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  • 51.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Dual polarised multibeam antenna1999In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 35, no 25, p. 2158-2160Article in journal (Refereed)
    Abstract [en]

    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

  • 52.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Evaluation of a clinical glare test based on estimation of intraocular light scatter.1991In: Optometry and Vision Science, ISSN 1040-5488, E-ISSN 1538-9235, Vol. 68, no 11, p. 881-7Article in journal (Refereed)
    Abstract [en]

    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.

  • 53.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Fiber optic point-source for in vivo measurement of light transmission and scattering in the eye1994In: OphthalmicTechnologies, Proc. SPIE 2126, 324-330 (Societ of Photo-Optical Engineers, Bellingham WA, 1994). / [ed] Societ of Photo-Optical Engineers, Bellingham WA, 1994, Vol. 2126, p. 324-330Conference paper (Refereed)
    Abstract [en]

    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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  • 54.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Glare and contrast sensitivity before and after Nd: YAG laser capsulotomy.1994In: Acta ophthalmologica, ISSN 0001-639X, Vol. 72, no 1, p. 27-32Article in journal (Refereed)
    Abstract [en]

    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.

  • 55.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Glare measurements before and after cataract surgery.1993In: Acta ophthalmologica, ISSN 0001-639X, Vol. 71, no 4, p. 471-6Article in journal (Refereed)
    Abstract [en]

    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.

  • 56.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Imaging through light scattering eye media: letter identification1994In: Proc.SPIE, Vol. 2079, p. 2079-2079Article in journal (Refereed)
    Abstract [en]

    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.

  • 57.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Intraocular light scattering in vision, artistic painting, and photography.1994In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 33, no 21, p. 4749-53Article in journal (Refereed)
    Abstract [en]

    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.

  • 58.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Letter imaging through light scattering eye media in the absence and presence of glaring light1994In: Vision and its application: OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1994). / [ed] Optical Society of America, Washington, 1994, p. 94-97Conference paper (Refereed)
    Abstract [en]

    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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  • 59.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Optical properties of diffractive, bifocal, intraocular lenses.1992In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 31, no 13, p. 2377-84Article in journal (Refereed)
    Abstract [en]

    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.

  • 60.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Performance analysis of applying up-link estimates in the down-link beamforming using a dual polarized array2000In: VTC2000-Spring. 2000 IEEE 51st Vehicular Technology Conference Proceedings (Cat. No.00CH37026), 2000, Vol. 2, p. 690-694 vol.2Conference paper (Refereed)
    Abstract [en]

    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

  • 61.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Plausibility of assuming ideal arrays for direction of arrival estimation1996In: IEEE Antennas and Propagation Society International Symposium. 1996 Digest, 1996, Vol. 2, p. 1364-1367 vol.2Conference paper (Refereed)
    Abstract [en]

    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.

  • 62.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Polarization diversity in CDMA1998In: 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, 1998, Vol. 4, p. 2236-2239 vol.4Conference paper (Refereed)
    Abstract [en]

    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.

  • 63.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Remissvar: Från analog till digital marksänd radio: en plan från digitalradiosamordningen (SOU 2014:77)2015Other (Other (popular science, discussion, etc.))
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  • 64.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    The 'light scattering factor'. Importance of stimulus geometry, contrast definition, and adaptation.1995In: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 36, no 11, p. 2313-7Article in journal (Refereed)
    Abstract [en]

    PURPOSE: Paulsson and Sjöstrand have suggested that the light scattering factor (LSF) can be estimated by using the equation: LSF = L/E (M2/M1-1). Here L is the space average luminance of the target, E is the illuminance of the glare source, and M2 and M1 are modulation contrast thresholds in the presence and absence of the glare source. To compensate for change of adaptation. Abrahamsson and Sjöstrand later modified the above equation by introducing a correction factor (CF): LSF = L/E ((CF) (M2/M1-1). The purpose of this study is to analyze the validity of the above equations.

    METHODS: The importance of stimulus geometry, contrast definition, background luminance, and glare illumination is studied through theoretical analysis and comparison with earlier studies. Stimulus geometry and contrast definition are studied through optical modeling. Adaptation is modeled according to the laws of Weber and DeVries-Rose.

    RESULTS: The choice of contrast definition may corrupt the result by a factor of 2. At background luminance levels above approximately 10 cd/m2, the Paulsson-Sjöstrand equation agrees well with theory. At lower background levels, the Abrahamsson-Sjöstrand equation is used with correction factors derived from adaptation measurements. Using this equation and earlier published data from glare testing performed at 2 cd/m2, the results are found to be in fair agreement with the light scattering theory.

