BE(IV) Electronics The following is the format for the question paper in DC Please Note that THERE WILL BE NO CHANGE in the paper style.

Transcription

1 BE(IV) Electronics The following is the format for the question paper in DC Please Note that THERE WILL BE NO CHANGE in the paper style. Elective: Digital Communication Section I Maximum marks : 100 Q1 a) In a PCM system, Signal Bandwidth is 4 KHz, Channel bandwidth is 25KHz, and S max /N q is to be greater than Design the system (4) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with Differential Manchester encoding. ii) How is signalling information incorporated in T1?. iii) State the rule for identifying stuffed bits in the M 12 output. iv) How does HDB3 encoding deal with long strings? v) Give the function of the discriminator in a channel vocoder. vi) Give the block diagram (only) of the regenerative repeater vii) For which of the following waveforms will you always observe slope overload in a linear delta modulator output? 1) Sine wave 2) Ramp waveform 3) Piecewise linear periodic waveform 4) Square wave 5) DC input starting at t = 0 viii) Which has greater probability of error: BPSK or QPSK? Why? (12) Q2 a) Explain how the duo-binary encoders attenuate sidelobes of the signal power spectrum (9) b) Explain principle of the early-late gate Bit synchroniser (8) Contd.

2 2 Q2 a) Describe the continuously variable slope δ modulator (CVSDM) (8) b) Explain OQPSK generation. Using signal space concepts, discuss its error probability (9) Q3 a) Compare MPSK and MFSK for same value of M. (8) b) Discuss the use of the Eye-Patterns (9) Q3 a) Explain why MSK output has a continuous phase. (9) b) Discuss QASK generation. (8) Section II Q4 a) Give the functions of the network independent layers in the ISO-OSI model (4) b) Answer any SIX (with figure and/or two or three sentences each) i) What is the topology in a walkie-talkie conference between two umpires and an ICC observer? ii) iii) iv) What is the difference between FDMA and CDMA? What is the difference between error control at the data-link and error control at the transport layers? If the CRC divisor has 16 bits, what is the length of the frame check sequence (FCS) appended to the frame? v) In sliding window protocol using 3 bit frame numbering, what is the largest number of frames which can be transmitted without receiving ACK? vi) vii) Give the fundamental difference between CSMA and ALOHA. What are piggy-backed acknowledgements?. viii) What kind of networks are 802.3, and 802.5? (12) Contd

3 3 Q5 a) Write a note on the Weiner filter (9) b) Explain the different ARQ mechanisms for error control (8) Q5 a) Write a note on the Token ring LAN. What physical layer precaution is taken to prevent breaking of the ring? How is priority managed?(9) b) What is the difference between bit and character oriented data link protocols? Give examples of each. Discuss briefly the HDLC frame types. (8) Q6 a) Explain the addressing system and DNS service in the Internet.. (8) b) Distinguish between virtual circuits and datagrams. Which layer of the Internet uses virtual circuits and which uses datagrams? Name and briefly give the descriptions of the highest level protocols in the Internet (9) Q6 a) Explain differences between bridge, router and gateway. Give a neat sketch illustrating where each is used. (9) b) Briefly discuss ISDN services and architectural components (8) -- END -- Contd

4 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA First Semester of BE III (Comp. Sc.) examination 2008 Wednesday, 9 th April, 3 PM to 6 PM Analog & Digital Communications Notes: -. (1) Answer the two sections in separate answer books. (2) Symbols & notations carry their usual meanings unless otherwise specified. (3) You may assume additional data if required, giving proper justification. Maximum Marks: 100 SECTION I Q1 [16] (a) Draw the diagram of a standard PCM transmitter and explain the individual blocks. How can PPM be derived from PWM? Explain their significance. (b) Explain the protocol which is used for long distance ( > 1000 ft) communication having multiple transmitters and receivers connected to the bus. (c) If the input signal is digitized using A/D converter, how will you decide the sampling frequency and sample time and hold time of the S & H block? (d) By what technique the data rate may be made greater than the bandwidth offered by the medium? Explain with an example. Q2 [9] (a) An 8 bit successive approximation converter has a clock of 100 KHz. Explain its operation and find its conversion time.(draw the diagram) If V R = 5 V, find its resolution and full scale voltage. (a) A 4-bit DAC has V R = 5V and digital input is Find Vo and the corresponding node voltages.what are the reasons for inaccuracies in this converter? Q2 (b) (b) [8] Explain the CRC-4 technique with an assumed message polynomial and draw the diagram to generate it. Explain HRC-VRC with 5 bytes of assumed data block. Q3 (a) Solve any three: [9] i. Explain the functions of the transport layer and data link layer in the OSI model showing their place in it. ii. Draw the ISDN frame and explain it. iii. What is meant by Random ALOHA and Slotted ALOHA? Which will have less data loss? Why? iv. Draw the diagram for RZ and Manchester coding. Explain the coding and state why they are preferred over NRZ. v. Draw the diagram of the interfaces in cellular communications within different systems. Page 1 of 2

