The game to play in wireless communications, when it conics to increasing spectrum efficiency, is eliminating interference. Currently, all cellular systems use frequency-division duplexing in an attempt to eliminate interference from adjacent cells. The use of many technologies has limited the effects of interference, but two types of interference remain. These are adjacent base-to-home mobile interference and adjacent mobile-to-home base interference. Time-division duplexing has not been used for mobile cellular systems because it is even more susceptible to different forms of interference. Not only is TDD subject to adjacent base-to-home mobile interference and adjacent mobile-to-home base interference; it also has to battle additional adjacent base-to-home base interference, and adjacent mobile-to-home mobile interference. Therefore, TDD can only be used for small confined area systems. Code-division duplexing is an innovative solution that can eliminate all four kinds of interference: adjacent base-to-home mobile, adjacent mobile-to-home base, adjacent base-to-home base, and adjacent mobile-to-home mobile in cellular systems. Eliminating each of these types of interference makes CDD the most spectrum-efficient duplexing system. This article will elaborate on a set of smart codes that will make an efficient CDD system a reality.
