Suchen und Finden
Wireless Networking Complete
von: Pei Zheng, Larry L. Peterson, Bruce S. Davie
Elsevier Trade Monographs, 2009
ISBN: 9780123785701 , 444 Seiten
Format: PDF, ePUB, OL
Kopierschutz: DRM
Preis: 65,95 EUR
Supporting Wireless Technologies
Pei Zheng
Lionel M. Ni
This chapter provides extensive coverage of existing mobile wireless technologies. Much of the emphasis is on the highly anticipated 3G cellular networks and widely deployed wireless local area networks (LANs), as the next-generation smart phones are likely to offer at least these two types of connectivity. Other wireless technologies that either have already been commercialized or are undergoing active research and standardization are introduced as well. Because standardization plays a crucial role in developing a new technology and a market, throughout the discussion standards organizations and industry forums or consortiums of some technologies are introduced. In addition, the last section of this chapter presents a list of standards in the wireless arena.
1.1 The Frequency Spectrum
The fundamental principle of wireless communication is electromagnetic wave transmission between a transmitter and a receiver. Signals are characterized by their frequencies in use. Multiple signals or noises of the same frequency will cause interference at the receiver. To avoid interference, various wireless technologies use distinct frequency bands with well-controlled signal power which are portions of the so-called frequency spectrum. As a scarce public resource, the frequency spectrum is strictly regulated by governments of countries around the world. In the United States, the Federal Communications Commission (FCC) has the responsibility of regulating civil broadcast and electronic communications, including the use of the frequency spectrum, and the National Telecommunications and Information Administration (NITA) administers the frequency use of the federal government. In Europe, the frequency spectrum is managed on a national basis, and the European Union (EU) members coordinate via the European Conference of Post and Telecommunications Administrations (ECPT) and the Electronic Communications Committee (ECC). Worldwide unified regulation of wireless communication is understandably difficult to achieve for various technological, economic, and political reasons. To this end, the International Telecommunications Union (ITU) has been formed as an international organization of the United Nation. The ITU allows governments and private sectors to coordinate development of telecommunication systems, services, and standards. In almost all countries, portions of the frequency spectrum have been designated as “unlicensed,” meaning that a government license is not required for wireless systems operating at these bands. In effect, wireless system manufacturers and service providers are required to obtain an exclusive license for a frequency band from regulatory bodies or resort to the use of the unlicensed spectrum. In either case, the emitted power of the wireless systems must comply with the power constraints associated with the regulations in question. In addition, frequency allocations of a country may change over time. (For the latest information regarding frequency allocation in the United States, see http://www.ntia.doc.gov/osmhome/allochrt.html.)
A radio signal is characterized by wavelength and frequency. In vacuum, the product of wavelength and frequency is the speed of light (about 3 × 108 m/sec); in general, a higher frequency means shorter wavelength. For example, visible light is in the frequency band of 4.3 × 1014 to 7.5 × 1014 Hz, with wavelengths ranging from 0.35 to 0.9 μm. Frequency modulation (FM) radio broadcasts operate within the frequency range of 30 to 300 MHz at wavelengths between 10 and 1 m.
The frequency spectrum can be divided into the following categories: very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF), ultra-high frequency (UHF), super-high frequency (SHF), extremely high frequency (EHF), infrared, visible light, ultraviolet, X-ray, gamma-ray, and cosmic ray, each of which represents a frequency band. Figure 1.1 shows the frequency spectrum up to the visible light band. Notice that in the context of electronic communication, there are two categories of transmission medium: guided medium (e.g., copper coaxial cable and twisted pair) and unguided medium (for wireless communication in the air). The guided medium carries signals or waves between a transmitter and a receiver, whereas the unguided medium typically carries wireless signals between an antenna and a receiver (which may also be an antenna). Nevertheless, each medium operates at a specific frequency band of various bandwidth determined by its physical characteristics. For example, coaxial cable uses many portions of frequencies between 1 KHz and 1 GHz for different purposes: television channels 2, 3, and 4 operate at frequencies from 54 to 72 MHz; channels 5 and 6 from 76 to 88 MHz; and channels 7 to 13 from 174 to 216 MHz. The optical fiber uses visible or infrared light as the carrier and operates at frequencies between 100 and 1000 THz.
