MIMO Configuration Research Articles

CPW fed optically transparent ultrawideband fractal MIMO terahertz antenna with meshed ground plane

Abstract An optically transparent UWB antenna element and its two-element pattern diversity MIMO configurations are presented in this paper. Three iterations of the quarter elliptical coplanar waveguide ground plane, rectangular microstrip feedline, and octagonal annular rings make up the antenna element. By metal meshing the ground planes and loading the radiator with several octagonal slots, the optical transparency is improved. It has a maximal achieved gain of 6.78 dBi and operates with steady radiation characteristics over the frequency spectrum of 4.52–28.64 THz (145.48%). The dimensions of the antenna element are 18 × 20.5 μm2. A metallic stub is positioned between two identical antenna components that are positioned orthogonally to one another to create a two-element pattern diversity MIMO antenna arrangement. The MIMO antenna is 20.5 × 42.5 μm2 in total. Its impedance bandwidth is 23.72 THz for port 2 and 22.68 THz for port 1. Using a rectangular stub results in an intraport isolation of >19 dB. Between the two ports, the planes in the radiation patterns have switched places. The diversity performance characteristics, which are considerably below the permissible limitations, are as follows: ECC > 0.01, CCL < 0.3 b/s/Hz, DG ∼ 10, TARC < 0 dB, MEG ∼ −3 dB, and 1≤VSWR_MIMO≤2. Compared to previously published structures, the suggested antenna structures have the advantages of smaller dimensions, a larger bandwidth, and improved optical transparency.

Physical analysis of high refractive index metamaterial-based radiation aggregation engineering of planar dipole antenna for gain enhancement of mm-wave applications

A metamaterial-incorporated high-gain and broadband dipole antenna is proposed for 5G mm-wave applications. The designed high refractive index metamaterial (HRIM) properties are presented in detail with supporting results. The proposed dipole antenna achieved broadband features, and the antenna gain increased significantly by incorporating HRIM in the electromagnetic (EM) wave propagation path. Besides, the EM wave aggregation engineering of utilizing the HRIM on the dipole antenna is analyzed using the electric field, magnetic field, and power flow distributions. Both conventional and HRIM-based dipole antenna (HRIMDA) were fabricated on thin (0.254 mm) Rogers RT5880 substrate material with a low dielectric constant of 2.2, where the noticeable gain enhancement by HRIM is observed. The measured results show the operational bandwidth (BW) from 23 to 38 GHz frequency, and the highest gain of 9.5 dBi is accomplished at 35 GHz frequency. Finally, a four-element MIMO configuration is numerically and experimentally analyzed where the isolation of the two conjugated MIMO elements is < − 20 dB. The MIMO parameters like envelop correlation coefficient (ECC) < 1 × 10–3 and diversity gain (DG) value of > 9.9 were also achieved. Hence, the proposed HRIM base dipole antenna is a potential candidate for 5G mm-wave applications.

Dual-Band Monopole MIMO Antenna Array for UAV Communication Systems.

This study proposes a compact, low-profile, four-port dual-band monopole multiple-input-multiple-output (MIMO) antenna array for unmanned aerial vehicle (UAV) communication systems. Each monopole antenna of the array features a modified T-shaped radiator configuration and is printed on a Rogers RT5880 substrate with compact dimensions of 134.96 mm × 134.96 mm × 0.8 mm. A four-element square MIMO configuration with sequential 0°, 90°, 180°, and 270° rotations was integrated smoothly into the UAV body. A prototype of the MIMO array was fabricated and experimentally evaluated, with measured results showing a close correlation to simulated results. The proposed dual-band monopole antenna demonstrated one of the widest impedance bandwidths of 46.15% at 2.4 GHz (2.04 to 3.25 GHz) IEEE 802.11b and 31.85% at 5.8 GHz (5.37 to 7.38 GHz) IEEE 802.11a on a thin 0.0064 λo substrate while achieving high transmission efficiency. The isolation of the proposed four-port MIMO design was measured at 23 dB at 2.4 GHz and 19 dB at 5.8 GHz. The MIMO array's total efficiency of each monopole antenna was measured at 96% at 2.4 GHz and 89% at 5.8 GHz. The design has measured diversity parameters such as an ECC below 0.01 and a DG of approximately 10. Based on these results, the proposed design suits the UAV communication system.