5 Q3 (b) State if True or False and justify (any four): [8] i. Reducing the cell size affects the hand off ii. At least 4 satellites are required to cover the earth. iii. CDMA has better reception quality as compared with GSM. iv. Subscriber location to local exchange the multiplexing technique used is FDM. v. Packet switching is more efficient than message switching. SECTION II Q4 (a) Explain the working principle of an envelope detector and show how diagonal peak clipping occurs. [8] (b) Derive the equation which shows power obtained in various components of an AM wave. In the same context explain merits and demerits of DSB-FC [8] Q4 (a) Explain the third method of SSB generation. Discuss its advantages and disadvantages. [8] (b) Draw the circuit diagram of the Foster-Seely discriminator and explain how an FM wave is detected using this circuit. [8] Q5 (a) Give block diagram for the generation and demodulation of a BPSK signal [8] (b) Compare Amplitude Modulation and Frequency Modulation [8] Q5 a) Describe various characteristics of a medium. What are the advantages of optical fiber? [8] b) Show how Phase Modulation can be generated using Frequency Modulation [8] Q6 a) A carrier frequency of 25 MHz and amplitude of 4 V is frequency modulated by a sinusoidal modulating signal of frequency 400 Hz. The maximum deviation is 10 KHz. Write the equation of the FM wave. [6] b) Explain the working principle of double balanced Ring modulator. [6] c) Explain ON-OFF Keying. Show that for modems using ASK technique the theoretical maximum speed is 1500 bps with full duplex mode of operation [6] Page 2 of 2

6 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) examination 2000 Thursday,11 th May 3 PM to 6 PM Elective: Digital Communication (NC) N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Section I Q1 a) In a PCM system, Signal Bandwidth is 4 KHz, Channel bandwidth is 25KHz, and S max /N q is to be greater than Design the system (4) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with Differential Manchester encoding. ii) How is signalling information incorporated in T1?. iii) State the rule for identifying stuffed bits in the M 12 output. iv) How does HDB3 encoding deal with long strings? v) Give the function of the discriminator in a channel vocoder. vi) Give the block diagram (only) of the regenerative repeater vii) For which of the following waveforms will you always observe slope overload in a linear delta modulator output? 1) Sine wave 2) Ramp waveform 3) Piecewise linear periodic waveform 4) Square wave 5) DC input starting at t = 0 viii) Which has greater probability of error: BPSK or QPSK? Why? (12) Q2 a) Explain how the duo-binary and Tamed FM encoders attenuate sidelobes of the signal power spectrum (9) b) Explain how the predictor in DPCM reduces the quantization noise power, and define predictor gain (8) Contd.

7 2 Contd

8 3 Q2 a) Describe the continuously variable slope δ modulator (CVSDM) (8) b) Explain OQPSK generation. Using signal space concepts, discuss its error probability (9) Q3 a) Compare MPSK and MFSK for same value of M. (8) b) Discuss the use of the Eye-Patterns (9) Q3 a) Explain why MSK output has a continuous phase. (9) b) Discuss the Integrate and dump receiver and show that it is a matched filter for rectangular pulse signals. (8) Section II Q4 a) What are the properties of the PN sequences used in Spread spectrum modulation? (4) b) Answer any SIX (with figure and/or two or three sentences each) i) What is the bandwidth of the FH/MFSK transmission during a given chip time? ii) iii) iv) What is the difference between slow and fast hopping spread spectrum What is the difference between error control at the data-link and error control at the transport layers? If the CRC divisor has 16 bits, what is the length of the frame check sequence (FCS) appended to the frame? v) In sliding window protocol using 3 bit frame numbering, what is the largest number of frames which can be transmitted without receiving ACK? vi) vii) Give the fundamental difference between CSMA and ALOHA. What are piggy-backed acknowledgements?. viii) What kind of networks are 802.3, and 802.5? (12) Contd

9 4 Q5 a) Explain the Fast FH Spread spectrum system. What are its advantages and disadvantages as compared with Slow FH and DS spread spectrum? (9) b) Explain the different ARQ mechanisms for error control (8) Q5 a) Write a note on the Token ring LAN. What physical layer precaution is taken to prevent breaking of the ring? How is priority managed?(9) b) What is the difference between bit and character oriented data link protocols? Give examples of each. Discuss briefly the HDLC frame types. (8) Q6 a) Explain the addressing system and DNS service in the Internet.. (8) b) Distinguish between virtual circuits and datagrams. Which layer of the Internet uses virtual circuits and which uses datagrams? Name and briefly give the functions of the highest level protocols in the Internet (9) Q6 a) Explain differences between bridge, router and gateway. Give a neat sketch illustrating where each is used. (9) b) Briefly discuss ISDN services and architectural components (8) -- END -- Contd

10 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) examination 2001 Saturday, 12 th May 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Section I Q1 a) A signal bandlimited to 3000 Hz. is sampled at 8000 samples/sec. A binary PCM signal is to be generated from the samples. If S/N q is required to be > 40 db, find minimum number of bits required per word and S/N q achieved. (4) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with B8ZS encoding. ii) If the T1 PCM word is , where is the companded sample value located (Quadrant, segment, level)? iii) Give (only) the frame format for the M12 multiplexer showing the locations of various control bits. iv) Give Block diagram for the QPSK transmitter. v) What is the difference between voiced and unvoiced speech sound? vi) Why is AQB (Backward adaptive quantization) preferred over AQF(Forward adaptive quantization) in ADPCM? vii) Name and sketch examples of the types of errors in linear delta modulation. viii) Which has greater error probability BFSK or MFSK? Why? (12) Q2 a) Derive the expression for the compressor characteristic for an ideal robust compander. (9) b) Write a note on the channel vocoder (8) Q2 a) Discuss the Early-Late gate synchroniser. (8) b) Give the block diagram of the duobinary system and Derive the transfer function of the duo-binary filter. Prove the decoding action of the duobinary receiver by giving appropriate truth tables / voltage levels. (9) Contd.

