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Data transmition security with BCH codes
Frolka, Jakub ; Tejkal, Vladimír (referee) ; Němec, Karel (advisor)
The bachelor thesis Data transmission security with BCH codes deals with class of random error correction cyclic codes which are able to protect data in binary form. BCH codes operate over algebraic structures called Galois fields. Encoding of these codes is same as encoding cyclic codes and can be used cyclic shift register, but decoding is more complex and can be done with many algorithms, in this thesis are mention three: Peterson algorithm, Matrix method and Berlekamp-Massey algorithm. In this thesis are described characteristics BCH codes, their usage in communication devices and their posibility implementation. An example BCH code which is able to correct four independent errors is created. This example is used for presentation of encoding and decoding methods. In the end is described implementation of data protection codec for FGPA devices.
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Decoding Barcode in Image in Real Time
Krupa, Martin ; Kajan, Rudolf (referee) ; Herout, Adam (advisor)
The goal of this thesis is to describe barcodes used in real world applications and to create application for real time detecting and decoding of chosen barcodes using computer vision. Normal linear barcode is first introduced, and then two dimensional matrix barcode is described with focus on its origin, usage and structure. Especially the process of localization, encoding and decoding of QR Code, which is chosen for future use in work, is described mainly. Also briefly description of computer vision and OpenCV library is available. Next the concept and implementation of application for localization and recognition of QR Codes is described. Finally description of testing, evaluation of thesis and ways of improvements are discussed.
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Advanced QR-Code reader for Android
Kubík, Martin ; Přinosil, Jiří (referee) ; Šmirg, Ondřej (advisor)
The aim of this diploma thesis was to created application for detection and decoding QR codes using devices with the Android Operating System. For preprocessing of the visual field camera is used OpenCV library. Designed preprocessing string searches a perspective transforms possible QR codes. This is suppressed a shape distortion QR code that would otherwise reduce the successful decoding. At the same time the preprocessing string applied unsharp mask, which reduces the effect of motion blur image caused by the camera motion. Thus preprocessing scene is finally decoded using ZXing library. Described manner it is possible to achieve a higher success rate detection and decoding of QR codes than other conventional QR readers.
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Kódování a efektivita LDPC kódů
Kozlík, Andrew ; Drápal, Aleš (advisor) ; Holub, Štěpán (referee)
Low-density parity-check (LDPC) codes are linear error correcting codes which are capable of performing near channel capacity. Furthermore, they admit efficient decoding algorithms that provide near optimum performance. Their main disadvantage is that most LDPC codes have relatively complex encoders. In this thesis, we begin by giving a detailed discussion of the sum-product decoding algorithm, we then study the performance of LDPC codes on the binary erasure channel under sum-product decoding to obtain criteria for the design of codes that allow reliable transmission at rates arbitrarily close to channel capacity. Using these criteria we show how such codes are designed. We then present experimental results and compare them with theoretical predictions. Finally, we provide an overview of several approaches to solving the complex encoder problem.
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Implementation of restoring method for reading bar code
Kadlčík, Libor ; Bartušek, Karel (referee) ; Mikulka, Jan (advisor)
Bar code stores information in the form of series of bars and gaps with various widths, and therefore can be considered as an example of bilevel (square) signal. Magnetic bar codes are created by applying slightly ferromagnetic material to a substrate. Sensing is done by reading oscillator, whose frequency is modulated by presence of the mentioned ferromagnetic material. Signal from the oscillator is then subjected to frequency demodulation. Due to temperature drift of the reading oscillator, the demodulated signal is accompanied by DC drift. Method for removal of the drift is introduced. Also, drift-insensitive detection of presence of a bar code is described. Reading bar codes is complicated by convolutional distortion, which is result of spatially dispersed sensitivity of the sensor. Effect of the convolutional distortion is analogous to low-pass filtering, causing edges to be smoothed and overlapped, and making their detection difficult. Characteristics of convolutional distortion can be summarized into point-spread function (PSF). In case of magnetic bar codes, the shape of the PSF can be known in advance, but not its width of DC transfer. Methods for estimation of these parameters are discussed. The signal needs to be reconstructed (into original bilevel form) before decoding can take place. Variational methods provide effective way. Their core idea is to reformulate reconstruction as an optimization problem of functional minimization. The functional can be extended by other functionals (regularizations) in order to considerably improve results of reconstruction. Principle of variational methods will be shown, including examples of use of various regularizations. All algorithm and methods (including frequency demodulation of signal from reading oscillator) are digital. They are implemented as a program for a microcontroller from the PIC32 family, which offers high computing power, so that even blind deconvolution (when the real PSF also needs to be found) can be finished in a few seconds. The microcontroller is part of magnetic bar code reader, whose hardware allows the read information to be transferred to personal computer via the PS/2 interface or USB (by emulating key presses on virtual keyboard), or shown on display.
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Barcodes Reading Library
Novohradský, Petr ; Přibyl, Bronislav (referee) ; Kubíček, Radek (advisor)
This work deals with the decoding of different types of barcodes in the image. Selected types of bar codes are described in detail. Presents an approach to decode linear and matrix bar codes. The practical part deals with the design and implementation of software library for reading selected types of bar codes in Java.
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Modelling of Network Coding in Wireless Networks
Svobodník, Petr ; Miloš, Jiří (referee) ; Kuder, Zenon (advisor)
During data exchange in the Point-to-Point wireless topology, in case where end nodes aren’t accessible directly, a relay is deployed. However, the basic approach to relays – Store-and-Forward – isn’t the way to reach the maximum throughput. Network Coding operation is performed by combining data words (packets) travelling through the network in opposite directions into one packet. End nodes, with knowledge of the data sent, can decode received packet. Packet exchange is then finished in shorter time which results in an increase of network throughput. There are more methods of Network Coding which differ from each other in the time requirements or the ability to work in a noisy channel. In this paper they will be described and compared.
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