Combined Antenna Research Articles

Fast Maximum Likelihood Detection of the Generalized Spatially Modulated Signals Using Successive Sphere Decoding Algorithms

The generalized spatial modulation (GSM) scheme is used in wireless communication to map each block of data bits to a set of spatially multiplexed (SMX) symbols and an index of transmit antenna combination (TAC) of active antennas. The SMX symbols are then transmitted simultaneously through the multiple active antennas. The detection of the GSM signals at the receiver side needs to recover both the SMX symbols and TAC index. To achieve maximum likelihood detection (MLD) of GSM signals with low complexity, two previous algorithms modify the computationally efficient sphere decoding algorithm (SDA) and needs to discriminate the SMX symbols from the null symbols transmitted by inactive antennas. In this letter, we propose a new successive SDA (SSDA) that employs multiple times of SDA though but does not need to process the null symbols during tree traversals. Particularly, when used together with the radius update and reordering of the multiple SDAs, our SSDA achieves great complexity reduction and is the fastest one among the algorithms that achieve exact MLD of GSM signals.

Practical User Selection With Heterogeneous Bandwidth and Antennas for MU-MIMO WLANs

User selection is one of the most important components for next generation multi-user multiple-input-multiple-output wireless local area networks. However, state-of-the-art approaches neglect the heterogeneity of users in the available bandwidth and the number of antennas, which diminishes their performance considerably. To tackle this challenge, we formulate a novel integer optimization framework to select the antennas of heterogeneous users simultaneously. With estimated signal-to-interference-and-noise ratio of users via channel vector projection, we propose a low-complexity branch-and-prune algorithm to search for the near-optimal combinations of user antennas. Our algorithm is compatible with legacy 802.11ac and is implemented on the software defined radio system. Extensive experiments show that our algorithm achieves around 95% of the optimal throughput and outperforms a benchmark scheme with a $1.18\boldsymbol \times $ gain in realistic indoor environments.

A low‐complexity architecture using diversity techniques for Internet of Vehicles with enhanced radio‐frequency performance

AbstractIn this article, we present a new architecture for the Internet of Vehicles (IoVs) that feature reduced system complexity and enhanced radio‐frequency (RF) performance. The proposed system requires no complex coding or selection algorithms, yet it significantly improves the received signal strength. We implement dual‐port antennas comprising a linearly polarized (LP) antenna and a circularly polarized (CP) antenna, which minimize the polarization loss between multipath signals and the receiving antenna. Using Wi‐Fi communications, we designed, fabricated, and examined a prototype system comprising seven circuit modules that employ spatial diversity and revised polarization diversity simultaneously. We test its performance using two antenna combinations with distinct peak gain characteristics. Our results show these antennas have highly desirable impedance matching and radiation properties and enhanced received signal strength compared to conventional techniques. As such, the proposed system can greatly improve signal quality and reliability in non‐line‐of‐sight (NLOS) IoV scenarios.

Beam pattern reconfigurable circularly polarized transmitarray antenna by rearrangement of sources

AbstractA novel method for a beam pattern reconfigurable circularly polarized (CP) transmitarray antenna based on passive metasurface is proposed by a rearrangement of source antennas. Two source antennas among eight source antennas are selected for the fine beam steering. The beam steering angle can be finely controlled by the positions and phase difference of the source. Moreover, this kind of transmitarray antenna can be utilized to generate multibeam by the combination of the source antennas for radiation to different directions. To verify its feasibility, the planar CP source antenna is designed to operate at 5.8 GHz. Also, the metasurface consists of four layer separated by four substrates to cover full transmission phase variation of 2π, and the metallic layers are designed to circular patches. As a result, the steering angle is experimentally observed at each 0, +20, and +40°, and dual beam radiating to −30 and +30° also is measured.

