Lattice-Code Multiple Access: Architecture and Efficient Algorithms

This paper proposes a lattice-code multiple-access (LCMA) scheme for K-user uplink systems. Each user encodes messages via 2^m-ary lattice codes mapped to 2^m-PAM. The receiver employs integer coefficients to compute integer linear combinations (ILCs) of messages, then reconstructs original data through novel low-complexity soft detection and single-user decoders. Key contributions include: 1) A soft detector calculating a posteriori probabilities of ILCs over lattices, enabling efficient belief-propagation decoding; 2) A bounded independent vectors problem (BIVP) framework to optimize ILC coefficients, solved by a rate-constrained sphere decoder outperforming traditional lattice reduction methods; 3) Optimized signature sequences designed via a targetswitching steepest descent algorithm. Simulations demonstrate LCMA's superiority over IDMA and SCMA in supporting higher user loads and achieving lower error rates, while avoiding successive interference cancellation or iterative detection.