He Ba

Feasibility and Benefits of Passive RFID Wake-Up Radios for Wireless Sensor Networks

Energy efficiency is one of the crucial design criteria for wireless sensor networks. Idle listening constitutes a major part of energy waste, and thus solutions such as duty cycling and the use of wake-up radios have been proposed to reduce idle listening and save energy. Compared to duty cycling, wake-up radios save more energy by reducing unnecessary wake-ups and collisions. In this paper, we investigate the feasibility and potential benefits of using passive RFID as a wake-up radio. We first introduce a physical implementation of sensor nodes with passive RFID wake-up radios and measure their energy cost and wake-up probability. Then, we compare the performance of our RFID wake-up sensor nodes with duty cycling in a Data MULE scenario through simulations with realistic application parameters. The results show that using a passive RFID wake-up radio offers significant energy efficiency benefits at the expense of delay and the additional low-cost RFID hardware, making RFID wake-up radios beneficial for many delay-tolerant sensor network applications.

Mobile computing - A green computing resource

Cloud computing provides an approach to accessing shared computing resources. However, a traditional cloud is composed of powerful but energy-hungry workstations. The growth of the population of mobile devices such as smart phones and tablets provides huge amount of idling computing power. In this paper, we describe the design and implementation of a mobile computing system prototype named GEMCloud that utilizes energy efficient mobile devices (e.g., smartphones and tablets) as computing resources. We evaluate the computing power and energy efficiency of the mobile devices through comprehensive experiments. The results show that a cloud computing system with enough mobile devices working cooperatively is able to save 55% to 98% of the energy consumption of conventional server-based clouds while providing comparable computing speed.

Range extension of passive wake-up radio systems through energy harvesting

Use of a passive wake-up radio can drastically increase the network lifetime in a sensor network by reducing or even completely eliminating unnecessary idle listening. A sensor node with a wake-up radio receiver (WuRx) can operate in an extremely low power sleep mode until it receives a trigger signal sent by a wake-up radio transmitter (WuTx). After receiving the trigger signal, the attached WuRx wakes up the sensor node to start the data communication. In this paper, we implement and compare the performance of three passive wake-up radio-based sensor nodes: 1) WISP-Mote, which is a sensor mote that employs an Intel WISP passive RFID tag as the WuRx; 2) EH-WISP-Mote, which combines a novel energy harvester with the WISP-Mote; and 3) REACH-Mote, which uses the energy harvester circuit combined with an ultra-low-power pulse generator to trigger the wake-up of the mote. Experimental results show that the wake-up range and wake-up delay for the EH-WISP-Mote are improved compared with the WISP-Mote, while providing the ability to perform both broadcast-based and ID-based wake-ups. On the other hand, the REACH-Mote, which can only provide broadcast-based wake-up, can achieve a much longer wake-up range than any known passive wake-up radio to date, achieving feasible wake-up at a range of up to 37 ft.

Use of Network Latency Profiling and Redundancy for Cloud Server Selection

As servers are placed in diverse locations in networked services today, it becomes vital to direct a clients request to the best server(s) to achieve both high performance and reliability. In this distributed setting, non-negligible latency and server availability become two major concerns, especially for highly-interactive applications. Profiling latencies and sending redundant data have been investigated as solutions to these issues. The notion of a cloudlet in mobile-cloud computing is also relevant in this context, as the cloudlet can supply these solution approaches on behalf of the mobile. In this paper, we investigate the effects of profiling and redundancy on latency when a client has a choice of multiple servers to connect to, using measurements from real experiments and simulations. We devise and test different server selection and data partitioning strategies in terms of profiling and redundancy. Our key findings are summarized as follows. First, intelligent server selection algorithms help find the optimal group of servers that minimize latency with profiling. Second, we can achieve good performance with relatively simple approaches using redundancy. Our analysis of profiling and redundancy provides insight to help designers determine how many servers and which servers to select to reduce latency.

