GB2405556A

GB2405556A - Performance enhancement in a portable communication device

Info

Publication number: GB2405556A
Application number: GB0320073A
Authority: GB
Inventors: Simon Fabri
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2003-08-27
Filing date: 2003-08-27
Publication date: 2005-03-02
Also published as: GB0320073D0

Abstract

A portable communication device comprises memory means for storing network search interval data and network search means for intermittently searching for a preferred network. The network search interval data is derived from the expected availability of a preferred network using, for example, network coverage information in conjunction with the detected location of the portable communication device. The network search interval represents an interval to elapse before the next search for the preferred network is initiated by the network search means. The time between successive searches for the preferred network by the network search means is varied using the network search interval data.

Description

PERFORMANCE ENHANCEMENT IN A PORTABLE COMMUNICATION DEVICE

FIELD OF THE INVENTION

The present invention relates to performance enhancement in a portable communication device. In particular, the invention relates to balancing the conflicting needs of improving standby time in a mobile telephone whilst reducing the time the mobile telephone is "campedH on a nonpreferred network, thereby maximising the time spent on a preferred network.

BACKGROUND TO THE INVENTION

Portable communication devices which connect to a network using a wireless link are well-known to those skilled in the art. In particular, suitable portable communication devices include mobile telephones and suitably equipped to laptop computers or PDAs (personal digital assistants).

It is increasingly common for portable communication devices to provide multi-frequency capability and/or multi-mode capability to equip the device to access one of a plurality of networks using one or more communication technologies.

Typically, use of one network by the mobile communication device is preferable in terms of cost and/or services offered. Roaming charges may be incurred if the device is used to make a call when camped on another network. An example of this is when a device is camped on a national roaming partner of the preferred, or "homer, network. In known mobile telephones, when this preferred network is unavailable because of a temporary lack of signal, lack of coverage in the particular location of the mobile communication device or the mobile communication device is utilising another network for whatever reason, a search for the preferred network is made at frequent intervals to attempt to minimise the time spent camped on another network. As calls made on a network other than the preferred network may incur additional charges, minimising time camped on a network other than the preferred network is clearly advantageous. By searching for the preferred network at frequent intervals, the standby time of the mobile handset may be significantly reduced. By "camped lo on" another network we mean any time when the mobile communication device is connected to a particular network enabling the mobile terminal to make calls and access services over mobile connections on the network, and enabling third parties to contact the mobile terminal over the network.

A representative search strategy for known mobile telephones is shown in the flow chart of figure 1. When the mobile telephone is switched on, it attempts to find a JO network to which it may connect to enable communication.

The mobile terminal searches for the preferred network.

If the preferred network is not available for any reason the search is widened to try to find an alternative available network to which the communication device is :5 permitted, and able, to connect. Assume then that the mobile telephone loses coverage of the preferred network or cannot access the preferred network. The mobile telephone searches for, and connects to, an alternative, suitable network 12. A search interval timer for JO measuring a predetermined fixed interval between searches for the preferred network is reset 14. A test of whether the timer has reached the predetermined fixed interval is made 16. Until the search interval has expired, the test timer is repeatedly applied and the mobile terminal :5 remains connected to the non-preferred network. If the test indicates that the fixed interval has expired, a search for the preferred network is initiated 18. If the preferred network is found, the mobile telephone connects to the preferred network 20 and disconnects from s any other network to which it was connected. If the preferred network is still not found by the search, the system loops back and resets the timer at step 14.

Typically the minimum and maximum search intervals are governed by the communications standard of the lo communications mode being employed.

However, we have appreciated that frequent searching for the preferred network is a drain on power and has a significant effect on the standby time available from the Is limited power supply of a portable communication device.

By standby time" we mean any time when the mobile terminal is not transmitting or receiving user data (voice or other) but is till accessible by the network with which it is registered such that the user may make outbound JO calls or use other services and the terminal is pageable by the network.

