UNIT I [ BEL-2007] [I.E.S-2007] [GATE-2014]

Transcription

1 UNIT I 1) In PCM, if the no. of quantization levels is increased from 4 to 64, then the band width requirement will approximately be increased---- times [ BEL-2007] [ ] A) 8 B) 16 C) 3 D)12 2) Pre emphasis circuit is used [ ] A) Noise in the channel B) repeaters in the channel C) limited band width of the channel D) Nonlinearity of the channel 3) The ultra high frequency (UHF) range extends from [ ] A) KHz B)3-30 KHz C) KHz D) KHz 4) The function of the input transducer in a communication system is [ ] A) To transmit the message signal B) to modulate the message signal C) To convert message sound signal into electrical signal D) none 5) Communication is the process of [ ] A) Keeping in touch B) broadcasting C) exchanging information D) none 6) PAM stands for [I.E.S-2007] [ ] A) Phase angle Modulation B) Phase amplitude Modulation C)Pulse amplitude Modulation D) Pulse angle Modulation 7) The communications medium causes the signal to be [ ] A) Amplified B) modulated C) attenuated D) interfered with 8) The process of transmitting two or more information signals simultaneously over the small channel is called [ ] A) Multiplexing B) telemetry C) detection D) modulation 9. Recovering information from a carrier is known as [ ] A) Demultiplexing B) modulation C) detection D) carrier recovery 10) Radio signals are made up of [ ] A) Voltages and current B) electric and magnetic fields C) Electrons and protons D) noise and data 11) Sampling Theorem finds applications in [ ] A) Amplitude Modulation B) Frequency Modulation C) PCM D) none 12) Indicate which of the following pulse modulation system is analog [ ] A) PCM B) differential PCM C) delta modulation D) None 13) In a PCM systems, the signal (t)={sin(100 πt+cos(100 πt))} is sampled at the Nyquist rate. The samples are processed by a uniform quantizer with step size 0.75V. The minimum data rate of the PCM system in bits per second is [GATE-2014] [ ] A) 200bps B)300bps C)400bps D)500bps 14) Quantizing noise can be reduced by increasing the number of samples per second. It is true A) Yes, it is B) no, it is not C) not necessarily D) none 15) In PCM a system, the quantization noise depends upon [ ] A) The number of quantization levels only B) the sampling rate only C) both D) none 16) The signal to quantization the noise ratio in PCM system depends upon [ ] A) Sampling rate B) number of quantization levels C) message signal band width D) none 17) Indicate which of the following systems is digital? [ ] A) pulse- position modulation B) pulse- code modulation C) pulse- width modulation D) pulse- frequency modulation 18) Quantizing noise occurs in [ ] A) time- division multiplex B) frequency- division multiplex

2 C) pulse- code modulation D) pulse- width modulation 19) A band-limited signal with a maximum frequency of 5 khz is to be sampled. According to the sampling theorem, the sampling frequency which is not valid is [ GATE-2013] [ ] A) 5 khz B)12 khz C) 15 khz D)20 khz 20) The biggest disadvantages of PCM [ ] A) Its inability to handle analog signals B) Its incompatibility with TDMC)The high error rate which is quantizing noise reduces D) The large bandwidth that is required for it 21) Pre emphasis is used to amplify [ ] A) Low frequencies B) High frequencies C)Both low and high D) none 22) The quantization noise is produced in [ ] A) All pulse modulation system B) PCM C) all modulation system D) none 23) One of the following systems is analog [ ] A) PCM B) delta C) differential PCM D) PAM 24) For an efficient communication in PCM system number of samples per second must at least Be equal to the highest modulating frequency. [ ] A) Twice B) Thrice C)a&b D) none 25) In PCM system output S/N increases with band width [ ] A) Linearly B) exponentially C) inversely D) none 26) A signal having uniformly distributed amplitude in the interval (-V to +V), is to be encoded using PCM with uniform quantization. The SNR is determined by the [GATE-1988 ] [ ] A)dynamic B)sampling C)number of quantizing levels D)power spectrum of signal 27) In a DM system, the granular noise occurs when the modulating signal [ ] A) increase rapidly B) remains constant C) decrease rapidly D) none 28) Quantization noise is produced in [ ] A) All pulse modulation system B) PCM C) all modulation system D) none 29) The main advantage of PCM signal is [ ] A) Lower bandwidth B) higher band width C) lower noise D) none 30) For transmission of normal speech signal the PCM channel needs a band width of [ ] A) 64 khz B) 8 khz C) 4 khz D) none 31) The minimum step-size required for a Delta-Modulation operating at 32K samples/sec to track the signal (here u(t) is the unit-step function) x(t)=125t{u(t) u(t 1)}+( t){u(t 1) u(t 2)} so that slope-overload is avoided would be [GATE-2006] [ ] A)2 10 B)2 8 C)2 6 D)2 4 32) The input to a linear DM having a step-size Δ=0.628 is a sine wave with frequency fm and peak amplitude Em. If the sampling frequency fs = 40 KHz, the combination of the sine-wave frequency and the peak amplitude, where slope overload will take place is Emfm [GATE-2003] [ ] A) 0.3 V 8 KHz B) 1.5 V 4 KHz C)1.5 V 3 KHz D)3.0 V 1 KHz 33) PCM system use non uniform quantization in order to [ ] A) Raise SNR for low level signals B) increase the maximum SNR C) Cut down the required band width of transmission 34) Granular noise is associated with [ ] A) PCM B) DPCM C) DM D) QAM 35) Signal to quantization noise ratio of a PCM system using 8-bit words for the analog signal that does not exceed its quantization boundary is [ ] A) 48 db B) 54 db C) 52.7dB D) 64 db 36) In PCM if the transmission path is very long [ ] A) Repeater stations are used B) pulse width may be increased C) Pulse amplitude is increased D) pulse spacing is reduced

