Abstract:
In the conventional wireless location system that synchronizes base stations by wireless communication, waveforms of a signal used for synchronization and of a signal used for delay measurement are the same, and therefore if there is a reflected wave in an earlier-sent signal, it becomes difficult to distinguish two kinds of signals, and accordingly location accuracy suffers degradation. Moreover, when two different waveforms are allocated to the two signals, a matched filter that supports the two waveforms becomes necessary, which inevitably makes a circuit size large. The invention is characterized in that signals having the same waveform but having different polarities are allocated to the synchronizing signal and the signal for delay measurement, respectively. This enables the two kinds of signals to be detected with one matched filter and also to be distinguished by simple means using polarity difference.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese application JP 2005-038568 filed on Feb. 16, 2005, the contents of which is hereby incorporated by reference into this application.  
       FIELD OF THE INVENTION  
       [0002]     This invention relates to a wireless base station of a location system that measures a position of a node having a function of wireless transmission, and a wireless base station of the system.  
       BACKGROUND OF THE INVENTION  
       [0003]     A concept of the sensor network that information collected by a small sensor terminal (node) is sent to a server through a wireless network is making substantial progress toward utilization in recent years by development of a circuit miniaturization technology using MEMS etc. and advent of new wireless communication systems.  
         [0004]     Although these small sensor nodes that eliminate the need for connection with cable are very flexible in terms of installation and operations, on the other hand, they need a technology of measuring positions of the sensors in order to specify a position where abnormality occurred. A typical method as the conventional node location method is methods of measuring a position using a signal from satellites, such as a GPS. However, these methods have a problem that they can only be used out-of-doors where radio waves from satellites are receivable and that they need an exclusive receiver and antenna, which makes the node large. As a location method that can be used indoors, there is a method in which a waveform of a radio wave transmitted from a node is recorded, a received timing of the signal is determined, and a node position is calculated from measurement results of received timings of a plurality of base stations (JP-A No. 189353/2003 (Patent document 1)). In order to acquire high location accuracy by this method, it is required to measure accurately received times of two kinds of signals, a synchronizing signal and a signal for delay measurement.  
       SUMMARY OF THE INVENTION  
       [0005]     In the conventional technology, since the signal used for obtaining a delay from the node to a base station and a signal used for synchronization between base stations are the same in waveform, if there exists a reflected wave for a signal being sent earlier, it becomes difficult to distinguish the two kinds of signals and accordingly location accuracy suffers degradation. Alternatively, if different waveforms are allocated to the two signals, there is a problem that a matched filter (MF) supporting two waveforms become necessary on the receiving side, and accordingly the circuit size becomes large.  
         [0006]     This invention is characterized in that two signals having the same waveform but having different polarities from each other are allocated to a synchronizing signal and a signal for delay measurement both of which are necessary to perform the location. The base station that receives the synchronizing signal and the signal for delay measurement enters the two kinds of input signals into the same matched filter, and calculates a correlation value for the same signal sequence. Since the two kinds of input signals have the same waveform, they can be detected by the matched filter using the same signal sequence, and the two signal outputs can be distinguished because of polarity difference of outputs. Timings at which the absolute value of this matched filter output becomes maximums in both polarities are detected as a received timing of the synchronizing signal and a received timing of the signal for delay measurement, respectively. For the matched filter here, both an analog filter and a digital filter are usable without causing any problem. In the case of a digital filter, a signal from an RF part is A/D converted before entering the filter and the matched filter output, as it is, is recorded in the memory. In the case of an analog filter, the signal from the RF part, as it is, is entered into the matched filter and its output is A/D converted and recorded in the memory.  
