University of Bremen

Displaying 1-40 of 53 results

  • White Papers // Feb 2014

    Detecting Hidden Encrypted Volume Files via Statistical Analysis

    Now-a-days various software tools have been developed for the purpose of creating encrypted volume files. Many of those tools are open source and freely available on the internet. Because of that, the probability of finding encrypted files which could contain forensically useful information has dramatically increased. While decoding these files...

    Provided By University of Bremen

  • White Papers // May 2012

    Compressive Sensing Multi-User Detection With Block-Wise Orthogonal Least Squares

    One challenging future application in digital communications is the wireless uplink transmission in sensor networks. This application is characterized by sporadic transmissions by a large number of sensors over a random multiple access channel. To reduce control signaling overhead, the authors propose that sensors do not transmit their activity states;...

    Provided By University of Bremen

  • White Papers // May 2012

    MTCLASS: Traffic Classification on High-Speed Links With Commodity Hardware

    Statistical traffic classification on high-speed, multi-Gb/s links has up to now been possible only with specialized, often proprietary, always quite costly hardware. In this paper, the authors present MTCLASS, a new, multi-threaded, modular Internet statistical traffic analysis engine capable of running in real-time on commodity hardware processing multi-Gb/s traffic aggregates....

    Provided By University of Bremen

  • White Papers // Jan 2012

    Improved HARQ Based on Network Coding and Its Application in LTE

    In this paper, a novel HARQ transmission scheme based on network coding is proposed for wireless unicast scenarios. Instead of retransmitting erroneous packets individually, a network coded packet constructed by the XOR of two erroneous packets is transmitted similar to network coding. In order to fully exploit the network coded...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Soft Information Relaying for Wireless Networks With Error-Prone Source-Relay Link

    Relays in wireless networks can be used to decrease transmit power while additionally increasing diversity. Distributed turbo coding as a special case of decode-and-forward is very powerful in relay networks when assuming error free decoding in the relay. In practical wireless networks, however, this assumption is only justiable if an...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Minimum MSE Relaying in Coded Networks

    In order to combine the advantages of Amplify-Forward (AF) and Decode-Forward (DF) in relay networks, several strategies have been developed making use of reliability information after decoding at the relay. The use of soft-output channel decoders enables forwarding reliability information for the decoded bits. This soft information can be forwarded...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Doppler-Compensation for OFDM Transmission by Sectorized Antenna Reception

    Rapidly time-varying channels are a major obstacle for successful data-transmission via OFDM. The resulting loss of orthogonality among neighboring subcarriers leads to inter-carrier-interference, which affects channel estimation. This in turn impedes the subsequent data detection. Literature contains numerous approaches to cope with this problem working either in time- or frequency-domain....

    Provided By University of Bremen

  • White Papers // Jan 2012

    A Doppler-Compensated Noncoherent OFDM-Transceiver With Sectorized Antenna Reception

    Frequency-selective fading channels are easily made use of by OFDM. Due to an increase of the symbol duration even channels with large delay spread can be utilized for data-transmission. However, if the channel additionally exhibits a large Doppler spread, a short symbol duration is desirable. Otherwise the channel's time-varying impulse...

    Provided By University of Bremen

  • White Papers // Jan 2012

    A Multiple-Symbol Turbo Detector for Coded M-DPSK Over Time-Varying Rayleigh Flat Fading Channels

    In the past few years, a number of publications concentrated on developing soft-in-soft-out algorithms for coded non-coherent detection, thereby enabling iterative processing and avoiding the need of channel estimation. This paper focuses on iterative non-coherent detection of convolutionally coded M- DPSK signals for time-variant Rayleigh flat fading channels without the...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Throughput Analysis of Per-Antenna Rate Control With Linear Chip-Level Equalization

    In this paper the achievable performance gains of Per-Antenna Rate Control (PARC) for Code Division Multiple Access (CDMA) transmission with different linear chip-level equalization algorithms are investigated. High Speed Downlink Packet Access (HSDPA) as a solution of a full packet-based transmission standard utilizes extensive multi-code operation especially in low-mobility scenarios....