    CONCLUSIONS: Glare testing using the Paulsson-Sjöstrand equation is found to be valid as long as the measurements are performed at high luminance levels (above 10 cd/m2), with targets of low spatiotemporal frequencies (e.g., 2 cpd and 1 Hz) and with the use of a properly chosen definition of contrast. At lower luminance levels, the Abrahamsson-Sjöstrand equation may be used with well-derived correction factors.

  • 65.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    The performance of polarization diversity antennas at 1800 MHz1997In: IEEE Antennas and Propagation Society International Symposium 1997. Digest, 1997, Vol. 2, p. 1368-1371 vol.2Conference paper (Refereed)
    Abstract [en]

    Cellular radio systems have been in operation since the early 1970s and are experiencing tremendous growth. However, a major problem for cellular systems is the multipath, or short-term fading. One way to combat multipath fading on the uplink is to implement a diversity scheme at the base station. Until recently this was done by using two separate antennas positioned some distance apart from each other. The disadvantage with this method, however, is that the antennas have to be separated by several wavelengths to receive "independently fading" signals. Thus the antenna systems become large. With polarization diversity two antennas are also used but there is no need for any physical separation between them. Instead the two antennas are polarized in two orthogonal polarizations, e.g., horizontal/vertical or /spl plusmn/45 degrees slanted. In a study by Lotse et al. (see IEEE VTS 46th Vehicular Technology Conference Proceedings, vol.3, p.1643-46, 1996) it was found that space diversity yields typically about 1 dB better "diversity gain" than polarization diversity. However, how different antenna parameters affect the results has to our knowledge never been studied. The authors aim to fill this void.

  • 66.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Verifying 3G License Coverage Requirements2011In: Advances in Vehicular Networking Technologies / [ed] Miguel Almeida, InTech , 2011, p. 339-356Chapter in book (Other academic)
    Abstract [en]

    In the beginning of the 21’st century, the 3rd generation mobile phone systems, 3G, were introduced all around the world. In most countries, spectrum for this technology was allocated through some kind of licensing procedure. In Europe, the prevailing approach was to allocatespectrum through auctions, a process which led to a situation where the European operators found themselves committed to pay a staggering 130Bilion Euros for their 3G licenses.However, in most European countries, the fee was not the only obligation put on thelicensee: A coverage, “roll-out” requirement was in many cases also connected to the license(Northstream, 2002). Typically, these coverage requirements required that the licenseescover a certain area at a certain point in time after that the licenses had been awarded.In order for the regulators to verify that the licensees had met the coverage requirement and,hence, complied with the regulation, a method for coverage verification was needed. Suchmethods have therefore since then been developed by several European regulators (e.g. PTS2004; ECC 2007). In this book chapter we describe some general underlying consideration for the verification of radio coverage in UMTS systems and in particular we describe the Swedishmethodology developed by the Swedish Telecom regulator Post & Telestyrelsen (PTS).

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  • 67.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Wave propagation in curved road tunnels1998In: 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, 1998, Vol. 4, p. 1876-1879 vol.4Conference paper (Refereed)
    Abstract [en]

    In the early seventies much work was done in order to understand the propagation loss of UHF waves in rectangular mine tunnels, using either waveguide methods or image techniques based on geometrical optics (GO). A simple and accurate model is needed for planning the deployment of mobile phone networks. The method presented a simple GO extension to the standard hybrid waveguide solution.

  • 68.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Bergek, Martin
    Wireless communication system for moving vehicles2013Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A wireless communication system for a moving vehicle, such as trains, is disclosed. The system includes at least one router in the moving vehicle for receiving and transmitting wireless voice communication and data communication to and from a stationary communication server outside the moving vehicle through an exterior mobile network. Further, the system includes at least one femtocell provided within the moving vehicle, and being connected to the router for wireless transferring of wireless voice communication and data communication between mobile terminals within the moving vehicle and the router. The at least one femtocell is controlled by a femtocell controller directly or indirectly connected to the communication server outside the moving vehicle.

  • 69.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Eriksson, Jon
    Mutual coupling effects on direction of arrival estimation1996In: In Radiovetenskaplig konferens, Luleå, Sweden 1996 / [ed] Lars H Zetterberg, 1996, p. 410-414Conference paper (Refereed)
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  • 70.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Garcia, J.
    Alfredsson, S.
    Brunström, A.
    On the impact of velocity on the train-to-earth MIMO propagation channel: Statistical observations and qualitative analysis2017In: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, IEEE conference proceedings, 2017, p. 1865-1866Conference paper (Refereed)
    Abstract [en]

    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.

