Channel Characterization and Emulation for Nonterrestrial Network Communications: Challenges and Solutions

Wireless networks have a key role in operational deployment, mobility, the flexibility of network organization and the variety of possible applications, in many cases being the only economically justified solution. Based on the above, for the deployment of wireless networks, the correct theoretical design of the wireless network is an important issue: the required number of devices, their characteristics, placement, energy characteristics of channels, distribution routes and coverage areas, etc. Correct theoretical analysis will ensure error-free construction of the network for the successful implementation of the tasks and will not lead to the need to attract additional material costs. One of the key tasks of wireless communication construction is a reliable assessment of the energy characteristics of a wireless communication channel. Modern global manufacturers of telecommunications equipment build both backbone equipment and equipment to cover WLAN (wireless local area networks) areas, based on IEEE 802.11 standards. One of the most modern standards of the IEEE 802.11 group is the IEEE 802.11ac standard, which is characterized by several improved technical characteristics compared to its predecessor IEEE 802.11n and older versions. That is why the task of evaluating the performance of modern wireless communication equipment based on IEEE 802.11ac standards and analyzing the evaluation of the energy characteristics of the communication channel to predict the parameters and performance characteristics of a point-to-point, point-to-multipoint or other wireless transmission systems within a certain wireless communication network. The following results of solving this problem are presented in this paper: – theoretical evaluation of the energy characteristics of the wireless communication channel. – laboratory studies of wireless communication equipment of the 802.11ac standard based on simulating a communication line using attenuators. – verification of the results of laboratory studies in field conditions based on the model for assessing the quality of communication in a wireless channel created based on the 802.11ac standard.

The article is devoted to the issues of improving the characteristics of radio communication channels and telemetry of unmanned aerial vehicles. It has been determined that the communication range depends not only on the modem, but also on the antennas, antenna cables, radio wave propagation conditions, external interference, and other reasons. The communication range is determined by such antenna parameters as the transmitter antenna gain and the receiver gain. The article defines the basic principles for improving the characteristics of radio communication channels and telemetry of unmanned aerial vehicles under various meteorological operating conditions, the effects of electromagnetic interference and terrain relief. It has been determined that to obtain the maximum possible communication range, it is necessary to use cables with the minimum possible attenuation and minimize the length of these cables. In the UAV body, the modem should be located as close as possible to the antenna. The degree of influence of the Earth's surface on the connection also depends on the height of the antennas. The higher the height of the antennas, the greater the distance that can be separated from the points without allowing objects or the underlying surface to fall into the significant zone. It is proposed to take into account the location of antennas, both on the ground and on board the UAV, so that during UAV maneuvers, at least for one of the UAV antennas on the NS - UAV antenna line there are no elements of the UAV design. Thus, it is determined that the loss of communication with the UAV of a certain range can be caused by a local decrease in field strength due to oscillations, thus, if you fly some more distance, the connection can be restored. The final loss of communication will occur only after a significant area is completely covered by objects on the ground or surface relief.

다음은 이 논문에서는 임펄스 잡음과 함께 다중경로 특성을 가진 수중 통신 채널에 대해, 확률거리 최소화와 델타함수열을 이용한 블라인드 적응등화 알고리듬을 소개하고 임펄스 잡음에 대한 강인성을 입증하였다. 기존의 자승평균오차 기반의 CMA는 임펄스 잡음 환경에서 다중경로 채널을 보상하지 못하는 현상을 보였고 엔트로피에 기반을 둔 코렌트로피 등화알고리듬도 일반적 변조방식에서 성능이 만족스럽지 못한 것으로 나타났으나, 델타함수열을 이용한 확률분포 거리최소화 방법은 이러한 임펄스 잡음 문제와 다중경로 채널 블라인드 등화문제를 동시에 해결함을 보였고, 임펄스 잡음에 대해 탁월한 강인성을 가짐을 이론적 분석과 함께 시뮬레이션 실험을 통해 입증하였다.

A novel graphic modeling method of obtaining the fingerprint characteristics of wireless communication channel was provided in the paper. Firstly, discrete Fourier transforms was carried on to the sample data of each channel. And then a three-dimensional image was generated by taking the frequency as X coordinates, the channel number as Y coordinates, and the frequency amplitude as Z coordinates. After the image had been applied to mathematical interpolation, amplitude normalization, extended maximum value filtering, numerical binarization and burr elimination, a binary valued image with fingerprint feature is obtained. Application results showed that this type of fingerprint image can effectively distinguish different scenes of wireless communication.

