Matrix Differential Calculus with Applications in Statistics and Econometrics

We study a certain random groeth model in two dimensions closely related to the one-dimensional totally asymmetric exclusion process. The results show that the shape fluctuations, appropriately scaled, converges in distribution to the Tracy-Widom largest eigenvalue distribution for the Gaussian Unitary Ensemble.

Shape Fluctuations and Random Matrices

In this chapter we deal with the following nonlinear fractional programming problem: 

$$P:\mathop{{\max }}\limits_{{x \in s}} q(x) = (f(x) + \alpha )/((x) + \beta )$$

where f, g: R n → R, α, β ∈ R, S ⊆ R n . To simplify things, and without restricting the generality of the problem, it is usually assumed that, g(x) + β + 0 for all x ∈ S,S is non-empty and that the objective function has a finite optimal value.

Nonlinear Fractional Programming

Radio waves carry both energy and information simultaneously. Nevertheless, radio-frequency (RF) transmissions of these quantities have traditionally been treated separately. Currently, the community is experiencing a paradigm shift in wireless network design, namely, unifying wireless transmission of information and power so as to make the best use of the RF spectrum and radiation as well as the network infrastructure for the dual purpose of communicating and energizing. In this paper, we review and discuss recent progress in laying the foundations of the envisioned dual purpose networks by establishing a signal theory and design for wireless information and power transmission (WIPT) and identifying the fundamental tradeoff between conveying information and power wirelessly. We start with an overview of WIPT challenges and technologies, namely, simultaneous WIPT (SWIPT), wirelessly powered communication networks (WPCNs), and wirelessly powered backscatter communication (WPBC). We then characterize energy harvesters and show how WIPT signal and system designs crucially revolve around the underlying energy harvester model. To that end, we highlight three different energy harvester models, namely, one linear model and two nonlinear models, and show how WIPT designs differ for each of them in single-user and multi-user deployments. Topics discussed include rate-energy region characterization, transmitter and receiver architectures, waveform design, modulation, beamforming and input distribution optimizations, resource allocation, and RF spectrum use. We discuss and check the validity of the different energy harvester models and the resulting signal theory and design based on circuit simulations, prototyping, and experimentation. We also point out numerous directions that are promising for future research.

Fundamentals of Wireless Information and Power Transfer: From RF Energy Harvester Models to Signal and System Designs

Radiative wireless power transfer (WPT) is a promising technology to provide cost-effective and real-time power supplies to wireless devices. Although radiative WPT shares many similar characteristics with the extensively studied wireless information transfer or communication, they also differ significantly in terms of design objectives, transmitter/receiver architectures and hardware constraints, and so on. In this paper, we first give an overview on the various WPT technologies, the historical development of the radiative WPT technology and the main challenges in designing contemporary radiative WPT systems. Then, we focus on the state-of-the-art communication and signal processing techniques that can be applied to tackle these challenges. Topics discussed include energy harvester modeling, energy beamforming for WPT, channel acquisition, power region characterization in multi-user WPT, waveform design with linear and non-linear energy receiver model, safety and health issues of WPT, massive multiple-input multiple-output and millimeter wave enabled WPT, wireless charging control, and wireless power and communication systems co-design. We also point out directions that are promising for future research.

Communications and Signals Design for Wireless Power Transmission

In this paper, we develop linear precoding methods for cognitive radio (CR) multi-user multiple-input multiple-output (MU-MIMO) broadcast systems where unlicensed secondary users (SUs) simultaneously use the same spectrum of the licensed primary user (PU). When the zero-forcing block diagonalization (ZF-BD) precoder is extended to the CR network, a noise enhancement problem occurs. Therefore, we propose a regularized BD precoder based on the minimum mean-square error (MMSE) criteria subject to zero interference constraint for the PU. As a result, the proposed MMSE-BD scheme improves the signal-to-interference-plus-noise ratio at each SU's receiver compared to the ZF-BD based method. Simulation results demonstrate that the proposed algorithm outperforms the ZF based technique by more than 5 dB at the sum-rate 10 bps/Hz for CR MU-MIMO downlink systems.

