25. October 2017 at 20:57 #8959SaraParticipant
Could you clarify for me what is the minimum and maximum possible value of the Bite Error Rate (BER) that maintains acceptable performance in LTE? and did the standard specify its values?
Sara26. October 2017 at 8:24 #8963Stefan PratschnerKeymaster
as you implicitly mentioned, the question of what is acceptable performance cannot be answered objectively but has to be defined by the standard. For the current LTE-A specification, this is given by a target Block Error Ratio (BLER) of 10%. This means that on average, one out of ten times, the decoding of a received codeword fails. To achieve this, the transmission parameters (CQI, RI, PMI) are adapted according to the channel state by the feedback algorithm.
However, as explained, the region of operation is defined in terms of BLER and not in terms of the BER.
Stefan12. November 2017 at 2:13 #9044SaraParticipant
Many thanks for your comments.
Regarding the (CQI ,RI and PMI). Just I want to know the steps of calculation for these reports and their format (in bits or real value ) and the names at each stage :
here my understanding:
At the UE:
Regarding the CQI report , the UE calculates the SNR value and then send this value in form of bits to the base station (BS) in wireless channel.
At the BS:
The value of CQI which in bits will estimated by the channel estimator and then from the table of the CQI the BS will know the required modulation and coding scheme (MCS). Then this value is used by the scheduler to increase or decrease MCSs. After that the BS will inform the UE about the new change ( here at this stage I don’t know what the BS will send to the UE as a feedback value?).
Regarding the RI and PMI I don’t know if they work in the same manner just like the CQI or not?
Please clarify for me how the process of exchanging this information happen between the UE and BS.
Sara29. November 2017 at 7:46 #9127Stefan PratschnerKeymaster
in the uplink, the BS can directly estimate the channel from pilots, transmitted by the UE. From this estimated channel, the receiver (for example zero forcing) can be found. With this information, the transmission parameters (CQI, PMI and RI) are calculated. Then these values are transmitted back to the UE via a control channel, that is not explicitly modeled in our simulator. Now, the signalled CQI, PMI and RI values are used by the UE for the next transmission.
For details on how to optimize the feedback parameters from the estimated channel, please refer to the following works
S. Schwarz, C. Mehlführer, M. Rupp:
“Calculation of the Spatial Preprocessing and Link Adaption Feedback for 3GPP UMTS/LTE”
S. Schwarz, M. Wrulich, M. Rupp:
“Mutual Information based Calculation of the Precoding Matrix Indicator for 3GPP UMTS/LTE”
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