Air Shower Detection by Arrays of Radio Antennas

Antenna arrays are beginning to make important contributions to high energy astroparticle physics supported by recent progress in the radio technique for air showers. This article provides an update to my more extensive review published in Prog. Part. Nucl. Phys. 93 (2017) 1. It focuses on current and planned radio arrays for atmospheric particle cascades, and briefly references to a number of evolving prototype experiments in other media, such as ice. While becoming a standard technique for cosmic-ray nuclei today, in future radio detection may drive the field for all type of primary messengers at PeV and EeV energies, including photons and neutrinos. In cosmic-ray physics accuracy becomes increasingly important in addition to high statistics. Various antenna arrays have demonstrated that they can compete in accuracy for the arrival direction, energy and position of the shower maximum with traditional techniques. The combination of antennas and particles detectors in one array is a straightforward way to push the total accuracy for high-energy cosmic rays for low additional cost. In particular the combination of radio and muon detectors will not only enhance the accuracy for the cosmic-ray mass composition, but also increase the gamma-hadron separation and facilitate the search for PeV and EeV photons. Finally, the radio technique can be scaled to large areas providing the huge apertures needed for ultra-high-energy neutrino astronomy.

Safety Assessment of Railway Vehicle Antenna Communication Management

In order to verify that multiple vehicle-mounted antennas do not appear electromagnetic interference due to integration on the same railway vehicle,an evaluation method suitable for electromagnetic compatibility of vehicle-mounted antennas is proposed. Based on the analysis of the forming factors of antenna interference and the changes of electromagnetic environment before and after loading,the combination of antennas that may produce electromagnetic interference is chosen.Then,the isolation between selected antennas is measured to supplement the evaluation data.Finally,the electromagnetic compatibility between antennas is evaluated by calculating the energy matching of transceiver antennas.The method has been applied to the development of railway vehicles.

A Novel Compact Quadruple-Band Indoor Base Station Antenna for 2G/3G/4G/5G Systems

This paper presents a quadruple-band indoor base station antenna for 2G/3G/4G/5G mobile communications, which covers multiple frequency bands of 0.8 - 0.96 GHz, 1.7 - 2.7 GHz, 3.3 - 3.8 GHz and 4.8 - 5.8 GHz and has a compact size with its overall dimensions of 204 × 175 × 39 mm 3 . The lower frequency bands over 0.8 - 0.96 GHz and 1.7 - 2.7 GHz are achieved through the combination of an asymmetrical dipole antenna and parasitic patches. A stepped-impedance feeding structure is used to improve the impedance matching of the dipole antenna over these two frequency bands. Meanwhile, the feeding structure also introduces an extra resonant frequency band of 3.3 - 3.8 GHz. By adding an additional small T-shaped patch, the higher resonant frequency band at 5 GHz is obtained. The parallel surrogate model-assisted hybrid differential evolution for antenna optimization (PSADEA) is employed to optimize the overall quadruple-band performance. We have fabricated and tested the final optimized antenna whose average gain is about 5.4 dBi at 0.8 - 0.96 GHz, 8.1 dBi at 1.7 - 2.7 GHz, 8.5 dBi at 3.3 - 3.8 GHz and 8.1 dBi at 4.8 - 5.0 GHz respectively. The proposed antenna has high efficiency and is of low cost and low profile, which makes it an excellent candidate for 2G/3G/4G/5G base station antenna systems.

Joint Antenna Selection and User Scheduling for Massive Multiuser MIMO Systems With Low-Resolution ADCs

The use of low-resolution data converters is regarded as a cost-effective solution to reduce the hardware complexity and power consumption of massive multiuser multiple-input and multiple-output (MIMO) systems. In this study, we focus on the problem of joint antenna selection and user scheduling (JASUS) in massive multiuser MIMO uplink systems, in which the base station (BS) is equipped with low-resolution analog-to-digital converters. We aim to simultaneously obtain the optimal BS antenna and user sets that maximize the system sum rate. However, finding the optimal solution to the JASUS problem requires an exhaustive search of all possible combinations of BS antennas and users, and this search incurs a combinatorial complexity that scales exponentially with the number of BS antennas and users. We address this problem by proposing a novel algorithm developed from the cross-entropy optimization (CEO) framework. The simulations produce promising results for the proposed CEO-based JASUS algorithm, which achieves a higher sum rate and a lower symbol error rate compared with other test algorithms.

