Tham khảo tài liệu 'recent advances in wireless communications and networks part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 230 Recent Advances in Wireless Communications and Networks handovers executed by the mobile node . nVHO . In the following we shall describe the overall mechanism in more details. Given a video application the QoS mapping process is accomplished by considering the relative prioritized packets to maximize end-to-end video quality. In the measurement phase each T seconds the MN gets samples of RSS and position as well as monitors Lev parameter for the video stream received from the current serving network. QoS monitoring is performed on the basis of the NR metrics1. In our scope NR technique addresses on audio and video flows evaluations to the receiver side although it could be also tuned and optimized by means of a full-reference metric applied to some low rate probe signals. In the QoS prioritization phase the probability to perform a handover is evaluated . PVHo . By opportunistically weighting the QoS-Lev parameter the handover probability will be mainly driven by QoS factors. The received video-streaming quality is monitored according to a subjective evaluation. On the basis of user preferences two appropriate QoS thresholds are defined called as Th1 and Th2 with Th1 Th2. Input RSS d Lev Output nVHO while T 0 do Measurement phase in SN if Lev Thi then First alarm to QDE QoS priorization phase Calculation of Pr - x VHO end Candidate network scanning phase List of target networks if Lev Th2 then Handoff initiation phase VQM Conversion phase Selection of a target network nVHO 1 VHO executed end end end end else I nVHO 0 no VHO executed end end Fig. 4. Multi-parameter QoS-based vertical handover pseudo-code 1 NR method presents some basic indicators for temporal and spatial analysis block distortion is evaluated by applying first a coarse temporal analysis for each frame to extract blocks potentially affected by artefacts produced by lost packets. Connectivity Support in Heterogeneous Wireless Networks 231 Traffic congestions transmission errors lost packets
