Viva Questions and Answers for Cellular Network (Unit I and II) - ENTC SSPU
Unit I: Introduction to Wireless Channel
Important Full Forms:
• LOS: Line of Sight
• NLOS: Non-Line of Sight
• LTE: Long Term Evolution
• OFDM: Orthogonal Frequency Division Multiplexing
• CSI: Channel State Information
• SISO: Single Input Single Output
Important Formulae:
Viva Questions and Answers:
Q1. What is a wireless channel?
Ans: Medium through which wireless signals travel between transmitter and receiver. It can
introduce distortion, delay, and noise.
Q2. What is Free Space Propagation?
Ans: Signal travels directly without obstacles. Power decays as inverse of distance squared
(d2d^2).
Q3. Define Path Loss.
Ans: Reduction in power density of the electromagnetic wave as it propagates through
space.
Q4. What is the Path Loss Exponent?
Ans: It indicates how fast the signal power decreases with distance. In free space, n = 2.
Q5. What is Multipath Propagation?
Ans: Multiple copies of signal reach receiver by reflection, scattering, diffraction.
Q6. What is meant by Fading?
Ans: Fluctuations in received signal strength due to multipath.
Q7. Difference between Fast and Slow Fading?
Ans:
• Fast Fading: Rapid fluctuations. Slow Fading: Gradual changes due to obstacles.
Q8. Explain types of Interference.
Ans:
• ACI (Adjacent Channel Interference): From nearby frequencies.
• CCI (Co-Channel Interference): Same frequency reused in different cells.
• ISI (Inter Symbol Interference): Overlapping of symbols in time.
Q9. What is Doppler Shift?
Ans: Change in frequency due to relative motion between transmitter and receiver.
Q10. Define Diversity.
Ans: Using multiple antennas or paths to improve communication reliability.
Q11. What is Channel Estimation?
Ans: Estimating the effects of the channel to correct distortions at receiver.
Unit II: Cellular Concepts
Important Full Forms:
• BTS: Base Transceiver Station
• MSC: Mobile Switching Center
• HLR: Home Location Register
• VLR: Visitor Location Register
• ISDN: Integrated Services Digital Network
• GSM: Global System for Mobile Communication
Important Formulae:
Viva Questions and Answers:
Q1. What is a Cellular System?
Ans: A wireless communication system divided into small regions called cells, each served
by its own base station.
Q2. What is Frequency Reuse?
Ans: Using the same frequency in different cells separated by sufficient distance to avoid
interference.
Q3. What are the advantages of Cellular Systems?
Ans: Increased capacity, reduced power consumption, better coverage.
Q4. Define Handoff.
Ans: Process of transferring an active call or data session from one cell to another.
Q5. Types of Handoff?
Ans:
• Hard Handoff: Break before make. Soft Handoff: Make before break.
Q6. What is a Cluster?
Ans: Group of cells that together use the entire set of available frequencies once.
Q7. What is Co-channel Interference?
Ans: Interference caused by reuse of the same frequency in nearby cells.
Q8. What is Adjacent Channel Interference?
Ans: Interference caused by signals in neighboring frequency bands.
Q9. Define Cell Splitting.
Ans: Dividing a congested cell into smaller cells to increase capacity.
Q10. What is a Base Station (BTS)?
Ans: Equipment that connects mobile devices to the network.
Q11. What is MSC (Mobile Switching Center)?
Ans: Central node responsible for routing calls and data.
Q12. Difference between HLR and VLR?
Ans:
• HLR: Stores permanent user data.
• VLR: Temporarily stores data of users currently visiting the area.
Quick Tip: Typical Values
• RMS Delay Spread: Microseconds (Outdoor), Nanoseconds (Indoor)
• Coherence Bandwidth: ~100 kHz (depends on environment)
• Path Loss Exponent: 2 (Free Space), >2 (Urban)
