Abstract:
A PDC communication controlling apparatus includes an audio processing section for converting a digital audio signal which has been encoded at a transmission rate of a personal digital cellular (PDC) into a digital audio signal at a transmission rate of a digital exchange network, a small radio base station controlling section accommodating a plurality of small radio base stations which are connected to PDC portable terminal units through radio circuits and which have different radio cover areas, the small radio base station controlling section managing the radio cover areas of the PDC portable terminal units, controlling calls, and controlling and managing the radio circuits, a network-side adaptor used in non-audio communications with the PDC portable terminal units, a PDC/network interface section connected to a private branch exchange through a plurality of communication paths, a time division switch for connecting the PDC/network interface, the audio processing section, the radio base station controlling section and the network-side adaptor and for switching the connection state thereof under the control of the small radio base station controlling section on time division basis.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a communication controlling apparatus in a local area radio system using a PDC (Personal Digital Cellular) portable terminal unit, in particular, to an audio/non-audio PDC communication controlling apparatus that is connected to a private branch exchange (PBX), that has the same service as a public PDC system, and that provides the service of the PBX. 
     2. Description of the Related Art 
     As the number of subscribers to digital portable telephone systems drastically increases, various new services are required. In addition, analog or digital telephone units used in offices and so forth require complicated wiring connections. Thus, fixed telephone units are inconvenient. To solve such problems, radio telephone systems have been constructed. 
     FIG. 6 is a schematic diagram showing the structure of a conventional radio telephone system as disclosed in Japanese Patent Laid-Open Publication No. Hei6-22360. 
     In the related art reference shown in FIG. 6, the radio telephone system is composed of a radio terminal unit  617  and a radio terminal unit controlling unit  600 . The radio terminal unit controlling unit  600  is connected to a private branch exchange (PBX) or the like (not shown). 
     The radio terminal unit controlling unit  600  comprises a radio terminal unit communication portion  615 , a controlling portion  601 , an exchange communication portion  604 , a two-wire/four-wire converting portion  610 , a hook relay switch  608 , a dial relay switch  609 , and a selecting switch  611 . A modular jack  619  can be used for both a two-wire type interface and a four-wire type interface of the PBX. With two-wire type signal lines  605 -R, the radio terminal unit controlling unit  600  is connected to the PBX. A bell detecting portion  607  detects a bell signal received from one of the signal lines  605 -R through a capacitor  606 . The controlling portion  601  generates a trigger signal. A DTMF (Dual Tone Multi-Frequency) signal generator  612  generates a DTMF signal. The selecting switch  611  selects the trigger signal or the DTMF signal and outputs the selected signal to the PBX or the like. 
     When an origination call, a termination call, a dialing signal, display data, and so forth are sent and received to/from the PBX, the controlling portion  601  controls the exchange communication portion  604 . Such data is transmitted to the radio terminal unit  617  through the radio terminal unit communication portion  615  and an antenna  616 . 
     An audio band signal is sent to the PBX through the radio terminal unit communication portion  615 , the two-wire/four-wire converting portion  610 , and the modular jack  619 . 
     The controlling portion  601  causes the radio terminal unit communication portion  615  to autonomously search a radio frequency free of an external interference and determine an operation frequency. In addition, the controlling portion  601  causes the radio terminal unit  617  to select a channel through the radio terminal unit communication portion  615 . 
     In other words, according to the related art reference, the controlling portion  601  determines whether or not the interface of the PBX is two-wire type or four-wire type, adaptively converts an audio band signal received from the radio terminal unit  617  into a particular signal, and autonomously determines an operation signal, thereby suppressing the operation frequency from interfering another unit and from being interfered by another unit. However, the radio terminal unit  617  of the system should be disposed in a radio cover area of the radio terminal unit controlling unit  600  accommodated in the PBX. 
     Thus, in the local area radio system composed of the PBX, the small radio base station, and the radio terminal unit, since communications are available only in the radio cover area of the radio base station accommodated in the PBX, the usability of the system is low. 
     In addition, since it is difficult to exchange a control signal among a plurality of terminal unit controlling units, while a radio terminal unit is moving, a user thereof cannot communicate to another user. 
     Moreover, due to the system structure, it is difficult to share the system with a non-audio communication (such as FAX and data communication) and an audio communication. 
