In Chapter 2, we have shown how to increase the degree of spectral reuse in an IEEE 802.16 mesh network. An integrated spectral reuse framework for centralized scheduling and a rout-ing tree construction scheme are developed. Compared to previous works, our framework is most complete in exploiting spectral reuse of IEEE 802.16 mesh networks in the sense that it takes dynamic traffic loads of SSs into account and integrates not only a bandwidth schedul-ing scheme but also a time-slot allocation scheme. In addition, a routschedul-ing algorithm with tree optimization is proposed. We have also developed an extension of our framework to support bandwidth requirements of real-time flows. Simulation results have shown that the proposed framework significantly improves the network throughput and the flow granted ratio compared with the specification in the IEEE 802.16 standard.
In Chapter 3, we have shown how to formulate the throughput given a path in which hosts roam around in a random walk model and the communication interfaces have the rate adaptive capability. As far as we know, this issue has not been carefully studied yet. Simulation results show that the proposed formulation can be used to evaluate path throughput accurately. We believe that the path throughput is a better metric than the traditional metrics, such as the hop count, for route selection in multi-rate ad hoc networks and that the proposed mechanism can be easily embedded into most of the current routing protocols for mobile ad hoc networks.
In Chapter 4, we have studied two contention-based request schemes for BE traffics in
IEEE 802.16 networks, which are heavily affecting the performance of BWA systems. Ana-lytical and simulation results show that our proposed scheme can significantly release request slot contention and efficiently minimize packet delivery delay. In particular, our investigation is useful for evolving a better request/grant mechanism for IEEE 802.16 networks.
Based on the results presented above, several directions may deserve further investiga-tion. First, more QoS factors of real-time flows such as delay constraints and jitters could be considered in the slot assignment strategy [41]. Second, flow differentiation rater than flow prioritization could be considered in the bandwidth allocation scheme to prevent non-real-time flows from starvation. Third, multi-path routing and distributed scheduling could be consid-ered to provide better performance. Finally, the limitation that a slot is only exclusively used for uplink or downlink throughout the whole network could be relaxed for better bandwidth efficiency.
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