11 2 Q3 a) Describe the QASK system and comment on its probability of error (8) b) Show that MSK is similar to BFSK and also to BPSK with help of derivations.(9) Q3 a) Discuss DPSK/ DEPSK transmission and reception - (9) b) ) In the signal constellation given below, S1 to S8 represent the signal points. determine (i)average symbol energy E s (ii)set of signals which have the minimum error probability (iii) Set of signals which have maximum error probability (iv)the expression for error probability for each set (v) Overall approximate P e for the system. (Do not evaluate error functions) (8) signal Constellation u2 S2 S S5 S S7 S8 S3-2 S4-3 u1 Section II Q4 a) Briefly describe the features of Asynchronous transmission. (4) b) Answer any SIX (with figure and/or two or three sentences each) i) What are the functions of the session layer? ii) iii) iv) Sketch the impulse response of a matched filter designed to receive a manchester encoded signal Give diagram of a structure for implementing a predictor of order N. Give the structures of the token and the data frames. v) Give an example situation in which the ENQ character is used in BiSynch vi) What is the function of the NT2 unit in ISDN?. vii) How can we identify class A, B or C internet addresses? viii) State the difference between a bridge and a repeater (12) Contd

12 3 Q5 a) Discuss the sliding window protocol. (9) Q5 b) Describe operation of the time slot interchange switch. (8) a) Describe medium access protocols suitable for use in i) Satellite linked network for Andaman islands administration and ii) wireless broadcast based MAN connecting university faculties at different locations within a city (9) b) Discuss priority management and functions of the monitor node in a token ring LAN.(8) Q6 a) Discuss the structure of the IP header and give the functions of various fields. (8) b) Describe typical layered structure of a TCP/IP network. Which protocol in the transport layer uses datagrams? Why? What is fragmentation and how is it controlled? Which internet protocol in transport layer uses virtual circuits? (9) Q6 a) Write notes on Weiner filter. (8) b) Give diagrams illustrating the exchange of frames in HDLC for the following cases, indicate type of frame and other relevant information.: i) Link set-up and disconnect ii) Two-way data exchange iii) Error recovery (9) -- END -- Contd

13 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination 2001 Wednesday, 7 th November 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Section I Q1 a) Describe the structure of the T1 frame. How is signalling information included and synchronising performed in T1 frames? (4) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with Manchester encoding. ii) Give the function of the M bits in M 12 multiplexer. iii) What does complete closure of the eye in an eye pattern indicate? iv) Give the function of the discriminator in a channel vocoder. v) State the rule for identifying stuffed bits in the M 12 output vi) Give block diagrams explaining the principle of AQB (Backward adaptive quantization) and AQF(Forward adaptive quantization) in ADPCM. vii) How does HDB3 waveform encoding eliminate long strings of 1 s? viii) Which has greater error probability: BFSK or BPSK? Why? (12) Q2 a) Write a note on DPCM. (8) b) Describe the Adaptive δ modulator (ADM) (9) Q2 a) Give a typical eye pattern and explain what information is conveyed by it. (8) b) Write a note on the adaptive vocoder. (9) Q3 a) Describe the BFSK system and comment on its probability of error (9) b) Give the block diagram of the MSK transmitter, and state without proof the major features of this system. What are its advantages? Where is it used? (8) Contd.

14 2 Q3 a) Discuss QASK transmission and reception - (9) b) ) From the signal constellation given below, determine (Do not evaluate error functions) 1. Average symbol energy E s 2. Sets of signals which have the same error probability 3. The error probability for each set 4. Overall approximate P e for the system. S1 to S8 represent the signal points (8) signal Constellation S4 S3 u2 2 S2 S u1-1 S5 S6-2 S7 S84 Section II Q4 a) Differentiate between Synchronous and Asynchronous transmission. (4) b) Answer any SIX (with figure and/or two or three sentences each) i) What are the functions of the data link layer? ii) iii) iv) Sketch the impulse response of a matched filter designed to receive a rectangular pulse NRZ encoded signal Give diagram of a structure for implementing a predictor of order N. Give the structures of the token and the data frames. v) Give an example of call establishment frame exchange in BiSynch vi) vii) What is the difference between B and D channels in ISDN? Give the Internet address formats for different sizes of networks? viii) State the difference between a bridge and a router (12) Q5 a) Explain difference between Go Back N and Selective Repeat ARQ. (9) Contd

15 3 b) Describe operation of the Time Division Multiplexed switch for circuit switching. (8) Q5 a) Write a note on CSMA (9) b) Discuss the main features of token bus networks following IEEE specifications.(8) Q6 a) Write a note on the IP header (8) b) State and briefly describe the major application layer protocols which use TCP/IP in the Internet. What is the DNS service? (9) Q6 a) Discuss Tapped Delay line adaptive filters. (8) b) Write a note on HDLC (9) -- END -- Contd

16 Slip No: 02 Exam Seat No: SECTION - II Q-4 (a) Write a note on (i) message switching, (ii) virtual circuits and datagrams. (b) Explain why multi-stage switching is preferred in circuit switching giving an example of a three stage switch. What is blocking? What is the condition for the switch in your example to be non-blocking? Q-4 (a) Explain the difference between (i) asynchronous and synchronous transmission and (ii) Stop & wait and Go Back N ARQ. (b) With the help of a neat diagram explain the operation of a TDMA switch. Q-5 (a) Give the functions of the layers in the ISO-OSI protocol stack. (b) What are the necessary properties of a CRC polynomial? A received bit stream is checked by CRC divisor Has there been an error? Q-5 (a) With the help of neat frame exchange diagrams explain how the following actions are performed by the BISYNCH point to point network:(i) link establishment / rejection (ii) Error-free data transfer (iii) error correction and (iv) Link termination. (b) Briefly discuss persistent and non-persistent CSMA methods of medium access control Q-6 (a) Explain the selective repeat ARQ. (b) Answer any four : i. Explain why CSMA is not used by satellite networks. ii. State the Bisynch command and response words and briefly give the function of each. iii. Explain the differences between error correction in the data link layer and th in transport layer. iv. Discuss advantages and disadvantages of flooding. v. What is the difference between TCP/IP network architecture and the ISO- OSI architecture? [8] [8] [8] [8] [8] [8] [8] [8] [6] [12]

