A most spectrum-efficient duplexing system: CDD
For increasing spectrum efficiency in telecommunication , we have to eliminate interference. At present, all cellular systems use FDD (Frequency Division Duplexing) in an attempt to eliminate the interference from the adjacent cells. But the adjacent base-tohome mobile interference still remains unsolved. the adjacent base-to-home mobile interference, the additional adjacent base-to-home base interference, and adjacent mobile-to-home mobile interference restricts the use of TDD (Time Division Duplexing). CDD (Code Division Duplexing) can eliminate all three kinds of interference; the adjacent base-to-home mobile, the adjacent baseto-home base, and the adjacent mobile- to- home in cellular systems. Thus it becomes the most spectrum efficient duplexing system.

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Methods and apparatus for wireless communication using code division duplex time-slotted CDMA
In a first technique in accordance with the invention, referred to as code division duplex (CDD) time-slotted CDMA, uplink and downlink portions of the system are separated using code division duplexing as well as the the users within a given cell are also separated using codes. Both the CDD and TDD techniques may make use of an electronically-steered beam . This is being designed to provide simultaneous coverage within a given cell for two or more users separated by codes.in accordance with the invention, referred to as orthogonal frequency division multiplexing (OFDM), uplink and downlink portions of the system are separated in frequency.
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