Zhongxiang Wei

Full-Duplex Versus Half-Duplex Amplify-and-Forward Relaying: Which is More Energy Efficient in 60-GHz Dual-Hop Indoor Wireless Systems?

We provide a comprehensive energy efficiency (EE) analysis of the full-duplex (FD) and half-duplex (HD) amplify-and-forward (AF) relay-assisted 60-GHz dual-hop indoor wireless systems, aiming to answer the question of which relaying mode is greener (more energy efficient) and to address the issue of EE optimization. We develop an opportunistic relaying mode selection scheme, where FD relaying with one-stage self-interference cancellation (passive suppression) or two-stage self-interference cancellation (passive suppression + analog cancellation) or HD relaying is opportunistically selected, together with transmission power adaptation, to maximize the EE with given channel gains. A low-complexity joint mode selection and EE optimization algorithm are proposed. We show a counter-intuitive finding that with a relatively loose maximum transmission power constraint, FD relaying with two-stage self-interference cancellation is preferable to both FD relaying with one-stage self-interference cancellation and HD relaying, resulting in a higher optimized EE. A full range of power consumption sources is considered to rationalize our analysis. The effects of imperfect self-interference cancellation at relay, drain efficiency, and static circuit power on EE are investigated. Simulation results verify our theoretical analysis.

Energy-Efficiency of Millimeter-Wave Full-Duplex Relaying Systems: Challenges and Solutions

Full-duplex (FD) relaying is a promising solution for fifth generation (5G) wireless communications due to its potential to provide high spectral efficiency (SE) transmission. However, FD relay nodes consume much higher power than half-duplex relay nodes, especially in millimeter (mm)-wave band. Therefore, energy-efficiency (EE) is an important issue to address for mm-wave FD relaying systems, which highlights the green evolution of 5G wireless communications. Existing FD relaying related research is SE-oriented, which is not efficient in cutting carbon footprint. This particle is different in that it addresses the critical EE challenges in implementing FD relaying in mm-wave systems, including low drain efficiency of power amplifier, high circuit power consumption, and additional power required by FD relays to mitigate self-interference. Based on the features of mm-wave communications, we outline a number of promising EE-oriented solutions for designing FD relaying enabled systems, including adaptive self-interference cancellation, transmission power adaptation, hybrid relaying mode selection, multi-input-multi-output (MIMO), and massive MIMO FD relaying. Some EE-oriented future research is also envisaged for mm-wave FD relaying systems.

Energy-Efficiency-Oriented Cross-Layer Resource Allocation for Multiuser Full-Duplex Decode-and-Forward Indoor Relay Systems at 60 GHz

Energy-efficiency (EE)-oriented green communication design is an important issue at 60 GHz due to high power consumption of devices working at such a high frequency. In this paper, we investigate EE-oriented resource allocation for full-duplex (FD) decode-and-forward relay-assisted 60-GHz multiuser indoor systems. In contrast to the existing spectral efficiency (SE)-oriented designs, our scheme maximizes the EE for a FD relaying system under cross-layer constraints, addressing the typical problems at 60 GHz, such as the intermittent signal blockage caused by the small wavelength of millimeter-wave. A low-complexity EE-orientated resource allocation algorithm is proposed, by which the transmission power allocation, subcarrier allocation, and throughput assignment are performed jointly across multiple users. Simulation results verify our analytical results and confirm that the FD relaying with the proposed algorithm achieves a higher EE than the FD relaying with SE-oriented approaches, while offering a comparable SE. In addition, a much lower throughput outage probability is guaranteed by the proposed resource allocation algorithm, showing its robustness against channel estimation errors. A full range of power consumption sources and imperfect self-interference cancellation are considered to rationalize our analysis.

Wireless Information and Power Transfer: Spectral Efficiency Optimization for Asymmetric Full-Duplex Relay Systems

To address the problem of unbalanced received signal-to-interference-and-noise ratio (SINR) at relay and destination nodes in wireless power transfer (WPT)- supported relay system, we propose a novel asymmetric full-duplex (FD) decode-and-forward (DF) WPT relay strategy, where the transmission time slots are not necessarily identical. By introducing asymmetric time slots, higher degree of freedom is obtained than the conventional symmetric WPT relay system. Furthermore, based on the asymmetric strategy, we develop a spectral efficiency (SE)- oriented resource allocation algorithm by jointly designing time slots, transmission power at source and relay. Simulation results show that the proposed asymmetric system demonstrates higher SE than the symmetric WPT-powered FD and the time- switching based FD relay systems. Besides, more energy can be harvested at the relay node by the proposed system benefiting from the enhanced degree of freedom, showing its applicability in WPT-powered relay systems.

