Patent Abstract:
A composite radio apparatus having two radio systems, comprises two antennas to be shared for a diversity operation of the two radio systems, and two antenna changeover switches for switching the two antennas, wherein the two antenna changeover switches serve to directly connect the two antennas to respective input/output sections of the two radio systems. In the composite radio apparatus according to the invention, the two antenna changeover switches are operated such that one of the antenna changeover switches connects one of the two antennas to the input/output section of one of the two radio systems when the other antenna changeover switch connects the other antenna to the input/output section of the other radio system.

Full Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a composite radio apparatus including two radio systems, and more particularly to a composite radio apparatus for carrying out a diversity operation in the respective radio systems. Moreover, the invention relates to a diversity switching method in the composite radio apparatus.  
           [0002]    In a radio communication, there has been employed a diversity technique in order to cope with fluctuation in the receiving signal power. According to the diversity technique, a plurality of antennas are connected to a radio apparatus such as a radio base station or a mobile terminal, so that it is switched into an antenna receiving a high receiving signal power depending on the fluctuation in the received power which is caused by fading to perform the communication, and the received radio wave signals are synthesized. In particular, there has been widely used an antenna switching type diversity receiving method which can be implemented with a simple circuit structure at a low cost.  
           [0003]    [0003]FIG. 5 is a diagram showing the schematic structure of a radio apparatus capable of carrying out a diversity reception. In FIG. 5, an antenna changeover switch  52  serves to switch a first antenna  53  and a second antenna  54  and to connect them to the input/output section (not shown) of a radio system  51 . The antenna changeover switch  52  is switched in response to switching signals  55   a  and  55   b  sent from an antenna switching control circuit  55 . The control signal  55   a  and the control signal  55   b  have an inversion relationship and serve to connect the first antenna  53  and the radio system  51 , and the second antenna  54  and the radio system  51  separately. The reason why the separate control signals are sent is that it might be necessary to set a rise time and a fall time for a time sharing slot individually in respect of the characteristic of the radio system. In this respect, another antenna changeover switch, which will be described below, has the same possibility. Separate control signals are sent, respectively. The radio apparatus in FIG. 5 switches the antenna changeover switch  52  in response to the control signals  55   a  and  55   b  and always carries out a receipt while retrieving the first antenna  53  or the second antenna  54  which has a higher received signal level in the case in which the diversity operation is to be executed.  
           [0004]    In a composite radio apparatus having two radio systems employing the diversity receiving method, the diversity operation can be carried out by using a common antenna.  
           [0005]    [0005]FIG. 6 is a diagram showing the schematic structure of a composite radio apparatus having two radio systems capable of carrying out the diversity reception. The composite radio apparatus in FIG. 6 includes a first radio system  61  and a second radio system  62  which carry out different radio communications, and a first antenna  65  and a second antenna  66  are switched and connected to input-output sections (not shown) of the first radio system  61  and the second radio system  62  by means of a system changeover switch  63  and an antenna changeover switch  64 . The system changeover switch  63  is switched in response to control signals  1   a  and  1   b  sent from a system switching control circuit  67  and the antenna changeover switch  64  is switched in response to control signals  2   a  and  2   b  sent from an antenna switching control circuit  68 .  
           [0006]    The control signal  1   a  serves to select the first radio system  61  and the control signal  1   b  serves to select the second radio system  62 . More specifically, the control signal  1   a  is set to be H and the control signal  1   b  is set to be L in the case that the first radio system  61  is to be selected, whereas the control signal  1   a  is set to be L and the control signal  1   b  is set to be H in the case in that the second radio system  62  is to be selected. Moreover, the control signal  2   a  serves to select the first antenna  65  and the control signal  2   b  serves to select the second antenna  66 . More specifically, the first antenna  65  is selected when the control signal  2   a  is H and the control signal  2   b  is L, whereas the second antenna  66  is selected when the control signal  2   a  is L and the control signal  2   b  is H.  
