Conference Papers

Overview

• M. Schnell, M. Werner, "Comparison Between Different Transmission Schemes for Mobile Radio Channels", Proc. of ISSSE'92, Paris, France, September 1992, pp. 705-70

• A. Wilde, M. Schnell, "Adaptive Resource Sharing for Satellite TDMA", Proc. of ECSC-3, Manchester, United Kingdom, November 1993, pp. 306-308
  

• M. Schnell, "Hadamard Codewords as Orthogonal Spreading Sequences in Synchronous DS CDMA Systems for Mobile Radio Channels", Proc. of ISSSTA'94, Oulu, Finland, July 1994, pp. 505-509

• M. Schnell, A. Wilde, "Adaptive Resource Sharing for Satellite TDMA", Proc. of PIMRC'94, Den Haag, The Netherlands, September 1994, pp. 1188-1191

• M. Schnell, A.J. Han Vinck, "Low Complexity Equalization with an Efficient Coding Scheme for Broadband Mobile Radio Systems", Proc. of Globecom'94, San Francisco, California, November 1994, pp. 16-21

• M. Schnell, "Interference Calculations for MC-SSMA Systems in Mobile Communications", Proc. of PIMRC'95, Toronto, Cananda, September 1995, pp. 158-163

• U.-C. Fiebig, F. Dolainsky, H. Reinel, M. Schnell, "Attenuation Measurements of the 40 GHz Beacon Signal of ITALSAT", Proc. of CEPIT'95, Rome, Italy, October 1995

• M. Schnell, S. Kaiser, "Diversity Considerations for MC-SSMA Systems in Mobile Communications", Proc. of ISSSTA'96, Mainz, Germany, September 1996, pp. 131-135

• U.C. Fiebig, M. Schnell, "40 GHz Measurement Campaign - Evaluation with Respect to System Design and Fade Countermeasures", Proc. of ECSC-4, Rome, Italy, November 1997, pp. 199-204

• U. Sorger, I. De Broeck, M. Schnell, "Interleaved FDMA - A New Spread-Spectrum Multiple-Access Scheme", Proc. of 1st Int. Workshop on Multi-Carrier Spread-Spectrum edited by K. Fazel and G.P. Fettweis, Kluwer Academic Publishers, Dordrecht 1997

• U. Sorger, I. De Broeck, M. Schnell, "Interleaved FDMA - A New Spread-Spectrum Multiple-Access Scheme", Proc. of ICC'98, Atlanta, Georgia, June 1998, pp. 1013-1017

• M. Schnell, I. De Broeck, "Application of IFDMA to Mobile Radio Transmission", Proc. of ICUPC'98, Florence, Italy, October 1998, pp. 1267-1272

• U.-C. Fiebig, M. Schnell, "Impact of Rain Attenuation on Satellite Broadcasting Systems at Ka-Band", Proc. of First Int. Workshop on Radiowave Propagation Modeling for Satcom Services at Ku-Band and Above, Noordwijk, The Netherlands, October 1998, pp. 261-265
  

• M. Schnell, I. De Broeck, "Interleaved FDMA: Equalization and Coded Performance in Mobile Radio Applications", Proc. of ICC'99, Vancouver, British Columbia, Canada, June 1999, pp. 1939-1944

• E. Haas, M. Schnell, "Development and Implementation of an Advanced Airport Data Link Based on Multi-Carrier Communications", Proc. of Third Int. Workshop on Multi-Carrier Spread-Spectrum edited by K. Fazel and S. Kaiser, Kluwer Academic Publishers, Dordrecht 2001

• E. Haas, M. Schnell, "Development of an Advanced Airport Data Link", Tagungsband Deutscher Luft- und Raumfahrtkongress, Hamburg, September 2001

• E. Haas, H. Lang, M. Schnell, "Development and Implementation of an Advanced Airport Data Link Based on Multi-Carrier Communications", Proc. of ISSSTA 2002, Prague, Czech Republic, September 2002, pp. 373-379

• E. Haas, M. Schnell, "Analysis of Compensation Methods for OFDM Implementation Effects", Proc. of WPMC 2002, Honolulu, Hawaii, USA, October 2002, pp. 1000-1004