    Provided By University of Bremen

  • White Papers // Jan 2012

    Performance Analysis of Maximum-Likelihood Semiblind Estimation of MIMO Channels

    Iterative channel estimation and data detection is a very useful method to improve the channel estimation quality without sacrificing the bandwidth efficiency. Since both the known training symbols (non-blind) and the unknown data symbols (blind) are used for channel estimation, corresponding techniques are referred to as semi-blind. If the channel...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Analysis of Semiblind Channel Estimation for FIR-MIMO Systems

    This paper deals with joint data detection and channel estimation for frequency-selective Multiple-Input Multiple-Output (MIMO) systems with focus on the analysis of the channel estimator. First, the authors present a scheme alternating between joint Viterbi detection and least squares channel estimation and analyze its performance in terms of unbiasedness. Since...

    Provided By University of Bremen

  • White Papers // Sep 2011

    Energy-Aware Design of Inter-Relay Cooperation for Distributed Relaying Networks

    The authors consider distributed relaying networks using Space-Time Block Codes (STBC) to exploit cooperative diversity. In order to mitigate the impact of error propagation for Decode-Forward (DF), an Inter-Relay Cooperation (IRC) scheme is proposed that allows message exchanges between the relays based on punctured channel codes. Specifically, one of the...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Relative Downlink Channel Calibration in OFDM Systems With CORDIC QR Decomposition

    Mismatched front-ends reduce the performance of precoding in multi-antenna OFDM systems, which results in a poor bit error rate. With a relative downlink channel calibration the transmission quality will be enhanced. An excellent calibration technique is based on a total least squares optimization problem. For the hardware implementation an efficient...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Effects of Downlink Channel Quantization on the Performance of Relative Calibration in OFDM Systems

    The application of calibration techniques mitigating the front-end impairments in adaptive multi-antenna TDD systems designed for very high data rates is of paramount importance. Excellent calibration purely based on signal processing can be achieved by means of relative calibration. There, additional estimated DL channel state information is required at the...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Enhanced Adaptive Downlink Transmission in MIMO-OFDM Systems by Hardware-Based Calibration

    In this paper, a hardware-based calibration scheme at the base station is used to mitigate the impact of the non-reciprocal transceivers in a Time Division Duplex (TDD) Multiple-Input-Multiple-Output Orthogonal-Frequency-Division-Multiplexing (MIMOOFDM) system. The calibration setup consists of two Single-Pole-Double-Throw (SPDT) switches to bypass the calibration and the data signals. Additionally, an...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Tracing Properties of UML and OCL Models With Maude

    The starting point of this paper is a system described in form of a UML class diagram where system states are characterized by OCL invariants and system transitions are defined by OCL pre- and post-conditions. The aim of the approach is to assist the developer in learning about the consequences...

    Provided By University of Bremen

  • White Papers // Jun 2011

    Decode-Quantize-Forward for OFDM-Based Relaying Systems

    In this paper, the authors present a new relaying protocol for coded OFDM-based relaying systems. The classical Decode-Forward (DF) protocol exploits the coding gain within the relay, however the overall performance suffers from error propagation in case of decodings errors at the relay as no reliability information about the Source-Relay...

    Provided By University of Bremen

  • White Papers // Jun 2011

    Two-Hop Relay-Systems With OFDM-IDM Space-Time Coding

    In mobile communication systems pathloss and shadowing are two of the main limiting factors. In order to overcome these effects, relaying has been identified as a very promising technique. In relay-systems additional nodes are introduced to the system, which are neither source nor destination of transmissions themselves. Instead their task...

    Provided By University of Bremen

  • White Papers // Apr 2011

    BER-Based Power Allocation for Decode-and-Forward Relaying With M-QAM Constellations

    In this paper, the authors develop a power allocation scheme for single-relay systems applying Decode-and-Forward (DF) based on the resulting Bit Error Rate (BER) at the destination. First, an analytical expression for the BER of M-QAM modulation considering estimation errors at the relay is derived. Based on this expression, the...

    Provided By University of Bremen

  • White Papers // Mar 2011

    Calibration for Single-Carrier PreFDE Transceivers Based on Property Mapping Principles

    In general, the unequal RF circuitry in the transmit and receive chains at the Base Station (BS) prevents the exploitation of the UpLink (UL) channel estimate for proper pre-equalization in Time Division Duplex (TDD) systems. To avoid additional transceiver hardware costs for matching networks, the idea of relative calibration was...