         [0007]     By allocating the signals having the same waveform but having different polarities from each other to the synchronizing signal and the signal for delay measurement, it becomes possible to detect the two kinds of signals with one MF and also distinguish the two signals easily by polarity difference. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a configuration diagram of a location system of a first embodiment of this invention;  
         [0009]      FIG. 2  is one example of a signal waveform of the first embodiment of this invention;  
         [0010]      FIG. 3  is a block diagram showing a position calculation flow of the first embodiment of this invention;  
         [0011]      FIG. 4  is a diagram of a message flow of the first embodiment of this invention;  
         [0012]      FIG. 5  is a block diagram of a reference station of the first embodiment of this invention;  
         [0013]      FIG. 6  is a block diagram of a base station of the first embodiment of this invention;  
         [0014]      FIG. 7  is a block diagram of a received timing measurement section of the first embodiment of this invention;  
         [0015]      FIG. 8  is a block diagram of a location system of a second embodiment of this invention;  
         [0016]      FIG. 9  is a block diagram showing a position calculation flow of the second embodiment of this invention; and  
         [0017]      FIG. 10  is a configuration diagram of a base station of the second embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0018]     A first embodiment of this invention will be described with reference to drawings.  FIG. 1  is a configuration diagram of a location system of the first embodiment of this invention. A node  01  is equipped with a function of transmitting a positioning signal  05  composed of a pulse or a pulse train. A reference station  02  is equipped with a function of transmitting a reference signal  06  for determining a reference time by wireless communication after receiving a signal from the node  01 . At this time, a reference signal shall be a pulse or a pulse train of the positioning signal transmitted from the node  01  whose polarity is inverted. Each base station  03  receives the positioning signal  05  transmitted by the node  01  and the reference signal  06  transmitted by the reference station  02 , and enters the received signals into a common matched filter (MF). Since the positioning signal  05  and the reference signal  06  have the same waveform but have inverted polarities to each other, the MF can detect both the positioning signal and the reference signal and obtain two outputs whose polarities are different. The base station  03  records the two outputs. The base station  03  obtains received times of the two signals from the MF outputs. A server  04  has information of coordinates of each of the base stations  03 , and is connected with each of the base stations  03  through a network  08 . The server  04  calculates a difference between the positioning signal received time and the reference signal transmitting time from received time information  07  that is information of signal reception times of the positioning signal and the reference signal both of which were obtained from each of the base stations through the network  08  and information on a distance between each of the base stations and the reference station, and calculates a position of the node  01  based on the information of the time difference and information of coordinates of each of the base stations  03 . In the case where position detection of the node is performed using a system in which base stations are not guaranteed to operate in synchronization, it is necessary to compensate an operation timing error between the base stations in some way. In this embodiment, a received timing of the reference signal  06  transmitted from the reference station  02  in a known position (or a distance from each of the base stations  03  is known) at the base station  03  whose position is known is measured, and by postulating that a shift of the received timing of the reference signal  06  resulting from a state where the base stations are asynchronous with one another affects the received timing of the positioning signal  05  similarly, the operation timing error between base stations is compensated.  
         [0019]      FIG. 2  shows one example of temporal waveforms of the positioning signal  05  and the reference signal  06  in the case where a UWB (Ultra Wide band) pulse signal is used. It is assumed that the reference signal has the same waveform as the positioning signal and the polarity of the whole signal is inverted to it.  
         [0020]      FIG. 3  shows a position calculation flow in this invention. First, the node  01  that is an object of the location transmits the positioning signal  05  towards the base station  03  and the reference station  02  (Step S 01 ). As a trigger of transmitting of this positioning signal, for example, there is a method for transmitting a signal for every fixed interval based on a timer attached to the node  01 . Moreover, as another example, there is also a method in which the node  01  transmits the positioning signal  05  in response to the positioning signal transmission instruction from the base station  03 . Alternatively, variation in sensor information or a fact that a residual amount of buffer for storing sensor information falls below a threshold may be used as a trigger to transmit the positioning signal.  
         [0021]     Each of the plurality of base stations  03  capable of receiving a signal from the node  01  enters the positioning signal  05  transmitted from the node  01  into its MF and records an output waveform from the MF (Step S 02 ). As an example of selection and adjustment of an MF to the input signal, there is a method in which positioning signal waveforms exclusively for each of a plurality of communication channels that the communication system can use are previously set up, and each base station has MFs that support the positioning signal waveforms of all the channels, respectively, enters the received signal into all the MFs, and adopts an MF that yields a maximum output. As long as the positioning signal  05  and the reference signal  06  have the same waveform, both a lone pulse and a pulse train are usable without causing any problem. Note that the MF shall support each signal; if the signal is a pulse train, the MF shall support the pulse train.  
