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This paper presents a mutual coupling reduction technique in a textile ultra-wideband (UWB) multiple-input–multiple-output (MIMO) antenna system implemented on a textile substrate. The compact textile UWB MIMO antenna consists of two patch antennas implemented on a felt textile substrate. The compact size and close placement of the antennas in a MIMO system cause higher mutual coupling which deteriorates the performance of the communication systems. To minimize the mutual coupling, Parasitic Elements and Defected Ground Structures are used in the designed textile UWB MIMO antenna. The MIMO antenna performed very well over almost the whole UWB frequencies ranging from 3.29 GHz to 13.3 GHz. The simulated and the measured parameters showed a good impedance matching with an impedance bandwidth of 133.4%. The results showed an improvement of 20 dB isolation at certain frequencies without impacting the reflection coefficient S11 and the antenna impedance bandwidth. The MIMO antenna has good diversity performance parameters in terms of Envelope Correlation Coefficient (ECC), Diversity Gain, Mean Effective Gain (MEG) and radiation pattern and the results indicate that the textile antenna is suitable for UWB MIMO applications. The overall size of the antenna is 30x60 mm2. Fully embroidered structure provides freedom of movement and comfort, so it is a good fit for Wireless Body Area Network applications. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) and visible light positioning (VLP) systems are usually designed separately to prevent mutual interference, while terminal mobility often introduces challenges that can degrade their performance. In this paper, we propose an integrated visible light communication and positioning (VLCP) scheme designed for mobile scenarios, encompassing both multiple-input–single-output (MISO) and multiple-input–multiple-output (MIMO) configurations. This scheme integrates both functionalities into a unified system. Utilizing decision feedback channel estimation (DFCE), we effectively estimate the dynamic channel state information (CSI) for both VLC and VLP, thereby potentially enhancing both communication and positioning performance. Simulation results across various routes verify the effectiveness of the proposed scheme. It is observed that when the terminal moves at 1 m/s, the VLCP scheme with DFCE can maintain reliable transmission quality, ensuring bit error rates (BERs) consistently below 1.3 × 10−2. Additionally, the mean positioning errors remain within the centimeter range in different routes, not exceeding 4.3 cm and 15.5 cm in the MISO and MIMO scenarios, respectively. [ABSTRACT FROM AUTHOR]

This study introduces a coplanar waveguide MIMO antenna design that offers both frequency and pattern reconfigurability. The antenna is intended for applications in WiMAX, WLAN, and X-Band. It is constructed using an FR4 substrate with dimensions of 1.6mm thickness and 0.025 loss tangent. Based on the proposed design, MIMO antennas can operate at 3.5 & 3.9GHz (WiMAX), 5.5 & 5.8GHz (WLAN) and 10.5 & 12.5GHz (X-Band). To accomplish this, two open-circuited 3mm x 3mm quatre wavelength transformers are linked to each radiator through PIN diodes. The performance enhancement of the reconfigurable MIMO antenna was fine-tuned utilizing microwave solvers in both CST and ADS. The system’s performance was validated through practical measurements. Furthermore, the analysis of diversity conducted on the suggested antenna reveals that the antenna has a low correlation coefficient (

A key aspect of the imaging capability of radar systems is the angular resolution, which is determined by the aperture size of the antenna array. Therefore technologies such as MIMO and especially radar networks consisting of multiple independent MIMO radar sensors seek to maximize the virtual aperture size. Depending on the range and velocity resolution of the MIMO radar network, multistatic aspects must be accounted for. So far, those multistatic effects were seen as errors, which must be compensated for in order to restore the classical DoA properties of the virtual aperture, described by the narrowband beam pattern. This paper shows that new virtual aperture designs with larger antenna spacings are possible while still preserving the angular ambiguity range of smaller antenna spacings, as long as the multistatic effects of distributed radar networks, namely radar networks whose virtual aperture is large in comparison to the range resolution, are correctly accounted for. The larger antenna element spacing enables larger aperture sizes leading to higher angular resolution. This paper illustrates that the well-known, Fourier Tranformation-based signal processing is unable to exploit this potential of distributed radar networks, and an computationally efficient approximated matched filter is proposed. This article presents a signal model for distributed radar networks, suitable signal processing, and a comparison to the well-known Fourier Transformation-based signal processing for compact radar networks. Both the signal model and the proposed signal processing are verified by measurements with a radar sensor network composed of 2 MIMO radar sensors operating in the automotive frequency range of $76 \,\mathrm{G}\mathrm{Hz}\,\mathrm{to}\, 81 \,\mathrm{G}\mathrm{Hz}$ providing 64 virtual channels with a range resolution of $0.03 \,\mathrm{m}$. The virtual aperture size of the radar network is ${\sim }0.5 \,\mathrm{m}$ with virtual antenna spacing of twice the wavelength, but the proposed signal processing still allows unambiguous DoA estimation within the full $180 \,\mathrm{^{\circ }}$ range.

