Motorola MOTOTRBO SYSTEM PLANNER Specifications download pdf (Page 42)

System Feature Overview 33

November, 2008

2.4.3.1 Performance Specifications

The definitions for some of the terms stated in the table above are as below:

• Cold start – A cold start scenario occurs when the radio is first powered up, and the GPS

receiver is attempting to acquire its first position lock. In this scenario, the GPS receiver only

has a valid almanac stored; it does not have any valid satellite ephemeris data nor valid real-

time clock synchronization. Almanac data is stored in a non-volatile (persistent) memory,

and is valid for approximately one year. The GPS receiver regularly updates the almanac

data; therefore it will always be valid unless the radio is powered off for more than one year.

The almanac data provides a mapping of the GPS satellites’ position in the sky in relation to

a real-time clock.

• Hot start – A hot start scenario occurs when the GPS receiver attempts to acquire a new

location fix after a previous fix had occurred recently. In this scenario, the GPS receiver has

valid satellite ephemeris data, a valid almanac, and valid real-time clock synchronization.

• TTFF – Time to First Fix indicates the time the GPS receiver takes to determine its first or

subsequent position lock. This is determined largely by the time taken to download a full

satellite ephemeris or satellite orientation packet with a data rate of 50 bits per second (bps),

as well as, how long it takes for the GPS receiver to reach the relevant satellite in its scan

list. In a cold start, the scan list includes all of the 24 orbiting satellites. The GPS receiver

samples each satellite for a certain amount of time to determine if it is visible or not before

moving to the next satellite. The receiver continues to do this until it detects a certain

number of visible satellites and can determine an approximate location, thus helping the

receiver to truncate the scan list. In a hot start, the receiver already has most, if not all, the

data needed to calculate its position. Therefore, no scanning is needed and minimal

downloading is necessary to calculate position, resulting in a lower time to acquire a

positional fix.

• Horizontal Accuracy – Horizontal Accuracy indicates a radius length from the reported

point location. The latitude and longitude reported is equivalent to a point in the center of a

circle, with the horizontal accuracy value as the radius of the circle. The true position should

be within this location range.

GPS Transmitter Portable Mobile

TTFF (Time to First Fix) Cold Start < 2 minutes < 1 minute

TTFF (Time to First Fix) Hot Start < 10 seconds

Horizontal Accuracy < 10 meters

Note: Accuracy specifications are for long-term tracking (95th percentile values > 5 satellites visible at

a nominal -130 dBm signal strength).

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Motorola MOTOTRBO SYSTEM PLANNER Specifications Page 42