NO310844B1 - Method and circuits for transferring data between a polling station and answering station - Google Patents

Abstract

The method described is intended for use in the transmission of data between interrogator and transponder stations (Q, R), the transponder station (R) preferably having a surface acoustic wave element (OFW) with a substrate suitable for conducting surface acoustic waves. The narrow-band interrogation pulses emitted by the interrogator station (Q) are modified in the transponder station (R) in such a way that the frequency spectrum of the modified interrogation pulses lies at least partly outside the frequency range of the unmodified interrogation pulses. The interrogation pulses are, for instance, fed to the surface acoustic wave element (OFW) in transponder station R1, for instance, via the input interdigital transducer (IDWi) and reflected as response pulses to the interrogator station (Q1) where signal components which lie in the frequency range of the response pulses are rejected. The response signals can thus be processed without interference occurring due to interrogation impulses emitted by other interrogator stations (Qx).

Description

The invention relates to a method according to the preamble of claim 1 as well as a transmission system suitable for carrying out the method according to claim 12.

Various interrogating and answering stations are known from the state of the art which carry out a two-way exchange of information with each other over a radio connection and which are used, among other things, for measurement and control purposes. From radar technology, there is e.g. known interrogators, which send interrogation pulses to transponders and thus receive the desired information in the form of response pulses.

From John Gosch, SAW TECHNOLOGY DRIVES AUTO ID, ROAD-TOLL SYSTEM, ELECTRONIC DESIGN of 26 April 1990, page 29, for example the use of SAW (surface acoustic wave) components is known in connection with the identification of cars that passing a checkpoint. The SAW components are then able to transform an arriving signal into a surface wave that propagates over the surface of the SAW component. Electro-acoustic transducers and reflectors are arranged on the surface of the SAW component, which are capable of converting part of the surface waves that pass them into electrical signals again. Each car to be identified in this connection has a SAW component on which a certain number of reflectors are placed at certain mutual distances on the surface of the SAW component in such a way that this SAW component differs from all further SAW components which used in other cars. This particular unique geometric arrangement of the reflectors also leads to an electrical relationship typical of each SAW component. That is to say, each SAW component that is impressed with a determined interrogation signal sends signals from the individual reflectors back to the interrogation station. With the typical arrangement of reflectors for each SAW component, the individual response signals are likewise returned with corresponding typical delays to the interrogation station. The responses given by a SAW component after receiving the interrogation signal, which occur in the form of several mutually time-shifted signals, are consequently also clearly different from the responses given by other SAW components.

Fig. 4 shows a possible course of the response pulse CWRD, which is emitted from the SAW component in response to a polling impulse AFI. In response to a single interrogation pulse AFI, the SAW component returns after a time delay in accordance with this a sequence of time-shifted pulses arriving at the interrogation station as code words.

From FR-A-2 624 677, a method for data transmission between interrogation and response stations, as well as a corresponding interrogation station and a corresponding response station, is known.

Problems can arise with this identification method if several non-centrally controlled polling stations Q are in operation close to each other. When e.g. a first polling station Q that has transmitted a polling pulse during a time interval Tr is connected to receive, and another polling station Q during this time interval Tr emits its own polling pulse, then there is a danger that the first polling station Q in addition to those from a response pulses transmitted by the associated response station receive a polling pulse from the other polling station Q. Such conditions can occur when using polling and response stations in railway technology, e.g. in large stations when several trains arrive at the same time or at an airport using several interrogation stations located close to each other. In the case of two or more parallel tracks, e.g. that in fig. 3 showed the problem that a polling pulse from polling station Q does not arrive at the associated answering station R, but also at another polling station Qx which is located on the neighboring track. Conversely, interrogation impulses from the interrogation station Qx could also reach the interrogation station Q and the response signals transmitted from the response station R to the interrogation station Q are superimposed. Although the disturbances are mainly due to the relatively strong polling pulses, reply signals arriving at nearby polling stations Qx or arriving from nearby reply stations Rx could also lead to disturbances of the communication. Since in order to ensure good transmission conditions, a relatively high transmission power is necessary, this problem is particularly disturbing.

In radar technology, it is also important that military stations that emit strong signals can be easily detected. Detected stations can consequently be disrupted by countermeasures.

The purpose of the present invention is therefore to specify a method and a transmission system which is suitable for carrying it out, with which the disturbances which could occur during the simultaneous operation of several polling stations can be prevented.

This purpose is solved by the features indicated in claims 1 and 12.

The method according to the invention allows the simultaneous operation of several polling stations which emit polling signals, without mutual interference occurring. The procedure consequently enables a high operational reliability of the communication system, which consists of all interrogation and response stations. Furthermore, there is the possibility of the transfer of changeable and unchangeable data between the interrogation and response station. The specified answering stations which are suitable for carrying out the method enable an advantageous modulation and demodulation of the signals which are respectively to be transmitted or received. Furthermore, the method can also reduce the detectability of stations that send out the interrogation or response signals.

In the following, for example, the invention will be explained in more detail in connection with a drawing. Fig. 1 shows a first of a transmitting and a receiving unit consisting of interrogation station.

Fig. 2 shows a first answering station consisting of a sending and a receiving unit.

Fig. 3 shows three rail-running vehicles passing a response station arranged on one of the tracks. Fig. 4 shows a possible signal sequence of inquiry and response signals resp. the course of the input and output signals in an answering station (see e.g. fig. 8).

Fig. 5 shows the course of the signals received and transmitted by the answering station.

Fig. 6 shows the sequence of controlled interrogation and response signals for two stations.

Fig. 7 shows search and detection signals in the frequency range.

Fig. 8 shows the sequence of interrogation and response signals in the time and frequency range.

Fig. 9 shows another interrogation station.

Fig. 10 shows another answering station.

Fig. 11 shows a third answering station.

In order to explain the method according to the invention, in the following two mutually corresponding interrogation and response stations Ql, RI will for example be described in more detail. Data is transmitted between the stations Ql, RI by means of modulated pulses. However, the method according to the invention can basically be used in all interrogation and response stations between which modulated carrier signals are transmitted. The preferred transmission of amplitude modulated carrier signals will be discussed in a later section.

