Antenna Downlink Research Articles

PCO and hardware delay calibration for LEO satellite antenna downlinking navigation signals

Augmentation of the Global Navigation Satellite System by low earth orbit (LEO) satellites is a promising approach benefiting from the advantages of LEO satellites. This, however, requires errors and biases in the satellite downlink navigation signals to be calibrated, modeled, or eliminated. This contribution introduces an approach for in-orbit calibration of the phase center offsets (PCOs) and code hardware delays of the LEO downlink navigation signal transmitter/antenna. Using the satellite geometries of Sentinel-3B and Sentinel-6A as examples, the study analyzed the formal precision and bias influences for potential downlink antenna PCOs and hardware delays of LEO satellites under different ground network distributions, and processing periods. It was found that increasing the number of tracking stations and processing periods can improve the formal precision of PCOs and hardware delay. Less than 3.5 mm and 3 cm, respectively, can be achieved with 10 stations and 6 processing days. The bias projections of the real-time LEO satellite orbital and clock errors can reach below 3 mm in such a case. For near-polar LEO satellites, stations in polar areas are essential for strengthening the observation model.

Optimal Configuration Mitigating Rayleigh-Backscattering-Induced Distortion in Radioastronomic Optical Fiber Systems

In the context of Radioastronomic applications where the Analog Radio-over-Fiber technology is used for the antenna downlink, detrimental nonlinearity effects arise because of the interference between the forward signal generated by the laser and the Rayleigh backscattered one which is re-forwarded by the laser itself toward the photodetector. The adoption of the so called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dithering</i> technique, which involves the direct modulation of the laser with a sinusoidal tone and takes advantage of the laser chirping phenomenon, has been proved to reduce such Rayleigh Back Scattering - induced nonlinearities. The frequency and the amplitude of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dithering tone</i> should both be as low as possible, in order to avoid undesired collateral effects on the received spectrum as well as keep at low levels the global energy consumption. Through a comprehensive analysis of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dithered</i> Radio over Fiber systems, it is demonstrated that a progressive reduction of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dithering tone</i> frequency affects in a peculiar fashion both the chirping characteristics of the field emitted by the laser and the spectrum pattern of the received signal at the fiber end. Accounting for the concurrent effects caused by such phenomena, optimal operating conditions are identified for the implementation of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dithering tone</i> technique in radioastronomic systems.

Error analysis of TAS‐OSTBC assisted downlink NOMA system over generalized η−μ fading Channel

SummaryIncorporation of multiple antennas in downlink non‐orthogonal multiple access (NOMA) system helps in achieving better performance by exploiting different diversity schemes. To this end, we propose a general framework of transmit antenna selection (TAS)‐assisted orthogonal space‐time block code (OSTBC) transmission for multiple NOMA users. We derive exact expressions of probability density function of the TAS‐OSTBC processed signal‐to‐noise ratio (SNR) at the output of maximum‐ratio combiner of the NOMA users. Using well‐known moment generating function approach, we evaluate the error performance of TAS‐OSTBC assisted NOMA users over generalized η−μ fading channel in presence of perfect and imperfect successive interference cancelation. We investigate the proposed system in different multi‐antenna scenarios and accordingly observe better error performance of the users by increasing the number of transmit and receive antennas. We perform their asymptotic analysis leading to full‐diversity order at high SNR. For numerical evaluation, we truncate the infinite series in derived results and examine the upper bound of truncation error. We evaluate nth moment of the output SNR and obtain channel quality estimation index as a performance measure of the proposed NOMA system. Moreover, we investigate the influence of power coefficients and fading parameters, η and μ, on the error performance of TAS‐OSTBC‐assisted NOMA users. We also compare the derived error performances with the existing schemes, wherein we observe that the proposed system shows remarkable improvement in the bit error rate (BER) of the NOMA users. For validation, we execute simulations which closely match with the derived analytical results.

