Smart Phone Ad hoc Network (SPAN) for Rescue Applications

Abstract

Natural disasters, large-scale emergency operations, and remote rescue missions share a common challenge: the collapse or unavailability of conventional communication infrastructure. Cellular networks, internet access points, and centralized servers become unreliable precisely when they are needed most. In such contexts, rescue teams require a lightweight, self-organizing, and infrastructure-independent communication system that can be deployed instantly using nothing more than the smartphones already in their hands. This thesis presents the complete design, architectural conception, and full Flutter/Dart implementation of SPAN RESCUE — a decentralized, peer-to-peer (P2P) mesh network application for Android. The system enables a group of smartphones to discover each other, form a local ad hoc network, and exchange structured messages in real time, without any reliance on the internet, external servers, or pre-configured infrastructure. Device discovery is accomplished through a hybrid mechanism combining Wi-Fi Direct P2P group formation with UDP broadcast beacons sent every 15 seconds on port 44444. Reliable data transport is achieved through persistent TCP socket connections on port 8888 managed by a dedicated group owner (GO), with UDP serving as an energy-efficient fallback mechanism. A store-and-forward queue preserves critical messages when connectivity is temporarily unavailable, and a bridge manager extends the mesh across multiple Wi-Fi Direct groups. The application architecture is organized into five distinct layers: the Flutter UI layer, the business logic layer (MeshService), the transport layer (WifiDirectService), a platform bridge layer connecting Dart to native Android Wi-Fi P2P APIs via MethodChannel, and the hardware layer. Four specialized helper modules — StoreForwardQueue, BridgeManager, MeshRouter, and P2pHelper — complete the system. The application provides four primary screens: a Mesh Map screen with a tactical radar overlay and OpenStreetMap integration; a Global Squad chat screen supporting text messages, voice messages, and SOS emergency alert cards; a Tactical AODV Topology screen for live mesh visualization; and a System Logs screen displaying real-time network events with ISO 8601 timestamps. Implementation in Flutter 3.x and Dart 3.x with a Kotlin native bridge required solving four categories of platform-specific challenges: null-pointer exceptions in the flutter_p2p_connection plugin when processing empty peer maps, non-deterministic group owner election across device manufacturers, delayed availability of P2P IP addresses after group formation, and battery optimization constraints affecting background UDP scan continuity. Validation across five Android devices from four different manufacturers confirmed correct operation of all core networking functions, SOS message propagation, and topology visualization.