    Provided By University of Bremen

  • White Papers // Feb 2011

    Outage Capacity Based Link Adaptation for BICM-OFDM With Imperfect CSI

    Adapting the modulation, power and channel code to the current channel state for OFDM systems is an important topic for future wireless data transmission to fully utilize the given channel conditions. The consideration of practical channel codes in Link Adaptation schemes is still under investigation, especially if imperfect knowledge of...

    Provided By University of Bremen

  • White Papers // Feb 2011

    Bit and Power Loading for Optical IM/DD Transmission

    Orthogonal Frequency Division Multiplexing (OFDM) is an established technique for equalization of the dispersion-dominated fiber-optical channel. The dispersive nature of the optical channel results in a frequency selective equivalent channel if Double SideBand (DSB) Intensity Modulation (IM) and Direct Detection (DD) is employed. In order to maintain the all pass...

    Provided By University of Bremen

  • White Papers // Jan 2011

    BER-Based Power Allocation for Amplify-and-Forward and Decode-and-Forward Relaying Systems

    In this paper, power allocation schemes are proposed for the total transmit power of the source and the relay in a triplet relaying system based on Bit Error Rate (BER) analysis. Considering Amplify-and-Forward (AF), Decode-and-Forward (DF) for relaying systems and Direct Transmission (DT) without relay, the authors perform a fair...

    Provided By University of Bremen

  • White Papers // Dec 2010

    Security in Open Model Software With Hardware Virtualisation - The Railway Control System Perspective

    Using the openETCS initiative as a starting point, the authors describe how open software can be applied in combination with platform-specific, potentially closed-source extensions, in the development, verification, validation and certification of safety-critical railway control systems. They analyze the safety and security threats presented by this approach and discuss conventional...

    Provided By University of Bremen

  • White Papers // Nov 2010

    Proposed a Method for Increasing the Delivery Performance in Dynamic Supply Network

    Supply network management adopts a systematic and integrative approach to managing the operations and relationships of various parties in a supply network. The objective of the manufactures in their supply network is to reduce inventory costs and increase customer satisfaction levels. One way of doing that is to synchronize delivery...

    Provided By University of Bremen

  • White Papers // Sep 2010

    Power Allocation for Adaptive Asymmetric Distributed MIMO Networks

    Distributed MIMO network topology is one of the most promising technologies in modern communication networks. Compared to classical Single Input Single Output (SISO) links, where information is broadcasted from one sender over huge distances, the distance between two points in multi-hop networks is rather small. By means of such relay...

    Provided By University of Bremen

  • White Papers // Aug 2010

    Security in Open Model Software With Hardware Virtualization - The Railway Control System Perspective

    Using the openETCS initiative as a starting point, this paper describes how open software can be applied in combination with platform-specific, potentially closed source extensions, in the development, verification, validation and certification of safety-critical railway control systems. This paper analyses the safety and security threats presented by this approach and...

    Provided By University of Bremen

  • White Papers // Jul 2010

    Low-Complexity Calibration of Mutually Coupled Non-Reciprocal Multi-Antenna OFDM Transceivers

    In adaptive Time Division Duplex (TDD) broadcast multi-antenna Orthogonal Frequency Division Multiplexing (OFDM) systems, non-reciprocal transceiver chains at the Base Station (BS) cause multi-user interference. This is due to the inappropriate spatial filter design at the BS based on the reverse link estimate. Hence, BS transceiver calibration is required. Provided...

    Provided By University of Bremen

  • White Papers // Jul 2010

    Robust Link Adaptation Using SNR-Outage Based Loading for BICM-OFDM

    In order to increase the data rate or power efficiency of OFDM systems several adaptive strategies to select the power, modulation and even code rate on a per subcarrier basis have been discussed in literature. The underlying assumption of perfect Channel State Information (CSI) at the transmitter, however, is hardly...

