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Smart grid network architectures Chapter 3 113

communication systems in SG applications. The main advantage provided by
wireless networks in the SG WANs is the presenting very wide coverage with
relatively low cost than that of the previous explained communication technol-
ogies. Furthermore, wireless communication technologies, especially cellular
communication technologies, can provide very high data rates for enabling
SG applications. Moreover, some of the wireless technologies are able to sup-
port mesh network scheme to improve reliability of the network. Before data are
conveyed, a connection to the wireless network is needed that may generally be
considered as a difficulty in the event of emergencies and outages. Long-term
latency may cause remarkable problems for real-time services of SG systems.
These issues are taken into account as the main problems of wireless technol-
ogies in SG WANs.

3.6 QoS requirements for SG networks
The SG communication networks should promote several developing applica-
tions to authorize monitoring, fault detection, protection and management trans-
actions [38]. If a fault occurs in any subsystem, it will cause a number of failures
since the SG is composed of many subsystems. The reliability of power systems
is crucial due to the fact that numerous contemporary systems need power grids
to maintain their functions. Therefore, power outages will frequently lead to a
series of failures for the systems requiring a stable power [39]. As a result of this
situation, there exists a growing need for monitoring and control of power grids.
On the other hand, SG applications and their environments call for specific QoS
performance requirements. The important QoS metrics for SG applications can
be sorted out as bandwidth, data rate, latency, reliability and security.
One of the most important QoS metrics is data rate that is related to how
speed the information can be transmitted among the SG equipment and commu-
nication networks. The reachable data rate can be estimated through Shannon
capacity theorem that is determined by both bandwidth and signal-to-noise ratio
(SNR). Measurement, control and management transactions, which operate
based on the SG communication networks, should be realized to accomplish
grid automation. If a data packet is conveyed over the communication network,
it experiences a delay due to the followed routes [26]. Therefore, a latency is
occurred for SG systems which is another significant issue for meeting the
QoS requirements. Even though the effect of latency in communication net-
works may be tolerated by some applications such as metering applications,
there also exist time-critical applications such as fault detection, protection
and control applications. Although several systems are insulated from each
other in contemporary power systems, a fault may lead to a series of failure.
Therefore, reliability of SG systems is very important QoS metric. In addition,
the reliability of SG systems should be ensured for both communication net-
work sites and power system sites. It is important to note that the reliability
of communication systems is not merely limited with connection outages since