“Our goal was to get the highest data rate possible, without compromising the fidelity of the signal,” says Dr. Alexandra Duel-Hallen, a professor of electrical and computer engineering at NC State and co-author of a paper describing the work.
Transmitting data within MANETs is challenging because every node that transmits and receives data is in motion – and the faster they are moving, the harder it is for the network to identify effective relay “paths” for transmitting data. This is because the power of the data-transmission channels fluctuates much more rapidly at high speed.
In other words, a transmitter may try to send a message through Relay A, because Relay A has a strong signal. However, because the transmitter and Relay A are both moving quickly, Relay A’s signal might be weak by the time the message actually gets there. And a weak signal could result in the message being garbled.
To address this issue, researchers developed a method to improve the ability of each node in the network to select the best path for relaying data, as well as the best for transmitting the data that ensures reliable reception.
When a node needs to transmit a message, it first measures the strength of transmissions it is receiving from potential relays. Those data are then plugged in to an algorithm that predicts which relay will be strongest when the message is transmitted. By predicting the strength of the relay, the algorithm also tells the node the rate at which it should transmit the data. If it tries to send too much data too quickly, the data quality will suffer – the data could be compromised. If the rate of data transmission is too slow, the network won’t be operating at peak efficiency.
The paper, “Enabling Adaptive Rate and Relay Selection for 802.11 Mobile Ad Hoc Networks,” will be presented at IEEE’s International Conference on Communications in Ottawa, June 10-15. The paper is co-authored by Neil Mehta, an NC State Ph.D. student; Duel-Hallen; and Dr. Wenye Wang, associate professor of electrical and computer engineering at NC State. The research was supported by the National Science Foundation and the U.S. Army Research Office.
Note to Editors: The study abstract follows.
“Enabling Adaptive Rate and Relay Selection for 802.11 Mobile Ad Hoc Networks”
Authors: Neil Mehta, Alexandra Duel-Hallen and Wenye Wang, North Carolina State University
Presented: June 12, 2012, at IEEE’s International Conference on Communications in Ottawa
Abstract: Mobile ad hoc networks (MANETs) are self-configuring wireless networks that lack permanent infrastructure and are formed among mobile nodes on demand. Rapid node mobility results in dramatic channel variation, or fading, that degrades MANET performance. Employing channel state information (CSI) at the transmitter can improve the throughput of routing and medium access control (MAC) protocols for mobile ad hoc networks. Several routing algorithms in the literature explicitly incorporate the fading signal strength into the routing metric, thus selecting the routes with strong channel conditions. While these studies show that adaptation to the time-variant channel gain is beneficial in MANETs, they do not address the effect of the outdated fading CSI at the transmitter. For realistic mobile node speeds, the channel gain is rapidly varying, and becomes quickly outdated due the feedback delay. We analyze the link throughput of joint rate adaptation and adaptive relay selection in the presence of imperfect CSI. Moreover, for an 802.11 network that employs geographic opportunistic routing with adaptive rate and relay selection, we propose a novel method to reduce the effect of the feedback delay at the MAC layer in the presence of Rayleigh fading. This method exploits channel reciprocity and fading prediction and does not require significant modification to the existing 802.11 frame structure. Extensive network simulations demonstrate that the proposed approach significantly improves the throughput, delay, and packet delivery ratio for high mobile velocities relative to previously proposed approaches that employ outdated CSI at the transmitter.
Matt Shipman | EurekAlert!
Between filter bubbles, uneven visibility and transnationality
06.12.2017 | Schweizerischer Nationalfonds SNF
New Technologies for A/V Analysis and Search
13.04.2017 | Fraunhofer-Institut für Digitale Medientechnologie IDMT
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong
Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...
An interdisciplinary group of researchers interfaced individual bacteria with a computer to build a hybrid bio-digital circuit - Study published in Nature Communications
Scientists at the Institute of Science and Technology Austria (IST Austria) have managed to control the behavior of individual bacteria by connecting them to a...
Physicists in the Laboratory for Attosecond Physics (run jointly by LMU Munich and the Max Planck Institute for Quantum Optics) have developed an attosecond electron microscope that allows them to visualize the dispersion of light in time and space, and observe the motions of electrons in atoms.
The most basic of all physical interactions in nature is that between light and matter. This interaction takes place in attosecond times (i.e. billionths of a...
Transistors based on carbon nanostructures: what sounds like a futuristic dream could be reality in just a few years' time. An international research team working with Empa has now succeeded in producing nanotransistors from graphene ribbons that are only a few atoms wide, as reported in the current issue of the trade journal "Nature Communications."
Graphene ribbons that are only a few atoms wide, so-called graphene nanoribbons, have special electrical properties that make them promising candidates for the...
08.12.2017 | Event News
07.12.2017 | Event News
05.12.2017 | Event News
08.12.2017 | Life Sciences
08.12.2017 | Information Technology
08.12.2017 | Information Technology