A novel asymmetric antipodal Vivaldi MIMO antenna

This communication describes the development and assessment of the genuine Antipodal Vivaldi MIMO antenna operating in the ultra-wideband spectrum. FR4 dielectric material, which is widely used in antenna designs and has characteristic features, is selected and used as a dielectric. The single antenna component has two asymmetric flares obtained with different parameters, and it also has a rectangular ground plane combined with a bottom flare. In the MIMO configuration, the single-antenna is built in a rotationally orthogonal way to generate a four-port system with the dimensions of 45 × 45 × 1 mm3. The vertical and horizontal stubs are added to the ground flare to obtain a common ground structure and increase the performance of the novel antenna design. It has a bandwidth of approximately 9 GHz, which starts from 2.85 GHz and ends at 11.8 GHz. The antenna has reasonable gain values and a high isolation value between the elements in the operation range. In this context, it is foreseen that the developed structure can be utilized in distinct multiport UWB applications.

Design and characterization of a meandered V-shaped antenna using characteristics mode analysis and its MIMO configuration for future mmWave devices

This study presents a novel four-element MIMO antenna system designed for the millimeter-wave (mmWave) spectrum. Each MIMO antenna element features a meandered V-shaped radiating structure fed by a 50Ω microstrip line and a partial ground plane with a square notch printed on a 0.254-mm thick RO5880 substrate. The characteristic mode analysis (CMA) of the antenna is done, which reveals that the antenna efficiently utilizes Mode 2, while Modes 1 and 4 also contribute to the resonance, resulting in a wideband response within the mmWave spectrum. A four-element pattern diversity MIMO configuration is developed to evaluate its suitability for MIMO communication, incorporating a connected ground-structure decoupling network to enhance isolation. The MIMO system achieves over 20 dB isolation between elements, with an impedance bandwidth ranging from 20.2 to 33.05 GHz and a peak gain of 6.6 dBi at 28 GHz. Fabrication and measurement validate the design, showing strong agreement with simulations. The MIMO performance metrics, including envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), and channel capacity loss (CCL), are within acceptable limits, suggesting that the proposed MIMO antenna system is a promising candidate for future mmWave applications.

A novel dual-band elliptical ring slot MIMO antenna with orthogonal circular polarization for 5G applications

This paper presents a dual-band 4-element multiple-input-multiple-output (MIMO) antenna featuring orthogonal circular polarization (CP) for Sub-6 GHz 5G applications. The single antenna combines a non-uniform width elliptical ring slot and a feed network, utilizing two L-shaped secondary feed lines to generate CP within the targeted frequency bands (3.55−3.80 GHz and 4.60−4.80 GHz). Using the single antenna as a unit antenna, a 4-element MIMO configuration is devised, employing a mirror technique for element placement to achieve orthogonal CP. This placement method effectively enhances coverage area and enlarges the 3-dB axial ratio bandwidth in the lower band (3.40–3.80 GHz). The common ground connections among elements are established via four strip lines. The antenna shows a good diversity performance considering the envelope correlation coefficient (ECC) result of less than 0.04 and isolation greater than 15 dB. The simulated gains of the MIMO antenna are 4 and 5 dBic in the respective bands. The single and MIMO antennas are fabricated, and the antennas’ performances are evaluated. A good agreement is observed between the measured and simulated results. The dual CP and diversity performances of the MIMO antenna make it more efficient for 5G wireless applications.

