5G-NR Interview Questions
- What is the main difference between 5G NR and LTE in terms of PHY design?
- Name and briefly describe the three main use cases for 5G NR.
- How does 5G NR address enhanced Mobile Broadband (eMBB)?
- What is the architecture of the 5G NR radio access network?
- What are the main building blocks of the 5G Core Network?
- Explain the concept of network slicing in 5G.
- What is SDAP and what function does it serve in NR?
- What entity is responsible for session management in 5G?
- What is the role of the AMF in 5G NR?
- Describe the difference between user plane and control plane in 5G NR.
- List the protocol layers in the 5G NR radio stack.
- What does the acronym NR stand for?
- List the major responsibilities of the 5G NR physical layer.
- What frequency ranges are defined for 5G NR, and what are their key differences?
- How do SA and NSA 5G deployments differ architecturally?
- What is a PDU Session in 5G NR?
- How does 5G enable seamless interworking with LTE?
- What is service-based architecture (SBA) in 5G?
- List the main reference points/interfaces in 5G NR.
- What is the difference between F1 and E1 interfaces?
- What is numerology in 5G NR?
- List all subcarrier spacings supported in 5G NR.
- How does numerology affect slot duration in NR?
- Define a mini-slot and explain its use case.
- Draw and explain the 5G NR radio frame structure.
- How does NR support multiple numerologies within a cell?
- Define slot, subframe, symbol, and TTI in NR context.
- What is an SSB and what does it contain?
- How are PSS, SSS, and PBCH mapped within an SSB?
- How many SSBs can be transmitted per SSB burst?
- What is the meaning and purpose of Point A in NR?
- Explain the difference between a CRB and a PRB.
- What is kSSB and why does it matter for SSB location?
- How is overall channel bandwidth divided in NR?
- What is a Bandwidth Part (BWP) in NR?
- Describe the benefits of BWP for UEs.
- How does BWP switching occur in 5G NR?
- What is CORESET and what does it enable in NR?
- List key differences between CORESET and the LTE control region.
- How are guard bands handled differently in NR versus LTE?
- List and briefly describe the main physical channels in NR.
- What is the function of PBCH in NR?
- Describe how the Master Information Block (MIB) is transmitted in NR.
- Which parameters are always present in the NR MIB?
- State the periodicity of MIB and SIB in 5G NR.
- How is SIB1 transmitted differently in NR versus LTE?
- What is PDCCH-ConfigSIB1?
- Define a search space in PDCCH configuration.
- How does UE acquire SIB1 in NR?
- What are the roles of BCCH and DL-SCH in system information broadcasting?
- What key info is included in SIB1 for 5G NR?
- How is SI scheduling different in NR compared to LTE?
- What is the Type0-PDCCH CSS set?
- How does a UE determine if a cell is SA or NSA based on SI?
- How is SIB1 delivered in SUL/SDL scenarios?
- What is the paging message, and what events trigger paging in NR?
- Compare the implementation of paging in LTE and NR.
- Describe DRX and paging occasions for power saving.
- How does a UE determine its own paging frame and subframe?
- Explain the role of SI request in NR.
- Why is RACH needed in 5G NR?
- What events can trigger a RACH procedure in NR?
- Describe all steps of a random access procedure in NR.
- Differentiate between contention-based and contention-free RACH.
- How is a PRACH preamble generated and transmitted?
- How many unique PRACH preambles are there in NR?
- What determines the preamble format in PRACH?
- What is the zeroCorrelationZoneConfig parameter?
- How does Ncs relate to PRACH collision avoidance?
- What is the function of the Root Sequence Index in PRACH?
- How is PRACH Configuration Index used for RACH occasions?
- Calculate the number of PRACH occasions for a typical configuration.
- What is contained in the Random Access Response (RAR)?
- How does contention resolution work in RACH?
- What is beam failure recovery in NR?
- How does RACH differ in SA vs NSA?
- How does the SSB beam association process relate to RACH?
- What fields are signaled in a RAR message?
- How does PRACH support multi-beam operation?
- How does the gNB differentiate UEs during RACH contention resolution?
- List all RRC states defined in 5G NR.
- Explain the purpose and benefits of the RRC INACTIVE state.
- Describe all possible state transitions between RRC states.
