Multiple-input Multiple-output (MIMO) Systems

In this paper, we propose a feedback-efficient hybrid precoding framework for wideband millimeter-wave (mmWave) multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. To mitigate the high cost of radio frequency (RF) chains and channel state information (CSI) feedback in large-scale antenna arrays, we first construct frequency-flat analog precoders by extracting dominant angle-of-arrival (AoA) and angle-of-departure (AoD) directions from sparse frequency-domain channels. For digital precoding, we design a quantized codebook using the Lloyd algorithm and develop a binary-search-based hierarchical interpolation algorithm that adaptively assigns codewords according to subcarrier correlation. The proposed method achieves sublinear feedback scaling by reducing the feedback overhead from O(K) to O(K/M +log M), where K is the number of subcarriers and M is the pilot spacing. Simulation results demonstrate that the proposed method achieves comparable or superior spectral efficiency and bit error rate (BER) performance to existing clustering and interpolation schemes, while significantly reducing computational complexity and exhibiting robustness under imperfect CSI.

This paper presents a conceptual architecture for directional flow regulation, phase-gradient management, and geometric stability in complex multi-input systems. The framework addresses a common systems problem: how to preserve coherence, symmetry, and internal stability while multiple active inputs interact under changing operational conditions. Instead of focusing on energy generation alone, the model focuses on how outputs are shaped, balanced, directed, and corrected in real time. The proposed architecture treats directional control as a coherence problem in which phase relationships, front-to-rear gradients, geometric preservation, and embedded feedback are all central to stable operation. The paper positions the framework as a theoretical control model for simulation, analog study, and advanced systems design rather than as an experimentally validated device. Its present-day relevance lies in control architectures, dynamic flow regulation, multi-variable feedback systems, and coherencesensitive engineering environments.

For 5G communication, this research suggests a small, broad band, 4-port multiple-input multiple-output (MIMO) antenna with an impedance bandwidth of 2.0 GHz (or 3.0-5.0 GHz). The n77, n78, and n79 bands are covered. The single antenna is realized by inserting the stubs and creating the 'HI' slot on the rectangle patch with the defect in the ground plane, using FR-4 substrate. Next, four MIMO antennas are built utilizing the reference antenna. Due to mutual interaction, implementing MIMO systems presents a substantial challenge: achieving good isolation between antenna parts in the confined space. To increase isolation with decoupling procedures, the four antennas are placed orthogonally to one another. Because the antennas are positioned orthogonally, the MIMO antenna has an isolation of 28.0 dB. The diversity gains (DG) and envelop correlation coefficient (ECC) are used to analyze the recommended antenna's diversity performance characteristics, and the results show that the values are 9.99 dB and 0.0003, respectively. The simulated S-parameters have been compared with orthogonal and adjacent positions of quad port MIMO antenna. Anritsu MS2037C VNA is used to measure the parameters, and HFSS software is used to simulate it.

Wireless communication systems are quickly evolving to fulfil the increasing need for higher spectral efficiency, lower latency, and seamless connectivity. Although the conventional multiple-input multiple-output (MIMO) architecture improves reliability and throughput, it still faces high hardware complexity, spectral inefficiency, and interference issues in dense environments. Existing solutions, such as double-sided microstrip patch antennas or 8×8 MIMO arrays, yield moderate improvements but are not flexible enough for next-generation networks. To overcome these limitations, this paper puts forward a slot-based distributed generalized spatial modulation (DGS-MIMO) framework, which integrates dynamic antenna subset activation and adaptive sub-band allocation. In this way, the number of radio frequency (RF) chains is reduced, power consumption is lower, and spectral utilization is improved. Experimental validation shows excellent impedance matching (return loss up to-36.29 dB), high gain (6.98 dB), high radiation efficiency, and low signal reflection (voltage standing wave ratio (VSWR) as low as approximately 1.03). These results prove the robustness and efficiency of the proposed system in comparison with conventional designs. Besides the performance enhancement, the framework has great potential to be applied in real-world 5G/6G applications, especially in internet of things (IoT) deployments and vehicular communication scenarios where scalability, energy efficiency, and reliability are important.

