System Planning Corporation GTLITEV3 Manuale Utente

GlobalTrak ™ 

GT Lite Operation and Maintenance Manual 

 

Without contact with GPS system time reference, the RTC maintains accurate time to within 3 
seconds per 1 year interval.  Time base shall be Coordinated Universal Time (UTC), formerly 

known as Greenwich Meridian Time (GMT). 

Always On mode allows the GSM receiver to remain on in an idle state.  This allows for 

incoming SMS messages to be received be the device at any time.  When an SMS is received 
the main processor wakes to process the message.  Incoming messages can be used to poll, 

reconfigure, or send other commands or data to the device.  Message types are listed in 
Section XXXXXXXXXX. 

GPS Receiver 

The GPS receiver within GT Lite has a very high sensitivity for use in outdoors and indoors.  
GPS can achieve consistent hot and warm fixes from far less than ideal scenarios such as 

within a pallet on a stuffed shipping container.  The GPS receiver will use a combination of 
highly sensitive receiver, internal correlators, and assistance data (A-GPS) to achieve this 

performance. 

The GPS receiver takes no longer than 45 seconds (95%) to get a position fix from a cold 

start and no longer than 10 seconds (95%) from a hot start (i.e., less than two hours since 
the last fix). 

The selected GPS achieves Standard Positioning Service (SPS) accuracy: 95% of position 
measurements within 10 meters of the true location. 

The antenna status is sensed, either connected or open circuit, only during the attempt for 
GPS fix.  If the antenna status goes from connected to disconnected, an alert is sent to the 
IMB. 

The GPS receiver is able to use assistance data received over the GSM network to aide in 
acquiring a GPS fix.  This data is received from Ublox, AssistNow service. 

There are two modes of operation for the GPS receiver:  Acquisition mode and tracking mode.  
They are explained below. 

Acquisition mode only powers the GPS module when a fix is needed.  This is typically with 
every wake cycle of the GT Lite, including periodic reports and aperiodic events. 

Tracking mode constantly powers the GPS module to always have a fresh fix.  This mode can 
be used if real time tracking is required.  Tracking mode starts in acquisition mode to get the 
first fix.  After the first fix is complete, the GPS receiver remains powered and tracking.  If the 

GT Lite loses the GPS fix while in tracking mode, it will enter acquisition mode to gain a new 
fix. 

  Prepared:  R. Straz 

Date: July 25, 2007 

 

Page 23 of 

139