3 37) In PCM the biggest disadvantage compared to analog modulation is [ ] A) Large bandwidth B) large noise C) inability to handle analog signals D) none 38) In an ADM system the output signal amplitudes for 1 s and 0 s are [ ] A) Fixed and repetition rate is also fixed B) fixed but the repetition rate is variable C) Variable and the repetition rates is also variable D) Variable but the repetition rate is fixed 39) In delta modulation, the slope overload distortion can be reduced by [GATE-2007] [ ] A) Decreasing the step size B) decreasing the granular noise C) decreasing the sampling noise D) Increasing the step size 40) For uniform quantization with 32 levels, the quantized output can be represented by n binary digits where n is [ ] A) 5 B) 8 C) 6 D) 4 Two Marks Questions: 1. What is meant by code word length? 2. State sampling theorem? 3. Define quantization? 4. Explain the importance of prediction in Differential pulse code modulation (DPCM)? 5. Discuss the noise effects in Delta Modulation? 6. Give the block diagram of DPCM? 7. Define multiplexing? 8. What is the transmission bandwidth of a PAM/TDM system? 9. What is meant by Nyquist rate? 10. Draw the block diagram of PCM scheme showing the elements required for the transmission? 11. Define pulse code modulation? 12. Discuss noise effects in PCM? 13. Explain Frequency Division Multiplexing? 14. Write any two differences between DM and DPCM? 15. What is meant by aliasing effect? 16. The signal to quantization noise ratio in a PCM system depends on which criteria? 17. What is the advantage of delta modulation over PCM? 18. What are the differences between ideal sampling and practical sampling? 19. What is meant by source encoder and decoder? 20. A) Define granular noise? B) Define slope overload distortion? Ten Marks Questions 1. A) Explain the DPCM system with neat diagram? B) What are the advantages disadvantages of DPCM? 2. A) Write the differences between PCM, DPCM, and DM? B) Explain ADPCM? 3. Explain the delta modulation with suitable diagram? 4. Explain slope overload distortion & granular noise? 5. A) Discuss the two major sources of quantizing error in DM systems? B) Draw and explain the block diagram of regenerative repeaters? 6. A) Derive the quantization noise in PCM? B) Derive the S/N ratio of PCM?