Scalability of MIMO Antennas: Assessing Gain and HPBW for Different Antenna Element Configurations

The design of Massive MIMO Antennas presents challenges due to their large size, which can impede the design process. Additionally, the arrangement of multiple antenna elements in Massive MIMO Antennas poses a challenge, as it surpasses the capabilities of simulation software and involves complex procedures. Therefore, to address these issues, a scalability technique utilizing array factor theory is employed to determine the relationship between the configuration of MIMO antennas and the corresponding values of gain and half-power beamwidth (HPBW). By utilizing a simpler MIMO Antenna array with incremental configurations, such as 2x2, 4x4, 8x8, and 16x16 MIMO element schemes, the array factor theory allows for the prediction of the gain and HPBW values for a Massive MIMO Antenna array with a specific configuration. This research aims to explore the scalability process and derive equations that relate the gain and HPBW values to the different MIMO configurations. The designed MIMO antenna arrangement is based on rectangular antennas with truncated corners and circular antennas with X slots, allowing for the investigation of various configurations operating at a frequency of 3.5 GHz.

Designing a Novel Hybrid Technique Based on Enhanced Performance Wideband Millimeter-Wave Antenna for Short-Range Communication.

This paper presents the design of a performance-improved 4-port multiple-input-multiple-output (MIMO) antenna proposed for millimeter-wave applications, especially for short-range communication systems. The antenna exhibits compact size, simplified geometry, and low profile along with wide bandwidth, high gain, low coupling, and a low Envelope Correlation Coefficient (ECC). Initially, a single-element antenna was designed by the integration of rectangular and circular patch antennas with slots. The antenna is superimposed on a Roger RT/Duroid 6002 with total dimensions of 17 × 12 × 1.52 mm3. Afterward, a MIMO configuration is formed along with a novel decoupling structure comprising a parasitic patch and a Defected Ground Structure (DGS). The parasitic patch is made up of strip lines with a rectangular box in the center, which is filled with circular rings. On the other side, the DGS is made by a combination of etched slots, resulting in separate ground areas behind each MIMO element. The proposed structure not only reduces coupling from -17.25 to -44 dB but also improves gain from 9.25 to 11.9 dBi while improving the bandwidth from 26.5-30.5 GHz to 25.5-30.5 GHz. Moreover, the MIMO antenna offers good performance while offering strong MIMO performance parameters, including ECC, diversity gain (DG), channel capacity loss (CCL), and mean effective gain (MEG). Furthermore, a state-of-the-art comparison is provided that results in the overperforming results of the proposed antenna system as compared to already published work. The antenna prototype is also fabricated and tested to verify software-generated results obtained from the electromagnetic (EM) tool HFSS.

RBFNN-based UWB 4×4 MIMO Antenna Design with Compact Size, High Isolation, and Improved Diversity Performance for Millimeter-Wave 5G Applications

Abstract The millimeter-wave spectrum has emerged as a compelling solution to address the pressing need for high-datarate&amp;#xD;capabilities in the development of 5G technology systems. Spanning between 20 GHz and 40 GHz, this spectrum&amp;#xD;encompasses several prominent frequency bands crucial for advancing 5G applications. In light of this, our study&amp;#xD;presents a thorough investigation into the design and performance of a compact cross-shaped slot broadband antenna,&amp;#xD;complemented by a 4×4 Multiple-InputMultiple-Output (MIMO) configuration tailored for 5G operations at&amp;#xD;28 GHz. The primary objective of this study is to develop an antenna system capable of achieving an extended bandwidth&amp;#xD;ranging from 20 GHz to 40 GHz, effectively covering the crucial frequency bands essential for 5G millimeterwave(&amp;#xD;mmWave) operations. To accomplish this, the optimization of antenna performance is meticulously carried out&amp;#xD;using the Radial Basis FunctionNeuralNetworks (RBFNN) model. The RBFNNmodel serves as a robust tool for establishing&amp;#xD;the intricate relationship between antenna dimensions, resonant frequency, and bandwidth. Subsequently,&amp;#xD;the developed RBFNN model is employed to predict optimal antenna dimensions, ensuring resonance at 28 GHz and&amp;#xD;meeting specified bandwidth targets. The single antenna is designed with a rectangular patch and a cross-shaped&amp;#xD;slot and is constructed on the low loss Rogers RT Duroid 5880 substrate. This design reaches an outstanding bandwidth&amp;#xD;of 19.5 GHz, and exhibits excellent radiation characteristics, with a high radiation efficiency of up to 99% and a&amp;#xD;corresponding gain of 5.75 dB. The antenna’s design and performance are rigorously designed using HFSS software,&amp;#xD;which is then compared to the results acquired using CST software. In addition, the proposed MIMO configuration&amp;#xD;offers excellent performance in terms of key features such as small size (16 × 16.2 mm2), very wide bandwidth of 20&amp;#xD;GHz, good gain of 6.75 high isolation exceeding 35 dB, and significant improvements in diversity performance measures&amp;#xD;such as Envelope Correlation Coefficient (ECC), Diversity Gain (DG), Channel Capacity Loss (CCL), Total Active&amp;#xD;Reflection Coefficient (TARC), and Mean Effective Gain (MEG). The potential of the proposed MIMO configuration&amp;#xD;for high-speed applications is particularly remarkable. Practical verification of the MIMO configuration is carefully&amp;#xD;carried out by fabrication andmeasurement. Experimental results strongly confirmthe effectiveness of the proposed&amp;#xD;antenna design, establishing it as a competitive challenger for 5G technology.