The rapid growth of wireless communications has created a significant demand for high through-put, seamless connectivity, and extremely low latency. To meet these goals, a novel technology - stacked intelligent metasurfaces (SIMs) - has been developed to perform signal processing by directly utilizing electromagnetic waves, thus achieving incredibly fast computing speed while reducing hardware requirements. In this article, we provide an overview of SIM technology, including its underlying hardware, benefits, and exciting applications in wireless communications. Specifically, we examine the utilization of SIMs in realizing transmit beamforming and semantic encoding in the wave domain. Additionally, channel estimation in SIM-aided communication systems is discussed. Finally, we highlight potential research opportunities and identify key challenges for deploying SIMs in wireless networks to motivate future research.

The stacked intelligent metasurface (SIM), comprising multiple layers of reconfigurable transmissive metasurfaces, is a promising solution for future wireless communication systems. In this paper, we explore the integration of SIM in a multi-antenna base station for application to downlink multi-user communications. Also, a realistic power consumption model for SIM-assisted systems is presented. Specifically, we focus on maximizing the energy efficiency (EE) for hybrid precoding design, i.e., the base station digital precoding and SIM wave-based beamforming. Due to the non-convexity and high complexity of the formulated problem, we employ the quadratic transformation method to reformulate the optimization problem and propose an alternating optimization (AO)-based joint precoding framework. Specifically, a successive convex approximation (SCA) algorithm is adopted for the base station precoding design. For SIM wave-based beamforming, two algorithms are employed: the high-performance semidefinite programming (SDP) method and the low-complexity projected gradient ascent (PGA) algorithm. In particular, the results indicate that, while the optimal number of SIM layers for maximizing the EE and spectral efficiency differs, a design of 2 to 5 layers can achieve satisfactory performance for both. Finally, numerical results are illustrated to evaluate the effectiveness of the proposed hybrid precoding framework and to showcase the performance enhancement achieved by the proposed algorithm in comparison to benchmark schemes.

Cell-free (CF) massive multiple-input multiple-output (mMIMO) systems are emerging as promising alternatives to cellular networks, especially in ultra-dense environments. However, further capacity enhancement requires the deployment of more access points (APs), which will lead to high costs and high energy consumption. To address this issue, in this paper, we explore the integration of low-power, low-cost stacked intelligent metasurfaces (SIM) into CF mMIMO systems to enhance AP capabilities. The key point is that SIM performs precoding-related matrix operations in the wave domain. As a consequence, each AP antenna only needs to transmit data streams for a single user equipment (UE), eliminating the need for complex baseband digital precoding. Then, we formulate the problem of joint AP-UE association and precoding at APs and SIMs to maximize the system sum rate. Due to the non-convexity and high complexity of the formulated problem, we propose a two-stage signal processing framework to solve it. In particular, in the first stage, we propose an AP antenna greedy association (AGA) algorithm to minimize UE interference. In the second stage, we introduce an alternating optimization (AO)-based algorithm that separates the joint power and wave-based precoding optimization problem into two distinct sub-problems: the complex quadratic transform method is used for AP antenna power control, and the projection gradient ascent (PGA) algorithm is employed to find suboptimal solutions for the SIM wave-based precoding. Finally, the numerical results validate the effectiveness of the proposed framework and assess the performance enhancement achieved by the algorithm in comparison to various benchmark schemes. The results show that, with the same number of SIM meta-atoms, the proposed algorithm improves the sum rate by approximately 275% compared to the benchmark scheme.

In this paper, the influence of the ground plane dimensions on the port-to-port isolation of two closelyspaced Universal Mobile Telecommunications System (UMTS) Planar Inverted-F Antennas (PIFAs) with and without neutralization line is first presented. Parametric studies show the existence of an optimal size of the ground plane allowing optimizing the isolation and the efficiency of the considered antenna system. The results obtained with this study are used in the second part to develop an efficient neutralized multi-antenna system for clamshelltype mobile phones. The obtained results, in terms of isolation, matching and diversity for the two possible configurations of the clamshell system in use namely the open and the closed states, show that good performance are obtained in the open state and preserved in the closed state. Prototypes of these two configurations are realized and measurement results are in good agreement with the simulations.