This letter presents a novel three‐port ultrawideband (UWB) multi‐input‐multi‐output (MIMO) antenna that covers the sub‐6 GHz (between 1.7 and 6 GHz) frequency band for wireless device applications. The proposed antenna consists of two parts: a dipole and two centrosymmetric slot antennas with shared structures. The radiating arm of the dipole can be reused as the large slot ground without increasing the size. The novel circular slot antenna etched on the radiator and circular microstrip feed line are designed to achieve wide impedance bandwidth. Meanwhile, four chamfers are loaded at the corners of the dipole to further optimize the impedance match in the whole frequency band. The physical dimension of the proposed three‐port MIMO antenna is 70 × 45 × 0.762 mm3. Experimental results validate that the reflection coefficient remains lower than −12 dB and the port isolation is better than 12 dB in the entire operational bandwidth without any decoupling network. The measured average peak gains are up to 5.6 dBi for all three ports, accompanied by a radiation efficiency of 90% across the frequency spectrum. With the advantages of simple design, high gain and high radiation efficiency, the proposed three‐element MIMO antenna design is well‐suited for implementation in UWB applications. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) has been envisaged as a key driving scheme for future wireless communication systems because of its huge connecting ability and superior spectrum efficiency. Integrating the concepts of Multiple-input-multiple-output (MIMO) into NOMA enhance the system capacity at the cost of hardware complexity. In this article, we consider an MIMO-NOMA-based system in which the users are partitioned to form a cluster. A beamforming vector that helps to maximize the channel gain has been designed to remove the inter-cluster interference. This work presents the effect of user pairing in downlink MIMO-NOMA systems. User pairing has a significant impact on the performance of MIMO-NOMA systems. Outage probability and Ergodic Capacity (EC) are analyzed for MIMO-NOMA systems. Exact outage probability expressions are provided for user pairing to reveal some useful insights that pairing two users with dissimilar channel conditions increases the probability that NOMA achieves a larger sum rate than traditional orthogonal multiple access (OMA) systems. This mathematical investigation is carried out by considering Nakagami-m fading channel. Furthermore, this notion of user pairing is presented for imperfect successive interference cancellation (SIC). Diversity order is also derived for the strong and weak users. Extensive simulation results are provided to validate the derived analytic expressions. Furthermore, it is also demonstrated that the EC of MIMO-NOMA systems is improved significantly when compared with traditional OMA systems. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is considered a key candidate technology for next-generation wireless communication systems due to its high spectral efficiency and massive connectivity. Incorporating the concepts of multiple-input-multiple-output (MIMO) into NOMA can further improve the system efficiency, but the hardware complexity increases. This study develops an energy-efficient (EE) subchannel assignment framework for MIMO-NOMA systems under the quality-of-service and interference constraints. This framework handles an energy-efficient co-training-based semi-supervised learning (EE-CSL) algorithm, which utilizes a small portion of existing labeled data generated by numerical iterative algorithms for training. To improve the learning performance of the proposed EE-CSL, initial assignment is performed by a many-to-one matching (MOM) algorithm. The MOM algorithm helps achieve a low complex solution. Simulation results illustrate that a lower computational complexity of the EE-CSL algorithm helps significantly minimize the energy consumption in a network. Furthermore, the sum rate of NOMA outperforms conventional orthogonal multiple access.

Non‐orthogonal multiple access (NOMA) is considered a key candidate technology for next‐generation wireless communication systems due to its high spectral efficiency and massive connectivity. Incorporating the concepts of multiple‐input‐multiple‐output (MIMO) into NOMA can further improve the system efficiency, but the hardware complexity increases. This study develops an energy‐efficient (EE) subchannel assignment framework for MIMO‐NOMA systems under the quality‐of‐service and interference constraints. This framework handles an energy‐efficient co‐training‐based semi‐supervised learning (EE‐CSL) algorithm, which utilizes a small portion of existing labeled data generated by numerical iterative algorithms for training. To improve the learning performance of the proposed EE‐CSL, initial assignment is performed by a many‐to‐one matching (MOM) algorithm. The MOM algorithm helps achieve a low complex solution. Simulation results illustrate that a lower computational complexity of the EE‐CSL algorithm helps significantly minimize the energy consumption in a network. Furthermore, the sum rate of NOMA outperforms conventional orthogonal multiple access. [ABSTRACT FROM AUTHOR]

Since the requirement of secure transmission for massive multiple-input–multiple-output (mIMO) is high, we consider a secure massive MIMO system in presence of multiple digital to analog converters (DACs). We deal with complicated performance analysis of the proposed system including a base station, a legitimate user, and an eavesdropper while these nodes are equipped with multiple antennas. In particular, we intend to present the closed-form expression for the ergodic secrecy rate of the system and also calculate the optimal power allocation for better performance gain. The simulation analysis shows that quantization bits, transmit signal to noise ratio at the base station, and power allocation plays a major role in enhancing the performance of the system.

Visible light communication (VLC) and visible light positioning (VLP) systems are usually designed separately to prevent mutual interference, while terminal mobility often introduces challenges that can degrade their performance. In this paper, we propose an integrated visible light communication and positioning (VLCP) scheme designed for mobile scenarios, encompassing both multiple-input–single-output (MISO) and multiple-input–multiple-output (MIMO) configurations. This scheme integrates both functionalities into a unified system. Utilizing decision feedback channel estimation (DFCE), we effectively estimate the dynamic channel state information (CSI) for both VLC and VLP, thereby potentially enhancing both communication and positioning performance. Simulation results across various routes verify the effectiveness of the proposed scheme. It is observed that when the terminal moves at 1 m/s, the VLCP scheme with DFCE can maintain reliable transmission quality, ensuring bit error rates (BERs) consistently below 1.3 × 10−2. Additionally, the mean positioning errors remain within the centimeter range in different routes, not exceeding 4.3 cm and 15.5 cm in the MISO and MIMO scenarios, respectively.

This paper intends to find out how to diminish the mutual coupling of closely spaced two-port antenna elements with a novel H-shaped EBG in the E-plane. The UWB MIMO antenna isolation is more than 20 dB in the entire operating frequency. The maximum isolation is up to 37 dB, obtained by the two-unit cell EBG placed between two CPW-fed antenna elements. Two-unit cell EBG is altering the current between radiating elements and enhancing up to 10 dB isolation. The proposed EBG decoupling MIMO antenna size is 35 mm × 22 mm and designed on the FR-4 substrate. The |S11| (in dB) varies from 3.4 to 10.4 GHz and covering most of UWB frequencies. This antenna has realized gain of more than 4 dB on a broader bandwidth with ECC and CCL under 0.01 and 0.35 bits/sec/Hz, respectively, across the entire 10 dB bandwidth. [ABSTRACT FROM AUTHOR]