Figure 1.1 The frequency spectrum (refer to the text for the exact frequency band allocated to each system).
Wireless communication operates at frequencies in the so-called radio spectrum, which is further divided into VLF, LF, MF, HF, VHF, UHF, SHF, and EHF. In addition, infrared data association (IrDA) is also used for short-range wireless communication. The following text discusses frequency bands at which existing mobile wireless technologies operate; notice that very often the frequency regulations enforce emitted power restrictions to avoid interference among wireless devices operating at the same frequency band.
1.1.1 Public Media Broadcasting
• Amplitude modulation (AM) radio: AM radio stations operate at a frequency band between 520 and 1605.5 KHz.
• FM radio: It uses the frequency band between 87.5 and 108 MHz.
• Shortwave (SW) radio: SW radio uses frequencies between 5.9 and 26.1 MHz within the HF band. The transmission of shortwave radio over a long distance is made possible by ionosphere reflection. HAM amateur radio, a popular activity enjoyed by over three million fans worldwide, relies on the HF band to communicate across the world.
• Conventional analog television: A quite small slice of VHF (30–300 MHz) and UHF (300–3000 MHz) has been allocated for analog television broadcasting. In the United States, each channel occupies a 6-MHz band. The first VHF channel, channel 2, operates at 54–60 MHz, whereas the last UHF channel, channel 69, operates at 800–806 MHz.
• Cable television: The frequency bands of channels 2–13 are exactly the same for both conventional television and cable television. Beyond those channels, cable television requires frequencies from 120 to 552 MHz for channels 13–78.
• Digital cable television: Channels 79 and above are reserved for digital cable broadcasting at frequencies between 552 and 750 MHz.
• Digital audio broadcasting (DAB): DAB is a standard developed by the EU for CD-quality audio transmission at frequencies from 174 to 240 MHz and from 1452 to 1492 MHz. In the United States, a technique called in-band on-channel (IBOC) is used to transmit digital audio and analog radio signals simultaneously with the same frequency band. The resulting services are generally marketed as high-definition radio.
• Direct broadcast satellite (DBS): The upper portion of the microwave Ku band (10.9–12.75 GHz) is used for direct satellite-to-receiver video and audio broadcasting. See Section 1.13 for more details regarding satellite communication.
• Satellite radio: Frequencies from 2320 to 2345 MHz have been allotted for satellite radio services in the United States. See Section 1.13 for more details regarding satellite communication.
1.1.2 Cellular Communication
• Global system for mobile (GSM): The two frequency bands used by GSM are 890–960 MHz and 1710–1880 MHz. They are sometimes referred to as the 900-MHz band and the 1800-MHz band.
• Code-division multiple access (CDMA): The IS-95 standard defines the use of the 800- and 1900-MHz bands for CDMA cellular systems.
• 3G wideband CDMA (WCDMA)/universal mobile telecommunications system (UMTS): Three frequency bands are allocated for 3G UMTS services: 1900–1980 MHz, 2020–2025 MHz, and 2110–2190 MHz.
• 3G CDMA 2000: This system reuses existing CDMA frequency bands.
1.1.3 Wireless Data Communication
• Wireless LANs: IEEE 802.11b operates at 902–928 MHz and 2400–2483 MHz, and the industrial, scientific, and medical (ISM) radio bands operate at 2.4 GHz in the United States. The IEEE 802.11b operates at 2400–2483 MHz in Europe, and at 2400–2497 MHz in Japan. IEEE 802.11a and HiperLAN2 use 5150–5350 MHz and 5725–5825 MHz, and the unlicensed national information infrastructure (U-NII) band operates at 5.8 GHz in the United States. They operate at 5150–5350 MHz and 5470–5725 MHz in Europe, and at 5150–5250 MHz in Japan. Section 1.10 discusses wireless LANs in more detail.
• Bluetooth:...
Alle Preise verstehen sich inklusive der gesetzlichen MwSt.