Fig. 1 shows a polling station Q1 which is arranged to emit polling pulses and receive response pulses. In response to a polling pulse, e.g. from the one in fig. 2 showed response station RI emitted a sequence of response pulses (see fig. 4). For data transmission, carrier frequency signals or polling pulses modulated depending on the data to be transmitted. Interrogation pulses that are sent to the response station RI are e.g. phase or frequency modulated. Signals that are reflected back to the interrogation station Ql, on the other hand, are phase and/or amplitude modulated. In the one in fig. 2 response station RI also has the possibility of position and length modulation of the reflected response pulses. That is that the response pulses can be reflected continuously or segmented at arbitrary times with adjustable pulse length.

In addition, a polling station Ql has an oscillator MCL, which is connected on the one hand to an encoder ENC and on the other hand via phase modulator PSK-M, a pulse modulator IPM, a control amplifier RAI and circulator C with an antenna A. The circulator C is further connected over a bandpass filter BPF and a detector DET with a decoder DEC. The output of the phase modulator PSK-M is also connected to the reference frequency inputs of the decoder DEC and the detector DET. The encoder ENC is connected to the control inputs of the phase modulator PSK-M and the pulse modulator IPM. It is known to those skilled in the art that the functions of the decoder DEC and the detector DET can be performed by a signal processor SPROC. Furthermore, the detector DET is arranged for emitting a control signal age to a control input on the control amplifier RAI, whereby the transmission power can be influenced depending on the detected data.

The circuit shown functions as follows:

The oscillator MCL supplies the phase modulator PSK-M controlled by encoder ENC with a continuous high-frequency signal which, depending on the data vd-t to be transmitted to the response station R, is phase modulated by the phase modulator PSK-M and transmitted to the pulse modulator IPM. With the phase modulator PSK-M, the phase of the transmitted pulses is changed stepwise from pulse to pulse depending on the data to be transmitted. This so-called phase-difference coding is described in more detail in Herter/Rocker, Nachrichtentechnik, first edition, Munich 1976, on page 209. The phase-difference coding allows a demodulation without carrier derivation, as the message is accommodated in the phase difference of two consecutive steps. It is therefore sufficient to compare the demodulation step of each arriving pulse with the previous one. In order to increase the transmission rate, several different phase steps are preferably used, e.g. 0°, 45°, 90°, 135°). The modulated high-frequency signal is transformed by the pulse modulator IPM, also controlled by the encoder ENC, into short pulses which, via the control amplifier RAI and the circulator C, are emitted to the antenna A and fed to e.g. the one in fig. 2 showed answering station RI. A sequence of response pulses sent by the answering station RI which is marked with fixed and/or variable data fd, vd-b is transmitted from the antenna A back over the circulator C and the bandpass filter BPF to the detector DET and on to the decoder DEC. The decoder DEC determines the transmitted data fd, vd-b from the signals emitted by the detector DET. The essential function of the bandpass filter BPF according to the invention will be described in a subsequent section (after the description of Figs. 2 and 11).

The one in fig. 2 response station RI houses a SAW component OFW1 where an input interdigital converter IDWi is arranged, respectively two offset reflectors RFT+45, RFT-45 and two output interdigital converters IDWa-1 and IDWa-2. The phase-modulated interrogation pulses are fed from the antenna A via a diplexer DX on the one hand to the input interdigital converter IDWi and on the other hand directly to the first input of a mixing stage MX-I and a mixing stage MX-Q, the second input of which is respectively connected to the output interdigital converter IDWa -1, IDWa-2 and whose output respectively with the input of a phase detector PD. The output interdigital converters IDWa-1 and IDWa-2 are arranged on the substrate and offset from each other by a quarter of the wavelength of the surface waves, so that the corresponding inputs of the mixing stage MX-I and MX-Q are supplied with two 90° mutually phase-shifted reference signals, each of which is mixed with the signal transmitted directly from the diplexer DX to the mixing stages MX-I, MX-Q. The surfaces formed by the input interdigital converters IDWi consequently arrive at the preferred reflectors RFT+45, RFT-45, offset with one-eighth of the wavelength of the surface waves (or corresponding to the desired degree of modulation). is arranged between the interdigital converters IDWi, IDWa-1 or IDWa-2 on the SAW component (OFW) and are there as response pulses over the input interdigital converter IDWi reflected back to the diplexer DX and on to the polling station Q. Furthermore, the surface waves arrive after a certain travel time to the output interdigital converters IDWa-1, IDWa-2. In this connection, the distance between the input and output interdigital converters IDWi, IDWa-1, IDWa-2 is chosen so that the travel time of the surface waves corresponds to the period duration of the pulse repetition frequency of the interrogation pulses. At the time when the interrogation signal delayed by the SAW component OFW arrives at the mixing stage, in each case the next interrogation pulse which is delivered from the diplexer DX directly to the mixing stage MX-I, MX-Q is available for demodulation. The demodulation takes place in the connection mentioned above, by a phase comparison of the signals emitted by the mixing stage MX-I, MX-Q. The local generation of a reference signal for the demodulation can thus be waived.

The diplexer DX is via a rectifier stage RECT and a threshold value connection DTH further connected to a control unit CU which is arranged for controlling an adjustable impedance IMP which, via one of the control units CU operated switch SW, can be connected to the reflectors RFT+45, RFT-45. When connecting the impedances, the reflection conditions of the reflectors RFT+45, RFT-45 can be set arbitrarily. In order to achieve maximum reflection values, the resistors IMP are selected in such a way that the self-capacitance of the reflectors RFT is compensated by an inductance selected depending on the operating sequence. In order to achieve minimal reflection values, capacitive resistors IMP or short-circuit loops are preferably selected. The degree of modulation can therefore also be changed arbitrarily by the amplitude modulation. The circuit design of the interdigital converters can take place in the same way. In order to optimize the method, it is preferred that the two reflectors RFT+45, RFT-45 can be simultaneously connected with an impedance. From the rectifier stage RECT, which emits a supply voltage Ub, a rectified signal is thereby sent to a threshold value circuit DTH by which it is determined whether there is a polling pulse and from which a corresponding signal is emitted to the control unit CU.

