Set Of Phase Shifts Research Articles

Energy-efficient resource allocation and user grouping for multi-IRS aided MU-MIMO system

In this paper, we consider a multiple-intelligent reflecting surface (IRS)-aided multi-user multiple-input-multiple-output (MU-MIMO) down-link communication system, wherein a base station (BS), equipped with multiple antennas, serves massive single-antenna users. In order to mitigate high inter-user interference, we divide all the users into a single near-user (NU) group and multiple cell-edge user (CEU) groups based on their connection with BS. In particular, we assign a single IRS for each CEU group such that the BS communicates and serves the set of CEUs using their corresponding IRS. Subsequently, we formulate a problem of energy-efficient resource allocation design subject to optimal beamforming design at BS and multiple IRS under given power constraints. Due to the non-convexity of the formulated resource allocation problem, we proposed two different alternating optimization frameworks which solve the joint optimization problem based on 1) minimum mean square error (MMSE) and Riemannian conjugate gradient (RCG) and 2) fractional programming and successive convex approximation techniques for active beamforming vectors at the BS and passive beamforming vectors for IRSs, respectively. Simulation results confirm that the MMSE-RCG-based resource allocation design attains fast convergence when compared to sequential fractional programming (SFP) based solution. Moreover, the MMSE-RCG attains better energy efficiency whereas the SFP renders better spectral performance. Nevertheless, both the proposed solution achieve 70%–80% better performance than random phase-shift settings.

Impact of the Refractive Index on the Achievable Rate of Liquid Crystal-Based Digital-RIS Indoor VLC Systems

In wireless networks, reconfigurable intelligent surfaces (RISs) have recently been proven to have a significant impact. The RIS has been incorporated into wireless communication systems to improve security, increase coverage, reduce interference, and improve transmission quality. Digital RIS (DRISs) have also proven to provide better reflection management. However, the impact of the DRIS intrinsic parameters on the system's achievable rate, has not yet been investigated. Due to their availability and easily reconfigurable properties, liquid crystals (LCs) appear as suitable materials for use in DRIS, specifically in optical communication systems. This paper analyzes the effect of the LC's refractive index on the achievable rate of LC-based DRIS indoor visible light communication systems. Based on a set of discrete phase shifts, required refractive indices have been evaluated. The reflected power and achievable rates are determined with respect to incoming light wavelengths at 510 nm, 550 nm, and 670 nm. According to the obtained numerical results, there is no linear relationship between refractive indices, corresponding transition coefficients, phase shifts, light power, and achievable rate.

Energy-Efficient Power Control and Beamforming for Reconfigurable Intelligent Surface-Aided Uplink IoT Networks

Recently, reconfigurable intelligent surface (RIS), a planar metasurface consisting of a large number of low-cost reflecting elements, has received much attention due to its ability to improve both the spectrum and energy efficiencies by reconfiguring the wireless propagation environment. In this paper, we propose an RIS phase shift and BS beamforming optimization technique that minimizes the uplink transmit power of the RIS-aided IoT network. Key idea of the proposed scheme, referred to as Riemannian conjugate gradient-based joint optimization (RCG-JO), is to jointly optimize the RIS phase shifts and the BS beamforming vectors using the Riemannian conjugate gradient technique. By exploiting the product Riemannian manifold structure of the sets of unit-modulus phase shifts and unit-norm beamforming vectors, we convert the nonconvex uplink power minimization problem into the unconstrained problem and then find out the optimal solution over the product Riemannian manifold. From the performance analysis and numerical evaluations, we demonstrate that the proposed RCG-JO technique achieves 94% reduction of the uplink transmit power over the conventional scheme without RIS.

Fitness landscape analysis and niching genetic approach for hybrid beamforming in RIS-aided communications

Reconfigurable intelligent surface (RIS) is a revolutionizing technology to achieve cost-effective communications. The active beamforming at the base station (BS) and the discrete phase shifts at RIS should be jointly designed to customize the propagation environment. However, current phase-shift setting methods ignore the non-separable property of phase shifts, degrading the performance, especially in cases with a large-sized RIS. To understand the problem characteristics related to the phase shifts and further tailor an eligible method with such characteristics, this paper, for the first time, analyzes the fitness landscape of the sum-rate maximization problem (maximizing the sum rate of users in a downlink multi-user multiple-input single-output system assisted by a RIS). Results show that the problem has a severe unstructured and rugged landscape, especially in cases with a large-sized RIS. This observation answers why current methods are ineligible and provides insightful guidance for designing a more intelligent method. With the landscape findings in mind, this paper introduces a niching genetic algorithm to solve the problem. In particular, the niching idea is employed to locate multiple local optima. These local optima act as stepping stones to facilitate approaching the global optima. Simulation results demonstrate that the proposed niching genetic algorithm obtains significant capacity gains over current methods in cases with large-sized RIS.