Dual-band MIMO antenna with low mutual coupling for 2.4/5.8 GHz communication and wearable technologies.

To satisfy the requirements of modern communication systems and wearables using 2.4/5.8 GHz band this paper presents a simple, compact, and dual-band solution. The antenna is extracted from a circular monopole by inserting various patches and stubs. The genetic algorithm is utilized to optimize the parameters and achieve the best possible results regarding bandwidth and gain. Afterward, a 2-port multiple-input-multiple-output (MIMO) configuration is created by positioning an identical second single element perpendicularly to the first one. The electrical size of the suggested MIMO configuration is 0.26 λL × 0.53 λL, where λL represents the free space wavelength at lower resonance of 2.45 GHz. The common ground technique is adopted to further reduce and achieve the accepted level of mutual coupling of the MIMO configuration. The presented MIMO antenna offers a low mutual coupling of < -27 dB with 0.2 envelope correlation coefficient (ECC). The antenna has a gain of around 6.2 dBi and 6.5 dBi at resonating frequencies of 2.45 GHz and 5.4 GHz. Furthermore, the specific absorption rate (SAR) analysis of the MIMO antenna offers a range inside of the standard values, showing its potential for On/Off body communications. The comparison with already published works shows that the proposed antenna achieves better results in either compact size or wide operational bandwidth along with low mutual coupling.

Dual-Band 2 × 1 Monopole Antenna Array and Its MIMO Configuration for WiMAX, Sub-6 GHz, and Sub-7 GHz Applications

This study introduces a cost-effective monopole antenna array and its MIMO configuration. The single element consists of a rectangular patch monopole featuring five circular slots at the center, accompanied by two thin slots at the top, offering a wide bandwidth (2–7.62 GHz) and a peak gain of 3.8 dBi. For gain improvement, a 2 × 1 antenna array is demonstrated. This antenna array exhibits dual-band behavior; spans from 2 to 3.71 GHz and from 5.9 to 7.54 GHz; covers the 2.5 GHz band (2.3–2.7 GHz), a significant portion of the n78 band (3.3–3.71 GHz), and the n96 band (5.925–7.125 GHz); and is assigned to WiMAX, sub-6 GHz, and sub-7 GHz applications, respectively. The antenna array achieves a peak gain of 6.47 dBi. Lastly, a two-element MIMO configuration derived from the 2 × 1 array is designed. Implementing a defected ground structure (DGS) on the ground plane plays a crucial role in enhancing the isolation from 7 dB to 20 dB. The presented MIMO antenna covers the desired frequency bands of 2.5 GHz, n78, and n96 with a peak gain of 7.5 dBi and high radiation efficiency (&lt;99%), which qualifies it for WiMAX, sub-6 GHz, and sub-7 GHz applications.

