Differential manchester encoding encoding midbit

Unformatted text preview: presenting 1 this is a differential encoding scheme used by IEEE 802.5 used Biphase Pros and Cons Biphase Con at least one transition per bit time and possibly two maximum modulation rate is twice NRZ requires more bandwidth Pros synchronization on mid bit transition (self clocking) has no dc component has error detection Modulation Rate Modulation D = modulation rate, baud R = data rate, bps b = number of bits per signal element Scrambling Scrambling use scrambling to replace sequences that would use produce constant voltage produce these filling sequences must produce enough transitions to sync be recognized by receiver & replaced with original be same length as original design goals have no dc component have no long sequences of zero level line signal have no reduction in data rate give error detection capability B8ZS and HDB3 B8ZS Digital Data, Analog Signal Digital main use is public telephone system has freq range of 300Hz to 3400Hz use modem (modulator-demodulator) encoding techniques Amplitude shift keying (ASK) Frequency shift keying (FSK) Phase shift keying (PK) Modulation Techniques Modulation Amplitude Shift Keying Amplitude encode 0/1 by different carrier amplitudes usually have one amplitude zero susceptible to sudden gain changes inefficient used for up to 1200bps on voice grade lines very high speeds over optical fiber Binary Frequency Shift Keying Keying most common is binary FSK (BFSK) two binary values represented by two different two frequencies (near carrier) frequencies less susceptible to error than ASK used for up to 1200bps on voice grade lines high frequency radio even higher frequency on LANs using co-ax Multiple FSK Multiple each signalling element represents more each than one bit than more than two frequencies used more bandwidth efficient more prone to error Phase Shift Keying Phase phase of carrier signal is shifted to phase represent data represent binary PSK binary two phases represent two binary digits differential PSK phase shifted relative to previous transmission phase rather than some reference signal rather Quadrature PSK Quadrature get more efficient use if each signal get element represents more than one bit element eg. shifts of π/2 (90o) eg. each element represents two bits split input data stream in two & modulate onto split carrier & phase shifted carrier carrier can use 8 phase angles & more than one can amplitude amplitude 9600bps modem uses 12 angles, four...
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