arXiv:2611.13449v1 Announce Type: cross Abstract: A feedback control policy is completely decentralized if the actuation signal at each location in space can be computed based only on state information from that location. For systems equipped with large numbers of spatially distributed sensors and actuators, completely decentralized controllers are desirable since they can be implemented in a communication and computation efficient manner, but generally perform worse than centralized counterparts. However, through a case study of Linear Quadratic Regulator (LQR) design for wave dynamics on a compact spatial domain, we show that careful design of system parameters to satisfy certain conditions causes a decentralized control policy to perform as well as any centralized policy. We then propose a spatially filtered $H_2$ norm to show that satisfying these conditions does not inherently degrade achievable closed-loop system performance, enabling simultaneous realization of both desirable performance and communication/computation efficiency via system-control co-design. Additional robustness analysis characterizes a range of system parameters such that the system interconnected with a decentralized controller maintains stability and near-optimal performance. Although our framework is derived for spatially continuous dynamics, we demonstrate that this theory can be leveraged to derive results for decentralization in finite-dimensional settings through a damped mass-spring example.