Abstract:
A master side communication apparatus and a slave side communication apparatus wherein the structure of a receiving part of the slave side communication apparatus is simplified to achieve a reduced size, a reduced power consumption and a reduced cost. The master side communication apparatus performs a communication in synchronism with the slave side communication apparatus having no synchronization timing adjusting function. A transport signal generating timing adjusting part of the master side communication apparatus acquires, from the slave side communication apparatus, synchronization signal generation timing information used when the slave side communication apparatus receives the transport signal from the master side communication apparatus. The transport signal generating timing adjusting part varies and adjusts, based on the acquired information, the transmission timing of the signal to be transmitted to the slave side communication apparatus. A transmitting part transmits the transport signal at the adjust transmission timing. The occurrence timing of the transport signal is varied and adjusted until the slave side communication apparatus becomes able to receive the transport signal from the master side communication apparatus.

Description:
TECHNICAL FIELD 
     The present invention relates to communication devices using wideband signals such as signals having pulse waveforms. 
     BACKGROUND ART 
     There is a rapid spread of devices compliant to wireless local area network (hereinafter, LAN) such as IEEE 802.11b standard established by the Institute of Electrical and Electronics Engineers based in the United States. Also, it is expected that a seamless network society will arrive where audio visual (hereinafter, AV) devices are connected with personal computers by a wireless network or other means. With this background, there is a demand for a technique to produce small and high-speed data communication devices at low cost. 
     As an approach to the technique, a communication system called Ultra Wide band (hereinafter, UWB) using a pulse-like modulation signal is drawing attention. 
       FIG. 11  is a block diagram of a UWB wireless device as an example of a conventional communication device. This conventional example includes a plurality of receiving systems. Antenna  1001  receives a signal, and amplifier/filter  1002  amplifies and filters the signal to remove unwanted signals. Automatic gain controller (hereinafter, AGC)  1003  controls the gain of the signal, and receiver systems  1011 A and  1011 B receive the gain-controlled signal. In receiver systems  1011 A and  1011 B, mixers  1004 A and  1004 B correlate the gain-controlled signal from AGC  1003  with pulse signals generated by pulse generators  1007 A and  1007 B, respectively. 
     Filters  1005 A and  1005 B filter the signals from mixers  1004 A and  1004 B, respectively, to remove unwanted signals. Analog/digital (hereinafter, A/D) converters  1006 A and  1006 B convert the filtered signals to digital signals. Controller  1010  determines the correlation and improves the correlation by controlling the timing of timing generators  1008 A and  1008 B with clock control signals and performing synchronization acquisition and holding of the signals received from controller  1010  and signals from local oscillation (hereinafter, LO) generators  1009 A and  1009 B, respectively. One example of this conventional communication device is disclosed in International Publication No. WO01/93442. 
       FIG. 12  is a block diagram showing a structure of another conventional communication device, and more specifically, a block structure of a UWB communication device. The block diagram of  FIG. 12  shows transmitter power control, which equalizes the electric power levels of signals that a communication device receives from a plurality of partner communication devices in the following manner. The communication device receives a reception signal from a partner communication device and returns the reception power level information obtained from the reception signal, thereby changing the transmission power depending on the partner communication device. 
     The transmitter power control is a technique not unique to UWB but used widely for wireless communication, and  FIG. 12  shows one example of the application of transmitter power control to UWB. In the communication device of this conventional example, receiver  2201  receives impulse trains transmitted from a plurality of other communication devices (unillustrated) via antenna  2205 , and measurer  2202  measures the reception characteristics. Measurer  2202  includes signal-to-noise ratio measurer  2202 A, reception signal intensity measurer  2202 B, and error rate measurer  2202 C. 
     These measurement results are used to detect the communication device that is required to control its transmission level. Information S 2202 , which indicates the detected communication device, is outputted to transmission-level-control-information generator  2203 . Transmission-level-control-information generator  2203  generates transmission level control information S 2203  to control the transmission level of the detected communication device, and transmitter  2204  transmits this information. This results in the control of the transmission level of the communication device that has received the transmission level control information. As a result, the reception characteristics of the impulse trains received from the plurality of other communication devices become equal to each other. This enables receiver  2201  to receive impulse trains transmitted concurrently from the plurality of other communication devices. An example of this conventional communication device is disclosed in Japanese Patent Unexamined Publication No. 2003-51761. 
     However, the conventional structure of International Publication No. WO01/93442 mentioned above includes a plurality of receiving systems and adjusts sync timing based on the correlation as described earlier. The structure requires that a plurality of receiving system signals be processed at high speed in a complicated decision flow. This might cause the receiver configuration to be complicated and large, thereby increasing the power consumption and price of the device. This is particularly difficult to achieve in a slave communication device such as a portable device. On the other hand, the conventional structure to control transmission power as described in Japanese Patent Unexamined Publication No. 2003-51761 mentioned above can reduce problems such as the inability to adjust sync timing due to signal interference (inability to pull into synchronism) and jitter increase during synchronization tracking. This structure, however, may still cause the receiver configuration to be complicated and large, thereby increasing the power consumption and price of the device. This is particularly difficult to achieve in a slave communication device such as a portable device. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to provide a slave communication device, such as a portable device, which has a simplified receiver configuration so as to be reduced in size, price, and power consumption by performing sync timing adjustment exclusively in a master communication device, which can be designed to be large. 