In this paper, we demonstrate the possibility to strongly modify the radiated fields of a UMTS handset by using a phased two-element PIFA array. The structure is composed of a 100x40 mm 2 metallic ground plane acting as the Printed Circuit Board (PCB) of the mobile phone. Two UMTS PIFAs are located at the top edge of this PCB. They are fed by a double Quasi-Lumped Coupler able to provide a 360° phase difference between its two outputs. By properly choosing the DC bias of the double Quasi-Lumped Coupler, we can set a specific phase difference between the two PIFAs. In this way the two-element array is able to radiate different electromagnetic fields. Simulated and measured radiation patterns in the two main planes of the chassis are presented for different phase differences. It is especially revealed that the novel twoantenna structure is able to radiate vertically-polarized electric fields in the azimuthal plane of the phone and horizontally-polarized electric fields in the same plane when changing the phase shift between the antennas from 0° to 180°. Potential applications are polarization-diversity techniques and Specific Absorption Rate reduction for handsets.

In this paper, we present the design and the measurement of MIMO meandered monopole antennas and the computation of their channel capacity performance. The initial proposed handset-system is composed of a meandered monopole operating in the LTE 700 MHz band, connected to a parasitic radiating element for the upper 2.5 GHz LTE band. Two antennas of the same kind are then closely positioned on the same 120x50 mm 2 Printed Circuit Board (PCB). A neutralization line connects the two antennas to enhance their port-to-port isolation in the 700 MHz band. The computation of the channel capacity performance in this band is based on propagation simulations performed with the GRIMM model from the CREMANT. Two system-prototypes are evaluated: one with the neutralization line for enhanced port-to-port isolation and a second without the neutralization exhibiting poor antenna-to-antenna isolation. It is demonstrated that the neutralization technique helps in giving a minimum improvement of 12% of the capacity performance of the handset-system, and a maximum improvement 46%, in the chosen environment.

Dans un contexte OFDM où le canal est sélectif en fréquence, on se propose d'optimiser la transmission de données scalables à la fois à l'issue de l'encodage source (nombre de classes à transmettre) et lors de l'encodage canal (protection inégale extrême contre les erreurs grâce aux rendements de code et aux modulations), sous une contrainte de qualité de service définie par l'utilisateur. Un algorithme répondant à ce problème d'optimisation, nomme FT-OFDM, est ici proposé et appliqué à la transmission de données de parole (MPEG-4). Les performances en terme de qualité perçue de la donnée reconstruite seront analysées et comparées à celles des schémas de protection inégale contre les erreurs actuels.

Antenna is a device with signal processing capability combining multiple antenna elements to optimize its radiation and reception patterns as per designed specifications. Smart antennas basically comprise of two functionalities, i.e., Direction of Arrival and Beamforming. This paper explains the estimation of Direction of Arrival using Bartlett method and a novel approach called MUltiple Signal Classification which takes advantage of orthogonal property and performs subspace computation. With a comparative study of both the algorithms, we shall prove the advantages of MUltiple Signal Classification over the Bartlett method with the aid of MATLAB.

En este artículo se presenta la aplicación MIMOGIS, basada en un Sistema de Información Geográfica (SIG), cuyo fin es facilitar la simulación de canales MIMO (Multiple-Input Multiple-Output). MIMOGIS es capaz de estimar la capacidad máxima teórica MIMO en entornos de propagación microcelulares e indoor. El modelo de propagación para estimar la función de transferencia del canal está basado en Óptica Geométrica (OG) y en la Teoría Uniforme de la Difracción (UTD). MIMOGIS permite el uso de cualquier tipo de configuración de arrays de antenas, tanto en transmisión como en recepción, ya que el usuario es capaz de introducir las coordenadas en 3 dimensiones (3D) de cada uno de los elementos que forman ambos arrays. Dirección General de Investigación (Consejería de Educación y Cultura de la Comunidad Autónoma de la Región de Murcia) por su financiación de este trabajo a través del proyecto con referencia 2I05SU0031), y a las empresa TECNICA y 102NOVADOC.

