1. Joint Access Point Placement and Channel Assignment for 802.11 Wireless LANs Xiang Ling School of Communication and Information Engineering University of Electronic Science and Technology of China Chengdu, China Kwan Lawrence Yeung Dept of Electrical and Electronic Engineering University of Hong Kong Hong Kong, China IEEE Wireless Communications and Networking Conference (WCNC) 2005

2. Outline Introduction Throughput estimation  Restrainers Objective Function (OF) Patching algorithm Simulations Conclusions

3. Introduction More and more multi-cell 802.11 WLANs are being deployed to provide seamless coverage Deciding AP placement and channel assignment become increasingly important

4. Introduction (cont.) [1] R.C.Rodrigues, G.R.Mateus, and A.A.F.Loureiro, “On the design and capacity planning of a wireless local area network,” IEEE/IFIP Network Operations and Management Symposium 2000.  AP Placement  Maximizing the total receiving signal strength

5. Introduction (cont.) [2] Y.Lee, K.Kim, and Y.Choi, “Optimization of AP placement and channel assignment in wireless LANs,” Proceedings of the 27th Annual IEEE Conference on Local Computer Networks, 2002.  Load balancing  Minimizing the load carried by the heaviest- loaded AP

6. Introduction (cont.) Goal  Consider the co-channel interference between cells AP placement Channel assignment  Throughput & Fairness

7. Throughput estimation [8] G.Bianchi, “Performance analysis of IEEE 802.11 distributed coordination function,” IEEE Journal on Selected Areas in Communications, vol. 18, no. 3, pp. 535~547, March 2000.

8. Throughput estimation (cont.)

9. Restrain criteria (a). Mobile terminals in MT 1 ’s radiating range (b). Mobile terminals located in AP 1 ’s interference range

10. Restrain criteria (cont.) (c). If MT 1 is in AP 2 ’s interference range, mobile terminals associated to AP 2 will restrain MT 1. (b). If AP 1 and AP 2 are so close that they can interfere with each other directly, mobile terminals associated to AP 2 are MT 1 ’s restrainers.

11. Throughput estimation (cont.)

12. Objective Function (OF) β approaches 1 when all THRs are the same β converges to 1/N when throughputs are heavily unbalanced

13. Patching algorithm

14. Example

15. Simulations NS-2 2 APs (Cells) MTs are uniformly distributed UDP / CBR / 1500-byte

16. System throughput

17. Fairness index

18. System throughput

19. Fairness index

20. OF values got by patching algorithm and exhaustive searching

21. Computation complexity

22. Conclusion This paper proposed an method to estimate the throughput of a multi-cell 802.11b WLAN system Co-channel overlapping between cells is considered in the estimation Patching algorithm reduce the computational complexity Simulation results show that better throughput and fairness are provided