Specifications to look for in GPS tracking unit

The GPS tracking unit comes in many different varieties. As the saying goes, one shoe doesn’t fit all, it’s true for tracking solution as well.
Get the basics of GPS tracking from earlier post here

This topic covers a few of the technical specifications that one must check before selecting the solution. The variance in these technical specifications also either increases or decreases the cost of the unit of whole.

The GPS/GPRS unit is an integrated unit with GPS Receiver functionality and GPRS/GSM data transmission facility. The location coordinates calculated by GPS module are transmitted to the server using the data communication channel provided by the GPRS or GSM.

The main functionality of GPS module is to

a. Calculate Location Coordinates – Latitude, Longitude
b. Calculate Altitude – above mean sea level
c. Calculate Direction Heading – Direction of the movement, e.g. SW, SE, NW, NE etc.
d. Speed calculation – based on changing the location coordinate over a period of time unit
e. Optionally calculate distance between two measurement points.
f. Dilution of Precision (DOP)– Measured as Horizontal, Vertical, Positional (3D), and Time Dilution of Precision. A DOP value between 2-5 is considered as good enough for the route navigation. Whereas the DOP value above 10 are considered poor and should be rejected.

GPS Accuracy and Limitations
Common Factors affecting the accuracy of GPS:
• GPS Technique employed (i.e.: Autonomous, WADGPS, DGPS, RTK, etc.)
• Surrounding conditions (satellite visibility and multipath)
• Number of satellites in view
• Satellite Geometry (HDOP, GDOP, PDOP etc.)
• Distance from Reference Receiver(s) (non-autonomous GPS i.e.: WADGPS, DGPS, RTK)
• Ionospheric conditions
• Quality of GPS receiver

The precision or accuracy quoted by many GPS manufacturers is often done using a statistic known as CEP (Circular Error Probable) and are usually tested under ideal conditions.
CEP is the radius of the circle that will contain approximately 50 percent of the horizontal position measurements reported by the GPS receiver. This also means that 50% of the positions reported by your GPS will be outside of this circle.

Due to this variation in the CEP and horizontal position calculations the distances measured using the location coordinates returned by the GPS unit may not be accurate and vary.

Minimum Specifications to Check in the technical document provided with the GPS tracking unit –

1. Calculation of Location coordinates with CEP < 5mts, More the value less the accuracy
2. Support for Remote Configuration OTA / SMS : Needed to troubleshoot, or control aided features
3. Power Supply – 9V – 24V, higher the range better are the chances that the unit won’t fail due to intermittent high voltages
4. Operation Temperature Range -10 deg. – 70deg
5. GPRS Class B and Class 12
6. Internal Battery Backup of upto 4 to 6 HRS
7. Support GSM Frequency Band 900/1800 MHZ

The above forms the basic and needed core specifications. Anything above it, is a value add to the device and make it feature rich.

So, next time you are on the task to decide the best solution for yourself or your organization, get the technical specifications and scan through it for the above. More likely the units with the above minimum specifications shall serve the purpose and work for long.

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