17 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination 2002 Friday, 17 th May 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Section I Q1 a) A baseband signal bandlimited to 3.4 KHz is sampled at 8 KHz. Design a PCM system for S/N q 40 db (6) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with Dibit (Polar Quaternary) encoding. ii) Give the structure of the M 12 multiplexer frame. iii) Sketch a typical eye pattern and indicate on it features which convey information about the quality of the transmission? iv) Give the block diagram of the receiver section of a channel vocoder. v) State how signaling information is included in T1 bit streams. vi) By how many dbs does the S/N q ratio change if the PCM word length is reduced by 2 bits?. vii) Give the advantages and disadvantages of Manchester encoding. viii) Which has greater error probability: MFSK or MPSK? Why? (12) Q2 a) Derive the expression for the S/N q ration in δ Modulation (DM). (9) b) Describe the operation of transmitter section of the channel vocoder with the help of a block diagram, and explain the functions of each block(8) Q2 a) Explain the operation of the Adaptive δ modulator (ADM) with block diagrams and waveforms (9) b) Define Predictor Gain in DPCM and describe the method of reducing quantization noise power. (8) Q3 Answer any three (15) a) Discuss the integrate and dump receiver b) Explain the blocks and their functions in the BPSK receiver. c) Compare BPSK and BFSK Page 1 of 2

18 d) Describe QPSK transmitter with block diagram and waveforms e) Discuss MPSK system 2 Section II Q4 a) Differentiate between Synchronous and Asynchronous transmission. (4) b) Answer any SIX (with figure and/or two or three sentences each) i) State the properties of Ortho-normal functions. ii) iii) iv) Give a circuit diagram of a matched filter for receiving a RF pulse Distinguish between a Stop and wait and Go Back N ARQ. Give the block diagram for a Weiner Filter and give the Weiner-Hopf equations. v) What is flooding? When is it used? vi) vii) Give the properties of PseudoNoise (i.e. PRBS) sequences. State the differences between DS and FH Spread spectrum viii) State the functions of the Session layer (12) Q5 a) Derive the expression for the impulse response of the matched filter (9) b) Distinguish between Packet switching and Circuit switching (8) Q5 a) What is the processing gain in DS spread spectrum? Derive. (9) b).explain the Union Bound approximation giving suitable examples of its use. (8) Q6 a) Compare and contrast i) LAN and WAN, ii) LAN and LAN (8) b) Briefly describe the various routing strategies used in packet switched networks (9) Q6 a) The following signal space locations represent the constellation of possible signals in a digital transmission. All signals are equi-probable. Find the average probability of error for the system expressed in terms of error function / complementary error function. The signal points are: (1,0), (1,1),(0,1),(-1,1),(-1,0),(-1,-1),(0,-1)and (1,-1) (8) b) Give the functions of the different layers in the ISO-OSI model (9) - - END -- Page 2 of 2

19 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination 2002 Friday, 17 th May 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Section I Q1 a) A baseband signal bandlimited to 3.4 KHz is sampled at 8 KHz. Design a PCM system for S/N q 40 db (6) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with Dibit (Polar Quaternary) encoding. ii) Give the structure of the M 12 multiplexer frame. iii) Sketch a typical eye pattern and indicate on it features which convey information about the quality of the transmission? iv) Give the block diagram of the receiver section of a channel vocoder. v) State how signaling information is included in T1 bit streams. vi) By how many dbs does the S/N q ratio change if the PCM word length is reduced by 2 bits?. vii) Give the advantages and disadvantages of Manchester encoding. viii) Which has greater error probability: MFSK or MPSK? Why? (12) Q2 a) Derive the expression for the S/N q ration in δ Modulation (DM). (9) b) Describe the operation of transmitter section of the channel vocoder with the help of a block diagram, and explain the functions of each block(8) Q2 a) Explain the operation of the Adaptive δ modulator (ADM) with block diagrams and waveforms (9) b) Define Predictor Gain in DPCM and describe the method of reducing quantization noise power. (8) Q3 Answer any three (15) a) Discuss the integrate and dump receiver b) Explain the blocks and their functions in the BPSK receiver. c) Compare BPSK and BFSK Page 1 of 2