Social Insurance Organizing Body is to protect community and Indonesian workers from health problems. Until 2010, many companies in Mataram City had not been a member of social insurance for workers because there was a lack of socialization in terms of the importance of health insurance for companies’ sustainability. This research aimed to identify factors influencing readiness of companies in implementing Social Insurance Organizing Body. This was analytic survey with cross-sectional approach. Samples were 113 company managers. Data were collected using a questionnaire and analyzed using the methods of univariate, bivariate, and multivariate (Linear Regression test). The result of this research revealed that percentage of respondents graduated from Diploma III was 27.4%, type of business based on the highest income level of a micro business (64.6%), and type of small business based on number of employees (90.3%). In addition, mostly respondents had low knowledge (52.2%), bad characteristics of innovation (50.4%), good communication channel (52.2%), bad social system (54%), bad promotion of reforming agent (50.4%), and unready company (54%). Furthermore, variables of knowledge (p=0.0001, r=0.898), characteristics of innovation (p=0.0001, r=0.888), communication channel (p=0.0001, r=0.886), social system (p=0.0001, r=0.894), and promotion of reforming agent (p=0.0001, r=0.704) had significant correlation with readiness of companies in implementing Social Insurance Organizing Body. Multivariate analysis showed that variables of knowledge, characteristics of innovation, communication channel and social system jointly influenced readiness of companies (F test= 223.404). As a suggestion, dissemination of information needs to be conducted among companies. Additionally, providing information in companies needs to be done by using a method of interpersonal communication. Provided information must be clear and complete.

Bit-error rate and eye diagram measurements have been the methods of choice in routine characterization of digital communication channels. The bit-error rate, however, does not provide insight into the digital channel's effect on transmitted signals, and in many situations the underlying assumptions behind eye diagram interpretation may not be justifiable. In order to supplement the conventional testing methods and improve upon their shortcomings, a general measurement tool has been developed to obtain direct statistical distributions of pulse shape parameters (distributions of the leading and trailing edge timing jitters and slopes, and the pulse peak heights) in addition to collections of severely degraded waveforms. The statistical distribution function contains a nearly complete picture of the noise process, which, in turn, reveals the mechanism of the noise generation process. Using this test setup, Gaussian time jitters of <;10 ps (FWHM) have been successfully measured.

The opportunity for correction of a continuous communication channel with constant parameters by the criterion of the maximum capacity is discussed. It is pointed that potential characteristics of the continuous communication channel should be taken into account, even when digital information transmission systems are synthesized. The problem of computation of the channel capacity with a random power transmission factor is stated and solved. The discrepancy between the existing criteria of the synthesis of linear systems and the problems solved by the systems of information transmission is demonstrated. A problem of synthesis of a linear system to increase the potential characteristics of the communication channel is stated.

In this article, a review on the use of unmanned aerial vehicles (UAVs) for retransmission has been conducted. The description of the basic network architecture and the main characteristics of communication channels are given. Various types of data transmission using UAVs, an approach to the organization of communication using unmanned aerial vehicles—short-range repeaters, which allows for information exchange in emergency situations, are considered. The general principles of UAV operation when used for weather monitoring, forest fire detection, traffic jam tracking, cargo transportation, use in rescue operations, etc., are analyzed. The advantages and disadvantages of such use of UAVs, the general architecture of communication systems and the place of the UAV in it, as well as the general characteristics of communication channels and types of data transmission are described. The technology was implemented using the example of establishing communication between separate units during training in a mountainous area using a low-flying UAV of the DJI Mavic Pro 2 type with suspended equipment for retransmission of radio signals SURECOM SR-112.

The V2V communications have been widely investigated. This paper studies the influence of different antenna locations on channel characterization for V2V communications. First of all, we carried out the channel measurement in urban with different antenna locations. Then, some typical channel parameters are extracted, such as power delay profile and path loss. Using these channel parameters, we analyze the effect of different antenna locations on channel characteristics in V2V communications. These results contribute to the design of the V2V communication system.

Using the low voltage power line network as a medium for signal communication, data transmission and information exchange offers a convenient and inexpensive solution for modern communication system. With its violent time-varying, strong interference and severe attenuation, the analyses of this communication channel become a challenging but important basic subjects for the sustainable development of L-PLC (Low-Voltage Power Line Communication) technology. In this paper, we point to bring fractal theory in the study of the characteristics of L-PLC channel. Firstly, the time series measured from L-PLC network are analyzed by R/S method which provides us a quantitative analysis of long-term time-dependence of the time series. Then, the changing curves of power spectrum and statistical moment of these time series are drawn, for the analyzing of multi-fractal characteristics of this channel. The results has showed: Hurst index of measured time series are greater than 0.5, fractal dimension is greater than 1.0, L-PLC channel has obvious fractal and chaotic characteristics; statistical moment is a nonlinear function, multi-fractal spectrum is strict symmetrical, the L-PLC channel has strong multi-fractal properties.