  • 71.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Karlsson, B.
    The story of Allgon: HF, VHF, cellular and microwave antennas during allmost 60 years2013In: 2013 7th European Conference on Antennas and Propagation (EuCAP), IEEE , 2013, p. 3171-3173Conference paper (Refereed)
    Abstract [en]

    Allgon, 'The Antenna Specialist', was a leading international design house and manufacturer of antennas for almost 60 years. The company was started in Stockholm in 1947 under the name of 'Antennspecialisten', by the Swedish engineer Torbjörn Cramner and his wife Veronica. In 1951 the company moved to Åkersberga north of Stockholm where its main facilities where located until the late 90's. During its life time the company designed and produced antennas for HF, VHF, Cellular and Microwave frequency bands, and for military, emergency, private and cellular radio systems. The company was in 2004 acquired by the US based company Powerwave but still today many of its original antenna designs are in production and many thousands of its base station antennas for mobile networks are still deployed all around the World.

  • 72.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Lindmark, Björn
    The evolution of base station antennas for mobile communications2007In: International Conference on Electromagnetics in Advanced Applications: ICEAA 07, IEEE conference proceedings, 2007, p. 85-92Conference paper (Refereed)
    Abstract [en]

    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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  • 73.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Lindmark, Björn
    Ahlberg, Mikael
    Dual Band Base Station Antenna Systems1998In: Broad Band Radio Access, Linköping, 1998, p. 69-74, article id 9Conference paper (Other academic)
    Abstract [en]

    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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  • 74.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Lundgren, L.
    Roos, D.
    Dielectric-loaded circular ridge waveguide applicator for hyperthermia1988In: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 1, no 6, p. 221-223Article in journal (Refereed)
    Abstract [en]

    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.

  • 75.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Smith, Gregory
    Shared Networks: Making Wireless Communications Affordable2005In: IEEE wireless communications, ISSN 1536-1284, E-ISSN 1558-0687, Vol. 12, no 2, p. 78-85Article in journal (Refereed)
    Abstract [en]

    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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  • 76.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Smith, Gregory
    The Benefits of network Sharing2005In: Radiovetenskap och Kommunikation: RVK 2005, 2005, p. 147-151Conference paper (Refereed)
  • 77.
    Beckman, Claes
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Thaung, Jörgen
    Sjöstrand, Johan
    In-vitro lens scatter measurements and glare testing1994Conference paper (Other academic)
  • 78. Bentley, F
    et al.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Dernirdjian, D
    Koile, K
    Darrell, T
    Perceptive presence2003In: IEEE Computer Graphics and Applications, ISSN 0272-1716, E-ISSN 1558-1756, Vol. 23, p. 26-36Article in journal (Refereed)
    Abstract [en]

    Perceptive presence systems automatically convey awareness of user states to a remote location or application without the user having to perform explicit commands or mode selection. The article describes a component-based architecture for creating presence applications using perceptual user interface widgets. Each widget performs a machine perception function, such as tracking a face or monitoring activity in a specific 3D location. Widgets provide an abstraction barrier between the perception algorithms and the needs of application writers. Two example applications developed using this framework are presented: one uses a luminous display to express a user’s availability for communication to a colleague at a remote location, and a second uses activity to control devices in a context-aware environment.

  • 79. Bentley, Frank
    et al.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Designing From Data: A Case Study From the Health Mashups Service2013In: Workshop on Informing Future Design via Large-Scale Research Methods and Big Data, 2013Conference paper (Refereed)
    Abstract [en]

    Instrumentation of mobile service interactions now allows for the ability to understand use in new ways and to base the design of system iterations as well as future services on data obtained from use “in the wild”over extended periods of time. This position paper will detail a few specific instances in the Health Mashupsproject where we were able to use usage data to improve the design and to create design implications to increase engagement in new services.

  • 80. Bentley, Frank
    et al.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Stephenson, Peter
    Levy, Laura
    Jones, Brian
    Robertson, Scott
    Price, Ed
    Catrambone, Richard
    Wilson, Jeff
    Health Mashups: Presenting Statistical Patterns between Wellbeing Data and Context in Natural Language to Promote Behavior Change2013In: ACM Transactions on Computer-Human Interaction, ISSN 1073-0516, E-ISSN 1557-7325, Vol. 20, no 5, p. 30-Article in journal (Refereed)
    Abstract [en]

    People now have access to many sources of data about their health and wellbeing. Yet, most people cannot wade through all of this data to answer basic questions about their long-term wellbeing: Do I gain weight when I have busy days? Do I walk more when I work in the city? Do I sleep better on nights after I work out? We built the Health Mashups system to identify connections that are significant over time between weight, sleep, step count, calendar data, location, weather, pain, food intake, and mood. These significant observations are displayed in a mobile application using natural language, for example, "You are happier on days when you sleep more." We performed a pilot study, made improvements to the system, and then conducted a 90-day trial with 60 diverse participants, learning that interactions between wellbeing and context are highly individual and that our system supported an increased self-understanding that lead to focused behavior changes.

