Research On Waveform Optimization And Receiving Methods Of SNCK Communication Systems

With the deeply development of the social information-based degree, the demand forcommunication system on capacity, quality and adaptability to different environmentbecomes higher and higher. Based on the technical ideas of the very minimum chirp keying(VMCK), using the strong multipath resolution and Doppler frequency shift inhibition of thefrequency modulation signal, a new non single frequency digital bandpass modulationmethod called sine non-linear chirp keying (SNCK) is proposed, and mainly studied from twoaspects of waveform optimization design and high efficiency receiving method.Firstly, two digital bandpass modulation methods are proposed based on non-linearfrequency modulation signal, called symmetric raised cosine keying (SRCK) and SNCK;Construct the mathematic models of the two modulation methods; Studied the correlationproperty, frequency domain characteristics and anti-noise ability of the two modulated signalsby theoretical derivation and simulation results, then selected SNCK as the subsequentresearch object.Secondly, mainly studied the internal connection between the SNCK modulationparameter configuration and mutual-correlation of modulated signal waveform samples.After setting up the mathematical model of the SNCK modulated signal waveform samplecorrelation, deduced the necessary condition for waveform orthogonal, and analyzed theorthogonality of the single and multiple frequency change cycle SNCK modulated signals.Deduced the mutual-correlation coefficient expression of the SNCK modulated signalwaveform samples, by introducing the Bessel function of the first kind to solve the doubletrigonometric function integral problem. Based on the analysis of the single frequency changecycle SNCK modulated signal orthogonality, proposed the orthogonal sine non-linear chirpkeying (OSNCK) modulation method, which has the minimum D value (the maximumbandwidth utilization), then analyzed its frequency domain characteristics and the coherentdemodulation error rate performance.Thirdly, in order to improve the noise suppression capability and bandwidth efficiency,mainly studied the memory property of the SNCK modulation and line spectrum removaltechnology of modulated signals. By adding memory property between symbols of the SNCKmodulated signals, proposed a memory sine non-linear chirp keying (MSNCK) modulation method. The MSNCK signals are demodulated using the Viterbi decoding algorithm, and byincreasing the memory correlation length to improve the anti-noise performance. Meanwhile,based on the orthogonal sinusoidal fitting method researched the harmonic line spectrumremoval method of the SNCK modulated signals. The method can improve the bandwidthefficiency and anti-noise ability of the SNCK modulated signals.Finally, focuses on the receiving method of the SNCK communication system, forfurther improve the channel adaptation of the modulated signals. By approximated SNCKmodulated signal waveform as segment linear frequency modulation (LFM) signal, usingdifference of fractional fourier transform (FRFT) domain convergent characteristics betweenLFM signal and noise, proposed pre-filtering method based on FRFT domain. The theoreticalanalysis and simulation results show that the filtering method can effectively improve thesignal-to-noise ratio improvement factor of the SNCK modulated signals. Meanwhile, inorder to improve the adaptability of the SNCK communication system for high dynamicenvironment, proposed a kind of noncoherent demodulation method for SNCKcommunication system based on FRFT. Compared with the coherent demodulation method,although this method has some incoherent loss, but the demodulation performance is notsensitive to the phase error, and even has strong suppression ability of Doppler frequencyshift and multipath interference suppression ability.