           [0007]    Next, the operation of the composite ratio machine in FIG. 6 will be described. First of all, the system changeover switch  63  is switched to the radio system side to be used in response to the control signals  1   a  and  1   b  in order to select the ratio system for carrying out the diversity reception. In the case that the diversity operation is to be carried out in this state, the antenna changeover switch  64  is switched in response to the control signals  2   a  and  2   b  and a receipt is always performed while retrieving the first antenna  65  or the second antenna  66  which has a higher received signal level.  
           [0008]    [0008]FIG. 7 is a diagram showing the state of the control signals  1   a ,  1   b ,  2   a  and  2   b  in the case in which the radio system is switched and the antenna is changed over in the composite radio apparatus of FIG. 6. FIG. 7 shows a time sharing operation in a transmitting slot T 1  and a receiving slot R 1  in the case in which the first radio system  61  is being operated, and the first antenna  65  is selected at time of a transmission and the second antenna  66  is selected at time of a receipt. More specifically, in the transmitting slot T 1 , the control signal  1   a  is set to be H, the control signal  1   b  is set to be L, the control signal  2   a  is set to be H and the control signal  2   b  is set to be L so that the first antenna  65  is selected. In the receiving slot R 1 , moreover, the control signal  1   a  is set to be H, the control signal  1   b  is set to be L, the control signal  2   a  is set to be L and the control signal  2   b  is set to be H so that the second antenna  66  is selected.  
           [0009]    However, the conventional composite radio apparatus is provided with the antenna changeover switch  64  for switching the antenna for the diversity operation and the system changeover switch  63  for radio system switching, and a transmitted/received signal is sent through the two switches including the antenna changeover switch  64  and the system changeover switch  63 . Therefore, there is a problem in that a receiving sensitivity is deteriorated due to an increase in a loss corresponding to one switch and a transmitted output is reduced at time of a transmission.  
           [0010]    Moreover, it is necessary to separately control the switching operations of the system changeover switch  63  and the antenna changeover switch  64 . For this reason, there is also a problem in that four control signals for the switching are required.  
         SUMMARY OF THE INVENTION  
         [0011]    The invention has been made to solve the conventional problems and has an object to provide a composite radio apparatus comprising two radio systems and two antennas to be shared for the diversity operation of the two radio systems and capable of reducing a loss in the switching of the antenna and the radio system. Moreover, the invention has another object to provide a diversity switching method capable of reducing a loss in the switching of the antenna and the radio system in the composite radio apparatus.  
           [0012]    The invention provides a composite radio apparatus having two radio systems, comprising two antennas to be shared for a diversity operation of the two radio systems, and two antenna changeover switches for switching the two antennas, wherein the two antenna changeover switches serve to directly connect the two antennas to respective input/output sections of the two radio systems.  
           [0013]    According to the composite radio apparatus, one switch is passed in a path formed by the antenna and the respective radio systems. Therefore, it is possible to reduce a loss caused by the passage through two switches in the conventional art. Moreover, switching control can easily be carried out.  
           [0014]    In the composite radio apparatus according to the invention, the two antenna changeover switches are operated such that one of the antenna changeover switches connects one of the two antennas to the input/output section of one of the two radio systems when the other antenna changeover switch connects the other antenna to the input/output section of the other radio system.  
           [0015]    By the execution of such switching, when one of the antennas is connected to one of the radio systems and is thus used, the same antenna is not connected to the other radio system. Therefore, it is possible to prevent an influence such as a reduction in a transmitted signal from being caused by a fluctuation in a load impedance.  
           [0016]    In the composite radio apparatus according to the invention, one of the antenna changeover switches serves to connect, by switching, the two antennas to either of the radio systems which is being operated.  
           [0017]    By the execution of such switching, it is possible to easily carry out the switching control of the antenna corresponding to a control system which is being operated or is to be operated.  
           [0018]    The composite radio apparatus according to the invention further comprises a matching circuit corresponding to the radio system between at least one of the antenna changeover switches and the input/output section of the radio system.  