     SUMMARY OF THE INVENTION 
     The present invention is made from the above-described point of view. An object of the present invention is to provide a PDC communication controlling apparatus that has the following features. A PDC portable telephone terminal unit instead of a conventional wired telephone unit used in an office is used in a local area radio system that will be increasingly used year after year. Thus, the PDC portable telephone terminal unit is used as an office telephone unit that has an extension communication function with high mobility. A plurality of PDC portable telephone terminal units can be connected to the PBX. Each PDC portable telephone terminal unit can transmit not only an audio band signal, but a non-audio signal (such as FAX and data). While a PDC portable telephone terminal is moving, it can transmit both an audio signal and a non-audio signal as with a conventional public PDC system. Moreover, services of the PBX are provided. Thus, the usability of a PDC portable telephone terminal unit can be further improved. 
     A first aspect of the present invention is a PDC communication controlling apparatus, comprising an audio processing means for converting a digital audio signal that has been encoded at a transmission rate of a personal digital cellular (PDC) into a digital audio signal at a transmission rate of a digital exchange network, a small radio base station controlling means accommodating a plurality of small radio base stations that are connected to PDC portable terminal units through radio circuits and that have different radio cover areas, the small radio base station controlling means managing the radio cover areas of the PDC portable terminal units, controlling calls, and controlling and managing the radio circuits, a network-side adaptor used in non-audio communications with the PDC portable terminal units, a PDC/network interface means connected to a private branch exchange through a plurality of communication paths, a time division switch for connecting the PDC/network interface, the audio processing means, the radio base station controlling means, and the network-side adaptor and for switching the connection state thereof under the control of the small radio base station controlling means on time division basis, wherein the small radio base station controlling means separates the PDC/network interface means from the network-side adaptor in the case that a termination call is an audio communication, places the network-side adaptor between the PDC/network interface means and the audio processing means in the case that the termination call is a non-audio communication, and loops back the communication path for an extension communication in the case that the termination call is a communication performed between the PDC portable terminal units. 
     A second aspect of the present invention is a PDC communication controlling apparatus, comprising an audio processing means for converting a digital audio signal that has been encoded at a transmission rate of a personal digital cellular (PDC) into a digital audio signal at a transmission rate of a digital exchange network, a plurality of small radio base stations having different radio cover areas, a small radio base station controlling means, connected to the small radio base stations, for managing the radio cover areas of PDC portable terminal units, controlling calls, and controlling and managing radio circuits, a network-side adaptor used in non-audio communications with the PDC portable terminal units, a PDC/network interface means connected to a private branch exchange through a plurality of communication paths, a time division switch for connecting the PDC/network interface, the small radio base station controlling means, and the network-side adaptor and for switching the connection state thereof under the control of the small radio base station controlling means on time division basis, wherein the small radio base station controlling means separates the PDC/network interface means from the network-side adaptor in the case that a termination call is an audio communication, places the network-side adaptor between the PDC/network interface means and the small radio base station controlling means in the case that the termination call is a non-audio communication, and loops back the communication path for an extension communication in the case that the termination call is a communication performed between the PDC portable terminal units. 
     The audio processing means preferably converts an audio signal that has been encoded at a transmission rate of 11.2 kbps, 7.05 kbps, or 3.675 kbps on the PDC side into an ADPCM (Adaptive Differential Pulse Code Modulation) audio signal at a transmission rate of 32 kbps on the digital exchange network side. 
     Thus, the audio processing means decodes and converts a PDC audio signal at a transmission rate of 11.2 kbps (full rate), 7.05 kbps (half rate), or 3.675 kbps (high efficiency) that has been encoded by a PDC portable terminal unit into an ADPCM signal at a transmission rate of 32 kbps. The resultant signal is sent to the PDC/network interface means by the time division switch. The signal is sent to the PBX through the PDC/network interface means. The PDC/network interface means can directly interface with the PBX. In other words, the PDC portable terminal unit can be connected as an extension unit to the PBX without need to modify the PBX. The PBX detects a destination telephone number from the signal received from the PDC portable terminal, sets a communication path to an external line or an extension line, and calls the telephone unit on the destination side (in the case that the PDC portable terminal unit originates a call). 
