Whisper: Fast Flooding for Low-Power Wireless Networks

This paper presents Whisper, a fast and reliable protocol to flood small amounts of data into a multi-hop network. Whisper relies on three main cornerstones. First, it embeds the message to be flooded into a signaling packet that is composed of multiple packlets. A packlet is a portion of the message payload that mimics the structure of an actual packet. A node must intercept only one of the packlets to know that there is an ongoing transmission. Second, Whisper exploits the structure of the signaling packet to reduce idle listening and, thus, to reduce the radio-on time of the nodes. Third, it relies on synchronous transmissions to quickly flood the signaling packet through the network. Our evaluation on the Flocklab testbed shows that Whisper achieves comparable reliability but significantly lower radio-on time than Glossy -- a state-of-the-art flooding algorithm. Specifically, Whisper can disseminate data in FlockLab twice as fast as Glossy with no loss in reliability. Further, Whisper spends 30% less time in channel sampling compared to Glossy when no data traffic must be disseminated

Improving practical sensitivity of energy optimized wake-up receivers: proof of concept in 65nm CMOS

We present a high performance low-power digital base-band architecture, specially designed for an energy optimized duty-cycled wake-up receiver scheme. Based on a careful wake-up beacon design, a structured wake-up beacon detection technique leads to an architecture that compensates for the implementation loss of a low-power wake-up receiver front-end at low energy and area costs. Design parameters are selected by energy optimization and the architecture is easily scalable to support various network sizes. Fabricated in 65nm CMOS, the digital base-band consumes 0.9uW (V_DD=0.37V) in sub-threshold operation at 250kbps, with appropriate 97% wake-up beacon detection and 0.04% false alarm probabilities. The circuit is fully functional at a minimum V_DD of 0.23V at f_max=5kHz and 0.018uW power consumption. Based on these results we show that our digital base-band can be used as a companion to compensate for front-end implementation losses resulting from the limited wake-up receiver power budget at a negligible cost. This implies an improvement of the practical sensitivity of the wake-up receiver, compared to what is traditionally reported.Comment: Submitted to IEEE Sensors Journa

Support for a long lifetime and short end-to-end delays with TDMA protocols in sensor networks

This work addresses a tough challenge of achieving two opposing goals: ensuring long lifetimes and supporting short end-to-end delays in sensor networks. Obviously, sensor nodes must wake up often to support short delays in multi-hop networks. As event occurs seldom in common applications, most wake-up are useless: nodes waste energy due to idle listening. We introduce a set of solutions, referred to as LETED (limiting end-to-end delays), which shorten the wake-up periods, reduce idle listening, and save energy. We exploit hardware features of available transceivers that allow early detection of idle wake-up periods. This feature is introduced on top of our approach to reduce idle listening stemming from clock drift owing to the estimation of run-time drift. To evaluate LETED and other MAC protocols that support short end-to-end delays we present an analytical model, which considers almost 30 hardware and software parameters. Our evaluation revealed that LETED reduces idle listening by 15x and more against similar solutions. Also, LETED outperforms other protocols and provides significant longer lifetimes. For example, nodes with LETED work 8x longer than those with a common TDMA and 2x-3x longer than with protocols based on preamble sampling, like B-MAC

Duty-cycled Wake-up Schemes for Ultra-low Power Wireless Communications

In sensor network applications with low traffic intensity, idle channel listening is one of the main sources of energy waste.The use of a dedicated low-power wake-up receiver (WRx) which utilizes duty-cycled channel listening can significantlyreduce idle listening energy cost. In this thesis such a scheme is introduced and it is called DCW-MAC, an acronym forduty-cycled wake-up receiver based medium access control.We develop the concept in several steps, starting with an investigation into the properties of these schemes under idealizedconditions. This analysis show that DCW-MAC has the potential to significantly reduce energy costs, compared to twoestablished reference schemes based only on low-power wake up receivers or duty-cycled listening. Findings motivatefurther investigations and more detailed analysis of energy consumption. We do this in two separate steps, first concentratingon the energy required to transmit wake-up beacons and later include all energy costs in the analysis. The more completeanalysis makes it possible to optimize wake-up beacons and other DCW-MAC parameters, such as sleep and listen intervals,for minimal energy consumption. This shows how characteristics of the wake-up receiver influence how much, and if, energycan be saved and what the resulting average communication delays are. Being an analysis based on closed form expressions,rather than simulations, we can derive and verify good approximations of optimal energy consumption and resulting averagedelays, making it possible to quickly evaluate how a different wake-up receiver characteristic influences what is possible toachieve in different scenarios.In addition to the direct optimizations of the DCW-MAC scheme, we also provide a proof-of-concept in 65 nm CMOS,showing that the digital base-band needed to implement DCW-MAC has negligible energy consumption compared to manylow-power analog front-ends in literature. We also propose a a simple frame-work for comparing the relative merits ofanalog front-ends for wake-up receivers, where we use the experiences gained about DCW-MAC energy consumption toprovide a simple relation between wake-up receiver/analog front-end properties and energy consumption for wide ranges ofscenario parameters. Using this tool it is possible to compare analog front-ends used in duty-cycled wake-up schemes, evenif they are originally designed for different scenarios.In all, the thesis presents a new wake-up receiver scheme for low-power wireless sensor networks and provide a comprehensiveanalysis of many of its important properties

Ferry Route Design with MAC Protocol in Delay Tolerant Networks

Delay Tolerant Networks(DTNs) are occasionally connected networks. They have high latency, long queuing time, limited resources and intermittent connectivity, which are different from traditional networks. They have been proposed to cope with challenges of communication in some extreme or special environments. Due to uncertainty of node mobility, application traffic demand and other factors, it is difficult to provide performance guarantee for a DTN where all nodes move arbitrarily. With controlled mobility, message ferry can be utilized to guarantee the network performance. MAC protocols developed for duty-cycled networks such as B-MAC,S-MAC, employ an extended preamble introduces X-MAC employs shortened preamble approach that retains the advantages of low power listening, namely low power communication, simplicity and a decoupling of transmitter and receiver schedules. Demonstrate through implementation and evaluation that xmac?s shortened preamble approach significantly reduces energy usage at both transmitter and receiver, reduces per-hop latency

Energy-efficient MAC protocols for wireless sensor networks: a survey

MAC Protocols enables sensor nodes of the same WSN to access a common shared communication channel. Many researchers have proposed different solutions explaining how to design and implement these protocols. The main goal of most MACs protocols is how to prolong lifetime of the WSN as long as possible by reducing energy consumption since it is often impossible to change or to recharge sensors’ batteries. The majority of these protocols designed for WSN are based on “duty-cycle” technique. Every node of the WSN operates on two periods: active period and sleep period to save energy. Until now (to our knowledge) there is no ideal protocol for this purpose. The main reason relies on the lack of standardization at lower layers (physical layer) and (physical) sensor hardware.  Therefore, the MAC protocol choice remains application-dependent. A useful MAC protocol should be able to adapt to network changes (topology, nodes density and network size). This paper surveys MAC protocols for WSNs and discusses the main characteristics, advantages and disadvantages of currently popular protocols