20 d) Describe QPSK transmitter with block diagram and waveforms e) Discuss MPSK system 2 Section II Q4 a) Differentiate between Synchronous and Asynchronous transmission. (4) b) Answer any SIX (with figure and/or two or three sentences each) i) State the properties of Ortho-normal functions. ii) iii) iv) Give a circuit diagram of a matched filter for receiving a RF pulse Distinguish between a Stop and wait and Go Back N ARQ. Give the block diagram for a Weiner Filter and give the Weiner-Hopf equations. v) What is flooding? When is it used? vi) vii) Give the properties of PseudoNoise (i.e. PRBS) sequences. State the differences between DS and FH Spread spectrum viii) State the functions of the Session layer (12) Q5 a) Derive the expression for the impulse response of the matched filter (9) b) Distinguish between Packet switching and Circuit switching (8) Q5 a) What is the processing gain in DS spread spectrum? Derive. (9) b).explain the Union Bound approximation giving suitable examples of its use. (8) Q6 a) Compare and contrast i) LAN and WAN, ii) LAN and LAN (8) b) Briefly describe the various routing strategies used in packet switched networks (9) Q6 a) The following signal space locations represent the constellation of possible signals in a digital transmission. All signals are equi-probable. Find the average probability of error for the system expressed in terms of error function / complementary error function. The signal points are: (1,0), (1,1),(0,1),(-1,1),(-1,0),(-1,-1),(0,-1)and (1,-1) (8) b) Give the functions of the different layers in the ISO-OSI model (9) - - END -- Page 2 of 2

21 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Saturday, 3 rd May Second Semester of BE IV (Electronics) Examination 2003 Elective: Digital Communication 3 PM to 6 PM N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Section I Q1 Q2 a) A speech signal has a total duration of 10 seconds. It is sampled at the rate of 8 KHz and encoded. The signal to quantization noise ratio is required to be 40 db. Calculate the minimum storage capacity needed to store the digitized speech signal. (6) b) Answer any six : (with figures or in two or three sentences each) i) Sketch the I/O characteristics of Mid-rise and Mid-tread uniform quantizers. ii) If a 128 level uniform quantizer has a signal to quantization noise ratio of 43.8 db, what will be the S/N Q ratio for a 32 level uniform quantizer? iii) How is Signaling information carried in T1 bit streams? iv) Give the function of the C bits in M12 multiplexer output. v) Give the eye diagram for perfect transmission of NRZ - Unipolar encoded bits over an infinite bandwidth noise free channel. vi) Give the commonly used value of A and equation of A-Law compander. vii) Represent using HDB3 code viii) Error probability of BFSK is same as that of 4FSK. True or False? Justify (12) a) Give the property of a robust Ideal compander and obtain the equation of its compressor. (8) b) Explain the similarities and differences between Delta modulation and DPCM(8) Q2 a) A linear Delta modulator is designed to operate with speech signals limited to 3.4 KHz. Sampling rate is 10 Nyquist frequency and step size is 100 mv. Determine the maximum amplitude of a 1 KHz test signal which will avoid slope overload. Derive the equations you have used. (8) b) Prove that overall frequency response of the Duobinary encoder is a half cycle Cosine function. (8) Page 1 of 2

22 2 Q3 Answer any two: (8+8) i) Comment on the Error probability of MPSK and compare it with MFSK ii) Explain π/4 -shifted QPSK iii) Describe the MSK transmitter. iv) Discuss the transmitting section of the Channel Vocoder. Section II Q4 a) Give the advantages and disadvantages of packet switching. (6) b) Answer any six: (with figure and/or two or three sentences each) i) Input SNR into a DS-SS receiver is 20 db and each bit duration is chipped into 4 chips. What is output SNR? ii) Sketch the block diagram of synchronizer for acquisition of DS-SS iii) Name and give the equations which yield coefficients of the Weiner Filter. iv) Define Slow and Fast FH-SS in terms of symbol rate and hop rate. v) What are the advantages and disadvantages of Flooding? vi) List differences between Pseudo-Noise sequences and pure noise sequences. vii) Carrier sensing was not feasible in ALOHA. Why? viii) What are the functions of the Transport Layer? (12) Q5 a) Comment on Adaptive Quantization and Adaptive Prediction. How are these used in ADPCM? (8) b) Write a note on Ethernet. (8) Q5 a) Show that Processing Gain in DS-SS is given by T b / T C (8) b) Distinguish between i) Asynchronous and Synchronous transmission ii) Connection Oriented and Connectionless transmission (8) Q6 a) Explain the Sliding Window flow control. (8) b) Comment on HDLC frame types and Control word formats. (8) Q6 a) Describe the CSMA methods, and list the steps used in each method. (8) b) What technique is used to reduce the number of switch-points in Circuit switched networks? What is the associated disadvantage? (8) -- END -- Page 2 of 2

23 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination 2003 Wednesday, 7 th November 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Q1 Section I a) How is signaling information included and synchronizing performed in T1 frames? (4) b) Answer any six (with figures or in two or three sentences each) i) Sketch the waveforms for the bit-stream with Manchester encoding. ii) Give the function of the M bits in M 12 multiplexer. iii) What does complete closure of the eye in an eye pattern indicate? iv) Give the function of the discriminator in a channel vocoder. v) State the rule for identifying stuffed bits in the M 12 output vi) Give block diagrams showing AQB (Backward adaptive quantization) and AQF (Forward adaptive quantization) in ADPCM. vii) How does HDB3 waveform encoding eliminate long strings of 1 s? viii) Which has greater error probability: BFSK or BPSK? Why? (12) Q2 a) Briefly discuss the signal to quantization noise ratio in PCM. (8) b) Describe the Adaptive δ modulator (ADM) (9) Q2 Q3 a) Give a block diagram and working of a delta modulator and explain what is slope overload. (8) b) Write a note on Duobinary encoding. (9) a) Give block diagrams and explain working of a BPSK transmitter. Comment on its probability of error (9) b) Give the block diagram of the QASK transmitter, and state without proof the major features of this system and explain its working. (8) Q3 a) Discuss MPSK transmission and reception - (9) b) Explain the use of the eye diagram in analysis of performance (8) Contd.

