Narrowband Channels Research Articles

Model Enhanced Learning Based Detectors (Me-LeaD) for Wideband Multi-User 1-bit mmWave Communications

Referring to the system equipped with single-bit converters, 1-bit mmWave communications is gaining increasing attention for its superb cost efficiency. However, the inherent non-linear distortion renders the detectors designed for classical transparent communications inapplicable, leading to an urgent need for novel detecting solutions dedicated to 1-bit systems. Although a few endeavours have been made towards learning-based (as opposed to the traditional model-based) detectors for multi-user (MU) 1-bit systems, they are exclusively limited to narrowband channels and fail to cope with the multi-path effects inevitable to mmWave systems. In this paper, we first design a learning-based detector (LeaD) for general wideband multi-user (wMU) scenarios. Though stemming from block-based detection, the classic workhorse for transparent systems, LeaD faces either unaffordable complexity or unacceptable data rate in 1-bit systems. Given the impracticability of block-based detection, we resort to the serial detection mechanism and henceforth devise a so-termed model-enhanced (Me-)LeaD by utilizing the channel delay-domain information. Me-LeaD can be further augmented by exploiting the channel angular-domain information. Underpinned by a judiciously tailored method for extracting tbe model information, the proposed Me-LeaD demonstrates a decent overall performance in general 1-bit wMU scenarios.

Estimation of electromagnetic compatibility of a narrow-band radio channel under the influence of unintended interference of the radar complicated pulse signals

The relevance of estimation of the electromagnetic compatibility (EMC) of narrow-band radio communication channels under the influence of unintended interference (UI) from radars with complex signals is due to the widespread use of both the first and second ones. At the same time, its equipment is often installed at the same carriers, which further complicates the task of providing EMC. The specificity of this situation is that narrow-band radio channels occupy a frequency band measured in few kilohertz, and the width of the spectrum of complicated signals used by radars is several and tens of megahertz. Under these conditions, during the preliminary estimation of the EMC, it is advisable to use the method of mathematical modeling and approximate a narrow-band radio receiving device (RRD) exposed to broadband UI with an equivalent circuit characterized with a given degree of accuracy by the parameters of this RRD. In this case, we used a chain approximation of the 4th order. This chain is represented by a system of differential equations that is solved in MATLAB. As a result of calculations, the dependence of the coefficient of suppression of unintended interference on the parameters of signals, interference and radio receivers was found. It was found that in the example under consideration, the suppression of unintended interference is at least 37 dB.

Leveraging Waveform Structure to Develop a Power Scalable AoA Estimation

In a mmWave mobile device, power consumption resulting from the high sampling rate is a primary concern for angle of arrival (AoA) estimation solutions. In this paper, we provide a power scalable solution for AoA estimation with structured waveforms in a narrowband channel. We design a set of pilot sequences that maintain orthogonality in sub-Nyquist sampling domains. We leverage the sequences’ structure to develop a variable rate decoupling algorithm to separate multiple sources at the receiver using partial knowledge about the pilots. The decoupling enables a feasible, low-complexity AoA estimation for digital architectures with flexible antenna array design. In this paper, we provide one such AoA estimation solution named ADELA for a linear antenna array design. Simulation results show that AoA estimation performance reaches the Cramer-Rao-Bounds (CRBs) for a range of SNRs. The proposed estimator with subsampling factors of 8 or less outperforms two examples of full rate virtual array AoA estimators for unknown waveforms: 2-level nested array and coprime filter bank estimators. Compared to these two examples of virtual array, our method offers an 8 times lower ADC power consumption, and a significantly lower computational complexity.