A novel ultra-compact four-port multiple-input-multiple-output (MIMO) cylindrical dielectric resonator antenna (DRA) with improved isolation is proposed for WLAN applications in this paper. The antenna is originally radiated with the assistance of two different excitation mechanisms to generate decoupled orthogonal modes. To further diminish the coupling field and improve the isolation, a suitable U-shaped slot is created on the common ground plane. Two additional rectangular slits are also etched to adjust the impedance matching of other ports. To better reveal the operating mechanism of the decoupling scheme, the common mode (CM) and differential mode (DM) impedance analysis methods between DRA ports are presented. The etched U-shaped slot can tune the impedance of CM and DM to be consistent to realize the decoupling. The antenna is simulated, fabricated, and tested to verify the decoupling mechanism. The results demonstrate that the isolation between ports 1 and 2 is enhanced from 5 dB to 23 dB, and other ports exhibit low coupling of better than 12 dB. Moreover, the antenna with the full size of 30 × 30 × 8.1 mm3 can be used either as a four-port DRA with a bandwidth of 300 MHz or as a two-port DRA with a bandwidth of 700 MHz, at a center frequency of 5.6 GHz. [ABSTRACT FROM AUTHOR]

A large-aperture radar composed of a multiple-input-multiple-output (MIMO) planar array can complete 3D through-wall imaging (TWI), but the simultaneous work of the multiple transceiver channels leads to difficulties in designing the hardware. In engineering, multiple transceiver channels are usually realized by time-division multiplexing (TDM) in MIMO radar, which is called TDM MIMO radar. A time delay will be introduced when the channels are switched, which will cause high sidelobes and position deviation in the 3D imaging of moving targets, also known as range migration. This paper proposes a motion compensation algorithm based on sparse array, designed to eliminate range migration in moving targets in 3D TWI scenes. In the proposed algorithm, the coincident array elements of the equivalent array are used as the compensation channels to calculate the position difference of the target, which can correct the remaining MIMO channels. The proposed algorithm is compared with no compensation, and the reference-channel-based motion compensation algorithm (RCMCA). According to the simulation and experimental results, the proposed motion compensation algorithm can effectively eliminate sidelobes, and keep the position deviation within 0.30 m in the 3D TWI of moving targets under the TDM MIMO radar, without increasing the system complexity. [ABSTRACT FROM AUTHOR]

In this paper, we investigate hybrid beamforming and resource allocation design problems for uplink millimeter wave (mmWave) multi-user (MU) massive multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. We propose three hybrid beamforming designs with dynamic streams assignment (DSA) integrated into the solution for the formulated resource allocation problem to maximize spectral efficiency. In the analog beamforming stage, three different designs are developed to maximize the channel gains of the equivalent baseband channel at each subcarrier, while the number of data streams is also determined for each mobile station (MS). Specifically, for the first design, the analog beamformers are designed to match the corresponding channel across the entire band for each MS. In the second one, to significantly reduce the complexity of the first design, we can completely avoid the matrix decomposition by selecting the appropriate set of array response vectors. The last design only performs singular value decomposition (SVD) on the channel of the center subcarrier to find the analog beamformers. In the digital beamforming stage, for the interference cancellation, the digital precoder and the combiner are obtained at each subcarrier using the block diagonalization (BD) and the coordinated transmit-receive processing method. We also develop fully-digital beamforming and another three hybrid beamforming schemes based on the existing algorithms as performance benchmarks. By being verified through numerical simulations, the spectral efficiency of the proposed schemes can be significantly improved after dynamically assigning the number of data streams for each MS. Moreover, simulations indicate the first and the third proposed hybrid beamforming designs can achieve a very competitive performance and even outperform the fully-digital design in some situations.

A novel customized $\pi $ -shaped split-ring resonator metasurface arranged in two configurations is presented to decouple $1\times 2$ and $1\times 4$ Millimeter-Wave (MMW) Magneto-Electric (ME) Dipole in the H-Plane with 1.6 mm ( $0.32\lambda $ at 60 GHz) inter-element spacing. The metamaterial unit cell is first designed to inhibit the propagation of coupled surface waves within the bandwidth of interest. A $5\times 2$ arrangement of this unit cell is carefully positioned on the top and bottom of the superstrate with 1 mm spacing ( $0.2\lambda $ at 60 GHz) between the antenna and the superstrate. In the $1\times 2$ array, a maximum measured mutual coupling reduction of 53 dB is observed within the 52–66 GHz bandwidth (23.7%). To further demonstrate the uniqueness of the metasurface, an $11\times 2$ configuration of this unit cell is arranged as a superstrate for the $1\times 4$ ME-dipoles. A maximum measured mutual coupling reduction of 40 dB is achieved without a considerable effect on the radiation characteristics. Parametric analysis is performed to confirm the uniqueness of this new decoupling structure. The proposed antenna exhibits measured high total efficiency (>89%), high gain (>8 dB), low envelope correlation coefficient ( $ < 0.0003$ ), and very good radiation characteristics throughout the entire bandwidth. The fabricated prototype antenna is measured to validate the simulation results. The proposed antenna is a good recommendation for V-band millimeter-wave MIMO applications like radar research.

This paper presents a dual-band split-ring structure that provides end-fire radiation characteristics for multi-input multi-output (MIMO) mm-wave 5G applications. The proposed single antenna element consists of a main split-ring resonator (SRR) directly fed using a high impedance microstrip transmission line. A lamda/4 transformer is employed to match the high impedance transmission line with a 50-ohm line. Two symmetric parasitic SRRs are used as directing elements to give end-fire radiation properties for the introduced antenna at the first resonant frequency. The parasitic SRRs are also utilized to produce the second resonant frequency by establishing a capacitive link with the main SRR. The single element antenna radiates at 24.5 and 28.5 GHz. A cross-shaped MIMO structure composed of four elements of the proposed antenna is introduced to improve the isolation of the MIMO system due to its orthogonal polarization characteristics. The proposed MIMO demonstrates acceptable values of gain and radiation efficiency, reaching 9.8 dB and 93%, respectively, at the first resonant frequency, and 8.7 dB and 95%, respectively, at the second band. MIMO performance is also studied, and the proposed MIMO system provides a very low envelope correlation coefficient of lower than $10^{-4}$ over the two operating frequency bands. A diversity gain is also calculated, it is around 10 dB over the two operating bands. The proposed high-isolation dual-band cross-shaped MIMO array is a promising candidate for millimeter-wave 5G applications.