24 2 Section II Q4 a) What are main features of Synchronous transmission? (4) b) Answer any SIX (with figure and/or two or three sentences each) 1. What are the functions of the physical layer? 2. List differences between Pseudo-Noise sequences and pure noise sequences. 3. What is the difference between MPSK and MFSK? 4. Name the ISO-OSI model layers. 5. Give the difference between datagram and virtual circuit. 6. What are the advantages of circuit switching? 7. List differences between WAN and LAN? 8. Define processing gain in a spread spectrum system. (12) Q5 a) Discuss generation of DS spread spectrum and give its advantages. (9) b) Describe slotted ALOHA system for accessing shared media. (8) Q5 a) Write a note on CSMA (8) b) Discuss the main features of HDLC. (9) Q6 a) State the Wiener-Hopf equations and discuss their application to adaptive filtering (9) b) Briefly describe IP address formats. What is the DNS service? (8) Q6 a) Briefly discuss various routing methods. (8) b) Write a note on ARQ error correction methods (9) -- END --

25 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Saturday, 8th May Second Semester of BE IV (Electronics) Examination 2004 Elective: Digital Communication 3 PM to 6 PM N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks: 100 Section I Q1 Q2 a) A sinusoidal signal is given by the expression s(t) = 3 cos (100πt). (i)find the signal quantization noise ration when this signal is quantized using 10 bit PCM, Also find (ii) the minimum number of bits required to achieve a signal to noise ratio of at least 40 db (6) b) Answer any six : (with figures or in two or three sentences each) i) Why is bit stuffing required in digital multiplexers? ii) Which has a higher transmission rate 16 PSK or 4 PSK? Why? iii) Bandwidth compression is realized in QPSK as compared to BPSK. Justify iv) Sketch the waveform for with dibit (polar quaternary) encoding. v) Give an example of antipodal signals and show their representation on signal space diagram. vi) Give the block diagram only of receiver section of a channel vocoder. vii) How does an adaptive equalizer work? viii) Sketch the output of a tapped delay line filter when its input is a narrow pulse. (12) a) Discuss the linear filter which maximizes SNR and minimizes Pe. How does it differ from a matched filter? (8) b) Find the duo-binary encoded signal for the data sequence (8) Q2 a) Describe the characteristics of the raised cosine filter. How does it help in achieving zero ISI? (8) b) Discuss the limitations of delta modulation in detail and suggest the remedy. (8) Q3 a) Compare MPSK and MFSK for the same value of M (8) b) Explain the terms (i) Idle channel noise and (ii) Tamed FM (8) Page 1 of 2

26 Q3 a) Describe the QASK system and comment on its probability of error. (8) b) Describe various considerations for selecting a particular waveform encoding scheme. Why is Bipolar format most widely used? (8) Section II Q4 a) Give the advantages and disadvantages of circuit switching. (6) b) Answer any six: (with figure and/or two or three sentences each) i) Does a TDM switch allow two pairs of users to be connected at the same instant of time? Justify. ii) What is common channel signaling? iii) What is a virtual circuit? iv) Give the structure of the Bi-Synch supervisory frame. v) Give the reason for the Time To Live (TTL) field in the IP header. vi) Why is it preferable to number the frames as 0 and 1 in stop and wait ARQ? vii) When is CSMA called 1-persistent? viii) Sketch a typical ISDN setup (12) Q5 a) Why is the sliding window protocol so called? Explain with the help of a suitable figure. (8) b) Describe the uses of the unnumbered frames and supervisory frames in HDLC. Give an annotated figure to illustrate HDLC frame exchanges to communicate a busy condition (8) Q5 a) Write a note on the token bus LAN (8) b) Discuss properties of pseudo-noise (PN) sequences with reference to DS-spread spectrum (8) Q6 Write Notes on any TWO of the following a) Aloha and Slotted Aloha b) Go-Back N (GBN) and Selective Repeat (SR) error control c) Fast Hop and Slow Hop FH-spread spectrum d) IP Address categories and DNS domain classification (16) -- END -- Page 2 of 2

27 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Q1 Section I a) Describe the structure of the T1 frame. How is signaling information included and synchronizing performed in T1 frame? (6) b) Answer any 5 (with figures or in two or three sentences each) i) Why is bit stuffing necessary in digital multiplexers? ii) What does complete closure of the eye in an eye pattern indicate? iii) Bandwidth compression is realized in QPSK as compared with BPSK. Justify. iv) Give the block diagram of the transmitter section in a channel vocoder. v) State the rules followed for HDB3 encoding vi) Give signal constellation for 8- PSK. vii) Give the waveform of the Manchester coded output for the string (10) Q2 a) Explain similarities and differences between Delta modulation and DPCM. (8) b) Prove that the overall frequency response of the duobinary encoder is a half cycle cosine function (9) Q2 a) Describe various considerations for selecting a particular waveform encoding scheme. Why is bipolar format most widely used? (8) b) Discuss QASK transmission and reception. (9) Q3 a) Discuss the Integrate and dump receiver (8) b) Describe MSK Transmitter (9) Q3 a) Explain how a CVSDM sytem works with help of block diagram (8) b) Write a note on the robust compander (9) Contd.

