A Frequency—Diversity Spread—Spectrum Multiple Access System with Random Signature Sequences

A new scheme for the spread-spectrum multiple access system named Frequency-Diver-sity Spread-Spectrum Multiple Access(FD-DDMA)system,is proposed.In this FD-SSMA sys-tem,the same information will be modulated on a group of mutually orthogonal frequency compo-nents(carriers)with a random signature sequence at the same time,and it will be demodulated by a coherent receiver for every component and then incorporated (ad if using frequency diversity)on the basis of this random sequence.The spectrum of the modulated signal is very close to that of a white-noise in a wider frequency band due to orthogonality for all frequency components and prop-erty of the random sequence,the system becomes a spread-spectrum one.The (Inverse)Fast Froier Transform(IFFT,FFT)can be applied in the system ,which provides additional flexibility.The performance in an asynchronous mode,such as ability of multiusers,anti-interferences ,is an-alyzed.     

HDTV传输的调制技术

本文旨在阐述高清晰度电视（ＨＤＴＶ）传输的调制技术，并对其国际现状作一较全面的概括。文中扼要地分析了ＨＤＴＶ传输的基本原理，在突出全数字式地面广播的情况下，简述了三种传输调制技术的思想和特点，最后，比较三种ＨＤＴＶ传输的调制技术并分析它们的发展趋势。