V
ARIOUS
G
REEN
C
OMMUNICATION
A
PPROACHES
Several approaches like Sleep Scheduling, OFDMA
networks, MIMO techniques, relay transmission and
resource allocation for signaling, to achieve the goal of
Energy Optimization in mobile wireless Communication
networks are discussed in this section of the paper.
A. MIMO
MIMO (multiple inputs and multiple outputs) is an
antenna technology for the wireless communication
systems. In this technique, multiple antennas are used on
both transmitter and receiver side [1]. In conventional
wireless communications, a single antenna is used at the
source, and another single antenna is used at the
destination. But in MIMO, the antennas at each end of the
communication circuits are combined to minimize errors
and optimize data speed. MIMO technology has attracted
attention in wireless communication as it offers the
significant increases in data throughput and link range
without additional bandwidth or increased transmit
power. Better reliability and higher transmission rates are
always anticipated in communication systems. MIMO is
one of the several forms of the smart antenna technology
[2]. MIMO technology uses multiple antennas to make
the use of reflected signals to provide gains in channel
robustness and throughput [3]. MIMO technology has
stimulated the efficacy of internet because of its possible
applications in digital television (DTV), wireless local
area networks (WLANs). Basic Diagram of MIMO is
shown in Fig.2.
Fig. 2. MIMO System.
MIMO antenna systems are a stupendous component
in the pursuit for broadband wireless systems with higher
capacity, performance, reliability, higher peak data rates,
high SNR, low level of latency which simply means
increased productivity with minimal resources to achieve
energy efficiency in wireless communication networks.
B. OFDMA and Resource Allocation
OFDMA refers to Orthogonal Frequency Division
Multiple Access, a special kind of Frequency Division
Multiplexing (FDM), which is used to allow the
transmission of high data rates with less complexity. In
OFDMA, carriers are orthogonal to each other which
makes it different from FDM [13]. In other words, we can
say that OFDM is multicarrier transport technology in
which frequency spacing is created using Fast Fourier
Transform [4, 5]. In OFDMA, system resource, such as
subcarriers and transmit power, needs to be properly
allocated to different users to achieve high performance.
OFDMA results in high spectral efficiency, resistant to
RF interference, lower multi-path distortion, enables
orthogonality in the uplink, enables single frequency
network coverage, adaptive modulation, frequency
diversity, reduces the amount of crosstalk in signal
transmissions, boost the speed of an Internet connection
over a standard telephone line. The two most commonly
used classes of dynamic resource allocation schemes are
rate adaptation (RA), which maximizes throughput, and
margin adaptation (MA), which minimizes total transmit
power. Thus, reducing the amount of energy consumed
which leads to energy efficient wireless communication.
Fig.3 shows the concept of OFDMA and Resource
Allocation.
Fig. 3. OFDMA and Resource allocation.
C. Sleep Scheduling
The large number of Base Stations (BSs) contributes a
significant portion of the whole network energy
consumption which mainly comes from the data server,
backhaul routers and the BSs. Therefore, it will be critical
to reduce the energy consumption of the BSs. Sleep
Scheduling is an energy efficient approach pertaining
software of BS, aiming at intelligent control of the
network elements which can conserve the battery energy
by switching ON or OFF the BS by monitoring the peak
time or high traffic hours/busy hours.
The objective of BS energy saving is to dynamically
minimize the number of active BSs to meet the traffic
variation in the network. This requires the traffic
distribution information of the whole network, both on
the space and time dimension to dynamically wake up
sleeping BSs according to the load condition of the active
BSs [6, 16].
D. Relaying
To achieve higher data rates, denser infrastructure is
needed by which distance between transmitter and
receiver can be decreased but if the concept of relaying is
implemented, then there will be no need of denser
infrastructure [14]. Apart from high data rates, other
benefits of deploying the concept of relaying are
improvement in coverage, coverage at cell edge and
coverage in shadow areas. A relay is similar to a repeater
and are basically low power base stations which enhance
coverage in areas where coverage is poor or to provide
coverage in rural areas without the need for a wired
2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 893 -