28 2 Section II Q4 a) Distinguish between synchronous and asynchronous transmission (6) b) Answer any 5 (with figure and/or two or three sentences each) 1. What are the functions of the Data Link layer? 2. give the properties of pseudo noise sequences in DS SS. 3. Name four application protocols which use the application layer in Internet. 4. Give the difference between datagram and virtual circuit. 5. What are the advantages of packet switching? 6. Distinguish between bus and ring topologies. 7. What is processing gain? (10) Q5 a) Discuss difference between DS and FH spread spectrum. (8) b) Distinguish between different varieties of CSMA. (9) Q5 a) Write a note on ALOHA and indicate its drawbacks and limitations (8) b) Why are error correcting codes not preferred in terrestrial digital communications? Discuss the Go back N ARQ technique for error correction. (9) Q6 a) Write a note on the CSMA-CD LAN (8) b) Write a note on Internet addressing and resolution of alphanumeric addresses into numeric IP addresses. (9) Q6 a) What is the sliding window protocol? What are its advantages? (8) b) Discuss (i) flooding (ii) Fixed routing and (iii) Adaptive routing methods. (9) -- END --

29 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE IV (Electronics) Examination 2005 Saturday, 7 th May 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Q1 Q2 Section I a) A digital system uses uniform quantization but non-binary transmission. The input signal range -1V to +1V is divided into segments with boundaries -1, -0.6, - 0.2, +0.2, +0.6 and +1 V, with quantization levels -0.8, -0.4, 0, +0.4, The five levels are transmitted respectively as 0, -cos(w o t), -(sinw o t), sin(w o t), cos(w o t). Which range of input signal values is most likely to be received with errors? (4) b) Answer any 8 (with figures or in two or three sentences each) i) Give the A-Law companding expressions and the commonly used value of A. ii) What does total closure of the eye in eye pattern indicate? iii) If input bit rate is f b what is the bandwidth required for BPSK? QPSK? iv) Justify the transmission bit rate of Mbps in the T1 system. v) State the rules for HDB3 coding. vi) Give signal constellation for QASK vii) Give the waveform of the Manchester coded output for the string viii) Sketch eye pattern for perfect reception of bits encoded by Manchester encoding ix) Sketch the typical analog compressor characteristic and equivalent variable step-size quantizer characteristic x) Distinguish between the waveforms and their spectra arising when you speak Ha and when you speak Na xi) Compare bandwidth and error probability of BPSK and BFSK (16) a) A TV signal having a bandwidth of 4.2 MHz is transmitted using a binary PCM system. Given that the number of quantization levels are 512, determine the (i) code word length (ii) minimum sampling frequency (iii) final bit rate (iv) output SNR (8) b) Explain the DPCM transmitter and explain the role of the predictor in it (7) Contd.

30 Q2 2 a) A signal 1V amplitude and 800 Hz frequency is transmitted by delta modulation. If sampling frequency is s/s, Determine minimum step size to avoid slope overload. Derive the expressions used (8) b) Discuss QASK generation. (7) Q3 a) Discuss the Integrate and Dump receiver (8) b) Describe total mean square error in PCM and show that as average P e tends to 0, output noise consists entirely of quantization noise (7) Q3 a) Describe the significance of the F, M, and C bits in the M12 multiplexer frame (8) b) Give the model for producing synthetic speech. (7) Q4 Section II a) What is a PN sequence and a maximum length sequence? List the properties of maximum length sequence (4) b) Answer any 8 (with figure and/or table and/or up to four sentences each) 1. In a Time slot interchange switch how is the interchanging of the time slots done? 2. Why is local area Cable TV network unsuitable for computer communication? 3. Give the disadvantages of circuit switching. 4. Differentiate between bit rate and symbol rate. 5. What is binary exponential back-off? 6. Distinguish between star and ring topologies. 7. When will the sliding window protocol cause the transmit window to contract? To expand? 8. What is the mechanism used in stop and wait ARQ to recover from lost ACK? 9. Distinguish between ALOHA and CSMA. 10. Give the functions of the Transport Layer. 11. What is piggy-backed acknowledgement? (16) Q5 a) Describe the DS/BPSK transmitter. (8) b) Explain the architecture of TCP/IP networks. (7) Q5 a) Discuss the different types of CSMA. (8) b) Compare and contrast packet switching and circuit switching (7) Q6 a) Write a short note on the performance of ARQ systems (8) b) Briefly discuss the various adaptive packet routing strategies. (7)

31 3 Q6 a) Explain the characteristic features of LAN, MAN and WAN. (8) b) Explain the CRC error detection procedure. (7)

32 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Q1 Q2 Q2 Q3 Section I a)describe the structure of the T1 and M12 frames. Explain how signaling information is carried in the T1 frame (6) b) Answer any 6 (with figures or in two or three sentences each) i) When is bit stuffing necessary in digital multiplexers? ii) How is the effect of excessive noise on eye pattern? Sketch. iii) Give the signal space constellation diagram for QASK. iv) Give the block diagram of the transmitter in a channel vocoder. v) State the rules followed for HDB3 encoding vi) State difference between voiced and unvoiced sounds. vii) Give the waveform of the Manchester coded output for the string viii) Give the block diagrams of the Duobinary encoder and decoder (12) a) Explain Delta modulation giving block diagram and analog and digital waveforms (8) b) Explain generation and reception of QPSK. Using signal space concepts derive the equation for the probability of error in QPSK (8) a) Describe various waveform encoding schemes. Briefly discuss important features of each (8) b) Show with derivations that MSK has similarities with FSK and PSK. (8) a) Describe the Integrate and dump receiver. Is it a matched filter for rectangular signals? Justify (8) b) Which has greater error probability QPSK or 4-FSK? Justify by deriving the probability of error expressions for both (8) Contd.