     At this point, the small radio base station (BS) and the radio circuit are controlled by the small radio base station (BS) controlling means. The PDC communication controlling apparatus handles a control signal on the control channel D ch different from the communication channel B ch. 
     At this point, the small radio base station (BS) controlling means manages the radio cover area of the PDC portable terminal unit and the frequency of the small radio base station. In the PDC communication controlling apparatus, the PDC portable terminal unit can be handed over. 
     The small radio base station (BS) converts the PDC control signal format into the network control signal format beforehand. The PDC communication controlling apparatus operates corresponding to the network control signal format. 
     When a non-audio communication (such as FAX/data) is performed, the audio processing means does not perform the encoding/decoding process, but directly send a non-audio signal to the time division switch. The time division switch detects a non-audio signal corresponding to a command received from the small radio base station (BS) controlling means and places the network-side adaptor (modem) in the communication path corresponding to the data type. The network-side adaptor (modem) has a function for terminating the PDC non-audio protocol and converting it into the network-side FAX/data communication protocol or vice versa (T.30, V42. bis etc.). 
     Thus, the PDC portable terminal unit can be disposed in the radio cover area of the PDC communication controlling apparatus. With the PDC portable terminal unit and the PBX, a local area radio system can be accomplished. In addition, the PDC portable terminal unit can have both services of the public PDC system and the PBX. 
     These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic diagram showing the structure of a preferred embodiment of the present invention; 
     FIG. 2 is a flow chart showing a radio circuit operation frequency determining process of a small radio base station (BS) controlling means  113 ; 
     FIG. 3 is a schematic diagram showing the structure of another embodiment of the present invention; 
     FIG. 4 is a flow chart showing a control process of a small radio base station (BS) controlling means  312 ; 
     FIG. 5 is a schematic diagram showing the structure of another embodiment of the present invention; and 
     FIG. 6 is a schematic diagram showing the structure of a related art reference. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic diagram showing the structure of a system according to an embodiment of the present invention. Referring to FIG. 1, reference numeral  100  is a private branch exchange (PBX). Reference numerals  101 ,  102 , and  103  are PDC communication controlling apparatuses. Reference numeral  104  is a group of small radio base stations. Reference numeral  105  is a group of PDC portable terminal units. 
     In this embodiment, a predetermined number of PDC communication controlling units can be accommodated to the PBX  100 . In other words, the PBX  100  treats all PDC portable terminal units that are in radio cover areas of the PDC communication controlling units  101 ,  102 , and  103  accommodated in the PBX  100  as extension units thereof. In FIG. 1, reference numeral  110  is a group of audio processing means. Reference numeral  111  is a time division switch. Reference numeral  112  is a PDC/network interface means. Reference numeral  113  is a group of small radio base stations (BS) controlling means. Reference numeral  114  is a group of network-side adaptors (modems). Reference numeral  115  is a group of FAX adaptors in the group of network-side adaptors  114 . Reference numeral  116  is a group of data communication adaptors. Reference numeral  131  is a D channel data bus for exchanging a control signal between the group of small radio base station (BS) controlling means  113  and the group of small radio base stations (BS)  104  or the group of PDC portable terminal units  105 . Reference numeral  132  is a B channel data bus for sending an audio signal or a non-audio signal. 
     The group of small radio base stations  104 , the group of PDC terminal units  105 , the group of audio processing means  110 , the group of small base station controlling means  113 , the group of network-side adaptors  114 , the group of FAX adaptors  115 , and the group of data communication adaptors  116  are composed of a plurality of small radio base stations, a plurality of PDC terminal units, a plurality of audio processing means, a plurality of small base station controlling means, a plurality of network-side adaptors, a plurality of FAX adaptors, and a plurality of data communication adaptors, respectively. However, in the following description, for simplicity, a single small radio base station  104 , a single PDC terminal unit  105 , an audio processing means  110 , a single small base station controlling means  113 , a single network-side adaptor  114 , a single FAX adaptor  115 , and a single data communication adaptor  116  will be described. 
     The number of small radio base stations (BS)  104  and the number of PDC portable terminals that can be accommodated in the audio processing means  110 , the small radio base station (BS) controlling means  113 , and the network-side adaptor (modem)  114  are predetermined. However, depending on an application, the number of PDC portable terminals accommodated in these means becomes large. In this case, a plurality of audio processing means  110 , a plurality of small radio base station (BS) controlling means  113 , and a plurality of network-side adaptors (modems)  114  are required. 
     In addition, when the number of PDC portable terminal units  105  becomes large, a plurality of PDC communication controlling apparatuses may be used. In FIG. 1, as an example, two PDC communication controlling apparatuses  102  and  103  are disposed. 
     Next, the operation of the system according to the embodiment shown in FIG. 1 will be described. 
     The operation frequency of the small radio base station (BS)  104  should be free from external interference. For example, when a plurality of small radio base stations (BS)  104  are adjacently disposed, the operation frequencies thereof may interfere with each other. To prevent such interference, the small radio base station (BS) controlling means  113  of the PDC communication controlling apparatus  101  manages the operation frequencies of all the small radio base stations (BS)  104  accommodated thereto. In addition, each small radio base station (BS)  104  has a transmitting/receiving antenna and detects interference corresponding to a data error ratio of the receiving portion. The small radio base station (BS) controlling means  113  has a blank frequency management table (not shown). With reference to the blank frequency management table, the small radio base station (BS) controlling means  113  manages the operation frequencies of the small radio base stations (BS)  104 . 
     FIG. 2 is a flow chart showing the operations of the small base station (BS) controlling means  113  and the small base station (BS)  104 . Next, with reference to FIG. 2, the operation of the system according to the embodiment shown in FIG. 1 will be described. 
     When the operation of the small radio base station (BS)  104  is started, it requests the small radio base station (BS) controlling means  113  to perform a channel scanning operation for blank frequency information (at step S 203 ). Thus, the small radio base station (BS) controlling means  113  performs the channel scanning operation and informs the small radio base station (BS)  104  of the blank frequency information (at step S 201 ). 
     The small radio base station (BS)  104  scans all frequencies corresponding to the received blank frequency information (at step S 204 ) and determines whether or not interference waves are present at individual frequencies (at step S 205 ). When an interference wave is present at a scanned frequency (namely, the determined result at step S 205  is Yes) (at step S 205 ), the small radio base station (BS)  104  informs the small radio base station (BS) controlling means  113  of the frequency at which an interference wave is present (at step S 206 ). The small radio base station (BS)  104  designates a channel on which the interference wave is the weakest as an operation channel (at step S 207 ), informs the small radio base station (BS) controlling means  113  of the designated channel (at step S 208 ), and determines the operation wave (at step S 210 ). 
     The small radio base station (BS) controlling means  113  stores the informed frequency as an operation unavailable frequency (at step S 202 ) and modifies the blank frequency table (at step S 209 ). 
     When the small radio base station (BS)  104  has detected an interference wave (at step S 211 ), it informs the small radio base station (BS) controlling means  113  of the interference frequency (at step S 212 ) and requests the small radio base station (BS) controlling means  113  for a blank frequency (at step S 213 ). 
     Thus, the small radio base station (BS) controlling means  113  searches an optimum blank frequency from the blank frequency table in the same manner as step S 201  and informs the small radio base station (BS)  104  of the searched frequency. The small radio base station (BS)  104  operates at the received blank frequency as the operation frequency and informs the small radio base station (BS) controlling means  113  of the operation frequency (at step S 208 ). 
     Thus, the small radio base station (BS) controlling means  113  modifies the blank frequency table corresponding to the informed operation frequency. Information is exchanged between the small radio base station (BS) controlling means  113  and the small radio base station (BS)  104  on the D channel  131 . 
     When an audio signal is communicated, the audio processing means  110  converts an encoded audio signal at a transmission rate of 11.2 kbps, 7.05 kbps, or 3.675 kbps on the PDC side into an ADPCM audio signal at a transmission rate of 32 kbps on the network side or vice versa. When a call is transmitted to an external line or a call is transmitted to an extension line in the PBX, the time division switch  111  sets a communication path to the PBX through the PDC/network interface means  112  so as to send an ADPCM audio signal. 
     When a call is transmitted between PDC portable terminal units accommodated in the same PDC communication controlling apparatus, the time division switch  111  loops back the communication path so as to accomplish an extension communication in the PDC communication controlling apparatus  101 . When an audio signal is communicated, the network-side adaptor (modem)  114  is not connected. 