  • 81.
    Berg, Miguel
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Access selection in partially Backhaul-limited multi-operator IEEE 802.11 networks2006In: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, Helsinki, 2006Conference paper (Refereed)
    Abstract [en]

    Radio resource management (RRM) across multiple, potentially competing, wireless networks has emerged as a salient feature for future generation system. Besides increased overhead, it will incur more complicated architectures and the question then becomes whether the gains of cooperative RRM (increased throughput, reliability, etc.) can justify these disadvantages. Herein we study potential gains that can be achieved by utilizing sophisticated algorithms in a scenario with two cooperating IEEE 802.11a networks, limited by either the wireless or wired link. Both best-effort (BE) and minimum bitrate (MBR) are treated and throughout the paper we use the rudimentary minimum path-loss (MPL) allocation as reference. Our results indicate that sophisticated access selection methods that besides path-loss, also account for AP load and potential constraints in the wired connection, can increase performance significantly. The maximum gain varies between 30-60% and 100-150% for BE and MBR traffic respectively and is typically obtained when there, on average, is one user per AP. We also studied the case where APs with constrained wired capacity connected (using the MPL criteria) to high-capacity APs in order to reroute traffic. Contrary to the approach in which advanced allocation principles is used, "loose" network integration is sufficient and even though it gave lower gains for BE data, the achievable rates for MBR data could be improved substantially.

  • 82.
    Berg, Miguel
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    On Selfish Distributed Access Selection Algorithms in IEEE 802.11 Networks2006In: IEEE VTS VEH TECHNOL CONF, 2006, p. 1097-1102Conference paper (Refereed)
    Abstract [en]

    An important question for future wireless networks is whether the prioritization between different accesses should be controlled by the networks or terminals. Herein we evaluate the performance of distributed access-selection algorithms where terminals are responsible for both AP selection and the necessary measurements. In particular, we focus on determining whether selfish distributed algorithms call perform as well as centralized ones (for comparison we include max-sum, max-min, proportional fair and minimum delay allocations). The study is conducted by time-dynamic simulations in a IEEE 802.11a network and its performance measures we use file transfer delay and supportable load at a maximum tolerable delay. Our results show that selfish algorithms can offer similar performance. both in terms of throughput and fairness, as the centralized schemes as long as they account for both path-loss and access point load. This is an important result and it suggests that terminal-controlled algorithms are Just as efficient as centralized schemes, which besides extensive measurements also require that AP exchange information, for improving the efficiency in WLAN networks. Compared with a minimum path-loss selection criteria, which is standard in the IEEE 802.11 family today, our distributed load-aware algorithm increases the maximum supportable load with more than 200 percent even after accounting for measurement time and estimation errors. With fast reselection during ongoing sessions the gains call be further increased with, typically, 20 percent.

  • 83.
    Berg, Miguel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    A Concept for Public Access to Privately Operated Cooperating Local Access Points2005In: IEEE Vehicular Technology Conference, New York: IEEE , 2005, p. 2959-2963Conference paper (Refereed)
    Abstract [en]

    For many future mobile communication scenarios, the traditional operators are believed to be unable or unwilling to support some services, mainly for cost reasons. Thus, there will always be gaps in the coverage and capacity of these systems.   This paper describes a non-conventional and low-cost concept for wireless access using privately operated local access points (LAPs) contributing to the public access, thus adding coverage and capacity in e.g. homes, offices and public hotspots.  The work has been performed in the EU-funded Ambient Networks (AN) project. A migration path is presented, starting with today’s LAPs for private-use-only to LAPs for public use, implementing the AN objective of “access for anyone to any network”. The main contributions in the paper are 1) the identification and analysis of re-use of fixed and wireless transport and access capacity using adhoc mesh networks between LAPs and 2) the use of network advertising &  discovery for LAP concepts.

  • 84.
    Blomgren, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Decentralized market-based radio resource management in multi-network environments2007In: IEEE VTS VEH TECHNOL CONF, 2007, p. 2884-2889Conference paper (Refereed)
    Abstract [en]

    For voice, an efficient radio resource management (RRM) essentially boils down to providing a predefined signal to interference ratio (SIR) at lowest cost possible and centralized schemes has, evidently, been an effective approach to address these problems. Delay-elastic data services, however, introduce both heterogeneous user requirements and possibilities for opportunistic RRM. One way, among others,to handle this would be to let autonomous trade-agents, acting on behalf of users, manage the radio resources, and this is our point of departure. We propose a market-based framework for decentralized RRM in environments populated by multiple, possibly heterogeneous, "access points" (APs), and the provided service for the users consists of file transfers. Resources (transmission time) are partitioned between users through a proportionally fair divisible auction. The problem at hand for the user (trade-agent), is then to determine how much resources it should purchase from the different APs in order to maximize its utility ("value for money"). Our results indicate that decentralized selfish bidding strategies are able to capitalize on temporary beneficial conditions and offer comparable performance with a centralized scheme (based on the 'mu C-rule') that requires knowledge about peak data-rates, queue lengths, and preferences for all users in the system.

