Abstract:
The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4 th -Generation (4G) communication system such as Long Term Evolution (LTE). In accordance with an aspect of the present disclosure, a method of transmitting data in a device to device communication system is provided. The method includes determining whether a security feature is applied to one or more packet data convergence protocol (PDCP) data units, configuring the one or more PDCP data units based on the determined result, and transmitting the one or more PDCP data units to one or more receiving user equipments (UEs).

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of an Indian provisional patent application filed on Oct. 30, 2014 in the Indian Patent Office and assigned Serial number 5430/CHE/2014, and of an Indian complete patent application filed on Oct. 7, 2015 in the Indian Patent Office and assigned Serial number 5430/CHE/2014, the entire disclosure of each of which is hereby incorporated by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to pro-se communication in 3 rd  generation partnership project (3GPP). More particularly, the present disclosure relates to generating a packet data convergence protocol (PDCP) protocol data unit (PDU) depending on whether or not security is applied during transmission. 
       BACKGROUND 
       [0003]    To meet the demand for wireless data traffic having increased since deployment of 4G (4 th -Generation) communication systems, efforts have been made to develop an improved 5G (5 th -Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. 
         [0004]    The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. 
         [0005]    In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. 
         [0006]    In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed. 
         [0007]    Device to device (D2D) communication is being studied in communication standard groups to enable data communication services between user equipments (UEs). During the D2D communication, a transmitting D2D UE can transmit data packets to a group of D2D UEs, broadcast data packets to all the D2D UEs, or send unicast data packets to a specific D2D UE. D2D communication between the transmitter and receiver(s) is connectionless in nature, i.e., there is no connection setup (e.g., no control messages are exchanged) between the transmitter and receiver before the transmitter starts transmitting the data packets. During the transmission, the transmitter includes a source identification (ID) and destination ID in the data packets. The source ID is set to the UE ID of the transmitter. The destination ID is the intended recipient of the transmitted packet. The destination ID indicates whether the packet is a broadcast packet or a unicast packet or a packet intended for a group. 
         [0008]      FIG. 1  is a schematic diagram illustrating a protocol stack for D2D communication according to the related art. 
         [0009]    Referring to  FIG. 1 , the packet data convergence protocol (PDCP) layer in the transmitter receives the data packets, i.e., Internet protocol (IP) packets or address resolution protocol (ARP) packets (PDCP service data units (SDUs)) from an upper layer. It secures the packet and also compresses the IP headers of IP packets. The processed packet PDCP protocol data unit (PDU) is sent to radio link control (RLC) layer. The RLC layer receives the PDCP PDUs (RLC SDUs) from the PDCP layer. It fragments the PDCP PDUs if needed and sends the RLC PDUs to a media access control (MAC) layer. The MAC layer multiplexes the RLC PDUs (or MAC SDUs) and sends the MAC PDU to a physical (PHY) layer for transmission on a PC5 interface (e.g., a wireless channel). 
         [0010]      FIG. 2  is a schematic diagram illustrating a PDCP PDU for D2D communication according to the related art. 
         [0011]    Referring to  FIG. 2 , the PDCP layer adds a PDCP header to each PDCP SDU. The PDCP header comprises of PDU type, pro-se group key (PGK) ID, pro-se traffic key (PTK) ID and PDCP sequence number (SN). The PDU type indicates whether the data in PDCP PDU is an ARP packet or an IP packet. In order to support the security a PGK is defined. PGK is specific to a group of D2D UEs. Multiple PGKs per group can be pre-provisioned in a UE. Each of these PGKs for the same group is identified using an 8 bit PGK ID. If a UE wants to send data packets to a group, then it derives a PTK from the PGK corresponding to that group. The PTK is identified using PTK ID. PTK is a group member specific key generated from the PGK. Each PTK is also associated with a 16 bit counter (or PDCP SN). The counter (or PDCP SN) is updated for every packet transmitted. 
         [0012]    The transmitter always adds the PDCP header with the PDU type, PGK ID, PTK ID and PDCP SN in every PDCP PDU. The receiver always parses these four fields in every PDCP PDU. The transmitter and receiver always encrypt/decrypt the data in PDCP PDUs respectively. 
