EC-503-B Mobile Communication - Nov 2022 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
   aWhat is the Cellular concept? Why hexagonal cells are used in cellular system? Describe the cellular system with the help of neat diagram.
   How to answer

   • Definition of cellular concept - frequency reuse with low-power cells
   • Reason for hexagonal cells - no gaps/overlap, tractable geometry, approximates circular coverage
   • Cellular system components - base station, MSC, mobile unit, channels
   • Neat diagram of cluster of hexagonal cells with base stations
2. 7 Marks
   bDefine frequency reuse. Explain the frequency reuse concept. What is the need of frequency reuse? What is frequency reuse factor?
   How to answer

   • Definition of frequency reuse
   • Frequency reuse concept - cluster size N, co-channel cells, reuse distance
   • Need - spectrum scarcity, capacity increase, interference management
   • Frequency reuse factor definition - 1/N and D/R relation
3. 7 Marks
   aDescribe handoff mechanism in cellular mobile system. What is its necessity? What are different handoff types?
   How to answer

   • Definition and purpose of handoff/handover
   • Handoff mechanism steps - signal measurement, threshold, hysteresis, channel switching
   • Necessity - mobility, maintain call continuity
   • Types - hard, soft, softer, intra/inter-cell, inter-system
4. 7 Marks
   bWhat are the various mechanisms for capacity increase in cellular system? Explain.
   How to answer

   • Need for capacity increase in cellular system
   • Cell splitting - microcells
   • Sectoring - directional antennas
   • Frequency borrowing, cell breathing, MIMO/SDMA if applicable
5. 7 Marks
   aDescribe the ground reflection propagation model for mobile radio propagation.
   How to answer

   • Two-ray ground reflection geometry - direct and reflected path
   • Assumptions - flat earth, d >> ht+hr
   • Path loss expression with ht, hr, d dependence
   • Break-point and d^4 law explanation
6. 7 Marks
   bUnder what conditions slow fading, fast fading, flat fading and frequency selective fading results? Explain.
   How to answer

   • Definitions of slow vs fast fading based on Doppler vs symbol rate
   • Flat vs frequency selective based on coherence bandwidth vs signal bandwidth
   • Conditions using coherence time and delay spread
   • Examples and effects on signal
7. 7 Marks
   aWhat do you understand by coherence bandwidth, Doppler spread and coherence time? Explain in detail.
   How to answer

   • Definition of coherence bandwidth, Doppler spread, coherence time
   • Relation Bc ~ 1/Tm, Tc ~ 1/Bd
   • Effect on fading type determination
   • Typical values and significance in system design
8. 7 Marks
   bExplain Clarke's model for flat fading in detail. Also discuss level crossing and fading statistics.
   How to answer

   • Clarke's scattering model assumptions - N plane waves, uniform AoA
   • Derivation of Rayleigh fading envelope and Doppler spectrum
   • Level crossing rate formula and average fade duration
   • Fading statistics - Rayleigh/Ricean distribution
9. 7 Marks
   aDescribe antennas used at cell site. Discuss unique situations of cell site antenna.
   How to answer

   • Types of cell site antennas - omni, sector, panel, diversity
   • Placement height, downtilt, location
   • Unique situations - rooftop, street microcell, indoor, hilly terrain
10. 7 Marks
    bWhat are the reasons/sources of co-channel interference? How it can be reduced?
    How to answer

    • Definition of co-channel interference and co-channel cells
    • Sources - frequency reuse, traffic load, antenna height, propagation
    • Effects on SIR and capacity
    • Reduction - larger reuse, sectoring, power control, smart antennas
11. 7 Marks
    aWhat is non-fixed channel assignment? Explain different types of non-fixed channel assignment algorithms.
    How to answer

    • Fixed vs non-fixed/dynamic channel assignment concept
    • Types - centralized, distributed, hybrid, borrowing
    • Algorithm operation and comparison
    • Advantages in traffic adaptability
12. 7 Marks
    bDraw the GSM architecture and explain each sub-system.
    How to answer

    • Block diagram of GSM - MS, BTS, BSC, MSC, HLR/VLR/EIR/AuC
    • Function of each sub-system
    • Interfaces Um, Abis, A
    • Call flow path explanation
13. 7 Marks
    aWhat multiple access scheme are used for GSM? Explain.
    How to answer

    • GSM uses FDMA/TDMA combination
    • 200 kHz carriers, 8 time slots per frame
    • Frequency hopping option
    • Explanation with frame/slot diagram
14. 7 Marks
    bFor GSM explain traffic channel control channel and frame structure.
    How to answer

    • Traffic channels TCH/F, TCH/H purpose
    • Control channels - BCCH, CCCH, DCCH types
    • GSM TDMA frame hierarchy - hyper, super, multi, frame, slot, burst
    • Diagram of frame structure
15. 7 Marks
    aCompare and explain slow frequency hopping and fast frequency hopping. Also describe the working of Frequency Hopped Spread Spectrum (FHSS).
    How to answer

    • Definition of slow vs fast frequency hopping
    • Comparison table - hopping rate vs symbol rate, diversity, complexity
    • FHSS working - hop sequence, synthesizer, de-hopping
    • Advantages - anti-jam, multipath resistance
16. 7 Marks
    bExplain call processing and handoff procedures in CDMA systems.
    How to answer

    • CDMA call processing steps - origination, paging, access, traffic
    • Pilot, sync, paging, traffic channels role
    • Handoff types - soft, softer, hard, idle
    • MAHO, rake receiver and power control in handoff