IEEE Consumer Electronics Magazine - November/December 2021 - 100

Special Section on Advances in Smart Cities
noise at the SEH with variance N0
2 , and N0 is the
noise power.
The SGC center in the SEH then performs the
maximum likelihood (ML) decoding and estiFigure
2. Generalized SGC framework:
Noncooperative and cooperative relay-aided
approaches.
The SGC scheme for the SEH is developed in
such a way that it has the ability to communicate
with different services in smart cities through
many options (e.g., directly and indirectly with
sellers or buyers). In the direct communication
framework, each buyer or seller can directly
communicate with the SEH as indicated in
Figure 2, which is known as the noncooperative
direct communication approach. At the same
time, the proposed SGC framework can facilitate
indirect communication where buyers or sellers
communicate with the SEH via inactive users or
ICT services, which is known as the cooperative
relay-aided communication where inactive users
or ICT services act as relay. A brief overview of
both the schemes for the proposed SEH is provided
in the following sections.
Noncooperative Direct Communication
In this scheme, each participant (seller or
buyer) directly shares energy excess/deficit
information to the SEH using separate time slots.
This means that ith participant at ith time slot
transmits the energy excess/deficit information,
which is packaged and modulated as xi ¼
fEi;Dig and the SGC center within the SEH in
Figure 2 receives this as
ySGC;i ¼ hi;SGCxi þ nSGC
(1)
where hi;SGC denotes the Rayleigh fading channel
gain coefficient with zero mean and variance vi,
nSGC is the zero mean additive White Gaussian
100
mates the energy excess/deficit information as
x^i. These decoded information are then sent to
the distributed control center (DCC) for performing
the appropriate energy sharing and initiating
energy trading activities, where it is decoded in
a similar manner as (1). The DCC updates the
control actions for different controllers accordingly
and the same applies for the energy trading
framework to start the energy sharing. This communication
system may fail or slow down if participants
are not within the communication
range of the SGC center. This will severely affect
the energy sharing and trading activities, which
can be overcome using the cooperative relayaided
communication system as discussed in
the following section.
Cooperative Relay-Aided Communication
The proposed cooperative relay-aided
scheme allows simultaneous information exchange
for more than one participant at a certain
time slot and the intermediate communication
relay receives the sum of these information. For
example, participants i and j transmit their
energy excess/deficit information and the kth
communication relay receives
yk ¼ hi;kxi þ hj;kxj þ nk
(2)
where all symbols have similar meanings as indicated
earlier on and channel gain coefficients
are between the respective service and intermediate
relay nodes. The relay node either performs
decode-and-forward to decode the sum of
signals or amplify-and-forward to directly forward
the signal to the SGC center. The intermediate
relay node forwards the estimated signal to
the SGC center after multiplying with some
known coefficients. The coefficients are chosen
in such a way that they are in the null space of
other participants channels. Now, the SGC center
estimates and shares the information with
the DCC and energy trading framework. Finally,
the communication framework with the DCC forwards
the decoded signals on energy sharing as
well as trading activities.
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IEEE Consumer Electronics Magazine - November/December 2021

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