Multimodal Robot/Human Interaction for Assisted Living

International Journal on Advances in Intelligent Systems, vol 2 no 2&3, year 2009, http://www.iariajournals.org/intelligent_systems/
reduce the packet loss by switching over among the
peers in case of congestion. On the other hand, the
randomized approach is showing packet loss and which
is due to the randomness in selecting and switching
over among the peers.
Packet loss can be considered the most crucial factor in
video decoding and, consequently, a determining factor
for video Quality of Experience (QoE). It is therefore
essential to verify that the P2P overlay is optimized
with this regard. Table 1 summarizes findings
published in [28], correlating packet loss ratio with
video streaming Quality-of-Experience (QoE), for the
case of single-layer coding. It is noticeable that any
value above around 14% leads to poor quality.
According to this table, the proposed method shows a
smooth video to the end-users.
Packet loss ratio (%)
14
12
10
8
6
4
2
0
Packet loss
ratio [%]
Proposed method Randomized method
c
0 5 10 15 20 25 30
Time ( s )
Figure11 - Packets loss ratio
QoE
acceptability
[%]
0 84 Smooth
Video quality playback
14 61 Brief interruptions
18 41 Frequent interruptions
25 31 Intolerable interruptions
31 0 Stream breaks
Table 1 Quality of experience acceptability
thresholds
Another important performance metric in video
streaming is end-to-end latency (or delay), which is
critical in the process of meeting strict playback
deadlines. In turn, this has a direct impact on quality of
service and quality of experience.
Figure 12 shows the average end-to-end delays of both
scenarios. Noticeably, our approach gives a lower
average latency (order of 0.02 seconds); also, we can
see that the delay is consistent, due to the fact that
connections are not chosen randomly. On the other
hand, delay in the randomized approach is fluctuating.
This variation in delay may in turn increase packet loss
with detrimental effect on QoE.
Figure 13 illustrates this attribute in terms of jitter. A
nearly constant jitter derives from the fact that peer
handover is governed by a prioritization process (based
on RTT values), which ensures that nearby nodes are
chosen first. The small variation in jitter in our
approach is due to the fact that we still need to force
handover even in the case of optimal connections, to
maintain a good computational load balance.
AVG.E2E Delay
AVG.Jitter (sec)
0.06
0.05
0.04
0.03
0.02
0.01
0
0.06
0.05
0.04
0.03
0.02
0.01
0
Proposed method Randomized method
0 5 10 15 20 25 30
Time ( s )
Figure12 - End-to-End Delay
Proposed method Randomized method
0 5 10 15 20 25 30
Time ( s )
Figure13 - Jitter
8.3 Quality of Experience
Finally, the objective and subjective quality of decoded
video under the proposed and randomized methods are
compared. The received packets are decoded using
error concealment of H.264/AVC encoder JM15. The
resulting PSNR is shown in fig. 14 comparing both the
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