         [0022]     The reference station  02  checks the positioning signal  05  from the node  01  has been received using the same MF as that of each of the base stations  03 . Then, the reference station  02  transmits the reference signal  06  to the surrounding base stations  03  (Step S 03 ). The reference signal  06  shall have the same waveform as the positioning signal  05  at the time of being transmitted from the node but have the inverted polarity to the positioning signal  05 . At this time, the reference signal  06  with the above-mentioned waveform may be stored in advance in the reference station  02 , or the system can use a method for recording the waveform of the positioning signal  05 , generating a reference signal whose polarity is inverted to the received waveform, and transmitting it to the base station. There is a method which comes under the scope of this invention in which the reference station  02  transmits the reference signal  06  when a fixed offset time elapsed in order to prevent the reference signal  06  from coinciding with a reflected wave of the positioning signal  05  transmitted from the node  01  at the time of transmitting the reference signal  06 . The base station  03  that received the signal of the reference station  02  enters also the reference signal  06  to the MF as in the case of the positioning signal  05  and records the reference signal together with the output waveform of the positioning signal  05  (Step S 04 ).  
         [0023]     Each base station obtains a received time T 1  of the positioning signal and a received time T 2  of the reference signal from the output waveform of the MF (Step S 05 ). As a method for detecting received times of the positioning signal and the reference signal, there is a method for obtaining times at which a maximum and a minimum of the MF output waveform to be recorded are received. Since the MF outputs of the positioning signal and the reference signal become opposite in polarity, if the MF shows a maximum at the time of receiving the positioning signal, the MF will show a minimum at the time of receiving the reference signal. On the contrary, if the MF shows a minimum at the time of receiving the positioning signal, the MF will show a maximum at the time of receiving the reference signal.  
         [0024]     If a signal with a polarity opposite to that of the earlier-received signal cannot be found, it is considered that either the positioning signal or the reference signal suffered signal polarity inversion on the way of a propagation path. As a method effective in the case where an opposite-polarity signal was not received in this way, there is a method in which a previously set-up threshold A for the absolute value of a signal amplitude is determined, the positioning signal and the reference signal are selected from signals whose amplitudes exceed A, and received times of these signals are obtained. As a method for selecting each signal, for example, there is a method in which first a signal whose amplitude is largest is selected and, after excluding signals whose received times are very close to that of the signal and that are considered as reflected waves, a signal whose amplitude is second largest is selected. Then, one of the two signals whose received time is earlier is determined as the positioning signal and the other whose received time is later is determined as the reference signal.  
         [0025]     Each of the base stations  03  sends to the server  04  the received time information  07  that includes several pieces of information: the positioning signal received time T 1 , the reference signal received time T 2 , an identifier of each of the base stations, an identifier of the node having sent the positioning signal, an identifier of the reference station having sent the reference signal, etc. As a method for acquiring the identifier information of the node and the reference station, there is a method in which after the node  01  sent the positioning signal  05  or after the reference station  02  sent the reference signal  06 , the node  01  or reference station  02  sends information including a fact that the signal was sent a little while ago and its identifier; if there did not come similar information from other node  01  or reference station  02  within a fixed period after receiving the positioning signal  05  or reference signal  06 , the base station  03  adopts that identifier; and if similar information was sent from one of a plurality of nodes  01  or reference stations  02 , one node  01  or reference station  02  among them is designated and instructed to send the positioning signal  05  or reference signal  06  again.  
         [0026]     Based on information on the reference signal detected time T 2  included in the received time information  07  sent from each of the base stations  03  and the known propagation delay T 3  that is elapsed for the signal to propagate between the reference station and the base station, a reference signal transmitting time T 4 =T 2 −T 3  at which the reference station transmitted the reference signal is obtained and designated as a reference time common to all the base stations (Step S 06 ).  
         [0027]     Next, a difference T 5 =T 1 −T 4  between the reference signal transmitting time T 4  and the positioning signal received time T 1  is obtained. Coordinates of the node  01  are calculated by the hyperbola intersection method using this information and coordinates of each base station (Step S 07 ). Incidentally, calculation procedures of calculating a position are described in detail in Patent document 1.  
         [0028]     Moreover, a method in which collision of a reflected wave of the positioning signal and the reference signal in the base station  03  is avoided by inserting a fixed offset time that extends until the reference station  02  transmits the reference signal  06  after the reception of the positioning signal  05  from the node  01  also comes under the scope of this invention. In this case, the base station  03  can achieve reduction in power consumption, reduction in a size of memory, etc. by halting received timing measurement of signals for a period corresponding to an offset time after receiving the positioning signal  05 .  
