| 1. |
- Ahlberg, M., et al.
(författare)
-
Downlink propagation measurements in the GSM 900 and 1800 MHz bands
- 1999
-
Ingår i: IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010). ; , s. 1506-1509 vol.3
-
Konferensbidrag (refereegranskat)abstract
- The authors investigate radio propagation in the GSM 900 and 1800 MHz bands in a typical Swedish suburban environment to determine whether or not it is practically feasible to co-site GSM 900 with GSM 1800 systems. They show that propagation in the GSM 1800 band is considerable higher (about 12 dB) than in the old GSM 900. In many cases this difference can be reduced by using dual band sector antennas with 3 dB higher gain at 1800 MHz. However, they also show that in small cells (radius <1000 m) this difference is of little concern and therefore it is possible to co-locate GSM 1800 sites within existing 900 MHz sites as a cost-effective way to increase the system capacity.
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| 2. |
- Alasali, Mohammad, et al.
(författare)
-
LTE MIMO Performance Measurements on Board Passenger Trains
- 2013
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Providing passenger internet on board trains with continuous connectivity at high speeds and over large rural distances is a challenging issue. A frequently used solution to the problem is to use an on board WiFi network connected to the 3G or 4G networks deployed outside the train. In order to be able to provide the capacity and the data rates that tomorrow's business travelers are expecting it has been suggested to use a combination of MIMO and carrier aggregation in the LTE-Advance standard. In this study, we practically investigate the plausibility of using MIMO functionality in an 900 LTE system when the receive antennas are mounted at a train roof about 4m above ground and the base stations antennas are on average placed 2.3km away from the track in towers with an average height of 45m and, hence, most of the time in line of site. It is found that along our test route MIMO is in practice supported by the radio channel at around 70% of the time when the train is travelling with an average speed of 185km/h and the MIMO antennas are mounted 10.5m apart.
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| 3. |
- Alasali, Mohammad, et al.
(författare)
-
LTE MIMO performance measurements on trains
- 2013
-
Ingår i: 2013 7th European Conference on Antennas and Propagation (EuCAP). - New York : IEEE. - 9788890701832 ; , s. 2327-2330
-
Konferensbidrag (refereegranskat)abstract
- Providing passenger internet on board trains with continuous connectivity at high speeds and over large rural distances is a challenging issue. A frequently used solution to the problem is to use an on board WiFi network connected to the 3G or 4G networks deployed outside the train. In order to be able to provide the capacity and the data rates that tomorrow's business travelers are expecting it has been suggested to use a combination of MIMO and carrier aggregation in the LTE-Advance standard. In this study, we practically investigate the plausibility of using MIMO functionality in an 900 LTE system when the receive antennas are mounted at a train roof about 4m above ground and the base stations antennas are on average placed 2.3km away from the track in towers with an average height of 45m and, hence, most of the time in line of site. It is found that along our test route MIMO is in practice supported by the radio channel at around 70% of the time when the train is travelling with an average speed of 185km/h and the MIMO antennas are mounted 10.5m apart.
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| 4. |
- Alasali, Mohammad, et al.
(författare)
-
Providing internet to trains using MIMO in LTE networks
- 2014
-
Ingår i: 2014 International Conference on Connected Vehicles and Expo, ICCVE 2014 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479967292 ; , s. 810-814
-
Konferensbidrag (refereegranskat)abstract
- Providing broadband passenger internet on board trains with continuous connectivity at high speeds and over large rural distances is a challenging issue. One solution to the problem is to use an onboard WiFi network connected to multiple 3G and 4G networks deployed outside the train and aggregate their combined capacity at the IP protocol level. In order to be able to provide the capacity and the data rates that tomorrow’s travelers are expecting, the future 4G standard (LTE-Advance) uses a combination of high order MIMO and carrier aggregation. In this study we use the Swedish company Icomera’s passenger internet system for our investigation. The system provides aggregation of multiple carrier and handover on an IP level. For about 10 years the system has in Sweden primarily been using multiple 3G communication links. However, here we present analysis and onboard measurements of a 2×2 MIMO channel to fast moving train in a live LTE 900 network. The results indicate that MIMO works surprisingly well and it is discussed that by combining 8×8 MIMO with carrier aggregation in future releases of 4G, it may be possible to bring gigabit internet connections to trains.
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| 5. |
- Andersson, Daniel, et al.
(författare)
-
M-Sequence UWB Radar for Industrial Applications
- 2010
-
Ingår i: Program of GigaHertz Symposium 2010, March 9-10, at Lund University.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ultra Wideband Radar has the potential of dramatically improving the control and surveillance of industrial processes in confined areas. An example is the application of UWB radar for surveillance of furnaces for heath treatment of steel billets developed by Radarbolaget in Gävle. In our installation at AB Sandvik Materials Technology, we have shown that by using a non-destructive UWB Radar technique it is possible to visualize in real-time the ongoing process inside the furnace behind a 0.5 m thick ceramic wall. Since the operating temperature inside the furnace is 1200 °C, there is today no other known method capable of visualizing the process for the operator of the furnace. The system is therefore designed to sustain high temperatures and powerful electromagnetic disturbances while performing measurement with wide dynamics and high stability. The design of this radar is based on the idea of transmitting a continuous m-sequence and then detecting the correlated impulse response (see figure below). The wide bandwidth is a requirement for obtaining high spatial accuracy and resolution but puts further requirements on the design of the antennas and the electronics. Our results show that with this technique it is possible to determine the deformation of the steel billets inside the furnace with an accuracy of less than 5 mm. The radar system is also able to detect deformations in the furnace wall The m-sequence radar has many advantages over other UWB radar technologies since it e.g. does not require many analogue components. Its performance is a result of the choice of code length, sampling rate and averaging. However, the resolution is still limited by the impulse response of the analogue antenna (ringing). In this paper system parameters that affect the overall performance of an m-sequence radar are reviewed and means of enhancing its performance are discussed.
