Digital Communication Question & Answers April 5, 2021 By WatElectronics This article lists 50+ Digital Communication MCQs for engineering students. All the Digital Communication Questions & Answers given below include a solution and link wherever possible to the relevant topic. Digital communication is the communication in which any message signal passed through digital devices. It is a communication system in which any type of information is sent digitally. Some examples of digital communication are Emailing on the computer, texting on a cell phone, fax, teleconferencing, video conferencing, etc. We require digital communication for internet/4G, and the processors also work on digital data. The digital communication systems are simpler and cheaper due to the advancements of IC technologies, the IC’s are reliable, cost-effective, and small in size. It is possible to use multiplexers in digital communication to merge speech, video, and other forms of data for transmission over a common channel. 1). The rearrangement of the data sequence is called _____ Line encoding Scrambling QAM None of the above None Hint 2). The modulation techniques are categorized into _________ Binary Signaling M-array Signalling Quadrature Amplitude modulation All of the above None Hint Read more about Modulation 3). In amplitude shift keying the 1 and 0 is denoted by _______ Acosωt, 1 Acosωct, 0 A cosωt,0 None of the above None Hint 4). The probability of error of amplitude shift keying is given by _______ Pe=1/4 erfc {E/4N0} Pe=1/2 erfc {E*4N0} Pe=1/2 erfc {E/4N0} None of the above None Hint Read more about Amplitude Shift Keying 5). The line encoding is classified into ______________ Unipolar, Bipolar Unipolar, polar Unipolar, Bipolar, Polar None of the above None Hint 6). The line encoding converts ________ Digital data to analog data Analog data to digital data Digital data to electrical signal/waveform None of the above None Hint 7). In unipolar line encoding 1 and 0 is represented as ________ 0 →1, 1 →-p(t) 0 →0, 1 →p(t) 0 →0, 1 →-p(t) None of the above None Hint 8). The properties of line encoding are _______ Transmission bandwidth Power efficiency Error detection & correction capability All of the above None Hint 9). Why scrambling is required? Data security Time extracting To access the unauthorized data All of the above None Hint 10). How many categories does the equalizer have? One Two Three Four None Hint 11). In bipolar line encoding 1 and 0 is represented as ________ 0 →1, 1 →-p(t) 0 →0, 1 →p(t) 0 →0, 1 →±p(t) None of the above None Hint Read more about Encoders 12). The change in amplitude of carrier in accordance to the digital message signal then it is called as _________ Phase Shift Keying Frequency Shift Keying Amplitude Shift Keying Binary Phase Shift Keying None Hint 13). The bit change corresponds to 450 phase change in _________ Quadrature Phase Shift Keying Frequency Shift Keying Amplitude Shift Keying Binary Phase Shift Keying None Hint 14). __________ is the non coherent mode of binary phase shift keying Quadrature Phase Shift Keying Differential Phase Shift Keying Amplitude Shift Keying Binary Phase Shift Keying None Hint 15). The maximum rate of information from transmitter to receiver is known as ___________ Information rate Code length Code efficiency None of the above None Hint 16). In polar line encoding 1 and 0 is represented as ________ 0 →1, 1 →-p(t) 0 → -p(t), 1 →p(t) 0 →0, 1 →±p(t) None of the above None Hint 17). The frequency of carrier signal is modified in accordance to the message signal then it is called as __________ Quadrature Phase Shift Keying Differential Phase Shift Keying Frequency Shift Keying Binary Phase Shift Keying None Hint 18). Which one comes under block code? Cyclic code Trellis code Turbo code None of the above None Hint 19). Which code doesn’t have memory? Block codes Trellis code Turbo code None of the above None Hint 20). Which code does have memory elements? Block codes Trellis code Turbo code Convolutional code None Hint Digital Communication Important MCQ’s for Students 21). When the phase of the carrier signal is varied in accordance to the message signal then it is called as _________ Quadrature Phase Shift Keying Differential Phase Shift Keying Frequency Shift Keying Binary Phase Shift Keying None Hint 22). The code efficiency in block code is denoted by ________ kn k/n k+n None of the above None Hint 23). The total number of non zero bits in code is known as _________ Code length Code height Code efficiency Code weight None Hint 24). The number of one’s in output code is even in ______ Even parity Odd parity Parity bit None of the above None Hint 25). ________ parity check detects only one error Horizontal parity check Vertical parity check Longitudnal parity check None of the above None Hint 26). Which one is the type of generation of cyclic code? Non systematic Systematic Cyclic code generation All of the above None Hint 27). In which type of cyclic code generation the position of parity bits are not defined? Non systematic Systematic Cyclic code generation All of the above None Hint 28). In which type of cyclic code generation the position of parity bits are well defined? Non systematic Systematic Cyclic code generation All of the above None Hint 29). _______ is the number of shifts over which single message bit influences the encoder output Code length Code height Code efficiency Code weight None Hint 30). _______ is a well defined, finite valued, real function on sample space Random variable Information rate Code efficiency None of the above None Hint 31). __________ parity check detects and corrects one error Horizontal parity check Vertical parity check Longitudinal parity check None of the above None Hint 32). The number of one’s in output code is odd in _______ Even parity Odd parity Parity bit None of the above None Hint 33). ________ is the collection of all possible outcomes of a random experiment Information rate Sample space Random variable None of the above None Hint 34). If each element in set A is mapped to separate element or a unique element in set B then it is called ___________ One One function Onto function One to function None of the above None Hint 35). If each element in set A is mapped to elements in set B and we don’t have an extra element in set B then it is called ___________ One One function Onto function One to function None of the above None Hint 36). The random variable takes continous value in an interval then it is called _________ Continuous random variable Continuous infinite random variable Discrete finite random variable Discrete infinite random variable None Hint 37). If there is a finite random variables in set A which are mapped to finite elements in set B then it is called as ______ Continous random variable Continous infinite random variable Discrete finite random variable Discrete infinite random variable None Hint 38). If first N elements of subset matched to the first N natural numbers then it is called as _________ Countable infinite random variable Continuous infinite random variable Discrete finite random variable Discrete infinite random variable None Hint 39). The poisson distribution function is discovered by ________ James Bernoulli Simon Denis Poisson Carl Friedrich Gauss None of the above None Hint 40). The Bernoulli distribution is discovered by _____ James Bernoulli Simon Denis Poisson Carl Friedrich Gauss None of the above None Hint Digital Communication Important MCQ’s for Interviews 41). ________ is used greatly in diverse fields, in central limit theorm, and sampling theorm Bernoulli distribution Gaussian distribution Poisson distribution Uniform distribution None Hint 42). The orthogonal frequency division multiplexing used in _________ Long Term Evolution (LTE) Long Term Evolution advanced World Wide Interoperability from Microwave Access (WIMAX) All of the above None Hint 43). The data rate transmission of orthogonal frequency division multiplexing is __________ High Low Medium None of the above None Hint 44). The data rate transmission of frequency division multiplexing is __________ High Very Low Medium None of the above None Hint 45). The voltage waveform which varies with time in an entirely unpredictable manner then it is called _________ Noise Code length QAM None of the above None Hint 46). The contaminated signal gives __________ Unwanted audio signal Unwanted video signal Both a and b None of the above None Hint 47). What are the advantages of digital communication systems? Simpler and cheaper Possibility of multiplexer High level of privacy All of the above None Hint 48). What are the disadvantages of digital communication systems? More transmission BW is required Sychronization is required High power consumption All of the above None Hint 49). In digital spread spectrum the input signal is modulated by ________ Phase Shift Keying Quadrature Phase Shift Keying Quadrature Amplitude Modulation