Research On Optimization Method Of Baseband Signal In Communication System

In recent years, with the rapid development of information technology and the wide application of mobile communication system, the spectrum resources are reducing dramatically, forcing people to develop new technology to improve the out-band inhibiting performance. This article puts forward fonctionelle of the optimization symbol signal which is based on the criterion of minimum out-of-band energy radiation. And basing on this fonctionelle, the baseband symbol signals in orthogonal systems are optimized. The optimized signal is quasi-constant envelope. And compared with traditional signals, occupied bandwidth by signals is narrowed very much, interference on adjacent channels made by signals is reduced and accordingly the bandwidth efficiency of communication signals is improved.In this paper, at the first the criterion of minimum out-of-band energy radiation is used to crease the fonctionelle of the optimized baseband symbol signal. Then getting approximate solution of the optimal fonctionelle is realized by using the numerical method, obtaining the optimized baseband symbol signals. And a detailed analysis of the impact of the accuracy of the signal is carried out with the number of Fourier series. Then the fonctionelle is limited with constraints, getting the optimization of baseband symbol signals of CPM system and partial response system in an orthogonal system,receiving waveform and energy spectral density curves of optimization baseband symbol signal. Compared with the MSK, the spectrum characteristic of the optimized signal is better than the MSK. For the optimized system, full response and partial response quadrature modulation systems are creased respectively, and corresponding coherent demodulation schemes are creased respectively, too.Then the curves of the demodulation signal, the modulated signal and the bit error rate are obtained. From the simulation results,it can be observed that the phase of the signal is continuous, constant envelope and the bit error rate is low, achieving the intended purpose.