Global Positioning System GPS Section, MOTOtalk

OVERVIEW: Global Positioning System (GPS) Section

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.

1.3Global 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.

1.4MOTOtalk

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.

1.5Bluetooth® 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.

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