A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

60 GHz Wireless Propagation Channels: Characterization, Modeling and Evaluation

To be able to connect wirelessly to the internet is nowadays a part of everyday life and the number of wireless devices accessing wireless networks worldwide are increasing rapidly. However, with the increasing number of wireless devices and applications and the amount available bandwidth, spectrum shortage is an issue. A promising way to increase the amount of available spectrum is to utilize frequency bands in the mm-wave range of 30-300 GHz that previously have not been used for typical consumer applications. The 60 GHz band has been pointed out as a good candidate for short range, high data rate communications, as the amount of available bandwidth is at least 5 GHz worldwide, with most countries having 7 GHz of bandwidth available in this band. This large bandwidth is expected to allow for wireless communication with bit rates up to 7 Gbit/s, which can be compared to the typical WLAN systems of today that typically provide bit rates up to 0.6 Gbit/s. However, the performance of any wireless system is highly dependent on the properties and characteristics of the wireless propagation channel. This thesis focuses on indoor short range wireless propagation channels in the 60 GHz band and contains a collection of papers that characterizes, models and evaluates different aspects that are directly related to the propagation channel properties. Paper I investigates the directional properties of the indoor 60 GHz wireless radio channel based on a set of indoor measurements in a conference room. In the paper, the signal pathways and propagation mechanisms for the strongest paths are identified. The results show that first and second order interactions account for the major contribution of the received power. The results also show that finer structures, such as ceiling lamps, can be significant interacting objects. Paper II presents a cluster-based double-directional channel model for 60 GHz indoor multiple-input multiple-output (MIMO) systems. This paper is a direct continuation of the results in paper I. The model supports arbitrary antenna elements and array configurations and is validated against measurement data. The validation shows that the channel model is able to efficiently reproduce the statistical properties of the measured channels. The presented channel model is also compared with the 60 GHz channel models developed for the industry standards IEEE802.15.3c and IEEE802.11ad. Paper III characterizes the effect of shadowing due to humans and other objects. Measurements of the shadowing gain for human legs, metallic sheets, as well as metallic and plastic cylinders are presented. It is shown that the shadowing gain of these objects are fairly similar and that the shadowing due to the metal cylinder can be determined based on the geometrical theory of diffraction. Next, the shadowing due to a water-filled human body phantom is compared with the shadowing due to real humans. The results show that the water-filled phantom has shadowing properties similar to those of humans and is therefore suitable for use in 60 GHz human body shadowing measurements. Paper IV presents a novel way of estimating the cluster decay and fading. Previously, the cluster decay has usually been determined by performing a simple linear regression, without considering the effects of the noise floor and cluster fading. The paper presents an estimation method which takes these effects into account and jointly estimates both the cluster decay and cluster fading. It is shown that this estimation method can greatly improve the estimated parameters. Paper V evaluates the capacity improvement capability of spatial multiplexing and beamforming techniques for 60 GHz systems in an indoor environment. In this paper, beamforming refers to conventional gain focusing in the direction of the strongest propagation path. The paper uses a capacity metric that only depends on the multi-path richness of the propagation channel and the antenna aperture size. In the paper, it is shown that, when the link budget is limited due to electrically small antennas and long Tx-Rx separation distances, beamforming approximates the capacity of spatial multiplexing. However, spatial multiplexing is a worthwhile option when Rx SNR is favorable and a higher peak data rate is required. Paper VI describes different methods for the clustering of wireless multi-path components. In the literature, the clustering method that is predominantly used is the K-means algorithm, or a power-weighted version of K-means, called K-power means. In this paper, we point out that K-means is a special case of a Gaussian mixture model (GMM). The paper presents a clustering method based on a GMM. This method is able to handle arbitrary cluster spreads in the different dimensions better than the K-means algorithm. A power-weighted version of the GMM is also presented. In addition to this, a mixture model based on asymmetric Laplace distributions is also presented, with and without power-weighting. Paper VII is based on channel measurements in a small and a large room, where the Tx and Rx arrays have dual polarized elements. Using these measurements, the cross-polarization ratio (XPR) of the multi-path components are characterized. This gives valuable information on how the MPCs are affected by the propagation channel. A statistical description of the XPR is also needed for the development of a propagation channel model that supports polarization. The paper also investigates the eigenvalue spreads for single and dual polarized elements. Furthermore, the measurements include LOS and NLOS measurement, where the NLOS scenarios include water-filled human presented in paper III. The results show that the capacity can be greatly improved if dual-polarized elements are used, and that the XPR values are in general higher compared to lower frequencies

Indoor wireless communications and applications

Chapter 3 addresses challenges in radio link and system design in indoor scenarios. Given the fact that most human activities take place in indoor environments, the need for supporting ubiquitous indoor data connectivity and location/tracking service becomes even more important than in the previous decades. Specific technical challenges addressed in this section are(i), modelling complex indoor radio channels for effective antenna deployment, (ii), potential of millimeter-wave (mm-wave) radios for supporting higher data rates, and (iii), feasible indoor localisation and tracking techniques, which are summarised in three dedicated sections of this chapter

SNR-based evaluation of coexistence in wireless system of hospital

Abstract. The wireless system (IEEE Std. 802.11) of North Karelian Central Hospital (NKCH) has been studied in the newly opened J2 building of the hospital. The measurements have been carried out using Ekahau Sidekick spectrum analyser and Ekahau Pro software. Signal propagation has been modelled in the control ward of the Emergency department because many coexisting systems are used with critical requirements of data communication over there. The analytical models have been developed to understand the radio-frequency (RF) signal propagation in the entire building. Measurements have also been carried out on the entire first floor, in the Department of the Abdominal Diseases on the ground floor and in the Children’s wards on the third floor. The multi-slope path-loss propagation models with shadowing have been generated based on the Received Signal Strength Indicator (RSSI) measurements for typical hospital environment at the 2.4 GHz and 5 GHz Industrial, Scientific, and Medical (ISM) band. The measurements have been carried out within the two predefined routes. The models have also been compared to the empirically derived path-loss models. The probability of signal outage has been calculated for both measured routes. The aggregate interference has been measured within the routes that cover the area where remarkable signal variations and the high level of interference has been indicated based on the heatmaps of Ekahau. The use of Ekahau Sidekick and Ekahau Pro software in the coexistence study has been described. The noise floor has been determined based on the averaged values of the six measurement campaigns. The local changes in signal strength of the desired signal and aggregated power of interference have been studied. The Signal-to-Interference Ratio (SIR) models have been generated within the measured routes. The rapid decreases of Signal-to-Noise Ratio (SNR) have been indicated on all measured floors of building J2. They have been studied and their effect on the network performance has been evaluated. The evaluation has been done by comparing the measured values of RSSI, SNR and SIR to the requirements of the respective Modulation and Coding Scheme (MCS). The link margins have been calculated based on the chosen bit error probability and the given SNR requirement of the respective MCS. The comparison between the measured RSSI readings and the required threshold of the respective MCS has been done using the defined shadowing as a link margin. It has been shown that the measured difference between the signal strength of the 2.4 GHz and 5 GHz bands has been caused by the reduced transmit power at the 2.4 GHz band. Based on the SIR measurements, it has been shown that the access points of the neighbouring building have contributed locally to the measured aggregate interference in the Control ward. However, the primary reason for the decrease of SIR at the 2.4 GHz band has been the decrease of desired signal power that has been contributed by the above mentioned reduced transmit power. The strong SNR drops have been indicated on every measured floor before the roaming has occurred.Sairaalan langattoman järjestelmän arviointi signaali-kohina-suhteen avulla. Tiivistelmä. Tässä diplomityössä on tutkittu Pohjois-Karjalan keskussairaalan (PKKS) langatonta verkkoa (IEEE Std. 802.11) äskettäin avatussa sairaalan laajennusosassa (J2-rakennus). Mittaukset on toteutettu käyttäen Ekahau Sidekick spektrianalysaattoria ja Ekahau Pro -ohjelmaa. Päivystyksen valvontaosasto on valittu tutkimuskohteeksi, koska siellä käytetään paljon eri teknologioihin perustuvia järjestelmiä, joiden välinen tiedonsiirto on luonteeltaan kriittistä. Luotujen mallien avulla rakennuksen langatonta toimintaympäristöä tutkitaan RF-järjestelmän (Radio-Frequency) näkökulmasta myös muissa mittausten kohteina olleissa tiloissa. Mittauksia on tehty myös valvontaosaston ulkopuolella 1. kerroksessa sekä 3. kerroksen lastenosastoilla ja Vatsakeskuksen tiloissa pohjakerroksessa. RSSI-mittausten perusteella on luotu radiotiehäviöihin perustuvat etenemismallit molemmilla käytössä olevilla ISM-taajuuskaistoilla (Industrial, Scientific and Medical bands). Varjostuminen ja etenemishäviökertoimen muutokset on otettu huomioon etenemismalleissa. Mittaukset on suoritettu ennalta määritellyillä reiteillä. Luotuja malleja on verrattu myös tutkimuskirjallisuudessa esitettyihin, empiirisesti johdettuihin etenemishäviömalleihin. Signaalikatkoksen todennäköisyys on laskettu molemmille reiteille 2.4 GHz:n taajuuskaistalla. Vastaanotetun häiriötehon summa on mitattu koko mallinnettavan tilan alueelle ulottuvien mittausreittien pohjalta. Mittausreitit on määritelty Ekahau Pron tuottamien kuuluvuus- ja häiriökarttojen avulla ottaen huomioon havaitut signaalitason vaihtelut. Ekahau Sidekick -spektrianalysaattorin ja Ekahau Pro -ohjelman käyttöä on kuvattu tämän tutkimuksen kontekstissa. Kohinataso on määritelty kaikissa kuudessa mittauskampanjassa mitattujen kohina-tehoarvojen keskiarvona. Paikallisten hyötysignaalinvoimakkuus- ja häiriötehovaihteluiden vaikutusta verkon suorituskykyyn on tutkittu ja molemmat mittausreitit kattavat SIR-mallit (Signal-to-Interference Ratio) on luotu. Kaikissa tutkituissa kerroksissa havaittuja äkillisiä signaali-kohinasuhteen vaihteluita on tutkittu ja niiden vaikutusta järjestelmän suorituskykyyn on arvioitu. Mitattujen hyöty- ja häiriösignaalivaihteluiden arviointi on toteutettu vertaamalla mittaamalla saatuja SNR- (Signal-to-Noise ratio), SIR- ja RSSI-arvoja (Received Signal Strength Indicator) eri tiedonsiirtonopeuksia käyttävien MCS-indeksien vaatimiin signaalinvoimakkuus- ja signaali-kohina-suhteen arvoihin. Kynnysarvoille on laskettu linkkimarginaalit käyttäen mitoitusvaatimuksena valittua bittivirhetodennäköisyyden arvoa. Mitattuja RSSI-arvoja on verrattu käyttäen linkkimarginaalina etenemismallinnuksessa määritettyjä varjostumisvaikutuksen arvoja. 2.4 ja 5 GHz:n taajuusalueiden välillä mitatun signaalinvoimakkuuseron on tutkimuksessa saatujen tulosten perusteella osoitettu olevan seurausta alennetusta lähetystehosta 2.4 GHz:n kaistalla. SIR-mittausten perusteella on todettu viereisen rakennuksen tukiasemien kasvattaneen vastaanotettua häiriötehosummaa valvontaosastolla paikallisesti. Ensisijainen syy mitattuihin SIR-arvojen vaihteluihin ovat kuitenkin alhainen signaalinvoimakkuus 2.4 GHz:n kaistalla, mikä osittain johtuu edellä kuvatusta alennetusta lähetystehosta. Voimakkaita SNR-vaihteluita on mitattu kaikissa kerroksissa ennen kuin päätelaite kytkeytyy uuteen tukiasemaan

