WO2007007124A1

WO2007007124A1 - A method of detecting downlink data destined for a mobile terminal

Info

Publication number: WO2007007124A1
Application number: PCT/GB2006/050185
Authority: WO
Inventors: Michael Gallagher; Ian Lasseter Phillips
Original assignee: Nokia Siemens Networks Gmbh & Co. Kg
Priority date: 2005-07-11
Filing date: 2006-07-04
Publication date: 2007-01-18
Also published as: GB2428350B; GB0514088D0; GB2428350A

Abstract

A method of detecting downlink data at a mobile terminal in a state which temporarily precludes receipt of the downlink data on a network (3) comprises sending an update message from the mobile terminal to a first base station (10); notifying the base station of a mobile terminal identifier; and on receipt of the notification, creating a virtual mobile terminal (14) in the network; registering the mobile terminal identifier and associated virtual mobile terminal location with the network; and redirecting received downlink data from the network to the virtual mobile terminal.

Description

A METHOD OF DETECTING DOWNLINK DATA DESTINED FOR A MOBILE

TERMINAL

This invention relates to a method of detecting downlink (DL) data destined for a mobile terminal (MT) in a state which temporarily precludes receipt of the downlink data on a network, in particular for networks using mobile internet protocol (mobile IP).

In a network operating with mobility protocols, with base stations which have an enhanced facility to control communication, there have been proposals to detect downlink data at whichever base station the MT was last attached to before entering the sleep state. The problem here is that if the sleeping MT moves away from this base station and the base station then suffers failure, downlink connectivity to the MT is lost, regardless of which base station the sleeping MT is currently in the vicinity of.

A centralised paging solution may enhance the robustness of this process, but the problem exists of how to temporarily redirect DL data to a centralised node so that the sleeping MT can be paged. Although traditional 2^nd and 3^rd generation networks operate a centralised paging approach, they also direct paging and mobility centrally, under network control, so that the problem of losing track of the base station that the mobile station is currently resident at, is avoided.

Networks that allow mobility to be controlled by the MT, for example, using Mobile IP either directly or by proxy, need to solve this problem, but there is no standard approach which is directly applicable.

In accordance with a first aspect of the present invention a method of detecting downlink data destined for a mobile terminal in a state which temporarily precludes receipt of the downlink data on a network comprises sending an update message from the mobile terminal to a first base station; notifying the base station of a mobile terminal identifier; on receipt of the notification, creating a virtual mobile terminal in the network; registering the mobile terminal identifier and associated virtual mobile terminal location with the network; and redirecting received downlink data from the network to the virtual mobile terminal. There are various situations in which there might be a temporary ceasing of receipt of downlink data, such as the phone disconnecting due to a poor signal, or even being switched off, such as on entry to an aircraft, but typically the state which temporarily precludes receipt of the downlink data is sleep mode.

Any identifier specific to the technology of the mobile network may be used, but preferably the mobile terminal identifier is a mobile internet protocol identifier. As part of a paging function, preferably, the update message is a location update message.

Preferably, the redirection of received downlink data comprises tunnelling downlink data to the paging function; and causing the paging function to issue a page request to one or more base stations. Since the mobile terminal may have moved on since first contacting the network, preferably, the page request is first issued to the base station which last received the location update message from the mobile terminal; and if the mobile terminal does not respond to the transmitted page request message, then page requests are sent to a number of base stations within a predetermined distance of the first base station. Any device requiring services from the network can operate this method, for example dedicated meter reading devices, but preferably the mobile terminal is one of a laptop, a personal digital assistant, or a mobile phone. These may incorporate the functionality of dedicated devices.

An example of a method of detecting downlink data at a mobile terminal in a state which temporarily precludes receipt of the downlink data on a network will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates a conventional approach to communication as a mobile device moves between base stations on a network;

Figure 2 illustrates location tracking using the method of the present invention; and,

Figure 3 is a block diagram of a paging function using the method of the present invention.