  • 85.
    Blomgren, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Demand-responsive pricing in open wireless access markets2007In: IEEE VTS VEH TECHNOL CONF, 2007, p. 2990-2995Conference paper (Refereed)
    Abstract [en]

    Radio resource management (RRM) across operator boundaries is emerging as a salient feature for wireless systems beyond 3G. Until recently, research has been confined to solutions where cooperating networks enter explicit sharing agreements that define how responsibilities and revenues should be divided. An alternative would be to share the infrastructure implicitly by establishing an open wireless access market wherein networks not only compete for users on a long-term time-scale, but also on a much shorter time-base. This could be realized with an architecture where autonomous trade-agents, that reside in terminals and access points (APs), manage the resources through negotiations. In this paper we develop a framework for studying demand-responsive pricing in contexts where APs with overlapping coverage compete for users. Resources are partitioned through a proportional fair divisible auction and our aim is to establish if, and when, an open market for wireless access can be se sustained. Compared to a scenario where APs cooperate, our results show that, an open access market results in better services at lower price which in the prolonging also yields more satisfied customers. As an effect demand will increase and, from the perspective of the APs, act as a counterbalance to the reduced prices. Thus, the revenue earned by the AN will be comparable to the one in which obtained through AP cooperation and monopoly (cartel) pricing. Generally speaking, the difference between the cooperative and noncooperative RRM is small when the demand is concave and increases with the convexity of demand.

  • 86.
    Blomgren, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cai, Rui
    Cai, Tao
    Distributed demand-aware access selection in wireless multi-cell data networks2007In: 2007 IEEE 18th International Symposium On Personal, Indoor And Mobile Radio Communications: Vols 1-9, 2007, p. 2888-2892Conference paper (Refereed)
    Abstract [en]

    Regardless of advances in transmission technology, wireless broadband access will result in that fewer active users can be supported in a given cell. This may, due to lower levels of statistical multiplexing, yield in an unbalanced network. For such contexts load aware access point (AP) selection (load balancing) has been proposed as a means to increase network performance. This paper evaluates the downlink capacity (maximum number of users that can be admitted given a throughput requirement) of distributed load aware AP selection criteria for a well planned network, where the expected number of users per cell coincide. We propose a market based algorithm in which AP selection is aided by market mechanisms. In contrast to most of the existing research, we account for that interference levels generated in different cells depend on user assignment, and therefore varies as terminals perform handoff. Compared to single-frequency systems where users base their selection on the received signal strength our results show that the downlink capacity can be increased with around 25 percent by introducing a channel plan in combination with demand, or load, aware AP selection criteria. This gain is fairly insensitive to the throughput requirement and does not come at the expense of uplink performance. To benefit from demand metrics it is, however, of paramount importance that the entire system bandwidth is not reused in all cells.

  • 87.
    Bratu, Vlad-Ioan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Self-optimization of Antenna Tilt in Mobile Networks2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The increased complexity of mobile networks, the need to deliver high data rate services and the variation of mobile traffic put a high burden on operation and maintenance in terms of extra workload and additional costs . New approaches to network optimization and management should be taken into account to increase network performance and reduce operational costs. Antenna tilt is a powerful parameter for optimization of a mobile network. It has direct impact on shaping the boundary of the serving cell and hence on the coverage and interference parameters of the network. With the introduction of Remote Electrical Tilt (RET) antennas, tilt optimization can be used in the context of self-optimization. This work discusses how base station antenna tilt can be used as a self-optimization tool for load-balancing and presents a framework for a self-optimization process that can be integrated into existing and future mobile networks. Tests using real traffic data proved that the self-optimization process can be used to correctly identify congested cells. Both link level and system level simulations are performed to determine the impact of tilt adjustments on network performance. The results show that antenna tilt can be an effective tool to achieve load-balance between neighbouring cells and thus increase the Grade of Service (GoS). Furthermore, different tilt adjustment procedures are discussed each with it's advantages and disadvantages. It is concluded that antenna tilt can be successfully used for self-optimization purposes and possible limitations and issues are discussed.

    Download full text (pdf)
    fulltext
  • 88.
    Bratu, Vlad-Ioan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Antenna Tilt Load Balancing in Self-Organizing Networks2013In: International Journal of Research in Wireless Systems, ISSN 2320-3617, Vol. 2, no 1, p. 21-26Article in journal (Other academic)
    Abstract [en]

    Base station antenna tilt is a powerful tuning parameter in traditional cellular network optimization. With theintroduction of Self-Organizing Networks (SON), this parameter may now be used also in the context of self-optimization.One envisioned scenario is load balancing (LB), where the coverage shaping properties of the antenna radiation pattern canbe used to control the cell borders. In this paper, a generalized framework for antenna tilt LB is presented and discussed. Inorder to assess the performance of antenna tilt as a tool for load balancing, simulations are performed to determine theeffect of tilt angle, vertical beamwidth and handover offset. The results show that there is a direct relation between theseparameters and the number of users that can be shifted towards neighboring cells. In conclusion, it is found that usingantennas with narrow vertical beamwidths together with small hand over offsets is an efficient way of performing loadbalancing but results also in high SIR variations.