This paper proposes a simple novel technique for self-isolating a MIMO antenna for mm-wave applications. MIMO antenna elements with inter-element separation of 0.2 mm ( $0.023\lambda $ at 35 GHz) and measured high isolation (>50 dB) are presented. By observing the concentration of surface waves on the radiating patch, several rigorously optimized slots of different shapes, positions, and dimensions are etched on the patch to enhance the inter-element isolation and increase the bandwidth within 28-37.5 GHz. The circuit models of the reference and proposed antennas have been presented. The coupling is measured by the level of the differences in the output voltage in both antennas. The novel mm-wave antenna exhibits high impedance bandwidth (>29%), high isolation (>50 dB), high efficiency (>90%), and low envelope correlation coefficient (< 0.005). Two configurations of MIMO antenna (i.e., $1\times 2$ and $1\times 4$ ) are fabricated and measured to validate the simulation outcomes. The single reference antenna has dimensions of 10x12 mm 2 while the 1x2 array has dimensions of 19x12 mm 2. The presented design is the first to exhibit such wideband isolation improvement without any external decoupling structure at the mm-wave frequency range, to the best of the authors’ knowledge.

Automotive radar pursues low cost and high performance, and especially hopes to improve the angular resolution under the condition of a limited number of multiple-input–multiple-output (MIMO) radar channels. Conventional time division multiplexing (TDM) MIMO technology has a limited ability to improve the angular resolution without increasing the number of channels. In this paper, a random time division multiplexing MIMO radar is proposed. First, the non-uniform linear array (NULA) and random time division transmission mechanism are combined in the MIMO system, and then a three-order sparse receiving tensor of a range-virtual aperture-pulse sequence is obtained during echo receiving. Next, this sparse three-order receiving tensor is recovered by using tensor completion technology. Finally, the range, velocity and angle measurements are completed for the recovered three-order receiving tensor signals. The effectiveness of this method is verified via simulations. [ABSTRACT FROM AUTHOR]

This brief proposes a novel decoupling method based on metallic sheets to improve inter-port isolation in dual-port single-element multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) systems. Two different structures, including an H-plane and an E-plane decoupled MIMO arrangement, have been investigated. The exploitation of metallic sheets can significantly impact the electromagnetic (EM) field distribution inside the dielectric resonator (DR) and restrict the strongest portion of the EM energy couple to the nearby slot. As a result, inter-port isolation can be improved significantly. As the single DR element is used and metallic sheets are embedded within the element, no additional footprint is required, making the MIMO antenna arrangements compact and simple. The outcomes convey a maximum enhancement in the inter-port isolation of the H-plane decoupled MIMO arrangement is about 23.45 dB, while that of the E-plane decoupled MIMO arrangement is about 17.08 dB across the operating frequency band. [ABSTRACT FROM AUTHOR]

In this letter, two compact, colocated, low-coupled, quad-polarized (QP) antennas are proposed based on two dual-mode radiation bodies to achieve compactness and high isolation. The first antenna obtains four polarizations by orthogonally placing two dual-mode loops; the second antenna includes a dual-mode loop and a miniaturized dual-polarized patch based on fractal structures inside the loop. To investigate the performance of QP multiple-input–multiple-output (MIMO) systems, channel parameters including correlation coefficients, degree of power balance, and channel capacities are analyzed based on the measured data. Results show that, high channel capacities can be achieved both in a realistic office room and a rich scattered reverberation chamber, which are very close to that of the 4 × 4 independently identically distributed (i.i.d.) Rayleigh channel. It is revealed that both correlation coefficient and degree of received power balance have strong influence on the performance of a MIMO system, which are related to the radiation properties of the antenna and the polarimetric characteristics of the propagation environment. [ABSTRACT FROM AUTHOR]

The complete multiple-input–multiple-output (MIMO) channel simulation in deterministic techniques can be a computationally intensive task, due to the inherent scenario's complexity and number of antennas. The spatial coherence among MIMO elements is a reasonable assumption to approximate the channel from a single point simulation. In this letter, a novel method to incorporate a geometrical approximation of the MIMO channel into a three-dimensional ray launching (3D-RL) algorithm is presented. The method is antenna type independent and the orientation of the array is embedded in the antenna representation. Relevant information of the MIMO channel characteristics like the root mean square (rms) delay spread, the maximum delay spread, phase and channel capacity are obtained and compared with the full 3D-RL simulation of the entire MIMO array, achieving 93.4% reduction in computational time. [ABSTRACT FROM AUTHOR]

In this article, a capacity-oriented envelope correlation coefficient (ECC) that incorporates a preferred channel model for assessing a multiple antenna system of a multiple-input-multiple-output (MIMO) mobile device is proposed. Originated from the rudimentary law of ergodic channel capacity, the ECC for multiple antennas (ECC-M) is proven to holistically reflect the impact of radiation patterns and total efficiencies of multiple antennas on channel capacity. The closed-form ECC-M expressions for Rayleigh fading channel model and ray-based spatial channel model are studied, leading to an easy-to-use ECC-M expression that approximately incorporates a realistic channel model. The correlation of the proposed ECC-M to the channel capacity is demonstrated through the Monte Carlo (MC) simulation of three four-element MIMO antenna testbeds in two channel models, showing that the antenna total efficiency and a realistic channel model involved in the ECC-M play an important role in assessing the performance of multiple antennas. It is justified that the difference in channel capacities of two multiple antenna systems is highly relevant to their ECC-Ms at high signal-to-noise ratios (SNRs). The proposed ECC-M is also experimentally validated through over-the-air (OTA) throughput measurement, revealing that the ECC-M can effectively assess the OTA performance of multiple antenna systems for MIMO terminal devices. [ABSTRACT FROM AUTHOR]