All of the above None Hint 50). In Frequency Hoping Spread Spectrum (FHSS), which is the effective method for coherent detection? Phase Shift Keying Quadrature Phase Shift Keying Quadrature Amplitude Modulation Frequency Shift Keying None Hint 51). The chip generator in digital spread spectrum is used to ____________ Generate code It can have barker codes It has digital output All of the above None Hint 52). What is fast hoping in frequency hoping spread spectrum? Tc < Tb Tc > Tb Tc = Tb All of the above None Hint 53). What is slow hoping in frequency hoping spread spectrum? Tc < Tb Tc > Tb Tc = Tb All of the above None Hint 54). The signal to interference ration in frequency hoping spread spectrum is given by _______ SIR=(B/m+1) (log2L/LRb) SIR=(B/m) (log2L/LRb) SIR=(B/m-1) (log2L/LRb) None of the above None Hint 55). The applications of frequency hoping spread spectrum are ________ Bluetooth JTRS Both a and b None of the above None Hint 56). In which multiple access scheme the bandwidth is limited? Frequency Division Multiple Access Code Division Multiple Access Time Division Multiple Access Both a and c None Hint 57). The issues in FDMA and TDMA resolved by ___________ Space Division Multiple Access Code Division Multiple Access Both a and b None of the above None Hint 58). What is the sampling principle of flat top sampling? Sample and hold circuit Multiplication Chopping None of the above None Hint 59). ________ is expection or expected value of random variable Mean Variance Standard deviation None of the above None Hint 60). In viterbi algorithm __________ decoder is used to decode the received data Instruction decoder Address decoder Binary decoder Trellis decoder None Hint Digital Communication Quiz Questions and Answers 61). The code word is a _______ Message bit Parity bit Combination of message and parity bit None of the above None Hint 62). The hamming code is given by _______ James Bernoulli Simon Denis Poisson Carl Friedrich Gauss RW Hamming None Hint 63). In hamming code we send data along with _____________ Parity bits Redandent bits Parity bits or Redundant bits None of the above None Hint 64). The hamming code is used to _________ Detect errors Correct errors Detect and correct error None of the above None Hint 65). The hamming code is represented by ________ (n, k) code (n, -k) code (-n, k) code None of the above None Hint 66). What is the sampling principle of natural sampling? Sample and hold circuit Multiplication Chopping None of the above None Hint 67). The number of parity bits in block code is n-1 then the code is referred to as _____ (n,0) (n,1) (n,1) c) (n,-1) None of the above None Hint 68). The limitation of capacity of channel to transmit information is referred as ______ Code word Channel capacity Code weight None of the above None Hint 69). The words belongs to a block code are called as _________ Code word Channel capacity Code weight None of the above None Hint 70). The entropy is defined as ______ E=Total information/ number of messages E=Total information-number of messages E=Total information* number of messages None of the above None Hint 71). ________ is the intelligence or ideal or message in information theory Code word Channel capacity Code weight Information None Hint 72). The ____________ is defined as the process of converting binary data to digital signal Data rate Line coding Code weight Information None Hint 73). ____________ is defined as the number of pulses per second Data rate Pulse rate Bit rate Information rate None Hint 74). ____________ is defined as the number of bits per second Data rate Pulse rate Bit rate Information rate None Hint 75). The sampled pulse amplitude modulation is off for most of the time in _________ Frequency Division Multiplexing Code Division Multiplexing Time Division Multiplexing Both a and c None Hint 76). The speech signal range is from ______ 300Hz-3.4KHz 200Hz-3.4KHz 300Hz-3.9KHz None of the above None Hint 77). What is the sampling principle of ideal sampling? Sample and hold circuit Multiplication Chopping None of the above None Hint 78). The block code repeats the information bits ________ times One time only Two times only Two or more times None of the above None Hint 79). The channel capacity by Shannon Hartley is given by _______ C= B log2 [1-S/N] C= B log2 [S/N] C= B log2 [1+S/N] None of the above None Hint 80). The noise interference in ideal sampling is _______ High Very high Less Very less None Hint Time's up