           [0019]    According to the composite radio apparatus, also in the case in which frequencies to be used for the two radio systems included in the composite radio apparatus are different from each other, it is possible to reduce a loss caused by the mismatching of an impedance through the connection switching.  
           [0020]    The invention provides a diversity switching method in a composite radio apparatus comprising two radio systems and two antennas to be shared in a diversity operation of the two radio systems, wherein one of the two antennas is directly switched and connected to an input/output section of one of the radio systems which is carrying out the diversity operation and the other antenna is directly switched and connected to an input/output section of the other radio system.  
           [0021]    According to the diversity switching method, it is possible to reduce a loss caused by the antenna switching through a simplified control method.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a diagram showing the schematic structure of a composite radio apparatus according to a first embodiment of the invention;  
         [0023]    [0023]FIG. 2 is a diagram showing the schematic structure of the composite radio apparatus according to the first embodiment of the invention;  
         [0024]    [0024]FIG. 3 is a table showing the relationship between control signals corresponding to a radio system to be used and an antenna;  
         [0025]    [0025]FIG. 4 is a diagram showing the state of the control signal in the composite radio apparatus according to the embodiment of the invention;  
         [0026]    [0026]FIG. 5 is a diagram showing the schematic structure of a radio apparatus capable of carrying out a diversity reception;  
         [0027]    [0027]FIG. 6 is a diagram showing the schematic structure of a conventional composite radio apparatus having two radio systems which can carry out the diversity reception; and  
         [0028]    [0028]FIG. 7 is a diagram showing the state of a control signal in the conventional composite radio apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    An embodiment of the invention will be described below with reference to the drawings.  
         [0030]    [0030]FIG. 1 is a diagram showing the schematic structure of a composite radio apparatus according to a first embodiment of the invention. The composite radio apparatus in FIG. 1 has a first radio system  11  and a second radio system  12  which carry out different radio communications, and a first antenna  15  and a second antenna  16  which are shared for the first radio system and the second radio system. The first antenna  15  and the second antenna  16  are directly switched and connected to an input/output section (not shown) of the first radio system by means of an antenna changeover switch  13  for the first radio system, and are directly switched and connected to the second radio system  12  by means of an antenna changeover switch  14  for the second radio system.  
         [0031]    The antenna changeover switch  13  for the first radio system and the antenna changeover switch  14  for the second radio system are switched in response to a control signal  10   a  of a first switching control circuit  17  and a control signal  10   b  of a second switching control circuit  18 . The antenna changeover switch  13  for the first radio system connects the first antenna  15  to the first radio system  11  by switching when the control signal  10   a  is H and the control signal  10   b  is L, and connects the second antenna  16  to the first radio system  11  by switching when the control signal  10   a  is L and the control signal  10   b  is H. Moreover, the antenna changeover switch  14  for the second radio system connects the second antenna  16  to the second radio system  12  by switching when the control signal  10   a  is H and the control signal  10   b  is L, and connects the first antenna  16  to the second radio system  12  by switching when the control signal  10   a  is L and the control signal  10   b  is H.  
         [0032]    The control signal  10   a  and the control signal  10   b  have an inversion relationship with each other when the switching control of the antenna changeover switch  13  for the first radio system and the antenna changeover switch  14  for the second radio system is carried out. Therefore, the first switching control circuit  17  and the second switching control circuit  18  may be collected into one switching control circuit and the control signals  10   a  and  10   b  having the inversion relationship with each other may be output.  
         [0033]    [0033]FIG. 3 shows the relationship between the control signals corresponding to the antenna to be connected to the radio system which is used. As shown in FIG. 3, during the use of the first radio system  12 , the control signal  10   a  is set to be H and the control signal  10   b  is set to be L when the first antenna  15  is to be selected, and the control signal  10   a  is set to be L and the control signal  10   b  is set to be H when the second antenna  16  is to be selected. During the use of the second radio system, moreover, the control signal  10   a  is set to be L and the control signal  10   b  is set to be H when the first antenna  15  is to be selected, and the control signal  10   a  is set to be H and the control signal  10   b  is set to be L when the second antenna  16  is to be selected.  
