1. Architectures and Algorithms for Future Wireless Local Area Networks  1 Chapter12345678910 Architectures and Algorithms for Future Wireless Local Area Networks Architectures and Algorithms for Future Wireless Local Area Networks PhD Defense 2012-12-14 Peter Dely

2. Architectures and Algorithms for Future Wireless Local Area Networks  2 Chapter12345678910 High speeds require small distances 2 Mbit/s 7000 Mbit/s 2 Carrier: 2.4 GHz Modulation: BPSK Channel: 20 MHz Carrier: 2.4 GHz Modulation: BPSK Channel: 20 MHz Carrier: 60 GHz Modulation: QAM256 Channel: 1800 MHz Carrier: 60 GHz Modulation: QAM256 Channel: 1800 MHz

3. Architectures and Algorithms for Future Wireless Local Area Networks  3 Chapter12345678910 AP selection with small WLAN “cells” Case 1: AP selection for mobility management 2

4. Architectures and Algorithms for Future Wireless Local Area Networks  4 Chapter12345678910 AP selection with small WLAN “cells” Case 2: AP selection for load balancing 2

5. Architectures and Algorithms for Future Wireless Local Area Networks  5 Chapter12345678910 Research questions 1.Which AP should a station select at a given time? 2.How to design and implement an architecture that enables fair resource distribution and mobility management? 3.How to estimate the quality of an AP?

6. Architectures and Algorithms for Future Wireless Local Area Networks  6 Chapter12345678910 Greedy is not always best Handover 6 Mbit/s 54 Mbit/s Given a certain “cost” for a handover, when is it beneficial to perform that handover? 4

7. Architectures and Algorithms for Future Wireless Local Area Networks  7 Chapter12345678910 Dynamic model finds best AP for the known future Mixed Integer Linear Program Solver 1. Which station uses which AP at what point in time 2. Which rate it can use for downloading Compute Describe system state Describe system characteristics Important constraints 1. Capacity of the wireless channel 2. Data transfer only after a station has been connected to an AP for a certain time Important parameters 1. Cost of a handover 2. Link rates between APs and stations 3. Interference Maximize minimum average throughput Objective 4

8. Architectures and Algorithms for Future Wireless Local Area Networks  8 Chapter12345678910 Evaluation scenario  Comparison of –Greedy –Hysteresis –k-Handover  Mobile stations “walk” on the corridors  Random waypoint with fixed waypoints  Comparison metric: –Normalized throughput –Relative to optimal solution with dynamic model –1 = Optimum 4

9. Architectures and Algorithms for Future Wireless Local Area Networks  9 Chapter12345678910 Mobility and handover costs reduce performance Impact of mobilityImpact of handover cost More mobility = Less performance Higher handover costs ~ Less performance 4

10. Architectures and Algorithms for Future Wireless Local Area Networks  10 Chapter12345678910 Internet AP selection in wireless mesh networks 5

11. Architectures and Algorithms for Future Wireless Local Area Networks  11 Chapter12345678910 Max-min fair rate allocations and single path routing cannot be found through a simple MILP Solution algorithm 1. Which traffic is sent via which route 2. Rates between the stations and the Internet 3. Which station uses which AP Compute Describe system state Describe system characteristics Important constraints 1. As in the pure AP scenario 2. Flow conservation constraints 3. Single-path routing constraints Important parameters 1. Network graph 2. Interference set 3. Association opportunities Max-min fair rate allocation Objective Mixed Integer Linear Program Solver Solve partial problem Reformulate Model 5 Max-min fair optimization is multi-objective optimization Standard algorithms are very slow  Design of heuristic MESHMAX-FAST(*)

12. Architectures and Algorithms for Future Wireless Local Area Networks  12 Chapter12345678910 MESHMAX-FAST* is better than a straight forward linear relaxation In 50% of cases, the performance is greater than 95% of the optimum 5 Better

13. Architectures and Algorithms for Future Wireless Local Area Networks  13 Chapter12345678910 MESHMAX-FAST is suitable for online optimization 5 Optimal solution: > 1000 seconds Optimal solution: > 1000 seconds MESHMAX-FAST*: < 10 seconds with comparable results MESHMAX-FAST*: < 10 seconds with comparable results

14. Architectures and Algorithms for Future Wireless Local Area Networks  14 Chapter12345678910 Research questions 1.Which AP should a station select at a given time? 2.How to design and implement an architecture that enables fair resource distribution and mobility management? 3.How to estimate the quality of an AP? 67

15. Architectures and Algorithms for Future Wireless Local Area Networks  15 Chapter12345678910 Internet A software defined mesh network OpenFlow Control Server Monitoring and Control Server  Build network graph  Run MESHMAX-FAST  Trigger actions at the OpenFlow control server  Build network graph  Run MESHMAX-FAST  Trigger actions at the OpenFlow control server  Configure routes  Configure rate shapers  Trigger handovers  Configure routes  Configure rate shapers  Trigger handovers  Programmable forwarding unit (OpenFlow)  Legacy routing protocol in a virtual network  Programmable forwarding unit (OpenFlow)  Legacy routing protocol in a virtual network 6

