Intelligent network searching for a multi mode phone

A dual or multi mode telephone can be connected to at least one cellular network or at least one cordless network. The telephone continuously monitors system information messages from said at least one cellular network and said at least one cordless network to maintain an idle mode connection. The telephone comprises first memory means for storing cell identification information about the cell in the cellular network concerned covering the telephone, and second memory means for storing cell identification information about the cells in the cellular network where the telephone has been covered by said at least one cordless network. The telephone furthermore comprises means for comparing the present cell identification information with the cell identification information stored in the second memory means, and means for enabling/disabling the cordless part of the telephone in dependence on said comparison.

BACKGROUND OF THE INVENTION
 The invention relates to a dual mode phone capable of establishing a
 connection to at least one cellular network or at least one cordless
 network, said phone continuously monitoring system information messages
 from said at least one cellular network and said at least one cordless
 network to maintain an idle mode connection.
 Users demand long standby times, because they find it cumbersome to have to
 recharge their portable telephone more than a couple of times a week. The
 manufacturers have worked intensely on reducing the energy consumption
 which is of no use to the user. Portable cellular telephones have many
 advantages, as they offer great mobility, which also applies to data
 transmission, good speech quality and good data safety (which applies to
 digital systems in particular).
 If the advantages of cellular networks are to be utilized in office
 environments and the like, this may take place e.g. via cordless systems,
 such as DECT. To avoid having to equip the staff with both a cordless
 telephone and a cellular telephone, it is attempted to integrate the two
 types in a so-called dual mode telephone, where the telephone in idle mode
 (ready to receive ingoing calls and to establish outgoing calls)
 continuously monitors the system information messages of the two networks.
 This requirement of continuous monitoring may have as a result that the
 telephone consumes energy in searching for a network, e.g. the DECT
 network, even though the telephone is outside the area covered by the
 network.
 SUMMARY OF THE INVENTION
 In accordance with this invention there is provided a method for use in
 network searching for a dual or multi mode telephone, capable of
 establishing a connection to at least one cellular network or at least one
 cordless network, said telephone monitoring system information messages
 from said at least one cellular network and/or said at least one cordless
 network to maintain an idle mode connection, said method comprising
 obtaining cell identification information about the cell in the cellular
 network concerned serving the telephone, comparing this cell
 identification information with cell identification information about the
 cells in the cellular network where the telephone is expected to be
 covered by said at least one cordless network, and enabling/disabling the
 cordless part of the telephone in dependence on said comparison.
 The telephone is hereby capable of determining its own position on the
 basis of information from the cellular network and comparing this position
 with a geographical area usually covered by a cordless network. If the
 telephone is outside this area, the cordless part of the telephone is
 automatically disabled.
 This disabling may be indicated to the user so that if he considers the
 disabling to be wrong, it can be manually overruled. The group of cellular
 cells providing cordless coverage can hereby be updated.
 Thus, a dual or multi mode telephone capable of intelligently shutting down
 the paging activity when this serves no purpose is provided.
 The invention also relates to a dual or multi mode telephone capable of
 establishing a connection to at least one cellular network or at least one
 cordless network, said telephone continuously monitoring system
 information messages from said at least one cellular network and said at
 least one cordless network to maintain an idle mode connection, said
 telephone comprising first memory means for storing cell identification
 information about the cell in the cellular network concerned covering the
 telephone, second memory means for storing cell identification information
 about the cells in the network where the telephone has previously been
 covered by said at least one cordless network, means for comparing the
 present cell identification information with the cell identification
 information stored in the second memory, and means for enabling/disabling
 the cordless part of the telephone in dependence on said comparison.
 The invention also relates to a dual mode telephone having means for
 sensing a mechanical interconnection between the telephone and
 predetermined accessory parts for enabling/disabling the cordless part of
 the telephone in dependence on said sensing, thereby overruling the cell
 identification information based enabling/disabling of the cordless part
 of the telephone. The telephone can hereby detect when it is placed e.g.
 in a car kit. The DECT system, e.g., requires that the telephone be moved
 only slowly. If a DECT telephone is placed in a car which begins driving,
 the telephone will be cut off because of fading caused by multi path
 propagation.

