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In the forthcoming 6G wireless networks, the explosive growth in the number of human-type devices and machine-type devices will result in the network densification including both end-device (ED) densification and base station (BS) densification. Owing to the unique features of the network densification, not only new challenging problems would be introduced, but also the techniques, used in conventional networks, would no longer be effective. In this article, the features of network densification in terms of both BS and ED densification are first explored, and new challenges and potential key technologies are introduced.

The paper aims to propose a sequence of steps that will allow multi-person tracking with a single UWB radar equipped with the minimal antenna array needed for trilateration. Its localization accuracy is admittedly limited, but on the other hand, thoughtfully chosen placement of antennas can increase the detectability of several humans moving in their immediate vicinity and additionally decrease the computational complexity of the signal processing methods. It is shown that the UWB radar measuring with high rate and fine range resolution in conjunction with properly tuned processing parameters can continually track people even in the case when their radar echoes are crossing or merging. Emphasis is given to the simplified method of the time-of-arrival (TOA) estimation and association and the novel method needed for antenna height compensation. The performance of the proposed human tracking framework is evaluated for the experimental scenario with three people moving closely in a small room. A quantitative analysis of the estimated target tracks confirms the benefits of suggested high antenna placement and application of new signal processing methods in the form of decreasing the mean localization error and increasing the frequency of correct target position estimations. [ABSTRACT FROM AUTHOR]

From the aspect of navigational safety and collision avoidance it is very important to be able to detect small maritime targets such as buoys and small boats. Ship's radar is supposed to detect these types of targets, however the ability of radar to detect such targets depends on several factors. The most important factors affecting the detection probability of small maritime targets are height of the antenna installation on the ship and radar cross section of the target. The methods of computation radar cross section are diverse and complicated, however, in this paper we apply our previously published numerical method for the RCS computation which had proven to be very accurate. Physically to find RCS of the target one has to find the solution of electromagnetic scattering problem. The numerical method relies on the combination of finite edge volume elements and finite edge boundary elements to obtain the solution of Maxwell equations. The radiation pattern of ships radar antenna is the source of excitation for the numerical method. At the end of the paper the RCS of small maritime targets as the function of antenna height is shown. These results can be used as a parameter in radar design, as well as the guideline for the height of installation of the ship's radar antenna above the sea.

Rain attenuation is the main practical problem that confronts wireless signals specifically when it uses millimeter-waves for fifth-generation (5G) communication systems. In addition, due to that the urban environments are characterized by many high buildings act as diffraction objects can block the signal path and produce non-line of sight (NLOS) situations. These diffraction materials can cause further considerable losses that disturb the received power at the 5G receiver. This paper proposes a new model can investigate the influence of both precipitation and diffraction phenomena on wireless point to point (PPT) communication systems. This new research work utilizes measured rainfall data and actual scenarios in an urban environment to simulate the wireless PPT system and examine the influence of rainfall and knife-edge diffraction (KED) on the performance of the PPT system and signal strength at the receiver. Several durations of exceedances of rain rates and various operation scenarios have been employed to study and analyze the status of 5G wireless system links. The results indicated that there is an exchange of the effect of rain and KED diffraction in the lower millimeter-waves compared to the higher millimeter-waves. This study declares that at higher frequency bands the rain attenuation is observed to be greater, the diffraction loss is higher, and the path loss is also larger compared to the effect of these three factors seen at lower frequency bands. Furthermore, specific carrier frequencies, as in the case of 60 GHz, undergo extra huge atmospheric absorption loss which can diminish the communication coverage of the PPT system link.

In this paper, we develop an innovative approach to quantitatively characterize the performance of ultra-dense wireless networks in a plethora of propagation environments. The proposed framework has the potential of simplifying the cumbersome procedure of analyzing the coverage probability and allowing the unification of single- and multi-antenna networks through compact analytical representations. By harnessing this key feature, we develop a novel statistical machinery to study the scaling laws of wireless networks densification considering general channel power distributions including small-scale fading and shadowing as well as associated beamforming and array gains due to the use of multiple antenna. We further formulate the relationship between network density, antenna height, antenna array seize and carrier frequency showing how the coverage probability can be maintained with ultra-densification. From a system design perspective, we show that, if multiple antenna base stations are deployed at higher frequencies, monotonically increasing the coverage probability by means of ultra-densification is possible, and this without lowering the antenna height. Simulation results substantiate performance trends leveraging network densification and antenna deployment and configuration against path loss models and signal-to-noise plus interference thresholds. [ABSTRACT FROM AUTHOR]

The arid climate regions, such as in Riyadh city (Saudi Arabia), are characterized by strong dust storms which can deteriorate the performance of wireless systems. In addition, due to that the accelerated growth in many high buildings in a modern city such as Riyadh creates non-line of sight (NLOS) conditions can be represented by diffraction mechanism causes also attenuation loss affects the received wireless signals. This paper presents a new modelling study on the influence of dust storm and diffraction mechanism on wireless point to point (P-to-P) communication links in Riyadh. This unique study uses measured dust storm data and real urban scenarios to simulate the wireless links and investigate the effect on receiver performance based on the receiver sensitivity criterion. Several frequencies allocated for the fifth-generation (5G) wireless systems have been utilized as operation frequencies. The results showed that there is an inverse proportional between the attenuation loss due to diffraction and the distance over which the signal travels between the transmitter and receiver particularly when either the transmitter or the receiver is more close to the diffraction object. This study reveals that higher frequencies lead to higher diffraction loss, higher dust storm loss as well as higher free space loss. Moreover, certain millimeter-wave frequencies, such as 60 GHz, experience very high losses due to atmospheric absorption that can only operate on very short link distances. Besides, there is a need for high-quality receivers, especially for very high operating frequencies.

The paper aims to propose a sequence of steps that will allow multi-person tracking with a single UWB radar equipped with the minimal antenna array needed for trilateration. Its localization accuracy is admittedly limited, but on the other hand, thoughtfully chosen placement of antennas can increase the detectability of several humans moving in their immediate vicinity and additionally decrease the computational complexity of the signal processing methods. It is shown that the UWB radar measuring with high rate and fine range resolution in conjunction with properly tuned processing parameters can continually track people even in the case when their radar echoes are crossing or merging. Emphasis is given to the simplified method of the time-of-arrival (TOA) estimation and association and the novel method needed for antenna height compensation. The performance of the proposed human tracking framework is evaluated for the experimental scenario with three people moving closely in a small room. A quantitative analysis of the estimated target tracks confirms the benefits of suggested high antenna placement and application of new signal processing methods in the form of decreasing the mean localization error and increasing the frequency of correct target position estimations.

Wireless power transfer (WPT) has drawn significant attention in the last decade and more and more literatures are arising on related research topics such as microwave power transfer and wireless powered communications network. The extremely low efficiency of WPT is regarded as the major bottleneck thus becoming the main task that researchers need to tackle. In this paper, we propose a novel distributed antenna power beacon (DA-PB) whose antennas are uniformly distributed on a circle with the same height when performing WPT. Closed-form expression of antenna height for DA-PB is derived to make the radio frequency (RF) electromagnetic radiation power density at any location of the charging cell lower than the safety level given by federal communications commission. In addition, we get the closed-form expression of average harvested direct current (DC) power per user in the charging cell for path-loss exponent 2 and 4. In order to maximize the average efficiency of WPT, the optimal radius for distributed antennas elements is derived when the path-loss exponent takes the typical value 2 and 4, which could be lower bound and upper bound for common path-loss exponent. Conventional colocated antenna (CA) PB is also analyzed as a benchmark for our proposed DA-PB. Simulation results verify our derived theoretical results. And it is shown that the proposed DA-PB indeed achieves larger average harvested dc power per user and efficiency of WPT than conventional CA-PB.

This study compared precipitable water vapor (PWV) of JRA-55 and GPS in Japan by considering different elevations in JRA-55 (geopotential height) and GPS (antenna height) because JRA-55's PWV is pointed out to be underestimated as a result of dry bias in the middle and upper troposphere in the forecast model. We selected 26 grid points of JRA-55 over Japanese islands and the respective nearest 26 GPS stations operated by the Geospatial Information Authority of Japan. First, we linearly converted the geopotential height of 26 grid points to air pressure at the antenna height, assuming the sea surface and 1500-m height corresponding to 1013.25 hPa and 850 hPa, respectively. We then calculated JRA-55's PWV by vertically integrating specific humidity in the pressure coordinate system using the antenna height from July 2010 through December 2012 (designated as "corrected PWV"). At 22 grid points among the 26, the geopotential height is higher than the antenna height, where the majority of the data of PWV provided by the JRA project was smaller than that retrieved from GPS. The underestimation of the corrected PWV decreased, although 65% of them remained underestimated. The underestimation of the corrected PWV increased in winter and decreased in summer. [ABSTRACT FROM AUTHOR]

• GPR penetration capability through a reinforced shield tunnel lining is evaluated. • A 400–600 MHz antenna is appropriate for the shield tunnel inspection using GPR. • The antenna polarization direction should be in the tunnel longitudinal direction. • The antenna stand-off height from the tunnel lining should be within 10 cm. Ground penetrating radar (GPR), as a recognized non-destructive testing method, has been widely applied to detect hidden defects behind a reinforced shield tunnel. However, the scattering of electromagnetic waves caused by the dense double-layer rebar meshes embedded in a tunnel lining severely influences GPR's detection capabilities. Selecting the appropriate antenna parameters is a crucial step before conducting GPR measurements. In this paper, the penetration capability of GPR waves is evaluated using a shield tunnel model made of two shield tunnel segments. The laboratory experimental results demonstrate that an antenna with a center frequency of 400–600 MHz is appropriate for detecting hidden defects behind the concrete segment. Regarding the antenna polarization direction, it is better to set it in the longitudinal direction of the shield tunnel since the rebar spacing is slightly larger than that in the circumferential direction. The antenna height from the concrete segment should be controlled within a fifth of the wavelength in air to compromise between the data quality and detection efficiency. The results will aid in determining antenna parameters when GPR is applied to inspect hidden defects behind a reinforced shield tunnel. [ABSTRACT FROM AUTHOR]

