GB2396526A

GB2396526A - Mobile station and method for selecting a radio frequency for call set-up

Info

Publication number: GB2396526A
Application number: GB0229542A
Authority: GB
Inventors: Mohamed Afkir
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2002-12-19
Filing date: 2002-12-19
Publication date: 2004-06-23
Anticipated expiration: 2022-12-19
Also published as: GB0229542D0; GB2396526B; AU2003283438A1; EP1582080A1; WO2004057889A1

Abstract

A mobile station (2), for use in a communication system comprising a plurality of cells (10), the mobile station being adapted to communicate with other mobile stations (4, 6) via a radio link to a base station (8), the mobile station (2) comprising: a controller (20); user interface circuitry (34,42,44); a first memory (50) divided into a plurality of areas (52,54,56,58) and adapted, in use, to store (52) the communication frequency (f) in use by the mobile station (2) in the present serving cell (10) and store records (54, LL) of the communication frequencies (f) used in previous serving cells; a second memory (60); means (20) for transferring the records from first memory (50) into second memory (60), thereby creating accumulated totals of the records, which are returned to the first memory; the mobile station (2) accessing different parts of the first memory (50) in a pre-determined sequence, in order to select one or more frequencies on which to attempt to set up a communication link with a base station. The invention allows rapid call set-up in a mobile communications network.

Description

1 2396526

Mobile Station and Method for selecting a radio freouencv for call shotgun Technical Field

The present invention relates to the field of mobile radio communication

systems. Backaround

Portable and mobile radios are normally arranged to communicate with one another through a base station. The radios and the base station are referred to as a Personal Mobile Radio (PMR) system. An example of such a system is the European TETRA PMR system. Mobile telephone systems have an analogous 1 5 design.

Several base stations may be linked together to form a network. A radio or phone can therefore communicate with any other that is within communication range of one of the base stations of the network.

In both mobile radio and mobile phone systems, the system's coverage area is normally subdivided into 'cells'. Each cell is a region served by a base station. A radio may communicate with another radio in the same or a different cell, via the . base station.

À "'' Some PMR radios are capable of communicating with other radios directly, In, without the communication passing through a base station. This mode of .. operation is referred to as Direct Mode Operation. Such communication is also À likely to be used by third and fourth generation communication systems, a 30 referred to as '3G' and '4G' systems, in addition to cellular communication.

. Henceforth the term 'mobile station' (MS) will be used to describe a portable or mobile radio or telephone that is capable of communication via a cellular communication system. Thus the term MS will cover portable- or mobile PMR

radios, mobile telephones, and 3G or 4G communication devices, wirelessly linked lap-top computers, or wirelessly linked personal digital assistants (PDA).

Figure 1 illustrates the general scheme of a PMR radio system 10. Portable 5 radios 2, 4 and 6 of figure 1 can communicate with a base station 8. Radios 2, 4 and 6 could equally well be mobile radios mounted in vehicles. Each of the radios shown in figure 1 can communicate through base station 8 with one or more other radios. If radios 2, 4 and 6 are capable of direct mode operation, then they may communicate directly with one another or with other radios, 10 without the communication link passing through base station 8. Cellular mobile phone systems, and 3G and 4G systems, have the same general arrangement as shown in Figure 1.

Portable and mobile radios are also known which can place calls through a base 15 station to telephone subscribers. These calls may be from the radio to either a POTS' landline telephone, or a mobile telephone.

A mobile station in a radio communication system will normally be able to place or receive a call through the base station that is nearest to its current location.

20 To enable movement between cells, each mobile station must clearly be able to establish communication with more than one base station. As base stations do not all operate on the same frequency, the mobile station must be able to communicate on a number of different frequencies.

25 There is a need to make operation of the portable or mobile radio simple. There is, for example, a particular need to reduce the time required for a user to set up a call to another radio or a telephone subscriber. This may be of particular advantage to public safety users of portable or mobile radios, and of great appeal to other users. Thus there is a need to minimise the time required for a 30 mobile station to set up a communication link on the frequency appropriate to the nearest base station.

Summarv of the Invention In accordance with the invention, a mobile station comprises the features of appended claim 1. Further in accordance with the invention, a method for a 5 mobile station to select a frequency with which to attempt to set up a call may comprise the steps of either of appended claims 11 or 12. Further advantageous features and steps of the invention are detailed in the dependent claims. 10 The invention allows rapid call set-up in a mobile radio communications system.