We have further appreciated that the desire to reduce the time spent camped on to a network other than the preferred network conflicts with the desire to maximise standby time. In some mobile communication devices, the search for the home network may draw a current an order of magnitude larger than the current drawn in idle mode. As a network search typically takes of the order of a few seconds, the impact on standby time caused by frequent searching is significant. 3s

SUMMARY OF THE INVENTION

We have appreciated that network coverage information; could be used in conjunction with the detected location of the portable communication device to calculate a location dependent search interval. Searching for the preferred network at a location dependent search interval rather than a fixed search interval may achieve a better balance in the compromise between maximising standby time and lo minimising time spent camped on a non-preferred network.

The invention is defined in the independent claims to I which reference is now directed. Preferred features of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a flowchart showing a known searching strategy for checking for coverage by a preferred network after to loss of coverage is detected; Figure 2 is a schematic coverage map for a notional network; Figure 3 is a schematic diagram showing the functional elements required in a mobile telephone embodying the Is invention; Figure 4 is a flowchart of the calculation of the search interval for a mobile telephone embodying the invention; Figure 5 is a schematic diagram showing the functional elements required in a mobile telephone embodying the invention in a second aspect; and Figure 6 is a flowchart of the calculation of the search interval for a mobile telephone embodying the invention in a second aspect.

DESCRIPTION OF A PREFERRED EMBODIMENT

The embodiment of the invention is a mobile telephone with; additional functionality to calculate a variable search s interval dependent on the location of the mobile telephone and coverage data for the preferred network. The calculation of the search interval may also take into account the motion of the mobile telephone relative to the coverage data describing the expected coverage of a lo preferred network at various locations.

Figure 2 shows a schematic coverage map 22 for a notional I network in a given locality. In figure 2, the road layout, cities, towns and villages are indicated and the Is coverage of a notional preferred network is shown by cross hatching 24. In the area at the bottom left 26 of the locality covered by the schematic coverage map of figure 2 no coverage is expected for the preferred network. It will be apparent to those skilled in the art that the so network coverage data need not necessarily take the form of a map but may be in any suitable format. For example, the coverage information may be stored in a database in which the expected coverage at a particular location is the data stored in the database and accessing the data Is requires indexing the database using a grid reference derived from determining the location of the mobile telephone. Many other suitable forms of coverage data and storage and access of the coverage data are possible and it is not intended to limit the invention to any particular type or format of coverage data. The coverage data will describe a plurality of separate areas in a larger environment and contain information describing the expectation of whether an area is covered by a particular network or not. The expectation may be qualitative or 3s quantitative.

Figure 3 shows schematically the functional elements required for calculating and implementing a variable; search interval for successive attempts to locate a preferred network when camped on another network. It will be understood by those skilled in the art that some or all of the functions of these elements could be implemented by a single, central processor or distributed over a number of processors. Some or all functions may be implemented lo in hardware and/or software. The purpose of figure 3 is therefore to aid the description of the elements required for the calculation and implementation of the variable I search interval. Other suitable implementations will be readily apparent to those skilled in the art.

The mobile telephone 30 is comprised of the usual components to allow bidirectional voice and/or image and/or text data to be communicated using a service provider's network. These elements are not shown in JO figure 3 but are well known in the field of mobile telephones. The mobile telephone 30 also comprises additional functionality to allow the interval for searching for the preferred network to be varied to suit the location of the mobile telephone given knowledge of :5 the preferred network coverage in a wider locale encompassing the location of the mobile telephone. In the schematic diagram of figure 3 these elements have been shown coupled to a bus 42 for transfer of data to and from each element. The remaining functional elements are location means 32, network search means 34, interval assessment apparatus 36, memory means 38 and transmitter/receiver 40.

The mobile telephone 30 is equipped with location determination means 32 for determining the location of the mobile telephone 30. The location may be an absolute location relative to a fixed reference system or may be relative to network coverage data describing the coverage; by the preferred network of the wider environment in which s the mobile phone is located. The location determination means may use the Global Positioning System (GPS) to determine the location of the mobile telephone in a method which would not require network assistance or may use any other suitable means to determine the location of the lo mobile telephone including requiring network assistance to determine its location. Network assistance may be used when GPS is employed to enhance the accuracy of the I location or the performance of the location determination calculation. Location means are well known to those Is skilled in the art and are not described in detail here.

