# Investigating Master-Slave Architecture for Underwater Wireless Sensor Network
## 1 Introduction  
Underwater Sensor Networks (UWSNs) have emerged as a field of research in recent years due to their applications for various purposes, e.g., monitoring water pollution, water quality testing, aquaculture, and exploration of geological resources (gas, oil, etc.). Such networks are composed of battery-powered nodes stationed in water to sense the environmental parameters, send them onwards to sink nodes floating on water and pass data to the monitoring station. These nodes can communicate using electromagnetic/radio signals, optical communication, and acoustic links. Electromagnetic communication is not suitable for underwater communication because of its limitation of higher attenuation resulting in higher absorption loss due to the conductivity of water. Similarly, optic signals are not supported by the aquatic environment because of the requirement of the direct line of sight between the sender and receiver [1]. The most suitable medium for underwater communication is the acoustic channel; however, there also exist several challenges, e.g., limited battery power, fading, limited bandwidth, high error rate [2].  
UWSNs communication's performance is gauged over several performance metrics including energy tax, Packet Delivery Ratio (PDR), End-to-End Delay (E2 ED), and Accumulated Propagation Distance (APD). These parameters are affected by various factors, e.g., void holes, energy holes, duplication of packets. Energy optimization is one of themain requirements for increasing the lifetime of a battery and overcoming other challenges such as void/energy holes, packet duplication, etc. The void/energy holes are created when a sender node cannot find other appropriate nodes for forwarding the received data packets due to the lack of information about the surroundings. Similarly, the duplication of packets happens when the source transmits data in the Omni direction which is received by all neighbor nodes for further transmission. Due to such data duplication, a significant fraction of energy is used in the transmission phase resulting in reduced network lifetime. The battery replacement of an underwater node after deployment is not feasible. Several routing protocols and schemes are proposed in the literature for efficient communication in UWSNs; however, each of them has its overheads as discussed in Section 2: Related Work. In particular, high energy consumption is still an important concern, and therefore, in this research work, we propose a new protocol, called \"An Efficient Routing Protocol based on Master-Slave Architecture for Underwater Wireless Sensor Network (ERPMSA-UWSN)\" focusing on energy optimization.  
Following are the main contributions of this research work:  
* Our proposed master-slave architecture helps to achieve lower energy consumption by limiting the broadcasting of packets to a specific region (set of nodes).
* We avoid packet duplication due to the suppression of nodes and the lack of multiple paths for transmission.
* We perform extensive simulation of our proposed protocol in various scenarios and demonstrate improvements in Packet Delivery Ratio (PDR) and energy tax.  
The rest of the manuscript is organized as follows: Section 2 contains a detailed discussion on the previous work regarding UWSN-based routing protocols. Section 3 identifies the problem statement that we aim to address in this research work. The proposed system model is presented in Section 4. Section 5 delineates the experimental setup and simulation results, performance comparison, and analysis of our proposed approaches. The paper is concluded in Section 6.