Media Streaming over Power-Controlled Wireless Links
Download
Report
Transcript Media Streaming over Power-Controlled Wireless Links
Control Mechanisms for Video
Streaming Wireless Links
Athina Markopoulou
Electrical Engineering Dept.
Stanford University
1
Real-Time Multimedia over Packet Networks
Characteristics
•
Continuous Stream Playout, Real-Time
t
src
ideally
t
rcv
t
src
network
t
rcv
loss
jitter
delay
Requirements
•
low loss, delay, delay jitter
2
Multimedia - Networking
Application
Network
Problems at the interface between multimedia
applications and underlying network
Control mechanisms
•
•
in the network and/or
at the end-systems
Challenges depend on underlying network(s)
3
The Bigger Picture
2
backbone
1
wireless
4
Media Streaming over Wireless Last-Hop
Wireline
Server
Mobile
Terminal
Streaming to
•
Access Point,
Server/Proxy
Wireless
laptops, cellphones, PDAs, wireless TV displays
Challenges
•
•
limited resources, time variation
strict application requirements
5
Example
Ideally
Tx
Tx
Rx
Rx
Play
Play
Tx
Control at the Tx
Tx
Rx
Rx
Play
Play
Over wireless
Control at the Rx
6
Problem Statement
N
p
i
Tx
Scenario
Objective
•
•
•
•
•
r
Rx
pre-stored media content at Tx.
interference i, according to a Markov chain with
deliver and play entire content
maximize the playout quality
minimize the power cost
7
System State and Controls
n
p
Tx
i
b
r
s(p,i) Rx
(p,r) = system controls in current time slot
(n,i,b, r’) = system state in current time slot
n = remaining packets at Tx
i = channel interference
b = available packets at Rx
r’ = playout rate in previous slot
8
System Controls at Tx
n
p
i
s(p,i) Rx
Tx
Control p: transmission power in current slot
•
s(p,i) : probability of successful reception
1
0.9
0.8
0.7
0.6
s(p,i)
r
b
0.5
0.4
•
Power Cost: Φ = p
–
–
battery lifetime
interference stress
0.3
0.2
0.1
0
0
2
4
6
8
10
SIR p/i
9
Dynamic Programming Formulation
System Evolution
Define
to be the
minimum expected cost-to-go
from n=N….
Power ·W + Quality
(n,i,b;r’)
·W
(p,r)
s(p,i)qij
(n-1,j,b+1-r;r)
(1-s(p,i))qij
(n,j,b-r;r)
… until n=0
10
Computing the Optimal Control
A stationary optimal solution (p*,r*) exists
and can be obtained by value iteration
Optimal policy:
•
•
table p*(n,i,b;r’) and r*(n,i,b;r’)
obtain offline & store in lookup table
11
Special Cases: Individual Controls
Scenario
Control at Tx
Control at Rx
No control
fix p
fix r=R
Power Control
adapt p
fix r=R
Power Control &
Re-buffering
adapt p
r in {0, R}
Playout Control
fix p
r in {0, r1, r2…R}
Re-buffering
fix p
r in {0, R}
Joint Control
adapt p
r in {0, r1, r2…R}
Similar formulations – obtain optimal policies
Compare: no control, special cases, joint control
12
Power-Quality Tradeoff (1)
No control
Better Performance
13
Power-Quality Tradeoff (2)
No control
Playout Only
14
Power-Quality Tradeoff (3)
No control
Playout Only
Power Only
Power+Rebuffering
15
Power-Quality Tradeoff (4)
No control
Playout Only
Joint control
Power Only
Power+Rebuffering
16
Heuristics
Why heuristics?
