The paper is concerned with communication within a team of players trying to coordinate in response to information dispersed among them. The problem is nontrivial because they cannot communicate all information instantaneously, but have to send longer or shorter sequences of messages, using coarse codes. We focus on the design of these codes and show that members may gain compatibility advantages by using identical codes, and that this can support the existence of several, more or less efficient, symmetric equilibria. Asymmetric equilibria may exist only if coordination across different sets of members is of sufficiently different importance. The results are consistent with the stylized fact that firm differ even within industries and that coordination between divisions is harder than coordination inside divisions. / Center for Innovation in Product Development at MIT under NSF Cooperative Agreement Number EEC-9529140.

We consider a communication system where two transmitters wish to exchange information through a central relay. The data is assumed to be transmitted over synchronized, average power constrained additive white Gaussian noise channels with a real input with signal-to-noise ratio (SNR) of snr. It has been shown that using lattice codes and lattice decoding, a rate of 1/2 log_2(1/2 plus snr) can be obtained asymptotically, which is essentially optimal at high SNR. However, there has been a lack of practical encoding/decoding schemes for the above mentioned system. We address this issue in this thesis by developing encoding/decoding strategies for the bidirectional relaying system using low-dimensional lattice codes. Our efforts are aimed at developing coding schemes which possess low computational complexity while at the same time providing good performance. We demonstrate two schemes using low-dimensional lattice codes. Both these schemes have their own advantages and are suitable for different classes of lattice codes. The two schemes are tested with different lattices and their performance is compared to that of other schemes for bidirectional relays. The first scheme is termed as demodulate and forward and it essentially consists of performing optimal estimation at the relay. It is primarily implemented with lattice codes of low rate and possesses low decoding complexity. When used with a two-dimensional hexagonal lattice, it achieves a gain of around 3.5 dB in comparison to other schemes like Analog network coding. The second scheme is the sphere decoding scheme which has been implemented with high-rate lattice codes. The sphere decoder is a low-complexity decoder which is used for decoding to a lattice point at the relay. We observe that as the dimensionality of the lattice code is increased, the performance of the sphere decoder for the bidirectional relay gets consistently better. The sphere decoder is also used at high SNR for those instances in which the low density lattice code(LDLC) decoder makes an error and it is found that the sphere decoder can correct around 90 percent of these errors at an SNR of 9.75 dB.

In quantum information processing, the information is stored in the state of quantum mechanical systems. Since the interaction with the environment is unavoidable, there is a need for quantum error correction to protect the stored information. Until now, the methods for quantum error correction were mainly based on quantum codes that rely on the arithmetic in finite fields. In contrast, this thesis aims to develop a basic framework for quantum error correcting codes over a class of rings known as the Frobenius rings. This thesis focuses on developing the theory of stabilizer codes over the Frobenius rings and provides a systematic construction of codes over these rings. A special class of Frobenius rings called finite chain rings will be the emphasis of this thesis. The theory needed for comparing the minimum distance of stabilizer codes over the finite chain rings to that over the fields is studied in detail. This thesis finally derives that the minimum distance of stabilizer codes over finite chain rings cannot exceed the minimum distance over the fields.

This is a research on orthogonal complementary codes, including complete complementary codes, super complementary codes, and generalized pairwise complementary code(GPC code). I discuss the properties of orthogonal complementary codes by the generation of orthogonal matries and realize its auto-correlation and cross-correlation are perfect. Apply orthogonal complementary codes on direct-sequence spreading system and offset stacked spreading system. In these two kinds of transmission, orthogonal complementary codes have the ideal auto-correlation and cross-correlation by way of direct-sequence spreading system, so it can solve multipath interference and multi-access interference effectively. While in offset stacked spreading system, orthogonal complementary codes have ideal cross-correlation. Modulating the offset chip time of offset stacked spreading properly can also solve multipath interference effectively. Moreover, GPC code keeps sub-ideal auto-correlation and cross-correlation, and it forsakes its ideal property to exchange for spreading codes with more users. In Chapter 2, we start to introduce complete complementary codes and its property to resist interferences in different transmission. Chapter 3 is the introduction of super complementary codes and its property to resist interferences in different transmission. Chapter 4 is the introduction of GPC code. We explain that GPC code forsakes its ideal property to exchange for spreading codes with more users. Chapter 5 is the introduce multi-rate orthogonal complementary codes and use 2D OVSF to suport different transmission speed.

