Digital Communication MCQ’SApril 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 encodingScramblingQAMNone of the aboveHintThe rearrangement of the data sequence is called scrambling, and it prevents unauthorized data. 2). The modulation techniques are categorized into _________Binary SignalingM-array SignallingQuadrature Amplitude modulationAll of the aboveHintThe modulation techniques are categorized into three types they are Binary Signaling, M-array Signaling, and Quadrature Amplitude modulation Read more about Modulation 3). In amplitude shift keying the 1 and 0 is denoted by _______Acosωt, 1Acosωct, 0A cosωt,0None of the aboveHintIn amplitude shift keying the 1 is denoted by Acosωct and 0 is denoted by 0 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 aboveHintThe probability of error of amplitude shift keying is given by Pe=1/2 erfc {E/4N0}, where Pe is the probability of error, erfc is the error function. Read more about Amplitude Shift Keying 5). The line encoding is classified into ______________Unipolar, BipolarUnipolar, polarUnipolar, Bipolar, PolarNone of the aboveHintThe line encoding is classified into three types they are polar line encoding, unipolar line encoding, and bipolar line encoding 6). The line encoding converts ________Digital data to analog dataAnalog data to digital dataDigital data to electrical signal/waveformNone of the aboveHintThe line encoding converts the digital data to electrical signal/waveform 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 aboveHintIn unipolar line encoding 1 represented as p(t) and 0 represented as 0 8). The properties of line encoding are _______Transmission bandwidthPower efficiencyError detection & correction capabilityAll of the aboveHintThe transmission bandwidth is as small as possible, the power efficiency is best in polar line encoding, and error detection & error correction capability is possible 9). Why scrambling is required?Data securityTime extractingTo access the unauthorized dataAll of the aboveHintThe scrambling is required for data security to avoid the unwanted or unauthorized data access 10). How many categories does the equalizer have?OneTwoThreeFourHintThe equalizer has three categories they are zero forcing equalizer, minimum mean equalizer, and adaptive equalizer. 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 aboveHintIn bipolar line encoding 1 represented as ±p(t) and 0 represented as 0 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 KeyingFrequency Shift KeyingAmplitude Shift KeyingBinary Phase Shift KeyingHintThe change in amplitude of carrier in accordance to the digital message signal then is called Amplitude Shift Keying 13). The bit change corresponds to 450 phase change in _________Quadrature Phase Shift KeyingFrequency Shift KeyingAmplitude Shift KeyingBinary Phase Shift KeyingHintThe bit change corresponds to 450 phase change in Quadrature Phase Shift Keying 14). __________ is the non coherent mode of binary phase shift keyingQuadrature Phase Shift KeyingDifferential Phase Shift KeyingAmplitude Shift KeyingBinary Phase Shift KeyingHintThe Differential Phase Shift Keying is the non-coherent mode of binary phase-shift keying, where the output encoded bit depends upon the previous bit 15). The maximum rate of information from transmitter to receiver is known as ___________Information rateCode lengthCode efficiencyNone of the aboveHintThe maximum rate of information from a transmitter to receiver is known as code length 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 aboveHintIn polar line encoding 1 represented as p(t) and 0 represented as -p(t) 17). The frequency of carrier signal is modified in accordance to the message signal then it is called as __________Quadrature Phase Shift KeyingDifferential Phase Shift KeyingFrequency Shift KeyingBinary Phase Shift KeyingHintThe frequency of carrier signal is modified in accordance with the message signal then it is called Frequency Shift Keying 18). Which one comes under block code?Cyclic codeTrellis codeTurbo codeNone of the aboveHintThe cyclic code is one type of block code 19). Which code doesn’t have memory?Block codesTrellis codeTurbo codeNone of the aboveHintThe block code doesn’t have memory elements because the output code depends upon the present message bit only 20). Which code does have memory elements?Block codesTrellis codeTurbo codeConvolutional codeHintThe convolutional code has memory elements because the output code depends upon the past elements alsoDigital 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 KeyingDifferential Phase Shift KeyingFrequency Shift KeyingBinary Phase Shift KeyingHintIn Binary Phase Shift Keying the phase of the carrier signal is varied in accordance with the message signal 