4 7. Explain the following line codes? A) Uni polar RZ&NRZ B) polar RZ&NRZ C)Manchester format D)polar quaternary 8. A) Draw and explain the block diagram of TDM system? B) What is meant by synchronization in TDM? 9. A) Draw the block diagram of digital communication system? Explain the each block? B) Write the advantages, disadvantages of digital communication? 10. A) Explain PCM transmitter and receiver? B) Write the advantages& disadvantaged in PCM? UNIT II 1) In a baseband communication link, frequencies up to 3500 Hz are used for, signaling. Using a raised cosine pulse with 75% excess bandwidth and for no inter-symbol interference, the maximum possible signaling rate in symbols per second is [GATE-2012] [ ] A)1750 B)2625 C)4000 D) ) The power spectral density of white Gaussian noise is [ ] A) N0/2 B) N0 C) 2/N0 D) 2 3) The shape of the impulse of a matched filter is similar to [ ] A) Input signal B) shape of output C) shape of square D) none 4) In matched filter erfc is a monatically.function [ ] A) Decreasing B) increasing C) equal D) none 5) The probability error of matched filter is does not depend upon [ ] A) Input signal B) shape of output C) shape of square D) shape of signal 6) Correlator is known as [ ] A) Correlates the received signal B) correlates the input signal C) A&B D) none 7) ISI means [ ] A) Inter symbol interference B) inter system interference C) Inter symbol inteferior D) All the above 8) The function which produces a zero ISI is called as.function [ ] A) Cosine B)sinc C) tan D) none 9) The process of sampling is called as [ ] A) Extraction B) interaction C) decoding D) encoding 10) The shape of the..pattern is shape of human eye [ ] A) Eye pattern B) eye symbol C) eye D) none 11) A Matched filter [ ] A) Minimizes the output S/N B) reduces the transmission energy requirement C) Minimizes the probability of error D) is unique for all signaling representations 12) For the digital data 1,0 represented as +V volts and - V volts respectively, which of the following can act as a Matched filter? [ ] A) Differentiator B) Integrator C) Sampling Circuit D) Bit synchronizer 13) An analog signal is band-limited to 4 KHz, sampled at the Nyquist rate and the samples levels are assumed to be independent and equally probable. If we transmit two quantized samples per second, the information rate [GATE-2011] [ ] A) 1 bit/sec B) 2 bits/sec. C) 3 bits/sec D) 4 bits/sec 14) Which of the following is a Causal system? [ ] A) Ideal LPF B) Matched filter C) Ideal BPF D) θ=0system with transfer function H(f) = 0 for 20KHz Q f Q 40KHz

5 15) A band limited signal is sampled at the Nyquist rate. The signal can be recovered by passing the samples through [ ] A) AN RC filter B)An envelope detector C)A PLL D) An ideal low-pass filter with the appropriate bandwidth 16) Nyquist's interval indicates [ ] A) The separation between the adjacent samples of the sampled signal B) Period of the sampling signal C) period of the base band signal D) Maximum separation between the adjacent samples of the sampled signal 17) Matched filter gives an impulse response which is [ ] A) zero for t>0 B) zero for t = 0 C) zero for t<0 D) None 18) A signal has frequency components from 300 Hz to 1.8 KHz. The minimum possible rate at which the signal has to be sampled is --- [GATE-1991] [ ] A) 360 samples/sec B) 3600 samples/sec C)36000 samples/sec D) 36 samples/sec 19) If the Nyquist's rate of a signal x (t) is fo, the Nyquists rate of its integral is [ ] A) fo B)fo/2 C) 2fo D)fo/4 20) The Nyquist interval for the signal x(t) =[ (Sin504t)/(4t) ] + [(Sin1004t)/(4t)]2 is A) 100/n sec B) n/200 sec C) n/100 sec D) 200/n An analog voltage in the range 0 to 8 V is divided in 16 equal intervals for conversion to 4-bit digital output. The maximum quantization error (in V) is [GATE-2014] [ ] A) 0.25V B) 0.025V C) 0.2V D)0.5V 22) If X(t) is a band limited signal with Nyquist`s rate of F0, then X(t).CosW0t is [ ] A) Band pass signal B) Band limited signal C) ofnyquist's rate 2F0 D) of band width Fo/2. 23) The impulse response of the filter matched to the input signal x(t)=u(t)-u(t-t) is A) x(t) B) x(-t) C) x(2t) D) 2.x(t) [ ] 24) When the noise is white Gaussian noise then optimum filter is called [ ] A) Gaussian filter B) matched filter C) white filter D) none 25) The S/N ratio of matched filter depends on [ ] A) 2E B) 2E/No C) No D) E 26) The channel B.W is equal to the B.W of message signal is called as [ ] A) Channel B) base band channel C) baseband D) none 27) The data transmission system which uses the base band channel is called as [ ] A) Pass band B) base band C) band D) none 28) The matched filter for rectangular pulse may be implemented using a circuit is called circuit A) Integrate B) Dump C) Integrate&Dump D) design [ ] 29) ISI will introduce errors in signal [ ] A) Transmitting B) Received signal C) detected D) none 30) The special value of bit rate Rb=2B0 is called [ ] A) Nyquist rate B)Nyquist interval C) Nyquist B.W D) ideal Nyquist channel 31) The special value of bit rate Rb=2B0, where B0 is called [ ] A) Nyquist rate B)Nyquist interval C) Nyquist B.W D) ideal Nyquist channe 32) The ideal base band transmission can be described by time or frequency domain is called [ ] A) Nyquist rate B)Nyquist interval C) Nyquist B.W D) ideal Nyquist channel l 33) In ideal channel the B0 is to bit rate [ ] A) Equal B) Half C) twice D) thrice 34) Base band M-ary PAM system requires bandwidth [ ] A) More B) less C) equal D) none

