GB2395621A

GB2395621A - Cellular network acquisition method and apparatus

Info

Publication number: GB2395621A
Application number: GB0226979A
Authority: GB
Inventors: Richard Ormson; Frederic Gabin; Darioush Downer; Osamu Yamashita; Nigel Legg
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2002-11-19
Filing date: 2002-11-19
Publication date: 2004-05-26
Anticipated expiration: 2022-11-19
Also published as: GB2395621B; GB0226979D0

Abstract

A method of finding a suitable network and cell in which to establish communications over that network comprises, monitoring signals from a plurality of cells 24, ranking cells in order according to a monitored signal characteristic 26, selecting the highest-ranked cell, comparing network information relating to that cell with information identifying prohibited networks 28 and, if the cell is in a prohibited network, identifying cells in the prohibited network neighbouring the cell 36, removing the cell and the neighbouring cells from the ranking 38, and selecting the new highest-ranking cell 40.

Description

239562 1

CELLULAR NETWORK ACQUISITION

METHOD AND APPARATUS

The present invention relates to a method and apparatus for use in 5 network acquisition for cellular communications devices.

Cellular communications devices such as cell phones, have become increasingly popular and widely adopted and in many instances have become the prime means of communication both for business and domestic 1 0 requirements.

As such usage becomes more widespread, potentially disadvantageous and limiting features of such devices become more apparent. For example, when a cell phone is first turned on, an acquisition procedure needs to be 15 conducted so that the cell phone can acquire the appropriate communications network and subsequently take part in a communications exchange over that network. The period between turning the cell phone on and actually acquiring the network does not generally go unnoticed by the user and comprises dead time as far as the user is concerned since no other operations over and above 20 network acquisition are conducted during that period. The longer the time period required to acquire the network, the more likely this period is to be noticed by the user and so as to lead to potential irritation.

Also, network acquisition procedures require the cell phone handset to expend a significant amount of power relative to power requirements arising merely for 25 communication procedures.

Indeed, in view of the different mobile communication modes that have arisen, and the subsequent requirement for cell phone handsets to offer dual mode, or indeed multimode, operability, it will become increasingly necessary for each 30 handset to search on more than one mode. Thus potential delays in network acquisition, and related user irritation, could become more frequently experienced. As explained further below network acquisition requires a search

through a set of frequencies - generally defined by a frequency band in an attempt to identify the most suitable cell of a network. With dual mode operation, there will be multiple sets of frequencies to search through in order not only to find the most suitable cell, but also the most suitable network given 5 the at least dual mode operability of the handset.

The present invention seeks to provide for a network acquisition method and apparatus which exhibits advantages over known such methods and apparatus. According to one aspect of the present invention there is provided a method of network acquisition for a cellular radio communications device comprising receiving signals from a plurality of cells, ranking the cells in order of suitability for acquisitions on the basis of a characteristic of the signals 15 received, selecting the highest ranked cell and comparing network information to which the selected cell belongs with network information identifying prohibited networks for the said communications device and, if the selected cell belongs to a prohibited network, including the further step of identifying cells which are neighbours to the selected cell on the prohibited network and 20 removing the neighbouring cells from the ranked cells prior to selecting a next highest ranked cell for attempted acquisition.

Advantageously, the characteristic of the received signals comprises signal strength, or a derivative thereof.

In one particular embodiment, the network information identifying prohibited networks is obtained from the Subscriber Identify Module (SIM) which carries information concerning the user of the device and the network(s) to be accessed. Once the final step of removing neighbouring cells to the 30 selected cell from the ranked cells and then selecting the next highest ranked cell is completed, network information associated with the said next highest ranked cell is likewise compared with network information identifying prohibited

networks and the related method steps repeated until such time as the device finds an appropriate cell to camp on.

The invention is particularly advantageous in that, by seeking to remove 5 the cells that neighbour an already identified problematic cell, from further processing during network acquisition, the time taken to acquire a network can be advantageously decreased, and the associated power requirements and the dead time experienced by the user can likewise be reduced as can the potential levels of irritation for the user.

The method can advantageously be employed in relation to an at least dual mode cellular radio communications device wherein potential time and power savings can prove important in view of the additional processing that might be required when discriminating between which of the two possible 15 modes is to be adopted for a communication exchange.

In accordance with a further arrangement, the method takes account of the fact that networks invariably use frequencies in blocks. If, there is a neighbour list containing frequencies A and B. both in the same band, one 20 band being GSM 900, another band being GSM1800 and so on, then it can be arranged that all frequencies from A to B are part of the incorrect network an can therefore be ignored.