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| 6. |
- Beckman, Claes, 1962-
(författare)
-
5G and its Implication for Rail
- 2019
-
Ingår i: Train Communicatins Systems 2019. - London.
-
Konferensbidrag (populärvet., debatt m.m.)
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| 7. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Antenna diversity for mobile telephones
- 1998
-
Ingår i: <em>IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36</em>, Atlanta, GA, 1998, pp. 2220-2223 vol.4.. ; , s. 2220-2223
-
Konferensbidrag (refereegranskat)abstract
- There have been several studies made on new diversity antennas for the mobile telephones. The main idea has been to have a built-in (planar) antenna working together with the conventional external. The purpose of this paper is to examine the concept of diversity further and to design two different concepts, one with two external antennas and one with an external antenna combined with an in-built. For evaluation a MATLAB program developed by the Center for Personkommunikation, CPK, in Aalborg, Denmark, is used. Given the radiation pattern from each antenna and the incoming field distribution from the environment, this program calculates the diversity performance of the system assuming that selection combining is used to combine the signals
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| 8. |
|
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| 9. |
- Beckman, Claes, 1962-
(författare)
-
Antenna-to-Antenna Isolation Measurements
- 1999
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this document we show results from measurements of the antenna-to-antenna isolation between different types of base station antenna configurations. The measurements are conducted on antennas for the GSM1800 band. However, since this band is relatively close to the IMT-2000 band it is reasonable to assume similar results for antennas to be used in this band.In this report we present measurement results from antennas with both vertical and slanted dual polarisation, and different horizontal beamwidths. The different antennas are shown in Table 1. The isolation is measured with the antennas positioned for some different configurations.
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| 10. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Base station antennas for mobile communications
- 2007
-
Ingår i: 2007 IEEE International Symposium on Antennas and Propagation.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This course gives the participants a general overview of the application, implementation and design of current and future base station antennas for mobile communications. It is aimed at microwave, RF- and antenna engineers in the wireless area, but also useful for researchers looking for relevant research topics and system engineers needing a deeper understanding of the antenna component of their system. The course explains underlying theoretical and practical implementation aspects of base station antennas in mobile communication networks of today and the future. The course is divided into three main parts: (i) System Aspects, (ii) BTS Antenna Design, (iii) Diversity and MIMO In the first part the fundamental parameters of a base station antenna are discussed in the context of radio network design. In particular we discuss parameters such as gain, radiation patterns, frequency bands and power handling and put them in the context of cell planning, propagation and capacity. In the second part a general overview of base station antenna design is given. In particular the design aspects of radiators, feed networks and reflectors are discussed. Furthermore, a general discussion of array synthesis for base station antennas is given. In the final part of the course we give an overview of the underlying theory of diversity and MIMO systems. In particular we discuss the requirements that these systems put on the base station antennas in order to be able to deliver the data rates expected from WiMAX and the long term evolution of 3G systems.
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| 11. |
- Beckman, Claes, Professor, 1962-, et al.
(författare)
-
Betänkande av Utredningen om radiospektrumanvändning i framtiden – Frekvenser i samhällets tjänst (SOU 2018:92)
- 2019
-
Annan publikation (populärvet., debatt m.m.)abstract
- KTH, har ombetts att ge sin syn på Betänkandet enligt ovan, ert diarienummer N2019/00192/D.Frågeställningarna faller innanför den utbildning och forskning som bedrivs inom KTH. Skolan har under lång tid varit ett nav inom utbildning, utveckling och forskning inom radiokommunikation och även hela system för trådlösa tjänster. Ett exempel är ”Wireless@kth”, som i samarbete med industri och myndigheter bedrivit forskning inom området trådlösa system sedan 2001. Forskare inom denna konstellation har berett frågan och lämnar nedanstående yttrande.
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| 12. |
- Beckman, Claes, Professor, 1962-, et al.
(författare)
-
Can local 5G networks using local spectrum be used as platform for digitalization of industrial systems and services?
- 2022
-
Ingår i: Proceedings 31st European Regional ITS Conference, Gothenburg, Sweden, June 2022.
-
Konferensbidrag (refereegranskat)abstract
- Local 5G spectrum licenses has recently attracted a great deal of attention and expectations from both industry and governments all over the world. One reason is the expectation that 5G local industrial networks using local spectrum can be used to support digitalization of industrial processes, and hence increase productivity of industrial use cases. In support of these expectations, governments all over the world have allocated spectrum for local 5G licensing in the 3.5GHz band with various conditions.This paper focuses on local 5G networks for "private" use, these non-public networks are commonly referred to as Non-Public Networks (NPNs). We present results and discussion about implications in three areas: Network capacity and cost for 5G NPN for industrial use; Allocation of local spectrum licenses; Ecosystem analysis of business models and value networks. For the two first areas our analysis indicates that previously identified questions related to radio-interference and co-existence between NPN and operator macro cell networks still seem to be challenging. It is unclear if 5G NPN using Time-Division Duplex (TDD) at the 3.5 GHz band can satisfy performance and operational needs in the field of industrial radio systems. Hence, the value of this type of local 5G licenses need to be further discussed.For the third area and the question “what actor is doing what?” we see a need to look more into solutions where different types of actors cooperate and contribute to different parts of the value network. This is in contrast to what is described in many papers and reports where the assumption is that one type of actor will take care of all or most of the roles.