  • 89.
    Bratu, Vlad-Ioan
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Base station antenna tilt for load balancing2013In: 2013 7th European Conference on Antennas and Propagation (EUCAP), New York: IEEE , 2013, p. 2039-2043Conference paper (Refereed)
    Abstract [en]

    The coverage shaping and interference reduction ability of base station antenna tilt are important tools in cellular network optimization. Through tilt changes, the coverage area of a serving cell may also be either reduced or expanded. Therefore, antenna tilt has the potential to be used for load balancing purposes. This paper gives an overview of base station antennas performance and antenna tilt. Simulations are performed in order to determine the impact of tilt changes when used for load balancing. The results show that while antenna tilt load balancing can improve the Grade of Service (GoS) in a congested cell, it will also influence the user bit rates and total cell throughput for both the congested cell and the neighbors.

  • 90.
    Bratu, Vlad-Ioan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Base Station Antenna Tilt for Load Balancing and Potential use in Self-Optimizating Networks2013Conference paper (Other academic)
    Abstract [en]

    The coverage shaping and interference reduction ability of base station antenna tilt are important tools in cellular network optimization. Through tilt changes, the coverage area of a serving cell may also be either reduced or expanded. Therefore, antenna tilt has the potential to be used for load balancing purposes. With the introduction of Self-Organizing Networks (SON) in the mobile communications, this parameter may now be used also in the context of self-optimization, to address the common situation where traffic has an uneven spatial distribution between serving cells. This work gives an overview of base station antennas and antenna tilt. Simulations are performed in order to determine the impact of tilt changes when used for load balancing. The effect of tilt angle, vertical beam width and handover offset are analyzed also. The results show that there is a direct relation between these parameters and the number of users that can be shifted towards neighboring cells. In conclusion, it is found that using antennas with narrow vertical beam widths together with small hand over offsets is an efficient way of performing load balancing but results also in high SIR. Although antenna tilt load balancing can improve the Grade of Service (GoS) in a congested cell, it will also influence the user bit rates and total cell throughput for both the congested cell and the neighbors.

  • 91.
    Bria, Aurelian
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Rembarz, Rene
    Ericsson Research,.
    Pöyhönen, Petteri
    Nokia Siemens Networks.
    Simon, Csaba
    Technical University Budapest.
    Miozzo, Marco
    Consorzio Ferrara Ricerche.
    Akhtar, Nadeem
    University of Surrey.
    Jennen, Ralf
    RWTH Aachen University.
    Validation of the Ambient Networks System Architecture2007In: Proceedings of the Second International Conference on Communications and Networking in China, ChinaCom 2007, IEEE , 2007, p. 784-791Conference paper (Refereed)
    Abstract [en]

    The Ambient Networks project develops a complete and coherent solution for control architectures in future networks. In particular, the concept of Ambient Control Space has been proposed to support a technology-agnostic, modular and dynamic control plane. The second phase of the project (2006-2007) has an increased focus on validation, where two complementary tracks are being followed: proof-of- concept prototyping and performance evaluation through simulations. The prototype modules, focusing on requirement engineering, were validated during the process of integrating them into a common control space prototype, which was later used to build the demonstration setups. The system performance evaluation through simulations deals with aspects such as capacity utilization, reachability, cost and performance trade-offs and also provides evidence that the additional AN features (e.g., composition) do not introduce excessive signaling overhead. We target different composition aspects, advertising & discovery, negotiation of composition agreements and their interaction with multi-radio access and mobility control. Our validation approach is based on several use cases.

  • 92.
    Bui, Minh N.
    et al.
    Concordia University.
    Jaumard, Brigitte
    Concordia University.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Mukherjee, Biswanath
    University of California - Davis.
    Design of a survivable VPN topology over a service provider network2013In: 2013 9th International Conference on the Design of Reliable Communication Networks (DRCN), IEEE conference proceedings, 2013, p. 71-78Conference paper (Refereed)
    Abstract [en]

