IU CH TIN HIU S ng dng Dng truyn d liu s trn mng in thoi cng cng 300Hz 3400Hz ASK Tor) K thut iu bin: Amplitude-Shift Keying (ASK) iu tn: Frequency-Shift Keying (F: Phase-Shift Keying (PSK)Digital AnalogFSKPSKQAMASK A cos( 2f t c ) s (t ) 0 binary 1 binary 0 Dng 2 bin khc nhau ca sng mang biu din mc logic 0 v 1 S dng mt tn s sgiao tip ang c s dng. ph hp trong truyn s liu tc thp (~1200bps trn knh thASKASKFSK A cos(2f1t c ) binary 1 s(t ) A cos(2f 2t c ) binary 0 S dng hai tn s sng mang: tn s cao tng ng mc 1, tn s thp tng ng mc 0. t 00bps hay thp hn trn mng in thoi C th dng tn s cao (3-30MHz) truyn trn sngFSKMultiple FSK Dng nhiu hn 2 tn s Bng thng c dng hiu qu- hn Kh- nng li nhiu hn Mi pBPSK A cos( 2 f c t ) s (t ) A cos( 2 f c t )binary 1 binary 0 Thay i pha ca sng mang Cho php ghp nhiu bit trn mt sng mang Phng php ny th400bps (2 bits), 4800bps (3 bits) hoc 9600bps (4 bits encoding per phase/amplitude change)BPSKQPSK A cos( 2 f c t 0 ) 00 A cos( 2 f c t 90 ) 01 s (t ) A cos( 2 f t 180 2 f t 270 ) 11 c 8 PSK Tng hiu qu- s dng ph Tng kh- nng tim n li.QAM (Quadrature Amplitude Modulation) Kt hp gia ASK v PSK Dng 2 b-n sao ca sng mang, mt c dch i gc q Mi sng ma Gi-i iu ch v kt hp cho d liu nh phn ban u8QAMPUSLE CODED MODULATION (PCM) nh l ly mu: Mt tn hiu lin tc theo thi gian x(t) c ph hu hn (f = fmax fmig nhng gi tr ri rc ti cc thi im t = kt (k = 0,1,,n), t l kho-ng cch gia hai lmu Ts .iu kin tn hiu thu c c sai s nh nht l ch u k ly mu Ts