Multi-node communication systems generally need an operating protocol to enable the nodes to communicate with each other. Two commonly used protocols are frequency domain multiplexing (FDM) and time division multiplexing (TDM).
The FDM protocol utilizes a different frequency “channel” for each node. In a TDM system the nodes take turns using a communication channel. The TDM protocol divides a communications channel into frames and it allocates each node one or more individual time slots in each frame. In general a system using a TDM protocol can scale to handle as many nodes as needed by merely adding additional time slots in each frame. The time clocks in all the nodes in a TDM system must be synchronized to a common time base so that each node knows when its respective time slot begins. Several conventional methods exist for synchronization of clocks in a TDM system. These include techniques such as: (a) a base station sends out a signal to one node at a time to indicate the beginning of that node's time slot, (b) clock signals embedded in the data packets to establish a common time base, (c) a phase locked loop (PLL) in each node that is synchronized to a ‘heartbeat’ signal, etc. The conventional methods in general require significant hardware and timing overhead in order to operate.