Channel Estimation for Ambient Backscatter Communication Systems with Massive-Antenna Reader

Ambient backscatter, an emerging green communication technology, has aroused great interest from both academia and industry. One open problem for ambient backscatter communication (AmBC) systems is channel estimation for a massive-antenna reader. In this paper, we focus on channel estimation problem in AmBC systems with uniform linear array (ULA) at the reader which consists of large number of antennas. We first design a two-step method to jointly estimate channel gains and direction of arrivals (DoAs), and then refine the estimates through angular rotation. Additionally, Cramer-Rao lower bounds (CRLBs) are derived for both the modulus of the channel gain and the DoA estimates. Simulations are then provided to validate the analysis, and to show the efficiency of the proposed approach.Comment: 5 figures, submitted to IEEE Transactions on Vehicular Technology, 29 March, 201

Optimum Reconfigurable Intelligent Surface Selection for Indoor and Outdoor Communications

The reconfigurable intelligent surface (RIS) is a promising technology that is anticipated to enable high spectrum and energy efficiencies in future wireless communication networks. This paper investigates optimum location-based RIS selection policies in RIS-aided wireless networks to maximize the signal-to noise ratio (SNR) for a power path-loss model in outdoor communications and an exponential path-loss model in indoor communications. The random locations of all available RISs are modeled as a Poisson point process (PPP). To quantify the network performance, the outage probabilities and average rates attained by the proposed RIS selection policies are evaluated by deriving the distance distribution of the chosen RIS node as per the selection policies for both power and exponential path-loss models. Feedback could incur heavy signaling overhead. To reduce the overhead, we also propose limited-feedback RIS selection policies by limiting the average number of RISs that feed back their location information to the source. The outage probabilities and average rates obtained by the limited-feedback RIS selection policies are derived for both path-loss models. The numerical results show notable performance gains obtained by the proposed RIS selection policies and demonstrate that the conventional relay selection policies are not suitable for RIS-aided wireless networks