Communications: directive radio wave systems and devices (e.g. – Radar transponder system
Reexamination Certificate
1999-08-25
2001-04-10
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
C342S044000, C342S051000
Reexamination Certificate
active
06215437
ABSTRACT:
BACKGROUND AND BRIEF DESCRIPTION OF THE PRIOR ART
The invention relates to a procedure for reading the data stored in a transponder which derives its supply energy from an RF interrogation pulse sent to it by an interrogation device and which transmits the data stored in it as an RF response signal modulated by these data. It furthermore relates to a transponder system for the execution of this procedure.
A transponder system is known from the EP 0 681 192 A2 which consists of two units, namely a transponder and an interrogation device. Data are stored in the transponder which may be read by means of the interrogation device. These data may, for example, serve to identify an object within which or to which the transponder is attached. The transmission of the data is in the form of RF signals, which means that reading the data and therefore, to give an example, the identification of the object to which the transponder is attached does not involve any physical contact.
The transponder of the known transponder system is a batteryless transponder which derives its supply energy from an RF interrogation pulse which is sent by the interrogation device. This RF interrogation pulse is rectified in the transponder and used to charge an energy store which in turn provides the supply energy required by the transponder in order to transmit the data stored in it in the form of RF response signals.
Due to this particularity it is obvious that the transmitting power of the transponder is rather low, which means that the range within which the data can still be read correctly by the interrogation device is limited. The greater the distance between the transponder and the interrogation device, the more feeble is the signal received by the retrieval device, so that, of necessity, interference frequencies receivable within the operating area of the transponder system tend to swamp the RF interrogation signal or at least components of this signal and, therefore, make a correct demodulation of the RF interrogation signal impossible.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a procedure and a transponder system of the type previously indicated which, even in the presence of interference frequencies within the operating frequency range and also where the distance between the transponder and the retrieval device is relatively great, still enables the RF interrogation signals to be correctly demodulated.
According to the invention, this requirement is satisfied in that in the interrogation device,
a) within a time period during which it has not caused the transponder by sending an RF interrogation signal to transmit the RF response signal, the background noise within the frequency range reserved for the signal transmission between the transponder and the interrogation device is received, and the background noise received is converted into a digital signal,
b) interference frequencies within the digital signal are acquired with which a signal with an amplitude exceeding a pre-determined threshold is received,
c) coefficients for an adaptive filter are computed on the basis of the interference frequencies that enable the passband characteristic of the filter to be adapted so as to suppress the interference frequencies acquired,
d) after the transmission of the RF interrogation pulse, an aggregate signal containing the RF response signal transmitted by the transponder and the superimposed background noise is received and converted into a digital signal,
e) the RF signal received is passed through the adaptive filter, tuned by means of the computed coefficients and
f) the filtered output signal from the adaptive filter is demodulated for the purpose of reading the data stored.
By means of the procedure according to the invention, firstly, the necessary preconditions are created so that any interference frequencies in the RF signal received by the retrieval device within the application frequency range are suppressed, so that subsequently an RF signal, freed from these interference frequencies, becomes available for demodulation to extract the data contained in it.
The transponder system according to the invention is characterised in that the interrogation device comprises the following:
I. An A/D converter which converts all analogue signals received by the interrogation device into digital signals,
II. an adaptive filter the passband characteristic of which is adjustable by means of filter coefficients,
III. a digital signal processor (DSP) which controls the procedural sequence and computes and sets the coefficients of the adaptive filter for the suppression of the interference frequencies contained in the background noise, and
IV. a demodulator which demodulates the signals filtered by the adaptive filter for the purpose of extracting the data transmitted by them.
Further advantageous developments of the invention are specified in the sub-claims.
REFERENCES:
patent: 3605029 (1971-09-01), Freedman
patent: 3617998 (1971-11-01), Freedman
patent: 4121102 (1978-10-01), Wilson
patent: 5134720 (1992-07-01), Gamgee et al.
patent: 5293399 (1994-03-01), Hefti
Aslanidis Konstantin O.
Hagl Andreas
Schurmann Josef H.
Brady III Wade James
Sotomayor John B.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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