    Provided By University of Bremen

  • White Papers // Jul 2010

    An Enhanced MIMO Hardware Demonstrator - Polarization Diversity in Adaptive OFDM Systems

    The performance of Multiple-Input Multiple-Output (MIMO) systems is affected by the spatial correlation properties, which depend on the array configuration and the channel characteristics. The configuration can be influenced by manipulating the radiation patterns of the antennas, the antenna spacing and the array geometry. To decrease the spatial correlation effects,...

    Provided By University of Bremen

  • White Papers // Mar 2010

    Quality Assessment for Listening-Room Compensation Algorithms

    In this contribution various objective measures that can be used to evaluate speech de-reverberation algorithms by means of Listening-Room Compensation (LRC) are compared to subjective listening tests. It is shown that technical measures describing the impulse responses are suitable for evaluation of such algorithms. Most signal-based objective measures fail to...

    Provided By University of Bremen

  • White Papers // Mar 2010

    Modeling and Formally Checking Workflow Properties Using UML and OCL

    In this paper a new metamodel for workflows is described by using UML. The underlying UML class diagram is formally extended with OCL pre- and postconditions for operations and OCL invariants for system states. The metamodel allows the developer to specify processes, activities in processes and temporal relations between them....

    Provided By University of Bremen

  • White Papers // Feb 2010

    Generalized Joint Channel Coding and Physical Network Coding for Two-Way Relay Systems

    In this paper, the authors present a generalized joint channel and physical layer network coding scheme for two-way relay systems, where the two sources A and B desire to exchange information from each other through the relay R simultaneously. Physical network coding scheme allows the relay to decode the network-coded...

    Provided By University of Bremen

  • White Papers // Feb 2010

    Comparison of Distributed LDPC Coding Schemes for Decode-and-Forward Relay Channels

    In order to approach the theoretical limit of the decode-and-forward strategy for the half-duplex relay channel, distributed LDPC coding schemes have been proposed. In these schemes, the code applied at the source should be decodable at the relay to yield correct parity bits. With the help of the parity bits...

    Provided By University of Bremen

  • White Papers // Feb 2010

    Iterative Pre-Compensation of I/Q Imbalances in an Adaptive 2.4 GHz MIMO-OFDM System

    Currently evolving communication standards, especially those using multi-antenna (MIMO) multicarrier modulation techniques, are based on the exploitation of Channel State Information (CSI) at the transmitter. The utilization of adaptive transmission schemes comes with a more sensitive behavior with respect to front-end imperfections. Direct-conversion architectures in turn allow for low-cost transceiver...

    Provided By University of Bremen

  • White Papers // Jan 2010

    Evaluation of Encoded MU-MISO-OFDM Systems in TDD Mode With Non-Ideal Channel Reciprocity

    In Multi-User Orthogonal Frequency Division Multiplexing (MU-OFDM) systems operating in Time Division Duplex (TDD) mode downlink pre-equalization can be applied relying on Channel State Information (CSI) from the uplink direction. Unfortunately, the prerequisite of channel reciprocity is usually not fulfilled due to non-reciprocal transceivers. Hence, this paper deals with a...

    Provided By University of Bremen

  • White Papers // Dec 2009

    Verifying UML/OCL Models Using Boolean Satisfiability

    Nowadays, modeling languages like UML are essential in the design of complex software systems and also start to enter the domain of hardware and hardware/software codesign. Due to shortening time-to-market demands, "First time right" requirements have thereby to be satisfied. This paper proposes an approach that makes use of Boolean...

    Provided By University of Bremen

  • White Papers // Nov 2009

    Optimal Sample Rate for Wireless Sensor Actuator Network

    In order to implement a wireless sensor network in process automation applications, it is needed to specify the sample rate for the sensors. Because of the hardware and power supply limitations, wireless sensors are applied to discrete event control system. In wireless sensor network the highest sample number is restricted...

    Provided By University of Bremen

  • White Papers // Jul 2009

    Opportunistic Distance-Aware Routing in Multi-Sink Mobile Wireless Sensor Networks

    Wireless sensor networks are a research area of growing importance within the wireless networks research community. One of the major issues in this area is the search for efficient routing methods. Most of the routing algorithms developed so far are limited to single-sink scenarios with no or limited mobility. This...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Relative Downlink Channel Calibration in OFDM Systems With CORDIC QR Decomposition

    Mismatched front-ends reduce the performance of precoding in multi-antenna OFDM systems, which results in a poor bit error rate. With a relative downlink channel calibration the transmission quality will be enhanced. An excellent calibration technique is based on a total least squares optimization problem. For the hardware implementation an efficient...