     When a non-audio signal is communicated, the audio processing means  110  does not perform the audio process, but directly sends the non-audio signal to a predetermined portion corresponding to a command received from the small radio base station (BS) controlling means  113 . However, in this case, the audio processing means  110  converts the non-audio signal at a transmission rate of 11.2 kbps on the PDC side into the signal at a transmission rate of 32 kbps on the network side. 
     Likewise, corresponding to a command received from the small radio base station (BS) controlling means  113 , the time division switch  111  is controlled so that the network-side adaptor (modem) is placed on the communication path. 
     The small radio base station (BS) controlling means  113  manages the radio cover area of the PDC portable terminal units  105  accommodated thereto. In the case that after a communication between a particular small radio base station (BS)  104  and a particular PDC portable terminal unit  105  is interrupted, the particular PDC portable terminal unit  105  transmits a communication request to another small radio base station (BS)  104 , the small radio base station (BS) controlling means  113  detects the communication request, restores the communication path of the particular PDC portable terminal unit  105 , and causes the time division switch  111  to set a new communication path. Thus, the call can be handed over (namely, the call is not disconnected, but resumed). 
     FIG. 3 is a schematic diagram showing the structure of a system according to an embodiment of the present invention. 
     Referring to FIG. 3, reference numeral  300  is a PDC communication controlling apparatus. Reference numeral  301  is a private branch exchange (PBX). Reference numeral  302  is a PDC mobile terminal unit. Reference numerals  303  and  304  are PDC small radio base stations (BS). 
     The embodiment shown in FIG. 1 is the maximum structure of the present invention, while the embodiment shown in FIG. 3 is the minimum structure thereof. The radio circuit format of the PDC small radio base stations (BS)  303  and  304  is a time division system having time slots  0  to  5 . The time slots  2  and  5  of each small radio base station (BS) are used for control channels on which a control signal is transmitted/received between a PDC portable terminal unit  302  and a PDC communication controlling apparatus  300 . 
     An audio processing means  310  in the PDC communication controlling apparatus  300  can accommodate two small radio base stations (BS)  303  and  304 . Each PDC communication controlling apparatus  300  can control up to eight (4×2=8) audio communications. The small radio base stations (BS)  303  and  304  and the PDC communication controlling apparatus  300  are connected with an ISDN circuit. 
     Reference numeral  311  is a time division switch that selects a communication path for an audio signal or a communication path for a non-audio signal. Reference numeral  312  is a small radio base station (BS) controlling means that controls the radio circuits of the small radio base stations (BS)  303  and  304 , calls, and the radio cover area of the PDC portable terminal unit  302 . Reference numeral  313  is a PDC/network interface means. Reference numeral  314  is a network-side adaptor (modem) used for a non-audio communication. The network-side adaptor  314  has FAX adaptors  317  and  318  and data communication adaptors  319  and  320 . Adaptors are disposed corresponding to individual non-audio communication services. Each adaptor is assigned one communication path. 
     The PDC/network interface means  313  in the PDC communication controlling apparatus  300  connects the PBX  301  and the PDC communication controlling apparatus  300  without need to modify the PBX  301 . Reference numeral  330  is a personal computer used in a non-audio communication. Reference numeral  331  is a card modem for a PDC portable terminal unit. The card modem  331  is connected to the personal computer  330 . The card modem  331  controls a PDC non-audio protocol with the network-side adaptor (modem)  314  through the PDC portable terminal unit  302 . 
     FIG. 4 is a flow chart showing the control operation of the small radio base station (BS) controlling means  312  that controls both an audio communication and a non-audio communication. Next, with reference to FIG. 4, the control operation will be described. 
     When the power of the small radio base station (BS)  303  is turned on, a frequency free from an interference wave is selected in the process shown in FIG.  2 . The selected frequency is used as an operation frequency of the small radio base station (BS)  303 . 
     When the PDC portable terminal unit  302  acquires the operation frequency, it exchanges a control signal with the small radio base station (BS) controlling means  112  and enters into a standby state. In other words, the PDC portable terminal unit  302  is placed in the radio cover area of the small radio base station (BS)  303 . Thus, the PDC portable terminal unit  302  enters into a standby state. In other words, the radio cover area of the PDC portable terminal unit  302  is managed by the small radio base station (BS) controlling means  312  accommodated in the PDC communication controlling apparatus  300 . 
