Optimized evolved node b (enb) handover in lte network

The present invention generally relates to mobile broadband networking technologies such as evolved 3GPP packet switching domains that provide IP connectivity using E-UTRAN (Evolved Universal Terrestrial Radio Access Network).

EPC (Evolved Packet Core) is an Internet Protocol (IP) -based core network defined by 3GPP, Release 8 for use in LTE (Long-Term Evolution) and other wireless network access technologies. The purpose of EPC is to provide an architecture that allows all Internet Protocol (IP) -based core networks to access various services. In LTE, the MME (Mobility Management Entity) feature provides an anchor for a mobile device (user device or "UE") as it moves through the system within the geographic area covered by the MME node. The EPC includes an MME and multiple access-independent gateways that route the user's datagram. The wireless access part of the LTE system is eNB (Evolved Node) B). Each eNB usually includes an antenna system along with a base station radio device. In addition to wireless transmitters and receivers, the eNB also includes resource management and logical control functions, which have traditionally been separated into base station controllers (BSCs) or wireless network controllers (RNCs). By including this additional feature, the eNBs communicate directly with each other, thereby eliminating the need for a mobile exchange system (MSC) or control unit (BSC or RNC). Communication between eNBs includes handovers. In the LTE standard, LTE eNB needs to perform both inter-eNB and intra-eNB handover procedures within E-UTRAN.

Femtocell is a radio access network element that supports a limited number of concurrent users in a home environment in a limited geographic area on one or more wireless interfaces of the GSM® / WCDMA family. is there. The 3G femto access point is called Home Node B (HNB). The CSG (Closed Subscriber Group) is used to describe a particular group of mobile devices that are allowed access to a particular femtocell. In LTE, a "home eNB" (HeNB) logical architecture may be implemented. The HeNB has a set of S1 interfaces that connect the HeNB to the EPC. In this way, the E-UTRAN architecture allows the home eNB gateway (HeNB GW) to extend the S1 interface between HeNB and EPC to support a large number of HeNBs.

The 3GPP specification requires the HeNB GW to relay all messages in the UE-related S1 application part between HeNB and MME. This requirement increases the amount of signaling that the EPC (ie MME and SGW (Serving Gateway)) needs to process. It is desirable to optimize UE handover between HeNBs connected to the same HeNB GW while reducing the amount of signaling to the EPC.

<p> This disclosure addresses this requirement in the art.</p>

<p> This disclosure describes a method of providing the LTE MME (mobility management entity) function of 3GPP E-UTRAN EPC (Evolved Packet Core) and an optimized intra-gateway handover operation that reduces signaling between GWs.</p><p> During operation, the HeNB gateway (GW) intercepts the handover request from the HeNB (source HeNB) and determines if the target cell is another HeNB (target HeNB) connected to the gateway. To do. (i) The target HeNB is in the same tracking area as the source HeNB (identified by the tracking area identifier (TAI)), (ii) the target HeNB is open or supports the CSG identifier specified by the source. , And (iii) If both the source HeNB and the target HeNB are using the HeNB GW S1-U interface, the HeNB GW handles the handover procedure locally with limited interaction with the MME. (i) the target HeNB is open or supports the CSG identifier indicated by the source, and (ii) the target HeNB is not in the same TAI as the source HeNB, or (iii) both the source HeNB and the target HeNB HeNB GW S1-U If you are not using the interface or you are using HeNB The GW still handles this locally by translating the handover procedure into an X2-based handover message to the MME. In both scenarios, despite the 3GPP requirement that the GW relays all handover messages to the MME, message transmission to and from the MME is minimized and / or reduced.</p><p> The above outlines some of the more subject-friendly features. These functions are merely examples. Many other favorable results can be obtained by applying the disclosed subject matter in various ways or by modifying the subject matter as described below.</p>

