Subject Code: 171004
GUJARAT TECHNOLOGICAL UNIVERSITY
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BE - SEMESTER-VII (OLD) EXAMINATION — WINTER 2018
Subject Name: Wireless Communication
Time: 10:30 AM TO 01:00 PM
Total Marks: 70
Date: 29/11/2018
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Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
Q.1 Give full forms of the following acronyms: HSCSD, GPRS, WLL, CDMA, WLAN, MAN, WAN. MARKS 07
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Q.2 Draw a neat sketch of GSM architecture and state the functions of the following: BSC, MSC, VLR, HLR, AUC. MARKS 07
Q.3 Explain the salient features of Bluetooth technology. MARKS 07
Q.4 Briefly discuss security threats in wireless network and suggest possible ways of protection. MARKS 07
OR
Explain the hidden-node problem and exposed-node problem in context of mobile ad-hoc networks. MARKS 07
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Q.4 Explain practical handoff considerations. MARKS 07
Q.5 A spectrum of 30 MHz is allocated to a wireless FDD cellular system which uses two 25 kHz simplex channels to provide full duplex voice and control channels. Compute the number of channels available per cell if a system uses (i) 4-cell reuse (ii) 7-cell reuse and (iii) 12-cell reuse. If 1 MHz of the allocated spectrum is dedicated to control channels, determine an equitable distribution of control channels and voice channels in each cell for each of the three systems. MARKS 07
OR
Explain the concept of cell sectoring and how it affects interference and system capacity. MARKS 07
For given path loss exponent (A) n=4 and (B) n=3, find the frequency reuse factor and the cluster size that should be used for maximum capacity. The signal to interference ratio (S/I) is required to be at least 15 dB for satisfactory system performance. There are six co-channel cells in the first tier and all of them are at the same distance from the mobile. Use suitable approximations. MARKS 07
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Explain salient features of CDMA. MARKS 07
Prove that for a regular hexagonal geometry, the frequency reuse ratio and cluster size are related by the relationship Q = (3N)1/2, where N=i2 +j2 +ij. MARKS 07
OR
Explain the working of RAKE receiver with neat diagram. MARKS 07
Derive an expression for total received field at a distance d for ground reflection model. MARKS 07
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Discuss GSM channel types in details. MARKS 07
In a cellular radio operating at 800 MHz, the transmitter and the receiver are separated by 500m from each other. The knife-edge diffraction object between them has a height of 30 m. The diffraction object is 100 m from transmitter. Find:
- The excess path length
- The phase difference corresponding to the excess path length.
- The Fresnel-Kirchhoff diffraction parameter.
- The radius of the second Fresnel zone.
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Q.5 (a) List types of diversity techniques and explain any two of them in 3-4 sentences. MARKS 07
(b) If a baseband binary message with a bit rate of 100 kbps is modulated by an RF carrier using BPSK. Calculate the following: MARKS 07
- Find the range of values required for rms delay spread of the channel such that the received signal is a flat-fading signal.
- If the modulation carrier frequency is 5.8 GHz, what is the coherence time of the channel for vehicle speed of 50 km/h.
- For your answer in part (ii), is the channel “fast” or “slow” fading?
- Given your answer in (ii), how many bits are sent while the channel appears static?
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