Enhancing 5G Sub-3.5 GHz Networks through Optimization of Microstrip Antenna Arrays with Sequential Rotation-Based MIMO using Machine Learning Techniques

The research concerns the design and optimization of microstrip antenna arrays with sequential rotation-based MIMO configurations for 5G sub-3.5 GHz networks. In total, the use of five optimization approaches was accessed, namely, Bayesian optimization, sparse learning, genetic algorithms, particle swarm optimization, and convolutional neural networks, to evaluate their efficiency in improving antenna properties. In general, Bayesian optimization outperformed the other methodologies most consistently, with the value of the average antenna gain ranging from 0.84 to 0.88, SNR between 14.8 and 15.3, and radiation efficiency ranging between 0.90 and 0.93. The use of sparse learning also ensured a high level of performance, with the average gain ranging between 0.80 and 0.85, and the values of SNR between 15.2 and 15.7. Thus, this approach showed the highest resistance to noise. Genetic algorithms, particle swarm optimization , and CNN are also quite close to each other in the efficiency of properties, with the average antenna gain value ranging between 0.85 and 0.89 and the value of SNR between 14.7 and 15.1. In overall, the results of the research show that there is a variety of available approaches to the optimization of antenna design, and each of them has a number of advantages that can be of use for the improvement of the properties and makes it possible to derive a solution that outweighs others in terms of several properties and the efficiency of its application.

Leveraging neuro-inspired AI accelerator for high-speed computing in 6G networks.

The field of wireless communication is currently being pushed to new boundaries with the emergence of 6G technology. This advanced technology requires substantially increased data rates and processing speeds while simultaneously requiring energy-efficient solutions for real-world practicality. In this work, we apply a neuroscience-inspired machine learning model called echo state network (ESN) to the critical task of symbol detection in massive MIMO-OFDM systems, a key technology for 6G networks. Our work encompasses the design of a hardware-accelerated reservoir neuron architecture to speed up the ESN-based symbol detector. The design is then validated through a proof of concept on the Xilinx Virtex-7 FPGA board in real-world scenarios. The experiment results show the great performance and scalability of our symbol detector design across a range of MIMO configurations, compared with traditional MIMO symbol detection methods like linear minimum mean square error. Our findings also confirm the performance and feasibility of our entire system, reflected in low bit error rates, low resource utilization, and high throughput.

Investigation of non-line-of-sight underwater optical wireless communications with wavy surface.

Underwater optical wireless communication (UOWC) systems have been widely researched to achieve high-speed and secure wireless communications. The non-line-of-sight (NLOS) UOWC system that uses the water surface to reflect signal light is widely studied to overcome the line-of-sight (LOS) channel limitation, particularly the channel blockage issue by marine biology or complex underwater topography. However, most previous NLOS UOWC studies have assumed a flat water surface or a general sine or cosine surface wave model for simplicity, leading to inaccurate performance estimations. In this paper, we build a theoretical NLOS UOWC framework with the Pierson wave model which considers both spatial correlation and time relativity information of wave incorporating wind speed, and investigate the signal-noise-ratio (SNR) and bit-error-rate (BER) performance. Results show that compared with the previous flat surface, the wavy surface can reduce the probability of achieving a satisfying signal level by up to 70%, affecting the performance of NLOS UOWC systems. Furthermore, we investigate the multiple-input-multiple-output (MIMO)-based NLOS UOWC under wavy surfaces. Results show that the MIMO principle can reduce the impact of the wavy surface, where the probability of achieving a satisfying signal level can be increased by up to 50% using the 2 × 4 MIMO configuration. However, results also show that further increasing the number of receivers may not further improve the system performance. The proposed model enables more accurate design and analysis of NLOS UOWC systems by accounting for the overlooked impact of wavy surfaces.