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| 13. |
- Beckman, Claes
(författare)
-
Center for RF-Measurement Technology
- 2008
-
Ingår i: Radio Science and Communication, RVK08.
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- In February 2006 the Centre for RF Measurement Technology was established at the University of Gävle (HIG). The long term objectives of the centre are to establish world leading research in the area of RF Measurement Technology, support education of radio engineers for local, national and international radio companies at HIG, become a natural collaboration partner for leading industry companies and universities and to support local and national small and middle sized companies in the radio business. Today the centre has collaboration with more than 15 national and international companies within 3 major projects in the field of RF measurement technology research spanning from power amplifiers and antennas to electromagnetic interference in industrial environments. The annual research budget is in the area of 10 MSEK. In addition to the research projects the centre also supports education and collaboration with local industry, high schools and community. The centre is located easy to find, well equipped laboratories in Gävle Technology Park, next to the University of Gävle campus.
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| 14. |
- Beckman, Claes, 1962-
(författare)
-
Comparison of three methods of evaluating glare.
- 1992
-
Ingår i: Acta ophthalmologica. - 0001-639X. ; 70:1, s. 53-9
-
Tidskriftsartikel (refereegranskat)abstract
- A Humphrey Automatic Refractor Model 570 was used to measure the impairment of visual acuity for low contrast optotypes as a result of glare for normal subjects and for subjects with cataracts. This was compared with a direct measure of intraocular light scatter as measured by a compensating technique and with a subjective assessment of glare determined by a questionnaire. Only a weak correlation (r = 0.28) was found between the decrease in low contrast letter acuity and intraocular light scatter. The subjective assessment of glare sensitivity was not correlated with the decrease in low contrast letter acuity, but correlated to some extent (r = 0.55) with the measurement of intraocular light scatter.
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| 15. |
- Beckman, Claes, 1962-
(författare)
-
Comparison of two glare measurement methods through light scattering modeling.
- 1992
-
Ingår i: Optometry and Vision Science. - : Ovid Technologies (Wolters Kluwer Health). - 1040-5488 .- 1538-9235. ; 69:7, s. 532-7
-
Tidskriftsartikel (refereegranskat)abstract
- Two methods used for evaluation of glare in patients with opacities of the ocular media are compared. One is a low contrast letter test and the other is a direct light scattering meter. Theoretical expressions for the measures obtained from the two different glare tests are derived in terms of the point spread function. Measurements on healthy test persons wearing diffusive glasses with known light scattering properties were in good agreement with the theory. Data from 26 cataractous eyes are presented and discussed in light of the theory.
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| 16. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Confocal fundus imaging with a scanning laser ophthalmoscope in eyes with cataract.
- 1995
-
Ingår i: British Journal of Ophthalmology. - : BMJ. - 0007-1161 .- 1468-2079. ; 79:10, s. 900-4
-
Tidskriftsartikel (refereegranskat)abstract
- AIMS/BACKGROUND: The study aimed to determine the influence of increased intraocular light scatter on the contrast in scanning laser ophthalmoscope (SLO) images and to examine to what extent SLO images can visualise the fundus through media opacities due to cataract.METHODS: Intraocular light scatter was estimated from measurements of letter contrast sensitivity before and after cataract surgery in five eyes. SLO images were obtained before and after surgery using confocal apertures of 1, 2, 4, and 10 mm, at laser wavelengths of 633 and 780 nm. Visibility of the fundus was determined by measurements of retinal contrast. SLO images were compared with standard fundus photographs.RESULTS: SLO images obtained before surgery revealed details of the retina that were unresolvable in the fundus photographs because of light scattering. By using one of the three smallest apertures, image contrast was further improved. However, no simple relations between aperture size, estimated light scatter, and image contrast could be found.CONCLUSION: SLO imaging was found to be superior to fundus photography for viewing the retina in eyes with cataract. Owing to the inhomogeneous nature of cataracts, the optimal choice of confocal aperture and laser wavelength is not simple and must be individualised.
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| 17. |
- Beckman, Claes, et al.
(författare)
-
Dielectric-loaded circular ridge waveguide applicator for hyperthermia
- 1988
-
Ingår i: Microwave and optical technology letters (Print). - : Wiley Subscription Services, Inc., A Wiley Company. - 0895-2477 .- 1098-2760. ; 1:6, s. 221-223
-
Tidskriftsartikel (refereegranskat)abstract
- An applicator for intracavitary hyperthermia treatment of cancer has been designed and tested. The applicator is a section of a dielectric-loaded circular ridge waveguide closed at both ends to form a transmission cavity. An aperture in the cavity wall can produce a directed heating of a tumor growing in the wall of a body cavity such as the vagina.
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| 18. |
- Beckman, Claes, 1962-
(författare)
-
Disputing Viking navigation by polarized skylight.
- 1994
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 33:21, s. 4754-5
-
Tidskriftsartikel (refereegranskat)abstract
- The widely held notion that the Vikings utilized polarization of skylight on overcast days for navigational purposes is demonstrated to have no scientific basis. The use of polarized skylight for navigation under partly cloudfree skies should be treated with caution and skepticism.