Big data driven information diffusion analysis and control in online social networks

Thanks to recent advance in massive social data and increasingly mature big data mining technologies, information diffusion and its control strategies have attracted much attention, which play pivotal roles in public opinion control, virus marketing as well as other social applications. In this paper, relying on social big data, we focus on the analysis and control of information diffusion. Specifically, we commence with analyzing the topological role of the social strengths, i.e., tie strength, partial strength, value strength, and their corresponding symmetric as well as asymmetric forms. Then, we define two critical points for the cascade information diffusion model, i.e., the information coverage critical point (CCP) and the information heat critical point (HCP). Furthermore, based on the two real-world datasets, the proposed two critical points are verified and analyzed. Our work may be beneficial in terms of analyzing and designing the information diffusion algorithms and relevant control strategies.

Semi-blind precoding aided ML CFO estimation for ICA based MIMO OFDM systems

We propose a semi-blind precoding aided maximum likelihood (ML) carrier frequency offset (CFO) estimation method and a precoding aided equalization based on independent component analysis (ICA) receiver structure for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication systems. By carefully designing a constant in the precoding process, the power between reference data and source data can be balanced to enable ML CFO estimation and ambiguity elimination for the ICA output signals at the receiver. This proposed semi-blind non-redundant structure is much more bandwidth-and-energy efficient than the pilot aided ML CFO estimation method, as no real-time training or extra transmission power is required. Simulation results show that the proposed scheme provides a bit error rate (BER) performance the same as the performance of the pilot aided ML CFO estimation method, and close to the ideal case with perfect channel state information (CSI) and no CFO.

Cross-layer energy-efficiency optimization for multiuser full-duplex decode-and-forward indoor relay networks at 60 GHz

Energy efficiency (EE) is an important issue at 60 GHz due to high power consumption of devices working at such high frequency. In this paper, we investigate EE optimization for full-duplex (FD) decode-of-forward (DF) relay-assisted 60 GHz multiuser indoor networks. In contrast to the existing spectral efficiency (SE) optimization, our scheme maximizes system EE for FD relaying system under cross-layer constraints, addressing the typical problems at 60 GHz, such as the effect of imperfect channel estimation due to serious signal blockage. A low-complexity EE-orientated optimization algorithm is proposed, by which the transmission power, subcarriers and throughput are allocated jointly across multiple users. Simulation results verify our analytical results and confirm that the proposed algorithm achieves a higher EE than the SE-oriented approach, while offering a comparable SE. Also, FD relaying with the proposed algorithm outperforms HD relaying in terms of both EE and SE. In addition, a much lower throughput outage probability is guaranteed by the proposed algorithm, showing its robustness against channel estimation errors. A full range of power consumption sources and imperfect self-interference cancellation are considered to rationalize our analysis.

Semi-blind full-duplex relay system with ICA based joint CFO mitigation and equalization

We propose a semi-blind independent component analysis (ICA) based receiver structure for an uplink orthogonal frequency division multiplexing (OFDM) based wireless system with multiple users, an amplify-and-forward (AF) relay in full-duplex mode, and a multi-antenna base station. We propose a one-step solution to mitigate multiple integer CFOs without explicit CFO estimation. Also, channel equalization is performed jointly with CFO mitigation by using ICA. A non-redundant precoding designed offline is applied to the transmitted signals, requiring no real-time training or extra transmission power, to enable integer CFO mitigation and ambiguity elimination for the ICA output signals at the base station. Simulation results show that the proposed scheme provides a bit error rate (BER) performance comparable to the ideal case with perfect channel state information (CSI) and no CFO. It is also much more robust against the fractional CFO estimation error than existing methods. Furthermore, the effect of imperfect self-interference cancellation at the full-duplex relay on performance is investigated.

Energy efficiency optimization for full-duplex relaying with hybrid self-interference cancellation in 60 GHz indoor wireless systems

An intensive analysis of energy efficiency (EE) is presented for full-duplex (FD) relay-assisted 60 GHz indoor wireless systems. It is proved that the EE of FD relaying systems is strictly quasi-concave or mono-increasing with respect to transmission power at source node, under a maximum transmission power constraint. We develop a hybrid self-interference cancellation scheme for the full-duplex relay, where one-stage interference cancellation (passive suppression) or two-stage interference cancellation scheme (passive suppression + analog cancellation) is opportunistically selected, together with transmission power adaptation, to maximize the instantaneous EE with given channel gains. A low-complexity optimization algorithm is proposed. We show a counter-intuitive finding that, with a relatively loose maximum transmission power constraint, the two-stage self-interference cancellation scheme is preferable to the one-stage solution, resulting in a higher optimized EE. Simulation results also show that FD relaying is much more energy efficient than half-duplex (HD) relaying.