1. College of Engineering Optimal Access Point Selection and Channel Assignment in IEEE 802.11 Networks Sangtae Park Advisor: Dr. Robert Akl Department of Computer Science and Engineering Sangtae Park Advisor: Dr. Robert Akl Department of Computer Science and Engineering

2. 10/28/2004 2 Outline IEEE 802.11 Overview IEEE 802.11 Network Design Issues Optimal Access Point Selection and Traffic Allocation Co-channel Interference Factor Optimal Channel Assignment Conclusions IEEE 802.11 Overview IEEE 802.11 Network Design Issues Optimal Access Point Selection and Traffic Allocation Co-channel Interference Factor Optimal Channel Assignment Conclusions

3. 10/28/2004 3 IEEE 802.11 Overview Transmission medium Formed in 1990 for wireless LANs Unlicensed industrial, scientific, and medical bands – 915 MHz, 2.4 GHz, 5 GHz 802.11 (1997) – 2.4 GHz, 1Mbps 802.11a (1999) – 5 GHz, 54 Mbps 802.11b (1999) – 2.4 GHz, 11 Mbps 802.11g (2003) – 2.4 GHz, 54 Mbps Transmission medium Formed in 1990 for wireless LANs Unlicensed industrial, scientific, and medical bands – 915 MHz, 2.4 GHz, 5 GHz 802.11 (1997) – 2.4 GHz, 1Mbps 802.11a (1999) – 5 GHz, 54 Mbps 802.11b (1999) – 2.4 GHz, 11 Mbps 802.11g (2003) – 2.4 GHz, 54 Mbps

4. 10/28/2004 4 IEEE 802.11 MAC Sublayer Protocol The 802.11 protocol stack architecture compared to OSI model

5. 10/28/2004 5 IEEE 802.11 MAC Sublayer Protocol IEEE 802.11 MAC layer architecture Distributed coordination function (DCF) - carrier sense multiple access with collision avoidance (CSMA/CA) with binary exponential backoff Point coordination function (PCF) IEEE 802.11 MAC layer architecture Distributed coordination function (DCF) - carrier sense multiple access with collision avoidance (CSMA/CA) with binary exponential backoff Point coordination function (PCF)

6. 10/28/2004 6 IEEE 802.11 Design Issues Designing 802.11 includes two major components: Placement of Access Points Coverage Ample bandwidth Channel assignment Minimize adjacent channel interference Minimize co-channel interference. Designing 802.11 includes two major components: Placement of Access Points Coverage Ample bandwidth Channel assignment Minimize adjacent channel interference Minimize co-channel interference.

7. 10/28/2004 7 Designing 802.11 wireless LANs Creation of service area map Placement of candidate APs Creation of signal level map Selection of the APs from candidate APs Assignment of radio frequencies to APs Creation of service area map Placement of candidate APs Creation of signal level map Selection of the APs from candidate APs Assignment of radio frequencies to APs

8. 10/28/2004 8 A service area map for a three story building with 60 demand clusters

9. 10/28/2004 9 A signal level map for a three story building with 14 APs

10. 10/28/2004 10 Candidate AP assignment graph for 14 APs and 20 demand clusters

11. 10/28/2004 11 AP Selection and traffic allocation Optimization Problem x ij = a binary variable; 1 when demand cluster i is assigned to AP j and 0 otherwise C i = the congestion factor B i = the maximum bandwidth of AP i T i = the average traffic load of a demand cluster i L = total number of demand cluster M = total number of candidate APs

12. 10/28/2004 12 Numerical Analysis Parameters 20 demand clusters and 14 APs in a three story building Number of users per demand cluster = between 1 and 10 (randomly chosen) Average traffic demand per user = 200 Kbps Maximum bandwidth of AP = 11 Mbps Average traffic load of a demand cluster i (T i ) = Average traffic demand per user x number of users at demand cluster i Parameters 20 demand clusters and 14 APs in a three story building Number of users per demand cluster = between 1 and 10 (randomly chosen) Average traffic demand per user = 200 Kbps Maximum bandwidth of AP = 11 Mbps Average traffic load of a demand cluster i (T i ) = Average traffic demand per user x number of users at demand cluster i

13. 10/28/2004 13 A signal level map for a three story building with 14 APs and 20 demand clusters

