Motorola i760, Field Service Manual

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OVERVIEW: Global Positioning System (GPS) Section
68P80400P94-O
1-5
1.3 Global Positioning System (GPS) Section
The U.S. Department of Defense (DoD) has built a 24-satellite constellation for the purpose of
pinpointing locations anywhere on the planet. The satellites circle the earth every 12 hours,
transmitting radio signals at a fixed frequency of 1575.42 MHz. The satellites share the 1575.42
MHz spectrum with each other through the use of CDMA modulation.
To determine a location on earth, a receiver must be built that can receive the simultaneous signals
from the satellites that are in view of the receiver and use that information to calculate the location
of the receiver. The receiver must pick up the signals from 4 satellites. Once the 4 satellites are
located, the receiver measures the time it took for the satellite signals to arrive. From this timing
information, the distance between the receiver and each satellite can be calculated. The four
satellites’ ephemeris data provide the satellite’s X, Y, and Z positions. The range, R, is the receiver
measurement made by calculating the time it took for the signal to reach the receiver. The user’s
position, (Ux, Uy, Uz), and the clock bias, Cb, is then calculated.
To use the GPS, a receiver that can receive the spread-spectrum signals must be built. The detected
signals are then converted from RF signals into appropriate digital input formats. These digital
inputs are processed and converted into position information. Once the position coordinates are
determined, they are communicated to the handset microprocessor and displayed on the screen or
transmitted to the base station as required.
1.4 MOTOtalk
The purpose of the MOTOtalk feature is to allow simple, direct, simplex two-way radio-to-radio
communications between subscriber units. It is a PTT (Push-To-Talk)- based feature that operates
like most any two-way radio might. A good basic model for operation is that of the Motorola
Talkabout product. What makes it quite different, however, is that it is digital in operation, which
allows for superior range and voice quality. It is also asynchronous in nature, and requires no
external source of synchronization for connections between units to be made.
1.5 SIM Cards
This unit is designed to work with a mini Subscriber Identity Module (SIM). The SIM card contains
all of the personal data required to access iDEN services. Data held by the SIM card includes:
•
Temporary Mobile Subscriber Identity
•
Services to which the user subscribes
•
PIN and unblocking codes
•
Call barring codes
The SIM card is also capable of storing phone numbers and names.
Available SIM cards for this unit are 64 kB and prepaid.
1.5.1 Removing and Inserting a SIM Card
NOTE:
When a SIM card is defective and must be replaced with a new one, the following
information will be erased: