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Is IEEE 802.11p V2X Obsolete Before it is Even Deployed? 33
generation. The paper concludes that DCC does not effectively limit channel load
and packet collisions. Another evaluation of the DCC mechanism performed with
message sizes from 100 to 600 bytes is presented in [23] and has similar findings.
It can be concluded that previous studies consistently find IEEE 802.11p to be
suboptimal for vehicular environments. However, it is the only standardized
VANET technology currently available. Therefore it would be worthwhile to assess
its scalability to decide whether it provides a viable intermediary solution until
better ones become available. The presented publications also lack to define a
realistic scenario. Packet sizes range from 100 to 600 Bytes and are, like the number
of ITS-Ss, often not comprehensible. To close this gap, we perform a performance
analysis of IEEE 802.11p using the ITS-G5 CA service as an application scenario.
3 The ETSI ITS-G5 Standard
The European market has its own DSRC standard, defined by the ETSI. The
physical layer is IEEE 802.11p with minor differences in frequency allocation. The
upper layers are derived from IEEE 1609, extending it with additional mechanisms
like DCC. ITS-G5 also introduces further layers into the model. Figure 1 depicts
the layer structure of ITS-G5. Two so-called basic services, CA and Decentralized
Environmental Notification (DEN), are also part of the standard. In this chapter we
briefly introduce the Access and Networking and Transport Layers as well as the
CA basic service. DEN is not covered as it is not considered in this evaluation.
3.1 Access Layer
The Access Layer encompasses the physical (PHY), MAC and Logical Link
Control (LLC) layers corresponding to OSI layers 1 and 2 [9]. The ITS-G5 PHY
Fig. 1 Layer model of
ITS-G5, only the parts
relevant to this evaluation are
shown (own figure after [9])