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The Global ETD Search service is a free service for researchers
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Showing 11 to 20 of 44 (0.094 seconds)Spelling suggestions: "subject:"collaborative 3research Centre 912"" "subject:"collaborative 1research Centre 912""
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Reduced Complexity Window Decoding Schedules for Coupled LDPC CodesHassan, Najeeb ul, Pusane, Ali E., Lentmaier, Michael, Fettweis, Gerhard P., Costello, Daniel J. 14 February 2013 (has links) (PDF)
Window decoding schedules are very attractive for message passing decoding of spatially coupled LDPC codes. They take advantage of the inherent convolutional code structure and allow continuous transmission with low decoding latency and complexity. In this paper we show that the decoding complexity can be further reduced if suitable message passing schedules are applied within the decoding window. An improvement based schedule is presented that easily adapts to different ensemble structures, window sizes, and channel parameters. Its combination with a serial (on-demand) schedule is also considered. Results from a computer search based schedule are shown for comparison.
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A high-throughput in-memory index, durable on flash-based SSDKissinger, Thomas, Schlegel, Benjamin, Böhm, Matthias, Habich, Dirk, Lehner, Wolfgang 14 February 2013 (has links) (PDF)
Growing memory capacities and the increasing number of cores on modern hardware enforces the design of new in-memory indexing structures that reduce the number of memory transfers and minimizes the need for locking to allow massive parallel access. However, most applications depend on hard durability constraints requiring a persistent medium like SSDs, which shorten the latency and throughput gap between main memory and hard disks. In this paper, we present our winning solution of the SIGMOD Programming Contest 2011. It consists of an in-memory indexing structure that provides a balanced read/write performance as well as non-blocking reads and single-lock writes. Complementary to this index, we describe an SSD-optimized logging approach to fit hard durability requirements at a high throughput rate.
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Capacity of Communications Channels with 1-Bit Quantization and Oversampling at the ReceiverKrone, Stefan, Fettweis, Gerhard 25 January 2013 (has links) (PDF)
Communications receivers that rely on 1-bit analogto-digital conversion are advantageous in terms of hardware complexity and power dissipation. Performance limitations due to the 1-bit quantization can be tackled with oversampling. This paper considers the oversampling gain from an information-theoretic perspective by analyzing the channel capacity with 1-bit quantization and oversampling at the receiver for the particular case of AWGN channels. This includes a numerical computation of the capacity and optimal transmit symbol constellations, as well as the derivation of closed-form expressions for large oversampling ratios and for high signal-to-noise ratios of the channel.
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Energy-Efficient In-Memory Database ComputingLehner, Wolfgang 27 June 2013 (has links) (PDF)
The efficient and flexible management of large datasets is one of the core requirements of modern business applications. Having access to consistent and up-to-date information is the foundation for operational, tactical, and strategic decision making. Within the last few years, the database community sparked a large number of extremely innovative research projects to push the envelope in the context of modern database system architectures. In this paper, we outline requirements and influencing factors to identify some of the hot research topics in database management systems. We argue that—even after 30 years of active database research—the time is right to rethink some of the core architectural principles and come up with novel approaches to meet the requirements of the next decades in data management. The sheer number of diverse and novel (e.g., scientific) application areas, the existence of modern hardware capabilities, and the need of large data centers to become more energy-efficient will be the drivers for database research in the years to come.
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| 15 |
Waiting for Locks: How Long Does It Usually Take?Baier, Christel, Daum, Marcus, Engel, Benjamin, Härtig, Hermann, Klein, Joachim, Klüppelholz, Sascha, Märcker, Steffen, Tews, Hendrik, Völp, Marcus 10 September 2013 (has links) (PDF)
Reliability of low-level operating-system (OS) code is an indispensable requirement. This includes functional properties from the safety-liveness spectrum, but also quantitative properties stating, e.g., that the average waiting time on locks is sufficiently small or that the energy requirement of a certain system call is below a given threshold with a high probability. This paper reports on our experiences made in a running project where the goal is to apply probabilistic model checking techniques and to align the results of the model checker with measurements to predict quantitative properties of low-level OS code.
