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Tham khảo tài liệu 'wimax, new developments 2011 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 290 WIMAX New Developments For rtPS and nrtPS connections when a new connection arrives the CAC module interacts with ARA in the DRA module and gets the current estimated bandwidth occupied by the ongoing rtPS and nrtPS connections ErtPS t and EnrtPS t which are the exponential moving average of ErtPS t and EnrtPS t mentioned in Eqn. 10 . If the sum of the estimated bandwidth used by the ongoing rtPS and nrtPS connections ErtPS t EnrtPS t and the estimated bandwidth to be used by the incoming connection ANrtPS or ANnrtPS is larger than a predefined upper threshold the incoming connection is rejected otherwise the connection is accepted with certain probability depending on the estimated bandwidth usage and the connection priority. Specifically when the estimated bandwidth occupancy is high or the priority of the incoming connection is low the acceptance probability is small and vice versa. A detailed description of the proposed CAC algorithm for rtPS connections is listed in pseudocode 3 where Ntmax and Ntmin are the maximum and minimum capacity threshold respectively and ErtPS 0 1 is a parameter that is used to differentiae class priorities. The same CAC algorithm is applied for nrtPS connections. Algorithm 3 Connection admission control algorithm for rtPS connections 1 if ErtPS t EnrtPS t ANrtPS Ntthax then 2 Reject the incoming connection 3 else if ErtPS t EnrtPS t ANrtPS Nfo then 4 Accept the incoming connection with probability prtPS 5 else 6 Accept the incoming connection with probability Nma _ ẼirtPS t ẼnrtPS t AN1rtPS ErtPS Nmax Nmin th th 7 end if For BE connections they are always accepted since they do not impose any QoS constraints. 6. Simulation Results and Discussions To evaluate the performance of the proposed downlink resource management framework for QoS scheduling in OFDMA based WiMAX networks a system-level simulation is performed in OPNET. 6.1 System Model We consider the downlink of a single-cell IEEE 802.16 system with OFDMA TDD operation. The