         [0029]     In addition, as a method for measuring a received timing, there is also a method in which direct waveforms of the positioning signal and the reference signal are searched and their received times are used, in addition to the method for simply using times at which the MF output becomes a maximum and a minimum, respectively. As a method for searching a direct wave, for example, there is a method of doing the following procedures. Two thresholds, a threshold B having a small absolute value and a threshold C having a large absolute value, are set up for polarity of either +1 or (−1), respectively; the received signal is determined surely as a desired signal at a time when the amplitude of the received signal exceeds the amplitude threshold C; assuming that the direct wave came earlier than that time point, the amplitude of the received signal earlier than the time point when the signal exceeded the threshold C is examined until the absolute amplitude becomes smaller than the threshold B; and by using a time at which the amplitude falls below the threshold B as a reference, an incoming time of the direct wave is estimated. Details of this method for measuring a received timing is disclosed in JP-A No. 014152/2002.  
         [0030]      FIG. 4  shows one example of a message flow in this invention. The node  01  transmits the positioning signal  05  at an arbitrary timing to the surrounding base stations ( 03   a - 03   c ) and the reference station  02 , and each base station records the MF output waveforms of the signal, respectively. Next, the reference station that received the positioning signal  05  transmits the reference signal  06 , and each of the base stations  03  records similarly an MF output waveform of the reference signal  06  from the reference station. Each base station obtains a received time of the positioning signal and a received time of the reference signal, respectively, and sends the received time information  07  including information of its identifier used for identifying the base station etc. to the server  04 .  
         [0031]     The server  04  estimates the signal transmitting time of the reference station from information on the received time of the reference signal included in the received time information  07  and a propagation delay from each of the base stations to the reference station that the server has. At this time, it also comes under the scope of this invention that the contents of the received time information that the base station sends to the server is a difference between the received time of the reference signal and the received time of the positioning signal and the server calculates a difference between the received time of the positioning signal and a transmitting time of the reference signal.  
         [0032]      FIG. 5  shows a configuration of the reference station in this invention. The reference station  02  consists of a signal generation section  21  for generating two signals of the two kinds of polarities, positive and negative, a reception determination section  22 , and a control section  23  in addition to an RF part including an antenna. When the reference station  02  received a signal, first the reception determination section  22  determines whether the received signal is the positioning signal  05 . If it is the positioning signal  05 , its waveform is stored and its polarity is determined. As a method for determining the positioning signal  05 , there is a method in which a plurality of MFs that support signals that are expected to be received are set up in advance, and a signal whose MF output is largest for the received signal is selected. When reception of the positioning signal  05  was checked, the control section  23  instructs the signal generation section  21  to generate the reference signal  06  having the same waveform as the stored waveform but having the inverted polarity to it, and a signal transmission timing. Regarding the timing of signal transmission, there is a method for transmitting the signal when a fixed offset time elapsed after the reception, in addition to the method for transmitting the signal immediately after the reception. The signal generation section  21  generates the reference signal  06 , and transmits the signal at a timing instructed by the control section  23 .  
         [0033]     Moreover, a method in which a signal whose polarity is opposite to a signal that the node  01  transmits is stored in advance and is transmitted as a reference signal permanently, regardless of a polarity of the waveform that the signal generation section  21  received, also comes under the scope of this invention. In this case, it is recommended that, when the positioning signal was received as with a polarity opposite to the normal case, the reference signal be also transmitted as with a polarity opposite to the normal case.  
         [0034]      FIG. 6  shows a configuration of the base station  03  in this invention. The base station  03  has: an MF  31  that supports waveforms of the reference signal and the positioning signal; a received timing measurement section  32  for measuring received timings of signals of the positioning signal, the reference signal, etc.; a wireless communication section  33  for performing usual wireless communication with the node etc.; memory  34  in which signal received timings and information obtained by communication are recorded; and a network section  35  for controlling communication to the server; in addition to the RF part including the antenna. Taking a signal sent from the RF part as an input, the MF  31  performs the sliding correlation processing with a previously determined signal sequence and outputs its results. At this time, a method in which the MF uses a signal sequence corresponding to an ID designated to each terminal as a signal sequence that the MF uses in correlation calculation, in addition to a specially determined signal sequence for the location, is one realization method for this invention. In either case, a signal from the base station and a signal from the reference station are entered into the same MF and used to calculate a correlation value with the same signal sequence. For the MF  31  in this stage, an analog filter and a digital filter are usable without causing any problem. In the case of a digital filter, a signal from the RF part is A/D converted before entering it into a filter and an MF output, as it is, is recorded in the memory  34 . In the case of an analog filter, a signal from the RF part, as it is, is entered into the MF  31 , and its output is A/D converted and recorded in the memory  34 .  
