Digital Signal Processing Reference
In-Depth Information
Figure 13-5.
Loss probability of UDP packets as a function of the error probability over the
802.11b wireless channel, when no TCP traffic sources are considered. The results are plotted for
different values of the maximum number of transmission attempts.
channel is small, say smaller than 0.003. More than 4 sources cannot be admit-
ted even in the presence of very good channel conditions.
Figure 13-5 shows the impact of the radio channel conditions on the loss prob-
ability of UDP packets of the video stream when different values of the maxi-
mum number of transmissions per MPDU are considered. The curves show that
some retransmissions are needed in order to keep the UDP packet loss proba-
bility to reasonable values. However, values of as small as 3 are already
enough to guarantee UDP loss probability smaller than 1%, even under bad
channel conditions.
4.3 Impact of the number of hops
In this section, we investigate the impact of the number of hops, i.e., relay
nodes, on the quality of service provided to the video and data services. As
sketched in Figure 13-1, the video source shares with the TCP flows the path
to the destination. We let the number of relay nodes increase from 1 (which
corresponds to the previous scenario) to 4. Correspondingly, the number of
hops in the path from the sources to the destination increases from 2 to 5. We
set the number of TCP connections to 2.
