Abstract:
The invention relates to a method for synchronizing clock pulse devices. According to this method, an emission unit emits at least one narrow-band distant signal; clock pulse devices of receiving units are pre-synchronized by coupling the same to the source of one such distant signal; the emission unit emits a wide-band measured signal after a defined waiting time, and the receiving units receive said signal; and the receiving units correlate the wide-band measuring signal with a homogeneously modulated comparison signal, the receiving time of the wide-band measuring signal and the deviation in the synchronization of the clock pulse devices being determined and compensated on the basis of the correlation result.

Description:
BACKGROUND 
       [0001]    The invention concerns a method for synchronization of clock pulse devices, in particular for the purpose of a precise position determination of an object in a radio-based positioning system. 
         [0002]    Measurement methods which are based on the TDOA (“Time Difference of Arrival”) principle are known according to  FIG. 1 . A transponder T to be localized thereby repeatedly emits a transponder signal T S  at certain points in time. This transponder signal T S  is then received at multiple M base stations whose positions are fixed and known. The M base stations BS 1 , BS 2 , . . . , BS M  possess means to precisely determine the arrival point in time of the transponder signal T S . For calculation of the position of the transponder T, the delay difference t 1 −t 2 , t 1 −t 3  or t 2 −t 3  of the transponder signal T S  between the transponder T and at least two base stations BS 1  and BS M  is evaluated. In order to be able to precisely measure the delay differences, it is necessary to let the clock pulse sources of the base stations BS to run synchronously among one another. For this, either a very elaborate real-time capable background network or highly-precise, long-term stable clocks is required. 
         [0003]    Coded signals are typically used as a transponder signal T S , and the determination of the arrival point in time of the signal T S  at the base stations BS ensues via a correlation with a signal known to the base station BS. Such a correlation is, however, very computation-intensive for broadband and radio-frequency signals. If the transponder T and base station BS participating in a measurement are not synchronized, this correlation must ensue continuously and in a real-time capable manner in each base station. This is, at present, only economically realizable for a limited bandwidth with digital circuits. 
         [0004]    A method for synchronization of a transmitter station and a receiver station that communicate with one another via a radio interface is known from German Patent Document DE 101 57 931 A1 (“DE &#39;931”), that discloses a system in which, in the transmitter station, a transmission signal is generated with a signal source and emitted via the radio interface and a corresponding reception signal is received in the receiver station by the radio interface and is evaluated using a receiver signal source signal from a signal source on the receiver side that is adapted to the sender-side signal source. 
         [0005]    For up-to-date adaptation of the synchronization between a transmission signal and a reception signal, similar modulations are applied to the transmission signal and the reception signal and both are intermixed with one another. The mixed signal is subsequently analyzed with regard to a frequency detuning. 
       SUMMARY 
       [0006]    The invention is based on the object to provide a method and/or an arrangement in which signals can be synchronized among one another such that a precise position determination of a radio station is ensured via the calculation of delay differences of these signals from one radio station and a plurality of others. 
         [0007]    The object is achieved via a method for synchronizing clock pulse devices, comprising: emitting, by a transmitter unit, at least one narrow-band pre-signal; pre-synchronizing clock pulse devices of receiver units to a source of the pre-signal via a coupling to such a pre-signal; emitting, by the transmitter unit, a broadband measurement signal after a specific wait time and receiving, by the receiver units, this signal; and correlating, by the receiver units, the broadband measurement signal with a similarly modulated comparison signal and, based on a correlation result, determining a reception point in time of the broadband measurement signal and a deviation of the synchronization of the clock pulse devices and this is compensated. 
         [0008]    As a solution, according to an embodiment of the invention, a method for synchronization of clock pulse devices is proposed in which:
       a transmitter unit emits at least one narrow-band pre-signal,   clock pulse devices are pre-synchronized to the source of the pre-signal via a coupling to such a pre-signal,   the transmitter unit emits a broadband signal after a specific wait time and the receiver units receive this signal,   the receiver units correlate the broadband measurement signal with a similarly modulated comparison signal and, based on the correlation result, the deviation of the synchronization of the clock pulse devices is determined and compensated.       
 
         [0013]    The clock pulse devices can also be designated as clocks. If a synchronicity of the clocks exists, a majority of the computation effort for determination of the arrival point in time of a signal whose original position is not known can be assumed by simple analog circuit elements. Since the synchronization ensues via radio communications, advantageously, no network cabling among the transmitter units and receiver units is necessary. 
