Jianjun Wen

A seamless handover for WSN using LMS filter

We propose a MAC protocol that supports the mobility of nodes in wireless sensor networks. The protocol enables burst transmission and seamless handover to achieve high throughput and to reduce packet delivery latency and packet loss. An adaptive filter continuously evaluates the RSSI values of received acknowledgment packets and decides whether a mobile node should transfer a communication to a nearby relay node with a better link quality. The handover process itself takes place without breaking an existing link. This paper presents the design, implementation and evaluation of the MAC protocol.

A Probabilistic Model for Estimating the Power Consumption of Processors and Network Interface Cards

Many of the proposed mechanisms aiming to achieve energy-aware adaptations in server environments rely on the existence of models that estimate the power consumption of the server as well as its individual components. Most existing or proposed models employ performance (hardware) monitoring counters and the CPU utilization to estimate power consumption, but they do not take into account the statistics of the workload the server processes. In this paper we propose a lightweight probabilistic model that can be used to estimate the power consumption of the CPU, the network interface card (NIC), and the server as a whole. We tested the models accuracy by executing custom-made benchmarks as well as standard benchmarks on two heterogeneous server platforms. The estimation error associated with our model is less than 1% for the custom-made benchmark whereas it is less than 12\% for the standard benchmark.

A link quality estimation model for energy-efficient wireless sensor networks

Understanding fluctuations of link quality in a wireless sensor network is useful for different reasons. For example, nodes can determine when and for how long they should transmit packets, so that they can reduce packet loss rate and the cost of retransmission (delay as well as power consumption). However, because the quality of a link depends on many factors, it cannot be known except in a probabilistic sense. In this paper we estimate the expected duration in which the quality of a specific link remains stable using the conditional distribution function of the signal-to-noise ratio (SNR) of received acknowledgment packets. We employ the expected duration to determine how long nodes should transmit packet in burst and how long they should refrain from contention. To develop our model, we deployed Imote2 sensor platforms in indoor and outdoor places and transmitted more than 70, 000 packets. We transmitted additional 16,900 packets to test our model. 90% of the time, our approach resulted in high packet delivery compared with the case in which packets were transmitted without knowledge of link quality fluctuations.

An Efficient Burst Transmission Scheme for Wireless Sensor Networks

This paper addresses link quality fluctuation and its impact on the packet delivery capacity of wireless sensor networks. Independent studies have previously confirmed that link quality fluctuates even in a static deployment and understanding stable durations, good and bad alike, can contribute to the efficient transmission of packets. We propose a two stage Markov model to characterise link quality fluctuation and to determine when and for how long nodes should transmit packets in burst. Both to develop and test our model, we deployed a wireless sensor network consisting of 14 nodes in a garden and transmitted more than 120,000 packets with different links. The experiment results confirm that our approach improved the packet delivery capacity of the links by up to 40% when compared with a baseline and by up to 25% when compared with a scheme that employs conditional distribution functions.

Adaptive Sleep-Time Management Model for WSNs

The energy consumption of a wireless sensor network affects its lifetime which in turn affects the scope and usefulness of the network. Most existing or proposed MAC protocols enable nodes to specify a duty cycle, so that they can sleep much of the time to save energy. However, only very few models exist to determine the appropriate time and duration of a sleep phase. Existing approaches rely on pre-calculated sleep durations or are difficult to implement on real platforms. We propose a runtime and adaptive model to estimate the sleep time and duration of wireless sensor nodes. Our model takes the statistics of incoming and outgoing packets at a relay node which is then supplied to a general queueing model. The model is lightweight and can be fitted into any existing MAC protocol. We have implemented our model for TelosB platform and TinyOS environment. We integrated our model with two existing protocols (TinyOS LPL MAC and XMAC) and compared the performance of these protocols with and without our model. The performance evaluation results show that the energy consumption of a relay node reduced by 11.4 - 64.8%. The overall throughput of the network increased by up to 24%. Moreover, our model readily responded to changes in packet traffic rate while at the same time increasing the packet transmission reliability by 64.5 - 67.4% for different traffic scenarios.