For the transmission of data vd-b to the interrogation station Q, the switch SW is controlled in such a way and the impedance IMP is set in such a way that the surface waves are either not reflected or, with respect to pulse length and amplitude, only partially reflected. In fig. 4 shows, for example, an interrogation pulse AFI which is delivered to the reflectors RFT+45, RFT-45 which are operated in such a way that parts of these pulses AFI pass and further parts (response pulses AWI1, ..., AWIn) are reflected. Those in fig. 4 shown response pulses AWI1, ..., AWIn have arbitrarily chosen time intervals, lengths and amplitudes. Furthermore, the phase positions of the response pulse AWI1, ..., AWIn are influenced by the choice of the activated reflector RFT+45; RFT-45. The response pulse AWI2 could e.g. be reflected from the reflector RFT+45 and the response pulse AWI4 from the reflector RFT-45.

For the transmission of data from the answering station RI to the interrogation station Q, the reflected signals could further be shifted between at least two phase positions (e.g. +/- 45° or +/- 90°) in a phase modulator depending on the binary data to be transmitted.

(Respective phase modulators or demodulators are described, for example, in Herter/Rocker, Nachrichentechnik - Ubertragung und Verarbeitung, Miinchen 1976, pages 181-218. As a phase modulator, the ring modulator shown on page 202, picture 2.4-27 can be used, for example. Phase modulation methods are further described in R. Måusl, Digitale Modulationsverfahren, Heidelberg 1991, chapters 3.3 and 3.4.) For demodulation of these phase-modulated signals, a reference signal is arranged in the interrogation station Ql which is used in each case for modulation of the interrogation signal and demodulation of the response signal. Moreover, the use of a pulse from the sequence of response pulses as a reference signal is possible. E.g. the phase position of the first pulse in the sequence is not changed. The phase positions of the subsequent pulses in the sequence can therefore be detected with respect to the first pulse in the sequence.

In fig. 11 shows a further response station R3 with a SAW component OFW3 which has an input interdigital converter IDWi and two mutually offset output interdigital converters IDWa-1, IDWa-2. The response pulses arrive at a response station R3 from the antenna A via the output OUT of a circulator Cx, a bandpass filter BF open to the bandwidth of the interrogation pulses as well as a diplexer DX to a rectifier stage RECT on the one hand and on the other hand to the input interdigital converter IDWi and via the SAW component OFW3 to the output interdigital converters IDWa-1, IDWa-2, which are connected via a switch SWtl to the input INP of the circulator Cx. The output interdigital converters IDWa-1 and IDWa-2 are offset from each other on the substrate by a quarter of the wavelength of the surface waves, so that the signals emitted from there are phase-shifted by 90° from each other. From the rectifier stage RECT which emits a supply voltage Ub, a rectified signal comes to the threshold value circuit DTH by which it is determined whether there is a polling pulse and from which a corresponding signal is emitted to the control unit CU whose output is connected to the control input on the switch SWtl. The output interdigital converter IDWa-1, IDWa-2 is also, as shown in fig. 2 preferably connected to a circuit which is suitable for detection of the transmitted data vd-t.

The function of the one in fig. The answering station shown in 11 must be explained in connection with that in fig. 4 for example showed the course of an interrogation pulse EFI and the corresponding response pulses AWI1, ..., AWIn. The shown interrogation pulse AFI, which has a narrow frequency spectrum, arrives practically unchanged at the input interdigital converter IDWi. With the only preferentially used band filter BF, only frequencies that fall outside the bandwidth of the polling pulse AFI are blocked. Over the switch SWtl which is controlled by the control unit CU, depending on the data to be transmitted, section-wise portions of the phase-shifted signals emitted by the output interdigital converters IDWa-1 and IDWa-2 are passed on to the input of the circulator Cx. The sequence of those in fig. 4 shown response pulses AWI1, ..., AWIn are consequently composed of pulses which, with regard to their temporal position, amplitude, length and phase position, are modulated. In the event that only an output interdigital converter IDWa-1 is used, the phase modulability is omitted.

In the case of two or more parallel tracks (see Fig. 3), the problem mentioned in the introduction is that the polling pulses from the polling station Ql do not reach the associated answering station RI, but also to a polling station Qx, which is located on a neighboring track. Conversely, the interrogation pulse from the interrogation station Qx could likewise reach the interrogation station Ql and superimpose the response signals transmitted from the response station RI to the interrogation station Ql. Although the disturbances mainly appear due to the relatively strong polling pulses, response signals arriving at nearby polling stations Qx or arriving from nearby polling stations Rx, could also lead to disturbances in the communication. According to the invention, these mutual disturbances occurring during the operation of several polling and answering stations are to be avoided. In order to avoid interference caused by extraneous interrogation pulses, the following procedural steps are accordingly arranged: From the interrogation station, narrowband interrogation signals are sent to the response station and the response signals are returned with a wide frequency spectrum and at least approximately the same center frequency. In the receiving stage of the interrogation station, components of the response signals whose frequencies lie within the frequency spectrum of the interrogation pulse are suppressed. Consequently, with these measures, all signals emitted by foreign interrogating stations can be suppressed, without the information transmitted from the answering to the interrogating station being lost.

From the polling station Ql, a narrowband polling pulse is sent out, the frequency spectrum of which in the response station RI is expanded by a non-linear circuit, after which the polling pulses modified in this way are sent over the delay line to the reflector RFT. Broadband response pulses are reflected from the reflector RFT and transmitted via the input interdigital converter IDWi and the antenna A to the interrogation station Ql. By the band-pass filter BPF arranged in the receiving stage in the interrogation station Ql, signal components whose frequencies lie in the range of the unmodified interrogation pulses are suppressed. In case the frequency range of the interrogation pulses is extended symmetrically, which is normally the case, then the blocking range of the bandpass filter BPF must be placed in the center of the frequency range of the response pulses. Since the response pulses, compared to the interrogation pulses, have a broadened frequency spectrum, the signal component that is not blocked by the bandpass filter BPF is sufficient to detect the interrogation pulses. The polling pulses of all polling stations Qx which work at the same frequency as the polling station Ql are then suppressed by the bandpass filter BPF. Disturbances that could be caused by foreign polling stations Qx are thus avoided.

