August 30, 2009 Reports and Slide Presentation: The reports and slide presentation from the Aug 30, 2009 meeting are provided here.

Airspace Sentinel Overview

Surreptitious wireless communications through "invisible wires" compromises the security of any room or building and their facilities. The objective of the Airspace Sentinel project is to make the invisible wireless airspace network activities "visible" by efficiently detecting unexpected RF power appearing in frequency bands throughout the useful RF spectrum.

The presence of wireless activity requires monitoring of the RF power appearing in each of the small frequency bands that might be used as a wireless channel. Figure 1 below illustrates qualitatively a brute force approach for implementing an airspace sentinel using a traditional spectral analysis styled function to extract the rf power in each of the individual small frequency bands of interest. Multiple extraction units operating on different frequency bands are shown, recognizing that the computational requirements will be considerable if full spectral analysis is used. Also shown is the base station (and management infrastructure) advising the sentinel regarding the legitimate frequency signals currently in use by the local wireless system. In this manner, the airspace sentinel can separate suspicious wireless activity from legitimate uses under the management of the base station. The large number of potential wireless channels combined with the large total bandwidth would require a substantial hardware system for this brute force approach.

Figure 1: Brute Force Approach

The research will identify and clarify realistic solutions, drawing on two major simplifications of the classical spectral analysis approach.

1. The Airspace Sentinel will make use of snapshots in time of airspace activity, acquiring the full spectrum wireless signal during that snapshot in time and using the time between snapshots to analyze the data stream acquired.
2. The Airspace Sentinel will emphasize detection of wireless activity (RF power in bands) over understanding the information contained in that RF signal. This converts the problem from information extraction to the simpler problem of energy detection.

These two simplifications provide a rich opportunity to establish efficient and cost effective solutions to the objective of monitoring the wireless airspace for unexpected activity. The research will combine innovative uses of signal processing algorithms and realizations along with scalable parallel architectures and scalable snapshot periods to provide a general solution applicable to a wide range of applications. Using the snapshot approach, the wireless receiver samples and digitizes the received RF signal during the "acquire" time period, after which that sampled and digitized RF signal is analyzed to determine RF energy in the smaller frequency bands. During the "analyze" period, creative uses of approaches such as decimation in frequency combined with intelligent implementation of the analysis in parallel hardware will be used to create an efficient RF narrowband energy detector. The computational algorithms will be developed consistent with an efficient implementation as a custom VLSI circuit, emulated using Xilinx Virtex 5 FPGAs. A simplified representation of a general architecture using these two simplifications is shown in Figure 2.