What is the 10% BLER target in LTE and NR?

There is a Buzz word which everyone says that BLER should be under 10%, but 10% of what?

There are two scenarios where BLER calculation is taken into account

– BLER Target for Radio Link Monitoring
– BLER Target for PDSCH decoding


In the Case of Radio Link monitoring, UE monitor’s the downlink link quality based on the reference signal in order to detect the downlink radio link quality of the camped cell.

3GPP Has defined two thresholds that define the entry and exit criteria when a UE can declare radio link failure and when it can exit the RLF.

Threshold Qout: Corresponds to out-of-sync block error rate (BLERout) which is 10% BLER of a hypothetical PDCCH transmission

Threshold Qin: Corresponds to in-sync block error rate (BLERin) which is 2% BLER of a hypothetical PDCCH transmission

In LTE UE measures the Cell-Specific reference signal (CRS) for downlink radio link monitoring were as

In NR UE measures either the SSB or CSI-RS ( if configured) for downlink radio link monitoring.

What is hypothetical PDCCH transmission?

3GPP has defined a list of PDCCH transmission parameters based on reference signal used for radio link monitoring in 38.133
It consists of DCI format, OFDM symbols, CCE, PRBs, SCS, REG bundle size, similar to a regular PDCCH transmission but with fixed values so UE can estimate the link quality based on these references values.

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