A CPW THz-MIMO antenna with reduced mutual coupling using Frequency Selective Surface for future wireless applications

In this article, we propose a novel THz-MIMO antenna system for future wireless applications. The performance of THz systems is prominently influenced by the MIMO configuration of the antenna. Increased signal attenuation and bit error rate (BER) are major hurdles to system performance at THz frequencies. MIMO antenna diversity techniques at the RF front end can significantly improve system performance. Toward this aim, this work attempts to develop a new THz-MIMO antenna system for future wireless applications. The proposed antenna uses a modified version of a traditional rectangular patch as the radiating element. The combination of a co-planar waveguide (CPW) feed structure and a modified stair-case radiator with an inverted L-shaped arch achieves excellent impedance matching between the feed line and the radiator, resulting in a broad bandwidth in the THz range. To evaluate the diversity performance of the antenna, both spatial and orthogonal 2-port antenna systems are designed and analyzed. Furthermore, isolation is enhanced by placing a frequency-selective surface (FSS) between the radiators of the proposed 4-port antenna. This design offers dual bandwidth, covering the ranges of 2.3–2.7 THz and 5.5–8.9 THz. The proposed antenna achieves very low mutual coupling (less than −30 dB), an extremely low envelope correlation coefficient (ECC) of 0.00001, and a low channel capacity loss (CCL) of 0.1 bps/Hz.

A dual-port, single-fed, integrated microwave and mm-wave MIMO antenna system with parasitic decoupling mechanism for 5G-enabled IoT applications

The integration of microwave and mm-wave antenna is recognized as a promising solution to ensure backward compatibility while effectively utilizing available space for 5G-enabled modern IoT devices. This paper proposed a very compact size multi-band dual-port MIMO antenna module, aiming to provide complete coverage in microwave frequency bands, including 2.4 GHz, 3.5 GHz, 5.3 GHz, and 7.5 GHz, along with 5G mm-wave bands such as 28 GHz. This is achieved through a common feedline by incorporating a semi-circular slotted monopole with strategically positioned quarter-wavelength metallic stubs on a partial ground plane. The proposed antenna exhibited -10 dB impedance bandwidths of 22.6% (2.16–2.71 GHz), 17.9% (3.36–4.02 GHz), 9.4% (5.18–5.69 GHz), 15.9% (7.29–8.55 GHz), and 15.5% (26.02–30.39 GHz) across diverse frequency bands. To attain compactness and high isolation capabilities, a composite three-dimensional parasitic element is employed as a decoupling structure to alleviate significant interference among closely positioned radiating elements. The proposed antenna provides radiation efficiency of > 85%, achieving necessary peak gains of 2.32 dBi, 3.46 dBi, 4.15 dBi, and 5.32 dBi at respective microwave frequencies. While in mm-wave frequency bands, radiation efficiency exceeds 95% having a measured realized gain of 6.2 dBi at 28 GHz. The proposed design successfully maintains an average isolation of > 28 dB in all frequency bands. The suggested MIMO configuration demonstrates outstanding diversity performance, which is evidenced by ECC, DG, MEG, CCL, and TARC.

PERFORMANCE ANALYSIS OF ACHIEVABLE BIT RATES IN RIS-ASSISTED MASSIVE MIMO NETWORKS AT 28 GHz BAND

Reconfigurable intelligent surface (RIS) technology is a smart way of controlling the radio signal propagation to improve the capacity and coverage of wireless networks. RIS tunes the phase shifts of the incident signals in a dynamic fashion. Channel modeling is an important aspect in RIS-based mmWave communication for the next-generation wireless networks. However, to achieve maximum benefit from RIS-assisted wireless systems, it is essential to provide accurate channel state information (CSI). But, it is very challenging to get accurate CSI because of large number of RIS elements, their passive nature, and the training overhead involved during the channel estimation. To overcome the higher training overhead, in this article we aimed to take advantage of the correlation and sparsity of channels in RIS-assisted channel estimation. The objective of this work is to propose a simplified channel model for the RIS-assisted physical channel of a massive multi-input-multi-output (mMIMO) wireless communication system and analyze its performance in terms of transmitted powers, MIMO configurations, and achievable bit rates. The simulated results proved that the strategic placement of RIS with optimal phase shifts and optimal MIMO configuration can enhance the maximum achievable rate. The achievable rates of the proposed channel modeling are compared with the existing state-of-the-art methods to prove its efficiency. Also, the combination of mMIMO technology along with RIS-assisted communication provides degrees of freedom in terms of signal coverage, energy consumption, and system complexity.

