Patent Publication Number: US-2005136835-A1

Title: Radio relay device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a radio relay device capable of relaying a data communication, telephone call and communication data for printing in a master-slave type of radio network.  
      2. Description of the Related Art  
      In recent years, various standards of the radio network have been specified, and the radio network is connected to another radio network in the same standard having various uses.  
      For example, as regards the Bluetooth (trademark) in the radio network standard, not only a computer but also a computer peripheral device such as a printer and scanner and an electronic device such as a facsimile device, audio device and cordless telephone can be connected to one another in the Bluetooth standard. Thus, the respective electronic devices are adapted to transmit/receive information, sound, and images.  
      In the Bluetooth, within a piconet which is the radio network, an electronic device which performs a main control of communication is communicated with other electronic devices called slaves under the control of the master. Further, in the Bluetooth, a single master is included in a single piconet, and slaves can be connected a plurality of piconets so that the slaves are connected to the masters in the plurality of piconets.  
      Further, in the Bluetooth, communication is carried out through radio waves. Therefore, if a plurality of electronic devices simultaneously perform the communication, collision of the respective transmission data occurs so that the communication cannot be done. In order to obviate such an inconvenience, transmission timings as time division slots are allotted to the respective devices, thereby preventing collision of transmission/reception data.  
      The cordless telephone which is an example of the device which can be connected to the piconet constitutes the piconet including a master as a parent device and slaves as child devices. A person can move anywhere within a radio wave reaching range to have a talk with another person using the cordless telephone. In addition, by providing a repeater serving as a radio relay device within the range of the piconet, the communication range of the child device can be enlarged so that the demand for the repeater may be increased more and more.  
      Where the repeater is connected to the parent device serving as the master, it operates as the slave. On the other hand, where the repeater is connected to the child device serving as the slave, it operates as the master.  
      Referring to  FIG. 10 , a conventional radio relay device will be explained.  FIG. 10  is a view showing the manner of connecting a repeater as an example of the conventional radio relay device to a radio network.  
      A repeater  100 , which operates as the conventional radio relay device, performs the relay for two cordless telephones. A child device  102  of the cordless telephone within a first piconet  101  as the radio network is connected to a parent device  104  of the cordless telephone in a second piconet  103  through the repeater  100 , thereby having conversation with a speaking partner connected to a public switched network  105 .  
      A PDA (Personal Digital Assistance)  107  within a third piconet  106  is connected to through the repeater  100  an internet through the public switched network  105  via a parent device  109  within a fourth piconet  108 .  
      First, the communication between the parent device  104  serving as a master and the repeater  100  serving as the slave is done as follows. The parent device  104  transmits a packet in synchronism with the clock of itself. The repeater  100  detects the timing of the clock of the parent device  104  on the basis of the packet received. In the transmission from the repeater  100  to the parent device  104 , the repeater  100  transmits the packet in synchronism the clock of the parent device  104  on the basis of the detected timing of the clock of the parent device  104 .  
      Next, the communication between the repeater  100  serving as the master and the child device  102  serving as the slave is done as follows. The repeater  100  transmits the packet in synchronism with its clock to the child device  102  serving as the slave. The child device  102  detects the timing of the clock of the repeater  100  on the basis of the packet received. In the transmission from the child device  102  to the repeater  100 , the child device  102  transmits the packet in synchronism with the clock of the repeater  100  on the basis of the detected timing of the clock of the repeater  100 .  
      The communication between the parent device  109  serving as the master and the repeater  100  serving as the slave is done as follows. The parent device  109  transmits the packet in synchronism with the clock of the parent device  109 . The repeater  100  detects the timing of the clock of the parent device  109 . In the transmission from the repeater  100  to the parent device  109 , the repeater  100  transmits the packet in synchronism with the clock of the parent device  109  on the basis of the detected timing of the clock of the parent device  109 . Likewise, between the repeater  100  and the PDA  107 , communication is done using the packet in synchronism with the timing of the clock of the repeater  100 .  
      In this way, in the case of the communication between the master and the slave, the slave can surely transmits the packet to the communication partner in such a manner that the slave transmits the packet in synchronism with the clock of the master.  
