Showing papers by "Deutsche Telekom published in 1997"

Multitone signals with low crest factor

Abstract: After an introductory discussion of real-valued and complex signals, it is shown that minimizing the crest factor (CF) of multitone signals is closely related to the construction of complex sequences with low sidelobes in their aperiodic autocorrelation function. Inspired by this observation, a lower bound on the achievable CF is derived. Four differing algorithms for the reduction of the CF of complex multitone signals are compared with each other by computer simulation. The preferred algorithm is presented in detail, and its convergence is proven. Examples of multitone signals with up to 15 tones and lower CF than previously reported in the literature are given.

Comparison between adaptive OFDM and single carrier modulation with frequency domain equalization

Abstract: The aim of the paper is to compare multicarrier and single carrier modulation schemes for radio communication systems. In both cases the fast Fourier transform (FFT) and its inverse are utilized. In the case of OFDM (orthogonal frequency division multiplexing), the inverse FFT transforms the complex amplitudes of the individual subcarriers at the transmitter into the time domain. At the receiver the inverse operation is carried out. In the case of single carrier modulation, the FFT and its inverse are used at the input and output of the frequency domain equalizer in the receiver. Different single carrier and multicarrier transmission systems are simulated with time-variant transfer functions measured with a wideband channel sounder. In the case of OFDM, the individual subcarriers are modulated with fixed and adaptive signal alphabets. Furthermore, a frequency-independent as well as the optimum power distribution are used.

Method for securing system protected by a key hierarchy

Abstract: A method for securing a system protected by a predefined hierarchy of cryptographic keys, and in particular, for securing a pay TV system, against unauthorized users. An individual cryptographic key assigned to a dishonest customer is determined by forming the intersection of at least two predefined subsets formed at different points in time and pertaining to the same hierarchical level.

The dependence of electromagnetic energy absorption upon human-head modeling at 1800 MHz

Abstract: The authors of a previously published paper on the dependence of electromagnetic (EM) energy absorption concluded that homogeneous modeling of the human head is suited for assessing the spatial-peak absorption for transmitters operating at 900 MHz or below. Additional studies became necessary for the frequency bands utilized by new mobile communications systems (i.e., 1.5 and 2.5 GHz) since some peripheral tissue layers have a thickness of the range of /spl lambda//4-/spl lambda//2. The results of the simulations combined with worst-case considerations confirmed the anticipated and more complex relationship between absorption and anatomical details at these higher frequencies. Nevertheless, a homogeneous representation of the head is suited for assessing the maximum specific absorption rate (SAR) in the head of the user of mobile telecommunication equipment (MTE) if the appropriate dielectric parameters are chosen.

Optical multi-channel separating filter with electrically adjustable photon crystals

Abstract: The invention relates to the structure of optical multi-channel separating filter based on electrically adjustable photon crystals. According to the invention, an electrically and/or light-adjustable filled photon crystal is used as an adaptable mirror. The properties of the photon crystal relating to their optical transmissibility can be influenced in selected regions by deliberate optical deformations in the photon crystal. This is preferably done by the application of a strong electric field. The light is coupled or decoupled via fixed photon mirrors arranged at an angle to the photon crystals. The optical separators of the invention are used in message switching technology networks. They facilitate service selection. The system of the invention is designed for very high packing density.

Diversity and equalization in frequency domain a robust and flexible receiver technology for broadband mobile communication systems

Abstract: A new receiver structure for broadband mobile communication systems is presented. Signals with block oriented single-carrier modulation are processed in frequency domain. By using a combination of diversity and equalization, an excellent receiver performance can be achieved even for time-variant and frequency-selective radio channels.

Rotation of the polarization plane in optical fibers

Abstract: The rotation of the polarization plane of a light wave traveling in an optical fiber that lies on a space curve based on parallel transport is described. An estimation of the effect due to winding the fiber is presented.

Symmetrical dispersion compensation for standard monomode-fiber-based communication systems with large amplifier spacing.

Abstract: Optical 10-Gbit / s return-to-zero pulse transmission in cascaded communication systems using dispersion compensation of the standard monomode fiber with large amplifier spacing is examined. It is shown that pulse distortions that are due to Kerr nonlinearity are significantly diminished by symmetrical ordering of the compensation sections when the total number of precompensation and postcompensation sections is equal. Repositioning of these sections is not critical.

Cascaded optical communication systems with in-line semiconductor optical amplifiers

Abstract: The optimization of the performance of installed standard-monomode fibers based optical transmission systems with in-line semiconductor optical amplifiers (SOA's) is reported in this paper. Both solitons and nonreturn-to-zero (NRZ) signals are studied and their capacities are compared. This investigation is based on numerical simulations by solving the nonlinear Schrodinger equations with the split-step method while the SOA is simulated with two different models that we show to be in a good agreement, transmissions over distances of the order of several hundreds of kilometers are shown to be possible, and very long distances can be reached especially if in-line sliding filters are used.