6 35) Base band M-ary PAM system requires power for their Pe [ ] A) More B) less C) equal D) none 36) Base band M-ary PAM system requires eye patterns [ ] A) (M+1) B) (M-1) C) M D) none 37)1.0 khz signal is sampled at the rate of 1.8 khz and the samples are applied to an ideal rectangular LPF with cut-off frequency of 1.1 khz, then the output of the filter contains [GATE-2015] [ ] A) T B )T-1 C)T+1 D) none 38) The height of eye opening defines [ ] A) Margin over noise B) Margin noise C) Margin under noise D) none 39) When the effect of ISI is severe the eye is completely [ ] A) Closed B) opened C) stacked D) none 40) When the effect of ISI is less the eye is completely [ ] A) Closed B) opened C) stacked D) none Two Marks Questions: 1. Explain the role of matched filter in baseband pulse transmission? 2. Give the Nyquist criterion for zero ISI? 3. How eye pattern obtained on the CRO? 4. List the effects of ISI? 5. What is meant by correlative coding? 6. How the raised cosine spectrum obtained in baseband transmission? 7. What is Nyquist Bandwidth? 8. Define ideal Nyquistchannel? 9. List the properties of matched filter? 10. What is the condition for zero intersymbol interference? 11. Explain baseband binary PAM system? 12. Write the drawbacks of binary PAM system? 13. Write the performance of data transmission system using eye pattern 14. Why intersymbol interference takes place in a channel? 15. Draw an illustrative figure to show the operation of a correlation receiver? 16. How to overcome the ISI problem? 17. Give 2 applications for eye pattern? 18. Define matched filter? 19. Explain the purpose of probability of error? 20. What is meant by intersymbol interference? Ten Marks Questions 1. A) State and prove the properties of matched filter? B) Show that the probability of bit error of matched filter receiver is given by 2. A) What do you understand by intersymbol interference? B) What are the factors responsible for it 3. A) Describe the baseband transmission of M-ary data. B) Give a brief explanation on modified duo binary signaling? 4. Derive the expression for the Nyquist criterion for distortion less baseband transmission in the absence of noise.?

7 5. Derive the mathematical expression for raised cosine spectrum.? 6. Derive the equation for probability error for a matched filter? 7. A) Give brief note on matched filter. B) Explain the rectangular pulse for a matched filter? 8. A polar NRZ waveform has to be received into the help of a matched filter. Here binary 1 is represented as a rectangular positive pulse. Also binary 0 is represented by a rectangular negative pulse.determine the impulse response of the matched filter. Also sketch it. 9. What is correlative coding? Explain its types 10. A) Explain the duo binary signaling scheme. B) Write a brief note on Eye pattern. UNIT III 1)The Auto-correlation function of White Noise is [ ] A) Impulse function B) Constant C) Sampling function D) Step function 2)A Binary communication system transmits equally likely 1's and 0's.A received '1' produces a voltage of 1V in the presence of Zero mean Gaussian noise with unity variance. A received '0' produces zero volts in the presence of same above noise. If the received signal is above the threshold, the decision is in favour of 1.The probability with which a transmitted 1 is received as 0 is [ ] A)Q(-0.5) B) Q(1) C) Q(-1) D) Q(0.5) 3)IfEb, the energy per bit of a Binary signal is 106 and the White noise PSD eta /2=105, then, the maximum output S/N in db is [ ] A) 13 B) 1 C) 20 D) 10 5)Noise with uniform PSD of N w/hz is passed through a filter with transfer function H(w)= 2.exp(-jwtD) followed by an ideal LPF with pass band over (0,B).The output [ ] Noise power in watts is A) 2NB B) 4NB C) 8NB D) 16NB 6)The probability density function of uniform noise extending from -1.5 v to +1.5 v is [ ] A) 1/3 B) 1/6 C) 2/3 D) 3/2 7)A modulation scheme with a densely packed constellation diagram is [ ] A) More energy efficient B) with more probability of error C) More power efficient D) with less probability of error 8)The noise in a communication channel is considered to be Gaussian random variable with mean=1 and variance = 3.The area enclosed by its pdf curve over (0,V) is [ ] A) 1 B) 2 C) 3 D) None 9)Zero mean, white Gaussian noise is passed through an Ideal LPF with pass band extending from - 5KHz to +5KHz. The output is zero at time t = [ ] A) 0.15sec B) 0.2sec C) 0.35 sec D) 0.55sec 10)The area enclosed by the density function of Gaussian Noise with mean=2 and variance of 5 is [ ] A) 2.5 B) 1 C) 3 D) 2 11) AWGN means [ ] A) Additive white Gaussian noise B) additive wheat Gaussian noise C) Additive white Gal noise D) none 12) Each multiplier is followed by a summer is called as [ ] A) Analyzer B) synthesizer C) vector D) all the above