<figref num="1">It is a simple block diagram of an EPC (Evolved Packet Core) -based network that deploys a home eNB gateway (HeNB GW) so that the S1 interface between HeNB and EPC can be scaled to support a large number of HeNBs.</figref><figref num="2">It is a time series diagram which shows the 1st Embodiment of this disclosure which reduces MME signaling in the handover procedure in HeNB gateway, and the source HeNB and the target HeNB are arranged in the same tracking area.</figref><figref num="3">It is a time series diagram which shows the 2nd Embodiment of this disclosure which reduces MME signaling in the handover procedure in HeNB gateway, and the source HeNB and the target HeNB are arranged in different tracking areas.</figref>

It is presumed that the following detailed description is familiar with the extension of E-UTRAN's General Packet Radio Service (GPRS) described in the standard specification 3GPP TS 23.401 of the 3GPP Mobile Broadband Standard. In particular, LTE E-UTRAN intra-handover is described in 3GPP TS 36.300.

As shown in FIG. 1, a typical LTE network 100 capable of implementing the disclosed handover technology is one coupled with MME102, SGW104, PGW106, HSS108, and HeNB gateway (HeNB GW) 112. It has a set of home-evolved nodes B (each HeNB). The MME102 is the primary control node for the LTE access network. While there are other features, the MME102 is responsible for paging procedures, including tracking and retransmission of idle mode UEs (user equipment). The serving gateway (SGW) 104 also acts as a mobility anchor for the user plane during e-node B inter-handover while routing and forwarding user data packets. The MME is responsible for selecting the UE's SGW during initial connectivity and during intra-LTE handovers, including relocation of core network (CN) nodes. The PDN gateway (PGW) 106 provides a connection from the UE to the external packet data network by being the entry and exit points for UE traffic. Home Subscriber Server (HSS: Home) Subscriber Server) 108 is a central database containing user-related and subscription-related information. HSS108 also provides mobility management, call and session establishment assistance, user authentication, and permissions.

The HeNB GW112 provides an S1-C and / or S1-U interface to the HeNB 110 connected to the gateway. The HeNB GW allows the S1 interface between HeNB and EPC to scale to support a large number of HeNB 110s. During operation, the HeNB GW will be the concentrator for the C plane, especially the S1-MME interface. The S1-U interface from HeNB can be terminated at HeNB GW or a direct logical U-plane connection between HeNB and S-GW can be used.

eNB is the wireless access part of the LTE system. As is well known, each eNB typically comprises at least one radio transmitter, receiver, control section, and power supply. In addition, eNBs typically perform a variety of software-based functions. For example, wireless resource management, access control, connection mobility management, resource scheduling, header compression, link encryption of user data streams, packet routing of user data towards the destination (usually to the EPC or other eNB), and handover (handover). It is a measurement report (to support the decision of).

LTE eNB needs to carry out the handover procedure within E-UTRAN. As can be seen in Figure 1, intra-E-UTRAN handover is used, for example, to perform a handover of UE114 from source e-node B116 to target e-node B (not shown), usually when the MME does not change. Uses X2-based handover messages. If there is no direct X interface between source e-node B and target e-node B, use the S1-based handover message transmission sequence. The home e-node B110, which is based on Release 8 of the 3GPP specification, does not provide an X2 interface and therefore uses S1-based handovers. During this handover procedure, the HeNB GW relays all messages to the MME, as described in the 3GPP specification, which is not desirable. To address this issue, HeNB GW A method of optimizing the in-GW handover procedure is implemented, which will be described below. This optimized GW handover procedure significantly reduces the amount of signaling to and from the MME relayed by the GW, thereby reducing EPC required performance, reducing network bandwidth and improving reliability. , Reduce costs.

<u style="single">Optimized Intra-HeNB GW Handover</u> A preferred method of this technique is illustrated in FIG. 2, which is a time series diagram showing a first embodiment of the present disclosure that reduces MME signaling during an intra-HeNB handover procedure. In this embodiment, the source HeNB200 and the target HeNB202 are located in the same tracking area (identified by the tracking area identifier, ie TAI), both coupled to the HeNB GW204 and using the HeNB GW's S1-U interface. .. The GW is coupled to the MME206 on the S1-C interface and to the SGW (not shown) on the S1-U interface. To enable optimization of the handover signaling of the present disclosure, the HeNB GW preferably stores the necessary data while establishing a signaling path between the UE (not shown) and the HeNB GW 204 and MME 206. This information includes, but is not limited to, a handover restriction list, security parameters, UE radio access capability data, and the like.