Efficient Online Burst Transmission Scheme for Wireless Sensor Networks

Wireless sensor networks supporting aggressive sampling in harsh environments (to deal with high packet loss or to provide reliable data from sensors such as 3D accelerometers and 3D gyroscopes) require transmission schemes which can achieve a relatively high throughput. Existing contention-based, low-power listening MAC protocols are not apt for these types of networks because their channel utilisation is considerably low. In this paper we propose a hybrid burst transmission scheme to achieve high throughput between static relay nodes, such as nodes deployed on a civil infrastructure (bridge or building). Our transmission scheme deals with link quality fluctuations and adaptively adjust the number of packets that can be transmitted in burst. Its essential features are relying on statistics that are obtained (1) offline and reflect the long-term characteristic of a link and (2) online and reflect the short-term link quality fluctuation. We experimentally compared our transmission scheme with two proposed state-of-the-art schemes in terms of throughput, transmission delay, packet loss, and energy consumption. We implemented all transmission schemes and integrated them into the TinyOS environment and the TelosB platform.

A System Architecture for Managing Complex Experiments in Wireless Sensor Networks

Several reproducible experiments are required before actual deployment of wireless sensor networks takes place if stable and predictable outcomes of protocols and data processing algorithms are desired. Considering the typical size of wireless sensor networks and the number of parameters that can be configured or tuned, conducting repeated and reproducible experiments can be both time consuming and costly. The conventional way of evaluating the performance of different protocols and algorithms under different network configurations is by changing the source code and reprogramming the testbed, which requires some effort. In this paper, we propose a traffic flow control management system that facilitates the execution of repeated experiments in an efficient and flexible way. We implemented our system on top of TinyOS for the TelosB platform and demonstrated the scope and usefulness of the system by conducting several experiments in two real testbeds.

Power-Latency Trade-offs in Virtualized Environments

The adoption of server virtualization and cloud computing has enabled high flexibility of service execution in the Internet. It also promises the efficient use of resources including power. At present, the cloud infrastructure (physical machines and cloud platforms) and the services employing the infrastructure are managed by independent entities. As a result, it is difficult to jointly configure hardware and software resources, which may introduce significant inefficiency of resource utilization. Often infrastructure providers over provision resources to accommodate a growing demand, but the cost of such inefficiency is gradually being felt by both parties. This paper experimentally examines the effect of system configuration (concurrency) on the power consumption and latency of a video hosting server. We find that the usefulness of concurrency is greatly influenced by the interplay of underlying leased resources and by the interaction of virtual machines with these resources. However, the exact nature of this interplay is difficult to quantitatively establish and, therefore, it is not presented to service providers. Our study encourages the scientific community to pay attention to this aspect and to undertake a more rigorous investigation based on practical observations.

MobiLab: A Testbed for Evaluating Mobility Management Protocols in Wireless Sensor Networks

Wireless sensor networks that support the mobility of nodes are finding applications in different areas such as healthcare, elderly care, and rehabilitation from total knee and hip replacement. However, these application areas also require reliable and high throughput networks. Considering the high fluctuation of link quality during mobility, protocols supporting mobile wireless sensor nodes should be rigorously tested to ensure that they produce predictable outcomes. In this paper we present a wireless sensor network testbed for carrying out repeated and reproducible experiments, independent of the application or protocol types which should be tested. The testbed consists of, among others, a server side control station and a client side traffic flow controller which coordinate interand intra-experiment activities. We fully implemented the testbed for the TinyOS and TelosB platforms. We employed Diddyborg robots for emulating different types of movement in indoor and outdoor environments. The paper includes also an extensive evaluation of the testbed and the performance of two mobility-aware MAC protocols. Received on 17 November 2016; accepted on 6 July 2017; published on 21 December 2017

MobiLab: A Testbed for Evaluating Mobility Management Protocols in WSN

Wireless sensor networks that support the mobility of nodes are finding applications in different areas such as healthcare, elderly care, and rehabilitation from total knee and hip replacement. However, these application areas also require reliable and high throughput networks. Considering the high fluctuation of link quality during mobility, protocols supporting mobile wireless sensor nodes should be rigorously tested to ensure that they produce predictable outcomes. In this paper we present a wireless sensor network testbed for carrying out repeated and reproducible experiments, independent of the application or protocol types which should be tested. The testbed consists of, among others, a server side control station and a client side traffic flow controller which coordinate inter- and intra-experiment activities. We fully implemented the testbed for the TinyOS and TelosB platforms. We employed Diddyborg robots for emulating different types of movements in indoor and outdoor environments. The paper includes also an extensive evaluation of the testbed.