GB2362544A - Filtering module for multi-mode communiction terminal - Google Patents

Abstract

To enable a communication terminal to operate in accordance with a number of differing telecommunication standards which may employ a range of different frequencies, the invention proposes the use of a removable filtering module specific to at least one communication standard which is coupled to a broadband transceiver of the terminal e.g. 810-2200MHz. Preferably, the filtering module is part of a data carrier, which may be a smart card such as a subscriber identity module (SIM) card 302, and comprises one or more of a receiver filter 410-414, a transmitter filter 420-424 and/or a duplexing filter 436-440. In order to operate the terminal in a particular telecommunication network, a SIM card 302 having the appropriate filtering module is selected and coupled to the terminal and on selection of the desired network, the required filters are switched-on. In addition to user selection, the terminal may monitor an air interface to determine an available telecommunication standard and switch-on the appropriate filters, if they are available within the filtering module of the attached SIM card 302. If the attached SIM card 302 does not support the standard, a message to this effect may be displayed to the user who may then obtain and attach the appropriate SIM card 302. With such a filtering module, there is no need for the terminal to contain complex and cumbersome filtering to cover all the present communication standards and future standards can be incorporated. The invention is applicable to standards such as GSM, PCS, IS-95 and cellular terminals, laptop computers or personal digital assistants (PDA).

Description

2362544 1 COMMUNICATIONS TERMINAL The present invention relates to a

communications terminal of the type that can operate in accordance with a number of telecommunication standards supported by a number of cellular communication systems.

A user of a mobile terminal has varying requirements depending upon where the user lives and travel habits of the user. At present, it is impossible to roam world-wide using a single mobile terminal, because present Second Generation and inu-ninent Third Generation mobile communication systems support incompatible telecommunication standards. Consequently, in order to make a truly universal mobile terminal capable of operating world-wide, the universal terminal needs to be able to support all present and future teleconununication standards.

Since it is impossible to foresee all possible future telecommunication standards that may immerge in the forthcoming years, it is necessary to ensure that the universal mobile terminal is based upon a flexible, softwarebased technology platform in order to achieve global roaming. Adaptive terminals are an example of the universal mobile terminal based upon a software-based technology platform.

Adaptive terminals have hardware which is reconfigurable by means of a standardised software download method. By downloading telecommunication standard-specific software to the adaptive terminal, the adaptive terrrfinal is able to adapt to different, or changing, standardisation requirements, in particular, radio access techniques and different service requirements.

2 However, the adaptive terminal has to operate in a range of ftequencies between about 8 10 to 2200 MHz. Consequently, in order to operate over all of this range of frequencies whilst meeting all the specifications of a required telecommunication standard, a Radio Frequency (RF) front end of a receiver of the adaptive terminal has to be very broadband, i.e. operate in the range of frequencies between about 8 10 to 2200 MHz.

In particular, an adaptive terminal having filters before conversion to intermediate frequency (IF) in the front end and a duplexing filter after an antenna (for Frequency Division Duplex (FDD) standards) capable of providing filtering operations in respect of all present telecommunications standards would be very complex and cumbersome in structure. Furthermore, any compromise with regard to complexity or size may impact upon the performance of the adaptive terminal. Therefore, even if it were possible to provide such filtering in the adaptive terminal, there would be no guarantee that the terminal would operate to a satisfactory standard in relation to future telecommunication standards.

It is therefore an object of the present invention to obviate, or at least mitigate, the above-described disadvantages in connection with adaptive terminals.

According to a first aspect of the present invention the present invention, there is provided a communication terminal comprising a broadband transceiver and a filtering module specific to at least one communication standard, wherein the filtering module is removably coupleable with the broad-band transceiver.

3 For the avoidance of doubt, it should be appreciated that the transceiver can be filterless, or can include at least one filter, provided that the at least one filter is not unique to the at least one communication standard.

Preferably, the filtering module is part of a data carrier. More preferably, the data carrier is a smart card. Very preferably, the smart card is a Subscriber Identity Module (SIM)..

Preferably, the filtering module comprises at least one receiver filter, at least one transmitter filter. The filtering module may also comprise at least one duplexing filter.

Preferably, the terminal further comprises a first selection means for selecting at least one of the at least one receiver filters.

Preferably, the terminal further comprises a second selection means for selecting at least one of the at least one transmitter filters.

Preferably, the tem-iinal further comprises a third selection means for selecting at least one of the at least one duplexing filters.