    Provided By University of Bremen

  • White Papers // Jun 2011

    Two-Hop Relay-Systems With OFDM-IDM Space-Time Coding

    In mobile communication systems pathloss and shadowing are two of the main limiting factors. In order to overcome these effects, relaying has been identified as a very promising technique. In relay-systems additional nodes are introduced to the system, which are neither source nor destination of transmissions themselves. Instead their task...

    Provided By University of Bremen

  • White Papers // Jun 2011

    Decode-Quantize-Forward for OFDM-Based Relaying Systems

    In this paper, the authors present a new relaying protocol for coded OFDM-based relaying systems. The classical Decode-Forward (DF) protocol exploits the coding gain within the relay, however the overall performance suffers from error propagation in case of decodings errors at the relay as no reliability information about the Source-Relay...

    Provided By University of Bremen

  • White Papers // Nov 2009

    Optimal Sample Rate for Wireless Sensor Actuator Network

    In order to implement a wireless sensor network in process automation applications, it is needed to specify the sample rate for the sensors. Because of the hardware and power supply limitations, wireless sensors are applied to discrete event control system. In wireless sensor network the highest sample number is restricted...

    Provided By University of Bremen

  • White Papers // Dec 2010

    Security in Open Model Software With Hardware Virtualisation - The Railway Control System Perspective

    Using the openETCS initiative as a starting point, the authors describe how open software can be applied in combination with platform-specific, potentially closed-source extensions, in the development, verification, validation and certification of safety-critical railway control systems. They analyze the safety and security threats presented by this approach and discuss conventional...

    Provided By University of Bremen

  • White Papers // Sep 2010

    Power Allocation for Adaptive Asymmetric Distributed MIMO Networks

    Distributed MIMO network topology is one of the most promising technologies in modern communication networks. Compared to classical Single Input Single Output (SISO) links, where information is broadcasted from one sender over huge distances, the distance between two points in multi-hop networks is rather small. By means of such relay...

    Provided By University of Bremen

  • White Papers // May 2012

    Compressive Sensing Multi-User Detection With Block-Wise Orthogonal Least Squares

    One challenging future application in digital communications is the wireless uplink transmission in sensor networks. This application is characterized by sporadic transmissions by a large number of sensors over a random multiple access channel. To reduce control signaling overhead, the authors propose that sensors do not transmit their activity states;...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Improved HARQ Based on Network Coding and Its Application in LTE

    In this paper, a novel HARQ transmission scheme based on network coding is proposed for wireless unicast scenarios. Instead of retransmitting erroneous packets individually, a network coded packet constructed by the XOR of two erroneous packets is transmitted similar to network coding. In order to fully exploit the network coded...

    Provided By University of Bremen

  • White Papers // Sep 2011

    Energy-Aware Design of Inter-Relay Cooperation for Distributed Relaying Networks

    The authors consider distributed relaying networks using Space-Time Block Codes (STBC) to exploit cooperative diversity. In order to mitigate the impact of error propagation for Decode-Forward (DF), an Inter-Relay Cooperation (IRC) scheme is proposed that allows message exchanges between the relays based on punctured channel codes. Specifically, one of the...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Effects of Downlink Channel Quantization on the Performance of Relative Calibration in OFDM Systems

    The application of calibration techniques mitigating the front-end impairments in adaptive multi-antenna TDD systems designed for very high data rates is of paramount importance. Excellent calibration purely based on signal processing can be achieved by means of relative calibration. There, additional estimated DL channel state information is required at the...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Enhanced Adaptive Downlink Transmission in MIMO-OFDM Systems by Hardware-Based Calibration

    In this paper, a hardware-based calibration scheme at the base station is used to mitigate the impact of the non-reciprocal transceivers in a Time Division Duplex (TDD) Multiple-Input-Multiple-Output Orthogonal-Frequency-Division-Multiplexing (MIMOOFDM) system. The calibration setup consists of two Single-Pole-Double-Throw (SPDT) switches to bypass the calibration and the data signals. Additionally, an...