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| 19. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Disputing Viking Navigation by Polarized skylight
- 1993
-
Ingår i: Light and Color in the Open Air, OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1993. - Washington DC. ; , s. 34-37
-
Konferensbidrag (refereegranskat)
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| 20. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Dual Band Base Station Antenna Systems
- 1998
-
Ingår i: Broad Band Radio Access. - Linköping. - 9163072254 ; , s. 69-74
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An analysis of the possibilities of using dualband antennas in cellular radio is presented. Results from simultaneous measurements at 900 MHz and 1800 MHz are presented and analyzed. Based on the measured results, a dual polarized, dual band base station antenna has been designed. Such an antenna proveides the opportunity to replace a 4 antenna space diversity installation with a single antenna, thereby reducing costs and tower space.
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| 21. |
- Beckman, Claes, 1962-
(författare)
-
Dual polarised multibeam antenna
- 1999
-
Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194 .- 1350-911X. ; 35:25, s. 2158-2160
-
Tidskriftsartikel (refereegranskat)abstract
- A dual polarised four-beam antenna array for the 1850-1990 MHz frequency band is presented. The polarisations are ±45° to vertical. The antenna has eight inputs corresponding to two orthogonal polarisations and four beams. The return loss and cross-polar isolation for a single Butler beam exceeds 15 and 22 dB, respectively. The radiation pattern is similar to an ideal Butler pattern and the cross-polarisation level is <-21 dB in the beams
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| 22. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Ett ödesval för regionen
- 2009
-
Ingår i: Gefle Dagblad. - Gävle. - 1103-9302. ; 6 februari
-
Tidskriftsartikel (populärvet., debatt m.m.)
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| 23. |
- Beckman, Claes, 1962-
(författare)
-
Evaluation of a clinical glare test based on estimation of intraocular light scatter.
- 1991
-
Ingår i: Optometry and Vision Science. - : Ovid Technologies (Wolters Kluwer Health). - 1040-5488 .- 1538-9235. ; 68:11, s. 881-7
-
Tidskriftsartikel (refereegranskat)abstract
- A glare test based on psychophysical estimation of intraocular light scatter and using a flickering, annular glare source was evaluated. The parameters determining the accuracy of the test were studied. In particular the influence of background light and flicker frequency were investigated and optimum values for best accuracy were found. Based on these findings a versatile and simple apparatus was constructed. Forty patients with various degrees of cataract were investigated in a clinical study. Patients, who subjectively experience severe glare problems, indeed show high glare values as measured with the apparatus. No obvious relation between visual acuity and glare score was found. In comparison with glare tests using a stationary glare source the use of a flickering glare source is advantageous in terms of sensitivity and accuracy.
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| 24. |
- Beckman, Claes
(författare)
-
Examining the performance of dul band base station antennas : What progress is being made?
- 1996
-
Ingår i: Integrating GSM & DCS 1800. - London : IIR.
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- The recent growth in cellular communications has rapidly created a need for more radio channels. In order to make better use of the available frequency bands new access techniques such as TDMA (Time Division Multiple Access), FDMA (Frequency DMA) and CDMA (Code DMA) have been introduced. Still, the need for new channels is strong and new frequency bands have therefore been allocated for future wireless communication systems. These new communication systems, e.g. the European Personal Communication Network (PCN: 1710-1880MHz) and the North American Personal Communication System (PCS: 1850-1990MHz), use frequencies about twice as high as their predecessors (e.g. AMPS: 824-894MHz and GSM: 880-960MHz). However, at a time when our downtown areas already are littered with basestation antennas, operators are not keen to install more. Therefore, dual-band antennas have gained an increased interest. They would allow the operators to replace two antennas for separate frequency bands with one only, thus, reducing the windload of the towers and perhaps most importantly reducing the cost of installation.
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| 25. |
- Beckman, Claes, 1962-
(författare)
-
Fiber optic point-source for in vivo measurement of light transmission and scattering in the eye
- 1994
-
Ingår i: OphthalmicTechnologies, Proc. SPIE 2126, 324-330 (Societ of Photo-Optical Engineers, Bellingham WA, 1994).. - Bellingham WA. ; , s. 324-330
-
Konferensbidrag (refereegranskat)abstract
- A fiber optic point-source was designed for in vivo measurement of light transmission and scattering. The point-source consists of an optical fiber, with a core diameter of about 8 um, mounted in a stainless steel cannula. At the tip of the cannula the entrance face of a 1 mm micro prism is fixed. The hypotenuse face of the prism is coated with aluminum and acts as a mirror reflecting the light out through the exit face. The arrangement allows light fed into the optical fiber to be emitted in a direction perpendicular to the axis of the cannula. The cannula is bent to allow its in vivo introduction into the eye at the posterior pole. The prism is positioned close to the retina along the optical axis of the eye. The light is transmitted through the eye in a reversed beam path (from vitreous towards cornea). In the vitreous, the light source emits within a numerical aperture of about 0. 1 allowing the exiting light to be well confined through the dilated pupil. After careful calibration of the light source, accurate measurements can easily be performed by positioning detector equipment outside the eye. The small size of the point-source (in the range of the eye's resolution) allows measurement of light scatter at both wide and narrow angles. With this intraocular fiber optic technique, it is possible to perform several types of experiments, including measurements of light transmission and scattering, and also studies of fluorescence phenomena in different parts of the ocular media.
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| 26. |
- Beckman, Claes, 1962-
(författare)
-
Glare and contrast sensitivity before and after Nd : YAG laser capsulotomy.