    Survivability in IP-over-WDM networks has alreadybeen extensively discussed in a series of studies. Up to date,most of the studies assume single-hop working routing of trafficrequests. In this paper, we study the multi layer survivable designof a logical topology in the context of multiple-hop workingrouting for IP layer traffic requests. The design problem iscomposed of two problems which are simultaneously solved:(i) Finding the most efficient or economical multi-hop routingof the IP traffic flows with different bandwidth granularitiesover the logical topology, which involves some traffic grooming,(ii) Ensuring that the logical topology is survivable throughoutan appropriate mapping of the logical links over the physicaltopology, if such a mapping exists.In order to solve such a complex multi layer resilient networkdesign problem, we propose a column generation ILP model. Itallows exploiting the natural decomposition of the problem andhelps devising a scalable solution scheme.We conducted numerical experiments on a German networkwith 50 nodes and 88 physical links. Not only we could solve muchlarger data instances than those published in the literature, butalso observe than multi-hop routing allows a saving of up to 10%of the number of lightpaths, depending on the traffic load.

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    DRCN-2013
  • 93. Buysse, Jens
    et al.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    De Leenheer, M.
    Dhoedt, B.
    Develder, Chris
    Improving energy efficiency in optical cloud networks by exploiting anycast routing2011In: NETWORK ARCHITECTURES, MANAGEMENT, AND APPLICATIONS IX / [ed] Wosinska, L; Sato, KI; Wu, J; Zhang, J, SPIE - International Society for Optical Engineering, 2011, p. 1-6, article id 83100XConference paper (Refereed)
    Abstract [en]

    Exploiting anycast routing significantly reduces optical network and server energy usage. In this work we present a case study showing that intelligently selecting destinations and routes thereto, while switching off unused (network) elements, cuts power consumption by around 20% and saves network resources by 29%.

    Download full text (pdf)
    fulltext
  • 94.
    Celik, Haris
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    On the feasibility of blind dynamic TDD in ultra-dense wireless networks2015In: IEEE Vehicular Technology Conference, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Abstract-Dynamic configuring of uplink and downlink switching point in time division duplex (TDD) systems is considered a promising solution to cope with the traffic variations caused by the burstiness of mobile broadband data. However, such dynamic TDD (D-TDD) requires fast inter-cell coordination which may be difficult to implement in ultra-densely deployed networks (UDNs). In order to explore the possibility of designing simplified UDN, we investigate the feasibility of uncoordinated and greedy TDD operation, namely blind D-TDD. It exploits the characteristics of UDN such as low average network utilization and similar transmit power for base stations (BS) and user equipment (UE). To reduce the impact of co- channel interference (CCI), the effect of beamsteering is also evaluated. Our results indicate that blind D-TDD outperforms traditional static TDD (S-TDD) when instantaneous traffic demands for uplink and downlink are highly asymmetric. Also, beamsteering exerts a significant influence on the feasibility of blind D-TDD.

  • 95.
    Châtaignier, Arnaud
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ahmed, Ashraf Awadelkarim Widaa
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Teslenko, Maxim
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Regulation development on licensed shared access and TV white spaces2014In: Der Open-Access-Publikationsserver der ZBW, Brussels: ITS , 2014Conference paper (Other academic)
    Abstract [en]

    For several years, the demand for data has increased. Furthermore, this is a growing trend. There are three ways to meet this demand. One option is to make the network denser; this implies large investments. We can work on improving the bandwidth efficiency; unfortunately, the channel limit is about to be reached[1]. Finally, the bandwidth allocated to telecommunication can be enlarged. Indeed, there are large spaces on spectrum which have been underused by the army or by the TV broadcasters. These players employ only a part of their allocated frequencies or use them only in a restricted area or time. Thus, regulatory frameworks are under construction to allow second users to exploit the locally unused frequencies without harming the incumbent. The two most advanced projects in this area are Licensed Share Access (LSA) and TV White Spaces (TVWS). Under LSA, an agreement is settled between an incumbent who underuses its spectrum (e.g: the Army) and one to several second users (share licensees). The agreement states, among other things, the area where the share licensees can deploy their networks and the conditions leading to its termination. In the case of TVWS, which takes advantage of the locally unused TV frequencies, the number of second users is unlimited and there is no direct contract with the incumbents (TV broadcasters and PMSE1 ). Instead, second users have to obtain the regulator authorization. Concretely, second users inform a database of their localization and the characteristics of their devices and will get in return available channels and power limitations. Even if there is a common understanding of these regulatory frameworks, regulators[2][3] are still working on the definition. This paper aims at presenting in several countries the trends in the regulation of TVWS and LSA. Aspects such as normalization, authorized uses, and allocated bandwidths will be highlighted. From this overall regulatory picture, this research will provide insight on the business development around TVWS and LSA.