- What is the significance of 5G-S-TMSI in paging?
- Name all types of SRBs in 5G NR and their usage.
- What is the role of SRB3?
- Which events trigger RRC connection setup in NR?
- Name and explain all messages exchanged during RRC connection setup.
- When and why does the UE request AS security activation?
- What are RRC procedures involved in mobility?
- How does inter-RAT mobility work at the RRC layer?
- What is the function of RRC Release in NR?
- What is the RRC re-establishment procedure and when is it used?
- Differentiate between RRC Reconfiguration and Re-establishment.
- Define a DRB in NR and its role.
- How are DRBs established for a new PDU session?
- What is contained in a UE Capability Information message?
- Why does the UE send measurement reports in NR?
- How is RRC signaling different in NSA mode versus SA mode?
- List at least three RRC timers and their functions.
- What types of mobility are supported in NR?
- Compare cell-level and beam-level mobility.
- Describe step-by-step the intra-NR handover process.
- How is inter-RAT handover to/from LTE performed in NR?
- What is the NSA (EN-DC) handover process?
- Explain the process and benefit of data forwarding during HO.
- Why are measurement gaps needed in NR?
- How does beam switching differ from handover?
- What is make-before-break handover?
- How does NR handle data reordering and duplication in HO?
- What is the sequence for dual connectivity handover?
- How does the UE report capability for inter-RAT HO?
- What is the role of NG-RAN in mobility?
- Describe the use of Xn interface in inter-gNB mobility.
- What are the responsibilities of AMF and SMF in HO?
- How is the security context handled in handover?
- Under which scenarios does the UE re-acquire SSB after handover?
- How does SUL impact handover decisions?
- What are the fast recovery steps for beam failure?
- What is the role of CRNTI in the HO process?
- List the core responsibilities of the NR MAC layer.
- How does the MAC map logical to transport channels?
- Explain the structure and function of MAC SDUs and CEs.
- What is the role of MAC in error correction?
- Define HARQ and its function in NR.
- How many HARQ processes are possible in NR?
- Compare HARQ management between NR and LTE.
- What is codebook-based feedback in NR HARQ?
- How does HARQ support mini-slots?
- How does flexible TTI affect HARQ operation?
- What is asynchronous HARQ, and how is it used?
- How does NR implement beam-specific HARQ retransmissions?
- How is DRX configured in NR?
- What improvements exist in NR DRX over LTE?
- How does MAC layer aid in beam management?
- Explain the scheduling request (SR) procedure in NR.
- How is logical channel prioritization handled?
- What is the purpose of MAC padding?
- How does MAC support QoS flows in NR?
- What is the procedure for buffer status reporting?
- Define a QoS flow in 5G NR.
- How are QoS flows mapped to IP packets in NR?
- What is the difference between GBR and non-GBR flows?
- Explain the meaning and function of 5QI.
- How does the scheduler handle QoS priorities in NR?
- What does the SDAP layer do?
- How is QoS support in NR improved over LTE?
- What is reflective QoS in NR?
- Name and describe the different PDU session types.
- How does network slicing interact with QoS management?
- What is the function of UL/DL packet marking in NR?
- What is ARP and how is it used in NR?
- How is QoS mapped when interworking with LTE?
- What is the limit on the number of QoS flows per session?
- How does the network perform dynamic QoS modification?
- Compare per-flow and per-bearer scheduling.
- How is ultra-low latency supported in NR QoS?
- What is the SDAP header and why is it important?
- Differentiate between session management and QoS management.
- List all physical DL/UL channels in NR.
- How are transport and physical channels mapped?
- What modulation schemes are supported in NR?
- What is the maximum supported modulation order?
- Where is polar coding used in NR?
- Where is LDPC used, and what are its benefits?
- Explain the MCS selection procedure in NR.
- What is the function of DMRS in NR?
- Explain the use of CSI-RS in downlink.
- What is PT-RS and its role?
- How does channel coding differ for control and data channels?
- What is slot aggregation?
- Describe the purpose of Rate Matching in NR.
- What is dynamic TDD and how is it managed in NR?
- Compare normal and extended cyclic prefix in NR.
- How does RNTI selection affect DCI decoding?
- List all reference signals in NR and their purpose.
- What is SRS and what function does it serve?
