| 1. |
- Coldrey, Mikael, 1972, et al.
(författare)
-
Higher order MIMO outdoor-to-indoor measurements using repeaters
- 2010
-
Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424425198
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present results from a outdoor- to-indoor MIMO measurement campaign where we study the effect of repeaters on singular values, spatial richness, capacity, and delay spread distributions. We present results from different repeater scenarios such as, e.g. different outdoor/indoor repeater deployments with single/dual polarized antennas. The measurements show that repeaters significantly enhance the received SNR while they increase the delay spread and decrease the spatial richness of the MIMO channel. However, the main conclusion is that a significant increase in channel capacity is attained when deploying repeaters mostly thanks to their ability to provide spatial multiplexing over the high-quality eigenmodes they may provide. The number of such eigenmodes is limited by the number of repeaters, deployment, and their antennas. © 2010 IEEE.
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| 2. |
- Ekström, Lars, 1959, et al.
(författare)
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Intervertebral disc response to cyclic loading--an animal model.
- 1996
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine. - 0954-4119. ; 210:4, s. 249-58
-
Tidskriftsartikel (refereegranskat)abstract
- The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 percent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the initial elastic response.
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| 3. |
- Haraldsson, Klas Tommy, et al.
(författare)
-
The Effects of Abstractable Hydrogen in Radical Photopolymerization of Maleate/Vinyl Ether Monomers Studied with EPR and Photo-RTIR
- 2010
-
Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 48:13, s. 2810-2816
-
Tidskriftsartikel (refereegranskat)abstract
- In this contribution, the influence of abstractable hydrogen on the kinetics of photopolymerized vinyl ether/maleate monomer formulations is reported. The effects of chain transfer on the polymerization rate were studied with photo real-time Infra Red (IR) for formulations composed of equimolar amounts of diethyl (DEMA) and three different vinyl ethers; methyl hexyl vinyl ether where the abstractable hydrogens adjacent to the vinyl functionality have been replaced with methyl groups, ethyl hexyl vinyl ether (EHVE) which has two easily abstractable alpha-hydrogens and triethylene glycol methyl vinyl ether (TEGMVE), which has several abstractable hydrogens. Four conclusions are drawn from these studies: (i) the vinyl ether/maleate kinetics differs significantly from the classical expression R-p = KI0.5, with recorded exponential factors of 0.84 +/- 0.04 in the absence of easily abstractable hydrogens; (ii) the presence of abstractable hydrogens significantly changes the kinetics of vinyl ether/maleate polymerizations with recorded exponential factors of 0.55 +/- 0.04 for EHVE/DEMA and 0.70 +/- 0.04 for TEGMVE/DEMA; (iii) the presence of easily abstractable hydrogens leads to a preferential consumption of maleates; and (iv) electron paramagnetic resonance studies show that vinyloxy-like radicals constitute the majority of the radicals in the systems with easily abstractable hydrogens.
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| 4. |
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| 5. |
- Harrysson, Fredrik, et al.
(författare)
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Evaluation of an Outdoor-to-In-Car Radio Channel with a Four-Antenna Handset and a User Phantom
- 2011
-
Ingår i: Vehicular Technology Conference VTC 2011-Fall.
-
Konferensbidrag (refereegranskat)abstract
- Based on static outdoor channel measurements we evaluate the influence of a vehicle on the MIMO radio channel, from a base station antenna array, to a multiple antenna handset in the hand of a user placed inside a test car. The measurement scenario is chosen to mimic a 2.6 GHz (LTE) macro-cell urban or rural scenario with two locations and orientations of the car, one at an open parking lot with a strong line-of-sight component, and one between buildings with no line-of-sight. The measurements are repeated several times with the user phantom plus handset positioned at the same spot within the car and with the car absent. Figures of the penetration loss, impact on fading statistics, mean delay, delay spread, terminal antenna correlation, eigenvalue distributions, as well as the performance of various hybrid diversity combining and spatial multiplexing schemes, are evaluated and compared with and without the vehicle present. It is found that the car make the channel statistics become more Rayleigh like and increases multipath channel richness, improving the potential of diversity gain and, to some extent, spatial multiplexing.
