Modern Wireless Communication Systems Research Articles

Analytical Nonstationary 3D MIMO Channel Model for Vehicle-to-Vehicle Communication on Slope

Vehicle-to-vehicle communication plays a strong role in modern wireless communication systems, appropriate channel models are of great importance in future research, and propagation environment with slope is one special kind. In this study, a novel three-dimensional nonstationary multiple-input multiple-output channel model for the sub-6 GHz band is proposed. This model is a regular-shaped multicluster geometry-based analytical model, and it combines the line-of-sight component and multicluster scattering rays as the nonline-of-sight components. Each cluster of scatterers represents the influence of different moving vehicles on or near a slope, and scatterers are, respectively, distributed within two spheres around the transmitter and the receiver. In this model, it is considered that the azimuth and elevation angles of departure and arrival are jointly distributed and conform to the von Mises–Fisher distribution, which can easily control the range and concentration of the scatterers within spheres to mimic the real-world situation well. Moreover, the impulse response and the autocorrelation function of the corresponding channel is derived and proposed; then, the Doppler power spectrum density of the channel is simulated and analyzed. In addition, the nonstationary characteristics of the presented channel model are observed through simulations. Finally, the simulation results are compared with measurement data in order to validate the utility of the proposed model.

An Improved Expectation Propagation Based Detection Scheme for MIMO Systems

Multiple-input Multiple-output (MIMO) technologies play an important role in modern and future wireless communication systems as they can improve the capacity without increasing the bandwidth. MIMO detection is one of the key technologies for MIMO system designs. MIMO detection schemes based on Message Passing (MP) algorithms have attracted extensive attention in recent years. The MIMO detection scheme based on Expectation Propagation (EP), which is also a kind of MP algorithms, has been proved to achieve the Bayes-optimal performance under the conditions of large system limit and compression rate threshold. However, there is improvement space for the detection performance of the EP algorithm when the conditions are not satisfied, which are the common cases in the practical applications. In this paper, when the conditions of the large system limit and compression rate threshold are not satisfied, we analyze the influences of two factors, the initial parameters selection and the moment matching strategy, on the performance of EP based detection scheme. As a result, we propose an improved EP detection scheme based on optimizing the two factors. Simulation results show that the proposed scheme outperforms the original EP detection scheme in different MIMO scenarios.

A Novel Modified Sparrow Search Algorithm with Application in Side Lobe Level Reduction of Linear Antenna Array

Antenna arrays play an increasingly important role in modern wireless communication systems. However, how to effectively suppress and optimize the side lobe level (SLL) of antenna arrays is critical for communication performance and communication capabilities. To solve the antenna array optimization problem, a new intelligent optimization algorithm called sparrow search algorithm (SSA) and its modification are applied to the electromagnetics and antenna community for the first time in this paper. Firstly, aimed at the shortcomings of SSA, such as being easy to fall into local optimum and limited convergence speed, a novel modified algorithm combining a homogeneous chaotic system, adaptive inertia weight, and improved boundary constraint is proposed. Secondly, three types of benchmark test functions are calculated to verify the effectiveness of the modified algorithm. Then, the element positions and excitation amplitudes of three different design examples of the linear antenna array (LAA) are optimized. The numerical results indicate that, compared with the other six algorithms, the modified algorithm has more advantages in terms of convergence accuracy, convergence speed, and stability, whether it is calculating the benchmark test functions or reducing the maximum SLL of the LAA. Finally, the electromagnetic (EM) simulation results obtained by FEKO also show that it can achieve a satisfactory beam pattern performance in practical arrays.

Fully connected feedforward neural networks based CSI feedback algorithm

In modern wireless communication systems, the accurate acquisition of channel state information (CSI) is critical to the performance of beamforming, non-orthogonal multiple access (NOMA), etc. However, with the application of massive MIMO in 5G, the number of antennas increases by hundreds or even thousands times, which leads to excessive feedback overhead and poses a huge challenge to the conventional channel state information feedback scheme. In this paper, by using deep learning technology, we develop a system framework for CSI feedback based on fully connected feedforward neural networks (FCFNN), named CF-FCFNN. Through learning the training set composed of CSI, CF-FCFNN is able to recover the original CSI from the compressed CSI more accurately compared with the existing method based on deep learning without increasing the algorithm complexity.