16. Architectures and Algorithms for Future Wireless Local Area Networks  16 Chapter12345678910 MESHMAX performance in real networks Testbed setup  IEEE 802.11a links, fixed PHY  Download from “Internet”  Gateways are connected via “DSL” Results with 6 Mbit/s GW links  SNR = Use AP with best signal  Hop-count = Use AP closest to GW  MESHMAX = Use optimal AP 6 1 2 3 4 5 6 8 9 7 10

17. Architectures and Algorithms for Future Wireless Local Area Networks  17 Chapter12345678910 Internet CloudMAC distributes MAC processing OpenFlow Controller Policy Application Virtual AP Virtual WLAN NIC Virtual AP Virtual WLAN NIC Virtual AP Virtual WLAN NIC Program switch 7

18. Architectures and Algorithms for Future Wireless Local Area Networks  18 Chapter12345678910 Internet CloudMAC enables simple handovers OpenFlow Controller Policy Application Virtual AP Virtual WLAN NIC Virtual AP Virtual WLAN NIC Virtual AP Virtual WLAN NIC Program switch Change flow table 7

19. Architectures and Algorithms for Future Wireless Local Area Networks  19 Chapter12345678910 CloudMAC reduces data loss during handovers Median reduction in packet loss from approx. 10000 to 3.5  Standard IEEE 802.11: scan and re-association  CloudMAC: Association state in Virtual AP  no reassociation 7

20. Architectures and Algorithms for Future Wireless Local Area Networks  20 Chapter12345678910 Research questions 1.Which AP should a station select at a given time? 2.How to design and implement an architecture that enables fair resource distribution and mobility management? 3.How to estimate the quality of an AP? 98

21. Architectures and Algorithms for Future Wireless Local Area Networks  21 Chapter12345678910 Finding the AP with the best link is hard 8 Interference Cross traffic

22. Architectures and Algorithms for Future Wireless Local Area Networks  22 Chapter12345678910 RSSI is not a good indicator for throughput 100% loss 0% loss 8

23. Architectures and Algorithms for Future Wireless Local Area Networks  23 Chapter12345678910 BEST-AP uses regular traffic for performance estimation BEST-AP Server Internet BW Estimation Handover BW Estimation 8

24. Architectures and Algorithms for Future Wireless Local Area Networks  24 Chapter12345678910 Dynamic AP selection with stationary users 8 Testbed setup  Two APs  Interference according to real traces Interference Results

25. Architectures and Algorithms for Future Wireless Local Area Networks  25 Chapter12345678910 Time Buffer Level Quality for current AP starts to decrease Connection completely breaks Video playout freezes Scan for new APs Connect to new AP Video playout resumes Evaluation with mobile users 9 Video freeze duration

26. Architectures and Algorithms for Future Wireless Local Area Networks  26 Chapter12345678910 BEST-AP reduces video freezes Testbed setup 9 Results  BEST-AP has fewer and shorter freezes than Linux  A dedicated scan card is not necessary

27. Architectures and Algorithms for Future Wireless Local Area Networks  27 Chapter12345678910 Summary of contributions 1.Theoretical study of AP selection problem –Considering handover costs –Wireless mesh backhauls 2.Architecture proposals and their implementation –For the centralized management of wireless mesh networks –For distributing MAC layer processing 3.Quality estimation of APs –Bandwidth estimation method –Improved video streaming 10

28. Architectures and Algorithms for Future Wireless Local Area Networks  28 Chapter12345678910 Future directions  Use other modeling frameworks –Convex optimization –Robust optimization  Unify architectures –Use CloudMAC in mesh networks –Integrate bandwidth estimation in system  Comprehensive tests in large networks –More realistic traffic loads –Scalability tests 10

29. Architectures and Algorithms for Future Wireless Local Area Networks  29 Chapter12345678910 Thank you! Watch this talk on youtube.com/kaumesh

30. Architectures and Algorithms for Future Wireless Local Area Networks  30 Chapter12345678910 Backup slides

31. Architectures and Algorithms for Future Wireless Local Area Networks  31 Chapter12345678910 … but this comes at a cost  From 2.4 GHz to 60 GHz  Higher path loss  Higher attenuation by walls etc.  From BSPK to QAM256  More constellations  More susceptible to noise  From 20 MHz to 160 MHz channels  Less spatial reuse  Higher energy use 2.4 GHz 60 GHz BSPKQAM256 3640444852566064 To achieve high speeds short distances between the AP and the stations are necessary. 2

32. Architectures and Algorithms for Future Wireless Local Area Networks  32 Chapter12345678910  Main idea: use predictions of the future for optimization  Optimize each time slot using the estimate of the future Using predictions to improve performance More estimation errors 4

33. Architectures and Algorithms for Future Wireless Local Area Networks  33 Chapter12345678910 MESHMAX-FAST improves performance 5

34. Architectures and Algorithms for Future Wireless Local Area Networks  34 Chapter12345678910 Key ideas of MESHMAX-FAST  Observation: APs are traffic aggregation points for many stations  Algorithm sketch: 1.Compute a multi-path solution between the APs and the stations 2.Assign stations to APs according to the capacity of the APs 3.Re-compute the multi-path solution and give priority to APs with many stations 4.Move stations to other APs if it increases the minimum rate 5.Repeat steps 3-4 until the minimum rate cannot be increased anymore 6.Finally, find a single-path for each station 5