Linear Precoder Designs for Cognitive Radio Multiuser MIMO Downlink Systems

This paper proposes a heterogeneous network topology, where the backhaul links are supported by massive multiple-input multiple-output systems with full-duplex (FD) modes. Communication is achieved in two phases. In the first phase, we equip macro cell (MC) base station (BS) with massive receive antennas and few transmit antennas and all small cell (SC) BSs with massive receive antennas and a single transmit antenna. In the second phase, a circulator switches the massive receive antennas into transmit antennas and transmit antennas into receive antennas. Under the assumption of imperfect channel state information and large antenna regime, closed-form expressions have been derived for the uplink/downlink achievable sum-rate. From the results, we check that the strength of self-interference (SI) and SC-to-SC interference which occur due to FD operation depends largely on the number of SCs. By increasing the number of SCs, achievable sum-rates also increase but require more antennas to overcome the deleterious effects of the SI and SC-to-SC interference. Based on our analytical results, a hybrid FD/half-duplex system is proposed according to the interferences and the number of antennas. Furthermore, using our system model, it is shown that the transmit power of the MC BS and the SC BSs can be scaled down proportionally to the massive number of receive antennas (first phase) and the massive number of transmit antennas (second phase) and still achieve a required rate.

Achievable Sum-Rate Analysis of Massive MIMO Full-Duplex Wireless Backhaul Links in Heterogeneous Cellular Networks

Link adaptation allows a communication system to adapt its transmission modes according to channel conditions. Although a maximum likelihood (ML) receiver for multiple-input multiple-output (MIMO) systems provides optimal performance, estimating its link performance has been a difficult problem. In this paper, we propose a new link performance abstraction technique for MIMO orthogonal frequency-division multiplexing systems with the ML receiver. The performance of ML detection (MLD) is estimated by employing capacity bounds of two simple linear receivers. Then, we give a simple parametrization to compute the desired per-stream signal-to-noise ratio (SNR) values, which can be applied for both vertically and horizontally coded MIMO systems. Based on the derived per-stream SNR estimates, the block error rate is obtained using the received-bit information rate metrics. We also examine the effect of imperfect channel estimation as well as spatial correlations among antennas. Finally, extensive simulation results show that the proposed method provides superior estimation accuracy in the MIMO-MLD link evaluation with very low computational complexity.

Link Performance Estimation Techniques for MIMO-OFDM Systems with Maximum Likelihood Receiver

It was shown by Cadambe and Jafar that the interference alignment (IA) algorithm achieves the theoretical bound on degrees of freedom (DOF) for interference channel systems. However, since this method addresses the precoder design problem from the DOF point of view, some optimization processes are additionally needed in order to improve the sum rate performance. In this paper, based on the IA method, we propose a two-stage optimization of the precoding and decoding matrices in the interference channels. Simulation results show that the proposed method significantly improves the sum rate of the conventional IA scheme while maintaining the optimality of the DOF.

A Two-Stage Precoding Method Based on Interference Alignment for Interference Channel Systems

This letter studies physical layer security (PLS) in non-orthogonal multiple access (NOMA) power line communication (PLC) networks A source node transmits information to two nodes of near and far users with different power allocations We consider two different cases of eavesdropping: internal and external The PLC channel and noise are modeled by correlated log-normal fading and Bernoulli-Gaussian random process, respectively We derive closed-form expressions for the secrecy outage probability (SOP) of both the internal and external cases by applying Gauss-Chebyshev quadrature, which are verified by Monte Carlo simulations We observe that higher impulsive noise degrades the SOP while higher channel correlation can improve the SOP In addition, the analytic results reveal the impact of power allocation on the SOP performance

Kyoung-Jae Lee

Papers

Linear Precoder Designs for Cognitive Radio Multiuser MIMO Downlink Systems

Achievable Sum-Rate Analysis of Massive MIMO Full-Duplex Wireless Backhaul Links in Heterogeneous Cellular Networks

Link Performance Estimation Techniques for MIMO-OFDM Systems with Maximum Likelihood Receiver

A Two-Stage Precoding Method Based on Interference Alignment for Interference Channel Systems

Secrecy Outage Analysis in NOMA Power Line Communications