     The master communication device of the present invention communicates in synchronization with a slave communication device with no sync timing adjustment feature and includes a transmission-signal-generation-timing adjuster and a transmitter. The transmission-signal-generation-timing adjuster receives sync signal generation timing information from the slave communication device, the sync signal generation timing information indicating a generation timing of a sync signal to be used when the slave communication device receives a transmission signal from the master communication device. The transmission-signal-generation-timing adjuster then changes and adjusts a transmission timing of a signal to be transmitted to the slave communication device based on the sync signal generation timing information thus received. The transmitter transmits the transmission signal at the transmission timing adjusted by the transmission-signal-generation-timing adjuster. The master communication device makes the transmission-signal-generation-timing adjuster adjust a generation timing of the transmission signal until the slave communication device can receive the transmission signal from the master communication device. 
     In this structure, timing adjustment can be performed in the master communication device with a sync timing adjustment feature. This enables components that are conventionally required on the receiver side of every device, such as multistage receiving-system branches and synchronization loops to be provided only in the master communication device. As a result, the slave communication device with no sync timing adjustment feature can have a simplified receiver configuration so as to be reduced in power consumption and price. 
     The master communication device of the present invention may use a variable delay unit capable of varying a delay time of a signal as the transmission-signal-generation-timing adjuster. This facilitates timing adjustment. 
     In the master communication device of the present invention, the transmitter may include a pulse generator capable of arbitrarily changing a pulse generation time, and a modulator for modulating pulses, the pulses being communication data to be transmitted to the slave communication device and being generated by the pulse generator. The transmission-signal-generation-timing adjuster may adjust at least one of the generation timing of the pulses and the generation timing of frames which are each a series of the communication data encoded. 
     In this structure, the timing adjustment for pulse and frame acquisition and holding (hereinafter, acquisition and holding can be collectively referred to as synchronization) is performed in the master communication device. This can reduce the number of receiving system branches and adjustment circuits for pulse and frame synchronization in the slave communication device. As a result, the slave communication device can have a simplified receiver configuration so as to be reduced in power consumption and price. 
     In the master communication device of the present invention, the transmission-signal-generation-timing adjuster may include a transmission timing storage for storing respective transmission timings corresponding to the plurality of slave communication devices. The transmitter may communicate with the plurality of slave communication devices at the respective transmission timings stored in the transmission timing storage. As a result, the master communication device can communicate with a plurality of slave communication devices. 
     The master communication device of the present invention may have a plurality of transmitters which communicate with the plurality of slave communication devices at the respective transmission timings from the transmission-signal-generation-timing adjuster, the respective transmission timings corresponding to the plurality of slave communication devices. As a result, the master communication device can communicate with a plurality of slave communication devices. 
     The slave communication device of the present invention with no sync timing adjustment feature communicates in synchronization with a master communication device with a sync timing adjustment feature. The slave communication device includes a sync signal generator, a correlator, a correlation detector, and a timing information transmitter. The sync signal generator generates a sync signal to be used upon receiving a transmission signal from the master communication device. The correlator correlates the transmission signal from the master communication device with the sync signal generated by the sync signal generator. The correlation detector detects correlation from an output of the correlator. The timing information transmitter transmits an output of the correlation detector as sync signal generation timing information. 
     With this structure, timing adjustment for pulse synchronization and frame synchronization can be all performed in the master communication device, so that the number of receiving system branches and adjustment circuits for pulse and frame synchronization can be minimized in the slave communication device. As a result, the slave communication device can have a simplified receiver configuration so as to be reduced in power consumption and price. 
     In the slave communication device of the present invention, the sync signal generation timing information may include pulse phase correlation for pulse synchronization. This structure enables the master communication device to be informed of the phase shift between the pulse signal of its own and the pulse signal for synchronous detection of the slave communication device, and to transmit a signal after adjusting the time corresponding to the phase shift. As a result, the slave communication device can achieve pulse synchronization without timing adjustment. 
     In the slave communication device of the present invention, the sync signal generation timing information may include correlation with a frame for frame synchronization. This structure enables the master communication device to be informed of the positional shift between the frame of the slave communication device and the signal transmission timing, and to transmit a signal after adjusting the time corresponding to the positional shift. As a result, the slave communication device can achieve frame synchronization without timing adjustment. 
     In the slave communication device of the present invention, the timing information transmitter may transmit the sync signal generation timing information by changing a reflection condition of the transmission signal from the master communication device. This structure enables the slave communication device to change the reflection condition of a transmission signal from the master communication device so as to reduce the power consumption of the transmission system when the slave communication device transmits sync signal generation timing information. 
     In the master communication device of the present invention, the transmitter may include a pulse generator for changing at least one of a shape and repetition intervals of generated pulses. Upon starting a synchronous operation with the slave communication device, the transmitter may transmit pulses with a high ease of synchronization acquisition first and then switch the pulses with pulses capable of precise synchronization. This structure enables synchronization to be established in a short time by switching between transmit pulses that can establish low-precision synchronization in a short time and transmit pulses that can establish high-precision synchronization. 
