We pres ent ex per i men tal re sults of a cha otic com mu ni ca tion sys tem that em ploys di rect mod u la tion, with the Chua's cha otic os cil la tor as a core of the trans mit ter block. The main re sult is that its pos si ble to re cover the in for ma tion sig nal if we mod u late over one state of os cil la tor and trans mit a dif fer ent state, avoid ing a cor re la tion be tween the in for ma tion sig nal and the cha otic carrier. Keywords: Cha otic com mu ni ca tion, cha otic car rier, chaos syn chro ni za tion, trans mit ter block, re ceiver block. ResumenSe presentan resul tados expe ri men tales de un sistema de comu ni ca ción caótico que emplea modu la ción directa, con el osci lador caótico de Chua como corazón del bloque trans misor. El prin cipal obje tivo es que es posible recu perar la señal de informa ción al modular un estado del osci lador y trans mitir un estado dife rente, evitando una corre la ción entre la señal de infor ma ción y la porta dora caótica. Descrip tores:Comu ni ca ción caótica, porta dora caótica, sincro ni za ción de caos, bloque trans misor, bloque receptor. Intro duc tionDe spite the fact that there ex ist sev eral con ven tional com mu ni ca tion sys tems, one main in ter est is to war rant pri vacy of the in for ma tion. In this as pect the cha otic com mu ni ca tion sys tems have been con trib uted to the se cure com mu ni ca tion area. Research in the last two de cades (Itho et al., 1995; Sushchik et al., 2000; Maybhate A. et al., 2003) in dicates that cha otic be hav ior has sev eral char ac ter is tics that makes it at trac tive for use in com mu ni ca tion systems as car rier sig nals. To men tion some ba sic Inves Inves tiga tiga ciones ciones Estudios e Estudios eRecientes Recientes

Synchronization of nonlinear systems forced by external signals is formalized as the response of a nonlinear filter. Sufficient conditions for a nonlinear system to behave as a filter are given. Some examples of generalized chaos synchronization are shown to actually be special cases of nonlinear filtering.

This work presents a forced synchronization phenomenon like the asymptotic correlated behavior between chaotic oscillators forced by an external signal. Different kinds of forced synchronization are presented and given a theoretical justification explaining why it is possible to find some of them. Numerical results are presented for different cases such as antisymmetric, lag, phase, and identical forced synchronization.