Method for relocating the diversity point of a mobile station in a radio access network

The invention relates to a method for relocating a mobile station with features according to claim 1 as well as a radio communication system with the features according to the preamble of patent claim 9.

Mobile radio communication systems can be divided into a core network CN, in which useful and signaling data of a plurality of terminals are transmitted over a wide range, and a radio access network RAN, which generally comprises a plurality of physical network nodes, Which is designed to convert data received from the terminals into a format suitable for transmission on the core network CN and, conversely, to adapt the format of the data received from the core network to the radio transmission and forward it to that radio station in the transmission area thereof The respective terminal is located.

Highly developed communication systems such as mobile radio systems (UMTS) or UMTS (Universal Mobile Telecommunications System) and data networks which are subject to the control of a packet transmission protocol, in particular the Internet protocol IP, enable a plurality of mobile stations to transmit a radio link in parallel To establish a network control device of the corresponding communication network and to use it for a data exchange with remote devices. In order to prevent a disturbing superposition of the signals of the many radio connections, the respective communication between the individual mobile stations and the respectively assigned network control device takes place, for example, via unambiguously assigned frequencies, within fixedly allocated time slots and / or with the aid of coded signals.

The data to be routed includes, on the one hand, user data, ie data to be transmitted between two users of mobile stations, and, on the other hand, signaling data which are generated and processed to control internal processes of the mobile radio communication system. Both types of data must be exchanged between the radio access network and a mobile station communicating with it.

In the radio access network, a distinction can be made between functionalities which are responsible for the transmission of user data and functionalities which are responsible for the transport of the signaling data. The former are referred to as user plane functions (UPF) and the latter as control plane functions (CPF).

The present invention is described below with reference to a UMTS-based mobile radio system. However, the properties of the system according to the invention can also be transferred to GSM-based mobile radio systems.

Each radio network control device has a plurality of user plane functions, each of which is allocated within the access network an address by means of which specific data packets for a particular mobile station are routed to the UPF communicating with this mobile station.

The exchange of signaling protocols in the radio access network is controlled by user equipment functions UEF, which can be located in a radio control server RCS, which forms a further physical node in the radio access network RAN.

When a mobile station moves completely out of the coverage area of ​​a base station of a radio network controller, this base station or the corresponding diversity branch must be removed from the so-called diversity tree, while conversely base stations or diversity branches without transmission interruption must be accepted when the mobile station In the overlap region thereof. Such a hand-over mechanism, in which the mobile station always communicates with a plurality of base stations, is referred to as a "soft handover".

In contrast, in a so-called "hard handover" the connection to a base station abruptly aborts and must be immediately transferred to another base station.

The present invention enables the relocation of a mobile station in both a soft and a hard handover.

A known solution for realizing the relocation or relocation of the diversity point in a radio access network is described below. FIG. 1 shows two states of such a network. A core network CN, which is connected to a serving radio network controller SRNC (serving radio network controller) and a destination radio network controller DRNC (Drift Radio Network Controller), is shown in each case. A plurality of radio stations or base stations BS are connected to both radio network control units DRNC and SRNC. The left figure shows a situation in which a mobile station UE moves from the area of ​​the operating radio network control unit SRNC into the area of ​​a targeted radio network control unit DRNC and is still fully assigned to the operating radio network control unit.

According to the illustrated fun purchase with two base stations BS of the targeted radio network control device DRNC, a data exchange of the mobile station UE with the core network CN takes place via the radio connections, via the connections between the corresponding base stations BS and the targeted radio network control device DRNC, via a connection Iur With the serving radio network controller SRNC and via a connection Iu with the core network CN or vice versa.

As soon as the conditions for a transfer or relocation are present, the previously targeted radio network controller DRNC takes over the function of the serving radio network controller SRNC, as shown in the right-hand illustration. The data communication of the mobile station UE with the core network CN now takes place directly from the mobile station UE via one of the corresponding base stations BS, via the serving radio network controller SRNC and via a connection Iu or vice versa.