This paper shows a micro-strip antenna based on the yagi antenna principle, both singly and in a matrix. The suggested antenna can operate at a frequency of 10 GHz, which is in the X-band, That suggested a return loss (S11) should be lessthan (-10 dB) and"the Voltage Stand Wave Ratio"(VSWR) should be lessthan 2. Two types of micro-strip Yagi antennas were simulated and compared by calculating the parameters (directivity, gain, parameter S11, VSWR). The first design consists of one antenna and the second consists of a group of two antennas. CST Microwave studio software 2019 was used for designing and simulation. The results were for antennas constructed for Gain (5.308dB) (9.682dB) and Directivity (6.016dB) (10.28), with the second Antenna outperforming the first antenna by a wide margin.

Network-coded cooperation (NCC) has recently gained interest as it improves the network throughput in multisource cooperative systems. NCC has been studied for singleantenna terminals only. Employing multiple-input multipleoutput (MIMO) techniques can significantly improve the performance of NCC systems. Furthermore, the existing relay selection (RS) strategies for NCC utilize the "max-min" end-toend (E2E) criterion. This selection strategy (called Strategy A) is complicated even for a network with single-antenna terminals as it requires global channel state information (CSI). This requirement makes it hard to implement RS-based NCC. To counter this issue, we introduce a new RS strategy (Strategy B), which utilizes only the local CSI (not global CSI), reducing the signaling overhead significantly without sacrificing the performance. The performance of MIMO-NCC under Strategy A and B is studied over independent and non-identically distributed (i.n.i.d.) Rayleigh fading channels. Relays and the destination are equipped with multiple antennas, whereas sources have single antenna. The exact outage probability expressions of the system under consideration are derived. The asymptotic outage expressions are further provided to obtain valuable insights into the practical system-design parameters such as the diversity order and coding gain. Furthermore, numerical results are provided in support of the analytical results.

In the 5G system, multiple input multiple output (MIMO) antennas for both transmitting and receiving ends are required. However, the design of MIMO antenna at 5G upper band is challenging due to the mutual coupling issues. Many techniques have been proposed to improve antenna isolation, however some of the designs have impacts on the antenna performance, especially on the gain and bandwidth reduction, or an increase in the overall size. Thus, a design with a detailed trade-off study shall be implemented. This article proposes a new C-shaped parasitic struc-24 ture around a main circular radiating patch of a MIMO antenna at 16GHz with enhanced isolation 25 features. The proposed antenna comprises two elements with separation 0.32λ edge to edge be-26 tween radiation parts placed in a linear configuration having an overall dimension of 15mm x 27 26mm. The C-shaped parasitic element is introduced around the main radiating antenna for better 28 isolation. Based on the measurement results, the proposed structure has significantly improved the 29 isolation from -23.86 dB to -32.32 dB and increased the bandwidth from 1150MHz to 1400MHz. For 30 validation, the envelope correlation coefficient (ECC) and the diversity gain (DG) are also measured, 31 giving 0.148dB and 9.89dB, respectively. Other parameters such as the radiation pattern, the total 32 average reflection coefficient and the mean effective gain are also calculated to ensure the validity 33 of the proposed structure. Based on the design work and analysis, the proposed structure is 34 proven to improve the antenna isolation and increase the bandwidth, while maintaining the small 35 overall dimension.

Resumo: O turismo de observação de aves é uma atividade econômica que tem grande sintonia com a proposta da Agroecologia. Os agricultores, se capacitados para a identificação de aves, podem atuar como guias facilitadores que ajudem aos observadores a encontrar as espécies desejadas. O objetivo desta pesquisa foi realizar o levantamento das aves do setor da Agroecologia do Instituto Federal de Brasília (IFB) e levantar o debate sobre a potencialidade da interação entre o turismo de observação de aves e propriedades que produzem em bases agroecológicas. Palavras-chave: turismo, renda, aviturismo.

