By taking advantage of a conformal mapping technique, we propose designs for various optical elements such as directional antennas, flat lenses, or bends. In contrast to most of the existing design approaches, the elements can be implemented with isotropic materials, thus strongly facilitating their fabrication. We furthermore generalize the concept and show that under certain conditions previously suggested devices consisting of anisotropic materials may be replaced by isotropic ones using an appropriate transformation. The designs are double-checked by full-wave simulations. A comparison with their anisotropic counterparts reveals a similar performance.

Abstract-In this work, a new energy-efficiency performance metric is proposed for MIMO (multiple input multiple output) point-to-point systems. In contrast with related works on energyefficiency, this metric translates the effects of using finite blocks for transmitting, using channel estimates at the transmitter and receiver, and considering the total power consumed by the transmitter instead of the radiated power only. The main objective pursued is to choose the best pre-coding matrix used at the transmitter in the following two scenarios : 1) the one where imperfect channel state information (CSI) is available at the transmitter and receiver ; 2) the one where no CSI is available at the transmitter. In both scenarios, the problem of optimally tuning the total used power is shown to be non-trivial. In scenario 2), the optimal fraction of training time can be characterized by a simple equation. These results and others provided in the paper, along with the provided numerical analysis, show that the present work can therefore be used as a good basis for studying power control and resource allocation in energy-efficient multiuser networks.

In this work, a novel technique which allows every transmitter in an interference network to have global channel state information (CSI) is proposed. The key feature of the proposed technique is that each transmitter acquires global CSI purely through the available feedback channel (i.e., a feedback of the received signal power). In the first step of the proposed technique, each transmitter uses several observations provided by the feedback channel to learn the channel gains perceived by its intended receiver. Secondly, this information is quantized, modulated, and transmitted to the other transmitters through the power levels used by the transmitters; the latter are indirectly observed through the received signal power. Hence, the interference is used as an implicit communication channel through which local CSI is exchanged. Once global CSI is acquired, it can be used to optimize any utility function which depends on it.

Energy-efficient communication protocols have become an important topic over the past two decades due to environmental issues, increased monetary costs of energy consumption, and limited battery capacities of sensors and mobile devices. In this context, we present a novel approach to design energy-efficient time-triggered communication policies for wireless networked control systems, while ensuring a given control performance. We consider a plant, modeled as a deterministic discrete-time linear system, which is controlled through a wireless network by an output-feedback law. We proceed by emulation, i.e., we construct the controller to stabilize the origin of the plant while ignoring communication constraints. Next, the wireless network is taken into account and we assume that the probability of packet drops depends on the transmission signal power. We introduce the notion of stochastic allowable transmission interval (SATI) to characterize stabilizing time-triggered transmission policies. We then explain how to minimize the average energy expenditure of the transmitting devices while satisfying the SATI constraints, thus ensuring the control requirements. Simulations results are provided to illustrate the trade-off between the communication and the control costs.