In this work, we investigate the measurement noise sensitivity and peaking problem of the extended state observer (ESO) under high-gain characteristics. For a class ofn-order nonlinear systems with measurement noise, a new variable-order filter and the corresponding filtered ESO (FESO) are constructed to achieve arbitrary suppression ability of measurement noise. Such a salient feature lies in the establishment of the variable-order filter with independent parameters such that the observer poles and the order of the proposed filter can be set arbitrarily by the designer, thereby allowing the user to predefine the suppression strength in prior by adjusting parameters. In addition, a peaking-free FESO is further proposed to eliminate the undesired peaking phenomenon during the transient state. Finally, a comprehensive numerical comparison is presented, and the proposed peaking-free FESO is applied to the drag-free spacecraft hardware in-loop platform. The simulation results reveal the advantages of the proposed scheme in measurement noise suppression and peaking elimination.

In smart building systems, the automatic control of devices relies on matching the sensed environment information to customized rules. With the development of wireless sensor and actuator networks (WSANs), low-cost and self-organized wireless sensors and actuators can enhance smart building systems, but produce abundant sensing data. Therefore, a rule engine with ability of efficient rule matching is the foundation of WSANs based smart building systems. However, traditional rule engines mainly focus on the complex processing mechanism and omit the amount of sensing data, which are not suitable for large scale WSANs based smart building systems. To address these issues, we build an efficient rule engine. Specifically, we design an atomic event extraction module for extracting atomic event from data messages, and then build a β-network to acquire the atomic conditions for parsing the atomic trigger events. Taking the atomic trigger events as the key set of MPHF, we construct the minimal perfect hash table which can filter the majority of the unused atomic event with O(1) time overhead. Moreover, a rule engine adaption scheme is proposed to minimize the rule matching overhead. We implement the proposed rule engine in a practical smart building system. The experimental results show that the rule engine can perform efficiently and flexibly with high data throughput and large rule set.

In Wireless Multimedia Sensor Networks (WMSNs), data fusion and collaborative in-network processing operations often require effective multimedia synchronization control. Extensive researches have been done in the traditional networks. Most of these works assume that there exists a powerful synchronization controller in the network. However, for WMSNs, the in-network processing of the multimedia content is usually performed based on the resource-constrained sensors. Traditional synchronization control algorithms fail to run on the low-end hardware platform. In this paper, we propose an adaptive synchronization control scheme with multi-level buffer to address this problem. Main contributions of this paper are as follows. (i) To overcome the resource constraint of WMSNs, we perform the synchronization control in a distributed way by combining the sensors in the stream transmission path. (ii) By evaluating the current network state, we adjust the level number of the buffer adaptively to balance the delay and delay jitter. (iii) Through analyzing the buffer state of each level, we propose an efficient packet scheduling scheme to reduce the delay jitter actively. (iv) We implement the proposed scheme and verify its effectiveness in our practical WMSNs platform. The experiment results show that the proposed scheme can maintain the streams synchronization effectively with the low-end sensors.

In Wireless Audio Sensor Networks (WASNs), many applications such as target tracking, data fusion and localization, often require precise synchronization among audio streams. Extensive researches have been done under the assumption that wireless channel is well enough and the cluster head is power supplied. However, these conditions can not be satisfied in many applications. When audio event occurs, the burst of data is usually coupled with a high packet loss rate. Besides, the cluster head is usually battery-powered, especially in the wild environment. In this paper, we propose a distributed audio synchronization scheme to address these challenges. By dynamically detecting the endpoint of the audio streams and marking the start point of the audio synchronization obviously at the reporting sensor, we can eliminate the sound propagation delay effectively and synchronize the audio streams precisely even under the high packet loss rate. Moreover, by handling the synchronization task in a distributed way, we can lighten the burden of the cluster head and prolong the lifetime of the whole network greatly. To improve the flexibility of the scheme, we also propose a self-adaptive algorithm which can adjust the parameters of the synchronization according to the network condition. Experimentally, we show that the proposed scheme can synchronize the audio streams under different conditions with low energy cost.

Video surveillance system, which can provide real-time display of the monitored scene and video playback, has been employed in many areas including: commercial security, accident investigation, law enforcement and emergency response. However, audio which carries important information not available in video is usually not taken seriously and used effectively. In this paper, we develop an enhanced surveillance platform by introducing the low-power wireless audio sensor networks (WASNs). We can obtain more comprehensive and precise monitoring without the limitation of the line-of-sight and lighting condition. Moreover, this platform is designed and built for providing key support to varieties of applications. This article describes the platform architecture, including design, implementation, and performance. We describe the audio sensor platform which can deliver high-quality audio over sensor network by multi-hops with low power requirement. In addition, we present the multimedia synchronization mechanism in the heterogeneous network which is the foundation of applications in the proposed platform. Our experiments include an in-depth analysis of the bottlenecks within the platform as well as measurements for the various components.

Wireless Audio Sensor Networks (WASNs) can provide event detection, object tracking and emergency response through cooperative audio sensor nodes. Effective collaboration of audio sensors requires precise synchronization among audio streams. Some researches have been done on the timestamp mechanism based on time synchronization ignoring propagation delay and many other researches have focused on the synchronization of simple gunshot or scream. However, for the synchronization of intermittent and fluctuating audio stream, there still exists many challenges. In this paper, we propose an effective audio synchronization scheme which can synchronize the intermittent audio streams adaptively while maintain low energy cost. On one hand, we obtain audio synchronization without global clock which save energy tremendously. On the other hand, by introducing a feedback loop mechanism, we can keep a high audio synchronization fidelity even when the audio source moves around and the sound strength varies with time. Furthermore, we discuss the extension for flexibility and scalability of this scheme when there exist several sound sources simultaneously or the audio source moves among clusters. Through experiments on a WASNs platform and simulations, we show that the proposed scheme is desirable to guarantee the accuracy of audio synchronization in practical environment with low energy cost.