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Campus Bus Tracking (Missouri State University)

Guest Blog posted by Corbin Campbell, Electronics Support Services Missouri State University
Just a little history, our Assistant Director of Public Safety had a project for me. Missouri State University had the ability to GPS track the shuttle bus fleet for the students, faculty, staff, and public safety. This was done using a wireless carrier and through a smartphone on each shuttle. The problem was the speed and the recurring data cost. We wanted to be able to track our shuttle fleet without the cellular cost and in real time. Other GPS systems that we looked at had cellular data fees and would only update once a minute. The cost of these systems were also not in the public safety budget. He knew there had to be some other options.  Being the campus radio guy, he thought that I might have seen something that would do what he wanted.  After some looking and talking with other GPS tracking  vendors, I came to the website of Raveon and the RV-M7-GX GPS modem. I knew that I had something that would do what I wanted but I wanted to to find out more.

bus tracking using gps radioI called Raveon and I started out with the tech support people since these are the guys that have to fix the problems.  After talking with them, I knew that I had to demo this product to see if the hype matched the product.  Sales at Raveon reviewed the project with me to make sure we had a good fit, and arranged to send us the proper gear for testing. A demo was programmed up on a UHF frequency that I had and the units were set up for 1 second updates. We used RavTrack PC for the interface and Google Earth for the mapping. After 30 minutes in the demo, we were sold. At that point Raveon sales located a contract our purchasing department could use and expedited a full system to meet our funding deadline.

In our full system installation, we are tracking 15 shuttles and our base unit is on the 20th floor of one of our buildings. We are tracking our shuttles every three seconds so we can add more shuttles without having to do a mass reprogramming. The shuttles use the combination GPS-UHF antennas to broadcast the data to the base station. The shuttle data is filtered, received, and converted to TCP\IP.  Networking tweaked the network to get the data to our Web Development team.  Web Development have taken the GPS data and created this custom map where students, faculty, and staff can pull up the shuttle locations, shuttle routes, speed, and direction. Just click on Shuttle Map and the route and you will see the bus stops and the icons that represent the shuttles. Web Development is also working on apps for the iPhone and Android to make it simple for students, faculty and staff.

I won’t say how much the system cost, but the system will pay for itself in less than two years from the savings in cellular data fees alone.

If you want to do GPS tracking this is the way to go.  If you don’t believe me, demo the product because the hardest thing that you will have to do is send it back!!!

P.S. Since we installed the system I have received multiple calls from my peers at other organizations.  They don’t believe we can track our fleet with 3 second updates, even though we see it live, and tell me I must be mistaken.  When I add that we do all of this without monthly service fees I think they write me off as a teller of tall tales.

Corbin Campbell
Electronics Support Services
campus bus tracking Missouri state

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GPS Tracking Service Comparison: RF versus Cellular

Common GPS vehicle tracking systems use “cellular” GSM/GPRS based transponders. Once the device calculates position from the GPS satellites the transponder transmits the position to the cellular GSM/GPRS network of receivers (cell towers) in the area.  At this point the GSM/GPRS system operator transports the data to your output device. Obviously the network operator charges a fee for this service, and is in control of your data as well.GPS Tracking Comparison: Radio Versus Cellular GSM/GPRS

Advantages of Radio-based Solutions

Radio-based solutions are different in that the radio transponders transmit position over a mobile radio frequency, typically designated by a government administrative agency for your exclusive use.  A GSM/GPRS system is not used; instead the operator of the radio system installs one or more receivers in position(s) around the area to be tracked. One receiver – or more exact: the connected RF antenna – is capable of covering an area of typically 10-25 mile radius from its own position, although this range might vary depending upon how high in elevation the receiving antenna is, and what the local terrain is like.

As the radio operator owns both the GPS position transmitters as well as the receiver(s), the fleet may transmit positions very frequently without concern for any fees, and with extremely fast delivery of data; allowing for true real-time position updates which common cellular solutions do not provide (or charge high fees for).

