What is Block Error Rate (BLER) in wireless or Mobile communication

Block Error Rate (BLER) Definition 

Block Error Rate (BLER) is a ratio of the number of erroneous blocks to the total number of blocks transmitted on a digital circuit.

                                     or

“Block Error Rate” or BLER is a measurement type of quality in telecommunication. Simple calculation of the measurement:

Formula to Calculate Block Error Rate (BLER)

BLER (in LTE) = Number of erroneous blocks / total number of received blocks

BLER is measured after channel de-interleaving and decoding by evaluating the Cyclic Redundancy Check (CRC) on each transport block.

Block Error Rate (BLER) is used in LTE/4G technology to determine the in-sync or out-of-sync indication during radio link monitoring (RLM). Normal BLER is 2% for an in-sync condition and 10% for an out-of-sync condition.

 

The calculation is based on CRC (Cyclic Redundancy Check) evaluation which is used for inspection of the transport blocks at the receiver side. CRC is attached to each transport block and sent by the transmitter, at the destination the transport block is cross-checked by the receiver. The transport block is successfully decoded if the attached CRC is matching the CRC calculated by the receiver.

 

The CRC is a technique used to detect errors in transport blocks.

 

If the calculation gives an undesired result then the receiver will feedback with a HARQ NACK message for asking for re-transmission. On the radio side, the typical BLER target is 10% which means the receiver should receive at least 90% successful transmission.

If the target is less than 10% then more re-transmission might be required and cause radio resource consuming.

 

“Error” is unavoidable in wireless communication due to several reasons.

 

Types of  Block Error Rate (BLER)

In many radio measurement tools, we can see two kinds of BLER: iBLER and rBLER

 
iBLER: Initial Block Error Rate

The ratio of data blocks with initial transmission errors to all initial transmission data blocks.

 

rBLER: Residual Block Error Rate

The ratio of data blocks with transmission errors after initial transmissions and retransmissions to all initial transmission data blocks.