GB2416960A

GB2416960A - Means and method for a mobile radio communications device to switch networks for emergency call establishment

Info

Publication number: GB2416960A
Application number: GB0417195A
Authority: GB
Inventors: Hamid Reza Falaki; Richard Ormson
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2004-08-02
Filing date: 2004-08-02
Publication date: 2006-02-08
Anticipated expiration: 2024-08-02
Also published as: GB0417195D0; GB2416960B

Abstract

A mobile radio communications device connected to a first network and wishing to make an emergency call, may be instructed to handover to a different network because the connected network has limited capacity, coverage or location-determining capabilities. The invention thus provides a mobile radio communications device, which is connected to a first network, with means to switch to a second network to establish an emergency call. The device searches for a cell of the second network having a signal power level above a threshold level and sends an emergency call establishment message to a cell identified by the search. Advantageously, the emergency call establishment message can be sent to the first cell identified as having a base transceiver station (BTS) channel exhibiting a receive signal strength (RSS) above a threshold level. The cell searching and call establishment of the invention is faster than that provided by conventional techniques.

Description

NETWORK SWITCHING FOR EMERGENCY CALL

ESTABLISHMENT AND RELATED MOBILE RADIO COMMUNCIATIONS

DEVICE

The present invention provides for a method of switching between mobile radio communications networks for the establishment of an emergency call and to a related mobile radio communications device.

Mobile radio communication devices, such as cellular phone handsets, offering at least dual mode operability are now commonly available.

Such dual mode operability can allow for access to both a third generation (3G) network such a UNITS network and a second generation (2G) network such as a GSM network.

To assist in the manner in which mobile radio communication devices can be employed in emergency situations, it is common for most cells of most 3G and 2G networks to allow for emergency call establishment. This is allowed even though the user of the mobile radio communications device might not subscribe to a particular network, nor indeed be connected to a particular network at the time the emergency call is to be established by way of that network.

For example, if, when a cell phone handset is camped onto a 3G network, an attempt is made at an emergency call, 3GPP standards allow for the network to redirect the emergency call if appropriate by way of a 2G network.

Such a switch in operation from the 3G to the 2G network can prove appropriate for a variety of reasons such as capacity and coverage limitations, or limitations relating to location-determining aspects arising in relation to the 3G network and which may itself result from the above-mentioned capacity and coverage issues.

If it is identified that a redirection to the 2G network is required, a signalling message is sent on the 3G network to the cell phone handset directing it to switch to the 2G network.

In view of the inherently important nature of an emergency call, it is of course desirable to establish the call with the 2G network as quickly as 1 0 possible.

However, limitations with regard to the speed of connection to the 2G network have been found to arise.

In particular, it is noted that the message sent on the 3G network to the cell phone handset and redirecting the handset to the 2G network may not actually contain any information about the one or more 2G networks that the cell phone handset should be able to make contact with. Further, the cell phone handset itself may not contain any information concerning which local 2G networks are available since, in accordance with some operational standards, power saving modes are initiated in which the monitoring of, for example, a 2G network is disabled if the signal quality arising on the 3G network is above a threshold level.

On this basis, it is appreciated that a situation can readily arise in which, in order to establish the emergency call, the cell phone handset requires rapid access to a 2G network but unfortunately has no information as to how and where to locate any such appropriate cell of such a network.

While one solution might be to execute a Public Land Mobile Network (PLMN) search as defined in various standards, disadvantages nevertheless exist. Such a search comprises a power-level search procedure followed by an attempt first to camp onto the cell exhibiting the strongest signal power level and then the cell exhibiting the next most strongest signal should the first attempt not succeed. It is however identified that such a search and connection procedure can take in the order of up to 30 seconds depending upon the number, and size of the radio bands covered.

Such delays are clearly inappropriate when an emergency call is to be established.

Even though attempts have been made previously to reduce such a delay, it is still found that delays of at least 10 seconds are experienced and which can prove inappropriate.

The present invention seeks to provide for a method of network switching for emergency purposes, and to a related mobile radio communications device, having advantages over known such methods and devices.

According to a first aspect of the present invention, there is provided a method of switching between networks in a mobile radio communications device for establishing an emergency call on a second network when connected to a first network and including the steps of: searching for a cell of the second network having a signal power level above a threshold level; and sending an emergency call establishment message to a cell identified by way of the said search.

The invention is advantageous in conducting an accelerated cell search procedure which takes advantage of the realisation that the mobile radio communications device is likely to be able to establish an emergency call on any network and cell permitting emergency access. Since it is a requirement for the vast majority of such networks and cells to permit emergency access, the accelerated search conducted in accordance with the present invention can prove fruitful in establishing an appropriate connection for the emergency call to be placed.

As will be appreciated, the search for a cell having a signal power level above a threshold level includes the step of comparing detected signal power levels against a predetermined threshold level.