For UMTS, version 99, 3GPP (3^approx Generation Partnership Project), a relocation function with the designation "Serving RNC Relocation" is standardized for the relocation. This solution allows the exclusive application of UMTS-specific protocols (3GPP TS 23.060). However, the relocation procedure performed so far is relatively complicated and time-consuming.

Out <patcit id="pcit0001" dnum="WO9847302A"><text>WO 98/47302</text></patcit> A method is known for transmitting data packets during a handover of a mobile station MS from an "old access point" to a "new access point". During the handover, data packets are temporarily stored at the "old access point", which should reach the "new access point" without loss of data. For the transmission, a "connection" between the "old access point" and the "new access point" is established dynamically, the device being controlled via an "ATM switch".

document <patcit id="pcit0002" dnum="WO0076170A"><text>WO 00/76170</text></patcit> Describes a use of a "Mobile Internet Protocol" in a GPRS network. One of two so-called "GPRS nodes" is assigned to one "foreign agent". A first "GPRS node" has access to the Internet via the "foreign agent" assigned to it and via a "home agent" assigned to it, whereby the "foreign agent" is connected to the "home agent" via a MIP tunnel. Accordingly, a second "GPRS node" has access to a private internet provider via the "foreign agent" assigned to it and via a "home agent" assigned to it, whereby also the "foreign agent" with the "home agent" via a MIP tunnel connected is.

It is an object of the present invention to reduce data packet loss during a relocation of a mobile station.

This object is achieved by the method for relocation with the features of patent claim 1 as well as by a communication system for carrying out such a method according to the features of patent claim 9.

Advantageous embodiments are the subject of dependent claims.

A method for relocating a mobile station with a low data packet loss in a radio communication network with at least first and second radio network control means, the management of the mobile station and / or the transmission of data to be transmitted to the mobile station from the first radio network controller (Handover) to the second radio network controller is particularly advantageous when data which after the handover is still arriving at the first radio network control unit or is temporarily stored there is, by utilizing a functionality of the first radio network controller to a corresponding functionality of the first radio network controller Second radio network control device and are forwarded from there to the mobile station.

The relocation of the mobile station, ie the establishment of the new transmission path between the core network and the mobile station, is carried out according to a further development of the invention using a mobile Internet protocol MIP. The current MIP standard is either IETF MIPv4 (RFC2002) or IETF MIPv6 (draft_IETF_mobileIP_Ipv6_12).

As functionality, by means of which the data are transmitted between the two radio network controllers, a mobile anchor function MAF is particularly suitable. A MAF is used, in particular, in large radio access networks in which too much time is required to reach the home agent. As a new entity, therefore, an MAF is provided in the radio network control devices. In this regard, reference is made to the IETF draft HMIPv4v6: draft_elmalki_soliman_HMIPv4v6_00.

As the client for performing the MIP registration of the mobile station, a virtual mobile host is preferably generated.

If the mobile station itself does not have a virtual mobile host, such a configuration is provided, for example, in the radio network controller, which acts as a (new) wireless radio network controller.

In conjunction with the handover, to set up a virtual mobile host in the operating wireless network controller, implementation in existing systems without complicated structural or programming adaptation.

The virtual host assumes the function which is dedicated to the mobile station according to the MIP standard with regard to the new registration and address management and also preferably assumes the function of an address memory and address manager for function-critical network-internal addresses.

After the virtual mobile host has been set up, it preferably registers with the home agent, the new local mobile anchor function, and the core network. In the solution in which the VMH is part of the mobile station, the planned IETF standard HMIP for the client function would have to be supplemented by a registration operation with the serving mobile anchor function.

According to a preferred development of the invention, the virtual mobile host is set up by a radio control server RCS and, in particular, by a subscriber device function UEF, which is part of the RCS.

In order to pass on data which still arrive at the second radio network control device after the handover or are temporarily stored there, the virtual mobile host transmits the address of the local MAF to the MAF of the first radio network control device.

The handover, ie the transfer of the administration to the second radio network controller, is preferably initiated by the mobile station.

