1. DARP: Distance-Aware Relay Placement in WiMAX Mesh Networks Weiyi Zhang *, Shi Bai *, Guoliang Xue §, Jian Tang †, Chonggang Wang ‡ * Department of Computer Science, North Dakota State University, Fargo § Department of Computer Science and Engineering, Arizona State University, Tempe † Department of Electrical Engineering and Computer Science, Syracuse University, Syracuse ‡ NEC Laboratories America, Princeton, USA IEEE INFOCOM 2011

2. Outline Introduction Motivation & Problem Observation & Goals System Model Solution for DARP: Distance-Aware Relay station Placement –LORC-MIS // lower tier –LORC-HS // lower tier –MUST // upper tier Simulation Conclusion

3. Introduction The emerging WiMAX technology is the 4G standard for –high-speed (up to 75Mbps) –long-range communications BS SS

4. Introduction IEEE 802.16j enhances IEEE 802.16e by the concept of mesh networks –Base Station (BS) –Relay Station (RS) –Subscriber Station (SS) BS RS SS RS SS

5. WiMAX 802.16j Relay Station –eliminate coverage hole –Range extension Introduction Internet Coverage Extension Coverage Hole Mobile Access Building Penetration SS RS BS RS SS

6. n Subscriber Stations (SS) –different user data rate requests Problem: –finding where to place a minimum number of relay nodes –to satisfy the certain performance requests Motivation SS BS SS

7. Observation – distance aware Signal to noise ratio (SNR) at receiver –SNR r = P r / N 0 –P r : power level at the receiver –N 0 : noise power is normally a constant SS user data rate requests: 35 Mbps

8. Observation – distance aware Two-ray ground path loss model –P r = P t G t G r H t 2 H r 2 d -  –P t : Transmission power (constant) –G t / G r : gains of transmitter/receiver antenna (constant) –H t /H r : heights of transmitter/receiver antenna (constant) –d : Euclidean distance between transmitter and receiver –  : attenuation factor (constant : 2~4) SS higher data rate requestlower data rate request

9. Goals Given a WiMAX mesh network –One BS –A set of SSs, S = {s 1, s 2, …, S n } –A set of distance requirements for the SSs, D = {d 1, d 2, …, d n } SS BS SS

10. Goals Solve the distance-aware relay placement (DARP) problem by a minimum number of RSs –Providing feasible coverage for each SS covered by at least one RS or BS –Each placed RS has enough data rate to relay traffic for each SS or another RS SS BS 25 Mbps RS  25 Mbps

11. System Model A WiMAX mesh network –n SSs, S = {s 1, s 2, …, S n } Distance requirements D = {d 1, d 2, …, d n } No routing and traffic relay capabilities –BS, is aware of the location and distance requirement of each SS SS BS SS

12. Solution for DARP problem Two-tiered relay model SS BS RS lower tier upper tier LORC-MIS LORC-HS MUST

13. LORC-MIS –LOwer-tier Relay Coverage – Maximal Independent Set based approximation solution SS lower tier

14. LORC-MIS First consider the SS with the smallest distance requirement –Highest user data rate requirement 1 2 3 4 5 C4C4 C5C5 C3C3 C1C1 C2C2 d2d2 d1d1 d3d3 d4d4 d5d5

15. LORC-MIS Construct a regular hexagon with 7 possible positions S2S2 d2d2 d

16. LORC-MIS Choose the point which covers most SSs S2S2 S5S5 S1S1 S4S4 S3S3

17. LORC-HS –LOwer-tier Relay Coverage – Hitting Set based approximation solution LORC-HS SS lower tier

18. LORC-HS Find the Minimum hitting set –to cover all SSs // {p 0, p 2 } –admits PTAS [18] s2s2 s1s1 s3s3 p3p3 p1p1 p0p0 p7p7 p6p6 p2p2 p4p4 p5p5 s0s0 S 0 ={p 0, p 1 } S 1 ={p 0, p 1, p 2, p 3, p 4, p 5, p 7 } S 2 ={p 2, p 3, p 4, p 5, p 6 } S 3 ={p 2, p 4, p 5, p 6, p 7 } [18] N. Mustafa and S. Ray, PTAS for geometric hitting set problems via local search, SCG’09, pp. 17-22.

19. MUST Minimum Upper-tier Steiner Tree upper tier BS RS

20. MUST The “MUST” ensures data rate for each individual SS or RS RS 3 RS 1 RS 2 BS A B C 15 16 18

21. MUST Construct a complete graph Assign edge weight w –Number of RSs RS 1 RS 2 BS d 1 =10 w=3 d 2 =5 10 2021 16 5 w=4 w=3

22. MUST Minimum spanning tree RS 1 RS 2 BS d1=5d1=5 w=3 d 2 =5 20 16 w=3

23. MUST Place RSs on edges RS 1 RS 2 BS d1=5d1=5 w=3 d 2 =5 20 16 w=3 5 4 5 5 5 444

24. Simulation Setup SSs are uniformly distributed in a square playing ground –2000  2000 –3000  3000 Distance requirements randomly distributed in [100,150] BS is deployed at the center of the field All figures illustrate the average of 10 test runs for various scenarios

25. Simulation

26. Simulation – lower-tier relay coverage

27. Simulation – upper-tier relay connectivity

28. Simulation

30. Conclusion This paper studies the Distance-Aware Relay Placement (DARP) problem –Multi-hop relay placement –Relay coverage –Relay connectivity TheEND Thanks for your attention !