Advantageously, the said search for a cell includes the step of searching for a Base Transceiver Station (BTS) channel having a received signal above a threshold level.

Advantageously, an emergency call establishment message is sent by way of the first cell identified as having a signal power over and above the said threshold level in accordance with the searching step.

The said threshold level is advantageously determined by data received as part of network messaging received from the network issuing the redirection command.

As a particular advantage of the present invention, it will be appreciated that no need arises to check for an appropriate PLMN since the connection can be controlled to be made only for emergency purposes and when the mobile radio communications device is to be used in an emergency mode.

According to another aspect of the present invention, there is provided a mobile radio communications device arranged for operation in connection with a first network and a second network and for establishing an emergency call on the said second network while connected to the said first network, the device further including means for searching for a cell on the second network having a signal power level above a threshold level, and being arranged to send an emergency call establishment message to a cell identified by the said means for searching.

From the aspects of the method outlined above, it will be appreciated that the mobile radio communications device can be advantageously arranged to conduct the said search by way of a comparison between measured ceil signal power levels and a predetermined threshold level.

In particular, the device is advantageously arranged to send an emergency call establishment message to the first cell identified as having a signal power level above the said threshold level.

Further, the mobile radio communications device is advantageously arranged to receive data determining the said threshold level within network messages received from the said first network.

The invention is described further hereinafter, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic block diagram of a mobile radio communications device in the form of a cell phone handset embodying the present invention; and Fig. 2 is a flow diagram illustrating the method embodying an aspect of the present invention.

Turning first to Fig. 1, there is illustrated in schematic form a cellular phone handset 10 employing standard front-end radio circuitry 12 and also a processing means 14 arranged to achieve the functionality of the present invention.

As will be described further in relation to Fig. 2, the handset, by way of its radio circuitry 12 receives a signalling message from a 3G network subsequent to the user trying to establish an emergency call connection, and which message instructs a handover connection of the handset to a 2G network.

Upon receipt of such a handover message, the processing arrangement 14 serves to establish an accelerated search procedure by means of which the handset 10 temporally searches for the first BTS channel it can identify with a received signal strength above a threshold value. Once having identified the first BTS channel having such a signal strength above the aforementioned threshold, the handset 10 is then arranged to send an emergency call establishment message to the cell associated with that BTS channel.

Again, in view of the above-mentioned accelerated search procedure, there is no need to search for an appropriate PLMN since the connection to be made in accordance with the present invention arises only in the emergency mode of the handset.

An emergency call which might not prove possible, nor appropriate, on the 3G network can therefore advantageously switched to a 2G network without suffering the potentially problematic and disadvantageous delays arising in the current state of the art.

A method of operation embodying the present invention is now described further with specific reference to Fig. 2.

Within Fig. 2, there is illustrated a flow diagram representing the main stages within a method embodying the present invention.

Thus, at step 16, the cell phone handset 10 of Fig. 1 receives a signalling message on the 3G network to which it is connected and requesting the handset 10 to switch to a 2G network so that the emergency call that the handset user wishes to place, can be established on the 2G network.

The method proceeds to step 18 where the handset 10 conducts a search for the first BTS channel it can find with a received signal strength above a threshold value.

The threshold value is advantageously determined on the basis of data I sent as part of the 3G network messaging and this advantageously allows the said threshold to be responsive to different radio environments.

Step 18 illustrates a first of two main aspects of the present invention and which can exhibit advantages over currently known search procedures.

For example, a standard power level search procedure generally involves making five measurements per frequency before an attempt to camp on to a particular network is made. Thus, since in accordance with step 18 only one measurement is required, this initial stage of the method of the present invention can prove to be in the region of five times faster than known procedures. In practice, the advantages can be rather more pronounced than suggested since, at any given location, there are likely to be in the order of four cells per network that exhibit a usable receive signal strength. Further, on an assumption that four networks will be available in any particular country, realistic expectations can therefore arise that it will be necessary to search only 1/16, of the frequency bands before a usable cell is found.

Thus, the present invention has the ability to accelerate the cell-search procedure by a factor of 80, i.e. 5 measurements x 16 frequency bands. On this basis, and for a typical dual-band handset, there is initial stage in the search procedure which generally takes in the order of 5 seconds can be advantageously reduced to 0.06 seconds.

Returning to Fig. 2, at step 20 one having identified a cell exhibiting the required, or greater, power level, the handset seeks to send an emergency call establishment message to that first cell so identified and in accordance with the search of step 18. Such connection to the first appropriate BTS channel identified requires over-the-air signalling and so cannot be achieved as quickly as the aforementioned step 18.

However, assuming again that four networks are available within any particular country, and on the expectation within the current state of the art that I a handset would find the correct network on at least the third attempt, advantages in the step relating to a connection to the BTS are however also achieved. Since, in accordance with the present invention, connection is to be made to the first cell offering an appropriate received signal level regardless of the actual network upon which the cell is found, the first connection will prove successful and so this part of the procedure illustrated by step 20 is expected to take no more than 1.5 seconds.

