133 research outputs found

    Coding theory, information theory and cryptology : proceedings of the EIDMA winter meeting, Veldhoven, December 19-21, 1994

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    Coding theory, information theory and cryptology : proceedings of the EIDMA winter meeting, Veldhoven, December 19-21, 1994

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    Asynchronous Communication: Exact Synchronization, Universality, and Dispersion

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    Recently, Tchamkerten and coworkers proposed a novel variation of the problem of joint synchronization and error correction. This paper considers a strengthened formulation that requires the decoder to estimate both the message and the location of the codeword exactly. Such a scheme allows for transmitting data bits in the synchronization phase of the communication, thereby improving bandwidth and energy efficiencies. It is shown that the capacity region remains unchanged under the exact synchronization requirement. Furthermore, asynchronous capacity can be achieved by universal (channel independent) codes. Comparisons with earlier results on another (delay compensated) definition of rate are made. The finite blocklength regime is investigated and it is demonstrated that even for moderate blocklengths, it is possible to construct capacity-achieving codes that tolerate exponential level of asynchronism and experience only a rather small loss in rate compared to the perfectly synchronized setting; in particular, the channel dispersion does not suffer any degradation due to asynchronism. For the binary symmetric channel, a translation (coset) of a good linear code is shown to achieve the capacity-synchronization tradeoff.National Science Foundation (U.S.) (Center for Science of Information Grant CCF-0939370

    Turbo Multiuser Detection Architectures

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    The discovery of Turbo Codes in 1996 by Berrou et. al. proved to be a huge boost for the research of channel coding. The Turbo Principle behind turbo codes was found to be applicable in other areas. One of these areas is Multiuser Detection. In this thesis, Turbo Multiuser Detection is investigated in order to answer two main questions. The questions concern the performance gain that is obtained when turbo multiuser detection is used instead of non-turbo multiuser detection and the convergence behavior of turbo multiuser detection. The performance gain is determined by comparing the bit-error-rate (BER) chart of a turbo multiuser detection architecture with the BER chart of a non-turbo multiuser detector. It was found that turbo multiuser detection results in a dramatical performance gain when Eb/N0 > 3 dB and more than one iteration is performed. The convergence behavior of turbo multiuser detection is analyzed with the help of EXIT charts. EXIT charts are recently proposed by S. ten Brink as a tool to analyze the convergence behavior of turbo architectures. EXIT charts are discussed in this thesis. An EXIT chart of a turbo multiuser detection architecture is created. From this chart, the minimum number of iterations to obtain the lowest BER possible are found.\ud EXIT charts are also used to analyze the difference of iterating aposteriori and extrinsic information in a turbo architecture. The analysis shows that EXIT charts of a-posteriori information give results, which contradict the results of simulations on turbo architectures

    Energy-efficient coding for high speed links

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    Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 76-77).Throughput and energy-efficiency of high-speed chip-to-chip interconnects present critical bottlenecks in a whole range of important applications, from processor-memory interfaces, to network routers. These links currently rely solely on complex equalization techniques to maintain the bit error rate lower than 10-15. While applicable to data rates up to 10 Gb/s on most links, this approach does not scale well to higher data rates or better energy-efficiency. The work described in the thesis shows that it may be possible to use coding techniques to share the burden of combating errors, while increasing the throughput of the link or improving its energy-efficiency. Since codes here attempt to alleviate the impact of partially correlated sources of error (like reflections interference, crosstalk and jitter), an experimental setup was created for characterization of link channel properties and performance gains from different codes. Four codes, specifically Hamming, BCH, Fire, and SEC-DED codes, are implemented and analyzed with various configurations (i.e. different blocksizes, data rates, and detection or correction). Most significantly, it is discovered that detection and retransmission of even the simple codes implemented in this project may be able to maintain a bit error rate of 10-15.by Maxine Lee.M.Eng

    Error-correction on non-standard communication channels

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    Many communication systems are poorly modelled by the standard channels assumed in the information theory literature, such as the binary symmetric channel or the additive white Gaussian noise channel. Real systems suffer from additional problems including time-varying noise, cross-talk, synchronization errors and latency constraints. In this thesis, low-density parity-check codes and codes related to them are applied to non-standard channels. First, we look at time-varying noise modelled by a Markov channel. A low-density parity-check code decoder is modified to give an improvement of over 1dB. Secondly, novel codes based on low-density parity-check codes are introduced which produce transmissions with Pr(bit = 1) ≠ Pr(bit = 0). These non-linear codes are shown to be good candidates for multi-user channels with crosstalk, such as optical channels. Thirdly, a channel with synchronization errors is modelled by random uncorrelated insertion or deletion events at unknown positions. Marker codes formed from low-density parity-check codewords with regular markers inserted within them are studied. It is shown that a marker code with iterative decoding has performance close to the bounds on the channel capacity, significantly outperforming other known codes. Finally, coding for a system with latency constraints is studied. For example, if a telemetry system involves a slow channel some error correction is often needed quickly whilst the code should be able to correct remaining errors later. A new code is formed from the intersection of a convolutional code with a high rate low-density parity-check code. The convolutional code has good early decoding performance and the high rate low-density parity-check code efficiently cleans up remaining errors after receiving the entire block. Simulations of the block code show a gain of 1.5dB over a standard NASA code

    On Linear Product Codes and Their Duals Scientific Report No. 4

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    Tensor products of linear codes, and product codes with dual cyclic component code

    Entropy of delta-coded speech

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    NASA Space Engineering Research Center for VLSI System Design

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    This annual report outlines the activities of the past year at the NASA SERC on VLSI Design. Highlights for this year include the following: a significant breakthrough was achieved in utilizing commercial IC foundries for producing flight electronics; the first two flight qualified chips were designed, fabricated, and tested and are now being delivered into NASA flight systems; and a new technology transfer mechanism has been established to transfer VLSI advances into NASA and commercial systems

    CNC Feed Drive Control

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    This document serves as the Final Design Report (FDR) for a senior project developed by our team: four senior Mechanical Engineering students and one computer engineering student at California Polytechnic State University, San Luis Obispo (Cal Poly). While the project was completed for, and sponsored by, Professor Simon Xing of Cal Poly, the remainder of the university’s controls professors will be indirectly benefited from this project. Our goal was to design and implement a functional CNC Feed Drive to be used for educational demonstrations and data collection. This document discusses our early product research and benchmark goals, which established constraints for our product design, as well as identifies our design process and conclusions. Through this evaluation of the feed drive form and function, we determined optimal system components - including a DC motor with rotary encoders, a ballscrew, linear bearings, and a load table with screws for fixturing. This FDR also discusses our design progression, beginning with the structural prototype and followed by a description of the final design. This will include the manufacturing steps taken, the front-end and back-end code generated and used to control the system, and the associated user’s manual. Lastly, this report will discuss the test procedures that we derived from the design verification requirements and include an overview of our test results. We conclude with our final acknowledgments, and we wanted to mention that we are extremely grateful to have worked on this project. The team has learned so much throughout the year, and we look forward to handing the prototype over to Professor Xing
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