Further Results on the Degrees of Freedom for Coprime MIMO Systems

Enhancing the degrees of freedom (DOFs) of MIMO systems has been a hotspot in communications. In this letter, a novel strategy to construct difference coarray of the sum coarray (DCSC) with heightened DOFs for coprime MIMO systems is put forward. Using the polynomial of DCSC, we reveal that DOFs expansion for sparse MIMO systems is a replicate-and-shift (RS) procedure, which explains the deficiency of overlapping lags caused by the consecutive DOFs in the difference coarray (DCA) as a moving period. To tackle this problem, the moving period is raised to the number of DOFs, so that the lags and holes in the forward and backward periods can perfectly complement each other. The range of consecutive DOFs (cDOFs) and the number of DOFs are then described in the closed-form expressions. The results show that the proposed strategy generates more DOFs than previous studies.