Daji Qiao

Heterogeneous ad hoc networks

The Heterogeneous Ad Hoc Networks (HANETs) are important components of the Internet of things, which become an inevitable trend in the future researches and applications. In recent years, the ad hoc networks have been widely employed in many fields, especially in environment monitoring, weapon control, intelligent transportation, smart city and other domains. HANETs consist of wireless sensor networks, smart ad hoc networks, wireless fidelity networks, telecommunication networks, vehicular ad hoc networks, etc. The digital information and physical objects are integrated through appropriate communication methods, thus new applications and services are created. Different applications use the independent network structures, which form a heterogeneous network platform and increase operational complexity of communication between each other. This paper presents a typical architecture of the large-scale HANETs, and investigates research advances of the current key technologies. To address existing issues, we suggest some potential solutions to deal with the current challenges, such as self-organization, big data transmission, privacy protection, data fusion and processing for large-scale HANETs.

A Robust Time Synchronization Scheme for Industrial Internet of Things

Energy-efficient and robust-time synchronization is crucial for industrial Internet of things (IIoT). Some energy-efficient time synchronization schemes that achieve high accuracy have been proposed recently. However, some unsynchronized nodes namely isolated nodes exist in the schemes. To deal with the problem, this paper presents R-Sync, a robust time synchronization scheme for IIoT. We use a pulling timer to pull isolated nodes into synchronized networks whose initial value is set according to level of spanning tree. Then, another timer is set up to select backbone node and its initial value is related to the distance to parent node. Moreover, we do experiments based on simulation tool NS-2 and testbed based on wireless hardware nodes. The experimental results show that our approach makes all the nodes get synchronized and gets the better performance in terms of accuracy and energy consumption, compared with three existing time synchronization algorithms TPSN, GPA, STETS.

A Practical PSM Scheme for Varying Server Delay

Today, many individuals use smartphones or other battery-powered mobile devices equipped with Wi-Fi to access the Internet. Since the network interface cards (NICs) often use a substantial portion of available energy, schemes such as the 802.11 power saving mode (PSM) have been used to limit the amount of time a NIC is awake in an operable state so as to extend battery life. However, since the NIC cannot retrieve packets while sleeping, PSM may negatively impact packet delay. These delays are also unbounded and can significantly increase communication time, particularly in a mobile environment where server delays may change drastically. To mitigate this, we present PSM-AW: a PSM with adaptive wake-up. PSM-AW is a client-side solution that allows the client device to sleep for a maximum time interval while still keeping a tight bound on performance. We present and prove a bound on performance using PSM-AW and demonstrate its effectiveness through extensive simulations and experiments.

Lifetime balanced data aggregation for the internet of things

A lifetime balanced data aggregation scheme for the Internet of Things, called LBA, is proposed.LBA adjusts the aggregation delays of neighboring devices in a collaborative manner.The lifetime between neighboring devices may be balanced without increasing the end-to-end delay.LBA is distributed, scalable, and able to dynamically adapt to the network changes in practice. Display Omitted This paper proposes LBA, a lifetime balanced data aggregation scheme for the Internet of Things (IoT) under an application-specified end-to-end delay requirement. In contrast to existing aggregation schemes, LBA aims to prolong the IoT network lifetime under network heterogeneity and dynamics, while ensuring the required data delivery delay. To achieve this goal in a distributed manner, LBA adaptively adjusts the aggregation delays of neighboring devices to balance the lifetime between them. As such balancing takes place in all neighborhoods, the minimal device lifetime in the network is increased gradually, thus prolonging the lifetime of the entire network. The effectiveness of LBA is demonstrated via extensive experiments on a testbed. Generally, when the network presents a higher degree of heterogeneity and dynamics, LBAs performance gain over a state-of-the-art non-adaptive data aggregation scheme becomes more significant, and the gap between LBAs performance and its theoretical upper bound gets smaller.

Optimized barrier location for barrier coverage in mobile sensor networks

Barrier coverage is an important application of sensor networks. This paper studies how to build a strong barrier with mobile sensors in which the maximum moving distance of sensors is minimized. Our work differs from others in the way the y-coordinate of the barrier is determined. We optimize the y-coordinate of the barrier instead of fixing it a priori. An efficient algorithm is proposed, in which the search space of the y-coordinate of the barrier is first discretized and then searched over iteratively. In the theoretical worst case, O(N4) iterations may be needed to find the optimal barrier location, where N is the number of sensors, but in practice, our algorithm requires less than O(N2) iterations, as confirmed in simulation.