A Trellis-Based Passive Beamforming Design for an Intelligent Reflecting Surface-Aided MISO System

In this letter, the downlink transmission of an intelligent reflecting surface (IRS)-assisted multiple-input single-output (MISO) system is investigated where the IRS elements are selected from a predefined discrete set of phase shifts. We minimize the mean square error (MSE) of the received symbols in the system via optimizing the phase shifts at the IRS jointly with beamforming vectors at the base station (BS) and equalizers at the user terminals. In order to find the optimal IRS phase shifts, a trellis-based structure is used that smartly selects the discrete phases. Moreover, for the sake of comparison, a semi-definite programming (SDP)-based discrete phase optimization is also presented. The BS beamformer and the optimal equalizers are determined via closed-form solutions. Numerical results demonstrate that the trellis-based scheme has better performance compared to other discrete IRS phase shift designs, such as SDP and quantized majorization-minimization technique, while maintaining a very low computational complexity.

A Closed Form Selected Mapping Algorithm for PAPR Reduction in OFDM Multicarrier Transmission

Nowadays, the demand for communication multi-carriers’ channels, where the sub-channels are made mutually independent by using orthogonal frequency division multiplexing (OFDM), is widespread both for wireless and wired communication systems. Even if OFDM is a spectrally efficient modulation scheme, due to the allowed number of subcarriers, high data rate, and good coverage, the transmitted signal can present high peak values in the time domain, due to inverse fast Fourier transform operations. This gives rise to high peak-to-average power ratio (PAPR) with respect to single carrier systems. These peaks can saturate the transmitting amplifiers, modifying the shape of the OFDM symbol and affecting its information content, and they give rise to electromagnetic compatibility issues for the surrounding electric devices. In this paper, a closed form PAPR reduction algorithm is proposed, which belongs to selected mapping (SLM) methods. These methods consist in shifting the phases of the components to minimize the amplitude of the peaks. The determination of the optimal set of phase shifts is a very complex problem; therefore, the SLM approaches proposed in literature all resort to iterative algorithms. Moreover, as this calculation must be performed online, both the computational cost and the effect on the bit rate (BR) cannot be established a priori. The proposed analytic algorithm finds the optimal phase shifts of an approximated formulation of the PAPR. Simulation results outperform unprocessed conventional OFDM transmission by several dBs. Moreover, the complementary cumulative distribution function (CCDF) shows that, in most of the packets, the proposed algorithm reduces the PAPR if compared with randomly selected phase shifts. For example, with a number of shifted phases U=8, the CCFD curves corresponding to the analytical and random methods intersect at a probability value equal to 10−2, which means that in 99% of cases the former method reduces the PAPR more than the latter one. This is also confirmed by the value of the gain, which, at the same number of shifted phases and at the probability value equal to 10−1, changes from 2.09 dB for the analytical to 1.68 dB for the random SLM.

Reconfigurable Intelligent Surface Optimization for Uplink Sparse Code Multiple Access

The reconfigurable intelligent surface (RIS)-assisted sparse code multiple access (RIS-SCMA) is an attractive scheme for future wireless networks. In this letter, for the first time, the RIS phase shifts of the uplink RIS-SCMA system are optimized based on the alternate optimization (AO) technique to improve the received signal-to-noise ratio (SNR) for a discrete set of RIS phase shifts. The system model of the uplink RIS-SCMA is formulated to utilize the AO algorithm. For further reduction in the computational complexity, a low-complexity AO (LC-AO) algorithm is proposed. The complexity analysis of the two proposed algorithms is performed. Monte Carlo simulations and complexity analysis show that the proposed algorithms significantly improve the received SNR compared to the non-optimized RIS-SCMA scenario. The LC-AO provides the same received SNR as the AO algorithm, with a significant reduction in complexity. Moreover, the deployment of RISs for the uplink RIS-SCMA is investigated.

