Design and implementation of virtual-single-length turbo decoder for multi-user parallel decoding

Dealing with multiple users in cellular basestation with multiple codewords of variable length is a challenging task in parallel decoding. Thus, a novel turbo decoder with variable codeword-based parallel decoding is proposed for the 3GPP LTE (4G) system. To make multi-user decoding more efficient, all users are aggregated into a single block with zero insertions where all users can be decoded in the same cycle. Different users are separated by additional zeros to decode in parallel and improve the hardware utilization. Moreover, a stationary boundary enhancement is utilized to exchange and update the decoded messages between different sub-blocks of codeword for the next decoding interaction. This scheme can balance the performance loss and decoding latency of variable codeword-based parallel decoding. The proposed turbo decoder has a maximum throughput of 280.5 Mbps (VC707) and 212 Mbps (ZC706), where the design has been integrated and tested with OpenAirInterface (OAI) 4G eNB in campus trials.