Digital Transmission & Analog Transmission. 1. DIGITAL-TO-DIGITAL CONVERSION. Digital Data -> Digital Signal Three techniques: line coding ( always needed ) block coding (working with NRZ-I) Scrambling (working with AMI). Figure 4.1 Line coding and decoding.
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r = number of data elements / number of signal elements
Baseline: running average of the received signal power
Constant digital signal creates low frequencies
Receiver Setting the clock matching the sender’s
Figure 4.8 Polar biphase: Manchester and differential Manchester schemes
Figure 4.9 Bipolar schemes: AMI (Alternate Mark Inversion) and pseudoternary
B8ZS substitutes eight consecutive zeros with 000VB0VB
HDB3 substitutes four consecutive zeros with 000V or B00V depending
on the number of nonzero pulses after the last substitution.
According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the signal.
What can we get from this:
1. we can sample a signal only if the signal is
2. the sampling rate must be at least 2 times the highest frequency, not the bandwidth
SNRdb= 6.02nb + 1.76 dB
nb: bits per sample
(related to the number of level L)
The minimum bandwidth of the digital signal is nb times greater than the bandwidth of the analog signal.
Bmin= nb x Banalog
Next bit is 1, if amplitude of the analog signal is larger
Next bit is 0, if amplitude of the analog signal is smaller
1. The transmission of binary data across a link can be accomplished in either parallel or serial mode.
2. In parallel mode, multiple bits are sent with each clock tick.
3. In serial mode, 1 bit is sent with each clock tick.
4. there are three subclasses of serial transmission: asynchronous, synchronous, and isochronous.
Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data.
B = (1+d) x S = (1+d) x N x 1/r
Analog-to-analog conversion is the representation of analog information by an analog signal.
Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us.
Example: radio stations
The total bandwidth required for AM can be determined from the bandwidth of the audio signal: BAM = 2B.
The total bandwidth required for FM can be determined from the bandwidth of the audio signal: BFM = 2(1 + β)B. β has a common value of 4
The total bandwidth required for PM can be determined from the bandwidth and maximum amplitude of the modulating signal:BPM = 2(1 + β)B.