We investigate the creation of linear block codes using Hadamard matrices for block fading channels. The aforementioned codes are very easy to find and have bounded cross correlation spectrum. The optimality is with respect to the metric-spectrum which gives a performance for the codes very close to optimal codes. Also, we can transform these codes according to different characteristics of the channel and can use selective transmission methods.

Reproduction de : Thèse doctorat : Electronique : Metz : 2003. / Titre provenant de l'écran-titre. Notes bibliographiques.

Ongoing technology improvements and feature size reduction have led to an increase in manufacturing-induced parameter variations. These variations affect various memory cell circuits, making them unreliable at low voltages. Memories are very dense structures that are especially susceptible to defects, and more so at lower voltages. Transient errors due to radiation, power supply noise, etc., can also cause bit-flips in a memory. To protect the data integrity of the memory, an error correcting code (ECC) is generally employed. Present ECC, however, is either single error correcting or corrects multiple errors at the cost of high redundancy or longer correction time. This research addresses the problem of memory reliability under adverse conditions. The goal is to achieve a desired reliability at reduced redundancy while also keeping in check the correction time. Several methods are proposed here including one that makes use of leftover spare columns/rows in memory arrays [Datta 09] and another one that uses memory characterization tests to customize ECC on a chip by chip basis [Datta 10]. The former demonstrates how reusing spare columns leftover from the memory repair process can help increase code reliability while keeping hardware overhead to a minimum. In the latter case customizing ECCs on a chip by chip basis shows considerable reduction in check bit overhead, at the same time providing a desired level of protection for low voltage operations. The customization is done with help from a defect map generated at manufacturing time, which helps identify potentially vulnerable cells at low voltage. An ECC based solution for tackling the wear out problem of phase change memories (PCM) has also been presented here. To handle the problem of gradual wear out and hence increasing defect rates in PCM systems an adaptive error correction scheme is proposed [Datta 11a]. The adaptive scheme, implemented alongside the operating system seeks to increase PCM lifetime by manifold times. Finally the work on memory ECC is extended by proposing a fast burst error correcting code with minimal overhead for handling scenarios where multi-bit failures are common [Datta 11b]. The twofold goal of this work – design a low-cost code capable of handling multi bit errors affecting adjacent cells, and fast multi bit error correction – is achieved by modifying conventional Orthogonal Latin Square codes into burst error codes. / text

It is believed that quantum computers would be able to solve complex problems more quickly than any other deterministic or probabilistic computer. Quantum computers basically exploit the rules of quantum mechanics for speeding up computations. However, building a quantum computer remains a daunting task. A quantum computer, as in any quantum mechanical system, is susceptible to decohorence of quantum bits resulting from interaction of the stored information with the environment. Error correction is then required to restore a quantum bit, which has changed due to interaction with external state, to a previous non-erroneous state in the coding subspace. Until now the methods for quantum error correction were mostly based on stabilizer codes over finite fields. The aim of this thesis is to construct quantum error correcting codes over finite Frobenius rings. We introduce stabilizer codes over quadratic algebra, which allows one to use the hamming distance rather than some less known notion of distance. We also develop propagation rules to build new codes from existing codes. Non binary codes have been realized as a gray image of linear Z4 code, hence the most natural class of ring that is suitable for coding theory is given by finite Frobenius rings as it allow to formulate the dual code similar to finite fields. At the end we show some examples of code construction along with various results of quantum codes over finite Frobenius rings, especially codes over Zm.

Thesis (M.A.R.)--Cincinnati Christian University, 2009. / Includes abstract and vita. Bibliography: l. 101-104.

Thesis (M.S.)--Pennsylvania State University, 2008. / Mode of access: World Wide Web.