<![CDATA[The demand for underwater communication is growing at a faster pace since few decades. Maximizing the communication performance and building efficient network architecture for underwater communication is a challenging task. Due to the reduced bandwidth, high error rate, noise, propagation delay, water currents and increased cost in the network topology, the existing communication techniques are not feasible for underwater communication. Research in high speed underwater transmission technology has become a primary need in today’s world. By using underwater acoustic sensor network high transmission distance can be achieved but with lower data rates, high power consumption, larger delays and with higher cost. Underwater Optical Communication can be used to increase data rates and lower delays but it suffers from high attenuation due to which it cannot be used for data transfer over larger distances. Research in the area of hybrid sensor networks is a challenging task and has many open research challenges, which needs to be solved. In this paper we discuss the various architectures of underwater communication. A comparative study is made on different routing protocols and localization algorithms. The challenges faced by acoustic and optical communication are also discussed.]]>