Performance of optimized routing in LEO intersatellite link networks

Abstract: An ATM based routing concept for LEO intersatellite link networks is proposed. The challenges arising from the complex time-variant ISL network topology are tackled by a discrete-time network model and routing procedure. The approach is based on the combination of a modified standard routing scheme and the ATM VPC concept. The routing scheme works completely off-line, i.e. prior to system operation. In a first step, a virtual topology is set up for all successive time intervals, providing instantaneous sets of alternative VPCs (paths) between all source-destination satellite pairs. In the second step, path sequences over a series of time intervals are chosen from that according to a certain optimization procedure. Two different optimization procedures are discussed in detail, and a numerical performance evaluation is presented for telephony service in an example ISL network (Iridium). The overall routing performance is evaluated in terms of remaining delay jitter due to inevitable path handover. The results show that optimized routing strategies are specifically capable of minimizing severe delay jitter, and thus in turn reduce the complexity of ATM based operation in a connection-oriented service environment.

Unrepeatered 40 Gbit/s RZ single channel transmission over 150 km of standard singlemode fibre at 1.55 [micro sign]m

Abstract: Unrepeatered 40 Gbit/s RZ single channel transmission over 150 km of standard singlemode fibre at 1.55 /spl mu/m is reported using passive dispersion compensation. The authors investigate the influence of signal power, the compensation scheme, and the word length. Error-free transmission (BER=10/sup -9/) is achieved with a receiver sensitivity of -27 dBm. Post-compensation allows for higher input powers and therefore for a higher system margin.

Robust voice-activity detection based on the wavelet transform

Abstract: This paper describes a new approach to voice-activity detection (VAD) which is based on the wavelet transform (WT). The algorithm utilizes the WTs flexibility in the time-frequency resolution to compute robust parameters for VAD decision. Furthermore, it exhibits a low complexity and can be easily adapted to operate as a pre-processor for many speech-coding algorithms. Two versions of the wavelet-transform-based VAD (WT-VAD) are tested against the VAD of the ITU-T G.729 Annex B (G729) and the VAD of the GSM enhanced full-rate codec (GSM), respectively. For a variety of background-noise types the WT-VAD shows superior noise robustness to signal-to-noise ratios above 10 dB.

AGGREGATION ERROR EFFECTS ON THE DISCRETE-SPACE p-MEDIAN MODEL: THE CASE OF EDMONTON, CANADA

Abstract: The spatial analysis literature recognizes three sources of aggregation error, termed Source A, Source B, and Source C, which affect models relying on distance measurements between populations and facilities. We consider these effects with respect to aggregating from census enumeration areas to census tracts, on a popular location model. We identify a further source of aggregation error, which we dub Source D error, arising from the representation of facility sites by discrete points. Source D effects are of the same magnitude as Source A and B combined, much greater than Source C effects. Source D error is further significant, because, unlike Source A and B error, it can be eliminated only by disaggregating. La litterature sur Vanalyse spatiale reconnait trois sources d'erreur d'agregation appelees erreurs de source A, B, et C. Ces erreurs influencent les modeles qui reposent sur des mesures de distance entre des populations et des installations. On considere les effets d'agregation des secteurs de denombrement en secteurs de recensement sur un modele de localisation courant. On identifie une quatrieme source d'erreur d'agregation appelee erreur de source D. Cette erreur decoule de la representation des sites des installations par des points discrets. Ses effets sont du meme ordre de grandeur que ceux des sources A et B combinees et beaucoup plus grands que les effets de source G. L'erreur de source D est d'autant plus significative a cause du fait que, contrairement aux erreurs de source A et B, elle ne peut etre eliminee que par la desagregation.

A device for inputting data

Abstract: The device comprises a grid of photodetectors which is coordinated with a grid of light-emitting picture elements. The light emitted by at least one of the picture elements is reflected to at least one of the photodetectors when an object approaches the device. The output signals produced by the photodetectors indicate which of the photodetectors have received reflected light.

Method of determining traffic data by means of mobile radio telephones

Abstract: The invention concerns a method of determining traffic data from vehicles which are each equipped with at least one decentralized unit having at least one mobile communication function and a function for obtaining time information as well as a storage facility. At least one central unit with control and processing functions is associated with a plurality of decentralized units. During travel, the decentralized unit receives and evaluates data characterizing the cells, and other radio and transmission data. Data characterizing a change of cell are recorded together with time marks.