     When the PDC portable terminal unit  302  originates a call, a control signal corresponding to the PDC protocol is transmitted to the small radio base station (BS)  303  through the time slots  2  and  5  of the radio circuit. 
     The small radio base station (BS)  303  converts the control signal corresponding to the PDC protocol into a control format corresponding to the network protocol. The resultant signal is sent to the small radio base station (BS) controlling means  312  through the audio processing means  310  and the ISDN D channel  340  (at step S 400 ). 
     The small radio base station (BS) controlling means  312  detects a destination telephone number of a call originated by the PDC portable terminal unit  302  and determines whether the designation of the call is an external line, an analog telephone unit in the PBX  301 , a digital telephone unit therein, or a PDC portable terminal unit  316  in the radio cover area of the small radio base station (BS)  312  (at step S 401 ). When the call is a communication between the PDC portable terminals  302  and  316 , the small radio base station (BS) controlling means  312  causes the audio processing means  310  to enter into the through mode regardless of whether the call is an audio communication or a non-audio communication (at step S 409 ). In addition, the small radio base station (BS) controlling means  312  causes the time division switch  311  to loop back the communication path (at step S 415 ). 
     Thus, the audio processing means  310  does not perform the audio process, but directly sends/receives the signal to a predetermined portion. When the call is not a communication performed between the PDC portable terminal units  302  and  316 , the small radio base station (BS) controlling means  312  determines whether the call is an audio communication or a non-audio communication (at step S 402 ). When the call is an audio communication, the small radio base station (BS) controlling means  312  determines whether the format of the radio circuit (transmission rate) is 11.2 kbps, 7.05 bps, or 3.675 bps (at step S 403 ). Depending on the format of the radio circuit, the audio process performed by the audio processing means  310  varies. Thus, the small radio base station (BS) controlling means  312  causes the audio processing means  310  to perform the process corresponding to the determined format of the radio circuit (at steps  404  to S 406 ). The audio processing means  310  performs the audio process corresponding to the required format of the radio circuit. 
     Thereafter, the small radio base station (BS) controlling means  312  sends required call control information to the PBX through the PDC/network interface means  313 . In addition, the small radio base station (BS) controlling means  312  causes the time division switch  311  to open the communication path  314  to the PBX  301  (at step S 407 ). The time division switch  311  connects the communication path corresponding to the command received from the small radio base station (BS) controlling means  312 . The PBX  301  connects a different communication path depending on whether the destination of the call is an external line, an analog telephone unit in the PBX  301 , or a digital telephone unit in the PBX  301 . 
     The above-described operation is performed in the case that the destination telephone number of the call is a telephone number of an external line or a telephone number accommodated in the PBX  301  and that the call is an audio communication. On the other hand, when the call is a non-audio communication as the determined result at step S 402 , the small radio base station (BS) controlling means  312  causes the audio processing means  310  to enter into the through mode (at step S 408 ) and determined whether or not the non-audio communication is a FAX communication or a data communication (at step S 410 ). Since the network-side adaptor (modem)  314  has FAX adaptors  317  and  318  and data communication adaptors  319  and  320  corresponding to service types and each adaptor is assigned one communication path, the network-side adaptor (modem)  314  can accommodate non-audio communications corresponding to the number of adaptors. 
     When the non-audio communication is a FAX communication as the determined result at step S 410 , the small radio base station (BS) controlling means  312  determines whether or not there is an available adaptor (at step S 412 ). When there is an available adaptor, the small radio base station (BS) controlling means  312  informs the time division switch  311  that the call is a FAX communication and causes the time division switch  311  to connect a relevant communication path to the FAX adaptors  317  and  318  of the network-side adaptor (modem)  314  (at step S 414 ). 
     When the non-audio communication is a data communication as the determined result at step S 410 , the small radio base station (BS) controlling means  312  determines whether there is an available adaptor (at step S 411 ). When there is an available adaptor, the small radio base station (BS) controlling means  312  informs the time division switch  311  that the call is a data communication so as to cause the time division switch  311  to connect a relevant communication path to the data communication adaptors  319  and  320  of the network-side adaptor (modem)  314  (at step S 413 ). 