In fig. 5a shows a polling pulse in the time range, as it is transmitted from the polling station Ql to the answering station RI. In fig. 5b, this narrowband a-v interrogation pulse is shown in the frequency range. In fig. 5c shows a modified interrogation pulse which has arisen by a temporal shortening of the one in fig. 5a showed polling pulse. For the sake of simplicity, a switch is arranged for this modification which is controlled in such a way that signal components which do not exceed an arranged threshold value are blocked. The switch is then only closed when the central part of the polling pulse exceeding the threshold value arrives. The threshold value corresponding to the desired broadening of the frequency spectrum can be chosen arbitrarily, preferably corresponding to approx. 2/3 of the maximum occurring signal amplitude. Fig. 5d shows the extended frequency spectrum for the modified polling pulse or the to the interrogation station Ql reflected response pulse. Fig. 5e shows the frequency spectrum of the response pulse after passing through the bandpass filter BPF in the interrogation station Ql. From this, it can be seen that the central part of the frequency spectrum, which includes the frequency range of the unmodified interrogation pulses, is blocked by the bandpass filter BPF.

Alternatively, the polling pulse can also be transmitted in its full length to a reflector or interdigital converter arranged on a SAW component which is thus activated and connected respectively to the transmitting and receiving antenna so that parts of the polling pulse that form the response pulse sequence are reflected to the polling station Ql. The response pulses generated in this way have, compared to the polling pulses for the above-mentioned reasons, likewise a broad frequency spectrum and can still be detected in the polling station Ql after passing through the bandpass filter BPF. This method and the associated answering station R can be used due to the mentioned advantages are also advantageously used without the use of the bandpass filter BPF which is used to suppress extraneous interrogation pulses.

The method according to the invention can also be used with particular advantage for the mutual transmission of signals on continuous waves (CW signals). The carrier signals for the data to be transmitted are modulated in the interrogation and response station Ql and R2 respectively in such a way that the total signal transmitted from the interrogation station Q2 has a smaller frequency spectrum than the total signal transmitted by the response station R2. This is preferably achieved by selecting a corresponding coding of the message data in stations Q2 and R2. Preferably, a two-stage frequency switching is chosen whereby the frequency of an oscillation changes between defined values which are assigned to logical states "1" and "0" for the data to be transmitted. The two frequency values for the data signal to be sent from the interrogation to the response station Q2 respectively R2 are consequently chosen lower than the frequency value for the data signal to be sent from the response to the interrogation station R2 respectively Q2.

In fig. 8a shows a series of data bits, such as is coded in stations Q2 and R2. For simplicity, the same bit sequence is chosen for the two transmission directions. The coded signals are shown in fig. 8b for the polling station Q2 and fig. 8c for the answering station R2. The coded signal in the interrogation station Q2 is switched between the frequencies fl and f2 and the coded signal in the response station R2 between the frequencies f2 and f3. The frequencies fl, f2 and f3 are therefore chosen much smaller than the frequency f5 for the carrier oscillation (fl, ..., D « fm), which is amplitude modulated with the coded signals. From the polling station Q2, there will be e.g. generated a carrier oscillation with a frequency of 850 MHz which is modulated with a data signal which switches between the frequency 75 kHz and 125 kHz. The carrier signal is preferably emitted with a power (e.g. 1W) which is so great that a supply voltage can be extracted from it in the response station R2 by rectification and filtering (see Fig. 2, voltage Ub). Furthermore, in the answering station R2, the carrier oscillation of the interrogation signal is preferably recovered and modulated with the data signal to be transmitted and which is switched between the frequency 75 kHz and 225 kHz. The carrier signal can also be suppressed before transmission to the polling station Q2. Typical frequency spectra of the interrogation (fig. 8d, line b) and response signals (see fig. 8d, line c) thus formed are shown in fig. 8d. It appears from this that the response signal in the spectral range of the interrogation signal has a very low power density. In the interrogation station Q2, the signal component occurring in this spectral range can therefore be blocked without disrupting the transmission of the data between the answering and interrogation station.

The data to be transmitted can also be supplied to a signal processor which emits a coded oscillation which has smooth transitions between signal components of different frequencies. With this loop formation of the frequency transition, a reduction of side maxima in the power spectrum is achieved. The frequency switching of a sine carrier is described, among other things, in R. Måusl, Digitale Modulationsverfahren, Heidelberg 1991, chapter 3.5.

The data to be transferred between the two stations Q2; R2 can also be converted from a "non-return-to-zero" to a "return-to-zero" format and supplied to a signal generator SG whose output signal is switched depending on the supplied data signal between two frequencies. The frequency values are selected for the interrogation station Q2 with a lower distance than for the response station R2. The "return-to-zero" format (described in P. Bocker, Datenubertragung, Springer-Verlag, Berlin 1978, page 23) is used because unwanted time intervals occur between the individual switching processes which cause the frequency spectra to change in an unacceptable manner.

With the method mentioned above, significant disturbances that could occur during the simultaneous operation of several polling and answering stations are taken care of. Of greater importance, however, are also problems that arise due to the case described below.

Especially when communicating with passive answering stations that reflect the interrogation signals unamplified, interrogation signals are emitted with high intensity to ensure that undisturbed communication is obtained even in unfavorable transmission conditions. However, strong interrogation signals as well as strong response signals formed therewith in good transmission conditions can cause interference, among other things, in further radio devices.

In the one in fig. 1 shown interrogation station Ql, the disturbing eavesdropping from the interrogation and response stations to foreign stations and radio devices is further reduced by the measures discussed below. According to the invention, the intensity of the arriving response signals is continuously measured by the detector DET in the interrogation station Ql and compared with a determined maximum value. Response signals that reach this maximum value can therefore be further processed without problems. Exceeding this maximum value due to the response signals therefore do not lead to an improvement in the transmission quality. From the detector DET, a signal age depending on the measured signal intensity is sent to the control input of the control amplifier RAI and regulates the amplification factor in such a way that the intensity of the arriving response signals never exceeds the determined maximum value. The intensity of the interrogation and response signals is consequently always kept at a minimum value at which the processing of the response signals in the interrogation station Q1 is still possible without problems.

