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 encoding Scrambling QAM None of the above HintThe rearrangement of the data sequence is called scrambling, and it prevents unauthorized data.2). The modulation techniques are categorized into _________ Binary Signaling M-array Signalling Quadrature Amplitude modulation All of the above HintThe modulation techniques are categorized into three types they are Binary Signaling, M-array Signaling, and Quadrature Amplitude modulation Read more about Modulation3). In amplitude shift keying the 1 and 0 is denoted by _______ Acosωt, 1 Acosωct, 0 A cosωt,0 None of the above HintIn amplitude shift keying the 1 is denoted by Acosωct and 0 is denoted by 04). 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 HintThe 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 Keying5). The line encoding is classified into ______________ Unipolar, Bipolar Unipolar, polar Unipolar, Bipolar, Polar None of the above HintThe line encoding is classified into three types they are polar line encoding, unipolar line encoding, and bipolar line encoding6). The line encoding converts ________ Digital data to analog data Analog data to digital data Digital data to electrical signal/waveform None of the above HintThe 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 above HintIn unipolar line encoding 1 represented as p(t) and 0 represented as 0 8). The properties of line encoding are _______ Transmission bandwidth Power efficiency Error detection & correction capability All of the above HintThe 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 security Time extracting To access the unauthorized data All of the above HintThe scrambling is required for data security to avoid the unwanted or unauthorized data access10). How many categories does the equalizer have? One Two Three Four HintThe 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 above HintIn bipolar line encoding 1 represented as ±p(t) and 0 represented as 0 Read more about Encoders12). 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 HintThe change in amplitude of carrier in accordance to the digital message signal then is called Amplitude Shift Keying13). The bit change corresponds to 450 phase change in _________ Quadrature Phase Shift Keying Frequency Shift Keying Amplitude Shift Keying Binary Phase Shift Keying HintThe bit change corresponds to 450 phase change in Quadrature Phase Shift Keying14). __________ 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 HintThe Differential Phase Shift Keying is the non-coherent mode of binary phase-shift keying, where the output encoded bit depends upon the previous bit15). The maximum rate of information from transmitter to receiver is known as ___________ Information rate Code length Code efficiency None of the above HintThe maximum rate of information from a transmitter to receiver is known as code length16). 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 HintIn 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 Keying Differential Phase Shift Keying Frequency Shift Keying Binary Phase Shift Keying HintThe frequency of carrier signal is modified in accordance with the message signal then it is called Frequency Shift Keying18). Which one comes under block code? Cyclic code Trellis code Turbo code None of the above HintThe cyclic code is one type of block code19). Which code doesn’t have memory? Block codes Trellis code Turbo code None of the above HintThe block code doesn’t have memory elements because the output code depends upon the present message bit only20). Which code does have memory elements? Block codes Trellis code Turbo code Convolutional code HintThe convolutional code has memory elements because the output code depends upon the past elements alsoDigital Communication Important MCQ’s for Students21). 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 HintIn Binary Phase Shift Keying the phase of the carrier signal is varied in accordance with the message signal22). The code efficiency in block code is denoted by ________ kn k/n k+n None of the above HintThe code efficiency in block code is denoted by k/n23). The total number of non zero bits in code is known as _________ Code length Code height Code efficiency Code weight HintThe total number of non zero bits in code is known as code weight24). The number of one’s in output code is even in ______ Even parity Odd parity Parity bit None of the above HintIn even parity the number of one’s in output code is even25). ________ parity check detects only one error Horizontal parity check Vertical parity check Longitudnal parity check None of the above HintThe vertical parity check detects only one error26). Which one is the type of generation of cyclic code? Non systematic Systematic Cyclic code generation All of the above HintThe nonsystematic, cyclic code generation and systems are the types of generations of cyclic code27). 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 HintIn non-systematic cyclic code generation, the position of parity bits are not defined28). 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 HintIn systematic cyclic code generation, the position of parity bits are well defined29). _______ is the number of shifts over which single message bit influences the encoder output Code length Code height Code efficiency Code weight HintThe code length is the number of shifts over which a single message bit influences the encoder output30). _______ is a well defined, finite valued, real function on sample space Random variable Information rate Code efficiency None of the above HintThe random variable is a well defined, finite valued, real function on sample space and it is always denoted by capital letters31). __________ parity check detects and corrects one error Horizontal parity check Vertical parity check Longitudinal parity check None of the above HintThe longitudinal parity check detects and corrects one error32). The number of one’s in output code is odd in _______ Even parity Odd parity Parity bit None of the above HintIn odd parity the number of one’s in output code is odd33). ________ is the collection of all possible outcomes of a random experiment Information rate Sample space Random variable None of the above HintThe sample space is the collection of all possible outcomes of a random experiment. Example {Head, Tail} on tossing a coin34). 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 HintIf each element in set A is mapped to a separate element or a unique element in set B then it is called One One function35). 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 HintIf 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=codomain36). 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 HintThe 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 variable Continous infinite random variable Discrete finite random variable Discrete infinite random variable HintIf 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 variable38). 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 HintIf 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 to39). The poisson distribution function is discovered by ________ James Bernoulli Simon Denis Poisson Carl Friedrich Gauss None of the above HintThe Poisson distribution function is discovered by Simon Denis Poisson40). The Bernoulli distribution is discovered by _____ James Bernoulli Simon Denis Poisson Carl Friedrich Gauss None of the above HintThe 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 theorm Bernoulli distribution Gaussian distribution Poisson distribution Uniform distribution HintThe Gaussian distribution is used greatly in diverse fields, in central limit theorem, and sampling theorem, it is also known as a normal distribution42). 