Characterization of 60 GHz Shadowing by Human Bodies and Simple Phantoms

The 60 GHz band is very prominsing for high data rate (>1 Gb/s) wireless systems operating at short ranges. However, due to the short wavelengths in this frequency band, the shadowing effects cuased by human bodies and furniture are severe and needs to be modeled properly. In this paper, we present an experimental, measurementbased characterization of the reflection and shadowing effects in the 60 GHz band caused by human bodies and various phantoms, in order to find simple phantoms suitable for use in human shadowing measurements. It is shown that a water-filled human phantom serves as a good choice for this purpose

Line-of-Sight Obstruction Analysis for Vehicle-to-Vehicle Network Simulations in a Two-Lane Highway Scenario

In vehicular ad-hoc networks (VANETs) the impact of vehicles as obstacles has largely been neglected in the past. Recent studies have reported that the vehicles that obstruct the line-of-sight (LOS) path may introduce 10-20 dB additional loss, and as a result reduce the communication range. Most of the traffic mobility models (TMMs) today do not treat other vehicles as obstacles and thus can not model the impact of LOS obstruction in VANET simulations. In this paper the LOS obstruction caused by other vehicles is studied in a highway scenario. First a car-following model is used to characterize the motion of the vehicles driving in the same direction on a two-lane highway. Vehicles are allowed to change lanes when necessary. The position of each vehicle is updated by using the car-following rules together with the lane-changing rules for the forward motion. Based on the simulated traffic a simple TMM is proposed for VANET simulations, which is capable to identify the vehicles that are in the shadow region of other vehicles. The presented traffic mobility model together with the shadow fading path loss model can take in to account the impact of LOS obstruction on the total received power in the multiple-lane highway scenarios.Comment: 8 pages, 11 figures, Accepted for publication in the International Journal of Antennas and Propagation, Special Issue on Radio Wave Propagation and Wireless Channel Modeling 201

Massive MIMO Extensions to the COST 2100 Channel Model: Modeling and Validation

To enable realistic studies of massive multiple-input multiple-output systems, the COST 2100 channel model is extended based on measurements. First, the concept of a base station-side visibility region (BS-VR) is proposed to model the appearance and disappearance of clusters when using a physically-large array. We find that BS-VR lifetimes are exponentially distributed, and that the number of BS-VRs is Poisson distributed with intensity proportional to the sum of the array length and the mean lifetime. Simulations suggest that under certain conditions longer lifetimes can help decorrelating closely-located users. Second, the concept of a multipath component visibility region (MPC-VR) is proposed to model birth-death processes of individual MPCs at the mobile station side. We find that both MPC lifetimes and MPC-VR radii are lognormally distributed. Simulations suggest that unless MPC-VRs are applied the channel condition number is overestimated. Key statistical properties of the proposed extensions, e.g., autocorrelation functions, maximum likelihood estimators, and Cramer-Rao bounds, are derived and analyzed.Comment: Submitted to IEEE Transactions of Wireless Communication

The COST IRACON Geometry-based Stochastic Channel Model for Vehicle-to-Vehicle Communication in Intersections

Vehicle-to-vehicle (V2V) wireless communications can improve traffic safety at road intersections and enable congestion avoidance. However, detailed knowledge about the wireless propagation channel is needed for the development and realistic assessment of V2V communication systems. We present a novel geometry-based stochastic MIMO channel model with support for frequencies in the band of 5.2-6.2 GHz. The model is based on extensive high-resolution measurements at different road intersections in the city of Berlin, Germany. We extend existing models, by including the effects of various obstructions, higher order interactions, and by introducing an angular gain function for the scatterers. Scatterer locations have been identified and mapped to measured multi-path trajectories using a measurement-based ray tracing method and a subsequent RANSAC algorithm. The developed model is parameterized, and using the measured propagation paths that have been mapped to scatterer locations, model parameters are estimated. The time variant power fading of individual multi-path components is found to be best modeled by a Gamma process with an exponential autocorrelation. The path coherence distance is estimated to be in the range of 0-2 m. The model is also validated against measurement data, showing that the developed model accurately captures the behavior of the measured channel gain, Doppler spread, and delay spread. This is also the case for intersections that have not been used when estimating model parameters.Comment: Submitted to IEEE Transactions on Vehicular Technolog