GPR Study of a Thrust-Fault in an Active Limestone Quarry (SW Slovenia)

After conducting a successful GPR pilot study in a tectonically complex area of the Karst Thrust Edge, a follow-up study was carried out. In the pilot study, the geometry and spatial extent of the Socerb thrust-fault, which separates limestone above from flysch below, were investigated using a 50 MHz antenna in the Črnotiče quarry. After one part of the quarry was deepened and widened, new flysch outcrops were exposed and GPR profiling was made possible in areas where the thrust contact could not be reached before. By comparing the first GPR results with the locations of new flysch outcrops, we found it reached the surface almost exactly where we had predicted. In order to gain new information about the location of the thrust contact, nine new profiles were recorded. In this newly deepened area, the thrust contact runs close to the surface, therefore a 250 MHz antenna was used in addition to the 50 MHz antenna in order to ensure an adequate level of resolution. This combination of antennas provided the depth penetration of 34 m as well as resolution high enough to obtain accurate information from the shallowest parts. GPR profiles were used to create a 3D model of the thrust-fault plane, providing information about the spatial position and lateral undulations of the thrust contact. The results provided new data about the geometry of the Socerb thrust-fault and correlated well with existing borehole data. The results also showed the importance of using appropriate antenna frequencies as other features capable of becoming hazardous during excavation (air-filled and sediment-filled karst caves) could otherwise be misinterpreted or overlooked. The follow-up research not only provides new data important for understanding the tectonic setting of the area, but also information needed for calculating exploitable material quantities and for planning safe excavation processes.

A simple low-complexity algorithm for generalized spatial modulation

Generalized spatial modulation (GSM) is an extension of spatial modulation which is significant for the next generation communication systems. Optimal detection process for the GSM is the maximum-likelihood (ML) detection which jointly detects the antenna combinations and transmitted symbols. However, the receiver is much more complicated than SM due to inter-antenna interference and/or increased number of combinations. Therefore, the computational complexity of the ML detection grows with the number of transmit antennas and the signal constellation size. In this letter, we introduce a novel and simple detection algorithm which uses sub-optimal method based on the least squares solution to detect likely antenna combinations. Once the antenna indices are detected, ML detection is utilized to identify the transmitted symbols. For obtaining near-ML performance while keeping lower complexity than ML detection, sphere decoding is applied. Our proposed algorithm reduces the search complexity while achieving a near optimum solution. Computer simulation results show that the proposed algorithm performs close to the optimal (ML) detection resulting in a significant reduction of computational complexity.

Solar Panel Integrated Circular Polarized Aperture-Coupled Patch Antenna for CubeSat Applications

In this letter, we propose to integrate a microstrip antenna with commercial solar cells for CubeSat applications where there is a small surface area available for a combination of antennas and solar cells. By placing the radiator for an aperture-coupled patch antenna under the solar cells, it is shown that a directional antenna system can be incorporated into a CubeSat without significant impact to the performance of the antenna. Considering stringent size restrictions involved in CubeSat designs, the proposed solution provides significant overall system size reduction and design flexibility. The solar cell integrated antenna is designed for operation in the 2.2–2.3 GHz space-to-Earth downlink band. Circular polarization is achieved by feeding two 90° rotated patches with a 90° phase offset signal. The results show very promising performance.

Ordering- and Partitioning-Aided Sphere Decoding for Generalized Spatial Modulation

In this study, low-complexity sphere decoding (SD) algorithms for generalized spatial modulation (GSM) are proposed. To reduce the computational complexity of the SD algorithm for GSM, layer ordering and transmit antenna combination (TAC) partitioning are employed. The layer ordering scheme determines the detection order of layers based on their reliabilities, which are measured by their minimum mean-square errors (MMSEs). In TAC partitioning, which is combined with the early termination technique, the likely TACs are selected by exploiting an MMSE-based weighting metric to reduce the search space. Simulation results demonstrate that the proposed ordering and partitioning aided SD schemes achieve nearly the same performance as the conventional SD scheme; however, they require significantly low complexity, especially in large GSM multiple-input-multiple-output systems and in the low SNR region.

A Compact Ultrawideband Antenna Based on Hexagonal Split-Ring Resonator for pH Sensor Application.

