Frequency switching is a fundamental capability for wireless communication systems. However, this capability is significantly constrained in backscatter systems. The difficulty is to generate tunable high-frequency modulation signals on a backscatter tag at an acceptable power budget. In this paper, we present Twaltz, a new design paradigm for backscatter communication that enables frequency switching across large frequency bands. By exploiting a low-power semiconductor device, i.e., tunnel diode, and carefully addressing its physical features, Twaltz generates oscillation signals up to 1.2 GHz while maintaining micro-watt level power consumption. Twaltz further facilitates on-tag oscillation signal stabilization and programmable oscillation frequency tuning. We prototype Twaltz on a PCB board, demonstrating its efficiency in cross-band communication for LoRa backscatter, and verifying its performance in concurrent transmission, channel hopping, and data transmission.

Most lightweight networks adopt simple feature fusion methods, such as element-wise addition, to achieve real-time speed. However, complex background and noise can affect these methods, making it difficult to locate objects accurately. At the same time, if a large number of channel connections are used to fuse the feature layer, the parameter quantity will increase dramatically. In this work, we propose a new network architecture with dense connection and feature filtering to tackle this problem. We introduce a feature filtering module (FFM) designed to implement feature fusion and filter features adaptively according to the global semantic information so as to reduce feature redundancy and aliasing after feature fusion. We verify the proposed network on CIFAR-10, CIFAR-100, Pascal VOC, and MS COCO. Compared with other state-of-the-art works, experimental results show that our network maintains lightweight while improving system accuracy on object recognition. In addition, our FFM can be applied to other models to improve the performance in object detection.

In recent years, wireless sensor networks have been used in a wide range of indoor localization-based applications. Although promising, the existing works are dependent on a large number of anchor nodes to achieve localizations, which brings the issues of increasing of the cost and additional maintenance. Inspired by the cross-technology communication, an emerging technique that enables direct communication among heterogeneous wireless devices, we propose an anchor-free distributed method, which leverages the installed Wi-Fi APs to calculate the distance instead of traditional anchor nodes. More specifically, for the asymmetric coverage of Wi-Fi and ZigBee nodes, we first design a progressive method, where the first unknown node estimates its location based on two Wi-Fi APs and a sink node, then once achieving its position, it acts as the alternative sink node of the next hop. This process is repeated until the new members can obtain their positions. Second, as a low-power technology, ZigBee signal may be submerged in strong signals such as Wi-Fi. To overcome this problem, a prime number is deployed to be the Wi-Fi broadcasting period based on the numerical analysis theory. Among lots of prime numbers, we have the opportunity to select an appropriate one with the relatively small packet collisions. Last, numerical simulations and experiments are performed to evaluate the proposal. The evaluation results show that the proposal can achieve decimeter level accuracy without deploying any anchor node. Moreover, the proposal demonstrates the anti-interference ability in the crowded open spectrum environment.

Emergency navigation is an emerging application of wireless sensor networks with significant research and social value. In order to ensure the safe and timely navigation of the evacuees, most of the existing works model navigation as a path-planning problem or movement decision support problem and adopt different metrics, such as the shortest route, the minimum exposure path, and the maximum safe distance. Without sufficient consideration of the dynamics of danger, the existing approaches are likely to cause users to move back and forth during navigation, known as oscillation. Frequent oscillations inevitably result in the user remaining in danger for a longer period of time, amplification of the user's panic, and eventual decrease in the chances of survival. In this paper we take users' oscillations in the dynamic environments into account and quantify the local success rate of navigation using a metric called ENO (Expected Number of Oscillations). We then propose OPEN, an oscillation-free navigation approach that minimizes the probability of oscillation and guarantees the success rate of emergency navigation. We implement OPEN and evaluate its performance through the trace from our system and extensive simulations. The results demonstrate that OPEN outperforms the current state-of-the-art approaches with respect to user safety and navigation efficiency.

Mobile software technologies have become increasingly important in building disaster response system to cope with natural and man-caused emergency situations. In this paper we present a context-aware disaster response system that analyzes the contextual information of public users and disaster environment, and then delivers customized instructions in an appropriate format to the mobile handsets of the public users in a timely manner. Compared to traditional disaster response systems and approaches, the proposed system can greatly improves the timeliness and efficiency of the instructions in the response by utilizing context awareness and mobile software technologies. Supporting evaluation results are also provided based on experiments that have been conducted on a software prototype which is developed to validate the proposed system.

Emergency navigation is an emerging application of wireless sensor networks with significant research and social values. In order to ensure the safety and timeliness of navigation for the users, most of the existing works model navigation as a path-planning problem and adopt different metrics, such as the shortest route, the minimum exposure path, and the maximum safe distance. Without sufficient consideration of the dynamics of danger, the existing approaches are likely to cause users to move back and forth during navigation, known as oscillation. Frequent oscillations inevitably result in the user remaining in danger for a longer period of time, amplification the user's panic, and eventual decrease in the chances of survival. In this paper we take users' oscillations in the dynamic environments into account and quantify the local success rate of navigation using a metric called ENO (Expected Number of Oscillations). We then propose OPEN, an oscillation-free navigation approach that minimizes the probability of oscillation and guarantees the success rate of emergency navigation. We implement OPEN and evaluate its performance through test-bed experiments and extensive simulations. The results demonstrate that OPEN outperforms the current state-of-the-arts approaches with respect to user safety and navigation efficiency.

In this paper, we have described a co-construction process model, in the context of a socio-technical framework, to support the collaborative engineering design. This paper has reviewed our previous work in building a co-construction model on the conceptual, logical, and analytical layers and then proposed an expanded Petri net representation that is developed toward a more comprehensive and operational co-construction model, which captures the key conceptual components of a collaborative engineering design process, describes the possible logic flow between these components, and analyzes their interaction in the design process. In this paper, we have also discussed a case study that was conducted in a real-life engineering design to validate our research. At the end of this paper, we emphasized the importance of this study and outlined the future directions of improving this study.