However, during the time during which polling and answering stations are not in contact with each other (proportion of time on average well over 99%), the polling station transmits with maximum power and range. This means that the end-of-transmission step must be carried out for a high permanent transmission power which may not be permitted by law and which may cause interference in other radio networks. According to the invention, these problems can be prevented by reducing the transmission power in communication-free operation in such a way that when approaching an answering station it is ensured that answering signals are triggered which can be detected with a sufficiently high degree of certainty. Upon detection of the first response signal, the transmission power is increased until the data transmission between the two stations Q and R is finished. The transmission power is then reduced again when, preferably within a fixed period of time, no response signals appear anymore. Thereby, it succeeds in reducing the transmission power to a minimum, except for very short periods of time (time proportion normally well below 1%). In terms of circuit technology, the transmission power is controlled, e.g. in the interrogation station Ql again over the control line AGC, which connects the detector DET (respectively the signal processor if used) with the control input of the control amplifier RAI. The two methods mentioned above are preferably used in combination with each other. That is to say, when the transmission power is increased, this is reduced again during the normally two-way data transmission if the intensity of the response signals exceeds the maximum value. This method for controlling the transmission power can also be used with advantage if polling and answering stations are used that are not equipped with SAW components or additional delay lines.

In fig. 6a shows a two-set ZK1 equipped with a polling station Q which e.g. moves at 100 km/h past a response station R arranged to reflect the interrogation pulses AFI. In this connection, the length KL where stations Q and R are in contact amounts to only a few metres. In the case of the interrogation station Q as shown in fig. 6, sends polling pulses AFI with constant amplitude over the total time range, from the answering station R those in fig. 6c showed response pulses AWI which assume a maximum value when the stations Q. and R are vertically above each other. As long as the polling station Q is located within the contact length KL, the overall data transfer must be completed, as a good transfer quality is only ensured within this. The interrogation pulse AFI which is emitted long before or after this zone of full transmission power is therefore no longer useful for communication with answering stations R, but may lead to disturbances in the station arranged on the neighboring tracks. According to the invention, as shown in fig. 6d transmission power greatly reduced and only increased when a first response pulse AWI sent from the response station R is detected. After a certain number of response pulses AWI (after termination of communication) have failed, the transmission power is again reduced. In case the maximum duration of the data transmission is known, the transmission power can also be increased only in this time period (see Fig. 6d, time period tf). The increase and decrease of the transmit power takes place practically without delay from one interrogation pulse to another, a first response pulse AWI which serves to raise the transmit power, also corresponds to those in fig. 6d showed interrogation pulses AFI to those of fig. 6c showed response pulses AWI. Until the first response pulse AWI is reduced corresponding to the reduced transmit power. In fig. 6f, the transmission power is therefore regulated in such a way that it in fig. 6e showed response pulse AWI does not exceed a fixed maximum value. Thereby, both the response pulse AWI and also the interrogation pulses AFI are reduced with regard to their amplitudes. As the ratio between the contact length KL and the distance between two response stations is very large (normally a factor of approx. 1000), mutual interference of the polling and response stations is largely eliminated by the above measures. That in fig. 6f indicated power level is preferably selected depending on the transmission conditions. In the event that the answering station R e.g. is covered by a layer of snow, possibly higher power levels must be selected. Preferably, in this connection, more than two power levels should be available.

In fig. 6, the regulation of the transmission power for pulsed signals is shown. However, the idea according to the invention can also be used for continuous wave signals in an analogue way. In the following, it will be described how low-power (continuous) search signals are first sent out, which, after contact with an answering station has been achieved, are replaced by high-power interrogation and possibly power supply signals.

In order to be able to easily detect the first response signals when approaching a response station R, a relatively low power search signal with two frequency lines (fig. 7, ssl and ss2) is preferably sent out, which e.g. is arranged symmetrically at a distance of 50 kHz to the frequency fm of the (suppressed) carrier signal. E.g. will be the received signal due to the power supply rectifier arranged in the response station R (fig. 2, RECT, fig. 10, RECT2) distorted non-linearly, whereby an intermodulation occurs. Thereby, two additional spectral lines are generated (Fig. 7, asi and as2) which can be easily detected in the interrogation station Q. The signals reflected from the surroundings have no additional spectral lines. In fig. 7, the search signals ssl, ss2 are shown with the detection signals asi, as2 formed in the response station R. A particularly advantageous feature of this search method is that the search signals ss can be radiated with low power, and that the possibly formed detection signals asi and as2 can still be detected simply and reliably. After the detection of the signals asi and as2, the interrogation is initiated in the interrogation station Q. With increased power, the interrogation signal is now emitted and preferably consists of a powerful carrier oscillation to supply energy to the answering station R and a data signal.

The described search and query mode is preferably connected sequentially with each other. However, a mutually independent application is also possible.

In the event that, despite the measures described above, signals from foreign stations cannot be suppressed in the input stage of the interrogation station Q, it must be ensured that the data imprinted thereon is discarded after a test. In fig. 3 runs on two parallel tracks TRI, TR2 two trains ZK1, ZK2. In this connection, train ZK1 has the serial number SN-0001 and train ZK2 has the serial number SN-0002. At the first track TRI, a response station RI is arranged which is charged with interrogation signals from the interrogation station Ql arranged in the train ZK1. In the event that, despite the measures described above, the response signals should be able to come from the response station RI to a questioning station Qx arranged in a train ZK2, false commands can come to the driver of the train ZK2. It is therefore essential that only the information about signals originating from an associated response station R is processed in the interrogation station Q.

In addition, each interrogation signal is provided with a ZK or for each polling station Q individual modulation. E.g. the modulation could be derived from the locomotive's serial number, a code word or preferably from the imprinted message data. By correlating the response signals reflected from the response station R with this code word, the first or second response station Ql or Qx is therefore easily determined whether the received signals correspond to the own interrogation signals and are to be further processed or suppressed. E.g. the received signal is correlated with an expected signal that exists in a memory. In the event that the resulting signal exceeds a predetermined threshold value, the signal is further processed. Advantageously, the response data sent from the interrogation to the response station, before and after the transmission, could be EXOR-linked with the interrogation data. In a one-time EXOR concatenation, the response data is reformatted into a bit sequence with checksum errors. Only at the second EXOR connection which takes place in the interrogation station Q after the transfer, is the response data correctly produced again. When verifying the checksum, it is ensured that the response data was transmitted correctly and originates from the corresponding response station. For this purpose, the transmission data must always be supplied at the same time as the response data to the exclusive-OR gate in the response or interrogation station R or Q. If it is known how many clocks the polling data has been delayed on the transmission paths and in the response station R where the first EXOR connection occurs, then the polling data in the polling station Q could be delayed by the same amount of time. E.g. the query data could be written into the register and read out again on arrival of the response data or after the time delay has elapsed.