Maximizing the Geometric Mean of User-Rates to Improve Rate-Fairness: Proper vs. Improper Gaussian Signaling

This paper considers a reconfigurable intelligent surface (RIS)-aided network, which relies on a multiple antenna array aided base station (BS) and an RIS for serving multiple single antenna downlink users. To provide reliable links to all users over the same bandwidth and same time-slot, the paper proposes the joint design of linear transmit beamformers and the programmable reflecting coefficients of an RIS to maximize the geometric mean (GM) of the users’ rates. A new computationally efficient alternating descent algorithm is developed, which is based on closed-forms only for generating improved feasible points of this nonconvex problem. We also consider the joint design of widely linear transmit beamformers and the programmable reflecting coefficients to further improve the GM of the users’ rates. Hence another alternating descent algorithm is developed for its solution, which is also based on closed forms only for generating improved feasible points. Numerical examples are provided to demonstrate the efficiency of the proposed approach.

On Actual Maximum Exposure From 5G Multicolumn Radio Base Station Antennas for Electromagnetic Field Compliance Assessment

The traditional approach of radio frequency electromagnetic field exposure compliance assessment is highly conservative when applied to radio base station antennas implementing dynamic beamforming. In this article, an analytical model based on the queuing theory with a hyperexponential service distribution time is developed to assess the time-averaged actual maximum downlink exposure of 5G multicolumn radio base station antennas by taking into account the effects of beam scanning over time in free space. Using the measured antenna radiation patterns, the 5G downlink antenna precoding codebook, and assuming a conservative user equipment distribution, the ratio of the actual maximum exposure to the theoretical maximum exposure with 100% traffic load and 75% time-division duplex downlink duty cycle is found to be less than 0.5 and 0.3 for four-transmitter and eight-transmitter radio base station antennas, respectively. These results show that assuming constant peak power transmission in a fixed direction leads to an overestimate of downlink exposure also from conventional antennas characterized by only a few transmitters in addition to massive multi-input multi-output products.

Design of C band antenna downlink system for monitoring Sentinel 1A signals on ground surface

The C band microwave signals are widely used for Earth observation in the field of remote sensing by using synthetic aperture radar sensor. The coverage of Indian regions by Sentinel 1A SAR sensor in interoferometric wide swath mode, provide an opportunity to research and conduct studies in remote sensing areas from urban planning to disaster management applications. The sensor acquired images undergo calibration test to confirm the quality requirements. The foremost significant step to ensure the availability of the signal of Sentinel 1A on the ground surface is by designing a antenna system which tracks and monitor the signal strength. In this context, the following stages are significant in signal monitoring system: satellite downlink budget calculation to ensure minimum signal strength, designing and configuring antenna system to receive the signals and measurement system such as spectrum analyser to monitor the signal strength. The paper presents the mathematical analysis of designing a down link for receiving Sentinel-1A SAR signals. An antenna subsystem is implemented which includes the design of the parabola antenna with horn feed and the simulation of the same using Matlab platform to confirm antenna parameters such as gain, directivity, VSWR and beam-width which meets the practical requirements

Effect of polarization on the link dynamics of a spinning low‐earth orbits satellite aligned with geomagnetic field

AbstractThis paper discusses the dynamic communication link aspects of IIT Madras student Satellite (IITMSAT). It is a Low‐Earth Orbits satellite which has limited Attitude Determination and Control System (ADCS) ability to align one of its body axes with the geomagnetic field in orbit. The ADCS of IITMSAT has no control over its spin with respect to the axis along the geomagnetic field. This has a destructive influence on the link aspects between the satellite and the ground station. As the satellite spins over its axis, given the two‐axis attitude control, the gain of the downlink antennas in the direction of the ground station vary all through the pass of the satellite over the ground station, which will, in turn, affect the signal received at the ground station. Similarly, the uplink is also affected. A rigorous analysis of the variation of the link strengths for uplink and downlink along typical passes of the satellite above a ground station located in Chennai, India, is presented, taking into account the geomagnetic field at the altitude of the orbit. This analysis helps in choosing the polarization (LHCP or RHCP) for uplink and stresses the need for polarization diversity at the ground station for downlink. This will ensure the link with the ground station remains robust through the pass of the satellite and hence achieving higher amounts of data transfer with the satellite. Further, this work helps design the satellite onboard antennas for better link performance, taking into account the ground station location and assisting in taking system‐level decisions for small satellite missions.

Integrating Metamaterial Antenna Node and LiFi for Privacy Preserving Intelligent COVID-19 Hospital Patient Management.