DETAILED DESCRIPTION OF THE INVENTION
 The invention will be explained below in connection with a dual mode
 telephone (DMT) for GSM/DECT; these systems, separately and in
 combination, have been or are being standardized under ESTI. GSM is the
 cellular system ensuring almost complete geographical coverage in the
 countries in which the telecommunication companies offer this service. The
 DECT system is usually for in-house use, e.g. in a company whose staff can
 then call internally via the cordless network and externally via the
 switchboard of the company.
 By using the information available from the GSM network it is possible to
 make a relative position determination of the DECT network in relation to
 the GSM network. The structure of cell identification information is
 determined by the GSM standard, and it comprises a mobile country code
 (MCC) identifying the country to which the network and thereby the cell
 belongs, a mobile network code (NC) identifying the network to which the
 cell belongs, a location area code (LAC) identifying an area in the
 network to which the cell belongs, and finally a cell identity (CI)
 identifying the cell within the area in the network to which it belongs. A
 base station system (BSS) or a network area is identified by an address in
 the form of a location area identification (LAI) comprising the address
 codes MCC, MNC and LAC. This address or identification code is unique to
 the network area which comprises a plurality of cells. Adding the cell
 identification code (CI) to the location area identification (LAI) gives a
 cell global identification (CGI) which is likewise unique to the cell.
 This structure is determined for GSM in ETS 300 523, paragraph 4.2.1. This
 information is transferred via the communication taking place between the
 portable terminal and the base station in the form of system information
 when the portable terminal is in idle mode.
 FIG. 2 shows schematically how the cells in the cellular network overlap
 each other. The GSM cells are shown to be hexagonal, but will have fluid
 borderlines in practice, as the network is designed to give satisfactory
 coverage to the greatest possible number of subscribers. This overlap
 between the GSM cells means that the portable terminal/telephone receives
 signals from several base stations at the same time. However, the terminal
 will camp on the cell from which it receives the best signal. The DECT
 cells will typically be defined within a building, as the DECT signals are
 rather vulnerable to fading caused by objects in motion.
 The DECT cells are typically quite small in relation to the GSM cells. The
 distance between a GSM base station and a portable terminal must not
 exceed 32 km, since, otherwise, the signals received from a portable
 terminal cannot be synchronized with the signals from other portable
 terminals. What FIG. 2 shows is that the dual mode telephone can expect
 that there will be DECT coverage if it communicates with the base stations
 in the GSM cells with cell global identification (CGI)=1, 3 and 4. If,
 instead, the dual mode telephone communicates with base stations in other
 cells, it will in general be impossible to have DECT coverage from the
 DECT system concerned.
 Table 1 shows an example of the relationship between DECT system coverage
 and the global cell information code, CGI, for the cells of the cellular
 GSM system, which also give coverage for the cellular part of the
 telephone. It will be seen that the dual mode telephone is assigned to
 four DECT networks, viz. one at the home of the telephone user (DECT
 home), one at his primary office (DECT office_1) which is close to the
 home, these two DECT networks being covered by the same GSM cell in some
 cases. Further, the telephone is assigned to a multi user DECT network at
 a shopping centre so that the user can make a call via this at the usual
 telephone rate. This network, too, has a partly coinciding GSM coverage
 with the two networks previously mentioned. Finally, the telephone is
 assigned to a DECT network at his secondary office (DECT office_2) which
 is located in another country and consequently has a CGI identification
 clearly different from the CGI identification of the three other networks,
 which differed only as regards the CI part.
 TABLE 1
 GSM address
 n cordless network MCC MNC LAC Cl
 1 DECT office_1 244 91 03b6 19.21
 2 DECT office_2 245 35 12d0 11
 3 DECT home 244 91 03b6 21.22
 4 DECT shopping center 244 91 03b6 20.21
 In order to communicate with a DECT network, the telephone must be assigned
 to the network and be given an ID code.
