TECHNICAL FIELD

The disclosure is directed to a connection re-direction method used by a user equipment (UE), a connection re-direction method used by a remote access node, a user equipment using the same method, and a remote access node using the same method.

BACKGROUND

Currently in 5G communication network, a gNB could be deployed in a central unit (CU)-distributed unit (DU) like topology in order to extend the network coverage and to reduce the network expenditure (CAPEX).FIG. 1shows a typical architecture used by a 5G communication network in which a gNB is deployed as having multiple parts including a gNB-head CU, a gNB-head DU, one or more gNB-remote DUs, and etc. One or more UEs could be attached to each of the multiple parts. The CU of a gNB hosting RRC, SDAP and PDCP. The DU of a gNB hosting RLC, MAC, and PHY. The gNB-head CU would connect with more than one gNB-remote DU at a time. Further, a UE may connect to multiple gNB-remote (DU) simultaneous for purposes including a dual connectivity (DC) operation.

In general, a gNB may contain a gNB-CU and one or more gNB-DUs. The gNB-CU would function as a logical node hosting radio resource control (RRC), service data adaptation protocol (SDAP) and packet data convergence protocol (PDCP) protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-DU would function as a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and the operation of the gNB-DU is partly controlled by gNB-CU. One gNB-DU may support one or multiple cells, but one cell is supported by only one gNB-DU. One gNB-DU is connected to only one gNB-CU. A backhaul connection is a connection between a gNB-CU and a gNB-DU, or a connection between two gNB-DUs. The direction toward the gNB-CU in the topology is referred to as upstream, the direction towards UE in the topology is referred to as downstream.

The communication network may handle the generation and delivery of system information (SI) by using the gNB-DU to generate and encode Master Information block (MIB) and System Information Block (SIB) 1, and the gNB-CU generates and encodes SI messages which contain all SIBs except SIB 1. The SI is then broadcasted, and the scheduling of the broadcasts of SI messages is carried out in the gNB-DU. As for the generation and delivery of paging messages, the communication network may use the gNB-CU to initiate a paging procedure by sending a paging message, and subsequently the gNB-DU may determine the final paging cycle for the UE.

One of the current challenges of the 5G communication network is that a gNB-DU may fail to connect. As shown inFIG. 2S201, such connection failure between a gNB-CU and one of the gNB-DUs may result in a radio access network (RAN) connection failure such as an RRC error or a PDCP error. From the perspective of a UE, the connection to the gNB appears to have remained, but the UE might be unable to detect the connection failures in the backhaul level based on a radio resource management (RRM) measurement such as in response to a UplinkInformationTransfer (i.e. NAS message) transmission failure which is a timer value measured in the unit of seconds. A connected UE may require a long period of time to detect a network connection failure such as in response to an expiration of the variable DataInactivityTimer (i.e. RRC connection failure and go into RRC_IDLE) which is set by a Long Term Evolution (LTE) system according to one of the set intervals including {s1, s2, s3, s5, s7, s00, s15, s20, s40, s50, s60, s80, s100, s120, s150, s180}. Similarly, a connected UE may also require a long period of time detect a network connection failure such as in response to an expiration of the variable discardTimer (i.e. PDCP SDU transmission failure) which is set by a New Radio (NR) system according to one of the set intervals including {ms10, ms20, ms30, ms40, ms50, ms60, ms75, ms100, ms150, ms200, ms250, ms300, ms500, ms750, ms1500, infinity}.

When a backhaul connection error occurs, all UEs served by a gNB-remote/DU would be impacted when the gNB-remote/DU has lost the connection with the gNB-head/CU, and such event may bring about a massive amounts of cell selections or RRC connection establishments for all the affected UEs. As seen in the example ofFIG. 3, when the gNB-remote 1/DU1 has lost its connection (S301) with the gNB-head/CU, the UE would need to transfer to RRC_IDLE and establish connections from scratch, even when the Secondary Cell Group (SCG) or PSCell (Primary Secondary Cell) was configured for the UE. The UE would then need to perform a cell selection in order to reestablish UE context and connections with the RAN or with core network (CN). As such, all the ongoing control plan (CP) and user plan (UP) traffic would be interrupted. Therefore, upon detecting a backhaul connection failure, a connection re-direction method would be needed to reduce the impact such backhaul connection failure.

SUMMARY OF THE DISCLOSURE

Accordingly, the disclosure is directed to a connection re-direction method used by a UE, a connection re-direction method used by a remote access node, a user equipment using the same method, and a remote access node using the same method.

In an aspect, the disclosure is directed to a connection re-direction method used by a UE. The method includes not limited to: receiving a network connection failure indication; and performing connection change procedure.

In an aspect, the disclosure is directed to a UE. The UE includes not limited to: a receiver; and a processor coupled to the receiver and configured to: receive, via the receiver, a network connection failure indication; and perform a connection change procedure.

In an aspect, the disclosure is directed to a connection re-direction method used by a remote access node. The method includes not limited to: detecting a backhaul connection failure of a backhaul connection with an upstream node; and transmitting a network connection failure indication from the downstream node in response to having detected the backhaul connection failure.

In order to make the aforementioned features and advantages of the present disclosure comprehensible, exemplary embodiments accompanied with figures are described in detail below. It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the disclosure as claimed.

It should be understood, however, that this summary may not contain all of the aspect and embodiments of the present disclosure and is therefore not meant to be limiting or restrictive in any manner. Also, the present disclosure would include improvements and modifications which are obvious to one skilled in the art.