For example, the article "Standardization of mobile phone positioning for 3G systems" by Yilin Zhao, IEEE Communications Magazine, vol 40, no. 7, July 2002, pp 108- 116 discusses several well-known mechanisms for to determining the location of a mobile phone.

In the embodiment shown schematically in figure 3, memory means 38 local to the mobile telephone 30 are provided for storing network coverage data to be used in conjunction Is with determined location of the mobile telephone 30 in the calculation of the variable search interval. The network coverage data relates specific locations with an expectation of whether or not a particular network is available at the location. The network coverage data may include data pertinent to the immediate location of the device as well as to the wider surrounding area of the device.

Network search means 34 are employed in known mobile Is telephones and ensure that a search is made for the preferred, or home, network at regular intervals set by L the manufacturer but falling within communication standard set limits. The functionality of known network search means was described with reference to figure 1. For the mobile telephone 30 embodying the present invention, the network search means 34 searches for the preferred network: in the known manner except that instead of using a fixed: search interval it uses a variable search interval set by: the interval assessment apparatus 36. : In a basic embodiment of the invention, the interval assessment apparatus 36 uses the location of the mobile telephone 30 determined by the location determination means 32 and the relevant network coverage data for the determined location and calculates the search interval to be used by the network search means 34 using an estimation of when network coverage is expected, based on the network coverage data and determined location. The extraction or selection of the relevant network coverage data for the JO determined location may be handled by the interval i assessment apparatus 36 or any suitable processor. The way in which the network coverage data relevant to the I determined location of the mobile telephone 30 is extracted depends on the way in which the network coverage data is arranged and stored.

The network coverage data is stored locally in the mobile telephone 30 in memory means 38. The network coverage data is effectively a "map" of expected network coverage JO of the preferred network for the general local area in which the mobile telephone 30 is currently located. If the mobile telephone 30 is moved so that it approaches the edge of the local coverage map, a new map centred on the new location of the mobile telephone 30 may be requested from the network and stored in memory means 38. - 9 -

Alternative ways of ensuring that the network coverage data includes the current location of the mobile telephone include the network periodically transmitting a map centred about the location of the mobile telephone 30 or, if memory is not an implementation concern in the mobile telephone 30, the memory means 38 may store one or more maps describing the coverage of the entire network.

However the network coverage data is stored or accessed it must be updated periodically to reflect changes in network lo coverage. New maps provided to the mobile telephone may not be centred on the current location but preferably include the current location.

Figure 4 is a flowchart showing steps in the operation of Is the preferred network search strategy of a mobile telephone embodying the invention in a first aspect.

Initiation of the preferred network search mode commences when a mobile telephone 30 previously registered with the preferred network loses coverage of the preferred network so or the mobile telephone 30 is powered on in an area where I there is no coverage by the preferred network 50. The current location of the mobile telephone is determined I using location means 32. The current location is stored.

The search interval indicating the time to elapse before a :5 further search for the preferred network is to be initiated must then be calculated. On the initial assumption that the loss of coverage may be temporary due to the telephone being in a area of borderline coverage or that the telephone is experiencing temporary loss of JO signal due to effects such as shadowing, the search interval, THpLMN, is set to the lowest value, TMIN, that may be used by the mobile telephone handset and the telephone resumes idle mode 52. The search interval timer counts until the search interval has elapsed at which point the network search means 34 initiates a search for the preferred network 54.

If coverage of the preferred network is available the s mobile telephone connects to the preferred network 56 and the preferred network search strategy is disabled until it is reactivated by loss of the preferred network. If the mobile telephone 30 is still out of coverage of the preferred network an appropriate, and variable, search lo interval must be determined. The new current location of the mobile telephone 30 is determined by the location determination means 32 and the relevant network coverage data for the current location is selected 58. A test of whether coverage is expected at the current location is Is made 60. If coverage is expected at the current location, the search interval is set to TMIN 62 and idle mode is resumed 68. If coverage is not expected at the current location, the search interval is set to a preset maximum value, TMAX 66. The preset maximum value may be stored in the mobile telephone. It may be updated by the network by downloading a new maximum value to the mobile telephone. Idle mode is then resumed 68. Operation then resumes at step 54 and continuously loops through steps 54 to 68 as appropriate until coverage of the preferred network is obtained and the mobile telephone has connected to the home network.

