| 1. |
- Bernado, Laura, et al.
(författare)
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Time- and Frequency-Varying K -Factor of Non-Stationary Vehicular Channels for Safety-Relevant Scenarios
- 2015
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Ingår i: IEEE Transactions on Intelligent Transportation Systems. - 1524-9050. ; 16:2, s. 1007-1017
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Tidskriftsartikel (refereegranskat)abstract
- Vehicular communication channels are characterized by a non-stationary time- and frequency-selective fading process due to fast changes in the environment. We characterize the distribution of the envelope of the first delay bin in vehicle-to-vehicle channels by means of its Rician $K$-factor. We analyze the time–frequency variability of this channel parameter using vehicular channel measurements at 5.6 GHz with a bandwidth of 240 MHz for safety-relevant scenarios in intelligent transportation systems (ITS). This data enables a frequency-variability analysis from an IEEE 802.11p system point of view, which uses 10 MHz channels. We show that the small-scale fading of the envelope of the first delay bin is Rician distributed with a varying K-factor. The later delay bins are Rayleigh distributed. We demonstrate that the K-factor cannot be assumed to be constant in time and frequency. The causes of these variations are the frequency-varying antenna radiation patterns, as well as the time-varying number of active scatterers, and the effects of vegetation. We also present a simple but accurate bimodal Gaussian mixture model, which allows to capture the K-factor variability in time for safety-relevant ITS scenarios.
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| 2. |
- He, Ruisi, et al.
(författare)
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Measurement-based analysis of relaying performance for vehicle-to-vehicle communications with large vehicle obstructions
- 2017
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Ingår i: 2016 IEEE 84th Vehicular Technology Conference, VTC Fall 2016 - Proceedings. - 9781509017010
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Konferensbidrag (refereegranskat)abstract
- It has been widely recognized that relaying is an important method for increasing the reliability and spectral efficiency of communications systems, and it is thus helpful for improving the performance of vehicle-to-vehicle (V2V) communication systems. However, designing and evaluating V2V relay networks require understanding the effect of shadowing, as this critically impacts the performance of the relay system. Even though the theoretic performances of various relaying schemes have been well investigated, there is a lack of empirical test that incorporates realistic shadowing effects. In this paper, we analyze the performance of relaying transmission in V2V scenarios based on measurements in scenarios where shadowing occurs through large vehicles such as buses. We investigate several potential locations for the relay nodes, and the measurements are performed with two static transmitters (TX) and one dynamic receiver (RX). Outage probabilities of several relaying schemes such as multi-hop decode-and-forward, multi-hop amplify-and-forward, and diversity-amplify-and-forward are estimated and discussed based on the measured instantaneous end-to-end signal-to-noise ratio (SNR). It is found that: (i) shadowing effect caused by the bus between V2V line-of-sight (LOS) links increases the outage probability for the non-LOS (NLOS) direct transmission; (ii) using relay node on the bus roof can significantly improve transmission, however, a strong shadowing effect may reduces the acceptable communication distance of relaying scheme; and (iii) the diversity-amplify-and-forward relaying scheme generally has the best performance. Our results can be used to design a relay system for V2V communications.
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| 3. |
- Karttunen, Aki, et al.
(författare)
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Censored Multipath Component Cross-Polarization Ratio Modeling
- 2017
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; 6:1, s. 82-85
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Tidskriftsartikel (refereegranskat)abstract
- In wireless channel measurements, the relatively weak cross-polarized multipath components (MPCs) are typically severely affected by the measurement noise level. As shown in this letter, the typical cross-polarization ratio (XPR) model parameter estimation, which ignores the existence of censored samples, may lead to significant errors. We demonstrate how to achieve accurate parameter estimates with a maximum likelihood estimator that properly takes into account both the measured XPRs and the censored samples. Also, a new XPR model is presented in which the average XPR is modeled as a function of the MPC excess loss. The new model is shown to be insensitive to the channel measurement noise level. A practical example with measured data in an indoor environment at 60 GHz demonstrates the utility of the approach.