- 1994
-
Ingår i: Acta ophthalmologica. - 0001-639X. ; 72:1, s. 27-32
-
Tidskriftsartikel (refereegranskat)abstract
- The benefits of Nd:YAG laser capsulotomy on visual performance were evaluated in 13 patients with after-cataract following extracapsular cataract extraction. Besides clinical evaluation we measured: visual acuity, letter contrast sensitivity with and without the presence of a circular glare source (glare angle: 8 degrees). Finally, the patients were asked to evaluate their subjective glare problems. In all patients, visual acuity had decreased markedly compared to measurements 2 months after cataract surgery. Before capsulotomy we observed impaired letter contrast sensitivity and increased intraocular light scatter compared to normals. Following capsulotomy, VA and contrast sensitivity both improved by a factor of 2. The subjective glare problems diminished, although most patients showed minor decreases in intraocular light scatter. The limited glare induced loss of letter contrast sensitivity, present before capsulotomy, remained after treatment. Our study indicates that after-cataract impairs resolution and contrast sensitivity without necessarily causing a marked increase in light scatter as measured at a large angle.
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| 27. |
- Beckman, Claes, 1962-
(författare)
-
Glare measurements before and after cataract surgery.
- 1993
-
Ingår i: Acta ophthalmologica. - 0001-639X. ; 71:4, s. 471-6
-
Tidskriftsartikel (refereegranskat)abstract
- The efficacy of cataract surgery in improving visual performance was evaluated in 10 patients by measuring changes in intraocular light scatter, contrast sensitivity and glare induced visual loss. Two different methods were used to estimate these functions before and after cataract extraction with implantation of a monofocal posterior intraocular lens. By one method intraocular light scattering was assessed. By the other, letter contrast sensitivity and glare induced visual loss were determined. Preoperatively most patients had various glare problems, glare induced visual loss and increased intraocular light scatter. Following surgery the letter contrast sensitivity increased by a factor of 3 or more (mean 4.3). The glare problems diminished or disappeared after surgery, although several patients still had increased intraocular light scattering and glare induced visual loss compared to normals. Postoperatively the contrast sensitivity both with and without glare had increased to a level where the glare induced visual loss did not create any visual problems.
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| 28. |
- Beckman, Claes, Professor, 1962-, et al.
(författare)
-
High Reliability Air-to-Ground Communication System based on Aggregation of Terrestrial Networks
- 2023
-
Ingår i: Proceedings - 2023 28th Asia Pacific Conference on Communications, APCC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 75-80
-
Konferensbidrag (refereegranskat)abstract
- Providing connectivity to helicopters and drones is a challenging issue both from a technical as well as financial perspective. One possible cost efficient solution to the problem is for the aircraft to connect directly to the already deployed terrestrial public networks and aggregate their combined capacity and coverage at the Internet Protocol (IP) level. In this study we equipped an Airbus helicopter H135 with external antennas from VITES GmbH, two Icomera 'X5/X6' multi-SIM routers, including Icomera's autonomous test and monitoring system 'Surveyor', and conducted multiple test flights over a rural area in southern Germany. The results showed that using Icomera's patented technology it is possible to connect a helicopter or a drone, flying at an altitude of 10.000 ft (3048 m), to multiple terrestrial public cellular networks. Thus, obtaining high capacity, large coverage and high reliability connections to the helicopter.
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| 29. |
- Beckman, Claes, 1962-
(författare)
-
Imaging through light scattering eye media : letter identification
- 1994
-
Ingår i: Proc.SPIE. - : SPIE. ; 2079, s. 2079-2079
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of intraocular light scatter on letter identification in the absence and presence of glaring light is studied through computer simulations and simple experiments on healthy test subjects wearing diffusive glasses with known light scattering properties. An explicit expression for the point-spread function of a cataractous eye is used to calculate retinal images. For estimating resolution in the calculated images an assumed neural contrast sensitivity function is needed. The function used is derived from measurements by Campbell and Green. Experimental results are in agreement with theory. The analysis shows that visual acuity is quite insensitive even to substantial diffusive scattering provided that glare sources are not present in the field of view. Comparing measurements of ‘letter size’ with measurements of ‘letter contrast’ the latter method is found to measure intraocular light scattering more sensitively.
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| 30. |
- Beckman, Claes, 1962-
(författare)
-
Implications of Dual Band Functionality on Base Station Antenna Development
- 1997
-
Ingår i: Dual Band/Multi Band '97. - London.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The recent growth in cellular communications has rapidly created a need for more radio channels. In order to make better use of the available frequency bands new access techniques such as TDMA (Time Division Multiple Access), FDMA (Frequency DMA) and CDMA (Code DMA) have been introduced. Still, the need for new channels is strong and new frequency bands have therefore been allocated for wireless communication systems.These new communication systems, e.g. the European Personal Communication Network (PCN: 1710-1880MHz) and the North American Personal Communication System (PCS: 1850-1990MHz), use frequencies about twice as high as their predecessors (e.g. AMPS: 824-894MHz and GSM: 880-960MHz). However, at a time when our downtown areas already are littered with antennas, operators are not keen to install more.One solution could be to replace existing GSM or AMPS antennas with dual band GSM/PCN or AMPS/PCS. This would reduce the windload of the towers, the number of feeder cables and the whole cost of tower installations. If the dual band antennas were to be dual polarized also, the four antennas today being needed for receiving the PCN and GSM bands in a sector, could actually be replaced by one only.
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| 31. |
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| 32. |
- Beckman, Claes, 1962-
(författare)
-
Intraocular light scattering in vision, artistic painting, and photography.
- 1994
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 33:21, s. 4749-53
-
Tidskriftsartikel (refereegranskat)abstract
- Light scattering in the eye is reviewed, and its influence on vision is discussed in some detail. Isotropic scattering and formation of halos around point sources are described with reference to theory and experiments. Artists usually take intraocularly scattered light into account when painting natural scenes. A method to achieve similar effects in photography by the use of diffraction filters in front of the camera lens is demonstrated. A number of photos that illustrate the effects of such filters are shown.