22). The code efficiency in block code is denoted by ________knk/nk+nNone of the aboveHintThe code efficiency in block code is denoted by k/n 23). The total number of non zero bits in code is known as _________Code lengthCode heightCode efficiencyCode weightHintThe total number of non zero bits in code is known as code weight 24). The number of one’s in output code is even in ______Even parityOdd parityParity bitNone of the aboveHintIn even parity the number of one’s in output code is even 25). ________ parity check detects only one errorHorizontal parity checkVertical parity checkLongitudnal parity checkNone of the aboveHintThe vertical parity check detects only one error 26). Which one is the type of generation of cyclic code?Non systematicSystematicCyclic code generationAll of the aboveHintThe nonsystematic, cyclic code generation and systems are the types of generations of cyclic code 27). In which type of cyclic code generation the position of parity bits are not defined?Non systematicSystematicCyclic code generationAll of the aboveHintIn non-systematic cyclic code generation, the position of parity bits are not defined 28). In which type of cyclic code generation the position of parity bits are well defined?Non systematicSystematicCyclic code generationAll of the aboveHintIn systematic cyclic code generation, the position of parity bits are well defined 29). _______ is the number of shifts over which single message bit influences the encoder outputCode lengthCode heightCode efficiencyCode weightHintThe code length is the number of shifts over which a single message bit influences the encoder output 30). _______ is a well defined, finite valued, real function on sample spaceRandom variableInformation rateCode efficiencyNone of the aboveHintThe random variable is a well defined, finite valued, real function on sample space and it is always denoted by capital letters 31). __________ parity check detects and corrects one errorHorizontal parity checkVertical parity checkLongitudinal parity checkNone of the aboveHintThe longitudinal parity check detects and corrects one error 32). The number of one’s in output code is odd in _______Even parityOdd parityParity bitNone of the aboveHintIn odd parity the number of one’s in output code is odd 33). ________ is the collection of all possible outcomes of a random experimentInformation rateSample spaceRandom variableNone of the aboveHintThe sample space is the collection of all possible outcomes of a random experiment. Example {Head, Tail} on tossing a coin 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 functionOnto functionOne to functionNone of the aboveHintIf each element in set A is mapped to a separate element or a unique element in set B then it is called One One function 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 functionOnto functionOne to functionNone of the aboveHintIf 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 Onto function i.e range=codomain 36). The random variable takes continous value in an interval then it is called _________Continuous random variableContinuous infinite random variableDiscrete finite random variableDiscrete infinite random variableHintThe continuous random variable will take Continuous value in an interval i.e X1-[1,2] X2-[3,4] X3-[4,5] 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 variableContinous infinite random variableDiscrete finite random variableDiscrete infinite random variableHintIf there is a finite random variable in set A which are mapped to finite elements in set B then it is called a discrete finite random variable 38). If first N elements of subset matched to the first N natural numbers then it is called as _________Countable infinite random variableContinuous infinite random variableDiscrete finite random variableDiscrete infinite random variableHintIf the first N elements of subset matched to the first N natural numbers then it is called a countable infinite random variable, the only condition is that it has to be countable, infinite then it has to be one-one and on to 39). The poisson distribution function is discovered by ________James BernoulliSimon Denis PoissonCarl Friedrich GaussNone of the aboveHintThe Poisson distribution function is discovered by Simon Denis Poisson 40). The Bernoulli distribution is discovered by _____James BernoulliSimon Denis PoissonCarl Friedrich GaussNone of the aboveHintThe Bernoulli distribution function is discovered by James BernoulliDigital Communication Important MCQ’s for Interviews 41). ________ is used greatly in diverse fields, in central limit theorm, and sampling theormBernoulli distributionGaussian distributionPoisson distributionUniform distributionHintThe Gaussian distribution is used greatly in diverse fields, in central