The initial screening was a phone interview.

Questions were based on the resume and covered CDMA, soft-handover, and OFDM.

I was then invited for an on-site interview.

The on-site interview consisted of discussions with 7 senior engineers.

Qualcomm is well-organized in conducting these interviews, so the only thing you need to worry about is being prepared and confident.

All the interviewers were extremely humble and nice. They will test your knowledge in all the areas mentioned in the job description and resume, so read through everything.

Here are the questions I was asked. I hope this helps.

• Difference between GSM and CDMA.
• Rake receiver – how do they combine signals?
• Draw a constellation diagram and explain the difference between 64-QAM and 16-QAM.
• What is the difference between TCP and UDP?
• What is fast retransmit in TCP?
• How does OFDM allow for high data rates compared to GSM? What is the trade-off?
• What is the trade-off of using a higher modulation scheme?
• How many non-overlapping channels are in 802.11? Name them.
• Explain RF planning and design.
• What is equalization? How is it done?
• Cyclic prefix.
• Does TCP use positive or negative acknowledgments?
• How are carriers made orthogonal in OFDM?
• What do you know about LTE/4G networks?
• What does an LTE phone do when it is switched on first?
• What does the capacity of a MIMO channel depend on?
• Why are 4x4 or 8x8 MIMO not implemented? (No space in phone hardware).
• Why is soft handover not used in GSM and LTE? (Spare time slots and sub-channels used are too precious to use for soft handover).
• Arrange in order of capacity: MIMO, SIMO, MISO.
• Although SIMO is better than MISO, it is more commonly used. Why is receive diversity not exploited? (No space on mobile phones to have multiple antennas).
• What are pico and femto cells?
• What is FDD and TDD?
• What is half rate in FDD and TDD?
• Lots of conceptual questions on frequency-selective fading in DSSS and OFDM.
• How is multipath mitigated in OFDM and DSSS?
• How does a receiver do demodulation?
• How does the receiver know when a transmission ends in TCP?
• What are pilot sequences? How are they used? (Used in OFDM).
• What does a 3dB gain/loss imply?
• What are Rayleigh and Rician fading?

During lunch, I was given a problem on how I would optimize the traffic at the access point used at the cafeteria. We discussed it during the entire time allotted for lunch.