Multiprojector Multicamera Structured Light Surface Scanner

Structured light surface scanners are usually limited to a single projector and cannot provide a full surface profile in a single scan. Multiple projectors must be employed to extend the imaging area over the whole surface of the imaged object. Using multiple projectors is a challenging problem due to inter-projector interference which make pattern decoding hard. We describe a practical approach to multi-projector structured light surface scanning based on sinusoidal fringe patterns and temporal phase shifting which allows simultaneous projector employment. In our approach a different set of temporal phase shifts is assigned to each projector to enable efficient and robust separation of observed combined patterns into the contributions of each projector. The proposed approach does not place any restrictions on projector placement nor on the upper limit of the number of projectors used. We demonstrate the applicability of the proposed approach on a structured light surface scanner comprised of three projectors and six cameras.

Architecture agnostic algorithm for reconfigurable optical interferometer programming.

We develop the learning algorithm to build an architecture agnostic model of a reconfigurable optical interferometer. A procedure of programming a unitary transformation of optical modes of an interferometer either follows an analytical expression yielding a unitary matrix given a set of phase shifts or requires an optimization routine if an analytic decomposition does not exist. Our algorithm adopts a supervised learning strategy which matches a model of an interferometer to a training set populated by samples produced by a device under study. A simple optimization routine uses the trained model to output phase shifts corresponding to a desired unitary transformation of the interferometer with a given architecture. Our result provides the recipe for efficient tuning of interferometers even without rigorous analytical description which opens opportunity to explore new architectures of the interferometric circuits.

Deterministic spatial search using alternating quantum walks

This paper examines the performance of spatial search where the Grover diffusion operator is replaced by continuous-time quantum walks on a class of interdependent networks. We prove that, for a set of optimal quantum walk times and marked vertex phase shifts, a deterministic algorithm for structured spatial search is established that finds the marked vertex with 100% probability. This improves on the Childs and Goldstone spatial search algorithm on the same class of graphs, which we show can only amplify to 50% probability. Our method uses $\ensuremath{\lceil}\frac{\ensuremath{\pi}}{2\sqrt{2}}\sqrt{N}\ensuremath{\rceil}$ marked vertex phase shifts for an $N$-vertex graph, making it comparable to Grover's algorithm for an unstructured search. It is expected that this framework can be readily extended to deterministic spatial search on other families of graph structures.

Phase shift approach for engineering desired radiation force: Acoustic pulling force example.

Phase shifts from scattering are used to analyze and engineer acoustic radiation forces. With the aid of phase shifts, analytical results for acoustic radiation forces can be simplified into compact and physically meaningful expressions, which can be used to develop a simplified procedure for the engineering of the radiation force. The desired radiation force can be fulfilled by a specific set of phase shifts up to a certain order, and then the required phase shifts can be fulfilled by engineering object and beam parameters. As an example, the phase shift approach is used to engineer the inner-to-outer radius ratio and the outer radius of a spherical shell to show how to use the phase shift method for the design of acoustic radiation forces. The example here is a force that is desired to pull particles against the propagation of a Bessel beam. A small paraxial parameter to pull a spherical shell is satisfied by in-phase scattering of monopole, dipole, quadrupole, octupole, and beyond. The example presented here is relatively simple yet reveals the advantages of the phase shift approach. The phase shift method can provide a simplified route for the design of acoustic tweezers using either traveling beams or standing waves.

The experimental identification method of the dynamic efficiency for frequency regulation algorithms of AEDs

The article proposes and substantiates a method for studying the dynamics of an asynchronous electric drives with frequency control from the input side of the signal for setting the speed of rotation of the electric motor. In this method, a constant speed reference signal is added to a harmonic variable frequency signal. The set of amplitude changes and phase shifts of velocity oscillations are the initial data for identifying the dynamics of the studied control method. The logic of this method is determined by the previously obtained nonlinear transfer function of the link that forms the mechanical moment in the asynchronous electric drive with frequency control. Experiments have shown the dynamic benefits of the drive with positive stator current feedback.

