WCDMA Block Coding – CRC
- Block coding is used to detect if there are any uncorrected errors left after error correction.
- The cyclic redundancy check (CRC) is a common method of block coding.
- Adding the CRC bits is done before the channel encoding and they are checked after the channel decoding.
- During the transmission, there are many interferences and fading. To guarantee
reliable transmission, system should overcome these influence through the channel
coding which includes block coding, channel coding and interleaving.
- Block coding: The encoder adds some redundant bits to the block of bits and the
decoder uses them to determine whether an error has occurred during the
transmission. This is used to calculate Block Error Ratio (BLER) used in the outer
loop power control.
- The CRC (Cyclic Redundancy Check) is used for error checking of the transport
blocks at the receiving end. The CRC length that can be inserted has four different
values: 0, 8, 12, 16 and 24 bits. The more bits the CRC contains, the lower is the
probability of an undetected error in the transport block in the receiver.
- Note that certain types of block codes can also be used for error correction, although
these are not used in WCDMA.