A node transmits/receives signals over first and second communication channels having non-equal propagation speeds. When node identifies reset signal received over first communication channel, it adjusts internal clock, transmits acknowledgement signal and initiates acknowledgement process. When reset signal not identified, node transmits reset signal over first communication channel and receives response signal from one node. If response signal is acknowledgement signal, acknowledgement process is initiated. If response signal is non-acknowledgement signal, internal clock is adjusted and acknowledgement process is initiated. In acknowledgement process, node determines distance to other nodes by measuring travelling time for signal over second communication channel exchanges distance information with other nodes, and fine tunes internal clock of each node when transmitting over first communication channel. Node's transceiver circuitry has radio frequency part to transmit/receive electromagnetic signals and acoustic part to transmit/receive acoustic signals. Each node determines distance in acknowledgement process.