Improve Energy Efficiency In Cooperative Medium Access Control Protocol For Wireless Networks

Cooperative communication has drawn a substantial attention in recent years due to the efficient and optimal utilization of constraint resources in dynamic wireless networks at a reduced infrastructural deployment and cost. In the medium access control (MAC) layer perspective, two major problems are associated with cooperative networks. The ability of cooperative MAC (CMAC) protocols to achieve multi-objective target orientation limit their adaptation to the future generation of wireless networks, since most of the existing protocols focus only on a single target objective. Besides, the sustainability of energy-constrained wireless networks due to limited energy supply capacity hinders their performance to ensure stable and reliable communication. These aforementioned problems limit the adaptation of the existing protocols to fit into the future generation of wireless networks. To adequately address these problems, two distinct CMAC protocols are proposed in this thesis to cater for the unpredictable and dynamic nature of the wireless network. Firstly, a new network lifetime-aware CMAC protocol named LEA-CMAC is proposed for energy-constrained wireless ad-hoc networks. An optimization problem is formulated with an objective of extending the lifetime of the network. The solution to this non-linear problem is provided in terms of optimal transmit power at the source and relay terminals in symmetric and asymmetric transmit power policies. The solution provided by this protocol is limited in terms of energy efficiency and network lifetime since the network totally rely on the helper nodes limited-powered batteries for their transmissions. Secondly, a novel CMAC protocol with radio frequency (RF) energy harvesting (EH) capability named EH-CMAC is proposed in a reactive relaying energy-constrained wireless ad-hoc networks to address the limitation in the earlier proposed LEA-CMAC protocol. The protocol possesses the ability to ensure a sustainable and reliable wireless connectivity in a dynamic wireless environment through the selection of an appropriate transmission mode that best suits the instantaneous network requirement. The protocol comprises of two distinct energy-efficient techniques namely, the outage probability quality-of-service (QoS) requirement and the transmit power optimization techniques which are applied in both traditional and EH relaying schemes. These techniques are selected and adapted based on the instantaneous network information and target objectives. In addition, a distributed and adaptive relay selection backoff process is proposed in each case to satisfy the available network information and achieve a multi-objective target oriented protocol. Through extensive simulation and comparison with existing CMAC protocols, the results show that LEA-CMAC extend the network lifetime by 85.67% over an existing CMAC protocol, while EH-CMAC extends the network lifetime by 90.99% over a traditional CMAC protocol. Thus, both protocols achieve a multi-objective target orientation under general circumstances

Trading Wireless Information and Power Transfer: Relay Selection to Minimize the Outage Probability

This paper studies the outage probability minimization problem for a multiple relay network with energy harvesting constraints. The relays are hybrid nodes used for simultaneous wireless information and power transfer from the source radio frequency (RF) signals. There is a trade-off associated with the amount of time a relay node is used for energy and information transfer. Large intervals of information transfer implies little time for energy harvesting from RF signals and thus, high probability of outage events. We propose relay selection schemes for a cooperative system with a fixed number of RF powered relays. We address both causal and non-causal channel state information cases at the relay--destination link and evaluate the trade-off associated with information/power transfer in the context of minimization of outage probability.Comment: IEEE GlobalSiP, 201

Wireless Energy Harvesting with Amplify-and-Forward Relaying and Link Adaptation under Imperfect Feedback Channel

Energy harvesting is an alternative approach to extend the lifetime of wireless communications and decrease energy consumption, which results in fewer carbon emissions from wireless networks. In this study, adaptive modulation with EH relay is proposed. A power splitting mechanism for EH relay is used. The relay harvests energy from the source and forwards the information to the destination. A genetic algorithm (GA) is applied for the optimisation of the power splitting ratio at the relays. Two scenarios are considered namely, perfect and imperfect feedback channels. Results show that the spectral efficiency (SE) degradation, which is due to an imperfect feedback channel, was approximately 14% for conventional relays. The use of energy harvesting results in a degradation in the performance of SE of approximately 19% in case of a perfect feedback channel. Finally, an increase in the number of energy harvesting relays enhances the SE by 22%