      However, the conventional radio relay device has the following disadvantage. The repeater  100  operating as the slave performs in synchronism with the parent device  104  serving as the master and also operates as the master for the child device  102 . Namely, the child device  102  performs the communication in synchronism with the repeater  100  serving as the master.  
      Where the repeater  100  relays a synchronous packet between the parent device  104  and the child device  102  in a line switched system in which the packet is periodically transmitted/received, if the clock frequency of the parent device  104  does not perfectly agree with but slightly deviates from that of the repeater  100 , the packets transmitted in synchronism with their respective clocks result in a step-by-step discrepancy in the transmission timings because of jitter due to the difference in the clock between the parent device  104  and the repeater  100 .  
      Namely, if the transmission timing of the packet transmitted from the parent device  104  to the repeater  100  and that of the packet transmitted from the repeater  100  to the child device  102  are shifted to the same timing, collision of the packets occurs.  
      In order to solve such a problem, JP-A-10-233730 discloses a radio relay device for relaying communication data between a first radio communication device (public base station) and a second radio communication device (cellular phone).  
      In accordance with the radio relay device disclosed in Patent Reference 1, when the difference in the transmission/reception timing between the public base station and cellular phone becomes less than a predetermined time, a control data for changing the transmission/reception timing is transmitted to the public base station so that overlapping of the transmission/reception timing between the public base station and the cellular phone can be avoided.  
      Further, in the relay station for relaying communication for a moving body terminal disclosed in JP-A-2002-359590, when the communication for the moving body terminal is relayed to a switching station through a plurality of relay stations, a signal is transmitted with the entire slot timings of the relay stations being in synchronism with one another and delayed by one slot for each relay station, or otherwise with the frequency of the signal received by each relay station being changed. In this manner, the communication with good response can be realized by the signal with less delay.  
      Meanwhile, in the radio relay device disclosed in Patent Reference 1, it is necessary to detect that the difference in the transmission/reception timing between the public base station and the cellular phone becomes less than the predetermined time. This leads to a problem of enlarging the circuit scale.  
      In addition, overlapping of the transmission/reception timing between the public base station and the cellular phone is avoided by transmitting the control data for changing the transmission/reception timing to the public base station. This complicates the communicating procedure.  
      In the case of the synchronous packet in the line switched system, since the communication is performed at prescribed slot intervals, changing the transmission/reception timing leads to deterioration in a data quality. Further, the Bluetooth does not have the control data of changing the transmission/reception timing as a measure. Thus, the radio relay device described in Patent Reference 1 cannot be applied to the radio network such as the Bluetooth.  
      Further, in the relay station disclosed in Patent Reference 2, since the packet is delayed by one slot for each of the plurality of relay stations, the delay of the packet increases with an increase in the number of the steps of the relay stations. Where the frequency of the packet to be transmitted is changed, it cannot be changed optionally because in the radio network such as the Bluetooth, the frequency used for transmission/reception is prescribed according to a frequency hopping.  
     SUMMARY OF THE INVENTION  
      In view of the above circumstance, this invention intends to provide a radio relay device with a small size and reduced cost which can prevent collision of communication data when the communication data are relayed in a plurality of radio networks.  
      This invention provides a radio relay device for receiving a synchronous packet in a line switched system transmitted from an electronic device serving as a master connected to a radio network and relaying, as the master, the synchronous packet thus received to another electronic device serving as a slave connected to another radio network different from the radio network, including: a synchronization timing detecting unit for detecting a synchronization timing synchronous with the electronic device serving as the master from the packet transmitted from the electronic device serving as the master; a timing correcting unit for computing a correcting value for correcting a timing of transmitting the packet to another electronic device on the basis of the timing detected by the synchronization timing detecting unit, wherein when a radio relay unit relays the synchronous packet transmitted from the electronic device serving as the master is relayed, it transmits the synchronous packet to the other electronic device at the timing corrected on the basis of the correcting value.  
