tailieunhanh - Quality of Service and Resource Allocation in WiMAXFig Part 9

Tham khảo tài liệu 'quality of service and resource allocation in wimaxfig part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | A Unified Performance Model for Best-Effort Services in WiMAX Networks 191 28 29 30 6. Saturated networks As defined in Section 1 saturated networks mean that each SS always has a packet to send. In other words p 1. Hence the outer set in Fig. 2 is not required for the saturation case and 3 becomes T 1 Bavg 1 27 Meanwhile the case S0 in Section 3 does not exist. Therefore the service time of an REQ X is equal to Y. For the same reason the service time of an successful REQ X is equal to Y . Obviously there is no need to calculate the waiting time in the queue of an REQ for saturated networks. So the delay of a packet can be changed to packet access delay as the time duration from the beginning of the request interval in which a request initiates the TBEB process till the end of the transmission of the packet which is given by Dsat Y Tre V. So the Laplace-Stieltjes transform of Dsat can be written as LDsat s Ly s Lv s e-sTRE. And the normalized network throughput for saturated works is given by _ _ự 1 jQ j Lj d 1 dQ j r sat d In order to verify this degenerated model for the saturated network the mean and variance of packet access delay and throughput against N with different W are plotted as Fig. 7 a to Fig. 7 c . It can be seen that the analytical and simulation results again match very well. 7. Conclusion In this chapter we have developed a unified performance model to evaluate the performances of the contention-based services in both saturated and unsaturated IEEE networks. Different from some related works which assume that the probability of an SS sending a bandwidth request is an input parameter our model takes into account the details of the backoff process to evaluate this probability. By solving two nested sets of fixed point equations we have obtained the failure probability of a bandwidth request and the probability that a subscriber station has at least one REQ to transmit. Based on these two probabilities the network throughput and the .