Method for processing transmitted and reflected signals for removing unwanted signals and noise from wanted signals

• US 5,144,313 A
• Filed: 04/24/1991
• Issued: 09/01/1992
• Est. Priority Date: 10/27/1988
• Status: Expired due to Term

• Current Assignee: Q-Free ASA
• Original Assignee: Steffen Kirknes
• Inventors: Kirknes, Steffen
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US07/690,498
• Time in Patent Office: 496 Days
• Field of Search: 342/44, 342/42
• US Class Current: 342/44
• CPC Class Codes: G01S 13/79 Systems using random coded signals or random pulse repetition frequencies , e.g. "Separation and Control of Aircraft using Non synchronous Techniques" [SECANT]

Abstract

In an identification system based on reflection of radar signals from a bit-coded transponder, the received signals are processed to remove unwanted signals and noise from the required, reflected and received signals that have a recurrent cycle. The reflected signals are extremely weak in relation to the unwanted signals and noise. A random bit sequencer and a time slot generator are used to generate a single phase modulated pulse train which is transmitted by an RF transmitter. The pulse train signal is received and reflected from a coded passive transponder back to a comparable receiver. The receiver demodulates the incoming reflected signal and directs the demodulated signal to an integrator array. An inverted signal from the receiver is also utilized. Synchronization of the transmitted and received signals is performed through a shift register while the bit sequencer controls a second integrator array. In this way, the unwanted signals and noise associated with the low power reflected signal is substantially eliminated.

Claims

1. A method in an identification system, wherein a radar signal is transmitted from a transmitter, said signal is arranged to be received by a mobile, bit-coded identification transponder which returns a coded signal that is received by a receiver;

the received coded signals are processed in order to remove unwanted signals and noise from the reflected, coded and wanted signals, wherein a pseudo-random bit sequence is used, characterized by comprising the steps of;

phase modulating the radar signal with a pseudo-random bit sequence,

dividing the modulated radar signal in time slots, forming a pulse train, which is transmitted,

passively reflecting from the transponder the transmitted pulse train signal, said transponder being encoded with binary coded information, and the reflected pulse train is modulated with the binary code of the transponder,

said receiver receiving and demodulating the reflected, coded pulse train signal using the same pseudo-random bit sequence and same time slots as were used at transmission, both of which being time delayed in order to demodulate the reflected pulse train signal to store, average and process the identification code from the bit-coded transponder for individual recognition.

2. A method in accordance with claim 1, characterized by said random bit sequence that is formed is different for each recurrent cycle.

3. A method in accordance with claim 1, characterized by the said binary-coded device reflecting the said pulse train signal at different times by means of the various bit positions in the device.

4. A method in accordance with claim 1, characterized by the demodulated signal being fed into a storage medium where the discrete values in the random bit sequence are able to control a device that opens for signals with a given bit value, and closes for signals that have the inverse value.

5. A method in accordance with claim 1, characterized by the random bit sequence being fed through a device that delays the values in time so that they are synchronized with the reflected signal.

6. A method in accordance with claim 5 characterized by the random bit sequence passing through a logical AND-gate operation prior to the delay device so that the storage device is blocked for signals outside the periods that equate the reflected pulse train.

7. A method in accordance with claim 1, characterized by the inverse demodulated signal being fed into the said storage medium, controlled by the inverse values of the said random bit sequence.

8. A method in accordance with claim 1, characterized by the said storage medium including the capability of storing a number of values which correspond to the number of bits in the reflecting device.

9. A method in accordance with claim 1, characterized by the said control signal being able to be extracted and used at different points in time, corresponding to the positions of the different bits in the reflecting device.

10. A method in accordance with claim 1, characterized by the said storage medium being designed so that a recurrent cycle of the received, demodulated and stored signal cycles are averaged over time.

13. A method in accordance with claim 1, characterized by the said storage medium including the capability of storing a number of values which correspond to the multiple of the number of bits in the reflecting device.

14. A method in accordance with claim 1, characterized by the said control signal being able to be extracted and used at different points in time which correspond to the multiple of the time delays between the bits in the reflecting device.

11. A device for filtering high frequency radar signals comprising;

a transmitter unit comprising an oscillator means and a generator means for generating a pseudo-random bit sequence, said transmitter unit being arranged to transmit a signal;

a remote binary coded transponder capable of reflecting at least a part of the transmitted signal;

a receiver unit arranged to receive and demodulate the transponder reflected signal; and

a controllable storage unit attached to said receiver unit;

characterized by the generator means of the transmitter unit being arranged to phase modulate the signal from the oscillator means, and the transmitting unit further comprises a time interval generator means, arranged to divide the phase modulated signal into a pulse train for transmission,

the transponder is individually binary coded to reflect a pulse train modulated with this code, and

the random bit sequence generator means and the time interval generator means are connected to at least one AND- gate having an output to at least one shift register, which is arranged to control the transmitter connected controllable storage medium.

12. A device according to claim 11, characterized by an invertor means is connected to the reflected, demodulated signal, and a second invertor means is connected to the random bit generator means for controlling the passage of the demodulated inverted signal to the storage medium.