Data Communication Unit 2

Digital-To-Digital ConversionLINE CODING: data element signal element

DATA RATE AND SIGNAL RATE The data rate is measured in bps (bits/sec). The data rate is also called bit rate. The signal rate is measured in baud. The signal rate is also called pulse rate, modulation rate, or baud rate.

Unipolar Scheme

Polar Scheme

Return to Zero (RZ)

BIPHASE Manchester and Differential Manchester

BIPOLAR SCHEMES (MULTILEVEL BINARY)(i)AMI (alternate mark inversion)

(ii)Pseudoternary

MULTILEVEL SCHEMES2B1Q (Two binary, one Quaternary)Transition Table

Previous level=positive Previous level=negativeNext bits Next level Next level

00 +1 -101 +3 -310 -1 +111 -3 +3

ANALOG TO DIGITAL CONVERSIONPulse Code Modulation (PCM)

1.Sampling:

2. Quantization:

3. Encoding:For example, if a sample has quantization code of 2, then it is encoded as 010, similarly, 5 is encoded as 101, and so on. The bit rate will be

SNRdB = 6.02nb + 1.76 dB

DIGITAL-TO-ANALOG CONVERSION

An analog signal carries 4 bits per signal element. If 1000 signal elements are sent per second, find the bit rate.

Amplitude Shift Keying (ASK)

Implementation

Frequency Shift Keying (FSK)

Implementation

Phase Shift Keying

Implementation

Quadrature PSK (QPSK)

Constellation Diagram

Quadrature Amplitude Modulation (QAM)

ANALOG-TO-ANALOG CONVERSION

Amplitude Modulation:

Frequency Modulation:

Phase Modulation: