1. HR/AB/VS, IIT-Bombay 1 Feb 8, 2006 An Opportunistic DRR (O-DRR) Uplink Scheduling Scheme for IEEE 802.16-based Broadband Wireless Networks Hemant Kr Rath, Abhijeet Bhorkar, Vishal Sharma Department of Electrical Engineering IIT-Bombay ICNGN-2006, IETE-Mumbai

2. HR/AB/VS, IIT-Bombay 2 Feb 8, 2006 Introduction The 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. HR/AB/VS, IIT-Bombay 3 Feb 8, 2006 IEE 802.16-based Networks The 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. HR/AB/VS, IIT-Bombay 4 Feb 8, 2006 IEE 802.16-based Networks Operation 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. HR/AB/VS, IIT-Bombay 5 Feb 8, 2006 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. HR/AB/VS, IIT-Bombay 6 Feb 8, 2006 O-DRR Scheduling Choosing 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. HR/AB/VS, IIT-Bombay 7 Feb 8, 2006 O-DRR Scheduling Operation 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. HR/AB/VS, IIT-Bombay 8 Feb 8, 2006 O-DRR Scheduling Bandwidth 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. HR/AB/VS, IIT-Bombay 9 Feb 8, 2006 O-DRR Scheduling The 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. HR/AB/VS, IIT-Bombay 10 Feb 8, 2006 Experiment With k=1, k=20

11. HR/AB/VS, IIT-Bombay 11 Feb 8, 2006 Experiment With k=50 Jain's Fairness Index

12. HR/AB/VS, IIT-Bombay 12 Feb 8, 2006 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. HR/AB/VS, IIT-Bombay 13 Feb 8, 2006 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. HR/AB/VS, IIT-Bombay 14 Feb 8, 2006 Thanks