1. EE360: Lecture 13 Outline Adaptive Techniques for Cellular
Introduction
Dynamic Channel and Resource Allocation
Area Spectral Efficiency
Adaptive Rate and Power
“On the performance of adaptive modulation in cellular systems”: Taek Chung
Adaptive CDMA
“Optimal power control law for multimedia multirate CDMA systems”: Anne Aaron

2. Dynamic Channel Allocation
Fixed channel assignments are inefficient
Channels in unpopulated cells underutilized
Handoff calls frequently dropped
Channel Borrowing
A cell may borrow free channels from neighboring cells
Changes frequency reuse plan
Channel Reservations
Each cell reserves some channels for handoff calls
Increases blocking of new calls, but fewer dropped calls
Dynamic Channel Allocation
Rearrange calls to pack in as many users as possible without violating reuse constraints
Very high complexity
“DCA is a 2G problem”

3. Dynamic Resource Allocation
Cellular system performance is improved by dynamically allocating resources as user locations, bandwidth and QOS requirements, and applications change.
BASE
STATION
Resources
Power
Rate
Codes
Channels
Base Stations
Access

4. Area Spectral Efficiency
BASE
STATION
A=.25D2p =
S/I increases with reuse distance.
For BER fixed, tradeoff between reuse distance and link spectral efficiency (bps/Hz).
Area Spectral Efficiency: Ae=SRi/(.25D2p) bps/Hz/Km2.

5. ASE with Adaptive Modulation
Users adapt their rates (and powers) relative to S/I variation.
S/I distribution for each user based on propagation and interference models.
Computed for extreme interference conditions.
Simulated for average interference conditions.
The maximum rate Ri for each user in a cell is computed from its S/I distribution.
For narrowband system use adaptive MQAM analysis

6. Propagation Model Two-slope path loss model:
Slow fading model: log-normal shadowing
Fast fading model: Nakagami-m
Models Rayleigh and approximates Ricean.
ASE maximized with reuse distance of one!
Adaptive modulation compensate for interference

7. Average Area Spectral Efficiency
ASE vs. Cell Radius
fc=2 GHz
101
100
D=4R
Average Area Spectral Efficiency
[Bps/Hz/Km2]
D=6R
D=8R
Cell Radius R [Km]

8. Variable Rate and Power
Narrowband systems (Taek)
Vary rate and power (and coding)
Optimal power control not obvious
CDMA systems (Anne)
Multiple methods to vary rate (VBR, MC, VC)
Optimization criteria
Maximize throughput/capacity
Meet different user requirements (rate, SIR, delay, etc.)
Maximize revenue

9. Summary
Adaptive techniques in cellular can improve significantly performance and capacity
Finding an optimal adaptation strategy is complicated by interference from other cells
Power control must balance link optimization with interference effects
Most 2.5 and 3G systems use adaptation