Collecting Data Over an Area of 25 Square Miles

Gathering data in a large and hostile environment is straightforward�transmitting and storing it are the real challenges.

Data acquisition projects are nothing new to B&B Technologies, now part of National Technical Systems. As a systems integrator, we have gathered brake data from sensors inside vehicles, simultaneously recorded dozens of missile re-entry vibration signals, and even monitored the projectile velocity and muzzle pressure of a 120-mm M1A1 tank cannon.

All of this experience helped when addressing a recent project. But in this case, we had to develop an innovative mix of modern communications technologies.

Our customer needed to perform outdoor tests of military equipment in a rugged environment over a 25 square mile area. The challenge was to reliably acquire data from these tests of custom electronic equipment and wirelessly send the data to a centralized SQL database for analysis and future storage.

Acquiring data from a portable device was the easy part. With portable notebook computers becoming more and more powerful and a growing variety of portable data acquisition devices available, it wasn�t too hard to find a suitable method of acquiring data.

The difficulty was finding a way to share the data in a timely fashion and store it in an organized manner. Ideally, we needed to put all the data acquisition devices on a single network to transfer the test results to a central database from which users could view the data at will. However, given the large geographical area and hostile conditions, there was no obvious way to solve this.

The solution came in the form of a high-speed broadband wireless network to communicate the data from the field to the central database. As shown in Figure 1, at the core of the network are Loea wireless radios that communicate at up to 1.25 Gb/s (see sidebar). Loea radios are used to link several remote wireless access points (APs) to the central network located in the same facility as the central data center.

Figure 1. Block Diagram Showing Communications Paths

Each AP has its own local 802.11g wireless network that communicates with data collection units (DCUs) in the field. Because of the number of separate tests that could be occurring at the same time, 40 DCUs were needed to acquire data simultaneously.

A DCU includes a laptop or tablet PC with data acquisition devices that collect the desired data and transmit it through an amplified 802.11 antenna to the AP through the radio link back to the central network and into the database.

The Loea radios enabled us to make a standard Windows network, which simplified the approach to building the application and transferring data from the DCUs to the central database. It allowed us to use an SQL database with Microsoft�s server, which hooks seamlessly into the software. As a result, we could use previously developed software protocols and off-the-shelf hardware solutions, saving a great deal of time and money in the development of the system.

The Solution in Detail
Because B&B Technologies is a select partner in National Instruments� (NI) Alliance Program, we are very familiar with the capabilities of the company�s hardware and software products. As a result, we chose to acquire data with NI�s USB-based DAQPad-6015.

This DAQPad version provides 16 single-ended or eight differential analog inputs and an aggregate 200-kS/s sampling rate with16-b resolution. The software measures up to eight analog voltages and controls eight digital lines, two counter/timer channels, and an RS-232 serial port. The counter/timer channels count events, measure frequency, or generate pulse trains. Figure 2 is a typical display showing acquired voltages.

Figure 2. Typical Signals Measured by the Data Acquisition System

DCUs are provided in either man-carried backpacks or all-terrain trucks. The man-carried DCUs have a battery life of only six hours. Because their mobility is somewhat limited, there is a better chance that the network connection can be maintained.

The truck-based DCUs can be recharged by the alternator in each truck, allowing them to run longer tests in the field. However, their greater mobility also increases the risk of moving out of range of the wireless network, delaying the transfer of data to the central database.

The AP
Each AP consists of a Loea high-speed wireless radio, an 802.11g local network, and a health monitoring system to ensure that the AP is working properly. Large solar panels and a propane generator provide the power.

The best choice for the health monitoring system was a combination PXI/SCXI chassis due to its compactness and high density of instrumentation. Each SCXI chassis contains modules for measuring high-voltage digital signals and thermocouples to record temperatures in and around each AP.

A pan-tilt-zoom camera connected to each AP allows users in the central data processing center to get a live view of the AP and its surroundings. A PXI video card captures this data digitally, and the software compresses the video data and sends it back to the central data center. Commands for the pan, tilt, and zoom functions are sent via an RS-485 serial connection from the PXI chassis to the camera.

