In Chapter 3 we noted that there is no such thing as a perfectly band limited signal. This fact has serious consequences in many places. For example, frequency is an economic commodity. The United States government regulates who can broadcast what signals in what bands. During the wireless revolution, for example, a bidding process was established to accommodate the various services providers. The highest bidder received the license to transmit their signal. In order to maximize the return on investment, the winner wants to serve as many customers as possible. In general, the allocated bandwidth is segmented into channels with a given group of subscribers assigned to a particular slot. One of the main problems is to avoid one channel from interfering with the next. This phenomenon is called adjacent channel interference. Here is the problem: Suppose that the amount of power spectral density generated by a signal in slot A is, say, 80 dB below the slot A carrier (dBc) as it spills into the next frequency slot B. Now suppose you are user B. You are talking to a transmitter source quite far away while the user on slot A is much closer. Then it can (and does) happen that the weak amount of spill from frequency slot A into slot B is greater than the direct signal power in frequency slot B. Slot B is blocked by slot A. This is called the near-far effect. Another system that suffers in the same manner is air traffic control...