In fig. 9, another interrogation station Q2 is shown which is suitable for carrying out the method steps described above. In this connection, the interrogation station Q2 is either operated in search or interrogation mode. In search mode, they should on fig. 7 shown search signals ssl, ss2 are transmitted and the possibly received intermodulation signals asi, as2 are detected. From an oscillator SO, a carrier oscillation with the frequency fm is generated for this, which via a signal divider SPL is delivered to a first input of a mixing stage MX1, whose output via an amplifier AMP, adding stage ADD and an antenna filter C (circulator) is connected to the antenna A The second input of the mixing stage MX1 is connected to a signal generator SG, (for example a direct digital synthesizer DDS or a signal processor) which in search mode sm emits a frequency fl and in polling mode tm depending on the blocking data qd switches between two frequencies fl, f2. Symmetrical to the carrier oscillation, the search signals ssl, ss2 consequently arise in the mixing stage MX1 (the carrier oscillation is preferably suppressed before emission). The one in fig. 9 shown control amplifier RA2 is in search mode sm not in operation.

Reflected (detection) signals asi, as2 arrive in the search mode via the antenna filter C, a bandpass filter BPF1, a mixing stage MX3, two bandpass filters BPF4, BPF5 and a rectifier RECT1 to a threshold circuit TH1 which is connected via a transmission unit XM to a control unit STCL. The other input of the mixing stage MX3 is via a phase shifter PHS connected to a mixing stage MX2, which is supplied on the one hand with the carrier oscillation fm and on the other hand via a switch SW2 a low frequency signal fo from an oscillator RO. The bandpass filter BPF1 suppresses own or foreign signals that are close to the frequency fm of the carrier oscillation or in the spectral range of the interrogation signals. In the mixing stage MX3, the received signals are mixed with the output signals (fm ± fo) of the mixing stage MX2, which is chosen so that the detection signal asi, as2 at the output of the mixing stage MX3 lies in the intermediate frequency range and has the lowest frequency of all signals in the formed signal mixture. In the event that the input signals are instead mixed with the frequency fm of the oscillator SO, the detection signals asi, as2 stand with the same coverage as with any third harmonic of the search signals ss. The measures taken consequently prevent the search signal ss from triggering a false detection message due to distortions in the reception branch, respectively due to resulting intermodulations. The search signals ss and any intermodulations can consequently be easily filtered out and thus separated from the detection signals. In the bandpass filters BPF4, BPF5, a wideband and a narrowband filtering takes place, before the signals are logarithmically rectified in the rectifier RECT1 and compared by the threshold value circuit TH1 with a threshold value. The possibly occurring identification of detection signals asi, as2, respectively signals that exceed the threshold value, is reported by the threshold value circuit TH1, for example via a transmission device, to a condition control STCL realized preferably in a processor PROC, which then triggers the interrogation sequence. In the sm search mode, the heterodyne principle mentioned above is therefore preferred.

In the polling mode, the oscillator SO emits an unmodulated signal via the control amplifier RA2 and via the mixing stage MX1 and the amplifier AMP a modulated signal at the carrier frequency fm via the adder stage ADD and the f-frequency filter C to the antenna A. The control amplifier RA2 is controlled by a control stage AGC in this connection in such a way that the response signal in one, for example, in fig. 10 shown response station R2 does not exceed a defined maximum value. When the control amplifier RA2 is switched on, the above-mentioned increase in transmission power is caused during the communication with the response station R2. By means of the signal generator, the mixing stage MX1 is supplied with FSK (frequency keyed) or MSK (minimum keyed) respectively biphase sine coded message data. The MSK method is described, for example, in R. Måusl, Digitale Modulationsverfahren, Heidelberg 1991, chapter 3.5 (image 3.38).

The response signals from the signal station R2 are sent from the antenna A via the bandpass filter BPF1 to the mixing stages MX3 and MX4, which are supplied with two 90° phase-shifted signals at the frequency fm. Using the homodyne principle in the interrogation mode tm, the transmitted response data from the mixing stage MX3 and MX4 are not emitted in the intermediate frequency range, but directly in the baseband and logarithmic amplifiers LG1, LG2 to a selection logic SEL. Logarithmic amplifiers are preferably chosen because the input signals in the present application can have very large level differences.

The response data emitted from the mixing stage MX3 and MX4 are in phase with each other, but their amplitude is, however, multiplied by the cosine of the receive phase angle. This means that depending on the phase angle (distance between antennas A to stations Q2 and R2), the signals alternately become zero and change their signs. The selection logic SEL now always selects the stronger of the two signals, corrects the sign change and transmits the selected, corrected signal via a demodulator DEM to a decoder DEC 1. The demodulator DEM and the decoder DEC1 as well as the state control STCL and an operating mode selector MODE are preferably integrated within a processor PROC . In addition, for the other EXOR connection mentioned above, the interrogation data is supplied to the decoder DEC 1, so that the decoded response data is emitted from the decoder DEC1.

Preferably, a further threshold value circuit TH2 is also arranged by which it is tested whether the received response data rd exceeds a determined threshold value and is suitable for further processing. The result of this test is then reported to the condition control STCL. The selection logic is further connected to a control circuit AGC which emits a control signal dependent on the measured signal intensity for the response data rd to the control amplifier RA2.

