Method for processing transmitted and reflected signals for removing unwanted signals and noise form wanted signals.

(74) Agent

Micro Design AS, Øyberget, 7580 Selbu, NO Steffen Kirknes, Selbu, NO

Curo AS, Lundamo (54) Designation Method and Device for Individual Identification (56) Published Publications United States (US) Patent Nos. 3981011, 4074263, 4194201, 3663935, 3706094.

(57) Summary

In an identification system based on teflections of radar signals from a bit-encoded transponder, the received signals are processed to remove unwanted signals and noise from the desired, reflected and received signals having a repetitive similar course. The reflected signal is extremely weak in relation to unwanted signal and noise. A transmitter unit (11) generates a signal which is phase modulated by a portion of a random binary number sequence (14) and divided into time slots by a device (15) to form a number of preferably different phase modulated pulse trains which are transmitted. These pulse trains are reflected from a coded passive transponder (12) back to a receiver (13) which demodulates the signal and leads it onto a controllable integrator array (16) controlled by said portions of a random binary number sequence (14) along with the time slot signal from device (15). Also, the inverted signal of the signal (18) is controlled on the integrator array, controlled by the inverted values ​​of said portions of a random binary number sequence (14) together with the time slot signal from device (15). The number sequence (14) and its inverted time delay are separately in each shift register (17) to be synchronized with the reflected signal. The integrator array (16) comprises a plurality of integrator links typically corresponding to the number of bits in the code contained on the transponder (12), controlled by extracting the number series (14) and its inverted at different locations in the shift registers (19). At each integrator stage, by repeating the signal, the desired signal is averaged, while at the same time noise and unwanted signal which is random and asynchronous will be strongly reduced. The signals from the integrator links can be read asynchronously.

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The invention relates to a method and apparatus for individual identification in the identification system, as described in the preamble of claim 1, respectively. 10.

The invention is contemplated for use in an identification system comprising a transmitter, mobile bit-coded passive transponders providing identification, and a receiver portion which together constitute the processing system.

The transponder mentioned may, for example, be realized in Surface Acoustic Wave (SAW) technology. This technology offers many benefits in this application, it is low cost, easy to manufacture, maintenance free, and independent of external power sources etc. But a transponder realized in this technology has a feature which is basically a weakness. There is a high loss of input, ie the reflected response signal is weak in relation to the received pulse received. This disadvantage is amplified by the use of a low power radar for the transmitter part to satisfy radiated power requirements in the frequency band used.

Taken together, this gives the effect on the desired signal back to the system's receiver part to be very low compared to unwanted signals, noise and intrinsic noise in the receiver.

Previously known solutions.

The traditional method of processing signals to improve the signal-to-noise ratio in the aforementioned applications is to digitize the reflected signal directly with an A / Dome converter and perform a digital processing. The processing takes place there by averaging the digital values ​​of the analog signal for several repeated courses of the response signal. This will improve the signal to noise ratio because the desired signal is the same for each course while the noise is different for each course. However, this method requires a powerful digital processing unit, powerful in terms of speed and computing power, to average over a sufficient number of processes. At the same time, the A / Jumper must be one of the fastest and most advanced types available. This solution allows the technology to set clear limits on how efficient the processing is. It will also have to use digital signal processors and A / D converters that are high in price.

Another traditional method used in radar technology is to use delay lines so as to delay the signal a course and means by summing these signals analogously. This method has a limitation that the number of averages that can be obtained is very low and that the averages are not synchronized with the process.

US Patent 3,706,094 describes a receiver in a low power radar monitoring system, wherein the receiver comprises equipment for analog processing of received, repeated pulse signals by dividing each pulse signal into a specified number of time slots in controlled gate circuits and by supplying an integrator signal from each gate circuit. , with the integration of the pulse signals repeatedly, the repetition frequency of the pulse signals being significantly higher than the low pass filter frequency of the integrators. When reading the integrator's outputs, the pulse signal is recovered from the responder. US 3,663,935 discloses the transmission of signals that are phase modulated with different codes at successive pulses. In the receiver, a warehouse performs a mediation process.

Through US 4,074,263 and US 4,194,201 there is known identification of transponders, which includes a pseudo-random number sequence used in modulation and demodulation at transmission, respectively. reception. However, here the pseudo-random code is information carrier, and the application consists of identifying either-or.

US 3,981,011 describes a system in which a transponder answers when it receives the pulse sequence for which it is encoded. The purpose is to detect multiple pieces in the same area. This system is an obstacle to performing mediation, as only one response can be received from each chip in a coding sequence. In many code combinations, the sequence becomes long and each tag code is rarely repeated.

The main object of the present invention is to provide a secure method and apparatus for individual identification in an identification system, without the disadvantages of the prior art.

According to the invention, this can be achieved by a method and apparatus as defined in the characterizing part of claim 1, respectively. 10. Further features of the invention are set forth in the other claims.

The present invention differs from the prior art in that an interaction between transmitted and reflected signals is used, in that a random binary number sequence modulates transmitted signal, and the same number sequence is used when the demodulated reflected signal is to be recovered. A large number, preferably different phase modulated pulse trains, are generated by dividing said random binary number sequence, and the same portions of said random binary number sequence are used to direct the demodulated reflected signal onto a storage medium, for example, an integrator link having an embodiment which is so that the medium will contain values ​​where the desired signal is averaged, while undesirable signal and noise are greatly reduced.

Advantages of using the invention.

The method used in the invention is to perform an analog mediation of the signal before it is digitized.

The advantages that are achieved compared to the traditional methods are that a very large processing capacity is obtained by using completely conventional and commercially readily available and affordable components. It has a capacity for speed and the number of repetitions of means that far exceed the traditional solutions mentioned above. At the same time, the lower readout rate will reduce the requirement for the Ά / D converter and, later, the digital processing unit to a very simple and conventional type so that commercial gain is achieved.

By using a bit sequence both to modulate the transmitted signal on the transmitter side and to control the storage and averaging of the demodulated reflected signal on the receiver side, all types of noise and unwanted signal are greatly reduced relative to the desired signal. Since said bit sequence is part of a random bit sequence, noise and unwanted signals will be greatly reduced even though they have an unfavorable repetitive course.

Furthermore, it is possible to achieve better power output by using phase-modulated, preferably different pulse trains rather than a single pulse, at the increased length of the pulse train, which is limited up to time until the first reflected pulse train.

Embodiment of the Invention

Furthermore, an example of an embodiment of the invention will be described with reference to the drawings, in which fig. 1 is a block diagram of one embodiment of the invention containing the major components included; FIG. 2 shows a more detailed representation of the transmitter portion of this embodiment; FIG. 3 shows a more detailed representation of the receiver and decoding portion of this embodiment; and FIG. 4 shows a representation in the schedule of transmitted and reflected signal in this embodiment of the invention.

The embodiment as shown in FIG. 1 comprises a transmitter unit 11, an identification tag 12 which is, for example, a passive SAW transponder, and a receiver unit 13 which is connected to an array 16 of integrator links. A device 14 forms a sequence of random binary numbers applied to transmitter unit 11 and a shift register 17 associated with the integrator array 16. A device 15 generates a time-limited signal which is applied to transmitter unit 11 and shift register 17.

The operation of this embodiment is as follows. Transmitter unit 11 transmits a phase-modulated pulse train received and reflected by the coded transponder 12, so that the reflected signal consists of a series of pulse trains, and spaces where pulse trains are missing, which together form an identity similar to the code of the transponder, consisting of phase-modulated pulse trains. This desired signal is received by receiver 13 which demodulates the signal and leads it to an integrator array 16 which is controlled by said sequence of binary numbers from device 14 together with the time slot from device 15.

