Encoding and Modulating

Different Conversion Schemes Encoding digitizing Modulating Modulating Digital Signal Analog Signal

Digital to Digital Encoding

Types of Digital to Digital Encoding NRZ- Nonreturn to zero RZ-return to zero

Unipolar Encoding It uses only one polarity, its has a voltage level taken as 0 and another is 1 Disadvantages DC Component Synchronization

Polar Encoding Uses two voltage levels NRZ- Nonreturn to Zero Level of the signal is always positive or negative. Two types of NRZ NRZ-L +ve voltage is represents a bit 0 NRZ-I Synchronization is provided RZ- Return Zero

NRZ-L and NRZ-I Encoding

RZ Encoding

Manchester and Diff. Manchester Encoding

Types of Bipolar Encoding

Bipolar AMI Encoding

B8ZS Encoding

HDB3 Encoding

Example Using B8ZS, encode the bit stream 10000000000100. Assume that the polarity of the first 1 is positive.

Analog to Digital Encoding

Pulse Amplitude Modulation (PAM)

Quantized PAM Signal

PCM

From Analog to PCM

From Analog to PCM

From Analog to PCM

From Analog to PCM

Digital to Analog modulation In digital to analog modulation two basics issues are defined: Bit/Baud rate & Carrier signal

Amplitude Shift Keying(ASK) The figure depicts operation of ASK modulation. As shown in the figure, binary 1 will be represented by carrier signal with some amplitude while binary 0 will be represented by carrier of zero amplitude(i.e. no carrier).ASK is susceptible to noise interference.

Amplitude Shift Keying(ASK)

Formulas for ASK For Half duplex the bandwidth remains the same as given For Full duplex: Bandwidth(BW)=Given Bandwidth/2 Formula for calculating carrier frequencies Fc(forward)=Fc(min)+Nbaud/2 Fc(backward)=Fc(max)-Nbaud/2

Frequency Shift Keying(FSK) The figure depicts the FSK modulation. As shown, binary 1 and 0 is represented by two different carrier frequencies. Figure depicts that binary 1 is represented by high frequency 'f1' and binary 0 is represented by low frequency 'f2'.

Frequency Shift Keying(FSK)

Formulas for FSK For Calculating the Bandwidth: BW=Baud rate+(Fc1-Fc0) For Calculating Bit rate or Baud rate Baud rate/Bit Rate=BW - (Fc1-Fc0) Where (Fc1-Fc0)-Difference between two carrier frequencies

Phase Shift Keying(PSK) Figure depicts Binary Phase Shift Keying modulation type of PSK. As shown in the figure, Binary 1 is represented by 180 degree phase of the carrier and binary 0 is represented by 0 degree phase of the carrier.

PSK Constellation

4-PSK Characteristics

Phase Shift Keying(PSK)

4-PSK

Bit Rate and Baud Rate

Analog to Analog Modulation

Amplitude Modulation

Frequency Modulation

Transmission of Digital Data Interfaces and Modems Digital Data Transmission DTE-DCE Interface Other Interface Standards Modems

Parallel Transmission

Serial Transmission

Asynchronous Transmission

Synchronous Transmission

DTEs and DCEs

DTE-DCE interface

Twisted-Pair Cable

Shielded Twisted-Pair Cable

Coaxial Cable

Fiber Construction

Refraction

Critical Angle

Reflection

Transmission Impairment Attenuation

Distortion:

Noise: