Patent Publication Number: US-2021185715-A1

Title: Data transmission method, device and system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present disclosure is a continuation of International Application No. PCT/CN2019/102603, filed Aug. 26, 2019, which claims priority to U.S. Provisional Application No. 62/722,812, filed Aug. 24, 2018, the entire disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of wireless communication technologies, and more particularly, to a data transmission method, device and system. 
     BACKGROUND 
     In legacy design in Long Term Evolution (LTE) Device to Device (D2D) and LTE Vehicle to X (V2X) specifications, sidelink has been specified for direct communication between User Equipments (UEs). Sidelink physical channels includes: Physical Sidelink Control Channel (PSCCH) and Physical Sidelink Shared Channel (PSSCH). PSSCH is used to carry data from a sending UE for sidelink communication, and PSCCH indicates resource and other transmission parameters used by a receiving UE for PSSCH.  FIG. 1  schematically illustrates a system architecture according to current specifications. A sidelink resource for a sending UE can be scheduled by a base station. E.g. a specific downlink control information (DCI) format (e.g. DCI format 5) is used to schedule the sidelink resource for PSCCH and PSSCH to the sending UE on PDCCH (Physical Downlink Control Channel). The sending UE shall inform the scheduling information for PSSCH in PSCCH to a receiving UE, and transmit its sidelink data in PSSCH to the receiving UE based on the scheduling information. 
     However, in the above solution, the latency will be large because the sidelink scheduling information is transmitted in two steps. In the first step, the sidelink scheduling information is transmitted to the sending UE from the base station, and in the second step, the sidelink scheduling information is transmitted the receiving UE from the sending UE. This will substantially increase the transmission latency. Moreover, in some deployment scenarios, the channel condition between the two UEs is so poor that the PSCCH is not reliable for forwarding the scheduling information. 
     Thus, the above solution may not meet the latency and reliability requirements of 5G the Ultra-Reliable and Low-Latency Communication (URLLC) service. The URLLC service has strict requirements on reliability and transmission delay. For example, the URLLC service needs to achieve 99.999% reliability within 1 ms. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     The present disclosure provides a transmission method, device and system. 
     In a first aspect, the present disclosure provides a data transmission method, which may comprise that a first terminal receives a first DCI from a network device, wherein the first DCI is configured to transport scheduling information of a sidelink between the first terminal and a second terminal; and the first terminal transmits sidelink data to the second terminal on a resource scheduled by the scheduling information; wherein the resource is obtained by the second terminal by receiving a second DCI from the network device and used by the second terminal for receiving the sidelink data. 
     In the second aspect, the present disclosure provides a data transmission method, which may comprise that a second terminal receives a second DCI from a network device, wherein the second DCI is configured to transport scheduling information of a sidelink between a first terminal and the second terminal; and the second terminal receives sidelink data from the first terminal on a resource scheduled by the scheduling information; wherein the resource is obtained by the first terminal by receiving a first DCI from the network device and used by the first terminal for transmitting the sidelink data. 
     In the third aspect, the present disclosure provides a data transmission method, which may comprise that a network device transmits a first DCI to a first terminal, wherein the first DCI is configured to transport scheduling information of a sidelink between the first terminal and a second terminal; and the network device transmits a second DCI to a second terminal, wherein the second DCI is also configured to transport scheduling information of the sidelink between the first terminal and the second terminal; wherein a resource scheduled by the scheduling information is used by the first terminal for transmitting sidelink data and by the second terminal for receiving the sidelink data. 
     In the fourth aspect, the present disclosure provides a terminal, which may comprise a receiver unit and a transmitter unit. Wherein the receiver unit is configured to receive a first DCI from a network device, and the first DCI is configured to transport scheduling information of a sidelink between the terminal and a second terminal; the transmitter unit is further configured to transmit sidelink data to the second terminal on a resource scheduled by the scheduling information; and the resource is obtained by the second terminal by receiving a second DCI from the network device and used by the second terminal for receiving the sidelink data. 
     In the fifth aspect, the present disclosure provides a terminal, which may comprise a receiver unit. Wherein the receiver unit is configured to receive a second DCI from a network device, and the second DCI is configured to transport scheduling information of a sidelink between a first terminal and the terminal; the receiver unit is further configured to receive sidelink data from the first terminal on a resource scheduled by the scheduling information; and the resource is obtained by the first terminal by receiving a first DCI from the network device and used by the first terminal for transmitting the sidelink data. 
     In the sixth aspect, the present disclosure provides a network device, which may comprise a transmitter unit. Wherein the the transmitter unit is configured to transmit a first DCI to a first terminal, and the first DCI is configured to transport scheduling information of a sidelink between the first terminal and a second terminal; the transmit is further configured to transmit a second DCI to a second terminal, wherein the second DCI is also configured to transport scheduling information of the sidelink between the first terminal and the second terminal; and a resource scheduled by the scheduling information is used by the first terminal for transmitting sidelink data and by the second terminal for receiving the sidelink data. 
     In the seventh aspect, the present disclosure provides an end to end data transmission system, which may include the terminal of the fourth aspect, the terminal of the fifth aspect and the network device of the sixth aspect. 
     This section provides a summary of various implementations or examples of the technology described in the disclosure, and is not a comprehensive disclosure of the full scope or all features of the disclosed technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the embodiments of the present disclosure more clearly, the following will briefly introduce the accompanying drawings required for describing the embodiments of the present disclosure. Apparently, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  schematically illustrates a system according to current specifications. 
         FIG. 2  schematically illustrates a data transmission system according to an embodiment of the present disclosure. 
         FIG. 3  schematically illustrates a flowchart of a data transmission method according to an embodiment of the present disclosure. 
         FIG. 4  schematically illustrates a flowchart of a data transmission method according to another embodiment of the present disclosure. 
         FIG. 5  schematically illustrates a flowchart of a data transmission method according to another embodiment of the present disclosure. 
         FIG. 6  schematically illustrates a flowchart of a data transmission method according to another embodiment of the present disclosure. 
         FIG. 7  schematically illustrates a terminal according to an embodiment of the present disclosure. 
         FIG. 8  schematically illustrates a terminal according to another embodiment of the present disclosure. 
         FIG. 9  schematically illustrates a network device according to an embodiment of the present disclosure. 
         FIG. 10  schematically illustrates a terminal device according to an embodiment of the present disclosure. 
         FIG. 11  schematically illustrates a terminal device according to another embodiment of the present disclosure. 
         FIG. 12  schematically illustrates a network device according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the disclosure will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. Exemplary embodiments of the disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of exemplary embodiments to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. 
     The described features, structures, or/and characteristics of the disclosure may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are disclosed to provide a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the disclosure may be practiced without one or more of the specific details, or with other methods, components and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure. 