Large Intelligent Surfaces With Discrete Set of Phase-Shifts Communicating Through Double-Rayleigh Fading Channels

Despite many studies already published on large intelligent surfaces (LIS), there are still some gaps in mathematical models in the face of possible scenarios. In this work, we evaluate the performance of a single-input single-output (SISO) system in which an LIS acts as a controllable scatterer. We consider that the direct link between the transmitting and receiving devices is non-existent due to a blockage. Quantization phase errors at the LIS are considered since a high precision configuration of the reflection phases is not always feasible. We derive exact closed-form expressions for the spectral efficiencies, outage probabilities, and average symbol error rate (SER) of different modulations schemes. We assume a more comprehensive scenario in which b bits are dedicated to the phase adjustment of the LIS' elements. Based on Monte Carlo simulations, we prove the excellent accuracy of our approach and investigate the behavior of the power scaling law and the power required to reach a specific capacity, depending on the number of reflecting elements. We show that an LIS with approximately fifty elements and four dedicated bits for phase quantization outperforms the conventional system without LIS.

Novel design for differential phase shifter structure by using multi‐section coupled lines

In this Letter, a new wideband differential phase shifter is proposed by using a multi-section coupled line structure. S-parameter circuit equations and design parameters are calculated using even/odd mode and transmission line analysis techniques for a set of phase shifters (from 0 to 90 with a step of 10°) of the proposed device. The proposed form is the first work that adds multi-section structures on the coupled line to provide any desired phase shift to the same reference line. In addition, for specific applications such as hyperthermia, the beamforming is ensured to be at small angle steps (10°) to focus the signal to the correct spot. The device is modelled with full-wave electromagnetic simulator Computer Simulation Technology (CST). Ten prototypes of differential phase shifters are designed, manufactured, and tested for the accuracy of simulation results. The simulated and measured results are in good agreement with the theory and show a bandwidth of 20.4%, 1 dB insertion loss across the 2.2–2.7 GHz frequency range.

Analysis of Possibility of Phase Shift Model Usage for Identification of Gas Leakage from Pipeline with Corrective Elements

Abstract Proposed method of leakage identification uses a parametric model in the form of signals phase shift (φ). Signals from the test stand will be used: r1, r2 - signals from the corrective elements connected to the tested pipeline, pressure signals x, mass flow y and simulated mass flow yw. For these signals, their auto and cross power spectral densities are determined: Sxx, Syy, Srr, Sxy, Sxr, Syr, which are the basis to determine spectral transfer functions described as the relations between these signals and next the phase shifts (φ). Thanks that, we get a large set of transfer functions, hence a large set of phase shifts between the measured.

Digital Predistortion of Millimeter-Wave RF Beamforming Arrays Using Low Number of Steering Angle-Dependent Coefficient Sets

This paper proposes a single-input single-output (SISO) digital predistortion (DPD) model for linearizing millimeter-wave (mm-wave) RF beamforming arrays. It starts with a dual-input power amplifier (PA) model that accounts for steering angle-dependent load modulation effects. This dual-input model is then transformed into a SISO model under the assumption of weak PA nonlinearity and RF beamforming architecture. The underlying coefficients of the SISO array model incorporate the beamforming weights, antenna cross-coupling, channel coefficients, and any possible phase-shifter gain variation with phase shift setting. An over-the-air (OTA) measurement setup is finally developed to validate the capacity of a SISO DPD model to linearize two different arrays-under-test with 4 and 64 elements and radiating mm-wave modulated signals with 320- and 800-MHz bandwidth. Although, in principle, the DPD coefficients should be retrained for each steering angle, experimental results have shown that the same set of coefficients can be used over a wide range of steering angles, and only a few sets of trained DPD coefficients are sufficient to minimize the distortion in a mm-wave RF beamforming array across a 120° steering range.