According to another aspect of the present invention there is provided a 25 cellular radio communications device including means for receiving signals from a plurality of cells and for ranking cells in order of suitability of acquisition on the basis of characteristics of the signals received, and further including means for selecting the highest ranked cell and comparing network information to which the selected cell belongs with network information identifying 30 appropriated networks for the said communications device, and arranged such that, if the selected cell is determinate as belonging to a prohibited network, identifying cells which are neighbours to the cell selected on the prohibited

network and removing the neighbouring cells from ranked cells prior to selecting a next highest ranked cell for attempted acquisition.

The invention is described further hereinafter, by way of example only, 5 with reference to the accompanying drawings in which: Fig. 1 is a flow diagram illustrating network acquisition steps as currently known in the art; and 10 Fig. 2 is a flow diagram illustrating network acquisition steps according to an embodiment of the present invention.

As will be appreciated under the 3GPP specification a handset is

required to search one entire radio technology (RAT) at a time. The relative 15 priority of RATsis set within the handset and so in a dual mode GSM/UMTS handset, an initial search of GSM or UMTS will be undertaken and the process will only look at the second RAT during initial selection if no suitable cells are found on the first RAT.

20 The initial search is a simple one, using signal strength, or a derivative thereof the cells are ranked in order of signal strength and the cell at the top of the list is assessed for suitability. This involves firstly checking against any prohibited networks listed in the SIM, and assuming this test is passed, attempting to camp on the cell. Either one of these two operations can result 25 in the handset determining that the cell is part of a network that is not allowed to use.

When a cell is found to be part of a prohibited network, the normal procedure is to defer to the cell with next highest signal strength and assess 30 that for suitability. This is potentially inefficient as this next cell could also be part of the prohibited network located.

Turning therefore to Fig. 1, there is illustrated a flow chart of the currently known procedures.

At step 10, the signal strength of the various signals coming from the 5 variety of cells is measured in the handset.

At step 12, the cells from which signals have been received are ranked in order of suitability based upon the signal strength values determined in step 10: the strongest signal leading to the highest ranked cell.

In step 12, the highest ranked cell is selected and, at step 14, the network information identifying the network with which that selected cell is associated is compared with network information within the SIM to determine whether or not the network associated with the selected cell is in fact a 15 prohibited network insofar as the particular communications device is concerned. If the network is found not to be prohibited, the process continues along 16 to step 18, and subsequent steps (not shown), relating to the attempt of the 20 device to camp on the selected cell and so acquire the related network.

However, if the information in the SIM indicates that the network associated with the selected cell is in fact prohibited to that particular device, then the procedure continues along 20 to step 22 which determines that the 25 next highest ranked cell from the ranking determined in step 12 be selected and it related network information be compared with that in the SIM in accordance with step 14.

As will be appreciated, insofar as the networks associated with the 30 ongoing selected cells are prohibited the process continuous in the loop represented by 14, 20, 22 and, irrespective of the number of times the procedure progresses around that loop, such repeated processing represents

a disadvantageous delay and also lead to disadvantageous power consumption. It is therefore proposed that, when a cell of a prohibited network is 5 found, the list of neighbours for that cell is read and those frequencies are removed from the list of cells to be assessed. This will prevent repeated attempts to camp onto the same incorrect network. The details of the cell initially found should be retained in the normal way to allow emergency calls if an allowed network cannot be found.

Turning now to Fig. 2, there is illustrated a procedure according to an embodiment of the present invention.

Here again, the strengths of the signals obtained from a variety of cells 15 is measured at step 24 and, at step 26, the cells are ranked in order according to the strength of their related signals.

At step 28, the highest ranked cell also found in step 26, and more particularly the information identifying the network associated therewith, is 20 compared with network information stored in the SIM and which indicates prohibited networks for the particular communications device. A particular network can also be identified as prohibited when an attempt is made to camp on to it. Thus, as an alternative, step 28 can comprise a step to camp onto a particular network and, should this fail, then the neighbours should be 25 removed in the same manner as discussed below when the SIM is found to provide identification of a prohibit network.

If the network associated with the selected cell is not prohibited, and the procedure continues, as with Fig. 1, via 30 to step 32, and subsequent steps 30 (not shown), at which the device attempts to camp on the selected cell.

However, if the network associated with the selected cell is prohibited, the method proceeds via 34 to step 36 at which cells from neighbours to the selected cell and on the same network are identified and, at step 38, removed from the list of ranked cells obtained at step 26.

The procedure then proceeds to step 40 where, of the remaining cells, the next highest ranked is selected and the procedure then continues via 42 to repeat step 28 in order to determine if the network with which the newly selected cell is associated is prohibited in accordance with the network 10 information stored in the SIM.

The procedure is then repeated as necessary.

However, as will be appreciated the loop provided by 34, 36, 38, 40 and 15 42 represents a means for determining that when the process next returns via 42 to step 28, it is more likely that the selected cell will be associated with the network not prohibited by information within the SIM.