     In the present disclosure, terms such as “connected” and the like should be understood broadly, and may be directly connected or indirectly connected through an intermediate medium, unless otherwise specified. The specific meanings of the above terms in the present disclosure can be understood by those skilled in the art on a case-by-case basis. 
     Further, in the description of the present disclosure, the meaning of “a plurality” is at least two, for example, two, three, etc., unless specifically defined otherwise. “And/or”, describing the association relationship of the associated objects, indicates that there may be three relationships, such as A and/or B, which may indicate that there are three cases of single A, single B and both A and B. The symbol “/” generally indicates that the contextual object is an “or” relationship. The terms “first” and “second” are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, features defining “first” and “second” may include one or more of the features either explicitly or implicitly. 
     It is to be understood that the technical solutions of the present disclosure may be used in various wireless communication systems, for example, Global System of Mobile communication (GSM), General Packet Radio Service (GPRS), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), LTE, LTE-Advanced (LTE-A), New Radio (NR) and so on. Furthermore, the communication between a terminal and a network device in the wireless communication network may be performed according to any suitable generation communication protocols, including , but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G) communication protocols, and/or any other protocols either currently known or to be developed in the future. 
     It is to be understood that the term “terminal” refers to any end device that can access a wireless communication network and receive services therefrom. The terminal may include user equipment (UE), which is also referred to as a mobile terminal or mobile user equipment and so on. The user equipment may be a mobile terminal such as a mobile telephone (also referred to as a cellular telephone) or a computer having a mobile terminal such as portable, pocket, hand-held, vehicle-mounted mobile apparatuses or a mobile apparatus with a built-in computer. 
     It is to be understood that the term “network device” refers to a device in a wireless communication network via which a terminal accesses the network and receives services therefrom. The network device may include a base station (BS), an access point (AP), a Mobile Management Entity (MME), a Multi-cell/Multicast Coordination Entity (MCE), a Access and Mobility Management Function (AMF)/User Plane Function (UPF), a gateway, a server, a controller or any other suitable device in the wireless communication network. The BS may be, for example, a base transceiver station (BTS) in the GSM or the CDMA, or may be a Node B in the WCDMA, or may be an evolutional Node B (eNB or e-NodeB) in the LTE or the LTE-A, or may be a gNB in the NR, and the present disclosure is not limited thereto. However, for ease of description, reference is made in following embodiments taking the eNB as an example. 
       FIG. 2  schematically illustrates data transmission system architecture according to an embodiment of the present disclosure. 
     Referring to  FIG. 2 , the data transmission system  10  comprises: a network device  11 , a first terminal  12  (which refers here to a sending terminal) and a second terminal  13  (which refers here to a receiving terminal). Communication between the network device  11  and the first terminal  12 , as well as communication between the network device  11  and the second terminal  13 , is implemented through a first-type air interface (e.g. a Uu Interface in cellular mobile communication). And communication between the first terminal  12  and the second terminal  13  is implemented through a second-type air interface (e.g. a sidelink air interface). 
     It can be understood that in the data transmission system  10 , there may be multiple first terminals and second terminals. A first terminal and a second terminal are respectively shown in  FIG. 2  only to exemplarily illustrate that a first terminal transmits data to a second terminal, instead of limiting the number of the first terminal and the second terminal. 
     The network device  11  may transmit a first DCI and a second DCI, for example on PDCCH, to the first terminal  12  and the second terminal  13 , respectively. 
     The first terminal  12  monitors the first DCI and receives a first sidelink scheduling information in the first DCI and the second terminal  13  monitors the second DCI and receives a second sidelink scheduling information in the second DCI. And then the first terminal  12  transmits sidelink data on a first time-frequency resource (e.g. on PSSCH) determined by the first sidelink scheduling information in the first DCI. The second terminal  13  receives the sidelink data on a second time-frequency resource (e.g. on PSSCH) determined by the second sidelink scheduling in the second DCI. The first time-frequency resource and the second time-frequency are mapped to the same physical resource in the sidelink between the first terminal  12  and the second terminal  13 . 
     It should be noted that the abovementioned sidelink data may include user data of the user plane, and may also include signaling or messages of the control plane. 
     In embodiments of the present disclosure, the first DCI and the second DCI may use the same DCI format (e.g. DCI format 5 defined for the scheduling of PSCCH). In order to distinguish the first DCI and the second DCI by a terminal (the first terminal  12  or the second terminal  13 ), the first DCI and the second DCI may include a field of identifier for DCI type to explicitly indicate different DCI types to the terminal. Therefore, the terminal can know whether the received DCI is used to schedule transmission resources or receive resources in the sidelink. For example, a first value of the identifier represents the first DCI and a second value of the identifier represents the second DCI. 
     In an alternative embodiment, the first DCI and the second DCI may use the different DCI format (e.g. new DCI format 5A and DCI format 5B) to indicate different DCI types to the terminal. 
     The first DCI may be with CRC scrambled by RNTI (Radio Network Temporary Identifier) of the first terminal  12 . And the second DCI may be with CRC scrambled by RNTI of the second terminal  13 . 
     In embodiments of the present disclosure, the first terminal  12  and the second terminal  13  may receive synchronization signals sent by each other. Optionally, the first terminal  12  and the second terminal  13  may send the synchronization signals to each other by broadcast, so that other second terminals  13  communicating with the first terminal  12  through the sidelink may receive the synchronization signals sent by the first terminals. 
     Wherein, the synchronization signal may include clock information (a transmit clock) and identity (ID) information. Therefore, when receiving the synchronization signals sent by each other, the first terminal  12  and the second terminal  13  may obtain the clock information and ID information of each other, and then the first terminal  12  and the second terminal  13  may complete synchronization. A synchronization process may refer to descriptions about synchronization in a conventional art and will not be elaborated in the embodiment of the disclosure. 
     In embodiments of the present disclosure, the first terminal  12  and the second terminal  13  may receive broadcast channels sent by the other. The first terminal  12  and the second terminal  13  may receive the broadcast channels of each other to determine transmission bandwidths of each other and determine whether they are within coverage of the network device  11  or not. 
     In embodiments of the present disclosure, the network device  11  may receive a resource request for the sidelink data transmission sent by the first terminal  12  before transmitting the first DCI and the second DCI to the first terminal  12  and the second terminal  13 , respectively. The resource request for the sidelink data transmission may be a scheduling request (SR) or a buffer status report (BSR). 
     In embodiments of the present disclosure, the network device  11  may also receive sidelink channel state information (CSI) from the second terminal  13  to feedback the channel quality information in sidelink before transmitting the first DCI and the second DCI to the first terminal  12  and the second terminal  13 , respectively. 
     The first sidelink scheduling information and/or the second sidelink scheduling information may include a field of frequency domain resource assignment and a field of time domain resource assignment. For the first DCI, the fields of frequency domain resource assignment and time domain resource assignment are configured to indicate, respectively, the frequency resource and the time resource in the sidelink allocated to the first terminal  12  for the sidelink transmission. And for the second DCI, the fields of frequency domain resource assignment and time domain resource assignment are configured to indicate, respectively, the frequency-domain resource and the time-domain resource in the sidelink allocated to the second terminal  13  for the sidelink reception. 
