Hi All, some steps to check for Throughput issues:
It depends on which MCS is allocated and number of RBs assigned based on MCS:
-> at High MCS index value (Range: 0 to 31), Modulation order will increase (Range: 2,4,6,8), size of Transport block also will increase.
What is allocated MCS against to the CQI
-> CQI: 1 to 6 (QPSK)
-> CQI: 7 to 9 (16 QPSK)
-> CQI: 10-15 (64 QPSK) for before Rel12.
If CQI value in between 10-15, the allocated MCS is 64 QPSK. Obviously will get good Throughput.
Padding in the MAC PDU.
-> Padding indicates that network doesn’t have any data to send.
Check RLC and PDCP Layer Retransmission.
Check for BSR (BUFFER STATUS REPORT), Index and allocated TranportBlock size.
-> BSR Range: 0 to 63
BSR : 0 -> No data
BSR : 63 -> Have high Buffer Data.
Check RLF,RACH ,Out of Sync Indications.
Check PHR Is insufficient.?
Check Retransmissions are discarded or not.
-> Initial BLER: When the eNB sends data to the UE and UE is unable to decode it, then it will send a HARQ NACK to the eNB. A NACK means that the eNB will have to retransmit the data and this NACK is considered IBLER or Initial Block Error.
-> Residual BLER: If the UE is unable to decode the data even after retransmission, the UE will send another NACK and the eNB will have to retransmit again. However, there is a limit to these retransmissions and usually they are configurable. Commonly, these retransmissions are set to 4 and after 4 retransmissions, the eNB will not retransmit at HARQ level and consider this as a Residual Block Error.
-> High BLER will effect on MCS and as well as low Throughputs .
Check DL BLER and UL BLER (It should be <10%).
Check Continuously DL Grants are coming or not from PHY Layer.
Check Link Balance: UE is sending RLC ACK, but because of poor RF conditions not allowing ENB to receive.