Physical principles of operation and basic capabilities of the four channel receiver 1288хк1т (mf-01)

In radar detection and radio navigation ensuring the reception of signals transmitted over the meteor channel of radio communication is often controversial[1-3]. Solving these problems requires the ability to synthesize precision signals directly[4, 5] for heterodyning systems in addition to modern analog-to-digital conversion devices, correlation analysis, and statistical processing of signal-noise complex. The step of adapting four channel receivers to dynamically changing conditions of transmitting information may include determining the composition of the signal-noise mixture, determining the phase characteristics of the communication channel, estimating the channel transmission rate, and obtaining QoS information. In addition, adaptation often implies the use of a logical channel control loop, which entails the need for complex feedback procedures. Software-defined radio systems are radio and telecommunication systems that can be tuned to an arbitrary frequency band and receive various types of modulated signal, consisting of programmable equipment with program control. SDR performs a significant part of digital signal processing on a conventional personal computer, signal processor or FPGA. In such systems and complexes, the parameters are changed by software configuration. The article considers the implementation of DDS for heterodyning an intermediate frequency signal on the FPGA basis for four channel receiver 1288хк1т (mf-01), which allows you to work with both narrow-band and wide-band communication channels (with simultaneous operation of 4 channels, the band can be expanded) and can be used in modern telecommunication communication systems.

Оценивание вероятностных характеристик приема сигналов с использованием моделей замираний при распространении по трансионосферным линиям.

Statistical models of narrow-band transionosphere channels, which determine the occurrence of signal fading due to random temporal and spatial fluctuations of the electron density of ionospheric irregularities, are considered. Fading models are based on the use of empirical relationships with respect to the distribution density of the amplitude of the signals at the output of the transionosphere channel as a random process. The parameters of empirical distribution densities (lognormal distribution, m-Nakagami distribution, Rician distribution) are related to the scintillation coefficient of signal fading. Using the considered models of signal fading, a technique is presented for estimating the probability of erroneous reception of digital signals with phase shift keying during reception. Using this technique, estimates of energy losses with respect to propagation in free space were made, reaching 0.001 for a scintillation coefficient value of 0.5 to 3 dB for signals with 2- and 4-phase shift keying.

Investigation of the Performance of TDoA-Based Localization Over LoRaWAN in Theory and Practice.

The paper deals with the localization in a low-power wide-area-network (LPWAN) operating long-range wide-area-network (LoRaWAN) technology. The LoRaWAN is, today, one of the most widely used connectivity-enabling technologies for the battery-powered smart devices employed in a broad range of applications. Many of these applications either require or can benefit from the availability of geolocation information. The use of global positioning system (GPS) technology is restrained by the bad propagation of the signal when the device is hidden indoors, and by energy consumption such a receiver would require. Therefore, this paper focuses on an alternative solution implying the use of the information readily available in the LoRaWAN network and application of the time difference of arrival (TDoA) method for the passive geolocation of end-devices in the network. First, the limits of geolocation services in networks that use narrow-band communication channels are discussed, as well as the relevant challenges faced by the TDoA approach. Then, we select five classic TDoA algorithms and evaluate their performance using simulation. Based on these results, we select the two providing the best accuracy (i.e., Chan’s and Foy’s). These algorithms were tested by the field measurements, using the specially designed low-cost gateways and test devices to estimate their real-life performance.

Analysis of the Underwater Multi-Path Reflections on Doppler Shift Estimation

For underwater target localization and tracking, accurate Doppler shift estimation is very important. In this letter, the analysis of the multi-path effect on Doppler shift estimation accuracy is conducted for the narrow-band acoustic underwater channels. We conducted comprehensive analysis on the performance of a widely used low-complexity Doppler estimation algorithm, and showed that the mean square estimation error decreases with sample length quadratically. Then we derived the Cramer-Rao lower bound, which also decreases quadratically with sample length. As a result, we concluded that the impact of multi-path effect is negligible for a sampling length of several seconds. The theoretical results are verified by numerical simulations.

Alternate hybrid precoding algorithm for wideband millimetre wave massive MIMO systems

Hybrid precoding, combining the digital and analogue precoding, is a key enabler to reach a compromise between system performance and hardware complexity in millimetre wave (mmWave) massive multiple-input multiple-output (MIMO) systems. Most previous studies on hybrid precoding considered narrowband channels. However, mmWave systems are expected to operate on wideband channels with frequency selectivity. In this study, the authors focus on the hybrid precoding design in mmWave massive MIMO systems using orthogonal frequency division multiplexing (OFDM). By transforming the hybrid precoding problem into a series of sub-problems, they propose a low-complexity algorithm to design the digital precoder and analogue precoder alternately. In particular, a phase pursuit method is introduced to seek this solution of analogue precoding matrix with the constant amplitude constraint. Simulation results and complexity evaluations reveal that the proposed algorithm can obtain better performance and lower complexity than some existing solutions in mmWave OFDM systems.

