An adaptive power control method to electromagnetic environment for PLC in cargo ships

Power-Line Communication (PLC) based Local Area Networks (LAN) in ships are one of the promising applications of the PLC technology. However, the unintentional-radiation is the serious problem for ship applications because the PLC system must coexist with the emergency communication system and shortwave broadcasting services. In this paper, a power control method of PLC modems depending on the radiation strength is proposed and examined in a training ship. It is proposed to use an antenna for shortwave radios and a wideband receiver (WBR) to measure the radiation strength. It is shown that the sensitivity of the WBR is 17 dB better than that of a spectrum analyzer. And by using the antenna, the WBR can be set up at any cabin in ship to measure the radiation strength. The proposed power-control algorithm consists of two modes, silent and power-control modes. After the environmental noise level is measured in the silent mode, the power level of PLC modems which cause the radiation is lowered to be the same level as the environmental noise level. If modems do not cause the radiation, their power level is raised as much as possible to guarantee the maximum possible throughput under the EMC regulation. By executing the silent mode occasionally, the controlled power level is adapted to the environmental noise level.