         [0014]    Base stations can be used as receiver units and transponders whose position is measured can be used as transmitter units. The transponder can be realized merely as a transmitter unit which itself receives no signal. Advantageously, only the base stations are synchronized among one another since these normally also have the possibility to receive clocked signals. 
         [0015]    For position determination of the transmitter unit, according to an embodiment of the invention, a method is provided in which
       a method for synchronization of clock pulse devices is executed as above, and   the arrival point in time of the broadband measurement signal is calculated based on the correlation result and the position of the transmitter unit can be determined via a comparison of the delays of the measurement signal received by the receiver units and transmitted by the transmitter unit.       
 
         [0018]    The method can be expanded in that a reference station with its own clock pulse source (the position of which reference station is known) emits a reference signal. This is received by the receiver units and the clock pulse devices of the receiver units synchronized on this reference signal. The reference station is advantageously fashioned as a transmitter unit in the form of a reference transponder. 
         [0019]    However, not only the receiver units but, rather advantageously, also the transmitter unit, can be synchronized from the reference transponder. For this, the transmitter unit must also be expanded as a receiver unit. Advantageously, this results in the base stations knowing at which point in time each transmitter unit transmits due to the coupling between the reference transponder and the transmitter unit or, respectively, transponder. The initial type of cited correlation in real time is therewith no longer necessary. The base stations can naturally likewise also serve as transmitter units, such that they can communicate among one another and, if applicable, pre-synchronize among one another. 
         [0020]    A radio communication arrangement can form the basis of and embodiment of the inventive method, which radio communication arrangement comprises:
       a transmitter unit and a plurality of transmitter and receiver units which respectively comprise a clock pulse device, a signal source and a radio interface,   a reference station whose position is known and which comprises a clock pulse device and a signal source via which reference signals of a predeterminable clock can be generated, whereby,   a synchronization of the clock pulse devices of the transmitter and receiver units can be achieved in that the delay differences of the reference signals that are to be expected are known to the plurality of transmitter and receiver units due to the known position of the reference station, and thus   the clock pulse devices of the transmitter and receiver units can be offset among one another in a uniform clocked state using a coupling to the clock pulses of the reference signals.       
 
         [0025]    It is advantageous when the radio communication arrangement is realized as a position measurement system or, respectively, as a radio-based positioning system in that distances between the transmitter and receiver units are measured. The position measurement system is advantageously to be used for the measurements of large distances, whereby in this case naturally the transmitter and receiver units exhibit a corresponding distance relative to one another. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0026]    Advantageous developments of the invention result from the following exemplary embodiments illustrated in the drawings. 
           [0027]      FIG. 1  is a block diagram illustrating a known radio communication arrangement with base stations and a transponder; 
           [0028]      FIG. 2  is a block diagram illustrating a radio communication arrangement with base stations, a transponder and a reference transponder; 
           [0029]      FIG. 3  is a timing diagram illustrating an embodiment for synchronization of clock pulse devices and for position determination of a transmitter unit with successions of pre-signals and measurement signals; and 
           [0030]      FIG. 4  is a block diagram illustrating a preferred design of transmitter and receiver units. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]      FIG. 2  shows how a reference transponder T Ref  is prepared at a known position. The base stations BS 1-M  are advantageously synchronized among one another with the aid of the arrangements and method described in DE &#39;931. For the devices which are used in this method from DE &#39;931, reference is made to  FIG. 4 . In this method, a transmitter station or, respectively, transponder SE, and a receiver station or, respectively, base station BS, are assumed to communicate with one another via an interface. In this arrangement, a transmission signal sig 1  is generated in the transmitter station with a signal source Sgen 1 , and is emitted via the interface. In the receiver station BS, a corresponding reception signal esig 1  is received by the interface and is evaluated using a receiver signal source signal sig 2  from a receiver-side signal source Sgen 2  adapted to the transmitter-side signal source Sgen 1 . 
         [0032]    The method is characterized in that a similar modulation is applied both to the transmission signal sig 1  and to the receiver signal source signal esig 1 , and the reception signal received in the receiver station BS is mixed with the receiver signal source signal sig 2  into a mix signal sigmix, and the mix signal is analyzed. Naturally the base stations BS must also serve as transmitter units for such a communication. After the base stations BS are at least roughly synchronized with one another, the values of the signal delay differences |t 4 −t 5 | between the reference transponder T ref  and a plurality of base stations BS 1-M  serve to synchronize the base stations more exactly among one another since the position of the reference transponder, and thus also the signal delay differences |t 4 −t 5 | to be expected, are known. The position of the transponder T can now be precisely determined via the synchronized base stations BS 1-M  in that delay differences |t 1 −t 2 | or |t 2 −t 3 | or |t 3 −t 1 | of the signal emitted by the transponder T to the base stations BS are evaluated. A triangulation or trilateration method can thereby be used for the position determination of the transponder T. 