According to a further preferred embodiment of the invention, data arriving at a radio network controller during the transfer of the administration are buffer-stored.

After the administration has been handed over, the resources of the mobile station are deleted in the first radio network controller, in particular the subscriber level function UPF.

The relocation of the mobile station is preferably carried out by means of the mobile Internet protocol MIPv6.

Advantageously, a radio communication system with at least first and second radio network control means for managing at least one mobile station, wherein the management of the mobile station and / or the transmission of data to be transmitted to the mobile station from the first radio network controller to the second radio network controller Radio network control device, the implementation of such a method, if at least one device is provided for performing the IP registration, such as, for example, a virtual mobile host.

The invention is explained in more detail below by way of example with reference to the accompanying drawings. Show it:<dl id="dl0001"><dt>FIG</dt><dd>The state of a radio network before or after a relocation of a mobile station according to the UMTS standard, version 99;</dd><dt>FIG</dt><dd>3 shows a schematic sequence of a relocation procedure according to an exemplary embodiment of the invention in an IP-based radio access network; and</dd><dt>Figures 3-5</dt><dd>Schematically the system states in a communication network during a relocation of the diversity point of a mobile station in a hard handover.</dd></dl>

As can be seen from FIGS. 1 and 2, the communications network according to FIG. 2 is essentially constructed as the communications network shown in FIG.

To distinguish the new technology, the radio network control devices SRNC and / or DRNC are subsequently referred to as serving or targeted sub-level servers S-UPS (Serving User Plane Server) or T-UPS (Target User Plane Server).

The core network CN has, inter alia, an integrated GPRS service node IGSN (Integrated GPRS Service Note, GPRS: General Packet Radio Service). This serves as a gateway or interface of the core network CN to the radio access network, which is generally referred to as the radio access network RAN. The radio access network RAN ​​has a multiplicity of devices relevant here, in particular the sub-level server UPS, via which connections with stationary or mobile subscriber stations UE are constructed and maintained. The base stations associated with the sub-level servers UPS are also part of the RAN, but not shown here.

Further devices in the radio access network RAN ​​are so-called routers R, which serve as interfaces to the so-called IP backbone, ie Internet protocol controlled remote lines or main lines.

Furthermore, the radio access network RAN ​​comprises subscriber device functions UEF (user equipment functions) for all signalings of a mobile station UE. Furthermore, a home agent (home agent), which is comparable to the home register in existing radio communication networks for registering a mobile subscriber or a mobile station UE, is located in the radio access network.

In the serving subscriber level server S-UPS, subscriber sub-functions UPF are present in the usual manner which are responsible for the transmission of useful data from a node (S-UPS) to a terminal.

In the exemplary embodiment illustrated here, a relocation method is proposed, in which a combination of radio-specific protocols, as known, for example, as UMTS-specific protocols, with IP-based protocols as described for example in the IETF standardized mobile protocol "Mobile IP Version 6 (MIPv6) "Are known.

In particular, an MIP protocol in conjunction with a protocol from a mobile radio system is used for signaling the transition of the management of the mobile station UE and / or the transmission of data to be transmitted to the mobile station UE from the S-UPS to the T-UPS.

The signaling protocols for a mobile station UE are handled in the radio access network RAN, as already mentioned, by the so-called subscriber device function UEF.

For the relocation of a mobile station using an MIP protocol, a virtual mobile host VMH is provided which serves as a client for the MIP registration.

Further, the sub-level server UPS includes a mobile anchor function MAF through which messages are routed from and to a mobile station UE.

The sequence of a relocation process is briefly explained below with reference to FIG.

When a mobile station UE logs in to the radio access network RAN ​​through a communication reception via a base station BS, an IP registration takes place for the mobile station UE at the home agent HA, the local mobile anchor function MAF and the core network CN, Station-directed data packets are routed via the S-UPS.

As long as the mobile station UE has a diversity leg, via which it is connected to a base station BS, which is connected to the serving subscriber server S-UPS, no new IP registrations are made for the mobile station UE.

