User's Manual

Galaxy Tracking Systems, L.L.C. Technical Documentation - VTU
Vehicles equipped with VTUs can be commanded to continuously report their position,
speed, and status.
For anti-theft and security related applications, the VTU can provide limited remote
control of vehicle systems (e.g., lights, horn or ignition), as well as automated and
manual alarms.
5.2 Fixed Components
The tracking system’s infrastructure is comprised a powerful transmitter, Central
Broadcasting Unit (CBU), and a host of fixed receivers, Fixed Tracking Units (FTUs),
placed strategically throughout the area of operations to ensure uninterrupted
communications to member vehicles. The CBU operates under the direct control of the
Central Command Center (CCC) which provides the primary operator interface to
command and control the system. The CBU transmits aiding data, system timing data and
VTU commands at precise intervals synchronized to GPS time.
Every VTU command requires an acknowledgment back to the CCC. The exact time and
interval at which the VTU is to transmit its response(s) is contained in the original VTU
command. Vehicle (VTU) transmissions are received by FTU(s) and forwarded by direct
cable connection or telephone line back to the CCC.
5.3 RF Transmission Scheme
Galaxy’s system currently supports sixteen radio channels. Each channel is comprised of
a receive / transmit frequency pair within the radio’s operating frequency range. Each
channel is divided using a Time Division Multiple Access (TDMA) transmission scheme
that begins on a one-hour boundary and repeats every 30 seconds. Each 30-second cycle
is divided into five six-second frames. The frames are further divided into 100 msec
“slots”.
The first six time slots of each frame are allocated to CBU transmissions. The remaining
time slots are allocated dynamically to specific VTUs under control of the command
center.
5.4 System Timing
Accurate time is required to maintain the TDMA transmission scheme employed for VHF
communications. All system components are synchronized to within a few milliseconds
of each other using the GPS 1 PPS output pulse.
Use or disclosure of data contained on this sheet is subject to the restriction on the title page of this report.