Raja Jurdak

A survey, classification and comparative analysis of medium access control protocols for ad hoc networks

Recent technological advances in wireless communications offer new opportunities and challenges for wireless ad hoc networking. In the absence of the fixed infrastructure that characterizes traditional wireless networks, control and management of wireless ad hoc networks must be distributed across the nodes, thus requiring carefully designed medium access control (MAC) layer protocols. In this article we survey, classify, and analyze 34 MAC layer protocols for wireless ad hoc networks, ranging from industry standards to research proposals. Through this analysis, six key features emerge: (1) channel separation and access; (2) topology; (3) power; (4) transmission initiation; (5) traffic load and scalability; and (6) range. These features allow us to characterize and classify the protocols, to analyze the tradeoffs produced by different design decisions, and to assess the suitability of various design combinations for ad hoc network applications. The classification and the tradeoff analysis yield design guidelines for future wireless ad hoc network MAC layer protocols.

Beep: 3D indoor positioning using audible sound

Rapid growth in the number of wireless enabled devices has led to an increased interest in location-aware applications. The backbone of such applications is provided by a location system. In this paper we present Beep, an indoor location system that senses audible sound. The use of audible sound makes our system cheap and easily deplorable to most existing roaming devices. Unlike positioning systems using ultrasound and infrared signals, Beep does not require the user to carry any kind of specialized hardware. Our system is based on standard 3D multilateration algorithms. However, the requirement of being able to locate existing devices, whose sound cards were not designed for high-precision signaling, introduces additional challenges to the location problem. This paper describes how those problems were solved and presents experimental results. Beep works with an accuracy of about 2 feet in more than 97% cases. The paper also describes a sensor deployment strategy that requires low sensor density and consequently low installation costs.

MERLIN: Cross-layer integration of MAC and routing for low duty-cycle sensor networks

Sensor network MAC protocols typically sacrifice packet latency to achieve energy efficiency. Such delays may well increase due to routing protocol operation. For this reason it is imperative that we attempt to quantify the end-to-end delay and energy consumption when jointly using low duty cycle MAC and routing protocols. In this paper, we present a comprehensive evaluation of MERLIN (MAC and efficient routing integrated with support for localization), a cross-layer protocol that integrates both MAC and routing features. In contrast to many sensor network protocols, it employs a multicast upstream and multicast downstream approach to relaying packets to and from the gateway. Simultaneous reception and transmission errors are notified by asynchronous burst ACK and negative burst ACK messages. A division of the network into timezones, together with an appropriate scheduling policy, enables the routing of packets to the closest gateway. An evaluation of MERLIN has been conducted through simulation, against both the SMAC and the ESR routing protocols (an improved version of the DSR algorithm). The results illustrate that the joint usage of both SMAC and ESR, in low duty cycle scenarios, causes extremely high end-to-end delays and prevents acceptable data delivery rate. MERLIN, as an integrated approach, notably reduces latency, resulting in nodes that can deliver data in a very low duty cycle, yielding a significant extension to network lifetime.

Adaptive Radio Modes in Sensor Networks: How Deep to Sleep?

Energy-efficient performance is a central challenge in sensor network deployments, and the radio is a major contributor to overall energy node consumption. Current energy- efficient MAC protocols for sensor networks use a fixed low power radio mode for putting the radio to sleep. Fixed low power modes involve an inherent tradeoff: deep sleep modes have low current draw and high energy cost and latency for switching the radio to active mode, while light sleep modes have quick and inexpensive switching to active mode with a higher current draw. This paper proposes adaptive radio low power sleep modes based on current traffic conditions in the network, as an enhancement to our recent RFID impulse low power wake-up mechanism. The paper also introduces a comprehensive node energy model, that includes energy components for radio switching, transmission, reception, listening, and sleeping, as well as the often disregarded micro-controller energy component to evaluate energy performance for both MicaZ and TelosB platforms, which use different MCUs. We then use the model for comparing the energy-related performance of RFIDImpulse enhanced with adaptive low power modes with BMAC and IEEE 802.15.4 for the two node platforms under varying data rates. The comparative analysis confirms that RFIDImpulse with adaptive low power modes provides up to 20 times lower energy consumption than IEEE 802.15.4 in low traffic scenario. The evaluation also yields the optimal settings of low power modes on the basis of data rates for each node platform, and it provides guidelines for the selection of appropriate MAC protocol, low power mode, and node platform for a given set of traffic requirements of a sensor network application.

U-MAC: a proactive and adaptive UWB medium access control protocol

Ultra wide band (UWB) technology has received increasing recognition in recent years for its potential applications beyond radar technology to communication networks. UWB is a spread spectrum technology that requires careful coordination among communicating nodes to jointly control link power and transmission rates. Here, we present ultra wide band MAC (U-MAC), an adaptive medium access control (MAC) protocol for UWB in which nodes periodically declare their current state, so that neighbors can proactively assign power and rate values for new links locally in order to optimize global network performance. Simulations comparing U-MAC to the reactive approach confirm that U-MAC lowers link setup latency and control overhead, doubles the throughput and adapts better to high network loads. Simulations also reveal that the basic form of U-MAC favors nodes that are closer to the receiver. As a result, we also introduce novel mechanisms that control the radius around a receiver within which nodes can have fair access to it. We show through simulations the effect of the mechanisms on the tradeoff between network throughput and fair access.