         [0035]     The base station enters a signal received by the RF part into the MF  31 , and monitors the reception of the positioning signal  05 . As a method for determining the reception of the positioning signal  05 , for example, the reception is determined by whether the absolute value of the amplitude of the MF  31  output exceeds a fixed threshold. When the reception of the positioning signal is checked, the MF  31  output, as it is, is sent to the memory  34  and the MF  31  output waveforms for the positioning signal  05  and the reference signal  06  are recorded. The received timing measurement section  32  obtains the received times of the positioning signal  05  and the reference signal  06  from the MF outputs stored in the memory  34 , and records the results in the memory  34 . The network section  35  sends to the server information of those signal received times and information on the identifiers of the node and the reference station. In the system where the reference station  02  inserts an offset time of a fixed interval between the reception of the positioning signal  05  and the transmission of the reference signal  06 , there can be used a method in which, when the amplitude of the output exceeded a fixed value, reception of the positioning signal  05  is determined, and writing of the MF output into the memory is halted for a time corresponding to the offset interval, whereby the memory quantity being used is curtailed.  
         [0036]      FIG. 7  shows one example of a configuration of the received timing measurement section. The received timing measurement section  32  consists of a maximum detection section  321 , a minimum detection section  322 , and a signal determination section  323 , wherein the maximum detection section- 321  and the minimum detection section  322  obtain a maximum and a minimum of the MF output stored in the memory  34  and reception times of these signals, respectively. The signal determination section  323  compares signal received times obtained from the maximum detection section  321  and from the minimum detection section  322 , sets an earlier received signal as a positioning signal and a later received signal as a reference signal, respectively, and records them together with their received times in the memory.  
         [0037]     For the received timing measurement section, in addition to one that uses a method for determining a maximum like this, one that has a function of estimating a received time of a direct wave by setting a time at which the amplitude of a received signal exceeds a threshold as a reference and searching a rise of the signal waveform is conceivable. Alternatively, there is a method where, if the reception of a signal whose polarity is opposite to that of the received signal cannot be checked, it is assumed that polarity inversion occurred in the propagation path, times at which large amplitude signals were detected are obtained among the MF outputs, and the received time of the positioning signal and the reference signal are obtained therefrom.  
       Second Embodiment  
       [0038]      FIG. 8  is a configuration diagram of a location system of a second embodiment of this invention. The node  01  is equipped with a function of transmitting the positioning signal  05  composed of a pulse or a pulse train. A base station  09  with a reference signal transmitting function is equipped with a function of transmitting the reference signal  06  used for fixing the reference time by wireless communication after receiving the positioning signal  05  from the node  01 . At this time, the reference signal shall be a pulse or a pulse train of the positioning signal transmitted from the node  01  whose polarity was inverted. The base station  03  receives the positioning signal  05  transmitted by the node  01  and the reference signal  06  transmitted by the base station  09 , and enters the received signals into a common matched filter (MF). Since the positioning signal  05  and the reference signal  06  have the same waveform but have inverted polarities to each other, the MF detects both the positioning signal  05  and the reference signal  06 , obtaining two outputs whose polarities are different. The server  04  has information on coordinates of each of the base stations  03 , and is connected with each of the base stations  03  through the network  08 . The server  04  calculates a difference between the positioning signal received time and the reference signal transmitting time from the received time information  07  on the positioning signal  05  obtained from each of the base stations  03  through the network  08  and the reference signal  06  and information on a propagation delay between each of the base stations and the reference station that the server has in advance, and then calculates a position of the node  01  based on the information of the time difference and information of coordinates of each of the base stations.  
         [0039]      FIG. 9  shows a position calculation flow of the second embodiment of this invention. First, the node  01  that is a target of the location transmits the positioning signal  05  to the base stations  03  and  09  (Step S 11 ). Each of the plurality of base stations  03  and  09  capable of receiving the signal of the node  01  enters the positioning signal  05  sent from the node  01  into its MF and records an output waveform from the MF (Step S 12 ).  
         [0040]     The base station  09  with the reference signal transmitting function transmits the reference signal  06  to the base station  03  that received the positioning signal  05 , after receiving the positioning signal  05  from the node  01  (Step S 13 ). The base station  09  records the reference signal transmitting time. The reference signals  06  shall be a signal whose waveform is the same as the waveform of the positioning signal  05  at the time of being transmitted from the node  01  but whose polarity is inverted to the positioning signal  05 . At this time, it is also possible to adopt a method in which a waveform of the positioning signal  05  is recorded, and a reference signal that is a received waveform whose polarity is inverted thereto is generated and transmitted to the base station.  