According to a second aspect of the present invention, there is provided a data carrier comprising a filtering module specific to at least one communication standard, wherein the filtering module is removably coupleable with a communication transceiver.

According to the present invention, there is also provided a method of operating a communication terminal comprising: coupling a data carrier to the communication terminal, and powering-up the communication terminal, the method being characterised by the steps of. providing a filtering module with the data carrier, the filtering module being specific to at least one communication standard.

4 Preferably, the method further comprises the steps of. selecting a communication network, and selecting filters within the filtering module to enable operation of the communication terminal in accordance with a communication standard from the at least one communication standard corresponding to the communication network selected.

It is thus possible to provide a communications terminal capable of operating over a wide range of frequencies between about 8 10 and 2200 MHz, whilst being capable of providing telecommunication standard specific filtering for operation within a particular sub-band of the wide range of frequencies.

Consequently, when a user first purchases the communication ten-ninal, the user is provided with a SIM card having the filtering module arranged to provide filtering operations to enable the handset to operate in accordance with the Global System for Mobile Communications (GSM), Personal Communications System (PCS) and IS-95 standards, thereby providing the user with the ability to use the communications terminal in Europe and the USA. Should the user need the communications terminal to operate in accordance with a different telecommunications standard, the user simply needs to contact a service provider from whom the communications terminal was purchased in order to obtain a new SIM card having a filtering module capable of providing the filtering necessary to enable the communications terminal to operate in accordance with the different telecommunications standard.

By providing standard specific filters capable of being separated from the rest of the transceiver hardware, the communications terminal becomes a fully universal mobile terininal which can be software configured to operate in accordance with any telecominunication standard, i.e. an adaptive terminal. Hence, the size of the communications terminal can be kept to a minimum, because hardware specific to supporting standards which are not required by the user is not incorporated into the communications terminal. Additionally, the design of the transceiver hardware for the communications tem-iinal becomes common, thereby reducing manufacturing costs. Of course, the user must subscribe to a network supporting the telecommunication standard and possess the correct SIM card having the appropriate filtering module.

At least one embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure I is a schematic diagram of a cellular communications system capable of supporting an embodiment of the invention; Figure 2 is a schematic diagram of a base station used in the cellular communications system of Figure 1; Figure 3 is a schematic diagram of a terminal constituting an embodiment of the invention:

Figure 4 is a schematic diagram of the terminal of Figure 3 in more detail, and Figure 5 is a flow diagram of the operation of the terminal of Figures 3 and 4.

Throughout the following description like parts will be identified by identical reference numerals.

In a cellular telecommunications system, for example, a GSM system 100 (Figure 1), a base station 102 supports a geographical area, or cell 104, 6 the base station 102 being in communication with a mobile handset 106 via a radio frequency (RF) interface 108.

As an example only, communications between the base station 102 and a Public Switched Telecommunications Network (PSTN) 110 can be supported by any telecommunications architecture 112 known in the art. A fixed-line telephone 114 is also coupled to the PSTN 110.

It should be appreciated that although reference has been made above to a particular type of handset, other terminals can be used instead of the base station 102 or the handset 106, including, for example, fixed cellular terminals, or laptop computers/Personal Digital Assistants (PDAs) suitably adapted to function within the GSM system 100. Similarly, although the fixed-line telephone 114 coupled to the PSTN 110 has been described above, other communications devices are envisaged, for example, a personal computer (PC) and a modem, or another mobile handset.

The base station 102 (Figure 2) comprises a base station antenna array 200 coupled to a base station duplexer 202. A first terminal of the base station duplexer 202 is coupled to a base station microprocessor 204 via a base station transmitter chain 206. Similarly, a second terminal of the base station duplexer 202 is coupled to the base station microprocessor 204 via a base station receiver chain 208.

The base station microprocessor 204 is coupled to a base station RAM 210. Information is communicated to and from other parts of the cellular network (not shown) by means of an 1/0 interface 212 coupled to the base station microprocessor 204.

Referring to Figure 3, the handset 106 comprises a front end portion, Pf, and a baseband portion, Pbb. The front end portion Pf, comprises a 7 broad-band receiver front end 3 10, a broad-band transmitter front end 312, and a data carrier, for example, a smart card such as a subscriber identity module (SIM) card 302. The SIM card 302 is adapted to have a first filter port 304, a second filter port 306 and a third filter port 308. The second filter port 306 and the third filter port 308 are coupled to the broad-band receiver RF front end 3 10 and the broad-band transmitter RF front end 312. The receiver front end 3 10 and the transmitter front end 312 are coupled to a base-band unit 314, constituting the base-band portion Pbb. The functionality of the receiver front end 3 10, the transmitter front end 3 12 and the base-band unit 314 is carried out by a rinicroprocessor 315. A display 316, the speaker unit 317, the keypad 318 and the microphone 320 are each coupled to the microprocessor 315. An antenna array 300 is coupled to the SIM card 302.

