Study On The Modem’s Techniques Of Very High-frequency Based On GFM

With the development of the tactical network,the construction of digital battlefield anddigital army requires that the tactical radios have to support the traditional phonic service as wellas the increasing service of digital data transimission.Therefore,it’s necessary and imperative toresearch and develop the digital radios. While the embedded waveform of the partial navy’sradios of the Ultra Short Wave supports the encrypted and unencrypted transmission of phoneand digital data,the problems of insufficient bandwidth and adaptability to use the waveform tothe channels will arise when the Internet protocols are running based on the current waveform.Atthe same time the electromagnetic environment of new mobile communication systems such asthe battlefield become more and more complex.The variety of modes and patterns ofelectromagnetic interfering against the fleet sometimes call for communicating stably anddependably in the harsh environment.As one of partial response system of CPM,Gaussian Minimum Shift Keying(GMSK) drawour attention more and more relying on its advantages of the less out-band radiation,the highlyefficiency of power and spectrum,the constant envelope.While the researches of most papersbelong to the class of digital modulation and coherent detection,it is unconvenient that theorthodox analog radios connect with these current digital radios.To meet the strict requirementsof which the tactical communication comes up with the signal spectrum,the paper presents a typeof MODEM,which has tight spectrum to transform the current analog radios to the digitalradios.We call it GFM(Gaussian Frequency Modulation),which adopts non-orhogonalmodulation and noncoherent detection.Based on the theoretic research of the MODEM of CPM and GMSK,the paper analyses thealgorithm of symbol-by-symbol and MLSD about the partial response.Using the Viterbialgorithm to avoid the ISI in the GFM’s model of Limiter-discriminator,we also simulate theBER curves of Gaussian waveform at different values of BT and timing offset.Aiming atdeconding serial concaterated trellis and using soft decoding methods at receiving end,the paperimproves the classical VA and gets soft Viterbi algorithm namely SOVA.The simulations indicateusing the SOVA could improve the decoding peroformance further. At last,based on the hardware platform of OMP-L138,we finish the design and implement of system project of MODEM.The paper adopts the way of theoretic analysis and computer simulation to indicate that themeasure of GFM MODEM expands the functions and applicational fields of original radios.Thesimulative result indicates that the measure of waveform designing and the mode of GFMmodem could direct the development of equipments of VHF subnet and supply the guidelines ofmanufacturing data transferring apparatuses of naval fleet.