Thus, when no coverage is expected the search for the preferred network is conducted on less frequent intervals.

Jo The search for the preferred network takes a significant amount of power which in turn reduces standby time. Hence by reducing the number of searches in a given period, the standby time may be increased. When coverage is not expected in the current location, the increased time between searches for the preferred network is beneficial in terms of overall performance which takes account of both the time spent camped on non-preferred networks and the effect on standby time of searching for the preferred network.

In a second, more sophisticated, arrangement of mobile telephone embodying the invention shown schematically in figure 5, previous and current locations of the mobile telephone, determined during the previous and most recent JO network searches, may be used in conjunction with the network coverage data to predict an entry interval representing the length of time it will take for the mobile telephone to enter an area covered by the preferred network. In figure 5, elements performing the same Is function as described above with reference to figure 3 are denoted by the same reference numeral.

The prediction of entry interval may be based on an average computed trajectory (or heading) and average JO computed speed of the motion of the mobile telephone and I may take account of road networks if it is appropriate given the apparent motion of the mobile telephone 30. 1 Prediction means 44 are provided for estimating the entry interval. The prediction means may be a separate, :5 dedicated processor or a central processor may be configured to function as the prediction means. The prediction means 42 uses location data from the location determination means 32 and network coverage data from the memory means or store 38 along with data representing the motion of the mobile telephone to predict when the mobile telephone 30 will enter an area covered by the preferred network. The entry interval is outputted from the prediction means 44 and used by the network search means 34 in a refined calculation of the search interval.

Figure 6 is a flowchart of the operation of the mobile telephone of figure 5. In figure 6, many of the steps are identical to those described above with reference to figure 4 and these steps are denoted by the same reference s numeral. Discussion of the operation of the search strategy for these steps (effectively steps 50 to 60, 62 and 68) is not repeated here and reference should be made to the relevant description for figure 4. After step 60 if the mobile telephone has still not entered an area of 0 expected coverage the mobile telephone uses the prediction means 44 to predict when the mobile telephone will enter an area of network coverage. A trajectory of the mobile telephone is determined based on the current and one or more previous locations 70. The search interval used immediately prior to the current search for the preferred network may be used to estimate a speed at which the mobile telephone is travelling. Based on the estimated speed, heading and distance along the heading to an area I of coverage by the preferred network the entry interval to may be predicted. The entry interval, TEXp is the duration before it is expected that the mobile telephone will enter an area of coverage by the preferred network.

A test is made to determine whether the entry interval, TEXp, is greater than the maximum allowable search interval, TMAX, 72. If TEXP > TMAX, then the search interval, THpLMn, is set to the value of TMAX 74 and operation at step 68 resumes as per the description in relation to figure 4. If TEXp is less than or equal to TMAX then the search interval, THpLMN, is set to the value of TEXp 76. TEXp is then checked against TMIN. If TEXp c TMIN, then TEXp is reset to THIN. Operation then resumes as per the description in relation to figure 4 at step 68.

Prediction of the trajectory of the mobile telephone in relation to the coverage of the preferred network may allow further improvements in overall performance to be obtained.

Implementing a variable search interval prevents the mobile telephone from searching frequently for the preferred network when there is no reasonable expectation of preferred network coverage. In a typical lo implementation, a beneficial effect on standby time may be obtained without incurring any substantial increase in the time spent camped on alternative networks.

It will be readily apparent to those skilled in the art that when the invention is used in a multi-mode device, such as a mobile telephone with 3G (third generation) capability and supporting GSM as a backup communication option for areas where there is no coverage of the newer I 3G technology, the preferred network may be use of a to particular network operator's service using the newer 3G technology to provide access to additional services and achieve improved performance compared with older technologies. The same network operator may provide a service using the older technology to support the user in :5 areas where there is no coverage of the newer technology.