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| 4. |
- Karttunen, Aki, et al.
(författare)
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Path loss models with distance-dependent weighted fitting and estimation of censored path loss data
- 2016
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 10:14, s. 1467-1474
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Tidskriftsartikel (refereegranskat)abstract
- Path loss models are the most fundamental part of wireless propagation channel models. Path loss is typically modelled as a (single-slope or multi-slope) power-law dependency on distance plus a log-normally distributed shadowing attenuation. Determination of the parameters of this model is usually done by fitting the model to results from measurements or ray tracing. The authors show that the typical least-square fitting to those data points is inherently biased to give the best fitting to the link distances that happen to have more evaluation points. A weighted fitting method is developed that emphasises the accuracy at the distance range that is consciously chosen by the user as most important for a system simulation. As a further important point that is typically not taken into account for path loss parameter extraction, the authors show that typically measurement data (but also ray tracing) is censored, i.e. path loss values above a certain threshold cannot be measured. The authors present examples of weighted fitting models, and models with and without the censored data, for 28 GHz channels in urban macrocells, and show that these effects have a significant impact on the extracted parameters and that the fitting accuracy can be improved with the presented methods.
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| 5. |
- Sangodoyin, Seun, et al.
(författare)
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Statistical Modeling of Ultrawideband MIMO Propagation Channel in a Warehouse Environment
- 2016
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 64:9, s. 4049-4063
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes an extensive propagation channel measurement campaign in a warehouse environment for line-of-sight (LOS) and nonline-of-sight (NLOS) scenarios. The measurement setup employs a vector network analyzer operating in the 2-8-GHz frequency band combined with an 8×8 virtual multiple-input multiple-output (MIMO) antenna array. We develop a comprehensive statistical propagation channel model based on high-resolution extraction of multipath components and subsequent spatiotemporal clustering analysis. The intracluster direction of departure (DoD), direction of arrival (DoA), and the time of arrival (ToA) are independent, both for the LOS and NLOS scenarios. The intracluster DoD and DoA can be approximated by the Laplace distribution, and the intracluster ToA can be approximated by an exponential mixture distribution. The intercluster analysis, however, shows a dependency between the cluster DoD, DoA, and ToA. To capture this dependency, we separately model the clusters caused by single and multiple bounce scattering along the aisles in the warehouse. The intercluster DoD distribution follows a Laplace distribution, while the cluster DoA conditioned on the DoD is approximated by a Gaussian mixture distribution. The model was validated using the capacity and delay-spread values.
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| 6. |
- Sangodoyin, Seun, et al.
(författare)
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Ultrawideband MIMO Channel Measurements and Modeling in a Warehouse Environment
- 2015
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Ingår i: IEEE International Conference on Communications. - 9781467364324 ; 2015-September, s. 2277-2282
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Konferensbidrag (refereegranskat)abstract
- This paper presents a detailed description of a propagation channel measurement campaign performed in a warehouse environment and provide a comprehensive channel model for this environment. Using a vector network analyzer (VNA), we explored both Line-of-sight(LOS) and Non-Line-of-sight (NLOS) scenarios over a 2-8 GHz frequency range. We extracted both small-scale and large-scale channel parameters such as distance-dependent pathloss exponent (n), frequency-dependent pathloss exponent (k), shadowing variance, and amplitude fading statistics of the channel. We also provide the clustering analysis of the channel impulse responses by using a modified Saleh-Valenzuela approach. Our model is validated by comparing the distributions of the root-mean-square (RMS) delay spread obtained from our model and measurement data, respectively. The model developed can be used for realistic performance evaluations of ultrawideband (UWB) communications and localization systems in warehouse environments.
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| 7. |
- Shafi, Mansoor, et al.
(författare)
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5G : A tutorial overview of standards, trials, challenges, deployment, and practice
- 2017
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716. ; 35:6, s. 1201-1221
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Tidskriftsartikel (refereegranskat)abstract
- There is considerable pressure to define the key requirements of 5G, develop 5G standards, and perform technology trials as quickly as possible. Normally, these activities are best done in series but there is a desire to complete these tasks in parallel so that commercial deployments of 5G can begin by 2020. 5G will not be an incremental improvement over its predecessors; it aims to be a revolutionary leap forward in terms of data rates, latency, massive connectivity, network reliability, and energy efficiency. These capabilities are targeted at realizing high-speed connectivity, the Internet of Things, augmented virtual reality, the tactile internet, and so on. The requirements of 5G are expected to be met by new spectrum in the microwave bands (3.3-4.2 GHz), and utilizing large bandwidths available in mm-wave bands, increasing spatial degrees of freedom via large antenna arrays and 3-D MIMO, network densification, and new waveforms that provide scalability and flexibility to meet the varying demands of 5G services. Unlike the one size fits all 4G core networks, the 5G core network must be flexible and adaptable and is expected to simultaneously provide optimized support for the diverse 5G use case categories. In this paper, we provide an overview of 5G research, standardization trials, and deployment challenges. Due to the enormous scope of 5G systems, it is necessary to provide some direction in a tutorial article, and in this overview, the focus is largely user centric, rather than device centric. In addition to surveying the state of play in the area, we identify leading technologies, evaluating their strengths and weaknesses, and outline the key challenges ahead, with research test beds delivering promising performance but pre-commercial trials lagging behind the desired 5G targets.
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| 8. |
- Witrisal, Klaus, et al.
(författare)
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High-accuracy localization for assisted living : 5G systems will turn multipath channels from foe to friend
- 2016
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Ingår i: IEEE Signal Processing Magazine. - 1053-5888. ; 33:2, s. 59-70
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Tidskriftsartikel (refereegranskat)abstract
- Asisted living (AL) technologies, enabled by technical advances such as the advent of the Internet of Things, are increasingly gaining importance in our aging society. This article discusses the potential of future high-accuracy localization systems as a key component of AL applications. Accurate location information can be tremendously useful to realize, e.g., behavioral monitoring, fall detection, and real-time assistance. Such services are expected to provide older adults and people with disabilities with more independence and thus to reduce the cost of caretaking. Total cost of ownership and ease of installation are paramount to make sensor systems for AL viable. In case of a radio-based indoor localization system, this implies that a conventional solution is unlikely to gain widespread adoption because of its requirement to install multiple fixed nodes (anchors) in each room. This article therefore places its focus on 1) discussing radiolocalization methods that reduce the required infrastructure by exploiting information from reflected multipath components (MPCs) and 2) showing that knowledge about the propagation environment enables localization with high accuracy and robustness. It is demonstrated that new millimeter-wave (mm-wave) technology, under investigation for 5G communications systems, will be able to provide centimeter (cm)-accuracy indoor localization in a robust manner, ideally suited for AL.
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| 9. |
- Zhang, Jianhua, et al.
(författare)
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Channel Models and Measurements for 5G
- 2018
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Ingår i: IEEE Communications Magazine. - 0163-6804. ; 56:12, s. 12-13
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Zhou, Lai, et al.
(författare)
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Geometry-Based Stochastic Channel Model for High-Speed Railway Communications
- 2019
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 68:5, s. 4353-4366
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Tidskriftsartikel (refereegranskat)abstract
- Reliable wireless communication links are a critical but challenging aspect for high-speed railway (HSR). To develop and analyze such systems, accurate models for the propagation channel are required. The radio channel properties in HSR scenarios are different from those in cellular scenarios not only due to the high velocity, but also due to the special construction elements and the type of surroundings along the train lines. We performed a measurement campaign at a carrier frequency of 2.4 GHz on the Guangzhou-Shenzhen dedicated high-speed train line in China. Motivated by the results from these measurements, we propose the concept of active scatterer region as an improvement for geometry-based stochastic channel models for HSR, to better describe the non-stationary properties of such channels. Further contributions to the total channel impulse response are also studied, including the line-of-sight component and the scattering component from overhead line poles. Each type of component is modeled and fully parameterized based on the measurement results.
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