Method and device for the remote operation and remote control of systems and apparatus via a telephone network

Abstract: The invention concerns a method wherein the establishment of connections between the base station and the adapters is made dependent on a unilateral authentication process. Before making his DTMF (dual tone multi-frequency dialling) selection, the user identifies himself with respect to the base station using coded data which comprise a 'key' and a 'secret' and are tested there for conformity with stored data concerning authorized persons. If conformity exists, readiness for connection to an adapter is acknowledged by means of a first ready signal. It is only then that, in a similarly coded manner, the adapter and type of actuation, which are acknowledged by status signals or a further ready signal, are selected. The method even enables critical functions with greater demands as concerns security to be remotely controlled via the public telephone network, for which dedicated lines would otherwise be necessary.

Pan-European optical networking using wavelength division multiplexing

Abstract: The development of the information society will require the introduction of high-capacity transport networks with high performance and low cost. There are currently two ACTS (Advanced Communications Technologies and Services program launched by the European Commission) projects addressing specifically the problem of trans-European optical transport networks using WDM (wavelength division multiplexing). Important issues addressed are the high capacity transmission on existing fiber infrastructure and the introduction of flexibility in the network through the use of optical cross-connects. If these networks become a reality, they could drastically change the evolution of both telecommunication and computer networking because of their transparency and the abundance of inexpensive bandwidth.

Position assignment in digital cellular mobile radio networks (e.g. GSM) derived from measurements at the protocol interface

Abstract: Measurements are carried out at the protocol interface between base transceiver station and base station controller unit for optimization of the base station subsystem in an existing digital mobile network. At this interface it is possible-in contrast to measurements at the air interface-to gain mass data (e.g. received power, BER, signaling information) with low expenditure. The collected data allow however, only for a very rough estimation of the terminal positions. In this paper a method is presented to assign measurement data from the protocol interface to the related location of the mobile with the aid of field strength prediction. The application of the position assignment method is demonstrated within the GSM network. To validate this approach measurements were taken from the German GSM D1 net and were compared with exact position assignments by means of GPS. On the base of location assignment methods there are new experimental possibilities available, e.g. identification of traffic hot spots or areas of bad interference conditions.

Method for the mechanical stabilization and for tuning a filter having a photonic crystal structure

Abstract: A method for mechanically stabilizing and for tuning a filter having a photonic crystal structure The cavities of the filter fabricated as a photonic crystal structure are filled with optically transparent material having an adjustable refractive index. The optical properties of the filter and, thus, the filtering action are adjusted by way of an electric field having a variable field strength. It is possible to produce small-dimensioned, narrow-band filter elements, which are finely tunable and tunable within a broad range, and to realize them as filter elements which are integrated with a high packaging density.

Method and device for checking accuracy of call data records in telecommunications systems

Abstract: A method and device for checking a telecommunication system ( 4 ) with respect to an accurate routine detection of system-internal call data records ( 13, 14 ). Various communications connections are established and later terminated between two subscriber stations ( 2,3 ) via the telecommunication system ( 4 ) on the basis of predefined communication parameters; further call data records ( 10 a ,10 b ) are independently prepared and saved from these communications connections at both of these subscriber stations ( 2,3 ); and the system-internal call data records ( 101013 ) for said communications connections that are routinely created by the telecommunications system ( 4 ) itself, are compared to the further call data records ( 10 a , 10 b ).

Uplink performance of a multicarrier-CDMA mobile radio system concept

Abstract: Currently the air interface of future mobile radio systems is the topic of worldwide investigations. In this context CDMA (code division multiple access) seems to be a promising candidate as an element of the air interface of future mobile radio systems. The combination of OFDM (orthogonal frequency division multiplexing) and CDMA for mobile radio transmission has been proposed by several authors for the downlink. So far, the more elaborate uplink of such OFDM-CDMA mobile radio concepts has only been the topic of few publications, since channel estimation and data detection are more complex than in the downlink. The uplink of an OFDM-CDMA mobile radio concept is investigated. A pilot tone based channel estimation technique is proposed and several detection techniques suitable for the approach are described. Simulation results are shown for the case of a single receiver antenna as well as for dual receiver antenna diversity. The simulation results indicate that the proposed concept is well suited for future mobile radio systems.

Method for the transmission of digital signals

Abstract: A method for the transmission of digital signals, particularly in the AM bands (broadcasting bands), with high-level modulation, preferably 32 APSK or 64 APSK, being used for data blocks to be transmitted. At the receiving end, time-periodic measurements of a noise are carried out and noise signals determined therefrom are subtracted from received signals.

Traffic data selection and filtering method

Abstract: The invention concerns a method of selecting and filtering traffic data in a mobile radiotelephone-assisted traffic data service. According to the invention, the traffic data are collected and prepared in a traffic-editing section of a central office and, depending on the extent of information desired, the user can select different retrieval modes as desired via a suitable mobile radiotelephone terminal and thus retrieve different traffic data from the central office. The information content of the traffic data retrieved is prepared by the central office specifically for the particular user, taking account of the location of the user at any given moment and/or the indication of a destination, and by specific filtering.

