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Position/Location Tracking and Communications Software Defined Radio (POSCOMM)

Network aided positioning solution in urban and other weak GPS signal environments

The GPS signals can be significantly attenuated, or even blocked, when they have to be received inside buildings, under foliage, in jamming, etc. The NAVSYS solution to this problem is to use network aiding with our POSCOMM, Position/Location Tracking and Communications Software Defined Radio (SDR).

The network aiding function requires the use of multiple “master” units to be operating in the network in locations where they have access to the GPS signals. These can be either other participants in the operation or pre-positioned “nodes” to provide coverage in areas where GPS has difficulty operating. These master units transmit a Time of Arrival (TOA) message which includes a pseudo-random sequence from which the time of arrival at the “slave” unit can be precisely determined. A message is also sent including the precise time of transmission of the TOA message and the precise location of the master unit based on the GPS observations. The TOA differenced with the time-of-transmission provides the slave unit with a pseudorange observation from each of the master unit’s locations. This can be used to solve for the position of the slave either using the TOA updates alone or using a combination of both the GPS and TOA observations.

Embeds easily into existing or sourced sensors

Because the GI-Eye system is a software platform it can be integrated to run on existing GPS, inertial, and visual sensors, reducing size and weight for your application. NAVSYS can also provide numerous sensors to meet the performance requirements of your application. Because of its modular design, it enables sensor upgrades over time with only software configuration changes.

POSCOMM Software Defined Radio
Position/Location Tracking and Communications Software Defined Radio
802.11b Network Data Link
802.11b network data link transfers PLT, TOA and network assist messages

System concept

The master units act as Pseudolites to aid the slave unit (remote unit) to navigate when the GPS signal is too small for direct tracking. The remote units can be configured to operate in any of the following navigation states.

  • GPS-only navigation (only uses GPS satellite observations)
  • Pseudolite-only navigation (only uses TOA pseudolite observations)
  • GPS/PL navigation (uses available GPS satellite and TOA pseudolites)


POSCOMM is a Software Defined Radio suitable for man-portable applications, which can support both the positioning and communication functions associated with the POSCOMM SDR. Since both the GPS and communications functions reside within common SDR hardware, they can be linked to provide a positioning capability that leverages both the GPS derived pseudo-range and carrier phase observations, and TOA observations derived from the communications channel. The POSCOMM unit includes a GPS front end and a communications transmit/receive front end. An 802.11b network data link is also included to transfer PLT, TOA and network assist messages as shown in the block diagram, above.



The POSCOMM SDR approach has the following advantages:

  • Provides a low cost hardware implementation including both GPS and communication functions in a single device.
  • Allows for power saving for man-portable operations through sharing of common components and through snapshot tracking (GPS DFE is only powered on when data is being collected).
  • Improves the GPS signal tracking capability by providing network assistance through the communication link to allow operation under low signal power conditions.
  • Improves GPS positioning performance by providing GPS corrections through the network.
  • Provides a back-up positioning capability using network aiding with TOA observations in the event of GPS signal drop-out.
  • Allows one-way TOA messaging to be used which significantly reduces the loading on the communications network.

GPS Frequency

1575.42 MHz (L1)

GPS Code

C/A (the system could be P(Y) configured)

GPS Channels

Six (with growth to 12)

GPS Signal Acquisition (Normal Mode-C/A) 32 dB-Hz
Maximum Dynamics 4 m/s, 1g
GPS Signal Acquisition (Network Assisted) 24 dB-Hz
GPS Signal Tracking (Normal Mode) 34 dB-Hz
GPS Signal Tracking (Network Assisted) 24 dB-Hz
Time to First Fix Normal Mode 40 secs
Time to First Fix Network Assisted Mode 10 secs
Reacquisition Time 10 secs
Remote PVT Accuracy 1m Horiz, 1m Vert, 0.03 m/s Vel.
Remote Unit Power Required

28 Watts with an additional watt when Pseudolite
(900 MHz) is transmitting

900 MHz Center Frequency 915 MHz
900 MHz Bandwidth 20 MHz (total)
900 MHz Channels Tracked 6
900 MHz Threshold Tracking 40 dB-Hz
900 MHz Transmitted Accuracy 1m relative to GPS reference signal
Wireless Data Link 802.11b
Wireless Bandwidth 80 MHz
Related Info



Indoor Navigation Using a Software Defined Radio.
Proceedings of SDR '08 Technical Conference, Washington, DC, Oct. 2008 (PDF: 265k)


Multipath Mitigation Algorithm Results Using TOA Beacons for Integrated Indoor Navigation.
Proceedings of ION GNSS 2008, Savannah, Georgia, Sep. 2008 (PDF: 1.2MB)


Integrated GPS/TOA Navigation using a Positioning and Communication Software Defined Radio.
Proceedings of IEEE/ION Position Location and Navigation Symposium, PLANS 2006, San Diego, CA, Apr. 2006 (PDF: 325k)


Design and Test Results of a Software Defined Radio for Indoor Navigation.
Proceedings of 2005 Software Defined Radio Technical Conference, Orange County, CA, Nov. 2005 (PDF: 365 KB)


Integrated GPS/TOA Navigation Using a Positioning and Communication Software Defined Radio
Proceedings of ION GNSS 2005, Long Beach, CA, Sept. 2005 (PDF: 403 KB)


Urban/Indoor Navigation using Network Assisted GPS.
ION 61st Annual Meeting, Cambridge, MA, June 2005 (PDF: 425 KB)


Software Defined Radio Test Bed for Integrated Communications and Navigation Applications.
2004 Software Defined Radio Technical Conference, Phoenix, AZ, Nov. 2004 (PDF: 271 KB)


PC/104 Test-Bed for Software GPS Receiver (SGR) and Software Defined Radio (SDR) Applications.
Proceedings of MPRG Symposium, Blacksburg, VA, June 2004 (PDF: 464 KB)


Position/Location Tracking and Communications Software Defined Radio (POSCOMM) (PDF: 158 KB)

Debbie Westra
toll free: 866.4.NAVSYS (866.462.8797)
or 719.481.4289

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