This invention proposes a scheme for the detection of downlink (DL) data for mobile terminals while they are temporarily unable to receive the data, for example when a terminal is in a sleep state. The invention is particularly directed to mobile networks operating mobility protocols specific to the technology of the mobile network, an example of which is networks using Mobile IP, but other mobility protocols can be used.

Fig. Ia illustrates a mobile device 1 in sleep mode, near to a first base station 2, BS-I, which can communicate with a mobile network 3. No data passes from the mobile device to the base station in sleep mode. In Fig. Ib, the mobile device has moved, so that it is now within the vicinity of a new base station 4, BS-2, so the mobile device 1 wakes up and notifies the network 3, via this base station 4 of the current location of the mobile device. New base station 4, BS-2 sends an indication to the network 3 that the mobile device resides within its territory. When data arrives at the network 3 for the sleeping mobile device 1, as shown in Fig. Ic, the network causes one or more base stations 4 to page the mobile device, which then wakes up to receive data.

Figs. 2 and 3 illustrate how the present invention deals with a device which is temporarily unable to detect downlink data in a system, so addressing the problems associated with a decentralised approach. Ordinarily in this situation, downlink data addressed to a particular mobile device is sent to the base station to which that mobile device was last connected and that base station detects the data and forwards the data to the most current location which it has. The most current location is obtained by tracking movement of the device since its last connection, so that every time the mobile device comes into range of a new base station, the mobile device wakes up and sends a message to itself, while the network still thinks that the mobile device is connected to the original base station. The only place where that mobile device's latest location is stored is in the base station at which the device was last connected, so if the base station fails, there is no knowledge of the mobile device at all. After a certain number of attempts, the network simply indicates that the connection has failed. To deal with this problem, a paging function is set up within the network to track the mobile device which is temporarily unable to receive data and also to detect downlink data. By transferring these functions to the network for situations where the data cannot be directed straight through to the mobile device, such as when it is in sleep mode, then the risk of losing contact with the device entirely is significantly reduced. The paging function within the network relies on a virtual representation of the mobile device created within the network which is able to receive, and thus detect, DL data on behalf of the real, but sleeping MT. One example of how this process is used for location tracking, i.e. maintaining a mapping of a sleeping MT to its location, is illustrated in Fig. 2.

A mobile terminal enters a sleep state. This may be done so 'silently', i.e. such that no other central network node needs to be informed. The MT 1 moves to a new base station 10 and sends a Location Update (LU) message 9 to the base station. An expanded LU message 11 is sent from the base station to a centralised paging function (PF) 8 within the network. The expanded message contains a mobile terminal identifier, for example, an internet protocol (IP) address of the MT 1 and location information that relates to the MT's position. The PF creates a virtual mobile terminal 14, also known as an emulated mobile client (EMC), or Mobile IP client in the example where Mobile IP is used as the mobility protocol, and this virtual terminal represents the MT while it is in the sleep state.

The virtual mobile terminal 14 registers with the Mobile IP Home Agent 18 responsible for the MT, such that subsequent DL data is tunnelled to the PF 8, acting as a Mobile IP Foreign Agent 16. The means used to identify and locate the Home Agent is not specified here. Mobile IP registration may actually be performed by the MT 1 or an entity acting on the MT's behalf that is not the EMC 14; although an EMC instance still needs to be created to act as the MT after this registration, and the registration also needs to redirect DL data to the PF, acting here as a Mobile IP Foreign Agent.

Fig. 2 shows how the paging function 8 and its components carry out location tracking. A tracking agent (TA) 12 is responsible for receiving the expanded LU messages 11 from the base station 10 and keeping a record of the MT IP address, or other identifier, and location information. The virtual mobile terminal 14 is created to represent the MT 1 while in sleep state and the MIP Foreign Agent 16 is used to assist in Mobile IP registration with the Mobile IP Home Agent and to terminate DL Mobile IP tunnels.

