signal (SRS) transmission.
A method of obtaining an uplink transmission timing for a user equipment (UE) in a non-terrestrial network (NTN) , the method comprising:

in a radio resource control (RRC) inactive mode or an RRC idle mode, initiating a random access (RA) procedure;

transmitting, to a serving cell of the NTN, a first message of the RA procedure;

receiving, from the serving cell, a first scheduling offset via a downlink control information (DCI) format 0_0 with cyclic redundancy check (CRC) scrambled by temporary cell radio network temporary identifier (TC-RNTI) ;

receiving, from the serving cell, a second message of the RA procedure, the second message including a second scheduling offset; and

applying the first scheduling offset and the second scheduling offset for a third message retransmission of the RA procedure.
The method of claim 11, further comprising:

determining whether the second message includes a fallback indication for indicating the UE to switch an RA type of the RA procedure to a 4-step RA type;

wherein applying the first scheduling offset and the second scheduling offset for the third message retransmission comprises applying the first scheduling offset and the second scheduling offset for the third message retransmission after determining the second message includes the fallback indication.
The method of claim 11, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the first scheduling offset and the third scheduling offset for a physical uplink shared channel (PUSCH) transmission.
The method of claim 11, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the third scheduling offset for a physical uplink control channel (PUCCH) transmission;

wherein the PUCCH transmission includes at least one of a hybrid automatic repeat request (HARQ) feedback transmission, a scheduling request (SR) transmission and a channel state information (CSI) transmission.
The method of claim 11, further comprising:

in a case that the UE enters an RRC connected mode from the RRC inactive mode or the RRC idle mode, receiving, from the serving cell, system information including the third scheduling offset, an RRC message including the third scheduling offset, or a downlink control information (DCI) format including the third scheduling offset; and

applying the third scheduling offset for a sounding reference signal (SRS) transmission.
A user equipment (UE) for obtaining an uplink transmission timing in a non-terrestrial network (NTN) , the UE comprising:

a processor; and

a memory coupled to the processor and storing a computer-executable program, wherein

when executed by the processor, the computer-executable program performs the method according to claim 1.
A user equipment (UE) for obtaining an uplink transmission timing in a non-terrestrial network (NTN) , the UE comprising:

a processor; and

a memory coupled to the processor and storing a computer-executable program, wherein

when executed by the processor, the computer-executable program performs the method according to claim 6.
A user equipment (UE) for obtaining an uplink transmission timing in a non-terrestrial network (NTN) , the UE comprising:

a processor; and

a memory coupled to the processor and storing a computer-executable program, wherein

when executed by the processor, the computer-executable program executes the method according to claim 11.