EC-802-B Wireless Communications - 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 the different types of wireless services and their requirements. Discuss the economic and social impact of wireless communication.
   How to answer

   • Types of wireless services: voice, data, multimedia, IoT, broadcast, emergency
   • Requirements: data rate, latency, coverage, mobility, QoS, reliability
   • Economic impact: growth, employment, new business models
   • Social impact: connectivity, education, healthcare, digital divide
2. 7 Marks
   bWhat are the key technical challenges in wireless communications? How do multipath propagation and user mobility affect system performance?
   How to answer

   • Key challenges: spectrum scarcity, fading, interference, mobility, power, security
   • Multipath propagation effects: ISI, fading, BER degradation
   • User mobility effects: Doppler, handoff, fast fading
   • Impact on system performance and mitigation need
3. 7 Marks
   aExplain the evolution of wireless communication from 1G to 5G. What are the major differences in services and requirements?
   How to answer

   • Evolution 1G analog to 2G digital to 3G data to 4G broadband to 5G massive connectivity
   • Services per generation: voice, SMS, internet, mobile broadband, URLLC/mMTC/eMBB
   • Requirements: data rate, latency, spectrum, capacity
   • Major differences in technology and applications
4. 7 Marks
   bWhat are the key spectrum limitations in wireless communication? How do they impact system design?
   How to answer

   • Limited spectrum, licensing, congestion
   • Path loss, interference, fading constraints
   • Impact on capacity, coverage, data rate
   • Design implications: reuse, multiple access, cognitive radio
5. 7 Marks
   aExplain the concept of coherence bandwidth and its relation to delay spread in wireless channels.
   How to answer

   • Definition of coherence bandwidth
   • Definition of delay spread / RMS delay spread
   • Inverse relation $B_c \approx 1/T_m$
   • Flat vs frequency-selective fading implication
6. 7 Marks
   bDerive the expression for the Doppler shift in a mobile wireless channel. How does velocity impact the Doppler shift?
   How to answer

   • Geometry of mobile, velocity, angle of arrival
   • Derivation of $f_d = (v/\lambda)\cos\theta$
   • Maximum Doppler shift $f_m = v/\lambda$
   • Velocity increases Doppler spread and fast fading
7. 7 Marks
   aDescribe small-scale fading and large-scale fading. How does Doppler shift impact wireless communication?
   How to answer

   • Small-scale fading: multipath, rapid fluctuations
   • Large-scale fading: path loss and shadowing
   • Doppler shift causes frequency dispersion and time selectivity
   • Effect on BER, handoff and reception
8. 7 Marks
   bDerive the expression for delay spread and coherence bandwidth in a wireless channel. How does delay spread affect system performance?
   How to answer

   • Power delay profile and RMS delay spread $\sigma_\tau$
   • Derivation of $B_c \approx 1/(5\sigma_\tau)$
   • Condition for ISI and frequency selectivity
   • Delay spread increases BER and limits data rate
9. 7 Marks
   aCompare narrowband, wideband, and directional channel models. Provide examples of their applications.
   How to answer

   • Definitions: narrowband vs wideband vs directional
   • Comparison on bandwidth, resolution, angular dependence
   • Application examples for each model
   • Summary table of differences
10. 7 Marks
    bExplain the process of channel sounding and describe different measurement methods used for characterizing wireless channels.
    How to answer

    • Purpose of channel sounding
    • Process: transmit probe, record impulse response
    • Methods: direct pulse, spread spectrum, frequency sweep
    • Parameters extracted for characterization
11. 7 Marks
    aDescribe the block diagram of a wireless transceiver. How do modulation and demodulation techniques impact system performance?
    How to answer

    • Block diagram: antenna, RF, IF, baseband, ADC/DAC, modem
    • Transmitter and receiver chain functions
    • Role of modulation/demodulation in spectral efficiency
    • Impact on BER, power and complexity
12. 7 Marks
    bExplain the impact of delay and frequency-dispersive fading on signal reception. How does it affect the error probability?
    How to answer

    • Delay dispersive fading causes ISI
    • Frequency dispersive fading causes time-selective fading
    • Effect on signal distortion and error floor
    • Increase in error probability and need for equalization
13. 7 Marks
    aCompare blind equalization and decision-directed equalization. When is blind equalization preferred?
    How to answer

    • Principle of blind vs decision-directed equalization
    • Comparison on training sequence, convergence, complexity
    • Advantages and limitations of each
    • Conditions preferring blind equalization
14. 7 Marks
    bWhat is Diversity? Explain microdiversity and macrodiversity. How does diversity improve signal reception?
    How to answer

    • Definition of diversity to combat fading
    • Microdiversity: space, frequency, time vs macrodiversity
    • Combining techniques concept
    • Improvement in SNR and reliability
15. 14 Marks
    Write short notes on any two of the followings.

    1. a)Antenna for mobile stations
    2. b)Data services in cellular communication
    3. c)TDMA and CDMA systems
    How to answer

    • Two topics selected with definition and principle
    • Key features, diagram or system aspects
    • Applications in wireless/cellular systems
    • Advantages and limitations