Yufei Jiang

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.

Low-Complexity Semiblind Multi-CFO Estimation and ICA-Based Equalization for CoMP OFDM Systems

We propose a low-complexity semiblind structure with multiple-carrier-frequency-offset (CFO) estimation and independent component analysis (ICA)-based equalization for multiuser coordinated multipoint (CoMP) orthogonal frequency-division-multiplexing (OFDM) systems. A short pilot is carefully designed for each user and has a twofold advantage. On the one hand, using the pilot structure, a complex multidimensional search for multiple CFOs is divided into a number of low-complexity monodimensional searches. On the other hand, the cross correlations between the transmitted and the received pilots are explored to allow simultaneous elimination of permutation ambiguity and quadrant ambiguity in the ICA equalized signals. Simulation results show that with a low training overhead of 1.6%, the proposed semiblind system not only outperforms the existing multi-CFO estimation schemes in terms of bit error rate (BER) and mean square error (MSE) of multi-CFO estimation but achieves a BER performance close to the ideal case with perfect channel state information (CSI) and no CFO at the receiver as well.

Semi-blind MIMO OFDM systems with precoding aided CFO estimation and ICA based equalization

We propose a semi-blind multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system, with a precoding aided carrier frequency offset (CFO) estimation approach, and an independent component analysis (ICA) based equalization structure. A number of reference data sequences are carefully designed offline and are superimposed to source data via a non-redundant linear precoding process, which can kill two birds with one stone, without introducing any extra total transmit power and spectral overhead. First, the reference data sequences are selected from a pool of carefully designed orthogonal sequences. The CFO estimation is to minimize the sum cross-correlation between the CFO compensated signals and the rest orthogonal sequences in the pool. Second, the same reference data enable elimination of the permutation and quadrant ambiguity in the ICA equalized signals by maximizing the cross-correlation between the ICA equalized signals and the reference data. Simulation results show that, without extra bandwidth and power needed, the proposed semi-blind system achieves a bit error rate (BER) performance close to the ideal case with perfect channel state information (CSI) and no CFO. Also, the precoding aided CFO estimation outperforms the constant amplitude zero autocorrelation (CAZAC) sequences based CFO estimation approach, with no spectral overhead.

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.

Low-Complexity Frequency Synchronization for ICA Based Semi-Blind CoMP Systems with ICI and Phase Rotation Caused by Multiple CFOs

We propose a low-complexity frequency synchronization approach for semi-blind independent component analysis (ICA) based coordinated multi-point (CoMP) orthogonal frequency division multiplexing (OFDM) systems, with multiple carrier frequency offsets (CFOs). The key idea is to introduce a short pilot for both multi-CFO estimation and ambiguity elimination in the ICA equalized signals. First, by minimizing the cross-correlation between original pilots and received pilots with implicit phase rotation correction, the one-dimensional search based CFO estimation can be performed without trial ICI compensation and channel state information (CSI). Second, by maximizing the real part of the cross-correlation between ICA equalized pilots and original pilots, the same pilots can be used again to eliminate the permutation and quadrant ambiguity in the ICA equalized signals. Simulation results show that, with a very low training overhead of 2%, the proposed multi-CFO estimation approach outperforms existing methods. Also, the proposed semi-blind CoMP system can achieve a bit error rate (BER) performance close to the ideal case with perfect CSI and no CFO.

Semi-blind CoMP system with multiple-CFO estimation and ICA based equalization

We propose an orthogonal frequency division multiplexing (OFDM) based semi-blind coordinated multi-point (CoMP) system, with a low complexity estimation approach for multiple carrier frequency offsets (CFOs), and an equalization structure based on the independent component analysis (ICA). Our work is different in that a small number of well-designed pilot symbols are employed to kill two birds with one stone. On the one hand, using the structure of pilots, a complex multi-dimensional search for multiple CFOs is divided into a series of low-complexity mono-dimensional searches. On the other hand, the cross-correlation between the transmitted and the received pilot symbols is explored to allow elimination of the remaining ambiguity in the ICA equalized signals. Simulation results show that with a low training overhead of 3.1%, the proposed semi-blind system can achieve a bit error rate (BER) performance close to the ideal case with perfect channel state information (CSI) and no CFO at the receiver.

Energy-efficient positioning for cellular networks with unknown path loss exponent

We propose a received signal strength (RSS) based energy-efficient positioning approach for cellular networks with unknown path loss exponent (PLE). A low-complexity searching algorithm is proposed for PLE estimation and a low-complexity lateration algorithm is proposed to provide the searching criteria. Simulation results show that the proposed positioning method achieves an accuracy similar to that of the nonlinear least square (NLS) algorithm, while requiring a much lower complexity.

ICA based joint semi-blind equalization and CFO estimation for OFDMA systems

We propose a joint independent component analysis (ICA) based equalization and carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiple access (OFDMA) systems, which requires only a single pilot, resulting in a very low spectral overhead. On the one hand, a low-complexity ambiguity elimination method is proposed in the ICA equalized signals. By designing and exploring a fixed order of correlation in the transmitted signals, the permutation ambiguity problem is solved, while the remaining quadrant ambiguity is eliminated by one pilot symbol. One the another hand, linear CFO estimation is performed with a closed-form solution based on the phase difference between adjacent rows in the CFO-corrupted channel structure. Simulation results show that the proposed semi-blind ICA based scheme not only outperforms some existing CFO estimation approaches, but also provides a bit error rate (BER) performance, comparable to the ideal case with perfect channel state information (CSI) and no CFO.

Joint semi-blind channel equalization and ICI mitigation for carrier aggregation based CoMP OFDMA systems with multiple CFOs

We propose a joint semi-blind equalization and inter-carrier interference (ICI) mitigation scheme for multiple carrier frequency offsets (CFOs) corrupted signals in carrier aggregation (CA) based multiple access coordinated multi-point (CoMP) systems with OFDMA. The CFO-induced ICI is mitigated implicitly via the independent component analysis (ICA) based semi-blind equalization, without requiring an explicit process of estimation of multiple CFOs. Only a small number of pilots are used to resolve the remaining indeterminacies in the ICA equalized signals, introducing a very low training overhead. Simulation results show that the proposed semi-blind ICA based equalization scheme provides a bit error rate (BER) performance closed to the ideal case with perfect CSI and no CFO, and also outperforms the approach with the constant amplitude zero autocorrelation (CAZAC) sequences based explicit CFO estimation.

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.