# RDSP: Rapidly Deployable Wireless Ad Hoc System for Post-Disaster Management
## 2 Related Work
Some algorithms monitor the link quality by measuring the signal-to-noise ratio (SNR) [26], bandwidth [27], or received signal strength indicator (RSSI) [28]. A threshold is set to trigger a deployment event. When the quality of the link falls below this limit, a fresh relay must be dropped by the user. For instance, a pre-defined threshold is used for all applications [26] and [28], whereas in [27], the threshold is set based on the bandwidth requirement of each application. In [28], the authors have proposed an ad hoc deployment system to efficiently communicate with victims during disasters. In the proposed system, two types of control information are used for the deployment of relay i.e., relay is deployed either because the link quality degradation is detected by the mobile user, or because an explicit relay deployment request is received by the mobile user from its neighbors. The disaster area could be sufficiently large; therefore, relays support multiple hop transmission to leverage end-to-end communication among each other. The command center is located on the outskirts of the incident region and members of the rescue team begin moving from the command center and move in separate directions into the incident scene. It is assumed that mobile users are connected with each other and with the command center at any time. A mobile rescue team member can drop a relay device if required to maintain connectivity. Each mobile user determines where and when a relay device should be deployed by running an algorithm and alerting the host user through some devices, such as blinking or strong light or sound, when it is necessary to unfold the network. Similarly, in [26], the authors proposed an algorithm where relays perform a rapid evaluation of a physical layer to decide on the deployment of the next relay. The relay constantly transmits probe packets to the relays that have been dropped before. A receiving relay responds with an acknowledgment packet if it is within the communication range. Then, through ACK reception, the transmitting relay calculates the SNR; if the value of the SNR drops below the threshold level, a new relay is dropped. The breadcrumb approach provides a suitable solution to extend the coverage area for rescue teams in disaster situations. However, this approach does not offer redeployment possibilities because the relays do not have their own mobility. Indeed, as mentioned in the above proposals, the first responders must drop breadcrumb devices to set up an ad hoc network. However, this is not necessarily the perfect solution. This is because when the first responders join the rescue operation, relay deployment is not their first priority. Hence, they may forget to drop a relay or merely miss the deployment signal. To solve this problem, an automatic breadcrumb dispenser is proposed in [29]. A Utility Function (UF)-based algorithm is proposed that sets criteria to deploy new breadcrumbs automatically. The UF based algorithm works as follows: the requester broadcasts a help message to initiate the algorithm. After receiving a help message, all the neighbors of requester send their data (number of breadcrumbs) to the requester. Following a predefined timeout, the requester calculates the value of each of its neighbors' utility functions and transmits a drop message to a neighbor with the highest UF value to deploy a new breadcrumb. As described above, the existing breadcrumb approaches only focus on the efficient deployment of breadcrumbs to enlarge the coverage area and eliminate the probability of network partitioning. These approaches, however, do not provide effective routing schemes to deliver emergency request messages with minimum latency to the command center. Indeed, these breadcrumb approaches utilize existing routing protocols already developed for mobile ad hoc networks. This is not, however, a perfect solution. This is because breadcrumb devices are utilized as battery-driven intermediate relays, and the current routing schemes can rapidly deplete the battery life of these devices.