Transcript Channel Access Algorithms with Active Link Protection for

Channel Access Algorithms with
Active Link Protection for
Wireless Communication
Networks with Power Control
Nicholas Bambos, Shou C. Chen,
Gregory J. Pottie
Agenda
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Overview
Motivation (Problem statement)
Foundation work
DPC/ALP algorithm
Properties of DPC/ALP algorithm
Extensions to algorithm VDO and FDO
Simulation results and extensions
Comments
Overview: DPC/ALP
• DPC: An Algorithm for transmit power control
–
–
–
–
Adaptive
Distributed
On-line
Different QoS levels
• ALP: Admission control algorithm
– Protect existing users form disruption
– Method for new users to enter wireless network
– “Smooth dynamics”
Motivation (Problem Statement)
• Power control with
– Entry and
– Egress from the
network
• While maintaining
QoS
– For existing users
Admissible?
Model
QoS constraint
SIRi 
Gii Pi
 i
G
P


 ij j i
i j
( I  F )P  U
P0
U  (
Fij 
 11
G11
 i Gij
Gii
,...)'
SIRi
Foundation Work: DPC
• Distributed Power Control
– P(k+1)=FP(k)+u Foschini and Miljanic
– P->P* where P*  ( I  F )1U
• But
– Convergence path may lead to “outage” or QoS
problems
• Alternative form:
i
Pi (k  1) 
Pi ( k )
SIRi
DPC/ALP Algorithm
• Based on DPC (above)
• Active link protection – Ensures existing
users QoS is maintained when new users are
added.
• Distributed admission control
• Extended – Voluntary drop out Mechanism
for “hot spots”
DPC/ALP Algorithm – continued
 i
Pi (k )
admitted
Pi (k  1) 
SIRi
  1 
Geometric power up
Pi (k )
Protection margin or buffer zone
new
Properties of DPC/ALP
• User is admitted when SIRi   i
– Once admitted continuously admitted
P(k  1)  P(k )
– bounded power overshoot
• New users
– Increasing SIR’s
– If admissible then admitted in bounded time
• But infinite power may be required

Admissibility vs. admissibility
DPC/ALP/VDO
• Voluntary Drop-Out
– When too many new users none wins
– Solution is one or more links backs off
• Types of VDO
– Coin flipping after a parameterized number of
tries
– Timer based
DPC/ALP/VDO/FDO
• Power constraint P max
• FDO – forced drop out
P max
)
– Active user nears max

– Signals local users seeking admission to drop
out
– Reduces contention for resources
(
,P
max
Simulation results
• VDO
– Increases number of users significantly
– Results in backlog of users not yet admitted
• Threshold effect for great enough arrival rate of new
users! Clogging effect
• VDO and FDO
– Decrease in time to admission
– Higher through-put
Hot spots
Congestion
control
Extensions
• Probing
– Predict admissibility from two SIR samples
SIRi 
1
X

k
Y
Solve for X Y
Admit after k= (log )1 (log X  log( 1  Y ))
Comments
• Dynamics of admission control
– Critical to ad-hoc networks
– Rapidly changing user group
• Results are very parameter sensitive