Feedback Mechanisms for Centralized and Distributed Mobile Systems

The wireless communication market is expected to witness considerable growth in the immediate future due to increasing smart device usage to access real-time data. Mobile devices become the predominant method of Internet access via cellular networks (4G/5G) and the onset of virtual reality (VR), ushering in the wide deployment of multiple bands, ranging from TVWhite Spaces to cellular/WiFi bands and on to mmWave. Multi-antenna techniques have been considered to be promising approaches in telecommunication to optimize the utilization of radio spectrum and minimize the cost of system construction. The performance of multiple antenna technology depends on the utilization of radio propagation properties and feedback of such information in a timely manner. However, when a signal is transmitted, it is usually dispersed over time coming over different paths of different lengths due to reflections from obstacles or affected by Doppler shift in mobile environments. This motivates the design of novel feedback mechanisms that improve the performance of multi-antenna systems. Accurate channel state information (CSI) is essential to increasing throughput in multiinput, multi-output (MIMO) systems with digital beamforming. Channel-state information for the operation of MIMO schemes (such as transmit diversity or spatial multiplexing) can be acquired by feedback of CSI reports in the downlink direction, or inferred from uplink measurements assuming perfect channel reciprocity (CR). However, most works make the assumption that channels are perfectly reciprocal. This assumption is often incorrect in practice due to poor channel estimation and imperfect channel feedback. Instead, experiments have demonstrated that channel reciprocity can be easily broken by multiple factors. Specifically, channel reciprocity error (CRE) introduced by transmitter-receiver imbalance have been widely studied by both simulations and experiments, and the impact of mobility and estimation error have been fully investigated in this thesis. In particular, unmanned aerial vehicles (UAVs) have asymmetric behavior when communicating with one another and to the ground, due to differences in altitude that frequently occur. Feedback mechanisms are also affected by channel differences caused by the user’s body. While there has been work to specifically quantify the losses in signal reception, there has been little work on how these channel differences affect feedback mechanisms. In this dissertation, we perform system-level simulations, implement design with a software defined radio platform, conduct in-field experiments for various wireless communication systems to analyze different channel feedback mechanisms. To explore the feedback mechanism, we then explore two specific real world scenarios, including UAV-based beamforming communications, and user-induced feedback systems

CPX based synthesis for binaural auralization of vehicle rolling noise to an arbitrary positioned stander-by receiver

Virtual reality is becoming an important tool for studying the interaction between pedestrians and road vehicles, by allowing the analysis of potentially hazard situations without placing subjects in real risk. However, most of the current simulators are unable to accurately recreate traffic sounds that are congruent with the visual scene. This has been recognized as a fault in the virtual audio-visual scenarios used in such contexts. This study proposes a method for delivering a binaural auralization of the noise generated by a moving vehicle to an arbitrarily located moving listener (pedestrian). Building on previously developed methods, the proposal presented here integrates in a novel way a dynamic auralization engine, thus enabling real-time update of the acoustic cues in the binaural signal delivered via headphones. Furthermore, the proposed auralization routine uses Close ProXimity (CPX) tyre-road noise signal as sound source input, facilitating the quick interchangeability of source signals, and easing the noise collection procedure. Two validation experiments were carried out, one to quantitatively compare field signals with CPX-derived virtual signal recordings, and another to assess these same signals through psychoacoustic models. The latter aims to assure that the reproduction of the synthesized signal is perceptually similar to one occurring on pedestrian/vehicle interactions during situations of street crossing. Discrepancies were detected, and emphasized when the vehicle is within close distance from the receiver (pedestrian). However, the analysis indicated that these pose no hindrance to the study of vehicle–pedestrian interaction. Improvements to the method are identified and further developments are proposed.This work was supported by the ‘‘Fundação para a Ciência e a Tecnologia” [PTDC/ECM-TRA/3568/2014, SFRH/BD/131638/2017, UIDB/04029/2020] This work is part of the activities of the research project AnPeB – ‘‘ANalysis of PEdestrians Behaviour based on simulated urban environments and its incorporation in risk modelling” (PTDC/ECM TRA/3568/2014), funded by the ‘‘Promover a Produção Científica e Desenvolvimento Tecnológico e a Constituição de Redes Temáti cas” (3599-PPCDT) project and supported by the ‘‘European Com munity Fund FEDER” and the doctoral scholarship SFRH/ BD/131638/2017, funded by ‘‘Fundação para a Ciência e a Tecnolo gia (FCT)”

Mobile 5G millimeter-wave multi-antenna systems

In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of Universitat Politècnica de Catalunya's products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to http://www.ieee.org/publications_standards/publications/rights/rights_link.html to learn how to obtain a License from RightsLink.Tesi en modalitat de compendi de publicacionsMassive antenna architectures and millimeter-wave bands appear on the horizon as the enabling technologies of future broadband wireless links, promising unprecedented spectral efficiency and data rates. In the recently launched fifth generation of mobile communications, millimetric bands are already introduced but their widespread deployment still presents several feasibility issues. In particular, high-mobility environments represent the most challenging scenario when dealing with directive patterns, which are essential for the adequate reception of signals at those bands. Vehicular communications are expected to exploit the full potential of future generations due to the massive number of connected users and stringent requirements in terms of reliability, latency, and throughput while moving at high speeds. This thesis proposes two solutions to completely take advantage of multi-antenna systems in those cases: beamwidth adaptation of cellular stations when tracking vehicular users based on positioning and Doppler information and a tailored radiation diagram from a panel-based system of antennas mounted on the vehicle. Apart from cellular base stations and vehicles, a third entity that cannot be forgotten in future mobile communications are pedestrians. Past generations were developed around the figure of human users and, now, they must still be able to seamlessly connect with any other user of the network and exploit the new capabilities promised by 5G. The use of millimeter-waves is already been considered by handset manufacturers but the impact of the user (and the interaction with the phone) is drastically changed. The last part of this thesis is devoted to the study of human user dynamics and how they influence the achievable coverage with different distributed antenna systems on the phone.Les arquitectures massives d'antenes i les bandes mil·limètriques apareixen a l'horitzó com les tecnologies que impulsaran els futurs enllaços sense fils amb gran ample de banda i prometen una eficiència espectral i velocitat de transmissió sense precedents. A la recent cinquena generació de comunicacions mòbils, les bandes mil·limètriques ja en són una part constitutiva però el seu desplegament encara presenta certes dificultats. En concret, els entorns d'alta mobilitat representen el major repte quan es fan servir diagrames de radiació directius, els quals són essencials per una correcta recepció del senyal en aquestes bandes. S'espera que les comunicacions vehiculars delimitin les capacitats de les xarxes en futures generacions degut al gran nombre d'usuaris simultanis i els requeriments estrictes en termes de fiabilitat, retard i flux de dades mentre es mouen a grans velocitats. Aquesta tesi proposa dues solucions per tal d'explotar al màxim els sistemes de múltiples antenes en tals casos: un ample de feix adaptatiu de les estacions bases quan estiguin fent el seguiment d'un vehicle usuari basat en informació de la posició i el Doppler i el disseny d'un diagrama de radiació adequat al costat del vehicle basat en una estructura de múltiples panells muntats a l'estructura del mateix. A més de les estacions base i els vehicles, un tercer element que no pot ser obviat en aquests escenaris són els vianants. Les generacions anteriors van ser desenvolupades al voltant de la figura d'usuaris humans i ara han de seguir tenint la capacitat de connexió ininterrumpuda amb la resta d'usuaris i explotar les capacitats de 5G. L'ús de frequències mil·limètriques també es té en compte en la fabricació de telèfons mòbils però l'impacte de l'usuari és completament diferent. La última part de la tesis tracta l'estudi de les dinàmiques de l'usuari humà i com influeixen en la cobertura amb diferent sistemes distribuïts d'antenes.Postprint (published version