PRIORITY 
     This application claims priority to U.S. Provisional Patent Application No. 61/846,653 filed on Jul. 16, 2013, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present invention relates to a communication system and an authentication method thereof. More particularly, the present invention relates to a wireless communication system and an authentication method thereof. 
     BACKGROUND 
     In recent years, the Long Term Evolution (LTE) technology of the 3rd Generation Partnership Project (3GPP) has been widely viewed as the basic architecture of the next generation of wireless communication systems. Under this architecture and in consideration of the security and capability, an authentication procedure must be accomplished between a User Equipment (UE), an Evolved Node B (eNodeB), a Mobility Management Entity (MME) and a Home Subscriber Server (HSS) during an attachment procedure performed by the UE. Therefore, it is conceivable that signaling exchanges generated between the UE, the eNodeB, the MME and the HSS during the authentication procedure will necessarily consume much time and many resources. 
     Accordingly, an urgent need exists in the art to provide a solution to simplify the signaling exchanges needed for the authentication procedure during the attachment procedure performed by a UE under the basic architecture of the LTE technology of 3GPP. 
     SUMMARY 
     A primary objective includes simplifying signaling exchanges needed for an authentication procedure during an attachment procedure performed by a UE under the basic architecture of the LTE technology of 3GPP. 
     To achieve the aforesaid objective, certain embodiments of the present invention include a wireless communication system, which comprises a UE, an eNodeB, an HSS and an MME. The MME is configured to, before the UE enters an attachment procedure, acquire an authentication vector from the HSS in advance and transmit a first authentication vector of the authentication vector to the UE and a second authentication vector of the authentication vector to the eNodeB in advance. The first authentication vector corresponds to the UE and the second authentication vector corresponds to the eNodeB. The eNodeB is configured to transmit a UE identifier to the UE, and the UE is configured to complete an authentication procedure with the eNodeB according to the UE identifier and the authentication vector. 
     To achieve the aforesaid objective, certain embodiments of the present invention include an authentication method for use in a wireless communication system. The wireless communication system comprises a UE, an eNodeB, an HSS and an MME. The authentication method comprises the following steps of: 
     (a) acquiring an authentication vector from the HSS in advance by the MME before the UE enters an attachment procedure; 
     (b) transmitting a first authentication vector of the authentication vector to the UE and a second authentication vector of the authentication vector to the eNodeB in advance by the MME before the UE enters the attachment procedure, wherein the first authentication vector corresponds to the UE and the second authentication vector corresponds to the eNodeB; 
     (c) transmitting a UE identifier to the UE by the eNodeB; and 
     (d) completing an authentication procedure with the eNodeB by the UE according to the UE identifier and the authentication vector. 
     According to the above descriptions, certain embodiments of the present invention include a wireless communication system and an authentication method thereof. More specifically, before a UE enters an attachment procedure, the present invention transmits information (e.g., an authentication vector) needed to be provided by an HSS during an authentication procedure to an MME in advance; and the MME also transmits the information to the UE and the eNodeB in advance. In this way, when the UE enters the attachment procedure, the authentication procedure will be simplified as being performed only between the UE and the eNodeB, so signaling exchanges needed in the conventional authentication procedure are effectively simplified. On the basis of the aforesaid operations, the present invention provides at least the following benefits: the load of the core network can be reduced; and the power consumption of the UE having a high switching frequency (e.g., a machine to machine device) can be reduced. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter, a brief description of the drawings is made, but this is not intended to limit the present invention. 
         FIG. 1  is a schematic structural view of a wireless communication system  1  according to an embodiment of the present invention; 
         FIG. 2  is a schematic view illustrating operations of the wireless communication system  1  shown in  FIG. 1 ; 
         FIG. 3  is a schematic view illustrating specific operations of an authentication procedure  461  shown in  FIG. 2 ; and 
         FIG. 4  is a flowchart diagram of an authentication method for use in a wireless communication system according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, the present invention will be explained with reference to example embodiments thereof. However, these example embodiments are not intended to limit the present invention to the examples, embodiments, environment, applications or implementations described in these example embodiments. Therefore, description of these example embodiments is only for purpose of illustration rather than to limit the present invention. In the attached drawings, elements unrelated to the present invention are omitted from depiction; and dimensional relationships among individual elements are illustrated only for ease of understanding but not to limit the actual scale. 
