The Implementation Of Maritime Mobile Communication System Using Ad Hoc Network

With the development of economy and shipping industry in our country, the number of transport vessels on sea is increasing as well. Shipping communication equipment plays an important role in daily navigation and distress alarm. But in the situations of cluster operation or sea rescue, channel congestion or calling out of service caused by poor coordination between ships seems inevitable. For this reason, based on the widespread use of VHF equipment, the article proposes and preliminarily realizes a solution in which the concept of mobile Ad Hoc network was applies to maritime mobile communications.Ad hoc network is a special non-center, no fixed base stations of self-organizing network. It can automatically distribute channels and provide network services between nodes in the network. Combining Ad hoc concept with VHF equipment in maritime communication will make the solution own both advantages which are low-cost and transmission stability from VHF equipment, and flexible network from Ad hoc. This solution could be a good choice to improve the performance of maritime communications.In this paper, the current developments in maritime communications are analyzed first. After a brief introduction of the GMDSS and AIS system, it discusses Ad hoc network's system principles and characteristics in detail, including analysis and comparison between routing protocol such as DSR, AODV, ABR and MAC protocol such as MACA, BAPU. Secondly, it proposes a project which is built an Ad hoc network in VHF-band, and focuses on the realization of that system. The C8051f020 microcontroller, advanced voice compression module, the third generation GPS module, and VHF-band digital video are used to constitute a terminal node in the project. The designs scheme of the system's MAC and routing protocol are also given, respectively. Finally, the hardware implementation is performed. The realized terminal node in the network can achieve data and voice transmission in accordance with protocols through 12.5 kHz bandwidth dual-channel in VHF band, which is fully compatible with the current function of GMDSS communications system.Experiments show that self-organization network nodes can complete data frame transmission and GPS signals reception. On the topology of three nodes which are placed on a straight line, the network throughput, network latency and other parameters are measured and analyzed. On this basis, two applications including daily communication and distress alarm are implemented. At last, through summarizing the current work, further improvements of system function and design of programs are given.