Motorola I580 ユーザーズマニュアル

ページ / 107
OVERVIEW:  Global Positioning System (GPS) Section
68P80401P05
5
be able to “handoff” from one coverage area to another as the user moves about during a call. 
Handoff is controlled by the iDEN system.
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
Bluetooth
®
 Wireless System
Bluetooth technology is used for short range wireless communications that do not require high data 
rates. The original usage models included telephone, headsets, low-data rate access point, file 
transfer, and automatic synchronization. The newer usage models have added human interface 
devices, remote control, print capability, cable replacements, and personal area networks.
Bluetooth devices use GFSK modulation in the 2.4 to 2.4835 GHz band. The channels have a 
bandwidth of 1MHz. Frequency hopping is used to provide immunity to interference. The master 
unit in a pico-net dictates the hopping sequence at a rate of 1600 hops per second. This translates to 
a 625 uS transmission. The maximum data rate through a Bluetooth device is 1Mb per second.