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Chiefly Symmetric: Results on the Scalability of Probabilistic Model Checking for Operating-System CodeBaier, Christel, Daum, Marcus, Engel, Benjamin, Härtig, Hermann, Klein, Joachim, Klüppelholz, Sascha, Märcker, Steffen, Tews, Hendrik, Völp, Marcus 10 September 2013 (has links) (PDF)
Reliability in terms of functional properties from the safety-liveness spectrum is an indispensable requirement of low-level operating-system (OS) code. However, with evermore complex and thus less predictable hardware, quantitative and probabilistic guarantees become more and more important. Probabilistic model checking is one technique to automatically obtain these guarantees. First experiences with the automated quantitative analysis of low-level operating-system code confirm the expectation that the naive probabilistic model checking approach rapidly reaches its limits when increasing the numbers of processes. This paper reports on our work-in-progress to tackle the state explosion problem for low-level OS-code caused by the exponential blow-up of the model size when the number of processes grows. We studied the symmetry reduction approach and carried out our experiments with a simple test-and-test-and-set lock case study as a representative example for a wide range of protocols with natural inter-process dependencies and long-run properties. We quickly see a state-space explosion for scenarios where inter-process dependencies are insignificant. However, once inter-process dependencies dominate the picture models with hundred and more processes can be constructed and analysed.
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Secure degrees of freedom on widely linear instantaneous relay-assisted interference channelHo, Zuleita K.-M., Jorswieck, Eduard 22 November 2013 (has links) (PDF)
The number of secure data streams a relay-assisted interference channel can support has been an intriguing problem. The problem is not solved even for a fundamental scenario with a single antenna at each transmitter, receiver and relay. In this paper, we study the achievable secure degrees of freedom of instantaneous relay-assisted interference channels with real and complex coefficients. The study of secure degrees of freedom with complex coefficients is not a trivial multiuser extension of the scenarios with real channel coefficients as in the case for the degrees of freedom, due to secrecy constraints. We tackle this challenge by jointly designing the improper transmit signals and widely-linear relay processing strategies.
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Interference Leakage Neutralization in Two-Hop Wiretap Channels with Partial CSIEngelmann, Sabrina, Ho, Zuleita K.-M., Jorswieck, Eduard A. 22 November 2013 (has links) (PDF)
In this paper, we analyze the four-node relay wiretap channel, where the relay performs amplify-and-forward. There is no direct link between transmitter and receiver available. The transmitter has multiple antennas, which assist in securing the transmission over both phases. In case of full channel state information (CSI), the transmitter can apply information leakage neutralization in order to prevent the eavesdropper from obtaining any information about the signal sent. This gets more challenging, if the transmitter has only an outdated estimate of the channel from the relay to the eavesdropper. For this case, we optimize the worst case secrecy rate by choosing intelligently the beamforming vectors and the power allocation at the transmitter and the relay.
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| 19 |
Secret key generation from reciprocal spatially correlated MIMO channelsJorswieck, Eduard A., Wolf, Anne, Engelmann, Sabrina 16 June 2014 (has links) (PDF)
Secret key generation from reciprocal multi-antenna channels is an interesting alternative to cryptographic key management in wireless systems without infrastructure access. In this work, we study the secret key rate for the basic source model with a MIMO channel. First, we derive an expression for the secret key rate under spatial correlation modelled by the Kronecker model and with spatial precoding at both communication nodes. Next, we analyze the result for uncorrelated antennas to understand the optimal precoding for this special case, which is equal power allocation. Then, the impact of correlation is characterized using Majorization theory. Surprisingly for small SNR, spatial correlation increases the secret key rate. For high SNR, the maximum secret key rate is achieved for uncorrelated antennas. The results indicate that a solid system design for reciprocal MIMO key generation is required to establish the secret key rate gains.
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| 20 |
Physical Layer Security vs. Network Layer Secrecy: Who Wins on the Untrusted Two-Way Relay Channel?Richter, Johannes, Franz, Elke, Engelmann, Sabrina, Pfennig, Stefan, Jorswieck, Eduard A. January 2013 (has links)
We consider the problem of secure communications in a Gaussian two-way relay network where two nodes exchange confidential messages only via an untrusted relay. The relay is assumed to be honest but curious, i.e., an eavesdropper that conforms to the system rules and applies the intended relaying scheme. We analyze the achievable secrecy rates by applying network coding on the physical layer or the network layer and compare the results in terms of complexity, overhead, and efficiency. Further, we discuss the advantages and disadvantages of the respective approaches.
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