A compact ultrawideband (UWB) antenna based on a hexagonal split-ring resonator (HSRR) is presented in this paper for sensing the pH factor. The modified HSRR is a new concept regarding the conventional square split-ring resonator (SSRR). Two HSRRs are interconnected with a strip line and a split in one HSRR is introduced to increase the electrical length and coupling effect. The presented UWB antenna consists of three unit cells on top of the radiating patch element. This combination of UWB antenna and HSRR gives double-negative characteristics which increase the sensitivity of the UWB antenna for the pH sensor. The proposed ultrawideband antenna metamaterial sensor was designed and fabricated on FR-4 substrate. The electrical length of the proposed metamaterial antenna sensor is 0.238 × 0.194 × 0.016 λ, where λ is the lowest frequency of 3 GHz. The fractional bandwidth and bandwidth dimension ratio were achieved with the metamaterial-inspired antenna as 146.91% and 3183.05, respectively. The operating frequency of this antenna sensor covers the bandwidth of 17 GHz, starting from 3 to 20 GHz with a realized gain of 3.88 dB. The proposed HSRR-based ultrawideband antenna sensor is found to reach high gain and bandwidth while maintaining the smallest electrical size, a highly desired property for pH-sensing applications.

Method for Radiation Center Position Measurements of a Combined Antenna in the Pulsed Mode

This paper proposes a method for measuring the position of radiation centers for an ultra-wideband combined antenna (CA) in the pulsed mode. The radiation centers for E- and H-planes of the antenna are determined. Antenna rotation in these planes, with respect to an arbitrary axis, results in the time delays (advances) of the recorded receiving pulses for various angles. The purpose of the measurements is to find the rotation axes providing minimum time delays of the radiated pulse registration at the receiving antenna for the largest possible range of observation angles. These rotation axes pass through local areas (radiation centers) in the antenna volume. Simple analytic formulas refining the position of the radiation center from an arbitrary measurement are proposed. In the simulations, a code based on the FDTD method was used. The CA has at least two radiation centers. Radiation center of the H-plane is located at 1/3–1/2 of the antenna length counting from its rear wall, slightly below the antenna’s half height. Radiation center of the E-plane is located near the aperture plane of the antenna, also slightly below the antenna’s half height.

Iterative Signal Detection for Large-Scale GSM-MIMO Systems

Generalized spatial modulations (GSM) represent a novel multiple input multiple output (MIMO) scheme, which can be regarded as a compromise between spatial multiplexing MIMO and conventional spatial modulations, achieving both spectral efficiency and energy efficiency. Due to the high computational complexity of the maximum likelihood detector in large antenna settings and symbol constellations, in this correspondence paper we propose a lower complexity iterative suboptimal detector. The derived algorithm comprises a sequence of simple processing steps, namely, an unconstrained Euclidean distance minimization problem, an element-wise projection over the signal constellation, and a projection over the set of valid active antenna combinations. To deal with scenarios where the number of possible active antenna combinations is large, an alternative version of the algorithm, which adopts a simpler cardinality projection, is also presented. Simulation results show that, compared with other existing approaches, both versions of the proposed algorithm are effective in challenging underdetermined scenarios where the number of receiver antennas is lower than the number of transmitter antennas.

Investigation of combining dipole antennas with three dimensional photonic crystals

The combination of dipole antennas and 3D diamond-structure photonic crystals is investigated by simulating method in this paper. The radiation frequency point of dipole antennas was selected to correspond to the reflection frequency point of the strongest energy in band gap. The results show that there is a good resonance performance in the range of band gap, which also indicate that in all direction the surface waves which propagate along the surface of the photonic crystals substrate can be suppressed because of the reflection the band gap. Moreover, coupling antenna has low return loss and improves the directionality compared to common dipole antenna. The EM waves are reflected and a high gain is attained, improving from 2.76 dB to 7.14 dB. Due to these merits of photonic crystals substrate, coupling antennas exhibit the excellent radiation performance, which will be widely utilized in communication field.

Control of Beam Direction for Substrate-Integrated Waveguide Slot Array Antenna Using Metasurface

The method to control the aperture phase distribution of antenna using a metasurface is proposed to point the antenna beam to desired directions. A $1\times 10$ substrate-integrated waveguide (SIW) slot array antenna directly integrated with the metasurface of double-layer miniaturized framed Jerusalem crosses is, for example, designed to achieve the oblique radiation beam in 30° at $Ka$ -bands. In order to achieve a full 360° transmission phase range, part of SIW slots are inverted to obtain additional 180° phase shift so that more than 400° phase shift range is realized. The measured results show that the beam directions are within 29.3 ± 1° from 34.25 to 35.75 GHz with a return loss better than 15 dB. The measured maximum gain is 12.1 dBi at 34.75 GHz. The combination of the array antenna and the metasurface features a low profile, simple structure, and flexible design for oblique beam application.

