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Power line communication technologies in smart grids Chapter 4 143

occurrence of burst errors that may be arisen from time and frequency depen-
dent noises. The mapping scheme of the ITU-T G.9902 is generally based on
coherent quadrature amplitude modulation (QAM) modulations with 1, 2, 3
or 4 bits per carrier, and channel estimation process is coped with the channel
estimation symbols located to the PHY frames.

4.4.1.2 MAC layer
The ITU-T G.9902 uses prioritized contention-based medium access that is a
CSMA/CA algorithm with four priority levels. While the three lower levels
(level 2, 1 and 0) are employed for user data frames, the highest priority (level
3) is exploited for beacons and emergency data transfers. In order to present
more dynamic network management, management communications are per-
formed via priority level 2 that is the highest level of application data priority.
There is also an optional and synchronized medium access opportunity. If it is
activated, the DM synchronously transmits network beacons. Each inter-beacon
interval may contain a series of contention-based and contention-free periods as
in IEEE 802.15.4 standard [85]. Since the MAC layer structure of the ITU-T
G.9902 is similar to the IEEE 1901.2 standard, both layer 2 and layer 3 routing
are also supported.

4.4.2 ITU G.9903 G3-PLC standard

In August 2009, Maxim Integrated Products, Inc. (United States) published the
G3-PLC specifications as an open specification to meet the requirements of
Electricit eR eseau Distribuion France (ERDF) in the SG applications such as
smart metering, AMI, home automation, HAN applications and further SG
applications. In order to develop and introduce specifications, certification pro-
cess and technology, several companies in the areas of utilities, system integra-
tors, meter manufacturers and silicon vendors with the leadership of ERDF
founded G3-PLC Alliance in 2011. The alliance standardized the specifications
as ITU-T Rec. G.9903 at the end of 2012, and several updates were released in
2014, 2015 and 2017, respectively. This standard characterizes PHY, MAC and
adaptation layers to authorize IP-based communication over LV and MV power
grids. In order to cope with more destructive noise scenarios, this standard
offers a variety of advanced properties such as adaptive tone mapping, two-
dimensional interleaving and robust mode. In addition, it can enable communi-
cations between LV and MV power systems, and vice versa. Furthermore, the
MAC layer structure developed for the IEEE 802.15.4 standard is adapted to
work on the PHY layer. While IPv6 over Low power Wireless Personal Area
Network (6LoWPAN) adaptation layer is also enabled to send IPv6 packets
over power line channels, the layer 2.5 mesh routing protocol is enabled to
detect best path among remote network nodes. Main technical parameters of
ITU-T G.9903 G3-PLC standard are given in Table 4.5.