Massive MIMO performance evaluation based on measured propagation data

Massive MIMO, also known as very-large MIMO or large-scale antenna systems, is a new technique that potentially can offer large network capacities in multi-user scenarios. With a massive MIMO system, we consider the case where a base station equipped with a large number of antenna elements simultaneously serves multiple single-antenna users in the same time-frequency resource. So far, investigations are mostly based on theoretical channels with independent and identically distributed (i.i.d.) complex Gaussian coefficients, i.e., i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in channels measured in real propagation environments. Channel measurements were performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a physically large aperture, and a practical uniform cylindrical array (UCA) which is more compact in size, both having 128 antenna ports. Based on measurement data, we illustrate channel behavior of massive MIMO in three representative propagation conditions, and evaluate the corresponding performance. The investigation shows that the measured channels, for both array types, allow us to achieve performance close to that in i.i.d. Rayleigh channels. It is concluded that in real propagation environments we have characteristics that can allow for efficient use of massive MIMO, i.e., the theoretical advantages of this new technology can also be harvested in real channels.Comment: IEEE Transactions on Wireless Communications, 201

A Measurement Based Shadow Fading Model for Vehicle-to-Vehicle Network Simulations

The vehicle-to-vehicle (V2V) propagation channel has significant implications on the design and performance of novel communication protocols for vehicular ad hoc networks (VANETs). Extensive research efforts have been made to develop V2V channel models to be implemented in advanced VANET system simulators for performance evaluation. The impact of shadowing caused by other vehicles has, however, largely been neglected in most of the models, as well as in the system simulations. In this paper we present a shadow fading model targeting system simulations based on real measurements performed in urban and highway scenarios. The measurement data is separated into three categories, line-of-sight (LOS), obstructed line-of-sight (OLOS) by vehicles, and non line-of-sight due to buildings, with the help of video information recorded during the measurements. It is observed that vehicles obstructing the LOS induce an additional average attenuation of about 10 dB in the received signal power. An approach to incorporate the LOS/OLOS model into existing VANET simulators is also provided. Finally, system level VANET simulation results are presented, showing the difference between the LOS/OLOS model and a channel model based on Nakagami-m fading.Comment: 10 pages, 12 figures, submitted to Hindawi International Journal of Antennas and Propagatio

Statistical Modeling and Estimation of Censored Pathloss Data

Pathloss is typically modeled using a log-distance power law with a large-scale fading term that is log-normal. However, the received signal is affected by the dynamic range and noise floor of the measurement system used to sound the channel, which can cause measurement samples to be truncated or censored. If the information about the censored samples are not included in the estimation method, as in ordinary least squares estimation, it can result in biased estimation of both the pathloss exponent and the large scale fading. This can be solved by applying a Tobit maximum-likelihood estimator, which provides consistent estimates for the pathloss parameters. This letter provides information about the Tobit maximum-likelihood estimator and its asymptotic variance under certain conditions.Comment: 4 pages, 3 figures. Published in IEEE Wireless Communication Letter

Channel Related Optimization of Wireless Communication Systems

This thesis deals with different optimization problems in the design of wireless communication systems. It is mainly directed to the design of systems based on multicarrier techniques and orthogonal frequency division multiplex, OFDM, but some of the problems apply to single carrier systems as well. The influence of different pilot patterns is analyzed when pilot symbol assisted modulation, PSAM, is used in OFDM systems. It is desirable to decrease the number of required pilot symbols and it is shown that the pilot pattern used plays a major role to enable reliable channel estimates from a small amount of pilot symbols. Rearrangement of the pilot pattern enables a reduction in the number of needed pilot symbols up to a factor 10, still retaining the same bit error performance. The effect of the number of sub-channels used in an OFDM system is analyzed with respect to resulting bit error rate. An analytical expression for the bit error rate on Rayleigh fading channels when interchannel interference, ICI, caused by channel changes during a symbol and energy loss due to the cyclic prefix are regarded. This expression is used to optimize the number of sub-channels, and thereby the sub-channel bandwidth (sub-channel spacing) in the system. It is argued that the system can be optimized neglecting the effect of imperfect channel estimation and on a worst case assumption for the Doppler frequency and signal to noise ratio. The benefits of using pre-compensation (precoding) in wireless time division duplex, TDD, systems are also investigated. The uplink channel estimate is used to compensate the channel impact on the downlink symbols. This enables less complex receiver structures in the mobile terminal since channel equalization is performed in the base station. Three different methods where amplitude and/or phase are adjusted are analyzed in terms of performance limits. Closed-form expressions for the QPSK bit error rate are given assuming a fully known channel. It is shown that pre-compensation is an attractive alternative to differential decoding. Phase-only compensation is preferred at low signal to noise ratios, while at high signal to noise ratios an order of magnitude improvement in the bit error rate can be obtained by including amplitude pre-compensation. All the analyses and optimizations are general and can be applied to any OFDM system

Effekter på foderintag, mjölkavkastning och energibalans hos mjölkkor som ger di parallellt med att de mjölkas i tidig laktation

The objective of this study was to compare the production level, feed intake and energy balance in early lactation of non-suckled cows against cows in a cow-driven cow-calf contact (CCC) system. CCC systems have become interesting to evaluate as they are thought to provide a more natural behaviour for both the cow and calf, several studies have reported higher growth and better health in calves kept in these systems. Reports on how the cows’ production and health are affected are fewer with varying results and often dependent on the type of contact system, type of feed and feeding management. There is also a need to evaluate potential difference in milking techniques, as the majority of reports are based on conventional machine milking and not from automatic milking systems (AMS). The production level on a farm is highly dependent on the animal’s welfare and a high feed intake supporting high production and energy status, therefor, the relationship between these factors are interesting to evaluate in a whole day contact system. Twenty-two treatment and nineteen control cows in different parities (12 vs. 6 first parity, 4 vs. 3 second parity, 6 vs. 7 older cows in treatment and control groups respectively), were included in the study between 4 and 50 days in milk (DIM). Daily observations of feed intake, feeding behaviour, milk yield from an automatic milking system (AMS) and body condition score (BCS) was collected, milk samples were taken every fortnight for analysing milk composition and blood samples were taken twice a week during the first two weeks postpartum for evaluation of non-esterified fatty acids. All cows were feed ad libitum of roughage from automatic feeders which enabled continuous recordings of the time spent eating and amount of eaten feed for each individual. Number of meals per day, visit duration, meal size, feeding rate and dry matter intake (DMI) was compared in order to study the feeding patterns between the two treatments. The results suggest that feed intake was similar in both treatments, while the treatment group had a more efficient feeding pattern. Treatment cows had fewer visits per day, longer meal durations, bigger meals, higher feeding rates and longer intervals between feedings. Harvested milk yield was significantly lower in the treatment group due to calf’s milk intake, however, when estimating the energy corrected milk (ECM) (based on the energy mobilization) both treatments had a similar milk production. The BCS was more stable in the treatment group compared to the control cows, also non-esterified fatty acids (NEFA) values were lower in this group, indicating the that the control group was less able to adapt their feed intake to the lactation during this period. The study period included in this thesis was short and occurred during early lactation, therefor it will be important for future studies to investigate the entire lactation to confirm these findings and get a better picture of the cow’s performance in these whole day CCC systems.Syftet med denna studie var att jämföra produktionsnivån, foderintaget samt energibalansen i tidig laktation mellan kor i ett ko-kalvsystem med kor som enbart mjölkas. Intresset att utvärdera ko-kalvsystem har ökat då systemen anses ge möjlighet till ett mer naturligt beteende hos både ko och kalv, exempelvis vid digivning. Flera studier har rapporterat om högre tillväxt och förbättrad hälsa hos kalvar som vistats tillsammans med modern och haft möjlighet att dia (Bar-Peled et al. 1997; Meyer et al. 2006; Johnsen et al. 2016), däremot är de rapporterade effekterna på kons produktion få och ofta varierande då det finns flera aspekter som kan skilja sig åt i dessa system. Produktionsnivån på en mjölkgård är i hög grad beroende av en god djurhälsa och ett högt foderintag som stimulerar en hög mjölkavkastning utan att påverka energibalansen, därmed är det av intresse att undersöka dessa aspekter i ett ko-kalvsystem. I studien inkluderades 22 behandlingskor och 19 kontrollkor i varierande laktationsnummer (12 vs. 6 förstakalvare, 4 vs. 3 andrakalvare, 6 vs. 7 äldre kor i behandlings- respektive kontrollgruppen), studien fortgick från dag fyra i laktationen till och med dag femtio. Dagliga observationer av foderintag, foderintagsmönster, mjölkavkastning från ett automatiskt mjölkningssystem (AMS) och hull samlades in tillsammans med mjölkprover varannan vecka samt blodprover som togs under fyra tillfällen första och andra veckan efter kalvning. Samtliga kor hade fri tillgång på grovfoder från automatiska fodertråg, dessa möjliggjorde att kontinuerliga data på foderintag kunde samlas in under hela försöket. Antal måltider per dag, besökstid, storleken på måltiden, äthastighet samt intaget av foder jämfördes mellan behandlingarna för att studera eventuella skillnader i foderintagsbeteendet. Resultatet tyder på att foderintaget var snarlikt i båda behandlingarna, dock antyder resultaten att behandlingskorna hade ett mer effektivt foderbeetende. Behandlingsgruppen åt färre måltider per dag, målen varade under en längre tid, de hade ett längre intervall mellan måltiderna hade en högre äthastighet. Mängden mjölk till mjölkningsroboten var signifikant lägre i behandlingsgruppen på grund av kalvarnas mjölkintag. Dock fanns ingen skillnad mellan grupperna i uppskattad energi korrigerad mjölk (ECM) (som baserats på energimobiliseringen). Behandlingskorna hade ett mer stabilt hull vilket bekräftades med lägre nivåer av icke-förestrade fettsyror (NEFA) i blodet jämfört med kontrollkorna, detta indikerar att kontrollkorna kan haft det svårare att anpassa foderintaget efter laktationen vid övergången från dräktighet till laktation. Studiens tidsperiod var kort och inkluderade endast de första sju veckorna i laktationen, framtida studier bör studera hela laktationen för att bekräfta resultaten i denna studie samt få en tydligare bild av hela laktationen och kornas produktion i ko-kalvsystem

Concentration Difficulties in the School Environment - with focus on children with ADHD, Autism and Down's syndrome

The overall aim of this thesis was to identify environmental factors that affect children with ADHD, autism, and Down's syndrome and their ability to concentrate in their learning environment at school. The issue of this research is not to dismiss any of the additional resources these children are in need of; instead it is to suggest how to arrange learning environments in the most supportive way possible based on the initial needs of these children. A pronounced ambition concerning the educational policy in Sweden is to organize an all-inclusive school, meaning that schools should be able to meet the needs of all children, irrespective of their capacities and conditions. However, there is no specific guidelines for the school environment as a learning environment considering these children's needs or the needs of those with concentration difficulties. The Human Environment Interaction-model was used to establish the structure of the approach of the thesis, especially concerning the review of previous research, the development of the questions at hand, but also as a holistic method way to fill possible gaps in earlier approaches. The research has been divided into four empirical studies. The first two studies served as a basis for possible principles of generalization and specifics for each disability concerning influences found in the school environment. In Study I, personal assistants and teachers working on a daily basis with children diagnosed with one of the disabilities were approached. In Study II the professionals approached were working at the Child and Adolescent Habilitation Services, thus having a different relation to the children than the informants in the first study. In both studies questionnaires were being used. The response from the 125 personal assistants and teachers, and 137 professionals at the Child and Adolescent Habilitation Services, revealed school-related environmental factors influencing the children in question and their ability to concentrate. The results sometimes showed different influences depending on which disability the children had. It was shown that aspect, such as, façade apertures and room passages, the view, acoustics, interior furnishing, seating arrangements, size of class and classroom, and decoration could influence the children's ability to concentrate, both positively and negatively. In Study III six group-work observations were carried out, revealing the need of individual adjustments. The results from that study also highlighted the difficulty in allocating already built classrooms to children with diminished cognitive abilities for the purpose of supporting their different needs. Finally, Study IV demonstrated the application of the principles within the building process, and that the participants tied to school projects in accordance with the cyclic building process has the potential to implement new knowledge. It may be concluded that these children's ability to concentrate are influenced by the features of their learning environment, which needs to be considered in the allocation of them in the school buildings. It was further concluded, that this knowledge should be implemented in the building process