Increasing the spatial resolution of cloud property retrievals from Meteosat SEVIRI by use of its high-resolution visible channel: evaluation of candidate approaches with MODIS observations

Abstract. This study presents and evaluates several candidate approaches for downscaling observations from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) in order to increase the horizontal resolution of subsequent cloud optical thickness (τ) and effective droplet radius (reff) retrievals from the native ≈3km×3km spatial resolution of the narrowband channels to ≈1km×1km. These methods make use of SEVIRI's coincident broadband high-resolution visible (HRV) channel. For four example cloud fields, the reliability of each downscaling algorithm is evaluated by means of collocated 1 km×1 km MODIS radiances, which are reprojected to the horizontal grid of the HRV channel and serve as reference for the evaluation. By using these radiances, smoothed with the modulation transfer function of the native SEVIRI channels, as retrieval input, the accuracy at the SEVIRI standard resolution can be evaluated and an objective comparison of the accuracy of the different downscaling algorithms can be made. For the example scenes considered in this study, it is shown that neglecting high-frequency variations below the SEVIRI standard resolution results in significant random absolute deviations of the retrieved τ and reff of up to ≈14 and ≈6 µm, respectively, as well as biases. By error propagation, this also negatively impacts the reliability of the subsequent calculation of liquid water path (WL) and cloud droplet number concentration (ND), which exhibit deviations of up to ≈89gm-2 and ≈177cm-3, respectively. For τ, these deviations can be almost completely mitigated by the use of the HRV channel as a physical constraint and by applying most of the presented downscaling schemes. Uncertainties in retrieved reff at the native SEVIRI resolution are smaller, and the improvements from downscaling the observations are less obvious than for τ. Nonetheless, the right choice of downscaling scheme yields noticeable improvements in the retrieved reff. Furthermore, the improved reliability in retrieved cloud products results in significantly reduced uncertainties in derived WL and ND. In particular, one downscaling approach provides clear improvements for all cloud products compared to those obtained from SEVIRI's standard resolution and is recommended for future downscaling endeavors. This work advances efforts to mitigate impacts of scale mismatches among channels of multiresolution instruments on cloud retrievals.

Modified Algorithm for Calculating the Ambiguity Function in the Problem of Estimating the Mutual Time Delays of Wideband Signals

Using the modified algorithm for calculating the ambiguity function, we consider the method of estimation of the mutual time delay of wideband signals, which are recorded by multiposition systems for determining the radiation-source location with the help of the space segment. It is based on the extraction of narrowband channels from the received signals and their further optimal quasi-coherent processing. The criterion of reliability and efficiency of the estimated mutual time delay by the proposed method is studied.

Iterative Analog-Digital Multi-User Equalizer for Wideband Millimeter Wave Massive MIMO Systems.

Most of the previous work on hybrid transmit and receive beamforming focused on narrowband channels. Because the millimeter wave channels are expected to be wideband, it is crucial to propose efficient solutions for frequency-selective channels. In this regard, this paper proposes an iterative analog–digital multi-user equalizer scheme for the uplink of wideband millimeter-wave massive multiple-input-multiple-output (MIMO) systems. By iterative equalizer we mean that both analog and digital parts are updated using as input the estimates obtained at the previous iteration. The proposed iterative analog–digital multi-user equalizer is designed by minimizing the sum of the mean square error of the data estimates over the subcarriers. We assume that the analog part is fixed for all subcarriers while the digital part is computed on a per subcarrier basis. Due to the complexity of the resulting optimization problem, a sequential approach is proposed to compute the analog phase shifters values for each radio frequency (RF) chain. We also derive an accurate, semi-analytical approach for obtaining the bit error rate (BER) of the proposed hybrid system. The proposed solution is compared with other hybrid equalizer schemes, recently designed for wideband millimeter-wave (mmWave) massive MIMO systems. The simulation results show that the performance of the developed analog–digital multi-user equalizer is close to full-digital counterpart and outperforms the previous hybrid approach.

