On VWDK Modulation Technology

Much attention is always paid to bandwidth efficiency in transmission, so it has an important meaning to explore in high efficiency modulations. In recent years, the bandwidth efficiency of Ultra Narrow Bandwidth (UNB) technologies, represented by Very Minimum Shift Keying (VMSK), has reached near a 100 bps/Hz. This dissertation mainly focuses on a sine-like VMSK modulation called Very-minimum Waveform Difference Keying (VWDK). By analysis and optimization of the VWDK modulation, and by joint research of bandwidth compression with signal demodulation, the confusion about the theoretic definition of signal bandwidth with its engineering provision has been clarified. Aimed at the theoretic bafflement brought by high efficiency transmission of UNB, extensions have been made to Shannon's channel capacity formula. Our research is as follows.Firstly the sine-like VMSK modulation is normalized by a change of its basic waveform, and its direct current component is removed. By working on this normalized modulation, a power spectra expression on VWDK is deduced, and it serves a theoretical preparation for later researches.Secondly, the unique orthogonal basic modulation waveform is found after study of symbol correlation on VWDK. Then its performance is analyzed. After further exploration of both power spectra and its theoretical expression of VWDK, the linear spectra in power spectra are adjusted, from which, the basic waveform and power spectra get optimized without any fall of demodulating capability.Thirdly, in pursuit of the narrower transmission bandwidth, the filters both for shaping in transmitter and for inversing in receiver are taken into account. A suitable filter group is designed leading to an optimized VWDK transmission system with greatly compressed bandwidth and tiny SNR cost. Besides, VWDK coding modulation system based on LDPC is also introduced.Aimed at both non-strictly band-limited signals and non-ideal sampling, Shannon's channel capacity formula is extended, which, to a certain extent, explains the bafflement that UNB transmission goes beyond the Shannon limit.Finally, by study of the mutual information between input and output, another channel capacity expression different from Shannon limit is deduced, by means of which the relations among waveform control parameter on VWDK, transmission bandwidth and channel capacity are expediently discussed.