Convolutional code is a non-blocking code
Block code: A code group of N symbols generated by the encoder in any specified period of time depends only on the k-bit input symbols in this period of time, and the supervision bits in the code group only supervise k of this code group. information bits.
The supervision bit of the block code only supervises the error condition of this group of symbols
Convolutional code: The n symbols generated by the encoder in any period of time depend not only on the k information bits in this period of time, but also on the information bits in the specified period of time before (N-1). At this time, the supervisory code bits supervise the information bits within this N period of time. The number of symbols associated with each other in encoding is nN.
The supervisory bits of non-block codes are related to multiple groups of symbols
The error correction performance of convolutional codes increases with the increase of N, while the error rate decreases exponentially with the increase of N.
Convolutional codes outperform block codes with the same encoder complexity.
Convolutional codes do not have the same rigorous mathematical analysis methods as block codes, and most of them are used to search for good codes through computers.
Although the convolutional code also encodes the k-bit information segment into an n-bit code group during encoding, the supervisory symbol is not only related to the current k-bit information segment, but also related to the previous m = (N – 1) information segment.
The supervision matrix H of the convolutional code is a semi-infinite matrix with a head and no tail.
The structure of every 3 (Note: n) columns of the matrix is the same, except that the last 3 columns are shifted down by two (Note: nk) rows from the first 3 columns.
For example, columns 4~6 are 2 rows lower than columns 1~3. From line 7 onwards, the left end of every two lines is 3 more "0" than the previous two lines.
Truncated H matrix