The invention may be of particular advantage for a mobile station that is operated in locations which were not foreseen before first use of the station.

Brief description of the drawings

Figure 1 illustrates an arrangement of portable and/or mobile radios and a base station. Figure 2 illustrates a mobile station in accordance with the present invention.

Figure 3 illustrates the contents of a first memory of a mobile station in accordance with the present invention.

À. À À 1. e. I.. a. Figure 4 illustrates the contents of a second memory of a mobile station in Àe 25 accordance with the present invention.

Àe ÀÀ À À. :... Detailed description of the Preferred embodiment

Àe À Figure 2 illustrates a mobile station in accordance with the present invention.

À À À À 30 The mobile station 2 of figure 2 may be either a portable- or a mobile (PMR) radio. The mobile station 2 may also be a mobile telephone, a 3G or 4G communication device, a wirelessly linked lap-top computer, or a wirelessly linked personal digital assistant (PDA). In use, the mobile station would typically be part of a cellular communication system, such as that shown in figure 1. The

cellular system would comprise at least one base station 8, and at least one mobile station 2.

The mobile station 2 of figure 2 can transmit speech from a user of the mobile 5 station. The mobile station comprises a microphone 34, which provides a signal for transmission by the mobile station. The signal from the microphone is transmitted by transmission circuit 22. Transmission circuit 22 transmits via switch 24 and antenna 26.

10 The transmitter 2 also has a controller 20, a RAM 50 and a permanent read-only memory 60. Controller 20 may be a microprocessor. RAM 50 provides a first memory. RAM 50 contains various different regions of memory, which are explained below in connection with figure 3. Permanent memory 60 provides a second memory, and may be a non-volatile Electrically Erasable Programmable 15 Read Only Memory (EEPROM). ROM 60 contains various different regions of memory, which are explained below in connection with figure 4.

The mobile station 2 of figure 2 also comprises a display 42 and keypad 44, which serve as part of the user interface circuitry of the mobile station. At least 20 the keypad 44 portion of the user interface circuitry is activatable by the user.

Voice activation of the mobile station, or other means of interaction with a user, may also be employed.

À. À À Signals received by the mobile station 2 are routed by the switch to receiving À - À 25 circuitry 28. From there, the received signals are routed to controller 20 and audio processing circuitry 38. A loudspeaker 40 is connected to audio circuit 38.

. Loudspeaker 40 forms a further part of the user interface.

Àe I A data terminal 36 may be provided. Terminal 36 would provide a signal À. .: 30 comprising data for transmission by transmitter circuit 22, switch 24 and antenna 26.

The mobile station 2 of the invention is suitable for use in a communication system, the communication system comprising a plurality of cells 10. An

s example of such a system is a TETRA network. The mobile station 2 is adapted to communicate with other mobile stations 4, 6 via a radio link to a base station 8 in a cell 10.

5 Figure 3 shows that the first memory 50 is divided into a plurality of areas 52,54,56,58.

Figure 4 shows the subdivision of the second memory 60 into a plurality of areas 62,64,66.

In use of mobile station 2, the first memory 50 is adapted to store the communication frequency f in use by the mobile station 2 in the present serving cell 10. Mobile station 2 uses a first area 52 of the first memory to do this, in what is marked as list 'L1' on figure 3.

The mobile station 2 also stores records of the communication frequencies f that the mobile station 2 has used in previous serving cells. These are stored in a second area 54 of the first memory 50. These records relate to the amount of usage of each frequency by the mobile station, typically since it was last 20 switched on. The frequencies stored are any frequencies with which the radio has communicated recently with a base station 8 of the cellular communications system 10. The records in second area 54 are a 'local list' LL.

In a preferred embodiment, second area 54, may record in list LL the number n 25 of occasions on which the mobile station connects to a base station 10 using a particular frequency f, and/or the total time t of connection using that frequency...DTD: The controller 20 transfers the records from the second area of the first memory . À 50 into the second memory 60. This transfer creates accumulated totals of the 30 records, which the controller 20 may calculate as part of the transfer. The accumulated totals are held in area 64 of second memory 60, shown as list 'L2 (Updated)' in figure 4. The frequencies may be stored as accumulated totals that are ranked in order by decreasing number n of occasions and/or total time t of connection.