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| 6. |
- Harrysson, Fredrik, et al.
(författare)
-
Experimental Investigation of the Directional Outdoor-to-In-Car Propagation Channel
- 2013
-
Ingår i: IEEE Transactions on Vehicular Technology. - 1939-9359. ; 62:6, s. 2532-2543
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract in UndeterminedThe demand for wireless channel models including realistic user environments is increasing. This motivates work on more detailed models that are reasonably simple and tractable but with adequatestatistical performance. In this paper, we present an investigation of the spatial outdoor-to-in-car radio channel at 2.6 GHz. Specifically, we investigate the performance of a multiple antenna smartphone mockup in the hand of a user. We evaluate and utilize a composite channel approach to combine measured antenna radiation patterns with an estimated spectral representation of the multipath channel outside and inside the car in two different scenarios. The performance of the method is investigated and comparisons with direct channel measurements are performed. Statistical and directional properties of the outdoorto-in-car channel are presented and analyzed. It is found that the composite method, despite nearfieldproblems when estimating plane-wave channel parameters in a very narrow environment, constitutes a tool that provides reasonably viable statistical results. In addition, we have found that the introduction of the car in the propagation environment increases scattering and eigenvalue dispersion while it decreases pairwise antenna signal correlation. These statistical properties are found to slightly increase the possible diversity and the spatial multiplexing gains of multiple antenna terminals when located inside cars. Thispositive effect, however, is small compared to the negative effect of car penetration loss.
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| 7. |
- Hult, E, et al.
(författare)
-
In vivo measurement of spinal column viscoelasticity--an animal model.
- 1995
-
Ingår i: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine. - 0954-4119. ; 209:2
-
Tidskriftsartikel (refereegranskat)abstract
- The goal of this study was to measure the in vivo viscoelastic response of spinal motion segments loaded in compression using a porcine model. Nine pigs were used in the study. The animals were anaesthetized and, using surgical techniques, four intrapedicular screws were inserted into the vertebrae of the L2-L3 motion segment. A miniaturized servohydraulic exciter capable of compressing the motion segment was mounted on to the screws. In six animals, a loading scheme consisting of 50 N and 100 N of compression, each applied for 10 min, was used. Each loading period was followed by 10 min restitution with zero load. The loading scheme was repeated four times. Three animals were examined for stiffening effects by consecutively repeating eight times 50 N loading for 5 min followed by 5 min restitution with zero load. This loading scheme was repeated using a 100 N load level. The creep-recovery behavior of the motion segment was recorded continuously. Using non-linear regression techniques, the experimental data were used for evaluating the parameters of a three-parameter standard linear solid model. Correlation coefficients of the order of 0.85 or higher were obtained for the three independent parameters of the model. A survey of the data shows that the viscous deformation rate was a function of the load level. Also, repeated loading at 100 N seemed to induce long-lasting changes in the viscoelastic properties of the porcine lumbar motion segment.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Hult, Tommy, et al.
(författare)
-
Active Suppression of Electromagnetic Fields Using a MIMO Antenna System
- 2003
-
Konferensbidrag (refereegranskat)abstract
- Active suppression of noise and vibrations is a well established field of research with many applications in acoustic and mechanical industries. In this paper we test some of these active control methods in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated is a model of a mobile telephone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to cancel out the electromagnetic field at a specific point in space (e.g. at your head).
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| 12. |
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| 13. |
- Hult, Tommy, et al.
(författare)
-
Analytical dual-link MIMO channel model using correlated correlation matrices
- 2010
-
Ingår i: Proceedings of the Fourth European Conference on Antennas and Propagation. - 9788476534724 - 9781424464319
-
Konferensbidrag (refereegranskat)abstract
- Analytical Multiple-Input Multiple-Output (MIMO) models are often attractive due to their low complexity when analyzing possibilities and limitations in the system. In this paper we outline a a possible dual link extension of an analytical MIMO channel model and investigate its suitability based on measurements of a dual link MIMO scenario. The extension is based on the correlation matrix distance (CMD) as a gauge to generate correlation matrices for the additional links of the multi-link scenario.
