3 g optimization interview topics
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  • 1. 3G Optimization Interview Topics 1. Important parts of Benchmarking Report a. RSCP Coverage b. Ec/Io Coverage c. CSSR d. DCR e. Retainability f. Handover (Mobility) g. Call Setup Time h. ASU Type i. 3G-2G Serving percentage j. IRAT Handover k. BLER and Quality statistics 2. UMTS Channels a. CPICH b. SCH c. AICH d. BCH – BCCH e. FACH – CCCH f. RACH – CCCH g. DCH – DCCH 3. HSDPA Channels a. HS-DPCCH (uplink signaling) b. HS-SCCH (downlink signaling) c. HS-PDSCH or HS-DSCH (data channel) 4. HSUPA Channels
  • 2. a. E-DPDCH b. E-DPCCH c. E-DCH d. E-AGCH e. E-RGCH f. E-HICH 5. Dropped Call Types a. Missing Neighbor b. Poor Coverage c. Pilot Pollution d. Congestion e. Not Radio Reasons f. Equipment Fault 6. Blocked Call Types a. Security and Authentication Mode Failure b. UE Issues c. Disconnect on RAB Setup d. Unavailable Resource e. UE Sensitivity Fault f. Unanswered RRC requests g. Barred Network 7. Major Network Problems a. Poor Coverage b. Poor Cell Dominance c. Pilot Pollution d. Missing Neighbors e. Corner Effects 8. Important Events in PS Call
  • 3. a. Attach and Detach b. PDP Context Activation c. Download and Upload d. Dual Mode 9. HSDPA Categories a. 3.6 Mbps – Cat 5 & 6 (5 HS-DSCH Codes) b. 7.2 Mbps – Cat 8 (10 HS-DSCH Codes) c. 14.4 Mbps – Cat 10 (15 HS-DSCH Codes) d. 21.1 Mbps – Cat 14 (15 HS-DSCH Codes, MIMO and 64 QAM) 10. Number of CE for PS 384 = 10 11. Number of Users for PS 384 = 3 12. HSDPA Factors a. Number of HSDPA Codes b. Number of HS-SCCH Codes c. Max HS-PDSCH Codes per Users d. Algorithm and Scheduling e. Number of HARQ Process 13. HSDPA Parameters a. HS-SCCH Power Offset b. Measurement Power Offset c. CQI Feedback Cycle, Power Offset d. ACK-NACK Power Offset e. Number of HARQ Process f. MAC-hs window size g. Tx- Rx Window size 14. HSUPA Parameters a. E-DPCCH to DPCCH Power Offset b. Happy Bit delay
  • 4. c. E-TFCI Power offset d. E-AGCH Channelization Code e. E-AGCH Power Offset 15. Reasons of Low Throughput in HSDPA: a. Poor RF Conditions (Low CQI) b. Frequent Serving Cell Change (Low CQI) c. Signaling Delay d. E1d setting issues e. TCP segment loss outside air interface f. TCP Tx/Rx window setting g. Iub Flow Control h. FTP server issues 16. HSDPA Scheduler Type a. Max C/I b. Round Robin c. Proportional Fair (mostly used) 17. Timers and Counters a. T300, N300 (2sec) RRC Connection Retransmission b. T312, N312 (1 sec) “In Sync” establishment c. T313, N313 (5 sec) “Out of Sync” Failure d. T314 (12 sec) Cell Update (CS) e. T315 (180 sec) Cell Update (PS) f. T302, N302 (1.2 sec) Cell Update Confirm 18. Resources for Each Call Type a. AMR SF 128 CE 1 (UL) 1(DL) b. VP SF 32 CE 3 (UL) 2 (DL) c. PS 128 SF 16 CE 5 (UL) 4 (DL) d. PS 384 SF 8 CE 10 (UL) 8 (DL)
