Microwave Transmission: 30 Technical Interview Questions and Answers

  1. What is the difference between TDM and Ethernet in microwave communication?
    Ans: TDM (Time Division Multiplexing) allocates fixed time slots for data streams, ideal for circuit-switched traffic like voice. Ethernet is packet-based, better for variable data loads and flexible bandwidth usage.

  2. What are the key layers in a microwave transmission system? Explain their roles.
    Ans: Key layers include Physical (signal transmission), Data Link (framing, error detection), and Network (routing). Together, they ensure reliable data delivery across microwave links.

  3. What is the difference between Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) links?
    Ans: LOS requires a clear direct path between antennas, offering better performance. NLOS uses reflection, diffraction, or scattering to establish connectivity in obstructed environments.

  4. How does Adaptive Modulation work in microwave radios?
    Ans: Adaptive Modulation dynamically adjusts modulation schemes (e.g., QPSK to 256-QAM) based on link quality, ensuring optimal performance under varying weather or interference conditions.

  5. What is channel planning in microwave, and why is it important?
    Ans: Channel planning assigns frequencies to avoid interference and ensure efficient spectrum use. It's crucial for maintaining high-quality communication and regulatory compliance.

  6. What is the difference between a microwave repeater and a passive reflector?
    Ans: A repeater amplifies and regenerates signals at midpoint; a passive reflector simply redirects signals without amplification, useful when power or active equipment isn't feasible.

  7. How does frequency planning work in a dense microwave network?
    Ans: Frequency planning prevents interference by assigning different frequencies based on site location, antenna direction, reuse distance, and regulatory constraints.

  8. What is XPIC (Cross Polarization Interference Cancellation) and how does it help?
    Ans: XPIC enables two signals on the same frequency using orthogonal polarizations. It cancels interference between them, effectively doubling channel capacity.

  9. What are the types of microwave topologies (e.g., ring, mesh, chain)?
    Ans: Chain is linear and simple; ring provides redundancy; mesh offers high availability and multiple paths, best for complex or critical communication networks.

  10. What is the role of a DCN (Data Communication Network) in microwave systems?
    Ans: DCN provides IP connectivity for monitoring and managing network elements remotely via NMS tools using protocols like SNMP.

  11. What is the function of IDU and ODU in a microwave link?
    Ans: The IDU (Indoor Unit) handles baseband processing and interfaces; the ODU (Outdoor Unit) transmits/receives RF signals through the antenna.

  12. What is IF loopback testing and when is it used?
    Ans: IF loopback tests internal radio functions by looping back the intermediate frequency signal. It's used during commissioning or troubleshooting to isolate issues.

  13. How do you troubleshoot a down microwave link?
    Ans: Verify power, physical connections, antenna alignment, configuration, alarms, and interference. Use loopbacks and RSL readings for root cause analysis.

  14. What is the function of a hop in microwave transmission?
    Ans: A hop is one microwave link between two sites. Multi-hop networks extend coverage over large areas by connecting several hops.

  15. What is ATPC (Automatic Transmit Power Control) and why is it used?
    Ans: ATPC reduces transmit power in good conditions to limit interference and extends equipment life. It increases power automatically in poor conditions.

  16. What causes multipath fading and how is it mitigated?
    Ans: Caused by reflected signals arriving out of phase, leading to signal cancellation. Mitigated using space diversity, equalizers, or adaptive modulation.

  17. How does Space Diversity improve link availability?
    Ans: It uses two antennas at different heights. If one experiences fading, the other likely remains unaffected, improving signal reliability.

  18. What is hitless switching in microwave systems?
    Ans: Hitless switching transfers traffic between working and protection paths without packet loss or noticeable impact, ensuring uninterrupted service.

  19. What is RSL (Received Signal Level) and what affects its value?
    Ans: RSL indicates signal strength at the receiver. Factors like distance, antenna alignment, weather, and obstacles affect it.

  20. What is BER (Bit Error Rate) in microwave links?
    Ans: BER measures the number of erroneous bits received. A lower BER means better link quality and data integrity.

  21. What are typical frequencies used in microwave communication?
    Ans: Common bands include 6, 7, 11, 13, 18, 23, 26, 38, and 80 GHz, selected based on distance, bandwidth, and licensing.

  22. What is a hybrid microwave link and where is it used?
    Ans: Hybrid links carry both legacy TDM and modern Ethernet/IP traffic. Useful in transitioning networks with mixed services.

  23. What is the difference between split-mount and all-indoor microwave radios?
    Ans: Split-mount separates IDU and ODU; all-indoor combines both inside. Choice depends on installation environment and cabling constraints.

  24. What is latency in microwave networks and how does it compare to fiber?
    Ans: Latency is transmission delay. Microwave usually has lower latency over short distances than fiber due to fewer hops and no routing.

  25. What is QoS in microwave transmission and how is it maintained?
    Ans: QoS ensures critical traffic gets priority. It's managed using traffic classification, queuing, shaping, and policing techniques.

  26. What is the use of FEC (Forward Error Correction) in microwave?
    Ans: FEC adds redundant bits allowing receivers to detect and correct errors, reducing retransmissions and improving link reliability.

  27. What is a microwave link budget and what factors are considered?
    Ans: It calculates expected signal levels considering transmit power, path loss, antenna gain, cable loss, and required fade margin.

  28. What are the licensing requirements for microwave bands in India?
    Ans: Most bands require WPC licensing. Applicants must follow norms, pay fees, and register links with SACFA clearance.

  29. What is alignment in microwave antenna installation and why is it critical?
    Ans: Proper alignment ensures signal hits the target antenna, maximizing RSL and minimizing interference and service disruption.

  30. What tools are used to monitor and maintain microwave links?
    Ans: Tools include Network Management Systems (NMS), spectrum analyzers, site alignment kits, loopback testers, and SNMP monitoring software.

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