In the paper a technique for designing antenna arrays composed of directional elements for direction-of-arrival (DOA) estimation is proposed. Especially this approach is applied for developing hybrid antenna arrays with increased accuracy which features digital spatial spectral estimation after preliminary analog beamforming. The earlier obtained explicit formula for calculating the Cramér-Rao lower bound (CRLB) which determines the relationship between the variance of the DOA-estimation and antenna elements' radiation patterns, array geometry, has been used. Main idea of the proposed technique is that it takes into account spatial pattern and gain of the antenna elements. The high gain unlike the number of the antenna elements or interelement distance is the most important factor which allows reducing the value of the DOA-estimation errors. A couple of the examples of calculating radiation patterns of antenna elements improving accuracy of DOA-estimation with super-resolution are provided in the paper. Proposed antenna arrays are modeled according to the method of moments (MoM). The values of the root mean square error after the DOA-estimation are obtained. It is shown that the resulting hybrid systems can reduce the error value in DOA-estimation with super-resolution.

The objective of this work is to develop a new tuning strategy for multivariable extended predictive control ͑EPC͒. A natural concern is the problem of ill conditionality in controlling multi-input multi-output ͑MIMO͒ systems. The main advantage of EPC is that it has a simple and effective tuning strategy that results in a well-conditioned system which can achieve tight closed-loop response. Moreover, unlike most existing model predictive control tuning strategies, the proposed strategy establishes a direct relationship between one main tuning parameter for each subprocess of the MIMO system. This tuning method has been derived based on the assumption of an infinite control horizon resulting in powerful stability for the nominal case and in the presence of model uncertainty. This tuning method is applicable to unconstrained multivariable processes, and was proven to have good control on nonsquare systems. The main features of the new tuning strategy are practically illustrated on a MIMO temperature system with improved control performance as compared to move suppressed predictive control.

Long Term Evolution (LTE) is the final release of third generation (3G) leading to the fourth generation (4G) network. The demand for a very high speed network connection is the driving force for this mobile network evolution. Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are strong multiple access scheme candidates for the downlink and uplink of the LTE and LTE-Advanced Networks with Orthogonal Frequency Division Multiplexing (OFDM) being adopted by third generation partnership project (3GPP) as the standard for modulation technique used in transmission of high data rate in LTE Networks. In this research, a Matlab and Simulink software package were used to model and design an LTE downlink physical layer simulator according to 3GPP specifications. The simulation was carried out for the single downlink, from one eNodeB to User Equipment (UE). The performance of different multi-antenna techniques (transmission modes) was exploited in Diversity scheme and mobility environment with the aim of maximizing LTE performance using Multiple-Input Multiple-Output (MIMO) Optimization. However, the result show that MIMO spatial multiplexing offers the best capacity gains at high SNR and Open Loop Spatial Multiplexing (OLSM) is more robust at high SNR followed by CLSM because of their ability to support high data throughput as well as multi-stream transmission. This research strengthens the belief that performance of different multi-antenna scheme configurations is better than single antenna scheme and that multi-stream transmission will be a practical method for improving the data throughput in LTE Networks than single stream transmission

A miniature Multiple Input Multiple Output (MIMO) Ultrawideband (UWB) antenna with C-band notch is recommended for wireless communications. The radiator is etched on an economical FR4 substrate and is 40 × 21 mm 2 in size. The antenna is comprised of a circularly notched rectangular patch embedded with an ellipse and is fed by a 50-Ω microstrip line. To reduce mutual coupling by <-18 dB throughout the whole operational bandwidth of 2.94-11.61 GHz without employing any coupling device, the two radiators are positioned side-by-side with a separation of 0.03 λ 0 (λ 0 is the wavelength at the lower cutoff frequency of 2.94 GHz). A U-type slit is cut into the patch to produce the band-notch at C-band across 3.63-4.15 GHz. Results from simulation and experiment concludes that the suggested radiator has a wide impedance bandwidth (S 11 <-10 dB) and strong mutual coupling (S 21 <-18 dB) between 2.94 and 11.61 GHz. Except at the notch frequency of 4 GHz, where the gain is-3.21 dBi, the peak gain and peak radiation efficiency are both 4.21 dBi and more than 82%, respectively. The measured envelope correlation coefficient (ECC) of 0.002, peak diversity gain (DG) of 9.999 dB, and mean effective gain (MEG) of less than-3 dB over operating band, along with the omnidirectional characteristics of the radiator, prove its suitability for use in wireless systems.