This can lead to an advantageous time and power savings as compared 20 with methods according to the current art.

Thus, the initial acquisition of a network can be accelerated, and the invention can also exhibit power saving aspects, and lead to a user experiencing less irritable dead time subsequent to turning on the mobile 25 communications device.

Claims

1. A method of network acquisition for a cellular radio communications device comprising receiving signals from 5 a plurality of cells, ranking the cells in order of suitability for acquisitions on the basis of a characteristic of the signals received, selecting the highest ranked cell and comparing network information to which the selected cell belongs with network information identifying prohibited 10 networks for the said communications device and, if the selected cell belongs to a prohibited network, including the further step of identifying cells which are neighbours to the selected cell on the prohibited network and removing the neighbouring cells from the ranked cells prior to selecting 15 a next highest ranked cell for attempted acquisition.

2. A method as claimed in Claim 1 wherein the said characteristic comprises signal strength.

20

3. A method as claimed in Claim 1, wherein the said characteristic comprises a derivative of signal strength.

4. A method as claimed in Claim 1, 2 or 3, wherein the network information identifying prohibited networks is 25 retrieved from the SIM associated with the device.

5. A method as claimed in any one or more of Claims 14, and including the step of comparing network information to which the selected next highest ranked cell belongs with 30 network information identifying the prohibited networks.

6. A method as claimed in any one or more of Claims 1-5, and arranged for use with an at least dual mode cellular communications device.

5

7. A method as claimed in any one or more of Claims 1-6, and including the step of retaining information relating to the cells identified as associated with prohibited networks.

8. A method as claimed in any one ore more of the 10 preceding claims wherein the identification of neighbouring cells on the prohibited network is conducted on the basis of identifying a range of frequencies between two frequencies contained in a neighbouring list.

15

9. A cellular radio communications device including means for receiving signals from a plurality of cells and for ranking cells in order of suitability of acquisition on the basis of characteristics of the signals received, and further including means for selecting the highest ranked cell and 20 comparing network information to which the selected cell belongs with network information identifying appropriated networks for the said communications device, and arranged such that, if the selected cell is determinate as belonging to a prohibited network, identifying cells which 25 are neighbours to the cell selected on the prohibited network and removing the neighbouring cells from ranked cells prior to selecting a next highest ranked cell for attempted acquisition.

30

10. A cellular communications device as claimed in Claim 9 is to operate in accordance with the method steps of any one or more of Claims 2-8.

A method of network acquisition for a cellular radio communication device substantially as hereinbefore described with reference to and as illustrated in Fig. 2 of 5 the accompanying drawings.

12. A cellular communication device substantially as hereinbefore described with reference to, and as illustrated, in Fig. 2 of the accompanying drawings.

Amendments to the claims have been filed as follows ll Claims 1. A method of network acquisition for a cellular radio communications device comprising receiving signals from 5 a plurality of cells, ranking the cells in order of suitability for acquisitions on the basis of a characteristic of the signals received, selecting the highest ranked cell and comparing information relating to the network to which the selected cell belongs with network information identifying 10 prohibited networks for the said communications device and, if the selected cell belongs to a prohibited network, including the further step of identifying cells which are neighbours to the selected cell on the prohibited network and removing the neighbouring cells from the ranked cells 15 prior to selecting a next highest ranked cell for attempted acquisition. 2. A method as claimed in Claim 1 wherein the said characteristic comprises signal strength.

4. A method as claimed in Claim 1, 2 or 3, wherein the 25 network information identifying prohibited networks is retrieved from the SIM associated with the device.

5. A method as claimed in any one or more of Claims 1-4, and including the step of comparing network information to 30 which the selected next highest ranked cell belongs with network information identifying the prohibited networks.

r 6. A method as claimed in any one or more of Claims 1-5, and arranged for use with an at least dual mode cellular communications device.

5 7. A method as claimed in any one or more of Claims 1-6, and including the step of retaining information relating to the cells identified as associated with prohibited networks.

15 9. A cellular radio communications device including means for receiving signals from a plurality of cells and for ranking cells in order of suitability of acquisition on the basis of characteristics of the signals received, and further including means for selecting the highest ranked cell and 20 comparing information relating to the network to which the selected cell belongs with network information identifying appropriated networks for the said communications device, and arranged such that, if the selected cell is determinate as belonging to a prohibited network, 25 identifying cells which are neighbours to the cell selected on the prohibited network and removing the neighbouring cells from ranked cells prior to selecting a next highest ranked cell for attempted acquisition.

30 10. A cellular communications device as claimed in Claim 9 is to operate in accordance with the method steps of any one or more of Claims 2-8.

11. A method of network acquisition for a cellular radio communication device substantially as hereinbefore described with reference to and as illustrated in Fig. 2 of 5 the accompanying drawings.