8 13) A group of integrators is called as [ ] A) Analyzer B) synthesizer C) vector D) all the above 14) The vector s i is also called as. [ ] A) System B) signal C) noise D) none 15) N-dimensional Euclidean space is called the. [ ] A) Signal vector B) system vector C) signal space D) none 16) The squared length of ant signal vector Si is [ ] A) Dot product B) inner product C) above a&b D) none 17) The vectors si&sk are.to each other [ ] A) Parallel B) perpendicular C) orthogonal D) none 18) In gram-schmidt orthogonalization procedure if N=M the signals are.., [ ] A) Linear B) nonlinear C) periodic D) non periodic 19) In gram-schmidt orthogonalization procedure if N<M the signals are [ ] A) Linear B) nonlinear C) periodic D) non periodic 20) δij is [ ] A)kronecker delta B) delta C) Necker D) none 21) For the designing of optimum receiver representation is used [ ] A) Geometric B) metric C) graphical D) none 22) In gram procedure modulated wave is divided into [ ] A) Discrete time B) continuous time C) A&B D) none 23) In the representation of set of energy signals is [ ] A) M B) N C) S D) E 24) If N=M the signals are [ ] A)linear B)non linear C)a&b D) none 25) If N<M the signals are [ ] A)linear B)non linear C)a&b D) none 26) In correlates the vector X is called as [ ] A)observation vector B) observation element C) a&b D) none 27) In correlates the vector Xj is called as [ ] A)observation vector B) observation element C) a&b D) none 28) The set of message points corresponding to signals is called as [ ] A)signal B) signal constellation C)a&b D)none 29) The average probability error is give by [ ] A)Pe B)Pa C)Ep D)none 30) A Matched filter [ ] A) Minimizes the output S/N B) reduces the transmission energy requirement C) Minimizes the probability of error D) is unique for all signaling representations 31) In a particular digital communication system application, the receiver designed is an optimum coherent receiver, the channel noise is white and bits are transmitted using rectangular pulses then which of the following statements would be inconsistent [ ] A) A correlator receiver B) a matched filter receiver C) dump receiver D)none 32) Matched filter gives an impulse response which is [ ] A) zero for t>0 B) zero for t = 0 C) zero for t<0 D) None 33) A Matched filter [ ] A) Maximizes output S/N ratio and increases the bit error probability B) Minimizes output S/N ratio and increases the bit error probability C) Minimizes output S/N ratio and decreases the bit error probability D) Maximizes output S/N ratio and decreases the bit error probability

9 34)Which of the following statements is correct? [ ] A) Matched filter is a unique system that can be used for any signaling format. B) Impulse response of a Matched filter is zero for t< 0. C) The output S/N of a Matched filter is independent of i/p signal energy D) The impulse response of a matched filter is same as the input signal 35) For the digital data 1,0 represented as +V volts and - V volts respectively, which of the following can act as a Matched filter? [ ] A) Differentiator B) Integrator C) Sampling Circuit D) Bit synchronizer 36) Which of the following is a Causal system? [ ] A) Ideal LPF B) Matched filter C) Ideal BPF D)System with transfer function 37) The impulse response of the filter matched to the input signal x(t)=u(t)-u(t-t) is A) x(t) B) x(-t) C) x(2t) D) 2.x(t) [ ] 38) The combination of matched filter with envelope detector is called as [ ] A)non coherent matched filter B) coherent matched filter C)a&b D) none 39) The output of a matched filter is [ ] A)sine B) cosine C) rectangular D) none 40) the matched filter output when [ ] A)θ=0 B) θ=180 C)a&b D) none Two Marks Questions: 1. Define Gaussian noise? 2. What is geometric representation of signals? 3. What is AWGN channel? 4. What is signal vector? 5. Define synthesizer? 6. What is analyzer? 7. What are the different types of noises occur in digital communication? 8. Draw the block diagram of integrator? 9. What is matched receiver? 10. What is the condition for orthogonal? 11. Why is prefiltering done before sampling? 12. What is signal constellation diagram? 13. Why do we require equalization for a communication system 14. Give the concept of Basis Function in Digital communication. 15. Explain the term optimum in digital communication. 16. Explain the term correlators. 17. What is the application of Gram Schmittorthogonalization procedure? 18. What is the meaning of signal space representation? 19. Define signal space and basis function 20. Define signaling set. Ten Marks Questions: 1. Explain the geometric representation of signals? 2. Explain the gram-schmidt orthogonalization procedure? 3. Explain the concept of AWGN channel?

