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Traffic Analysis and Design of Wireless IP Networks phần 7

để hỗ trợ một số lượng lớn các dòng vào một liên kết tốc độ cao. Chúng tôi có thể tìm thấy một số thay đổi khác nhau để WFQ. Ví dụ, WFQ dựa trên lớp giao các gói dữ liệu đến hàng đợi dựa trên phân loại gói dữ liệu người dùng định nghĩa (ví dụ, bằng cách sử dụng bit ToS IP). | Analytical Analysis of Multimedia Mobile Networks 213 Ah h c 7.39 where the new call rate a c and handover rate h c are given by 7.35 and 7.33 respectively. State departure rate ft can be calculated according to 4.119 that is ft ftc fth where ftc and fth are the call completion rate in the cell and the call handover rate to the neighboring cells respectively. By solving the Markov state diagram by using birth-death processes 5 we can calculate call-dropping probability. For that purpose we need to obtain the handover-blocking probability. Blocking of a handover happens when all logical channels at the target cell are busy or the number of idle channels is less than the bandwidth requirements for that call . Hence handover-blocking probability equals the probability that the system is in state C as shown in Figure 7.2. The total offered traffic in Erlangs to a cell is A A ft while A2 A iJft is the handover traffic in Erlangs. From the Markov chain we obtain the steadystate probabilities P j A7P 0 j Ac Afc A p 0 j j c 1 7.40 0 j c 1 Using 7.40 we can calculate the probability P 0 that is the probability that there are no allocated channels in the cell. Then we can obtain the probability that the system i.e. the cell has allocated j channels by P j 1 y A y Ac A2 i 0 i i c 1 i Ac A2-c j c i y A y i 0 Ỉ i c 1 C Ac A2 0 j c j c 1 7.41 Handover-blocking probability is equal to the probability that all logical channels in the cell are busy. Therefore it is given by Ac ACC -c PFh C c C y A .ỉ i c Ac A2 7.42 i 0 214 Traffic Analysis and Design of Wireless IP Networks If we use the above relation to calculate PFh we can calculate the calldropping probability PD by using 7.14 . New call blocking probability is C Pb i P j j c C i j c Ac A2-c j c_ C i A S Ac A2 7.43 i 0 1 In a special case when A A2 7.43 becomes the Erlang-B formula which is widely used in the dimensioning of telecommunication networks refer to Chapter 4 . The explanation of this phenomenon is simple. If we do .