tailieunhanh - CDMA truy cập và chuyển mạch P1

Introduction One of the basic concepts in communication is the idea of allowing several transmitters to send information simultaneously over a communication channel. This concept is described by the terms multiple access and multiplexing. The term multiple access is used when the transmitting sources are not co-located, but operate autonomously as a multipoint-to-point network, while when the transmitting sources are co-located, as in a point-to-multipoint network, we use the term multiplexing. . | CDMA Access and Switching For Terrestrial and Satellite Networks Diakoumis Gerakoulis Evaggelos Geraniotis Copyright 2001 John Wiley Sons Ltd ISBNs 0-471-49184-5 Hardback 0-470-84169-9 Electronic 1 The Generalized CDMA Introduction One of the basic concepts in communication is the idea of allowing so votail i E i t ni f i s to send information simultaneously over a communication channel. This concept is described by the terms multiple access and multiplexing. The term multiple access is used when the transmitting sources are not colocated but potatto autonomously as a multipoint-to-point network while when the transmitting sources are codocated as in a point-to-multipoint network we use the term multiplexing. There are several techniques for providing multiple aceess ad mult plexirig wliicli bolorig to one ot two basic categories the orthogonal and the pseudo-orthogonal PO division multiple accesses. In orthogonal multiple access the communication channel is divided into sub-channels or user channels which are mutually orthogonal . are not interfering with each other. In pseudo-orthogonal multiple access on the other hand there is interference between user channels since they are not perfectly orthogonal to each other. The traditional Time Division and Frequency Division Multiple Access methods TDMA and FDMA as well as the Orthogonal Code Division Multiple Access O-CDMA are orthogonal multiple accesses while the conventional asynchronous CDMA is a pseudo-orthogonal multiple access. Orthogonal division multiple access is achieved by assigning an orthogonal code or sequence to each accessing user ortllogoual co Se-so iuoucoo are presented in Chapter 2 . Orthogonal sequences provide complete isolation between user channels. However they require synchronization so that all transmissions arrive at the receiver at a given reference time global synchronization . Pseudo-orthogonal multiple accesses such as the asynchronous CDMA are implemented with pseudo-random .