Abstract:
A communications system for a motor vehicle in which the hands-free device for a mobile phone is integrated into an audio or information system of the motor vehicle such as a car radio. The voice and/or data transmission between the mobile phone and the hands-free device takes place over an additional short-range radio link. A transceiver for this short-range radio link is contained both in the car radio and in the mobile phone. The need to install additional connection interfaces is thus eliminated. In addition, the need to couple the mobile phone to the hands-free device using a cable is eliminated. This has the advantage that the mobile phone can remain, for example, in the driver&#39;s pocket. The coupling between the mobile phone and car radio occurs automatically if the mobile phone moves into the range of the short-range radio link of the car radio.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a communications system of a motor vehicle having a mobile phone with a first transceiver device for communicating on a first radio link between the mobile phone and a stationary transceiver system of a mobile radio system. The communication system preferably includes an audio and/or information system that is installed in the motor vehicle and has a receiver and an audio output unit and a microphone for implementation of a hands-free function. Voice and/or data transmission takes place between the mobile phone and the audio and/or information system over a wireless link. It is possible to output voice calls which are received at the mobile phone via the audio output unit. 
     2. Description of the Related Art 
     In order to operate mobile phones in motor vehicles safely when driving, hands-free devices are used which permit the driver to make a telephone call without having to hold the mobile phone. Such a hands-free device contains at least one microphone for picking up the voice of the driver or of another vehicle occupant and a loudspeaker for outputting the voice of the calling party. Appropriate hands-free devices can be mounted as stand-alone units in a vehicle and are connected to the mobile phone by means of an interface. 
     Because most motor vehicles have an audio system, as a rule a radio unit, solutions are known which also make use of the radio unit&#39;s loudspeakers for the hands-free device. In this case, a connection must be made between the radio unit and the mobile phone, and it is thus necessary to provide a mount for the mobile phone in the vehicle. The implementation of such a hands-free device is work-intensive, in particular when it is retrofitted in the motor vehicle, and requires cables to be laid. 
     WO 96/32783 discloses a hands-free device with which the installation effort can be reduced. For this purpose, an interface is provided which is connected to the mobile phone. The interface contains a transmitter unit for wireless transmission of the incoming voice signals of a telephone call to a radio unit in the vehicle. The signals that are transmitted by the interface are picked up by the radio unit&#39;s antenna and converted into audio signals in the radio receiver. These audio signals are fed to the loudspeakers via an amplifier. The transmission between the interface and the radio unit is carried out at any desired radio frequency in the AM or FM range. During an incoming call, the driver can thus listen to the incoming voice signals via the loudspeaker of the radio unit after he has selected the correct reception channel. The microphone is located in the interface mount. In this way, a hands-free device is implemented using a conventional radio unit which reduces the cabling complexity. 
     Nevertheless, in this hands-free device as well, the basic installation of the mount with the interface initially must be carried out in the motor vehicle. In addition, in each case the mobile phone has to be connected to the interface, with the result that every time the mobile phone is used in the motor vehicle certain handling steps are required. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a communications system which includes an audio and/or information system, in particular a radio unit, and a mobile phone, with a hands-free function in such a way that no additional installation effort in the motor vehicle is necessary and even on each occasion when the mobile phone is used in the motor vehicle for the first time at the beginning of a journey, no additional handling steps, such as for example connecting the mobile phone to an interface, are required. 
     A further object of the invention consists in providing a radio unit which is adapted to the requirements of such a communications system according to the invention. A further object consists in specifying a method for convenient operation of a hands-free device of a motor vehicle. Other objects and advantages of the present invention will be apparent from this Summary and the following Detailed Description. 
     These objects are achieved in a communications system of the generic type in a motor vehicle by a second transceiver that is integrated into the mobile phone, and the audio and/or information system contains not only the receiver but also a transmitter for setting up a second radio link as a bidirectional short-range radio link between the second transceiver of the mobile phone and the audio or information system. 
     In the communications system according to the invention, both incoming and outgoing voice and/or data signals are transmitted between the mobile phone and the audio or information system over a radio link. This ensures that no additional mechanical installation effort is required for the hands-free device. In contrast, the hands-free device is integrated completely into the car or information system. The need to connect the mobile phone to an interface or the like before each journey is also eliminated completely. With the communications system according to the invention, the mobile phone can therefore remain, for example, in the driver&#39;s pocket or any other convenient location within the automobile. 
