Method on Supporting Traffic Offload for Mobile Wireless Relay

項目	內容
所屬技術領域	With the rapid development of science and technologies, wireless communication technologies have been widely applied in various environments. In order to provide a wider service scope, the primary wireless communication technologies all adopt relay technologies to provide a handover mechanism for moving stations and to correspondingly process transmission paths of the stations after handover. However, for the stations moving at a high speed, the conventional processing mechanism has shortcomings. Now, the shortcomings of the conventional processing mechanism in the high-speed moving environment will be described with the Long Term Evolution (LTE) technology as an example. In the LTE architecture, a relay node (RN) may be deployed in a carriage of a train moving at a high speed to serve user equipment (UE) in the carriage.
所欲解決之問題	The demand of traffic offloading is increased as the number of UEs under a Mobile Relay (MRN) increases. It’s suggested to consider the aspect of offloading in determining a suitable architecture for MRN. This PV addresses the support of LIPA and SIPTO for MRN.
解決問題之技術手段	The key in designing traffic offloading for the UEs under MRN is the deployment of UE’s L-GW (Local Gateway), which is used for PDN connectivity-based LIPA and SIPTO. Two typical deployments of UE’s L-GW are (1) UE’s L-GW located at MRN (denoted by UE_L-GW@MRN), and (2) UE’s L-GW collocated with MRN’s P-GW (denoted by UE_L-GW@MRN_P-GW). It is assumed that MRN’s P-GW is equipped with SGi interface to the Internet. Therefore, for the case of UE_L-GW@MRN_P-GW, UE’s L-GW is accordingly equipped with SGi, which is the breakout for both LIPA and SIPTO in the case. For the case of UE_L-GW@MRN, UE’s L-GW is the breakout for LIPA. However, since there is no SGi at MRN, it is necessary to find SGi at another device for SIPTO traffic. It is proposed that MRN’s P-GW is a good choice providing SGi for UE’s L-GW. For the purpose of providing SGi, MRN’s P-GW is functioning as MRN’s L-GW. Therefore, two-stage breakout for SIPTO traffic (uplink) is implemented by firstly UE’s L-GW and secondly MRN’s L-GW. From the aspect of LIPA and SIPTO support, major alternatives of MRN architecture in TR. 36.836 can be classified into the following three groups: (1) Alt.1 and eAlt.2-3, in which MRN’s P-GW is located in EPC, (2) Alt.2 and eAlt.2-2, in which MRN’s P-GW is located at the Initial DeNB, (3) eAlt.2-1, in which MRN’s P-GW is located at the Target DeNB and (4) Alt.4, in which L-GW is not collocated with MRN’s PGW. There are six combinations by paring the three groups of alternatives with the two cases of UE’s L-GW deployment.
對照先前技術之功效	For deployment cost, the case of UE_L-GW@MRN requires added L-GW function at MRN in all MRN alternatives, which should be seen as low cost. There is no extra deployment cost for the case of UE_L-GW@MRN_P-GW for all MRN alternatives. For LIPA efficiency, the case of UE_L-GW@MRN outperforms the case of UE_L-GW@MRN_P-GW over all MRN alternatives. Moreover, the lowest LIPA efficiency is seen for Alt.1 & eAlt.2-3 in the case of UE_L-GW@MRN_P-GW, due to the standalone MRN’s P-GW in EPC. For SIPTO efficiency, the lowest SIPTO efficiency is seen again for Alt.1 & eAlt.2-3 due to the same reason as in LIPA efficiency. For group mobility support, the case of UE_L-GW@MRN does not require re-connection of UE’s LIPA and SIPTO PDN connection after MRN moves to a new DeNB, since UE’s L-GW remains the same in the case of MRN handover. For standardization effort, since the baseline of reference is R10, only Alt.1 suffers. Alt.2, Alt.2 enhancements (i.e. eAlt.2-1 and eAlt.2-2) and Alt.4 with UE_L-GW@MRN are better choice among all options.