Justified vs. ad-hoc heuristics
•
mimic properties of optimal control
Steps
•
•
•
Power-only heuristic
Playout-only heuristic
Joint power-playout heuristic
17
Power Heuristic
n
p
i
r
Fix playout r=R
s(p,i) Rx
Tx
Optimal power:
Backlog pressure X(n,i,b)
•
b
n=N
has structural properties:
X
^
Heuristic: approximate X
•
mimicking those properties
n=1
b
18
Playout - today
n
p
i
fix p
Tx
B2
s(p,i)
s(i)
Rx
B1
r=R/2
r=R
b
r
r=0
Purpose: choose r(b)
Fixed Threshold Heuristic
•
•
L thresholds for buffer occupancy b
r
r=rl
r=0
Bl
r=R
Bl+1
BL
b
19
Playout Heuristic
B2
i
s(i)
Rx
r=R
B1
r=R/2
b
r
r=0
Observation: channel not taken into account yet
Adaptive Threshold Heuristic
•
•
adapt rate
and adapt thresholds
20
Joint Power-Playout Heuristic
n
p
Tx
•
•
•
•
•
i
s(p,i)
b
r
Rx
Tx side:
^
compute X(n,b)
compute power p:
Rx side:
estimate i, compute p and s(p,i)
adjust thresholds, compute playout r
feedback to Tx
21
Joint heuristic performs well
Optimal Playout
Optimal Power+Rebuffering
Joint Heuristic
Joint Optimal
22
Demo: no-control vs. joint heuristic
For the same
interference scenario
For the same power
consumption
Compare the playout
quality
original
no control
Joint heuristic
23
Comparison Details
Controls off
Joint Heuristic
24
Wireless Video - Summary
Contributions
•
•
•
Joint power-playout control
Modeled in a dynamic programming framework
Developed simple, efficient heuristics
Extensions
•
•
•
•
Additional Channels and Responsive Interference
Additional Controls
Content-Aware Control
Apply to protocols (802.11h)
“Joint Power-Playout Control Schemes for Media Streaming over Wireless
Links”, in IEEE Packet Video 2004, Markopoulou joint work with Y.Li,
N.Bambos, J.Apostolopoulos
25
Extension: adding more controls
control
scheduling
n
R(t)
Tx
b
Rx
Additional Controls:
•
Tx: control scheduling
–
•
how many units to transmit and which to drop
Rx: motion-aware playout
–
content-aware
playout (r)
slowdown video scenes with low or no motion
Results:
•
•
trade-off: playout speed variation vs. distortion
effect of playout variation is less perceived
“Joint Packet Scheduling and Content-Aware Playout Control for Media
Streaming over Wireless”, invited paper in IEEE MMSP 2005, A.
Markopoulou joint work with Y.Li, N.Bambos, J.Apostolopoulos
26
Example of Motion-Aware Playout
Motion-aware playout
Motion-unaware playout
27
Future Directions
Multimedia over IP
•
•
Network Dependability
•
•
Cross-layer optimization
Content distribution
From traditional QoS to Reliability & Security
Measurements for diagnosis and control
Network shared by independent selfish entities
•
•
•
Network-adaptive applications
How bad is selfish routing?
Selfishness in other contexts?
Interaction …
28
Appendix
29
Responsive Interference - Setup
Primary Media link, background PCMA links
Pairs of Tx-Rx randomly chosen from area
(500x500 wrapped in a torus)
Background: geometric durations, Bernoulli
arrivals
Free space path loss G~1/d^4, noise 1^(12)
Estimate I using previous timeslot
N=100, initial 5slots, buffer B=10
Heuristic gains: 60% in power, 66% in QoS
30
Responsive Interference- Power
31
Responsive Interference- Quality
32
Adding mode control: (p, m, r)
Add a control m:
• Packets transmitted in a time slot
Add a cost Psi(m)
Modify
Bellman equations
33
Power-only heuristic
Fix playout r=R and find optimal power p*
•
similarly to [B&R (1997), B&K(2000), B&Li(2004)]
•
where
p*
X
i
aggres
sive
soft
backoff
hard
backoff
Heuristic: approximate X, plug it in p.
34
[Performance evaluation cont’d]
Simulated other channels
Simulated responsive interference
Found low sensitivity to r-parameters
35