无线通信与网络(课后习题答案) Wireless_Communications_&_Networking

CHAPTER 2 TRANSMISSION FUNDAMENTALS A NSWERS TO QUESTIONS 2.1 A continuous or analog signal is one in which the signal intensity varies in a smooth fashion over time while a discrete or digital signal is one in which the signal intensity maintains one of a finite number of constant levels for some period of time and then changes to another constant level. 2.2 Amplitude, frequency, and phase are three important characteristics of a periodic signal. 2.3 2π radians. 2.4 The relationship isλf= v, whereλ is the wavelength, f is the frequency, and v is the speed at which the signal is traveling. 2.5 The spectrum of a signal consists of the frequencies it contains; the bandwidth of a signal is the width of the spectrum. 2.6 Attenuation is the gradual weakening of a signal over distance. 2.7 The rate at which data can be transmitted over a given communication path, or channel, under given conditions, is referred to as the channel capacity. 2.8 Bandwidth, noise, and error rate affect channel capacity. 2.9 With guided media, the electromagnetic waves are guided along an enclosed physical path, whereas unguided media provide a means for transmitting electromagnetic waves through space, air, or water, but do not guide them. 2.10 Point-to-point microwave transmission has a high data rate and less attenuation than twisted pair or coaxial cable. It is affected by rainfall, however, especially above 10 GHz. It is also requires line of sight and is subject to interference from other microwave transmission, which can be intense in some places. 2.11 Direct broadcast transmission is a technique in which satellit

e video signals are transmitted directly to the home for continuous operation.