Ergodic Capacity Evaluation of Multi-Hop Decode-and-Forward MIMO-OFDM Relaying Network

Spatial diversity plays a significant role in wireless communication systems, including the Fourth Generation (4G) and Fifth Generation (5G) systems, and it is expected to be a fundamental part of the future wireless communication systems as well. The Multiple-Input Multiple-Output (MIMO) technology, which is included in the IEEE 802.16j standard, still holds the most crucial position in the 4G spectrum as it promises to improve the throughput, capacity, spectral, and energy efficiency of wireless communication systems in the 2020s. This makes MIMO a viable technology for delay constrained medical and health care facilities. This paper presents an approximate closed-form expression of the ergodic capacity for the Decode-and-Forward (DF) protocol MIMO-Orthogonal Frequency Division Multiplexing (OFDM) relaying network. Although MIMO-OFDM is highly valuable for modern high-speed wireless communication systems, especially in the medical sciences, its performance degrades in multi-hop relay networks. Therefore, in this paper, an approximate closed-form expression is derived for an end-to-end ergodic capacity of multi-hop DF MIMO-OFDM wireless communication system has been presented. Monte-Carlo simulations are conducted to verify the performance of the presented analysis regarding the capacity (bits/s/Hz) for different SNR-dB values for single, 2 × 2, 4 × 4, and multi-hop DF MIMO-OFDM systems. The presented results provide useful insights for the research on the end-to-end ergodic capacity evaluation.

Relative Bitrate Estimation of Multi-Channel Connectors Based on RF and EMC Parameters

The need for higher information rates has been increasing due to the rise of modern wireless communication systems. A practical bitrate analysis for RF communication media, without prior information about coding or modulation, is still not thoroughly investigated. The major aim of this paper is to propose a practical approach for estimating the bandwidth-dependent channel capacity for multi-channel high-speed data connectors. The well-known Shannon-Hartley theorem is adopted for this purpose where a detailed signal-to-noise-and-interference S/(N+I) analysis is carried out in terms of scattering and EMC parameters obtained from simulations and measurements in the baseband.

ОБЗОР ИССЛЕДОВАНИЙ АДАПТИВНОГО ФОРМИРОВАНИЯ ДИАГРАММЫ НАПРАВЛЕННОСТИ И ЦИФРОВОЙ ОБРАБОТКИ СИГНАЛОВ

Introduction: Recently, there has been an active development of algorithms for adaptive beamforming. Such work is required in order to improve the efficiency of receiving a useful signal, especially in mobile communication systems. This article provides an overview of research on this topic. Papers devoted to the improvement of the classical least mean square algorithm, blind signal separation methods, antenna selection algorithms in MIMO systems and other topics of adaptive signal processing are presented. Practical relevance: Adaptive beamforming is a key development for modern wireless communication systems, in particular 5G. Increasing requirements that impose a limitation on the spectral bandwidth of the signal and its center frequency with limited signal power lead to the strategy of forming a narrow signal transmission beam, thereby increasing the energy efficiency of signal transmission and reducing the overhead associated with the reception of various interference. This article provides an overview of studies on this topic. The results of the analysis of works devoted to the improvement of the classical algorithm for minimizing the mean square error, blind signal separation, antenna selection algorithms in systems of several antennas, and other topics of adaptive signal processing are presented. Discussion: It is shown that the main directions of research are focused on the improvement of classical diagramming algorithms, as well as on the improvement of methods for receiving digital signals in MIMO systems. Algorithms for recognizing the type of signal modulation, an algorithm for blind separation of second-order signals, an improved algorithm for automatic gain control, an algorithm for suppressing noise-like interference, and an algorithm for estimating radiation pattern parameters were also considered.

A Compact Triple Band EBG Using Interdigital Coplanar Waveguide Structure for Antenna Gain Enhancement

A new triple band EBG unit cell with compact size has been designed, fabricated, and tested. The proposed EBG unit cell is based on a square mushroom-like EBG (M-EBG) structure with an interdigital coplanar waveguide (ICPW). With this technique, the size of the proposed ICPW-EBG structure has been reduced from λ/2 to λ/4 compared with the conventional M-EBG unit cell dimension, which is 18 × 18 mm2. The proposed unit cell was designed in order to respond for three frequency bands at 1.8 GHz, 2.45 GHz, and 3.7 GHz. An array of 10 × 10 unit cell was also designed as a reflector with an overall dimension of 181.8 × 181.8 mm2. The dipole antennas were implemented over the designed reflector with a short distance of λ/8 to radiate electromagnetic wave. The simulation results showed that the ICPW-EBG reflector can improve directivity of the dipole antenna to be 9.12 dB at 1.8 GHz, 9.02 dB at 2.45 GHz, and 8.40 dB at 3.7 GHz. The measurement directivities agreed well with simulation results including 8.72 dB at 1.8 GHz, 8.56 dB at 2.4 GHz, and 8.1 dB at 3.7 GHz. This is the first design of triple band EBG unit cell with 50% size reduction compared with the conventional structure at the same frequency. The designed ICPW-EBG reflector with dipole antenna results in the triple band operation, low-profile and high gain suitable for modern wireless communication systems.