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| 14. |
- Hult, Tommy, et al.
(författare)
-
Application of Space-Time Signal Processing and Active Control Algorithms for the Suppression of Electromagnetic Fields
- 2011
-
Ingår i: Applied Signal and Image Processing. - Hershey : IGI Global. - 9781609604776 ; , s. 45-60
-
Bokkapitel (refereegranskat)abstract
- Several studies have been conducted on the effects of radiation on the human body. This has been especially important in the case of radiation from hand held mobile phones. The amount of radiation emitted from most mobile phones is very small, but given the close proximity of the phone to the head it might be possible for the radiation to cause harm. The suggested approach involves the use of adaptive active control algorithms and a full space-time processing system setup (i.e. multiple antennas at both the transmitter and receiver side or MIMO), with the objective of reducing the possibly harmful electromagnetic radiation emitted by hand held mobile phones. Simulation results show the possibility of using the adaptive control algorithms and MIMO antenna system to attenuate the electromagnetic field power density.
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| 15. |
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| 16. |
- Hult, Tommy, et al.
(författare)
-
Assessment of Multipath Propagation for a 2.4 GHz Short-Range Wireless Communication System
- 2007
-
Konferensbidrag (refereegranskat)abstract
- In this paper we assess the multipath propagation effects of a short-range wireless device operating at 2.4 GHz in an indoor office environment. The investigations are carried out using FEM simulations and measurement trials for NLOS and LOS propagation scenarios. The FEM simulations will also be used for assessing the influence on propagation when doors are opened or closed. Finally, we investigate a single-input multiple-output (SIMO) antenna receive diversity system utilizing different combining techniques to improve the performance over a fading radio channel in a NLOS propagation environment. Simulation results show that a substantial diversity gain would be achieved by using this system. © 2007 IEEE
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| 17. |
- Hult, Tommy, et al.
(författare)
-
CAPACITY OF A SATELLITE DIVERSITY SYSTEM EMPLOYING MULTIPLE POLARIZATIONS
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with satellite diversity techniques in order to increase the data rates in satellite communication systems. Simulation results show that by exploiting the additional multiple polarization channels and satellite diversity we can achieve considerable capacity gain compared to the single satellite case.
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| 18. |
- Hult, Tommy, et al.
(författare)
-
CAPACITY OF MULTIPLE HAP SYSTEM EMPLOYING MULTIPLE POLARIZATIONS
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we investigate the potential increase in capacity of HAP (High Altitude Platforms) communication systems using compact MIMO antenna array configurations in conjunction with HAP diversity techniques. In addition, we evaluate the system performance for different separation angles between HAPs. Simulation results show that the HAP diversity system provides superior performance compared to the single HAP case.
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| 19. |
- Hult, Tommy, et al.
(författare)
-
COMBINED POLARIZATION AND SATELLITE DIVERSITY FOR HIGH DATA RATE COMMUNICATIONS
- 2006
-
Konferensbidrag (refereegranskat)abstract
- This paper addresses the potential gain of using multiple-input multiple-output (MIMO) principle in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. In addition, we investigate the effect of using different compact MIMO polarization antenna configurations and power control on the information theoretic capacity of the total transmission channel of the satellite system.
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| 20. |
- Hult, Tommy, et al.
(författare)
-
Compact MIMO Antennas and HAP Diversity for Enhanced Data Rate Communications
- 2007
-
Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using various compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to enhance the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. Simulations also show the existence of an optimum separation angle between HAPs that maximizes capacity. © 2007 IEEE.
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| 21. |
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| 22. |
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| 23. |
- Hult, Tommy, et al.
