Abstract:
A circuit arrangement for a mobile radio unit of a motor vehicle has a first mobile radio module for mobile radio transmission according to a first mobile radio standard, and a second mobile radio module for mobile radio transmission according to a second mobile radio standard, the first mobile radio module having a communication interface which is intended to interchange control and useful data and is connected to an electrical connection for electrically connecting the circuit arrangement to an external processor unit. The first mobile radio module has an additional interface which is used to electrically connect the first mobile radio module to a communication interface of the second mobile radio module, which communication interface is designed to interchange control and useful data. Reliable mobile radio transmission is enabled for voice data and other digital useful data with little development and circuit complexity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to International Application No. PCT/EP2013/002044 filed on Jul. 11, 2013 and German Application No. 10 2012 014 547.0 filed on Jul. 21, 2012, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The invention relates to a circuit arrangement for a mobile radio unit of a motor vehicle, having two mobile radio modules which are designed for mobile radio transmission according to different mobile radio standards. The invention also includes a motor vehicle with a mobile radio unit having the circuit arrangement. Finally, the invention also relates to a method for operating the circuit arrangement. 
     In a motor vehicle, for example an automobile, telephony and Internet connection are possible only via a radio link to a mobile radio network. In this case, a mobile radio unit provided in the motor vehicle for this purpose couples a control processor of the motor vehicle, for example a processor of an infotainment system, to the antenna system. During transmission, the mobile radio unit generates the analog mobile radio signals from the useful data (voice data or other digital data) output by the control processor and, during reception, extracts useful data from mobile radio signals received by the mobile radio unit via the antenna system and passes said data to the control processor. The conversion between the analog mobile radio signals and the digital useful data is effected using so-called mobile radio modules which are commercially available under the designation GSM module (GSM—Global System for Mobile Communications), UMTS module (UMTS—Universal Mobile Telecommunications System) or LTE module (LTE—Long-Term Evolution). When developing a mobile radio unit for a motor vehicle of a particular series, it is necessary to stipulate the mobile radio standards, that is to say GSM, UMTS or LTE for instance, for which mobile radio transmission by the mobile radio unit is intended to be enabled. Although younger mobile radio standards have the advantage here that they can be presumably used for longer, it may be disadvantageous that all data services have not yet been reliably implemented. In connection with the LTE mobile radio standard for example, it is known that the standard provided in LTE for voice transmission VoLTE is currently not supported by the mobile radio networks. In order to transmit voice, an LTE module must switch to an older mobile radio standard. In contrast, a mobile radio standard which is older in comparison affords the advantage that the available systems are established and tried and tested and therefore operate reliably. If a mobile radio unit is used with an older mobile radio standard for many years, it may emerge, however, that the customers feel the mobile radio unit to be out of date since younger mobile radio standards have become established in the meantime. 
     In connection with mobile radio devices, for instance mobile telephones, it is known practice to provide a dual mode in which voice data or other useful data can be transmitted using UMTS or GSM, for example. In this case, such a mobile radio device has two mobile radio modules, for example a GSM module and a UMTS module. In order to set up a connection for useful data transmission (voice data or equally other useful data), an attempt is first of all made to set up a connection using the mobile radio module with the younger mobile radio standard, that is to say the UMTS module. If no UMTS connection is possible, a changeover is made to the mobile radio module with the older mobile radio standard, that is to say the GSM module, and the latter is used to set up the connection. 
     SUMMARY 
     One possible object is to provide a mobile radio unit for a motor vehicle, which mobile radio unit enables reliable mobile radio transmission for voice data and other digital useful data with little development and circuit complexity. 
