Effects of Call Arrival Rate and Mobility on Network Throughput in MultiCell CDMA

1
Effects of Call Arrival Rate and Mobility on
Network Throughput in Multi-Cell CDMA

• Manju Hegde, Robert Akl, Paul Min
• Washington University
• St. Louis, Missouri USA

2
Outline

• CDMA Capacity and Inter-cell Effects
• Feasible Region
• Mobility Model and Blocking
• Net Revenue
• Implied Costs
• Effects of Mobility
• Maximization of Subscribers
• Maximization of Revenue
• Shaping Feasible Region

3
Probability of Outage

• Single Cell
• Multiple Cells

4
Probability of Outage
5
Gaussian Approximation

• We approximate the Poisson by a Gaussian
  variable with the same mean and variance

6
Probability of Outage for Multiple Cells

• Iji Inter-cell interference from cell j to cell
  i.

7
Nine Cell Network
8
Probability of Outage For Each Cell
9
Inter-Cell Interference
10
Soft Handoff

• User is permitted to be in soft handoff to its
  two nearest cells.

11
Soft Handoff
12
Inter-Cell Interference Factor

• Kji per user inter-cell interference factor
  from cell j to cell i
• nj users in cell j produce an amount of
  interference in cell i equal to njKji

13
Feasible Region
14
Total Offered Traffic

• New call arrival process to cell i is Poisson.
• Total offered traffic to cell i is

15
Handoff Rate
16
Probability of State n
17
Fixed Point
18
Net Revenue W

• Revenue generated by accepting a new call
• Cost of a forced termination

19
Implied Costs

• Find derivative of W wrt new call arrival rate
• Capture knockon effect of increases in an arrival
  rate
• Maximize net revenue for a given blocking
  probability vector

20
Three Cell Network
21
Blocking in Cell 3
22
Normalized Arrival Rate
23
Net Revenue W1 C2
24
Net Revenue W1 C10
25
Optimization of Subscribers

• Best Scenario

26
Optimization of Subscribers

• Worst Scenario
• For all values of the arrival rates summing to
  S, the blocking probabilities do not exceed the
  threshold.

27
Maximized Subscribers
28
Optimization of Net Revenue
29
Maximized Net Revenue
30
Shaping Feasible Region

• Increases capacity
• Fine tune the nominal power of the users through
  PCF
• PCF defined for each cell
• PCF is a design tool to maximize the capacity of
  the entire network

31
Power Compensation Factor

• Interference is linear in PCF
• Allows us to reshape the Feasible Region.

32
Equal Number of Users
33
Implied Cost
34
Shaping with PCF
35
Two Cell Network
Mobility
36
Feasible Region
37
Shaped Feasible Region
38
Maximized Subscribers
39
Maximized Net Revenue
40
Conclusions

• For a given network topology we calculate
• Inter-cell and intra-cell interference and
  Feasible Region
• Maximized net revenue
• Maximized subscriber capacity
• Effects of Mobility
• Shape feasible region to increase maximized net
  revenue and subscriber capacity

41
Future Work

• Design Problem given a user demand
  distribution, what are the optimal location and
  coverage of Base Stations to
• Maximize Net Revenue
• Maximize Subscriber Capacity