OFDMA Networks: The subcarriers and powers can be allocated according to user’s requirement. BS dynamically controls the resource allocation in two categories – Rate Adaptation (RA) which maximized thru put and Margin Adaptation (MA) which minimizes the total transmitted power. The frequency diversity is yet to be exploited with the consideration of circuitry consumption for frequency-selective fading channels which aids in reduction in energy consumption. The existing research on energy-efficient OFDMA is mainly being focused on the uplink scenarios or mobile terminal sides; however this effort should be put on the downlink or BS for the greener design target.

MIMO Techniques: It has been found that multiple antennas enhance both reliability and capacity of MIMI systems. MIMO can be used with single or multiple users like in SU-MIMO, MU-MIMO, CoMP. Although MIMO techniques improve system capacity and spectral efficiency in wireless system, the energy consumption is high. This energy expense is checked in circuitry components, adaptively altering the number of active antennae according to need.

Relay Transmission: Relay offers network performance and energy saving. Resource allocation schemes are applied for enhancing the relay nodes and their output in the network. The relay nodes in transmission schemes can either amplify-and-forward or detect-and-forward. The performance depends on the transmission strategies, node locations, data rate used in each node, hop number, power allocation and number of nodes in the between transmitter and receiver. The optimization in these parameters helps to achieve highly energy efficient wireless networks. Relaying can be done with pure relay systems or with cooperative relay systems depending upon the complexity of network resources and build of the network.

Resource Allocation in Data Communication: The separation of signaling and data symbol designs does not optimize the system performance. The joint resource allocation between signaling and data symbols is, thus, very important for energy-efficient design (Li, et al). Many miniature attributes of the data communication systems are considered to implement optimal resource allocation, so that maximum energy-efficiency could be obtained. However, the study on resource allocation between signaling and data symbol is still an open issue in energy-efficient wireless networks.

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