         [0013]    In some D2D communication systems, whether or not to apply the security (e.g., encryption and/or integrity protection) can be configurable. In the case that the transmitter does not apply security, then the related art approach does not work as the receiver always assumes that data is encrypted in every PDCP PDU and using the PDCP security information in the PDCP header, the receiver derives the security keys and decrypts the data. 
         [0014]    In some D2D communication system, a UE can be in coverage of network and another UE can be in out of network coverage. UE in coverage of network can receive the security configuration information from the network, while out of coverage UE must rely on pre-configuration or may not apply security in the absence of security configuration information. In the case that the receiving UE is in coverage and always assumes that data is encrypted in every PDCP PDU then communication will fail as the receiver attempts to decrypt the PDU which is not encrypted. 
         [0015]    Thus, there is a need for a method to generate the PDCP PDU depending on whether or not the security is applied. Further, it is required to reduce the overhead in the radio interface by avoiding transmitting redundant information, especially when security is not applied, then it is not required to send the security information in the PDCP header. 
         [0016]    The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure. 
       SUMMARY 
       [0017]    Aspects of the present disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a method of performing device to device communication between user equipments (UEs). 
         [0018]    In accordance with an aspect of the present disclosure, a method of transmitting data in a device to device communication system is provided. The method includes determining whether a security feature is applied to one or more packet data convergence protocol (PDCP) data units, and configuring the one or more PDCP data units based on the determined result, and transmitting the one or more PDCP data units to one or more receiving user equipments (UEs). 
         [0019]    In accordance with an aspect of the present disclosure, a method of receiving data in a device to device communication system is provided. The method includes receiving one or more packet data convergence protocol (PDCP) data units, and processing the one or more PDCP data units configured based on whether a security feature is applied to one or more packet data convergence protocol (PDCP) data units. 
         [0020]    In accordance with an aspect of the present disclosure, an apparatus of transmitting data in a device to device communication system is provided. The apparatus includes a controller for determining whether a security feature is applied to one or more packet data convergence protocol (PDCP) data units and configuring the one or more PDCP data units based on the determined result, and a transmitter for transmitting the one or more PDCP data units to one or more receiving user equipments (UEs). 
         [0021]    In accordance with an aspect of the present disclosure, an apparatus of transmitting data in a device to device communication system is provided. The apparatus includes a receiver for receiving one or more packet data convergence protocol (PDCP) data units, and a controller for processing the one or more PDCP data units configured based on whether a security feature is applied to one or more packet data convergence protocol (PDCP) data units. 
         [0022]    Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0024]      FIG. 1  is a schematic diagram illustrating a protocol stack for device to device (D2D) communication according to the related art; 
           [0025]      FIG. 2  is a schematic diagram illustrating a packet data convergence protocol (PDCP)protocol data unit (PDU) for D2D communication according to the related art; 
           [0026]      FIG. 3  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure; 
           [0027]    FIG. 4  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure; 
           [0028]      FIG. 5  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure; 
           [0029]      FIG. 6  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure; 
           [0030]      FIG. 7  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure; 
           [0031]      FIG. 8  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure; 
           [0032]      FIG. 9  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure; 
           [0033]      FIG. 10  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure; and 
           [0034]      FIG. 11  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure. 
       
    
    
       [0035]    Throughout the drawings, like reference numerals will be understood to refer to like parts, components, and structures. 
       DETAILED DESCRIPTION 
       [0036]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those or ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
         [0037]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents. 
         [0038]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0039]    It will be further understood that the terms “includes”, “comprises”, “including” and/or “comprising” when used in this specification, specify the presence of stated features, integers, operations, elements and/or components, but do not preclude the presence or addition of one or more other features integers, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations and arrangements of one or more of the associated listed items. 
         [0040]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Any name or term (which is registered trademark/copyright) used in the specification is only for the purpose of explaining the present disclosure and not for any commercial gain. 
         [0041]    The present disclosure describes a method to generate the packet data convergence protocol (PDCP) protocol data unit (PDU) depending on whether or not a security feature is applied during pro-se communication in 3 rd  generation partnership project (3GPP). 