Passive wake-up radios: From devices to applications

Energy efficiency is one of the most important criteria in the design of a wireless sensor network. Sensor nodes are usually battery-powered and thus have very limited lifetime. In this paper, we introduce a novel passive wake-up radio device named WISP-Mote that uses a passive RFID tag as a wake-up receiver for a traditional sensor node. We characterize the WISP-Mote with field tests in different operating environments and present the wake-up probabilities based on the distance between the wake-up transmitter and receiver. We then perform simulations to compare the performance of a network with WISP-Motes and with duty-cycling of the sensor nodes, using the wake-up probabilities measured in our field tests. Additionally, potential applications that can benefit from WISP-Motes are discussed, and the advantages of using WISP-Motes are identified by simulation results based on these application scenarios. Results show that the wake-up radio sensor networks have great potential over duty-cycling approaches for energy efficiency, while providing similar latency and packet delivery performances.

The Cloudlet Accelerator: Bringing Mobile-Cloud Face Recognition into Real-Time

A mobile-cloud architecture provides a practical platform for performing face recognition on a mobile device. However, using a mobile-cloud architecture to perform real-time face recognition presents several challenges including resource limitations and long network delays. In this paper, we determine three approaches for accelerating the execution of the face recognition application by utilizing an intermediate device called a cloudlet. We study in detail one of these approaches, using the cloudlet to perform pre-processing, and quantify the maximum attainable acceleration. Our experimental results show up to a 128x improvement in response time when appropriate cloudlet hardware is used.

Extending volunteer computing through mobile ad hoc networking

Volunteer computing provides a practical and low cost solution to the increasing computational demands of many applications. Recent advancements in mobile device processing capabilities, combined with the energy efficiency of the mobile devices, make their inclusion in a distributed computing architecture particularly appealing. However, the intrinsic requirement of Internet connectivity to participate in volunteer computing limits the direct adoption of mobile devices due to service availability or related costs to connect to the Internet. In this paper, we propose and implement a novel computational architecture that extends the ability of mobile devices to participate in volunteer computing through ad hoc networking. By introducing decentralized task distribution points, mobile devices are invited to join the computation via device to device communication, removing the requirement for an Internet connection. Using a prototype implementation running on Android devices, we investigate the impact of a promising ad hoc communication technology, namely WiFi Direct, and two task distribution algorithms with different computation and communication overheads, under various scenarios. Experimental results show that our proposed approach is feasible with only minor additional energy consumption at the decentralized task distribution points.

BaNa: A hybrid approach for noise resilient pitch detection

Pitch is one of the essential features in many speech related applications. Although numerous pitch detection algorithms have been developed, as shown in this paper, the detection ratio in noisy environments still needs improvement. In this paper, we present a hybrid noise resilient pitch detection algorithm named BaNa that combines the approaches of harmonic ratios and Cepstrum analysis. A Viterbi algorithm with a cost function is used to identify the pitch value among several pitch candidates. We use an online speech database along with a noise database to evaluate the accuracy of the BaNa algorithm and several state-of-the-art pitch detection algorithms. Results show that for all types of noises and SNR values investigated, BaNa achieves the best pitch detection accuracy. Moreover, the BaNa algorithm is shown to achieve around 80% pitch detection ratio at 0dB signal-to-noise ratio (SNR).

Sleeping Techniques for Reducing Energy Dissipation

Sensors have limited resources such as energy, computational power and bandwidth, and thus they require protocols and techniques that are resource aware and energy efficient. As energy waste through idle listening, retransmissions and overhearing are some of the primary causes of reduced lifetime in wireless sensor networks, sensor sleeping is critically important. Sleeping techniques prolong the network lifetime by placing components of the sensor node into a sleep mode while aiming to minimize the impact on application performance. Sensor sleeping can be applied to different layers of the protocol stack, and a cross-layer sleep manager can orchestrate sleeping in multiple layers simultaneously. In this chapter, the importance of sensor sleeping, the various sleeping techniques proposed and the applications using these approaches are discussed.

Passive RFID-Based Wake-Up Radios for Wireless Sensor Networks

This article describes the history of the Wireless Identification and Sensing Platform (WISP) program. It describes the research motivating the creation of the WISP, its development process, the decision to open source its design, and the creation of the WISP Challenge, a program to make WISPs available to univer-sity researchers. The article then surveys WISP-related research performed by the author’s group, by collaborators, and by others who received WISPs through the WISP Challenge or via other channels