 small frequency band used to separate two adjacent frequency bands. Cochannel interference, sometimes also referred to as narrowband interference, is due to other nearby systems (say, AM/FM broadcast) using the same transmission fre- quency. This can be minimized by dynamic channel allocation techniques. The most common noise impairment in data transmission is the linear addition of wideband noise with a constant spectral density (expressed as watts per hertz of bandwidth) Channel Receiver Block Booster Threshold Retrieved Equalizer Decision Amplifier Circuit Signal Amplifier/ Amplifier/ Repeater Repeater Timing Extractor Fig. 2.10 Regenerator at the receiver block, including the equalizer. Chapter 2 Data Transmission and a Gaussian distribution of amplitude. Wideband Gaussian noise (also called white noise) comes from many natural sources, such as the thermal noise or shot noise. Thermal noise arises from the random agitation of electrons because of temperature variations in the electronic device. Shot noise is generated at the receiver and is caused by the random varying velocity of elec- tron movement under the influence of externally applied potentials or voltages at terminals or electrodes. It is similar to thermal noise in that it has a Gaussian distribu- tion and a flat power spectrum. It differs, however, in that it is not directly affected by temperature. Its magnitude is proportional to the square root of the direct current through the device and thus can be a function of signal amplitude. Other common types of noise include impulse noise and intermodulation noise. Impulse noise is the effect of an external electromagnetic disturbance, faults, or flaws in the communication system. This type of noise will happen suddenly for a short period of time and will be represented as a spike in the transmitted signal. Impulse noise consists of short spikes of power having an approximately flat frequency response over the spectrum range of interest. It is considered to be a voltage increase of 12 dB or more above 