     In the master communication device of the present invention, the pulse generator may change a width of the generated pulses. Upon starting a synchronous operation with the slave communication device, the transmitter may transmit pulses having a width large enough to have the time to be correlated by the slave communication device first and then switch the pulses with short-width pulses capable of precise synchronization. With this structure, low-precision synchronization is established in a short time with an increased pulse width and then high-precision synchronization is established with a reduced pulse width. This results in a reduction in synchronization time to achieve high-speed communication. 
     In the master communication device of the present invention, the pulse generator may change repetition intervals of the generated pulses. Upon starting a synchronous operation with the slave communication device, the transmitter may transmit pulses with short repetition intervals so as to transmit the pulses at frequent intervals first, and then switch the pulses with pulses with long repetition intervals capable of precise synchronization. In this structure, the repetition intervals are shortened to increase the chance of detecting correlation, and high-precision synchronization is established after low-precision synchronization is established in a short time. This can reduce the synchronization time to achieve high-speed communication. 
     In the master communication device of the present invention, the pulse generator may change repetition intervals of the generated pulses. Upon starting a synchronous operation with the slave communication device, the transmitter may transmit pulses with a high peak voltage and long repetition intervals so as to transmit the pulses at infrequent intervals first, and then switch the pulses with pulses with short repetition intervals. In this structure, the peak value of each pulse can be increased by making the pulse repetition intervals longer. This prevents the signal from being buried in noise, allowing pulse synchronization to be established in a short time although it is low precision. After this, the pulse peak value is lowered and the pulse repetition intervals are made shorter to establish high-precision synchronization. This results in a reduction in the synchronization time to achieve high-speed communication. 
     In the master communication device of the present invention, the repetition intervals may be changed intentionally and arbitrarily so as to control the transmission timing, and the distance to the slave communication device may be calculated based on the time elapsed to obtain the sync signal generation timing information. This structure can calculate the distance between the devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a structure of a master communication device and a slave communication device of a first embodiment of the present invention. 
         FIG. 2  is a block diagram showing another structure of the master communication device and the slave communication device of the first embodiment. 
         FIG. 3  is a block diagram showing another structure of the master communication device and the slave communication device of the first embodiment. 
         FIG. 4  is a block diagram showing a structure of a master communication device and a slave communication device of a second embodiment of the present invention. 
         FIG. 5  is a block diagram showing another structure of the master communication device of the second embodiment. 
         FIG. 6  is a block diagram showing a structure of a master communication device and a slave communication device of a third embodiment of the present invention. 
         FIG. 7  is a diagram of pulse waveforms in a master communication device of a fourth embodiment of the present invention. 
         FIG. 8  is a diagram of pulse waveforms in a master communication device of a fifth embodiment of the present invention. 
         FIG. 9A  is a diagram of a first pulse waveform indicating the operation of the master communication device of the fifth embodiment. 
         FIG. 9B  is a second pulse waveform diagram indicating the operation of the master communication device of the fifth embodiment. 
         FIG. 9C  is a third pulse waveform diagram indicating the operation of the master communication device of the fifth embodiment. 
         FIG. 10  is a communication signal sequence diagram of a master communication device and a slave communication device of a sixth embodiment of the present invention. 
         FIG. 11  is a block diagram showing a structure of a conventional communication device. 
         FIG. 12  is a block diagram showing a structure of another conventional communication device. 
     
    
    
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           101 ,  201 ,  301 ,  401 ,  501 ,  1201  master communication device 
           102 ,  202 ,  302 ,  303 ,  502 ,  1202  slave communication device 
           103 ,  215 ,  307 A,  307 B,  511  transmitter 
           104  transmission-signal-generation-timing adjuster 
           105  sync-signal-generation-timing-information receiver 
           106  reception signal demodulator 
           107  sync signal generator 
           108  sync-signal-generation-timing-information transmitter 
           203 A,  203 B,  203 C,  203 D,  216 A,  216 B,  503 ,  516 A,  516 B,  1208 ,  1211 , 
           1222 ,  1223  antenna 
           204 ,  208 ,  405 A,  405 B,  1203 ,  1213  pulse generator 
           205 ,  210 ,  407 A,  407 B,  1204 A,  1204 B modulator 
           206 ,  209 ,  406 A,  406 B,  1210 A,  1210 B,  1210 C encoder 
           207 ,  305 ,  306 A,  306 B,  402 ,  512  receiver 
           211 ,  506  correlation signal generator 
           212 ,  505 ,  1212 A,  1212 B correlator 
           213 ,  507 ,  1214 A,  1214 B pulse acquisition-and-correlation determiner 
           214 ,  1217 A,  1217 B frame acquisition-and-correlation determiner 
           304  generation timing storage 
           403  out-of-sync information distributor 
           404 A,  404 B generation timing adjuster 
           408  synthesizer 
           504  reflection condition changer 
           508 A switch 
           509  transmission data generator 
           510  distributor 
           513  delay unit 
           1205 A,  1205 B rectangular wave generator 
           1206 A,  1206 B,  1206 C,  1206 D variable delay unit 
           1207 A,  1207 B,  1207 C bandlimiting filter 
           1209 A,  1209 B data 
           1215 A,  1216 B,  1220 A,  1220 B determiner 
           1215 B,  1216 A,  1219 A,  1219 B integrator 
           1218 A,  1218 B code correlator 
           1221  received-power detector 
       
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described as follows with reference to drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a block diagram showing a structure of a master communication device and a slave communication device of a first embodiment of the present invention. The present embodiment is provided with a single master communication device and a single slave communication device. 
