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CDMA truy cập và chuyển mạch P7

Network Access and Synchronization Overview As we have described in Chapters 3 and 6, the SS/CDMA uses orthogonal CDMA in both uplink and downlink. The orthogonal CDMA can reject the interference between the user traffic channels and thus maximize the system capacity. However, the use of orthogonal CDMA in the uplink requires a network-wide synchronization of all satellite receptions (global synchronization). The accuracy of the synchronization at steadystate and the speed at which synchronization is acquired depends on the propagation environment, i.e. the channel condition, the mobility of the end user, the propagation delay, etc | 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 7 Network Access and Synchronization 7.1 Overview As we have described in Chapters 3 and 6 the SS CDMA uses orthogonal CDMA in both uplink and downlink. The orthogonal CDMA can reject the interference between the user traffic channels and thus maximize the system capacity. However the use of orthogonal CDMA in the uplink requires a network-wide synchronization of all satellite receptions global synchronization . The accuracy of the synchronization at steadystate and the speed at which synchronization is acquired depends on the propagation environment i.e. the channel condition the mobility of the end user the propagation delay etc. There are several examples in which synchronous CDMA orthogonal or quasi-orhtogonal attempted for use in the uplink or inbound channel. One such example is presented in reference 1 in which synchronous CDMA is proposed for mobile satellite applications. In another example presented in reference 2 orthogonal CDMA is recommended for the inbound and outbound links in terrestrial wireless applications. In this reference it is also shown by simulation that the required synchronization jitter from a reference time should not exceed 10 of the chip length for orthogonal CDMA operation. This result has also been verified analytically in Chapter 2. Such a requirement can be achieved easily if the CDMA system has a relatively narrow band and low user mobility. The system presented in reference 3 has a chip rate of 0.65 Mc s or a chip length of Tc 1.538 s corresponding to a propagation distance of 460 meters and the cell radious is 230 meters. The synchronization subsystem to meet the above requirement may then be simple. On the other hand a wideband orthogonal CDMA requires a substantial effort in acquiring and maintainingsynchronization especially in a .