We consider a downlink multi-user scenario and investigate the use of reconfigurable intelligent surfaces (RISs) to maximize the dirty-paper-coding (DPC) sum rate of the RIS-assisted broadcast channel. Different from prior works, which maximize the rate achievable by linear precoders, we assume a capacity-achieving DPC scheme is employed at the transmitter and optimize the transmit covariances and RIS reflection coefficients to directly maximize the sum capacity of the broadcast channel. We propose an optimization algorithm that iteratively alternates between optimizing the transmit covariances using convex optimization and the RIS reflection coefficients using Riemannian manifold optimization. Our results show that the proposed technique can be used to effectively improve the sum capacity in a variety of scenarios compared to benchmark schemes.

The article presents a 2-port multiple-input multiple-output (MIMO) antenna array designed for millimeter-wave band operation, specifically optimized for Vehicle-to-Everything (V2X) applications. To enhance performance, a novel approach employing two types of metasurfaces on a single plate is utilized. The first metasurface, based on a loop structure, aims to improve the frequency bandwidth, while the second metasurface, utilizing a composite right/left-handed (CRLH) design, focuses on reducing mutual coupling. These two steps result in an improved frequency bandwidth exceeding 45% and a decreased structure width of about 50% compared to other designs. Notably, the compact nature of these metasurfaces, measuring approximately 32 × 3 mm 2 , is a significant feature that reduces manufacturing costs. The arrayed antenna, with 20 series elements, is suitable for medium-range radar in V2X applications, although our method is generally applicable to other ranges. Additionally, the radiation pattern exhibits a 40-degree beam rotation within the frequency bandwidth, making it well-suited for V2X applications. The results demonstrate impressive diversity performance, with a consistent maximum gain of 16 dB across the entire frequency bandwidth of approximately 68 GHz to 82 GHz, representing an 18.2% coverage. [ABSTRACT FROM AUTHOR]

A novel ultra-compact four-port multiple-input-multiple-output (MIMO) cylindrical dielectric resonator antenna (DRA) with improved isolation is proposed for WLAN applications in this paper. The antenna is originally radiated with the assistance of two different excitation mechanisms to generate decoupled orthogonal modes. To further diminish the coupling field and improve the isolation, a suitable U-shaped slot is created on the common ground plane. Two additional rectangular slits are also etched to adjust the impedance matching of other ports. To better reveal the operating mechanism of the decoupling scheme, the common mode (CM) and differential mode (DM) impedance analysis methods between DRA ports are presented. The etched U-shaped slot can tune the impedance of CM and DM to be consistent to realize the decoupling. The antenna is simulated, fabricated, and tested to verify the decoupling mechanism. The results demonstrate that the isolation between ports 1 and 2 is enhanced from 5 dB to 23 dB, and other ports exhibit low coupling of better than 12 dB. Moreover, the antenna with the full size of 30 × 30 × 8.1 mm3 can be used either as a four-port DRA with a bandwidth of 300 MHz or as a two-port DRA with a bandwidth of 700 MHz, at a center frequency of 5.6 GHz.

A large-aperture radar composed of a multiple-input-multiple-output (MIMO) planar array can complete 3D through-wall imaging (TWI), but the simultaneous work of the multiple transceiver channels leads to difficulties in designing the hardware. In engineering, multiple transceiver channels are usually realized by time-division multiplexing (TDM) in MIMO radar, which is called TDM MIMO radar. A time delay will be introduced when the channels are switched, which will cause high sidelobes and position deviation in the 3D imaging of moving targets, also known as range migration. This paper proposes a motion compensation algorithm based on sparse array, designed to eliminate range migration in moving targets in 3D TWI scenes. In the proposed algorithm, the coincident array elements of the equivalent array are used as the compensation channels to calculate the position difference of the target, which can correct the remaining MIMO channels. The proposed algorithm is compared with no compensation, and the reference-channel-based motion compensation algorithm (RCMCA). According to the simulation and experimental results, the proposed motion compensation algorithm can effectively eliminate sidelobes, and keep the position deviation within 0.30 m in the 3D TWI of moving targets under the TDM MIMO radar, without increasing the system complexity.

In this article, outage probability (OP) of a joint transmit-and-receive antenna selection (JTRAS) scheme is analyzed in multiple-input–multiple-output nonorthogonal multiple-access-based downlink energy harvesting (EH) relaying networks. In this dual-hop and amplify-and-forward relaying-based network, since the first and second hops are types of single-user and multiuser systems, respectively, the optimal JTRAS and suboptimal majority-based JTRAS schemes are employed in the first and second hops. The theoretical OP analysis is carried out over Nakagami-m fading channels in the cases of perfect and imperfect successive interference cancellation. An asymptotic OP expression is also obtained at a high signal-to-noise ratio regime. Finally, Monte Carlo simulations are performed to substantiate the accuracy of the theoretical analysis. It is shown that the optimal power splitting ratios at the EH relay are different for users and the users with good channel conditions have minimum optimal ratios. [ABSTRACT FROM AUTHOR]

This letter presents a dual-element multiple-input–multiple-output antenna for applications in the very high frequency band. A compact geometry of microstrip line-fed radiators engaging 0.04 $ \times $ 0.04 ${{\boldsymbol{\lambda }}}^2$ footprint at 150 MHz was fabricated on an FR-4 substrate and tested in the anechoic chamber. Good circularly polarized radiation patterns were generated by employing two corner-fed meander lines and integrating slots at strategic locations of the ground. A dielectric strip was stacked above the substrate and between the two meandered elements to enable $ -$ 10 dB impedance bandwidth of 24%. In the operating frequency band from 133 to 169 MHz, the proposed antenna offered axial ratio of <3 dB, mutual coupling of >-25 dB, gain of $\sim $ 3 dBi, efficiency (${\boldsymbol{\eta }}$) of $\sim $ 80%, envelope correlation coefficient of $ < $ 0.5 and diversity gain of $\sim $ 10 dB. [ABSTRACT FROM AUTHOR]

