GB2413737A

GB2413737A - Reducing frequency of network search if no network is detected

Info

Publication number: GB2413737A
Application number: GB0418584A
Authority: GB
Inventors: Ashley Wheeler
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2004-08-19
Filing date: 2004-08-19
Publication date: 2005-11-02
Anticipated expiration: 2024-08-19
Also published as: GB2413737B; GB0418584D0

Abstract

An apparatus for prolonging battery life in a mobile communication device comprising means for executing a search for a communication network, means for confirming that no communication network is available if the executed search is negative, means for entering into a sleep mode during which a reduced number of searches are executed if no communication network is available, means for detecting movement of the device and means for re-commencing of execution of searches for the network in dependence on movement of the device being detected. This is especially advantageous where a user will be within an area of no network coverage for a long period of time. In this case, any network search will fail and therefore shorten battery life unnecessarily.

Description

APPARATUS FOR PROLONGING BATTERY LIFE IN A MOBILE

COMMUNICATION DEVICE

The present invention relates to an apparatus for prolonging battery life in a mobile communication device and in particular to prolonging battery life by reducing the network search activity while the device is out of range of the network.

The battery life of a mobile handset is one of the parameters that is under constant improvement by handset manufacturers. The demand by users for more features on their handsets and longer talk time and standby time has put pressure on mobile handset manufacturers to minimise use of power unnecessarily. Many handsets conserve battery power by turning off hardware components or reducing the activity of these components when they are not required. Standards that define both the second and third generation mobile phone technologies are designed in such a way as to maximise the opportunities for handsets to conserve battery power, in particular, when they are idle.

The current standards require that when a mobile handset loses synchronization (i.e. moves out of coverage) from the Public Land Mobile Network (PLMN) on which it previously had a normal service, it must make searches for the same or another PLMN on which normal service can be resumed. It is essential that a communication device can communicate with a PLMN in order that it can operate in the usual way. In situations when no PLMN can be identified by the handset, or no PLMN is available which can provide normal service, the handset will operate in a "limited service state" or a "no service state". In a "limited service state" the handset identifies and synchronises with an acceptable cell from a PLMN which is not able to provide a normal service. Typically, only emergency calls may be made in this state. In a "no service state", no cell from any network can be detected by the communication device and not even emergency calls can be made from the device.

In both the "limited service state" and the "no service state", the mobile communication device must perform some periodic search of local networks in case a suitable PLMN becomes available that can provide a normal service to the communication device. Second and third generation standards require that, in this situation, devices should "minimise the time taken to find new available PLMNs while maintaining battery life, discontinuous search schemes may be used" (GSM 03.22, section in 3.7). Of course, it is important that communication devices identify a suitable PLMN as soon as possible.

Known handsets perform a scaling back search in which a full PLMN search is performed frequently, for example every few seconds, immediately after normal service has been lost. However, as time goes on without identifying a suitable PLMN the time period between full PLMN searches is increased. By increasing the duration of time between searches the device avoids using unnecessary battery power on unsuccessful searches. The scaling back search is used since it is possible that the handset may be stationary in an area of no coverage in which case performing a full PLMN search every few seconds will be fruitless and will drain the battery unnecessarily. Infrequent PLMN searches are made to ensure that if the handset does move into an area in which a suitable PLMN is available then the communication device will identify the PLMN and resume normal service.

Although the scaling back search reduces the number of unnecessary PLMN searches there are disadvantages with operating in this way when the device moves out of coverage of the network. Firstly, if the handset is stationary in an area in which there is no suitable network coverage, then any search that is performed will fail and, therefore, battery power will be consumed unnecessarily.

Therefore, despite the fact that the device is running fewer searches, any searches that are run in this situation will waste battery power unnecessarily.

Secondly, since the time duration between searches increases with the length of time that the device has been out of coverage of the network, if a handset does move back into coverage then it may be a number of minutes before the device executes a full network search. Therefore, there will be an unnecessary delay before communication with the network is re-established.

Both situations are unfavourable to the user since the user requires minimum power wastage and also requires that he is in touch with the network whenever he is in an area of coverage. A typical example when these disadvantages occur is when a handset owner lives in an area in which no suitable network coverage is provided but he regularly travels and works in an area in which suitable coverage is available. At night, when he returns home, if he leaves his handset switched on in a stationary position, where service will never be obtained, the device will continue to make full network searches periodically and thus use unnecessary battery power.

We have appreciated that power is used unnecessarily when a mobile communication device searches for networks when it is positioned in an area in which no network provides suitable coverage for normal operation. Furthermore, we have appreciated that it is important that the communication device searches for, and connects to, a network as soon as it moves into an area in which coverage is provided.

