The RavTrack system architecture compared to common “cellular” GSM/GPRS tracking systems.

Most GPS 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 in the area.  At this point the GSM/GPRS system owner/operator transports the data to your HQ tracking location.  Obviously they charge a fee for this service, and are in control of your data as well.

RavTrack is different in that the RavTrack 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 RavTrack system installs one or more RavTrack receivers in position(s) around the area to be tracked.  One receiver is capable of covering an area commonly of 10-25 mile radius from its own position, although this range varies a good deal depending upon how high in elevation the receiving antenna is, and what the local terrain is like.

As the RavTrack 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.

Many users of RavTrack install just one receiver, and mount it high atop a building, antenna tower, or point of elevation to cover the tracking area.  This area is often 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, RavTrack can work anywhere GPS satellite lock can be acquired.  In fact, the entire system can be mobile and any fleet member can receive GPS reports from other fleet members in radio range, even while all are traveling at high speeds.

If a larger area of coverage is needed, or the tracking HQ is not at a good location for area reception, a single RavTrack repeater may be established at a preferred location where the repeater then wirelessly relays the transmissions it receives to the tracking HQ.  If the area of coverage is very large, then multiple receivers may be installed and connected together as well as to the tracking HQ 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.

There is little doubt that the RavTrack system offers significant performance advantages and other benefits over GSM/GPRS based systems.   Primarily the decision to install RavTrack versus an alternative system comes down to the area of tracking coverage required and the size of the fleet involved.  RavTrack can handle very large fleets.  However, when the area of coverage required is vast, requiring a large number of receivers, and the fleet itself is small, 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.

For a point-by-point comparison of RavTrack versus GSM/GPRS “cellular” vehicle tracking systems please refer to this tech blog article: http://ravtrack.com/GPStracking/553/553/

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.

A comparison of GPS tracking and AVL systems.  RavTrack versus cellular GSM or GPRS.

Most GPS tracking systems use a “cellular” wireless telephone carrier system to collect position information from the fleet in the field and transport that information back to headquarters.  You may see acronyms such as GSM or GPRS describing the system.  The RavTrack system uses a very different approach, that of local user based radio.  These two approaches will often appeal to different types of users.  However, one thing is clear; if RavTrack can meet your needs it is by far the superior choice over cellular.  Here are some of the most common reasons why.

Total cost of ownership

Every cellular system has recurring service fees, typically on a per vehicle per month basis.  The RavTrack system has no monthly fees.  Consider how long they will want to have a tracking system.  Likely you will want it “forever” and you should recognize that once you have RavTrack installed you have no more expenses.  In some cases it may cost more to initially purchase and install RavTrack versus a cellular system but over several years time it can cost much less, even if the monthly fees the operators charge are not very high. 

Also, RavTrack protects your tracking system from budget cuts.  If you determine RavTrack and the celluar systems both cost the same over 3 years, RavTrack is the only of the two systems you know you can keep.  If you are forced to cut your budget next year or later, then your cellular system, and any investment you have made is at risk.  RavTrack is not at risk.

Performance

RavTrack will provide very frequent and very fast updates.  Both are important.  With RavTrack you can hear back from the fleet at very frequent intervals.  How does this compare to the cellular system?  Perhaps you feel frequent updates are unimportant, but if later things change can the cellular system even provide these faster updates?  If so, does the monthly charge increase?

RavTrack updates are not only frequent but fast as well.  When a vehicle sends the current position with RavTrack you can receive this position right away (often less than one second later).  Many cellujlar systems will take 15 seconds, 30 seconds, or even several minutes before the operator receives the position report from the vehicle

Both of these factors are important to operations that serve in emergencies such as police, fire, and ambulance.

Capability

With RavTrack you can track fleet fleet or personnel from other vehicles or mobile posts?  Any RavTrack vehicle can receive from the other vehicles or personnel automatically, and with a proper display can see the other members on a map in real time.  Even personnel on foot can be provided a hand-held display.  Almost no other system has this capability.  This is an important benefit to supervisors in the field or any time teams need to work together.  You can have this capability now, or add it later.  You do not lose this capability, nor general tracking capabilities if part or all of your fleet travels into an area where cellular service is not available.

Reliability

The celllular service is a shared service used both for voice and data.  Any high demand or peak use of the cellular system, either at a single receiver or on the system overall, such as can be caused by a disaster or just a popular event, can overwhelm the cellular system and may cause the system to be too overloaded to be useful for tracking.  Often, this occurs when you need your tracking capabilities most.  The RavTrack system is dedicated to your fleet and not subject to peak use concerns.

Security

RavTrack messages can be encrypted with 128 bit AES, making them indecipherable to outside parties.  Furthermore, RavTrack data is stored only on the customer devices and not available to unauthorized users, including those that might be in a 3^rd party data center.

Powerful Software

RavTrack PC software is extremely rich with features, unmatched by most other software packages.  RavTrack provides extensive geofences, rules, and alarm capabilities.  RavTrack PC enables sophisticated user security measures to ensure only the right people have access to important information, and features in depth historical logging, playback, and reporting capabilities.  For a detailed list of RavTrack PC features and functions refer to http://ravtrack.com/RavTrack-PC-Functions.html

Flexibility

As the customer you are always in control of the RavTrack system and can make adds, deletes, and changes whenever you need.  You do not have to submit a request to a vendor and wait for the vendor to perform (or mis-perform) on either routine on uncommon requests.  Furthermore, as a RavTrack software implementation is specific to each customer and not shared, we are capable of providing you something unique or special to meet your individual needs, and do not need to be concerned about a specific change affecting other parties.

Adaptability

With RavTrack you are not limited to the map your vendor provides.  Almost any map can be converted into a RavTrack map, including aerial photographs!  Choose the map or view that best meets your needs, when you need it.  If your environment changes RavTrack allows you to bring in the latest map with the latest data, providing uncompromised adaptability.

Options

The RavTrack system is supported by more than 10 other software packages from parties other than Raveon, giving you far more choices than any other system on the market.  Most cellular systems provide only one software option.

The RavTrack system includes devices for both vehicles as well as personnel.  Many other systems only provide equipment to track vehicles.

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.

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.”

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.

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.

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.

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.

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.