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182 From smart grid to internet of energy

for various processes such as channel selection algorithm and CCA. The
zero value of detected ED means that the received signal power is 10 dB
above the receiver sensitivity level.
l Link Quality Indication (LQI): The LQI determines a quality measure for
data packets and it is considered for every received data packet. While this
transaction can be accomplished by using various techniques, the most
widely preferred techniques are ED method, signal-to-noise ratio (SNR)
estimation or the combination of these two methods. It is worth noting that
the IEEE 802.15.4 standard does not specify how the LQI parameter will be
used neither on the network layer nor on the application layer. The minimum
and maximum values of this parameter show the quality range depend on the
detectable signals by receivers. Furthermore, it is also desirable that distri-
bution of the LQI values is uniform within the range.
l Clear Channel Assessment (CCA): The CCA transaction can be performed
over several methods that are ED, carrier sense, a combination of ED and
carrier sense methods, and ALOHA. In the first method (in ED), the channel
is considered as busy if an energy level is detected larger than the predeter-
mined threshold. In the second method, the CCA reports an occupied chan-
nel when it detects a modulated signal including spreading characteristic of
the standard. In addition, it is worth noting that the energy level of the per-
ceived signal is ignored in the carrier sense method. In third method, the
CCA reports an occupied channel if it perceives a modulated signal having
spreading characteristics and energy level is detected larger than the prede-
termined threshold. In fourth mode (in ALOHA), the CCA will ever report a
free channel.
l Channel Frequency Selection: Even though there exist 27 wireless channel
alternatives in the standard, only a part of channels is allowed to be used by a
network. Thus, PHY layer should be able to set its radio dynamically.

5.3.1.2 MAC layer of IEEE 802.15.4 standard
The MAC layer comprises two services called MAC data service and MAC
management service. The former service empowers MAC protocol data units
(MPDUs) for receiving and/or transmitting data across the PHY data service.
The major features of the MAC layer can be listed as guaranteed time slot
(GTS) management, beacon management, frame validation, acknowledged
frame delivery, channel access, association, and disassociation. In addition,
the layer presents several chances to carry out appropriate security schemes
for different type applications. There are two channel access methods in the
IEEE 802.15.4 standard, which are named as beacon-enabled method and
non-beacon method. If unslotted carrier sense multiple access with collision
avoidance (CSMA/CA) is employed, the standard requires the use of non-
beacon mode. In the event of the slotted CSMA/CA is employed, the standard
requires the use of beacon-enabled mode where PAN coordinator periodically