Embodiments of the present invention detect when the device is positioned in an area in which network coverage is not available and then executes network searches at a reduced rate. In certain embodiments of the invention the rate is zero. The device then monitors movement of the device. If no motion is detected the device is assumed to be in the same location in which no network coverage is provided. However, if movement of the device is detected, then the device re- commences its network searches in order to identify, and connect to, a network as soon as that network provides suitable coverage. The ability of the invention to detect movement and re-commence network searches enable the device to search for and identify a network as soon as it provides adequate coverage. The invention reduces power wastage by not executing searches when it is in a location of non-coverage and re- commences network searches as soon as motion of the device is detected.

Preferred embodiments of the present invention execute infrequent searches while the device is stationary in an area which has previously been determined as having no suitable network coverage. These infrequent searches are executed in case the loss of coverage was only temporary due to some network fault at either a local cell level or within the core network. Further embodiments of the invention execute these infrequent searches at regular intervals.

Still further embodiments of the invention increase the time period between network searches when movement is detected if, after movement is detected, the device remains positioned within an area of no network coverage. The advantage provided by such an embodiment is that power usage is reduced if the device is moving within an area in which no network coverage is provided since movement does not indicate that coverage has returned, only that it might have returned.

The invention is now defined in its various aspects in the appended claims to which reference should now be made.

An embodiment of the invention is now described in detail with reference to the accompanying figures in which: Figure 1 shows a mobile communication device in operation when communicating with a network.

Figure 2 is a flow diagram showing the steps taken when implementing an embodiment of the present invention.

Figure 3 is a block diagram showing the components within an embodiment of the present invention.

Figure 1 shows a communication device 10 operating in a typical cell network.

Typically, a cell network includes a plurality of base stations 20, 30, 40. Some of the base stations may belong to PLMNs (networks) that the terminal is allowed to use (i.e. can provide normal service) and other base stations may belong to PLMNs that the terminal is not allowed to use (i.e. cannot provide normal service). Typically, the device will set up a communication link with the base station of an allowable PLAIN which provides the strongest signal. The device will monitor signals from the non-serving base stations periodically in order to assess which allowable base station is providing the strongest signal. As the device moves it may move to an area in which the network coverage from the serving base station grows weak and coverage from other base stations is stronger. It may also move into an area in which no visible base station is able to provide suitable network coverage. If all visible base stations belong to disallowed PLMNs then the terminal enters the 'limited service' state. If no base stations are visible, the device enters a "no service" state.

In figure 2, the device experiences normal service from the PLMN at 200. At this stage the device will be in range of a base station that can provide coverage for the network on which the device is operating. At 205 the device loses normal service. Typically normal service will be lost due to the device moving out of range of the base station providing normal service. However, there may be other reasons why coverage is lost for example the signals may be blocked or there may be a problem with the network or the particular base station.

Once normal service is lost at 205 the device executes a PLMN search at 210.

During the PLMN search the device executes a search of all PLMNs to try to identify a PLMN that is able to provide it with a normal service. If the device identifies a suitable PLMN at 215 then it communicates with that PLMN at 220 and resumes normal operation at 200. However, if no suitable PLMN is found at 215 the device executes a number of PLMN searches at 230 to confirm that the handset really has lost coverage of the network and that this is not a transient condition in which network coverage has only been lost temporarily. The number and frequency of these confirmatory network searches can be chosen by the manufacturer or the user and can be fine tuned as part of the implementation of the invention. If the further network searches confirm that network coverage has been lost the device enters a state of "sleep" at 240 (i.e. a state of minimal power consumption).

Once the device has entered a sleep mode at 240, the handset starts to monitor the movement of the device at 250. Embodiments of the invention include a simple passive motion detection device, such as a non-mercury tilt switch or some form of vibration detector, in order to determine whether the device has moved since it has entered the "sleep" mode. Preferred embodiments of the invention include motion detecting components which have a very low quiescent current in order to minimise battery power consumption during the "sleep" mode.

Furthermore, preferred embodiments of the invention incorporate motion detecting devices which do not require the CPU to be running any software in order to detect motion. Again, this will reduce unnecessary battery power consumption during the "sleep" mode.

If no motion is detected the handset remains in a state of "sleep". During this sleep period the device executes PLMN searches at a reduced rate since the device assumes that it remains in an area of no suitable network coverage. Since the device has not moved since it was determined that it was positioned in an area of no suitable coverage the device assumes that monitoring of the networks When motion of the device is detected at 260, the CPU is interrupted, i.e. woken up, and full PLMN searches are re-commenced at 210. Thus, the device is able to react quickly to movement in order that it can re-commence searches and detect when the device moves back into an area of suitable network coverage such that the device can resume normal operation.