         [0033]    The reference transponder T ref  comprises at least one signal source and a radio interface. It is also provided with a clock pulse source which clocks the signal source. The reference transponder can thus serve as a clock master for all remaining transmitter and receiver units so that the signals originating from these units are synchronized among one another. In order to be able to achieve an even higher precision, a plurality of reference transponders T ref  can naturally be used. 
         [0034]    A development of the invention exists in that the transponder T to be localized (thus not only the base stations BS M ) is also synchronized to a specific clock master, for example, the reference transponder. The transponder signal should thereby be a coded signal, such that at which point in time (relative to the clock of the clock master) each transponder transmits is known to all base stations per se or via a radio data transmission. The very elaborate correlation with this broadband measurement signal no longer has to ensue in a real-time capable manner, but rather can be implemented offline after a data recording. The computational effort or, respectively, the bandwidth of the signal to be evaluated can also be reduced by orders of magnitude via mixing processes as they are described in DE &#39;931 and via evaluation of the mix signal. 
         [0035]      FIG. 3  is a timing diagram showing the course of a series of signals for synchronization of radio stations. In this situation, there is no longer only one special clock master; rather, every transponder, regardless of whether it is a reference transponder or a transponder to be localized, takes on this function as needed. The localization process thereby runs as follows: 
         [0036]    Each transponder that would like to initialize a measurement emits an initially very narrow-band pre-signal V 1 , whereby in  FIG. 3 , the frequency spectrum or, respectively, the frequency axis is identified with f. In the normal case, all base stations implement a real-time correlation; this should detect this pre-signal V 1 . Each base station BS that detects such a pre-signal V 1  synchronizes to the source of this pre-signal V 1  according to the method from DE &#39;931. After a specific wait time T w  known to the base station, the transponder T then sends the actual broadband measurement signal V 3 . 
         [0037]    The pre-signal V 1  advantageously also comprises some further information such as identification number of the transponder and specifications about the wait time T w  between pre-signal V 1  and measurement signal V 3  or also the time duration until the emission of the next signal. In a wholly unsynchronized state, the pre-signal V 1  is advantageously repeated slightly time-shifted at least once to increase the assurance of detection of a pre-signal V 2 . The repetition signal is designated with V 2 . The wait time T r  should be selected such that it corresponds to approximately half of the modulation duration T of the pre-signal. 
         [0038]    A preferred embodiment of the invention exists in that not only are various base stations synchronized to the respective active transponders with the pre-signals V 1  and V 2 , but rather, a reference transponder at a known position also receives the pre-signals V 1  and V 2  and likewise synchronizes to these pre-signals using these. After a specific wait time T w , the transponder then sends the actual broadband measurement signal V 3 . 
         [0039]    The reference transponder likewise sends a similarly-modulated broadband reference measurement signal RV 3  offset by a very small time shift relative to T w . The time offset is selected such that it is distinctly smaller than the length of the broadband measurement signals V 3 . In the arrangement shown in  FIG. 4 , both the broadband measurement signal V 3  and the broadband reference measurement signal RV 3  are then simultaneously mixed with sig 2  in the base stations BS. Two signal components—one originating from the transponder and one originating from the reference transponder—are now found in the signal sigmix, using which two signal components the arrival times of and the time difference between the transponder signal and the reference transponder signal RV 3  can be determined very exactly in each base station BS. The position of the transponder T can then be determined very well based on the arrival times or, respectively, time differences. 
         [0040]    An alternative would be visible in that all participants are synchronized not to a transponder but rather to a reference transponder. The reference transponder would then, for its part, have to provide (via sending of identification signals (addressing specific transponder addresses)) that no more than one transponder emits a measurement signal at the same time. 
         [0041]    It is preferred that the position of the transponder to be localized is calculated after various base stations BS have received both the signals of the reference transponder described with respect to  FIG. 2  and of the transponder to be localized. 