Often radio users install just one receiver, and mount it high atop a building, antenna tower, or point of elevation to cover the tracking area. This area might be a city, an open pit mine or other remote area, or a fleet of boats where the group can be tracked by other boats in the fleet. Since the entire system operates independently from any GSM/GPRS network, radio modems can work anywhere GPS satellite lock can be acquired.  In fact, the entire system can be mobile and – in case of Raveon’s M7-GX series radios – any fleet member can receive GPS reports from other fleet members in radio range, even while all are moving at high speeds.

Large Area Coverage

If a larger area of coverage is needed, or the tracking headquarters is not at a good location for area reception, a single radio repeater may be established at a preferred location where the repeater then wirelessly relays the transmissions it receives to the central tracking location. If the area of coverage is very large, then multiple receivers may be installed and connected together as well as to a central location via an IP backbone, which can include either a private network or the public internet.  The determination of the proper receiver layout is based principally upon the area the system must cover for effective fleet tracking, as well as the local terrain.

Primarily the decision to install a radio-based tracking solution versus a common cellular system comes down to the area of tracking coverage required and the size of the fleet involved. Even the area of coverage required is vast, requiring a large number of receivers, and the fleet itself is small, and the cost per vehicle may become prohibitive.  In these cases the operator must rely on a pre-installed network of GSM/GPRS system receivers owned and operated by another entity and pay their monthly fees. If GSM/GPRS service coverage is poor then an expensive communications satellite relay may be a considered alternative.

See this complete comparison of RF versus GSM/GPRS “cellular” vehicle tracking systems.

For more information about the RavTrack system:

  • Attend our webinar where we introduce the technology and provide an overview of the system.
  • View a list of some of our Customers. We partner with many diverse companies and government agencies.
  • Learn more about how the RavTrack system is designed by viewing the asset tracking infographic.
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Fast GPS reporting with TDMA timeslots

Fast GPS reporting with TDMA timeslots

RavTrack is very fast at reporting the positions of even large fleets over a single radio channel because each RavTrack transponder is assigned a specific time slot in which to transmit, avoiding interference which may occur if multiple devices were permitted to transmit simultaneously. The fact that all transponders share a “common clock” via the GPS satellite signals allows us to assign a unique timeslot to each device, yet maintain timing coordination over a large fleet of devices.

RavTrack timeslots are built on 50 millisecond increments by factory default, athough 10msec granularity can be achieved with newer firmware versions. For the purposes of illustration we will assume each time slot must be a multiple of 50msec. The specific size of your time slot is typically determined by the bandwidth/transmission rate of your particular transponder and the presence or absence of a repeater.

Most FCC licenses granted in the USA are for narrowband (12.5KHz) channel spacing. The associated RavTrack transponders operate quite well at 4800 baud transmission rate (factory default), although slower rates can be used. These transponders can complete a position report transmission in about 64msec, so a 100msec timeslot would be the factory default when no repeater is in the system. If your license permits wideband (25KHz) channel spacing, and your transponders are capable of wideband operation, the factory default transmission rate is 9600 baud. In this instance a position transmission can be completed in about 32msec, so a 50msec timeslot is typically used when no repeater is in the system.

If your system uses a store-and-forward repeater you need to make each timeslot longer so that once a vehicle reports, the repeater has sufficient time to receive, process, and repeat the transmission on “quiet air” before the next vehicle transmission occurs. In a 9600 baud system a 100msec timeslot may be used if you are not encrypting your transmissions, but with encryption a 150msec time slot should be used, as the repeater needs a bit more time to process an encrypted message than an unencrypted message. In a 4800 baud system using a repeater a 200msec timeslot may be used whether or not you are encrypting the position transmissions.

Timeslots are numbered starting at zero, and the zero time slot is reserved by the system. Thus you can start numbering your transponder time slots at slot 1 (0001). In a system using 100msec timeslots the first second is completed once time slots 0 through 9 are used (10 time slots total). For this reason, up to 9 vehicle transmissions can be completed in the first second, and in this example your fleet size would be limited to a total of 9 vehicles if you need the entire fleet to report each second. As the reserved zero time slot only occurs at the start of any particular TDMA cycle, cycles longer than 1 second would allow the addition of 10 more time 100msec slots for each second added to the cycle. Thus a fleet using 100msec time slots can provide reports from 19 vehicles every 2 seconds, 29 vehicles every 3 seconds, and so forth. Similar logic applies to other RavTrack timing schemes.