UMTS-specific mobility functions are responsible for adding or removing diversity branches during a soft handover.

The removal of diversity branches is usually initiated by satellite telecommunication messages from the mobile station UE.

When the subscriber device function UEF detects that the last diversity branch has been removed between the mobile station UE and the serving subscriber server S-UPS, the UEF generates a subscriber sub-function UPF in the targeted sub-sub-server T-UPS as shown in FIG Indicated by an arrow.

Similarly, when the UEF receives a request for a hard handover, the subscriber device function UEF generates a subscriber sub-function UPF in the targeted sub-sub-server T-UPS.

In addition, the subscriber device function UEF sends the targeted subscriber server UPS the message of setting up a virtual mobile host VMH (which may also be part of the newly established UPF). The newly created virtual host VMH can start MIP registration.

At the Internet Protocol level, the transmission path between the core network CN and the mobile station UE is changed by a MIP registration process initiated by the new serving subscriber server S-UPS. In this case, the virtual mobile host VMH registers with the local MAF, as indicated by the arrow 2, with the local MAF, as indicated by the arrow 3, with the local MAF, and with the core network, as indicated by the arrow. The MIP registration may alternatively be executed by a MIP client function provided in the mobile station UE.

In addition, the MIP client function (the virtual mobile host VMH) sends a connection update to the mobile anchor function (MAF) of the formerly serving subscriber server S-UPS whereby the downstream transmitted data is redirected to the targeted sub-slave server T-UPS as indicated by arrow 4 . The connection update particularly contains the address of the mobile anchor function MAF of the targeted subscriber subscriber T-UPS.

As a result, data packets which are still on the way to the old serving subscriber server S-UPS or are buffer-stored can still reach the mobile station via the connection between the two mobile anchor functions MAF (arrow 6) Time is maintained. Deletion of the last diversity branch or the last connection takes place only after the expiry of a changeover time after the transfer of the administration.

Finally, the subscriber device function UEF instructs the old serving subscriber server S-UPS to clear the resources for the mobile station UE (arrow 5).

With regard to the UMTS selected as the basic communication system, reference is made, in particular, to the principles and registration functions, in particular to the publications IETF spec "mobility support in IPv6", draft-ietf-mobile IP-IPv6-12. The integration of MIPv6 offers a variety of advantages:

It allows a device to send data packets to a mobile station UE with a fixed IP address, this fixed IP address being independent of the actual instantaneous connection point of this mobile station UE to the IP network, in our case of the connection to the base station BS of the radio access network RAN. This means, in particular, that the subscriber level protocol layers above the Internet protocol IP are relieved of the effect of changes in IP addresses.

Furthermore, MIPv6 software is available as a commercial IP software so that development work can be saved.

The solution described above can be used, in particular, in a distributed IP-based RAN architecture in which functions on the subscriber level and functions on the control level are distributed over several physical nodes.

In order to implement the relocation method according to the invention, it is proposed to exchange a part of the standard IP mechanisms in order to speed up the relocation procedure and, on the other hand, to modify the UMTS functionality in order to prevent packet losses during the relocation procedure.

The sequence of a relocation for setting up a new operating subscriber server UPS in the case of a hard handover is explained below with reference to FIGS.

FIG. 3 shows the situation in which a first sub-sub-server SUPS is the serving subscriber server, and a second sub-sub-sub-server TUPS is the targeted sub-sub-server. The subscriber device functions UEF are arranged in the radio control server RCS, which is a physical node. The present radio access network RAN ​​has a distributed architecture. The subscriber sub-functions related to a single mobile station UE are presented as dedicated sub-sub-functions UPFd (dedicated user plane functions). These assigned subscriber functions UPFd are each managed in a subscriber server UPS. The functional blocks VMH, PDCP, RLC, MAC, MDF and FP are sub-functions of the entity UPFd.

The associated subscriber sub-functions UPFd are generated by corresponding control sub-messages, as described above.