Upon receipt from a base station 10 of an expanded LU message 11 in the paging function 8, the following steps occur. The TA 12 receives the expanded LU message 11, and may authenticate it by interaction with a central server (not shown). The TA 12 causes 13 a new EMC 14 to be created, to represent the MT 1. The EMC 14 registers with the MIP Home Agent 18, or other mobility protocol anchor, using the Home Address of the MT.

The second stage of the process is paging, i.e. the process of signalling to the MT to wake up at its current location, be that a specific sector, base station, or group of base stations. An example of a Page Request operation may be summarised in the following steps, illustrated in Fig.3. The Mobile IP Home Agent 18, or other mobility protocol anchor, receives 20 DL data for the MT 1. The Home Agent 18 tunnels 21 the data to the MIP Foreign Agent 16, resident at the paging function 8.

The PF issues a Page Request 26 to the base station 10 that the last Location Update message was received from and if the MT 1 does not respond within a configurable time period, the PF 8 issues Page Requests 26 to the location that the MT last issued a location update from, which may constitute several base stations 10, 11, 12. The MT 1 receives the Page Request 26 and wakes up, performing Mobile IP re- registration with the Home Agent 18. The serving base station issues an indication to the PF of the current serving base station and the PF 8 tunnels all received data for the MT 1 to the serving base station.

The paging function components involved in generation of page requests include the emulated mobile client (EMC) 14, created to represent the MT while in sleep state; the tracking agent (TA) 12, responsible for recording the current location of the MT 1; the paging agent (PA) 24, responsible for liaising 25 with the TA to determine the base station, or base station area, that the MT last updated its location from, for resolving the base station area (if required) to a set of one or more base stations 10, 11, 12, and for generating and sending Page Request messages 26 to this set of base stations. The MIP Foreign Agent 16 is used to terminate DL Mobile IP tunnels 21 from the Home Agent 18, and forward 22 received DL data to the appropriate EMC 14.

The following steps occur within the PF 8 when generating Page Requests. The Mobile IP Home Agent 18 receives 20 DL data destined for the sleeping MT 1. The Home Agent tunnels 21 the DL data to the PF Mobile IP Foreign Agent (FA) 16 and the Mobile IP FA recovers the DL data from the Mobile IP tunnel 21, then forwards the data to the EMC 14 which is currently acting on the MT's behalf. The EMC sends 23 a trigger signal to the PA 24 which retrieves 25 current location information from the TA 12, and generates a list of 'target' base stations 10, 11, 12. Page Request messages 26 are generated and sent first to the last known base station, then to all base stations within the last known location sub-area, and finally to all base stations within the last known location area. A confirmation is sent from the currently serving base station of the (now active) MT to the EMC. All received DL data is tunnelled from the EMC to the base station, which then forwards the data to the MT. The PF then deletes the EMC instance. Advantages of the present invention are that centralisation of the paging function enhances the robustness of the paging process and provides resilience against base station failure.

Claims

1. A method of detecting downlink data at a mobile terminal in a state which temporarily precludes receipt of the downlink data on a network, the method comprising sending an update message from the mobile terminal to a first base station; notifying the base station of a mobile terminal identifier; on receipt of the notification, creating a virtual mobile terminal in the network; registering the mobile terminal identifier and associated virtual mobile terminal location with the network; and redirecting received downlink data from the network to the virtual mobile terminal.

2. A method according to claim 1 , wherein the state which temporarily precludes receipt of the downlink data is sleep mode.

3. A method according to claiml or claim 2, wherein the mobile terminal identifier is a mobile internet protocol identifier.

4. A method according to claim 2 or claim 3, wherein the update message is a location update message.

5. A method according to any preceding claim, wherein the redirection comprises tunnelling downlink data to the paging function; and causing the paging function to issue a page request to one or more base stations.

6. A method according to claim 5, wherein the page request is first issued to the base station which last received the location update message from the mobile terminal; and if the mobile terminal does not respond to the transmitted page request message, then page requests are sent to a number of base stations within a predetermined distance of the first base station.

7. A method according to any preceding claim, wherein the mobile terminal is one of a laptop, a personal digital assistant, or a mobile phone.