     The following is a description of the structure of master communication device  101  and slave communication device  102 . Master communication device  101  is a device with a sync timing adjustment feature, and includes transmitter  103 , sync-signal-generation-timing-information receiver  105 , and transmission-signal-generation-timing adjuster  104 . Transmitter  103  generates a transmission signal of the master communication device. Sync-signal-generation-timing-information receiver  105  receives sync signal generation timing information from slave communication device  102 . Transmission-signal-generation-timing adjuster  104  determines the transmission timing based on the sync signal generation timing information received. 
     On the other hand, slave communication device  102  is a device with no sync timing adjustment feature, and includes reception signal demodulator  106 , sync signal generator  107 , and sync-signal-generation-timing-information transmitter  108 . Reception signal demodulator  106  receives and demodulates a signal from master communication device  101 . Sync signal generator  107  generates a sync signal to be used for the synchronization with the signal from master communication device  101  when reception signal demodulator  106  demodulates the reception signal. Sync-signal-generation-timing-information transmitter  108  detects and determines the correlation between the reception signal and the sync signal, and transmits the result as sync signal generation timing information to master communication device  101 . 
     The following is a description of the operation of the master communication device and the slave communication device of the present embodiment. When master communication device  101  communicates with slave communication device  102 , slave communication device  102  can receive and demodulate a transmission signal (hereinafter, signal “A”) from master communication device  101  under the following condition. The signal “A” received by slave communication device  102  must be synchronous with a sync signal generated by sync signal generator  107  of slave communication device  102 . Examples of the synchronization requirement include agreement in signal phase, agreement in frequency, agreement in frame position, and agreement in code sequence. 
     In slave communication device  102 , sync signal generator  107  generates the sync signal at any timing. Reception signal demodulator  106  correlates and demodulates the sync signal and the received signal “A”. However, without timing adjustment, the sync signal and the received signal “A” are not synchronized with each other. This is why timing adjustment is necessary to meet the aforementioned synchronization requirements (such as agreement in signal phase, agreement in frequency, agreement in frame position, and agreement in code sequence). Although the details will be described later, slave communication device  102  does not have a sync timing adjustment feature and only performs the generation of a signal for timing adjustment. The timing adjustment is performed by master communication device  101 . 
     In slave communication device  102 , the sync signal generation timing information, which is a signal for timing adjustment, is generated by sync-signal-generation-timing-information transmitter  108  based on the received signal “A” and the sync signal, and transmitted to master communication device  101 . 
     The sync signal generation timing information includes the correlation between the signals, the strength of received power, and the error rate of the reception signal. The sync signal generation timing information is received by sync-signal-generation-timing-information receiver  105  of master communication device  101 . Sync-signal-generation-timing-information receiver  105  reads out out-of-sync information between the signal “A” transmitted from its own station (master communication device  101 ) and the signal “A” received by slave communication device  102 . The out-of-sync information is inputted to transmission-signal-generation-timing adjuster  104 . Transmission-signal-generation-timing adjuster  104  changes the transmission timing of its own station (master communication device  101 ) so as to achieve synchronization with slave communication device  102 . 
       FIG. 2  is a block diagram showing a more specific structure of the master communication device and the slave communication device of the present embodiment. In master communication device  201 , transmission data to be transmitted to slave communication device  202  is encoded using a code sequence generated by encoder  206 . The transmission data can be data used only for the establishment of synchronization. Although the transmission data is encoded by encoder  206  before being transmitted in the present embodiment, encoding is not essential. 
     The encoded transmission data is composed of pulses generated by pulse generator  204 , modulated by modulator  205 , and transmitted from antenna  216 A. The transmission data transmitted from master communication device  201  is received (hereinafter, reception signal) by antenna  203 A of slave communication device  202  that is a communication partner. The reception signal is then correlated with a correlation signal for synchronization by correlator  212 . The correlation signal for synchronization is generated by correlation signal generator  211  including encoder  209 , pulse generator  208 , and modulator  210 . Then, pulse acquisition-and-correlation determiner  213  detects the deviation or correlation between the pulses generated by pulse generator  208  and the pulses of the reception signal, and outputs the result to transmitter  215  as pulse phase shift information or the phase correlation information. 
     Frame acquisition-and-correlation determiner  214  detects the deviation or correlation between the code sequence generated by encoder  209  and the code sequence of the reception signal, and outputs the result to transmitter  215  as frame deviation information or frame correlation. One example of the frame acquisition is the agreement between the code sequence which is encoded in the transmitter side of master communication device  201  and the code sequence generated by encoder  209  of slave communication device  202 . Decoding cannot be performed even if the same code sequences are used, unless the code sequences are started at the same time. Therefore, the coincidence of the start positions is regarded as frame synchronization. Transmitter  215  transmits the received “frame deviation information” to master communication device  201 . 
     Master communication device  201  demodulates the deviation information received by receiver  207  so as to change and adjust the time of generation of pulses and a code sequence in pulse generator  204  and encoder  206 , respectively, according to the deviation time. These series of operations are repeated until synchronization is established. When the synchronization is established, transmitter  215  transmits data to master communication device  201 , whereas receiver  207  receives data from slave communication device  202 . 
