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Previous Year Exam Questions for Wireless Communication - WC of 2018 - BPUT by Ruparani Mahapatra

  • Wireless Communication - WC
  • 2018
  • PYQ
  • Biju Patnaik University of Technology Rourkela Odisha - BPUT
  • Electronics and Communication Engineering
  • B.Tech
  • 405 Views
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Registration No : Total Number of Pages : 03 B.Tech. PET7J001 7th Semester Regular Examination 2018-19 WIRELESS COMMUNICATION SYSTEMS BRANCH : ECE, ETC Time : 3 Hours Max Marks : 100 Q.CODE : E049 Answer Question No.1 (Part-1) which is compulsory, any EIGHT from Part-II and any TWO from Part-III. The figures in the right hand margin indicate marks. Q1 a) b) c) d) e) f) g) h) i) j) Q2 a) b) Part- I Short Answer Type Questions (Answer All-10) Why do paging systems need to provide low data rates? How does a low data rate lead to better coverage? What is bleed over and cell dragging phenomenon in wireless communication? Consider a transmitter which radiates a carrier frequency of 1900 MHz. For a vehicle moving with 80 km/h, compute the received carrier frequency if the mobile is moving directly away from the transmitter? How the bandwidth efficiency affected, if the average bit energy and transmission bit rate both becomes doubles and transmission bandwidth increased four times? A mobile is located 5 km away from base station and uses a vertical λ/4 monopole antenna with a gain of 2.55 dB. The carrier frequency used for this system is 900 MHz. The electric field at 1 km from the transmitter is measured to be 10 V/m. Find the received power at the mobile if the height of the transmitter antenna is 50 m and received antenna is 1.5 m above ground. Define Fraunhofer region. Find the far-field distance for an antenna with maximum dimension of 1 m and operating frequency of 2GHz. What are the main advantages of spread spectrum transmission over fixed frequency transmission? If a normal GSM time slot consists of 10 trailing bits, 20 training bits, two traffic bursts of 40 bits of data and 12 guard bits, with bit duration of 3.692 µs. Then find the slot duration and frame efficiency. (2 x 10) What are the main advantages of GMSK that led to its adoption for second generation GSM mobile telephones? What range of frame number, is sent with base station identity code during SCH burst?If in a normal GSM transmission 20 super-frames are sent, then what will be total time required to complete the process? Part- II Focused-Short Answer Type Questions- (Answer Any Eight out of Twelve) Discuss the similarities and differences between a conventional cellular radio system and a space-based (satellite) cellular radio system. What are the advantages and disadvantages of each system? Which system could support a larger number of users for a given frequency allocation? Why? How would this impact the cost of service for each subscriber? In cellular radio system, a signal to interference ratio of 14 dB is required for satisfactory forward channel performance. Assume that there are 6 co-channels cells in the first tier, and all of them are at the same distance from the mobile. Then calculate what is the frequency reuse factor and cluster size that should be used for (6 x 8)

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c) d) maximum capacity for the following two case: a. path loss exponent n = 4 b. path loss exponent n = 3 A hexagonal cell within a 7-cell system has a radius of 1.2 km. A total of 140 channels are used within the entire system. If the load per user is 0.026Erlangs, and λ = 1 call/hour, compute the following for an Erlang C system that has a 5% probability of a delayed call. (Given that traffic intensity = 13.0 Erlangs ). a. How many users per square kilometer will this system support? b. What is the probability that a delayed call will have to wait for more than 10 seconds? c. What is the probability that a call will be delayed for more than 10 seconds? While designing a cellular system, how are co-channel and adjacent channel interferences are kept under control? What is the role of S/I ratio and Q in this? e) Prove that in the 2-ray ground reflected model, ∆= f) What causes ‘fading’ in a radio channel and how does it affect digital transmissions? Explain the difference between 'flat' fading and 'frequency-selective' fading and state what is meant by the ‘coherence bandwidth’. Determine the proper spatial sampling interval required to make small-scale propagation measurements which assume that consecutive samples are highly correlated in time. How many samples will be required over 10 m travel distance if f c = 2100 MHz and v = 60 m/s. How long would it take to make these measurements, assuming they could be made in real time from a moving vehicle? What is the Doppler spread BD for the channel? g) ′′ − ′ = . h) Explain the different features of FDMA system. i) The GSM TDMA system uses a 270.833 kbps data rate to support 8 users per frame. a. What is the raw data rate provided for each user? b. If guard time, ramp-up time, and synchronization bits occupy 10.1 kbps, determine the traffic efficiency for each user. Calculate the capacity and spectral efficiency of the DS-CDMA system with an omni-directional cell using the following data: bandwidth efficiency=0.9, frequency reuse efficiency=0.45, capacity degradation factor=0.8, voice activity factor =0.4,information bit rate=18 kbps, Eb/Io=7 dB,one-way system bandwidth=12 MHz. Neglect other source of interferences. j) k) l) With suitable schematic diagram explain GPRS protocol stack. How much of the original GSM network does GPRS need? Which element of the network perform data transfer? Justify your answer. Part-III Q3 Q4 Long Answer Type Questions (Answer Any Two out of Four) How to improve coverage and capacity in cellular systems. Explain in detail. Assume a mobile traveling at a velocity of 15 m/s receives two multipath components at a carrier frequency of 900 MHz. The first component is assumed to arrive at fk = 0 with an initial phase of 00 and a power of -60 dBm, and the second component which is 3 dB weaker than the first component is assumed to arrive at fk = 1 µs, also with an initial phase of 00. If the mobile moves directly towards the direction of arrival of the first component and directly away from the direction of arrival of the second component, a. Compute the narrowband instantaneous power at time intervals of 0.1 sec from 0 second to 0.5 second. b. Compute the average narrowband power received over this observation interval. c. Compare average narrowband and wideband received powers over this interval. (16) (16)

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Q5 a) b) Explain the capacity of Space Division Multiple Access. A CDMA cellular system uses SDMA, and multiple cells are used, where each cell shares the same radio channel. Consider propagation path loss exponents of n = 2, 3, and 4, and determine the number of simultaneous users that can be supported at an average probability of error of 10-2. Assume K = 511 and 6 dB of directionality is provided by the base station for each user. (8) (8) Q6 a) b) Draw the GSM system architecture and write the function of each block. What is the cut-off frequency of the baseband. Gaussian, pulse-shaping filter used in the GSM system?In the normal GSM time slot, why would the 26 equalizer training bits be placed in the middle of the frame rather than at the beginning? What is the reason for having an 8.25 bit guard period after the data bursts? (8) (8)

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