If your fleet is quite large and you want faster updates than the 100msec timeslot scheme allows, you can double your fleet size if local regulations allow you to use wideband transmissions that yield a 50msec time slot.  In many deployemnets a fleet can scale much larger and still preserve fast report cycles simply by using multiple frequencies.  As transponders on different frequencies will not interfere with one another even if transmitting simultaneously, a properly architected system using five frequencies can report five times faster than the same system using only one frequency.

When setting up your fleet timing it is a good idea to leave a little extra capacity in your timing scheme to allow the easy addition of new vehicles to the fleet.

Finally, if you want to use the RavTrack transponders to transmit not only position data, but extra data as well (e.g. from an on-board telemetry device), you will need longer time slots to send this extra data. Please contact us in this regard, and we are happy to help you in architecting a solid system.

For a more technical programming perspective on TDMA time slots as used by RavTrack see the following articles: http://ravtrack.com/GPStracking/tdma-transmission-overview/361/  

http://ravtrack.com/GPStracking/tdma-time-slots/71/ 

or consult your technical manual.

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TDMA Transmission Overview

TDMA, or Time-Division-Multiple-Access is a very effective way of allowing a lot of radios to share one radio channel.  Used extensively in GSM cellular and APCO public-safety systems, TDMA excels at allowing quick and reliable access to radio channels.  It allows 2-10 times more radios to share a radio channel than conventional carrier-sense methods.  This allows 2-10 times more tracking radios on one channel, as compared to radios that do not have TDMA capability.

The following diagram illustrates how it works.

When a RV-M7 GX wants to report its position and status, it waits until its assigned time-slot, and then transmits its data.  By default, TDMA time slot positions are assigned by unit-ID, so RV-M7 GX with ID 1 uses the first slot, and ID 2 uses the second slot, and so on.  This default slot assignment can be overriden by the SLOTNUM command or by using Raveon’s Radio Manager software, allowing each GX to have an ID that is different than the slot assignment.

A TDMA “Frame” time is the time it takes all units to transmit once.  This is configured with the TDMATIME xx command.  The factory default is 10 seconds, so every 10 seconds, each RV-M7 GX may transmit.  The TDMA frame must be set long enough for all units to transmit.  For example, if you have 50 RV-M7s, and use 200mS TDMA slots, then the TDMATIME should be set to 10 seconds.  The simplest way to set it the TDMATIME is to make it equal to the TXRATE, the rate you wish to report position

The duration of a TDMA time slot is programmed into the RV-M7 GX with the SLOTTIME command. If SLOTTIME is set to 200 milliseconds (factory default), then every 10 seconds, the RV-M7 will have a 200mS window to report its position in.

All TDMA frames are synchronized automatically in all RV-M7 GX Transponders to the top of the minute.  Slot 0, frame 0 is at the top of each minute. They use the internal GPS receiver to determine the current time, and calculate when their are supposed to transmit their position and status information.

A unit may be allocated additional time slots.  The SLOTQTY command sets the number of slots each unit receives.  It is normally set to 1.

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Who’s Tracking You? GPS Tracking Security

GPS vehicle tracking is a powerful technology that can speed emergency response, improve efficiency, and provide a safety link to support personnel.  Raveon Technologies sells real real-time tracking system so business, agencies, and commanders, can track their personnel, assets and vehicles.

Raven’s private tracking system uses a very secure AES encryption algorithm, so that only authorized radios can track the GPS transponders.  It would be bad, and maybe even disastrous if GPS tracking were not secure.  Law enforcement, military, and security forces use GPS tracking to do their job and GPS tracking provides extra security for their operations.  And if the bad guys were able to track them, their operations and their lives could be in jeopardy.

This is why Raveon takes GPS tracking security very seriously, and tracking systems based upon less-secure communication methods should be carefully considered.  Most all other GPS tracking systems us cellular radio technology, such as GSM networks to send their data.  Anyone using a public GSM system must carefully assess all aspects of the system’s security.

