Communication apparatus comprising a plurality of mobile communication devices arranged for peer-to-peer communication using TDMA, the arrangement being such that a said device wishing to transmit uses a time slot in each TDMA time-frame used for transmission, the time slot in each frame being the same and wherein the communication devices include means for synchronization to the same TDMA time frame using a synchronization signal, the synchronization signal being transmitted by a said communication device or a GPS satellite. |