GB2434716A

GB2434716A - Reconfiguring a radio link

Info

Publication number: GB2434716A
Application number: GB0601601A
Authority: GB
Inventors: Thomas Malcolm Chapman
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2006-01-27
Filing date: 2006-01-27
Publication date: 2007-08-01
Anticipated expiration: 2026-01-27
Also published as: GB0601601D0; GB2434716B

Abstract

A method of reconfiguring a radio link between a mobile device (3) and a base station (2) comprises determining a requirement for a reconfiguration of the radio link and sending a reconfiguration instruction (4) from a controller (1) to a mobile device (3) and an associated base station (2). The mobile device (3) sends a notification (11) to the base station (2) that it is about to reconfigure and the mobile device (3) and the base station (2) then implement the reconfiguration substantially simultaneously.

Description

A METHOD OF RECONFIGURING A RADIO LINK BETWEEN A MOBILE

DEViCE AND A BASE STATION This invention relates to a method of reconfiguring a radio link between a mobile device and a base station, in particular for 3R generation (3G) communication systems.

In a 3G universal mobile telecommunications system (UMTS) network, there is a procedure called "Radio Link (RL) Reconfiguration" which is used from time to time, in particular with respect to call setup. Currently, the procedure for implementing RL Reconfiguration occurs at a future activation time. However, proposals have been made in a new procedure for the 3rd generation partnership project (3GPP) to have an activation time NOW. When activation time NOW is used, the mobile device, or user equipment (UE), switches configuration as soon as it is able to. After receiving a reconfiguration message, the base station, or Node B, continues to transmit the old downlink (DL) configuration until it detects that the UE has switched configurations.

The Node B detects a change in configuration by means of detecting an uplink (UL) change in scrambling code. However this proposal has some drawbacks. Firstly, there is extra complexity for the Node B, which must detect two scrambling codes, the old and the new. Secondly, in between the UE changing configuration and the Node B switching DL configuration, there is a short time during which a DL radio link failure could occur.

In accordance with a first aspect of the present invention, a method of reconfiguring a radio link between a mobile device and a base station comprises determining a requirement for a reconfiguration of the radio link; and sending a reconfiguration instruction from a controller to a mobile device and an associated base station; wherein the mobile device sends a notification to the base station that it is about to reconfigure; and wherein the mobile device and the base station then implement the reconfiguration substantially simultaneously.

Preferably, the radio link comprises an uplink and a downlink between the mobile device and the base station.

Preferably, the reconfiguration instruction comprises a change from a first uplink to a second uplink and from a first downlink to a second downlink.

Preferably, the notification from the mobile device to the base station is sent on the first uplink.

Preferably, the notification is sent via physical layer signalling.

Preferably, the notification is sent on a dedicated physical control channel In one embodiment, the notification comprises a preset transport format combination indicator value.

Alternatively, the notification comprises feedback mode indicator bits, or the notification comprises a change in a pilot sequence sent by the mobile device.

Preferably, the notification is repeated.

This invention is particularly applicable to 3GPP and therefore, preferably, the controller comprises a radio network controller, the base station comprises a node B and the mobile device comprises a user equipment.

In accordance with a second aspect of the present invention, a communication system comprising a controller, a base station and a mobile device, wherein the system is adapted to carry out the method of the first aspect.

An example of a method of reconfiguring a radio link between a mobile device and a base station will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a method of radio link reconfiguration; and, Figure 2 illustrates a method of reconfiguring a radio link in accordance with the method of the present invention.

In physical channel reconfiguration of 3GPP, parameters of both downlink and uplink physical channels are reconfigured in order to switch from a signalling bearer to a target bearer. A significant amount of the time taken relates to the setting of an activation time, which has to allow for the worst case on the signalling. A faster means of implementing such a procedure, as recently proposed in 3GPP is to define a modified procedure with activation time NOW. When activation time NOW is used, then a terminal, or UE, switches configuration as soon as it is able to. After receiving the reconfiguration message, a base station, or Node B, continues to transmit an old downlink (DL) configuration until the node B detects that the UE has switched configurations, which occurs by means of detecting an U L change in scrambling code.

However this proposal adds extra complexity for the Node B, which must detect two scrambling codes and also gives rise to the problem that in between the UE changing configuration and the Node B switching DL configuration, there is a short time during which a DL radio link failure could occur.

This can be illustrated by reference to Fig. 1, in which a conventional system comprises, for example, a server or radio network controller (RNC) 1, a base station or node B 2, and a terminal 3. The server determines that reconfiguration is required and sends a radio link reconfiguration command signal 4 to the node B and the terminal as shown in Fig. 1 A. At this stage the node B and the terminal are communicating using an old downlink (DL) 5 and an old uplink (UL) 6 configuration. Conventionally, when the RNC decided a reconfiguration was needed, it set a time in future at which the reconfiguration was intended to happen. Since this time had to cover for the worst case of how long the message takes to get through and be implemented, it was frequently larger than actually necessary.

