1. Flexible Allocation of Capacity in Multi-Cell CDMA Networks Robert Akl, Manju Hegde, Mort Naraghi-Pour*, Paul Min Washington University, St. Louis, MO *Louisiana State University, Baton Rouge, LA

2. 2 Outline Capacity and Probability of Outage Calculation of inter-cell interference Capacity region Power compensation factor Effects of different cell sizes Optimization of capacity Flexible allocation of capacity Results

3. 3 Nine Cell Network

4. 4 Probability of Outage For Each Cell

5. 5 Probability of Outage for Single Cell

6. 6

7. 7 Gaussian Approximation We approximate the Poisson by a Gaussian variable with the same mean and variance:

8. 8 I ji : Inter-cell interference from cell j to cell i. Probability of Outage for Multiple Cells

9. 9 Shadow and Rayleigh Fading Assume power control overcomes both large scale path loss and shadow fading, but not Rayleigh fading. The average of the Rayleigh fading is the shadow fading on that path.

10. 10 Inter-Cell Interference

11. 11 Soft Handoff User is permitted to be in soft handoff to its two nearest cells.

12. 12 Soft Handoff

13. 13 Inter-Cell Interference Factor K ji : per user inter-cell interference factor from cell j to cell i n j users in cell j produce an amount of interference in cell i equal to n j K ji K ii are not necessarily zero because of soft handoff, users in cell i can cause inter-cell interference to cell i.

14. 14 Capacity Region

15. 15 Capacity Region Capacity region: set of all feasible user configurations Uniform capacity: n i = c 1 for all i Two level capacity: m 1 cells have capacity c 1 and m 2 cells have capacity c 2 where m 1 + m 2 = M

16. Example: 2 Cell Network K ij BS-1BS-2 BS-104.0130 BS-20.06170

17. Capacity Region

18. 18 Power Compensation Factor Fine tune the nominal power of the users PCF defined for each cell PCF is a design tool to maximize the capacity of the entire network

19. 19 Power Compensation Factor Interference is linear in PCF

20. 20 Sensitivity Analysis Derivative of capacity function with respect to the PCF Capture effect of increases in PCF in one cell on the capacity of whole network Tool to flexibly distribute capacity between cells

21. 21 Sensitivity Analysis For uniform capacity case:

22. 22 Sensitivity Analysis

23. 23 Optimization Optimize the sum capacity: the sum of the capacities of the cells Constraint: PCF between a min and a max Use the derivatives in steepest descent algorithm New PCF is the factor that the nominal power needs to be increased by for every cell Each PCF is used by its Base Station in the Closed Loop Power Control

24. 24 Optimization of Uniform Capacity

25. 25 Optimization of Two-Level Capacity

26. Capacity Region

27. Hard Handoff vs. Soft Handoff HHBS-1BS-2BS-3CapOptPCF BS-100.3303.5734171.00 BS-20.33103.4204171.00 BS-30.0760.07204174.53 SHBS-1BS-2BS-3CapOptPCF BS-10.1060.1160.60317261.00 BS-20.1170.0990.59117261.00 BS-30.0660.0630.00617262.56

28. 28 Seven Cell Network

29. 29 Probability of Outage For Each Cell

30. 30 Optimization Uniform capacity –C1: 11 (PCF=1) to 20 (PCF Optimized) –Sum capacity: 77 to 140 Two-level capacity –Small cells: 14 (PCF=1) to 22 (PCF Optimized) –Large cells: 7 (PCF=1) to 11 (PCF Optimized) –Sum capacity: 77 to 121

31. 31 Flexibility in Capacity Allocation Case 1: Result: sum capacity of 150.

32. 32 Flexibility in Capacity Allocation Case 2: Result: sum capacity of 152 but capacity of cell three drops from 20 to 13.

33. 33 Flexibility in Capacity Allocation Case 3: Result: cell three has a capacity of 25 but sum capacity drops to 143.

34. 34

35. 35 Conclusions Power Compensation Factor is a design tool to: –Flexibly distribute the capacity allocation between cells –Optimize the capacity of a network –Maximize the capacity of a single cell –Easy to implement in an existing network –Does not require the relocation or addition of Base Stations.

36. 36 Future Work Pilot Power determines the cell geometry which determines the inter-cell and intra-cell interference Determine the sensitivity of capacity with respect to Pilot Power Determine the sensitivity of capacity with respect to Base Station location Complete Design: Location, forward power, reverse power.