In this case, the preferred network will be the 3G network provided by the service provider rather than the GSM network. The adjustment of the search interval in the manner described above serves the same purpose in multi mode devices as in multi-frequency devices.

In alternative embodiments, the network coverage data may be stored other than in the mobile telephone 30. For example, the network coverage data could be stored in a database on a server associated with the home network and a number of other networks. The mobile telephone 30 may query the database via any available network, using the location of the mobile telephone to access the relevant portion of the network coverage data. The actual location determination may be performed by apparatus at the portable phone either in a stand alone capacity or in conjunction with network assistance using a UE-based (where "UK" means user equipment) technique.

lo In another embodiment, the determination of the location of the mobile phone may be performed by the network in conjunction with assistance from the mobile phone using a UE-assisted location technique. Techniques for UE-based and UE-assisted location of the mobile communication device are known in the field and are not described here in detail.

Whilst the embodiment of mobile telephone described includes interval assessment apparatus for performing the calculation of the network search interval, this functionality may be provided by the network rather than at the portable communication device. A processor associated with the preferred network but accessible by the mobile telephone handset over roaming partner networks :5 may use the location of the portable communication device and the expected network coverage for the preferred network to calculate the network search interval. Network search interval data may then be transmitted to the portable communication device for use by the network So search means to adapt and control the interval between successive searches for the preferred network. This scheme would require co- operation between the preferred network and partner networks to ensure that the information required to determine a location dependent search interval was made available to the mobile telephone via the partner network.

The invention is clearly applicable to portable communication devices other than mobile telephones and these are within the scope of the invention. With respect to the above description, it is to be realised that equivalent apparatus and methods are deemed readily apparent to one skilled in the art, and all equivalent lo apparatus and methods to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous Is modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, to falling within the scope of the invention.

It should be noted that the features described by reference to particular figures and at different points in the description may be used in combinations other than those particularly described or shown. All such modifications are encompassed within the scope of the invention as set forth in the following claims.

Claims

1. A portable communication device for use with a network, the portable communication device comprising: a) memory means for storing network search interval data derived from the expected availability of a network and representing an interval to elapse before a search for the network is to be To initiated; and b) network search means, coupled to the memory means, for intermittently searching for the network, wherein the network search means is configured to use the network search interval data to vary the interval between successive searches for the network.

2. A portable communication device according to claim l, further comprising: c) interval assessment apparatus, coupled to the memory means, the interval assessment apparatus being configured to: (i) receive data representing the location of the portable communication device; (ii) receive network coverage data representing the coverage of a network in the vicinity of the portable communication device; (iii) use the data representing the location of the portable communication device and the network coverage data to calculate a network search interval; and (iv) output network search interval data to the memory means.

3. A portable communication device according to claim 2, wherein the interval assessment apparatus is s configured to use data representing the location of the portable communication device at the time of the last network search.

4. A portable communication device according to any lo of the preceding claims, further comprising location determination means, coupled to the memory means, for determining the location of the portable communication device and outputting data representing the location of the portable communication device.

5. A portable communication device according to claim 4, wherein the location determination means is configured to use network assistance over a communication channel establishable between the portable communication device and a network to determine the location of the portable communication device.

:5

6. A portable communication device according to claim 1, further comprising: c) interval assessment apparatus, coupled to the memory means, the interval assessment apparatus being configured to: (i) receive entry interval data representative of the estimated time of arrival of the portable communication device in a location of expected network coverage; (ii) use the entry interval data to calculate network search interval data; and - 18 (iii) output the network search interval data to the memory means.

7. A portable communication device according to claim 6, further comprising prediction means, coupled to the interval assessment apparatus, configured to: (i) receive location data representative of the location of the portable communication device at a plurality of intervals; lo (ii) receive network coverage data representing the coverage of a network; (iii) use the location data and the network coverage data to calculate entry interval data representing the estimated time of arrival of the portable communication device in an area of network coverage; and (iv) output the entry interval data for use by the interval assessment apparatus.