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 HintThe 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 __________ High Low Medium None of the above HintThe data rate transmission of orthogonal frequency division multiplexing is very high because the bandwidth is very high in OFDM when compared to frequency division multiplexing44). The data rate transmission of frequency division multiplexing is __________ High Very Low Medium None of the above HintThe 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 _________ Noise Code length QAM None of the above HintThe voltage waveform which varies with time in an entirely unpredictable manner then it is called noise46). The contaminated signal gives __________ Unwanted audio signal Unwanted video signal Both a and b None of the above HintWhenever the signal is contaminated, then the signal is added with the noise, so the contaminated signal gives unwanted audio/ video/ picture disturbances47). What are the advantages of digital communication systems? Simpler and cheaper Possibility of multiplexer High level of privacy All of the above HintThe 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 encryption48). What are the disadvantages of digital communication systems? More transmission BW is required Sychronization is required High power consumption All of the above HintThe 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 Keying Quadrature Phase Shift Keying Quadrature Amplitude Modulation All of the above HintIn 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 Keying Quadrature Phase Shift Keying Quadrature Amplitude Modulation Frequency Shift Keying HintThe 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 code It can have barker codes It has digital output All of the above HintThe 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 < Tb Tc > Tb Tc = Tb All of the above HintWhen 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 period53). What is slow hoping in frequency hoping spread spectrum? Tc < Tb Tc > Tb Tc = Tb All of the above HintWhen 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 period54). 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 HintThe 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 rate55). The applications of frequency hoping spread spectrum are ________ Bluetooth JTRS Both a and b None of the above HintIn Bluetooth we find 625 times frequency hopes in one second, Joint Tactical Radio System (JTRS ), these are popular methods in FHSS56). 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 HintIn Frequency Division Multiple Access and Time Division Multiple Access the bandwidth is limited, due to limited bandwidth it requires high spectral efficiency57). The issues in FDMA and TDMA resolved by ___________ Space Division Multiple Access Code Division Multiple Access Both a and b None of the above HintIn 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 CDMA58). What is the sampling principle of flat top sampling? Sample and hold circuit Multiplication Chopping None of the above HintThe flat-top sampling works based on the principle of sample and holds the circuit59). ________ is expection or expected value of random variable Mean Variance Standard deviation None of the above HintMean is expection or expected value of random variable and it is denoted by µ60). In viterbi algorithm __________ decoder is used to decode the received data Instruction decoder Address decoder Binary decoder Trellis decoder HintIn 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 Answers61). The code word is a _______ Message bit Parity bit Combination of message and parity bit None of the above HintThe codeword is a combination of message and parity bits62). The hamming code is given by _______ James Bernoulli Simon Denis Poisson Carl Friedrich Gauss RW Hamming HintThe hamming code is given by RW Hamming63). In hamming code we send data along with _____________ Parity bits Redandent bits Parity bits or Redundant bits None of the above HintIn hamming code, we send data along with parity bits or redundant bits64). The hamming code is used to _________ Detect errors Correct errors Detect and correct error None of the above HintThe hamming code is used to detect the error as well as correct the error65). The hamming code is represented by ________ (n, k) code (n, -k) code (-n, k) code None of the above HintThe hamming code is represented by (n, k) code where n represents total bits and k represents message bits66). What is the sampling principle of natural sampling? Sample and hold circuit Multiplication Chopping None of the above HintThe natural sampling works based on the principle of chopping67). 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 HintThe 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 word Channel capacity Code weight None of the above HintThe limitation of the capacity of the channel to transmit information is referred to as channel capacity69). The words belongs to a block code are called as _________ Code word Channel capacity Code weight None of the above HintThe words that belong to a block code are called a code word70). 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 HintThe entropy is defined as a ratio of total information by a number of messages, where entropy is denoted by E71). ________ is the intelligence or ideal or message in information theory Code word Channel capacity Code weight Information HintThe 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 signal Data rate Line coding Code weight Information HintLine coding is defined as the process of converting binary data to digital signal73). ____________ is defined as the number of pulses per second Data rate Pulse rate Bit rate Information rate HintThe pulse rate is defined as the number of pulses per second74). ____________ is defined as the number of bits per second Data rate Pulse rate Bit rate Information rate HintThe bit rate is defined as the number of bits per second75). 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 HintIn time-division multiplexing, the sampled pulse amplitude modulation is off for most of the time76). The speech signal range is from ______ 300Hz-3.4KHz 200Hz-3.4KHz 300Hz-3.9KHz None of the above HintThe speech signal range is from 300Hz-3.4KHz, the maximum frequency will be bandwidth that is 3.4kHz77). What is the sampling principle of ideal sampling? Sample and hold circuit Multiplication Chopping None of the above HintThe ideal sampling works based on the principle of multiplication78). The block code repeats the information bits ________ times One time only Two times only Two or more times None of the above HintThe block code repeats the information bits two or more than two times79). 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 HintThe 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 power80). The noise interference in ideal sampling is _______ High Very high Less Very less HintThe noise interference in ideal sampling is very high compared to natural sampling Time is Up! Time's up