     Changes and adjustments in the time of generation of the pulses and code sequence in pulse generator  204  and encoder  206  can be performed by changing the generation timing in pulse generator  204  and encoder  206 , or by combining pulse generator  204  and encoder  206  with a delay unit having a variable delay amount. 
     As described hereinbefore, in the master communication device and slave communication device of the present embodiment, sync timing adjustment is performed exclusively in the master communication device, which can be designed to be large. This allows the slave communication device such as a portable device to have a simplified receiver configuration, thereby being reduced in size, price, and power consumption. 
     The aforementioned structure performs pulse synchronization (acquisition and holding) and frame synchronization (acquisition and holding) such as a code sequence. Alternatively, it is possible to have a structure that performs either pulse synchronization or frame synchronization. In the present invention, sync timing variability (modification) means the ability to detect the timing of a reception signal and to adjust the timing difference with its own station. A device that cannot detect or adjust the timing of a reception signal is regarded as a sync timing invariable device even if it has a delay unit having a variable delay amount. 
     Although there is no description about modulation scheme used for communication, there is no limitation to communication system. Examples of the modulation scheme include On-Off Keying (hereinafter, OOK), Biphase Shift Keying (hereinafter, BPSK), Quadrature Phase Shift Keying (hereinafter, QPSK), and Pulse Position Modulation (hereinafter, PPM). 
       FIG. 3  is a block diagram showing another structure of the master and slave communication devices of the present embodiment with OOK modulation and BPSK modulation. Master communication device  1201  and slave communication device  1202  both have a transmitting function and a receiving function. Similar to the former embodiment, slave communication device  1202  does not have a sync adjustment feature, and sync adjustment about communication is performed by master communication device  1201 . 
     First, the transmitting function of master communication device  1201  will be described as follows. The main components to execute the transmitting function are pulse generator  1203  and modulator  1204 A. Pulse generator  1203  can be realized by various ways and composed of rectangular wave generator  1205 A, variable delay  1206 A, and bandlimiting filter  1207 A. Rectangular wave generator  1205 A generates a rectangular wave signal from which transmit pulses are generated and which determines the repetition frequency and pulse width of the transmit pulses. 
     Rectangular wave generator  1205 A generally uses as a reference signal an output of an unillustrated crystal oscillator having a high frequency stability. The reference signal is multiplied to generate a signal having a high repetition frequency, and the pulse width is adjusted by combining the delay unit with a comparator. This results in a rectangular wave signal having an arbitrary repetition frequency and an arbitrary pulse width. The generated rectangular wave signal is delayed by a certain period of time by variable delay unit  1206 A. Later, the signals with communication frequencies are selected by bandlimiting filter  1207 A, amplitude-modulated by modulator  1204 A, and transmitted by antenna  1208 . The delay time of variable delay unit  1206 A will be described later as the operation of the timing adjustment. Modulator  1204 A can be a circuit such as a switch or a mixer. 
     In the case of BPSK modulation, a mixer or the like is used because phase information is required. The modulated signal to be applied to modulator  1204 A is outputted from data  1209 A. The source of the data can be information inside the communication device or information received from an external device such as a personal computer (hereinafter, PC) and a network. 
     The present embodiment includes encoder  1210 A for data encoding; however, encoder  1210 A is unnecessary when data is not encoded. The output of encoder  1210 A is inputted as a modulated signal to modulator  1204 A after being delayed by a certain period of time by variable delay unit  1206 B. The delay-time setting operation of variable delay unit  1206 B will be described later. 
     The following is a description of the receiving function of slave communication device  1202 . Antenna  1211 A receives a reception signal and inputs it to correlator  1212 B, which multiplies the signal by a template signal generated by pulse generator  1213  and generates a receiving correlation signal. Pulse generator  1213  can be composed of rectangular wave generator  1205 B and bandlimiting filter  1207 B. The receiving correlation signal is inputted to pulse acquisition-and-correlation determiner  1214 B and determined whether it is a desired signal or not. 
     Pulse acquisition-and-correlation determiner  1214 B may be composed of integrator  1215 B and determiner  1216 B. The receiving correlation signal is integrated by integrator  1215 B for a predetermined period of time, and threshold-detected by determiner  1216 B so as to be outputted as the result of the correlation determination. Also, the difference between the receiving correlation signal and the threshold is outputted as phase shift information. The output of the correlation determination is inputted to frame acquisition-and-correlation determiner  1217 B so as to be correlated with the code sequence. 
     Frame acquisition-and-correlation determiner  1217 B may be composed of code correlator  1218 B, integrator  1219 B, and determiner  1220 B. Code correlator  1218 B multiplies the output of the correlation determination by the code sequence. Integrator  1219 B integrates the multiplied result for a predetermined period of time, and determiner  1220 B performs threshold detection to output the result of the frame correlation as received data and also outputs the difference between the receiving correlation signal and the threshold as frame deviation information. 
     Slave communication device  1202  may include received-power detector  1221  so as to operate a circuit only when a signal reception is detected. The circuit to be operated in this case can be pulse generator  1213 . 
     The following is a description of the transmitting function of slave communication device  1202 . Information to be transmitted by slave communication device  1202  includes information generated by data  1209 B itself as well as phase shift information and frame deviation information. These different kinds of information are synthesized by data  1209 B, encoded by encoder  1210 C, and inputted to modulator  1204 B. Modulator  1204 B modulates the pulse generated by pulse generator  1213  with the information obtained from encoder  1210 C. The output is transmitted from antenna  1222 . 
