Adaptive Multi-Band DMR-Based System for Data Transmission in Civil Defence Monitoring and Alerting

Abstract The continuity of national civil defence warning systems requires resilient backup communication channels that remain operational under crisis conditions, including long-term evolution (LTE) outages and intentional interference. This work presents the design and evaluation of a narrowband digital mobile radio (DMR)-based backup system employing a novel multi-band software-defined radio (SDR) transceiver architecture. Unlike conventional fixed-band implementations, the proposed prototype integrates five parallel radio frequency (RF) chains (150 MHz, 430 MHz, 868 MHz, 1.2 GHz, and 2.4 GHz), each equipped with dedicated filtering and antennas, thereby enabling rapid band switching without hardware replacement. Experimental point-to-point tests over a 6 km line-of-sight link, combined with Monte Carlo interference simulations, demonstrate frequency-dependent performance trends and validate the resilience benefits of multi-band operation. A methodological contribution of this study is the equalization of effective isotropic radiated power (EIRP) across all channels using calibrated attenuators, which allows for fair cross-band comparison of metrics such as received signal strength indicator (RSSI), bit error rate (BER), and packet delivery ratio. The results confirm that very high frequency and ultra high frequency bands remain the most reliable foundation for long-range telemetry, while higher frequencies serve as auxiliary reserves. The proposed SDR-based multi-band approach enhances system survivability by enabling dynamic adaptation to spectrum congestion or electronic countermeasures, offering a practical and cost-efficient foundation for nationwide deployment of backup siren control networks.