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| 33. |
- Beckman, Claes, 1962-
(författare)
-
Letter imaging through light scattering eye media in the absence and presence of glaring light
- 1994
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Ingår i: Vision and its application: OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1994).. - Washington. ; , s. 94-97
-
Konferensbidrag (refereegranskat)abstract
- In cataractous eyes, part of the incomming light is directly transmitted through the optical media and part is scattered or absorbed by opacities in the lens. Wide angle, diffusively scattered light results in a veiling luminance which mhich mainly reduces
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| 34. |
- Beckman, Claes M. E., 1962
(författare)
-
Studies in Physiological Optics and Microwave Hyperthermia
- 1993
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the optics of the eye, the sky and microwave induced hyperthermia treatment of cancer. Light scattering in normal eyes is reviewed and its influence on vision is discussed in some detail. It is noted that artists usually take intraocularly scattered light into account when depicting scenes, and a photographic method to achieve similar effects is demonstrated. A new method for in vivo light scattering measurements in living rabbit eyes is presented and preliminary results are reported. Using both theoretical models and clinical measurements the importance of increased light scattering for retinal image quality is studied in cataractous eyes. In the analysis an assumed neural contrast sensitivity function is used, derived from results from previous investigations. The analysis shows that visual acuity is quite insensitive even to substantial diffusive scattering provided that glare sources are not present in the field of view. Different glare test methods are studied. A versatile and simple apparatus for clinical glare testing is constructed. It utilizes a flickering glare source and is optimized for maximum accuracy. A diffractive, bifocal intraocular lens is studied through computer simulation, optical bench measurements, and visual acuity testing. This lens combines a traditional intraocular lens with a blazed Fresnel lens structure on one of its surfaces, supposedly allowing the patient good distant as well as near vision. It is found that a pupil displacement of the order of 1 mm considerably reduces the lens' resolution. A possible side-effect of new headlights for cars, which utilize ultraviolet radiation, is intraocular stray-light increase, a study of which is reported. The widely held notion that the Vikings utilized polarization of skylight on overcast days for navigational purposes is demonstrated to have no scientific basis. A microwave applicator for intracavitary hyperthermia treatment of cancer is designed and tested. The applicator is a section of a dielectric-loaded circular ridge waveguide closed at both ends forming a transmission cavity. An aperture in the cavity wall produces a directed heating of a tumour growing in the wall of a body cavity such as the vagina.
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| 35. |
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| 36. |
- Beckman, Claes, 1962-, et al.
(författare)
-
On the impact of velocity on the train-to-earth MIMO propagation channel : Statistical observations and qualitative analysis
- 2017
-
Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings. - : IEEE conference proceedings. - 9781538632840 ; , s. 1865-1866
-
Konferensbidrag (refereegranskat)abstract
- We provide measured data collected from 97 trains completing over 7000 journeys in Sweden showing that the throughput over LTE is impacted by train velocity. In order to explain these observations we assume that the underlying causes can be found in the implementation of the MIMO system into LTE Rel. 8 and the diffuse scattering of signals from ground reflections.
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| 37. |
- Beckman, Claes, 1962-
(författare)
-
Optical properties of diffractive, bifocal, intraocular lenses.
- 1992
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 31:13, s. 2377-84
-
Tidskriftsartikel (refereegranskat)abstract
- The resolution of diffractive, bifocal, intraocular lenses was studied with regard to pupil displacement and diameter size through computer simulations, bench measurements, and patient vision-acuity measurements. Good agreement was obtained between these three methods of investigation. In particular, we find that pupil displacements of the order of 1 mm reduce the resolution considerably for these lenses.
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| 38. |
- Beckman, Claes, 1962-
(författare)
-
Performance analysis of applying up-link estimates in the down-link beamforming using a dual polarized array
- 2000
-
Ingår i: VTC2000-Spring. 2000 IEEE 51st Vehicular Technology Conference Proceedings (Cat. No.00CH37026). ; , s. 690-694 vol.2
-
Konferensbidrag (refereegranskat)abstract
- Most of the current and future mobile communications systems are frequency duplex systems, i.e. the up- and down-link are separated in frequency. Since the effect of the radio channel is not constant with frequency, this potentially limits the capacity gain using adaptive antennas. We use 150 MHz measurement data to simulate adaptive beamforming in a suburban environment. The information from the up-link at 1741 MHz is used for beamforming at this frequency as well as on the down-link at 1839 MHz. Our results show a reduction in C/I improvement of up to 10 dB between the up- and down-link
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| 39. |
- Beckman, Claes, 1962-
(författare)
-
Plausibility of assuming ideal arrays for direction of arrival estimation
- 1996
-
Ingår i: IEEE Antennas and Propagation Society International Symposium. 1996 Digest. ; , s. 1364-1367 vol.2
-
Konferensbidrag (refereegranskat)abstract
- In order to fulfil the increasing demands on capacity and coverage of mobile communication systems smart or intelligent antennas have been suggested. These antennas increase the spectral efficiency of a wireless system by using arrays of antenna elements to shape RF signals in particular directions. Generally, smart antennas can be divided into two approaches: switched multi-beam and adaptive. Adaptive antennas utilize sophisticated signal processing algorithms to continuously distinguish between the desired signal, multipath and interfering signal as well as to calculate their direction of arrival (DOA). This makes it possible to smoothly track users with main lobes and interferers with nulls and thereby constantly maximizing the SINR (signal-to-interference and noise ratio). The DOA is one of the most important parameter for an adaptive antenna system to estimate. It is also the main subject of this paper. We establish whether or not it is plausible to assume the array to be ideal (which is often assumed in array signal processing theory) when the received signals are actually collected with a physical array consisting of standard folded dipoles. In doing so we first measured the element patterns (or steering vectors) of a twelve element antenna array. The results were then used in array signal processing simulations. The performance of two DOA estimation algorithms, MUSIC and ESPRIT, are studied and compared.
