s. This limits the transmission range and network coverage. The other is the variability of path loss as a function of distance. A device must adjust its transmission power as it moves nearer to or farther from a receiver, to ensure that (1) the received power level is sufficiently large for correct detection and (2) it does not transmit too much power and deplete its battery. As a result, power control processes have become essential in wireless communications. Power control is also important in combat- ting signal fading in the time and frequency domains, topics which are outside the scope of this text. Diversity Reception A technique to mitigate signal fading is through diversity combining. Diversity combining is based on a premise that if a signal can be received through two (or more) independently faded paths the combined signal is less faded as a trough in one path is compensated by a possible peak in another. Independent reception of signals may be accom- plished through several means, including employing multiple receiver antennas. Because the probability that all paths may fade at the same time is significantly less than the probability that a single path fades, the overall combined signal experiences less fading. This is illustrated below, where the stronger of two fading paths is selected, and as a result the combined signal has fewer instances of signal fading. Terrestrial Broadband Wireless Telecommunications Selection diversity combined Path 2 Path 1 Case Study 10.1: Indoor Office Wireless Communications Systems The 1980s witnessed the growth of office automation and usage of desktop computers, on-line printers and databases. However most offices were not wired for the necessary local area networking infrastructure and equipment. While most offices had been wired for internal and external telephony, the new data communications infrastructure required significant investment in cables and wiring and reconfiguration of office layout. This motivated research into wireless local area networking. The wire