Energy-Efficient Resource Allocation in SWIPT Enabled NOMA Systems

In this paper, we investigate joint power allocation and time switching (TS) control for energy efficiency (EE) optimization in a TS-based simultaneous wireless information and power transfer (SWIPT) non-orthogonal multiple access (NOMA) system. Our aim is to optimize the EE of the system whilst satisfying the constraints on maximum transmit power, minimum data rate and minimum harvested energy per-terminal. The considered EE optimization problem is formulated and then transformed according to the duality of broadcast channels (BC) and multiple access channels (MAC). The corresponding non-linear and non-convex optimization problem, involving joint optimization of power allocation and time switching factor, is difficult to solve directly. In order to tackle this problem, we develop a dual-layer algorithm where a convex programming-based Dinkelbach's method is proposed to optimize the power allocation in the inner-layer and an efficient search method is then applied to optimize the TS factor in the outer-layer. Numerical results validate the theoretical findings and demonstrate that significant performance gain over orthogonal multiple access (OMA) scheme in terms of EE can be achieved by the proposed algorithm in a SWIPT-enabled NOMA system

Joint 3D Trajectory Design and Time Allocation for UAV-Enabled Wireless Power Transfer Networks

This paper considers a rotary-wing unmanned aerial vehicle (UAV)-enabled wireless power transfer system, where a UAV is dispatched as an energy transmitter (ET), transferring radio frequency (RF) signals to a set of energy receivers (ERs) periodically. We aim to maximize the energy harvested at all ERs by jointly optimizing the UAV's three-dimensional (3D) placement, beam pattern and charging time. However, the considered optimization problem taking into account the drone flight altitude and the wireless coverage performance is formulated as a non-convex problem. To tackle this problem, we propose a low-complexity iterative algorithm to decompose the original problem into four sub-problems in order to optimize the variables sequentially. In particular, we first use the sequential unconstrained convex minimization based algorithm to find the globally optimal UAV two-dimensional (2D) position. Subsequently, we can directly obtain the optimal UAV altitude as the objective function of problem is monotonic decreasing with respect to UAV altitude. Then, we propose the multiobjective evolutionary algorithm based on decomposition (MOEA/D) based algorithm to control the phase of antenna array elements, in order to achieve high steering performance of multi-beams. Finally, with the above solved variables, the original problem is reformulated as a single-variable optimization problem where charging time is the optimization variable, and can be solved using the standard convex optimization techniques. Furthermore, we use the branch and bound method to design the UAV trajectory which can be constructed as traveling salesman problem (TSP) to minimize flight distance. Numerical results validate the theoretical findings and demonstrate that significant performance gain in terms of sum received power of ERs can be achieved by the proposed algorithm in UAV-enabled wireless power transfer networks

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

MIMO wireless communications in frequency selective fading channels

Multiple-input multiple-output (MIMO) wireless communication system exploits the multiple spatial channels to achieve higher data rate or improved performance in multipath fading environment. Various MIMO systems have been proposed recently, where the most well developed and promising schemes are the Vertically-layered Bell Laboratories Layered Space-Time (V-BLAST) system, the Space-Time Trellis Code (STTC), and the Space-Time Block Code (STBC). These schemes assumed flat fading channels, and exploration into frequency selective fading channels is a challenging and necessary footstep for practical high-speed realization. In this thesis, we investigate these MIMO systems in frequency selective fading channels, and propose several schemes using maximum likelihood sequence estimator (MLSE) to combat this performance limiting impairment. The V-BLAST system in these channels is investigated first and three layered detection techniques are proposed, namely the Zero-Forcing Maximal Ratio Combining (ZF-MRC), the Layered Maximum Likelihood Detection (L-MLD), and the Group Maximum Likelihood Detection (G-MLD). In addition, we propose the imaginary transmit antenna idea to facilitate the derivation of these schemes, and the imaginary receive antenna idea to reduce the number of receiving antennas. Analysis showed that the L-MLD and G-MLD schemes outperform other existing solutions. In our second contribution, we analyze the STTC with ML equalization and detection (MLED), and with the orthogonal frequency division multiplexing (OFDM) over frequency selective fading channels. Their performance bounds are derived and their code design criterions, receiver complexity and other issues are compared and discussed. From this analysis, we found that both schemes have different advantages over each other and in particular, the STTC MLED is more preferable in short delay spread channels. However, the STTC MLED assumes perfect channel knowledge in the receiver, but channel estimation is required in practice. To provide reliable channel estimates and reduce unnecessary computations in conventional receivers, we propose a novel Expectation-Maximization (EM) receiver that performs channel gain, channel order, and sequence estimation. Simulation results showed that the proposed scheme outperforms the conventional receiver with lesser complexity, and is highly robust in various channel environments. Finally, we study the concatenation of trellis-coded modulation with Time-Reversal STBC (TR-STBC) for frequency selective fading channels, and obtain a sub-optimal code design criterion. From the simulation results, the concatenated system with the proposed codes achieves better performance with lesser complexity than STTC over the same channel environment