Temel Engin Tuncer

Object reconstruction from in-line Fresnel holograms without explicit depth focusing

We propose two computational techniques for extracting object cross-sectional shape information from digitized in-line Fresnel holograms that do not require prior knowledge of object depths but recover relative depth information along the way. The first algorithm is applicable to hologram segments involving a single particle only. It is based on estimating Fourier transform magnitude and phase of the particle from those of the hologram segment. The second algorithm conducts a joint inverse filtering and depth search procedure so as to minimize (or maximize) a binariness (or a concentration) criterion defined over the output object function. It is applicable to multiple-particle, multiexposure holograms as well. The proposed techniques are illustrated on synthesized holograms and their practical limitations are discussed.

Antenna Selection and Hybrid Beamforming for Simultaneous Wireless Information and Power Transfer in Multi-Group Multicasting Systems

In this paper, low-cost alternatives to full digital beamforming, namely, antenna selection and hybrid beamforming, are proposed for simultaneous wireless information and power transfer in a multi-group multicasting scenario. The joint problem can be outlined as the design of beamformer weight vectors and power splitting ratios in order to satisfy both signal-to-interference-plus-noise-ratio and harvested power constraints at each user with minimum transmission power. We first develop an efficient algorithm for antenna selection by converting the original mixed integer programming problem into a continuous one and adapting feasible point pursuit-successive convex approximation. Second, a new hybrid beamforming structure is presented for multi-group multicasting. Both continuous and discrete-phase hybrid beamformers are considered in this content. Two algorithms for continuous-phase case are developed by employing two competing techniques. In addition, a special two-bit discrete-phase hybrid beamformer design is considered for practical systems. The integer constraints are converted into linear equality and inequalities for this specific structure and an efficient algorithm is designed. The proposed algorithms are compared for different scenarios revealing some interesting characteristics of each technique.

Max–Min Fair Resource Allocation for SWIPT in Multi-Group Multicast OFDM Systems

Simultaneous wireless information and power transfer is considered for multi-group multicasting OFDM systems. Each user has the energy harvesting capability through a power splitter (PS). The power and subcarrier allocation at the base station is done such that the minimum signal-to-noise ratio among the users for each subcarrier is maximized while user needs for harvested power are satisfied. The optimization of PS ratios in addition to resource allocation is realized in a joint manner. It is shown that the problem can be cast in a convex optimization form for the given subcarrier sets. In order to determine the subcarrier sets, an efficient subcarrier allocation algorithm is proposed. It is shown that the proposed method performs very close to the exhaustive search, which gives the optimum solution.

A fast and automatically paired 2-dimensional direction-of-arrival estimation using arbitrary array geometry

A new approach is proposed for two-dimensional (2-D) direction-of-arrival (DOA) estimation with arbitrary array geometries, which is based on array interpolation. The method provides automatically paired source azimuth and elevation angle estimates. Furthermore it is possible to estimate D sources with D+1 sensor. 2-D array interpolation errors are minimized by using Wiener formulation. Proposed method is applied to the two planar arrays; uniform circular array (UCA) and uniform isotropic (IU) V-shaped array. It seen that the method can find closed form, automatically paired azimuth and elevation angles. Simulation results are presented verifying the efficacy of the method.

Direction of Arrival Estimation in Non-Uniform Linear Arrays for Wide Band Signals

Direction of arrival estimation of wideband signals takes an important place in both literature and practical applications. Although there are several studies on this topic, behavior of non-uniform linear arrays (NLA) for wideband signals was not investigated comprehensively. In this paper performance of Root-MUSIC algorithm is studied for wideband signals using NLA and a new approach is proposed. This new approach decreases the mean square error of the arrival angle estimation using Wiener formulation and initial estimate of the arrival angles. Advantages of NLA use for wideband signals are presented via several simulations.

Optimum QoS-Aware Beamformer Design for Full-Duplex Relay With Self-Energy Recycling

In this letter, we introduce quality of service-aware beamformer design for full-duplex wireless-powered relay with self-energy recycling. In the first phase of communication, the information signal is transmitted from the source to the relay. In the second phase, the relay forwards this signal using beamforming while it harvests energy via self recycling and from the source. The aim is to satisfy the signal-to-noise ratio requirement of the destination with minimum transmission power from the relay’s own battery. A closed-form solution for the optimum relay beamformer is derived and the feasibility conditions are obtained. The effects of different system parameters on the relay’s performance are discussed in the simulation results.

Relay-assisted beamforming for multicast systems with energy harvesting capability

In this paper, multi-group multicasting scenario is considered where single antenna sources transmit their own information to different groups of users with the help of single antenna relays. Users have energy harvesting capability, i.e., a part of the received signal is used for information decoding while the rest is used for energy harvesting. Beamforming is performed by the relays which use amplify-and-forward protocol. The design of complex relay coefficients and power splitting ratios for the users is studied and the resulting nonconvex optimization problem is converted into a form suitable for quadratically constrained quadratic programming. In this paper, phase-only beamforming is also considered and both problems are solved iteratively.

Two-bit hybrid beamforming for broadcasting

In this paper, a hybrid system consisting of analog and digital beamformers is proposed to reduce the hardware complexity of full digital beamforming. In analog beamforming part, specially chosen two-bit radio frequency (RF) phase shifters are used. Two-bit structure enables the conversion of the discrete optimization problem to a continuous programming form which gives faster and more efficient solution. The optimization problem is formulated as a quadratic-cost problem and is solved iteratively by exact penalty and semidefinite programming. Simulation results show that the proposed method performs with considerable efficiency and effectiveness.

Direction of arrival estimation in non-uniform linear arrays forwide band signals with colored noise

There are several studies in literature that investigated the direction of arrival estimation of wide band signals. In our previous study [1] using array interpolation in non-uniform linear arrays (NLA) for estimating arrival direction of wideband signals via Wiener formulization and initial estimate of the arrival angles is proposed as a new approach. During the array interpolation it was assumed that variances of noise and signals are known. In this study, it is assumed that variances of both signal and noise are unknown as in practical applications. Signal to noise power ratio (SNR) is extracted from the information recorded by only antenna sensors and this SNR information is used in array interpolation operation. In addition to that, in this study colored noise case is also considered. Performance increase of direction of arrival estimation is observed when estimating and using the SNR values of each frequency bin during the colored noise case.

Uniform and non-uniform V-shaped arrays for 2-D DOA estimation

In this study, a new method for optimum design of uniform and non-uniform V-shaped arrays is presented for azimuth and elevation angle estimation. The proposed design method finds an optimum angle between the linear sub-arrays of the V-array by using the Cramer-Rao bound (CRB) where statistical coupling effect between azimuth and elevation angle estimation is considered. This method can be used to obtain directional and isotropic angle performances for uniform and non-uniform V-arrays. For non-uniform isotropic V-array symmetric and non-symmetric design examples are given. Furthermore the modelling error for the sensor positions is also investigated. The direction of arrival (DOA) performance comparisons of designed V-arrays and uniform circular array (UCA) are also presented and it is shown that the designed arrays have better DOA accuracy.