In the core network CN, the integrated GPRS service node serves as a gateway to the radio access network RAN. The integrated GPRS service node converts downstream user data into IP data packets which have the address of the virtual mobile host VMH as the destination address and the address of the integrated GPRS service node as the source address.

The virtual mobile host has a local IP address, usually referred to as a care-of address, and thus registers with the home agent HA, the mobile anchor function MAF, and the integrated GPRS service node, whereby data transmitted in the down- And arrive at the IGSN node, to the local mobile anchor function MAF and to the virtual mobile host. The VMH decapsulates the IP data packets and transmits the user data to the base station. In the upward direction, the virtual mobile host VMH processes the user data received via the radio link (via the node B) and sends it directly to the IGSN service node.

Starting from this system state, the relocation of the serving subscribers' server is described below.

Upon activation from the mobile station UE, the radio control server RCS stimulates the relocation procedure by generating a virtual mobile host VMH at the targeted subscriber server T-UPS via a U-ser_Plane_Setup instruction, as shown in FIG. This instruction creates terminal-specific instances in a subscriber level function UPFd, in particular, the instances PDCP, RLC, MAC, and VMH in the targeted subscriber server T-UPS.

The radio control server also commands the base station BS to establish a radio link. In this state, upstream data from the mobile station UE can reach the IGSN service node via the radio link, the base station BS, and the targeted sub-server T-UPS.

Downstream data received from the formerly serving subscriber server S-UPS can no longer be forwarded via the radio link and must be temporarily stored in the mobile anchor function MAF of the S-UPS.

In order to forward the data to the mobile station, the new virtual mobile host automatically sends connection updates (address messages) to the MAF of the T-UPS, to the HA, and to the IGSN service nodes. In addition, the virtual mobile host VMH sends a connection update to the MAF of the S-UPS, thereby registering the address of the mobile anchor function MAF of the T-UPS as a new care-of address. In this state (Figure 4), the data packets still on the way to the S-UPS or buffered data packets are transmitted from the MAF of the S-UPS to the MAF of the T-UPS, thereby transferring them to the assigned subscriber sub-function UPFd in the T-UPS, Mobile station UE.

Data packets arriving at the IGSN service node or home agent HA (not shown) are now routed directly to the MAF of the T-UPS and from there to the mobile station UE.

The targeted subscriber server T-UPS informs the radio control server RCS that the handover has been completed (as far as the T-UPS is concerned). This is done by submitting a response UP_setup response.

As shown in FIG. 5, the radio control server RCS clears the associated sub-sub-function UPFd in the serving sub-sub-server UPS upon receipt of the UP_setup response, and then issues a message UP_freigeben to the S-UPS.

After S-UPS has received the UP_release request, it waits until corresponding buffer stores are empty before the previously serving subscriber server S-UPS removes the associated sub-sub-function UPFd including the VMH, VMH, and answers the UP_request request with a UP_freigeben_response message.

Reference list

<dl id="dl0002" compact="compact"><dt>UE</dt><dd>Mobile Station</dd><dt>MDF</dt><dd>Macro diversity function</dd><dt>SRNC</dt><dd>Operating wireless control unit</dd><dt>DRNC</dt><dd>Targeted radio control device</dd><dt>CN</dt><dd>core network</dd><dt>R</dt><dd>routers</dd><dt>HA</dt><dd>Home agent</dd><dt>UEF</dt><dd>subscriber device function</dd><dt>RCS</dt><dd>radio control server</dd><dt>IGSN</dt><dd>Integrated GPRS service node</dd><dt>RAN</dt><dd>radio access network</dd><dt>VMH</dt><dd>Virtual mobile host</dd><dt>BS</dt><dd>base station</dd><dt>S-UPS</dt><dd>Operating subscriber server</dd><dt>T-UPS</dt><dd>Targeted subscriber server</dd><dt>UPFd</dt><dd>Assigned subscriber level function</dd><dt>MAF</dt><dd>Mobile anchor function</dd><dt>MAC</dt><dd>Media access control level</dd></dl>