Wireless Multihop Communications for First Responder Connectivity


Michael Souryal, Johannes Geissbuehler, Luke Klein-Berndt, Leonard Miller, Nader Moayeri


Wireless multihop communication technologies are envisioned for use in public safety operations to dynamically provide flexible and robust communications in challenging environments.  This research targets the data communication needs of first responders entering a building where conventional radios are unable to maintain connectivity with the incident command center outside the building.  Using detailed indoor propagation studies, the objective of this work is to develop algorithms for real-time multihop network creation as first responders enter and move about a building, and to utilize this network to monitor and relay vital health signs back to incident command.


Current first responder radio communication technologies are susceptible to interruption and disconnection due to propagation loss of the radio signal with distance and obstructions, especially in large buildings with metal construction.  Multihop networks use intermediate nodes to relay the signal over multiple, shorter hops from source to destination.  By constantly measuring the state of the wireless link, inexpensive relays can be dropped as "breadcrumbs" at appropriate points along a first responder's path into a building to maintain multihop communications with the outside.  Challenges include developing accurate real-time link state measurement techniques, determining the optimal placement of wireless breadcrumbs, and adapting to time-varying environmental conditions to maintain end-to-end connectivity.


We have performed detailed propagation studies using two wireless networking platforms, 900 MHz Crossbow Motes and 2.4 GHz 802.11b transceivers.  Stationary experiments with a network of transceivers have been conducted to determine the viability of rapid link assessment based on received signal strength measurements and signal-to-noise ratio measurements.  Mobile experiments with a transceiver on a vehicle were performed to assess the variability of link state with motion and to determine adequate sampling rates for link measurement.  Additional experimental results reveal the effects of transceiver height and antenna orientation.  Work is in progress on developing breadcrumb dropping algorithms using one-hop polling by the mobile node of neighboring nodes.


Michael R. Souryal

(Advisor:  Nader Moayeri)

Advanced Network Technologies Division (892)

Information Technology Laboratory

National Institute of Standards and Technology

100 Bureau Drive, Mail Stop 8920

Building 820, Room 442

Gaithersburg, MD  20899-8920

Tel:  (301) 975-4342

Fax:  (301) 590-0932


Sigma Xi member:  No

Category:  Engineering