      In this configuration, in communication with the other electronic device serving as the slave, the relay apparatus can communicate with the other electronic device at the corrected timing so that the packet transmission/reception for the electronic device serving as the master and that for the other electronic device serving as the slave are executed at the timing synchronous with the clock of the electronic device serving as the master. Thus, it is possible to prevent the transmission timings of the packet from gradually shifting to the same timing, thereby preventing collision of packets. Further, in a simple configuration, synchronization of the packets can be taken so that the communicating procedure or circuit for changing the transmission timing using e.g. a control data is not required. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a view showing the configuration in which a repeater which is an example of the radio relay device according to an embodiment of this invention is connected to radio networks.  
       FIG. 2  is a view of the construction of the repeater which is an example of the radio relay device according to an embodiment of this invention.  
       FIG. 3  is a timing chart showing the relationship between the format of a packet used in the Bluetooth and clocks.  
       FIG. 4  is a flowchart for explaining the method of computing a correcting value which represents a deviation from the timing synchronous with the master in the packet received by a repeater from a master.  
       FIG. 5  is a view showing an example of the contents of a timing correcting buffer.  
       FIG. 6  is a flowchart for explaining the transmission timing synchronous with the master when a synchronous packet is transmitted from the repeater.  
       FIG. 7  is a view showing in detail the correction of the packet transmission timing in the repeater.  
       FIG. 8  is a view showing an example of the communication in which a parent device and child device and the parent device and PDA are relayed by a repeater, respectively.  
       FIG. 9  is a view showing packet transmission timings in detail in the case where two relays are concurrently by the repeater.  
       FIG. 10  is a view showing the configuration in which a repeater which is an example of a conventional radio relay device is connected to radio networks. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Now referring to the drawings, an explanation will be given of an embodiment of this invention.  FIG. 1  is a view showing the configuration in which a repeater which is an example of the radio relay device according to an embodiment of this invention is connected to radio networks.  
      In the example shown in  FIG. 1 , a repeater  1  which is a radio relay device belongs to four radio networks, i.e. a first piconet  101 , a second piconet  103 , a third piconet  106  and a fourth piconet  108 . In the first piconet  101  and third piconet  106 , a repeater  1  serves as a master. In the second piconet  103 , the repeater  1  serves as a slave and is connected to a parent device  104  serving as a master. In the fourth piconet  108 , the repeater  1  serves as the slave and is connected to a parent device  109  serving as the master.  
      A child device  102  of the cordless telephone within the first piconet  101  as the radio network is connected to the parent device  104  of the cordless telephone through the repeater  100 , thereby having conversation with a speaking partner connected to a public switched network  105 .  
      A PDA (Personal Digital Assistance)  107  within the third piconet  106  is connected through the repeater  100  to an internet through the public switched network  105  via a parent device  109  within the fourth piconet  108 .  
      Where the repeater  1  relays a packet from the parent  104  and child device  102  between which an audio data is transmitted/received, in the second piconet, the repeater  1  serving as the slave receives the packet transmitted from the parent device  104  serving as the master, and in the first piconet, the repeater  1  serving as the master transmits the received packet to the child device  102  serving as the slave.  
      Likewise, where the repeater  1  relays the communication data from an internet to the parent device  109  and PDA  107 , in the fourth piconet  108 , the repeater  1  serving as the slave receives the packet transmitted from the parent device  109  serving as the master and in the third piconet  106 , the repeater  1  serving as the master transmits the received packet to the PDA  107  serving as the slave.  
      Next, referring to  FIG. 2 , an explanation will be given of the configuration of a repeater which is an example of the radio relay device according to an embodiment of this invention.  FIG. 2  is a block diagram of the repeater which is an example of the radio relay device according to the embodiment of this invention.  
      A repeater  1  includes an antenna  10 , a radio unit  11  for performing transmission/reception of a signal in a time divisional communicating system, a synchronization correlator  12 , a received packet analyzing unit  13 , a received packet processing unit  14 , a transmitted packet creating unit  15 , a synchronizaton timing detector  16 , a timing correcting unit  17 , a clock counter  18 , a bit counter  19 , a timing correcting value buffer  20  and a communication control unit  21 .  
      The antenna  10  receives a packet transmitted via a radio wave from another electronic device connected to a radio network or transmitted directly or a repeater device which is a relay device.  