For a system in which the activation time is NOW, the node B continues to transmit using only the old DL configuration and it is assumed that the terminal 3 is slower than the base station 2, so the next step, shown in Fig. 1 B, is for the terminal 3 to immediately implement the configuration change by changing to a new UL 7 and sending an RL Reconfiguration Complete signal 8 to the server I indicating that it has changed to the new UL. Part of the configuration of this new uplink is that it has a new scrambling code. When the node B 2 detects that the old scrambling code of the UE has changed to the new one, then the node B is triggered to change from the old DL 6 to a new DL configuration in response.

On successful completion of the change to the new downlink 9, the base station 2 and terminal 3 are communicating via the new UL 7 and new downlink 9. The base station sends an RL Reconfiguration Complete 10 message to the server, as shown in Fig. 1C.

There are problems with the proposed procedure using activation time NOW, as described above, since when the terminal 3 changes to the new UL 7, the terminal expects the downlink 6 to change accordingly. However, it takes a finite time for the node B 2 to notice the change in scrambling code and to make the change in DL itself, giving rise to possible errors, e.g. due to a downlink failure before the base station can send its RL Reconfiguration Complete message. This method also means that the base station has to deal with increased complexity because of the need to detect two scrambling codes.

The present invention addresses this problem enabling the benefits of reduced call setup time to be enjoyed, without incurring additional complexity at the Node B, or risking the loss of downlink. It is particularly important to reduce signalling delays in the communications networks, because these have a significant impact on user experience, so there is pressure from operators to reduce these delays. The time required for call setup is of particular concern in this respect, as it can run into seconds and so be very noticeable to the user.

In the present invention, as described with reference to Fig. 2A, the server sends an RL Reconfiguration command signal 4 to the terminal 3 and base station 2 which are communicating via old uplink 5 and downlink 6. The node B continues to use the old DL configuration until notified otherwise and the terminal takes steps to change its configuration as soon as possible, but instead of relying on the base station, or node B 2 to notice a change in scrambling code, indicating that the uplink has changed, the present invention requires the terminal 3 to signal to the base station using the old uplink 5 that the terminal is about to change to a new uplink configuration, as shown in Fig. 2B. Thus, the new uplink 7 and new downlink 9 come into use at the same time, as shown in Fig. 2C. The base station and terminal send back RL Reconfiguration Complete signals 12, 13 to the server once they are ready to use the new configuration.

In one embodiment of the present invention, physical layer signalling using medium access control (MAC) or higher layers provides an indication on the dedicated physical control channel (DPCCH) to indicate to the base station that the terminal is about to change its UL configuration. The signalling is sent immediately in advance of the configuration change. To reduce the possibility for errors, the signalling is optionally repeated or transmitted with slightly higher power.

The signalling of the change from the terminal might be by way of setting feedback indicator mode (FBI) bits of the DPCCH, assuming that closed loop transmit diversity is not used for the previous signalling channel; or by using a specially assigned transport format combination indicator (TFCI) value, where the signalling radio access bearer (RAB) is revised to include a special TFCI value to indicate that the new configuration is about to be implemented, or by using a change in a pilot sequence sent by the terminal The use of signalling immediately prior to the new configuration allows for the Node B to change the DL configuration at the same time the UL configuration changes and hence removes the risk of a DL radio link failure that exists with the currently proposed solution. Also the use of signalling TFCI or FBI means that there is no increase in Node B complexity for this procedure, as would be the ease if a change in scrambling code has to be detected.

The invention uses signalling immediately prior to implementing the new configuration in the terminal to ensure that the base station reconfigures at the same time as the terminal. Physical layer signalling is used to optimise the Node B response to a physical channel reconfiguration and in one embodiment a special TFCI value is used to signal completion of a higher layer procedure.

Claims

CLAIMS

I. A method of reconfiguring a radio link between a mobile device and a base station; the method comprising determining a requirement for a reconfiguration of the radio link; and sending a reconfiguration instruction from a controller to a mobile device and an associated base station; wherein the mobile device sends a notification to the base station that it is about to reconfigure; and wherein the mobile device and the base station then implement the reconfiguration substantially simultaneously.

2. A method according to claim 1, wherein the radio link comprises an uplink and a downlink between the mobile device and the base station.

3. A method according to claim 2, wherein the reconfiguration instruction comprises a change to from a first uplink to a second uplink and from a first downlink to a second downlink.

4. A method according to claim 3, wherein the notification from the mobile device to the base station is sent on the first uplink.

5. A method according to any preceding claim, wherein the notification is sent via physical layer signalling.

6. A method according to any preceding claim, wherein the notification is sent on a dedicated physical control channel 7. A method according to any preceding claim, wherein the notification comprises a preset transport format combination indicator value.

8. A method according to any of claims 1 to 6, wherein the notification comprises feedback mode indicator bits.

9. A method according to any of claims 1 to 6, wherein the notification comprises a change in a pilot sequence sent by the mobile device.

10. A method according to any preceding claim, wherein the notification is repeated.

11. A method according to any preceding claim, wherein the controller comprises a radio network controller, the base station comprises a node B and the mobile device comprises a user equipment.

12. A communication system comprising a controller, a base station and a mobile device, wherein the system is adapted to carry out the method of any preceding claim.