This paper studies a lattice-code based multiple-access (LCMA) framework, and develops a package of processing techniques that are essential to its practical implementation. In the uplink, $K$ users encode their messages with the same ring coded modulation of $2^{m}$-PAM signaling. With it, the integer sum of multiple codewords belongs to the $n$-dimension lattice of the base code. Such property enables efficient \textit{algebraic binning} for computing linear combinations of $K$ users' messages. For the receiver, we devise two new algorithms, based on linear physical-layer network coding and linear filtering, to calculate the symbol-wise a posteriori probabilities (APPs) w.r.t. the $K$ streams of linear codeword combinations. The resultant APP streams are forwarded to the $q$-ary belief-propagation decoders, which parallelly compute $K$ streams of linear message combinations. Finally, by multiplying the inverse of the coefficient matrix, all users' messages are recovered. Even with single-stage parallel processing, LCMA is shown to support a remarkably larger number of users and exhibits improved frame error rate (FER) relative to existing NOMA systems such as IDMA and SCMA. Further, we propose a new multi-stage LCMA receiver relying on \emph{generalized matrix inversion}. With it, a near-capacity performance is demonstrated for a wide range of system loads. Numerical results demonstrate that the number of users that LCMA can support is no less than 350\% of the length of the spreading sequence or number of receive antennas. Since LCMA relaxes receiver iteration, off-the-shelf channel codes in standards can be directly utilized, avoiding the compatibility and convergence issue of channel code and detector in IDMA and SCMA.
翻译:本文研究基于 lattice 代码的多存取 (LCMA) 框架, 并开发一套对其实际执行至关重要的处理技术。 在上行链接中, $K 用户将信息编码成相同的环码调制 $2 ⁇ m} $- PAM 信号。 有了它, 多编码词的整数总和属于基代码的 $- dimenasion 套件。 这些属性可以高效计算 $K$ 用户信息的线性组合 。 对于接收器来说, 我们设计了两种新的算法, 以直线物理层网络编码和线性过滤为基础, 用直线码编码编码将信息编码编码编码编码编码编码编码编码编码成 $q$( textitutitleitit {algebrial binning) 。 最后, 我们设计了两个新的算法算法, 以直线端网络网络网络网络网络编码为基础网络编码为基础, 所有用户的代号代号都以后后一级 IM IMA 的代号表示 IMA 新的代号 IMA 新的 的代碼的代码 代码的代号 正在恢复。