Light fidelity (LiFi) and wireless fidelity (WiFi) can be applied with the same network under the different constraints, which is suitable for COVID-19 surveillance in hospitals. The LiFi network is a high-capacity and security platform. A COVID-19 surveillance system using LiFi is proposed, which consists of two switching modes: communication and surveillance. Firstly, the communication targets are to accommodate the electromagnetic interference (EMI) immunity and high-capacity and security data transmission, where secondly the COVID-19 surveillance can be applied. In operation, the up and downlink system uses a metamaterial antenna embedded by Mach Zehnder interferometer (MZI). An antenna consists of silver bars embedded at the microring center with two-phase modulators at its sides. The entangled source namely a dark soliton is applied to form the transmission, where the information security based on quantum cryptography can be managed. By using the suitable parameters, the whispering gallery modes (WGMs) are generated and the up and downlink nodes are formed. The input information is multiplexed with time to form the multiplexed signals, where the big data transmission (40 Pbit {mathrm{s}}^{-1}) can be employed. By using the surveillance mode, the plasmonic antenna can be applied for temperature and electric force sensors, which can offer the disinfectant spray and temperature sensor for COVID-19 applications. The optimum plasma force sensitivity is 0.16 N kg−1 mW−1. The center frequencies of 191.48 THz and 199.41 THz are obtained for uplink and downlink antennas, respectively. The optimum temperature sensitivity is 0.05 rads−1 °C−1. In conclusion, the novelty of proposed work is that the integrated sensor circuits are employed for COVID-19 surveillance in the hospital. The fuzzy-based system is designed for critical patient monitoring alert using this surveillance and management inside the hospital for COVID-19 patients.

Low-Profile Dual-Polarized Isoflux Antennas for Space Applications

Design, realization, and measurements of an X-band antenna for data downlink (DDL) from low Earth orbit (LEO) satellites are presented. This antenna has an isoflux radiation pattern and operates in dual circular polarization with cross-polar discrimination (XPD) higher than 18 dB on the operational bandwidth. Two solutions are first proposed: one realized by a metasurface with circular strips printed on a dielectric slab and another realized by concentric metallic corrugations. Starting from a basic scattering mechanism of a self-complementary ring-type metasurface excited by a perfectly polarized source, both these antennas are designed by optimizing an equivalent anisotropic impedance surface excited by a short hat feed. The corrugated antenna is realized and measured, confirming that the performances are compliant with the requirements for next-generation DDL antennas.

Joint Design of Reconfigurable Intelligent Surfaces and Transmit Beamforming Under Proper and Improper Gaussian Signaling

This paper considers a network consisting of a multiple antenna array access point serving multiple single antenna downlink users with the assistance of a reconfigurable intelligent surface (RIS). The reflecting coefficients of the RIS can be programmed to ensure that the signals reflected from the RIS elements add coherently at the users. The joint design of these programmable reflecting coefficients and transmit beamforming to maximize the users' worst rate is addressed. Under either proper Gaussian signaling (PGS) or improper Gaussian signaling (IGS), the design poses a very computationally challenging nonconvex problem. Based on their exactly penalized optimization reformulation, which incorporates the computationally intractable unit-modulus constraints on the reflecting coefficients into the optimization objectives, new iterative algorithms of low computational complexity, which converge at least to a locally optimal solution, are developed. The provided simulations show not only the benefit of using the RIS, but also the advantage of IGS over PGS in delivering higher rates to users.

Spin-wave generation using MZI embedded plasmonic antennas for quantum communications

Spin wave generation formed by a soliton pulse within MZI embedded plasmonic antennas has been proposed. A soliton is the orthogonal (entangled) source that can be configured as the vertical and horizontal components in the same way as the polarization components. A dark soliton of wavelength 1.55 µm is selected and fed into the MZI input. The dark-bright soliton pulse entered into the upper and lower branches to form uplink and downlink antennas. The whispering gallery mode (WGM) can be generated by controlling the two side ring phase modulators. The gold grating surface is excited by the WGM input form the circuit, from which the electric dipoles oscillated. The trapped electrons by soliton pulses transmitted. The dipole oscillation of the antennas identified by plasma frequencies (Bragg wavelengths), which can form the spin-waves. The simulation programs are Optiwave and Matlab programs, from which the used parameters are selected from the realistic device parameters. The simulation results obtained show that the transmission bandwidth of 600 GHz with the antenna directivity of 7.78, and 4.63 for the uplink and downlink respectively and antenna gain (power) of 1.13 dB, and 1.07 dB for the uplink and downlink respectively. The transmission signals and power stability are confirmed by the transmission entanglement. The quantum sensor networks can also be applied, where the trend of the sensor sensitivity linearity is achieved.

