Data and Signals Data and Signals * Data must be transformed into electromagnetic signals prior to transmission across a network. * Data and signals can be either analog or digital. * A signal is periodic if it consists of a continuously repeating pattern. * Each sine wave can be characterized by its amplitude, frequency, and phase. * Frequency and period are inverses of each other. * A time-domain graph plots amplitude as a function of time. * A frequency-domain graph plots each sine wave’s peak amplitude against its frequency. * By using Fourier analysis, any composite signal can be represented as a combination of simple sine waves. * The spectrum of a signal consists of the sine waves that make up the signal. * The bandwidth of a signal is the range of frequencies the signal occupies. Bandwidth is determined by finding the difference between the highest and lowest frequency components. * Bit rate (number of bits per second) and bit interval (duration of 1 bit) are terms used to describe digital signals. * A digital signal is a composite signal with an infinite bandwidth. * Bit rate and bandwidth are proportional to each other. * The Nyquist formula determines the theoretical data rate for a noiseless channel. * The Shannon capacity determines the theoretical maximum data rate for a noisy channel. * Attenuation, distortion, and noise can impair a signal. * Attenuation is the loss of a signal’s energy due to the resistance of the medium. * The decibel measures the relative strength of two signals or a signal at two different points. * Distortion is the alteration of a signal due to the differing propagation speeds of each of the frequencies that make up a signal. * Noise is the external energy that corrupts a signal. * We can evaluate transmission media by throughput, propagation speed, and propagation time. * The wavelength of a frequency is defined as the propagation speed divided by the frequency. |
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