 A flow diagram illustrating the method of the invention is shown in FIG. 3.
 When the dual mode telephone searches for coverage from a predetermined
 DECT network in order to be able to switch to idle mode in DECT, it will
 already be in GSM idle mode, whereby it will receive GSM messages, which
 takes place in stage 20. The controller of the telephone detects the CGI
 part of the message, which takes place in stage 21. It is checked in stage
 22 whether the telephone has arrived at a new GSM cell or not. If this is
 not the case, the controller jumps back to search for the next CGI
 information. If the telephone has arrived at a new cell, a search for DECT
 coverage is started if CGI matches. Since the telephone may be connected
 to several different DECT networks, a counter is set at the value 0 in
 stage 23. The contents of the counter are counted one up in stage 24, and
 then the controller checks in stage 25 whether the GSM cell concerned is
 comprised by the group of cells which have so far provided DECT coverage
 for the DECT network which is searched for. This is done by comparing the
 cell information of the cell concerned with the cell information of the
 cell group.
 Stage 25 forms part of a scanning loop which successively scans for DECT
 networks which provide DECT coverage in the GSM cell concerned. This is
 done by checking whether CGI for the GSM cell concerned matches the GSM
 cell identification of the DECT network shown in table 1. If this is not
 the case, the next DECT network is checked, which is done by counting n
 one up in stage 30. As long as no DECT coverage is found, this is
 continued until all networks have been checked, which is detected in stage
 31, in which n is compared with n.sub.max, which is 4 in the case shown in
 connection with table 1.
 If no matching between the CGI identification and the possible DECT
 networks is detected, the controller jumps to stage 32, where it is
 indicated to the user that it is not possible to obtain DECT coverage.
 This indication may be in the form of a sound signal (beep) combined with
 representation on a display. Then, in stage 33 the user has the
 opportunity of deciding whether the telephone is to go on with its search
 or not. As a default facility, the telephone may switch to pure single
 mode, which means GSM alone. This is done in stage 34, and the telephone
 remains in this mode until the user decides to start a new search for DECT
 coverage, or the telephone itself initiates a new search because of the
 arrival at a new GSM cell. However, it will frequently be advantageous to
 use a timer to search for DECT coverage at intervals of e.g. 10 minutes
 and to check whether the GSM cell matches the stored CGI information for
 the DECT system--which should be done for a period of 30 to 60 minutes as
 default. In a preferred embodiment, the telephone selects this mode
 automatically if the user has not decided to go on with his search within
 a predetermined period of time.
 If in stage 33 the user wants the telephone to continue searching for DECT
 coverage, he is to state in stage 35 whether all accessible systems are
 still be scanned, or whether a specific DECT network is to be searched
 for. Further, the user must state whether he wants a search until coverage
 is found or a search of fixed duration. Default will usually be a search
 for all systems for a period of time. Depending on the selection, the
 controller goes to stage 23 to scan, or to stage 27 to search for a
 specific DECT network.
 It is checked in stage 27 whether DECT coverage can be found, and if this
 is the case, the controller enables the DECT paging part of the telephone,
 which takes place in stage 26, thereby entering the DECT idle mode, which
 takes place in stage 29. The telephone will hereby be a dual mode
 telephone proper. However, prior to this, it has been checked in stage 28
 whether the cell information is consistent with the cell information list
 of the group of cells which have so far given DECT coverage for the DECT
 network which is searched for. If this is not the case, the cell
 information list is updated, which takes place in stage 38.
 It was checked in stage 27 whether DECT coverage could be found, and if
 this is not the case, the search for the DECT system is repeated a number
 of times within a period t.sub.max, which may e.g. be of a duration of
 some minutes, as default. It is checked in stage 36 whether the time spent
 on the search exceeds t.sub.max, and the search is continued as long as
 this is not the case. If t.sub.max is exceeded, the controller concludes
 that the DECT network concerned provides no coverage at the location
 concerned, and checks in stage 37 whether there are still networks to
 which the telephone is assigned, and whose coverage has not been checked.