Unmanned aerial vehicle (UAV) is considered as an important component for future communication networks. In this paper, an air-to-ground (A2G) channel sounder is designed and implemented for UAV communication channel measurement and characterization. The channel impulse response (CIR) extraction is implemented on a field programmable gate array (FPGA) to improve extraction efficiency. Based on the channel characteristics under measured (or baseline) scenarios, a transfer learning neural network (TNN) framework is also proposed to predict the channel characteristics of other unmeasured (or transferred) scenarios. In the proposed framework, the baseline matrices of neural network parameters are obtained from the measurement data of baseline scenarios. The ray tracing (RT) simulation data is only used to obtain the extrapolation matrices where we utilize imperfect digital map and do not require a highly accurate RT simulation. Then the neural network driven by the baseline and extrapolation matrices is used to predict the channel characteristics of transferred scenarios. To verify the proposed prediction method, the channel characteristics including path loss, K-factor, and root mean square delay spread of a near-urban scenario are firstly measured. Then, the corresponding channel characteristics of a transferred dense-urban scenario are predicted by the proposed TNN method and validated by the measurement data. It is shown that the predicted channel characteristics are well consistent with the measured ones.

There is an increasing demand on wireless communications in subway tunnels to provide video surveillance and sensory data for security, maintenance and train control, and to offer various communication or entertainment services (e.g., Internet, etc.) to passengers as well. The wireless channel in tunnels is quite unique due to the confined space and the waveguide effects. Modeling the channel characteristics in tunnels is critically important to design or optimize subway wireless communication systems. This paper investigates the key radio channel characteristics of a subway tunnel in Beijing, China, such as the path loss, root mean square (RMS) delay spread, K-factor, channel stationarity, RMS Doppler spread, and channel capacity. Our field measurements show that channel characteristics in tunnels are highly location-dependent and there exists a dominant path in line-of-sight (LOS) scenarios as well as in non-line-of-sight (NLOS) scenarios, which is quite different from that in the land mobile communications. In the straight section of the subway tunnel, the measured path loss exponents at 2.45 GHz and 5.7GHz are 1.58 and 1.62, respectively.

Regarding the new demands and challenges of sixth-generation (6G) mobile communications, wireless networks are undergoing a significant shift from traditional terrestrial networks to space-air-ground-sea-integrated networks. Unmanned aerial vehicle (UAV) communications in complicated mountainous scenarios are typical applications and have practical implications, especially in emergency communications. In this paper, the ray-tracing (RT) method was applied to reconstruct the propagation scenario and then acquire the wireless channel data. Channel measurements are also conducted in real mountainous scenarios for verification. By setting different flight positions, trajectories, and altitudes, channel data in the millimeter wave (mmWave) band was obtained. Important statistical properties, such as the power delay profile (PDP), Rician K-factor, path loss (PL), root mean square (RMS) delay spread (DS), RMS angular spreads (ASs), and channel capacity were compared and analyzed. The effects of different frequency bands on channel characteristics at 3.5 GHz, 4.9 GHz, 28 GHz, and 38 GHz bands in mountainous scenarios were considered. Furthermore, the effects of extreme weather, especially different precipitation, on the channel characteristics were analyzed. The related results can provide fundamental support for the design and performance evaluation of future 6G UAV-assisted sensor networks in complicated mountainous scenarios.

In this paper, we present a comprehensive channel modeling and characterization study for visible light communications. Our study is based on ray tracing, which allows for an accurate description of the interaction of rays emitted from the lighting source within a specified confined space. Contrary to existing works, which are mainly limited to ideal Lambertian sources and purely diffuse reflections, our approach is capable of obtaining channel impulse responses (CIRs) for any nonideal sources, as well as specular and mixed specular–diffuse reflections. Furthermore, we can precisely reflect the presence of objects (e.g., furniture) and wavelength-dependent reflection characteristics of surface materials (e.g., ceilings, floor, walls, and furniture) in a channel study. As case studies, we consider a number of indoor environments with various dimensions and different surface materials, i.e., plaster, gloss paint, wood, aluminum metal, and glass. We further consider various scenarios with different transmitter specifications (i.e., single versus multiple transmitters and array type) and receiver specifications (i.e., location and rotation). For each environment, we obtain CIRs and present a channel characterization study where channel parameters, such as channel DC gain, root mean square (RMS) delay spread, coherence bandwidth, and mean excess delay, are obtained. We also make one-to-one comparisons between infrared and visible-light CIRs for the same environments to emphasize the differences between two optical bands.

Underwater communication technology has seen significant development in recent years, with a focus on finding efficient and secure techniques for exploring the underwater world. While acoustic and electromagnetic waves have limitations in water, the use of optical communication has become a focus of research due to its high bandwidth and low delay. Research has shown that blue and green lights are absorbed less than other wavelengths in water, making them suitable for underwater optical communication. In recent years, people have been working with optical communication in harsh environments. The optical system and the acoustic system have been combined to achieve certain development. Several high-speed underwater laser transmission systems have also been developed, with varying transfer rates and distances. This paper focuses on the theory of underwater optical systems and their communication channel characteristics.