Multi-rate relaying for performance improvement in IEEE 802.11 WLANs

It is well known that the presence of nodes using a low data transmit rate has a disproportionate impact on the performance of an IEEE 802.11 WLAN. ORP is an opportunistic relay protocol that allows nodes to increase their effective transmit rate by replacing a low data rate transmission with a two-hop sequence of shorter range, higher data rate transmissions, using an intermediate node as a relay. ORP differs from existing protocols in discovering relays experimentally, by optimistically making frames available for relaying. Relays identify themselves as suitable relays by forwarding these frames. This approach has several advantages compared with previously proposed relay protocols: Most importantly, ORP does not rely on observations of received signal strength to infer the availability of relay nodes and transmit rates. We present analytic and simulation results showing that ORP improves the throughput by up to 40% in a saturated IEEE 802.11b network

Max-min Fairness in 802.11 Mesh Networks

In this paper we build upon the recent observation that the 802.11 rate region is log-convex and, for the first time, characterise max-min fair rate allocations for a large class of 802.11 wireless mesh networks. By exploiting features of the 802.11e/n MAC, in particular TXOP packet bursting, we are able to use this characterisation to establish a straightforward, practically implementable approach for achieving max-min throughput fairness. We demonstrate that this approach can be readily extended to encompass time-based fairness in multi-rate 802.11 mesh networks

The Design and Analysis of a Wireless LAN Relayed Frame Protocol Extension

Computing stations networked on wireless LANs (wLANs) typically have a limited range of mobility: the station must always be within an access point’s coverage area. If a station moves outside of that area, and if it is unable to locate another base station within its range to perform a handover of communication connectivity responsibility, then it will ex perience a disruption in network services until it migrates into the coverage area of another wLAN. Typical causes for such losses of service include station migration to outside of the wLAN’s coverage area, changing environmental conditions, and “holes” within the cumu lative cell coverage area of multiple access points. There could be several mobile stations simultaneously sharing the network in a wLAN. Each station may be stationary or in motion for part or all of its service life. How ever, in order to use the wLAN, it must be within service range of a access point. Theoreti cally, if a station is outside the access point’s coverage area, yet its own radio signal is within range of one of the stations which has connectivity with an access point, the isolated station could relay its network negotiations and traffic through a relay station which has direct communication with the access point. Therefore, the station nearer to the base sta tion acts as a relay point for the isolated station out of the access point’s range. In this thesis, the author proposed, the design of a MAC Frame Relaying Protocol Extension which enables this type of dynamic relaying of network frames between stations in wLANs. It requires additional logic in the networking process on both the access point and the stations involved (both relay station and the isolated station) to support the bidirec tional forwarding of network traffic, and the definition of several new message types to support relay connection setup and data exchange. Both cryptography and digital signature concepts are employed to make secure the process of establishing of a relayed network session, and the exchange of data between the end stations. To verify the validity of the protocol extension and to measure its performance, the protocol extension was implemented into an existing and widely accepted wireless network standard, IEEE 802.11. To study its effectiveness and impact on the wLAN protocol, the network simulation software, OPNET, was used. An existing model of IEEE 802.11 was enhanced with the additional logic introduced by the protocol extension. Through simulation, it is proved that the logic presented by the protocol extension is able to function. In addition, the impact to overall network performance, and the quality of service the isolated station experiences during a relayed network session were quantita tively analyzed. Through the OPNET simulation, it was found that overall wLAN perfor mance diminished a moderate amount, while the isolated station experienced a far smaller level of throughput when engaged in a relayed network session, than it did in a normal network session

STiCMAC: A MAC Protocol for Robust Space-Time Coding in Cooperative Wireless LANs

Relay-assisted cooperative wireless communication has been shown to have significant performance gains over the legacy direct transmission scheme. Compared with single relay based cooperation schemes, utilizing multiple relays further improves the reliability and rate of transmissions. Distributed space-time coding (DSTC), as one of the schemes to utilize multiple relays, requires tight coordination between relays and does not perform well in a distributed environment with mobility. In this paper, a cooperative medium access control (MAC) layer protocol, called \emph{STiCMAC}, is designed to allow multiple relays to transmit at the same time in an IEEE 802.11 network. The transmission is based on a novel DSTC scheme called \emph{randomized distributed space-time coding} (\emph{R-DSTC}), which requires minimum coordination. Unlike conventional cooperation schemes that pick nodes with good links, \emph{STiCMAC} picks a \emph{transmission mode} that could most improve the end-to-end data rate. Any station that correctly receives from the source can act as a relay and participate in forwarding. The MAC protocol is implemented in a fully decentralized manner and is able to opportunistically recruit relays on the fly, thus making it \emph{robust} to channel variations and user mobility. Simulation results show that the network capacity and delay performance are greatly improved, especially in a mobile environment.Comment: This paper is a revised version of a paper with the same name submitted to IEEE Transaction on Wireless Communications. STiCMAC protocol with RTS/CTS turned off is presented in the appendix of this draf

A multichannel relay MAC protocol for IEEE 802.11 wireless LANs

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109605/1/dac2526.pd

Fly-By-Wireless for Next Generation Aircraft: Challenges and Potential solutions

”Fly-By-Wireless” paradigm based on wireless connectivity in aircraft has the potential to improve efficiency and flexibility, while reducing weight, fuel consumption and maintenance costs. In this paper, first, the opportunities and challenges for wireless technologies in safety-critical avionics context are discussed. Then, the assessment of such technologies versus avionics requirements is provided in order to select the most appropriate one for a wireless aircraft application. As a result, the design of a Wireless Avionics Network based on Ultra WideBand technology is investigated, considering the issues of determinism, reliability and security