The one in fig. 10 shows answering station R2 has an antenna A with two connection lines AZ1, AZ2. Over the first connection line AZ1, the interrogation signals are led to a rectifier stage RECT2, generated as detection signal asi, as2 and emitted over the antenna A. From the output of the rectifier stage RECT2, the rectified signals are delivered to a filter circuit SBG and on the other hand via a bandpass filter BPF6 to a clock generator TRG and a decoder DEC2. In this connection, the supply voltage for the response station R2 is supplied from the filter circuit SBG. The clock generator TRG generates the clock signal of the interrogation data qd emitted by the decoder DEC2 which is delivered to an encoder stage CD1, in which the first EXOR connection of the response data rd with the interrogation data qd takes place as described above. The response data rd is thereby either read out by a memory component ROM or by a data buffer BFF and via a multiplexer MPL supplied to the code stage CD1. The memory component ROM is preferably programmable at the installation location of the answering station R2. For this, a programming device PRG is preferably arranged, which can be supplied via a frame antenna FA with the data rd2 to be stored. Normally, a number of telegrams are thereby added to the storage component ROM, one of which can be selected over a line tsel and a decoder DEC3.1 encoder stage CD2, the encoder stage CD1 transmits the data preferably modulated according to the MSK (minimum shift keying) method and led to the control input of a switching transistor ES W, at the output of which a quarter-wave line arranged, for example, on a surface wave component SAW which is connected on one side to the connection line AZ2 and on the other side to earth, can be short-circuited. Thereby, the connection line AZ2 can be extended with the quarter-wave line depending on the response data. Signals that pass through the quarter-wave line twice (back and forth) are phase-shifted by 180° compared to signals that are reflected by the short-circuited quarter-wave line at the end of the connection line AZ2. In this connection, the quarter-wave line is preferably connected to the second connection line AZ2 via a bandpass filter. The carrier frequency of the polling signal is then transmitted over the second connection branch AZ2, sign-modulated by means of its connected quarter-wave line and transmitted back over the antenna A to the polling station Q2. In the response station R2, there is also a state control STCL2 which controls all processes, especially the time-correct EXOR connection. The bandpass filter BPF8 has a wide pass curve so that the aforementioned response signal (see fig. 8d) can be transmitted to the interrogation station Ql. Further modulation methods as well as the choice of corresponding frequencies to realize the above-mentioned invention can be determined by experts.

Claims (20)