     The following is a description of the receiving function of master communication device  1201 . A reception signal received by antenna  1223  is multiplied by a template signal by correlator  1212 A so as to form a correlated signal. This template signal is obtained as follows. The rectangular wave generated by rectangular wave generator  1205 A is formed into a data sequence by data  1209 A; encoded by encoder  1210 B; provided with an initial delay by variable delay units  1206 C and  1206 D; and formed into a signal in a desired frequency band by bandlimiting filter  1207 C. 
     The correlated signal, which is the output of correlator  1212 A, is inputted to pulse acquisition-and-correlation determiner  1214 A to determine the correlation. When there is a predetermined correlation, the pulse position is regarded to be acquired and the determination of the code correlation is started. On the other hand, when there is no predetermined correlation, the amount of delay of variable delay unit  1206 D is changed by a predetermined amount. 
     Pulse acquisition-and-correlation determiner  1214 A may determine the presence or absence of correlation by allowing integrator  1216 A to perform integration only by a predetermined period of time, and determiner  1215 A to perform threshold detection. The amount of delay of variable delay unit  1206 D is changed. The code correlation can be determined using frame acquisition-and-correlation determiner  1217 A, which can be composed of code correlator  1218 A, integrator  1219 A, and determiner  1220 A. 
     A signal exceeding the threshold of determiner  1220 A is determined to be code correlated and becomes received data. When the correlation is low, the amount of delay of variable delay unit  1206 C is changed. The amount of delay of variable delay unit  1206 C to be changed may be about the same as the distance between the pulses. The change of the amount of delay is continued until the correlation exceeds the threshold. 
     The received data of master communication device  1201  includes the phase shift information and frame deviation information of slave communication device  1202 . The amount of delay of variable delay units  1206 A and  1206 B are changed based on these pieces of information. When the amount of delay to be changed is determined, a calculation formula or a table is used to convert the phase shift information and the frame deviation information of slave communication device  1202  indicating the output values of determiners  1216 B and  1220 B to a predetermined amount of delay. As described above, slave communication device  1202  never performs timing adjustment using a variable delay unit. 
     Although the aforementioned description is focused on pulse communication, the present invention is also applicable to communication with a sine wave and is particularly effective to communication such as CDMA requiring frame synchronization. In a phase locked loop generally performed in communication with a sine wave, the above-described pulse acquisition-and-correlation determiner may be equipped with a phase difference detection circuit that is used in a general phase locked loop. This enables the present invention to be applied to frequency synchronization by detecting a frequency difference and then outputting the difference as phase shift information. 
     Second Exemplary Embodiment 
       FIGS. 4 and 5  are block diagrams showing structures of a master communication device and a slave communication device of a second embodiment of the present invention. The present embodiment differs from the first embodiment in that the master communication device of each of  FIGS. 4 and 5  communicates in synchronization with a plurality of slave communication devices. 
     In  FIG. 4 , master communication device  301  includes pulse generator  204 , modulator  205 , encoder  206 , antenna  216 A, antenna  216 B, generation timing storage  304 , and receiver  305 . Slave communication device  302  includes antenna  203 A, antenna  203 B, receiver  306 A, and transmitter  307 A. Slave communication device  303  includes antenna  203 C, antenna  203 D, receiver  306 B, and transmitter  307 B. 
     As described in detail in the first embodiment, the master communication device with a timing adjustment feature performs communication synchronously with slave communication devices with no timing adjustment feature. In this case, when there are a plurality of slave communication devices with no sync timing adjustment feature, the master communication device with the timing adjustment feature is required to perform communication synchronously with the respective slave communication devices. Two examples will be described below. 
     In  FIG. 4 , master communication device  301  stores the sync timing with slave communication device  302  and the sync timing with slave communication device  303  in ingeneration timing storage  304 , which is a transmission timing storage. Master communication device  301  changes or adjusts the generation timing of pulses and a code sequence in pulse generator  204  and encoder  206  at the transmission timing corresponding to the respective communication partners. In the case of pulse communication, the pulse generation time in communication time is short enough to generate all the signals for the plurality of communication partners by one pair of pulse generator  204  and encoder  206 . 
       FIG. 5  shows another structure of the master communication device that generates a plurality of sync timings. Master communication device  401  shown in  FIG. 5  differs from the one shown in  FIG. 4  by having more than one functional block. While the structure shown in  FIG. 4  has a single pulse generator  204 , the structure shown in  FIG. 5  has two pulse generators  405 A and  405 B. Similarly, while the structure of  FIG. 4  has a single encoder  206 , the structure of  FIG. 5  has encoders  406 A and encoder  406 B. Similarly, while the structure of  FIG. 4  has a single generation timing storage  304 , the structure of  FIG. 5  has generation timing adjuster  404 A and generation timing adjuster  404 B. In the structure of  FIG. 5 , out-of-sync information received is distributed for the respective communication partners by out-of-sync information distributor  403 , thereby performing the timing change and adjustment separately depending on the communication partner. 
