The Turbo encoder in LTE is a systematic parallel concatenated convolution code (PCCC) with two 8-state constituent encoders and one Turbo code contention free internal inter-leaver. Where the encoders are based on RSC (Recursive Systematic Convolution) codes and their generator polynomial is given by
G=[1, g0/g1],
where g0=[1011] (feedback) and g1=[1101] (feedforward).
Structure of the LTE Turbo encoder (dotted lines are for trellis termination:
As can be seen in Figure the output of the LTE Turbo encoder consists of three parts, a systematic bit and two parity bits. The systematic bit is the untouched input bit. The first parity bit is the output of the first convolution encoder with the original input as input and the second parity bit is the output of the second convolution encoder after interleaving.
Turbo coding is used in LTE for following channels: UL-SCH (Uplink Shared CHannel), DLSCH (Downlink Shared CHannel), PCH (Paging CHannel) and MCH (Multicast CHannel).
