Direct-sequence spreading was initially considered for defense applications such as jamming-resistant communication and low probability of intercept communication. The realization that it could also be a multiple-access technique led to its exploration and eventual adaptation as a mode for achieving mobile wireless communication or cellular telephony. This chapter provides an overview of basic issues in cellular telephony and a description of how CDMA is typically administered.
Today, widespread use of wireless communication has been made possible by the adoption of a cellular structure. As in conventional landline telephony, the connection between two users for a voice conversation requires a communication path or channel between them. For example, if a link is to be established between two telephones on a small campus using conventional telephony, it is done through a private exchange or telephone switch . If the telephones are widely separated, by a few hundred kilometers for example, coordination among several switches is required to establish the connection. When a call is initiated, the calling instrument first contacts its switch through a wired connection.
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