Sparse Extended Vector Coding for Short Packet URLLC

Sparse vector coding (SVC) has gained recognition due to its high reliability and low latency in short packet communications. This letter proposes a sparse extended vector coding (SE-SVC) scheme. It uses partial index bits to select non-zero positions (NZPs) via index modulation, and then evenly distributes remaining bits across these NZPs for per-position extension. This yields a small index table with almost no loss in sparse vector length for given bit streams. To enhance coding efficiency, we pair these NZPs and implement constellation swapping between their two allocated constellations during non-zero element generation of these NZPs, thereby encoding one additional bit per pair. This simplified constellation allocation maintains low receiver-side matching complexity, ensuring the proposed scheme's transmission reliability. Simulation results show that compared to state-of-the-art SVC schemes, the proposed SE-SVC scheme can simultaneously reduce encoding/decoding delay while maintaining high transmission reliability.