This paper describes ExOR,an integrated routing and MAC protocol that increases the throughput of large unicast transfers in multi-hop wireless networks. ExOR chooses each hop of a packet's route after the transmission for that hop, so that the choice can reflect which intermediate nodes actually received the transmission. This deferred choice gives each transmission multiple opportunities to make progress. As a result ExOR can use long radio links with high loss rates, which would be avoided by traditional routing. ExOR increases a connection's throughput while using no more network capacity than traditional routine.ExOR's design faces the following challenges. The nodes that receive each packet must agree on their identities and choose one forwarder.The agreement protocol must have low overhead, but must also be robust enough that it rarely forwards a packet zero times or more than once. Finally, ExOR must choose the forwarder with the lowest remaining cost to the ultimate destination.Measurements of an implementation on a 38-node 802.11b test-bed show that ExOR increases throughput for most node pairs when compared with traditional routing. For pairs between which traditional routing uses one or two hops, ExOR's robust acknowledgments prevent unnecessary retransmissions,increasing throughput by nearly 35%. For more distant pairs, ExOR takes advantage of the choice of forwarders to provide throughput gains of a factor of two to four.

/pdf/exor-opportunistic-multi-hop-routing-for-wireless-networks-2hu6r88tiv.pdf

ExOR: opportunistic multi-hop routing for wireless networks

Hofmeister phenomena: an update on ion specificity in biology.

This paper describes Extremely Opportunistic Routing (ExOR), a new unicast routing technique for multi-hop wireless networks. ExOR forwards each packet through a sequence of nodes, deferring the choice of each node in the sequence until after the previous node has transmitted the packet on its radio. ExOR then determines which node, of all the nodes that successfully received that transmission, is the node closest to the destination. That closest node transmits the packet. The result is that each hop moves the packet farther (or average) than the hops of the best possible pre-determined route.The ExOR design addresses the challenge of choosing a forwarding node after transmission using a distributed algorithm. First, when a node transmits a packet, it includes in the packet a simple schedule describing the priority order in which the potential receivers should forward the packet. The node computes the schedule based on shared measurements of inter-node delivery rates. ExOR then uses a distributed slotted MAC protocol for acknowledgements to ensure that the receivers agree who the highest priority receiver was.The efficacy of ExOR depends mainly on the rate at which the reception probability falls off with distance. Simulations based on measured radio characteristics [6] suggest that ExOR reduces the total number of transmissions by nearly a factor of two over the best possible pre-determined route.

/pdf/opportunistic-routing-in-multi-hop-wireless-networks-5agpgp9lby.pdf

Opportunistic routing in multi-hop wireless networks

Definitive diagnosis of prion disease currently requires postmortem brain tissue. Now, Ryuichiro Atarashi and colleagues have discovered an assay that can identify prions in human cerebrospinal fluid. This assay could allow for diagnosis of disease in living humans.

/pdf/ultrasensitive-human-prion-detection-in-cerebrospinal-fluid-2s58on3y7d.pdf

Ultrasensitive human prion detection in cerebrospinal fluid by real-time quaking-induced conversion

Charged and polar groups, through forming ion pairs, hydrogen bonds, and other less specific electrostatic interactions, impart important properties to proteins. Modulation of the charges on the amino acids, e.g., by pH and by phosphorylation and dephosphorylation, have significant effects such as protein denaturation and switch-like response of signal transduction networks. This review aims to present a unifying theme among the various effects of protein charges and polar groups. Simple models will be used to illustrate basic ideas about electrostatic interactions in proteins, and these ideas in turn will be used to elucidate the roles of electrostatic interactions in protein structure, folding, binding, condensation, and related biological functions. In particular, we will examine how charged side chains are spatially distributed in various types of proteins and how electrostatic interactions affect thermodynamic and kinetic properties of proteins. Our hope is to capture both important historical developments and recent experimental and theoretical advances in quantifying electrostatic contributions of proteins.

Electrostatic Interactions in Protein Structure, Folding, Binding, and Condensation

We develop an anycast mechanism at the link layer for wireless ad hoc networks. The goal is to exploit path diversity in the link layer by choosing the best next hop to forward packets when multiple next hop choices are available. Such choices can come from a multipath routing protocol, for example. This technique can reduce transmission retries and packet drop probabilities in the face of channel fading. We develop an anycast extension of the IEEE 802.11 MAC layer based on this idea. We implement the protocol in an experimental proof-of-concept testbed using the Berkeley motes platform and S-MAC protocol stack. We also implement it in the popular ns-2 simulator and experiment with the AOMDV multipath routing protocol and Rician fading channels. We show that anycast performs significantly better than 802.11 in terms of packet delivery, particularly when the path length is large or fading is substantial.