Deterministic Modeling of Indoor Stairwells Propagation Channel

A deterministic approach is presented for modeling a wireless propagation channel in a stairwell environment. The ray-tracing method is used to find the reflected and diffracted rays with the highest contribution to the total received power at a given location. Most significant reflected rays occur at the surfaces of specific steps of the stairwell and the surrounding lateral walls, while most significant diffracted beams emanate from the edges of steps located between transmitter and receiver antennas. The uniform theory of diffraction is used to calculate the diffracted contributions from the edges, whereas the multiple diffractions are calculated using heuristic diffraction coefficients. Unlike the reported models, the proposed model is deterministic and focuses on the radio propagation within stairwells at the X-band frequencies range. Experimental validation is performed using two types of antennas, horns and patches, for an operating frequency of 10 GHz. Simulated results of narrowband and wideband radio channels showed a good agreement with the experimental ones. The correlation coefficient between measured and simulation results is around 80% on average, and the residual errors between measured and simulated total received power results are less than 13%, which means that the proposed model has fair accuracy for such complex environments.

On-Board Fast and Intelligent Perception of Ships With the “Jilin-1” Spectrum 01/02 Satellites

Acquisition of information on ocean-going vessels is important for trade, shipping safety and assessing illegal behavior, and so on. Optical remote sensing satellites have become important for the above tasks because of its advantages of a large swath width, high resolution and independence from ground basic resources. Relying on the “Jilin-1” Spectrum 01/02 satellites, this paper proposes an on-board processing system for ship information acquisition and is studied with the relevant methods. The main modules include data analysis, image preprocessing, target area recommendation, target detection, and longitude and latitude calculation of the ship. The paper utilizes a narrow-band communication channel to send a message to the user when the offshore ship's length is more than 70 m. The satellite-ground experiment shows that the information was acquired within 4 minutes from the intelligence system working to the operator getting the ship's information. The delay of information acquisition is reduced from a few hours in previous systems to a few minutes in this system. This paper the first attempt at intelligent on-board information processing in the field of commercial aerospace.

An Improved Off-grid Channel Estimation Scheme for Lens Antenna Arrays in mmWave Systems

Abstract In this paper, we propose an improved off-grid channel estimation scheme for lens antenna arrays in mmWave systems. This scheme belongs to the spatial domain channel estimation. In the scheme, we first design a two-stage antenna selection algorithm based on the sparsity of mmWave channels as well as the optical focusing characteristic. Next, we exploit off-grid channel estimation to calculate the dimension reduction matrix and the angle of arrival of received signals. Unlike beam domain estimation, our scheme is suitable for wideband and narrowband channel matrix estimation. Simulation results show that our proposed scheme can achieve better estimation accuracy as the existing spatial scheme at much lower hardware overhead.

Bringing It Indoors: A Review of Narrowband Radio Propagation Modeling for Enclosed Spaces

Small cells are now widely deployed indoors to address hot-spot areas where capacity uplift is needed. This deployment leads to the increase of wireless networks as a challenge to service demands of personal communication systems, which has inspired the scientific community to work towards understanding and predicting in-building radio wave propagation performance. Despite this, only a few reviews have attempted to overview channel modeling for specific indoor environments and even fewer outline remarks that include a methodology for designing and planning indoor radio systems. Consequently, a comprehensive survey of indoor narrowband channel models is presented, spanning more than 30 years of continuous research to overview and contrast significant developments including their disadvantages, and proposing a new taxonomy to analyze them. Finally, remarks on indoor radio propagation modeling with a vision for future research opportunities are presented.

