In the field of high-speed power line communications, there are three major standards; ISO/IEC 12139-1, IEEE 1901-2010, and ITU-T G.99xx. However, they are not interoperable because of having their own physical and MAC layer specification. Actually, they cannot even avoid interfering with each other because they are using the same frequency band of 1 ~ 30 MHz. In this paper, a common signaling mechanism is suggested which uses multi-carrier partitioning and carrier sensing, so that all standards can be coexisted by sharing time resource. The suggested mechanism has been compared with the ISP protocol which is included in IEEE and ITU-T standard for coexistence.