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| 40. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Polarization Diversity Antennas
- 1997
-
Ingår i: Antenn 97. ; , s. 59-65
-
Konferensbidrag (refereegranskat)abstract
- In this study we investigate how different types of base station antenna polarization configurations, horizontal/vertical and slanted ±45 degrees, affect the diversity performance in different environments at 1800 MHz. The performance is determined by measurements where envelope cross-correlation, mean signal levels and diversity gain are studied in urban and suburban small-cell environments. The results are compared with a two branch space diversity scheme, where the antennas are horizontally separated by 20l. The correlation values are in general low, less than 0.7 for more than 90% of the measurements. The horizontal/vertical system suffers though from differences in mean branch signal levels, compared to the ± 45° and space diversity system which always have comparable mean signal levels. The diversity gain of both dual polarized antenna systems are in general about 1dB less than the gain of spatial diversity. The ± 45° scheme performs also about 1dB better than the horizontal/vertical scheme in the urban area. The results indicates that the ± 45° dual polarized scheme can be attractive in situations where hand-held portables are dimensioning for the cell planning.
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| 41. |
- Beckman, Claes, 1962-
(författare)
-
Polarization diversity in CDMA
- 1998
-
Ingår i: IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36. ; , s. 2236-2239 vol.4
-
Konferensbidrag (refereegranskat)abstract
- Since down-town areas are rapidly becoming littered with antennas, it is of great interest for operators to keep their contribution of antennas to a minimum. Dual polarized antennas may be a solution to reduce the number of antennas, and still obtain a satisfactory antenna diversity gain. However, in order for them to be competitive with space diversity configurations, the diversity gain obtained using dual polarized antennas must be comparable to the that obtained from space diversity. The purpose of this study is to analyse the diversity performance of a DS-CDMA system employing /spl plusmn/45 /spl deg/ dual polarized antennas, for different environments. A system model is presented and analysed.
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| 42. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Radio Propagation in Curved Road Tunnels
- 1998
-
Ingår i: Nordic Radio Symposium on Broadband Radio Access, NRS98 (Saltsjöbaden), 1998.. ; , s. 41-46
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This report investigates radio propagation in curved road tunnels at a mobile communications frequency of 925 MHz. This is done by comparing simulations with measurements taken in Norwegian road tunnels. The simulations are based on a simple model derived from geometrical optics and hybrid waveguide modes. The simulations agree well with measurements, indicating that the proposed model is reasonably good.
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| 43. |
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| 44. |
- Beckman, Claes, 1962-, et al.
(författare)
-
Shared Networks : Making Wireless Communications Affordable
- 2005
-
Ingår i: IEEE wireless communications. - : IEEE. - 1536-1284 .- 1558-0687. ; 12:2, s. 78-85
-
Tidskriftsartikel (refereegranskat)abstract
- In the wake of the substantial financial commitments incurred by European and other UMTS network operators in the form of licence fees, licensees have turned to network sharing as a means of reducing the capital requirements needed to bring 3G services to market. The reception from European regulators has been mixed, due to concerns that this inhibits competition, slow buildout, or otherwise result in reduced consumer benefits. The authors believe that the generic product life cycle model provides insights that indicate that network sharing, within an appropriately constructed regulatory framework, is not a threat to vigorous competition in the 3G industry, and in fact is one of the keys to stimulating the development of advanced, ubiquitous, affordable services.
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| 45. |
- Beckman, Claes, Professor, 1962-, et al.
(författare)
-
Starlink and Cellular Connectivity under Mobility : Drive Testing Across the Arctic Circle
- 2024
-
Ingår i: 2024 Wireless Telecommunications Symposium, WTS 2024. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350317886
-
Konferensbidrag (refereegranskat)abstract
- Low Earth Orbit (LEO) satellite networks such as Starlink can provide broadband connectivity in sparsely populated regions, including those located in arctic and subarctic regions. However, only satellites in a subset of inclination planes can serve these northern regions. In order to evaluate Starlink connectivity in these geographically extreme regions, we perform a drive test across the arctic circle measuring Starlink and cellular connectivity. We analyze the results with regards to Starlink throughput characteristics including the effects of the 15 second reconfiguration interval, and compare the throughput and connectivity. Starlink generally provide better throughput, with around 10x better median throughput than our comparison cellular network. However, the low tail of the distribution is less impressive with more frequent connectivity losses. Our results also show that the combination of Starlink and cellular has the potential to provide considerable gains in aggregated connection reliability and tail throughput. We additionally discuss policy implications relating to state subsidy policies designed to ensure that the whole population has access to broadband connectivity.
