Multiple access schemes for third-generation wireless networks.

摘要

This thesis addresses several link and network layers issues for third generation wireless communication systems. Although the problems originated from different situations, all of them share a common objective which is to maximize the throughput or capacity of the system. In addition, we try to guarantee different qualities of service to different traffic types and make the system flexible so that it can adapt to different situations, such as non-uniform traffic loads.; Firstly, the problem of joint admission and switching for a novel satellite switched code division multiple access (SS/CDMA) demand assignment system is considered. Three joint admission and switching schemes, namely optimum, sub-optimum and random schemes, are proposed. We find that in the CDMA satellite system we consider, close to optimum performance can be achieved by the low-complexity sub-optimal or random scheme. This translates into a 10% to 15% improvement in system capacity over a time division multiple access (TDMA) based system employing an algorithm with similar complexity.; Secondly, the power control problem of an overlaid/underlaid CDMA system for third generation wireless networks is investigated. The transmitted power and the transmission rate of the users in both the overlaid and underlaid systems are controlled so that the resultant interference is kept low enough that the two systems can coexist and the total capacity is increased. Through the overlaid/underlaid approach, we can guarantee a certain capacity or quality of service within a small neighborhood of an existing system. This can be used to, for example, alleviate the high traffic load in an urban area.; Thirdly, a multiple access protocol called packet reservation inhibit sense multiple access (PR-ISMA) is proposed to support short burst data service in third generation CDMA wireless communication systems. Three variants of the protocol are considered and their performances are compared with that of slotted Aloha. Numerical results show that the proposed scheme outperforms slotted Aloha which is being used in some of the second generation wireless personal communication systems (PCS) and presently considered for most third generation systems.; Finally, a new multiple access protocol called time reuse capture access (TRCA) is proposed which takes advantage of the burstiness of the traffic to provide a higher throughput than that can be achieved otherwise by a fixed allocation scheme. As a result, more resources (i.e. time slots) can be dynamically allocated to a cell with a higher traffic load or to a user that requires retransmissions to provide a more reliable communication link.