As shown in FIG. 2, the handover procedure starts in step 1, and the source HeNB200 issues a handover request message to the GW204. In step 2, the GW204 sends a path switch request message to MME206, which responds in step 3 with a path switch acknowledgment message (Path Switch Request Ack). message) is returned. In step 4, the GW204 issues a handover request message to the target HeNB202, and in step 5, the target HeNB responds to the GW204 with a handover request acknowledgment message. In step 6, the GW204 issues a handover command message to the source HeNB200, and the source HeNB responds to the GW204 with an eNB state transfer message in step 7. In step 8, the GW204 issues an eBN status transfer message to the target HeNB202, and the target HeNB responds to the GW204 with a handover notification message in step 9. In step 10, the GW204 issues a UE context release command to the source HeNB200. The source HeNB200 responds to GW204 with a UE context release completion message in step 11. This completes a typical handover sequence.

In the absence of the optimization techniques disclosed herein, the GW204 relays each of the signaling messages (to and from the MME) in steps 1 and 4-11 (to ensure 3GPP compliance). .. Such an operation is described by having the HeNB GW204 determine whether the handover request message can be processed "locally", i.e., without having to relay all the messages to and from the MME. Makes it unnecessary. According to this first embodiment, this determination (that the local handover process can be performed) is made when all of the following conditions are satisfied. That is, (i) the target HeNB202 is in the same tracking area as the source HeNB200 (identified by the tracking area identifier (TAI)), and (ii) the target HeNB202 is open or the CSG identifier specified by the source 200. (Iii) Both the source HeNB and the target HeNB use the HeNB GW S1-U interface. In such cases, and with this disclosure, HeNB The GW204 handles the handover procedure locally and in a limited interaction with the MME. In this particular embodiment, as shown in FIG. 2, this limited interaction is simply by sending a passswitch request message (step 2) and receiving a passswitch request acknowledgment message (step 3). is there. Although these messages are traditional, those skilled in the art will appreciate that the messages themselves are used here in a manner different from their typical usage. That is, according to the present disclosure, these standardized messages are effectively repurposed to facilitate local handover procedures. In this exemplary scenario, the purpose of steps 2 and 3 is to ensure security key synchronization between the UE and the source HeNB and the target HeNB.

Alternative uses of these standardized messages are preferred but not essential. Other alternative solutions can be used. So, for example, one variant defines a new message instead of extending the S1 message or reusing the pathswitch request. In another variant, the handover request message (step 1) and the handover request message (step 4) can be extended to pass the current HeNB used by the source HeNB 200 (to the target HeNB 202). In yet another variant of this method, the MME204 may be programmed to provide multiple security contexts once the UE context is established on the HeNB via the HeNB GW. These latter options eliminate the need to use steps 2 and 3 of Figure 2, which further reduces the impact on MME.

FIG. 3 is a time-series diagram showing a second embodiment of the present disclosure that reduces MME signaling during the Intra-HeNB GW handover procedure, in which the source HeNB and the target HeNB are located in different tracking areas. In this embodiment, both the source HeNB and the target HeNB are connected to the HeNB GW304, and the target HeNB 302 is open or supports the CSG identifier indicated by the source HeNB 300. Either or both of the following conditions differ from the first embodiment (ie, FIG. 2). That is, the source HeNB 300 and the target He NB 302 are not located in the same tracking area, or at most one (but not both) uses the HeNB GW's S1-U interface. In this case as well, the GW304 is connected to the MME306 on the S1-C interface and the SGW (not shown) on the S1-U interface, as in the embodiment of FIG. Again, and to enable optimization of the handover signaling of the present disclosure, the HeNB GW304 is a UE (not shown) and a HeNB. It is preferable to store the necessary data while establishing the signaling path between GW304 and MME306.

