Custom Wireless Networking over Standard Physical Layers, 10-R9753

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Principal Investigator
Michael S. Moore

Inclusive Dates:  10/01/07 – 03/31/09

Background - Wireless networking for personal and business computing has become ubiquitous in the past several years due to standards such as IEEE 802.11 (WiFi). Product companies have invested large amounts of capital to develop electronics to implement the standard, and chip sets are commercially available that implement 802.11. This has been driven by the size of the market and the work that has been put into the development of the standard.

Some military and space applications have a need for two-way wireless networks in environments in which 802.11 and other standards will not suffice. For instance, wireless links that must traverse very long distances require a protocol that will not be affected by large propagation delays. Developing new standard protocols from the ground up for these environments is very costly and delays the insertion of wireless networks into these application areas.

Approach - The goal of this research was to develop a technique for leveraging the investment in standards, such as 802.11, to develop highly customized wireless protocols for applications with vastly different signal environments than that for which the standard was developed. The objective was to develop a demonstration system that leverages 802.11 electronics in a target environment with long distances (up to 150 nautical miles) and high closing speeds between the radios (high Doppler effect). The approach is to use the physical layer electronics developed to support the 802.11 standard, but replace the collision avoidance-based Media Access Control (MAC) and link layers with a custom, scheduled protocol with deterministic behavior.

Accomplishments - The research products of this effort include a novel link and MAC protocol called Dynamic Time Division Multiple Access (DTDMA), a simulation of the DTDMA protocol in relevant operational scenarios, an embedded implementation of the DTDMA link and MAC layer protocol, and progress toward a fully integrated DTDMA radio.

The protocol has been successfully simulated using the OPNET® networking simulation package. A laboratory demonstration of a DTDMA protocol has been implemented in a radio network controller prototype, which runs on an embedded platform and implements an interface to the physical layer electronics using the serial peripheral interface (SPI) standard. Several electronics modules that implement 802.11a-compatible orthogonal frequency division multiplexing (OFDM) radios were procured, evaluated, and tested. Although it was outside of the expected accomplishments of this project, the team came close to accomplishing a fully integrated DTDMA radio. Incompatibilities in the SPI interfaces of the modules remain, and the integration could be completed in follow-on work.

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