     The radio link between the mobile phone and the audio and/or information system is a short-range radio link, with the result that the transmission preferably also takes place on different frequencies or with different transmission methods than the transmission on the first radio link between the mobile phone and a stationary transceiver system of the mobile radio system. 
     The information system can be, in particular, a navigation or telematic system with voice input and output which is present in the vehicle. Because radio receivers are, however, used in motor vehicles today to an even greater extent, it is, in particular, preferred to use a radio unit as audio system in the described communications system. The radio unit then contains not only its conventional receiver unit for receiving radio signals but also a transceiver unit for transmitting signals between the radio unit and the mobile phone. The transmission between the mobile phone and the radio unit takes place here on frequencies outside the frequency bands of the radio signals. 
     The radio unit contains all the electronic components that are essential for the hands-free device. These are, in particular, components for automatically switching over to the hands-free function or else an electronic system for preventing feedback between the voice output via the loudspeakers and the voice input via the microphone. The microphone can, in particular, also be provided in the radio unit itself. However, so that it is not necessary to pay attention to the placing of the microphone in the vicinity of a speaker in the motor vehicle when the radio unit is being positioned in the vehicle, the radio unit has a microphone input, and the microphone is arranged at a different location in the motor vehicle. Suitable installation locations for the microphone in the motor vehicle are, in particular, the inside roof lining of the vehicle, the A pillar, the dashboard or the center console, the sun visor or the interior mirror. In order to obtain a good signal-to-noise ratio it is also possible to embody the microphone, in particular, as a directional microphone. The external microphone can be connected to the radio unit via a cable connection, but, in particular, a wireless link is also advantageous here. The latter may, in particular, be an infrared or radio connection. 
     The radio transmission between the radio unit and the mobile phone takes place preferably at frequencies of more than 2 GHz. The transmission then lies above the usual frequencies for radio links between the mobile phone and a stationary transceiver system of a mobile radio system and also above the frequency bands for radio signals. The transmission power of the transmitter device for the connection within the vehicle between the mobile phone and radio unit can be kept very low. 
     A range for the short-range radio link of approximately 10 m is considered adequate. In this context, a radio link using the Bluetooth method is particularly significant. The Bluetooth method has been developed in conjunction between various companies as a short-range communications method with ranges of typically 10 m. Ranges up to approximately 100 m are possible options. The transmission power of 1 mW is very low. The 2.4 GHz frequency band is preferably provided for transmission. The method can be used to implement data rates up to one megabit/sec. The low current demand of only 0.3 mA in the standby mode is of particular interest. As a result, a Bluetooth receiver in the radio unit can continuously be kept in the standby mode. Even if the vehicle is not used for a relatively long time, no significant loading of the battery arises. 
     As a result of the fact that the standby mode is also permanently possible in the motor vehicle, the driver does not need to perform any particular steps to activate the hands-free device when he enters the motor vehicle with his mobile phone. Instead, with the method which is described later, the hands-free device is activated automatically. A control element with which the driver can accept a call that is received at the mobile phone is provided on the radio unit. This corresponds to the known procedure when a telephone call is received at the mobile phone itself. With the communications system according to the invention, the driver does not need to carry out any further steps. 
     In one particular embodiment there is provision for the mobile phone to be capable of being operated by means of control elements of the radio unit. This means, in other words, that when the driver wishes to make a call he can dial the number of the other party by operating the control elements on the radio unit. In this case also, it is not necessary for the driver to pick up the mobile phone or for the mobile phone to be located directly within his reach. 
     However, in one particular preferred embodiment, the bidirectional transmission of data and voice calls between the mobile phone and the radio unit also makes it possible for the mobile phone to be used, for example, by other vehicle occupants as a remote control for the radio unit or for other devices connected to the radio unit in the vehicle. 
     In one alternate preferred embodiment of the communications system there is provision for the radio unit to be connected to, or equipped with, a voice recognition system, in order to process voice commands. As a result, when the driver wishes to make a call he can use voice commands to inform the communications system of the party he wishes to contact. For example, to do this, the driver merely speaks the name of the desired other party. The telephone number which is associated with the aforesaid name is then stored in the communications system, and in particular in the radio unit of the communications system or else in the mobile phone. When the word spoken is recognized by the voice recognition system, the associated telephone number is then automatically dialed and the voice connection is set up. The voice recognition system can also be integrated in the mobile phone itself. 