Base Station Antenna Selection for Low-Resolution ADC Systems

For low-resolution analog-to-digital converter (ADC) systems, only high-complexity receive antenna selection has been developed and transmit antenna selection has been limited to a single antenna selection in prior work. In this paper, we propose low-complexity receive antenna selection algorithms and analyze transmit antenna selection by considering antenna selection at a base station with large antenna arrays and low-resolution ADCs. For downlink antenna selection, we show a selection criterion with zero-forcing precoding equivalent to a perfect quantization system; sum rate increases with number of selected antennas; derivation of the sum rate loss function from using a antenna subset; and sum rate loss reaches a maximum at a point of total transmit power and decreases beyond that point to converge to zero. For wideband orthogonal-frequency-division-multiplexing (OFDM) systems, our results hold when entire subcarriers share a common subset of antennas. For uplink antenna selection, we generalize a greedy antenna selection criterion; propose a quantization-aware fast antenna selection algorithm using the criterion; and derive a lower bound on sum rate achieved by the proposed algorithm. For wideband OFDM systems, we extend our algorithm and derive a lower bound on its sum rate. Simulation results validate theoretical analyses and show increases in sum rate over conventional algorithms.

Dual-Codebook Precoding Selection for LTE-A System

Long-term evolution advanced (LTE-A) is currently the most popular 4G wireless communication system worldwide. LTE-A system defines eight transmit antennas in downlink and adopts the precoding matrices to reduce the effect of interference and improve the received signal quality at the receiver. In this paper, three algorithms adopting the unique overlapped angle of direction of the beams for the LTE-A precoding matrices and the Euclidean Norm relation are proposed to reduce the calculations during precoding selection. Computer simulations and experiment results show that the proposed low-complexity precoding selection method can reduce more than 70% computational complexity and still maintains a good bit error rate performance compared with literary full search method.

Interleaved Training and Training-Based Transmission Design for Hybrid Massive Antenna Downlink

In this paper, we study the beam-based training design jointly with the transmission design for hybrid massive antenna single-user (SU) and multiple-user (MU) systems where outage probability is adopted as the performance measure. For SU systems, we propose an interleaved training design to concatenate the feedback and training procedures, thus making the training length adaptive to the channel realization. Exact analytical expressions are derived for the average training length and the outage probability of the proposed interleaved training. For MU systems, we propose a joint design for the beam-based interleaved training, beam assignment, and MU data transmissions. Two solutions for the beam assignment are provided with different complexity-performance tradeoff. Analytical results and simulations show that for both SU and MU systems, the proposed joint training and transmission designs achieve the same outage performance as the traditional full-training scheme but with significant saving in the training overhead.

Power allocation scheme and spectral efficiency analysis for downlink non‐orthogonal multiple access systems

In this study, the authors investigate the power allocation (PA) problem and spectral efficiency (SE) analysis for the single antenna downlink non-orthogonal multiple access (NOMA) system under the sum rate maximising criteria with minimum rate constraints (SRMC-MRC). For the PA problem, they propose the duality scheme for SRMC-MRC which is considered as the optimal solution for the PA problem on one orthogonal subband in the single antenna NOMA system. They propose the specific user rate maximising criteria with minimum rate constraints (SURMC-MRC) scheme to decrease the computational complexity of SRMC-MRC. The PA problem on one subband under SURMC-MRC is proved to be equivalent to SRMC-MRC. Numerical results show that both the SE and fairness performance for SURMC-MRC can strictly approach to those of the duality scheme in the whole signal-to-noise ratio (SNR) region. They prove that NOMA under SRMC-MRC can obtain SE performance advantage in the high SNR region but accompany with some disadvantages in the low SNR region over the orthogonal multiple access system. This conclusion is verified through numerical results under different parameter conditions.

