Digital Signal Processing Reference
In-Depth Information
Figure 13-7.
Average delay of UDP packets as a function of the number of relay nodes, when
two TCP traffic sources are considered. The results are plotted for different values of the error
probability over the wireless channel.
acceptable quality of service to the video users increases. In Figure 13-9 the
PSNR is plotted versus the number of relay nodes for different values of the
playout buffer under average error probability equal to Even if the
channel is good, tight delay constraints are difficult to meet when the number
of hops is large, say larger than 3. For example, very low quality is provided
with a constraint of 150 ms when only 3 hops are needed to reach the destina-
tion. These results suggest that, in a multi-hop network scenario, high-quality
real-time video can be provided only under loose delay constraints and limited
distance (in terms of number of hops) between source and destination.
Finally, we assess the impact of the number of relay nodes on the perfor-
mance of data traffic. The throughput achieved by TCP connections is shown
in Figure 13-10. The increase of both loss probability and delay makes the TCP
throughout drastically decrease with the number of relay nodes.
5. CONCLUSIONS
The behavior of H.264-coded video transmission over a wireless 802.11b ad
hoc network scenario has been analyzed. The influence of some of the main
parameters involved in the transmission system has been studied by means of