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| 46. |
- Beckman, Claes, 1962-
(författare)
-
Svar till PTS konsultation inför planerad tilldelning av frekvensutrymme i 2,3- och 3,5 GHz-banden samt tilldelning av frekvensutrymme för lokala tillstånd
- 2019
-
Annan publikation (populärvet., debatt m.m.)abstract
- KTH, Skolan för elektroteknik och datavetenskap (EECS) har beretts möjlighet att ge sin syn på PTS ”Konsultation inför planerad tilldelning av frekvensutrymme i 2,3- och 3,5 GHz-banden samt tilldelning av frekvensutrymme för lokala tillstånd”, PTS DNR 18-8496.KTH anser att det är olyckligt att PTS frångår principen om teknikneutrala band. Vi förstår att i detta fall finns inga alternativ men råder PTS att arbeta för att framtida spektrumtilldelning sker på teknikneutral basis då inlåsning av frekvensband till specifika tekniker inte bidrar till innovation.TDD medger ett mer effektivt utnyttjande av spektrum i fallet då nedlänkstrafik dominerar. Denna vinst måste dock vägas mot det faktum att co-ordinering och synkronisering av och mellan operatörernas nät hämmar konkurrensen. En möjlig framtida lösning är att 3.5 bandet enbart används för nedlänk och att upplänk sker i annat band (tex 1800 bandet). Slutligen så bör spektrumvillkoren vara oberoende av de nu existerande aktörerna. För att även öppna upp för flera och ev nya operatörer så föreslår vi att hela bandet 3,4 - 3,8GHz bjuds ut vid denna auktion.
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| 47. |
- Beckman, Claes, 1962-, et al.
(författare)
-
The Benefits of network Sharing
- 2005
-
Ingår i: Radiovetenskap och Kommunikation. ; , s. 147-151
-
Konferensbidrag (refereegranskat)
|
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| 48. |
- Beckman, Claes, et al.
(författare)
-
The evolution of base station antennas for mobile communications
- 2007
-
Ingår i: International Conference on Electromagnetics in Advanced Applications.
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- During the last two decades, mobile telephony has virtually exploded around the world. Whereas fixed telephony has merely around 800 milion phone lines globally, cellular mobile telephony has today close to 4 bilion subscribers less than 20 years after the introduction of digital mobile telephony! In the centre of a mobile cell is the base station antenna whose vertical and horizontal beam pattern creates the borders. The first base station antennas deployed for cellular communications were omni-directional in the horizontal plane. These antennas are typically based on stacked circular dipole elements fed by a series feed network. However, as the need for capacity increased more radio channels were being used and the radio networks soon reconfigured to 3 sector systems. The base station antennas in these type of systems typically has half power beam widths in the horizontal plane of around 65 degrees and the elements are fed by corporate feed networks. Through the choice of antenna length and the selection of vertical element positions and excitations a broad range of antenna gains and vertical beam patterns can be achieved. We show that for a linear array the gain is mainly determined by the vertical and horizontal beam widths but reduced by losses in the feed network. The electrical down tilt is needed to provide good coverage within the desired cell and is preferred to mechanical down tilt as it is independent of horizontal angle. Remotely adjustable electrical down tilt is also available today and an important cost saver during the expansion part of a network. As we will see, system requirements on reduced channel interferencemlead to a simple expression for the necessary phase shift in such an array. Due to the rapid increase in subscribers it was soon realized by the regulators around the world that one frequency band for digital mobile communications was not enough to provide the capacity needed. Therefore, in the mid 90-ties second frequency bands were introduced in both North America and Europe. Since operators are not keen to put up bigger towers and more antennas, ´this development called for dual-band antennas. The introduction of the UMTS band in the beginning of this millennium of course then called for triple band functionality! Traditionally the diversity is achieved by using two receive antenna branches separated in space. In mobile phone networks, all base stations for macro cellular communications incorporate diversity on the up-link. Otherwise it would be virtually impossible to communicate with a low power mobile over the rapidly fading channel. Since space diversity uses two horizontally separate antennas positioned about 20 wavelengths apart it become soon of interest for the operators to incorporate polarization diversity. With polarization diversity only one dual polarized antenna is used for each sector at the base. In order to ensure good polarization diversity it is necessary and sufficient to have symmetrical patterns with equal power in horizontal and vertical polarization. In 3G it is of great interest to strengthen the up- and down-links in order to be able to increase the data rates from today’s 16kbit/s (voice) to a wireless broadband of around 10Mbits/s. However, in the Long Term Evolution of 3G, LTE, data rates of up to and around 100MBits/s are expected. In order accomplish this diversity at the base station will not be enough but complemented by multiple branch reception and transmission at both the base station and the mobile terminal (Multiple-Input-Multiple-Output, MIMO systems). For such arrays it is of interest to reduce the mutual coupling between elements. Although the mutual coupling could be compensated for by perfect channel estimation it is still of interest to reduce the coupling in practice in order to be able to handle the mismatch loss. In order to do so the use of e.g. corrugations, hard and soft surfaces as well as Electronic Band Gap, EBG materials for the inclusion into the antenna structure has been studied. In conclusion we find that the base station antenna has developed dramatically during the last two decades and base station antenna technology may become a key enabler for the Long Term Evolution of 3G.
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| 49. |
- Beckman, Claes, 1962-, et al.
(författare)
-
The evolution of base station antennas for mobile communications
- 2007
-
Ingår i: International Conference on Electromagnetics in Advanced Applications. - : IEEE conference proceedings. - 9781424407675 ; , s. 85-92
-
Konferensbidrag (refereegranskat)abstract
- This paper gives a general overview of the design of base station antennas for mobile communications. It explains underlying theoretical and practical implementation aspects in mobile communication networks of today and the future. In the first part the fundamental parameters of a base station antenna are discussed in the context of radio network design. In particular we discuss parameters such as gain, radiation patterns, frequency bands and power handling and put them in the context of cell planning, propagation and capacity. In the final parts of the paper we give an overview of the underlying theory of diversity and MIMO systems.
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| 50. |
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