1. Rahul Jain Advisor: Dr. Bhaskaran Raman IIT Bombay. Comprehensive Evaluation of The SIR-Based Interference Mapping Strategy

2. Wireless Mesh Network (WMN)  Self tuned and self organized network of “Mesh routers” & “Mesh client”.  Provide low cost broadband internet access to static or mobile hosts. Source: http://research.microsoft.com/mesh/

3. Issue with TDMA WMNs Less throughput How to improve throughput of TDMA WMN ? Parallelism Enabling simultaneous transmissions of packets at multiple sender-receiver pairs.

4. Parallelism is fundamentally limited by interference

5. Cause of Interference 1. Wifi interferers  These are interferers (usually include other 802.11 nodes) that transmit in the same band and in the same physical area. 2. Non-wifi interferers  These are interferers (Bluetooth nodes, Microwave ovens) that transmit in the same band and same area.

6. Type of Interference

7.  Carrier sense (Sending) Interference  Hidden terminal (Receiving) Interference  Multi-way Interference

8. Carrier sense (Sending) Interference

9. Hidden terminal (Receiving) Interference

10. Multi-way Interference

11. Effect of interference  Capacity of wireless network.  Routing protocol.  Optimal channel assignment.  Packet scheduling (knowledge of interference needed in Order to schedule transmission in the network to achieve fairness).

12. Problem Statement 1. Comprehensive evaluation of the SIR-based interference mapping strategy, on an outdoor mesh network. 2. Evaluating the usefulness of interference information is in practice, for TDMA scheduling, or link channel selection. i. As an extension to [6] work.

13. Pradeep’s work [6] In [6] Pradeep et al. presented study of pair-wise interference and proposed a SIR metric for automated estimation of interference for 802.11b Wireless Mesh Networks. [6] evaluated their metric in a 3-node out-door mesh network. We will evaluate SIR metric in a wireless TDMA 802.11a/g based outdoor mesh network.

14. Existing Work 1. J. Padhye, S. Agarwal, V. N. Padmanabhan, L. Qiu, A.Rao, and B.Zill. “Estimation of Link Interference in Static Multi- hop Wireless Network,” In Proceedings of IMC, 2005. 2. S. M. Das, D. Koutsonikolas, Y. C. Hu, and D. Peroulis. “Characterizing Multi-Way Interference in Wireless Mesh Networks,” in WiNTECH, Sep 2006. 3. C. Reis, R. Mahajan, M. Rodrig, D. Wetherall, and J. Zahorjan, “Measurement-Based Models of Delivery and Interference in Static Wireless Networks,” in ACM SIGCOMM, Sep 2006

15. Existing Work 4. A. Kashyap, S. Ganguly, and S. Das, “A Measurement- Based Approach to Modeling link capacity in 802.11- based Wireless Networks,” in ACM MOBICOM, Sep 2007. 5. Dragos Niculescu, “Interference Map for 802.11 Network,” in IMC, Oct 2007. 6. Pradeep Gopaluni, Mtech thesis “A Study of Pair-Wise Interferenceand Automated estimation of interference for 802.11b Wireless MeshNetworks”, Dept of Computer Science, IIT Kanpur, July 2008.

16. Our work  All previous work consider only indoor environment, but [6] and our work will focus on outdoor environment.  We will use SIR-based interference mapping strategy, in contrast to [1], [2] and [4].  [1], [2], [5] did experiments for 802.11a, [4] did experiments for both 802.11a and 802.11b, [6] did experiments for 802.11b, we will verify for 802.11 a/b/g.

17. Our work  Target network need O(n 2 ) measurement steps in [1], [2], [5], but our work, [6] and [4] requires O(n) steps.  [1], [2], [4] provides model to estimate interference but [5] and our work extract useful information to build interference map in order to perform TDMA scheduling, channel assignment and routing.  [1], [2], [4], [5] and [6] performed experiments in CSMA network, we will perform experiments in TDMA mesh network.