      The radio unit  11  carries out the transmission/reception of a signal in a time divisional system using a frequency band from 2.402 GHz to 2.480 MHz called an ISM (Industry Science Medical). The radio unit  11  also modulates transmitted data in a binary frequency shift keying system and demodulates the data on the basis of the signal received in the same system.  
      The synchronization correlator  12  has a buffer for storing the received packets, which stores one bit for each packet and monitors whether or not the received packet is a packet directed to the repeater  1  on the basis of the access code which is a leading segment of the packet. If the synchronization correlator  12  determines that the received packet is the packet directed to the repeater  1 , it sends the packet to the received packet analyzing unit  13 .  
      The received packet analyzing unit  13  analyzes an SCO packet in a line switched system mainly used for synchronous communication of audio data and an ACL packet in a packet switched system used for asynchronous communication such as data transmission/reception.  
      The received packet processing unit  14  processes the SCO packet received in the line switched system and the ACL packet received in the packet switched system. The transmitted packet creating unit  15  receives transmitted data from the communication control unit  21  and creates the packet in conformity with the format of the SCO packet and the ACL packet on the basis of the received data.  
      The synchronization timing detector  16  detects, on the basis of the packet received from the synchronization correlator  12 , the timing (T) when reception of the preamble and synchronous word included in the access code which is the leading segment of the packet has been completed, thereby creating an interruption for the timing correcting unit  21 .  
      The clock counter  18  creates a fundamental clock used within the piconet. The clock CL created by the clock counter  18  is called a Bluetooth clock having a period of 312. 5 μs. A two-period time (625 μs) of the clock CL constitutes a single slot. For example, where the master performs the transmission during an even slot, the slave perform the transmission during an odd slot. Namely, in a minimum slot communication (transmission during the single slot and the reception during the single slot), a transmission timing comes every 1.25 ms and a reception timing comes every 1.25 ms.  
      The bit counter  19  counts 1 μs pulses and produces a counted value which returns from a maximum “1249” to “0”. The clock counted by this bit counter  19  is a fundamental clock for correcting a drift called a “slot offset” on the basis of the data transmitted from the electronic device which is a communication partner.  
      Generally, the master performs the communication at its own clock and timing. Therefore, in the minimum slot communication, the time from 0 to 624 of the value of the bit counter is a transmission period whereas the time from 625 to 1249 is a reception period. By correcting the value in its own bit counter to remove the discrepancy between the master and the slave, the slave adapts its transmission period to the time from 625 to 1249 of the value of the bit counter in the master.  
      Where the packet is received from the master, when the timing correcting unit  17  receives, from the synchronization timing detector  16 , an interruption indicative of the detection of the synchronization timing, it reads the correcting value, i.e. the slot offset from the bit counter  19 , and stores this correcting value in the timing corrected value buffer  20 .  
      Where the packet is transmitted in synchronism with the master, the timing correcting unit  17  reads the correcting value from the timing correcting value buffer  20 , and informs the communication control unit  21  of the timing obtained by correcting the value in the bit counter  19  on the basis of the above correcting value.  
      The timing correcting value buffer  20  is a storage unit for storing the correcting value i.e. the slot offset and for storing the electronic device with an identified communication partner corresponding to the slot offset from a Bluetooth address (BD_ADDR).  
      The communication control unit  21  executes the whole control for the synchronization correlator  12 , received packet analyzing unit  13 , received packet processing unit  14  and transmitted packet creating unit  15 .  
      Further, in the relay of data between the parent device  104  and child device  102  which communicate the SCO packet, for the communication with the parent device  104  serving as the master, the communication control unit  21  operates as the slave by returning the packet at the timing in synchronism with the packet from the parent device  104 . Also, for the communication with the parent device  104  also, the communication control unit  21  performs the control of communicating the SCO packet at the timing in synchronism with the parent device  104 . In short, the timing correcting unit detects the drift in the clock of the SCO packet received from the parent device  104 , and in the transmission to the parent device  104  and the child device  102 , the communication control unit  21  transmits the SCO packet at the timing obtained by correcting the clock CL created by the clock counter  18  on the basis of the correcting value acquired from the drift.  