     In an alternative embodiment of the present disclosure, the first sidelink scheduling information and/or the second sidelink scheduling information may only include a field of frequency domain resource assignment or a field of time domain resource assignment. For example, if the time domain resource used for sidelink transmission is pre-configured, only a field of frequency domain resource assignment is present; conversely, if the frequency domain resource used for the sidelink transmission is pre-configured, only a field of time domain resource assignment is present. 
     In an alternative embodiment of the present disclosure, the first sidelink scheduling information and/or the second sidelink scheduling information may include a field of resource block assignment to indicate the time-frequency domain resource in the sidelink. The field of resource block assignment is configured to indicate the resource block in the sidelink for the sidelink transmission or reception. In the sidelink, for example, a physical resource block may be defined as N symb   SL  consecutive SC-FDMA symbols in the time domain and N sc   RB  consecutive subcarriers in the frequency domain. A physical resource block in the sidelink thus consists of N symb   SL ×N sc   RB  resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain. 
     It is noted that the frequency-domain resource for the sidelink transmission and reception shall be determined by the first terminal&#39;s active bandwidth part for sidelink transmission and the second terminal&#39;s active bandwidth part for sidelink reception. Similarly, the time-domain resource for the sidelink transmission and reception shall be based on the time-domain resource set/table configured to the first terminal  12  and the time-domain resource set/table configured to the second terminal  13 . 
     The first DCI and the second DCI may further include a field of modulation and coding scheme. This field is configured to indicate the modulation and coding scheme of the sidelink data transmitted in the sidelink. The first terminal encodes and modulates the sidelink data to be sent by using the modulation and coding scheme, and the second terminal uses the modulation and coding scheme to demodulate and decode the received sidelink data. It should be noted that if the MSC is pre-configured, the field of modulation and coding scheme would be not present in the first DCI and the second DCI. 
     In embodiments of the present disclosure, the first DCI and the second DCI may further include a field of carrier indicator. It should be understood that this field is included in the DCI only when both the first terminal  12  and the second terminal  13  support multiple carriers or carrier aggregation. this field indicates the component carrier index of the frequency-domain resource for the sidelink transmission and reception. That is, the first terminal  12  transmits the sidelink data on the carrier indicated by the first DCI, and the second terminal receives the sidelink data on the carrier indicated by the second DCI. 
     In embodiments of the present disclosure, the first DCI and the second DCI may further include a field of redundancy version. For the first DCI, the field of redundancy version is configured to indicate the redundancy version of the sidelink data for the first terminal transmission; and for the second DCI, the field of redundancy version is configured to indicate the redundancy version of the sidelink data for the second terminal reception. 
     In embodiments of the present disclosure, the first DCI and the second DCI may further include a field of HARQ (Hybrid Automatic Repeat Request) process number. For the first DCI, the field of HARQ process number is configured to indicate the HARQ process number of the sidelink data for the first terminal transmission; and for the second DCI, the field of HARQ process number is configured to indicate the HARQ process number of the sidelink data for the second terminal reception. 
     In embodiments of the present disclosure, the second DCI may further include a field of HARQ timing indicator. This field is only present in the second DCI, which indicates to the second terminal  13  the timing for transmit HARQ-ACK/NACK for the received sidelink data. 
     A HARQ-ACK or HARQ-NACK is transmitted by the second terminal  13  after receiving the data transmitted by the first terminal  12 . The HARQ-ACK or HARQ-NACK may be transmitted to the network device  11  or to the first terminal  12 . If the HARQ-NACK of the sidelink data is transmitted to the network device  11 , the network device  11  can directly transmit the retransmission resource of the sidelink through the first DCI and the second DCI to the first terminal  12  and the second terminal  13 . And if the HARQ-NACK of the sidelink data is transmitted to the first terminal  12 , the first terminal has to transmit retransmission resource request for retransmitting the sidelink data, which will cause more retransmission delays. 
     In embodiments of the present disclosure, the first DCI may further include a field of TPC (transmission power control command). This field is only present in the first DCI, which indicates to the first terminal  12  to adjust transmission power of the sidelink data. 
     In embodiments of the present disclosure, the first DCI may further include a field of CSI-RS (channel state information reference signal) resource indicator. This field is only present in the first DCI, which indicates to the first terminal  12  the resource for transmitting CSI-RS to the second terminal  13 . 
     In embodiments of the present disclosure, the second DCI may further include a field of SRS (sounding reference signal) resource indicator. This field is only present in the second DCI, which indicates to the second terminal  13  the resource for transmitting SRS to the first terminal  12 . 
     In embodiments of the present disclosure, the first DCI and the second DCI may further include a field of PUCCH resource indicator. For the first DCI, the PUCCH resource indicator is configured to indicate first PUCCH resource for transmitting a first uplink control information (UCI) corresponding to the sidelink data to the network device  11  by the first terminal  12 . And for the second DCI, the PUCCH resource indicator is configured to indicate second PUCCH resource for transmitting second UCI corresponding to the sidelink data to the network device  11  by the second terminal  12 . 
     The first UCI may comprise at least one of scheduling request, buffer status report, service type or QoS requirement. And the second UCI comprises at least one of HARQ-ACK/NACK for the received sidelink data, the sidelink channel state information report. 
     The first PUCCH resource may be based on PUCCH resource set configured for the first terminal  12 . And the second PUCCH resource may be based on PUCCH resource set configured for the second terminal. 
     In embodiments of the present disclosure, the first DCI and the second DCI may further include a field of frequency hopping flag and a field of frequency hopping parameters/configurations. The frequency hopping flag is configured to indicate to the first terminal  12  and the second terminal  13  whether the first terminal  12  shall perform PSSCH frequency hopping or not, and the frequency hopping parameters/configurations are configured to indicate to the first terminal  12  and the second terminal  13  the frequency hopping parameters/configurations for the sidelink data if the frequency hopping flag indicates that the first terminal  12  shall perform PSSCH frequency hopping. 
     In embodiments of the present disclosure, the first DCI and the second DCI may further include a field of sidelink MIMO transmission parameters/configurations. This field of the sidelink MIMO transmission parameters/configurations is configured to indicate to the first terminal  12  and the second terminal  13  the sidelink MIMO transmission parameters/configurations for the sidelink data. 
     In embodiments of the present disclosure, the first DCI may further include a field of timing advance indication. This field is only present in the first DCI, which is configured to indicate to the first terminal  12  the timing advance for transmitting the sidelink data. 
     In embodiments of the present disclosure, the second DCI may further include a field of group destination ID. This field is only present in the second DCI, which is configured to indicate to the second terminal  13  the group destination ID for the sidelink data. 