Digitally Assisted 28 GHz Active Phase Shifter With 0.1 dB/0.5° RMS Magnitude/Phase Errors and Enhanced Linearity

This brief presents a new digitally assisted vector-summing phase shifter (DA-VSPS) featuring high accuracy and enhanced linearity. It begins by highlighting the RF performance degradation of traditional DA-VSPSs operating at millimeter-wave frequencies due to the large number of unit-cells and the significant underlying parasitics. Then, a new DA-VSPS topology is proposed to mitigate this source of performance degradation using analog variable-gain amplifiers with digitally assisted current sources. A study of the accuracy and linearity of the proposed DA-VSPS is conducted to inform the choice of the optimal parameters (number of unit-cells and load impedance) that maximize the RF performance while minimizing the implementation complexity. A proof-of-concept prototype was implemented in 45 nm silicon-on-insulator CMOS technology. The measurement results demonstrated a 1-dB RF bandwidth from 27 to 33 GHz, root-mean-square magnitude and phase errors of 0.1 dB and 0.5° to 0.6°, respectively, while covering 360° of phase shifts at 5° resolution. Furthermore, the measured group delay and input 1dB compression point are maintained within ± 4 ps and >2.2 dBm, respectively, at any phase shift settings.

Acoustic radiation force expansions in terms of partial-wave scattering phase shifts: Extended applications

When evaluating radiation forces on spheres in sound fields, the interpretation of analytical results is greatly simplified by retaining the use of s-function notation for partial-wave coefficients imported into acoustics from quantum scattering theory. This facilitates easy interpretation of various scattering efficiency factors [L. Zhang and P. Marston, J. Acoust. Soc. Am. 140, EL178 (2016)]. This also facilitates the correction of certain plane-wave results [H. Olsen et al., J. Acoust. Soc. Am. 30, 633 (1958)] and the force parameterization for a broader class of wavefields. For situations in which dissipation is negligible, each partial-wave s-function becomes characterized by a single parameter: a phase shift. These partial-wave phase shifts are associated with scattering by plane traveling waves; the incident wavefields of interest (progressive and standing wavefields and beams) are separately parameterized. (When considering outcomes, the method of fabricating symmetric objects having a desirable set of phase shifts becomes a separate issue.) The existence of negative radiation force “islands” for beams reported in 2006 by Marston is manifested. Elementary standing and traveling wave force expressions are also recovered. This approach also manifests the utility of conservation theorems [P. Marston and L. Zhang, J. Acoust. Soc. Am. 139, 3139 (2016)]. [Work supported by ONR.]

Overview of the End-of-Mission Observation Experiments of Precipitation Radar Onboard the Tropical Rainfall Measuring Mission Satellite

Special experiments using the Precipitation Radar (PR) onboard the Tropical Rainfall Measuring Mission satellite during descent after the orbital maintenance fuel was depleted are reported in this paper. In these special observation experiments, a 90° yaw maneuver experiment, a wide swath width experiment, and the dense sampling experiments were carried out. The key operation of these experiments was a large change in the phase shifter settings of the transmitter and receiver, which was not tested before or after the launch. In addition, the 90° yaw experiment required the special operation of the satellite, whereas the other two experiments were implemented by changing only the PR operation. During the experiments, the PR was operated, and the expected data were obtained. The preliminary results suggest the possibility of future radar observation from space, and the results of these experiments will be utilized as basic data to improve the algorithm of the dual-frequency PR onboard the Global Precipitation Measurement mission core satellite and the design of future spaceborne PRs.

A 260 MHz IF Sampling Bit-Stream Processing Digital Beamformer With an Integrated Array of Continuous-Time Band-Pass Modulators

We propose an ADC-digital codesign approach to IF sampling digital beamforming (DBF) that combines continuous-time bandpass ${\Delta \Sigma }$ modulators (CTBPDSMs) and bit-stream processing (BSP). This approach enables power- and area-efficient DBF by removing the need for digital multipliers and multiple decimators. The prototype beamformer digitizes eight 260 MHz IF signals at 1040 MS/s with eight CTBPDSMs, and performs digital down conversion and phase shifting with only multiplexers directly on the undecimated CTBPDSM outputs. With two sets of phase shifters, the prototype simultaneously forms two independent beams. Each phase shifter is controlled by a 12 bit programmable complex weight to provide a total of 240 phase-shift steps. By constructively combining inputs from eight elements, an 8.9 dB SNDR improvement is achieved, resulting in an array SNDR of 63.3 dB over a 10 MHz bandwidth. Fabricated in 65 nm CMOS, the eight-element two-beam prototype beamformer is the first IC implementation of IF sampling DBF. It occupies $\text{0.28}\;\text{mm}^{ 2}$ , and consumes 123.7 mW.