Digital Signal Processing Reference
In-Depth Information
Figure 13-6.
Loss probability 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.
In Figure 13-6, the UDP packet loss probability is plotted versus the number
of relay nodes for three different values of the average error probability over the
radio channel. As expected, the UDP loss probability increases with the number
of relay nodes. The performance deterioration is limited when the number of
relay nodes increases from 3 to 4 relay nodes, since the distance between the
first and the last relay node is in this case large enough to allow for concurrent
undisturbed transmissions.
The UDP packet average delay is shown in Figure 13-7 under the same sce-
nario. The delay increase due to the higher number of hops makes it unfeasible
to provide interactive video services (end-to-end delay smaller than 150 ms)
with 4 relay nodes, while with 3 relay nodes that objective that can be achieved
only under good channel conditions; i.e., when the error probability over the
radio channel is lower than 0.5%.
As a more accurate measure of the quality of service perceived by video users,
the PSNR is plotted in Figure 13-8 versus the number of relay nodes for different
channel conditions; the playout buffer is set to 1 s, which represents a suitable
value for typical streaming scenarios. The quality decreases with the error prob-
ability and acceptable service can be provided only under very good channel
conditions. Clearly, as the delay constraint tightens, the difficulty to provide