  • 5. 19. Event Thresholds a. E1a 3dB b. E1b 6dB c. E2d -12dB and -101 dBm d. E2f -10dB and -99dBm 20. NASTAR a. Network performance and monitoring tool b. SQL Based c. Collect data from M2000 d. Data storage up to 3 months e. Supports 5 RNC and 6000 Cells 21. NASTAR Inputs: a. RNC performance data M2000 / BAM b. Project Parameters Manual c. Configuration Parameters M2000 d. CHR Data M2000 / BAM e. Interference data M2000 / BAM f. Coverage Data LMT client g. NodeB performance data M2000 22. NASTAR Analysis: a. Performance Analysis b. Neighbor Cell Analysis c. Call Drop Analysis d. Pilot Pollution Analysis e. Interference Analysis f. Resource Monitoring i. CPU Utilization ii. Iub Utilization
  • 6. iii. Traffic Load iv. Cell Load 23. Monitoring Levels a. Level 1 – Statistics, Alarm Logs (M2000) b. Level 2 – Sample tracing, CHR (M2000 and NASTAR) c. Level 3 – DT Data, Single UE Tracing 24. NASTAR Performance Data: a. RAN Counters (KPI) b. Call History Records (CHR) CDR Analysis c. System History Records (SHR) Cell Status d. Real-Time User Monitor (RUM) IMSI Tracing e. Real-Time System Monitor (RSM) Load, Inference, etc 25. NASTAR Counters: a. For calculating Call Drop Rate b. For calculating Handover Success Rate 26. LMT Trace Message Levels: a. To or From NodeB NBAP b. To or From CN RANAP c. To or From UE RRC 27. Throughput Types in Actix a. Payload L1 with CRC blocks b. Throughput L1 without CRC blocks c. PDU throughput MAC/RLC Interface d. SDU throughput RLC/RRC Interface or RLC/PDCP Interface L1 Throughput > PDU Throughput > SDU Throughput 28. Signal Flow (R99 MO)
  • 7. a. RRC Connection Request (UL-CCH) i. TMSI and LAI info ii. LAC iii. PSC info including Ec/Io and RSCP level iv. Establishment cause (CS, PS, VP) b. RRC Connection Setup (DL-CCH) i. S-RNTI ii. RLC Mode (AM, UM, TM) iii. Transport Channel Type iv. Timers and Parameters c. RRC Connection Setup Complete (UL-DCCH) i. Domain Identity (CS or PS) ii. Security Parameter supported d. Initial Direct Transfer (UL-DCCH) i. Notification and Capabilities of UE ii. Mobile TMSI e. Downlink Direct Transfer (DL-DCCH) i. RAND Value, Authentication f. Uplink Direct Transfer (UL-DCCH) i. Authentication Response g. Security Mode Command (DL-DCCH) i. Ciphering and Integrity
  • 8. h. Security Mode Complete (UL-DCCH) i. Response from UE i. Uplink Direct Transfer (UL-DCCH) i. Authentication Code j. Downlink Direct Transfer (DL-DCCH) i. CC Call Proceeding k. Radio Bearer Setup (DL-DCCH) i. Transport Channel Info l. Radio Bearer Setup Complete (UL-DCCH) i. Response from UE m. Downlink Direct Transfer (DL-DCCH) i. Alerting n. Downlink Direct Transfer (DL-DCCH) i. CC Connect o. Uplink Direct Transfer (UL-DCCH) i. Connect Acknowledgement 29. Load Control a. Load Monitoring (LDM) b. Load Reshuffling (LDR)
