EC-503-B Mobile Communication - Jun 2025 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 relation
   • Draw hexagonal cellular layout and 19-cell reuse pattern marking co-channel cells
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
   • Illustrate measurement and decision flow between MS, BS and MSC
   • Explain hard, soft, softer, intra/inter-cell, inter-system handoffs
3. 7 Marks
   aExplain foliage losses and propagation in near-in-distance.
   How to answer

   • Define foliage loss and its causes
   • Explain near-in-distance propagation mechanism
   • Summarize empirical models and 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 $B_c \approx 100\,kHz$ to find $T_s > 1/B_c$
   • Calculate maximum symbol rate $R_s \approx B_c$ for minimal ISI
5. 7 Marks
   aDiscuss the small scale multipath propagation.
   How to answer

   • Define small-scale fading and multipath
   • Explain time, frequency and spatial variation effects
   • Describe factors: multipath propagation, Doppler, impulse response
6. 7 Marks
   bExplain frequency management and channel assignment.
   How to answer

   • Define frequency management objectives
   • Explain fixed, dynamic and hybrid channel assignment
   • Discuss borrowing, blocking and handoff strategies
7. 7 Marks
   aWhat are the different multiplexing techniques?
   How to answer

   • Define multiplexing vs multiple access
   • List FDMA, TDMA, CDMA, SDMA, OFDM
   • Brief principle and application of each
8. 7 Marks
   bExplain frame structure.
   How to answer

   • Define frame and its need in TDMA/TDM systems
   • Describe sync, control and traffic slots structure
   • Give example GSM frame structure with diagram
9. 7 Marks
   aExplain spread spectrum multiple access in detail.
   How to answer

   • Define spread spectrum principle and processing gain
   • Explain FHSS and DSSS with diagrams
   • Explain SSMA code separation for multiple users
10. 7 Marks
    bDescribe Code Division Multiple Accessing (CDMA). Also discuss output power limit and control in CDMA.
    How to answer

    • Define CDMA principle with orthogonal/pseudo-noise codes
    • Explain forward/reverse link and power control need
    • Discuss output power limit and open/closed loop control
11. 7 Marks
    aExplain Clarke's model of flat fading.
    How to answer

    • State assumptions of Clarke's flat fading model
    • Derive Rayleigh envelope and Doppler spectrum
    • Explain uniform scattering and E-field derivation
12. 7 Marks
    bList the various techniques used to expand the capacity of a cellular system and explain.
    How to answer

    • List cell splitting, sectoring, microcells, borrowing
    • Explain principle of each capacity expansion method
    • Compare gain vs interference/trade-offs
13. 7 Marks
    aWhat is CDMA? Write advantages of CDMA over FDMA for TDMA technologies.
    How to answer

    • Define CDMA, FDMA and TDMA access principles
    • Compare capacity, interference, handoff and security
    • List advantages of CDMA: soft capacity, multipath diversity, privacy
14. 7 Marks
    bIf $B_t$ is 12.5 MHz $B_{guard}$ is 10 kHz and $B_c$ is 30 kHz. Find the number of channels available in an FDMA system.
    How to answer

    • State FDMA channels formula $N = (B_t - 2B_{guard})/B_c$
    • Substitute $B_t=12.5\,MHz$, $B_{guard}=10\,kHz$, $B_c=30\,kHz$
    • Compute number of channels available
15. 14 Marks
    Write short note on (any two):

    1. i)Multiple input multiple output system
    2. ii)Orthogonal frequency division multiplexing
    3. iii)Diversity (spatial)
    How to answer

    • Select any two: MIMO, OFDM, spatial diversity
    • Define principle, block diagram and benefits
    • Give applications in 4G/5G mobile communication