       FIG. 3  schematically illustrates a flowchart of a data transmission method according to an embodiment of the present disclosure. The method may be applied, for example, to the data transmission system  10  in  FIG. 2 . 
     Referring to  FIG. 3 , the method  20  comprises: 
     In Step S 202 , the network device  11  transmits a first DCI and a second DCI to the first terminal  12  and the second terminal  13 , respectively. 
     In embodiments of the present disclosure, before Step S 202 , the first terminal  12  and the second terminal  13  may receive synchronization signals sent by each other. Optionally, the first terminal  12  and the second terminal  13  may send the synchronization signals to each other by broadcast, so that other second terminals  13  communicating with the first terminal  12  through the sidelink may receive the synchronization signals sent by the first terminals. 
     Wherein, the synchronization signal may include clock information (a transmit clock) and identity (ID) information. Therefore, when receiving the synchronization signals sent by each other, the first terminal  12  and the second terminal  13  may obtain the clock information and ID information of each other, and then the first terminal  12  and the second terminal  13  may complete synchronization. A synchronization process may refer to descriptions about synchronization in a conventional art and will not be elaborated in the embodiment of the disclosure. 
     In embodiments of the present disclosure, before Step S 202 , the first terminal  12  and the second terminal  13  may receive broadcast channels sent by the other. The first terminal  12  and the second terminal  13 may receive the broadcast channels of each other to determine transmission bandwidths of each other and determine whether they are within coverage of the network device  11  or not. 
     In embodiments of the present disclosure, the network device  11  may receive a resource request for the sidelink data transmission sent by the first terminal  12  before Step S 202 . The resource request for the sidelink data transmission may be a scheduling request (SR) or a buffer status report (BSR). 
     In embodiments of the present disclosure, the network device  11  may also receive sidelink channel state information (CSI) from the second terminal  13  to feedback the channel quality information in sidelink before Step S 202 . 
     The first terminal  12  monitors the first DCI and receives a first sidelink scheduling information in the first DCI. 
     The first DCI may be with CRC scrambled by RNTI of the first terminal  12 . 
     The second terminal  13  monitors the second DCI and receives a second sidelink scheduling information in the second DCI. 
     The second DCI may be with CRC scrambled by RNTI of the second terminal  13 . 
     In embodiments of the present disclosure, the first DCI and the second DCI may use the same DCI format (e.g. DCI format 5 defined for the scheduling of PSCCH). In order to distinguish the first DCI and the second DCI by a terminal (the first terminal  12  or the second terminal  13 ), the first DCI and the second DCI may include a field of identifier for DCI type to explicitly indicate different DCI types to the terminal. Therefore, the terminal can know whether the received DCI is used to schedule transmission resources or receive resources in the sidelink. For example, a first value of the identifier represents the first DCI and a second value of the identifier represents the second DCI. 
     In an alternative embodiment, the first DCI and the second DCI may use the different DCI format (e.g. new DCI format 5A and DCI format 5B) to indicate different DCI types to the terminal. 
     The details of the first DCI and the second DCI have been explained above, and will not be described again here. 
     In Step S 204 , the first terminal  12  transmits sidelink data on a first time-frequency resource determined by the first sidelink scheduling information in the first DCI. 
     The second terminal  13  receives the sidelink data on a second time-frequency resource determined by the second sidelink scheduling in the second DCI. The first time-frequency resource and the second time-frequency are mapped to the same physical resource in the sidelink between the first terminal  12  and the second terminal  13 . 
     It should be noted that the abovementioned sidelink data may include user data of the user plane, and may also include signaling or messages of the control plane. 
     According to the data transmission method of the embodiment of the disclosure, the network device may transmit the first DCI to the first terminal and the second DCI to the second terminal at the same time. In addition, separate DCIs are defined for the sidelink transmission and reception respectively, so that the first terminal and the second terminal can obtain the scheduling information at the same time. Thus the transmission latency can be substantially reduced. And the scheduling information for the second terminal is transmitted by the network device, which can substantially improve the reliability of the scheduling information transmission. Therefore, the spectral efficiency and robustness of the sidelink communication system can be substantially enhanced. 
       FIG. 4  schematically illustrates a flowchart of a data transmission method according to another embodiment of the present disclosure. The method may be applied, for example, to the first terminal  12  in  FIG. 2 . 
     Referring to  FIG. 4 , the method  30  comprises: 
     In Step S 302 , the first terminal  12  receives a first DCI from a network device (e.g. the network device  11  in  FIG. 2 ). 
     Wherein, the first DCI is configured to transport scheduling information of the sidelink between the first terminal  12  and a second terminal (e.g. the second terminal  13  in  FIG. 2 ) 
     The first DCI may comprise: frequency domain resource assignment, time domain resource assignment and modulation and coding scheme. 
     In embodiments of the present disclosure, before Step S 302 , the first terminal  12  and the second terminal  13  may receive synchronization signals sent by each other. Optionally, the first terminal  12  and the second terminal  13  may send the synchronization signals to each other by broadcast, so that other second terminals  13  communicating with the first terminal  12  through the sidelink may receive the synchronization signals sent by the first terminals. 
     Wherein, the synchronization signal may include clock information (a transmit clock) and identity (ID) information. Therefore, when receiving the synchronization signals sent by each other, the first terminal  12  and the second terminal  13  may obtain the clock information and ID information of each other, and then the first terminal  12  and the second terminal  13  may complete synchronization. A synchronization process may refer to descriptions about synchronization in a conventional art and will not be elaborated in the embodiment of the disclosure. 
     In embodiments of the present disclosure, before Step S 302 , the first terminal  12  and the second terminal  13  may receive broadcast channels sent by the other. The first terminal  12  and the second terminal  13  may receive the broadcast channels of each other to determine transmission bandwidths of each other and determine whether they are within coverage of the network device  11  or not. 
     In embodiments of the present disclosure, the network device  11  may receive a resource request for the sidelink data transmission sent by the first terminal  12  before Step S 302 . The resource request for the sidelink data transmission may be a scheduling request (SR) or a buffer status report (BSR). 
     In embodiments of the present disclosure, the network device  11  may also receive sidelink channel state information (CSI) from the second terminal  13  to feedback the channel quality information in sidelink before Step S 302 . 
     The first terminal  12  monitors the first DCI and receives a first sidelink scheduling information in the first DCI. 
     The first DCI may be with CRC scrambled by RNTI of the first terminal  12 . 
     The details of the first DCI have been explained above, and will not be described again here. 
     In Step S 304 , the first terminal  12  transmits sidelink data to the second terminal  13  on a resource scheduled by the scheduling information. 
     The resource may be determined according to the frequency domain resource assignment and the time domain resource assignment by using the modulation and coding scheme. 
