GPS Sensor Specifications-Sensitivity, TTFF (Time to First Fix), Form factor, number of channels

This page covers GPS Sensor Specifications viz. sensitivity, TTFF (Time to First Fix), number of channels, form factor, power consumption, update rate, output type, supply voltage, current consumption etc.


• Sensitivity is the minimum power at which GPS sensor functions as desired.
• It is expressed in dBm.
• dBm refers to power ratio in decibels of measured power referenced to 1 milliwatt.

TTFF (Time to First Fix)

• It is measure of time required for GPS receiver to acquire satellite signals and navigation data and calculate position solution (called "fix"). In other words, it is the time required to obtain an initial fix from a satellite.
• Each GPS satellite transmits a message once in 30 seconds. It has two parts viz. ephemeris and almanac. Ephemeris data is used to calculate position of each satellite in orbit. Almanac provides information about time/status of entire satellite constellation.
• TTFF (Time to First Fix) value depends on different scenarios viz. cold start, warm start and hot start.
• During cold start, it is 12.5 minutes. GPS receiver takes such long time as only small part of Almanac is included in a GPS message and hence it requires about 25 messages to get full almanac. The 25 messages require about 12.5 minutes. Here cold start means GPS module was off for sometime and there has been no data in the memory.
• During warm start, it is 30 seconds to couple of minutes.
• During hot start, it is between 0.5 to 20 seconds.

Number of Channels

• It is the number of satellites GPS receiver module housing GPS sensor can track simultaneously.
• Early GPS receivers could sense only 4 channels.
• Modern GPS sensors may be able to deal with 22.

Form Factor

• This is the size of a chip, often determined by dimensions of ceramic antenna on top of it.
• Dimensions may be 15 mm x 15 mm or larger.

Power Consumption

• It is expressed in milliwatts.
• manufactured GPS module consumes 82 mWatt (during acquisition of satellite signals) and 66 mWatt (during tracking).
• Typically voltage of 4 V DC chipset consumes about 20mA.

Update Rate

• The number of position measurements per second.
• 1 update per second is usual while certain GPS chips require even faster updates.
• The frequency of updates is expressed in Hz.

Output Type

• It is TTL level serial which provides NMEA data output.
• Usually 4800 or 9600 bps baudrate is used for decoding.
• It uses {8 bits, no parity, 1 stop bit} for decoding satellite received data.

Supply Voltage

• It is usually below 5 V DC.

Current Consumption

• It is higher during satellite acquisition.

Refer application note on interfacing of GPS sensor >> with Arduino Uno board with pin to pin block diagram and source code.


GPS Sentences  GPS Sensor function and working  What is GPS system?  GPS vs AGPS  GPS Frame Structure  GPS vs GPRS  GPS Basics Tutorial  GPS Antenna  GPS Receiver Module  GPS Satellite  GPS Tracking System 

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