     The small radio base station (BS) controlling means always monitors whether or not the network-side adaptor (modem)  314  is being used. When there is no available adaptor at steps S 411  and S 412 , the small radio base station (BS) controlling means  312  informs the PDC portable terminal unit  302  or the PDC portable terminal card modem  331  through the small radio base station (BS)  303  of service unavailable information (at step S 416 ). 
     When the call is received from an external line or a telephone unit accommodated in the PBX  301 , the small radio base station (BS)  303  converts a signal corresponding to the protocol of the external line or the telephone unit in the PBX  301  into a signal corresponding to the protocol of the PDC and terminates the call to the PDC portable terminal unit  302 . As with the origination call of the PDC portable terminal unit  302 , the small radio base station (BS)  312  determines the radio circuit format corresponding to the protocol of the PDC and controls the audio processing means  310 . When the call is a non-audio communication, the small radio base station (BS) controlling means  312  causes the audio processing means  310  to connect the network-side adaptor (modem)  314 . When the call is an audio communication, the small radio base station (BS) controlling means  312  causes the audio processing means  310  to disconnect the network-side adaptor (modem)  314 . 
     FIG. 5 is a schematic diagram showing the structure of a system according to another embodiment of the present invention. 
     As with the embodiment shown in FIG. 3, the system shown in FIG. 5 comprises a PDC communication controlling apparatus  500 , a private branch exchange (PBX)  501 , and small radio base stations  503  and  504 . Likewise, the PDC communication controlling apparatus  500  comprises a small radio base station (BS) controlling means  512 , a PDC/network interface means  513 , a time division switch  511 , and a network-side adaptor (modem)  514 . In this embodiment, instead of the audio processing means  310  shown in FIG. 3, audio processing means  505  and  506  are disposed in the small radio base stations (BS)  503  and  504 , respectively. The small radio base station (BS) controlling means  512  has an ISDN interface means  517  that separates or combines an audio/non-audio signal on a B channel and a control signal on a D channel. The functions and operations of a PDC portable terminal unit  502 , a personal computer  530 , a card modem  531 , and a PDC portable terminal unit  516  are the same as those of the PDC portable terminal unit  302 , the personal computer  330 , the card modem  331 , and the PDC portable terminal unit  316  shown in FIG. 3, respectively. 
     According to the embodiment shown in FIG. 5, the structure of the PDC communication controlling apparatus can be simplified. In the embodiment shown in FIG. 3, the small radio base station (BS) controlling means  312  controls the audio processing means  310 , the time division switch  311 , the radio cover areas of the PDC mobile terminal units  302  and  316 , and the small radio base stations (BS)  303  and  304 . However, in the structure shown in FIG. 5, since the control of the audio processing means can be omitted, the process of the small radio base station (BS) controlling means  512  can be alleviated. 
     As described above, the present invention has the following effects. 
     As a first effect of the present invention, with the PDC communication controlling apparatus, a control signal corresponding to a PDC protocol can be converted into a control signal corresponding to a network protocol or vice versa. A PDC audio signal can be encoded or decoded to/from an ADPCM signal at a transmission rate of 32 kbps. With a FAX/data communication adaptor connected to a PDC portable terminal unit, a signal corresponding to a non-audio protocol on the PDC side can be converted into a signal corresponding to a non-audio protocol on the network side. Thus, a non-audio communication can be accomplished. An audio communication path can be switched to a non-audio communication path or vice versa. In addition, since the radio cover areas of PDC portable terminal units are managed, various functions such as a hand-over function of PDC portable terminal units accommodated in the same PDC communication controlling apparatus or the same private branch exchange (PBX) can be accomplished. 
     Thus, almost the same functions as a public PDC system can be accomplished. When the PDC communication controlling apparatus and the small radio base station (BS) are disposed in a building or a factory, PDC portable terminal units used in the public PDC system are accommodated in the PDC communication controlling apparatus, the same service as the public PDC system can be accomplished. In addition, as with a conventional local area radio system and an office telephone system, the PDC portable terminal units can be used as extension terminal units of the PBX. 
     As a second effect of the present invention, when the audio processing means group, the network-side adaptor group, and the small base station (BS) controlling means group are disposed in the PDC communication controlling apparatus according to the present invention, the structure of the small radio base stations (BS) disposed in various places such as buildings and factories can be simplified. Thus, the PDC communication controlling apparatus can be easily disposed. 
     Although the present invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.