  • 9. c. Overload Congestion Control (OCL) 30. Load Reshuffling Actions: a. First Action – Code Tree Reshuffling b. Second Action – Inter Frequency HO c. Third Action – BE Service Rate reduction d. Fourth Action – Renegotiation of QoS real time services 31. Scanner vs UE Data Scanner is used to scan all carriers and DL Scrambling codes, while UE measures only codes of informed cells (through BCH and measurement control Neighbor List) 32. INTER RAT Types: a. IRAT Handover (CS) b. IRAT Cell Change Order (PS) 33. Call Flow for IRAT Handover: a. RRC Measurement Report UL b. Physical Channel Reconfiguration DL c. Physical Channel Reconfiguration Complete UL d. Handover from UTRAN Command GSM DL e. Handover Complete 34. Call Flow IRAT Cell Change Order a. RRC Measurement Report UL b. Physical Channel Reconfiguration DL c. Physical Channel Reconfiguration Complete UL d. Cell Change Order from UTRAN DL e. Immediate Assignment DL f. Authentication Response UL g. TMSI Relocation Complete UL 35. Compressed Mode Methods a. SF/2 (CS, PS) Code Compression
  • 10. b. HLS (PS only) Higher Layer Scheduling 36. IRAT HO due to Overload – event 3A 37. Physical Channel Reconfiguration Message details a. gsm-Carrier RSSI Measurement b. gsm-Initial BSIC Identification c. gsm-BSIC Reconfirmation 38. Huawei Tools : a. Genex U-Net (Planning and Simulation) b. Genex WCDMA Probe (Drive Testing and Logging) c. Genex Assistant (Post Processing) 39. Huawei NodeB Type a. BTS3812 (GSM BTS upgradable to WCDMA) b. BTS3900 A (Macro Indoor) c. BTS3900 E (Macro Outdoor) d. BTS3900 C (Indoor Compact – Micro) e. DBS3900 (Distributed NodeB with BBU and RRU)
  • 11. 1. The output of coverage planning is needed for which one of the following processes? A. Code planning. B. Transmission planning. C. Propagation model tuning. D. Loading field measurements. Answer: A 2. If the cell range of 12.2 kbps voice service with 141.9 dB path loss is 2.3 km, what is the size of the cell area with omni-directional site (k factor for site area is 2.6)? A. 12.2 km? B. 13.8 km? C. 15.9 km? D. 16.6 km?NP Answer: B 3. Which one of the following services has the HIGHEST processing gain? A. 12.2 kbps AMR voice. B. 64 kbps RT data. C. 64 kbps NRT data. D. 384 kbps NRT data. Answer: A 4. Which one of the following parameters can be measured with a UE connected measurement system but NOT with a scanner measurement system? A. P-CPICH Ec/No. B. BLER. C. SIR. D. Scrambling code. Answer: B 5. The possible pilot pollution area can be detected from which one of the following? A. Ec/No lower than target and low number of scrambling codes seen. B. Ec/No lower than target and high number of scrambling codes seen. C. Ec/No higher than target and low number of scrambling codes seen. D. Ec/No higher than target and high number of scrambling codes seen. Answer: B 6. How can capacity (interference) be improved? A. Usage of transmission diversity. B. Increasing transmission power of UEs. C. Decreasing speed of UEs. D. Increasing SHO. Answer: A 7. For the use of a shared antenna line between GSM and WCDMA, what is needed? A. Coupler or splitter. B. One shared BTS for GSM and WCDMA. C. Same output power both GSM and WCDMA. D. Diplexer or triplexer. Answer: D 8. Which one of the following is NOT a method to decrease inter-system interference? A. Tighter filtering for the Tx signal of GSM BTS. B. Proper frequency planning in GSM. C. Usage of shared antenna line. D. Careful antenna selection and placing.