10 4. Explain with a neat diagrams and derivations prove that the correlation receiver and matched filters give the same result. 5. Explain the coherent detection noise of signals? 6. Explain the correlation receiver with neat diagram? 7. Explain the probability error in correlation receiver? 8. Write a brief note on signal constellation diagram. 9. Explain the optimum receiver with neat diagram? 10. Explain the probability error of optimum receiver. UNIT IV 1) In 8-PSK system, adjacent phasors differ by an angle given by( in degrees) [ ] A) n/4 B) n/8 C) n/2 D) n/6 2) A BPSK system is transmitting data at a rate of 1Mbps.The minimum B.W and the Baud rate of the above system is [ ] A)1MHz, 1Mbps B) 0.5MHz, 1Mbps C) 0.5MHz,0.5MbpsD) 1MHz, 0.5Mbps 3) Adjacent phasors in M-ary PSK system differ in Phase by [ ] A) n/m B) 2n/M C) M D) 2M 4) Orthogonal PSK means [ ] A) DPSK system B) Offset-QPSK C) Non-Offset D) 8-PSK system 5) The band width of BFSK is [ ] A) 4Fb B) 2Fb C)Fb D)None 6) The band width of BPSK is [ ] A) 4Fb B) 2Fb C)Fb D) None 7) The band width of DPSK is [ ] A) 4Fb B) 2Fb C)Fb D) None 8) The noise immunity of BFSK is [ ] A)High B) low C) higher than BPSK D) None 9)Quardrature multiplexing is [ ] A) High B) low C) higher than BPSK D) None 10) The noise immunity of DPSK is [ ] A)High B) low C) higher than BPSK D) None 11) Probability error of BFSK is [ ] A) High B) low C) higher than BPSK D) None 12) Probability error of BPSK is [ ] A) High B) low C) higher than BPSK D) None 13) Probability error of DPSK is [ ] A) High B) low C) higher than BPSK D) None 14) The variable characteristic of BFSK is [ ] A) Amplitude B) frequency C) phase D) None 15) The variable characteristic of BPSK is [ ] A) Amplitude B) frequency C) phase D) None 16) The variable characteristic of BASK is [ ] A) Amplitude B) frequency C) phase D) None 17) OOK means [ ] A)On off keying B) on on keying C) off off keying D) None 18) BASK is also called as [ ] A)On off keying B) on on keying C) off off keying D) None

11 19) Quadrature phase amplitude keying is also called as [ ] A) QAM B) QPM C) QPSK D)Mary 20) The minimum band width required for a BPSK signal is equal to [ ] A) Bit rate B) Baud rate C) signal bandwidth D) none 21) The following digital modulation techniques which have lowest bit error probability is[ ] A) 8PSK B)BPSK C)DPSK D)QPSK 22) The Band width efficiency of 8-PSK system is [ ] A) 2 B) 3 C) 4 D) 5 23) Error probability of FSK is [ ] A) B) C) D) None 24) Error probability of PSK is [ ] A) B) C) D) None 25) Error probability of QSK is [ ] A) B) C) D) None 26) Error probability of ASK is [ ] A) B) C) D) None 27)The Band width efficiency of 16 QAM systems is [ ] A) 4 B) 1 C) 2 D) 3 28) A digitally Modulated carrier in QPSK system is [ ] A)Energy Signal B) Power signal C) both energy and power signal D) Neither energy nor power signal 29) The advantage of Offset QPSK is [ ] A) Amplitude variations are less pronounced B) band width occupied is less C) Less transmitted power D) probability of error is less 30) The energy of the two possible signals in a BPSK system is [ ] A) AB B) AB2 C) A2Tb D)ATb 31) Non-coherent detection of FSK signal results in [ ] A) More band width occupancy B) more probability of error C) Energy efficiency than BPSK D) less probability of error 32) Baud rate for a BFSK system is [ ] A) Half of the bit rate B) twice the bit rate C) same as the bit rate D) one fourth the bit rate 33) The possible signal sets in which of the following systems are orthogonal [ ] A) PSK over (0,TB) B) PSK over (0,TB) C) DPSK over (0,2TB) D) QPSK over (0,TB) 34) Mathematical representation of ASK for 0 is [ ] A) B) C) π t D) π t 35)... is most effected by noise [ ] A) ASK B) PSK C) FSK D) DPSK 36) Quardrature multiplexing is [GATE-98] [ ] A) the same as FDM B) the same as TDM C) combination of FDM & TDM 37) For a given data rate, the bandwidth B P of a BPSK signal and the bandwidth B 0 of the OOK signal are realated as [ GATE-98] [ ] A) B P =B 0 /4 B) B P =B 0 /2 C) B P =B 0 D) B P =2B 0

