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%

Channel estimation, synchronisation and contention resolution in wireless communication networks

In the past decade, the number of wireless communications users is increasing at an unprecedented rate. However, limited radio resources must accommodate the increasing number of users. Hence, the efficient use of radio spectrum is a critical issue that needs to be addressed. In order to improve the spectral efficiency for the wireless communication networks, we investigate two promising technologies, the relaying and the multiple access schemes. In the physical (PHY) layer of the open systems interconnect (OSI) model, the relaying schemes are capable to improve the transmission reliability and expand transmission coverage via cooperative communications by using relay nodes. Hence, the two-way relay network (TWRN), a cooperative communications network, is investigated in the first part of the thesis. In the media access control (MAC) layer of the OSI model, the multiple access schemes are able to schedule multiple transmissions by efficiently allocating limited radio resources. As a result, the contention-based multiple access schemes for contention resolution are explored in the second part of the thesis. In the first part of the thesis, the channel estimation for the two-way relay networks (TWRNs) is investigated. Firstly, the channel estimation issue is considered under the assumption of the perfect synchronisation. Then, the channel estimation is conducted, by relaxing the assumption of perfect synchronisation. Another challenge facing the wireless communication systems is the contention and interference due to multiple transmissions from multiple nodes, sharing the common communication medium. To improve the spectral efficiency in the media access control layer, a self-adaptive backoff (SAB) algorithm is proposed to resolve contention in the contention-based multiple access networks

Channel estimation, synchronisation and contention resolution in wireless communication networks

In the past decade, the number of wireless communications users is increasing at an unprecedented rate. However, limited radio resources must accommodate the increasing number of users. Hence, the efficient use of radio spectrum is a critical issue that needs to be addressed. In order to improve the spectral efficiency for the wireless communication networks, we investigate two promising technologies, the relaying and the multiple access schemes. In the physical (PHY) layer of the open systems interconnect (OSI) model, the relaying schemes are capable to improve the transmission reliability and expand transmission coverage via cooperative communications by using relay nodes. Hence, the two-way relay network (TWRN), a cooperative communications network, is investigated in the first part of the thesis. In the media access control (MAC) layer of the OSI model, the multiple access schemes are able to schedule multiple transmissions by efficiently allocating limited radio resources. As a result, the contention-based multiple access schemes for contention resolution are explored in the second part of the thesis. In the first part of the thesis, the channel estimation for the two-way relay networks (TWRNs) is investigated. Firstly, the channel estimation issue is considered under the assumption of the perfect synchronisation. Then, the channel estimation is conducted, by relaxing the assumption of perfect synchronisation. Another challenge facing the wireless communication systems is the contention and interference due to multiple transmissions from multiple nodes, sharing the common communication medium. To improve the spectral efficiency in the media access control layer, a self-adaptive backoff (SAB) algorithm is proposed to resolve contention in the contention-based multiple access networks

Tomlinson Harashima precoding design for non-regenerative MIMO relay networks

In this paper we consider the design of minimum mean square error (MMSE) transceivers for non-regenerative multiple input multiple output (MIMO) relay systems. Our design utilises Tomlinson Harashima precoding (THP) at the source along with linear processors in each stage of the network. Assuming full channel state information (CSI) is available at each node in the network the various processors are jointly optimised to minimise the system arithmetic mean square error (MSE) whilst abiding by average power constraints at both the source and relay terminals in the network. Simulations show that the proposed schemes outperform existing methods in terms of bit error ratio (BER)

Spectral-energy efficiency trade-off of relay-aided cellular networks

Wireless communication networks are traditionally designed to operate at high spectral e ciency with less emphasis on power consumption as it is assumed that endless power supply is available through the power grid where the cells are connected to. As new generations of mobile networks exhibit decreasing gains in spectral e ciency, the mobile industry is forced to consider energy reform policies in order to sustain the economic growth of itself and other industries relying on it. Consequently, the energy e ciency of conventional direct transmission cellular networks is being examined while alternative green network architectures are also explored. The relay-aided cellular network is being considered as one of the potential network architecture for energy e cient transmission. However, relaying transmission incurs multiplexing loss due to its multi-hop protocol. This, in turn, reduces network spectral e ciency. Furthermore, interference is also expected to increase with the deployment of Relay Stations (RSs) in the network. This thesis examines the power consumption of the conventional direct transmission cellular network and contributes to the development of the relay-aided cellular network. Firstly, the power consumption of the direct transmission cellular network is investigated. While most work considered transmitter side strategies, the impact of the receiver on the Base Station (BS) total power consumption is investigated here. Both the zero-forcing and minimum mean square error weight optimisation approaches are considered for both the conventional linear and successive interference cancellation receivers. The power consumption model which includes both the radio frequency transmit power and circuit power is described. The in uence of the receiver interference cancellation techniques, the number of transceiver antennas, circuit power consumption and inter-cell interference on the BS total power consumption is investigated. Secondly, the spectral-energy e ciency trade-o in the relay-aided cellular network is investigated. The signal forwarding and interference forwarding relaying paradigms are considered with the direct transmission cellular network taken as the baseline. This investigation serves to understand the dynamics in the performance trade-o . To select a suitable balance point in the trade-o , the economic e ciency metric is proposed whereby the spectral-energy e ciency pair which maximises the economic pro tability is found. Thus, the economic e ciency metric can be utilised as an alternative means to optimise the relay-aided cellular network while taking into account the inherent spectral-energy e ciency trade-o . Finally, the method of mitigating interference in the relay-aided cellular network is demonstrated by means of the proposed relay cooperation scheme. In the proposed scheme, both joint RS decoding and independent RS decoding approaches are considered during the broadcast phase while joint relay transmission is employed in the relay phase. Two user selection schemes requiring global Channel State Information (CSI) are considered. The partial semi-orthogonal user selection method with reduced CSI requirement is then proposed. As the cooperative cost limits the practicality of cooperative schemes, the cost incurred at the cooperative links between the RSs is investigated for varying degrees of RS cooperation. The performance of the relay cooperation scheme with di erent relay frequency reuse patterns is considered as well. In a nutshell, the research presented in this thesis reveals the impact of the receiver on the BS total power consumption in direct transmission cellular networks. The relayaided cellular network is then presented as an alternative architecture for energy e cient transmission. The economic e ciency metric is proposed to maximise the economic pro tability of the relay network while taking into account the existing spectral-energy e ciency trade-o . To mitigate the interference from the RSs, the relay cooperation scheme for advanced relay-aided cellular networks is proposed