(författare)
-
Estimation of the TOA performance of Loran-C
- 2004
-
Konferensbidrag (refereegranskat)abstract
- Loran-C is a navigational aid that relies on the ability to make correct estimates of the Times of Arrival (TOAs) of signals received over a noisy radio channel. How good is the performance of Loran-C in this respect? Is it close to optimal? Are there perhaps better estimation techniques available than we currently employ? In this paper we use Estimation Theory to find the optimal limit of the accuracy of TOA estimates, for a given signal-to-noise ratio (SNR). Specifically, we compute the Cramer-Rao Lower Bound (CRLB) which specifies the absolute minimum error variance that can be achieved by an unbiased estimator. From the CRLB we can estimate the best repeatable accuracy that can be attained using a set of TOAs. We compute here the CRLBs for the TOA of a Loran-C signal with both Additive White Gaussian Noise (AWGN) and Additive Coloured Gaussian Noise (ACGN). We then employ the Maximum Likelihood Estimator (MLE) and compare its results with that of CRLB. Simulation results show that the MLE approaches the minimum variance obtained by CRLB for SNR values of practical and reliable Loran-C operation.
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| 24. |
- Hult, Tommy, et al.
(författare)
-
HAP Diversity and Compact MIMO Antennas for High Data Rate Communications
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP diversity and OFDM techniques in order to increase the data rates in HAP communication systems. Simulation results show that the MIMO system provides superior performance as compared to the single HAP case.
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| 25. |
- Hult, Tommy, et al.
(författare)
-
Indoor Propagation Simulation using FEM for Short-Range Wireless Communication Systems Operating at 2.4 GHz
- 2005
-
Konferensbidrag (refereegranskat)abstract
- In this paper we investigate the wave propagation effects of a short-range wireless device, like the Bluetooth, in an indoor office environment. Specifically, we investigate line of sight (LOS) and non line of sight (NLOS) propagation scenarios and verify the theoretical statistics of the fading using real measurements and finite element method (FEM) simulations of the environment. The simulations are also used for assessing the impact on propagation when doors are opened or closed. In addition, we also investigate the improvement in performance resulting from receive diversity gain of a system employing multiple receive antennas with various combining techniques.
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| 26. |
- Hult, Tommy, et al.
(författare)
-
MIMO ANTENNA APPLICATIONS FOR HIGH ALTITUDE PLATFORMS
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. Simulation results show that the MIMO system provides superior performance as compared to the single HAP case.
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| 27. |
- Hult, Tommy, et al.
(författare)
-
MIMO Antenna Applications for LEO Satellite Communications
- 2005
-
Konferensbidrag (refereegranskat)abstract
- This paper addresses the potential gain of using multiple antennas and MIMO-OFDM techniques in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. In addition, we investigate the effect of using different compact MIMO polarization antenna configurations and power control on the information theoretic capacity of the total transmission channel of the satellite system.
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| 28. |
- Hult, Tommy, et al.
(författare)
-
MIMO applications for interference mitigation in multiple high altitude platform WCDMA systems
- 2009
-
Ingår i: 2009 IEEE 70Th Vehicular Technology Conference Fall, Vols 1-4. - Anchorage : IEEE. - 1090-3038. ; , s. 1172-1176
-
Konferensbidrag (refereegranskat)abstract
- In this paper we investigate the possibility of multiple HAP coverage of a common cell area. In particular we study the uplink system performance since it is considered as a worst case scenario. In order to obtain further enhancement (interference mitigation) we also apply space-time diversity techniques, such as Single-Input Multiple-Output (SIMO) receive diversity or Multiple-Input Multiple-Output (MIMO) diversity, to improve the spectrum reuse in the multiple HAP scenario. We will show the level of improvement using SIMO and MIMO algorithms, the practical limits on the number of HAPs and SIMO/MIMO system dimension in response to traffic demands and the type of service used.
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| 29. |
- Hult, Tommy, et al.
(författare)
-
MIMO for HAPs : an idea whose time has come
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP diversity techniques in order to increase the data rates in HAP communication systems. Simulation results show that the MIMO system provides superior performance as compared to the single HAP case
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| 30. |
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| 31. |
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| 32. |
- Hult, Tommy, et al.
(författare)
-
MULTIPATH PROPAGATION ASSESSMENT FOR A 2.4 GHZ SHORT-RANGE WIRELESS COMMUNICATION SYSTEM
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we assess the effects of multipath propagation on the link performance of a short-range wireless device, like the Bluetooth, in an indoor office environment. Specifically, we analyze the non line of sight (NLOS) propagation scenario and confirm the theoretical statistics of the fading using real measurements and finite element method (FEM) simulations of the environment. The simulations are also used for assessing the impact of multipath propagation when doors are opened or closed. In addition, we also investigate the improvement in performance resulting from receive diversity gain of a system employing multiple receive antennas with various combining techniques.
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| 33. |
- Hult, Tommy, et al.
(författare)
-
Novel Applications of MIMO Antenna System for Active Suppression of Electromagnetic Fields
- 2005
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Active suppression of noise and vibrations is a well established field of research with many applications in acoustic and mechanical industries. In this report we test some of these active control methods combined with MIMO antenna system in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated is a model of a mobile phone equipped with one ordinary transmitting antenna and a number of actuator-antennas which purpose is to cancel out the electromagnetic field at a specific volume in space (e.g. at the human head) while maintaining a predefined level of the overall output power of the system. This power control is achieved through the use of a quadratic constraint on the active control algorithm. In addition, we will also investigate the impact of MIMO antenna parameters and carrier frequency on the performance of the system. Simulation results show the promise of using the adaptive control algorithms and MIMO system to attenuate the electromagnetic field power density.
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| 34. |
- Hult, Tommy
(författare)
-
Novel Applications of Space-Time Processing for Wireless Systems
- 2006
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Space-time processing techniques have emerged as one of the most promising areas of research and development in wireless communications. Space-time processing signifies the signal processing performed on a system consisting of several antenna elements, whose signals are processed adaptively in order to exploit both the spatial (space) and temporal (time) dimensions of the radio channel. Space-time processing techniques can be applied at the transmitter, the receiver or both. The use of space-time signal processing can significantly improve average signal power, mitigating fading, and reduce inter-symbol interference and co-channel interference. This can significantly improve capacity, coverage and quality of wireless systems. In this thesis we expand the scope of space-time processing by proposing novel applications in wireless communications. These include the reduction of possibly harmful electromagnetic radiation from mobile phones, enhancing link quality for Bluetooth links in indoor office environments, and increasing the spectral efficiency of satellite communication systems. Several studies have been conducted on the effects of radiation from hand held mobile phones. The amount of radiation emitted from most mobile phones is minute, but given the close proximity of the phone to the head it might be possible for the radiation to cause harm. In Part I, we suggest the use of adaptive signal processing algorithms combined with a MIMO (multiple-input multiple output) antenna system to decrease the electromagnetic radiation inside a certain volume in space (e.g. the the human head). In addition, we investigate the impact of MIMO antenna parameters, carrier frequency and power constraint on the performance of the system. Over the last decade there has been an explosive growth in the use of wireless mobile communications. Today we find users with mobile phones, wireless PDA's, MP3 players, and wireless headphones to connect to these devices. In Part II, we investigate the wave propagation effects of a short-range wireless device, such as the Bluethooth technology. Specifically, we assess the fading phenomenon for Bluetooth link in indoor office environment by simulation of different propagation scenarios, and use measurement results to confirm our findings. In addition, we investigate the improvement in performance resulting from receiver diversity gain of a system employing multiple receive antennas with various combining techniques. The need for high-speed, high-quality bandwidth efficient mobile communications is constantly increasing. In Part III, we address the potential gain of using MIMO antenna system in combination with OFDM (orthogonal frequency division multiplexing) in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. In addition we investigate the effect of using different compact MIMO polarization antenna configurations and power control on the information theoretic capacity of the total transmission channel of the satellite system.
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| 35. |
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| 36. |
- Hult, Tommy, et al.
(författare)
-
Performance of a multiple HAP system employing multiple polarization
- 2010
-
Ingår i: Wireless Personal Communications. - : Springer. - 0929-6212 .- 1572-834X. ; , s. 105-117
-
Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. In addition, we evaluate the performance of the system for different separation angles between HAPs, and determine the optimal separation angle that maximizes the total capacity of the system. © 2008 Springer Science+Business Media, LLC.
