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

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Control Mechanisms for Video Streaming Wireless Links

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Control mechanisms for video streaming wireless links

Control Mechanisms for Video Streaming Wireless Links

Athina Markopoulou

Electrical Engineering Dept.

Stanford University


Real time multimedia over packet networks

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

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


The bigger picture

2

1

The Bigger Picture

backbone

wireless


Media streaming over wireless last hop

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


Example

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

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


System state and controls

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


System controls at tx

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


Dynamic programming formulation

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

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

Special Cases: Individual Controls

  • Similar formulations – obtain optimal policies

  • Compare: no control, special cases, joint control


Power quality tradeoff 1

Better Performance

Power-Quality Tradeoff (1)

No control


Power quality tradeoff 2

Power-Quality Tradeoff (2)

No control

Playout Only


Power quality tradeoff 3

No control

Playout Only

PowerOnly

Power+Rebuffering

Power-Quality Tradeoff (3)


Power quality tradeoff 4

No control

Playout Only

Power Only

Power+Rebuffering

Power-Quality Tradeoff (4)

Jointcontrol


Heuristics

Heuristics

  • Why heuristics?

  • Justified vs. ad-hoc heuristics

    • mimic properties of optimal control

  • Steps

    • Power-only heuristic

    • Playout-only heuristic

    • Joint power-playout heuristic


Power 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


Playout today

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


Playout heuristic

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


Joint power playout heuristic

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

Joint heuristic performs well

Optimal Playout

Optimal Power+Rebuffering

Joint Heuristic

Joint Optimal


Demo no control vs joint heuristic

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


Comparison details

Controls off

Comparison Details

  • Joint Heuristic


Wireless video summary

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

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

Example of Motion-Aware Playout

Motion-aware playout

Motion-unaware playout


Future directions

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

Appendix


Responsive interference setup

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- Power


Responsive interference quality

Responsive Interference- Quality


Adding mode control p m r

Adding mode control: (p, m, r)

  • Add a control m:

    • Packets transmitted in a time slot

  • Add a cost Psi(m)

  • Modify

  • Bellman equations


Power only heuristic

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

[Performance evaluation cont’d]

  • Simulated other channels

  • Simulated responsive interference

  • Found low sensitivity to r-parameters


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