     The inventor proposes a circuit arrangement that comprises two mobile radio modules for mobile radio transmission according to two different mobile radio standards. One of the mobile radio modules, referred to here as the first mobile radio module, is preferably a UMTS module or an LTE module. The UMTS module may also simultaneously support GSM and the LTE module may also simultaneously support UMTS and GSM. The designations UMTS/GSM module and LTE/UMTS/GSM module are introduced for this purpose. In contrast, the second mobile radio module is preferably a GSM module. Each of the mobile radio modules has, in a manner known per se, a communication interface for interchanging control and useful data. The communication interface is those contacts and the logic of the respective mobile radio module linked to the latter, via which the mobile radio module interchanges useful data with local devices and the mobile radio module can be controlled by local devices. In order to connect the circuit arrangement to the remaining on-board electronics, the circuit arrangement has an electrical connection. In this case, only the communication interface of the first mobile radio module is connected to this connection. In other words, it is only possible for an external processor unit, for example a control processor of an infotainment system of the motor vehicle, to directly interchange control and useful data with the communication interface of the first mobile radio module via the electronic connection. In contrast, in the proposed circuit arrangement, the second mobile radio module is not directly connected to the electrical connection of the circuit arrangement. Instead, the first mobile radio module has an additional interface which is used to electrically connect the first mobile radio module to the communication interface of the second mobile radio module. In other words, the first mobile radio module is situated, in terms of circuitry, between the electrical connection and the second mobile radio module. The external processor unit mentioned can therefore communicate with the second mobile radio module only indirectly via the first mobile radio module. 
     The circuit arrangement has the advantage that the electrical connection for connecting the circuit arrangement to the vehicle electronics must have comparatively few signal lines, namely only those lines needed for interchanging control and useful data with a single communication interface. Nevertheless, mobile radio transmission using two different mobile radio standards is enabled in the circuit arrangement. 
     The inventor also proposes a motor vehicle that accordingly has a mobile radio unit which comprises one embodiment of the circuit arrangement. In this case, a control processor of the motor vehicle, which is set up to interchange data with a mobile radio network, that is to say the control processor of the infotainment system for example, may be coupled in the described manner to the communication interface of the first mobile radio module via the electrical connection of the circuit arrangement. In this case, the control processor must be advantageously designed only for communication with the first mobile radio module. 
     In order to make it possible for the control processor to use the second mobile radio module, the the inventor proposes a method according that provides for the first mobile radio module to receive a control command at its communication interface, as can be transmitted, for example, from the control processor to the communication interface of the first mobile radio module for the purpose of setting up a call (telephony) or setting up a connection for an Internet connection. The first mobile radio module then examines the received control command in order to determine whether the latter is intended for the first or second mobile radio module. In the second case, that is to say if a connection is intended to be set up via the second mobile radio module, the first mobile radio module then controls the second mobile radio module according to the received control command via its additional interface. As a result, the second mobile radio module then initiates call setup or connection setup. 
     It is possible to determine whether a particular control command is intended for the first or second mobile radio module in different ways. On the one hand, the external control processor may be set up to transmit corresponding signals to the first mobile radio module in order to expressly indicate thereby which mobile radio module is intended to execute the control command. 
     However, another advantage results if the first mobile radio module itself decides whether it is intended to execute the received control command itself or whether it is intended to cause the second mobile radio module to execute the control command. This is because the control software of the external control processor then does not have to be designed to control two different mobile radio modules. In order to enable such independent assignments of a control command to the first or second mobile radio module by the first mobile radio module, the first mobile radio module can check, for example, which of the two mobile radio modules can presumably be used to set up a radio link with a better signal-to-noise ratio. Similarly, it is possible to stipulate that, in principle, a call for telephony is intended to be set up by the second mobile radio module, that is to say a GSM module in particular, while digital useful data which differ from voice signal data are intended to be effected, in principle, using the first mobile radio module, that is to say the UMTS module or the LTE module in particular. The first mobile radio module preferably has a control device which is set up to itself generate the control commands for controlling the second mobile radio module and to transmit said commands to the second mobile radio module via the additional interface. This results in the advantage that the external processor unit need not be designed to control the second mobile radio module. 
     In order to make it possible to interchange the actual useful data, that is to say the voice data or the non-voice-related digital data, between the second mobile radio module and the external processor unit, the method can be developed by designing the first mobile radio module to transmit useful data between its communication interface and its additional interface, that is to say to loop through the useful data. In this case, provision may be made for direct transmission or transmission using a buffer. For example, a digital voice signal, for example a PCM signal (PCM—Pulse Code Modulation), may be interchanged between the external processor unit and the second mobile radio module. During transmission by the first mobile radio module, signal processing can also be carried out by the first mobile radio module in this case. 