14. 10/28/2004 14 Candidate AP assignment graph

15. 10/28/2004 15 Average Traffic Load T1T1 1,600 Kbps T 11 1,400 Kbps T2T2 2,000 Kbps T 12 2,000 Kbps T3T3 800 Kbps T 13 1,800 Kbps T4T4 T 14 400 Kbps T5T5 1,200 Kbps T 15 400 Kbps T6T6 T 16 2,000 Kbps T7T7 800 Kbps T 17 200 Kbps T8T8 400 Kbps T 18 800 Kbps T9T9 1,800 Kbps T 19 800 Kbps T 10 1,600 Kbps T 20 400 Kbps

16. 10/28/2004 16 Results of the optimization AP selection graph

17. 10/28/2004 17 Optimal Access Point Selection and Traffic Allocation

18. 10/28/2004 18 Congestion factor of 14 APs with 15, 20, 25, and 30 demand clusters

19. 10/28/2004 19 Average congestion across the networks as the number of demand clusters is increased

20. 10/28/2004 20 Channel Assignment Problem Frequency and channel assignments ChannelsFrequencyChannelsFrequency 12.412 GHz82.447 GHz 22.417 GHz92.452 GHz 32.422 GHz102.457 GHz 42.427 GHz112.462 GHz 52.432 GHz122.467 GHz 62.437 GHz132.472 GHz 72.442 GHz142.484 GHz

21. 10/28/2004 21 802.11b Channel Overlap Blue – noise from room 1 Red – noise from room 6 Yellow – noise from room 11 Only 3 quite rooms available; 1, 6, and 11 Blue – noise from room 1 Red – noise from room 6 Yellow – noise from room 11 Only 3 quite rooms available; 1, 6, and 11 Rooms in Party (11 rooms)

22. 10/28/2004 22 802.11b Channel Overlap Only 3 non-overlapping channels: 1, 6, and 11.

23. 10/28/2004 23 Co-channel Interference Factor Relative percentage gain in interference between two APs as a result of using overlapping channels. For example if we used channels 1 and 2 we would have 80% interference Channels 1 and 5 would have 20% interference Channels 1 and 6 would have 0% interference Relative percentage gain in interference between two APs as a result of using overlapping channels. For example if we used channels 1 and 2 we would have 80% interference Channels 1 and 5 would have 20% interference Channels 1 and 6 would have 0% interference F i = the channel assigned to AP i c = the overlapping channel factor, which is 1/5 for 802.11b

24. 10/28/2004 24 Types of Channel Interference Adjacent channel interference: inversely proportional to the distance Co-channel interference: directly proportional to the co- channel interference factor Adjacent channel interference: inversely proportional to the distance Co-channel interference: directly proportional to the co- channel interference factor

25. 10/28/2004 25 Channel Assignment Optimization Problem V = the total interference at AP i I ij = the relative interference that AP j causes on AP i w ij = co-channel interference factor between AP i and AP j d ij = the distance between AP i and AP j m = a pathloss exponent c = the overlapping channel factor K = the total number of available channels

26. 10/28/2004 26 Channel Assignment using channels 1, 6, and 11 only APChannelInterferenceAPChannelInterference 110.00643810.01101 260.008589110.00303 3110.002491010.00878 4110.005461160.00662 510.008781260.00635 660.0041813110.00558 760.009181410.00913

27. 10/28/2004 27 Channel Assignment Map using channels 1, 6, and 11 only

28. 10/28/2004 28 Optimal Channel Assignment APChannelInterferenceAPChannelInterference 110.00549850.00954 2110.00797960.00472 360.005801010.00638 460.0071511 0.00638 51 12110.00557 6110.003951360.00857 7100.009721410.00603

29. 10/28/2004 29 Optimal Channel Assignment Map

30. 10/28/2004 30 The relative interference of APs when using only channels 1, 6, and 11 and optimal assignment

31. 10/28/2004 31 Average interference across the networks as the number of APs is increased

32. 10/28/2004 32 Conclusions Our Access Point Selection optimization balances the load on the entire network By minimizing the bottleneck APs, we can get better bandwidth utilization for the whole network, which result in higher throughput We define a co-channel interference factor that captures the interference in overlapping channels. Our Channel Assignment optimization minimizes the interference at each AP By optimally using more than just the 3 non- overlapping channels, the average interference across the network can be reduced Our Access Point Selection optimization balances the load on the entire network By minimizing the bottleneck APs, we can get better bandwidth utilization for the whole network, which result in higher throughput We define a co-channel interference factor that captures the interference in overlapping channels. Our Channel Assignment optimization minimizes the interference at each AP By optimally using more than just the 3 non- overlapping channels, the average interference across the network can be reduced

33. 10/28/2004 33 Thank You!! Questions?