Resource Allocation in Topology Management of Asymmetric Interference Networks

Most existing works of interference alignment focus on symmetric networks. When the difference of path loss is considered in asymmetric networks, topology management needs to be carefully designed for interference-alignment-based interference networks. Using topology management, the network is separated into an interference alignment subnetwork and some spatial multiplexing subnetworks. In this paper, antenna selection and power allocation techniques are exploited to further improve the performance of topology management in asymmetric interference networks. First, the antenna selection technique is applied to interference alignment subnetworks. Through fully utilizing the redundant antennas, more optional antenna combinations can be provided to achieve the diversity gain. Then, based on the geometric programming framework, the transmitted power is allocated among transmitters of both the interference alignment and spatial multiplexing subnetworks, to optimize the spectrum efficiency of the network. Based on these two techniques for the topology management scheme, the joint optimization of antenna selection and power allocation is developed through a stepped resource allocation optimization strategy to further improve the performance with low computational complexity. Simulation results are presented to show the effectiveness of the proposed algorithms.

Simulation modeling and analysis of the hop count distribution in cognitive radio ad-hoc networks with beamforming

Due to the spatial–temporal spectrum mobility in cognitive radio ad-hoc networks (CRAHNs), multi-hop communication paths among secondary users have to detour or even be disconnected to avoid interfering with primary users. Consequently, the hop count in CRAHNs shows distinguishing characteristics compared with those in conventional ad-hoc networks (AHNs). Although the influences of beamforming on the connectivity of CRAHNs have been studied in the literature, no research works on investigating the hop count in cognitive environment under the joined effect of beamforming have been conducted. In this paper, we model CRAHNs where SUs are equipped with directional antennas as geometric random graphs and then propose a framework for simulation analysis of the hop count distribution. Our proposed framework comprises of two components. The first one is an algorithm which finds all possible paths between two random secondary users selected as source node and destination node then returns the hop count of the shortest path between them by using the random values of node location and active state, antenna gain, and channel fading as input data. The second one is a methodology which returns the hop count distribution and connection probability of these two nodes from vast number of examined random network topology trials. We show that the hop count and the connectivity between two secondary users greatly depend on the number of antenna elements of directional antenna. Moreover, only a specific combination of direction antenna and beamforming scheme gives better performance than omnidirectional antenna. The observed results in this paper provide useful guidelines on designing and evaluating hop count based applications in CRAHNs with beamforming.

Transmit Antenna Combination Optimization for Generalized Spatial Modulation Systems

Generalized spatial modulation (GSM), where both the transmit antenna combination (TAC) index and the amplitude phase modulation (APM) symbols convey information, is a novel low-complexity and high efficiency multiple-input multiple-output (MIMO) technique. In conventional GSM (C-GSM), the legitimate TACs are selected randomly to transmit the APM symbols. However, the number of the TACs must be a power of two, hence the excess TACs are discarded, resulting in wasting some resource. To address these issues, in this paper, an optimal TAC set-aided enhanced GSM (E-GSM) scheme is proposed, where the optimal TAC set is selected with the aid of the channel state information (CSI) by maximizing the minimum Euclidean distance. Furthermore, a hybrid mapping GSM (HM-GSM) scheme operating without CSI knowledge is investigated, where the TAC selection and bit-to-TAC mapping are both taken into consideration for optimizing the average Hamming distance. Finally, an enhanced high throughput GSM (E-HT-GSM) scheme is developed, which makes full use of all the TACs. This scheme is capable of achieving an extra one bit transmission rate per time slot. Moreover, the rotated phase is employed and optimized for the reused TACs. Our simulation results show that the proposed E-GSM system and HM-GSM system are capable of outperforming the C-GSM system. Furthermore, the E-HT-GSM system is capable of obtaining one extra bit transmission rate per time slot compared with the C-GSM system.