     Although mention has been made hitherto, and will also be made below, essentially of a radio unit, the communications system can, as an audio and/or information system, also include other devices. In addition to the navigation or telematic system already mentioned, said equipment may be in this context, for example, also a CD player and the like. In particular, the radio unit can and will as a rule also interact with other audio systems and/or said audio systems can and will be integrated into the radio unit. 
     Navigation systems are used to inform the driver of a suitable route to his destination. Navigation systems are known as so-called onboard or also as offboard navigation systems. In the case of onboard navigation systems, the calculation and display of a route is carried out completely with components present in the vehicle. In offboard navigation systems, data is transmitted, for example, from the route network from an external station into the motor vehicle. This will be carried out, in particular, by means of the mobile phone. However, in all cases it is desirable for the navigation systems also to include current traffic reports in the routine calculation. The system is then referred to as a dynamic navigation system. The traffic reports can then be transmitted on broadcast radio channels (for example RDS-TMC) or on a mobile radio network. 
     In another exemplary embodiment, the communications system according to the invention is therefore connected to a navigation system or contains such a system. In order to implement a dynamic navigation system, the radio unit is configured to pass on to the navigation system traffic, driving or route information that is received either from a radio station or via the mobile phone. 
     In order to filter the incoming traffic information, it is also advantageous if the mobile phone contains a position-determining means, for example a GPS receiver or a system for evaluating the position by means of the mobile radio network (cellular positioning). This also simultaneously facilitates the emission of an emergency call, because the precise position of the vehicle can be communicated together with the emergency call. 
     As has already been mentioned, the mobile phone can also be used as a remote control by virtue of the transmission of data to the radio unit. However, it is possible not only to set functions of the radio unit by remote control but also to control other vehicle functions if the respective device is connected to the radio unit via a suitable bus. 
     A motor vehicle radio unit according to the invention for use in the communications system described above has an input unit, a receiver for receiving radio signals within specific frequency bands and means for converting the received radio signals into audio signals by means of an audio output unit. The invention provides for a further receiver unit and a transmitter unit which is connected to the further receiver unit to be additionally integrated into the radio unit. The further receiver unit and the transmitter unit are configured to connect an external device in wireless fashion over a bidirectional short-range radio link. 
     Voice signals which are received by means of the further receiver unit are output by means of the audio output unit, and the transmission using the short-range radio link takes place outside the frequency bands of the radio signals. As a result of the transceiver device, integrated into the radio unit, for a bidirectional short-range radio link, the radio unit can connect to a multiplicity of units which have an appropriate device. In addition to the mobile phone already mentioned above, the external unit may be, in particular, a personal computer. If the radio unit is connected, for example, to a navigation system, or contains the navigation system, the driver can work out his route at home on the personal computer. The information does not then need to be transferred manually from the personal computer to the navigation system or to be transferred over a cable which has to be specially installed. Instead, the transmission can take place in wireless fashion over the short-range radio link to the radio unit, and from there to the navigation system. 
     The external unit may also be, in particular, a headset. The headset is connected directly to the radio unit over the short-range radio link. In this way, individual vehicle passengers can, for example, listen to a music channel over the headset. The headset can, in particular, also contain control elements, for example for setting specific functions of the radio unit or the volume. The transmission between the radio unit and the headset takes place over the wireless short-range radio link in the same way as described above in conjunction with the mobile phone. Further examples of external devices are external display and control components, an audio or video device or else a door opener, such as, for example the garage door. 
     In the latter case, the driver can then transmit a signal to the garage door over the short-range radio link by activating an appropriate key on the radio unit. The garage door contains a corresponding receiver and a motor for closing and opening the door. 