This letter provides an effective solution to deal with the radar cross section (RCS) and mutual coupling of the multiple-input–multiple-output (MIMO) antenna simultaneously. A wideband reflective type polarization converter (PC) is designed and its strategic placement in between the antenna elements of the two-element MIMO antenna has been conceived to mitigate these two issues concurrently. The antenna elements of the proposed MIMO antenna are placed at a proximal distance of 0.088 λ from each other. The proposed MIMO architecture ensures a maximum coupling reduction of 46 dB compared to the conventional MIMO across 4.4–8 GHz. The PC surface reduces the reflection of copolarized waves and enhances cross-polarized reflection. A supercell formed by a unit cell of PC and its 90° rotated counterpart causes phase cancellation of cross- polarized reflected waves, which contributes to wideband RCS reduction by a maximum value of 7 dB. The alignment of PC cells in a column between the adjacent antenna elements causes a reduction in the mutual coupling due to introduction of an extra coupling path and cross-polarization conversion. A good agreement between the simulated and measured results validates this concept of the proposed MIMO design with low RCS and mutual coupling. [ABSTRACT FROM AUTHOR]

This article proposed a compact dual-element MIMO (multiple-input-multiple-output) antenna system working in 1.575 GHz (Global Positioning System)/4.5 GHz (5G)/5.8 GHz (Wireless Local Area Network)/6.4 GHz (Satellite communication) with relatively high isolation. The proposed antenna element consists of compact inverted-F antenna with meandered arm. One side of the T-shaped monopole antenna is extended and meandered while the other side is grounded to form the IFA structure. Meandering of the arm is responsible for the quad-band response. The proposed structure is simulated and fabricated on a FR4 substrate with an overall dimension of (0.23 λ0 × 0.09 λ0 × 0.004 λ0) and edge-to-edge separation of the two patches is 0.04 λ0, where λ0 is the wavelength at lower resonating frequency (1.575 GHz) of the proposed antenna. The high isolation is achieved by incorporating two inverted L-shaped strips and a narrow slot in the ground plane. Envelope correlation co-efficient (ECC) and channel capacity loss (CCL) are within their acceptable limits. Other different diversity parameters are evaluated and the results are satisfactory for MIMO applications. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) communications is expected to be a critical enabler of distributed computing in edge networks at scale. A key challenge in providing this capability is the requirement for judicious management of the heterogeneous communication and computation resources that exist at the edge to meet processing needs. In this paper, we develop an optimization methodology that considers the network topology jointly with device and network resource allocation to minimize total D2D overhead, which we quantify in terms of time and energy required for task processing. Variables in our model include task assignment, CPU allocation, subchannel selection, and beamforming design for multiple-input multiple-output (MIMO) wireless devices. We propose two methods to solve the resulting non-convex mixed integer program: semi-exhaustive search optimization, which represents a “best-effort” at obtaining the optimal solution, and efficient alternate optimization, which is more computationally efficient. As a component of these two methods, we develop a novel coordinated beamforming algorithm which we show obtains the optimal beamformer for a common receiver characteristic. Through numerical experiments, we find that our methodology yields substantial improvements in network overhead compared with local computation and partially optimized methods, which validates our joint optimization approach. Further, we find that the efficient alternate optimization scales well with the number of nodes, and thus can be a practical solution for D2D computing in large networks. [ABSTRACT FROM AUTHOR]

Intelligent reflecting surfaces (IRSs) are promising enablers for high-capacity wireless communication systems by constructing favorable channels between the transmitter and receiver. However, general, accurate, and tractable outage probability analysis for IRS-aided multiple-input-multiple-output (MIMO) systems is not available in the literature. In this paper, we first characterize the distribution of the mutual information (MI) for IRS-aided MIMO systems by capitalizing on large random matrix theory (RMT). Based on this result, a closed-form approximation for the outage probability is derived and a gradient-based algorithm is proposed to minimize the outage probability with statistical channel state information (CSI). We also investigate the diversity-multiplexing tradeoff (DMT) with finite signal-to-noise ratio (SNR). Based on these theoretical results, we further study the impact of the IRS size on system performance. In the high SNR regime, we provide closed-form expressions for the ergodic mutual information (EMI) and outage probability as a function of the IRS size, which analytically reveal that the benefit of increasing the IRS size saturates quickly. Simulation results validate the accuracy of the theoretical analysis and confirm the increasing cost to improve system performance by deploying larger IRSs. For example, for an IRS-aided MIMO system with 20 antennas at both the transmitter and receiver, we need to double the size of the IRS to increase the throughput from 90% to 95% of its maximum value. [ABSTRACT FROM AUTHOR]

This paper describes a singly-fed circularly polarized rectangular dielectric resonator antenna (RDRA) for MIMO and 5G Sub 6 GHz applications. Circular polarization was achieved for both ports using a novel-shaped conformal metal strip. To improve the isolation between the radiators, a "S" shaped defective ground plane structure (DGPS) was used. In order to authenticate the estimated findings, a prototype of the suggested radiator was built and tested experimentally. Over the desired band, i.e., 3.57–4.48 GHz, a fractional impedance bandwidth of roughly 36.63 percent (−10 dB as reference) was reached. Parallel axial ratio bandwidth of 28.33 percent is achieved, which is in conjunction with impedance matching bandwidth. Between the ports, isolation of −28 dB is achieved Gain and other far-field parameters are also calculated and found to be within their optimum limits [ABSTRACT FROM AUTHOR]