limit theorem, and sampling theorem, it is also known as a normal distribution 42). The orthogonal frequency division multiplexing used in _________Long Term Evolution (LTE)Long Term Evolution advancedWorld Wide Interoperability from Microwave Access (WIMAX)All of the aboveHintThe orthogonal frequency division multiplexing used in four-generation wireless communication applications such as LTE, LTE advanced, WIMAX, etc. 43). The data rate transmission of orthogonal frequency division multiplexing is __________HighLowMediumNone of the aboveHintThe data rate transmission of orthogonal frequency division multiplexing is very high because the bandwidth is very high in OFDM when compared to frequency division multiplexing 44). The data rate transmission of frequency division multiplexing is __________HighVery LowMediumNone of the aboveHintThe data rate transmission of frequency division multiplexing is very low because the bandwidth is less in FDM 45). The voltage waveform which varies with time in an entirely unpredictable manner then it is called _________NoiseCode lengthQAMNone of the aboveHintThe voltage waveform which varies with time in an entirely unpredictable manner then it is called noise 46). The contaminated signal gives __________Unwanted audio signalUnwanted video signalBoth a and bNone of the aboveHintWhenever the signal is contaminated, then the signal is added with the noise, so the contaminated signal gives unwanted audio/ video/ picture disturbances 47). What are the advantages of digital communication systems?Simpler and cheaperPossibility of multiplexerHigh level of privacyAll of the aboveHintThe digital communication systems simpler and cheaper due to the advancements of IC technologies, possible to use a multiplexer, high level of privacy due to data encryption 48). What are the disadvantages of digital communication systems?More transmission BW is requiredSychronization is requiredHigh power consumptionAll of the aboveHintThe disadvantages of digital communication systems are more transmission BW is required, synchronization is required, and it consumes more power 49). In digital spread spectrum the input signal is modulated by ________Phase Shift KeyingQuadrature Phase Shift KeyingQuadrature Amplitude ModulationAll of the aboveHintIn the digital spread spectrum, the input signal could be modulated by PSK, QPSK, and QAM. 50). In Frequency Hoping Spread Spectrum (FHSS), which is the effective method for coherent detection?Phase Shift KeyingQuadrature Phase Shift KeyingQuadrature Amplitude ModulationFrequency Shift KeyingHintThe Frequency Shift Keying used in FHSS because it is the effective method for coherent detection, because the cost of PSK, QAM, and QPSK are very costly for coherent detection 51). The chip generator in digital spread spectrum is used to ____________Generate codeIt can have barker codesIt has digital outputAll of the aboveHintThe chip generator in the digital spread spectrum is used to generate code, and it can have barker codes and its output is in terms of digital form that may be in terms of [+1, -1] 52). What is fast hoping in frequency hoping spread spectrum?Tc < TbTc > TbTc = TbAll of the aboveHintWhen the bit period is greater than the chip period then it is fast hoping, where Tc is the chip period, and Tb is the bit period 53). What is slow hoping in frequency hoping spread spectrum?Tc < TbTc > TbTc = TbAll of the aboveHintWhen the chip period is greater than the bit period then it is slow hoping, where Tc is the chip period, and Tb is the bit period 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 aboveHintThe signal to interference ratio in FHSS is given by SIR=(B/m+1) (log2L/LRb), where B is the system bandwidth, m is the number of users, L is the number of orthogonal codes, and Rb is the signaling rate 55). The applications of frequency hoping spread spectrum are ________BluetoothJTRSBoth a and bNone of the aboveHintIn Bluetooth we find 625 times frequency hopes in one second, Joint Tactical Radio System (JTRS ), these are popular methods in FHSS 56). In which multiple access scheme the bandwidth is limited?Frequency Division Multiple AccessCode Division Multiple AccessTime Division Multiple AccessBoth a and cHintIn Frequency Division Multiple Access and Time Division Multiple Access the bandwidth is limited, due to limited bandwidth it requires high spectral efficiency 57). The issues in FDMA and TDMA resolved by ___________Space Division Multiple AccessCode Division Multiple AccessBoth a and bNone of the aboveHintIn FDMA and TDMA the bandwidth is limited and due to limited bandwidth we can observe narrowband spectrum and concentrated spectrum all these issues solved by using CDMA 58). What is the sampling principle of flat top