     Wherein, the resource is obtained by the second terminal  13  by receiving a second DCI from the network device  11 , and the resource is used by the second terminal for receiving the sidelink data. 
     The second DCI may comprise: the frequency domain resource assignment, the time domain resource assignment and the modulation and coding scheme. 
     According to the data transmission method of the embodiment of the disclosure, the network device may transmit the first DCI to the first terminal and the second DCI to the second terminal at the same time. In addition, separate DCIs are defined for the sidelink transmission and reception respectively, so that the first terminal and the second terminal can obtain the scheduling information at the same time. Thus the transmission latency can be substantially reduced. And the scheduling information for the second terminal is transmitted by the network device, which can substantially improve the reliability of the scheduling information transmission. Therefore, the spectral efficiency and robustness of the sidelink communication system can be substantially enhanced. 
       FIG. 5  schematically illustrates a flowchart of a data transmission method according to another embodiment of the present disclosure. The method may be applied, for example, to the second terminal  13  in  FIG. 2 . 
     Referring to  FIG. 5 , the method  40  comprises: 
     In Step S 402 , the second terminal  13  receives a second DCI from a network device (e.g. the network device  11  in  FIG. 2 ). 
     Wherein, the second DCI is configured to transport scheduling information of a sidelink between a first terminal (e.g. the first terminal  12  in  FIG. 2 ) and the second terminal  13  and comprises: frequency domain resource assignment, time domain resource assignment and modulation and coding scheme 
     In embodiments of the present disclosure, before Step  5402 , the first terminal  12  and the second terminal  13  may receive synchronization signals sent by each other. Optionally, the first terminal  12  and the second terminal  13  may send the synchronization signals to each other by broadcast, so that other second terminals  13  communicating with the first terminal  12  through the sidelink may receive the synchronization signals sent by the first terminals. 
     Wherein, the synchronization signal may include clock information (a transmit clock) and identity (ID) information. Therefore, when receiving the synchronization signals sent by each other, the first terminal  12  and the second terminal  13  may obtain the clock information and ID information of each other, and then the first terminal  12  and the second terminal  13  may complete synchronization. A synchronization process may refer to descriptions about synchronization in a conventional art and will not be elaborated in the embodiment of the disclosure. 
     In embodiments of the present disclosure, before Step S 402 , the first terminal  12  and the second terminal  13  may receive broadcast channels sent by the other. The first terminal  12  and the second terminal  13  may receive the broadcast channels of each other to determine transmission bandwidths of each other and determine whether they are within coverage of the network device  11  or not. 
     In embodiments of the present disclosure, the network device  11  may receive a resource request for the sidelink data transmission sent by the first terminal  12  before Step S 402 . The resource request for the sidelink data transmission may be a scheduling request (SR) or a buffer status report (BSR). 
     In embodiments of the present disclosure, the network device  11  may also receive sidelink channel state information (CSI) from the second terminal  13  to feedback the channel quality information in sidelink before Step S 402 . 
     The second terminal  13  monitors the second DCI and receives a second sidelink scheduling information in the second DCI. 
     The second DCI may be with CRC scrambled by RNTI of the second terminal  13 . 
     The details of the second DCI have been explained above, and will not be described again here. 
     In Step S 404 , the second terminal  13  receives sidelink data from the first terminal  12  on a resource scheduled by the scheduling information. 
     The resource may be determined according to the frequency domain resource assignment and the time domain resource assignment. 
     Wherein, the resource is obtained by the first terminal  12  by receiving a first DCI from the network device  11  and used by the first terminal for transmitting the sidelink data. 
     The first DCI may comprise: the frequency domain resource assignment, the time domain resource assignment and the modulation and coding scheme. 
     According to the data transmission method of the embodiment of the disclosure, the network device may transmit the first DCI to the first terminal and the second DCI to the second terminal at the same time. In addition, separate DCIs are defined for the sidelink transmission and reception respectively, so that the first terminal and the second terminal can obtain the scheduling information at the same time. Thus the transmission latency can be substantially reduced. And the scheduling information for the second terminal is transmitted by the network device, which can substantially improve the reliability of the scheduling information transmission. Therefore, the spectral efficiency and robustness of the sidelink communication system can be substantially enhanced. 
       FIG. 6  schematically illustrates a flowchart of a data transmission method according to another embodiment of the present disclosure. The method may be applied, for example, to the network device  11  in  FIG. 2 . 
     Referring to  FIG. 6 , the method  50  comprises: 
     In Step S 502 , the network device  11  transmits a first DCI to a first terminal (e.g. the first terminal  12  in  FIG. 2 ). 
     Wherein, the first DCI is configured to transport scheduling information of a sidelink between the first terminal  12  and a second terminal  13 . 
     In Step S 504 , the network device  11  transmits a second DCI to a second terminal (e.g. the second terminal  13  in  FIG. 2 ). 
     Wherein, the second DCI is also configured to transport scheduling information of the sidelink between the first terminal  12  and the second terminal  13 . The first DCI and the second DCI comprises: frequency domain resource assignment, time domain resource assignment and modulation and coding scheme; for the first DCI, the frequency domain resource assignment and the time domain resource assignment is configured to indicate time-frequency resource for the sidelink data transmission; and for the second DCI, the frequency domain resource assignment and the time domain resource assignment is configured to indicate the time-frequency resource for the sidelink data reception. 
     In embodiments of the present disclosure, before Step S 502 , the first terminal  12  and the second terminal  13  may receive synchronization signals sent by each other. Optionally, the first terminal  12  and the second terminal  13  may send the synchronization signals to each other by broadcast, so that other second terminals  13  communicating with the first terminal  12  through the sidelink may receive the synchronization signals sent by the first terminals. 
     Wherein, the synchronization signal may include clock information (a transmit clock) and identity (ID) information. Therefore, when receiving the synchronization signals sent by each other, the first terminal  12  and the second terminal  13  may obtain the clock information and ID information of each other, and then the first terminal  12  and the second terminal  13  may complete synchronization. A synchronization process may refer to descriptions about synchronization in a conventional art and will not be elaborated in the embodiment of the disclosure. 
     In embodiments of the present disclosure, before Step S 502 , the first terminal  12  and the second terminal  13  may receive broadcast channels sent by the other. The first terminal  12  and the second terminal  13 may receive the broadcast channels of each other to determine transmission bandwidths of each other and determine whether they are within coverage of the network device  11  or not. 
     In embodiments of the present disclosure, the network device  11  may receive a resource request for the sidelink data transmission sent by the first terminal  12  before Step S 502 . The resource request for the sidelink data transmission may be a scheduling request (SR) or a buffer status report (BSR). 
     In embodiments of the present disclosure, the network device  11  may also receive sidelink channel state information (CSI) from the second terminal  13  to feedback the channel quality information in sidelink before Step S 502 . 
     In embodiments of the present disclosure, the first DCI and the second DCI may use the same DCI format (e.g. DCI format 5 defined for the scheduling of PSCCH). In order to distinguish the first DCI and the second DCI by a terminal (the first terminal  12  or the second terminal  13 ), the first DCI and the second DCI may include a field of identifier for DCI type to explicitly indicate different DCI types to the terminal. Therefore, the terminal can know whether the received DCI is used to schedule transmission resources or receive resources in the sidelink. For example, a first value of the identifier represents the first DCI and a second value of the identifier represents the second DCI. 
     In an alternative embodiment, the first DCI and the second DCI may use the different DCI format (e.g. new DCI format 5A and DCI format 5B) to indicate different DCI types to the terminal. 
     The first DCI may be with CRC scrambled by RNTI (Radio Network Temporary Identifier) of the first terminal  12 . And the second DCI may be with CRC scrambled by RNTI of the second terminal  13 . 
     According to the data transmission method of the embodiment of the disclosure, the network device may transmit the first DCI to the first terminal and the second DCI to the second terminal at the same time. In addition, separate DCIs are defined for the sidelink transmission and reception respectively, so that the first terminal and the second terminal can obtain the scheduling information at the same time. Thus the transmission latency can be substantially reduced. And the scheduling information for the second terminal is transmitted by the network device, which can substantially improve the reliability of the scheduling information transmission. Therefore, the spectral efficiency and robustness of the sidelink communication system can be substantially enhanced. 
     The following is embodiments of the device of the present disclosure, which can be used to carry out the method embodiments of the present disclosure. For details not disclosed in the embodiment of the device of the present disclosure, please refer to the method embodiments of the present disclosure. 
       FIG. 7  schematically illustrates a terminal according to an embodiment of the present disclosure. The terminal may be the first terminal  12  in  FIG. 2 . 
     Referring to  FIG. 7 , the terminal  60  comprises: a receiver unit  602  and a transmitter unit  604 . 
     The receiver unit  602  is configured to receive a first DCI from a network device (e.g. the network device  11  in  FIG. 2 ), wherein the first DCI is configured to transport scheduling information of a sidelink between the terminal  60  and a second terminal (e.g. the second terminal  13  in  FIG. 3 ) and may comprise: frequency domain resource assignment, time domain resource assignment and modulation and coding scheme. 
     The transmitter unit  604  is configured to transmit sidelink data to the second terminal on a resource scheduled by the scheduling information. For example, the resource may be determined according to the frequency domain resource assignment and the time domain resource assignment by using the modulation and coding scheme. 
     Wherein the resource is obtained by the second terminal by receiving a second DCI from the network device and used by the second terminal for receiving the sidelink data. 
     The second DCI may comprise: the frequency domain resource assignment, the time domain resource assignment and the modulation and coding scheme. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: redundancy version and HARQ process number; for the first DCI, the redundancy version is configured to indicate the redundancy version of the sidelink data for the terminal  60  transmission and the HARQ process number is configured to indicate the HARQ process number of the sidelink data for the terminal  60  transmission; for the second DCI, the redundancy version is configured to indicate the redundancy version of the sidelink data for the second terminal reception and the HARQ process number is configured to indicate the HARQ process number of the sidelink data for the second terminal reception. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: PUCCH resource indicator; for the first DCI, the PUCCH resource indicator is configured to indicate first PUCCH resource for transmitting a first UCI corresponding to the sidelink data to the network device by the terminal  60 ; for the second DCI, the PUCCH resource indicator is configured to indicate second PUCCH resource for transmitting second UCI corresponding to the sidelink data to the network device by the second terminal. 
     In embodiments of the present disclosure, the first UCI comprises at least one of scheduling request, buffer status report, service type or QoS requirement. 
     In embodiments of the present disclosure, the first PUCCH resource is based on PUCCH resource set configured for the terminal  60 . 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: frequency hopping flag and frequency hopping parameters/configurations; the frequency hopping flag is configured to indicate to the terminal  60  and the second terminal whether the terminal  60  shall perform PSSCH frequency hopping or not, and the frequency hopping parameters/configurations are configured to indicate to the terminal  60  and the second terminal the frequency hopping parameters/configurations for the sidelink data if the frequency hopping flag indicates that the terminal  60  shall perform PSSCH frequency hopping. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises at least one of carrier indicator, sidelink MIMO transmission parameters/configurations or identifier for DCI; for first DCI, the carrier indicator is configured to indicate a component carrier index of the terminal  60 ; and for the second DCI, the carrier indicator is configured to indicate a component carrier index of the second terminal; the sidelink MIMO transmission parameters/configurations are configured to indicate to the terminal  60  and the second terminal the sidelink MIMO transmission parameters/configurations for the sidelink data; and the identifier for DCI is configured to indicate to the terminal  60  and the second terminal the received DCI is the first DCI or the second DCI. 
     In embodiments of the present disclosure, the first DCI further comprises at least one of TPC command, CSI-RS resource indicator or timing advance indication; the TPC command is configured to adjust transmission power of the sidelink data for the terminal  60 , the CSI-RS resource indicator is configured to indicate the terminal  60  resource for transmitting CSI-RS to the second terminal, and the timing advance indication is configured to indicate to the terminal  60  the timing advance for transmitting the sidelink data. 
     It is important to note that, in the embodiment of the disclosure, the receiver unit  602  may be implemented by a receiver (e.g. the receiver  1004  in  FIG. 10 ) and the transmitter unit  604  may be implemented by a transmitter (e.g. the transmitter  1006 ). 
       FIG. 10  schematically illustrates a terminal device according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 10 , a terminal device  100  may include a processor  1002 , a receiver  1004 , a transmitter  1006  and a memory  1008 , wherein the memory  1008  may be configured to store a code executed by the processor  1002  an the like. 
     Each component in the terminal device  100  is coupled together through a bus system  1010 , wherein the bus system  1010  includes a data bus, and further includes a power bus, a control bus and a state signal bus. 
     The processor  1002  typically controls overall operations of the terminal device  100 , such as the operations associated with display, data communications and recording operations. The processor  1002  may include one or more processors to execute instructions to perform all or part of the steps in the above described methods. Moreover, the processor  1002  may include one or more modules which facilitate the interaction between the processor  1002  and other components. 
     The memory  1008  is configured to store various types of data to support the operation of the terminal device  100 . Examples of such data include instructions for any applications or methods operated on the terminal device  100 , contact data, phonebook data, messages, pictures, video, etc. The memory  1008  may be implemented using any type of volatile or non-volatile memory devices, or a combination thereof, such as a static random access memory (SRAM), an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), a programmable read-only memory (PROM), a read-only memory (ROM), a magnetic memory, a flash memory or a magnetic or optical disk. 
     The receiver  1004  is configured to receive an electromagnetic signal received by the antenna. The main function of the receiver is to select the frequency components it needs from the numerous electromagnetic waves existing in the air, suppress or filter out unwanted signals or noise and interference signals, and then obtain the original useful information after amplification and demodulation. 
     The transmitter  1006  is configured to generate and modulate the RF current and transmit the radio waves through the antenna. 
     In embodiments of the present disclosure, the transmitter  1006  and receiver  1004  may be implemented as a transceiver. 
     The terminal  60  illustrated in  FIG. 7  and the terminal device  100  illustrated in  FIG. 10  may implement each process implanted by the first terminal  12  in the abovementioned method embodiments and will not be elaborated herein to avoid repetitions. 
       FIG. 8  schematically illustrates a terminal according to another embodiment of the present disclosure. The terminal may be the second terminal  13  in  FIG. 2 . 
     Referring to  FIG. 8 , the terminal  70  comprises: a receiver unit  702 . 
     The receiver unit  702  is configured to receive a second DCI from a network device (e.g. the network device  11  in  FIG. 2 ), wherein the second DCI is configured to transport scheduling information of a sidelink between a first terminal (e.g. the first terminal  12  in  FIG. 2 ) and the terminal  70  and may comprise: frequency domain resource assignment, time domain resource assignment and modulation and coding scheme. 
     The receiver unit  702  is further configured to receive sidelink data from the first terminal on a resource scheduled by the scheduling information. For example, the resource is determined according to the frequency domain resource assignment and the time domain resource assignment. 
     The resource is obtained by the first terminal by receiving a first DCI from the network device and used by the first terminal for transmitting the sidelink data. 
     The first DCI may comprise: the frequency domain resource assignment, the time domain resource assignment and the modulation and coding scheme. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: redundancy version and HARQ process number; for the first DCI, the redundancy version is configured to indicate the redundancy version of the sidelink data for the first terminal transmission and the HARQ process number is configured to indicate the HARQ process number of the sidelink data for the first terminal transmission; for the second DCI, the redundancy version is configured to indicate the redundancy version of the sidelink data for the terminal  70  reception and the HARQ process number is configured to indicate the HARQ process number of the sidelink data for the terminal  70  reception. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: PUCCH resource indicator; for the first DCI, the PUCCH resource indicator is configured to indicate first PUCCH resource for transmitting a first UCI corresponding to the sidelink data to the network device by the first terminal; for the second DCI, the PUCCH resource indicator is configured to indicate second PUCCH resource for transmitting second UCI corresponding to the sidelink data to the network device by the terminal  70 . 
     In embodiments of the present disclosure, wherein the second UCI comprises at least one of HARQ-ACK/NACK for the received sidelink data, the sidelink channel state information report. 
     In embodiments of the present disclosure, the second PUCCH resource is based on PUCCH resource set configured for the terminal  70 . 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: frequency hopping flag and frequency hopping parameters/configurations; the frequency hopping flag is configured to indicate to the first terminal and the terminal  70  whether the first terminal shall perform PSSCH frequency hopping or not, and the frequency hopping parameters/configurations are configured to indicate to the first terminal and the terminal  70  the frequency hopping parameters/configurations for the sidelink data if the frequency hopping flag indicates that the first terminal shall perform PSSCH frequency hopping. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises at least one of carrier indicator, sidelink MIMO transmission parameters/configurations or identifier for DCI; for first DCI, the carrier indicator is configured to indicate a component carrier index of the first terminal; and for the second DCI, the carrier indicator is configured to indicate a component carrier index of the terminal  70 ; the sidelink MIMO transmission parameters/configurations are configured to indicate to the first terminal and the terminal  70  the sidelink MIMO transmission parameters/configurations for the sidelink data; and the identifier for DCI is configured to indicate to the first terminal and the terminal  70  the received DCI is the first DCI or the second DCI. 
     In embodiments of the present disclosure, the second DCI further comprises at least one of SRS resource indicator, HARQ timing indicator or group destination ID; the SRS resource indicator is configured to indicate to the terminal  70  resource for transmitting SRS to the first terminal, the HARQ timing indicator is configured to indicate to the terminal  70  the timing for transmitting HARQ-ACK/NACK for the received sidelink data, and the group destination ID is configured to indicate to the terminal  70  the group destination ID for the sidelink data. 
     In embodiments of the present disclosure, the terminal  70  further comprises: a transmitter unit  704 , wherein the transmitter unit  704  is configured to transmit the HARQ-ACK/NACK for the received sidelink data to the network device based on the timing. 
     It is important to note that, in the embodiment of the disclosure, the receiver unit  702  may be implemented by a receiver (e.g. the receiver  1104  in  FIG. 10 ) and the transmitter unit  704  may be implemented by a transmitter (e.g. the transmitter  1106 ). 
       FIG. 11  schematically illustrates a terminal device according to another embodiment of the present disclosure. 
     As illustrated in  FIG. 11 , a terminal device  110  may include a processor  1102 , a receiver  1104 , a transmitter  1106  and a memory  1108 , wherein the memory  1108  may be configured to store a code executed by the processor  1102  an the like. 
     Each component in the terminal device  110  is coupled together through a bus system  1110 , wherein the bus system  1110  includes a data bus, and further includes a power bus, a control bus and a state signal bus. 
     The processor  1102  typically controls overall operations of the terminal device  110 , such as the operations associated with display, data communications and recording operations. The processor  1102  may include one or more processors to execute instructions to perform all or part of the steps in the above described methods. Moreover, the processor  1002  may include one or more modules which facilitate the interaction between the processor  1102  and other components. 
     The memory  1108  is configured to store various types of data to support the operation of the terminal device  110 . Examples of such data include instructions for any applications or methods operated on the terminal device  110 , contact data, phonebook data, messages, pictures, video, etc. The memory  1108  may be implemented using any type of volatile or non-volatile memory devices, or a combination thereof, such as a static random access memory (SRAM), an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), a programmable read-only memory (PROM), a read-only memory (ROM), a magnetic memory, a flash memory or a magnetic or optical disk. 
     The receiver  1104  is configured to receive an electromagnetic signal received by the antenna. The main function of the receiver is to select the frequency components it needs from the numerous electromagnetic waves existing in the air, suppress or filter out unwanted signals or noise and interference signals, and then obtain the original useful information after amplification and demodulation. 
     The transmitter  1106  is configured to generate and modulate the RF current and transmit the radio waves through the antenna. 
     In embodiments of the present disclosure, the transmitter  1106  and receiver  1104  may be implemented as a transceiver. 
     The terminal  70  illustrated in  FIG. 8  and the terminal device  110  illustrated in  FIG. 11  may implement each process implanted by the second terminal  13  in the abovementioned method embodiments and will not be elaborated herein to avoid repetitions. 
       FIG. 9  schematically illustrates a network device according to an embodiment of the present disclosure. The network device may be the network device  11  in  FIG. 2 . 
     Referring to  FIG. 9 , the network device  80  comprises: a transmitter unit  802 . 
