Page 218 - From Smart Grid to Internet of Energy

Emerging wireless communication for smart grid applications Chapter 5 193

is intended to support star topology in infrastructure mode. Nonetheless, IEEE
802.11 based standards supporting mesh network scheme may be revised for
supporting the IEEE 802.11ah to extend network with wider coverage. The
CSMA/CA technology, which is an advanced version of CSMA technology
employed in Ethernet, is exploited in MAC layer of this standard. Firstly, the
CSMA/CA method senses the channel, and then data transmission is performed
if the channel is idle. In the event of the channel is busy, station should wait
for a while until continuing transmission completes, which is called as
contention period.
IEEE 802.11e-2005 characterizes the MAC procedures to assist LAN
applications with QoS requirements. The mentioned procedures are related to
transmitting audio, voice and video over the WLANs. It provides remarkable
improvements for delay constrained environments.
IEEE 802.11s defines several protocols for IEEE 802.11 stations to create
self-configured multi-hop networks that are able to serve in both broadcast/mul-
ticast and unicast data transmission. This standard promotes Hybrid Wireless
Mesh Protocol (HWMP) that is a routing protocol based on Ad hoc On-demand
Distance Vector (AODV). This standard is generally employed in outdoor
applications required wide coverage.
The coverage areas and operating frequencies of the IEEE 802.11 based
standards are illustrated in Fig. 5.9 while technical specifications of them are
listed in Table 5.2.

FIG. 5.9 Coverage comparison of IEEE 802.11 standards.