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In this article, we investigate the problem of distributed coherent beamforming in wireless networks where multiple distributed transmitters adjust the phases of their signals to form a directional and targeted communication link to a client receiver. The quality-of-service (QoS) and security are key components of robust and secure wireless networks. Although the security can be improved by exploiting information about potential adversaries, such information may not be available in practical networks since the adversaries are often passive. Therefore, we introduce transmission strategies which not only send a confidential message by forming a beam towards the client but also broadcast interference with the aim of obfuscating adversaries without having any information about them. Since the interference may degrade the QoS of the client, the transmitters radiating the interference steer a null to the client to alleviate the interference. We develop two algorithms. The first assumes that a subset of the transmitters send the confidential message in the direction of the client via coherent beamforming. Then, the others transmit interference while creating a null towards the client. In the second, each node transmits both the confidential message and interference simultaneously. Two different client feedback scenarios are considered, two-bit and rich feedback. Both of the proposed algorithms can be performed in a fully distributed manner without any knowledge about potential adversaries. Numerical simulations in both microwave and low-very high frequency (low-VHF) bands validate the effectiveness of the proposed schemes.

Direction of arrival (DoA) estimation has wide-ranging applications and is particularly challenging in complex propagation environments. Conventional approaches estimate the DoA based on the phase of the impinging signal on a sensor array. This approach has several challenges: for example, it requires tight synchronization among array elements and the estimated DoA is sensitive to multipath and to correct specification of the array geometry. In this paper, we develop a principled Bayesian DoA estimation algorithm based on the received signal strength gradient. We present algorithms for clustering, spatial- and model-based outlier detection and removal, and proper uncertainty quantification, which yield an estimator robust to non-uniform shadowing, multipath, and errors in antenna position. Physics-based full-wave simulations and experiments in the 2.4 GHz and 40 MHz bands illustrate the utility of our approach.