The SIM card 302 contains a computer (not shown) and a memory chip (not shown). The SIM card 302 is the size of a credit-card or can also take the fonn of a cut-down version to fit into smaller handsets. For GSM, the SIM card 302 contains subscriber parameters, holds personal data used by the subscriber, holds subscriber personal telephone numbers, identifies the subscriber to the network, provides security via a Personal Identification Number (PIN), retains information on the last cell in which the phone was operated, frequency of base channel and cell location, as well as stores short messages from the network. The most important function of the SIM card 302 is to identify the subscriber to the network for various known purposes, for example, billing and determining privileges of the subscriber. The SIM card 302 is essential for making non-emergency use of the handset 106.

Referring to Figure 4, the handset 106 comprises a superheterodyne transceiver comprising the broad-band receiver RF front end 3 10 having a down-conversion unit 400, for conversion to IF, IF filtering and conversion to base-band of received signals. The superheterodyne transceiver also comprises the broad-band transmitter RF front end 312 having an upconversion unit 402 for up-conversion and modulation of baseband signals. Although, in this example, the handset 106 comprises a superheterodyne transceiver, it should be appreciated that other transmitter, receiver or transceiver structures can be employed. However, any other transinitter, receiver or transceiver structures needs to be adaptable so that filters necessary for correct operation of the handset 106 in accordance with at least one given telecommunication standard can be easily replaced, preferably by a user of the handset 106.

Consequently, the SIM card 302 includes a filter module comprising a first bank of filters 404, a second bank of filters 406 and a bank of duplexing filters 408. The first bank of filters 404 comprises a first receiver filter 410, a second receiver filter 412 and a third receiver filter 414. An input terminal of each of the first, second and third receiver filters 410, 412, 414 is coupled to a respective first, second and third output terminal of a first receiver switch 416. An output terminal of each of the first, second and third receiver filters 410, 412, 414 is coupled to a respective first, second and third input terminal of a second receiver switch 418. An output terminal of the second receiver switch 418 is coupled to the down-conversion unit 400 via the second filter port 306.

The second bank of filters 406 comprises a first transmitter filter 420, a second transmitter filter 422 and a third transmitter filter 424. An input terminal of each of the first, second and third transmitter filters 420, 422, 424 is coupled to a respective first, second and third output terminal of a first 9 transmitter switch 426. An input terminal of the first transmitter switch 426 is coupled to the up-conversion unit 402 via the third filter port 308. An output terminal of each of the first, second and third transmitter filters 420, 422, 424 is coupled to a respective first, second and third input terminal of a second transmitter switch 428.

An input terrrfinal of the first receiver switch 416 is coupled to an output terminal of a low noise amplifier 428, an input terminal of the low noise amplifier 428 being coupled to an output terminal of a second duplexer switch 434, via the second filter port 306, and an output terminal of a power amplifier 430. An input tem-iinal of the power amplifier 430 is coupled to an output terminal of the second transmitter switch 428.

A first, second and third output tem-iinal of the first duplexer switch 434 is respectively coupled to a first duplexing filter 436, a second duplexing filter 438 and a third duplexing filter 440. An output terminal of the first, second and third duplexing filter 436, 43 8, 440 are respectively coupled to a first, second and third output terminal of a first duplexer switch 432, an output terminal of the first duplexer switch 432 being coupled to the antenna array 300 via the first filter port 304.

Additionally, the base-band unit 314 is coupled to a subscriber parameter store 442 provided in the SIM card 302. Although not shown, the base-band unit 314 is also coupled to the first and second receiver switches 416, 418, the first and second transmitter switches 426, 428 and the first and second duplexer switches 432, 434 in order to control switching of filters.

Although, in the above example, a first bank of filters 404, a second bank of filters 406 and a bank of duplexing filters 408 are provided, each comprising a plurality of filters, one or more of the first bank of filters 404, the second bank of filters 406 and the bank of duplexing filters 408 can be replaced by an appropriate respective single filter. The handset 106 is, in the above example, provided with banks of filters to enable the handset 106 to operate in accordance with more than one telecommunication standard.

