Technical Bulletin April Opticom GPS System Verifying GPS coverage in a Fire Station

Transcription

1 Technical Bulletin April 2011 Opticom GPS System Verifying GPS coverage in a Fire Station

2 Background Opticom GPS System radios require a GPS 3D or WAAS fix in order to operate. In order for the Opticom GPS radio to transmit and request preemption as soon as possible after pulling out of the fire station, a minimum level of GPS coverage needs to be maintained while the vehicle is parked in the fire station. This is because data is constantly being downloaded to the GPS receiver that allows it to find the GPS satellites quickly upon startup. This data is called ephemeris data. This data becomes obsolete after four hours unless it is continually updated. Once this data is obsolete, the GPS receiver may take up to 45 seconds to find the satellites and achieve a 3D fix. Opticom GPS vehicle equipment should be wired directly to the vehicles battery so that their GPS receivers are always on and able to continually download ephemeris data. In order for the ephemeris data to be received, the signal strength for any given satellite needs to be 18 or above. Ideally we will see many satellites with strong signals inside of the fire station. However we can still keep the initial acquisition time low if we see some satellites with signal strength of at least 18. This procedure describes how to verify this. Equipment Needed 1. Opticom GPS vehicle assembly with vehicle simulator box, antenna and magnet mount. Or a vehicle with Opticom GPS vehicle equipment permanently installed. 2. Laptop computer running the On-site software with cable. Procedure 1. Set-up and connect the Opticom GPS Vehicle Assembly in a test vehicle. 2. Equipment should be plugged in, parked (or driven around) outside with a good view of the sky and allowed to operate at least ½ prior to beginning the check. Note: It is important that the almanac information in the GPS receiver be current for your location. By allowing the unit to remain outside with a good view of the sky and remain powered on for ½ hour prior to starting the verification, you will insure that the latest almanac for the area that you are in has been downloaded. 3. Start the On-site software and connect the cable from the PC port on the front of the Vehicle control unit to your computer. 4. Click on the Current Activity button. 5. Select the GPS Status tab and observe GPS coverage. 6. Drive the test vehicle into the fire station and observe the GPS coverage. 7. Shut all of the doors and observe the GPS coverage for five minutes. 8. Close the GPS status screen. 9. Unplug the vehicle control from the cigarette lighter for several minutes and then reconnect. The longer it is unplugged the more accurately you will simulate a vehicle being parked inside for long periods of time 10. Start the GPS status screen and observe GPS coverage. 11. Use the criteria listed below to determine if GPS coverage is adequate.

3 Characteristics to look for 1. Strong Signal Strength (see dbhz column) a. The higher the GPS signal strength the better. b. Signal strength should be above 18 dbhz for ephemeris data to be received. c. If only a few satellites have signal strength above 18 dbhz you have marginal coverage and acquisition time may be longer. This is the most important criteria. If you see good signal strength after step 11 above, GPS coverage is adequate to keep acquisition time to a minimum. 2. Many satellites in view a. The number of satellites that are visible is always changing. b. Generally you should see eight or more, usually no more than twelve. c. You will likely see more satellites outside in the open than you will inside of a fire station. 3. Low Dilution Numbers a. Low values for Horizontal and Position Dilution are desirable and indicate good GPS reception. b. See the Excellent GPS Coverage screen shot below for an example of good dilution numbers.

4 Figure 1 Excellent GPS Coverage Many satellites in view WAAS fix Very low dilution values High signal strength Fire vehicle should acquire GPS almost immediately upon exit of fire station. Figure 2 Good GPS Coverage A good number of satellites in view 3D fix Fairly low dilution values Good signal strength Fire vehicle should acquire GPS almost immediately upon exit of fire station.

5 Figure 3 Marginal GPS coverage A fair number of satellites in view 3D fix Fairly high dilution values Low signal strength, some below 18 dbhz Fire vehicle may take some time (probably less than 30 seconds) to acquire GPS upon exit of fire station. Figure 4 No GPS coverage 2D fix High dilution values No signal strength Fire vehicle will take some time (probably less than 60 seconds) to acquire GPS upon exit of fire station. Please contact Global Traffic Technologies Technical Service at if you have any questions.

6 Important Notice to Purchaser: EXCEPT FOR THE LIMITED WARRANTIES SET FORTH IN THIS DOCUMENT, GLOBAL TRAFFIC TECHNOLOGIES (GTT) MAKES NO OTHER WARRANTIES AND EXPRESSLY DISCLAIMS ALL OTHER WARRANTIES, WHETHER EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, ANY WARRANTY AS TO MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. GTT will, at its sole option, repair, replace or refund amounts paid for any Opticom TM System component found to be defective in materials or manufacture during the warranty period. GTT warrants future system operability coverage as described herein. This warranty shall not apply to any Opticom TM system components which have been (1) repaired or modified by persons not authorized by GTT; (2) subjected to incorrect installation, misuse, neglect or accident; (3) damaged by extreme atmospheric or weather-related conditions, flood, fire, vandalism, crime or other events beyond the reasonable control of GTT; or (4) subjected to events or use outside the normal or anticipated course. IN NO EVENT SHALL GTT BE LIABLE FOR ANY INJURY (INCLUDING, WITHOUT LIMITATION, PERSONAL INJURY), DEATH, LOSS, OR DAMAGE (INCLUDING, WITHOUT LIMITATION, PROPERTY DAMAGE), WHETHER DIRECT, INDIRECT, INCIDENTAL, SPECIAL, CONSEQUENTIAL, OR OTHERWISE, ARISING OUT OF THE USE OR INABILITY TO USE, REPAIR OR FAILURE TO REPAIR, ANY GTT PRODUCT, REGARDLESS OF THE LEGAL THEORY ASSERTED. THE REMEDIES SET FORTH IN THIS DOCUMENT ARE EXCLUSIVE. Sale and use of the Opticom TM System is expressly restricted to authorized agencies of government customers, within their specific jurisdictions. However, because the signal generated by the Opticom system may not be exclusive, GTT does not warrant exclusive activation by purchaser. Authorized users who desire to use or coordinate use of the Opticom TM system with that of other jurisdictions must first obtain the prior written approval of each authorized user in the jurisdiction where use is sought. Since the availability of a GPS signal is out of GTT s control and is required for Opticom TM GPS system operations, GTT does not warrant against Opticom TM GPS system failures due to the unavailability of the GPS signal for any reason. Global Traffic Technologies, LLC Global Traffic Technologies Canada, Inc. Opticom and the GTT logo are trademarks of Global 7800 Third Street North 157 Adelaide Street West Traffic Technologies, LLC St. Paul, Minnesota Suite 448 Used under license in Canada Toronto, ON M5H 4E7 Please recycle. Printed in the U.S.A Canada Global Traffic Technologies, LLC All rights reserved B