 If this is the case, the controller jumps back to stage 24, where a search
 for the next DECT network is initiated in that the value "n" is counted
 one up, and then coverage for this DECT network is searched for. If the
 telephone is designed to search for a DECT network for e.g. up to 30
 minutes before giving up, the loop may advantageously be designed to scan
 for the DECT networks, to pause, and to scan again. If CI is 21, the
 search for the DECT systems in table 1 will proceed as follows: 1, 3, 4,
 pause, 1, 3, 4, pause, and so on until t.sub.max is reached or DECT
 coverage is obtained.
 If it was established in stage 37 that a search had been conducted for all
 the DECT networks to which the telephone was assigned, the controller
 jumps to stage 32.
 The DECT system is not suitable for terminals moving at a high speed.
 Therefore, the dual mode telephone of the invention is adapted to detect
 when it is placed in e.g. a car kit. This detection takes place in stage
 38, and it is already used today for volume control by the hands free
 function.
 If a change in status is detected, it is checked in stage 39 whether the
 telephone was placed in the car kit or removed from it. If the telephone
 was placed in the car kit (connected), the telephone switches to GSM
 single mode (stage 34). Assuming that the telephone was in dual mode, the
 switch from the dual mode function in stage 29 to the single mode function
 in stage 34 is shown in dashed line. Even if the telephone was in search
 mode, it will switch to single mode in stage 34.
 If, on the other hand, the telephone was removed from the car kit
 (disconnected), it switches from GSM single mode (stage 34) to search mode
 in stage 23, which is shown in dashed line.
 If the DECT coverage in stage 29 is lost without a change in CGI and
 without the telephone being placed in the car kit, the telephone will
 automatically try to re-establish the DECT coverage (with the same DECT
 system) by jumping back to stage 25, which is indicated in dashed line.
 When the telephone operates in dual idle mode (stage 29) and a change in
 CGI occurs (because of roaming in the GSM system), the telephone remains
 in the dual mode state (stage 29), but will register the new CGI.
 The invention has been explained above in connection with a GSM/DECT dual
 mode telephone, but it may be used in all types of dual mode or multi mode
 telephones, where a search for network coverage may be automatically
 prevented on the basis of the knowledge of the position of the telephone,
 if it is already clear that this search will be in vain.
 FIG. 4 moreover shows the most important parts of a preferred embodiment of
 a dual mode telephone, said parts being essential to the understanding of
 the invention. A controller 12 is provided with a microprocessor 11. A
 microphone 16 records the user's speech, and the resulting analog signals
 are A/D-converted in an ADC in a converter unit 14 before it is
 speech-encoded in a code/encode unit 13. The encoded speech signal is
 transferred to the physical layer processor 11, which e.g. supports the
 DECT/GSM terminal software.
 The processor 11 also constitutes the interface to the peripheral units 10
 of the apparatus, including the display and the keypad (as well as SIM,
 data, power supply, RAM, ROM, etc.) The processor 11 communicates with the
 RF part 17 via a baseband unit 18. In addition to transmitting data,
 packed in accordance with the standard concerned, to the RF part, the
 controller also controls the oscillator frequency so that the packet
 concerned is transmitted at the correct transmission frequency. The
 reception is controlled correspondingly.
 The baseband unit 18 is a baseband converter, which moreover performs a
 channel equalizer function. The audio code/encode unit 13 speech-decodes
 the signal which is transferred from the controller 12 to the earpiece 15
 via a DAC in the converter unit 14. Thus, it is the controller 12 which
 controls the communication in the telephone and messages in idle mode.
 Thus, it is also the controller 12 which carries out the method of the
 invention. In the preferred embodiment, the method is implemented as
 software which is executed under the control of the controller 12.
 The present invention includes any novel feature or combination of features
 disclosed herein either explicitly or any generalisation thereof
 irrespective of whether or not it relates to the claimed invention or
 mitigates any or all of the problems addressed.
 In view of the foregoing description it will be evident to a person skilled
 in the art that various modifications may be made within the scope of the
 invention.