- Describe how PUSCH resources are allocated.
- How is dynamic uplink scheduling achieved in NR?
- What is DCI and its purpose in NR?
- Explain all DCI formats defined in NR.
- How does aggregation level impact DCI decoding?
- Define CCE and REG.
- What is blind decoding in DCI detection?
- Differentiate between UE-specific and common search space.
- What is CORESET#0?
- How does NR enable PDCCH scheduling for URLLC?
- What are Control Channel Elements (CCEs)?
- How does DCI enable uplink and downlink scheduling?
- Compare PDCCH mapping in LTE and NR.
- How does BWP configuration impact PDCCH search?
- How is a paging indication signaled in NR?
- How are CORESET and BWP related?
- Define beamforming and its significance in NR.
- How does UE select the best beam during access?
- Explain analog, digital, and hybrid beamforming.
- What is the function of CSI-RS in beam management?
- Describe beam failure detection and recovery.
- How is massive MIMO realized in NR?
- List all spatial multiplexing types in NR.
- What is the maximum number of MIMO layers in NR?
- How does SSB beam sweeping work?
- How does scheduler assign beams to UEs?
- Compare reciprocity-based and feedback-based beamforming.
- What is a CRI and how is it used?
- What is a multi-TRP and its advantages?
- Define SSBRI and its application.
- How does multi-TRP enhance reliability in NR?
- What is EN-DC and what advantages does it offer?
- How does secondary node addition occur in NSA?
- Explain MCG and SCG in EN-DC context.
- What is MR-DC?
- How are bearers managed in dual connectivity?
- How does HO differ between NSA and SA?
- How are SRB and DRB setup in dual connectivity?
- What is the X2/Xn interface role in DC?
- How does DC affect UE battery life?
- How does NR manage fallback to LTE?
- Compare NSA and SA attach call flows.
- How is data path selection achieved in dual connectivity?
- What is an LTE anchor cell in NSA?
- What is SCG failure and how is it handled?
- What is the effect of non-ideal backhaul in EN-DC?
- Explain carrier aggregation in 5G NR.
- How is SUL configured in NR?
- What is SDL and why is it important?
- How does a UE choose between UL and SUL?
- What is inter-band CA?
- What challenges exist for CA in mmWave?
- What is the role of multi-band SSBs?
- How is spectral efficiency maximized in CA deployments?
- What is the max number of carriers supported in NR CA?
- What is DSS and how does it operate?
- Explain cross-carrier scheduling in NR.
- How is SUL handover performed?
- How does NR manage power across aggregated carriers?
- What is the carrier indicator field in DCI?
- What is the importance of band combinations in CA?
- How is NAS security activated in NR?
- Which algorithms are used for ciphering/integrity in NR?
- Describe the process of security key derivation in NR.
- What is the role of the 5G AKA procedure?
- How is security context managed differently in NR and LTE?
- How is security context transferred during inter-RAT HO?
- What is AS/NAS security separation?
- Explain NGAP security in NR.
- What is integrity protection and how is it ensured?
- How is replay protection implemented in NR?
- Name unique security threats in 5G NR.
- What are SUCI and SUPI in NR?
- How is user plane security handled for split bearers?
- What is the function of SEAF in authentication?
- When and how are session keys renewed in NR?
- What RRM measurements are mandatory in NR?
- How does UE report RSRP, RSRQ, SINR in NR?
- What is CQI in NR and how is it reported?
- List all standard measurement events in NR.
- Explain events A1-A5 in NR.
- What is beam-specific measurement reporting?
- How does the gNB configure measurement reporting?
- How are measurement gaps managed in NR?
- How are inter-frequency measurements performed in NR?
- List at least five KPIs for 5G NR optimization.
- What is BLER and how is it used for link adaptation?
- Name typical causes of RACH failure.
- How is handover failure detected in NR?
- Define Radio Link Failure (RLF) in NR.
- What tools are used for protocol testing in NR?
- How do you debug paging failures?
- What error counters exist in NR layers?
- How is throughput measured and optimized?
- What are challenges in mobility optimization for NR?
- Which KPIs indicate poor QoS?
- What are the key differences between “Reference Point” and “Service-Based” architecture in 5G Core?
- What is the function of the Network Exposure Function (NEF)?