Since the second memory 60 is non-volatile, these accumulated records remain available even after the mobile station has been switched off. They are therefore available to the mobile station, e.g. on switching on the mobile station 5 at the beginning of a work shift.

The accumulated totals from area 64 of the second memory are returned by controller 20 to the third area 56 of the first memory 50. This occurs typically when the radio is switched on.

However, prior to first use of mobile station 2, area 64 of the second memory 60 may contain an initial list of frequencies. This list may then be transferred immediately to the third area 56 of first memory 50, as soon as the mobile station is first used. The initial list typically has a number of frequencies, for 15 example 32, stored in it. These frequencies are those that the user or the provider of the mobile station believed would be useful in the region where the mobile station was likely to be used. Such a list has been provided in prior art

mobile communication devices. Because it is set up before first use, such an initial list has the disadvantage that it will be of limited value if the mobile station 20 moves out of the area in which the user had initially expected to use it. It will also become out of date if, for example, cells are subdivided as network load grows. ÀÀ In a preferred embodiment, the initial list in area 64 of second memory 60 À 25 contains pre-programmed frequencies, ranked in descending order of the À.. probability of the mobile station being able to make a connection on each lo frequency. In this case, the means 20 for transferring the records from area 54 of the first memory 50 into the second memory 64, in use of the mobile station, Àe are adapted to overwrite the pre-programmed frequencies, the lowest ranked À. À À 30 pre-programmed frequencies being over-written first.

The first memory 50 also has a fourth area 58. The fourth area stores a predetermined frequency of one base station 10.

Area 62 of second memory 60 may store the most recent value of the frequency held in list L1, from first area 52 of the first memory. Area 66 of second memory 60 may store the value in list L3, from fourth area 58 of the first memory.

Because second memory 60 is permanent, it will retain the values held in areas 5 62 and 66, even when the mobile station is powered down. These values can then be transferred respectively into areas 52 and 58 of first memory 50, as soon as the mobile station is powered up again. Controller 20 may perform this transfer. 10 FreouencY selection In use, mobile station 2 accesses different parts of the first memory 50 in a pre determined sequence, in order to select one or more frequencies on which to attempt to set up a communication link with a base station 8.

In a preferred embodiment of the invention, the mobile station selects first the frequency stored in first region 52 of first memory 50. This will be the frequency of the base station with which the mobile station has most recently been in communication. If attempts to use the frequency in region 52 to set up a call fail, then the mobile station will attempt to make communication using the first frequency in the third area 56 of first memory 50. The mobile station will then use further frequencies from third area 56, as required, to try and set up a call.

À À... À.. If the mobile station is unable to set up a communication with any base station ale. using frequencies from the first 52 and third 56 areas of the first memory, then it tries the single frequency stored in the fourth area 58 of the first memory.

À.e . À. À À 30 The fourth area 58 of the first memory may store only one frequency in its list L3'. From this frequency, the mobile station can calculate all possible frequencies that the radio communication system has available for communication with base stations. The mobile may be adapted to try further frequencies successively, the further frequencies being spaced from the

frequency stored in the fourth area by integer multiples of a fixed frequency increment. This fixed frequency increment may be preferably about 25kHz, a typical channel spacing.

5 So, when selecting frequencies in order to attempt to set up a communication link with a base station, the controller 20 of the mobile station is adapted to access the frequencies from the first memory in the sequence: (i) the frequency stored in the first area 52 of the first memory 50; then 10 (ii) access successively the frequencies f stored in the third area of the first memory 56, in the said decreasing order; and then (iii) the frequency stored in the fourth area 56.

Example of frequency selection from a Motorola radio The following sequence is used by one Motorola radio product: 1. Try frequency from L1. If contact is not made with a Base Station (BS), then go to step 2.

2. Try all the frequencies from L2, one by one. There may be up to 32 20 frequencies. If no BS found, then go to step 3.

3. List L3 specifies a frequency from which to start, for example 420.000 Mhz. It also specifies a number of frequencies, e.g. 200. The radio will try the first 32 frequencies from 420.000 Mhz. If no BS found, then: À À-Try L1, if no BS found, then 25 -Try the second 32 frequencies of L3, if no BS found then À.. -Try L1, if no BS found, then -Try the third 32 frequencies of L3, if no BS found then......

and repeat this cycle, until the end of L3. If no BS found then go to step 4.

. 4. Go to a further list L4. This frequency list is similar to L3, having a frequency . 30 from which to start, and the number of frequencies. The purpose of L4 is to have another point at which to start. This may start at a small offest frequency from L3, i.e. less than the channel spacing. It will allow the radio to search the full range of frequencies. The sequence for searching is similar to that in step 3 above.

General features The controller 20 may transfer the records from the second area 54 of first 5 memory 50 into the second memory 60, under user control. This may be by means of the user interface circuitry 34,42,44. However, the controller 20 may transfer the records automatically from the second area 54 of first memory 50 into the second memory 60. This transfer may be at times that are pre-

programmed into the codeplug of the mobile station, and/or when the user 10 switches off the mobile station. Conventionally, the codeplug is part of the second memory 60. The predetermined times may be, for example, every 24 hours, or after any 6 hours of use.

Methods of the invention The mobile station 2 selects a frequency with which to attempt to set up a call via a radio link to a base station 8 in a cell 10 of a cellular communication network, by: a) providing both a first memory 50 divided into a plurality of areas 52,54,56,58, 20 and a second memory 60; b) in use of the mobile station: (i) storing 52, in the first memory, the communication frequency f in use by I. the mobile station in the present serving cell; and À À- (ii) storing 54, in the first memory, a local list LL of records of the 25 communication frequencies f that the mobile station has used in previous . ..: serving cells; À ale. c) transferring the local list records LL from the first memory into the second memory, thereby creating accumulated totals of the records, and returning the accumulated totals to the first memory; and À - À 30 d) accessing different parts 52, 56 of the first memory in a predetermined sequence, in order to select one or more frequencies on which to attempt to set up a communication link with a base station.

In an alternative embodiment of the invention, the mobile station 2 selects a frequency with which to attempt to set up a call, by: a) storing, in a first area 52 of the first memory 50, the communication frequency in use by the mobile station in the present serving cell 10; 5 b) storing, in a third area 56 of the first memory 50, communication frequencies that the mobile station has used in previous serving cells, the communication frequencies being arranged in an ordered list, the communication frequencies and the order of the list being obtained from the second memory 60; c) the mobile station accessing in succession the first area 52 and then the 10 third area 56 of the first memory, in order to select frequencies with which to attempt to set up a communication link with a base station.

. A.- here À. À À À e. À -.. À À.e À Àe À À e À À-

Claims

1. A mobile station (2) for use in a communication system, the communication system comprising a plurality of cells (10), whereby the mobile station (2) is 5 adapted to communicate with other mobile stations (4, 6) via a radio link to a base station (8) in a cell (10), the mobile station (2) comprising: a) a controller (20); 10 b) user interface circuitry (34,42,44); c) a first memory (50), the first memory being divided into a plurality of areas (52,54,56,58);

15 d) a second memory (60); e) the first memory (50) being adapted, in use of the mobile station (2), to: (i) store (52) the communication frequency (0 in use by the mobile station (2) in the present serving cell (10); and 20 (ii) store records (54, LL) of the communication frequencies (A that the mobile station (2) has used in previous serving cells; . fly means (20) for transferring the records from the first memory (50) into the À Àsecond memory (60), thereby creating accumulated totals of the records, which 25 are returned to the first memory; À - À À - À Àe À ale. 9) the mobile station (2) being adapted, in use, to access different parts of the first memory (50) in a pre-determined sequence, in order to select one or more À. frequencies on which to attempt to set up a communication link with a base 30 station.

2. A mobile station (2) in accordance with claim 1, wherein: a) in use of the mobile station, the first memory (50) is adapted to store, in a first area (52), the communication frequency 0) in use by the mobile station (2) in the present serving cell (10), and is adapted to store, in a second area 5 (54, LL), records of the number (n) of occasions on which the mobile station connects to a base station (10) using a particular frequency (in, and/or the total time (t) of connection using that frequency (fl; and b) the second memory (60) is adapted to store (64) the frequencies (fl, transferred from the second area (54,LL) of the first region, as accumulated 10 totals that are ranked in order by decreasing number (n) of occasions and/or total time (t) of connection.

3. A mobile station (2) in accordance with claim 2, comprising: (a) means (20) for transferring the ranked accumulated totals from the second 15 memory (60) back to a third area (56) of the first memory (50), preferably on switching on the mobile station (2); and (b) when selecting frequencies with which to attempt to set up a communication link with a base station (10), the controller (20) of the mobile station is adapted to, in sequence: 20 (i) access the frequency stored in the first area (52) of the first memory (50); and then (ii) access successively the frequencies (in stored in the third area (56) of the , first memory, in the said decreasing order.