    Provided By University of Bremen

  • White Papers // Apr 2011

    BER-Based Power Allocation for Decode-and-Forward Relaying With M-QAM Constellations

    In this paper, the authors develop a power allocation scheme for single-relay systems applying Decode-and-Forward (DF) based on the resulting Bit Error Rate (BER) at the destination. First, an analytical expression for the BER of M-QAM modulation considering estimation errors at the relay is derived. Based on this expression, the...

    Provided By University of Bremen

  • White Papers // Feb 2011

    Outage Capacity Based Link Adaptation for BICM-OFDM With Imperfect CSI

    Adapting the modulation, power and channel code to the current channel state for OFDM systems is an important topic for future wireless data transmission to fully utilize the given channel conditions. The consideration of practical channel codes in Link Adaptation schemes is still under investigation, especially if imperfect knowledge of...

    Provided By University of Bremen

  • White Papers // Feb 2011

    Bit and Power Loading for Optical IM/DD Transmission

    Orthogonal Frequency Division Multiplexing (OFDM) is an established technique for equalization of the dispersion-dominated fiber-optical channel. The dispersive nature of the optical channel results in a frequency selective equivalent channel if Double SideBand (DSB) Intensity Modulation (IM) and Direct Detection (DD) is employed. In order to maintain the all pass...

    Provided By University of Bremen

  • White Papers // Jan 2011

    BER-Based Power Allocation for Amplify-and-Forward and Decode-and-Forward Relaying Systems

    In this paper, power allocation schemes are proposed for the total transmit power of the source and the relay in a triplet relaying system based on Bit Error Rate (BER) analysis. Considering Amplify-and-Forward (AF), Decode-and-Forward (DF) for relaying systems and Direct Transmission (DT) without relay, the authors perform a fair...

    Provided By University of Bremen

  • White Papers // Mar 2011

    Calibration for Single-Carrier PreFDE Transceivers Based on Property Mapping Principles

    In general, the unequal RF circuitry in the transmit and receive chains at the Base Station (BS) prevents the exploitation of the UpLink (UL) channel estimate for proper pre-equalization in Time Division Duplex (TDD) systems. To avoid additional transceiver hardware costs for matching networks, the idea of relative calibration was...

    Provided By University of Bremen

  • White Papers // Jul 2010

    Low-Complexity Calibration of Mutually Coupled Non-Reciprocal Multi-Antenna OFDM Transceivers

    In adaptive Time Division Duplex (TDD) broadcast multi-antenna Orthogonal Frequency Division Multiplexing (OFDM) systems, non-reciprocal transceiver chains at the Base Station (BS) cause multi-user interference. This is due to the inappropriate spatial filter design at the BS based on the reverse link estimate. Hence, BS transceiver calibration is required. Provided...

    Provided By University of Bremen

  • White Papers // Jul 2010

    An Enhanced MIMO Hardware Demonstrator - Polarization Diversity in Adaptive OFDM Systems

    The performance of Multiple-Input Multiple-Output (MIMO) systems is affected by the spatial correlation properties, which depend on the array configuration and the channel characteristics. The configuration can be influenced by manipulating the radiation patterns of the antennas, the antenna spacing and the array geometry. To decrease the spatial correlation effects,...

    Provided By University of Bremen

  • White Papers // Jul 2010

    Robust Link Adaptation Using SNR-Outage Based Loading for BICM-OFDM

    In order to increase the data rate or power efficiency of OFDM systems several adaptive strategies to select the power, modulation and even code rate on a per subcarrier basis have been discussed in literature. The underlying assumption of perfect Channel State Information (CSI) at the transmitter, however, is hardly...

    Provided By University of Bremen

  • White Papers // Feb 2010

    Generalized Joint Channel Coding and Physical Network Coding for Two-Way Relay Systems

    In this paper, the authors present a generalized joint channel and physical layer network coding scheme for two-way relay systems, where the two sources A and B desire to exchange information from each other through the relay R simultaneously. Physical network coding scheme allows the relay to decode the network-coded...