     In one exemplary embodiment, the method has the following method steps: 
     1. Mutual identification of a radio unit and a mobile phone when the mobile phone enters the radio coverage area of the radio unit; 
     2. Switching of the hands-free device into the standby mode; and 
     3. Activation of the hands-free device for the transmission of incoming or outgoing mobile radio data between the mobile phone and the radio unit; 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below with reference to exemplary embodiments and the drawing, in which: 
         FIG. 1  illustrates an overview of an exemplary communications system according to the present invention; 
         FIG. 2  illustrates a block circuit diagram of an exemplary embodiment of a radio unit and of a mobile phone; 
         FIG. 3  illustrates a flowchart of a method sequence for an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an overview of an exemplary embodiment of a communications system according to the invention. The communications system contains a radio unit  1  and a mobile phone  2 . The mobile phone  2  has, in a manner known per se, a plurality of control elements  3  and a display unit (display)  4 . For example, a telephone number is dialed, an incoming telephone call is accepted, a telephone directory is called etc. using the control elements  3 . The selected telephone number and further status information items are displayed, for example, on the display  4 . Mobile radio signals are received and emitted using the mobile radio antenna  5 . 
     The radio unit  1  has a plurality of groups of control elements  6 ,  7 ,  8 . The volume of the radio unit, for example, can be set using the control element  6 . Further functions, such as the selection of a stored transmitter, can be carried out using the control elements  7 . The control elements  8  are embodied as a numerical keypad and thus correspond largely to the control elements  3   a  of the mobile phone  2 . The control elements  8  can thus be used to dial a telephone number. The radio receiver also has a display unit (display)  9 . In radio mode, the selected transmitter and other status information, for example, are displayed on the display  9 . When a telephone number is dialed using the control elements  8 , the telephone number dialed can be displayed on the display  9 . When there is an incoming call, the telephone number of the calling party can likewise be displayed on the display  9 . Instead of the display of the telephone number, it is also possible to display the name of the calling party on the display  9  if assignments of names and telephone numbers are stored in a storage element of the radio receiver or of the mobile phone. 
     The radio receiver  1  also has a radio antenna  10  for receiving radio signals. Loudspeakers  11  are connected, as audio output unit, to the radio unit  1 . In addition, a microphone  12  is integrated into the radio unit  1 . The radio unit  1  is connected to the mobile phone  2  over a short-range radio link, with the result that the radio unit  1  with the microphone  12  and the loudspeakers  11  serves as a hands-free unit for the mobile phone  2 . An incoming call can be accepted at the mobile phone  2  by activating the control element  7   a  on the radio unit  1 . Because, in addition, it is also possible to dial a telephone number using the control elements  8  of the radio unit  1 , the mobile phone can be placed at any desired location within the vehicle for both incoming and outgoing telephone calls. In particular, it is not necessary to plug the mobile phone  2  into a special mount or to set up a cable connection between the mobile phone  2  and the radio unit  1 . 
     During a telephone call, the audio signals of the voice of the driver or of another vehicle occupant are converted into electrical signals by means of the microphone  12  and transmitted to the mobile phone  2  over the short-range radio link. From the mobile phone  2 , the transmission is carried out in a known way over the mobile radio antenna  5  to a stationary mobile radio station of a mobile radio system. The incoming voice signals of the other party are received by the mobile radio antenna  5  and passed on from the mobile phone over the short-range radio link to the radio unit and output there by means of the loudspeakers  11 . 
       FIG. 2  shows a simplified block circuit diagram of the radio unit  1  and of the mobile phone  2 . The radio unit  1  contains a control unit (MMI)  13  which has, for example, the control elements  6 ,  7  and  8  in  FIG. 1 . The control unit  13  is connected to a microprocessor unit (CPU)  14 . The CPU  14  converts the signals coming from the control unit  13  into control commands. In order to receive broadcast radio channels, the radio unit  1  has a radio antenna  10  which is connected to a radio receiver unit  15 . The radio receiver unit  15  is actuated by the CPU  14 , for example to select the radio signals of a specific transmitter. In the radio receiver unit  15 , the radio signals which are received via the radio antenna  10  are converted into voice frequency (VF) signals in a known fashion. 
     The voice frequency signals are amplified in a VF controller and amplifier  16  and fed to the loudspeakers  11  for audio playback. In addition, the radio unit  1  contains a drive  17 , with the result that, for example, music can be played back from a CD or from a music cassette. The drive  17  is also actuated by the CPU  14 . The voice frequency signals which are output by the drive  17  are fed to the VF controller and amplifier  16  and then also output by means of the loudspeakers  11 . In this respect the radio unit comprises known embodiments of a conventional car radio. 