• I. Cosovic, M. Schnell, "Time Division Duplex MC-CDMA for Next Generation Mobile Radio Systems", Proc. of TELFOR 2002, Belgrade, Yugoslavia, November 2002, pp. 216-219

• I. Cosovic, M. Schnell, A. Springer, "Combined Pre- and Post-Equalization for Uplink Time Division Duplex MC-CDMA in Fading Channels", Proc.  of Fourth Int. Workshop on Multi-Carrier Spread-Spectrum edited by K. Fazel and S. Kaiser, Kluwer Academic Publishers, Dordrecht 2004

• I. Cosovic, M. Schnell, A. Springer, "On the Performance of Different Channel Pre-Compensation Techniques for Uplink Time Division Duplex MC-CDMA", Proc. of VTC-Fall 2003, Orlando, Florida, USA, October 2003

• I. Cosovic, M. Schnell, A. Springer, "Pre-Compensation of Fading Channels for Uplink Time Division Duplex MC-CDMA Systems", Proc. of ECWT 2003, Munich, Germany, October 2003, pp. 51-54

• A. Arkhipov, M. Schnell, "The Influence of User Frequency Offset on the Up-link Performance of SS-MC-MA", Proc. of ECWT 2003, Munich, Germany, October 2003, pp. 451-454

• I. Cosovic, M. Schnell, A. Springer, "Countermeasures for Reducing the Influence of Frequency Offset on Uplink MC-CDMA", Proc. of WPMC 2003, Yokosuka, Japan, October 2003, pp. 171-175

• A. Arkhipov, M. Schnell, "Performance Evaluation of SS-MC-MA Up-link Transmission with User Frequency Offsets", Proc. of European Wireless 2004, Barcelona, Spain, February 2004, accepted for publication

• I. Cosovic, A. Arkhipov, M. Schnell, "Pre-Equalization in Combination with Transmit Diversity for OFDMA Code-Division Multiplexing Systems in Fading Channels", Proc. of VTC-Spring 2004, Milan, Italy, May 2004, accepted for publication

• I. Cosovic, M. Schnell, M. Dukic, A. Springer, "Analysis of the Performance Degradation in Uplink MC-CDMA Systems with Doppler Induced Frequency Offsets", Proc. of ICC 2004, Paris, France, June 2004, accepted for publication
  

Abstracts

• Comparison Between Different Transmission Schemes for Mobile Radio Channels

  In this paper direct-sequence (DS) spread-spectrum (SS) techniques with binary phase-shift keying (BPSK) modulation applied to mobile radio channels are investigated and compared with conventional narrowband and broadband BPSK on the basis of their bit error rate (BER). Considering idealized equivalent low-pass systems, lower bounds for the BERs, the so-called matched filter bounds (MFBs), are calculated. These as well as the corresponding BERs obtained by Monte Carlo simulations are used to compare the different transmission schemes. The results show that DS-SS signals are a suitable choice for a digital mobile radio transmission scheme. They exploit the multipath diversity due to the broadband transmission suppressing simultanously the intersymbol interference (ISI) to a very high extent. Thus, good error performance can be achieved without using, for example, a costly Viterbi equalizer in the receiver. Moreover, the simulations show that the MFBs are thight lower bounds in the case of DS-SS transmission.
  
  

• Hadamard Codewords as Orthogonal Spreading Sequences in Synchronous DS CDMA Systems for Mobile Radio Channels

  This paper addresses the question if orthogonal spreading sequences, especially Hadamard codewords, can improve the performance of synchronous direct-sequence code-division multiple-access systems applied in a mobile radio environment. For this purpose, the correlation properties of Hadamard codewords are determined and performance simulations are carried out. The results show, that Hadamard codewords have rather poor autocorrelation properties and very inhomogeous crosscorrelation properties ranging from excellent up to very poor depending on which codeword is considered. The performance simulations reveal a behaviour similar to the crosscorrelation properties. Using additional scrambling the autocorrelation properties are improved and the crosscorrelation properties are made more homogenous yielding performance results similar to those obtained for conventional spreading using Gold-codes or preferentially phased Gold-codes.
  