/pdf/exploiting-path-diversity-in-the-link-layer-in-wireless-ad-3o9mecp2y6.pdf

Exploiting path diversity in the link layer in wireless ad hoc networks

Accurate interference models are important for use in transmission scheduling algorithms in wireless networks. In this work, we perform extensive modeling and experimentation on two 20-node TelosB motes testbeds -- one indoor and the other outdoor -- to compare a suite of interference models for their modeling accuracies. We first empirically build and validate the physical interference model via a packet reception rate vs. SINR relationship using a measurement driven method. We then similarly instantiate other simpler models, such as hop-based, range-based, protocol model, etc. The modeling accuracies are then evaluated on the two testbeds using transmission scheduling experiments. We observe that while the physical interference model is the most accurate, it is still far from perfect, providing a 90-percentile error about 20-25% (and 80 percentile error 7-12%), depending on the scenario. The accuracy of the other models is worse and scenario-specific. The second best model trails the physical model by roughly 12-18 percentile points for similar accuracy targets. Somewhat similar throughput performance differential between models is also observed when used with greedy scheduling algorithms. Carrying on further, we look closely into the the two incarnations of the physical model -- 'thresholded' (conservative, but typically considered in literature) and 'graded' (more realistic). We show via solving the one shot scheduling problem, that the graded version can improve `expected throughput' over the thresholded version by scheduling imperfect links.

A measurement study of interference modeling and scheduling in low-power wireless networks

To investigate how the heterogeneity inherent in the formation of worm-like amyloid fibrils by the mouse prion protein is modulated by a change in aggregation conditions, as well as to determine how heterogeneity in reaction leads to heterogeneity in structure, the amyloid fibril formation reaction of the protein at low pH was studied in the presence of various salts. It is shown that β-rich oligomers of different sizes and structures are formed at low and high NaCl concentrations, as determined by Fourier transfer infrared (FTIR) spectroscopy and dynamic light scattering (DLS). The worm-like fibrils formed from the β-rich oligomers at low and high NaCl concentrations also differ in their internal structure, as determined by FTIR measurements. The apparent rate constant for the formation of the worm-like amyloid fibrils shows a very steep sigmoidal dependence on NaCl concentration, suggesting that the effect occurs because of the binding of many ions. The effect of salt in modulating the kinetics of worm-...

Salt-induced modulation of the pathway of amyloid fibril formation by the mouse prion protein.

Evidence for stepwise formation of amyloid fibrils by the mouse prion protein.

We develop an anycast mechanism at the link layer for wireless ad hoc networks. The goal is to exploit path diversity in the link layer by choosing the best next hop to forward packets when multiple next hop choices are available. Such choices can come from a multipath routing protocol, for example. This technique can reduce transmission retries and packet drop probabilities in the face of channel fading. We develop an anycast extension of the IEEE 802.11 MAC layer based on this idea. We implement the protocol in an experimental proof-of-concept testbed using the Berkeley motes platform and S-MAC protocol stack. We also implement it in the popular ns-2 simulator and experiment with the AOMDV multipath routing protocol and Ricean fading channels. We show that anycast performs significantly better than 802.11 in terms of packet delivery, particularly when the path length or effect of fading is large. Further we experiment with anycast in networks that use multiple channels and those that use directional antennas for transmission. In these networks, deafness and hidden terminal problems are the main source of packet loss. We implemented anycast as extension of 802.11 like protocols that were proposed for these special networks. We are able to show that anycast is capable of enhancing the performance of these protocols by simply making use of the path diversity whenever it is available.

/pdf/exploiting-path-diversity-in-the-link-layer-in-wireless-ad-1044z7m8m1.pdf

Shweta Jain

Papers

Exploiting path diversity in the link layer in wireless ad hoc networks

A measurement study of interference modeling and scheduling in low-power wireless networks

Salt-induced modulation of the pathway of amyloid fibril formation by the mouse prion protein.

Evidence for stepwise formation of amyloid fibrils by the mouse prion protein.

Exploiting path diversity in the link layer in wireless ad hoc networks