Pilot power adaptation for tomographic channel estimation in distributed MIMO systems

In distributed multiple-input multiple-output (D-MIMO) systems, the improvements of spectral and energy efficiencies rely heavily on the accuracy of the channel state information (CSI). In order to enhance the accuracy of CSI acquisition, the problem of pilot design in a D-MIMO system is addressed in this study. In particular, the authors focus on the optimisation of pilot power adaptation in a single-cell D-MIMO system with multiple users served in orthogonal resources. Under the concept of tomographic channel estimation, the problem of pilot power adaptation aiming at maximising the lower bound of the sum capacity is formulated. As the computational complexity of solving the problem is relatively high due to the mutual coupling constraints, the dual decomposition technique is introduced to decouple the constraints and reduce the complexity via parallel computation. An effective pilot power adaptation scheme is further proposed by using the projected subgradient method. The superiority and effectiveness of the proposed scheme are illustrated by the simulation results.