In certain embodiments of the invention, no PLMN searches are made during the sleep mode. However, it is possible that the loss of coverage at 205 is only temporary and may be due to some network fault at either a local level or within the core network. In this case, the above algorithm would conclude that coverage has been permanently lost if the confirmation PLMN searches at 230 are negative when, in fact, the device would be able to return to normal operation at a later time without any need for the handset to move. To account for this situation, preferred embodiments of the invention execute infrequent network searches while the handset remains stationary. Such searches enable the device to resume operation with the network if the network does re-appear in this way at a later time. The regularity of these measurements can be determined on an individual handset basis by the user or be pre-programmed during manufacture. Typically, the searches would be executed more infrequently than the back searches used in known devices and thus the invention would still provide a significant power saving over known systems.

It is also possible that, on detection of movement, the handset has moved in an area of permanent non-coverage. In this case, the above algorithm could result in frequent PLMN searches in areas of non-coverage. If a device is moving in an area of non-coverage the device would lose coverage with the network, execute confirmation PLMN searches and enter a sleep mode. The constant movement of the device would trigger the device to exit the sleep mode immediately and execute PLMN searches. In an area of non-coverage, the PLMN searches would again be negative and the device would enter sleep mode once more only to be woken up immediately when motion is detected. In this situation, the device would be using power unnecessarily since any network search in the area of non- coverage would produce a negative result. To account for this situation, preferred embodiments of the present invention include some intelligence in the motion detection initiated searches. For example, preferred embodiments of the invention do not exit the sleep mode if motion is detected within a pre-determined time period after entering the sleep mode. Embodiments may increase this time period if a negative search is taken after exiting the sleep mode. This period may be increased up to a maximum time period if negative searches are taken after exiting the sleep mode on successive occasions. The time period is increased in a similar manner to the scaling back searches discussed above. For example, after entering the sleep mode no searches can be triggered by movement for X seconds. If the searches triggered by movement, the first time the devices leave the sleep mode, are negative then no further searches can be triggered until X+5 seconds after re-entering the sleep mode. The time period can be increased if the device executes negative searches after exiting the sleep mode on successive occasions. The advantage of this feature is that continuous movement does not trigger continuous searching if the device is moving in an area of non coverage. This feature helps to save power since movement does not necessarily indicate that coverage is available, only that it might be.

As an example, an embodiment of the invention may perform a predefined number of confirmation PLMN searches at 230, for example 3 or 5 searches, to confirm that coverage has been permanently lost. Typically, each PLMN search lasts between 4 and 10 seconds depending on whether any PLMNs are detected.

If the PLMN searches produce negative results then any subsequent search would only be triggered by movement of the handset. In a situation where the handset was stationary for a two hour period in an area of noncoverage, then only a total of 12 seconds of PLMN search would have taken place.

In contrast, in known systems when coverage is lost the handset performs a full 2G PLMN search every x seconds where x is initially 5 seconds and increases by 5 seconds each time a search is negative up to a maximum of 3 minutes.

Therefore, over a period of 2 hours when the handset is stationary in an area of non-coverage, the handset will perform 57 PLMN searches. With each search lasting between 4 and 10 seconds, a minimum of 3.8 minutes of continuous PLMN search will have taken place over the 2 hour period. This example shows that the present invention provides considerable power saving over typical known systems.

Figure 3 shows the device 300 having an antenna 310. The device incorporates suitable hardware and software for executing network searches 320. The device also includes a trigger 330 which controls the timing at which the searches are executed. The trigger is connected to the internal clock 340 to control the periodic monitoring of the network and is also connected to a motion detector 350. When embodiments of the invention are in a "sleep" state and motion is detected, the motion detector advises the trigger that a network search should be executed.

Claims

1. A method for prolonging battery life in a mobile communication device comprising the steps of; executing a search for a communication network, confirming that no communication network is available if the executed search is negative, entering a sleep mode during which a reduced number of network searches are executed if no communication network is available, and detecting movement of the device, and re-commencing execution of searches for a communication network when movement of the device is detected.

2. A method for prolonging battery life in a mobile communication device according to claim 1 wherein the reduced rate is zero.

3. A method for prolonging battery life in a mobile communication device according to claim 1, wherein network searches are executed infrequently during the sleep period.

4. A method for prolonging battery life in a mobile communication device according to claim 3, wherein the infrequent network searches are executed at periodic intervals.