  

• Adaptive Resource Sharing for Satellite TDMA

  In this paper, a method to improve the link quality of a satellite TDMA network using adaptive resource sharing is presented. The TDMA network considered is an experimental 20/30 GHz satellite network operated via the german satellite DFS KOPERNIKUS. Adaptive resource sharing provides a means to distribute a common resource within a network. The common resource in a TDMA system is an additional time slot. This spare time is used for lowering the code rate and/or the data rate. This results in better link quality and/or better link availability. Another resource used is the uplink transmit power to compensate for uplink fades. This paper describes the adaptive resource sharing strategy and the uplink power control implemented in the experimental 20/30 GHz TDMA satellite network.
  
  

• Low Complexity Equalization with an Efficient Coding Scheme for Broadband Mobile Radio Systems

  In this paper, different low complexity equalization schemes applied to mobile radio channels are investigated and compared. Using Monte Carlo simulations for the bit error rates the performance losses of the different low complexity equalization schemes in comparison to ideal equalization represented by the matched filter bound are determined. It is shown, that considerable complexity reduction is possible with a performance loss of less than 1 dB under the assumption that the appropriate receiver structure is chosen. Moreover, a single-parity-check encoding scheme with low complexity soft decoding is presented which achieves a coding gain of about 2.8 dB at a bit error rate of P_b = 10^-4.
  
  

• Interference Calculations for MC-SSMA Systems in Mobile Communications

  The other-user interference of a Multi-Carrier Spread-Spectrum Multiple-Access system applying conventional detection is considered. The investigations refer to the synchronous uplink, i.e. the synchronous transmission from the mobile stations to the base station in a mobile communications system. Under the assumption of independent Rayleigh fading the probability density function of the interference signal is calculated analytically and it is shown that the resulting probability density function can be well approximated by a Gaussian distribution. Moreover, refering to the bit error rate formula for the single-user case a closed-form expression for the bit error rate in the case of other-user interference is derived using the Gaussian approximation method. The analytical results are validated by Monte-Carlo simulations.
  
  

• Attenuation Measurements of the 40 GHz Beacon Signal of ITALSAT

  This paper gives an overview of the attenuation measurement compaign for the 40 GHz beacon signal of ITALSAT carried out at the Institute for Communications Technology, DLR, Oberpfaffenhofen. The measurements currently focus on the 40 GHz beacon signal of ITALSAT. Furthermore, the 20 GHz beacon signal of DFS KOPERNIKUS is recorded. A short description of the experimental earth station and of the recording concept is given. Moreover, the statistical evaluation of the recorded data is described and some results are reported.
  
  

• Diversity Considerations for MC-SSMA Systems in Mobile Communications

  In this paper, the diversity gain achievable with MC-CDMA transmission in mobile communications is investigated. It is shown that only a certain amount of diversity is available depending on the transmission bandwidth and the transmission channel. For example, a diversity of about D=7 can be achieved for a typical mobile radio application. As a consequence, a modified MC-CDMA transmission scheme is investigated which allows the use of short spreading sequences, e.g. L=8 chips, without loosing diversity. Due to the short spreading sequences maximum likelihood multi-user detection can be applied at the receiver with acceptable effort. This detection strategy achieves a bit error rate of about 1x10^-3 in a system with maximum number of simultaneously transmitting users at a signal-to-noise ratio of 12 dB whereas for a simple detector applying equal-gain-combining the bit error rate is about 3x10^-2.
  
  

• 40 GHz Measurement Campaign - Evaluation with Respect to System Design and Fade Countermeasures

  The purpose of this contribution is to present results of the DLR propagation measurement campaign of the 40 GHz beacon of ITALSAT. The results are based on a two-years data collection. Presented are cumulative distributions of the attenuation, probability of outage, distributions of the fade slope and distributions of the 3 dB time duration where seasonal and diurnal variations are shown. The presented data is the basis for both system design and development of fade countermeasures.
  
  

• Interleaved FDMA - A New Spread-Spectrum Multiple-Access Scheme (MC-SS'97)

  In this paper, a new spread-spectrum multiple-access scheme applicable for both the uplink and the downlink of a mobile radio communications system is proposed, which is termed ``Interleaved Frequency-Division Multiple-Access''. This new scheme can be viewed as a special kind of a multicarrier spread-spectrum multiple-access scheme, since each user is assigned a different set of orthogonal frequencies. The orthogonality between the different users is maintained at the receiver, even in time-dispersive channels. Thus, there is no multiple-access interference. However, the cost to avoid multiple-access interference is to allow for intersymbol interference and therefore an equalization is required at the receiver. This article describes the new spread-spectrum multiple-access scheme as well as the optimum receiver structure.
  
