Transmit only for dense wireless networks.

摘要

As the size and cost of embedded wireless devices decreases, researchers and technology companies find an ever-growing number of applications in health and safety, environmental monitoring, and agriculture. The goal of many of these applications is to simultaneously monitor more things at finer time or spatial granularity than was previously practicable. Progress in the size and cost of ICs has made these applications possible, but new wireless protocols must be developed to leverage this modern hardware for multi-year, dense, "always on" deployments.;These applications have requirements that are not currently addressed, most importantly energy efficiency in mobile and dense deployments, because transmitter lifetime and system maintainability may be more important than the low latency or high reliability that are paramount in current wireless systems. Current wireless protocols, such as CSMA, favor channel throughput and packet transmission success without considering the energy efficiency and utility of energy hungry feedback mechanisms such as channel sensing and packet acknowledgements. A protocol that extends the lifetime of sensors by years at the cost of occasional sensing delays (measured in seconds) from packet loss is preferable in many emerging applications. In this dissertation one such approach, called Transmit Only, is introduced. Transmit Only is shown to achieve years of lifetime on current commercially available hardware by consuming just over 20mA per year on a chip doing both sensing and data transmission.;We also show that Transmit Only can remain energy efficient even as transmitter density increases. Although packet collisions increase with the number of transmitters in a Transmit Only system, we show that careful placement of multiple receivers can maximize the capture effect and reduce actual packet loss. For example, in a sensor network with 1000 transmitters offering 100% channel load, with just five receivers the transmitters successfully convert 80% of their radio energy into successfully transmitted bits.;This dissertation will demonstrate that the drawbacks of Transmit Only, namely multiple receivers and no packet delivery guarantees, are easily worth the benefits in efficient energy usage and lifetime, transmitter simplicity, and high throughput at very high offered loads and transmitter densities.