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Hemant Kr Rath, Abhijeet Bhorkar, Vishal Sharma Department of Electrical Engineering IIT-Bombay

Hemant Kr Rath, Abhijeet Bhorkar, Vishal Sharma Department of Electrical Engineering IIT-Bombay ICNGN-2006, IETE-Mumbai. An Opportunistic DRR (O-DRR) Uplink Scheduling Scheme for IEEE 802.16-based Broadband Wireless Networks. Introduction The Broadband Networks. Wire-line Broadband Access

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Hemant Kr Rath, Abhijeet Bhorkar, Vishal Sharma Department of Electrical Engineering IIT-Bombay

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  1. Hemant Kr Rath, Abhijeet Bhorkar, Vishal Sharma Department of Electrical Engineering IIT-Bombay ICNGN-2006, IETE-Mumbai An Opportunistic DRR (O-DRR) Uplink SchedulingScheme for IEEE 802.16-based BroadbandWireless Networks

  2. IntroductionThe Broadband Networks • Wire-line Broadband Access • Optical Fiber, DSL • Wireless Broadband Access • Using IEEE 802.16 Standard Services (known as WiMax) • Wire-line vs. Wireless • Fast Deployment • Dynamic Sharing of Bandwidth • Low Cost

  3. IEE 802.16-based NetworksThe Basics • Operating Frequency Band • 10-66 GHz • Line of Sight • Single carrier modulation • Insignificant Multi-path Propagation • Static • 2-11 GHz • Non Line of Sight Propagation • Significant Multi-path Propagation • Static/mobile • 25-28 MHz Bandwidth • 120 Mb/s Raw Data Rate

  4. IEE 802.16-based NetworksOperation • Multipoint-to-multipoint • Mesh network • Point-to-multipoint • One Base Station (BS) connected to the core network and multiple Subscriber Stations (SS) • BS Polls the SSs before allocating resources (slots) • DAMA-TDMA based system • Each Frame is divided into 2-parts • Uplink and Downlink sub-frame • Requests and grant mechanism • SS sends its requests during the control slots of the uplink sub-frame • Slot grants are communicated to SSs during control slots in the downlink sub-frame Requests Grants

  5. Open Issues in WiMax Networks Scheduling • Scheduling in both uplink and downlink are open • In the downlink, the scheduling is easier • In the uplink, scheduling is difficult • BS does not have the information of queues of all SSs • The channel between the BS and SS are varying • WiMax is not a work conserving scheme • Scheduling algorithms of wireline/wireless network are not usable We suggest a polling-based O-DRR scheduling scheme

  6. O-DRR SchedulingChoosing Polling interval ‘k’ • The polling interval ‘k’ is a function of • Delay requirement, Fairness measure and Efficiency of the system • As ‘k’ increases • System becomes more efficient, but it is less fair • May not satisfy delay requirements • Service provider should select a ‘k’ • Optimum for a set of relative fairness and delay • Both efficiency and fairness are balanced • ‘k’ can be different for different set of traffic classes • Should we go for a single 'k' or multiple 'k'?

  7. O-DRR SchedulingOperation of O-DRR • DRR Scheduling • For a particular ‘k’, at the polling instant • BS checks the SINR of all the SSs and finds schedulable users • Called as eligible set (Channel and Active Queue) • The eligilble set is fixed for ‘k’ frames • After ‘k’ frame, BS again finds out the new eligible set • Assumption • channel is static during a frame • For each subsequent frame in the scheduling epoch • BS schedules, using Opportunistic Deficit Round Robin • The membership of the schedulable set changes dynamically from frame to frame during a scheduling epoch • BS schedules an SS, iff it is in the eligible set and it's SINR is more than the threshold

  8. O-DRR SchedulingBandwidth assignment in O-DRR • The O-DRR scheduling algorithm runs at the BS • BS allocates slots to SSs in a deficit round robin fashion • Based on the net allocation of slots, we mark the SSs as lagging/leading • The scheduling process is opportunistic, as the BS assigns slots in an opportunistic manner

  9. O-DRR SchedulingThe Algorithm • Uplink Scheduling using DRR • If SINR < SINR_th • Check for connectivity • If “connected” • Mark as “lagging” and assign its BW to other “Leading” flows • Continuously Monitor the status • When SINR > SINR_th • Re-mark as “leading” and assign more BW • Take the slots of previous “leading” flows • Provides Dynamic Slot Allocation

  10. ExperimentWith k=1, k=20

  11. ExperimentWith k=50 Jain's Fairness Index

  12. Discussion • The Scheduling is done in the MAC layer • It is a cross layer scheduling involving PHY and MAC layer • Jain's Fairness index remains above 90% for various ‘k’ • It is possible to tradeoff fairness for delay • O-DRR ensures delay requirements of users • Single class of traffic • For multi-class traffic some modification in the scheduling process needs be done

  13. Future Work • Analysis and Simulation for multi-class traffic • With same ‘k’ and different ‘k’ • Packet drop analysis for delay sensitive traffic • Multi-rate users (SSs) based on channel condition • For a particular channel condition SS needs to select a particular modulation scheme and hence a data rate • Needs modification in the scheduling scheme

  14. Thanks

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