EC-503-B Mobile Communication - Nov 2023 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aExplain frequency reuse concept with the help of proper cellular diagram. Also draw a cellular system with 19-cell reuse and locate the co-channel cells for this system.
   How to answer

   • Define frequency reuse and reuse factor N
   • Explain co-channel cells and reuse distance D/R formula
   • Sketch hexagonal cellular layout and 19-cell reuse with co-channel cells marked
2. 7 Marks
   bIllustrate the MAHO technique and Queuing concept in hand off. Also explain the different types of handoff in mobile communication.
   How to answer

   • Define MAHO and queuing for handoff
   • Explain handoff procedure steps
   • List and explain types of handoff e.g. hard, soft, intra/inter-cell
3. 7 Marks
   aExplain foliage losses and propagation in near-in-distance.
   How to answer

   • Define foliage loss causes
   • Explain near-in-distance propagation mechanism
   • Summarize frequency/distance dependence
4. 7 Marks
   bIf the coherence bandwidth is calculated as 100 kHz in the given radio channel of 900 MHz frequency, calculate the maximum symbol rate that can be transmitted over this channel that will suffer minimal intersymbol interference.
   How to answer

   • State relation between coherence bandwidth and symbol period
   • Use $B_c = 100\,kHz$ to find $T_s > 1/B_c$
   • Calculate maximum symbol rate $R_s \approx B_c$ for minimal ISI
5. 7 Marks
   aExplain Cell splitting and Concept of frequency channels.
   How to answer

   • Define cell splitting need for capacity
   • Explain splitting procedure and radius reduction
   • Explain concept of frequency channels
6. 7 Marks
   bElaborate dynamic channel assignment and compare its advantages and disadvantages with the fixed channel assignment.
   How to answer

   • Define fixed vs dynamic channel assignment
   • Explain DCA operation
   • Compare advantages and disadvantages in table
7. 7 Marks
   aExplain GSM with the help of proper network architecture block diagram. Also give brief view of various Interface standards in GSM.
   How to answer

   • Draw GSM network architecture block diagram (MS, BTS, BSC, MSC, HLR/VLR)
   • Explain function of each subsystem
   • List interface standards Um, Abis, A, etc.
8. 7 Marks
   bExplain frame structure.
   How to answer

   • Define GSM frame hierarchy
   • Explain TDMA frame, multiframe, superframe
   • Mention time slots and burst structure
9. 7 Marks
   aDescribe forward and reverse CDMA channels.
   How to answer

   • List forward CDMA channels (pilot, sync, paging, traffic)
   • List reverse CDMA channels (access, traffic)
   • Explain function of each channel
10. 7 Marks
    bIn IS-95 CDMA, assume K = 20 users share the same 1.25 MHz channel. The chip rate for each user is 1.2288 Mcps and each user has a baseband data rate of 13 kbps. If a maximum $E_b/N_0$ of 7.8 dB is provided for each user and the PN code lengths are 32,678 chips ($2^{15}$), find the bit error probability for a user. What is the processing gain of IS-95?
    How to answer

    • Compute processing gain $G_p =$ chip rate / data rate
    • Use $E_b/N_0 = 7.8\,dB$ to estimate BER for BPSK/QPSK
    • State PN length $2^{15}=32678$ effect
11. 7 Marks
    aExplain Clarke's model of flat fading.
    How to answer

    • State assumptions of Clarke's model (N plane waves, uniform AoA)
    • Derive Rayleigh fading statistics / Doppler spectrum
    • Explain flat fading implication
12. 7 Marks
    bWith the help of block diagram describe the basic cellular system and discuss its performance criteria.
    How to answer

    • Draw basic cellular system block diagram (transmitter, receiver, switching)
    • Explain components function
    • Discuss performance criteria: voice quality, service, interference
13. 7 Marks
    aWhat is co-channel interference? What is the main reason for it? How can be co-channel interference be reduced?
    How to answer

    • Define co-channel interference and C/I
    • Explain main reason: frequency reuse
    • List reduction methods: larger N, sectoring, power control, smart antenna
14. 7 Marks
    bIn a mobile radio environment, for hilly terrain of height H = 100 m, the average cell site antenna height is about 50m, the mobile antenna height is about 3m and the communication path length is 5 km. Find the incident angle and the slope angle.
    How to answer

    • State knife-edge / hilly terrain geometry
    • Use heights H=100m, hb~50m, hm~3m and d=5km to find angles
    • Calculate incident angle and slope angle formulas
15. 14 Marks
    Write a short note on any two:

    1. i)Trunking and grade of service
    2. ii)Free space propagation model
    3. iii)GSM traffic channel
    4. iv)Mobile to Mobile propagation
    How to answer

    • Select any two topics from i-iv
    • Define key terms and model/diagram
    • Give applications and significance