Generic Constraint-Free Design of Sparse MIMO System for Enhanced Localization of Targets

Recently, the multiple input multiple output (MIMO) system uses sparse arrays to generate a long co-array with higher degrees of freedom (DOFs) for direction of arrival (DOA) estimation. However, most of the existing sparse MIMO have design limitations, lack a generic approach, and generate many holes in co-array, especially with coprime sparse arrays. To this end, we propose a ubiquitous MIMO (U-MIMO) system, which employs a new supplementary tri-level (STiL) receiver (Rx) and a transmitter (Tx) of increased inter-element spacing. The STiL scheme can be designed for any number of Rxs and applies to different sensor arrays. The inter-element spacing of the proposed Tx is increased by the total number of virtual lags in the difference co-array of STiL Rx to produce a longer sum co-array of the difference co-array (SCDC) for the U-MIMO system. As a result, the proposed approach not only overcomes the design constraints but achieves higher DOFs with no or minimum number of holes in SCDC, even when coprime arrays are used. The closed-form expressions are provided for precise sensor locations and calculating the DOFs. Simulation results validate the effectiveness of the U-MIMO system using different sensor arrays.