SÄHKÖ- JA TIETOTEKNIIKAN OSASTO SÄHKÖTEKNIIKAN KOULUTUSOHJELMA IMPLEMENTATION OF FREQUENCY HOPPING CODE PHASE SYNCHRONIZATION METHOD FOR AD HOC NETWORKS

Anti-jamming capability and protection against undesired interception are key priorities in ad hoc networks for secure applications. These features are supported by spread spectrum (SS) techniques such as frequency hopping (FH). In a frequency hopping ad hoc network, the phase of the hopping sequence is typically derived from the local time reference (clock reading) of each node. Therefore, network-wide time synchronization is needed in order to get the nodes to simultaneously switch to the same frequency channel, i.e., hop synchronously. Due to the characteristics of ad hoc networks there is no centralized control, e.g., no unambiguous entity, to define a common time reference. Thus, a distributed decision has to be made between the nodes as to whose local time reference is chosen as the common time reference for other nodes to synchronize to. For that purpose, there has to be a predefined procedure for frequency hopping nodes to exchange synchronization information out-of-phase, e.g., through a control channel