MAC Protocol Implementation on Atmel AVR for Underwater Communication

Underwater acoustic communication is widely used in many areas to collect the data from different kinds of sensors deployed underwater or send control information to remote nodes. However, there are many challenges for underwater communication systems because of the characteristics of acoustic propagation in the underwater environment, such as Doppler spread, ambient noise, fading, high propagation delay, limited bandwidth, wave effect and multipath. MAC protocol, as a developed protocol for Ethernet networks, has been introduced into underwater communication by many researchers and lots of work has been done on the improvement of MAC protocol for throughput and energy efficiency purposes. In general, MAC protocols can be roughly divided into two categories: contention-free protocols and contention-based protocols. Contention-free protocols include TDMA,FDMA and CDMA, where communication channels are separated in time, frequency or code domains. It is common wisdom that FDMA is unsuitable for underwater sensor networks because of the narrow available bandwidth. There are some researches on TDMA and CDMA for underwater networks. However, some problems inherent in these methods have not been well addressed in acoustic networks. For example, the synchronization problem in TDMA and near-far problem in CDMA. Thus, the feasibility of these protocols in underwater sensor networks is unclear. Contention-based protocols includes random access methods and collision avoidance methods. In a random access protocol, e.g., Aloha, the sender sends packets without coordination. Thus packet avoidance is totally probabilistic. While in a collision avoidance protocol, the sender and receiver capture the medium through control packet exchange before data transmission. There are many collision avoidance protocols, among which RTS/CTS-based protocols are widely used. The performance of random access methods and RTS/CTS-based approaches in underwater sensor networks is determined by many factors. In this implementation, I developed Aloha and RTS/CTS-based MACA protocols on a Atmel AVR device in our targeted underwater network and evaluated their performance in the shallow water.