A single fed wideband mode‐reconfigurable OAM metasurface CP antenna array with simple feeding scheme

In this paper, a low-profile mode reconfigurable orbital angular momentum (OAM) circular polarization (CP) array antenna is presented, which consists of 2 × 2 elements and a single feed network. Each element is a metasurface subarray composed of 4 × 4 square patchs. The vias in the subarray produces 90° phase difference between x- and y- polarizations, and CP is realized. Both the 90° phase-shifting reconfigurable feed network and broadband 180° phase shift by the mirror images are used to generate the OAM helical phase. The OAM modes l can be dynamically switched between l = +1 and l = −1 by controlling operation states of p-i-n diodes in the feed network. The CP and OAM impedance bandwidths are 13.3% (from 5.8 to 6.6 GHz). The peak gains for the two modes are 9.4 dBi. The developed array antenna has the following advantages of the least pin diode number, high gain, small size, lowest divergence angle, wideband CP, low cross-polarization and low fabrication cost. Therefore, the proposed antenna is very promising for modern high-speed and large capacity wireless communication systems.

Beamformed Radio Link Capacity Under Positioning Uncertainty

Beamforming is one of the key technologies for achieving the high performance criteria in various modern and future wireless communications systems, in particular at the millimeter wave frequencies. In order to avoid or reduce the large signaling overhead and corresponding latency related to beam-training procedures, location-based beamforming utilizing available position information has been proposed. In this paper, by using the available position probability density function of a receiving device, we derive and analyze the capacity of a beamformed radio link, without and with beam-sweeping based beam training. Through the analysis, we show that by adjusting the beamforming and/or beam-training parameters appropriately, the radio link capacity can be optimized with respect to the prevailing positioning accuracy, and thus optimal utilization of radio resources is achieved with minimal radio access latency.

Design of a High-Efficiency GaN High-Electron Mobility Transistor Microwave Power Amplifier

This study presents a design procedure to obtain high-efficiency for microwave power amplifier. The designed amplifier uses a GaN high electron mobility transistor as an active device. Matching networks including input and output networks are realized using Megtron6 substrate microstrip lines. The designed amplifier operates at 2.1 GHz band. The simulated results show that the amplifier delivers a maximum power-added efficiency of 73.2% at output power and power gain of 47.8 dBm and 13.8 dB, respectively. This promising designed performance makes this amplifier to be an excellent candidate for use in modern wireless communication systems like radar, mobile network, and satellite communications.

Wideband antennas on glass reinforced epoxy materials

The wideband antennas have presented in this paper. The proposed antennas have a tunable, able to provide the multiband applications; which also offered the various modern wireless communication systems. It consists of two different shapes of (EF and ΨU) conductive strips; stack on Epoxy based composite substrate in the array pattern. It has offered the resonant of 4.87 GHz and 5.42 GHz, with Fractional Bandwidth (FBW) of 24.64% and 23.33% respectively. These proposed antennas have a compact dimensional of 18.64x17.92x1 mm2. Hence, these prototypes have validated with respective wideband frequencies of the measurement analysis. These proposed antennas have effectively offered the Ultra Wide-Band (UWB) bands of operation, which includes the Industry, Scientific and Medical applications.

