RAU optimization for UMTS URA connected state

Details RAU optimization for UMTS URA connected state RAU optimization for UMTS URA connected state

2000-08-21

2004-07-20

Vanderpuye, Kenneth (Department: 2661)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S328000, C370S338000, C455S436000

Reexamination Certificate

active

06765890

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to routing area updates (RAUs) that take place as a mobile terminal moves from one radio access coverage area to another, and particularly to such movement when the mobile terminal is in a so-called standby mode in which no data is being transmitted or received.
BACKGROUND OF THE INVENTION
GSM (Global System for Mobile Communications) radio coverage, which may also be referred to as second generation (2G) radio coverage, is quite extensive today. During the introduction of UMTS (Universal System for Mobile Telecommunications), which may also be referred to as third generation (3G) radio coverage, UMTS radio coverage is expected to be limited to urban areas. Thus UMTS radio coverage will cover only parts of the more extensive GSM radio coverage areas. Even within UMTS coverage areas, the UMTS radio coverage cannot be expected to be contiguous. For example, given that the frequency used for UMTS is higher than that for GSM, the in-building penetration will not be as good as GSM. This will result in small pockets (such as inside buildings) without UMTS coverage within the overall UMTS coverage area. Thus, only GSM radio coverage will be available in these pockets.
A dual mode GSM and UMTS mobile terminal (a mobile terminal is referred to as user equipment (UE) in UMTS) can communicate using either one of the two radio access systems. If a dual mode mobile terminal communicating via the UMTS radio link goes out of UMTS coverage, to an area with only GSM coverage, it can expect to continue the communication via the GSM radio link, but with a consequential degradation of service. Similarly a dual mode mobile terminal in an area with only GSM radio coverage which moves into an area with UMTS coverage can expect to switch to the UMTS radio link to improve service.
Thus as a dual mode mobile terminal moves around within radio access areas, changes in the type of radio access can be expected as the available radio access systems change. As the mobile terminal moves between radio access areas, routing area updates occur to notify the necessary support network of the new position of the mobile in the routing area associated with the particular radio access type. Changing between two radio access systems involves additional signalling and can also lead to outages during the transition between the two systems. The impact of the additional signalling and outages depends on the network architecture and the protocols chosen.
Packet data communication can be bursty, and there can consequentially be long periods when a mobile terminal is not sending or receiving data. When a mobile terminal is in packet communication mode in the GSM network, it is communicating via the GPRS interface. A certain time-out period after sending the last packet, the mobile terminal will transfer to a standby state. In the UMTS network, after a certain time out period of no activity, the terminal will first transfer to a so-called ‘UTRAN Registration Area (URA) connected’ state. In the URA connected state, the connection between the mobile terminal and the UTRAN is maintained on the Iu link. After a longer period of time, the context in the UTRAN which identified the link to the mobile can be removed and the Iu connection torn down. While the state of the mobile terminal after the Iu connection has been torn down has not been given any specific name in the UMTS standards, it shall be referred to herein as a UMTS standby state.
In the proposed implementations of both the GSM and UMTS standby states, a mobile terminal always performs a routing area update as it moves between radio access system coverage areas at all times, even when it is in the standby state.
SUMMARY OF THE INVENTION
The present invention provides an improved technique for reducing unnecessary routing area updates, which still ensures the location of a mobile terminal is known when the mobile terminal starts data communication after being in a standby state.
According to the present invention there is provided in a packet radio access network architecture having a common routing area controlled by a core network and supported by a first wireless access system and a second wireless access system a method of controlling routing area updates, wherein in at least the first radio access system there is provided a mode of operation in which a radio link is maintained between a mobile terminal and the first radio access system after completion of a data transmission, a routing area update only taking place if the mobile is located in the second radio access system routing area when the next data transmission is initiated, wherein if packet transmission is initiated by the network the first radio access system receives a paging request, and responsive to receipt of the paging request the first radio access system pages the core network common routing area.
The first radio access system may page the core network common routing area by sending a paging request to the core network.
Responsive to the paging request, the core network may send a paging request to the second radio access system.
The first radio access system may be a UMTS system and the second radio access system may be a GSM system. The UMTS system may generate a RNTI paging signal to the common routing area, and the core network may generate a P-TMSI paging signal to the core network routing area.
The core network may generate a modified paging signal to the second routing area based on the RNTI paging signal.
The mobile terminal may respond to the paging signal with a routing area update.
If packet transmission is initiated by the mobile, the packet transmission initiation may include a routing area update.
Thus a mobile terminal (or user equipment) moving back and forth between a 2G environment and a 3G environment without sending any data will not generate any signalling. This frequent switching between 2G and 3G environments is likely to happen at the edges of the patchy 3G coverage areas.
This allows almost all of the 2G and 3G implementation of the serving GPRS support nodes (SGSNs) to be kept separate. The routing area update (RAU) performed before sending any data from the new access network will result in the context transfer from the 2G to the 3G and also the set up of the proper state machines and protocol stack.


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European Search Report, dated Jan. 26, 2000.

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