      Further, in the relay of data between the parent device  109  and PDA  107  which communicate the ACL packet, for the communication with the parent device  109  serving as the master, the communication control unit  21  operates as the slave by returning the packet at the timing in synchronism with the packet from the parent device  109 . On the other hand, for the communication with the PDA  107 , the communication control unit  21  operates as the master to performs the control of communicating the ACL packet at the slot timing created on the basis of the clock in the repeater  1 . In short, for the transmission to the parent device  109 , the timing correcting unit  17  detects the drift in the clock of the ACL packet received from the parent device  109 , and the communication control unit  21  transmits the ACL packet at the timing obtained by correcting the clock CL created by the clock counter  18  on the basis of the correcting value acquired from the drift. On the other hand, for the transmission to the PDA  107 , without correcting the clock, the communication control unit  20  performs the transmission/reception of the ACL packet at the timing in synchronism with the clock peculiar to the repeater  1  created by the clock counter  18 .  
      These units inclusive of the received packet analyzing unit  13 , received packet processing unit  14 , transmitted packet creating unit  15 , clock counter  18 , bit counter  19 , communication control unit  21 , synchronization timing detector  16  and timing correcting unit  17  can be constructed by a gate array, MPU (Micro Processing Unit), ROM (Read Only Memory) storing a control program, or RAM (Random Access Memory) used for read/write for a program.  
      The timing correcting buffer  20  may be constructed by a SRAM (Static Random Access Memory) or DRAM (Dynamic Random Access Memory) which is rewritable.  
      Now referring to FIGS.  1  to  5 , an explanation will be given of the operation of the radio relay device according to an embodiment of this invention.  
       FIG. 3  is a view showing the relationship between the format of a packet used in the Bluetooth and clocks.  FIG. 4  is a flowchart for explaining the method of computing a correcting value which a drift from the timing synchronous with the master in the packet from the master received by the repeater.  FIG. 5  is a view showing an example of the contents of the timing correcting value buffer  20 .  FIG. 6  is a flowchart for explaining the timing synchronous with the master when the packet is transmitted from the repeater.  
      The packet used in the Bluetooth includes an SCO packet which is a synchronous packet in the line switched system and an ACL packet in the packet switched system. These packets each is composed of an access code, a packet header and a payload. The master timing is extracted from the access code at a leading segment of each of these packets transmitted from the parent device  104  or  109  serving as the master. The access code is composed of a preamble of 4 bits of binary 1 and 0 repeatedly arranged, a synchronous word which is an identifier of 64 bits called a Bluetooth address and a trailer of 4 bits of binary 1 and 0 repeatedly arranged like the preamble.  
      The packet header contains a parameter necessary to manage the communication. The payload contains audio data of a speech, data to be communicated, and a control command, etc.  
      The repeater  1  serving as the slave monitors whether or not the packet received by the synchronization correlator  12  is a packet of the radio network to which the repeater  1  is connected, and whether the AM_ADDR of the packet received by the received packet processing unit  14  represents the packet directed to the repeater  1 . If it is determined that the received packet is a packet directed to the repeater  1 , the synchronization timing detecting unit  16  creates an interruption at the timing having detected the final bit of the preamble and synchronous word, thereby reading the value at this time from the bit counter  19  and recognizing a clock drift from the master on the basis of the value thus read.  
      In the example, at the timing of the final bit ( 68 ) of the synchronous word, the value of the bit counter is “34” so that there is a drift of 34 μs. Thus, the timing of the final bit of the synchronous word of the packet transmitted from the master represents the clock drift in the slave.  
      Next, an explanation will be given of the method for detecting a correcting value of the clock drift from the master when the repeater  1  serving as the slave receives the packet.  
      In  FIG. 4 , in S 10 , when the radio unit  11  receives the packet transmitted from the parent device  104  or  109  serving as the master, the synchronization correlator  12  accumulates the data within the packet one bit by one bit to monitor whether or not the packet received is directed to the repeater  1  on the basis of the information of the preamble and the synchronous word of 64 bits.  
      In S 20 , the synchronization timing detecting unit  16  returns to S 10  until the timing of the final bit of the synchronous word of the packet accumulated is detected. If the synchronization timing detecting unit  16  detects the final bit of the synchronous word which represents the synchronization timing with the master, it creates an interruption indicative of the clock synchronization for the timing correcting unit  17 .  
      In S 30 , in response to the creation of the interruption from the synchronization timing detecting unit  16 , the timing correcting unit  17  reads the value of the clock form the bit counter  19 .  
      In S 40 , the timing correcting unit  17  performs the processing of computing the value N when “68” is subtracted from the value in the bit counter  19 . For example, in the case of  FIG. 3 , since the drift is “34”, the value of N is “−34”.  
      In S 50 , the timing correcting unit  17  determines whether or not the value of N is not smaller than 0. If N is smaller than “0”, in S 60 , N is adopted as the correcting value M as it is. Therefore, since N is “−34”, M is “−34”.  
      If N is not smaller than “0”, in S 70 , the timing correcting unit  17  computes the value when “1249” is subtracted from N, and adopts the value thus obtained as the correcting value M.  
      In S 80 , the timing correcting unit  17  stores, in the timing correcting value buffer  20 , the correcting value M so as to correspond to the information identifying the master. Namely, where the repeater  1  communicates with a plurality of masters, the timing correcting unit  17  individually stores the correcting value M so as to correspond to the information for identifying the respective masters.  FIG. 5  shows an example of the contents of the timing correcting value buffer  20  in which the correcting value M is stored so as to correspond to the information of identifying the masters. In the example shown in  FIG. 5 , since “1215” is stored as the correcting value M used for communication with the parent device  109  serving as the master, M: 1215  is adopted as the timing correction for the slot during which the repeater executes the transmission/reception for the parent device  109 . M:  56  is adopted as the timing correction for the slot during which the repeater  1  executes the transmission/reception for the parent device  104 .  
      Incidentally, the device name for identifying the master corresponds to the BD_ADDR and a device class of the FHS packet transmitted from the master at the time of calling. The device class is a region for defining the kind of a 24 bit device stored in the FHS packet, in which the kind of each of a computer, telephone and audio device and its detailed information are stored in their codes. For this reason, the device class as well as BD_ADDR can be employed as the device name for identifying the master.  
      Next, referring to  FIGS. 6 and 7 , an explanation will be given of the timing correction in the cases where the repeater  1  serving as the slave returns the packet to the parent device and where the repeater  1  serving as the master transmits the SCO packet to the child device.  
      In S 100 , the timing correcting-unit  17  reads out the correcting value M from the timing correcting value buffer  20 . In the case of  FIG. 3 , M is “−34”. In S 110 , the timing correcting unit  17  reads out the value of the bit counter  19 .  
      In S 120 , the timing correcting unit  17  computes a sum of the read value of the bit counter  19  and “−34”. The timing correcting unit  17  waits for the timing when the sum reaches “0”, and when “0” is detected, informs the communication control unit  21  of this fact.  
      In S 130 , in response the information from the timing correcting unit  17 , the communication control unit  21  instructs the transmitted packet creating unit  15  to start the transmission of the packet for the parent device and the transmission of the packet for the child device. Thus, the SCO packet or ACL packet is transmitted through the radio unit  11 .  
       FIG. 7  shows the corrected timings of starting the transmission of the SCO packet for the parent device and child device in the repeater  1 . The repeater  1  performs the communication in the transmission/reception slot which is switched every two periods of the fundamental clock CL (Bluetooth clock) created by the clock counter  18  and employed in the piconet as described above. In this case, as seen from  FIG. 7 , the time difference a from when the repeater (slave) receives the SCO packet transmitted from the parent (master) to when the repeater returns the SCO packet to the parent device is the time difference corrected by the timing correcting unit  17 . The time difference b from when the repeater receives the SCO packet transmitted from the parent device to when the repeater  1  transmits the SCO packet to the child device is also the time difference corrected by the timing correcting unit  17 . In this way, the packet transmission timing is corrected by the timing correcting unit  17  so that the SCO packet is transmitted at the time position deviated from the normal transmission/reception slot of the repeater.  
      Also in the case where the packet transmitted from the parent device (master) is the ACL packet, the time difference unit the repeater returns the ACL packet to the parent device is corrected by the timing correcting unit  17 . As a result, when the packet transmitted by the repeater  1  is either the SCO packet or the ACL packet, the repeater  1  can transmit the packet in synchronism with the communication clock of the parent device.  
      Next, referring to  FIG. 8 , an explanation will be given of an example of the communication relayed by the repeater  1  between the parent device  104  and the child device  102  and between the parent device  109  and the PDA  107 . In the example shown in  FIG. 8 , the repeater  1  relays the communication of the SCO packet of the audio data in the line switched system between the parent device  104  and the child device  102 , and also relays the ACL packet in the packet switched system between the other parent device  109  and the PDA  107 .  
      In this case, the repeater  1  serving as the slave transmits/transmits the SCO packet in synchronism with the communication clock of the parent device  104  serving as the master. As regards the timing of the slot for the transmission/reception between the repeater  1  and the parent device  104 , the transmission/reception for the repeater  1  accords with the transmission timing of the parent device  104 . Further, as regards the timing of the slot for the transmission/reception between the repeater  1  and the child device  102 , the child device  102  serving as the slave accords with the transmission timing of the repeater  102 .  
      In this case, as described above, the repeater  1  transmits the SCO packet to the child device  102  at the slot timing obtained by correcting the clock CL created by the clock counter  18 , i.e. the system clock of the repeater  1  using the correcting value. In this way, since the transmission timing of the repeater  1  for the child device  102  is corrected to be always synchronous with the transmission timing of the parent device  104 , it is possible to prevent the transmission timings of the packet from gradually shifting to the same timing.  
      Further, in order that the PDA  107  can access the home page on an internet through the parent device  109 , the repeater  1  relays the communication of the ACL packet in the packet switched system between the PDA  107  and the parent device  109 . In this case, the repeater  1  serving as the slave transmits/receives the ACL packet in synchronism with the communication clock of the parent device  109  serving as the master. Further, the repeater  1  serving as the master communicates with the child device  102  in synchronism with the timing of the bit counter  19 , i.e. the system clock of the repeater  1 . In the communication of the ACL packet between the parent device  109  and PDA  107 , the PDA  107  reads the home page on its screen in a DH1 packet employed for request of transmission of a page or communication of a text, and in a DH3 packet employed for communication of a large quantity of data such as an image.  
      Thus, the repeater  1  can relay the parent device  104  with the child device  102  while transmitting/receiving the SCO packet in the line switched system (synchronous communication) for audio communication, and can also relay the parent device  109  with the PDA  107  while transmitting/receiving the ACL packet in the packet switched system (asynchronous communication) for data communication.  FIG. 9  shows in detail the SCO packet transmission starting timings for the parent device  104  and the child device  102  and the ACL packet transmission starting timings for the parent device  109  and the PDA  107  in the case where the repeater  1  concurrently performs two relays.  
      Where the repeater  1  performs the relay for a plurality of parent devices, since the clock of the repeater  1  deviates from that of the parent device  104  or  109 , initially, the transmission timings can be designed to not overlap. However, with passage of time, the transmission timings of the respective devices will overlap so that collision of the packets may occur. However, in this invention, where the packet (SCO or ACL) transmitted from the parent devices is returned to the respective parent devices, since the packet is transmitted in synchronism with the communication clock of each of the parent devices, there is very little possibility that the transmission timings of the repeater  1  and each parent device overlap owing to the drift of the clocks. Further, in the communication of the ACL packet (asynchronous) between the parent device  109  and the repeater  1 , the transmission timing of the repeater is made synchronous with the communication clock of the parent device  109 . On the other hand, in the communication between the repeater  1  and the PDA  107 , as described in  FIG. 9 , since the repeater  1  serving as the master transmits the packet in synchronism with the clock CL of the repeater itself, the repeater  1  can select the transmission slot for the PDA  107  at a suitable timing position not overlapping (not too dose) with the transmission/reception of the other parent devices.  
      Thus, even where the repeater  1  performs a plurality of relays in which the SCO packets in the line switched system (synchronous communication) and the ACL packets in the packet switched system (asynchronous communication) are mixed, useless consumption of time can be minimized while avoiding collision of the packets, thereby improving the communication efficiency.