CDMA

1. CDMA Network DesignCDMA Network Design
Robert Akl, D.Sc.

2. OutlineOutline
 CDMA overview and inter-cell effects
 Network capacity
 Sensitivity analysis
– Base station location
– Pilot-signal power
– Transmission power of the mobiles
 Numerical results

3.  How to match cell design to user
distribution for a given number of base
stations?
– CDMA network capacity calculation
– Reverse signal power and power control
– Pilot-signal power
– Base station location
Problem StatementProblem Statement

4. CDMA Capacity IssuesCDMA Capacity Issues
 Depends on inter-cell interference and
intra-cell interference
 Complete frequency reuse
 Soft Handoff
 Power Control
 Sectorization
 Voice activity detection
 Graceful degradation

5. Relative Average Inter-CellRelative Average Inter-Cell
InterferenceInterference
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6. Soft HandoffSoft Handoff
 User is permitted to be in soft handoff to
its two nearest cells.

7. Soft HandoffSoft Handoff
[ ]
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8. Inter-Cell Interference FactorInter-Cell Interference Factor
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9. Capacity RegionCapacity Region
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10. Network CapacityNetwork Capacity
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 Transmission
power of mobiles
 Pilot-signal power
 Base station
location

11. Power Compensation FactorPower Compensation Factor
 Fine tune the nominal
transmission power of
the mobiles
 PCF defined for each
cell
 PCF is a design tool
to maximize the
capacity of the entire
network

12. Power Compensation Factor (PCF)Power Compensation Factor (PCF)
 Interference is linear in PCF
 Find the sensitivity of the network
capacity w.r.t. the PCF
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13. Sensitivity w.r.t. pilot-signal powerSensitivity w.r.t. pilot-signal power
 Increasing the pilot-signal power of one
cell:
– Increases intra-cell interference and decreases
inter-cell interference in that cell
– Opposite effect takes place in adjacent cells

14. Sensitivity w.r.t. LocationSensitivity w.r.t. Location
 Moving a cell away from neighbor A and
closer to neighbor B:
– Inter-cell interference from neighbor A
increases
– Inter-cell interference from neighbor B
decreases

15. Optimization using PCFOptimization using PCF
.,...,1for
,0)(
,1subject to
capacity)(network,max
1
max
1
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ββ
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=

16. Optimization using LocationOptimization using Location
.,...,1for
,0
),(
subject to
capacity)(network,max
)(
1
1
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17. Optimization using Pilot-signal PowerOptimization using Pilot-signal Power
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,0
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subject to
capacity)(network,max
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1
1
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18. Combined OptimizationCombined Optimization
.,...,1for
,0)(
),(
,1subject to
capacity)(network,max
1
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1
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19. Twenty-seven Cell CDMATwenty-seven Cell CDMA
NetworkNetwork
 Uniform user
distribution profile.
 Network capacity
equals 559
simultaneous
users.
 Uniform placement
is optimal for
uniform user
distribution.

20. Three Hot Spot ClustersThree Hot Spot Clusters
 All three hot spots
have a relative user
density of 5 per
grid point.
 Network capacity
decreases to 536.
 Capacity in cells 4,
15, and 19,
decreases from 18
to 3, 17 to 1, and 17
to 9.

21. Optimization using PCFOptimization using PCF
 Network capacity
increases to 555.
 Capacity in cells 4,
15, and 19,
increases from 3 to
12, 1 to 9, and 9 to
14.
 Smallest cell-
capacity is 9.

22. Optimization using Pilot-signal PowerOptimization using Pilot-signal Power
 Network capacity
increases to 546.
 Capacity in cells 4,
15, and 19,
increases from 3 to
11, 1 to 9, and 9 to
16.
 Smallest cell-
capacity is 9.

23. Optimization using LocationOptimization using Location
 Network capacity
increases to 549.
 Capacity in cells 4,
15, and 19,
increases from 3 to
14, 1 to 8, and 9 to
17.
 Smallest cell-
capacity is 8.

24. Combined OptimizationCombined Optimization
 Network capacity
increases to 565.
 Capacity in cells 4,
15, and 19,
increases from 3 to
16, 1 to 13, and 9 to
16.
 Smallest cell-
capacity is 13.

27. Combined Optimization (m.c.)Combined Optimization (m.c.)
 
.,...,1for
,
,0)(
),(
,1subject to
capacity)(network,max
min
1
max
1
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=

30. Combined Optimization (m.c.)Combined Optimization (m.c.)
 Network capacity
increases to 564.
 Capacity in cells 4,
15, and 19,
increases from 3 to
17, 1 to 17, and 9 to
17.
 Smallest cell-
capacity is 17.

34. ConclusionsConclusions
 Solved cell design problem: given a user
distribution, found the optimal location
and pilot-signal power of the base stations
and the reverse power of the mobiles to
maximize network capacity.
 Uniform network layout is optimal for
uniform user distribution.
 Combined optimization increases network
capacity significantly for non-uniform user
distribution.