A Modulation Of Physical Layer Based On FH-OFDM In Self-organized Network

Ad hoc network is a special kind of wireless mobile self-organized network without cable infrastructure. It has been widely used in fields of military communication and data collection from disaster areas, so more and more attentions have been given to its research. The paper discusses a modulation of physical layer aimed at the security in Ad hoc network. The FH-OFDM(Frequency-Hopped Orthogonal-Frequency-Division Multiplexing) is adopted in this paper.Based on expatiation of Frequency-Hopping Spread Spectrum(FHSS) and OFDM technical theory, synchronous method and performance also analyzed respectively. Considering the special application of Ad hoc network, FH-OFDM communication system adopts differential modulation OFDM, it doesn't require channel estimation,and bit error rate(BER) performance has been simulated. According to the structure of the FH-OFDM signal and the system request under the FH circumstance, an ML(Maximum Likelihood) synchronization algorithm is applied here. And the simulation shows that the method can realize the joint synchronization of the timing and frequency offset with high speed and accuracy of estimation achieved. At last, the paper also discusses interactive synchronization in Ad hoc network which is achieved by the exchange and interaction control of the time benchmark between the nodes. This can improves the network's reliability.