    Provided By University of Bremen

  • White Papers // Dec 2009

    Verifying UML/OCL Models Using Boolean Satisfiability

    Nowadays, modeling languages like UML are essential in the design of complex software systems and also start to enter the domain of hardware and hardware/software codesign. Due to shortening time-to-market demands, "First time right" requirements have thereby to be satisfied. This paper proposes an approach that makes use of Boolean...

    Provided By University of Bremen

  • White Papers // Mar 2010

    Modeling and Formally Checking Workflow Properties Using UML and OCL

    In this paper a new metamodel for workflows is described by using UML. The underlying UML class diagram is formally extended with OCL pre- and postconditions for operations and OCL invariants for system states. The metamodel allows the developer to specify processes, activities in processes and temporal relations between them....

    Provided By University of Bremen

  • White Papers // Aug 2010

    Security in Open Model Software With Hardware Virtualization - The Railway Control System Perspective

    Using the openETCS initiative as a starting point, this paper describes how open software can be applied in combination with platform-specific, potentially closed source extensions, in the development, verification, validation and certification of safety-critical railway control systems. This paper analyses the safety and security threats presented by this approach and...

    Provided By University of Bremen

  • White Papers // Apr 2009

    Justifying Common European Action Through Human Rights And Security: A Conceptual Perspective On Europe As An Actor In The World

    Human Rights as a justification for action in the international realm are often juxtaposed with justifications that rely on the concept of security, in particular the security of the own polity. It is equally common to consider human rights justifications as a rhetorical devise to legitimate action which is 'Actually'...

    Provided By University of Bremen

  • White Papers // Jul 2011

    Tracing Properties of UML and OCL Models With Maude

    The starting point of this paper is a system described in form of a UML class diagram where system states are characterized by OCL invariants and system transitions are defined by OCL pre- and post-conditions. The aim of the approach is to assist the developer in learning about the consequences...

    Provided By University of Bremen

  • White Papers // Nov 2010

    Proposed a Method for Increasing the Delivery Performance in Dynamic Supply Network

    Supply network management adopts a systematic and integrative approach to managing the operations and relationships of various parties in a supply network. The objective of the manufactures in their supply network is to reduce inventory costs and increase customer satisfaction levels. One way of doing that is to synchronize delivery...

    Provided By University of Bremen

  • White Papers // Jul 2009

    Opportunistic Distance-Aware Routing in Multi-Sink Mobile Wireless Sensor Networks

    Wireless sensor networks are a research area of growing importance within the wireless networks research community. One of the major issues in this area is the search for efficient routing methods. Most of the routing algorithms developed so far are limited to single-sink scenarios with no or limited mobility. This...

    Provided By University of Bremen

  • White Papers // Mar 2010

    Quality Assessment for Listening-Room Compensation Algorithms

    In this contribution various objective measures that can be used to evaluate speech de-reverberation algorithms by means of Listening-Room Compensation (LRC) are compared to subjective listening tests. It is shown that technical measures describing the impulse responses are suitable for evaluation of such algorithms. Most signal-based objective measures fail to...

    Provided By University of Bremen

  • White Papers // Feb 2010

    Comparison of Distributed LDPC Coding Schemes for Decode-and-Forward Relay Channels

    In order to approach the theoretical limit of the decode-and-forward strategy for the half-duplex relay channel, distributed LDPC coding schemes have been proposed. In these schemes, the code applied at the source should be decodable at the relay to yield correct parity bits. With the help of the parity bits...

    Provided By University of Bremen

  • White Papers // Feb 2010

    Iterative Pre-Compensation of I/Q Imbalances in an Adaptive 2.4 GHz MIMO-OFDM System

    Currently evolving communication standards, especially those using multi-antenna (MIMO) multicarrier modulation techniques, are based on the exploitation of Channel State Information (CSI) at the transmitter. The utilization of adaptive transmission schemes comes with a more sensitive behavior with respect to front-end imperfections. Direct-conversion architectures in turn allow for low-cost transceiver...

    Provided By University of Bremen

  • White Papers // Jul 2009

    Influence of Non-Reciprocal Transceivers at 2.4 GHz in Adaptive MIMO-OFDM Systems

    In this paper, the impact of nonreciprocal transceivers is demonstrated by measurement results for different adaptive transmission strategies in a time division duplex MIMO-OFDM system. These strategies rely on the Channel State Information (CSI) at the transmitter, thus requiring either appropriate feedback or reciprocity of both communication links. The measurements...

