High Order Multi-User MIMO Subspace Detection

An efficient high order multi-user multiple-input multiple-output (MU-MIMO) subspace detector is proposed. The detector employs joint modulation classification (MC) and subspace detection (SD), by which the modulation type of the interferer is estimated, while multiple decoupled streams are individually detected. The algorithmic contributions are on two levels. First, the preprocessing channel matrix decomposition overhead is reduced, using special layer ordering followed by permutation-robust QR Decomposition and elementary matrix operations. Second, a hierarchical MC scheme is proposed, comprising feature-based and near-optimal likelihood-based classifiers, as well as a classifier that always assumes the interfering modulation type to be a fixed high order quadrature amplitude modulation. An efficient hardware architecture that realizes the proposed algorithms is presented. Simulations demonstrate that depending on the channel condition, one of the proposed schemes can achieve near interference-aware performance with a minimum complexity overhead.