實施方式	Embodiment 1: L-GW@MRN Basic features for this deployment are listed as follows: (1)UE’s L-GW is collocated at MRNNC。 (2)UE establishes LIPA session and SIPTO session with its L-GW (3)For LIPA, UE’s L-GW extracts the incoming IP packet’s destination address and finds the corresponding UE’s radio bearer to carry the packet to a local UE. (4)For SIPTO, two-stage breakout is implemented by UE’s L-GW and MRN’s L-GW. UE’s SIPTO traffic (in the case of uplink) reaches UE’s L-GW and is tunneled by MRN’s bearer from MRN to MRN’s L-GW, where the traffic is routed to the Internet through SGi interface.     (A) L-GW@MRN in Alt.2 To fit the deployment in Alt.2, MRN’s L-GW is collocated with MRN’s P-GW at the Initial DeNB, which is the first DeNB MRN attaches to. Steps in the signaling procedure are explained in the following. A. Procedure of LIPA PDN connection establishment: 1.UE initiates and sends PDN Connectivity Request (Step 1) to UE’s MME to establish a PDN connection for LIPA. UE’s MME performs LIPA authorization to decide whether the UE is allowed to use LIPA or not according to the UE subscription data and the LIPA capability of the UE’s eNB (i.e. MRN). The MME might reject the PDN Connectivity Request if the LIPA authorization fails. After successful LIPA authorization, UE’s MME uses the appropriate L-GW address provided in S1-AP signaling to select the L-GW collocated with eNB (i.e. MRN). Optionally, the PDN Connectivity Request can be triggered by UE’s MME with PDN Connectivity Setup Indication (Step 0). 2.UE’s MME performs the Create Session process and sends Create Session Request to UE’s L-GW by way of UE’s S-GW (Step 2 & Step 3). The process is finished when UE’s MME receives Create Session Response from UE’s L-GW (Step 4 & Step 5). 3.Upon reception of Create Session Response, UE’s MME sends S1-AP Bearer Setup Request along with the message of PDN Connectivity Accept to MRN acting as UE’s eNB (Step 6). The messages of RRC Connection Reconfiguration and RRC Connection Reconfiguration Complete are exchanged between MRN and UE for establishment of the default radio bearer and dedicated bearer(s) (Step 7 & Step 8), and MRN sends the S1-AP Bearer Setup Response message to UE’s MME (Step 9). 4.UE sends Direct Transfer message to MRN (Step 10), and MRN sends the message of PDN Connectivity Complete to UE’s MME (Step 11). 5.Finally, the messages of Modify Bearer Request and Modify Bearer Response are exchanged between UE’s MME and UE’s S-GW (Step 12 & Step 13), and the procedure of LIPA PDN connectivity establishment is finished. B. Procedure of SIPTO PDN connection establishment: The procedure for SIPTO PDN connection establishment for the most part is the same as the procedure for LIPA presented in Sec. 2.1-A. The only difference is the additional steps of Step 3.1 and Step 3.2. In the case of SIPTO, UE’s L-GW requests MRN (Step 3.1) to setup PDN Connectivity or GTP tunnel with MRN’s L-GW to provide virtual SGi interface. The procedure for MRN acting as a UE to set up PDN connection with MRN’s L-GW. (B) L-GW@MRN in Alt.1 To fit the deployment of L-GW@MRN in Alt.1, MRN’s L-GW is collocated with MRN’s P-GW in EPC. Rather than collocated at the Initial DeNB in Alt.2, MRN’s P-GW is a standalone device in Alt. 1, but the procedure of PDN connection establishment for both LIPA and SIPTO is the same as in Alt.2. Embodiment 2: L-GW@DeNB In this deployment, UE’s L-GW is located at DeNB. LIPA and SIPTO session is set up from UE to UE’s L-GW by way of MRN’s bearer as in the regular PDN connection from UE to UE’s P-GW. Therefore, the uplink path of LIPA and SIPTO is as follows: UE -> MRN -> MRN’s P-GW -> UE’s L-GW. (A) L-GW@DeNB in Alt.2 To fit the deployment in Alt.2, two variants are proposed: L-GW@Initial_DeNB (variant 1) and L-GW@Target_DeNB (variant 2), where the Target DeNB is the current DeNB MRN is attached to. The following procedures for setting up LIPA and SIPTO PDN connection apply to both variants. A.Procedure of LIPA PDN connection establishment The only difference is UE’s L-GW is collocated at the Initial DeNB (variant 1) or at the Target DeNB (variant 2). B.Procedure of SIPTO PDN connection establishment UE’s L-GW internally requests the Initial DeNB (variant 1) or the Target DeNB (variant 2) to properly configure the SGi interface. (B) L-GW@DeNB in Alt.1 To fit the deployment of L-GW@DeNB in Alt.1, UE’s L-GW is located at the Target DeNB. A.Procedure of LIPA PDN connection establishment (ref. Figure 18): The procedure is almost the same as Sec. 2.1-A. The only difference is UE’s L-GW is collocated at the Target DeNB. B.Procedure of SIPTO PDN connection establishment (ref. Figure 18): The procedure for SIPTO PDN connection establishment for the most part is the same as the procedure for LIPA presented in Sec. 3.2-A. The only difference is the additional step of Step 3.1, in which UE’s L-GW internally requests the Target DeNB to properly configure the SGi interface. Embodiment 3: L-GW@EPC In this deployment, UE’s L-GW is located in EPC. LIPA and SIPTO session is set up from UE to UE’s L-GW by way of MRN’s bearer as in the regular PDN connection from UE to UE’s P-GW. Therefore, the uplink path of LIPA and SIPTO is as follows: UE -> MRN -> MRN’s P-GW -> UE’s L-GW. (A) L-GW@EPC in Alt.2 To fit the deployment of L-GW@EPC in Alt.2, UE’s L-GW is located in EPC as a standalone entity. A. Procedure of LIPA PDN connection establishment : The only difference is UE’s L-GW is a standalone device in this case. B. Procedure of SIPTO PDN connection establishment (B) L-GW@EPC in Alt.1 To fit the deployment of L-GW@EPC in Alt.1, two variants are proposed: (1) standalone UE’s L-GW (variant 1), or (2) UE’s L-GW collocated with MRN’s P-GW (variant 2). The following procedures apply to both variants. A.Procedure of LIPA PDN connection establishment :  The procedure is almost the same as Sec. 2.1-A. The only difference is UE’s L-GW is a standalone device (variant 1) or collocated with MRN’s P-GW (variant 2). B.Procedure of SIPTO PDN connection establishment : The case of standalone L-GW in Alt.1 is very similar to the case of L-GW@EPC in Alt.2, therefore the procedure of SIPTO for variant 1 is the same . For variant 2, the procedure is almost the same except the difference of the addition Step 3.1, in which UE’s L-GW internally requests MRN’s P-GW to properly configure the SGi interface.