Confining Wi-Fi Coverage: A Crowdsourced Method Using Physical Layer Information

Many small businesses and public areas offer free Wi-Fi access, but may wish to restrict network access only to their customers or patrons inside the physical property. Unfortunately, due to the nature of wireless networks, this is difficult to accomplish. We develop and implement CLAC, a Crowdsourced Location aware Access Control scheme using physical layer information to address this challenge. It crowdsources both channel state information (CSI) and received signal strength (RSS) of already validated users to classify future users. We propose and use two CSI metrics in CLAC: CSI Cross-Antenna Stability Metric and CSI Cross-Frame Stability Metric, which summarize well the spatial and temporal CSI characteristics respectively. CLAC is evaluated in an office and a classroom. Evaluation results show that CLAC performs well in both environments, allowing most valid users inside the area to access the network, while the chance that invalid users outside the boundary may access the network is small.

EDAD: Energy-centric data collection with anycast in duty-cycled wireless sensor networks

Recent efforts in applying anycast techniques to duty-cycled wireless sensor networks have shown promising results in terms of reduced delay and energy consumption. This paper further increases the energy savings by introducing EDAD, an energy-centric cross-layer data collection protocol designed for anycast communications in asynchronously duty-cycled wireless sensor networks. EDAD uses a new anycast routing metric, EEP, that minimizes the expected energy consumed along the path of a packet and automatically adapts to network settings. Simulation results show that EDAD consumes less energy than similar existing protocols, while maintaining a comparable delay and high delivery rate.

Cost-efficient barrier coverage with a hybrid sensor network under practical constraints

Barrier coverage is a natural application of sensor networks in which sensors are deployed to detect intruders or protect crucial resources. In this paper, we consider a hybrid sensor network with a two-phase deployment, in which less-expensive static sensors are first randomly deployed in an area, and then more-expensive mobile sensors are deployed to fill coverage gaps. We use a probabilistic model to take into account the practical constraints of detection probability and false positives. We propose an iterative scheme that finds a sensor deployment strategy that minimizes the total sensor cost. Our scheme makes use of a graph transformation and includes speed-up strategies. We present simulation results that verify the correctness of the proposed scheme and demonstrate the effectiveness of the speed-up strategies.

BladeMAC: Radio duty-cycling in a dynamic, cyclical channel

As wind energy continues to expand to new frontiers in terms of the location, number, and size of wind turbines, the industry has begun to seek smarter operations and management solutions. Wireless sensing nodes could provide a low-cost platform to support a variety of applications designed to reduce the levelized cost of energy and increase the safety of wind turbines. However, a wireless sensor node deployed on a wind turbine blade would have an extremely limited energy supply. To combat this limitation, we present BladeMAC, a new MAC-layer protocol designed for sensor nodes deployed on rotating wind turbine blades. BladeMAC overcomes a unique cyclical channel problem to allow a sensor node attached to a rotating blade to opportunistically and efficiently offload its data to a sink node attached to the turbine tower. We have implemented and evaluated BladeMAC using Contiki OS and the Cooja simulation tool. We present results showing that BladeMAC effectively deals with the cyclical channel problem at a wide range of data arrival intervals, and that BladeMAC is insensitive to rotation speed and rotation speed fluctuations.

A lifetime-balancing MAC protocol under the end-to-end delay requirement

This article presents lifetime-balancing medium access control (LB-MAC), a new medium access control (MAC) protocol with embedded adaptivity for asynchronous, duty cycle sensor networks. Different from existing sensor network MAC protocols that usually focus on reducing energy consumption and extending lifetime of individual sensor nodes, LB-MAC aims at prolonging the network lifetime under a certain end-to-end delay requirement. It achieves this goal by dynamically tuning a comprehensive set ofMAC parameters. LB-MAC is a distributed, lightweight, and scalable solution, as the required control information is only exchanged locally between neighbors. LB-MAC has been implemented in TinyOS and evaluated on a sensor network testbed with extensive experiments. Results show that LB-MAC is able to yield a significantly longer network lifetime than state-of-the-art MAC protocols such as X-MAC, RI-MAC, and SEESAW, while meeting the end-to-end delay requirement, andmaintaining comparable levels of data delivery ratio and average nodal power consumption.