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| 37. |
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| 38. |
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| 39. |
- Hult, Tommy, et al.
(författare)
-
Power Constrained Space-Time Processing for Suppression of Electromagnetic Fields
- 2005
-
Ingår i: Journal of Communication Software and Systems. - Split : Croatian Communications and Information Society. - 1845-6421 .- 1846-6079. ; 1:1
-
Tidskriftsartikel (refereegranskat)abstract
- Active suppression of noise and vibrations is a well established field of research with many applications in acoustic and mechanical industries. In this paper we investigate the possibility of applying these adaptive active control methods with the aim of lowering the electromagnetic power density at a specific volume in space using the superposition principle and space-time processing employing the full MIMO (Multiple Input Multiple Output) antenna system setup. The application that we evaluated is a model of a mobile phone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to cancel out the electromagnetic field at the human head while maintaining a predefined level of the overall output power of the system. This power control is achieved through the use of a quadratic constraint on the active control algorithm. Simulation results show the promise of using the adaptive control algorithms and MIMO system to attenuate the electromagnetic field power density
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| 40. |
- Hult, Tommy
(författare)
-
Space-Time Processing Applications for Wireless Communications
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless mobile communication networks are rapidly growing at an incredible rate around the world and a number of improved and emerging technologies are seen to be critical to the improved economics and performance of these networks. The technical revolution and continuing growth of mobile radio communication systems has been made possible by extraordinary advances in the related fields of digital computing, high-speed circuit technology, the Internet and, of course, digital signal processing. Improved third generation (3G) and future generation wireless communication systems must support a substantially wider and enhanced range of services with respect to those supported by second generation and basic 3G systems. The never-ending quest for such personal and multimedia services, however, demands technologies operating at higher data rates and broader bandwidths. This combined with the unpredictability and randomness of the mobile propagation channel has created many new technically challenging problems for which innovative, adaptive and advanced signal processing techniques may offer new and better solutions. Space-time processing techniques have emerged as one of the most promising areas of research and development in wireless communications for the efficient utilization of the physical mobile radio propagation channel. Space-time processing signifies the signal processing performed on a system consisting of several antenna elements, whose signals are processed adaptively in order to exploit both the spatial (space) and temporal (time) dimensions of the radio channel. This can significantly improve the capacity, coverage, quality and energy efficiency of wireless systems. This thesis expands the scope of space-time processing by proposing novel applications in wireless communication systems. These include the reduction of possibly harmful electromagnetic radiation from mobile phones, enhancing the quality of Bluetooth links in indoor office environments, increasing the spectral efficiency of satellite and the novel high altitude platforms (HAPs) communication systems, enhancing the coverage and capacity of integrated multiple-HAP 3G systems, and improving the energy efficiency of cooperative wireless sensor networks. The performance of these systems is assessed by theoretical analysis, by computer simulations under a range of propagation environments including realistic channel models, advanced commercial electromagnetic modeling software, and a proposed novel multi-channel simulator suitable for various space-time applications.
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| 41. |
- Hult, Tommy, et al.
(författare)
-
Suppression of EM Fields using Active Control Algorithms
- 2004
-
Ingår i: Radioengineering. - Brno, Czech Republic : Brno University. - 1210-2512 .- 1805-9600. ; 13:3, s. 22-25
-
Tidskriftsartikel (refereegranskat)abstract
- Active methods for attenuating acoustic pressure fields have been successfully used in many applications. In this paper we investigate some of these active control methods in combination with a MIMO antenna system in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated in this paper is a model of a mobile phone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to reduce the electromagnetic field at a specific area in space (e.g. at the human head). Simulation results show the promise of using the adaptive active control algorithms and MIMO system to attenuate the electromagnetic field power density.
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| 42. |
- Hult, Tommy, et al.