It should be appreciated that reference to "ports" implies the presence, where appropriate, of more than one terminal.

In operation (Figure 5), a user possessing the handset 106 determines at least one telecommunication network in which the handset 106 is to be operated. The user then acquires the SIM card 302 having an appropriate filter module to enable operation of the handset 106 in the at least one telecommunication network. The SIM card 302 is then brought into operative coupling (step 500) with the handset 106 according to any technique known in the art. In the present example, physical coupling of the SIM card 302 to the handset 106 via the first, second and third filter Ports 304, 306, 308 enables the first bank of filters 404, the second bank of filters 406 and the bank of duplexing filters 408 to be coupled to the processor 315 to enable operation of the handset 106.

Subsequently, the user selects (step 502), for example via the keypad 318, the telecommunication network in which the handset 106 is to operate. Software within the handset 106 then electronically switches (step 504) the first and second receiver switches 416, 418, the first and second transmitter switches 426, 428 and the first and second duplexer switches 432, 434 in order to connect a correct one of the first, second or third receiver filters 4 10, 412, 414 to the low noise amplifier 428 and the down-conversion unit 400, a correct one of the first, second and third transmitter filters 420, 422, 424 to the power amplifier 430 and the upconversion unit 402, and a correct one of the first, second or third duplexing filters 436, 438, 440 between the low noise amplifier 428, the power amplifier 430 and the antenna array 300.

Once the correct filters have been switched in-circuit, the handset 106 is able to transmit and receive signals (506) in the band of frequencies assigned to the selected telecommunication network operating in accordance with a corresponding telecommunication standard. If a different telecommunication standard is supported by the filtering module and is required by the user, a different network (if available) operating in accordance with the different telecommunication standard can be selected by repeating steps 502 and 404.

Although, in the above example, the user selects the telecommunication network, the handset 106 can be arranged to monitor an air interface in order to determine an available telecommunication standard. During this monitoring period, the bank of duplexing filters 408 required for FDD standards and the second bank of filters 406 are not necessary and the broad-band receiver front end 3 10 can function correctly without the need for the bank of duplexing filters 408 and the second bank of filters 406. Once the available teleconununication standard has been determined, the correct filters in the first bank of filters 404, the second bank of filters 406 and, if the available telecommunication standard is an FDD standard, the bank of duplexing filters 408 can be switched in.

In both of the above telecommunication standard selection techniques described above, if the SIM card 302 does not contain the correct filters required for the selected telecommunication standard, the display 316 can be arranged to display a message to the user to this effect and advise the user to obtain an appropriate SIM card from a Service Provider.

12

Claims (1)

1. A communication terminal comprising a broad-band transceiver and a filtering module specific to at least one communication standard, wherein the filtering module is removably coupleable with the broad-band transceiver.

   2. A terminal as claimed in Claim 1, wherein the filtering module is part of a data carrier.

   3. A terminal as claimed in Claim 2, wherein the data carrier is a smart card.

   4. A terminal as claimed in Claim 3, wherein the smart card is a Subscriber Identity Module (SIM).

   5. A terminal as claimed in Claim 1, wherein the filtering module comprises at least one receiver filter and at least one transmitter filter.

   6. A terminal as claimed in Claim 1, wherein the filtering module comprises at least one duplexing filter.

   7. A terminal as claimed in Claim 5, further comprising a first selection means for selecting at least one of the at least one receiver filter.

   13 8. A terminal as claimed in Claim 5, further comprising a second selection means for selecting at least one of the at least one transmitter filter.

   9. A terminal as claimed in Claim 6, further comprising a third selection means for selecting at least one of the at least one duplexing filter.

   10. A data carrier comprising a filtering module specific to at least one communication standard, wherein the filtering module is rernoveably coupleable with a communication transceiver.

   A method of operating a communication terminal comprising: coupling a data carrier to the communication terminal, and powering-up the communication terminal, the method being characterised by the steps of. providing a filtering module with the data carrier, the filtering module being specific to at least one communication standard.

   12. A method as claimed in Claim 11, further comprising the step of.. selecting a communication network, and selecting filters within the filtering module to enable operation of the communication terminal in accordance with a communication standard from the at least one communication standard corresponding to the communication network selected.

   13. A communication terminal substantially as hereinbefore described with reference to Figures 3 and 4.

   14 14. A method of operating a communication terminal substantially as hereinbefore described with reference to Figure 5.