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

Iterative Decoding And Detection For CDMA Systems On Non-Gaussian Channels

The presence of impulsive non -Gaussian noise in multiple access channels presents a challenge to the operation of iterative/turbo multiuser receivers without proper mitigating measures. Thus, the study is extended to impulsive non-Gaussian channels whereby it is found that the performance of Gaussian iterative/turbo multiuser receivers seriously degrades when the underlying noise density function departs from Gaussianity

Optimization of Multi-objective Resource Allocation Problem in Cognitive Radio LTE/LTE-A Femtocell Networks Using NSGA II

In LTE/LTE-A networks, femtocells are used to improve service coverage in indoor environments. Cognitive radio allows femtocell users to share the available spectrum with primary macrocell users. However, some issues arise because of the coexistence between femtocells and macrocells. These issues include but not limited to mitigating interference and fair distribution of network resources. In this paper, we use NSGA II to solve a multi-objective optimization problem that maximizes resource utilization while minimizing interference and guaranteeing fairness among users in a femtocell LTE/LTE-A network. Simulation results show that the proposed scheme improves the multi-objective function score by 8% and enhances the overall performance of the network

On the Efficiency of MIMO Transmission with Channel State Information Feedback

A channel state information (CSI) feedback algorithm based on scalar quantization is proposed for a multiple-input multiple-output (MIMO) transmission. The performance of the proposed algorithm is evaluated using the effective transmission rate, which incorporates the effect of the CSI feedback overhead on transmission time. Besides that, the power consumed due to the computational complexity of the CSI feedback algorithm is taken into account together with the transmit power when evaluating the energy efficiency. We compare our proposed algorithm to other typical CSI feedback algorithms under correlated channel conditions. Simulation results show that the proposed algorithm enables practical MIMO transmission to achieve an relative transmission rate at 95% of the ideal rate

Trade-Off Performances in Multiuser MIMO Networks with Quantized CSI Feedback

Multiuser multiple-input multiple-output transmission is identified as one of the promising techniques to vastly increase the transmission rate especially in densely deployed networks where inter-user interference is a major issue. To achieve this, channel state information (CSI) is needed to ensure accurate precoder design at the transmitter in order to effectively mitigate inter-user interference. However, the CSI is usually estimated at the receiver and, after quantization, is sent back to the transmitter. The feedback of quantized CSI incurs additional overhead which then leads to trade-off performances between transmission rate and energy efficiency. We will analyze this trade-off and propose the economy efficiency metric as a potential tool to determine the best operating point when the network is jointly optimized using transmission rate and energy efficienc

Improved Joint Cell Association and Interference Mitigation for LTE-A Heterogeneous Networks

Existing cell association do not jointly consider load balancing and throughput maximization for efficient resource allocation in Long Term Evolution-Advanced heterogeneous networks. In this paper, a hybrid cell range extension-almost blank subframe (CRE-ABS) scheme is proposed, which exploits the information of distance and signal-to-interference-plus-noise ratio (SINR) to perform cell association and executes partial muting. Results show that the proposed scheme achieves better performance compared to the baseline scheme in terms of throughput and network load balancing

Design of Wilkinson power divider at 28 GHz for 5G applications

A power divider plays a significant function in antenna’s feeding network. Many types of power divider exist yet there are only a few existing studies of Wilkinson power dividers at high frequencies (28 GHz) for 5G communications systems. This paper presents a tapered 2-way Wilkinson power divider that operates in Malaysia's 5G wireless communication band (28 GHz). CST microwave studio is used to design, simulate, and optimize the tapered 2-way Wilkinson divider. The simulation results show resonance around 23.5-37.9 GHz. The operating frequency of 28 GHz resulted in power division with a 3.2 dB insertion loss and has an isolation of 19.21 dB. The design can be made wideband with equal power division at each output port by adding an extra resistor along the tapered line to reduce output return loss and isolation, as demonstrated in this paper

Performance of Practical Multiuser MIMO Networks with Limited CSI Feedback

Efficient channel state information (CSI) feedback is crucial in practical multiuser multiple-input multiple-output (MU-MIMO) networks for effective interference mitigation. In this study, a CSI feedback scheme using random scalar quantization (RSQ) for MU-MIMO networks is proposed. The analytical expression for the quantization noise variance of the RSQ CSI feedback scheme is presented. Next, the lower bound of the relative transmission rate for the MU-MIMO network with RSQ CSI feedback is derived. Using a unified transmission framework, trade-off between the relative transmission rate and energy efficiency of the MU-MIMO network with RSQ CSI feedback is depicted. In a fully loaded network, it is shown that MU-MIMO with RSQ CSI feedback outperforms that of random vector quantization and sparse compression CSI feedback schemes by as much as 38% and 19%, respectively