Multi-frequency alarm system receiver with interference detection

• US 20080001731A1
• Filed: 06/29/2006
• Published: 01/03/2008
• Est. Priority Date: 06/29/2006
• Status: Active Grant

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Eskildsen, Kenneth G.
• Granted Patent: US 7,642,910 B2
• Time in Patent Office: Days
• US Class Current: 340/539.1
• CPC Class Codes: G08B 25/10 using wireless transmission systems G08B25/009 takes precedence
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal

Abstract

An alarm system receiver that is capable of receiving signals transmitted from wireless intrusion detectors at more than one frequency and automatically switching from receiving at one frequency to receiving at a different frequency based on the detection of an interference signal. The alarm system receiver senses a first signal, filters the sensed first signal at a first frequency, demodulates the filtered first signal at the first frequency, and determines if a first interference signal is present in the demodulated first signal for a predetermined time. If the first interference signal is not present in the demodulated first signal, it processes the demodulated first signal as an alarm system signal. If the first interference signal is present in the demodulated signal, the alarm system receiver senses a second signal, filters the sensed second signal at a second frequency, demodulates the filtered second signal at the second frequency, and processes the demodulated second signal as an alarm signal. The alarm system receiver consists of an antenna, more than one filter, more than one local oscillator for providing oscillator signals at the predetermined frequencies, a demodulator for inputting one of the oscillator signals and a corresponding one of the filtered signals to provide a demodulated signal, and an interference detection circuit for inputting the demodulated signal, determining if an interference signal is present in the demodulated signal, and providing an interference detection signal.

Claims

1. A method of receiving signals from a wireless intrusion detector comprising the steps of

a. sensing a first signal;

b. processing said first signal at a first frequency to determine if a first interference signal is present in said first signal for a predetermined time;

c. if said first interference signal is not present in said first signal for said predetermined time, then further processing said first signal as an alarm system signal, and

d. if said first interference signal is present in said first signal for said predetermined time, then

i. sensing a second signal, and

ii. processing said second signal at a second frequency as an alarm signal.

2. The method of claim 1 wherein the step of processing said first signal at a first frequency to determine if a first interference signal is present in said first signal for a predetermined time comprises the steps of

i. filtering said sensed first signal at said first frequency to provide a filtered first signal,

ii. demodulating said filtered first signal at said first frequency to provide a demodulated first signal, and

iii. determining if a first interference signal is present in said demodulated first signal for a predetermined time;

and

further wherein the step of processing said second signal at a second frequency as an alarm signal comprises the steps of;

i. filtering said sensed second signal at said second frequency to provide a filtered second signal, and

ii. demodulating said filtered second signal at said second frequency to provide a demodulated second signal, and

iii. processing said demodulated second signal as an alarm signal.

3. The method of claim 2 further comprising, after said step of demodulating said filtered second signal at said second frequency, the step of determining if a second interference signal is present in said demodulated second signal for a predetermined time, and if said second interference signal is present in said demodulated second signal for said predetermined time, then not processing said demodulated second signal as an alarm signal.

4. The method of claim 3 further comprising the steps of:

a. sensing a subsequent signal,

b. filtering said sensed subsequent signal at a subsequent frequency to provide a filtered subsequent signal,

c. demodulating said filter subsequent signal at said subsequent frequency to provide a demodulated subsequent signal,

d. determining if a subsequent interference signal is present in said demodulated subsequent signal for a predetermined time,

e. if said subsequent interference signal is not present in said demodulated subsequent signal for said predetermined time, then processing said demodulated subsequent signal as an alarm system signal, and

f. if said subsequent interference signal is present in said demodulated subsequent signal for said predetermined time, then repeating steps a through f for a predetermined number of times.

5. The method of claim 1 wherein said first frequency is 345 MHZ.

6. The method of claim 1 wherein said second frequency is 315 MHZ.

7. The method of claim 4 wherein said subsequent frequency is between 260 Mhz and 460 Mhz.

8. The method of claim 4 wherein said subsequent frequency is the same as said first frequency.

9. The method of claim 1 wherein said predetermined time is 2 seconds.

10. The method of claim 1 wherein said first interference signal is present if said interference signal is greater than [41.66 (μ

V/m)/MHz]*F-7083.33 μ

V/m, where F is said first frequency.

11. The method of claim 3 wherein said second interference signal is present if said interference signal is greater than [41.66 (μ

V/m)/MHz]*F-7083.33 μ

V/m, where F is said second frequency.

12. The method of claim 3 further comprising the steps of generating and transmitting an interference message if said first or said second interference signal is present in said demodulated signal for said predetermined time.

13. An alarm system receiver comprising:

a. an antenna for sensing signals,

b. processing circuitry adapted to

i. process a first signal at a first frequency to determine if an interference signal is present in said first signal for a predetermined time,

ii. process the first signal as an alarm system signal if the interference signal is not present in said first signal for a predetermined time, and

iii. process a second signal at a second frequency as an alarm system signal if said interference signal is present in said first signal for a predetermined time.

14. The alarm system receiver of claim 13, wherein said processing circuitry comprises:

a. more than one filter for filtering said sensed signals at predetermined frequencies comprising the first frequency and the second frequency,

b. more than one local oscillator for providing oscillator signals at said predetermined frequencies,

c. a demodulator for inputting one of said oscillator signals and a corresponding one of said filtered signals to provide a demodulated signal, and

d. an interference detection circuit for inputting said demodulated signal, determining if an interference signal is present in said demodulated signal, and providing an interference detection signal, wherein said interference detection signal is used to select one of said oscillator signals and a corresponding one of said filtered signals for demodulating.

15. The alarm system receiver of claim 14 further comprising:

a. a slicer circuit for generating a quantized demodulated signal, and

b. a microcomputer for inputting said quantized demodulated signal and processing said quantized demodulated signal as an alarm signal.

16. The alarm system receiver of claim 15 wherein said microcomputer inputs said interference detection signal, further processes said interference detection circuit, and provides a frequency select signal.

17. The alarm system receiver of claim 16 further comprising analog switches for selecting one of said oscillator signals and one of said filtered signal to be inputted into said demodulator wherein the selection is based on said frequency select signal.

18. The alarm system of claim 13 wherein said predetermined frequencies are frequencies between 260 MHz and 470 MHz.

19. The alarm system receiver of claim 14 wherein said interference detection circuit determines if an interference signal is greater than a predetermined threshold for a predetermined time.

20. The alarm system of claim 19 wherein said predetermined threshold is [41.66 (μ

V/m)/MHz]*F-7083.33 μ

V/m, where F is said predetermined frequency.

21. The alarm system of claim 19 wherein said predetermined time is two seconds.