       Embodiment 1 
       [0042]      FIG. 3  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure. 
         [0043]    Referring to  FIG. 3 , in this method of the present disclosure, the transmitter adds the same PDCP header irrespective of whether or not a security feature (e.g., ciphering) is applied on the data (i.e., PDCP service data unit (SDU)) by a PDCP entity. In an embodiment of the present disclosure, the pro-se configuration information provided by the network (which is stored in the secure element (e.g., a universal integrated circuit card (UICC)) of the device) indicates to PDCP whether or not security feature (e.g. ciphering) should be applied to PDCP SDUs for a particular destination identification (ID), for all destination IDs, or for a particular PDU SDU type (e.g., a relay SDU, signaling SDU, address resolution protocol (ARP) SDU, etc.). In an embodiment of the present disclosure, whether or not to apply a security feature (e.g., ciphering) is configured by the pro-se key management function or pro-se function in the network. In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not a security feature (e.g., ciphering) should be applied to PDCP SDUs by the PDCP entity. Whether or not a security feature (e.g., ciphering) should be applied to PDCP SDUs can be indicated for a particular destination ID, for all destination IDs, or for a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). Upper layer may indicate not to apply a security feature in PDCP if the security is already applied to the PDCP SDU at the upper layer. If the security feature is applied, then PDCP generates the PDCP PDU by adding the PDCP header and including the PDU type, pro-se group key (PGK) ID and pro-se traffic key (PTK) ID and PDCP sequence number (SN) values associated with the PDCP SDU in the PDCP PDU. If the security feature is not applied, then PDCP generates the PDCP PDU by adding the PDCP header and setting the PDU type associated with the PDCP SDU in the PDCP PDU. The PGK ID and PTK ID are set to predefined values. In one embodiment of the present disclosure, they can be set to zeroes. In another embodiment of the present disclosure, they can be set to ones. The pre-defined values of PGK ID and/or PTK ID indicated in the PDCP header when the security feature is not applied are used to identify (i.e., should be excluded from values used to identify PGK and PTK when the security is applied) PGK and PTK when the security feature is applied. In an embodiment of the present disclosure, the PDCP SDUs are not numbered if the security is not applied, and the PDCP SN in the PDCP header is set to a pre-defined value. The pre-defined value can be zero. 
         [0044]    In an embodiment of the present disclosure, the transmitter determines if a security feature is to be applied on a PDCP SDU or not, at operation  301 . At operation  302 , the security feature is either applied or not based on the information received from the operation  301 . If the security feature is applied, at operation  303 , PDCP entity encrypts the PDCP SDU. PDU Type and PDCP SN are set to the corresponding values associated with PDCP SDU. At operation  304 , PGK ID is set in the PDCP header to the PGK ID of the PGK or some least significant bits (LSBs) of the PGK ID of the PGK which was used to generate PTK used for securing this PDCP SDU. At operation  305 , the PTK ID is set to the PTK ID of the PTK which was used to generate a pro-se encryption key (PEK) used for securing this PDCP SDU. The encrypted PDCP SDU is transmitted together with PDCP header to a receiver. 
         [0045]    If a security feature is not to be applied, PDCP entity does not encrypt the PDCP SDU. PDU type is set to the corresponding value associated with PDCP SDU at operation  306 . At operation  307 , the PGK ID is set in the PDCP header to predefined values (e.g., zeros or ones). At operation  308 , the PTK ID is set in the PDCP header to predefined values (e.g., zeros or ones). At operation  309 , PDCP SDUs are not numbered and the PDCP SN in the PDCP header is set to a pre-defined value (e.g., zeros or ones). The unencrypted PDCP SDU is transmitted together with PDCP header to the receiver. 
         [0046]      FIG. 4  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure. 
