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Control Mechanisms for Video Streaming Wireless Links. Athina Markopoulou Electrical Engineering Dept. Stanford University. t. src. t. src. ideally. t. network. rcv. t. rcv. loss. jitter. delay. Real-Time Multimedia over Packet Networks. Characteristics

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Control Mechanisms for Video Streaming Wireless Links

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Control Mechanisms for Video Streaming Wireless Links

Athina Markopoulou

Electrical Engineering Dept.

Stanford University


t

src

t

src

ideally

t

network

rcv

t

rcv

loss

jitter

delay

Real-Time Multimedia over Packet Networks

  • Characteristics

    • Continuous Stream Playout, Real-Time

  • Requirements

    • low loss, delay, delay jitter


Multimedia - Networking

  • 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)

Application

Network


2

1

The Bigger Picture

backbone

wireless


Wireline

Wireless

Access Point, Server/Proxy

Mobile Terminal

Server

Media Streaming over Wireless Last-Hop

  • Streaming to

    • laptops, cellphones, PDAs, wireless TV displays

  • Challenges

    • limited resources, time variation

    • strict application requirements


Ideally

Over wireless

Tx

Tx

Rx

Rx

Play

Play

Control at the Tx

Control at the Rx

Tx

Tx

Rx

Rx

Play

Play

Example


Problem Statement

p

i

r

N

  • Scenario

    • pre-stored media content at Tx.

    • interference i, according to a Markov chain with

    • deliver and play entire content

  • Objective

    • maximize the playout quality

    • minimize the power cost

Tx

Rx


p

i

r

n

b

s(p,i)

Tx

Rx

System State and Controls

(p,r) = systemcontrolsin current time slot

(n,i,b, r’) = systemstatein current time slot

n = remaining packets at Tx

i = channel interference

b = available packets at Rx

r’ = playout rate in previous slot


r

b

Rx

System Controls at Tx

p

i

n

s(p,i)

Tx

  • Control p: transmission power in current slot

    • s(p,i) : probability of successful reception

    • Power Cost: Φ = p

      • battery lifetime

      • interference stress


from n=N….

Quality

Power

·W +

·W

… until n=0

Dynamic Programming Formulation

  • System Evolution

  • Define to be the minimum expected cost-to-go

(n,i,b;r’)

(p,r)

(1-s(p,i))qij

s(p,i)qij

(n-1,j,b+1-r;r)

(n,j,b-r;r)


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


Special Cases: Individual Controls

  • Similar formulations – obtain optimal policies

  • Compare: no control, special cases, joint control


Better Performance

Power-Quality Tradeoff (1)

No control


Power-Quality Tradeoff (2)

No control

Playout Only


No control

Playout Only

PowerOnly

Power+Rebuffering

Power-Quality Tradeoff (3)


No control

Playout Only

Power Only

Power+Rebuffering

Power-Quality Tradeoff (4)

Jointcontrol


Heuristics

  • Why heuristics?

  • Justified vs. ad-hoc heuristics

    • mimic properties of optimal control

  • Steps

    • Power-only heuristic

    • Playout-only heuristic

    • Joint power-playout heuristic


r

b

n

Tx

Rx

n=N

X

n=1

b

Power Heuristic

p

i

Fix playout r=R

s(p,i)

  • Optimal power:

  • Backlog pressure X(n,i,b)

    • has structural properties:

  • Heuristic: approximate

    • mimicking those properties

^

X


B2

B1

p

i

n

fix p

r

s(p,i)

s(i)

Tx

r=R/2

r=R

r=0

r=R

r=rl

r=0

BL

Bl

Bl+1

b

Playout - today

b

r

Rx

  • Purpose: choose r(b)

  • Fixed Threshold Heuristic

    • L thresholds for buffer occupancy b


B2

B1

i

r=R/2

r=R

r=0

Playout Heuristic

b

r

s(i)

Rx

  • Observation: channel not taken into account yet

  • Adaptive Threshold Heuristic

    • adapt rate

    • and adapt thresholds


p

n

Tx

Joint Power-Playout Heuristic

i

r

b

s(p,i)

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

^


Joint heuristic performs well

Optimal Playout

Optimal Power+Rebuffering

Joint Heuristic

Joint Optimal


Demo: no-control vs. joint heuristic

no control

  • For the same interference scenario

  • For the same power consumption

  • Compare the playout quality

Joint heuristic

original


Controls off

Comparison Details

  • Joint Heuristic


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


Extension: adding more controls

control scheduling

content-aware playout (r)

R(t)

n

b

Tx

Rx

  • Additional Controls:

    • Tx: control scheduling

      • how many units to transmit and which to drop

    • Rx: motion-aware playout

      • 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


Example of Motion-Aware Playout

Motion-aware playout

Motion-unaware playout


Future Directions

  • Multimedia over IP

    • Cross-layer optimization

    • Content distribution

  • Network Dependability

    • 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 …


Appendix


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


Responsive Interference- Power


Responsive Interference- Quality


Adding mode control: (p, m, r)

  • Add a control m:

    • Packets transmitted in a time slot

  • Add a cost Psi(m)

  • Modify

  • Bellman equations


X

p*

hard backoff

aggressive

soft backoff

i

Power-only heuristic

  • Fix playout r=R and find optimal power p*

    • similarly to [B&R (1997), B&K(2000), B&Li(2004)]

    • where

  • Heuristic: approximate X, plug it in p.


[Performance evaluation cont’d]

  • Simulated other channels

  • Simulated responsive interference

  • Found low sensitivity to r-parameters


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