     The transmitter unit  802  is configured to transmit a first DCI to a first terminal (e.g. the first terminal  12  in  FIG. 2 ), wherein the first DCI is configured to transport scheduling information of a sidelink between the first terminal and a second terminal (e.g. the second terminal  13  in  FIG. 2 ). 
     The transmitter unit  802  is further configured to transmit a second DCI to a second terminal, wherein the second DCI is also configured to transport scheduling information of the sidelink between the first terminal and the second terminal. 
     A resource scheduled by the scheduling information is used by the first terminal for transmitting sidelink data and by the second terminal for receiving the sidelink data. 
     The first DCI and the second DCI may comprise: frequency domain resource assignment, time domain resource assignment and modulation and coding scheme; for the first DCI, the frequency domain resource assignment and the time domain resource assignment is configured to indicate time-frequency resource for the sidelink data transmission; and for the second DCI, the frequency domain resource assignment and the time domain resource assignment is configured to indicate the time-frequency resource for the sidelink data reception. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: redundancy version and HARQ process number; for the first DCI, the redundancy version is configured to indicate the redundancy version of the sidelink data for the first terminal transmission and the HARQ process number is configured to indicate the HARQ process number of the sidelink data for the first terminal transmission; for the second DCI, the redundancy version is configured to indicate the redundancy version of the sidelink data for the second terminal reception and the HARQ process number is configured to indicate the HARQ process number of the sidelink data for the second terminal reception. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: PUCCH resource indicator; for the first DCI, the PUCCH resource indicator is configured to indicate first PUCCH resource for transmitting a first UCI corresponding to the sidelink data to the network device  80  by the first terminal; for the second DCI, the PUCCH resource indicator is configured to indicate second PUCCH resource for transmitting second UCI corresponding to the sidelink data to the network device  80  by the second terminal. 
     In embodiments of the present disclosure, the first UCI comprises at least one of scheduling request, buffer status report, service type or QoS requirement. 
     In embodiments of the present disclosure, the second UCI comprises at least one of HARQ-ACK/NACK for the received sidelink data, the sidelink channel state information report. 
     In embodiments of the present disclosure, the first PUCCH resource is based on PUCCH resource set configured for the first terminal and the second PUCCH resource is based on PUCCH resource set configured for the second terminal. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises: frequency hopping flag and frequency hopping parameters/configurations; the frequency hopping flag is configured to indicate to the first terminal and the second terminal whether the first terminal shall perform PSSCH frequency hopping or not, and the frequency hopping parameters/configurations are configured to indicate to the first terminal and the second terminal the frequency hopping parameters/configurations for the sidelink data if the frequency hopping flag indicates that the first terminal shall perform PSSCH frequency hopping. 
     In embodiments of the present disclosure, the first DCI and the second DCI further comprises at least one of carrier indicator, sidelink MIMO transmission parameters/configurations or identifier for DCI; for first DCI, the carrier indicator is configured to indicate a component carrier index of the first terminal; and for the second DCI, the carrier indicator is configured to indicate a component carrier index of the second terminal; the sidelink MIMO transmission parameters/configurations are configured to indicate to the first terminal and the second terminal the sidelink MIMO transmission parameters/configurations for the sidelink data; and the identifier for DCI is configured to indicate to the first terminal and the second terminal the received DCI is the first DCI or the second DCI. 
     In embodiments of the present disclosure, the first DCI further comprises at least one of TPC command, CSI-RS resource indicator or timing advance indication; the TPC command is configured to adjust transmission power of the sidelink data for the first terminal, the CSI-RS resource indicator is configured to indicate the first terminal resource for transmitting CSI-RS to the second terminal, and the timing advance indication is configured to indicate to the first terminal the timing advance for transmitting the sidelink data. 
     In embodiments of the present disclosure, the second DCI further comprises at least one of SRS resource indicator, HARQ timing indicator or group destination ID; the SRS resource indicator is configured to indicate to the second terminal resource for transmitting SRS to the first terminal, the HARQ timing indicator is configured to indicate to the second terminal the timing for transmitting HARQ-ACK/NACK for the received sidelink data, and the group destination ID is configured to indicate to the second terminal the group destination ID for the sidelink data. 
     In embodiments of the present disclosure, the network device  80  further comprises: a receiver unit  804 , wherein the receiver unit  804  is configured to receive the HARQ-ACK/NACK for the received sidelink data from the second terminal. 
     It is important to note that, in the embodiment of the disclosure, the receiver unit  804  may be implemented by a receiver (e.g. the receiver  1204  in  FIG. 10 ) and the transmitter unit  802  may be implemented by a transmitter (e.g. the transmitter  1206 ). 
       FIG. 12  schematically illustrates a network device according to another embodiment of the present disclosure. 
     As illustrated in  FIG. 12 , a network device  120  may include a processor  1202 , a receiver  1204 , a transmitter  1206  and a memory  1208 , wherein the memory  1208  may be configured to store a code executed by the processor  1202  an the like. 
     Each component in the network device  120  is coupled together through a bus system  1210 , wherein the bus system  1210  includes a data bus, and further includes a power bus, a control bus and a state signal bus. 
     The processor  1202  typically controls overall operations of the terminal device  120 , such as the operations associated with display, data communications and recording operations. The processor  1202  may include one or more processors to execute instructions to perform all or part of the steps in the above described methods. Moreover, the processor  1202  may include one or more modules which facilitate the interaction between the processor  1202  and other components. 
     The memory  1208  is configured to store various types of data to support the operation of the terminal device  120 . Examples of such data include instructions for any applications or methods operated on the terminal device  120 , contact data, phonebook data, messages, pictures, video, etc. The memory  1208  may be implemented using any type of volatile or non-volatile memory devices, or a combination thereof, such as a static random access memory (SRAM), an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), a programmable read-only memory (PROM), a read-only memory (ROM), a magnetic memory, a flash memory or a magnetic or optical disk. 
     The receiver  1204  is configured to receive an electromagnetic signal received by the antenna. The main function of the receiver is to select the frequency components it needs from the numerous electromagnetic waves existing in the air, suppress or filter out unwanted signals or noise and interference signals, and then obtain the original useful information after amplification and demodulation. 
     The transmitter  1206  is configured to generate and modulate the RF current and transmit the radio waves through the antenna. 
     In embodiments of the present disclosure, the transmitter  1206  and receiver  1204  may be implemented as a transceiver. 
     The network device  80  illustrated in  FIG. 9  and the network device  120  illustrated in  FIG. 12  may implement each process implanted by the network device  11  in the abovementioned method embodiments and will not be elaborated herein to avoid repetitions. Exemplary embodiments have been specifically shown and described as above. It will be appreciated by those skilled in the art that the disclosure is not limited the disclosed embodiments; rather, all suitable modifications and equivalent which come within the spirit and scope of the appended claims are intended to fall within the scope of the disclosure.