JO

8. A portable communication device according to claim 7, wherein the prediction means is further configured to use the location data and knowledge of the time instances when the location data was determined to determine an approximate trajectory Is of the portable communication device and use the approximate trajectory in conjunction with the network coverage data to calculate the entry interval data.

9. A portable communication device according to any of claims 2 to 8, wherein the interval assessment apparatus is further configured to adjust the calculated network search interval data if the calculated network search interval exceeds a maximum value.

10. A portable communication device according to any of claims 2 to 9, wherein the interval assessment apparatus is further configured to adjust the calculated network search interval data if the i calculated network search interval is less than a minimum value.

11. A portable communication device according to any lo of claims 2 to 10, wherein the interval assessment apparatus is configured to receive network coverage data over a communication channel establishable between the portable communication device and a network.

12. A portable communication device according to any of claims 2 to 10, wherein the memory means is configured to store network coverage data.

JO

13. Interval assessment apparatus for determining a variable network search interval for use by a portable communication device in varying the time between searches for a preferred network when the portable communication device is not registered :5 with the preferred network, the interval assessment apparatus comprising: ' a) memory means for storing network coverage data L representing the coverage of a network at a plurality of locations; b) output means for outputting network search interval data for transmission to a portable communication device; and c) a processor, coupled to the memory means and to; the output means, the processor configured to: ; (i) receive location data representing the location of a portable communication device; (ii) use the location data and network coverage data to determine a location dependent network search interval for a portable communication device; and (iii) output the location dependent network search interval for transmission to a portable communication device.

14. Interval assessment apparatus according to claim 13, further comprising location determination means, coupled to the processor, configured to determine the location of the portable communication device in conjunction with location assistance data originating from the portable communication device and to output the location data to the processor.

JO

15. Interval assessment apparatus according to either claim 13 or claim 14, wherein the interval assessment apparatus is hosted remotely from a portable communication device.

:5

16. Interval assessment apparatus according to claim 15, wherein the remotely hosted interval assessment apparatus and a portable communication device are configured to communicate data over a communication channel establishable between the JO portable communication device and a roaming partner network to the preferred network.

17. Interval assessment apparatus according to any of claims 13 to 16, wherein the interval assessment apparatus is located on a preferred network and is accessible by a portable communication device via a communication channel establishable between the portable communication device and a roaming partner network to the preferred network.

18. A method of determining a variable network search interval for use by a portable communication device to control initiation of a search for a preferred network, the method comprising the steps lo of: a) storing network search interval data derived from the expected availability of a preferred network and representing an interval to elapse before a search for the preferred network is to be initiated; b) using the network search interval data to adjust the interval between successive searches for the preferred network.

lo

19. A method according to claim 18, further comprising the preliminary steps: (i) receiving data representing the location of a portable communication device; (ii) receiving network coverage data :5 representing the coverage of a network in the vicinity of the portable communication device; (iii) using the data representing the location of the portable communication device and the network coverage data to calculate a network search interval; and (iv) outputting network search interval data for subsequent storage.

20. A method according to claim 19, further comprising the preliminary step of determining the location of the portable communication device and outputting data representing the location of the portable communication device. t s

21. A method according to claim 18, further comprising the preliminary steps of: (i) receiving entry interval data representative of the estimated time of arrival: of the portable communication device in a location lo of expected network coverage; (ii) using the entry interval data to calculate l network search interval data; and l (iii) storing the network search interval data. I Is

22. A method according to claim 21, further comprising the preliminary steps of: (i) receiving location data representative of the location of the portable communication device] at a plurality of intervals; lo (ii) receiving network coverage data representing the coverage of a network; (iii) using the location data and the network coverage data to calculate entry interval data r representing the estimated time of arrival of the as portable communication; and (iv) storing the entry interval data.

23. A method of determining a variable search ' interval for use in a portable communication L device to control initiation of a search for a ' preferred network, the method substantially as 3 hereinbefore described with reference to any of figures 2 to 6.

24. A portable communication device substantially as hereinbefore described with reference to any of figures 2 to 6. :

25. A mobile terminal substantially as hereinbefore described with reference to any of figures 2 to 6.