Multi-frequency alarm receiver with interference detection
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Solution Overview
Problem
Security system receivers using single frequency transmitters are susceptible to in-band interference, while frequency hopping systems are complex and costly, necessitating a solution that combines the benefits of frequency hopping with the simplicity and cost-effectiveness of single frequency systems.
Innovation Solution
An alarm system receiver capable of receiving signals at multiple frequencies and automatically switching to a different frequency upon detecting interference, utilizing multiple filters and local oscillators, along with a microcomputer for processing and selecting the appropriate frequency, to ensure reliable signal reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single frequency transmitter is used, then the system has lower cost and less complex hardware, but it is susceptible to in-band interference
Solution Approach 1:
The receiver dynamically switches between different frequency bands (first frequency and second frequency) based on interference detection. The system transitions from a static single-frequency reception to a dynamic multi-frequency reception, allowing it to adapt to interference conditions while maintaining simple hardware architecture.
Solution Approach 2:
The system changes the operating frequency parameter from a fixed single frequency to a variable multi-frequency mode. By detecting interference at the current frequency and switching to an alternative frequency, the system modifies the frequency parameter to maintain reliable communication without requiring complex frequency hopping hardware.
2Reliability
If a frequency hopping transmitter is used, then the system is less susceptible to in-band interference, but the electronics become much more complex and costly
Solution Approach 1:
The frequency range is segmented into distinct bands (first frequency and second frequency) with a frequency separation of at least 10 MHz. Instead of continuously hopping through many frequencies, the system divides the spectrum into discrete segments and switches between them, simplifying the electronics while maintaining interference resistance.
Solution Approach 2:
The invention extracts only the essential frequency switching capability needed to avoid interference, removing the complex frequency hopping algorithm and extensive frequency table management. By taking out only the necessary multi-frequency reception capability with a minimum 10 MHz separation, the system achieves interference resistance with simplified electronics.
3Ease of operation
If the receiver stays tuned to one frequency, then the reception is simple, but it cannot detect or avoid interference signals
Solution Approach 1:
The system implements feedback by monitoring the received signal quality at the current frequency and automatically switching to an alternative frequency when interference is detected. This closed-loop approach maintains reception simplicity while providing automatic interference avoidance through the interference detection and frequency switching mechanism.
Data Source
AI summary
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.