18. SIR-based Mapping scheme  There exists strong correlation between the received signal strength at a particular receiver from different senders and the amount of interference that each of them exerts upon the other.  Signal to Interference ratio (SIR) is practically the difference between the sender and receiver RSSI in dBm.  Due to Variability of RSSI[8], SIR can be determined by taking discrete convolutions [6].

19. Interference Map  Collection of data structures, map contains delivery ratio matrix, carrier sense matrix and hidden terminal matrix.  Used for Channel Assignment, Routing and Scheduling links in a WMN.  Periodic re-generation possible that  Reflect changes in network.  Reflect changes in interference pattern.

20. Solution approach

21. Proposed Campus Test-bed Source: google earth

22. Experiments

23. Calibration of the devices  Experiments to identify “Variability” in live wireless network.  Calibrate the card’s transmit power using an RF power meter to verify that offered power range is same as observed.  Experiments to identify dependency of interference on specific hardware.

24. Which link to use ?  Network with n number of nodes, have O(n 2 ) links. In practice all links does not exists either they have no connectivity or packet loss rate is very high.  Consider link (L AB ), between two nodes A, B. A transmits alone for 30 seconds, while B listening and vice-versa, this data gives us packet loss between link (L AB ) and (L BA ) respectively (P AB ) and (P AB ), than we will use ETX [8] metric to determine the existence of the link.

25. SIR calculation  SIR is practically the difference between the sender and receiver RSSI in dBm.  Due to Variability of RSSI [8], SIR can be determined by taking discrete convolutions [6]. P x = RSSI distribution of x node P y = RSSI distribution of y node K = RSSI value

26. Work done so far  Technical Reading Interference Mapping strategy  Common Exercise we have installed different version of Linux kernel (linux- 2.4.20.19, linux-2.4.25.4) on to soekris. We made some modification to madwifi(madwifi-0.9.4) code to make it suitable for: Get per packet level statistics Disabling acknowledgement and back-offs

27. Timeline for Stage - II  Establishment of proposed test-bed  Calibration of devices (control experiments)  Identifying Links  SIR-calculation for 802.11a/g based TDMA mesh network  Building data-structures for interference map delivery ratio matrix & hidden terminal matrix.

28. Thank you

29. References 1. J. Padhye, S. Agarwal, V. N. Padmanabhan, L. Qiu, A.Rao, and B.Zill. “Estimation of Link Interference in Static Multi- hop Wireless Network,” In Proceedings of IMC, 2005. 2. S. M. Das, D. Koutsonikolas, Y. C. Hu, and D. Peroulis. “Characterizing Multi-Way Interference in Wireless Mesh Networks,” in WiNTECH, Sep 2006. 3. C. Reis, R. Mahajan, M. Rodrig, D. Wetherall, and J. Zahorjan, “Measurement-Based Models of Delivery and Interference in Static Wireless Networks,” in ACM SIGCOMM, Sep 2006.

30. References 4. A. Kashyap, S. Ganguly, and S. Das, “A Measurement-Based Approach to Modeling link capacity in 802.11-based Wireless Networks,” in ACM MOBICOM, Sep 2007. 5. Dragos Niculescu, “Interference Map for 802.11 Network,” in IMC, Oct2007. 6. D. S. J. D. Couto, D. Aguayo, J. C. Bicket, and R. Morris. A high throughput path metric for multi-hop wireless routing. In Proc. of ACM MobiCom, 2003.

31. References 7. Dattatraya Gokhale, Sayandeep Sen, Kameswari Chebrolu, and Bhaskaran Raman, “On the Feasibility of the Link Abstraction in (Rural) Mesh Networks,” in The 25th Annual Conference on Computer Communications (IEEE INFOCOM), Phoenix, Arizona (USA), April 2008. 8. Pradeep Gopaluni, Mtech thesis “A Study of Pair-Wise Interference and Automated estimation of interference for 802.11b Wireless Mesh Networks”, Dept of Computer Science, IIT Kanpur, July 2008.

32. Our work  We will evaluate SIR metric in a wireless TDMA 802.11a/g based outdoor mesh network.  We will use information about interference to build a Interference Map, that will help in TDMA scheduling, routing etc

33. Experiments  Calibration of the devices  Which link to use ?  SIR calculation  Building Interference Map