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Emerging wireless communication for smart grid applications Chapter 5 191

Wi-Fi that is developed by Wi-Fi Alliance [35]. The Wi-Fi term has been cre-
ated by the Wi-Fi Alliance to present more attractive name rather than the IEEE
802.11 technology. The Wi-Fi Alliance that is formed to promote the technol-
ogy in 1999 is a non-profit international association of several carriers, vendors,
service providers, manufacturers and other related companies. Furthermore, it
also manages certification and interoperability issues. The Wi-Fi technology
characterizes an upper layer protocol by using IP for enabling wireless commu-
nications over the Internet. Even though the Wi-Fi and IEEE 802.11 terms may
be employed mutually, there exist minor differences among them. The IEEE
802.11 is a collection of standards, which identifies several fundamental func-
tionalities such as PHY layer, MAC layer, protocols, authentication, QoS and so
on. On the other hand, the Wi-Fi Alliance determines technical specifications by
referring to IEEE 802.11 standards and manages certification process of devices
that ensures interoperability. In addition, Wi-Fi certified devices are immedi-
ately able to contact with each other thanks to Wi-Fi Direct technology devel-
oped by the Alliance that is presently activated in many smart devices such as
smartphones, tablets and notebooks. Furthermore, the Wi-Fi Alliance
researches in several issues to provide performance improvements in terms
of data rate, security, QoS and hardware based issues [36–38].
The family of IEEE 802.11 standards characterizes the PHY and MAC
layers, and supports IP addressing. The most popular standards of IEEE
802.11 family are 802.11a, 802.11b, 802.11g, 802.11n, and recently released
802.11ah. IEEE 802.11 networks are intended to function in unlicensed fre-
quencies and they are serving on the ISM bands by generally using 2.4 and
5 GHz carrier frequencies. In addition, below 1 GHz and above 60 GHz fre-
quency bands are presently being taken into account for the PHY layer charac-
terization. Several PHY layer specifications, FHSS, DSSS and OFDM methods
are exploited by the IEEE 802.11 standards. The FHSS based systems allocate
the 2.4 GHz band into sub-channels where each sub-channel has 1 MHz band-
width. In addition, transmitter devices dynamically vary the channels by
employing predefined sequence sets in the standard. An improved channel uti-
lization method is the DSSS technique that is also exploited in Code Division
Multiple Access (CDMA) systems. Firstly, data are multiplied with a chip
sequence in this method and then, either differential binary phase shift keying
(DBPSK) or differential quadrature phase shift keying (DQPSK) modulation
scheme is used to convey data. Complementary code keying (CCK) modulation
scheme may be used to advance data rates of the DSSS, which is called as high
rate DSSS (HR/DSSS). In addition, there are some standards based on IEEE
802.11 employing OFDM method that is a combination of mapping and multi-
plexing method. This method uses many orthogonal sub-carriers in order to
carry data.
A generalized MAC frame format of the standard is illustrated in Fig. 5.8.In
addition to the MAC data frame, standard also utilizes RTS and CTS control
frames.