- Describe the role and use case of the Network Function Repository Function (NRF).
- What are the advantages of splitting CU into Control Plane (CP) and User Plane (UP) functions?
- What are the typical deployment options for distributed unit (DU) and central unit (CU)?
- Explain the practical impact of passive vs. active antennas in gNB design.
- What is CP-UP separation and why is it important for cloud-native 5G?
- Describe “base station class” distinctions in 5G and give an example of each.
- How is the Xn interface different from X2, and what are their primary use cases?
- Explain the F1 interface and its impact on CU-DU splits.
- What triggers the use of the E1 interface in gNB deployments?
- How is the NG interface structured and what protocols does it carry?
- What does “Fl split” mean in 5G RAN architecture?
- Describe the difference between User Plane and Control Plane protocol stacks in NR.
- Outline the steps in Registration Management in 5G SA mode.
- What is the process of Access Control in 5G NR and how does it protect the network?
- What is a PDU session and how does it differ from an LTE bearer?
- Explain the principle of “edge computing” in 5G and the role of the UPF.
- What are “micromodes” in the context of 5G NR?
- How does the network determine UE capabilities during registration?
- Explain the difference between IMSI and 5G-GUTI for UE identity.
- What is a SUPI and how is it concealed over the air interface?
- What is SUL (Supplemental Uplink) and in which scenarios is it useful?
- What challenges are associated with mmWave propagation in 5G NR?
- How do operating bands and band combinations affect UE design complexity?
- What is “quasi co-location” and where is it used in NR?
- How does 5G NR handle TDD pattern switching in the field?
- How are antenna ports numbered and mapped to beams?
- What are the practical considerations for deploying massive MIMO in dense urban environments?
- What is the main advantage of using “multi-user MIMO” in NR?
- How is beamforming different in FR1 and FR2?
- What is a “beam group” in beam management?
- What is a virtual resource block (VRB) and how does it relate to PRBs?
- What is the purpose of the “frequency raster” in 5G NR?
- How does synchronization raster differ from channel raster?
- What determines the maximum channel bandwidth in a given NR band?
- What are the uplink waveform options in NR and their respective pros/cons?
- How does the use of cyclic prefix (CP) affect the NR air interface?
- In what cases is DFT-s-OFDM preferred over CP-OFDM in NR?
- What is the benefit of “mini-slot” scheduling for URLLC?
- Describe the complete mapping of downlink channels to physical resources in NR.
- What is the function of the SS/PBCH block and how is it scheduled?
- How does the NR SSB burst set support initial access and beam management?
- What are the CORESET configuration parameters and how do they influence control coverage?
- What is a reserved resource in the PDSCH and why is it important?
- How does pre-emption work for dynamic multiplexing in NR?
- What is “resource block bundling” and its role in interference management?
- Explain the role and design of phase tracking reference signals (PT-RS).
- How does repetition improve reliability in the downlink?
- Explain PRACH generation for “long” and “short” sequence formats.
- What is the background and evolution of PRACH design from LTE to NR?
- What is a “PUCCH group” and how does it relate to uplink control resource allocation?
- Compare all PUCCH formats in NR and their appropriate use cases.
- How are uplink shared channels (PUSCH) resource allocations performed?
- What are the key parameters for SRS configuration and what do they optimize?
- What steps comprise the beam management framework in NR?
- How does “PMI beam selection” work for closed-loop MIMO?
- What triggers a beam failure recovery procedure and how is it executed?
- Explain “uplink beam refinement” and its importance for coverage.
- What measurements are used to support downlink vs. uplink beam refinement?
- How are beam IDs signaled and tracked at the gNB and UE?
- What is the difference between SS-RSRP and CSI-RSRP?
- Describe the calculation of SS-SINR and its typical range.
- What is Layer 3 filtering and why is it important for measurement reporting?
- What is event A6 and in what scenario is it triggered?
- What is event B2 and its use case in inter-RAT mobility?
- How does the network configure measurement reporting periodicity?
- Describe the paging procedure in NR step by step.
- What are the mechanisms for cell reselection in 5G NR?
- How is absolute priority used in cell reselection decisions?
- What is a “mobility state” and how does it affect reselection timers?
- What is the format and function of the NR PLMN selection procedure?
