Bandwidth is determined by the range of frequencies that can be carried on a facility or the range of radio frequencies that a signal will occupy. Bandwidth refers to the amount of spectrum available to transport information. Narrowband, also referred to as baseband, implies a single channel. Wideband, also referred to as broadband, implies the use of multiple channels.
It is important to note that bandwidth is most often limited by regulation rather than technology. That is, the politics and business of spectrum allocationrather than the physical attributes of a given frequency bandoften determine which frequencies are made available and who obtains the licenses to use them.
The maximum physical capacity of a transmission channel can be determined by using Shannon's Law, which describes the relationship between the primary limiting factors in a transmission channelbandwidth and noise. This formula is
C = W log2 (1 + S/N)
where C is the capacity of a channel (in bits per second), W is the bandwidth of the channel (in Hertz), and S/N is the signal-to-noise ratio. The more bandwidth there is available, the more bits per second can be sent on the channel. The more noise that is present, the fewer bits per second the channel will be able to carry.
As mentioned earlier in this chapter, as radio signals travel through the air, they lose power and encounter interference from other signals as well as environmental disturbances. The level of noise affects how efficiently the radio signal can be encoded and, therefore, how many bits per second can be carried on one cycle of radio bandwidth; this is referred to as the bandwidth efficiency. Noise is measured by the signal-to-noise ratio. As the power of the signal is reduced, the signal-to-noise ratio degrades, and the potential for error therefore increases.
Part I: Communications Fundamentals
Telecommunications Technology Fundamentals
Traditional Transmission Media
Establishing Communications Channels
Part II: Data Networking and the Internet
Data Communications Basics
Local Area Networking
Wide Area Networking
The Internet and IP Infrastructures
Part III: The New Generation of Networks
Broadband Access Alternatives
Part IV: Wireless Communications
Wireless Communications Basics
WMANs, WLANs, and WPANs
Emerging Wireless Applications