Offline Node-to-Node Communication in Infrastructure-Restricted Environments: A Thematic Review

The selected literature shows that offline node-to-node communication is a system-design problem rather than a choice of radio alone. BLE provides a practical starting point for discovery and short-range communication, but a BLE scan is not a mesh network. Wi-Fi Direct can support local device-to-device links, yet group management and multi-hop routing require additional software and platform-specific evaluation. Emergency and opportunistic networking studies highlight the importance of resilience, fairness, persistence, and delivery under intermittent contact. IoT-assisted and cross-technology approaches offer possible extensions, but they introduce additional infrastructure and implementation complexity. For ResQNet, the defensible contribution at this stage is an explicitly scoped Android BLE discovery prototype and a research plan for progressing toward reliable messaging. The next technical milestones are application-specific node identification, direct message exchange, acknowledgement, and controlled performance measurement. Store-and-forward, multi-hop relay, Wi-Fi Direct, and fixed IoT nodes should be presented as future extensions until implemented and validated. A broader, documented literature search and reproducible site-oriented experiments are the necessary next steps. The most useful future contribution would be a transparent empirical evaluation that reports not only successful communication but also failure modes, energy cost, environmental sensitivity, and limitations relevant to industrial digester areas.

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