     An embodiment of the present invention (called “a first embodiment” for short) is a wireless communication system.  FIG. 1  is a schematic structural view of the wireless communication system. As shown in  FIG. 1 , the wireless communication system  1  conforms to the basic architecture of the LTE technology of 3GPP. Under this basic architecture, the wireless communication system  1  comprises at least one UE  11 , at least one eNodeB  13 , at least one MME  15  and at least one HSS  17 . The basic architecture refers to standards that are formulated in accordance with the LTE series technologies, and the LTE series technologies comprise the LTE technology, the LTE-advanced technology and the predecessor technologies of the LTE technology. The predecessor technologies include, for example, a Universal Mobile Telecommunications System (UMTS) or a Global System for Mobile Communications (GSM) and etc. 
     Furthermore, the aforesaid basic architecture may be divided into two parts, namely, an access network and an Evolved Packet Core (EPC). Specifically, the access network comprises the UE  11  and the eNodeB  13 , and the EPC comprises the MME  15  and the HSS  17  as well as at least one Serving Gateway (S-GW) and at least one Packet Data Network Gateway (P-GW). Because the S-GW and the P-GW are not directly related to this embodiment, they are not depicted in the drawings. Furthermore, basic operations, the communication manner and the connections of the UE  11 , the eNodeB  13 , the MME  15 , the HSS  17 , the S-GW and the P-GW can all be known from the standards formulated in accordance with the LTE series technologies, so only contents directly related to the present invention will be described hereinafter. 
       FIG. 2  is a schematic view illustrating operations of the wireless communication system  1 . As shown in  FIG. 2 , before the UE  11  enters an attachment procedure  46  with the eNodeB  13 , the MME  15  and the HSS  17 , the MME  15  has acquired an authentication vector  20  from the HSS  17  in advance and has transmitted a first authentication vector  201  of the authentication vector  20  to the UE  11  and a second authentication vector  202  of the authentication vector  20  to the eNodeB  13  in advance. The first authentication vector  201  corresponds to the UE  11  and the second authentication vector  202  corresponds to the eNodeB  13 . The authentication vector  20  may comprise any authentication information needed to be provided by the HSS  17  when the UE  11  performs the attachment procedure  46 . For example, this authentication information may comprise but not limited to, the Random Number (RAND), the Expected Response (XRES), the Access Security Management Entity (K ASME ), the Authentication Token (AUTN) and etc. The first authentication vector  201  and the second authentication vector  202  may comprise all or a part of the contents of the authentication vector  20 . 
     The MME  15  may acquire the authentication vector  20  from the HSS  17  in advance through an authentication data procedure  40 . More specifically, during the authentication data procedure  40 , the MME  15  may send an authentication data request signaling to the HSS  17 , and then the HSS  17  may transmit an authentication data response signaling which comprises the authentication vector  20  to the MME  15  in response to the authentication data request. 
     After having acquired the authentication vector  20 , the MME  15  may transmit the first authentication vector  201  to the UE  11  in advance through a detachment procedure  42 . The attachment of the UE  11  must be accomplished through an attachment procedure, and the detachment of the UE  11  must be accomplished through a detachment procedure. Therefore, in this embodiment, the MME  15  has transmitted the first authentication vector  201  to the UE  11  in advance during a previous detachment procedure performed by the UE  11 . However, in other embodiments, the MME  15  may also transmit the first authentication vector  201  to the UE  11  through other procedures than the detachment procedure  42 . 