A Single-Layer Low-Profile Broadband Metasurface Antenna Array for Sub-6 GHz 5G Communication Systems

This article presents a planar, low-profile, and single-layer metasurface (MTS)-based wideband 4 × 4 array antenna operating in the 5G sub-6 GHz band. The proposed antenna consists of 4 × 4 unequal size MTS unit cells fed by a simple parallel microstrip feed network in the form of a thin strip cross dipole. The wide impedance bandwidth (IBW) and improved boresight gain characteristics are realized due, respectively, to the excitation of multiple TM resonance modes that are closely spaced and the relatively large lateral size that supports in-phase currents. With an overall size of 1.40λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×1.22λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.054λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the center frequency of 5.64 GHz), the proposed antenna realizes an IBW of 41.13% (4.48-6.80 GHz), a peak boresight gain of 10.14 dBi, low cross-polarization in the E- and H-planes, and higher front-to-back ratio. Because of the advantages of low-profile, planar and single-layer structure, as well as equal E- and H-planes 3 dB beamwidth, the proposed antenna is a competitive candidate for several modern wireless communications systems, including 5G in the sub-6 GHz band.

Dual Frequency Electronically Controlled Radiation Beam Reconfigurable slotted Antenna for Detection of a Stationary or Nonstationary Target

A dual-frequency and radiation pattern reconfigurable microstrip patch antenna for detecting a stationary as well as a non-stationary target is described. Six angular patches, that collectively form a circular shape, are used. All the six patches radiate one by one after a fixed interval of time and their feed controlling is done by six PIN diodes. The switching of PIN diodes is controlled by an embedded biasing network. This antenna provides radiation beam scanning characteristics. It gives the main lobe scanning at every 60o clockwise (or anticlockwise) continuously by applying a signal to patches one by one. The purpose of introducing the slot is to get the radiation pattern in the desired direction since by changing the length, width, and position of the slot, the direction of the radiation pattern can be controlled. The slotted antenna operates in a C band with two frequencies 4.21 GHz and 4.82 GHz and provides a radiation pattern, 90o apart from each other. The scanning rate of 0.6 deg/ms is obtained; however, the scanning rate can be changed with the help of ATMEGA 2560 microcontroller. This compact Microstrip patch antenna can be widely used for short-range applications i.e. ground surveillance radar, missile control, mobile battlefield surveillance for military and many other applications in a modern wireless communication system. The designed antenna along with the switching application will be able to track the stationary as well as a non-stationary target.

Miniaturized Wideband Planar Antenna Using Interembedded Metasurface Structure

One kind of interembedded metasurface (MS) structure is proposed and applied to realize miniaturized wideband MS antennas (MSA). Different from conventional MSA, the proposed interembedded MSs are formed by etching slots on the radiating patch with various sawtooth schemes rather than rectangular gaps. Consequently, the resonance frequency of MSA can be decreased due to introducing those interdigital-like capacitances, while obvious miniaturization can be realized accordingly. By optimizing the parameters of the sawtooth radiating slots, a miniaturized antenna using cross-shaped interembedded MS is proposed, achieving an impedance bandwidth of 35.08% and a high gain of about 8.25 dBi with a compact overall size of 0.66λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.66λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Moreover, one further miniaturized antenna using modified cross-shaped interembedded MS is also presented, realizing a larger impedance bandwidth of 41.35% and a high gain of about 6.62 dBi with a smaller aperture of 0.48λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.48λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Compared with conventional MSA, 42% overall size reduction and larger bandwidth can be obtained. The design approach may provide a feasible solution to realize compact MSAs with the unique advantages of large bandwidth, low profile, low cost, and easy fabrication. Due to above good features, the proposed antenna can be a promising candidate for applications in modern wideband wireless communication systems.

Design Method for Compact Multifunctional Reconfigurable Filtering Power Divider on a New Tunable Three-Port Multi-Mode Topology

In this paper, a new effective approach is proposed to design compact multifunctional reconfigurable filtering power divider (FPD) based on a developed tunable multi-mode FPD topology. Different from conventional tunable FPD method by cascading tunable filter with power divider (PD), and double tunable filtering structures based on the tunable FPD method, it provides one promising solution of high operation performance, miniaturization and design flexibility enhancement etc., for industrial multi-functional modern wireless communication systems. By reformulating the traditional coupling matrix in terms of element-variable coupling coefficients for the developed tunable FPD topology, bandwidth (BW), center frequency (CF), as well as power division ratio (PDR) tuning are well accounted, which can help guide a new class of tunable FPD designs. For demonstration, a new second-order tunable FPD with only one common ring loaded coupled line tunable resonant unit is implemented as an example without losing generality. Higher-order tunable FPD case is further discussed and investigated by freely generalizing the FPD structure through the adoption of different tunable resonant units without dramatically increasing circuit complexity and size. Experimental results indicates that an improved performance (wider tuning range for CF, BW and PDR with nice isolation and matching), a very compact size and flexible design are achieved in the proposed work, which stands out from those in the literature.

