Digital Communication Interview Questions

Digital Communication & Electronics Interview Questions

  • Anuj Awasthi
  • 04th Jun, 2022

Digital Communication Interview Questions

1) What is Digital communication?

Digital communication is a mode of communication where the information or the thought is encoded digitally as discreet signals and electronically transferred.

2) What is Dibit?

Any one of four patterns from two consecutive bits: 00, 01, 10 and 11. Using phase modulation, a dibit can be modulated onto a carrier as a different shift in the phase of the wave.

3) What is Pulse Code Modulation?

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony, and other digital audio applications.

4) Define Nyquist rate?

The Nyquist rate or frequency is the minimum rate at which a finite bandwidth signal needs to be sampled to retain all of the information. For a bandwidth of span B, the Nyquist frequency is just 2 B.

5) What is difference in DPCM and DM?

DPCM: DPCM stands for Differential Pulse Code Modulation, is same as Pulse Code Modulation technique used for reworking analog signal into digital signal. Differential Pulse Code Modulation has moderate signal to noise magnitude relation.

DM: A delta modulation (DM or Δ-modulation) is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance. In delta modulation, the transmitted data are reduced to a 1-bit data stream.

6) What is Quantization in digital signal processing?

Quantization in digital signal processing is the procedure of mapping a sizable pair of input values into a smaller set – for instance, rounding values for some unit of precision. It is a tool or algorithmic function that performs quantization is termed a quantizer.

7) Enlist different types of Quantization?

There are two types of Quantization - Uniform Quantization and Non-uniform Quantization.

The type of quantization in which the quantization levels are uniformly spaced is termed as a Uniform Quantization.

The type of quantization in which the quantization levels are unequal and mostly the relation between them is logarithmic, is termed as a Non-uniform Quantization.

8) What is Delta Modulation?

A delta modulation (DM or Δ-modulation) is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance. ... The analog signal is approximated with a series of segments.

9) List different types of Data Encoding?

Data Encoding is the process of converting the data or a given sequence of characters, symbols, alphabets etc., into a specified format, for the secured transmission of data.

Different types of Data Encoding Techniques that are available are

  • Digital-to-Digital Encoding
  • Analog to Digital
  • Digital to Analog
  • Analog to Analog

10) What is Inter Symbol Interference?

In telecommunication, intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effects like noise, thus making the communication less reliable.

11) What is Amplitude Shift Keying and Frequency Shift Keying?

Amplitude-shift keying (ASK): It is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, the binary symbol 1 is represented by transmitting a fixed-amplitude carrier wave and fixed frequency for a bit duration of T seconds.

Frequency-shift keying (FSK): It is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information.

12) What is MPSK ?

M-ary Phase Shift Keying - or MPSK - is a modulation where data bits select one of M phase-shifted versions of the carrier to transmit the data. Thus, the M possible waveforms all have the same amplitude and frequency but different phases. The signal constellations consist of M equally spaced points on a circle.

13) What is Pseudo-Noise Sequence?

A pseudo-noise code (PN code) or pseudo-random-noise code (PRN code) is one that has a spectrum similar to a random sequence of bits but is deterministically generated.

14) What is matched filter?

The matched filter is the optimal linear filter for maximizing the signal-to-noise ratio (SNR) in the presence of additive stochastic noise. Matched filters are commonly used in radar, in which a known signal is sent out, and the reflected signal is examined for common elements of the out-going signal.

15) What is Half-Duplex Communication System?

In half-duplex systems, the transmission and reception of information must happen alternately. While one point is transmitting, the other must only receive it. Walkie-talkie radio communication is a half-duplex system, this is characterized by saying “over” at the end of a transmission to signify that the party is ready to receive information.

16) When Granular noise occurs?

Granular or Idle noise occurs when the step size is too large compared to a small variation in the input signal. This means that for very small variations in the input signal, the staircase signal is changed by a large amount (Δ) because of the large step size.

17) What is Correlative level coding?

Correlative level coding is used to transmit a baseband signal with the signaling rate of 2Bo over the channel of bandwidth Bo. This is made physically possible by allowing ISI in the transmitted in controlled manner. This ISI is known to receiver. The correlative coding is implemented by duobinary signaling and modified duobinary signaling.

18) What are eye pattern?

An eye pattern or eye diagram is an oscilloscope display in which a digital signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep.

19) What is baseband signal?

A baseband signal is an original transmission signal that has not be modulated, or has been demodulated to its original frequency. Most telecommunications protocols require baseband signals to be converted, or modulated, to a higher frequency so they can be transmitted over long distances.

20) What is hamming distance?

While comparing two binary strings of equal length, Hamming distance is the number of bit positions in which the two bits are different. The Hamming distance between two strings, a and b is denoted as d(a,b). It is used for error detection or error correction when data is transmitted over computer networks.

21) What is a convolution code?

A convolutional code is a type of error-correcting code that generates parity symbols via the sliding application of a boolean polynomial function to a data stream.

22) What is Binary Golay codes?

In mathematics and electronics engineering, a binary Golay code is a type of linear error-correcting code used in digital communications.The binary Golay code, along with the ternary Golay code, has a particularly deep and interesting connection to the theory of finite sporadic groups in mathematics.

These codes are named in honor of Marcel J. E. Golay whose 1949 paper introducing them has been called, by E. R. Berlekamp, the "best single published page" in coding theory.

23) What is jamming margin?

The jamming margin usually is considered as the jamming power to the signal power, it is a figure of merit and that provides a measure that how vulnerable your system is to interference.

24) What is Frequency-hopping spread spectrum?

Frequency-hopping spread spectrum is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both transmitter and receiver.

25) What is line code? List some properties of Line Coding?

A line code is a code used for data transmission of a digital signal over a transmission line. This process of coding is chosen so as to avoid overlap and distortion of signals such as inter-symbol interference.

Some Properties of Line coding are

  • As the coding is done to make more bits transmit on a single signal, the bandwidth used is much reduced.

  • For a given bandwidth, the power is efficiently used.

  • The probability of error is much reduced.

  • Error detection is done and the bipolar too has a correction capability.

  • Power density is much favorable.

  • The timing content is adequate.

  • Long strings of 1s and 0s is avoided to maintain transparency.

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