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    fulltext
  • 96.
    Dahlberg, Christian
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Liu, Zhicheng
    KTH, School of Electrical Engineering (EES). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Pradini, Aidilla
    KTH, School of Electrical Engineering (EES). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    A Techno-Economic Framework of Spectrum Combining for Indoor Capacity Provisioning2013In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), IEEE conference proceedings, 2013, p. 2759-2763Conference paper (Refereed)
    Abstract [en]

    Spectrum combining refers to utilizing multiple types of spectrum authorization options for a wireless network. The approach is considered as an essential ingredient of high-capacity provision in the coming years. This paper presents a techno-economic framework to analyze capacity and cost of different spectrum combining options. We focus on indoor environments where the traffic demand is expected to be extremely demanding. We describe various spectrum options such as licence-exempt, light licensing, and licensed shared access (LSA). Then, we compare various combinations of these options with increasing traffic demand over time. In terms of capacity provisioning, this framework is based on the idea that spectrum combining must be done at the right time, that is when the existing deployment can no longer satisfy capacity demand. For the cost analysis, most relevant cost drivers are included in a cost structure which becomes the backbone of this framework. The proposed framework can help network providers determine the most cost-effective spectrum acquisition strategy which can meet capacity demand in indoor environments.

  • 97. Darrell, T. J.
    et al.
    Yeh, T.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Photo-based mobile deixis system and related techniques2004Patent (Other (popular science, discussion, etc.))
  • 98.
    Devlic, Alisa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab).
    Lungaro, Pietro
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Kamaraju, Pavan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab).
    Segall, Zary
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Energy consumption reduction via context-aware mobile video pre-fetching2012In: Proceedings - 2012 IEEE International Symposium on Multimedia, ISM 2012, IEEE , 2012, p. 261-265Conference paper (Refereed)
    Abstract [en]

    The arrival of smartphones and tablets, along with a flat rate mobile Internet pricing model have caused increasing adoption of mobile data services. According to recent studies, video has been the main driver of mobile data consumption, having a higher growth rate than any other mobile application. However, streaming a medium/high quality video files can be an issue in a mobile environment where available capacity needs to be shared among a large number of users. Additionally, the energy consumption in mobile devices increases proportionally with the duration of data transfers, which depend on the download data rates achievable by the device. In this respect, adoption of opportunistic content pre-fetching schemes that exploit times and locations with high data rates to deliver content before a user requests it, has the potential to reduce the energy consumption associated with content delivery and improve the user's quality of experience, by allowing playback of pre-stored content with virtually no perceived interruptions or delays. This paper presents a family of opportunistic content pre-fetching schemes and compares their performance to standard on-demand access to content. By adopting a simulation approach on experimental data, collected with monitoring software installed in mobile terminals, we show that content pre-fetching can reduce energy consumption of the mobile devices by up to 30% when compared to the on demand download of the same file, with a time window of 1 hour needed to complete the content prepositioning.

  • 99.
    Devlic, Alisa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab).
    Lungaro, Pietro
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Segall, Zary
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Evaluation of energy profiles for mobile video prefetching in generalized stochastic access channels2014In: Mobile and Ubiquitous Systems: Computing, Networking, and Services: 10th International Conference, MOBIQUITOUS 2013, Tokyo, Japan, December 2-4, 2013, Revised Selected Papers, Springer, 2014, p. 209-223Conference paper (Refereed)
    Abstract [en]

    This paper evaluates the energy cost reduction of Over-The-Top mobile video content prefetching in various network conditions. Energy cost reduction is achieved by reducing the time needed to download content over the radio interface by prefetching data on higher data rates, compared to the standard on demand download. To simulate various network conditions and user behavior, a stochastic access channel model was built and validated using the actual user traces. By changing the model parameters, the energy cost reduction of prefetching in different channel settings was determined, identifying regions in which prefetching is likely to deliver the largest energy gains. The results demonstrate that the largest gains (up to 70%) can be obtained for data rates with strong correlation and low noise variation. Additionally, based on statistical properties of data rates, such as peak-to-mean and average data rate, prefetching strategy can be devised enabling the highest energy cost reduction that can be obtained using the proposed prefetching scheme.

  • 100.
    Dinc, Ergin
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Vondra, Michal
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Multi-user Beamforming and Ground Station Deployment for 5G Direct Air-to-Ground Communication2017In: Globecom 2017 - 2017 IEEE Global Communications Conference, Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    On-board of aircraft is one of the last venues without high-speed connectivity, which makes it an important problem to address for both industry and academia. To this end, direct air-to-ground communications (DA2GC), where communication link is provided via direct link between aircraft and ground station, is a promising solution to provide high capacity and low latency backhaul capacity for aircraft. In this paper, we investigate the ground station deployment problem to provide 1.2 Gbps average backhaul capacity for each aircraft. The feasible operation points for the key network parameters: the number of ground stations, antenna array size, transmit power and bandwidth, are calculated. In addition, we propose a multi-user beamforming algorithm for dual-polarized hybrid DA2GC antenna arrays, and derive a tractable expression for the DA2GC cell throughput.

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