         [0041]     The base station  03  that received the signal of the base station  09  enters the reference signal  06  into its MF similarly as in the case of the positioning signal  05  and records the MF output together with the output waveform of the positioning signal (Step S 14 ). Each of the base stations  03  obtains a difference between the positioning signal received time T 1  and the reference signal received time T 2  from the output waveform of its MF (Step S 15 ).  
         [0042]     Each of the base stations  03  sends the received time information  07  including information of the positioning signal received time T 1 , the reference signal received time T 2 , the identifier of each of the base stations, an identifier of a node that sent the positioning signal, an identifier of the base station that sent the reference signal, etc. to the server  04 . As a method for acquiring identifier information of the node  01  and the base station  09 , there is a method in which, after the node  01  sent the positioning signal  05  or after the base station  09  sent the reference signal  06 , the node  01  or base station  09  sends information of a fact that the signal was sent a little while ago and its identifier to the base station  03 . If there does not come similar information from other node  01  and base stations  09  within a fixed time after receiving the positioning signal  05  or the reference signal  06 , the base station  03  adopts the identifier, if there was sent similar information from the plurality of nodes  01  and base stations  090 , one of the nodes  01  or base stations  090   a  is designated and instructed to send the positioning signal  05  or the reference signal  06  again.  
         [0043]     The server  04  calculates the coordinates of the node  01  that sent the positioning signal  05  based on the received time information  07  sent from each of the base stations  03  and known coordinates of each of the base stations ( 03  and  09 ). For the received time information  07  sent from each of the base stations ( 03  and  09 ), the server obtains the reference signal transmitting time T 4 =T 2 −T 3  when the reference-signal-transmitting base station sent the reference signal based on the reference signal detected time T 2  and a known propagation delay T 3  that is elapsed for the signal to propagate between the reference-signal-transmitting base station  09  and the base station in concern (Step S 16 ).  
         [0044]     Next, a difference T 5 =T 1 −T 4  between the reference signal transmitting time T 4  and the positioning signal received time T 1  is calculated. In this stage, regarding also the base station  09  having transmitted the reference signal  06 , a difference between the reference signal transmitting time T 4  and the positioning signal received time T 1  of the base station is obtained. Using these pieces of information and coordinates of each of the base stations, the coordinates of the node  01  is calculated by the hyperbola intersection method (Step S 17 ).  
         [0045]      FIG. 10  shows a configuration of a base station  09  with the reference signal transmitting function in this invention. The base station  09  has: the MF  31  that supports the waveforms of the reference signal and the positioning signal; the received timing measurement section  32  for measuring received timings of signals of the positioning signal and the reference sign transmitted from other base station, etc.; the wireless communication section  33  for performing usual wireless communication with the node  01  etc.; the memory  34  for recording a signal received timing and information obtained by communication; a signal generation section  91  for generating two signals of the two kind of polarities, positive and negative; and the network section  35  for controlling communications to the server; in addition to the RF part including the antenna.  
         [0046]     The base station enters a signal received by the RF part into the MF  31  and monitors the reception of the positioning signal  05 . As a method for determining whether the positioning signal was received, for example, there is a method for determining it by checking whether an absolute value of the amplitude of the MF output exceeded a fixed threshold. When the reception of the positioning signal  05  was checked, the MF output is recorded in the memory  34 , and the signal generation section  91  transmits the reference signal  06 . At this time, inserting a fixed offset interval between the reception of the positioning signal and the transmission of the reference signal also comes under the scope of this invention. The received timing measurement section  32  obtains a received time of the positioning signal  05  from the MF output recorded in the memory, and records the received time in the memory together with the transmitting time of the reference signal  06 . The network section  35  sends to the server  04  information of the received time of the positioning signal, the transmitting time of the reference signal, an identifier of the received node, and a fact that the network section  35  sent the reference signal.  
         [0047]     Since the application of the technology of this invention to a wireless location system can reduce the number of matched filters necessary in the base station, the invention can realize miniaturization and lower cost of the base station. Moreover, since the processing on the matched filter outputs is simple, such as detection of a maximum value and a minimum value, the technology of this invention is expected to shorten a calculation time necessary for the location and make smaller the power consumption of the base station.