Energy-efficient multi-hop medical sensor networking

Wireless sensor networks represent a key technology enabler for enhanced health care and assisted living systems. Recent standardization eorts to ensure compatibility among sensor network systems sold by dierent vendors have produced the IEEE 802.15.4 standard, which specifies the MAC and physical layer behavior. This standard has certain draw-backs: it supports only single-hop communication; it does not mitigate the hidden terminal problem; and it does not coordinate node sleeping patterns. The IEEE 802.15.4 standard design philosophy assumes that higher layer mechanisms will take care of any added functionality. Building on IEEE 802.15.4, this paper proposes TImezone COordinated Sleep Scheduling (TICOSS), a mechanism inspired by MERLIN [2] that provides multi-hop support over 802.15.4 through the division of the network into timezones. TICOSS is cross-layer in nature, as it closely coordinates MAC and routing layer behavior. The main contributions of TICOSS are threefold: (1) it allows nodes to alternate periods of activity and periods of inactivity to save energy; (2) it mitigates packet collisions due to hidden terminals belonging to nearby star networks; (3) it provides shortest path routing for packets from a node to the closest gateway. Simulation experiments confirm that augmenting IEEE 802.15.4 networks with TICOSS doubles the operational lifetime for high trac scenarios. TICOSS has also been implemented on the Phillips AquisGrain modules for testing and eventual deployment in assisted living systems.

Multi-Hop RFID Wake-Up Radio: Design, Evaluation and Energy Tradeoffs

Energy efficiency is a central challenge in battery- operated sensor networks. Current energy-efficient mechanisms employ either duty cycling, which reduces idle listening but does not eliminate it, or low power wake-up radio, which adds complexity and cost to the sensor platform. In this paper, we propose a novel mechanism called RFIDImpulse that uses RFID technology as an out-of-band wake-up channel for sensor networks. RFIDImpulse is an on-demand mechanism that enables nodes to sleep until they have to send or receive packets. It relies on IEEE 802.15.4 radio to emulate an RFID reader at a sender node, and on an off-the-shelf RFID tag attached to the external interrupt pin of each sensor node. The sender can simply activate the receivers tag before sending it data packets. This setup enables both radio and microcontroller to go into deep sleep mode until they need to be active. We develop an analytical model to evaluate the energy tradeoffs of RFIDImpulse, and then evaluate the mechanism against BMAC and IEEE 802.15.4 in high and low traffic scenarios. The results confirm that RFIDImpulse reduces the energy consumption relative to both protocols for low and medium traffic scenarios, and they reveal the thresholds for adaptive activation of RFIDImpulse based on traffic load.

Software Acoustic Modems for Short Range Mote-based Underwater Sensor Networks

Most recent work in underwater network development has relied on using expensive commercial acoustic modems or on building custom transceivers for each application to establish acoustic communication links among the sensors. Using commercial modems or designing custom hardware may require prohibitive monetary or time investment for many applications. Our work proposes the design of software acoustic modems that can utilize built-in microphones and speakers on the relatively cheap Tmote Invent platforms. The built-in Tmote hardware and the software modem enable acoustic communication in a short range shallow water network. In this paper, we present the initial design and architecture of our acoustic communication system which targets environmental monitoring applications. Our experiments with generic acoustic hardware to profile this underwater communication channel reveal that the channel favors frequencies below 3 Khz, a result which guides the design choices for our FSK software modem. We perform experiments with our software modem/generic hardware system to explore the systems data transfer capability. The data communications experiments confirm the systems capability of transferring information in the order of tens of bits per second for a communications range of up to 10 meters.

Software Modems for Underwater Sensor Networks

The prohibitive monetary cost and high power consumption of existing acoustic hardware represent an obstacle for underwater sensor network deployment efforts. To address this issue, we propose underwater networks that rely on widely available speakers and microphones in electronic devices, coupled with software modems, to establish acoustic communication links. In this paper, we analytically and empirically explore the potential of this acoustic communication system for the underwater environment with a generic PC microphone as a receiver and with the Tmote Invent sensor module speaker as a transmitter. After waterproofing the components with elastic membranes that provide suitable coupling with the water, our experiments profile the hardware communication capability in a controlled aquatic environment. The medium profiling results expose the favorable frequencies of operation for the hardware, enabling us to design a software FSK modem. The experiments to evaluate the data transfer capability of our 8-frequency FSK software modem in the underwater channel yield an error-free channel capacity of 24 bps, and they also demonstrate that the system supports data rates up to at least 48 bps within a transmission range of 17 m.

BlockChain: A Distributed Solution to Automotive Security and Privacy

Interconnected smart vehicles offer a range of sophisticated services that benefit the vehicle owners, transport authorities, car manufacturers, and other service providers. This potentially exposes smart vehicles to a range of security and privacy threats such as location tracking or remote hijacking of the vehicle. In this article, we argue that blockchain (BC), a disruptive technology that has found many applications from cryptocurrencies to smart contracts, is a potential solution to these challenges. We propose a BC-based architecture to protect the privacy of users and to increase the security of the vehicular ecosystem. Wireless remote software updates and other emerging services such as dynamic vehicle insurance fees are used to illustrate the efficacy of the proposed security architecture. We also qualitatively argue the resilience of the architecture against common security attacks.