- What is prioritized random access and when is it used?
- How does timing advance procedure differ between PUSCH and PUCCH?
- How does the network command power control for uplink PUCCH and SRS?
- How is UE power class determined and used in scheduling?
- What are the mechanisms for downlink power control in NR?
- What is the relationship between PHR (Power Headroom Reporting) and UL scheduling?
- What is Radio Link Monitoring (RLM) and how does it contribute to link reliability?
- What is the definition and detection method for radio link failure in NR?
- What is discontinuous reception (DRX) and how is it configured for both idle and connected modes?
- What is the architecture and flow of Voice over NR (VoNR)?
- Describe EPS fallback and its triggers in SA NR.
- What is RAT fallback and how is it managed during call setup?
- Explain the steps of LTE RRC idle mode procedure when integrated with 5G NR.
- Walk through the EN-DC secondary cell addition procedure.
- What is the initial context setup procedure and its key messages?
- How is Xn-based handover performed in NR?
- What is the function of RRC Connection Release in dual connectivity scenarios?
- How is the NR-ARFCN calculated from center frequency?
- What is a GSCN and why is it needed in NR initial access?
- Explain the role of PCI allocation in NR planning.
- What steps are involved in throughput expectation and capacity planning?
- How do slot formats affect planning for different numerologies?
- How does CSI reference signal planning optimize beamforming performance?
- What considerations are required for PRACH planning in a multi-cell network?
- What is the process for tracking area planning and optimization?
- What is Dynamic Spectrum Sharing (DSS) and what are its deployment challenges?
- How does DSS affect SSB scheduling and legacy LTE users?
- Compare the use and over-the-air protection of IMSI, IMEI, SUPI, SUCI in NR.
- What is the process of 5G-S-TMSI assignment and update?
- How is I-RNTI used in random access procedures?
- If a UE reports repeated RLF, what are the main troubleshooting steps?
- How would you analyze a sudden increase in PRACH failures across a sector?
- How do you optimize DRX settings for maximum battery life in NB-IoT vs. eMBB UEs?
- How do you plan PCI for a dense urban grid to avoid collision and confusion?
- If VoNR MOS scores are low, what protocol layers and measurements do you investigate?
- How would you investigate high HARQ NACK rates in FR2 deployments?
- What KPIs would you monitor during a drive test for a greenfield 5G deployment?
- If handovers fail only for high-speed UEs, what configuration parameters do you review?
- How would you identify and resolve coverage holes in a mmWave cluster?
- What are the use cases and deployment models for private 5G NR networks?
- How can 5G NR be leveraged for ultra-precise indoor positioning?
- What are the security challenges unique to network slicing?
- How do open RAN (O-RAN) architectures impact interoperability testing?
- What steps are necessary for a UE to support both NR and NB-IoT in a dual-mode configuration?
- What is the principle of RedCap (Reduced Capability NR) and what scenarios require it?
- What is the expected impact of quantum computing on NR encryption schemes?
- What is the main function of network exposure function (NEF) for 3rd-party integration?
- How will distributed MIMO (D-MIMO) change the landscape of cell planning?
- What are the regulatory and policy implications of DSS for legacy networks?
- If your cell site reports abnormal ARFCN conflicts after a spectrum refarm, what steps do you take?
- What is your approach to detecting and resolving ghost PCI events in a live NR network?
- If a site’s Xn interface repeatedly fails, but F1 is healthy, what troubleshooting do you perform?
- How would you test DRX performance in both idle and connected mode in a lab?
- What actions do you take if SSB detection fails at the cell edge, but midcell performance is normal?
- A UE in EN-DC mode suddenly drops all NR bearers but keeps LTE—what logs and traces do you review?
- How would you validate end-to-end throughput performance for an NR FWA deployment?
- If uplink grant-free transmissions suddenly experience high BLER, what layers do you check first?
- If a regulator suddenly mandates new lower power limits for FR2, what features/protocols are affected?
- How do you test and validate phase tracking reference signals in real field conditions?
- What approach do you recommend for PCI planning in overlapping NR/LTE coverage zones?
- How do you ensure MIB/SIB compatibility for multi-vendor gNB deployments?
- If you had to explain 5G NR to a high school student, how would you do it in one minute?