Lecture in Wireless WANs: Cellular Telephone and Satellite Networks

Review for Wireless WANs: Cellular Telephone and Satellite Networks

Definition of Terms

Cellular telephony provides communication between two devices. One or both may be mobile.
A cellular service area is divided into cells.
Reusing cells is cells with the same number in a pattern that can use the same set of frequencies.
A mobile switching center coordinates communications between a base station and a telephone central office.
Handoff - If the strength of the signal diminishes, the MSC seeks a new cell that can better accommodate the communication. The MSC then changes the channel carrying the call (hands the signal off from the old channel to a new one).
In a hard handoff, a mobile station only communicates with one base station. When the MS moves from one cell to another, communication must first be broken with the previous base station before communication can be established with the new one. This may create a rough transition.

In Soft Handoff, a mobile station can communicate with two base stations at the same time. This means that, during handoff, a mobile station may continue with the new base station before breaking off from the old one.
Roaming means, in principle, that a user can have access to communication or can be reached where there is coverage.
Advanced Mobile Phone System (AMPS) is a first-generation cellular phone system.
AMPS is an analog cellular phone system using FDMA.
Digital AMPS CD-AMPS) is a second-generation cellular phone system that is a digital version of AMPS.
D-AMPS, or IS-136, is a digital cellular phone system using TDMA and FDMA.
Global System for Mobile Communication (GSM) is a second-generation cellular phone system used in Europe.
GSM is a digital cellular phone system using TDMA and FDMA.
Interim Standard 95 (IS-95) is a second-generation cellular phone system based on CDMA and DSSS.
IS-95 is a digital cellular phone system using CDMA/DSSS and FDMA.
The third-generation cellular phone system will provide universal personal communication.
A satellite network uses satellites to provide communication between any points on earth.
A satellite network is a combination of nodes, some of which are satellites, that provides communication from one point on the Earth to another. A node in the network can be a satellite, an Earth station, or an end-user terminal or telephone.
An artificial satellite needs to have an orbit, the path in which it travels around the Earth.
The orbit can be equatorial, inclined, or polar.
A footprint is the area on earth at which the satellite aims its signal.
Transmission from the earth to the satellite is called the uplink. Transmission from the satellite to the earth is called the downlink.
Based on the location of the orbit, satellites can be divided into three categories: geostationary Earth orbit (GEO), low-Earth-orbit (LEO), and middle-Earth-orbit (MEO).
A geosynchronous Earth orbit (GEO) is at the equatorial plane and revolves in phase with the earth.
Global Positioning System (GPS) satellites are medium-Earth-orbit (MEO)satellites that provide time and location information for vehicles and ships.
Iridium satellites are low-Earth-orbit (LEO) satellites that provide direct universal voice and data communications for handheld terminals.
The Iridium system has 66 satellites in six LEO orbits, each at an altitude of 750 km.
Iridium is designed to provide direct worldwide voice and data communication using handheld terminals, a service similar to cellular telephony but on a global scale.
The main difference between Iridium and Globalstar is the relaying mechanism. Iridium requires relaying between satellites. Globalstar requires relaying between satellites and earth stations.
Teledesic satellites are low-Earth-orbit satellites that will provide universal broadband Internet access.
Teledesic has 288 satellites in 12 LEO orbits, each at an altitude of 1350 km.