(författare)
-
The Effect of Mutual Coupling on a High Altitude Platform Diversity System Using Compact Antenna Arrays
- 2010
-
Ingår i: International Journal of Antennas and Propagation. - : Hindawi Publishing Corporation. - 1687-5869 .- 1687-5877. ; 2010
-
Tidskriftsartikel (refereegranskat)abstract
- We analyze the destructive effects of mutual coupling and spatial correlation between the separate antenna elements on a combined diversity system consisting of multiple HAPs (High-Altitude Platforms) employing various compact MIMO (Multiple-Input Multiple-Output) antenna array configurations, in order to enhance the mutual information in HAP communication links. In addition, we assess the influence of the separation angle between HAPs on system performance, and determine the optimal separation angles that maximize the total mutual information of the system for various compact MIMO antennas. Simulation results show that although the mutual information is degraded by mutual coupling and spatial correlation, the proposed HAP diversity system still provides better performance compared to a nondiversity system for all tested scenarios.
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| 43. |
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| 44. |
- Hult, Tommy, et al.
(författare)
-
THE IMPACT OF MIMO ANTENNA SYSTEM AND CARRIER FREQUENCYON ACTIVE CONTROL SUPPRESSION OF ELECTROMAGNETIC FIELD
- 2004
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Konferensbidrag (refereegranskat)abstract
- There have been several studies done, with conflicting results, on the effects of cell-phone radiation on the human body. The amount of radiation emitted from most cell phones is very minute. However, given the close proximity of the phone to the head, it is entirely possible for the radiation to cause harm. If you want to be on the safe side, the easiest way to minimize the radiation you are exposed to is to position the antenna as far from your head as possible. Utilizing a hands-free kit, a car-kit antenna or a cell phone whose antenna is even a couple of inches farther from the head can do this most effectively. This paper makes a contribution to that discussion by proposing a new approach by employing adaptive active control algorithms combined with a Multiple-Input Multiple-Output (MIMO) antenna system to suppress the electromagnetic field at a certain area in space. We will also investigate the effects of the size and number of MIMO antenna elements and test the algorithms at different carrier frequencies (e.g., other GSM bands and UMTS).
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| 45. |
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| 46. |
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| 47. |
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| 48. |
- Hult, Tommy
(författare)
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WCDMA Uplink Interference Assessment from Multiple High Altitude Platform Configurations
- 2008
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Hindawi Publishing Corporation. - 1687-1472 .- 1687-1499. ; vol. 2008:Special Issue on Advanced Communication Techniques and Applications for High-Altitude Platforms
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the possibility of multiple high altitude platform (HAP) coverage of a common cell area using a wideband code division multiple access (WCDMA) system. In particular, we study the uplink system performance of the system. The results show that depending on the traffic demand and the type of service used, there is a possibility of deploying 3-6 HAPs covering the same cell area. The results also show the effect of cell radius on performance and the position of the multiple HAP base stations which give the worst performance.
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| 49. |
- Kolmonen, Veli-Matti, et al.
(författare)
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Measurement-based evaluation of interlink correlation for indoor multi-user MIMO Channels
- 2010
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 9, s. 311-314
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe properties of the single-link multiple-input-multiple- output (MIMO) propagation channels have been analyzed in many studies based on extensive propagation measurements. In this letter, we extend the measurement-based analysis to dual-link MIMO propagation channels. Here, we examine interlink correlation by evaluating the correlation of eigenvectors obtained from multiple MIMO links. We also investigated how the physical propagation phenomena produced the interlink correlation. Results indicate that interlink correlation may exist. Sometimes it is found to be very high also for far separated receive units, depending on similarity of dominant propagation mechanisms between multiple MIMO links and also on antenna array properties.
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| 50. |
- Mohammed, Abbas, et al.
(författare)
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Detection and minimisation of ionospheric interference in Loran-C receivers
- 2009
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Konferensbidrag (refereegranskat)abstract
- The subspace eigen-decomposition algorithms are applied to the problem of detecting ionospheric interfering signals affecting the performance of Loran-C receivers. In particular, we are interested in measuring the delay of these interfering Loran-C skywave components. The performance of these algorithms are evaluated and compared with our Fourier-based method. The simulation results show that many of the subspace eigen-decomposition algorithms yields good estimation accuracy and that they can also operate successfully with noisy signals.
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