     The transmission of the useful data between the communication interface of the first mobile radio module and its additional interface is expediently enabled by a transfer device which can electrically connect mutually corresponding connections of the communication interface and of the additional interface directly to one another, for example, or else can also transmit data, for example, using intermediate buffering. Audio data can be transmitted, for example, by coupling the audio connections of the two communication interfaces via the intermediate interface. 
     The operation of two independent mobile radio modules previously also required the provision of two SIMs (SIM—Subscriber Identity Module). In this context, one development of the circuit arrangement provides for the first mobile radio module to be designed to serially receive identification data relating to a user from a SIM via a connection of its communication interface. This then makes it possible to transmit the identification data via an individual electrical interface. For example, the transmission can be effected according to the USB standard (USB—Universal Serial Bus). The CDC/ACM (Communication Device Class/Abstract Control Model) specification provided within the scope of the USB standard can be used here in particular. 
     In the circuit arrangement, the two mobile radio modules are preferably arranged on a common plug-in card. The circuit arrangement can then be installed, for example, in a conventional control unit in which a slot for a plug-in card with only one individual mobile radio module is provided. 
     Another advantageous development of the circuit arrangement makes it possible to operate both mobile radio modules using one antenna system, as is provided for the operation of an individual mobile radio module with antenna diversity. Such an antenna system generally comprises a main antenna and a secondary antenna, the main antenna having a transfer characteristic which is more favorable for a radio link, in particular lower directivity. For this purpose, the main antenna is generally arranged on a roof of the motor vehicle. In contrast, in order to enable antenna diversity, the secondary antenna may be arranged at a shielded location, for example in the bumper, since the practice of arranging two antennas on the roof is generally undesirable. In order to now make it possible to use the main antenna for both mobile radio modules, one embodiment of the circuit arrangement provides a switching device which connects the first mobile radio module to a main antenna connection of the circuit arrangement and at the same time connects the second mobile radio module to a secondary antenna connection of the circuit arrangement in a first switching state and conversely couples the first mobile radio module to the secondary antenna connection and couples the second mobile radio module to the main antenna connection in a second switching state for radio signal transmission. While the second mobile radio module, for instance the GSM module, thus does not transmit any telephony data, but rather only interchanges monitoring data with a GSM mobile radio station, the switching device can be left in the first switching state for this purpose and the monitoring data can be interchanged via the secondary antenna. 
     At the same time, the complete antenna diversity is available for the first mobile radio module since the first mobile radio module can use both the main antenna and (via a further antenna line) the secondary antenna for reception without disturbing the second mobile radio module. When the second mobile radio module is activated, for instance in connection with a call setup or in the event of an incoming call, the second mobile radio module can then be coupled to the main antenna by switching the switching device to the second switching state. In the meantime, the first mobile radio module can still continue to use the secondary antenna for reception or transmission with reduced bandwidth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  shows a schematic illustration of a preferred embodiment of the proposed motor vehicle; and 
         FIG. 2  shows a schematic illustration of a mobile radio unit as can be installed in the motor vehicle from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     In the example explained below, the described components of the motor vehicle and of the mobile radio unit each represent individual features of the invention which should be considered independently of one another and each also develop the invention independently of one another and therefore can also be considered to be part of the invention individually or in a combination other than the combination shown. Furthermore, the described embodiments can also be supplemented with further features of the features of the invention which have already been described. 
       FIG. 1  shows a motor vehicle  10  which may be an automobile, for example. A mobile radio unit  12  and a control device  14  are installed in the motor vehicle  10 . The mobile radio unit  12  can emit digital data in the form of a mobile radio signal  16  via a main antenna  18  and possibly a secondary antenna  20  and can demodulate mobile radio signals received via the antennas  18 ,  20  and can extract the useful data contained in the mobile radio signals. 
     The mobile radio unit  12  therefore makes it possible to convert between the analog mobile radio signals from the antenna  18 ,  20  and the digital data interchanged between the mobile radio unit  12  and the control device  14 . The digital data may be, for example, voice data from a telephone  22  or digital data from a computer  24 , for example an on-board computer for reading emails or viewing websites. The control device  14 , the telephone  22  and the computer  24  may be part of an infotainment system  26 . The telephone  22  may also be a device which is outside the vehicle and communicates with the control device  14  using a Bluetooth connection, for example. The computer  24  may also be a device outside the vehicle, for example a laptop, which communicates with the control device  14  via a cable connection or a radio link (WLAN—Wireless Local Area Network). 