This study presented an implementation of weighted-polarization multiple-input–multiple-output (MIMO) antenna for wireless body area networks at 2.45 GHz. The weight function determined by considering the variation in the cross-polarization power ratio (XPR) and the antenna tilt angle was realized by a two-way power divider (PD), where tunable power ratio range of proposed PD could not only cross the boundary of equal power ratio (k2 = 1), but also maintain a wide tunable range at the same time. The patch array antenna fed by the proposed PD consists of microstrip lines, capacitors, resistors, and varactor diodes can overcome the polarization mismatch in dynamic off-body channel due to the variation in radio-propagation environment and human movement by adjusting the bias voltages. The experiment of 2 × 2 MIMO channel capacity was conducted using a three-dimensional spatial fading emulator. The measured and simulated results are in good agreement. Under the considered condition of arm-swinging angle and the XPR, the tunable power ratio range of proposed PD can be realized from −1.25 dB to 20 dB; therefore, it is suitable for radio-frequency control antenna to obtaining high data transmission in future wearable MIMO applications. [ABSTRACT FROM AUTHOR]

Automotive radar pursues low cost and high performance, and especially hopes to improve the angular resolution under the condition of a limited number of multiple-input–multiple-output (MIMO) radar channels. Conventional time division multiplexing (TDM) MIMO technology has a limited ability to improve the angular resolution without increasing the number of channels. In this paper, a random time division multiplexing MIMO radar is proposed. First, the non-uniform linear array (NULA) and random time division transmission mechanism are combined in the MIMO system, and then a three-order sparse receiving tensor of a range-virtual aperture-pulse sequence is obtained during echo receiving. Next, this sparse three-order receiving tensor is recovered by using tensor completion technology. Finally, the range, velocity and angle measurements are completed for the recovered three-order receiving tensor signals. The effectiveness of this method is verified via simulations.

A rigorous analysis of the concept of coupling manipulation utilizing two antennas suited to modern smartphone devices in talk position for voice calls is presented. By using the optimum relative phase between the elements, they can substantially reduce the specific absorption rate (SAR) but still maintain efficiency due to the splitting of power between them and by exploiting a suitable level of interelement coupling. The same antenna elements can still be used for multiple-input–multiple-output (MIMO) when not in talk position without heavily degrading their fundamental capacity limit, but this is of secondary importance. The concept could be applied to frequency ranges used in mobile communications from 1.8 to 6 GHz where the ground plane has sufficient form factor. Extensive simulations using two planar inverted-F antennas (PIFAs) operating at 2.4 GHz are carried out to demonstrate conceptually how two antennas can be optimized to reduce SAR by over 50% compared to a single antenna element. SAR reduction is maintained regardless of the user’s head composition and how they are handling the device in a talk position. Antenna prototypes are measured and compared to verify the capacity when the handset is used away from the body with two MIMO terminal antennas. [ABSTRACT FROM AUTHOR]

Cluster-based channel modeling has gradually become a trend in the development of a channel model, since it is a good compromise between accuracy and complexity. However, most of the existing clustering algorithms require prior knowledge of clusters, initialization, and threshold choices. An accurate and automatic cluster identification algorithm is therefore highly desirable for channel modeling. In this article, adaptive kernel-power-density (AKPD) and support vector machine-assisted AKPD (SVM-AKPD) algorithms are proposed. First, a new distance-based metric is proposed to calculate an adaptive-K for each multipath component (MPC), in which the AKPD can be used in scenarios where we have a complex distribution of MPCs, especially for the cluster with small MPCs. Furthermore, the SVM is applied in clustering by the full partition of MPCs’ feature space to overcome the limitation of the AKPD, where the MPCs lying at a large distance from the cluster centroids will be clustered into surrounding clusters when the clusters are closely spaced in the AKPD. Finally, the performance of the proposed AKPD and SVM-AKPD is validated with measured and simulated channels data at millimeter waveband, respectively. Both numerical simulations and experimental validation results are provided to demonstrate the effectiveness and robustness of the proposed algorithm. The proposed algorithms enable applications in multiple-input–multiple-output (MIMO) channels with no prior knowledge about the clusters, such as number and initial locations. It also does not need to adjust cluster parameters manually and can be implemented for cluster-based channel modeling with a fairly low complexity. [ABSTRACT FROM AUTHOR]

Multiple-input–multiple-output (MIMO) technology is one of the most widely used communication technologies. However, with the increasing number of antennas, the complexity of the MIMO wireless communication receiver becomes higher and higher. On the other hand, the complex communication channels also raise up a great challenge to the reliability of the communication receiver system. With the rapid development and wide application of deep learning, it has been applied in the field of communication to solve some problems that are difficult to solve by the traditional methods, and thereby, improves the reliability of communication systems. Inspired by this idea, this article reviewed the signal processing process of the MIMO receiver system from the perspective of system reliability. Based on deep learning, the signal processing modules of the receiver system are jointly optimized, which changes the information recovery process of the traditional receiver and proposes the intelligent receiver for MIMO communication. In order to verify the system reliability of the intelligent receiver, this article analyzes it from the aspects of antenna numbers and channel conditions. The influence of different implementation methods of the intelligent receiver on the system reliability is also analyzed. Simulation results show that the proposed intelligent receiver for the MIMO wireless communication can recover information with a lower bit error rate and higher reliability compared with the traditional receiver under different conditions and antenna configurations. [ABSTRACT FROM AUTHOR]