  • 12. Answer: C 9. The most appropriate reason for Power control headroom is to: A. improve the downlink reception. B. maintain the fast power control at the cell edge. C. compensate slow fading. D. increase the transmitting power of user equipment (Ue). Answer: B 10. What is the MAXIMUM number of P-CPICH signals, of similar strength, that the UE should measure? A. 1 WBTS cell. B. 2 WBTS cells. C. 3 WBTS cells. D. 4 WBTS cells. Answer: C 11. Considering 1 site (3 cells) with 1 only one carrier per cell, how many traffic hardware channels are needed if in the site the active users are: 1.8 voice, 0.7 CS64, 0.7 PS64 and 1 PS384 and knowing that for each connection the following hardware channels apply: 1 for voice, 4 for CS64, 4 for PS64 and 16 for PS384 are needed? A. 4 B. 13 C. 24 D. 37 Answer: C 12. Considering 1 site (3 cells) with 1 only one carrier per cell, what is the downlink throughput (in Kb/s) PER CELL if in the site the active users are: 1.8 voice, 0.7 CS64, 0.7 PS64 and 1 PS384? A. 64.94. B. 165.19. C. 194.82. D. 514.76. Answer: B 13. For what reason should the power control strategy be changed? A. UE location. B. UE type. C. UE service. D. UE speed. Answer: D 14. Which one of the following network planning tasks is NOT normally performed with a radio network planning tool? A. Coverage planning. B. Traffic calculation. C. Hardware channel calculation. D. Monte Carlo Simulation. Answer: C 15. The Node B antenna gain is 17 dB and receiver sensitivity 112 dBm, radiated power (EIRP) of user equipment (Ue) is 18 dBm and feeder cable loss is 3 dB. What is the MAXIMUM path loss? A. 114 dB B. 116 dB C. 144 dB D. 147 dB Answer: C
  • 13. 16. If the cell radius is 2 km and the required service area is 100 km2,how many 3-sector sites (in coverage-limited case) are needed to provide the service for the area (k factor for site area is 1.95)? A. 5 B. 8 C. 13 D. 19 Answer: C 17. What is the interference margin for 50% and 90% network loads? A. 3.0 dB and 10.0 dB. B. 5.0 dB and 1.5 dB. C. 3.0 dB and 7.0 dB. D. 4.0 dB and 10.0 dB. Answer: A 18. When applying the free space propagation loss formula both for GSM 1800 and WCDMA, what APPROXIMATELY is the propagation loss difference between the systems, if the distance from the BTS is 1500 meters? (Use frequency 2100 MHz for WCDMA.) A. 5.5 dB. B. 1.3 dB. C. 7.4 dB. D. 13.4 dB. Answer: B 19. Which one of the following does NOT make the UL adjacent channel interference worse? A. UE transmitting with maximum power. B. UE uses hard handover. C. Other operator BTS in a bad location. D. Own BTS transmitting with high power. Answer: D 20. The required Eb/No value is dependent on which one of the following factors? A. Base station antenna gain. B. Speed of the user equipment (Ue). C. Fast fading margin. D. Body loss. Answer: B
  • 14. 1- What are the main KPI to measure the performance of 3G cell - Accessibility ( RRC , RAB , CSSR) - Retainability (speech , Video , PS DCR) - Mobility (SHO , IRAT HO success rate) 2- What resources affect HSDPA throughput in 3G system - (DL power, DL code and transport capacity) 3- What parameter tuning can be done to improve HSDPA throughput in any 3G cell - increase the DL channelization codes for HSDPA - changing the scheduling algorisms 4- How can we reach 21 Mbps in P7 - 15 codes in DL and 64 QAM 5- what is the usage of the following signaling messages in RRC protocol - Actives setup updates (ADD/Remove/Replace RL in SHO) - RB reconfiguration (channel switching between Cell_DCH and Cell_FACH RRC stats) - Physical channel reconfiguration (IF HO) 6- what is the use of GPEH tool in Ericsson system - tool used to record RAN and internal events in Ericsson system and the tracing files can be analyzed by TEMS visualization 7- what types of congestion can affect the services accessibility in any 3G cell - DL power ( AMR - Directed retry - reducing High R.99 RAB users SFxx parameters) - UL/DL CE ( reducing High R.99 RAB users SFxx parameters) - DL code (reducing static codes for HSDPA –AMR-Directed retry) - Transport capacity 8- what is the difference between RSCP and EC/No measures for pilot channel - RSCP is received signal code power for CPICH channel - Ec/No is The received energy per chip divided by the power density in the band . it reflects the quality of CPICH channel 9- what is the difference of using 2nd carrier and high power amplifier in expanding the capacity for any 3G cell - 2nd carrier gives capacity in DL power and DL codes
  • 15. - High power Amplifier gives capacity in DL power only 10- what is the max bit rate that can be achieved in UL when using 10ms EUL and 2 ms EUL - 1.5 Mbps for 10 ms EUL - 5.76 for 2 ms EUL 11- how many HSSCCH channel can be configured in HSDPA cell ( - Four that allows four users per TTI