Suburban Fixed Wireless Access Channel Measurements and Models at 28 GHz for 90% Outdoor Coverage

Achieving adequate coverage with high gain antennas is key to realizing the full promise of the wide bandwidth available at cm/mm bands. We report extensive outdoor measurements at 28 GHz in suburban residential areas in New Jersey and Chile, with over 2000 links measured for same-street link types (vegetation blocked LOS) from 13 streets and other-street link types (true NLOS) from 7 streets, using a specialized narrowband channel sounder at ranges reaching 200 m. The measurements, applicable to fixed wireless access, involved a 55$^\circ$ transmit antenna placed on the exterior of a street-facing window and a 10$^\circ$ receive horn antenna spinning on top of a van mast at 3 m height, emulating a lamppost-mounted base station. Measured path gain-distance dependence is well represented by power-law models, and azimuth gains at the base are degraded through scattering by more than 4.3 dB for 10% of links. It was found that, with 51 dBm EIRP at the base station and 11 dBi antenna at an outdoor mounted terminal, 1 Gbps downlink rate can be delivered up to 100 m from a base station deployed in the same street with 90% coverage guarantee.

Beyond NDVI- Spectral indexing of biomass

The use of both terrestrial and satellite sensors often lacks the specific knowledge that makes them more effective. There are many reasons for this, one of them is agricultural digitalization to facilitate data availability and shortened automatic spectral indexing, but interpretation requires special remote sensing and agricultural knowledge. The absence of this complex knowledge, will result in misleading or incorrect solutions and on the other hand the existing technical possibilities cannot be exploited by the farmers. The application and calculation of the wide and narrow band channel VIs were presented on two agricultural test areas. The purpose of this publication is to briefly introduce the technical capabilities of vegetation indices based on a Hungarian test site and thereby reduce potential misinterpretation.

Doppler Shift Characterization of Wideband Mobile Radio Channels

The prevailing approach for characterizing the Doppler shift (DS) of mobile radio channels assumes the transmission of an unmodulated carrier. This consideration is valid for the analysis of narrowband channels, but its pertinence is questionable in regards to the modeling of wideband channels. In this correspondence, we redefine the DS from a time-frequency analysis perspective that does not depend on the aforementioned assumption. We systematically demonstrate that the DS can be characterized by the instantaneous frequency of the channel transfer function. This generic definition makes evident a fundamental aspect of the DS that is seldom acknowledged, namely, the DS is a frequency-varying quantity. We show that the second-order statistics of wideband mobile radio channels are non-stationary due to the DS's frequency variations. In addition, we present numerical results of a case study showing that such non-stationarities can cause significant system performance degradations.

Research Of Optimization Algorithms Used In Mimo-Ofdm Systems

Orthogonal Frequency Diνision Multiplexing (OFDM) technology is used to split large amount of data into several parallel narrowband channels with different frequencies orthogonally such that interference is reduced. Multiple Input M𝒖ltiple Output (MIMO) technology uses diversity ƫechnique such that capɑcity of the system and data throughput can be improved. Thereby combining both the technologies as MIMO-OFDM achieves great spectral efficiency and it is the most advanced technology in broadband wireless communication. Ƭhe channel estimation techniques like Leaşt Square Estimation (LSE) algorithm is used to estimate the channel and the performancе of MIMO-OFDM system is еvaluated on the basis of Bit Error Ratе (BER) and MеanSquarе Error (MSE) by using MATLAB simulation. Further enhancement can be achieved by applying optimization algorithms, in this paper to find the optimum solution Partic1e Swɑrm Optimization Algorithm (PSO) is uti1ized when the pilots are placed randomly. Simulation outcome show that PSO algorithm outperforms the LSE when random pilots are used for MIMO-OFDM systems.

Setup for characterising the spectral responsivity of Fabry–Pérot-interferometer-based hyperspectral cameras

Hyperspectral cameras capture the spectral power distribution of the objects in the imaged view via dozens of narrow-band spectral channels of the camera. Knowledge of the spectral responsivity of the channels is essential when interpreting the acquired hyperspectral data and assessing its reliability. The spectral responsivity of the camera channels may vary within the image area. This paper presents a measurement setup and data analysis routine for characterising the spectral responsivity of a hyperspectral camera. This method was used to characterise the spectral responsivity of a Fabry–Pérot-interferometer-based hyperspectral camera. The characterisation method implemented in this study was able to reveal several channel leaks in the measured wavelength range. In the image area there is an approximately 1.5 nm shift in the channel wavelengths, and up to 10% variation in the channel bandwidths. The expanded uncertainties (k = 2) for the measured channel bandwidths, sensitivities and wavelengths were 7.9%, 9.5% and 0.64 nm, respectively.