Teemu Vanninen

Frequency hopping mobile ad hoc and sensor network synchronization

The time synchronization is one of the main issues in frequency hopping mobile ad hoc networks (FH MANET) or time synchronous wireless sensor networks (TWSN). In the former case a network wide time reference is needed in FH code phase synchronization and in the latter case, e.g., in time stamping of the sensed phenomenon. Herein, a distributed decision making method (s) that solves the problems considering initial time synchronization, FH code phase synchronization, late-entry nodes and subnetwork merging cases of tactical FH MANETs and TWSNs is proposed. One of the starting points is a recently developed robust control channel method that enables the nodes to exchange the necessary synchronization messages prior the frequency hopping synchronism, i.e., out-of-phase. The proposed method is master free and based on node identifiers and local information that a node collects from the surroundings, namely local density and local data-activity. Simulation results are given that prove the functionality and the potentiality of the proposed methods.

FH-Code Phase Synchronization in a Wireless Multi-Hop FH/DSSS Adhoc Network

A military ad hoc network has to have a good LPI (low probability of intercept) and LPJ (low probability of jamming) capabilities. These requirements can be met by using a combined frequency hopping/direct sequence (FH/DS) spread spectrum (SS) system. Due to characteristics of an ad hoc network, the network wide synchronization has to be achieved distributely, which makes especially FH-code phase synchronization a challenging task. Here, we present an FH-code phase synchronization method suitable for very long FH-codes and unknown code-patterns. The synchronization data is spread using a specific synchronization DS-code (DS(s)-code), i.e., the control channel is in the code-space. Synchronization messages are broadcasted periodically to allow single nodes or subnetworks with different FH-code phases to synchronize as a one network. Divergent synchronization hops are not needed, thus providing excellent LPI & LPJ properties. In order to achieve and maintain a common FH-code phase a network time synchronization algorithm has to be used. Simulations of an ad hoc network with a simple network time synchronization algorithm has been made and the results are presented in this paper. The simulations prove that the chosen algorithm can maintain a common timing at a satisfactory level as long as the connectiveness in a network is tolerable. The effects of clock drift and the synchronization message size have also been studied

A demonstration of frequency hopping ad hoc and sensor network synchronization method on warp boards

Despite of the fact that the time synchronization is one of the main issues in frequency hopping mobile ad hoc networks (FH MANET) or time synchronous wireless sensor networks (TWSN), it seems to be a rarely issued research subject. In the former case a network wide time reference is needed in FH code phase synchronization and in the latter case, e.g., in time stamping of the sensed phenomenon. Herein, a previously developed, simulated and published (by the authors) network time and FH code phase synchronization method that is a MANET compliant is demonstrated in a real-time environment on wireless open-access research platforms (WARP). The time or FH code phase synchronization process consists of both initial synchronization and synchronization maintaining phases. The proposed initial decision making method is master free and based on node identifiers (ID) and local information that a node collects from the surroundings. The synchronization is maintained by regularly transmitted (and received) synchronization messages. The demonstration cases are organized so that the frequency hopping characteristics of the waveform are shown together with the algorithms ability to conduct an initial synchronization, the synchronization maintaining and late-entries to the existing network. Further, a payload data-streaming with the synchronized FH waveform is demonstrated.

Demonstration of synchronization method for frequency hopping ad hoc network

Anti-jamming capability and protection against interception are key priorities in wireless mobile ad hoc networks (MANETs) or sensor networks for military applications. These features are supported by spread spectrum (SS) techniques such as frequency hopping (FH). In an FH ad hoc network, the phase of hopping sequence, i.e., FH-code phase is typically derived from the local 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. In this paper, a rarely issued distributed FH-code phase synchronization method for an FH MANET is implemented and demonstrated on wireless open-access research platforms (WARPs). In the earlier studies the considered method has been investigated to be military compliant in the anti-jamming and low probability of detection -sense. Herein, the measurements are reported for static scenarios of two and three nodes. Sufficient time synchronization is managed to be preserved for the frequency hopping operations in the presence of the measured clock drifts. Furthermore, it is shown that the system is able to maintain the FH-code phase synchronization as long as the clock errors are less than half the dwell time.