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A Cross-Layer Scheduling Algorithm With QoS Support in Wireless Networks Qingwen Liu, Student Member, IEEE, Xin Wang, Member, IEEE, and Georgios B. Giannakis, Fellow, IEEE IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 55, NO. 3, MAY 2006 報告者：李宗穎 1 Outline • • • • • Introduction System Architecture Scheduler Design Simulation Conclusion 2 Introduction • 802.11, 802.16, and 802.15 networks support multimedia services with different QoS requirement • channel capacity in wireless networks is time varying due to multipath fading • Paper define a priority function (PRF) depend on the 1) wireless channel quality, 2) QoS satisfaction, and 3) service priority across layers 3 Network Configuration • Star topology is also used to describe the connections between each relay station and multiple SS in mobile ad hoc networks and wireless sensor networks 4 Wireless link from BS to SS • A buffer is implemented at the BS for each connection and operates in a FIFO mode • The AMC (Adaptive Modulation and Coding) controller follows the buffer at the BS 5 • AMC selector is implemented at the SS Transmission modes in the IEEE 802.16 Standard • At the MAC, each packet is mapped to a symbol block containing Nb/Rn symbols • At the PHY, each frame is divided into Nc + Nd time slots 6 Processing units at MAC and PHY 7 QoS Architecture at the MAC • Unsolicited grant service (UGS) EX: VoIP… • Real-time polling service (rtPS) EX: MPEG video and video stream… • Nonreal-time polling service (nrtPS) EX: FTP… • Best effort (BE) EX: HTTP、Email… 8 AMC Design at the PHY • To simplify the AMC design, paper approximate the PER expression in AWGN channels • AMC design guarantees that the PER (Packet Error Rate) is less than or equal to P0 9 Scheduling UGS Connections • The AMC design is not adopted for UGS Nr = Nd – NUGS Nr：availability time slot Nd：all time slot to transmit data NUGS：UGS connections time slot 10 Scheduling rtPS Connections • Fi(t) is the delay satisfaction indicator Fi(t) = Ti − ΔTi −Wi(t) + 1 Ti = maximum latency ΔTi = guard time region Wi(t) = longest packet waiting time • ψi(t) is the PRF for connection i at time t 11 Scheduling nrtPS Connections • Fi(t) is the rate satisfaction indicator ηi(t) = average rate at time t ηi = minimum reserved rate • ψi(t) is the PRF for connection i at time t 12 Scheduling BE Connections • ψi(t) is the PRF for connection i at time t • The priority of QoS classes is rtPS > nrtPS > BE βrtPS > βnrtPS > βBE 13 Desirable Features • Efficient bandwidth utilization • Delay bound Ti is provided for rtPS connections • Throughput is guaranteed for nrtPS connections • Implementation complexity is low • Flexibility is provided • Scalability is achieved 14 Simulation Parameter Setting The frame length is Tf = 1ms Packet length at the MAC is fixed to Nb = 128bytes Simulation time = 60000ms MAX delay MIN Thoughput PER SNR β rtPS-1 30ms 2Mbps 0.01 15dB 1.0 rtPS-2 50ms 1Mbps 0.01 20dB 1.0 nrtPS-1 - 6Mbps 0.001 15dB 0.8 nrtPS-2 - 3Mbps 0.001 20dB 0.8 BE-1 - - 0.001 16dB 0.6 BE-2 - - 0.001 18dB 0.6 15 Result Nr=3 rtPS nrtPS BE 16 Result Nr=2 rtPS nrtPS BE 17 Result Nr=1 rtPS nrtPS BE 18 Conclusions • Paper developed a cross-layer scheduling algorithm at the MAC layer for multiple connections with diverse QoS requirements • Future works, scheduling multiple connections each time may lead to better performance 19