Analytical Non-Stationary Satellite to Aircraft Channel Modeling over Open Area Based on Regular Shaped Geometry-Based Stochastic Model

Channel modeling is crucial to the development and evaluation of modern wireless communication systems including satellite communication system, since there might be critical safty-of-life applications. Also, the channel model is of great importance to the performance evaluation of mobile communication systems. In recent years, encouraged by the widely application of unmanned aerial vehicles, the research on channel modeling for aerial and aeronautical communications attract lots of interests. In the published articles, stationary and non-stationary channel models have been developed for air-to-ground communications based on regular shaped geometry-based stochastic model (RS-GBSM). The modeling of air-to-air or satellite-to-aircraft (S2A) communication is still quite simple or completely lacking. For obtaining more precise model of S2A channel, this paper presents an analytical non-stationary S2A channel mode based on RS-GBSM with considerations on line-of-sight path, specular reflection path, and ground scattering path. Analytical expressions of the channel impulse responses, the transfer functions, the auto-correlation functions, and the Doppler power spectrum density based on 3-path model are derived and simulated. Also, the distributions of the path antennation, the path delay, and the normalized Doppler shift based on uniform distribution of the scatterers are derived, simulated and fitted.

Differentially Fed Dielectric Resonators: Applications in Filters and Antennas

With the rapid development of wireless communication technology, high-performance miniaturized RF circuits are becoming more complicated, and more functions and signals are being packed into a small, tight space, resulting in a significant level of electromagnetic (EM) interference and signal crosstalk. In modern wireless communication systems, a higher signal-to-noise ratio is desirable and can be attained using differential signals and circuits. Using the differential technique, commonmode (CM) interference is rejected, enhancing signal transparency. Thus, lots of attention has been drawn to differential/balanced circuits, owing to their advantages over traditional single-ended circuits, such as immunity to interference, high reliability, considerable output power, harmonic suppression, and so on [1]. Corresponding to this trend, differential topologies have been used to design basic and key devices for RF front-end systems, such as filters [2], [3], power dividers [4], antennas [5], [6], and active components [7].

PROPERTIES AND FORMATION OF OFDM AND DERIVED SIGNALS

The article discusses the technology of forming signals used in mobile, information and telecommunication systems, and also provides an analysis of promising technologies that can be used in wireless communication systems of broadband access. It is shown that the widely used modulation scheme with orthogonal frequency division (OFDM) has a number of drawbacks, which can lead to a decrease in system performance. Alternative technologies for generating signals are presented, in particular, a technology based on windowed signal processing (W-OFDM), a technology based on time division (w-OFDM); UFMC technology and others to eliminate the disadvantages of OFDM technology. New points of view are proposed on the use of multi-carrier transmission technology in the form of multiplexing with orthogonal frequency division (in order to increase the security of modern wireless broadband access communication systems from external and internal threats), a class of non-linear discrete cryptographic sequences to form a physical data carrier – signal.

Low computational complexity methods for decoding of STBC in the uplink of a massive MIMO system

Reducing the computational complexity of the modern wireless communication systems such as massive MIMO configurations is of utmost interest. In this paper, we propose algorithms which can be used to accelerate matrix inversion and reduce the complexity of common spatial multiplexing schemes in massive MIMO systems. Here, we specifically investigate the performance of the proposed methods in systems that utilize STBC (Space-Time Block Code) in the uplink of dynamic massive MIMO systems for different scenarios. A multi-user system in which the base station is equipped with a large number of antennas and each user has two antennas is considered. In addition, users can enter or exit the system dynamically. For a given space-time block coding/decoding scheme, the computational complexity of the receiver will be significantly reduced by employing the proposed methods. The first approach is utilizing Neumann series to approximate the inverse matrix for linear decoders. The second tactic is reducing the computational complexity of the STBC decoders when a user is added to system or removed from it. In the proposed schemes, the matrix inversion for ZF and MMSE decoding is derived from inversing a partitioned matrix and Woodbury matrix identity. Furthermore, the suggested techniques can be utilized when the number of users is fixed but the CSI changes for a particular user. The mathematical equations for both approaches are derived and the complexity of the suggested methods is compared to the direct computation of the inverse matrix. Moreover, the performance of the proposed algorithms is evaluated in terms of the system BER (bit error rate). Evaluations confirm the effectiveness of the proposed approaches.