Thus it will be appreciated that the complete search and connection procedure reduce the current best delays of in the region of ten seconds to a value of well under two seconds.

The present invention therefore takes advantage of the ability of the handset to make an emergency call on any network or cell if that network/cell permits emergency access. Since most networks/cells are required to permit such emergency access, the advantages offered by the present invention can be readily realised. Standard search procedures therefore currently employed within the state of the art are not necessary and accelerated search of the present invention can be advantageously performed.

Potentially delays that can arise when attempting to establish an emergency call are therefore advantageously avoided.

Claims

Claims 1. A method of switching between networks in a mobile radio

communications device for establishing an emergency call on a second network when connected to a first network and including the steps of: searching for a cell of the second network having a signal power level above a threshold level; and sending an emergency call establishment message to a cell identified by way of the said search.

2. A method as claimed in Claim 1, wherein the search for a cell having a signal power level above a threshold level includes the step of comparing detected signal power levels against a predetermined threshold level.

3. A method as claimed in Claim 1 or 2, wherein the said search for a cell includes the step of searching for a Base Transceiver Station channel having a receive signal strength above a threshold level.

4. A method as claimed in Claim 3, wherein a emergency call establishment message is sent to the first cell identified as having a signal power over and above the said threshold level in accordance with the searching step.

5. A method as claimed in Claim 1, 2, 3 or 4, said threshold level is determined by data received as part of network messaging received in relation to the said first network.

6. A mobile radio communications device arranged for operation in connection with a first network and a second network and for establishing an emergency call on the said second network while connected to the said first network, the device further including means for searching for a cell on the second network having a signal power level above a threshold level, and being arranged to send an emergency call establishment message to a cell identified by the said means for searching.

7. A device as claimed in Claim 6, and arranged to conduct the said search by way of a comparison between measured cell signal power level and a predetermined threshold level.

8. A device as claimed in Claim 6 or 7, and arranged to send an emergency call establishment message to the first cell identified as having a signal power level above the said threshold level.

9. A device as claimed in Claim 6, 7 or 8, and arranged to receive data determining in the said threshold level within network messages received from the said first network.

10. A method of switching between networks in a mobile radio communications device for establishing an emergency call and substantially as hereinbefore described and with reference to, and as illustrated in Fig. 2 of the accompanying drawings.

11. A mobile radio communications device substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 of he accompanying drawing.

Amendments to the claims have been filed as follows 1. A method of switching between networks in a mobile radio communications device for establishing an emergency call on a second network when connected to a first network and in which the first network rejects an attempt to establish an emergency code and including the steps of: the first network notifying the handset of the presence of an appropriate second network; searching in the device for a cell of the notified second network having a signal power level above a threshold level; and sending an emergency call establishment message to a cell identified by way of the said search.
2. A method as claimed in Claim 1 and including the step of the first network notifying the handset of details of cells of the second network.
3. A method as claimed in Claim 1 or 2, wherein the search for a cell having a signal power level above a threshold level includes the step of comparing detected signal power levels against a predetermined threshold level.
4. A method as claimed in Claim 1, 2 or 3, wherein the said search for a cell includes the step of searching for a Base Transceiver Station channel having a receive signal strength above a threshold level.
5. A method as claimed in Claim 4, wherein a emergency call establishment message is sent to the first cell identified as having a signal power over and above the said threshold level in accordance with the searching step.
6. A method as claimed in any one or more of Claim 1 to 5, wherein said threshold level is determined by data received as part of network messaging received in relation to the said first network.
7. A mobile radio communications device arranged for operation in connection with a first network and a second network and for establishing an emergency call on the said second network while connected to the said first network and after the first network has rejected an attempt to establish an emergency call, the device being arranged to receive notification via the first network of the presence of an appropriate second network and further including means for searching for a cell on the notified second network having a signal power level above a threshold level, and being arranged to send an emergency call establishment message to a cell identified by the said means for searching.
8. A device as claimed in Claim 7 and arranged to receive notification of details of cells of the second network.
9. A device as claimed in Claim 7 or 8, and arranged to conduct the said search by way of a comparison between measured cell signal power level and a predetermined threshold level.
10. A device as claimed in Claim 7, 8 or 9, and arranged to send an emergency call establishment message to the first cell identified as having a signal power level above the said threshold level.
11. A device as claimed in Claim 7, 8, 9 or 10, and arranged to receive data determining in the said threshold level within network messages received from the said first network.
12. A method of switching between networks in a mobile radio communications device for establishing an emergency call and substantially as hereinbefore described and with reference to, and as illustrated in Fig. 2 of the accompanying drawings.
13. A mobile radio communications device substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 of he accompanying drawing. . ë :' :.

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