Ann. Telecommun. (2017) 72:173–188 DOI 10.1007/s12243-017-0560-0 On energy efficiency in underwater wireless sensor networks with cooperative routing Ashfaq Ahmad 1 · Sheeraz Ahmed 1 · Muhammad Imran 2 · Masoom Alam 1 · Iftikhar Azim Niaz 1 · Nadeem Javaid 1 Received: 6 February 2016 / Accepted: 4 January 2017 / Published online: 26 January 2017 © Institut Mines-T´ el´ ecom and Springer-Verlag France 2017 Abstract In this paper, we exploit cooperative communi- cation for designing an energy-efficient routing algorithm in underwater wireless sensor networks (UWSNs). Each network node is equipped with a single omnidirectional antenna and multiple node coordinates while taking advan- tage of spatial diversity. This research work is limited in scope to amplify-and-forward (AF) scheme at the relay node and fixed ratio combining (FRC) strategy at the receiver node. Cooperative diversity at the physical layer and multi- hop routing at the network layer enable us to formulate minimum energy routing as a joint optimization of the transmission power at physical layer and link selection at the network layer. Simulations results show that our proposed cooperative energy-efficient routing for UWSN (Co-EEUWSN) performs better than the selected non- cooperative routing protocols (depth-based routing (DBR) and energy-efficient DBR (EEDBR)) and cooperative DBR (Co-DBR) in terms of packet delivery ratio, end-to-end delay, and energy efficiency. Keywords Cooperative communication · Relay sensor node · Routing protocol · Multi-hop · Single-hop · Diversity · Energy consumption · Packet delivery ratio  Nadeem Javaid nadeemjavaid@comsats.edu.pk www.njavaid.com 1 COMSATS Institute of Information Technology, Islamabad, Pakistan 2 King Saud University, Riyadh, Saudi Arabia 1 Introduction Radio waves are very quickly absorbed in water limiting their propagation range and data rate. Similarly, light waves are infeasible due to high dispersion in the under water (UW) environment. In these networks, acoustic waves are the most feasible means for communicating over adequate distances. However, new progresses achieved in UW acous- tic (UWA) communications make reliable data transmission across several meters conceivable. Many investigations have been made towards discovering new networking solutions for underwater wireless sensor networks (UWSNs), includ- ing acoustic channel modeling, physical layer transmission analysis, and networking protocols [1]. UWSNs exhibit many unique features like slow propaga- tion speed, variable link quality, low available bandwidth, high end-to-end delay, and limited battery capacity. These constraints pose many challenges in devising transmission- efficient, energy-saving, and low-delay routing protocols for UWSNs [2]. Introduction of cooperation in WSNs has recently gained attention. It exploits the broadcast nature of the wireless medium for the design of energy-efficient routing algorithms [5]. Depth-based routing (DBR) [1] is a non-cooperative receiver-based routing protocol in which source node broadcasts its data to all its neighbors. Among the neighbors, one forwarder is selected on the basis of minimum depth from the sink. Hence, data is routed from source to destination over a single noisy link in a multi-hop fashion. Due to noise and multipath fading in UW envi- ronment, the transmitted signal suffers high a bit error rate (BER). DBR is improved in [2], the energy-efficient DBR (EEDBR), where local depth information along with resid- ual energy of sensor nodes is used to select the optimal for- warder to achieve load balancing. Redundant transmissions