sampling?Sample and hold circuitMultiplicationChoppingNone of the aboveHintThe flat-top sampling works based on the principle of sample and holds the circuit 59). ________ is expection or expected value of random variableMeanVarianceStandard deviationNone of the aboveHintMean is expection or expected value of random variable and it is denoted by µ 60). In viterbi algorithm __________ decoder is used to decode the received dataInstruction decoderAddress decoderBinary decoderTrellis decoderHintIn the Viterbi algorithm trellis decoder is used to decode the received data, the Viterbi algorithm is a method of decoding convolution codesDigital Communication Quiz Questions and Answers 61). The code word is a _______Message bitParity bitCombination of message and parity bitNone of the aboveHintThe codeword is a combination of message and parity bits 62). The hamming code is given by _______James BernoulliSimon Denis PoissonCarl Friedrich GaussRW HammingHintThe hamming code is given by RW Hamming 63). In hamming code we send data along with _____________Parity bitsRedandent bitsParity bits or Redundant bitsNone of the aboveHintIn hamming code, we send data along with parity bits or redundant bits 64). The hamming code is used to _________Detect errorsCorrect errorsDetect and correct errorNone of the aboveHintThe hamming code is used to detect the error as well as correct the error 65). The hamming code is represented by ________(n, k) code(n, -k) code(-n, k) codeNone of the aboveHintThe hamming code is represented by (n, k) code where n represents total bits and k represents message bits 66). What is the sampling principle of natural sampling?Sample and hold circuitMultiplicationChoppingNone of the aboveHintThe natural sampling works based on the principle of chopping 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 aboveHintThe number of parity bits in block code is n-1 then the code is referred to as (n,1) 68). The limitation of capacity of channel to transmit information is referred as ______Code wordChannel capacityCode weightNone of the aboveHintThe limitation of the capacity of the channel to transmit information is referred to as channel capacity 69). The words belongs to a block code are called as _________Code wordChannel capacityCode weightNone of the aboveHintThe words that belong to a block code are called a code word 70). The entropy is defined as ______E=Total information/ number of messagesE=Total information-number of messagesE=Total information* number of messagesNone of the aboveHintThe entropy is defined as a ratio of total information by a number of messages, where entropy is denoted by E 71). ________ is the intelligence or ideal or message in information theoryCode wordChannel capacityCode weightInformationHintThe information is the intelligence or ideal or message in information theory and the message form could be electrical, speech or voice, picyures or image, video, text signal, etc. 72). The ____________ is defined as the process of converting binary data to digital signalData rateLine codingCode weightInformationHintLine coding is defined as the process of converting binary data to digital signal 73). ____________ is defined as the number of pulses per secondData ratePulse rateBit rateInformation rateHintThe pulse rate is defined as the number of pulses per second 74). ____________ is defined as the number of bits per secondData ratePulse rateBit rateInformation rateHintThe bit rate is defined as the number of bits per second 75). The sampled pulse amplitude modulation is off for most of the time in _________Frequency Division MultiplexingCode Division MultiplexingTime Division MultiplexingBoth a and cHintIn time-division multiplexing, the sampled pulse amplitude modulation is off for most of the time 76). The speech signal range is from ______300Hz-3.4KHz200Hz-3.4KHz300Hz-3.9KHzNone of the aboveHintThe speech signal range is from 300Hz-3.4KHz, the maximum frequency will be bandwidth that is 3.4kHz 77). What is the sampling principle of ideal sampling?Sample and hold circuitMultiplicationChoppingNone of the aboveHintThe ideal sampling works based on the principle of multiplication 78). The block code repeats the information bits ________ timesOne time onlyTwo times onlyTwo or more timesNone of the aboveHintThe block code repeats the information bits two or more than two times 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 aboveHintThe channel capacity by Shannon Hartley is given by C= B log2 [1+S/N], where C is the channel capacity, B is the bandwidth of the channel, N is the noise power 80). The noise interference in ideal sampling is _______HighVery highLessVery lessHintThe noise interference in ideal sampling is very high compared to natural sampling Time is Up!