         [0047]    Referring to  FIG. 4 , in an embodiment of the present disclosure, the receiver knows whether or not the security feature is applied to the PDCP SDU based on configuration information received from a network (which is stored in the secure element (UICC) of the device). In an embodiment of the present disclosure, whether or not the security feature (e.g., ciphering) is applied is configured by the pro-se key management function or pro-se function in the network. In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not the security feature is applied to PDCP SDUs. If the security feature is applied, the PDCP entity parses the PDCP header and determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header. The PDCP entity also parses the PDCP header and determines the PDCP SN. If the security feature is not applied, then the PDCP entity ignores the PTK ID and PGK ID fields in the PDCP header. In an alternate embodiment of the present disclosure, wherein PDCP SDUs are not numbered if the security feature is not applied, then the PDCP entity ignores the PDCP SN, PTK ID, and PGK ID fields in the PDCP header. 
         [0048]    In an embodiment of the present disclosure, the receiver process the data received from the transmitter to determine if security feature is applied on the PDCP SDU or not based on configuration information from a pro-se function or pro-se key management function, at operation  401 . At operation  402 , a check is performed of whether or not the security feature is applied based on the information received from the operation  401 . At operation  403 , the PDCP entity parses the PDCP header and determines the PDCP SN, PGK, and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header when the security feature is applied. At operation  404 , the received PDCP SDU is decrypted and sent to upper layer. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, non-access stratum (NAS) protocol, pro-se protocol, application, internet protocol (IP), ARP protocol, and signaling protocol. 
         [0049]    At operation  405 , the PDCP SDUs are not numbered if the security feature is not applied, and the PDCP entity ignores the PDCP SN, PTK ID, and PGK ID fields in the PDCP header. In an alternate embodiment of the present disclosure at operation  405 , the PDCP entity ignores the PTK ID and PGK ID fields in the PDCP header when the security feature is not applied. At operation  406 , the PDCP entity sends the received PDCP SDU to upper layer without decryption. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, NAS protocol, pro-se protocol, application, IP protocol, ARP protocol, and signaling protocol. 
         [0050]      FIG. 5  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure. 
         [0051]    Referring to  FIG. 5 , in this embodiment of the present disclosure, the receiver determines whether or not the security feature is applied to the PDCP SDU based on the PGK ID and/or PTK ID field values in the PDCP header. If the PGK ID and/or PTK ID are set to predefined values, then the PDCP entity interprets that the security feature is not applied to the PDCP SDU; otherwise, it interprets that the security feature is applied to the PDCP SDU. In an alternate embodiment of the present disclosure, the receiver determines whether or not the security feature is applied to the PDCP SDU based on the PDCP SN and/or PGK ID and/or PTK ID field values in the PDCP header. If the PDCP SN and/or PGK ID and/or PTK ID are set to the predefined values, then the PDCP entity interprets that the security feature is not applied to the PDCP SDU; otherwise, it interprets that the security feature is applied to the PDCP SDU. 
         [0052]    At operation  501 , the receiver reads the PGK ID and/or PTK ID information in the received PDCP header. At operation  502 , a check is performed of whether the PGK ID and/or PTK ID is set to the pre-defined values. At operation  503 , the receiver observes that the security feature is applied to PDCP SDU when the PGK ID and/or PTK ID is not set to the pre-defined values. In an alternate embodiment of the present disclosure, at operation  501 , the receiver reads the PDCP SN and/or PGK ID and/or PTK ID information in the received PDCP header. At operation  502 , a check is performed of whether the PDCP SN and/or PGK ID and/or PTK ID is set to the pre-defined values. At operation  503 , the receiver observes that the security feature is applied to the PDCP SDU when the PDCP SN and/or PGK ID and/or PTK ID is not set to the pre-defined values. The PGK and PTK used for securing the PDCP SDU are determined based on the PTK ID and PGK ID in the PDCP header. At operation  504 , the received PDCP SDU is decrypted and sent to the upper layer. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, NAS protocol, pro-se protocol, application, IP protocol, ARP protocol, and signaling protocol. 
         [0053]    At operation  505 , the receiver observes that the security feature is not applied to the PDCP SDU when the PGK ID and/or PTK ID is set to the pre-defined values. Alternately, at operation  505 , the receiver observes that the security feature is not applied to the PDCP SDU when the PDCP SN and/or PGK ID and/or PTK ID is set to the pre-defined values. The received PDCP SDU is sent to upper layer without decryption. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, NAS protocol, pro-se protocol, application, IP protocol, ARP protocol, and signaling protocol. 
       Embodiment 2 
       [0054]      FIG. 6  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure. 
         [0055]    Referring to  FIG. 6 , in this embodiment of the present disclosure, the transmitter adds a different type of PDCP header depending on whether or not the security feature (e.g., ciphering) is applied on the data (i.e., a PDCP SDU). In an embodiment of the present disclosure, the pro-se configuration information provided by the network (which is stored in the secure element (UICC) of the device) indicates to PDCP whether or not the security feature (e.g., ciphering) should be applied to PDCP SDUs by the PDCP entity for a particular destination ID, all destination IDs, or a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). In an embodiment of the present disclosure, whether or not to apply the security feature (e.g., ciphering) is configured by the pro-se key management function or pro-se function in the network. In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not the security feature should be applied to PDCP SDUs. Whether or not the security feature (e.g., ciphering) should be applied to PDCP SDUs, can be indicated for a particular destination ID, for all destination IDs, or for a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). Upper layer may indicate not to apply the security feature in PDCP if the security is already applied to the PDCP SDU at the upper layer. If the security feature is applied, then PDCP generates the PDCP PDU by adding the PDCP header and setting the PDU type, PGK ID, PTK ID, and PDCP SN associated with the PDCP SDU in the PDCP PDU. If the security feature is not applied, then PDCP generates the PDCP PDU by adding the PDCP header wherein the PDCP header comprises of PDU type and PDCP SN fields only. These fields are set to the PDU type and PDCP SN associated with the PDCP SDU in the PDCP PDU. The PGK ID and PTK ID are not included in the PDCP header. 
         [0056]    In an embodiment of the present disclosure, an indicator is provided in the PDCP header which indicates whether or not the PGK ID and PTK ID are included in the PDCP header. 
         [0057]    At operation  601 , the transmitter determines if the security feature is to be applied on the PDCP SDU or not. At operation  602 , the security feature is either applied or not, based on information received from the operation  601 . At operation  603 , the PDCP entity encrypts the PDCP SDU and the PDCP header is added to data, i.e., a PDCP SDU, which comprises of only PDU type, PGK ID, PTK ID, and PDCP SN when the security feature is applied. At operation  604 , the PDU type and the PDCP SN are set to the corresponding values associated with the PDCP SDU. At operation  605 , the PGK ID in the PDCP header is set to the PGK ID of the PGK which was used to generate the PTK used for securing this PDCP SDU. At operation  606 , the PTK ID is set to the PTK ID of the PTK which was used to generate the PEK used for securing this PDCP SDU. The encrypted PDCP SDU is transmitted together with the PDCP header to the receiver. 
         [0058]    At operation  607 , the PDCP entity does not encrypt the PDCP SDU. The PDCP header is added to the data, which comprises of only the PDU type and PDCP SN, when the security feature is not applied. At operation  608 , the PDU type and the PDCP SN are set to the corresponding values associated with the PDCP SDU. The unencrypted PDCP SDU is transmitted together with PDCP header to the receiver. 
         [0059]      FIG. 7  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure. 
         [0060]    Referring to  FIG. 7 , in this embodiment of the present disclosure, the receiver already knows whether or not the security feature is applied to the PDCP SDU based on configuration information received from a network (which is stored in the secure element (UICC) of the device). In an embodiment of the present disclosure, whether or not the security feature (e.g., ciphering) is applied is configured by the pro-se key management function or pro-se function in the network. In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not the security feature is applied to PDCP SDUs. If the security feature is applied, the PDCP entity parses the PDCP header comprising of the PDU type, PGK ID, PTK ID, and PDCP SN. The PDCP entity then determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header. If the security feature is not applied, then the PDCP entity parses the PDCP header comprising of the PDU type and PDCP SN (as the receiver knows that the PGK ID and PTK ID are not included in the PDCP header). 