     The detachment procedure  42  may be initiated by one of the UE  11  and the MME  15 . In a case when the detachment procedure  42  is initiated by the UE  11 , the UE  11  may transmit a detach request signaling to the MME  15 , and then the MME  15  may transmit a detach accept signaling which comprises the first authentication vector  201  to the UE  11  in response to the detach request signaling. On the other hand, in a case when the detachment procedure  42  is initiated by the MME  15 , the MME  15  may transmit a detach request signaling which comprises the first authentication vector  201  to the UE  11 , and then the UE  11  may transmit a detach accept signaling to the MME  15  in response to the detach request signaling. 
     After having acquired the authentication vector  20 , the MME  15  may transmit the second authentication vector  202  to the eNodeB  13  in advance through a UE context release procedure  44 . As described above, the detachment of the UE  11  must be accomplished through a detachment procedure; and after the UE  11  is detached, the resource needed for the UE  11  may be released by the eNodeB  13  through the UE context release procedure  44 . Therefore, during the UE context release procedure  44 , the eNodeB  13  may transmit a UE context release command signaling to the MME  15 , and then the MME  15  transmits a UE context release complete signaling which comprises the second authentication vector  202  to the eNodeB  13  in response to the UE context release command. 
     If the UE  11  is to enter the attachment procedure  46  with the eNodeB  13 , the MME  15  and the HSS  17  after the first authentication vector  201  is received by the UE  11  and the second authentication vector  202  is received by the eNodeB  13 , an authentication procedure  461  needed in the attachment procedure  46  will be simplified as being performed only between the UE  11  and the eNodeB  13 . More specifically, during the attachment procedure  46 , the eNodeB  13  may transmit a UE identifier  22  to the UE  11  so that the eNodeB  13  identifies the UE  11  according to the UE identifier  22 . In other embodiments, the eNodeB  13  may also transmit the UE identifier  22  to the UE  11  in advance before the UE  11  enters the attachment procedure  46 . After the UE identifier  22  is received by the UE  11 , the UE  11  can complete an authentication procedure  461  with the eNodeB  13  according to the UE identifier  22  and all or a part of the contents of the authentication vector  20 . 
       FIG. 3  is a schematic view illustrating specific operations of the authentication procedure  461 . As shown in  FIG. 3 , the UE  11  may transmit an authentication request message  4610  to the eNodeB  13  according to the UE identifier  22 . Then, the eNodeB  13  may confirm the identity of the UE  11  according to the authentication request message  4610  and transmit an authentication response message  4612  to the UE  11  according to the authentication request message  4610 . The authentication request message  4610  transmitted to the eNodeB  13  may directly carry the UE identifier  22 . However, the authentication request message  4610  transmitted to the eNodeB  13  may not carry the UE identifier  22  but carry other information which is related to the UE identifier  22  and allows the eNodeB  13  to identify the identity of the UE  11 . Then, the UE  11  may transmit an authentication result message  4614  to the eNodeB  13  according to the information of the first authentication vector  201  and the authentication response message  4612 . For example, the UE  11  may calculate a response (RES) according to a random value and an authentication symbol comprised in the first authentication vector  201  and then transmits the RES to the eNodeB  13  by carrying the RES in the authentication result message  4614 . After the authentication result message  4614  is received by the eNodeB  13 , the eNodeB  13  may determine whether the RES is consistent with the expected RES comprised in the authentication vector  20 . If it is determined that the two RESs are consistent with each other, the eNodeB  13  may transmit an authentication success message  4616  to the UE  11  according to the authentication result message  4614  to notify the UE  11  that the authentication procedure is successful. 
     According to the basic architecture of the LTE technology of 3GPP, the UE  11  must complete a radio resource control connection setup procedure with the eNodeB  13  during the attachment procedure  46  performed by the UE  11 . Therefore, the authentication procedure  461  may be incorporated into the radio resource control connection setup procedure. However, in other embodiments, the authentication procedure  461  may also be performed separately from the radio resource control connection setup procedure. 
     In as case where the authentication procedure  461  is incorporated into the radio resource control connection setup procedure, the authentication request message  4610  may be considered as a radio resource control connection request message, the authentication response message  4612  may be considered as a radio resource control connection setup message, the authentication result message  4614  may be considered as a radio resource control connection setup complete message, and the authentication success message  4616  may be considered as a radio resource control connection reconfiguration message. 