The aim of this paper is to evaluate and compare impacts of mechanical and electrical down tilt angles of antenna systems to the downlink performance of the sulaymaniya base station. By depending on same height, in three dimensions. The effect of mechanical and electrical antenna down tilt angles have been studied in terms. Simulation studies are performed for sulaymaniya base station. Using the same height measurement by power meter simulator modeling of electrical and mechanical antenna tilt and propagation in three dimensions.In this paper a comparison made between the mechanical and electrical tilt antenna angle for five different intersite directions by choosing Alinaji, Ashty new , Bakhtiary, Industry, and Shoqakan sitesin sulaymaniya base station, using the same height, in three sectors. Simulation results indicate that optimum down tilt angle depends on the network environment also showed that different environments may lead to different optimization results in terms of capacity and coverage performance.

Three-dimensional (3D) multi-input-multi-output (MIMO) is one of the enabling technologies for next-generation mobile communication. As the elevation angle in the 3D MIMO channel model might vary against the height of the base station (BS) antenna, it should be considered within channel modeling. In this paper, the impact of antenna height on the channel characteristics of the 3D MIMO channel is investigated by using the intelligent ray launching algorithm (IRLA). Three typical street scenarios, i.e., the straight street, the forked road, and the crossroad, are selected as benchmarks. The joint and marginal probability density functions (PDFs) of both the elevation angle of departure (EAoD) and the elevation angle of arrival (EAoA) are obtained through simulations. Moreover, the elevation angle spread (AS) and the elevation delay spread (DS) under various antenna heights are jointly discussed. Simulation results show that the characteristics of the PDFs of EAoD will vary under different street scenarios. It is observed that in order to obtain the maximum or minimum value of the AS and the DS, the BS antenna should be deployed at half of the building height. [ABSTRACT FROM AUTHOR]

In this paper, we present a new and significant theoretical discovery. If the absolute height difference between base station (BS) antenna and user equipment (UE) antenna is larger than zero, then the network performance in terms of both the coverage probability and the area spectral efficiency will continuously decrease toward zero as the BS density increases in ultra-dense networks (UDNs). Such findings are completely different from the conclusions in the existing works, both quantitatively and qualitatively. In particular, this performance behavior has a tremendous impact on the deployment of the 5th-generation UDNs. Network operators may invest large amounts of money in deploying more network infrastructure only to obtain even less network capacity. This paper’s results reveal that one way to address this issue is to lower the BS antenna height to the UE antenna height. However, this requires a revolutionized approach of the BS architecture and deployment, which is also explored in this paper. [ABSTRACT FROM PUBLISHER]

In this paper we propose an outlier detection approach for GNSS vector networks based on the specific direction (i.e., SD approach), along which the test statistic constructed reaches the maximum. We derive the unit vector of this specific direction in detail, and prove that the unit vector is the same as that determined by the outlier estimates in three-dimensional (3D) approach, while the distribution of the maximum test statistic in this direction is the square root of Chi-squared distribution. Therefore, eliminating an outlier along this specific direction can get the same result as that of eliminating all three components of outlier vector in 3D approach. The mathematical equivalence of SD approach and 3D approach is further demonstrated by a real GNSS network. Moreover, preliminary application of the SD approach to detect the abnormal antenna height measurement is carried out in terms of numerical simulations of multiple baseline solutions, and it shows that the SD approach can effectively detect baselines that are directly infected by corresponding receiver antenna height errors.

This paper completes the fundamental development of the basic coherent entities in radar polarimetry for coherent reciprocal scattering involving polarized wave states, antenna states, and scattering matrices. The concept of antenna polarization states as contravariant spinors is validated from fundamental principles in terms of Schelkunoff’s reaction theorem and the Lorentz reciprocity theorem. In the general bistatic case, polarization states of different wavevectors must be related by the linear scattering matrix. It is shown that the relationship can be expressed geometrically, and that each scattering matrix has a unique complex scalar invariant characterizing a homographic mapping relating pairs of transmit/receive states for which the scattering amplitude vanishes. We show how the scalar invariant is related to the properties of the bistatic Huynen fork in both its conventional form and according to a new definition. Results are presented illustrating the invariant $k$ for a range of spheroidal Rayleigh scatterers. [ABSTRACT FROM PUBLISHER]