12 38) The bit rate of a digital communication system is R kbits/s. The modulation used is 32-QAM. The minimum bandwidth required for ISI free transmission is [GATE-2013] [ ] A) R/10 Hz B) R/10 khz C) R/5 Hz D) R/5 khz 39) For a bit of 8kbps, the possible values of the transmitted frenquencies in a coherent binary FSK system are [GATE-2002] [ ] A)16-20 KHz B) KHz C) KHz D) KHz 40) The message bit sequence input to DPSK moulator is 1,1,0,0,1,1. The carrier phase during the reception of the first two message bits is π, π.the carrier phase for the remaining four message bits is [GATE-88] [ ] A) π, π,0, π B) 0,0, π, π C) π, π,0, 0 D) 0, π, π, π Two Marks Questions: 1. Why PSK always preferable over ASK in coherent detection? 2. Define coherent digital modulation technique? 3. Define ASK 4. What is meant by DPSK? 5. What is the difference between PSK and FSK? 6. What is the major advantage of coherent PSK over coherent ASK? 7. Highlight the major difference between a QPSK & MSK signal 8. List the advantages of Passband transmission 9. Bring out the difference between coherent & non coherent binary modulation scheme 10. Write the two differences between DPSK and BFSK? 11. Define non-coherent digital modulation technique? 12. Give a brief note on BPSK? 13. Explain the role of QPSK? 14. What are the two forms of synchronization required for the operation of coherent detector? 15. What is meant by offset QPSK 16. What is meant by Probability of error & Bit Error Rate 17. What does 8-QAM & 16-QAM means? 18. Write the two differences between QPSK and BPSK? 19. What are the advantages of M-ARY PSK over BPSK? 20. Explain the types of digital modulation techniques? Ten Marks Questions: 1. A) Explain the generation and detection of BPSK. B) Discuss in brief about Non-coherent detection of binary FSK 2. A) Compare all the digital modulation techniques. B) Derive the probability of error for a coherent QPSK system. 3. A) Explain with a neat diagrams M-ary PSK transmitter and receiver. B) What is the bandwidth of M-aryPSK? 4. A) Draw the block diagram of QASK transmitter and receiver and explain the operation. B) What is the bandwidth of M-ary QASK? 5. A) Explain the power spectrum of BPSK, BFSK? B) Bandwidth of BPSK, BFSK. 6. A) Explain the power spectrum of QPSK, DPSK? B) How will you differentiate binary PSK and MPSK, explain with block diagrams. 7. A) Explain the pass band transmission model with neat diagram? B) Compare pass band transmission with band pass transmission.

13 8. A) Explain the generation and detection of DPSK. B) Derive the probability of error for DPSK. 9. Draw the block diagram of QPSK transmitter & receiver and explain each block in detail. 10. A) Explain the generation and detection of BFSK B) Derive the probability of error for BFSK. UNIT V 1) Error control coding is a practical way to achieve.bit rate [ ] A) High B) low C) equal D) none 2) In error detection and correction adding extra bits is known as [ ] A) Parity bits B) error bits C) correction bits D) all the above 3) The coded words contain the bits [ ] A) Data B) check C) data and check D) none 4) The error correcting codes are [ ] A) Block B) convolution C) a& b D) none 5) In FEC the encoded data produces bit rate [ ] A) High B) low C) equal D) none 6) In ARQ additional channel is also called as [ ] A) Back B) feedback C) a&b D) none 7) The probability error of ARQ system is [ ] A) High B) small C) equal D) none 8) In block codes the extra bits are bits [ ] A) Parity B) redundant C) code D) None 9) The convolution codes require [ ] A) Register B) memory C) MUX D) none 10) The errors that occur in a random manner are error [ ] A) Random B) burst C) fire D) none 11) The alternative technique for correcting the burst errors are [ ] A) Interleaving B) inter mission C) a&b D) none 12) Source encoding in a data comunicatin system is done in order to [GATE-92] [ ] A) enhance the information transmission B) band pass filters and envelop rate detectors C) conserve the transmitted power D) discriminator detection 13) The distance between the two code words is distance [ ] A) Signal B) code C) hamming D) code rate 14) The ratio of message to transmit bits is called [ ] A) Code efficiency B) code C) signal D) code rate 15) Cyclic codes are codes [ ] A) Linear B) non linear C) signal D) none 16) The convolution codes are used to [ ] A) Detection B) correction C) A&B D) none 17) The encoding of convolution codes by using [ ] A) MUX B) DMUX C) shift register D) register 18) Convolution encoding is convolution [ ] A) Binary B) octal C) hex D) decimal 19) Code rate r [ ] A) B) C) k+n D) kn 20) The graphical representation of convolution encoding is [ ]

