Deep-fading hole avoidance for secure region detection using channel state information

One of the critical challenges in many wireless systems is the deep fading hole problem where signals interfere destructively to create an abrupt change in signal amplitude due to multipath fading. In this work, we tackle this challenge in the context of secure region detection (SRD) problem. Specifically, we propose SHARD, a novel hole avoidance technique that analyzes channel state information (CSI) to significantly improve the accuracy of CSI-based SRD. SHARD identifies potential fading holes in CSI amplitude, and removes an unreliable portion of data while utilizing the remaining unaffected part. To compensate for the loss of information, we define phase-distance for reliable use of time-varying CSI phase, and neighboring reference points are utilized for accurate matching. Our real-world experiments show that SHARD can achieve a near-perfect 99.96% true-negative ratio (successfully rejecting devices not in the secure region) and an excellent true-positive of 98.01% for practical usage, significantly better than state-of-the-art prior work. We believe our ideas can be generalized to many RF-based localization systems to mitigate the deep fading hole problem and improve their accuracy.