How do convolutional codes work for error correction?

Convolutional codes generate output bits from current and previous input bits using shift registers and XOR operations. Described by (n,k,K) where n=output bits, k=input bits, K=constraint length. Code rate R=k/n. Unlike block codes, they operate on continuous streams. Decoding uses Viterbi algorithm (maximum likelihood, finds path through trellis with minimum distance to received sequence). Error correction capability depends on free distance. Used in deep-space communication, GSM, and 802.11a/g. Combined with interleaving for burst error correction.