     While the structure of  FIG. 4  has a single modulator  205 , the structure of  FIG. 5  has modulator  407 A and modulator  407 B. Receiver  402  of  FIG. 5  corresponds to receiver  305  of  FIG. 4 . In this structure, the two functional blocks generate transmission signals separately, so that the transmission signals are synthesized by synthesizer  408  and transmitted from a single antenna  216 A. Having a plurality of transmission systems unlike the structure of  FIG. 4  is likely to increase the device in size, but can reduce the number of pulses and code sequences, in other words, reduce the speed. 
     As described hereinbefore, in the master and slave communication devices of the second embodiment of the present invention, sync timing adjustment is performed exclusively in the master communication device, which can be designed to be large. This allows the slave communication device such as a portable device to have a simplified receiver configuration, thereby being reduced in size, price, and power consumption. 
     The master communication device of the present embodiment includes synthesizer  408 ; however, it is alternatively possible to provide each transmission system with an antenna instead of a synthesizer. 
     Third Exemplary Embodiment 
       FIG. 6  is a block diagram showing a structure of a master communication device and a slave communication device of a third embodiment of the present invention. The present embodiment differs from the first embodiment in that the sync signal generation timing information, which is out-of-sync information, is transmitted by the reflected wave of a signal transmitted from the master communication device by changing the terminal condition of the receiving antenna of the slave communication device. 
     In  FIG. 6 , slave communication device  502  which performs reception includes reflection condition changer  504  for changing the terminal condition of antenna  503 . In slave communication device  502 , correlator  505  correlates the reception signal and the correlated signal generated by correlation signal generator  506 . Pulse acquisition-and-correlation determiner  507  detects the correlation so as to generate a correlation state signal, which is the sync signal generation timing information. When the correlation is low, that is, when there is no synchronization, switch  508 A is switched to transmit the correlation state signal. 
     The correlation state signal is returned by making reflection condition changer  504  reflect the transmission signal from master communication device  501  by alternately switching between a matched impedance of 50Ω and a short-circuit impedance of 0Ω. As a result, the correlation state signal is received and demodulated by receiver  512  of master communication device  501 . A correlated signal at the time of demodulation is generated by making distributor  510  distribute the signal of transmission data generator  509  and delay unit  513  give a delay corresponding to the propagation time of the signal because master communication device  501  receives the signal transmitted from its own station. 
     Antenna  516 A of master communication device  501  corresponds to antenna  216 A; antenna  516 B corresponds to antenna  216 B; and transmitter  511  corresponds to modulator  205 . 
     As described hereinbefore, in the master and slave communication devices of the third embodiment of the present invention, sync timing adjustment is performed exclusively in the master communication device, which can be designed to be large. This allows the slave communication device such as a portable device to have a simplified receiver configuration, thereby being reduced in size, price, and power consumption. The description hereinabove does not include the modulation scheme for communication with a reflected wave; however, it is possible to use OOK, BPSK, PPM or the like. 
     Fourth Exemplary Embodiment 
       FIG. 7  is a diagram of pulse waveforms in a master communication device of a fourth embodiment of the present invention and shows examples of the pulse waveform of a signal transmitted for synchronization. The present embodiment differs from the first embodiment in that at the time of generation timing adjustment, synchronization is achieved by changing the pulse width of pulses to be transmitted. Waveform  1  of  FIG. 7  is a correlated signal of the slave communication device, and waveform  2  of  FIG. 7  shown in dashed line is a transmission signal waveform from the master communication device. These signals are synchronized by performing generation timing adjustment in such a manner as to change the generation timing of dashed-line waveform  2  of  FIG. 7  to the solid-line waveform by Δt. However, for example in pulse communication, it is difficult to calculate a time lag of Δt because the waveforms overlap each other only for a short time and have no correlation for a long time. 
     To overcome this problem, waveform  3  of  FIG. 7  having a large pulse width is used as a transmission signal. Waveform  3  of  FIG. 7  has a pulse width large enough to have a correlation with waveform  1  of  FIG. 7  and can be synchronized with waveform  1  at either timing of its three repetition periods. Repeated correlations are performed between waveform  1  and waveforms  4  and  5  of  FIG. 7  which have a slightly reduced pulse width. Finally, synchronization is completed between waveform  1  and waveform  6  of  FIG. 7  which is exactly correlated with waveform  1 . 
     In the aforementioned structure, sync adjustment is performed by changing the pulse width of pulses to be transmitted by the master communication device, which can be designed to be large. This allows the slave communication device such as a portable device to have a simplified receiver configuration, thereby being reduced in size, price, and power consumption. 
     The present embodiment describes the example of serially-connected wave elements which are equal in amplitude and phase; however, it is alternatively possible to change the amplitude so that the envelope can be, for example, Gaussian Mono Pulse. It is also possible to change phase and frequency between the center and both ends or between the former half and the latter half of pulses. This enables the correlation position to be estimated based on the difference in amplitude and phase in positions such as the former half and the latter half of a pulse signal after the pulse signal is correlated. 
     Fifth Exemplary Embodiment 
       FIG. 8  is a diagram of pulse waveforms in a master communication device of a fifth embodiment of the present invention.  FIGS. 9A to 9C  are diagrams of pulse waveforms indicating the operation of the master communication device of the present embodiment and show examples of the waveform of a signal which is transmitted to be synchronized with the slave communication device. The present embodiment differs from the fourth embodiment in that generation timing adjustment is performed by changing not the pulse width but the number of pulses to be transmitted. 
