Research Of The Method Of Improving Communication Signal Spectrum Efficiency

As communication technology is improved rapidly, fewer spectrum resources can beused, so, improving the bandwidth efficiency becomes an important aspect of study anddifferent kinds of modulation systems with high bandwidth efficiency are proposed；what’smore, in a lot of communication environments (for example, satellite communication systemsand deep space communication systems), because of the existence of non-linearcommunication channels, modulated signals are needed to have the constant or quasi-constantenvelope characteristic to reduce spectrum expansion. So, many modulation systems with thecharacteristics of constant or quasi-constant envelope and high bandwidth efficiency areproposed, such as, MSK, GMSK and FQPSK. And in this paper, based on the foundation of afonctionelle model, an optimized high bandwidth efficiency signal is proposed and the signalis used as the basedand modulation signal to realize quadrature modulation. The modulatedsignal has the characteristics of quasi-constant envelope and high out-of-band spectral roll-offrate. Compared with traditional signals, occupied bandwidth by signals is narrowed verymuch, interference on adjacent channels made by signals is reduced and accordingly thebandwidth efficiency of communication signals is improved.In this paper, at the first the criterion of minimum out-of-band energy radiation is used tocrease the fonctionelle model of the optimized baseband symbol signal, and the fonctionelle islimited with constraints. The fonctionelle model is creased in two conditions of the signalwith intersymbol interference and without intersymbol interference, and with the introductionof the Fourier series the optimized baseband symbol signal with high bandwidth efficiency isfound by solving the fonctionelle minimum. Then, the characteristics of spectrum and PAPR(peak-to-average power ratio) of the found signals are analysed and compared with MSK andQPSK signal. In view of the two conditions of the signals with intersymbol interference andwithout intersymbol interference, full response and partial response quadrature modulationsystems are creased respectively, and corresponding coherent demodulation schemes arecreased respectively, too. At last, the simulation of quadrature modulation and coherentdemodulation is realized with MATLAB, the simulation results demonstrate that the methodis available.