Verfahren zur routenplanung und zielführung von fahrzeugen

Abstract: Die Erfindung betrifft ein Verfahren zur Routenanfrage und Zielfuhrung von Fahrzeugen unter Anwendung eines oder mehrerer Ortungsverfahren, eines in Form einzelner Wegesegmente in einer Zentrale elektronisch gespeicherten Wegenetzes und eines in der Zentrale angesiedelten Routenplanungs- und/oder Optimierungsmoduls. Das Verfahren is dadurch gekennzeichnet, dass ein Mobilkommunikationssystem, bestehend aus Mobilfunk-Netz und Mobilfunk-Endgeraten verwendet wird, in der Zentrale eine Routenplanung auf Benutzeranfrage stattfindet, wobei die Routenplanung nach anfrage- und/oder fahrzeug- und/oder benutzerindividuellen Optimierungskriterien erfolgt, in der Zentrale eine Zielfuhrungswurzel generiert wird, in welcher als wichtige Information eine routenindividuelle Verkettung und Sequenz von Wegesegmenten enthalten ist, in der Zentrale aus der Zielfuhrungswurzel und Zusatzinformationen eine individuelle Routenbeschreibung generiert wird, welche zum Endgerat ubertragen und dort weitgehend autark abgearbeitet wird.

Method and device for accurately dating an electronic document

Abstract: In a method for verifying the instant that a transaction is implemented or that a document is created, signed, sent and/or received, it is provided for a time marker to be inserted into the document in a tamper-proof manner, and for the time marker to correspond to a time stamp taken from a non-adjustable clock. An arrangement for performing the method is also provided.

Verfahren und Anordnung zur Information mobiler Teilnehmer

Abstract: Beschrieben wird ein Verfahren zur Information mobiler Teilnehmer, wobei auf Anfrage und/oder automatisch Daten zwischen einer Zentraleinheit und einer mobilen Teilnehmereinheit ubertragen werden. Ebenso wird eine Anordnung zur Information mobiler Teilnehmer beschrieben, wobei mindestens eine Zentraleinheit sowie mindestens mehrere mobile Teilnehmereinheiten vorgesehen sind.

Degradation of multicarrier and single carrier transmission with frequency domain equalization due to pilot-aided channel estimation and frequency synchronization

Abstract: The performance of multicarrier and single carrier modulation schemes is compared for wideband mobile radio communication systems. In both cases the fast Fourier transform (FFT) and its inverse are utilized. The transmission systems are simulated with time-variant transfer functions measured with a wideband channel sounder. In case of OFDM, the individual subcarriers are modulated with fixed and adaptive signal alphabets. In particular, the systems are compared with respect to the degradation due to pilot-aided channel estimation and carrier frequency synchronization.

Picture-transmitting remote object inspection system

Abstract: A remote object inspection system has a picture-taking system arranged at the site of the object (43) to be examined, an observation station located at a distance therefrom for evaluating the pictures and remote controlling the picture-taking system, and an intermediate, narrow band telecommunication path of transmission (7). According to the invention, a unit (42) for determining the state of the system constantly detects the total, picture transmission-relevant state of the system and automatically controls the picture data compression and/or reduction and/or the number of telecommunication channels used in a transmission bundle depending on the detected data, in order to achieve the desirable picture quality in the momentary situation and the best possible on-line picture appearance. The invention has applications for example in telemicroscopy, tele-endoscopy and telesonography.

Method and switching device for billing in telecommunications networks

Abstract: An administratively optimized process and/or system for metering communication tariffs which—with the aid of a flat-rate-calculating computer, which is connected to an associated exchange for customer terminals—carries out automatic administratively optimized metering of communication tariffs. Such automatic, administratively optimized metering of communication tariffs is suitable both for digitized, as well as for analog communication networks, implemented as wire-bound, radio-based or laser-assisted, terrestrial or satellite networks. Each terminal is connected to a communication meter which is sealed or otherwise protected against manipulation and can be read off using telemetry or, when prompted, by the customer using a special meter-reading card. The flat-rate-calculating computer processes the information pertaining to consumed volumes of information in three ways. First, it compares the current values with the specified process breadths and, if process alarm limits have been exceeded, generates a process alarm; it checks the current consumption values for a possible trend development and generates an indicator alarm in response to a limit-value exceeding trend. It stores the charge information, process behavior and alarms in a system memory for documentation purposes. At a predetermined time or if there is a special need, it calculates a new flat-rate value which corresponds to the changed communication behavior of the particular customer or group of customers. For the purpose of control, the flat-rate-calculating computer is connected to an operator terminal having a record printer.