     The structure and the method of operation of the mobile radio unit  12  are explained in more detail below. 
     The mobile radio unit  12  may be in the form of a plug-in card  28  which can be inserted into a slot (not illustrated) of a control device of the motor vehicle  10 . The mobile radio unit  12  has an electrical connection  30  with a plurality of electrical contacts which are used to interchange signals between the mobile radio unit  12  and the control device  14 . A voltage supply  32  is also supplied with the vehicle electrical system voltage (for example 12 V) of the motor vehicle  10  via the connection  30 . The mobile radio unit  12  has two mobile radio modules, namely an LTE module  34  and a GSM module  36  in the present example. The LTE module  34  may also additionally support the UMTS and GSM standards. Instead of the LTE module  34 , the mobile radio unit  12  may also have a UMTS module or an HSPA module. The UMTS or HSPA module may also additionally support the GSM standard. In this example, the LTE module  34  is used to transmit digital useful data from the computer  34  and from other computers of the motor vehicle  10  and to receive useful data for these devices. The GSM module  36  is used to provide telephone connections. Provision may also be made for the GSM module  36  to be used for telephony only when it is identified that this function currently cannot be provided by the LTE module  34 . 
     Each mobile radio module  34 ,  36  has a sheet metal housing for shielding radio-frequency radiation, said housing containing digital circuits and analog amplifiers in order to output antenna signals for the antennas  18 ,  20  at analog outputs  38 ,  40 ,  44  and to receive corresponding antenna signals from the antennas  18 ,  20 . The analog outputs  38 ,  40 ,  44  are connected to antenna connections  48 ,  50  for the antennas  18  and  20  via a changeover device  46 . The changeover device  46  has controllable switches which, in a switching position, make it possible to connect the analog outputs  38 ,  40  of the LTE module  34  to one of the antenna connections  48 ,  50  in each case. In this switch position, the LTE module  34  uses both antennas  18 ,  20  to receive mobile radio signals  16  using antenna diversity. In this switch position, the analog connection  44  of the GSM module  36  is connected to the secondary antenna  20  via which the GSM module  36  receives monitoring data from surrounding GSM mobile radio stations. In a second switch position of the changeover device  46 , the analog connections  38 ,  40  of the LTE module  34  are connected to the secondary antenna  20 . In this switch position, the LTE module  34  uses only the antenna  20  for transmission and reception. In the meantime, the analog connection  44  of the GSM module  36  can be connected to the main antenna  18 . The digital connection  42  may be an output for displaying a GSM burst. When emitting a GSM burst, the changeover device  46  may initiate protective measures against overloading of the analog connections  38 ,  40 , for example. The analog connection  44  is for general transmission and reception. As a result, the GSM module  36  can use the better transmission and reception properties of the main antenna  18  to transmit telephony data. The digital connection  42 ′ is used to change over the analog connections  38 ,  40 ,  44  to the analog connections  48 ,  50 . 
     The changeover device  46  also comprises electrical components for impedance matching between the analog connections  38  to  44  and the antennas  18 ,  20 . 
     Although digital useful data, on the one hand, and telephony data, on the other hand, can be transmitted in the mobile radio unit  12  using the two different mobile radio modules  34 ,  36 , the connection  30  has only connecting contacts for interchanging data between the control device  14  and the mobile radio module  34 . There is no need for any further data lines for interchanging data with the GSM module  36  in the connection  30 . 
     The connection  30  is connected to connection contacts of the LTE module  34 , inter alia, via five physical lines, referred to as SIM lines  52  here, a USB line  54  for serial data transmission, a control line  56  and an audio line  58 . The connection contacts together form a communication interface  60  of the LTE module  34 . 
     The GSM module  36  has a comparable communication interface  62 , as is known per se from the related art. The connection contacts of the communication interface  62  are not directly connected to the connection contacts of the connection  30 . Instead, the communication interface  62  is connected to further connection contacts of the LTE module  34  at least via a control line  64 , an audio line  66  and SIM lines  68 . In order to connect the lines  64 ,  66 ,  68  to the LTE module  34 , it is possible to use connection contacts of the LTE module  34  which can be freely configured by appropriately programming the LTE module  34 . The connection contacts used overall form an additional interface  70  of the LTE module  34 . 
