How to debug the Throughput issues?

Hi All, some steps to check for Throughput issues:

  1. 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.

  2. 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.

  3. Padding in the MAC PDU.
    -> Padding indicates that network doesn’t have any data to send.

  4. Check RLC and PDCP Layer Retransmission.

  5. 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.

  6. Check RLF,RACH ,Out of Sync Indications.

  7. Check PHR Is insufficient.?

  8. 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 .

  9. Check DL BLER and UL BLER (It should be <10%).

  10. Check Continuously DL Grants are coming or not from PHY Layer.

  11. Check Link Balance: UE is sending RLC ACK, but because of poor RF conditions not allowing ENB to receive.

Hello Raju,

what do you mean by Buffer status report. Is it any OSS KPI or DT KPI?

can you elaborate more on this point.

Buffer status report (BSR) is a MAC layer control will carry the information on the amount of data available for each Logical Channel Group (LCG) from UE to eNB.

This not related to OSS KPI Or DT KPI.Its related to the MAC layer concept.

BSR : Whenever ENB assign the grants to the UE , UE will send the stored data in the buffer to the ENB.

Hi Raju,
Thank you for a good analysis about throughput .
How do we check that Buffer Status Report?