Networking Reference
In-Depth Information
Figures 4.14 and 4.15 focus on the simulations in an urban
environment. Thus, Figure 4.14 represents the packet loss
depending on the density of the vehicles in the case of an
urban topology, for LTE4V2X-C and DCP. This figure clearly
shows the extremely high packet loss that DCP suffers from.
In fact, this decentralized approach creates less optimized
clusters. The vehicles are not directly warned of the changes
in topology. The simple cluster members can therefore send
packets to non-existing nodes, and the CHs can miss the
inclusion of a new node in the cluster. Moreover, with
LTE4V2X, all of the nodes are synchronized with the help of
the cluster update packet (sent periodically by the eNodeB in
the LTE network). As far as DCP goes, it must try to
synchronize the nodes without the help of a fixed
infrastructure. Thus, this lack of synchronization, associated
with the high dynamics of the network, provokes serious
packet loss when the volume of the data exchanged in the
VANET becomes significant. The packet loss observed in
LTE4V2X remains constant, even at a high vehicle density.
This can be explained by the fact that the loss is caused by
the intrinsic dynamics of the network (the eNodeB cannot
update the clusters more than once a second, and it can
happen that the configurations need a higher updating
frequency for the clusters).
Figure 4.15 represents the useful flow depending on the
vehicle density in the case of an urban topology, for
LTE4V2X-C and DCP. Two different curves were traced for
each protocol, in order to be able to distinguish the flows of
the LTW network from those of the vehicular network. This
figure clearly shows that LTE4V2X generates a very low
useful flow in the 802.11p network, and a relatively high
useful flow in the LTE network. To understand this behavior,
we must consider Figure 4.14. DCP indeed suffers from an
extremely high packet loss, and we therefore obtain a low
flow for DCP, given that a large part of the useful data is lost
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