         [0042]      FIG. 4  shows how a transmitter unit SE sends a transmission signal sig 1  via a signal generator Sgen 1 , which transmission signal sig 1  is radiated via the transmission antenna A T  to the base station BS. The form of the signal sig 1  is permanently preset. It is advantageous when sig 1  is a frequency-modulated signal (for example a FMCW signal). The frequency modulation can ensue linearly, step-by-step, or in digital stages. Such signals are advantageously used as they are also described in DE &#39;931. The base station BS is uniformly designed in large parts. A signal sig 2  is generated here in the same manner as in the transmitter unit SE. 
         [0043]    The signal received via the antenna A R , which signal was previously generated by the transmitter unit SE, is mixed with sig 2  with a mixer MIX. The mix signal sigmix is supplied to an evaluation and control unit ASE that evaluates the mix signal sigmix. 
         [0044]    A further embodiment is to likewise expand the unit previously designated as a transponder with similar receiver mechanism like the base station. After the base station is synchronized (as already described before) using the pre-signals V 1  and V 2  and has received the actual measurement signal and calculated the arrival point in time and the exact synchronization parameters according to DE &#39;931, the base station now, for its part, generates a response signal (based on the arrival point in time and the synchronization parameters) that is now sent to the transponder after a stipulated time span and is received by this transponder and, as provided before, the arrival point in time of the response signal is calculated. The response signal has a modulation nearly identical to sig 1  and is mixed (as described for the base station or in DE &#39;931) with a modulated signal like sig 1  (advantageously, like V 3  in  FIG. 3 ), and the arrival point in time is calculated from the remaining signal. 
         [0045]    The signal delay, and thus the radio channel length, and thus the separation between base station and transponder, can then be calculated from the time difference between query and response under consideration of the stipulated time span. This advantageously occurs using a generally known rough time of flight (RTOF) method. In typical systems without the synchronization according to the method, this method breaks down in all cases in that two spatially separate systems cannot agree upon exact time spans, in particular not on longer time spans, since their clock bases are not identical. However, a highly-precise compensation of the clocks can ensue via the synchronization. 
         [0046]    Since here the actual measurement information (namely, the separation value) is acquired in the transponder, it makes sense to exchange the nomenclature and to name the transponder so expanded as the base station and the base station the transponder. In many applications, it can also be reasonable to hold the expanded transponder stationary and to operate the base station mobile. An advantage of this arrangement is that the direct distances between two stations are measured and not delay differences (thus delays of 3 participants) as in the time difference of arrival (TDOA) principle. This direct delay measurement immanently enables a highest-possible flexibility—for example, even this exchange capability of the functions—and harmonizes in a particular manner with typical communication systems in which the communication also runs normally between only two participants. This method is therefore particularly well suited for apparatus in self-organizing radio networks or in sensor networks. 
         [0047]    It is also noted that the cited RTOF arrangement, according to the embodiment, is also very well suited for a transponder or, respectively, RFID (radio frequency identification) systems, since with them, the delay between a base station and a transponder can be determined. If the transponder additionally transmits an identification code, it is thus a clearly-improved identification system since not only the identity but rather also the distance of the object with the specific identity can be determined. This supplementary information can be used very advantageously in the field of automation technology, logistics, or in access or security systems. 
         [0048]    For the purposes of promoting an understanding of the principles of the invention, reference has been made to the preferred embodiments illustrated in the drawings, and specific language has been used to describe these embodiments. However, no limitation of the scope of the invention is intended by this specific language, and the invention should be construed to encompass all embodiments that would normally occur to one of ordinary skill in the art. 
         [0049]    The present invention may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions. For example, the present invention may employ various integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, and the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. Similarly, where the elements of the present invention are implemented using software programming or software elements the invention may be implemented with any programming or scripting language such as C, C++, Java, assembler, or the like, with the various algorithms being implemented with any combination of data structures, objects, processes, routines or other programming elements. Furthermore, the present invention could employ any number of conventional techniques for electronics configuration, signal processing and/or control, data processing and the like. The word mechanism is used broadly and is not limited to mechanical or physical embodiments, but can include software routines in conjunction with processors, etc. 
         [0050]    The particular implementations shown and described herein are illustrative examples of the invention and are not intended to otherwise limit the scope of the invention in any way. For the sake of brevity, conventional electronics, control systems, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent exemplary functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. Moreover, no item or component is essential to the practice of the invention unless the element is specifically described as “essential” or “critical”. Numerous modifications and adaptations will be readily apparent to those skilled in this art without departing from the spirit and scope of the present invention.