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.
Interview Question Categories
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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?
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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?
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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?
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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?
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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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