An Experimental and Analytical Study on the Improvement of False Path-switching in Auxiliary Radio Communication System Repeaters Using Digital Multichannel Filtering

Vollständiger Abstract

Worum geht es in dieser Arbeit?

Korean fire-safety standards such as the National Fire Performance Code (NFPC) 505 and the National Fire Technical Code (NFTC) 505 require that auxiliary radio communication systems do not impede digital radios. However, most repeaters and line amplifiers are analog path-switching devices driven by carrier detection, which respond to input power rather than signal identity. This study quantifies false path-switching vulnerabilities and proposes structural and institutional remedies. The mechanism was formulated as a frequency-blind threshold model, and a bench test was performed on a KC (Korea Certification) conformity-assessed commercial repeater by injecting unmodulated continuous-wave (CW) and real-modulated Digital Mobile Radio (DMR) signals from a commercial Type-2 license-free radio into the receiver (RX) port with a power sweep. A DMR signal only six channels (75 kHz) away from the fire channel falsely captured the RX path at −79 dBm, 1 dB above the minimum detectable level (MDL). A 1 MHz-offset CW did likewise at −65 dBm; lowering the MDL by 5 dB shifted both thresholds by exactly 5 dB, confirming the threshold-selectivity decomposition. A digital multichannel filtering repeater combining spectrum detection and synchronization, polyphase filter-bank finite impulse response (FIR) filtering, and least-mean-squares (LMS) adaptive notch filtering was proposed. Analytical calculations without hardware implementation predicted that channel-selective filtering would raise the equivalent false-switching threshold by the stopband attenuation (60 dB or more) and nonlinearly improve DMR synchronization retention. As conformity assessment does not test switching selectivity, supplementary fire-performance test items, including an off-channel false-switching immunity test, should be introduced into the type-approval and inspection framework; prototype validation can be conducted in the future.