Performance Enhancement of VLC-NOMA Employing Beamforming Function based Vehicle-to-Multivehicle Communication System

The realm of vehicular safety applications driven by communication has surfaced as a paramount approach for elevating road safety standards. The adoption of Vehicular VLC (V-VLC) is rooted in its multifaceted advantages, making it a preferred choice for integrating both illumination and data transmission. Beyond its highly secure attributes, V-VLC boasts virtues such as demonstrating low complexity, and ensuring immunity to radio frequency (RF) interference. The core premise of this study revolves around the proposition of a novel system that synergistically integrates NOMA into V-VLC networks to amplify spectral efficiency, harnesses beamforming techniques to bolster Signal-to-Noise Ratio (SNR), and leverages Successive Interference Cancellation (SIC) to curtail interference. An exhaustive analysis of this system configuration is provided, accompanied by the derivation of a precise Signal-to-Interference-plus-Noise Ratio (SINR) expression tailored to the proposed scenario. This paper not only delves into the nuanced aspects of NOMA performance at the receiver but also delves into critical dimensions such as the influence of transmitter-receiver distance, elevation disparity between transmitter and receiver, and the impact of diverse channel conditions on received power and BER VS. Eb/No for different MIMO configurations.

Expectation-maximization vector approximate message passing-based frequency-domain turbo equalization for underwater acoustic communications.

Channel equalization plays a crucial role in single-carrier underwater acoustic (UWA) communications. Recently, a frequency-domain turbo equalization (FDTE) scheme enabled by the vector approximate message passing (VAMP) algorithm, was proposed, and it outperformed classic linear minimum mean square error FDTE at acceptable complexity cost. The operation of the VAMP-FDTE requires knowledge of noise power, which is predetermined before the equalization starts. In practice, however, it is difficult to obtain prior knowledge of noise power due to factors of unknown channel estimation errors and dynamic underwater environments. Motivated by this fact, we propose an enhanced VAMP-FDTE scheme, which learns the noise power knowledge during the equalization process via the expectation-maximization (EM) algorithm. The EM-based noise power estimation makes use of intermediate results of the VAMP-FDTE and, thus, only incurs a small extra computational overhead. The improved VAMP-FDTE, named EM-VAMP-FDTE, was tested by experimental data collected in shallow-sea horizontal UWA communication trials with MIMO configuration. It showed better performance than the existing VAMP-FDTE scheme, attributed to the online noise power learning.

Analyzing the Performance of Millimeter Wave MIMO Antenna under Different Orientation of Unit Element.

In this paper, a compact and simplified geometry monopole antenna with high gain and wideband is introduced. The presented antenna incorporates a microstrip feedline and a circular patch with two circular rings of stubs, which are inserted into the reference circular patch antenna to enhance the bandwidth and return loss. Roger RT/Duroid 6002 is used as the material for the antenna, and has overall dimensions of WS × LS = 12 mm × 9 mm. Three designs of two-port MIMO configurations are derived from the reference unit element antenna. In the first design, the antenna element is placed parallel to the reference antenna, while in the second design, the element is placed orthogonal to the reference element of the antenna. In the third design, the antenna elements are adjusted to be opposite each other. In this study, we analyze the isolation between the MIMO elements with different arrangements of the elements. The MIMO configurations have dimensions of 15 mm × 26 mm for two of the cases and 15 mm × 28.75 mm for the third case. All three MIMO antennas are made using similar materials and have the same specifications as the single element antenna. Other significant MIMO parameters, including the envelope correlation coefficient (ECC), diversity gain (DG), channel capacity loss (CCL), and mean effective gain (MEG), are also researched. Additionally, the paper includes a table summarizing the assessment of this work in comparison to relevant literature. The results of this study indicate that the proposed antenna is well-suited for future millimeter wave applications operating at 28 GHz.