Modem Test Engineer Interview Question – Apple, Qualcomm

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When you are preparing for a Modem Test Engineer interview for companies like Apple, Google, Qualcomm, and MediaTek, you should expect a combination of technical and behavioral questions. Interviewer focus will be on understanding your expertise in modem technologies, wireless protocols, testing methodologies, and problem-solving skills.

Modem Test Engineer Interview Question for Apple, Google and Qualcomm

Interview Question Categories

  • Technical Knowledge

    • What is the difference between LTE, 5G NR, and Wi-Fi in terms of modems testing requirements?
    • Can you explain MIMO and its significance ?
    • How would you go about testing a 3G/4G/5G modem? What specific metrics or parameters do you focus on?
    • Explain RF, SNR in the performance of a modem? How do you test and optimize it?
    • Describe the purpose and process of a throughput test for a wireless modem.
    • What is the handover process in mobile networks, and how do you test this feature in a modem?

  • Tools and Test Equipment

    • What testing equipment have you used in your previous roles e.g. signal generators, network analyzers, traffic simulators, etc.?
    • How do you use a base station emulator in the modem testing process?
    • Have you worked with tools like QXDM, Test UT, or Keysight/Anritsu/Spirent for modem testing? How would you approach testing using such tools?

  • Test Methodology

    • Describe scenario where you had to perform protocol conformance testing for a modem
    • Explain how you approach automating modem tests.
    • What scripting languages or tools have you used for automation?
    • How do you ensure repeatability and reliability in your test results?
    • How do you handle testing in real-world network conditions vs. a simulated environment?

  • Scenario-Based Questions:

    • Imagine you are testing a new modem that has inconsistent performance in different geographic regions (e.g., poor reception in rural areas). How would you investigate and fix the issue?
    • You are tasked with testing a new 5G modem that supports both standalone (SA) and non-standalone (NSA) modes. How would you structure your testing to cover both modes thoroughly?

  • Behavioral Questions:

    • Describe a challenging modem test project you worked on? How did you overcome the challenges?
    • How do you handle competing priorities when testing a modem under tight deadlines?
    • Give an example of when you had to collaborate with cross-functional teams e.g., hardware, software, RF engineers) during modem testing?

Below are the list of Question I encountered while appeared for an Interview at Apple.

  • Area of expertise?
  • What feature you have work at L2?
  • How to create call flow script in TM500?
  • What is MIB & SIB Periodicity in LTE?
  • Other SIB Periodicity?
  • What is periodicity and repetition in definition for MIB?
  • Difference between TM3 and TM4 MIMO configuration in LTE?
  • Given the scenario, where TM3 is used and where TM4 MIMO configuration is used?
  • Which DCI format is used for TM3 and TM4 ?
  • SIB Modification Procedure?
  • 5G NR Experience Brief?
  • What all frequency bands you have working for 5G NR ?
  • What is new thing in 5G PDCP compare to 4G?
  • What is new Layer SDAP application in 5G SA?
  • Re-ordering which layer is responsible in 5G SA ?
  • What is a MAC-CE  and its bit map for CA?
  • What are RRC Establishment causes?
  • What is use of RRC Establishment causes high priority access?
  • UE Cell selection and reselection procedure?
  • Cell Reselection parameters and their uses?
  • CA Band Classes and band definition?
  • What is FGI in 4G and Feature Set in 5G?
  • What are different UE Categories?
  • What is difference between Cat-M and Cat-0 UE?
  • What is the advantage and disadvantage of NB-IoT?
  • What is RRC Suspend feature is NB-IoT?
  • What are RRC Inactive state in 5G NR and how it works?
  • Does cell reselection happens in RRC Inactive state?
  • RAN Area Notification feature in 5G?
  • Beam Selection and Beam Switching procedure ?
  • Subcarrier spacing and Frequency band relation in 5G?
  • Question on Base Station Simulator like call box CMW 500?
  • Question on UE Simulator TM500?
  • Python Expertise?
  • Tools used like QXDM, Sanjole, Channel Emulator expertise?
  • What is use of N26 Interface and why we need N26 interface in 5G?
  • What is redirection feature for for Voice in 5G?
  • Why EPS fallback is required ?
  • What is PDU Session and PDU session ID?
  • What is use of Tracking Area Update feature?
  • Handover Procedure Call flow, different event definition with example?
  • Explain Inter beam mobility procedure?
  • Neighbor Relation Table (NRT) parameters for Handover?
  • Meas Object, Report Config and Meas ID relation?
  • CBRA and CFRA RACH Procedure?
  • RACH Parameter like RACH Config Index, PRACH Format?
  • RACH parameter for FDD and TDD?
  • TCI and Quasi-Colocation Concept ?
  • PCFICH Channel in 4G, Why it is not required in 5G?
  • Concept of COREST?
  • No. of Test Case/Volume Handled by the You?
  • Who design the test case, Pass/Fail Criteria?
  • Test case flavor like throughput, mobility, Voice?
  • What kind of issue observed during throughput testing?
  • How to troubleshoot low throughput issue layer wise, explain the steps?
  • How TDD and FDD duplexing can impact the peak throughput?
  • How subcarrier spacing can impact peak throughput?
  • What type of configuration changes can be done to get best latency like SR periodicity, SCG or MCG Bearer Configuration, QoS Configuration etc,
  • What is performance testing?
  • How to test Radio Conformance?
  • How PUSCH nominal power can impact the throughput performance?
  • How to test DRX feature without UE logging tool?
  • What is timing advance, how to test timing advance from UE prospective.
  • UE SSB selection and RACH? Beam Mobility and measurement of other SSBs?
  • What all tool you have worked like Keysight, Qualcomm etc.?
  • What is NSA deployment and Why it is useful for the operator to choose NSA?
  • How data flow happens in NSA protocol stack?
  • An application required high data rate and low latency, What type of spilt bearer configuration is useful? – Dedicated bearer with SCG-only bearer configuration
  • What is K values (K0, K1 and K2) in 5G NR?
  • How can we make PDSCH more robust?
  • What are different DMRS configuration?

Tips for Preparing Modem Test Engineer:

  • Understand the technologies: Be prepared to explain wireless communication standards, such as LTE, 5G NR, and Wi-Fi protocols, as well as testing principles like modulation, RF characteristics, and throughput.
  • Hands-on experience: Highlight any practical experience you have with tools like QXDM, Keysight, Anritsu, or network simulators. Show how you’ve used them in real-world testing scenarios.
  • Company culture: Research each company’s focus and products. Understanding the specifics of their modem-related technologies (like Apple’s focus on iPhones, Qualcomm’s Snapdragon modems, or MediaTek’s chipsets) can help you tailor your answers.
  • Problem-solving skills: Be ready to provide examples of how you solved specific issues during modem testing and how you approach debugging.

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