Chapter 16 Wireless WANs: Cellular Telephone and Satellite Networks

Chapter 16 of Data Communications and Networking by Behrouz A. Forouzan, titled "Wireless WANs: Cellular Telephone and Satellite Networks", discusses wireless WAN technologies, focusing on cellular networks and satellite communication systems. Below are the detailed notes from the chapter:

1. Cellular Telephony

• Definition: Cellular telephony provides communication between two mobile units or between a mobile and a stationary unit. It operates by dividing the service area into cells, with each cell having its own antenna and a base station (BS) controlled by a mobile switching center (MSC).

• Components:

  1. Mobile Station (MS): A device like a mobile phone.

  2. Base Station (BS): The antenna in each cell that connects to the mobile stations.

  3. Mobile Switching Center (MSC): Coordinates communication between BSs and connects them to the telephone network.

1.1 Frequency-Reuse Principle

• Frequency Reuse: The available spectrum is divided into channels, which are reused in non-adjacent cells to increase the number of simultaneous users. This method is designed to avoid interference between adjacent cells.

1.2 Transmitting and Receiving

• Cellular systems use duplexing to allow simultaneous sending and receiving of data. Frequencies are divided into uplink (mobile to base station) and downlink (base station to mobile) channels.

1.3 Roaming and Handoff

• Roaming: The ability to move from one cell to another without losing the connection.

• Handoff: The process of transferring a mobile unit's communication from one BS to another as it moves between cells. There are two types:

  1. Hard Handoff: The connection is broken before the next one is established.

  2. Soft Handoff: The mobile unit is connected to more than one BS during the handoff process.

1.4 Generations of Cellular Systems

• First Generation (1G): Analog cellular systems that use frequency modulation for voice communication, such as Advanced Mobile Phone System (AMPS).

• Second Generation (2G): Digital systems like Global System for Mobile Communications (GSM) and IS-95 (CDMA). These systems provide better quality, data services (SMS), and higher capacity through digital modulation.

  • GSM: A TDMA-based system that uses 124 channels, each 200 kHz wide, allowing for 8 users per channel.

  • IS-95 (CDMA): Based on code division multiple access (CDMA), allowing multiple users to share the same bandwidth by encoding each user's signal uniquely.

• Third Generation (3G): Designed for multimedia communication, 3G systems provide high data rates and global roaming. The IMT-2000 standard specifies voice quality similar to the PSTN and data rates up to 2 Mbps for stationary users.

2. Satellite Networks

• Definition: Satellite networks consist of artificial satellites that enable communication between distant points on Earth. Satellites work like base stations, covering areas known as footprints.

2.1 Satellite Orbits

• Satellites are categorized based on their orbit:

  1. Geostationary Earth Orbit (GEO): Satellites remain in fixed positions relative to the Earth’s surface, located at 35,786 km altitude. They cover large areas, ideal for TV and long-distance communication.

  2. Medium Earth Orbit (MEO): Satellites located between GEO and low Earth orbit (LEO), typically used for GPS systems.

  3. Low Earth Orbit (LEO): Satellites located at altitudes between 500 and 2,000 km. They are used for mobile communication and low-latency services like Iridium and Globalstar.

2.2 Categories of Satellites

• GEO Satellites: Offer broad coverage, primarily used for broadcasting and point-to-point communication.

• MEO Satellites: Offer better latency than GEO, often used for GPS.

• LEO Satellites: Provide low-latency communication, often used in systems like Iridium for global mobile services.

2.3 Iridium and Globalstar

• Iridium: A constellation of 66 LEO satellites that provides global voice and data communication. Iridium uses a network of interconnected satellites to relay calls between users.

• Globalstar: Similar to Iridium but uses a combination of satellites and ground stations for communication, reducing the number of satellite-to-satellite hops.

3. Summary

• Cellular telephony systems rely on cell division and frequency reuse to handle large numbers of users.

• The evolution from 1G to 3G has greatly increased the capabilities of cellular networks, from analog voice communication to high-speed multimedia services.

• Satellite networks provide global coverage and are vital for both communication and navigation services, with different types of orbits catering to different applications.

These detailed notes cover the essential concepts of cellular telephony and satellite networks as explained in Chapter 16【7:16†source】【7:0†source】【7:5†source】【7:12†source】.