Wi-Fi based position information communicating methods, vehicle mounted communication devices, and pedestrian devices are provided. One of the methods includes: a communication device mounted on a first vehicle determining whether position information of a second vehicle, whose distance to the first vehicle is shorter than a first predetermined distance, is received within a first predefined time period; and if no, broadcasting position information of the first vehicle in a first 802.11 management frame. By employing the methods, pedestrian detection rate may be improved and wireless channel congestion may be mitigated.