14 A) Code tree B) code trellis C) state diagram D) all the above 21) The compact graphical representation of convolution encoding is [ ] A) Code tree B) code trellis C) state diagram D) all the above 22) The decoding methods of convolution codes are [ ] A) Viterbi B) feedback C) sequential D) all the above 23) The path of the decoded signal with minimum metric is path [ ] A) Surveying B) surviving C) front D) back 24) The metric diversion effect is used for reducing the [ ] A) Memory B) registers C) A&B D) none 25) The minimum distance between the codes vectors is called [ ] A) free distance B) fire distance C) code distance D) none 26) The code dimension depends on [ ] A) n B) k C) L D) All the above 27)Parity check codes are applicable for no of errors [ ] A) Even B) odd C) no D) none 28) Code rate is given by [ ] A) B) C) D) 29) The hamming distance between code vectors & is [ ] A) 5 B) 4 C) 2 D) 3 30) To detect up to S errors/word the minimum distance required is [ ] A) B) t C) D) t 31) The channel encoder adds.. Bits to the original message [ ] A) Extra B) redundant C) parity D) all above 32) In ARQ system when an error is detected the decoder sends a [ ] A) NAK B) ACK C) request D) PAK 33) The code vector can be represented as [ ] A) X=(M C) B) X=MG C) both a&b D) none 34) The generator matrix is given as [ ] A) B) C) D) 35) The Viterbi algorithm operates on principle [ ] A) Like hood B) Lake hood C) A&B D) A&B 36) Check vector is given as [ ] A) C = MP B) C=MG C) botha&b D) none 37) Weight of the code vector [ ] A) 3 B) 4 C) 2 D) 5 38) Linear block codes are represented as [ ] A) (n,k,l) B) (n,l,k) C) (n,k) D) (k,n) 39) In tree diagram the graph move upward if the input is [ ] A) 0 B) 1 C) 2 D) 3 40) In ARQ system if no error is detected the decoder sends a [ ] A) NAK B) ACK C) request D) none Two Marks Questions: 1. Explain Interleaving. 2. Explain convolutional coding. 3. What is the use of syndromes explain syndrome decoding?

15 4. What are convolutional codes how they are different from block codes. 5. What is constraint length for convolutional encoders. 6. Explain Repetition codes. 7. Explain even and odd parity coding with suitable example? 8. Explain the encoder of (7,4) Hamming code with suitable diagram? 9. What are the types of error control methods? 10. How many coding techniques are used for transmission the digital data? 11. Define Parity & Parity check code. 12. Define the term Hamming distance in coding. 13. What is meant by code efficiency? 14. Write about code tree and trellis diagram for convolution encoder. 15. Define the term Constraint length (K) in convolutional code. 16. Define the term Metric in Viterbi Algorithm. 17. Define the term Surviving path in Viterbi Algorithm. 18. List the advantages of convolutional codes over block codes? 19. Give the relation between Euclidean distance and partition in trellis code modulation. 20. Define the following terms a) Codeword b) Minimum Distance c) code vectors d)hamming Distance Ten Marks Questions: 1. Construct a tree diagram, state diagram &trellies diagram for the input sequence and determine the output sequence. 2. A generator matrix for a (6, 3) block code is given below [ ] A) List all the code vectors B) Find out minimum distance & weight C) How many errors can be detected &corrected. 3. A) The generator polynomial of a (15,11) hamming code is defined by: g(x) = 1+X+X 2. Develop an encoder and syndrome calculator for this code, using a systematic form of the code. B) write short notes on Hamming codes and burst error codes 4. What are the types of parity check codes explain with neat diagrams and also their advantages and disadvantages 5. The parity check matrix for a (7, 4) block code is given below [ ] A) Find the generator matrix(g) B) List all the code vectors. 6. Draw and explain the block diagram of ARQ system in detail and write about various types of ARQ systems. 7. The Generator matrix(g) for a (7, 4) block code is given below [ ] A) Find the Parity check matrix(g) B) Find code vectors for any eight messages 8. A) Explain the concept of interleaving.

16 B) Discuss in brief about sequential decoding of convolutional codes. 9. A) What is FEC and explain in detail? B) Explain the matrix representation of linear block codes? 10. For a systematic (7, 4) linear block code the sub matrix P is given as P= [ ] Detect & correct the error using syndrome vector for the code vectors A) B)