     Furthermore, the radio unit  1  contains a transceiver device  18  with an antenna  19  for setting up a short-range radio link to the mobile phone  2 . The transceiver  18  is also actuated by the CPU  14 . The transceiver  18  is connected to the VF controller and amplifier  16 . In this way, voice signals which are received at the antenna  19  from the mobile phone  2  over the short-range radio link are passed on to the VF controller and amplifier  16  via the transceiver  18  and are output by means of the loudspeakers  11 . Voice signals of the driver or of a front seat passenger are picked up by the microphone  12  and fed via the VF controller and amplifier  16  to the transceiver  18  and the antenna  19  and transmitted over the short-range radio link to the mobile phone  2 . 
     The mobile phone  2  has a mobile radio antenna  5  which is connected to a first transceiver unit  20  for mobile radio signals. The transceiver unit  20  is actuated by a CPU  21 . The received mobile radio signals are converted in the transceiver unit  20  into VF signals which are fed to a VF controller and amplifier  22 . In the conventional mobile radio mode, the VF signals are output by means of a loudspeaker  23  which is integrated into the mobile phone. During conventional operation of the telephone, the voice signals of the telephone user are fed via the microphone  24  of the mobile phone  2  to the VF controller  22  and passed on from there via the transceiver unit  20  and the mobile radio antenna  5  to a stationary mobile radio station and ultimately to the other party. The mobile phone also has, as is known, a control unit  24  for selecting a telephone number and further telephone functions. A mobile phone which is suitable for the communications system according to the invention also has a second transceiver  25  which is connected to an antenna  26 . The transceiver  25  is connected to the VF controller and amplifier  22  and is actuated by the CPU  21 . 
     Mobile radio signals which are received via the mobile radio antenna  5  can thus be passed on via the first transceiver unit  20  to the VF controller and amplifier  22  after conversion into VF signals, and transmitted from said VF controller and amplifier  22  to the transceiver  25 . From the transceiver  25 , the VF signals are transmitted via the antenna  26  over a short-range radio link at a frequency of, for example, 2.4 GHz to the antenna  19  of the radio unit  1  and are output from there by means of the loudspeakers  11  in a fashion which has already been described. Conversely, the voice signals which are transmitted from the antenna  19  of the radio unit over the short-range radio link are picked up by the antenna  26  of the mobile phone  2  and passed onto the VF controller via the transceiver  25 . In the transceiver  25 , the radio signals are converted into VF signals. From the VF controller  22 , the VF signals are then passed on to the first transceiver unit  20 . After conversion of the incoming VF signals into mobile radio signals in the transceiver unit  20 , they are ultimately transmitted again to the stationary mobile radio station via the mobile radio antenna  5 . 
     In the exemplary embodiment, the transceivers  18  and  25 , respectively, preferably operate using the Bluetooth method which is known in the art. As a result, ranges of the short-range radio connection of typically 10 meters, sufficient for application in a motor vehicle, are obtained. The transceivers are implemented here in the form of a microchip. 
     Both in the radio unit  1  and in the mobile phone  2 , the devices are controlled by means of the respective CPU  14  and  21 . In this respect,  FIG. 3  illustrates a method sequence which describes the function of the radio receiver and of the mobile phone as a communications system with integrated hands-free device. Moreover, the CPU  14  controls the conventional functions of a radio receiver  1 . In an analogous way, the CPU  21  also controls the conventional functions of a mobile phone  2 . 
       FIGS. 3   a  and  3   b  show, by way of example, the method sequence in the communications system for incoming or outgoing telephone calls or data transmission, the connection between  FIGS. 3   a  and  3   b  being made at the position indicated by “1”. In describing the method it is assumed that the mobile phone is switched on (method step  101 ). The driver, together with the mobile phone, approaches the motor vehicle or enters the motor vehicle and thus enters the radio cell of the radio unit which is installed in the vehicle as a car radio (step  102 ). The radio cell being conditioned by the range of the radio link. At this time, the car radio is normally switched off but the short-range radio link is in the standby mode (step  103 ). After the driver, together with the mobile phone, enters the radio cell of the car radio, mutual identification of the radio stations in the mobile phone and in the car radio takes place in step  104 . 