Fig. 2 shows a more detailed representation of the transmitter part. It consists of an oscillator 21 which generates a fixed frequency signal. This signal is phase modulated by a random binary number sequence from device 14. The completed modulated signal is divided into pulse trains by means of an open / close device 23, controlled by time slots from a device 15. The pulse trains are then amplified by an amplifier 24 before being transmitted.

Fig. 3 shows a more detailed representation of the receiver and the decoding part. In the receiver 13, the signal is demodulated, to a phase-coded and time-coded signal 31a, unwanted noise is superimposed. In this example of embodiment of the invention, the signal 31a enters a switch 36a which directs the signal 31a into an integrator link 37. This integrator link 37 may, for example, consist of RC filters with a time constant that is very high relative to the time of a single one. signal progress (ex. 10,000 times).

The binary number sequence from device 14 and the time slot signal from device 15 form the inputs of an AND gate 32a, where the output goes to a shift register 33a, which thus receives exactly the same number series as that used in the transmitter to form the phase modulated pulse train. This binary number sequence is then clocked across the shift register 33a by an external clock signal (not shown in the figure). It is possible to extract a signal at different positions on the shift register 33a, i.e. after certain time intervals after the signal is fed into the shift register 33a. When the time interval corresponding to the time delay for the first bit of transponder 12 has elapsed, the signal is taken out of the shift register and controls the switch 36a which opens respectively. closes for demodulated signal 31a from receiver 13 and onto integrator link 37.

The signal 31a is inverted by inverter 34 to a signal 31b which is also fed to the integrator link.

37. This is done by passing the random binary number sequence 14 through an inverter 35 to a second shift register 33b and taken out at a position correspondingly in the first shift register 33a and controls switch 36b to open, respectively. closes for the inverted signal 31b onto integrator link 37. Switches 36a and 36b may e.g. controlled in such a way that a logic 1 in the number sequence 14 causes the switch for the non-inverted signal 31a from the receiver to open and the switch for the inverted signal 31b to close; if a logical 0 occurs in the number sequence 14, the opposite will occur.

In the time intervals where pulse trains are not formed from transmitter 13 by the signal from device 15 having the value logically 0, AND gates 32a and 32b will always have logic 0 on the output, which in turn causes both switch 36a and 36b to be open. , to prevent unwanted noise from entering the integrator link.

The integrator array 16 is formed by a number of integrator links 37, typically corresponding to the number of bits or multiples of the number of bits in the reflecting device 12. The individual integrator links 37 can be read at any time after the desired number of pulse trains has been processed. This reading can take place asynchronously and without having to take into account what has happened before.

Fig. 4 shows a representation in the schedule of how two pulse trains are emitted from transmitter 11 and reflected from transponder 12, in an example where transponder 12 has a resolution of four bits. In this example, transponder 12 is encoded with binary number sequence 1101.

First pulse train 41a is a phase modulated signal, modulated by a first portion of a random binary number sequence from device 14, with a length determined by the time slot formed by device 15. This first pulse train 41a is received by transponder 12 and reflected where it is coded to logic 1. . Since the transponder in this example has code 1101, the reflected signal will form a pattern as shown in 41b in that bit 1, bit 2 and bit 4 reflect a pulse train, while bit 3, which has a logical value of "0, will not reflect any signal . The reflected pulse trains 41b can and will overlap for the different bit positions without having any negative consequences for the result.

After receiving the last reflected pulse train, a new second pulse train will be sent out. This pulse train is phase modulated by a second, preferably different from the first, portion of a random binary number series from device 14, printed for a certain time determined by the time slot of device 15. This second pulse train 42a is reflected from transponder 12 in a similar manner as in the first one. case, forming a series of reflected pulse trains 42b.

A large number of pulse trains, corresponding to pulse trains 41a and 42a, but preferably phase-modulated in various ways, can be emitted, reflected, received, and fed into the integrator array 16 so that the desired signal is averaged and the undesired signal which is random and asynchronous will be greatly reduced.