WCDMA Interview Questions and Answers

This page provides a WCDMA questionnaire set prepared by experienced specialists in the WCDMA domain. These top 10 WCDMA interview questions and answers will help engineers seeking WCDMA/UMTS jobs to crack the interview on their first try. These questions are also very useful as viva questions.

Question-1. What is CDMA? Explain different versions as per 3GPP releases.

Answer-1 : CDMA (Code Division Multiple Access) is a digital cellular technology which allows multiple users to share the same frequency band by assigning unique codes to each communication. In 3GPP, CDMA was introduced with Release 99 as part of UMTS standard.

Question- 2. What is the basic difference between CDMA and GSM?

Answer-2 : CDMA assigns unique codes to users, allowing multiple users to share the same frequency band simultaneously. GSM, on the other hand, divides frequencies into time slots, assigning each user a specific time slot on a specific frequency

Question- 3. Differentiate CDMA technique with respect to TDMA and FDMA.

Answer-3:

• FDMA (Frequency Division Multiple Access): Allocates separate frequencies to each user.​
• TDMA (Time Division Multiple Access): Allocates separate time slots to each user.
• CDMA (Code Division Multiple Access): Allocates unique codes to each user. ​

Question-4. What is the difference between EV-DO and EV-DV?

Answer-4: EV-DO (Evolution Data Optimized), EV-DV (Evolution Data and Voice)

Question- 5. What is spread spectrum?

Answer-5 : It is technique in which signal is transmitted over bandwidth significantly larger than the minimum required. Increases robustness against interference and makes information more secured.

Question- 6. What is compressed mode in WCDMA?

Answer-6: Compressed mode in WCDMA introduces transmission gaps which allows UE to perform measurements on the other frequencies or RATs without requiring dual receivers.

Question- 7. What is the difference between QPSK and OQPSK?

Answer-7 : QPSK stands for Quadrature Phase Shift Keying and OQPSK stands for Offset QPSK.

Question- 8. Explain WCDMA frame structure.

Answer-8: WCDMA radio frame is about 10 ms long and consists of 15 slots, each having duration of about 0.666 ms.

Question- 9. What are the physical, transport, and logical channels in WCDMA? Explain the function of each.

Answer-9:

• Logical Channels: Define the type of information transmitted, such as control or user data.​
• Transport Channels: Describe how and with what characteristics data is transferred over the air interface.​
• Physical Channels: Represent the actual transmission over the air, including modulation and coding.

Question- 10. What is the function of the channelization code, scrambling code, and synchronization code?

Answer-10 :

• Channelization Code: Used to separate different physical channels within the same cell.​
• Scrambling Code: Distinguishes transmissions from different cells or UEs, aiding in interference reduction. ​
• Synchronization Code: Assists UEs in detecting and synchronizing with the network during initial access.

Question- 11. What is the difference between DSSS and FHSS?

Answer-11 : DSSS stands for Direct Sequence Spread Spectrum where as FHSS stands for Frequency Hopping Spread Spectrum.