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• <br /> 3. Transition sites are needed for frequency reuse. Antennas mounted on tall support structures <br /> sometimes create a problem in frequency reuse because they "see" everything and overlap <br /> into the next cell site's coverage area. In order to control frequency reuse problems, these tall <br /> structures must be removed and replaced by transition sites. Transition sites allow the <br /> cellular company to increase the capacity of calls and maintain coverage simultaneously. <br /> Analog and Digital Technologies <br /> Traditionally, cellular phones have utilized analog transmission signals. In the analog technology, <br /> voice messages are electronically replicated and amplified as they are-carried from the transmitting <br /> antenna to the receiving antenna. A problem with this technology is that the amplification <br /> procedure tends to pick up "noise," sometimes making the message difficult to hear. • <br /> In order to diminish this noise and to provide greater calling capacity per channel, the cellular <br /> industry is beginning to use digital transmission signals. hi the digital technology, voice messages <br /> are converted into digits (zeroes and ones)that represent sound intensities at specific points in time. <br /> Because natural pauses in the conversation are eliminated, more calling capacity becomes available <br /> from the same amount of spectrum, thus reducing the need for new sites. An added benefit is that <br /> the background noise that is generally heard in the analog system becomes inaudible. As illustrated <br /> in Figure 9, the graphic difference between the two technologies is that analog signals are <br /> transmitted as continuous waves while digital technology converts the analog signal to binary <br /> digits. <br /> S <br /> Figure 9 <br /> TRANSMISSION SIGNALS <br /> ANALOG SIGNAL <br /> DIGITAL SIGNAL • <br /> 0 1 0 1 1 0 0 1 . 1 0 0 1 0 1 0 <br /> There are currently two forms of digital technology: time division multiple access (TDMA) and • <br /> code division multiple access (CDMA). Both of these forms of digital technology attempt to <br /> provide multiple access over one frequency, or channel. While TDMA is expected to increase <br /> calling capacity three to ten times over analog technology, CDMA is expected to increase calling <br /> capacity by ten to twenty times. <br /> Whereas cellular telephone carriers are in the process of converting to the digital technology, <br /> ESMR is already using it and PCS will come on line with it. <br /> 17 <br />