Graph: Figure 17: Measured ECC of UWB-MIMO antenna-1 and UWB-MIMO antenna-2. 4 Conclusions A goblet-shaped quad-notched band antenna was introduced as a prototype antenna. 2 Design of the goblet-shaped quad band-notched UWB antenna 2.1 Antenna structure Firstly, a goblet-shaped UWB antenna with quad NBs is designed as a prototype antenna. Utilizing three CSRR slots and two C-like symmetrical metal stubs, the antenna can minimize interruption from 3.5 GHz WiMAX, 5.3 GHz lower band WLAN, 5.8 GHz upper band WLAN and 8.3 GHz X-band. Keywords: band-notched; CSRR; multiple-input-multiple-output (MIMO); ultra-wideband (UWB) EN band-notched CSRR multiple-input-multiple-output (MIMO) ultra-wideband (UWB) 317 329 13 05/09/22 20220601 NES 220601 1 Introduction In 2002, Federal Communications Commission (FCC) allocated 3.1-10.6 GHz band for ultra-wideband (UWB) applications [[1]]. [Extracted from the article]

Attitude information can be utilized for beam tracking in millimeter-wave (mmWave) analog beamforming. It provides the direction of arrival (DOA) information of the user equipment (UE) when it rotates, and thus, significantly reduces the overhead of beam searching. However, in digital beamforming (DBF), the transceivers are not designed based on DOAs, which makes it more challenging to utilize attitude information to reduce system overhead. In this article, we propose an attitude information aided DBF algorithm. Specifically, based on the clustered channel model, we derive the relationship between channel variation and the attitude of UE during the rotation. Furthermore, it is proved that only the transmitter at UE requires to be redesigned after the rotation, while the receiver at base station does not. Compared with the joint transceiver design, the performance loss is generally trivial. Therefore, we propose an AIA digital transmitter design algorithm for uplink transmission with equal power allocation. The spectral efficiency performance can approximate the optimal joint transceiver design performance without real-time channel state information. We also extend the method to unequal power allocation case and propose the algorithm with water-filling power allocation. Finally, simulation results are presented to examine the effectiveness of proposed algorithms. [ABSTRACT FROM AUTHOR]

Recent works in the field of space modulation hardware have demonstrated the ability to realize different implementations using the RF-switch. The existing family of implementations, referred to at space modulation techniques (SMTs), offers a variety of realizations that can fit different application needs. Generally, higher spectral efficiency is attained while power consumption, cost, and receiver computational complexity are traded off for variant configurations. As well, all SMTs introduced to-date achieve realizations through a single spatial dimension, where implementations transmitting only spatial symbols do not require an RF-chain. A recently introduced new technique called signed quadrature spatial modulation (SQSM) adds a second spatial dimension that increases the spectral efficiency without the need for nonspatial symbols. In this article, novel hardware design models based on SQSM are introduced adding more techniques to the family of SMTs. The introduced models are compared in terms of cost, power, and computational complexity against quadrature space shift keying that has shown the most favorable traits in past comparisons against other SMTs. [ABSTRACT FROM AUTHOR]

This letter investigates the isolation of a multiple-input–multiple-output (MIMO) antenna system, consisting of two circularly polarized antennas with opposite rotating senses. The challenge in achieving a high isolation for this type of antenna system is analyzed and discussed. Based on this, a low-profile wideband design is proposed and demonstrated, in which the role of the decoupling structure is also explained. As a validation, an antenna prototype is fabricated and measured. The operating bandwidth, in which $|S_{11}|$ and axial ratio are respectively less than –10 and 3 dB, is 8.3% (5.2–5.65 GHz). Within this band, the measured peak realized gain in the broadside direction is 6.2 dBi and the isolation is better than 26 dB. In comparison with other related works, the proposed antenna has one of the smallest spacing while maintaining high isolation characteristics in a relatively wide bandwidth with a low-profile structure. [ABSTRACT FROM AUTHOR]

Polarization selectivity has a great impact on multiple-input–multiple-output (MIMO) relay channels. In this letter, the channel capacity of MIMO relay channels is analyzed, revealing the polarization dependency of multipath components. Polarization optimization schemes are proposed, including a regular optimization and a dynamic weight particle swarm optimization (DWPSO) for MIMO relay channels. The performance analysis shows that the DWPSO can significantly improve the link capacity of MIMO relay channels based on the COST 2100 channel model. This study indicates that it is necessary to optimize the polarization direction of MIMO relay channels. [ABSTRACT FROM AUTHOR]

Millimeter wave (mmWave) communication and multiple-input multiple-output (MIMO) are two important technologies for future communication systems. Hybrid precoding and combining have been used to reduce the cost and the power consumption of traditional full digital precoding and combining for mmWave MIMO systems. In this paper, we consider a fully-connected hybrid precoding architecture with finite resolution phase shifters in the design. Basically, we first obtain the phases of optimal precoder and combiner, which are obtained through the singular value decomposition (SVD) operation of channel vectors. Then, these phases are used to construct the RF precoder and combiner. After the RF precoder and combiner are achieved, the digital precoder and combiner can be calculated by the least squares solutions. The simulation results show that the proposed algorithms improve the capacity and reduce the complexity compared with the existing orthogonal matching pursuit (OMP)-based algorithm. Besides, an adaptive solution is further proposed to save computational time with competitive performance. With the adaptive solution, the full SVD process is not required for the weighting coefficient updating at every time slot. [ABSTRACT FROM AUTHOR]

A composite antenna with wide impedance bandwidth and enhanced isolation for multiple-input-multiple-output (MIMO) applications is introduced in this article. A simple conformal-strip fed rectangular dielectric resonator (rDR) with a conducting conformal-patch, which provides wide impedance bandwidth (3.21-6.19 GHz), is utilized as an antenna element. The proposed MIMO antenna is formed by arranging two symmetrical composite antenna elements side by side along with a simple decoupling structure (based on a wide rectangular slot and two metallic strips) in between them. The proposed MIMO antenna delivers good inter-port isolation (greater than 18 dB) over the entire operating bandwidth. Also, a well satisfactory outcome of the envelope correlation coefficient (ECC) is obtained over this bandwidth. Moreover, the proposed antenna exhibits a stable broadside directional radiation pattern over the entire operating bandwidth. [ABSTRACT FROM AUTHOR]