Research On Dehopping Of Frequency Hopping Communication System

Frequency Hopping(FH) communication techniques have been widely used not only in military communications but also in mobile communications such as GSM, Home RF and Bluetooth, with anti-jamming and multiple access capabilities.FH communication is one kind of spread spectrum communication. This article analyses it in theory, which proves that frequency hopping communication is feasible and practical. And there are three core parts in FH communication, which are FH sequence generator, FH synthesizer and FH synchronization. Two block diagrams for FH communication system are given based on the difference in data modulation. The generation and application of frequency hopping pattern in FH communication system are introduced.Then three traditional theories on implement of frequency hopping synthesizer are introduced. And the principle and characteristic of Fractional-N phase locked loop frequency synthesis based on∑Δmodulation are discussed emphatically. Besides, the performance of Fractional-N phase locked loop frequency synthesis based on∑Δmodulation is emulated and analysed in practice. FH synthesizer only reveals its advantage in anti-jamming with appropriate FH sequence, so this kind of FH sequence is described briefly.The design of FH synchronization is another key technique in FH communication system. And it is also the key for dehopping. The implement and characteristic of many kinds of synchronization techniques are introduced in this paper. Specially the synchronization method of self-synchronization and the synchronization method with synchronization header are discussed in detail. All kinds of synchronization need acquistion, recognition and tracking. A new synchronization method of self-synchronization is proposed, which is realized by measuring pulse wide in digital PLL.Finally, a successful FH communication system is designed which uses techniques including Fractional-N phase locked loop frequency synthesis based on ∑Δmodulation, M-sequence and Self-synchronization. The ADF7020-1 realizes the RF channal and∑Δmodulation, which is a single RFIC. Because of the architecture of high performance single-chip plus CPLD, it is easy to relize acquistion, recognition and tracking of synchronization. And the single-chip is Atmega88 produced by ATEML company, which realizes intelligent control and processing. CPLD is EPM3128 produced by ALTERA company, which can realize the quickly hopping and synchronization by its parallel process ability. And this system performs rather well in FH communication system. Some circuits and conclusion of simulation are given.