Given the channel features or objectives below. For each part, tell which line c

Question

Given the channel features or objectives below. For each part, tell which line code(s) is (are) the best choice(s). (a) The channel frequency response has a null at f = 0 hertz. (b) The channel has a passband from 0 to 10 kHz and it is desired to transmit data through it at 10,000 bits/s. (c) At least one zero crossing per bit is desired for synchronization purposes. (d) Built-in redundancy is desired for error-checking purposes. (e) For simplicity of detection, distinct positive pulses are desired for ones and distinct negative pulses are desired for zeros. (f) A discrete spectral line at the bit rate is desired from which to derive a clock at the bit rate.

Explanation / Answer

a) Ans:- Unipolar encoding only makes use of one polarity, i.e. positive voltage, to represent a binary 1 and it uses an idle line to represent a binary 0, i.e. zero voltage.

c)Ans:-Non Return to Zero (NRZ)

As its name implies Non Return to Zero (NRZ) encodes a signal that is always positive or negative but never zero.

b,d,f) Ans:- Inverting NRZ (NRZ-I)

Inverting NRZ (NRZ-I) works by using the inversion of the voltage level to represent the binary 1. Therefore, it is the change in the voltage level rather than the actual polarity that signifies a binary 1. If the next bit is a one there will be a voltage change and if it is a zero then there will be no change.

This type of NRZ can offer some synchronisation or timing because a series of binary ones will result in a series of inversions that can be used by the receiving end to resynchronise its timer.

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