     The following is a description of increasing the number of pulses by the master communication device of the present embodiment with reference to  FIG. 8 . Waveform  1  of  FIG. 8  is a correlated signal of the slave communication device, and waveform  2  of  FIG. 8  shown in dashed line is a transmission signal waveform from the master communication device. These waveforms can be synchronized with each other by changing the waveform generation timing of dashed-line waveform  2  of  FIG. 8  by Δt so as to be overlapped with the solid-line waveform. While the fourth embodiment increases the pulse width, the present embodiment uses waveform  3  of  FIG. 8  having a large number of pulses as a transmission signal. Waveform  3  of  FIG. 8  has a large number of pulses and can be correlated with waveform  1  of  FIG. 8 . Waveform  3  of  FIG. 8  can be synchronized with waveform  1  by either one of the two pulses. Then, correlation is performed between waveform  1  and waveforms  4  and  5  of  FIG. 8  having a slightly reduced number of pulses. Finally, synchronization is completed between waveform  1  and waveform  5  of  FIG. 8  which is exactly correlated with waveform  1 . 
     The following is a description of reducing the number of pulses by the master communication device with reference to  FIGS. 9A to 9C . When the signal power-to-noise power ratio is large, the noise power can be ignored and the reception signal has a waveform shown in  FIG. 9A . However, in such a case that the communication distance is large; that another device is in operation near the slave communication device; or that the master communication device itself causes loud noise, the noise power becomes so large relative to the signal power that the signal is buried in noise as shown in  FIG. 9B . This makes it difficult to detect a signal that is not yet synchronized or correlated. 
     To overcome this problem, a signal is transmitted by reducing the number of pulses and increasing the peak voltage of each pulse as shown in  FIG. 9C . The high peak voltage allows the ratio of the signal power to the noise power to be larger regardless of the small number of pulses. This facilitates the detection, demodulation, and hence synchronization of signals. 
     As described hereinbefore, in the present embodiment, sync adjustment to change the number of pulses to be transmitted is performed by the master communication device, which can be designed to be large. This allows the slave communication device such as a portable device to have a simplified receiver configuration, thereby being reduced in size, price, and power consumption. 
     Sixth Exemplary Embodiment 
       FIG. 10  is a communication signal sequence diagram of a master communication device and a slave communication device of a sixth embodiment of the present invention and shows examples of signal timing. The present embodiment uses the master communication device and the slave communication device of either one of the first to fifth embodiments so as to describe a method for calculating the distance between the communication devices using a sync signal sequence and a sync-check signal sequence. 
     When a sync signal sequence shown in signal example  1  of  FIG. 10  is transmitted from the master communication device and synchronously received by the slave communication device, the slave communication device transmits as sync signal generation timing information, signal example  2  of  FIG. 10  which is a sync-check signal sequence. Signal example  3  of  FIG. 10 , which is the sync-signal-check signal sequence, reaches the master communication device with a delay corresponding to a flying time. When the distance between communication devices is measured, the master communication device transmits a signal example  4  of  FIG. 10  by adding a signal sequence for distance measurement, which is a signal different from a sync signal sequence. 
     Upon receiving the signal containing an async signal, the slave communication device returns the signal indicating asynchronization shown in signal example  5  of  FIG. 10 . The master communication device includes a flying time calculator (unillustrated) for calculating the time difference between the signal for distance measurement and the signal indicating asynchronization in the receiver as shown in signal example  6  of  FIG. 10 . The flying time calculator calculates the flying time and the distance between the communication devices. The flying time can be easily calculated using the time difference between the signal transmitted from the master communication device and the return signal from the slave communication device. In short, the flying time is the time obtained by subtracting the response time in the slave communication device from the time difference. The flying time can be reduced in half to obtain a flying time for a signal to be transmitted from the slave communication device to the master communication device or from the master communication device to the slave communication device. The distance can be calculated from the flying time by multiplying the flying time by the speed of electromagnetic wave. 
     The internal delay between the reception of the signal for distance measurement and the return of the signal indicating asynchronization by the slave communication device can be subtracted from the time difference if the slave communication device previously measures the internal delay and informs the master communication device of it. 
     As described hereinbefore, in the master and slave communication devices of the present embodiment, sync timing adjustment is performed exclusively in the master communication device, which can be designed to be large. This allows the slave communication device such as a portable device to have a simplified receiver configuration, thereby being reduced in size, price, and power consumption. The use of the signal for sync timing adjustment achieves a master communication device and a slave communication device, each of which can measure the distance between itself and another communication device. 
     INDUSTRIAL APPLICABILITY 
     As described hereinbefore, in the master and slave communication devices of the present invention, timing adjustment is performed in the master communication device with a sync timing adjustment feature. This can provide components that are conventionally required on the receiver side of every device such as multistage receiving-system branches and synchronization loops only in the master communication device. As a result, the slave communication device with no sync timing adjustment feature can have a simplified receiver configuration, thereby being reduced in power consumption and price. The master and slave communication devices of the present invention can be usefully applied to data communication devices, UWB wireless devices, and the like. In these devices, wide band signals such as signals having pulse waveforms are used to create a seamless network by wirelessly connecting AV devices and personal computers to each other.