         [0034]    When one of the antennas is connected to one of the radio systems for use, a load impedance fluctuates so that a transmitted signal is reduced if the same antenna is connected to the other radio system. For example, in the case in which the control signal  10   a  is set to be H, the control signal  10   b  is set to be L and the first antenna  15  is connected to the first radio system during the use of the first radio system  12 , the above problem arises when the first antenna  15  is also connected to the second radio system. In the composite radio apparatus in FIG. 1, however, if the control signal  10   a  is set to be H and the control signal  10   b  is set to be L, the second antenna  16  is connected to the second radio system  12  and the first antenna  15  is disconnected from the second radio system  12  so that the above problem does not arise.  
         [0035]    Next, the operation of the composite radio apparatus in FIG. 1 will be described by taking, as an example, a switching operation in transmitting and receiving timings in a radio system using a time sharing method. FIGS. 4A and 4B are diagrams showing the states of the control signals  10   a  and  10   b  in a transmitting slot T 1  and a receiving slot R 1  in the time sharing method. FIG. 4A shows a state obtained when the first radio system  11  is used and FIG. 4B shows a state obtained when the second radio system  12  is used, and both the drawings show the case in which the first antenna  15  is selected at time of a transmission and the second antenna  16  is selected at time of a receipt.  
         [0036]    When the control signals  10   a  and  10   b  are brought into the state shown in FIGS. 4A and 4B, the radio system to be used and the first antenna are connected to each other in the transmitting slot T 1  and the radio system to be used and the second antenna are connected to each other in the receiving slot R 1  during both the use of the first radio system  11  and the use of the second radio system  12 .  
         [0037]    In the composite radio apparatus shown in FIG. 1, in the case in which frequencies to be used by the two radio systems are different from each other, the mismatching of an impedance might be caused by the connection switching of the radio system through the antenna switching circuit, resulting in an increase in a loss.  
         [0038]    [0038]FIG. 2 is a diagram showing the schematic structure of a composite radio apparatus according to a second embodiment of the invention, in which the mismatching of an impedance is not caused also when frequencies to be used by two radio systems included in the composite radio apparatus are different from each other. The composite radio apparatus of FIG. 2 is the same as the composite radio apparatus in FIG. 1 except that a first matching circuit  21  is provided between a first radio system  11  and an antenna changeover switch  13  for a first radio system and a second matching circuit  22  is provided between a second radio system  12  and an antenna changeover switch  14  for a second radio system.  
         [0039]    The first matching circuit  21  serves to carry out frequency matching corresponding to a frequency to be used by the first radio system  11  and the second matching circuit  22  serves to carry out frequency matching corresponding to a frequency to be used by the second radio system  11 . By thus providing the matching circuits  21  and  22  corresponding to the frequencies to be used by the respective radio systems between the radio system and the antenna changeover switch, it is possible to reduce a loss caused by the mismatching of the impedance also when the frequencies to be used by the two radio systems are different from each other.  
         [0040]    While the first matching circuit  21  and the second matching circuit  22  are provided in FIG. 2, only one of them may be provided. In that case, a first antenna  15  and a second antenna  16  are set to correspond to a frequency to be used by the radio system on the side where the matching circuit is not provided.  
         [0041]    As described above, according to the invention, it is possible to provide a composite radio apparatus capable of reducing a loss in the switching of the antenna and the radio system. Moreover, it is possible to provide a diversity switching method capable of reducing a loss in the switching of the antenna and the radio system in the composite radio apparatus.  
         [0042]    According to the invention, furthermore, the matching circuits corresponding to the frequencies to be used by the respective radio systems are provided between each of the radio systems and the antenna changeover switch. Also in the case in which the frequencies to be used by the two radio systems constituting the composite radio apparatus are different from each other, consequently, it is possible to reduce a loss caused by the mismatching of an impedance in a diversity operation sharing the antenna.

Technology Classification (CPC): 7