     Control software of the LTE module  34  can form a transfer device  72  which can be used to selectively transmit data either between the communication interface  60  and a processing unit  74  of the LTE module  34  or between the communication interface  60  and the additional interface  70 . In the latter case, this makes it possible, for example, to forward voice data, which are transmitted in the form of PCM data, for example, from the telephone  22  to the LTE module  34  via the control device  14  on the audio line  58 , to the GSM module  36  via the audio line  66 . Equally, control commands from the control device  14  can be redirected onto the monitoring line  64  via the monitoring line  56 . 
     In connection with control of the GSM module  36  or else in connection with processing of the audio data, provision may also be made for the processing unit  74  to directly independently output GSM control commands or processed audio data to the GSM module  36  via the intermediate additional interface  70 . 
     Identification data relating to the user from a respective SIM (SIM 1  and SIM 2 ) are needed to operate the mobile radio modules  34 ,  36 . The two SIMs are arranged outside the mobile radio unit  12  on at least one SIM card (UICC—Universal Integrated Circuit Card) which can respectively be situated in a slot in the motor vehicle  10 . The connection  30  only has the five physical lines of the SIM lines  52  in order to forward the data from the SIM 1  to the communication interface  60  of the LTE module  34 . The identification data from the second SIM, SIM 2 , may be transmitted to the LTE module  34  without the need for a further five lines for this purpose. The USB line  54  is designed, as a serial communication interface, to receive identification data from the second SIM (SIM 2 ) in the form of serially transmitted data, for example using a CDC-ACM driver of the LTE module  34 . The LTE module  34  is designed to transmit the identification data received via the USB line  54  to the GSM module  36  via the SIM lines  68 . The SIM lines  68  may again be, for example, the customary five physical lines for the standard transmission of identification data from a SIM card. 
     One SIM card in each case would actually have to be provided for use of the LTE module  34  and GSM module  36 . However, provision may also be made for two SIM fields of the same SIM card to be used, as is known, for example, from the SuperSIM product from the company NowGSM. 
     The mobile radio unit  12  may have a further connection for an additional SIM card  76 . The manufacturer of the motor vehicle  10  can set up such a communication connection between control devices of the motor vehicle  10  and a service station for the motor vehicle outside the motor vehicle, for example, using the LTE module  34  without this being at the motor vehicle user&#39;s expense. For example, such a software update can be transmitted by the motor vehicle manufacturer to control devices of the motor vehicle  10 . In order to be able to use the SIM card  76 , the mobile radio unit  12  may have a switch  78  which is changed over using control logic (not illustrated) of the motor vehicle  10 . 
     In the case of future implementation of LTE in the vehicle, technical difficulties will be expected according to experience, with the result that it is desirable to have a redundant solution or a fallback solution. The example shows how both an LTE module and a GSM module can be arranged in a mobile radio unit, in particular on a single plug-in card. Both modules share two antennas. One antenna has better reception properties than the other antenna. If necessary, the antenna with the better reception properties is connected to the LTE or GSM module. For example, during a telephone call, the antenna with the better reception properties can be connected to the GSM module. The GSM module preferably controls the changeover logic of the antennas, that is to say the switching device. 
     The LTE module can be connected to a control processor of a control device, which is not on the plug-in card, via control lines which can likewise be operated using the USB standard. The control for the GSM module is looped through the LTE module using the transfer device and/or is also accordingly influenced by the LTE module if necessary. Equally, the LTE module can be connected to the signal processor which is not on the plug-in module via a digital audio connection. Audio signals for the GSM module are then looped through the LTE module or are also accordingly influenced by the latter if necessary. 
     Fewer signal lines than in the case of a conventional connection of two mobile radio modules would be needed to connect the plug-in card. In addition, the control processor of the control device need not bear the computation load for controlling two mobile radio modules. The computation load for controlling the GSM module is moved to the LTE module. 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  69 USPQ2d 1865 (Fed. Cir. 2004).