On the Design of Efficient Lattice-Code based Multiple Access
Tao Yang, Fangtao Yu, Qiuzhuo Chen, Rongke Liu · 2023
This paper studies a lattice-code based multiple-access (LCMA) system. In the uplink,$K$users encode their messages with the same 2m-ary ring code mapped to 2m- PAM, belonging to the ensemble of lattice codes. All users transmit simultaneously. The receiver attempts to compute$K$independent streams of integer-combinations (ICBs) of the users' messages. For this, 1) we establish and solve a new “bounded independent vectors problem” (BIVP) which identifies a near-optimal set of coefficient vectors w.r.t. the ICBs, outperforming existing LLL and HKZ lattice reduction methods; 2) we put forth new LCMA soft detection algorithms, which calculate the a posteriori probability w.r.t. the ICB over the lattice. The per-user complexity is of order less than O(K), suitable for massive access of$K$being large. The soft detection outputs are forwarded to$K$ring-code decoders to recover the messages. With our developed techniques, LCMA is shown to support a significantly higher load of users and exhibits an improved frame error rate over state-of-the-art IDMA and SCMA schemes. Such advanced functionality are achieved with just parallel processing and$K$single-user decoding operations.