We present an electromagnetic simulation of a practical mobile terminal with a two-port MIMO antenna on left and right sides of the head. The computed far-field patterns include the effect of head and hand phantoms. We show that the far-field patterns on the two sides are strongly correlated if they are presented in the coordinate system of the phone, but they are completely uncorrelated in the coordinate system of the environment. I.

Resumo: A agricultura familiar camponesa é marcada por conflitos e as inovações da agricultura latifundiária restritivas às necessidades de comunidades assentadas. Entretanto, o desenvolvimento da matriz científica da Agroecologia amplia as possibilidades sociotécnicas. O objetivo geral deste relato é compartilhar a experiência desenvolvida no Assentamento Milton Santos por meio das Tecnologias Sociais (TS). O objetivo específico é apresentar um dispositivo de baixo custo para monitoramento de compostagem caseira. A metodologia seguiu os princípios da Educação Popular com visitas de campo, coleta de dados e validação participativa. Os resultados apontam para um incremento da adubação usual pelo uso do dispositivo, demonstrando como as TS fortalecem redes sociotécnicas essenciais. Este trabalho faz parte do projeto "Agroecologia, tecnologias de produção orgânica em assentamentos rurais e educação popular", fomentado pelo CNPq e desenvolvido no âmbito do Núcleo de Estudos em Agroecologia, Educação e Sociedade

A method to characterize the memory effects in a nonlinear concurrent dual-band transmitter is presented. It is an extension of the conventional two-tone test for power amplifiers to concurrent dual-band transmitters. The output signal of a concurrent dual-band transmitter is affected not only by intermodulation (IM) products but also by cross-modulation (CM) products. In one frequency band, the transmitter is excited by a two-tone signal which frequency separation is swept. In the second band, the transmitter is concurrently excited by another two-tone signal with slightly wider frequency separation. The frequency difference of the two signals is fixed during the frequency sweep. The two-tone test is made at different power levels. The upper and lower third-order IM and CM products are measured. The asymmetry between the upper and lower third-order IM and CM products are measures of the transmitter's memory effects. The measurement results show that the memory effects are more dominant in the third-order IM products than in the CM products. An error analysis and system calibration was performed and measurement results for two different devices are presented.

A method to characterize the memory effects in a nonlinear concurrent dual-band transmitter is presented. It is an extension of the conventional two-tone test for power amplifiers to concurrent dual-band transmitters. The output signal of a concurrent dual-band transmitter is affected not only by intermodulation (IM) products but also by cross-modulation (CM) products. In one frequency band, the transmitter is excited by a two-tone signal which frequency separation is swept. In the second band, the transmitter is concurrently excited by another two-tone signal with slightly wider frequency separation. The frequency difference of the two signals is fixed during the frequency sweep. The two-tone test is made at different power levels. The upper and lower third-order IM and CM products are measured. The asymmetry between the upper and lower third-order IM and CM products are measures of the transmitter's memory effects. The measurement results show that the memory effects are more dominant in the third-order IM products than in the CM products. An error analysis and system calibration was performed and measurement results for two different devices are presented.

This paper proposes three novel models for behavioral modeling and digital pre-distortion (DPD) of nonlinear 2 2 multiple-input multiple-output (MIMO) transmitters in the presence of crosstalk. The proposed models are extensions of the singleinput single-output generalized memory polynomial model. Three types of crosstalk effects were studied and characterized as linear, nonlinear, and nonlinear & linear crosstalk. A comparative study was performed with previously published models for the linearization of crosstalk in a nonlinear 2 2 MIMO transmitter. The experiments indicate that, depending on the type of crosstalk, the selection of the correct model in the transmitter is necessary for behavioral modeling and sufficient DPD performance. The effects of coherent and partially noncoherent signal generation on the performance of DPD were also studied. For crosstalk levels of 30 dB, the difference in the normalized mean square error and adjacent channel power ratio was found to be 3-4 dB between coherent and partially noncoherent signal generation.