     After successful identification, the car radio electronics can automatically be switched to the standby mode (step  105 ). However, as an alternative, manual activation of the car radio electronics is also provided in step  110 . Then, in step  106 , status messages are transmitted between the mobile phone and the car radio. If the driver then wishes to make a telephone call, he can dial the desired telephone number using the control elements of the radio unit (step  107 ). Then, in step  108 , the telephone number is dialed over the short-range radio link to the mobile phone. As an alternative, in step  114 , the telephone number can also be dialed directly at the mobile phone. 
     Then the mobile radio link is set up in step  109 . The radio transmission of the mobile radio data subsequently takes place in step  116 . The telephone call can be made here using the hands-free device which is integrated in the radio unit (step  117 ). However, the telephone call can also alternatively be made using the mobile phone (step  125 ). By appropriately activating keys on the radio unit or on the mobile phone it is possible here to switch between making a call using the hands-free device or making one using the mobile phone. The radio transmission of the mobile radio data to the stationary mobile radio station also continues (step  118 ) after such a switchover. In the case of a telephone call which is initially being made using the hands-free device, said call can be transferred using the mobile phone by activating a respective control element of the mobile phone in step  119 . 
     If the call is made using the mobile phone, it can be transferred to the hands-free device by activating a respective control element on the radio unit in step  121 . The telephone call can be terminated either using a control element of the mobile phone (step  120 ) or using a control element of the radio unit (step  122 ). 
     If an external telephone call is received at the mobile phone  2  (step  123 ), there is initially a status transmission to the radio unit so that audio and/or visual signaling takes place. The driver can then accept the incoming telephone call using a control element of the radio unit (step  126 ). The telephone call is made here using the hands-free device (step  117 ), and the mobile radio data are transmitted (step  118 ). Alternatively, in step  124 , the call can also be accepted using a control element of the mobile phone, and the telephone call can be made using the mobile phone (step  125 ). The call is terminated or transferred to the mobile phone or to the hands-free device in the fashion previously described in method steps  119  to  122 . 
     Exemplary steps of the method according to the invention are thus the mutual identification of the radio stations when the mobile phone enters the radio coverage area of the radio unit and the switching on of the standby mode of the hands-free device. The transmission of status messages over the short-range radio link and the activation of the hands-free device for the transmission of incoming or outgoing mobile radio data or calls between the mobile phone and the radio unit are additional exemplary method steps. Furthermore, it is preferred that telephone calls can be accepted or made either at the mobile phone or at the hands-free device in the radio unit. 
     Additionally, there are also a multiplicity of modifications and options of the method. For example, in step  103 , the radio link does not have to be continuously switched to the standby mode. Instead, the standby mode can be switched on, for example, when the vehicle doors are opened by means of the central locking system or the ignition of the motor vehicle is switched on. 
     In one particular preferred embodiment of the invention it is possible for specific setting operations to be performed on the vehicle or on devices in the vehicle after the car radio electronics have been switched to the standby mode in step  105 . Examples of such automatic, predefined switching procedures are, the switching on or off of the hands-free function, the selection of a specific station key on the radio unit, and thus of a specific radio transmitter, specific audio settings or the deactivation of an antitheft system of the car radio. Such operations relating to the vehicle itself may comprise activation of the central locking system with automatic unlocking of the vehicle doors, a specific seat setting or the deactivation of the vehicle antitheft system. These functions may be performed automatically or else switched remotely by manual means using the mobile phone (step  112 ). 
     In further specific alternate embodiments, status displays of the radio unit or of the telephone link may be displayed on the display of the radio unit (step  111  or  115 ,  127 ). There is also provision for the hands-free device to be switched to a mute setting if the telephone call is made using the mobile phone (step  128 ). 
     It will be appreciated by those skilled in the art that the radio links described herein may be embodied in other alternate electromagnetic transmission links, such as, for example, via a wireless infrared transmission communication link. This embodiment would be particularly advantageous to eliminate undesired cross-talk between adjacent vehicles using similar systems. In such an embodiment, the user need only place the infrared transceiver unit of the phone near or simply facing a corresponding unit located in the motor vehicle. 
     The communications system according to the invention, the radio unit according to the invention and the method according to the invention have been explained by reference to an exemplary embodiment having a plurality of variants. At the same time, a multiplicity of further refinements is possible without departing from the basic concept of the invention as detailed in the claims below.