  

• Interleaved FDMA - A New Spread-Spectrum Multiple-Access Scheme (ICC'98)

  In this paper, a new spread-spectrum multiple-access scheme applicable for both the uplink and the downlink of a mobile radio communications system is proposed, which is termed "Interleaved Frequency-Division Multiple-Access''. This scheme combines the advantages of spread-spectrum and multicarrier transmission. Moreover, it can be viewed as a special kind of a multicarrier spread-spectrum scheme where user discrimination is done using frequency-division multiple-access. The multiple-access capability is achieved by assigning to each user a different set of orthogonal subcarriers. The orthogonality between the different users is maintained at the receiver, even in time-dispersive channels resulting in no multiple-access interference. However, the cost to avoid multiple-access interference is to allow for intersymbol interference and therefore an equalization is required at the receiver.
  
  

• Application of IFDMA to Mobile Radio Transmission

  Recently, "Interleaved Frequency-Division Multiple-Access'' (IFDMA) has been introduced which is a new spread-spectrum multiple-access scheme showing several advantages over other multiple-access schemes. In this paper, the application of IFDMA to mobile radio transmission is considered. Especially, the frequency-diversity achievable with IFDMA taking into account the influence of pulse shaping is investigated. As a result, maximum diversity can be achieved with a set of IFDMA parameters which enables maximum-likelihood detection at the receiver. Therefore, maximum-likelihood detection is proposed for IFDMA and investigated using Monte-Carlo simulations. In comparison with multicarrier code-division multiple-access IFDMA shows an even better performance whereas having additional advantages, such as avoiding large crest factors.
  
  

• Interleaved FDMA: Equalization and Coded Performance in Mobile Radio Applications

  Recently, "Interleaved Frequency-Division Multiple-Access" (IFDMA) has been introduced as a new spread-spectrum multiple-access scheme for mobile communications. In this paper, performance results for uncoded and coded mobile radio transmission taking into account different equalization techniques are presented. As a result, equalization reduces the effects of intersymbol interference significantly. Uncoded IFDMA applying optimum equalization performs even better than uncoded multicarrier code-division multiple-access applying maximum-likelihood multi-user detection. Moreover, in the case of coded IFDMA transmission coding gains up to 6.8 dB at a bit-error-rate of 10^-4  are achieved using a standard convolutional code.
  
  

• Development and Implementation of an Advanced Airport Data Link Based on Multi-Carrier Communications

  In this paper, both the concept and the demonstrator implementation of an advanced airport data link is described. The proposed data link is used to establish the necessary data exchange for future surface movement guidance and control systems on airports and, therefore, is designed to be a high capacity, high rate data link.
  
  

• Development of an Advanced Airport Data Link

  In this paper, both the concept and the demonstrator implementation of an advanced airport data link is described. The proposed data link is used to establish the necessary data exchange for future surface movement guidance and control systems on airports and, therefore, is designed to be a high capacity, high rate data link.
  
  

• Development and Implementation of an Advanced Airport Data Link Based on Multi-Carrier Communications

  In this paper, both the concept and the demonstrator implementation of an advanced airport data link is described which is used for data exchange between pilots and controllers in future surface movement guidance and control systems on airports. To fulfil future airport capacity requirements, the proposed data link has to be a high capacity, high rate data link. Therefore, the data link design is based on multi-carrier code-division multiple-access which is a flexible and highly efficient multiple-access transmission technique suitable for mobile communications in fading conditions. Both simulation results with typical aeronautical channel scenarios and bit error rate measurements using the demonstrator hardware show the suitability of multi-carrier code-division multiple-access for aeronautical communications within the airport and its vicinity. Moreover, implementation effects which degrade the performance are identified and countermeasures are proposed and investigated. The results show that a reduction of the implementation loss of up to 2 dB is achievable by applying appropriate countermeasures.