Herein, we focus on convergent 6G communication, localization and sensing systems by identifying key technology enablers, discussing their underlying challenges, implementation issues, and recommending potential solutions. Moreover, we discuss exciting new opportunities for integrated localization and sensing applications, which will disrupt traditional design principles and revolutionize the way we live, interact with our environment, and do business. Regarding potential enabling technologies, 6G will continue to develop towards even higher frequency ranges, wider bandwidths, and massive antenna arrays. In turn, this will enable sensing solutions with very fine range, Doppler, and angular resolutions, as well as localization to cm-level degree of accuracy. Besides, new materials, device types, and reconfigurable surfaces will allow network operators to reshape and control the electromagnetic response of the environment. At the same time, machine learning and artificial intelligence will leverage the unprecedented availability of data and computing resources to tackle the biggest and hardest problems in wireless communication systems. As a result, 6G will be truly intelligent wireless systems that will provide not only ubiquitous communication but also empower high accuracy localization and high-resolution sensing services. They will become the catalyst for this revolution by bringing about a unique new set of features and service capabilities, where localization and sensing will coexist with communication, continuously sharing the available resources in time, frequency, and space. This work concludes by highlighting foundational research challenges, as well as implications and opportunities related to privacy, security, and trust.

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Convergent Communication, Sensing and Localization in 6G Systems: An Overview of Technologies, Opportunities and Challenges

In this paper, real measurements were conducted to investigate the impact of rain on the propagation of millimeter waves at 26 GHz. The measurements were accomplished using a microwave fifth generation radio link system with 1.3 km path length implemented at Universiti Teknologi Malaysia Johor Bahru, Malaysia. The implemented system consisted of Ericsson CN500 mini E-link, radio unit, rain gauge, and data logger. The measurements were attained and logged daily for a continuous year, with 1-min time intervals. Next, the MATLAB software was used to process and analyze the annual rain rate and rain attenuation, including for the worst month. From the analyzed results, it was found that at 0.01% percentage of time, the rain rate was 120 mm/hr; while the specific rain attenuation was 26.2 dB/km and the total rain attenuation over 1.3 km was 34 dB. In addition, the statistics acquired from the measurements for the worst month were lower than what was predicted by the international telecommunication union (ITU) model; around 51% and 34% for the rain rate and rain attenuation, respectively. The average percentage of error calculated between the measurements and predicted results for the rain rate and rain attenuation were 143% and 159%, respectively. Thus, it can be concluded that the statistics for the worst month in Malaysia is lower than what was predicted by the ITU model.

Real Measurement Study for Rain Rate and Rain Attenuation Conducted Over 26 GHz Microwave 5G Link System in Malaysia

With the challenge to form the networks of the Intelligent Transportation Systems (ITS), both technologies of vehicles and wireless communication are required to be connected tightly. In terms of wireless communication, the communication system in the terahertz (THz) frequency range with ultra-large bandwidth is a potential technology to support very high-data-rate wireless transmission at the age of beyond fifth-generation mobile communications (B5G). In this paper, the carrier frequency of 300 GHz with 8 GHz bandwidth vehicle-to-infrastructure (V2I) channel is characterized for the urban and highway scenario, respectively. The self-developed ray-tracing (RT) simulator is employed with the calibrated electromagnetic (EM) parameters. Since the wavelength of carrier frequency approaches the diameters of raindrops and snowflakes, the significant influence of the precipitation on the channel characterization is studied in our work as well. The large-scale parameters of the THz V2I channel, including path loss, Rician K-factor, root-mean-square (RMS) delay spread, and angular spreads are explored in the target scenarios under sunny, rainy, and snowy conditions, respectively. The channel characteristics studied in this paper can be used to support the link-level and system-level design for the future THz vehicular communications.

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Characterization for the Vehicle-to-Infrastructure Channel in Urban and Highway Scenarios at the Terahertz Band

Next generations of satellite communication systems demand the use of high frequency bands and the effect of the troposphere at these frequencies has a major impact in the signal attenuation. In this context, the objective of the work presented in this paper is to take advantage of the Weather Research and Forecasting (WRF) system, capable of providing reanalysis and forecasts at high resolution, to be able to simulate the atmospheric conditions, to finally estimate the signal attenuation for slant path satellite links beyond 10 GHz. This is of paramount importance to effectively supplant the lack of measurements for the design of new satellite systems.

http://ieeexplore.ieee.org/iel7/6526699/6546197/06546505.pdf

Use of WRF model to characterize propagation effects in the troposphere

Terahertz (THz) communications are envisioned as a key technology for the sixth-generation wireless communication system (6G). However, it is not practical to perform large-scale channel measurements with high degrees of freedom at THz frequency band. This makes empirical or stochastic modeling approaches relying on measurements no longer stand. In order to break through the bottleneck of scarce full-dimensional channel sounding measurements, this paper presents a novel paradigm for THz channel modeling towards 6G. With the core of high-performance ray tracing (RT), the presented paradigm requires merely quite limited channel sounding to calibrate the geometry and material electromagnetic (EM) properties of the three-dimensional (3D) environment model in the target scenarios. Then, through extensive RT simulations, the parameters extracted from RT simulations can be fed into either ray-based novel stochastic channel models or cluster-based standard channel model families. Verified by RT simulations, these models can generate realistic channels that are valuable for the design and evaluation of THz systems. Representing two ends of 6G THz use cases from microscopy to macroscopy, case studies are made for close-proximity communications, wireless connections on a desktop, and smart rail mobility, respectively. Last but not least, new concerns on channel modeling resulting from distinguishing features of THz wave are discussed regarding propagation, antenna array, and device aspects, respectively.

Towards 6G: Paradigm of realistic terahertz channel modeling

Humidity remains in the atmosphere even on bright days. Water of all three states can be found naturally in the atmosphere: liquid (rain, fog, and clouds), solid (snowflakes, ice crystals), and gas (water vapour). Water in any state is an obstacle in the link of the electromagnetic wave. When the wave passes through the water particles, a part of its energy is absorbed and a part is scattered. Therefore the electromagnetic wave is attenuated. Prediction of the influence of these factors is very important in radio system design. Attenuation due to rain, fog, and clouds can lead to the perturbations of the wireless, mobile, satellite and other communications. Another problem is the refractive index of the atmosphere, which affects the curvature of the electromagnetic wave path and gives some insight into the fading phenomenon. The anomalous electromagnetic wave propagation can cause disturbances to radar work, because variation of the refractive index of the atmosphere can induce loss of radar coverage. Accurate prediction of losses due to these factors can ensure a reliability of the radio system, decrease an equipment cost, furthermore, the radio systems can become less injurious to health of people. When there are no possibilities to gather data for calculations of the specific attenuation due to rain, clouds and fog, and atmospheric refractive index, the values recommended by the International Communication Union’s Radiocommunication sector (ITU-R) can be used. But the recommended values are not always exact. In design of the radio links, the most desirable operating frequencies are below 10 GHz, because in such cases atmospheric absorption and rainfall loss may generally be neglected (Freeman, 2007). However, in most countries, the frequency-band below 10 GHz is highly congested. In addition, high frequencies provide larger bandwidth, narrower beam width, good resolution and smaller component size (Bhattacharyya et al., 2000). Therefore, the operating frequencies of 10 GHz and above are often used in design of radio systems. The higher the operating frequency, the greater attenuation due to hydrometeors (rain, cloud, fog, snow, and etc.) is observed (Tamosiūnaitė et al., 2010a). In (Ishimaru, 1978), it was mentioned that the electromagnetic wave attenuation due to snow is less than attenuation due to rain, and that the attenuation due to dry snow may be neglected

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Atmospheric Attenuation due to Humidity

The increase of data traffic, a demand for high-speed reliable mobile networks and congested frequency bands raised both technological and regulatory challenges. Therefore, the fifth-generation mobile network (5G) is being developed. Recently, researchers have focused on a very promising terahertz (THz) band (frequencies from 100 GHz to 30 THz), which will allow fast transmission of huge amounts of data. However, transmission distance is limited due to atmospheric attenuation, as THz waves undergo significant absorption by water vapor and oxygen molecules in the atmosphere. Moreover, THz waves are very vulnerable by precipitation. Furthermore, the path of the propagating waves changes due to variations of the atmospheric refractive index. Nevertheless, the THz networks could be perfect candidates for fiber-to-THz bridges in difficult-to-access areas. The aim of this chapter is to present the possibilities and challenges of the THz networks from a point of view of atmospheric attenuation. The results show that simulations of the atmospheric attenuation using real-time data are a powerful tool that should complement technological basis, as it will help to foresee possible failures, extend transmission distance and improve reliability of the THz and other high-frequency broadband wireless networks.

/pdf/atmospheric-attenuation-of-the-terahertz-wireless-networks-5et126igfl.pdf

Atmospheric Attenuation of the Terahertz Wireless Networks

In Vilnius, the daily and the seasonal variations of the radio refractivity values have been computed at the Earth surface in the years 2005-2010 and at the heights up to 1.2 km in November 2010. The International Telecommunications Union - Radiocommunications Sector (ITU-R) model was used for calculation of the radio refractive index according to the peculiarities of climatic conditions of Lithuania. As a result of obtained data analysis, the days with more variable meteorological parameters have been chosen for more detailed investigation. The radio refractivity gradient has been computed at the heights starting from the Earth surface up to 1.2 km above the ground, using the meteorological data measured at those heights. The variation of radio refractivity and its gradient are influenced by the changes in air's humidity and temperature in most part. Ill. 7, bibl. 17, tabl. 1 (in English; abstracts in English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.111.5.349

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Variation of Radio Refractivity with Height above Ground

The peculiarities of the climatic conditions in the Baltic Sea Region are reviewed According to the values of rain rates measured in the Lithuanian Weather Stations with the 10- minute's integration time, a relation between the rain rate and the annual precipitation has been derived The model for one-minute rain rate calculation on the months starting from May up to September in Lithuania has been presented The values of the electromagnetic waves attenuation due to the rain have been determined The cloud attenuation has been computed by using the meteorological data measured at the ground level The semi empirical method has been used The values of the speciflc attenuation under conditions of cloud cover have been determined Knowledge of the electromagnetic waves attenuation due to rain and clouds is desirable while planning the communication systems, especially at frequencies of 10GHz and above Most of the methodologies for the prediction of rain attenuation on radio waves paths require the knowledge of the rain rate R-value Rain rate data is presented in units of length per unit time (in millimeters per hour), but in practice it is measured over intervals of typically one minute, flve minutes, hour or yearlong In (1), it was mentioned that the integration time ¢t (time between the readings of the values of rainfall amount) is important parameter and it can change the R-value Most of the rain attenuation prediction methods require one-minute rain rate value One-minute rain rate (mm/h) is the rainfall for one minute (mm/min) multiplied by 60 Rainfall rate is highly variable Therefore, the rain rate and rain attenuation are analyzed for concrete climatic conditions However, the electromagnetic waves attenuation due to rain under the Baltic Sea Region climatic conditions has been analyzed not enough (2,3) The electromagnetic waves attenuation due the clouds, as far as we know, has been not analyzed under Lithuanian climatic conditions The main goals of this paper were to determine the one-minute value of rain rate by using ten-minutes rainfall amount data measured in the Lithuanian Weather Stations and to estimate the values of the electromagnetic waves attenuation due to the rain and the clouds 2 THE PECULIARITIES OF THE CLIMATIC CONDITIONS IN THE BALTIC SEA REGION The climate of Baltic Sea Region (BSR) is speciflc BSR, being in the transition geography zone from Baltic Sea climate to Atlantic and continentals East Europe climate, may be distinguished for its variable climate The average amount of precipitation in the BSR is 679mm The average nebulosity in the region is 50% The minimal nebulosity (46%) occurs in spring (4) The increase of nebulosity is going from north to south In this paper we analyze Lithuanian climate more particularly The climate of Lithuania is deflnable as middling cold, with the snowy winters There are 20{30 thaw days even in mid-winter In Lithuania, humid weathers predominate all over the year The annual precipitation in rainy wet year is almost twice higher than in dry year The values of annual rainfall measured in the localities of Lithuania are presented in Table 1 The showers are observed in the warm period of the year Such climate is typical climate of the middle part of the East Europe The climate of the west part of Lithuania (for example, of Klaipeda) is specifled as the moderate warm climate The average temperature of the coldest month is more than i3 - C Such type of the climate is dominating in the West Europe Vilnius is one of the cloudiest localities of Lithuania There are about 100 overcast days in the year

https://www.piers.org/piersonline/pdf/Vol4No3Page321to325.pdf

The Influence of the Climatic Peculiarities on the Electromagnetic Waves Attenuation in the Baltic Sea Region

Seasonal and daily variations of radio refractivity have been analyzed in the localities of Lithuania. The method proposed in the Recommendation of International Telecommunication Union (ITU) has been used. The local meteorological data have been used in calculation of radio refractivity. The values of radio refractivity have been determined in Vilnius, Kaunas, Klaipėda, and Mažeikiai. The meteorological data collected in February, April, July and October have been used. The highest values of the radio refractivity have been observed in Klaipėda in the year 2009. In July 2009, the values of the radio refractivity were highest in all localities investigated here and over all the time of the day.

http://ieeexplore.ieee.org/iel5/5523194/5540324/05540617.pdf

Milda Tamosiunaite

Papers

Atmospheric Attenuation due to Humidity

Atmospheric Attenuation of the Terahertz Wireless Networks

Variation of Radio Refractivity with Height above Ground

The Influence of the Climatic Peculiarities on the Electromagnetic Waves Attenuation in the Baltic Sea Region

Determination of radio refractivity using meteorological data