         [0061]    At operation  701 , the receiver determines if the security feature is to be applied on PDCP SDU or not based on configuration information from pro-se function. At operation  702 , the security feature is either applied or not based on information received from the operation  701 . At operation  703 , the PDCP entity parses the PDU type, PGK ID, and PDCP SN from the beginning of the PDCP PDU, and determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header. At operation  704 , the received PDCP SDU is decrypted and sent to upper layer. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, NAS protocol, pro-se protocol, application, IP protocol, ARP protocol, and signaling protocol. 
         [0062]    At operation  705 , the PDCP entity parses the PDU type and PDCP SN from the beginning of the PDCP PDU. Alternately, at operation  705 , the PDCP entity parses the PDU type from the beginning of the PDCP PDU. At operation  706 , the received PDCP SDU is sent to upper layer. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, NAS protocol, pro-se protocol, application, IP protocol, ARP protocol, and signaling protocol. 
       Embodiment 3 
       [0063]      FIG. 8  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure. 
         [0064]    Referring to  FIG. 8 , in this embodiment of the present disclosure, the transmitter adds a different type of PDCP header depending on whether or not the security feature is applied on the data (i.e., a PDCP SDU). In an embodiment of the present disclosure, the pro-se configuration information provided by the network (which is stored in the secure element (UICC) of the device) indicates to PDCP whether or not the security feature should be applied to PDCP SDUs by the PDCP entity for a particular destination ID, all destination IDs, or a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). In an embodiment of the present disclosure, whether or not the security feature (e.g., ciphering) is applied is configured by the pro-se key management function or pro-se function in the network. In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not the security feature should be applied to PDCP SDUs. Whether or not the security feature (e.g., ciphering) should be applied to PDCP SDUs, can be indicated for a particular destination ID, for all destination IDs, or for a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). Upper layer may indicate not to apply the security feature in PDCP if the security is already applied to the PDCP SDU at the upper layer. If the security feature is applied, then PDCP generates the PDCP PDU by adding the PDCP header and setting the PDU type, PGK ID, PTK ID, and PDCP SN associated with the PDCP SDU in the PDCP PDU. If the security feature is not applied, then PDCP generates the PDCP PDU by adding the PDCP header, wherein the PDCP header comprises of the PDU type only. The field PDU type is set to the PDU type associated with the PDCP SDU in the PDCP PDU. The PGK ID, PTK ID, and PDCP SN fields are not included in the PDCP header. The PDCP SN is not maintained since the security feature is not applied. 
         [0065]    In an embodiment of the present disclosure, an indicator is provided in the PDCP header which indicates whether or not the PGK ID, PTK ID, and PDCP SN are included in the PDCP header. 
         [0066]    At operation  801 , the transmitter determines if the security feature is to be applied on PDCP SDU or not. At operation  802 , the security feature is either applied or not based on information received from the operation  801 . At operation  803 , the PDCP entity encrypts the PDCP SDU, and the PDCP header is added which comprises of only the PDU Type, PGK ID, PTK ID, and PDCP SN when the security feature is applied. At operation  804 , the PDU Type and PDCP SN are set to the corresponding values associated with the PDCP SDU. At operation  805 , the PGK ID in the PDCP header is set to the PGK ID of the PDG which was used to generate the PTK used for securing this PDCP SDU. At operation  806 , the PTK ID is set to the PTK ID of the PTK which was used to generate the PEK used for securing this PDCP SDU. The encrypted PDCP SDU is transmitted together with the PDCP header to the receiver. 
         [0067]    At operation  807 , PDCP entity does not encrypt the PDCP SDU and the PDCP header is added which comprises of only the PDU type, when the security feature is not applied. At operation  808 , the PDU type is set to the corresponding value associated with the PDCP SDU. The unencrypted PDCP SDU is transmitted together with the PDCP header to the receiver. 
         [0068]      FIG. 9  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure. 