The camera controller application in the AP acts as a server, allowing client applications running from the central data center to retrieve the live video data and send pan, tilt, and zoom commands to control the camera. This is done seamlessly through the broadband wireless network link. Figure 3 is a view of one AP�s surroundings.

Figure 3. Remote Camera Image Showing the Surroundings of an AP

Software Application
Since the main purpose of the application was to acquire data, NI�s LabVIEW was a suitable platform on which to develop the software. The tools for low-level TCP/IP communications and image acquisition made it an appropriate choice.

The application stores all the acquired data locally in case the DCU is disconnected from the network. A separate application runs in parallel in the background constantly looking for data on the hard drive. When it sees new data, it sends it in chunks to the central database and deletes it from the DCU once it has been successfully transferred. Figure 4 shows how data flows among the various parts of the system.

Figure 4. Software Application Flowchart

A database also allows the user to independently configure settings for each DCU and store them in a central location. These settings include which types of measurements to take, the settings of each data acquisition channel, and the speed of data acquisition.

The DCU retrieves its settings from the database each time it is powered on so users in the central data center can change settings locally. Users out in the field in difficult environments do not need to make any adjustments while testing.

Data Storage and Viewing
A Loea radio in the central data processing center connects the SQL database to the high-speed wireless network. The database consists of 2-TB servers connected to a domain controller running Microsoft�s SQL Server. The overall storage of the system is approximately 6 TB of data.

The application running in the central data center allows the user to read the data from the database, reassemble the data, and view the data. Using the power of SQL queries, data can be quickly displayed despite the large amount stored in the database.

The application also includes the camera controller, network pinging, and the AP health monitoring utilities. The camera controller shows live data from any of the connected APs and remotely controls the camera�s pan, tilt, and zoom functions.

The network pinging utility sends a network ping to devices on the network, verifying that devices are connected to the network. This utility proves to be quite useful when trying to diagnose potential problems with network connectivity.

The AP health monitoring utility views live data transmitted from the APs to the central database. From here, the user can monitor AP input and output voltages, power consumption, and temperatures.

When we started this project, there were many concerns about the adequacy of the system�s bandwidth and whether it could handle all the data being transferred. Although this system still is in its initial testing phase, the results so far seem promising.

We have established wireless networks and acquired data in remote locations once thought unimaginable. Testing has shown that five DCUs and four APs transmitting simultaneously can be supported. Phase two of the system, which will expand our wireless coverage in different areas and increase the number of DCUs and APs considerably, now is underway.

The customer is pleased with the success to date and even has considered using some of the technology in other applications. For example, the success with remote wireless cameras may lead to a project used to track aircraft.

Microwave Link

The Loea wireless radio uses a pair of millimeter wavebands at the 71.0- to 76.0-GHz and 81.0- to 86.0-GHz frequencies to communicate via full duplex Gigabit Ethernet (GbE). Simultaneous 1.25-Gb/s transmit and receive data rates are supported over distances of 1 km with 99.999% availability regardless of the weather.

Because the radio operates in frequency bands that have little sensitivity to environmental conditions, it doesn�t share the restrictions of free space optics (FSO) that can offer only 99.9% availability to roughly 500 m. Oxygen absorption associated with FSO�s 60-GHz operating frequency is a major limiting factor. The 60-GHz band also is license free, which means that interference from other users, especially in densely populated metropolitan areas, always is possible.

About the Author
Chris Cahoon is a senior system integrator at National Technical Systems where he has worked for five years. He received a B.S. in physics from the University of Colorado. During his career, Mr. Cahoon has integrated test systems for many customers including Sandia National Labs, Los Alamos National Laboratory, L3 Communications Ocean Systems, and Spacelabs Medical Devices in Seattle. National Technical Systems, 6610 Gulton Ct. N.E., Albuquerque, NM 87109, 505-345-9499, e-mail: [email protected]

October 2006

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