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.

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.

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.”

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.

Raveon’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.

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.

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.