tailieunhanh - Mobile and wireless communications network layer and circuit level design Part 2

Tham khảo tài liệu 'mobile and wireless communications network layer and circuit level design part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Call Admission Control in Mobile and Wireless Networks 21 total revenue obtained while in Sherif Habib Nagshineh Kermani 2000 an adaptive resource allocation scheme is proposed to maximize bandwidth utilization and attempt to provide fairness with a generic algorithm. In general when a call arrives in a certain cell the network may either have enough resources to provide bandwidth between the minimum and the maximum demand or be congested that is it cannot provide the minimum bandwidth requested by the new call. In the first case the call is admitted whereas in the second bandwidth adaptation CAC algorithms also known as rate-adaptive schemes are applied to determine an optimal resource allocation aiming at serving as many users as possible while reducing the admission failure probability. This is accomplished by reducing the rate of some users when possible as much as required to accommodate the new call. In some bandwidth adaptation CAC schemes this procedure is followed only for handoff or for call requests of high priority SCs Tragos Tsiropoulos Karetsos Kyriazakos 2008 Lindemann Lohmann Thummler 2004 . However it should be mentioned that user rates cannot be reduced below the minimum rate values required to assure QoS thus when all users operate at their lowest bandwidth requirement a new call request will be rejected. Rate degradation may be enforced according to a prioritization or to a non-prioritization scheme. In the former the rate degradation policy is first applied to the SC calls of the lowest priority. If the resources released are still not sufficient for the admission of a new call the calls of the next priority level are examined. In the non-prioritization schemes all calls served with higher rates than their minimum bandwidth demand reduce their rate to admit the call request. A useful metric in QoS renegotiation CAC schemes is the degradation ratio which is defined as the ratio of the number of degraded calls to the number of ongoing calls Kwon