    Provided By University of Bremen

  • White Papers // Jul 2009

    Link Adaptation for MIMO-OFDM With Partial CSI

    The discussion of bit and power loading algorithms for Multiple Input Multiple Output (MIMO) systems often neglects the requirement of perfect channel state information to perform singular value decomposition. Especially in multi-carrier systems like Orthogonal Frequency Division Multiplex (OFDM) a vast amount of feedback is necessary to facilitate such a...

    Provided By University of Bremen

  • White Papers // Jul 2009

    Calibration of Non-Reciprocal Transceivers for Linearly Pre-Equalized MU-MISO-OFDM Systems in TDD Mode

    This paper deals with a relative calibration approach in terms of non-reciprocal transceivers in a multi-user MISO-OFDM TDD broadcast scenario where linear pre-equalization strategies are applied. The calibrated system, which is achieved by solving a total least squares problem, is compared with robust minimum mean square error pre-equalizer designs. Simulation...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Soft Information Relaying for Wireless Networks With Error-Prone Source-Relay Link

    Relays in wireless networks can be used to decrease transmit power while additionally increasing diversity. Distributed turbo coding as a special case of decode-and-forward is very powerful in relay networks when assuming error free decoding in the relay. In practical wireless networks, however, this assumption is only justiable if an...

    Provided By University of Bremen

  • White Papers // Jan 2012

    Minimum MSE Relaying in Coded Networks

    In order to combine the advantages of Amplify-Forward (AF) and Decode-Forward (DF) in relay networks, several strategies have been developed making use of reliability information after decoding at the relay. The use of soft-output channel decoders enables forwarding reliability information for the decoded bits. This soft information can be forwarded...

    Provided By University of Bremen

  • White Papers // Jan 2009

    Improving the Performance of BICM-OFDM Systems in Presence of HPA Nonlinearities by Efficient Bit and Power Loading

    The usage of Orthogonal Frequency Division Multiplexing (OFDM) allows to adapt the available time-frequency grid to the current channel conditions. To exploit the offered degrees of freedom many bit and power loading algorithms were introduced. However, they do not include channel coding in the optimization. Similar to conventional multicarrier schemes...

    Provided By University of Bremen

  • White Papers // Mar 2009

    Performance Evaluation of Joint Power and Time Allocations for Adaptive Distributed MIMO Multi-Hop Networks

    Distributed Multiple Input Multiple Output (MIMO) multihop networks are proven to achieve superior performance in terms of data throughput and communication reliability. In this paper a low-complexity adaptive relaying scheme is considered in order to achieve robust end-to-end (e2e) communications. For this system optimal as well as near-optimal efficient resource...

    Provided By University of Bremen

  • White Papers // Feb 2009

    Linearisation of Transmitter and Receiver Nonlinearities in Optical OFDM Transmission

    In this paper, linearisation of transmitter and receiver nonlinearities of an optical Intensity Modulation/Direct Detection system using digital signal processing is presented and analyzed. The system performance is estimated on basis of the signal-to-interference-and-noise ratio. Furthermore, the bit error performance of a linearised system is compared to a non-linearised one....

    Provided By University of Bremen

  • White Papers // Apr 2009

    Adaptive Distributed MIMO Multi-Hop Networks With Optimized Power and Time Allocation

    Distributed Multiple-Input Multiple-Output (MIMO) multi-hop relaying is a promising technology to achieve high-quality end-to-end (e2e) link performance by providing cooperative diversity. The application of low-complexity space-time codes offers improved coverage, data rates, and reliability. However, efficient transmission protocols and enhanced resource allocation schemes are required to exploit these advantages. Specifically,...

    Provided By University of Bremen

  • White Papers // Feb 2009

    Adaptive BICM-OFDM Systems

    Link Adaptation for Orthogonal Frequency Division Multiplex (OFDM) systems is an important topic to achieve higher spectral efficiencies or better error rate performance. However, channel coding has been neglected previously, only gaining some attention recently. In this paper, an overview over existing techniques and algorithms to adapt Bit Interleaved Coded...

    Provided By University of Bremen