5. A method for prolonging battery life in a mobile communication device according to claims 1, 2, 3, or 4 comprising the further step of increasing the time period between executing network searches if the network search is negative after the network searches have been recommenced.

6. A method for prolonging battery life in a mobile communication device according to claim 5 wherein the time period between executing network searches is increased if a network search is negative within a predetermined time after re-commencing execution of the searches.

7. A method for prolonging battery life in a mobile communication device according to claims 1, 2, 3, 4, 5 or 6, wherein the step of confirming is performed by executing confirmation network searches before entering the sleep mode but after detecting that no network is available.

8. A method for prolonging battery life in a mobile communication device according to any preceding claim in which the step of checking for movement of the mobile communication device is executed using a passive motion detection device.

9. A method for prolonging battery life in a mobile communication device according to claim 8, in which the passive motion detection device is a non mercury tilt switch.

10. A method for prolonging battery life in a mobile communication device according to claim 8, in which the passive motion detection device is a vibration detector.

11. A method for prolonging battery life in a mobile communication device, substantially as herein described with reference to the accompanying figures.

12. An apparatus for prolonging battery life in a mobile communication device comprising; means for executing a search for a communication network, means for confirming that no communication network is available if the executed search is negative, means for entering into a sleep mode during which a reduced number of searches are executed if no communication network is available, means for detecting movement of the device, and means for re-commencing of execution of searches for the network in dependence on movement of the device being detected.

13. An apparatus for prolonging battery life in a mobile communication device according to claim 12 wherein the reduced rate is zero.

14. An apparatus for prolonging battery life in a mobile communication device according to claim 10 wherein the network searches are executed infrequently during the sleep period.

15. An apparatus for prolonging battery life in a mobile communication device according to claim 14 wherein the infrequent network searches are executed at periodic intervals.

16. An apparatus for prolonging battery life in a mobile communication device according to claims 12, 13, 14 or 15 wherein the time period between executing searches for communication network searches is increased if the network search is negative after the network searches have been re-commenced.

17. A method for prolonging battery life in a mobile communication device according to claim 16 wherein the time period between executing network searches is increased if a network search is negative within a predetermined time after re-commencing execution of the searches.

18. An apparatus for prolonging battery life in a mobile communication device according to claims 12, 13, 14 or 15 wherein the means for confirming executes confirmation network searches before entering the sleep mode but after detecting that no network is available.

19. An apparatus for prolonging battery life in a mobile communication device according to any of claims 12, 13, 14, 15 or 16 wherein the means for detecting movement of the mobile communication device is a passive motion detector.

20. An apparatus for prolonging battery life in a mobile communication device according to claim 19 in which the passive motion detection device is a non mercury tilt switch.

21. An apparatus for prolonging battery life in a mobile communication device according to claim 19 in which the passive motion detection device is a vibration detector.

22. An apparatus for prolonging battery life in a mobile communication device, substantially as herein described with reference to the accompanying figures.

d-e e '. ,

# c. Amendments to the claims have been filed as follows 1. A method for prolonging battery life in a mobile communication device comprising the steps of; executing a search for a communication network, confirming that no communication network is available if the executed search is negative, entering a sleep mode during which a reduced number of network searches are executed if no communication network is available, and detecting motion of the device using a motion detector, and recommencing execution of searches for a communication network when motion of the device is detected by the motion detector.

6. A method for prolonging battery life in a mobile communication device according to claim 5 wherein the time period between executing network searches is increased if a network search is negative within a predetermined time after re-commencng execution of the searches.

e. e 8 6 8 C . ', a 8 - ' /3 7. A method for prolonging battery life in a mobile communication device according to claims 1, 2, 3, 4, 5 or 6, wherein the step of confirming is performed by executing confirmation network searches before entering the sleep mode but after detecting that no network is available.

8. A method for prolonging battery life in a mobile communication device according to any preceding claim in which the step of detecting motion of the mobile communication device is executed using a passive motion detection device.

12. An apparatus for prolonging battery life in a mobile communication device comprising; means for executing a search for a communication network, means for confirming that no communication network is available if the executed search is negative, means for entering into a sleep mode during which a reduced number of searches are executed if no communication network is available, motion detector for detecting motion of the device, and means for re-commencing of execution of searches for the network in dependence on motion of the device being detected.

e eve# are e e e a ae e a a a. a e e sea e e a 14. An apparatus for prolonging battery life in a mobile communication device according to claim 10 wherein the network searches are executed infrequently during the sleep period.

19. An apparatus for prolonging battery life in a mobile communication device according to any of claims 12, 13, 14, 15 or 16 wherein the motion detector is a passive motion detector.