     Another embodiment of the present invention (called “a second embodiment” for short) is an authentication method for use in a wireless communication system. The wireless communication system may comprise at least one UE, at least one eNodeB, at least one HSS and at least one MME. For example, the second embodiment may be an authentication method for use in the wireless communication system  1  of the first embodiment.  FIG. 4  is a flowchart diagram of the authentication method. As shown in  FIG. 4 , the authentication method comprises: a step S 21  of acquiring an authentication vector from the HSS in advance by the MME before the UE enters an attachment procedure; a step S 23  of transmitting a first authentication vector of the authentication vector to the UE and a second authentication vector of the authentication vector to the eNodeB in advance by the MME before the UE enters an attachment procedure, wherein the first authentication vector corresponds to the UE and the second authentication vector corresponds to the eNodeB; a step S 25  of transmitting a UE identifier to the UE by the eNodeB; and a step S 27  of completing an authentication procedure with the eNodeB by the UE according to the UE identifier and the authentication vector. 
     In other embodiments, the step S 21  may further comprise the following step of: acquiring the authentication vector from the HSS in advance by the MME through an authentication data procedure before the UE enters an attachment procedure. 
     In other embodiments, the step S 23  may further comprise the following step of: transmitting the first authentication vector to the UE in advance by the MME through a detachment procedure before the UE enters an attachment procedure. Optionally, the detachment procedure may be initiated by one of the UE and the MME. 
     In other embodiments, the step S 23  may further comprise the following step of: transmitting the second authentication vector to the eNodeB in advance by the MME through a UE context release procedure before the UE enters an attachment procedure. 
     In other embodiments, the step S 27  may further comprise the following steps of: transmitting an authentication request message to the eNodeB by the UE according to the UE identifier; transmitting an authentication response message to the UE by the eNodeB according to the authentication request message; transmitting an authentication result message to the eNodeB by the UE according to the first authentication vector and the authentication response message; transmitting an authentication success message to the UE by the eNodeB according to the authentication result message. 
     In other embodiments, the authentication procedure may be a radio resource control connection setup procedure, the authentication request message may be a radio resource control connection request message, the authentication response message may be a radio resource control connection setup message, the authentication result message is a radio resource control connection setup complete message, and the authentication success message may be a radio resource control connection reconfiguration message. 
     In addition to the aforesaid steps, the authentication method of the second embodiment can also execute steps corresponding to all the operations of the wireless communication system  1  of the first embodiment. The method in which the second embodiment executes these corresponding steps will be readily appreciated by those of ordinary skill in the art based on the explanation of the first embodiment, and thus will not be further described herein. 
     According to the above descriptions, the present invention provides a wireless communication system and an authentication method thereof. More specifically, before a UE enters an attachment procedure, the present invention transmits information (e.g., an authentication vector) needed to be provided by an HSS during an authentication procedure to an MME in advance; and the MME also transmits the information to the UE and the eNodeB in advance. In this way, when the UE enters the attachment procedure, the authentication procedure will be simplified as being performed only between the UE and the eNodeB, so signaling exchanges needed in the conventional authentication procedure are effectively simplified. On the basis of the aforesaid operations, the present invention provides at least the following benefits: the load of the core network can be reduced; and the power consumption of the UE having a high switching frequency (e.g., a machine to machine device) can be reduced. 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.
A wireless communication system and an authentication method thereof are provided. The wireless communication system includes a User Equipment (UE), an Evolved Node B (eNodeB), a Home Subscriber Server (HSS), and a Mobility Management Entity (MME). Before the UE enters an Attachment Procedure, the MME is configured to acquire an Authentication Vector from the HSS in advance, and transmit, based on the Authentication Vector, a first Authentication Vector corresponding to the UE to the UE and a second Authentication Vector corresponding to the eNodeB to the eNodeB in advance. The eNodeB is configured to transmit a UE identifier to the UE. The UE is configured to complete an Authentication procedure with the eNodeB according to the UE identifier and the Authentication Vector.