1. Procedure for data transmission between interrogation and response stations (Q, R) which are arranged for receiving and transmitting carrier frequency signals, characterized in that interrogation signals are sent from the interrogation to the response station (Q; R) whose frequency spectrum lies within the frequency spectrum of the response signals that are transmitted from the response to the interrogation station (R; Q), that signal components of received signals whose frequencies lie within the frequency spectrum of the interrogation signal are blocked in the receiving part of the interrogation station (Q), and that the remaining signal components of any received response signals, in which information transmitted from the response until the polling station (R; Q) is completely contained, is further processed in the polling station (Q) if the quality of the transmission path corresponds to the requirements set. 2. Procedure according to claim 1, characterized in that the frequency spectra of the interrogation and response signals are obtained by suitable modulation of the occurring carrier signals, which at least have approximately the same carrier frequency, and that this suitable modulation is obtained in particular by the coding of the data that is transmitted according to an FSK, MSK or PSK method. 3. Procedure according to claim 2, characterized in that the data to be transferred between the two stations (Q; R) is converted from a "non-return-to zero" to a "return-to-zero" format and delivered to a signal detector (SG) whose output signal depending on the transmitted data signal is switched between two frequencies; whose values are chosen for the blocking station (Q) with a smaller distance than the frequency values assigned for the answering station (R), and that the carrier signals are modulated with the signals coded in this way. 4. Procedure according to claim 1, characterized in that the response station (RI) has at least one delay line, preferably a SAW component (OFW) which is provided with a substrate suitable for conduction of surface waves, on which at least one input interdigital converter (IDWi) and at least one reflector (RFT) are arranged and/or at least one output digital converter (IDWa), that narrowband interrogation pulses are transmitted from the interrogation to the response station (Ql; RI) which are modified in the response station (RI) in such a way that the frequency spectrum of the modified interrogation pulses at least partially falls outside the frequency range of the unmodified polling pulses, and that the interrogation pulses over the input interdigital converter (IDWi) are delivered to the SAW component (OFW) and reflected to the interrogation station (Ql). 5. Procedure according to claim 4, characterized in that the change in the frequency spectrum of the unmodified interrogation pulses in the response station (R) is achieved by suppressing signal components of the interrogation pulses whose intensity does not exceed a fixed threshold value, or by at least unaltered interrogation pulses being fed to an optionally activatable reflector (RFT +45; RFT-45) or at least to an output interdigital converter (IDWa-1, IDWa-2) which can optionally be connected to the antenna (A) and at which sections of the interrogation pulses are reflected to the interrogation station (Q) depending on the data that must be transferred. 6. Procedure according to claim 4, characterized in that corresponding to the data to be transmitted (vd-t; vd-b), the unmodified interrogation pulses in the interrogation station (Q) are phase modulated and/or the response pulses in the response station (R) are position, length, phase, and/or amplitude modulated, and that the signals to be transmitted are demodulated in the receiving stage to the response station (R) or the interrogation station (Q) respectively and/or that the response pulses are routed through one of two mutually offset output interdigital converters (IDWa-1, IDWa-2) to the antenna (A) or sections of the interrogation pulses are reflected by one of two mutually offset, optionally activateable reflectors (RFT+45; RFT-45) back to the antenna (A). 7. Procedure according to claim 6, characterized in that the phase-modulated interrogation pulses in the response station (RI) are transmitted to the first input of a mixing stage (MX-1; MX-Q) and as a reference the surface wave component (OFW), delayed by the period length of the interrogation pulse repetition frequency, to two mutually offset output interdigital converters (IDWa -1, IDWa-2) which supplies two 90° phase-shifted signals to the other input of the mixing stage (MX-1 and MX-Q respectively), and that the mixed signals in the mixing stage (MX-l, MX-Q) are supplied each input on a phase detector (PD). 8. Method according to one of the preceding claims, characterized in that each polling station (Q) with time intervals Tp emits periodic polling pulses or sequences of polling pulses to an assigned response station (R) and which are modulated individually differently, preferably corresponding to a code word and correlated with the received signals, and that only the received signals that correlate with the transmitted signals are further processed. 9. Method according to one of the preceding claims, characterized in that the response data to be transferred from the response to the interrogation station (RQ) is first EXOR-connected in the response station (R) and then in the interrogation station (Q) with the interrogation data to be transmitted from the interrogation to the response station (R, Q) and that the response data in the interrogation station (Q) is only further processed if their checksum is correct. 10. Method according to one of the preceding claims, characterized in that a search signal is generated in the interrogation station (Q) with two frequency lines (ssl, ss2) which lie symmetrically about a center frequency, that the search signal is transmitted to the response station (R) and there is distorted in such a way that two additional frequency lines (asi, as2) arise symmetrically to the center frequency, and that the resulting signal is transmitted to the interrogating station (Q) and it is determined therein about the frequency lines (asi, as2), which indicate an achieved contact between interrogating and answering stations (Q, R), are contained in the signal mix. 11. Method according to one of the preceding claims, characterized in that the transmission power in the interrogation station (Q) is kept at a reduced value as long as there is no contact between the interrogation and response stations (Q, R) (search mode), that the transmission power in the interrogation station ( Q) after contact has been achieved between the interrogation and response station (Q, R) is increased for the data transfer (interrogation mode), and that the transmission power in the interrogation station (Q) is preferably controlled or regulated in such a way that the response signals do not exceed a fixed maximum value. 12. Transfer system suitable for carrying out the method according to claim 1, and comprising a polling station (Ql, Q2) which has an oscillator (MCL) which via a modulator (PSK-M, MX1), connected to a control device (ENC, SG), is connected to a circulator (C), connected to an antenna ( A) and to a receiving stage (DET, DEC), and which further includes an answering station (RI, R2, R3) having a component (OFW) connected to an antenna (A), which component is suitable for reflection of the signals received by the interrogating station (Ql, Q2), which signals can be modulated before retransmission in the answering station (RI, R2, R3) by means (CU, SW, IMP, RFT; CD2, ES W; CU, SWtl, IDW), characterized in that a pulse modulator (IPM) is arranged in the transmission path for the interrogation station (Ql, Q2) which transforms a supplied signal into interrogation pulses, that means (SW, SWtl; ESW) are arranged in the answering station (RI, R2, R3) for to increase the bandwidth for the reflected signals, and that a bandpass filter (BPF) is arranged in the receiving path for the interrogation station (Ql, Q2) which blocks signal components of received signals whose frequencies lie within the frequency spectrum of the interrogation pulses sent out by the interrogation station (Ql, Q2). 13. Transmission system according to claim 12, characterized in that the component (OFW) arranged in the response station (RI, R2, R3) is a surface wave filter comprising an input interdigital converter (IDWi) connected to an antenna (A), as well as at least one reflector (RFT) and/or at least one output interdigital converter ( IDWa), and that in order to achieve an extension of the bandwidth of the response signals formed by the interrogation pulse, means (SW; SWtl; ESW) are arranged which serve to shorten and segment the interrogation pulse to be reflected. 14. Transmission system according to claim 13, characterized in that the antenna (A) is connected via a controllable switch to the input interdigital converter (IDWi), or that a switch (SW; SWtl) controlled by a control unit (CU) is arranged for bandwidth expansion and for data transmission, over which one or one of two mutually offset output interdigital converters (IDWa-1; IDWa-2) can be connected via a circulator (Cx) with the antenna (A) or a reflector (RFT+45; RFT-45) with an impedance (IMP). 15. Transmission system according to claim 13 or 14, characterized in that means (RECT, DHT) are arranged which are suitable for determining the arrival of an interrogation pulse and reporting this to the control unit (CU), which according to the data as vd-b to be transmitted and/or the time position of the interrogation pulse , is suitable for timely operation of the switches (SW; SWtl). 16. Transmission system according to one of claims 12-15, characterized in that the interrogation station (Q2) comprises an oscillator (SO, MCL) which, via a mixing stage (MX1), an amplifier (AMP) and a circulator (C) is connected to an antenna (A), in which the mixing stage (MXl) is further connected or can be connected to a signal generator (SG) which is arranged for the generation of search signals (ss), that the circulator (C) further over a bandpass filter (BPF1) and an intermediate frequency stage (MX3, BPF4, PHS, MX2, RO) is connected to a filter and detection stage (BPF5, RECT1, TH1) in which the detection signals (as) formed in a response station (R2) by intermodulations of the search signals (ss) are detected and returned to the interrogation station (Q2). 17. Transmission system according to one of claims 12-16, characterized in that the interrogation station (Q2) comprises an oscillator (SO) which on the one hand over a mixing stage (MX1) and an amplifier (AMP) and on the other hand over a control amplifier (RA ) is connected to an adder stage (ADD) and further over a circulator (C) with an antenna (A), the mixing stage (MX1) being connected or can be connected to a signal generator (SG) which is arranged for emitting FSK -, MSK- or PSK-coded data, the circulator (C) also being connected via a bandpass filter (BPF1), a demodulation stage operating according to the homodyne principle (MX3, MX4, BPF3, BPF4, PHS, SO) and respectively a control amplifier (LG1, LG2), with a selection logic (SEL) which emits the power amplifier at the output of the control amplifier (LG1, LG2) signal corrected for sign to a demodulator (DEM) which is arranged for the recovery of the unmodulated data. 18. Transmission system according to claim 17, characterized in that the detector (DET) or a control stage (AGC) connected to the selection logic (SEL) is suitable for measuring the intensity of the received response signals and for emitting a control signal dependent thereon which can be supplied via a control line (AGC) to a control input on the control amplifier (RAI; RA ) and with which the transmission power is regulated in such a way that the received response signals do not exceed a fixed maximum value and/or by which the transmission power depending on the received signals is switched between at least two power stages. 19. Transmission system according to claim 18, characterized in that the output power of the control amplifier (RAI; RA2) can be at least partially reduced as long as there is no contact between the interrogation and response stations (Q, R) and/or that the interrogation signals to be emitted can be modulated corresponding to a code word, and that the reception stage of the interrogation station (Q) is carried out so that the received signals can be correlated with the code word and preferably supplied to a threshold value circuit. 20. Transmission system according to claim 12, characterized in that the answering station (R2) comprises an antenna (A) which is connected to a rectifier (RECT2) which is connected via a bandpass filter (BPF6) to a clock generator (TRG) and decoder (DEC2) with a by a switch (ESW) short-circuitable quarter-wave line (A./4) which terminates a wire (AZ2) connected to the antenna (A) to which the interrogation signals are modulated reflected, with an encoder stage working according to the FSK, MSK or PSK method which can be supplied with the data to be transmitted is supplied and whose output is connected to the control input of the switch (ESW), and the input of the code stage (CD2) can preferably be connected to a data buffer (BFF) or a memory component (ROM) via a multiplexer.