What is BLER (Block Error Rate)?
Definition
BLER (Block Error Rate) is the percentage of transmitted data blocks that are received incorrectly and fail error detection (CRC check) after decoding.
It is a key performance metric in 4G and 5G wireless systems.
Formula
BLER = (Number of incorrectly received blocks) / (Total transmitted blocks)
Example:
If 100 transport blocks are transmitted and 10 fail CRC:
BLER = 10 / 100 = 10%
What is a Block?
- Data is transmitted in Transport Blocks (TB)
- Each TB contains multiple code blocks (LDPC coded)
- If CRC fails, the entire TB is considered erroneous
Why is BLER Important?
- Determines throughput
- Affects retransmission rate (HARQ)
- Impacts link adaptation efficiency
- Influences overall user experience
Target BLER in 5G
- Target BLER after first transmission ≈ 10%
- After HARQ retransmissions → close to 0%
The 10% target balances spectral efficiency and retransmission cost. Operating below that wastes capacity, while above increases HARQ overhead.
BLER vs BER
| BLER | BER |
|---|---|
| Block-level error | Bit-level error |
| Used in link adaptation | Used in theoretical analysis |
| Practical metric in 5G | More academic metric |
What Causes High BLER?
- Low SINR
- Poor channel estimation
- Wrong MCS selection
- Interference
- RF impairments (phase noise, IQ imbalance)
- Frequency offset
How is BLER Reduced?
- Lower MCS
- HARQ retransmissions
- Better precoding (MMSE instead of ZF)
- Improve channel estimation
- Increase DMRS density
Summary
BLER is the probability that a transport block fails CRC after decoding. In 5G, link adaptation targets around 10% BLER at first transmission because it balances spectral efficiency and retransmission cost.