33 2 Q3 a) Explain any adaptive δ modulation system with help of block diagram (8) b) Derive the equation of the characteristic of a robust compander. (8) Section II Q4 a) Distinguish between Data Link and Transport layers (6) b) Answer any 6 (with figure and/or two or three sentences each) 1. What are the functions of the Network layer? 2. Give the properties of pseudo noise sequences in DS SS. 3. Name four application protocols which use the application layer in Internet. 4. Give the difference between Stop & Wait and Selective Repeat ARQ. 5. What are the advantages of circuit switching? 6. Distinguish between datagrams and virtual circuits. 7. Sketch and label layers in a TCP/IP data communication system. 8. Differentiate between fast hopping and slow hopping FHSS systems (12) Q5 Q5 a) Explain the term Processing Gain and derive its expression for DS Spread Spectrum. (8) b) Explain the different variations of CSMA. How does CSMA differ from ALOHA (8) a) Write a note on Slotted ALOHA and explain why it performs better than simple ALOHA (8) b) Explain Go Back N ARQ and derive the expression for its throughput (8) Q6 a) Discuss the Token Bus LAN (8) b) Explain the operation of a Time Slot Interchange switch. (8) Q6 a) What is the Sliding Window protocol? Explain with an example. (8) b) Explain the classes of Internet addresses and discuss DNS system for IP address resolution. (8) -- END --

34 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE III/IV (Electronics) Examination 2006 Thursday, 4 th May 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Q1 Section I a) A speech signal has a total duration of 10 seconds. It is sampled at the rate of 8 KHz and encoded. The signal to quantization noise ratio is required to be 40 db. Calculate the minimum storage capacity needed to store the digitized speech signal (6) b) Briefly answer any SIX i) Give the advantages and disadvantages of Manchester encoding ii) What information may be provided by eye pattern? Show with sketches. iii) Give the signal space constellation diagram for 3-FSK. iv) Give the function of the discriminator in a channel vocoder. v) State the characteristic function defining u-law companding vi) When does granular noise arise in delta modulation? vii) Differentiate between BPSK and DPSK. viii) Give the block diagrams of the Duobinary encoder (12) Q2 a) Derive and discuss the signal-to-quantization noise ratio in PCM. (8) b) Explain generation of MSK. (8) Q2 a) Describe various waveform encoding schemes. Briefly discuss important features of each (8) b) Write a note on Adaptive Delta Modulation. (8) Q3 a) What is CRC? Explain how it is performed. (8) b) Explain duo-binary encoding and give the block diagrams of duo binary encoder and decoder (8) Q3 a) Describe the operation of the transmitter section of the channel vocoder with the help of a block diagram, and explain the functions of each block. (8) b) Discuss the characteristics of (i) A- law and (ii) robust (ideal) compander. (8) Contd.

35 2 Section II Q4 a) Discuss differences between OSI model and TCP/IP model (6) b) Answer any SIX 1. What are the functions of the session layer? 2. Why do IP packets have a time to live (TTL) field? 3. Give the bit formats for IP addresses of type A and C 4. Why do stop and wait ARQ packets carry numbers 0 or What are the disadvantages of circuit switching? 6. Explain the significance and use of the poll/final bit in HDLC. 7. Differentiate between ALOHA and Slotted ALOHA 8. Why is padding field required in some LAN frames? (12) Q5 a) Derive the throughput efficiency for the Stop-&-Wait and GBN ARQs. (8) b) Discuss Non persistent and p-persistent CSMA and explain the binary exponential backoff procedure. (8) Q5 a) Derive the condition for a three stage switch to be non-blocking (8) b) Explain HDLC frame types and give examples showing their use. (8) Q6 a) Discuss the function of the monitor bit, reservation bits and priority bits in LAN (8) b) Derive the expression for the processing gain in DS Spread Spectrum (8) Q6 a) Write a note on X.25 virtual circuit numbering conventions. (8) b) Discuss.the IP header. (8) -- END --

36 THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA Second Semester of BE IV (Electronics) Examination 2007 Thursday, 26 th April 3 PM to 6 PM Elective: Digital Communication N.B.: i) Answer the two sections in separate answer-books. ii) Maximum marks are given in brackets to the right of the question. iii) Suitable assumptions may be made with due justification. Maximum marks : 100 Q1 Q2 Q2 Section I a) A binary channel with bit rate of R b =36000 bits/second is available for PCM voice transmission. Find appropriate values of the sampling rate fs, the number of quantizing levels L and the number of binary digits n assuming f max = 3.2 KHz (6) b) Briefly answer any SIX i) Show that for a T1 carrier system the frame length is 193 bits ii) Explain the importance of the timing circuit in a regenerative repeater. iii) What is the data rate for a QPSK modem operating at 1200 bauds? Justify. iv) Show that the performance of a DPCM system can be improved by using a predictor. v) Prove that the magnitude of detection error depends on the position of the vi) incorrectly detected pulse in a symbol. Adding an integrator in the input improves slope overload avoidance in a delta modulator. Justify. vii) What is a matched filter?. viii) Differentiate between the spectra of voiced and unvoiced speech. a) With the help of a constellation diagram prove that 8 QAM can tolerate larger phase errors compared to 8-PSK. Also discuss generation of QAM signal. (8) b) Show that the spectrum of RRC filter helps in reducing ISI by limiting the transmission bandwidth. (8) a) Describe methodologies due to which it has become possible to achieve a SNR of 80 db over the dynamic range of 40 db in voice communication (8) b) Explain with a block diagram the working principle of an Adaptive Equalizer. (8) (12) Contd.