Joint beamforming and compressed sensing for uplink grant-free access

Compressed sensing (CS)-based techniques havebeen widely applied in the grant-free non-orthogonal multipleaccess (NOMA) to a single-antenna base station (BS). In thispaper, we consider the multi-antenna reception at the BS foruplink grant-free access for the massive machine type communi-cation (mMTC) with limited channel resources. To enhance theoverloading performance of the BS, we develop a general frame-work for the synergistic amalgamation of the spatial divisionmultiple access (SDMA) technique with the CS-based grant-freeNOMA. We derive a closed-form statistical beamforming and adynamic beamforming scheme for the inter-cluster interferencesuppression when applying SDMA. Based on this, we furtherdevelop a joint adaptive beamforming and subspace pursuit (J-ABF-SP) algorithm for the multiuser detection and data recovery,with a novel sparsity level decision method without the accurateknowledge of the noise level. To further improve the datarecovery performance, we propose an interference cancellation-based J-ABF-SP scheme (J-ABF-SP-IC) by using the initial signalestimates generated from the J-ABF-SP algorithm. Illustrativesimulations verify the superior user detection and signal recoveryperformance of our proposed algorithms in comparison withexisting CS-based grant-free NOMA techniques.