Frequency Hopping Wireless Mobile Self-organizing Network Clock Synchronization Protocol

Wireless Mobile Ad Hoc network(MANET) is a intergration of mobile communications and computer networks. Frenquency hopping is a spread spectrum Technique(FHSS). Frenquency hopping wireless Ad Hoc network combines the two techonologies, it possesses a lot of advantages, such as flexible, efficient, strong.Above all, frequency synchronization is essential for communications. The IEEE 802.11 standards support the peer-to-peer mode Independent Basic Service Set(IBSS), which is an Ad Hoc network with all its stations within each other's transmission range. In an IBSS, it is important that all stations are synchronized to a certain clock. So clock synchronization is essential for the MAC layer power management. If frequency hopping spread spectrum is used in the physicallayer, clock synchronization is needed to ensure that all stations "hop"at the same time, frenquency hopping communications rely on clock synchronization.As clock synchronization is important for many applications in an IEEE 802.11 based mobile Ad Hoc network, an accurate clock synchronization protocol for MANET is critical to the performance of these applications. IEEE 802.11 standards first specify a Timing Synchronization Function for the MANET, which is the base of the following synchronization protocols, according to it, hosts accomplish clock synchronization by exchanging timing information periodically, a station adopts the timing in a received beacon if the received time is larger (later) than the station's own TSF timer.But the accuracy of clock synchronization is heavily restricted by the transportation delay and the propagation delay, which due to unaccurate timestamp. And if the numbers of hosts in an MANET increase, by analyzing the beacon generation procedure, it is shown that the stations may fail to successfully transmit beacon frames due to beacon contention. As a result, some stations in the IBSS may become so out of synchronization with others that power management or FHSS can not work properly. When the number of stations in an IBSS is not very small, there is a non-negligible probability that stations may get out of synchronization. The more stations, the higher probability and the larger ratio of asynchronism, so the accuracy and scalability of clock synchronization protocols in multihop Ad Hoc networks are the focus of the study.To solve the problems elaborated in the above chapter, a new algorithm named UDTSP(Uniform Distribution Timing Synchronization Protocol) is proposed in this paper, according to the protocol, a host collects the clock information of its neighbors and use these information as a reference to update its own clock, the host can also adjust its frequency deviation automatically. Simulations are based on the OFDM system and run in the NS2 environment,the results show that the networks can achieve fast convergence, the max clock offset can be controlled in less 30us, UDTSP performs effectively in the multihop environment.