In 2009, a German computer engineer announced that he’s deciphered the 21-year old 64-bit encryption algorithm that protects the GSM standard.  According to the New York Times, the German encryption expert “aimed to question the effectiveness of the 21-year-old G.S.M. algorithm” and its use to protect the world’s GSM based GPS Tracking communications.  Having the code itself isn’t enough to eavesdrop, but it certainly helps people along the path. The GSM Association responded by calling the publication “theoretically possible but practically unlikely.”

OpenLock

It may be only a matter of time before the technology is readily available to eavesdrop on GSM communications.   Right now, it is believed that only the US military and certain foreign governments have the ability to eavesdrop on GSM communications.  Technology marches on, and the security of GPS tracking using GSM networks may be left behind.

See www.ravtrack.com for mor information about secure, private GPS tracking.

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GPS Position Accuracy

The accuracy of a position determined by using a GPS receiver is limited by the accuracy of the GPS signal itself.  The US government controls the precision of the GPS signals sent from the GPS satellite constellation.   It varies from day to day, and the following graph shows historically, how precise the GPS position information is.

gpsaccuracyRaveon’s GPS transponders utilize the WAAS signal, so accuracies of 2-3 meters are possible.  Laboratory tests with the M7 series of GPS transponders confirm that this is possible, but typically, the accuracy is in the 3-5 meter range.

If the GPS transponder is located indoors, or if there are very tall buildings near the transponder, the accuracy will be degraded due to multipath of the GPS signal.

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Tracking Alerts via SMS

Your Raveon RavTrack PC GPS Tracking System can send “Rule Alert Messages” via email when triggered by a GPS tracking rule.  GPS tracking Rules may be based upon vehicle speed, proximity, idle time, geo-fences, and many other conditions.   When a rule alert is triggered, the rule alert messages may be sent to any email address.

Often, users wish to send an alert to a mobile device using Short Messaging Services (SMS).  Cell phones, Blackberries, iPhones, and many other mobile communication devices can receive SMS messages.  And sending a Rule Alert Message to them is very simple.

To send a GPS tracking alert from RavTrack PC (Raveon’s GPS tracking software),  configure the “mail to” address to send the alert message to, to the mobile-devices wireless carrier’s email server, using the telephone number of the mobile device as the email address.  Different wireless carriers use different email address formatting (See list below), but in general, the email address will be something like:
760-555-1212@txt.att.net    where 760-555-1212 is the telephone number of the subscriber.

The domain listed after the @ sign depends upon the carrier, and the list below shows some common carriers and their email domain names.

Verizon: 10digitphonenumber@vtext.com
AT&T: 10digitphonenumber@txt.att.net
Sprint: 10digitphonenumber@messaging.sprintpcs.com
T-Mobile: 10digitphonenumer@momail.net
Nextel: 10digitphonenumber@messaging.nextel.com
Cingular: 10digitphonenumber@cingularme.com
Virgin Mobile: 10digitphonenumber@vmobl.com
Alltel: 10digitphonenumber@message.alltel.com
CellularOne: 10digitphonenumber@mobile.celloneusa.com
Omnipoint: 10digitphonenumber@omnipointpcs.com
Qwest: 10digitphonenumber@qwestmp.com
MetroPCS: 10digitphonenumber@mymetropcs.com
Bell Canada: 10digitphonenumber@txt.bellmobility.ca
Telus: 10digitphonenumber@msg.telus.com

Remember, SMS is a short-message service, and the carrier may break long messages up into multiple short messages.   SMS is often not free, and the users of SMS must pay a per-message fee.  The recipient of the GPS tracking alert SMS may be billed by the wireless carrier for each alert message received.

The email server and address that the Rule Alerts are emailed to is configured in RavTrack PC by selecting  FILE>PROGRAM PROPERTIES and then clicking on the “SERVERS” tab.  On the Servers tab, you will see the boxes to fill-in the email address and email server information.

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About This GPS Tracking Blog

This site is a web log for information about Raveon’s Real-Time GPS Tracking system called RavTrack.  It is a repository full of usefull information about GPS tracking technology, and particularily real-time tracking using VHF/UHF radio technology. 

Users of Raveon’s GPS tracking system are welcome to post helpful information about the products or their systems, or simply highlight projects they use Raveon’s real-time GPS tracking systems in.