As shown in FIG. 3, the handover procedure of this embodiment starts in step 1, and the source HeNB 300 issues a handover request message to the GW 304. In step 2, the GW304 issues a handover request message to the target HeNB 302, and the target HeNB responds to the GW 304 with a handover request acknowledgment message in step 3. In step 4, the GW304 issues a handover command message to the source HeNB300, and the source HeNB responds to the GW304 with an eNB state transfer message in step 5. In step 6, the GW304 issues an eBN status transfer message to the target HeNB 302, and the target HeNB responds to the GW304 with a handover notification message in step 7. In step 8, GW304 issues a passswitch request message to MME306, and MME returns a passswitch request acknowledgment message in step 9. In step 10, the GW304 issues a UE context release command to the source HeNB300. The source HeNB300 responds to GW304 with a UE context release completion message in step 11. This completes a typical handover sequence.

In contrast to the embodiment of FIG. 2, in the embodiment of FIG. 3, the pass switch request message (step 8) and the pass switch request acknowledgment message (step 9) are used in the conventional manner. Primarily, these messages are used in this embodiment to ensure that the UE and MME remain in sync and to pass location information.

According to the embodiment of FIG. 3, the HeNB GW also performs a "local" process of handover. However, the determination that the local handover process can be executed is made when all of the following conditions are satisfied. That is, (i) the target HeNB302 is open or supports the CSG identifier indicated by the source HeNB300, and (ii) the target HeNB302 is not in the same TAI as the source HeNB300, or (iii) the source HeNB or Target HeNB does not use the HeNB GW S1-U interface. If these conditions are met, the HeNB GW processes the handover procedure locally, preferably by translating it into an X2-based handover message to the MME. Here, MME message transmission (steps 8-9) is required, but the technique nevertheless does not require traversing messages 1-7 and 10-11 between MME and GW, and with MME. Meet the goal of reducing the amount of messages sent.

Therefore, even in the embodiment of FIG. 3, message transmission to and from the MME is reduced regardless of the 3GPP requirement that the GW relays all handover messages to the MME.

HeNB GW is preferably implemented as hardware, i.e., one or more processors, computer memory, and software executed by the processors to perform the functions described above. Therefore, it is preferable that the functions shown in FIGS. 2 and 3 are executed as software, for example, as program instructions executed by a processor, on each of the machines necessary for performing the above-described operations. Each machine is optionally equipped with relevant data structures and utilities (eg, communication routines, database routines, etc.) to facilitate communication, control and storage functions.

HeNB provides the functionality described herein. GW is carried out on machines equipped with hardware and software systems. The handover function described above can be practiced, usually in software, on one or more such machines. In general terms, machines typically include commodity hardware and software, storage devices (eg, one or more disks, arrays, etc.) and memory (RAM, ROM, etc.). The specific machine used in the network is not limited. A given machine is the network interface described above (including, but not limited to, S1-C, S1-U and other interfaces), and software that connects the machine to other components of the radio access network in the usual way. including. More generally, the techniques described herein together facilitate or provide the functionality of the invention described above, a set of computer-related entities (systems, machines). , Processes, programs, libraries, features, etc.). In a typical embodiment, the HeNB-GW comprises one or more computers. A typical machine comprises commodity hardware, an operating system, an application run-time environment, and multiple applications or processes and related data that provide the functionality of a given system or subsystem. As mentioned above, this function can be performed on a stand-alone node or across a set of distributed machines.

The handover technique can be performed on other nodes in the network, such as the HeNB node and the MME itself.

As long as the GW can determine that the handover request message can be processed locally, there is no requirement to implement the specific handover message transmission protocol described above in FIG. 2 or FIG.

Having described the present invention, the following claims will be described.

100 LTE network 102,206,306 MME 104 SGW 106 PGW 108 HSS 110 HeNB 112 Home Evolved Node B Gateway (HeNB GW) 114 UE 116 Source enode B 200,300 Source HeNB 202,302 Target HeNB 204,304 HeNB GW