An omnidirectional PIFA for downlink and uplink satellite applications in C‐band

ABSTRACTIn this article, we present a dual band planar inverted‐F antenna (PIFA) for downlink and uplink satellite systems in C‐band frequency range. The proposed antenna is fabricated on an FR4 substrate with dielectric constant of 4.4. By cutting a pair of T‐shaped slits in the ground plane, and also by embedding a meander‐line slit in the ground plane a good dual‐band operation antenna can be achieved. The measured impedance bandwidth for 10 dB return loss is from 3.625–4.200 GHz (14%) and 5.850–6.425 GHz (9%), covering the down/up links of satellite communications. Simulated and experimental results obtained for this antenna show that the proposed PIFA has good antenna gain and radiation behavior in the operation bands. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2684–2686, 2014

Full-duplex bidirectional transmission of 10-Gb/s millimeter-wave QPSK signal in E-band optical wireless link

We experimentally demonstrated full-duplex bidirectional transmission of 10-Gb/s millimeter-wave (mm-wave) quadrature phase shift keying (QPSK) signal in E-band (71-76 GHz and 81-86 GHz) optical wireless link. Single-mode fibers (SMF) are connected at both sides of the antenna for uplink and downlink which realize 40-km SMF and 2-m wireless link for bidirectional transmission simultaneously. We utilized multi-level modulation format and coherent detection in such E-band optical wireless link for the first time. Mm-wave QPSK signal is generated by photonic technique to increase spectrum efficiency and received signal is coherently detected to improve receiver sensitivity. After the coherent detection, digital signal processing is utilized to compensate impairments of devices and transmission link.

Joint Power and Antenna Selection Optimization in Large Cloud Radio Access Networks

Large multiple-input multiple-output (MIMO) networks promise high energy efficiency, i.e., much less power is required to achieve the same capacity compared to the conventional MIMO networks if perfect channel state information (CSI) is available at the transmitter. However, in such networks, huge overhead is required to obtain full CSI especially for Frequency-Division Duplex (FDD) systems. To reduce overhead, we propose a downlink antenna selection scheme, which selects S antennas from M>S transmit antennas based on the large scale fading to serve K\leq S users in large distributed MIMO networks employing regularized zero-forcing (RZF) precoding. In particular, we study the joint optimization of antenna selection, regularization factor, and power allocation to maximize the average weighted sum-rate. This is a mixed combinatorial and non-convex problem whose objective and constraints have no closed-form expressions. We apply random matrix theory to derive asymptotically accurate expressions for the objective and constraints. As such, the joint optimization problem is decomposed into subproblems, each of which is solved by an efficient algorithm. In addition, we derive structural solutions for some special cases and show that the capacity of very large distributed MIMO networks scales as O\left(K\textrm{log}M\right) when M\rightarrow\infty with K,S fixed. Simulations show that the proposed scheme achieves significant performance gain over various baselines.

Design of linear precoder for multiuser MIMO system with spatial correlation and imperfect CSI

AbstractMinimum mean square error (MMSE) based linear precoder in multiple antenna downlink wireless communication system with imperfect channel state information (CSI) at the base station (BS) is considered in this paper. The CSI available at the BS is modelled by incorporating antenna correlation at the BS, channel estimation error variance and temporal correlation coefficient. If the temporal correlation coefficient is known at the BS, the current CSI can be updated. To improve the performance of the system, the future channel is predicted using two‐dimensional MMSE prediction. In this paper, the proposed MMSE linear precoder is designed by considering the imperfect CSI and two‐dimensional predicted CSI. The computer simulation results validate the bit error rate performance of the proposed system when compared to the previously proposed precoders, which consider channel estimation error variance only. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The Safety Production Monitoring System Based on LTE in Coal Mine

A new safety production monitoring schemes and emergency rescue communication system based on LTE technology for coal mine is introduced, which mainly responsibility is conveying video data of disaster scene and ensuring the two-way communication of mobile terminal and emergency communication car. The schemes include to use of TDD full-duplex mode to make uplink configuration as much time slot resources as possible, SC– FDMA for uplink multi-access technologies and OFDMA for Downlink. Considering the terminal ability, MIMO antennas of uplink and downlink antennas is available. At the same time we adopt HARQ and adaptive modulation coding technology to improve reliability and transmission efficiency. The Performances of link level are simulated aiming at transmitting schemes. Respectively use QPSK, 16QAM, 64QAM three methods of modulation, the simulation results show that the LTE technology can satisfy the requirements of data rate, BER and delay for wireless communication under emergency environment in coal mine.