Abstract Event causality extraction is a challenging task in natural language processing (NLP), which plays an important role in event prediction, scene generation, question answering and textual entailment. Most existing methods focus on extracting single‐scale (such as phrase) event causality, while fails to extract multi‐scale (such as word, phrase, sentence) event causality. To fill the gap, we propose multi‐scale event causality extraction via simultaneous knowledge‐attention and convolutional neural network (KA‐CNN). First, knowledge‐attention takes N‐gram embedding as input and takes semantic features, fused with prior knowledge through causal associative link network (CALN), as output. Second, multi‐scale CNN is designed with word embedding as input and semantic feature of corpus as output. Third, bidirectional long short‐term memory with conditional random field (BiLSTM + CRF) is conducted after concatenation of features from knowledge‐attention and multi‐scale CNN. Finally, we compare our results with other baselines. The experimental results show that our proposed method shows promising result in extracting multi‐scale event causality.

Nowadays, Unmanned Aerial Vehicles (UAVs) are playing increasingly important roles in agriculture, rescuing and surveillance due to their small size, low cost and strong adaptability. Coverage Path Planning (CPP) is a fundamental problem for UAV applications, which means to find a path covering all the targets or regions of interest. Researches on CPP in a single region have been studied for decades, but rare to be devoted to covering multiple scattered regions of multiple UAVs. This paper proposes an attempt to solve this problem in a short time and take the task balance of multiple UAVs into account meanwhile. This work constructs a model for multiple UAVs to cover scattered regions firstly. In view of the high computational complexity of the precise solution, we keep innovating a heuristic measure based on the model to make the solving process feasible. To settle the problem of imbalanced time consumption caused by super regions, we improve the previously built model furthermore. A series of experiments validated that the presented approaches exhibit the effectiveness and balance of time consumption in diverse scenarios.

Today, most spectrum allocation algorithms use conflict graphs to capture interference conditions. The use of conflict graphs, however, is often questioned by the wireless community for two reasons. First, building accurate conflict graphs requires significant overhead, and hence does not scale to outdoor networks. Second, conflict graphs cannot properly capture accumulative interference. In this paper, we use large-scale measurement data as ground truth to understand how severe these problems are and whether they can be overcome. We build “practical” conflict graphs using measurement-calibrated propagation models, which remove the need for exhaustive signal measurements by interpolating signal strengths using calibrated models. Calibrated models are imperfect, and we study the impact of their errors on multiple steps in the process, from calibrating propagation models, predicting signal strengths, to building conflict graphs. At each step, we analyze the introduction, propagation, and final impact of errors by comparing each intermediate result to its ground-truth counterpart. Our work produces several findings. Calibrated propagation models generate location-dependent prediction errors, ultimately producing conservative conflict graphs. While these “estimated conflict graphs” lower spectrum utilization, their conservative nature improves reliability by reducing the impact of accumulative interference. Finally, we propose a graph augmentation technique to address remaining accumulative interference.

Most spectrum distribution proposals today develop their allocation algorithms that use conflict graphs to capture interference relationships. The use of conflict graphs, however, is often questioned by the wireless community because of two issues. First, building conflict graphs requires significant overhead and hence generally does not scale to outdoor networks, and second, the resulting conflict graphs do not capture accumulative interference. In this paper, we use large-scale measurement data as ground truth to understand just how severe these issues are in practice, and whether they can be overcome. We build "practical" conflict graphs using measurement-calibrated propagation models, which remove the need for exhaustive signal measurements by interpolating signal strengths using calibrated models. These propagation models are imperfect, and we study the impact of their errors by tracing the impact on multiple steps in the process, from calibrating propagation models to predicting signal strength and building conflict graphs. At each step, we analyze the introduction, propagation and final impact of errors, by comparing each intermediate result to its ground truth counterpart generated from measurements. Our work produces several findings. Calibrated propagation models generate location-dependent prediction errors, ultimately producing conservative conflict graphs. While these "estimated conflict graphs" lose some spectrum utilization, their conservative nature improves reliability by reducing the impact of accumulative interference. Finally, we propose a graph augmentation technique that addresses any remaining accumulative interference, the last missing piece in a practical spectrum distribution system using measurement-calibrated conflict graphs.

A Vehicular Sensor Network (VSN) may be used for urban environment surveillance utilizing vehicle- based sensors to provide an affordable yet good coverage for the urban area. The sensors in VSN enjoy the vehicle's steady power supply and strong computational capacity not available in traditional Wireless Sensor Network (WSN). However, the mobility of the vehicles results in highly dynamic and unpredictable network topology, leading to packet losses and distorted surveillance results. To resolve these problems, we propose a cooperative data sensing and compression approach with zero inter-sensor collaboration overhead based on sparse random projections. The algorithm provides excellent reconstruction accuracy for the sensed field, and by taking advantage of the spatial correlation of the data, enjoys much smaller communication traffic load compared to traditional sampling algorithms in wireless sensor networks. Real urban environment data sets are used in the experiments to test the reconstruction accuracy and energy efficiency under different vehicular mobility models. The results show that our approach is superior to the conventional sampling and interpolation strategy which propagates data in an uncompressed form, with 4-5dB gain in reconstruction quality and 21-55% savings in communication cost for the same sampling times.

Environmental surveillance applications usually require a long living cycle of sensor nodes, especially when they are powered by non-charged batteries. Inspired by cellular automata, we propose a non-cluster based topology control method to prolong the lifetime of wireless sensor networks. Differing from the traditional cluster-based methods, our approaches lead a special way to maintain longer system lifetime by sacrificing a small proportion of network coverage and connectivity degrees. The demonstration contains both theoretical simulation and system-level experiment, which will be instructive for future study.