Question

a. Describe TWO (2) advantages and TWO (2) disadvantages of digital transmission. (CO1: PO1 - 4 marks)

Answer 1

a) Solution:

Advantages of Digital Transmission

1. Noise Immunity: Digital signals are inherently less susceptible than analog signals to interference caused by noise because with digital signals it is not necessary to evaluate precise amplitude, frequency or phase. Instead pulses are evaluated during the precise time interval and simple determination is made whether the pulse is above or below a prescribed reference level.

2. Resistant to additive Noise: Digital transmission systems are more resistant to analog system to additive noise because they use signal regeneration rather than signal amplification. Noise produced in electronic circuit is additive, therefore S/N ratio deteriorates each time an analog signal is amplified.

3. Multiplexing: Digital signals are better suited than analog signals for processing and combining using a technique multiplexing.

Disadvantages of Digital Transmission:

1. More Bandwidth Requirement: The transmission of digitally encoded original analog signal. BW is one of the important aspects of any communication system because it is costly and limited.

2. Extra Circuitry for encoding and Decoding: Analog signals must be converted to digital pulses prior to transmissions and converted back to their original analog form at receiver, thus require additional circuitry for encoding and decoding.

3. Require Synchronization: Digital transmissions require precise time synchronization between the clocks in transmitter and receiver.

d) solution:

(d) solution Sampling dute 9000 samples / sec. ato No of channels = 24 3 Z No of bits per each Sample 7 No of bits per flame (24x1) + , y parity 169 bits framing bit (i) Line speed in Sec speed of the line is number Se Cond of bits per transmitted by the line during its transmission . speed =( Number of bits per frame) x ( sampling rate - 169 X 9000 speed 1.52 Mb/sec. R (ii) minimum Ny quist Band width R6 1.52 Mb/s Transmission Bandwidth 7 Bw 217.142 Kb/vec.