         [0069]    Referring to  FIG. 9 , in this embodiment of the present disclosure, the receiver already knows whether or not the security feature is applied to the PDCP SDU based on configuration information received from network (which is stored in the secure element (UICC) of the device). In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not the security feature is applied to PDCP SDUs. If the security feature is applied, the PDCP entity parses the PDCP header comprising of the PDU type, PGK ID, PTK ID, and PDCP SN. The PDCP entity then determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header. If the security feature is not applied, then the PDCP entity parses the PDCP header comprising of the PDU type only (as the receiver knows that the PGK ID and PTK ID are not included in the PDCP header). 
         [0070]    At operation  901 , the receiver determines if the security feature is to be applied on PDCP SDU or not based on configuration information from pro-se function. At operation  902 , the security feature is either applied or not based on information received from the operation  901 . At operation  903 , the PDCP entity parses the PDU type, PGK ID, PTK ID, and PDCP SN from the beginning of the PDCP PDU, and determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header, when the security feature is applied. At operation  904 , the received PDCP SDU is decrypted and sent to upper layer. 
         [0071]    At operation  905 , the PDCP entity parses the PDU type from the beginning of the PDCP PDU. At operation  906 , the received PDCP SDU is sent to upper layer. 
       Embodiment 4 
       [0072]      FIG. 10  is a flowchart illustrating a PDCP entity operation in the transmitter for generating the PDCP PDU according to an embodiment of the present disclosure. 
         [0073]    Referring to  FIG. 10 , in this embodiment of the present disclosure, the transmitter adds a different type of PDCP header depending on whether or not the security feature is applied on the data (i.e., a PDCP SDU). In an embodiment of the present disclosure, the pro-se configuration information provided by the network (which is stored in the secure element (UICC) of the device) indicates to PDCP whether or not the security feature should be applied to PDCP SDUs for a particular destination ID (which can be a group ID), all destination IDs, or a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). In an embodiment of the present disclosure, whether or not the security feature (e.g., ciphering) is applied is configured by the pro-se key management function or pro-se function in the network. In an embodiment of the present disclosure, the upper layer indicates to PDCP whether or not the security feature should be applied to PDCP SDUs. Whether or not the security feature (e.g., ciphering) should be applied to PDCP SDUs, can be indicated for a particular destination ID, for all destination IDs, or for a particular PDU SDU type (e.g., a relay SDU, signaling SDU, ARP SDU, etc.). Upper layer may indicate not to apply the security feature in PDCP if the security is already applied to the PDCP SDU at the upper layer. If the security feature is applied, then PDCP generates the PDCP PDU by adding the PDCP header and setting the PDU type as secured (for example, if the PDU type indicates ARP and IP packets, then two additional types indicating unsecured ARP and unsecured IP are defined) and further adds the PGK ID, PTK ID, and PDCP SN associated with the PDCP SDU in the PDCP PDU. If the security feature is not applied, then PDCP generates the PDCP PDU by adding the PDCP header, wherein the PDCP header comprises of the PDU type only. The field PDU type is set to the PDU type associated with the PDCP SDU in the PDCP PDU as unsecured (i.e., the security feature is not applied). The PGK ID, PTK ID, and PDCP SN fields are not included in the PDCP header. The PDCP SN is not maintained since the security feature is not applied. 
         [0074]    In an alternate embodiment of the present disclosure, an indicator can be in the PDCP header which indicates whether or not the PGK ID, PTK ID, and PDCP SN are included in the PDCP header. 
         [0075]    At operation  1001 , the transmitter determines if the security feature is to be applied on PDCP SDU or not. At operation  1002 , the security feature is either applied or not based on information received from the operation  1001 . At operation  1003 , the PDCP header is added, which comprises of the PDU type, PGK ID, PTK ID, and PDCP SN when the security feature is applied. At operation  1004 , the PDU type and PDCP SN are set to the corresponding values associated with the PDCP SDU. 
         [0076]    At operation  1005 , the PGK ID in the PDCP header is set to the PGK ID of the PGK which was used to generate the PTK used for securing this PDCP SDU. At operation  1006 , the PTK ID is set to the PTK ID of the PTK which was used to generate the PEK used for securing this PDCP SDU. 
         [0077]    At operation  1007 , the PDCP header is added to data, which comprises of only the PDU type, when the security feature is not applied. At operation  1008 , the PDU type is set to the corresponding value associated with the PDCP SDU. 
         [0078]      FIG. 11  is a flowchart illustrating a PDCP entity operation in the receiver according to an embodiment of the present disclosure. 
         [0079]    Referring to  FIG. 11 , in this embodiment of the present disclosure, the PDCP entity parses the PDCP header comprising of the PDU type, and based on the received PDU type knows whether or not the security feature is applied. If the PDU type indicates that the security feature is applied, then the PDCP entity further parses the PDCP header comprising of the PGK ID, PTK ID, and PDCP SN. The PDCP entity then determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header. If the security feature is not applied (based on the PDU type), then the PDCP entity further process the data packet without decrypting the packet (or verifying the message authentication code (MAC-I)). 
         [0080]    At operation  1101 , the receiver processes the data received from transmitter to determine if the security feature is applied on PDCP SDU or not based on the PDU type in the received PDCP header. At operation  1102 , a check is performed of whether or not the security feature is applied based on information received from the operation  1101 . At operation  1103 , the PDCP entity parses the PGK ID, PTK ID, and PDCP SN from the beginning of the PDCP PDU, and determines the PGK and PTK used for securing the PDCP SDU based on the PTK ID and PGK ID in the PDCP header, when the security feature is applied. At operation  1104 , the received PDCP SDU is decrypted and sent to upper layer. 
         [0081]    At operation  1105 , the received PDCP SDU is sent to upper layer without decryption, when the security feature is not applied. In an embodiment of the present disclosure, the upper layer includes, but is not limited to, NAS protocol, pro-se protocol, application, IP protocol, ARP protocol, and signaling protocol. 
       Embodiment 5 
       [0082]    In an embodiment of the transmitter operation of the present disclosure, the transmitter adds a different type of PDCP header (as explained in solutions 1 to 4) depending on whether or not the security feature is applied on the data (i.e., a PDCP SDU). In an embodiment of the present disclosure, the pro-se configuration information provided by the network (which is stored in the secure element (UICC) of the device) indicates to the PDCP entity whether or not the security feature should be applied to the PDCP SDUs for a particular destination ID (which can be a group ID). 
         [0083]    In an embodiment of the receiver operation of the present disclosure, the receiver knows whether or not the security feature is applied to the PDCP SDU based on configuration information received from pro-se function during the service authorization. Further the configuration information indicates, whether or not a particular device within a group will apply the security feature. For example, there are four devices (D 1 , D 2 , D 3 , D 4 ) within a group performing D2D communication, where D 1 , D 2 , and D 3  are subscribed for transmission and D 4  is subscribed for only reception. In D 4 , the network configuration information indicates that, D 1  and D 3  will apply security feature and D 2  will not apply security feature. In this case, when D 4  receives data packets from D 1  and D 3 , it knows the security feature will be applied and when D 4  receives data packets from D 2  it knows the security feature is not applied. The network decides the configuration information based on the device capability, subscription (i.e., a low priority device), and like so. 
       Embodiment 6 
       [0084]    In an embodiment of the present disclosure during the transmitter operation, the transmitter adds a different type of PDCP header (as described in embodiments 1 to 4) depending on whether or not the security feature is applied on the data (i.e., a PDCP SDU). In an embodiment of the present disclosure, the transmitting device decides whether or not the security feature should be applied to the PDCP SDUs based on an application (for example, whether or not the application applies the security feature, applications sensitivity), an upper layer protocol (for example, if the upper layer protocol(s) is real-time transport protocol (RTP) and/or user datagram protocol (UDP) and/or hypertext transfer protocol over secure socket layer (HTTPS), no security feature will be applied), its security capability, and like so. 
         [0085]    In an embodiment of the present disclosure, during the receiver operation, the receiver already knows whether or not the security feature is applied to the PDCP SDU based on configuration information received from pro-se function during the service authorization. Further, the configuration information may indicate whether or not a particular device within a group will apply the security feature. In an embodiment of the present disclosure, based on the indication/information received in the data packets, the receiver knows whether or not the security feature is applied (for example, using pre-defined values in the security information fields, based on the PDU type value in the PDCP header). 
         [0086]    While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.