Providing protocol adaptation in CDMA ATM wireless local loop
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The goal of this thesis is to provide a design alternative to the user-plane wireless protocols of wireless asynchronous transfer mode (WATM) by making use of a flexible multiple access scheme, multieode direct-sequence code division multiple access (MC-CDMA). On a radio link, supporting multimedia applications with WATM demand additional requirements that are not present in wired ATM networks. In order to meet these requirements, we need improved communication technology, high computing speed, and an efficient and robust communication protocol. Protocol design is a fundamental issue in communication applications. A distributed implementation of such applications is derived from a given functional specification of the overall system. The design starts from a specification of the target system in textual form and is manually broken down into a set of functional blocks. After the functional decomposition, the communication protocol that interacts among these blocks is defined. Integrating heterogeneous traffic in a wireless environment is a major issue that needs to be resolved before wireless ATM technology can be realized. Moreover, the unstable wireless link and the mobile environment cause the radio link to be less reliable and constantly varying. These conditions demand the wireless protocols to be robust, efficient, and flexible. This thesis provides a design alternative for the wireless protocols of WATM that can operate over a multicode CDMA substrate. In the implementation of this thesis, CDMA channels are simulated to operate simultaneously, three of them carrying traffic of different traffic classes in forward direction and a feedback channel carrying traffic in the reverse direction from the receiver. The performances of these channels are tabulated. The feedback from the receiver is used to update a global table that maintains updated radio link conditions. The transmitting applications and transmitter side protocol layers can refer to link conditions in the status table in order to adapt their operations to suit the wireless environment prevailing at that point of time. Appropriate adaptations that can promote multimedia applications are performed. The underlying idea in providing adaptation is that the user can compromise a brief quality degradation rather than cause an abrupt shutdown of the service. The simulation results and the adaptation effects on the user experience are presented in later chapters. Experimental results are very encouraging and show that supporting multimedia applications on wireless devices is not too far from reality.