Here are some of the questions to expect in LTE interview, fellow experts can add to this list:
1) Used Multiple access Techniques?
O-FDMA – In Downlink
SC-FDMA – In Uplink
2) Used Subcarrier Spacing?
15KHz
3) No. of Bandwidths vs Resource Blocks?
(1 Radio Frame = 10 Subframe)
(1 Radio Frame = 10ms)
(1 Subframe = 1ms so, 10 SF = 10ms)
(1Subframe = 2 Time slots)
(10 Subframe = 20 Time slots/ 1 SF = 0.5ms)
1.4Mhz 6RBs
3 MHz 15RBs
5 MHz 25RBs
10 MHz 50RBs
15 MHz 75RBs
20 MHz 100RBs
4) CQI (Channel Quality Indicator)
SINR(UE)–>CQI–>>MCS(eNodeB)
Range : 0 to 15
Subrange : 0 -> out of Range
1 to 6 : QPSK
7 to 9 : 16QAM
10 to 15 : 64QAM
Note: QPSK & QAM are Modulation Schemes.
5) LTE Events?
A1, A2, A3, A4, A5, A6, B1, B2.
A1: Serving Coverage/Quality is better than Threshold.
A2: Serving Coverage/Quality is Worse than Threshold.
A3: Neighbor Cell coverage becomes better than Serving cell coverage by an offset.
A4: Neighbor Cell Becomes better than a Threshold.
A5: Serving Cell Becomes worse than Threshold-1, while Neighbor Cell Becomes better than Threshold-2.
A6: Neighbor Cell Becomes better than a secondary cell by an offset (In CA Case)
B1: Inter-System Neighbor(Other RAT- 2G/3G/CDMA)Cell becomes better than Threshold.
B2: Serving Cell becomes worse than a Threshold-1 while Inter System Neighbor Cell becomes better than Threshold-2.
Here is a brief definition of the terms used above:
Threshold: It is used when measurement of serving & Neighbor cells are not compared and while taking decision to trigger measurement report both or one cell measured independently.
for example: A1, A2.
Offset: Offset is the parameter that makes serving cell look better than the actual measurement of it compare to neighbor cell.
Hysteresis: It is the Parameter which is used to make Neighbor Cell look worse than the current measured value.
It helps UE to make sure that neighbor cell is strong enough and if the network triggers a handover after receiving the measurement report from the UE, handover to target cell will successful.
6) MIB Periodicity in LTE?
40ms generation Periodicity with 10ms retransmission Periodicity.
7) What are LTE Idle Mode Parameters?
qHyst : Cell Reselection Parameter that defines the hysteresis value in the Intra-Frequency Cell ranking criteria
tReselectionEutra: Cell Reselection Timer value for an Eutra Frequency.
sIntraSearch: Threshold for Intra Frequency Measurement.
Note: qHyst and tReslectionEutra parameters can be tuned together to ensure that UE reselect cells as early as possible without experiencing ping-pong Reselection.
-> By decreasing sIntraSearchP/sNonIntraSearchP from higher to lower value are making aggressive cell selection.
8) RRC Failure Reasons?
-> Bad RF Conditions.
-> Congestion ( SRS, PUCCH, PUSCH, PDCCH, High PRB)
-> Interference (UL RSSI), Overshooting
-> Transmission Issue
-> High BLER
-> Wrong Parameter Configuration
-> Timer T300 Value too small and other.
-> RACH Power & Mobility Setting.
-> Hardware Issue.