- 25

4. A mobile station (2) in accordance with claim 2 or claim 3, wherein: A (i) in advance of the first use of the mobile station, the second memory (64) contains pre-programmed frequencies, ranked in descending order of the probability of the mobile station being able to make a connection on each frequency; and À. - .: 30 (ii) the means (20) for transferring the records from the first memory (50) into the second memory (64) are adapted to overwrite the pre-programmed frequencies, the lowest ranked pre-programmed frequencies being over-

written first.

5. A mobile station (2) in accordance with any previous claim, wherein the first memory (50) is random access memory (RAM), and the second memory (60) is permanent memory, preferably non-volatile Electrically Erasable Programmable Read Only Memory (EEPROM).

6. A mobile station (2) in accordance with any previous claim, wherein the means (20) for transferring the records from the first memory (50) into the second memory (60) are activatable by the user, by means of the user interface circuitry (34, 42,44).

7. A mobile station (2) in accordance with any of claims 1-5, wherein the means (20) for transferring the records from the first memory (50) into the second memory (60) are adapted to transfer the records automatically, at times pre programmed into the codeplug of the mobile station and/or when the user 15 switches off the mobile station, the codeplug being part of the second memory (60).

8. A mobile station (2) in accordance with any previous claim, wherein: (a) in use of the mobile station, the first memory (50) has a fourth area (58), the 20 fourth area storing a predetermined frequency of one base station (10); and (b) when selecting frequencies in order to attempt to set up a communication link with a base station, the controller (20) of the mobile station is adapted to access the frequencies from the first memory in the sequence: (i) the first area (52); then 25 (ii) the third area (56); (iii) the fourth area (58); . c) when the mobile station has unsuccessfully attempted to set up a communication link with a base station using the frequency from the fourth area, the mobile station is adapted to then try further frequencies successively, the À. - .: 30 further frequencies being spaced from the frequency stored in the fourth area by integer multiples of a fixed frequency increment, the fixed frequency increment being preferably 25kHz.

9. The mobile station (2) of any previous claim being a portable- or mobile (PMR) radio, a mobile telephone, a 3G or 4G communication device, a wirelessly linked lap-top computer, or a wirelessly linked personal digital assistant (PDA).

10. A cellular communication system comprising at least one base station (8), and at least one mobile station (2) in accordance with any previous claim.

11. A method for a mobile station (2) to select a frequency with which to attempt 10 to set up a call, the call being via a radio link to a base station (8) in a cell (10) of a cellular communication system, the method comprising: a) providing both a first memory (50), the first memory being divided into a plurality of areas (52,54,56,58), and a second memory (60); b) in use of the mobile station (2): (i) storing (52), in the first memory (50), the communication frequency (f) in use by the mobile station (2) in the present serving cell (10); and (ii) storing (54, LL), in the first memory (50), records of the 20 communication frequencies 0) that the mobile station (2) has used in previous serving cells; . c) transferring the records from the first memory (50) into the second memory À À- (60), thereby creating accumulated totals of the records, and returning the Àe 25 accumulated totals to the first memory; À. À À I. d) accessing different parts of the first memory (50) in a pre-determined sequence, in order to select one or more frequencies on which to attempt to set Àe . up a communication link with a base station.

. .: 30

12. A method for a mobile station (2) to select a frequency with which to attempt to set up a call, the call being via a radio link to a base station (8) in a cell (10) of a cellular communication system, the method comprising: 5 a) the mobile station (2) storing, in a first area (52) of a first memory (50), the communication frequency in use by the mobile station in the present serving cell (1 o); b) the mobile station (2) storing, in a third area (56) of the first memory (50), 10 communication frequencies that the mobile station has used in previous serving cells (10), the communication frequencies being arranged in an ordered list, the communication frequencies and the order of the list being obtained from a second memory (60); 15 c) the mobile station accessing in succession the first area of the first memory (50) and then the third area of the first memory (56), in order to select frequencies with which to attempt to set up a communication link with a base station. 20

13. A mobile station (2) substantially as hereinbefore described with reference to, or as illustrated by, any of figures 2 of the drawings.

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