Transcript Real-time transmission in ad-hoc networks

Multi-Path Multimedia
Transmission
in Ad-hoc Networks
Related Work
Marcin Michalak
[email protected]
Agenda
• ad-hoc networks
• multi-path
– routing
– content
• experimental results
• references
• summary
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Environment
• ad-hoc networks – no infrastructure,
multihop, multi-path, mobile, wireless
• users want good quality
• real need for QoS – network may get
congested
• not much to rely on…
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Important parameters
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delay (~ no. hops)
jitter
available bandwidth
stability of path
packet error rate
congestion
ad-hoc: all variable
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Multi-Path
• independent paths - independent loss
probability
“it has been observed that for multi-path transmission
the end-to-end application sees a virtual average path
which exhibits a smaller variability in quality than any of
the individual paths”  more is better
how to do it?:
 routing issue – getting multiple paths
 content issue – dividing content
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Multipath Routing
• Current algorithms already provide
information about multiple routes, but only
use one at a time
• Transmission:
– redundant: data + error correction
– non-redundant: all paths transmit data
• some promising work on Internet, using
relays
• load balancing (but interference)
• still a very open issue
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Path Selection
node-
• correlation factor: no. of links
connecting 2 paths
• paths should be unrelated, to
avoid interference (sharing same
link):
a) two node-disjoint, unrelated
paths
b) node-disjoint, 7-related
c) link-disjoint
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Path Selection (2)
• shared-channel model
• the larger c.f., the larger
delay – interference
Path should be:
• node-disjoint
• short
• have small correlation factor
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Experimental Results
• 50 nodes
• 1500m x 500m field
• 900s simulation time
• TX range 250m
• speed 5-10 m/s
• CBR: 512B / 250ms
• pause time 0-900 s
•delay including queue
and propagation
improvement limited under pause time 300s
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SMR – Split Multipath Routing
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Sung-Ju Lee (HP) and Mario Gerla (UCLA)
on-demand discovery
using request/reply cycles
goal: build maximally disjoint paths
2 routes: shortest delay + max disjoint
(shortest hop)
• source routing
• per-packet allocation
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SMR - Simulation
• SMR-1: route recovery when any of the
routes is invalidated
• SMR-2: only when both are invalidated
• comparison to DSR – single path
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SMR – Packet Delivery Rate
SMR-2
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SMR-1
DSR
GloMoSim
50 mobile hosts
(1000 m)2 area
prop. range 250m
channel 2Mbps
run 300 sec
speed 0-10 m/s
simulation ends on 300 s....
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SMR – End-to-End Delay
DSR
• 300 s seems to
be a limit?
• DSR uses longer
paths
SMR-1
SMR-2
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Coding possibilities
• Single Description
• Reference Picture Selection (RPS) –
from H263+
• Multiple Description (MD)
• layered coding (+ARQ) – good for mcast
• Video Redundancy Coding
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Multiple Description Coding
(MDC)
• Code video into a number of descriptions, each of
roughly equal importance
• Properties:
– receiving either bitstream gives good quality
– receiving both bitstreams gives highest quality
Original
Video
Decoder 1
Good Quality
Video
Decoder 2
Highest Quality
Video
Decoder 3
Good Quality
Video
Stream 1
MD Coder
Stream 2
(from HP slides – John Apostolopoulos)
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Results (Panwar ...)
• MD coding works well for low-error links
• Layered Coding + ARQ is better for
high-error links, but increases delay
packet loss rate
(3%,3%)
(10%,10%)
(5%,10%)
RPS
31.3
27.5
28.8
Layer Coding + ARQ 31.1
29.4
30.6
MDMC
31.3
26.8
27.9
VRC
30.1
24.8
25.3
Average PSNR of Decoded Images (dB)
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References
• “Split Multipath Routing with Maximally Disjoint Paths
in Ad hoc Networks”, Sung-Ju Lee & Mario Gerla
• “Real-Time Voice Communication over the Internet
Using Packet Path Diversity”, Liang, Steinbach,
Bernd Girod, Stanford University
• “On-Demand Multipath Routing for Mobile Ad Hoc
Networks”, Kui Wu and Janelle Harms, University of
Alberta
• “Video Transport over Ad-hoc Networks Using
Multiple Paths”, S.Lin, Y.Wang, S.Mao and S.Panwar
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Summary
• multi-path transmission seems to be a
good solution – better quality, lower
average delay
• not only for multimedia
• several video coding techniques
• many issues still open
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Questions?
– is this all as good as presented?
?
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