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Wobble modifications and other features in transfer RNA important for decoding and reading frame maintenanceNäsvall, Joakim January 2007 (has links)
Transfer RNA (tRNA) is the adaptor molecule responsible for bringing the correct amino acid to the ribosome during protein synthesis. tRNA contains a number of modified nucleosides, which are derivatives of the four normal nucleosides. A great variety of modifications are found in the anticodon loop, especially at the first (wobble) position of the anticodon. According to Crick’s wobble hypothesis, a uridine at the wobble position of tRNA recognize codons ending with A and G. Uridine-5-oxyacetic acid (cmo5U34), found at the wobble position of six species of tRNA in Salmonella enterica, have been predicted to expand the codon recognition of uridine to include U-ending, but not C-ending codons. To study the function of cmo5U34 we have identified two genes, cmoA and cmoB, which are required for the synthesis of cmo5U34 in tRNA. We have shown that the proline, alanine and valine tRNAs containing cmo5U34 are capable of reading codons ending with any of the four nucleotides, while the threonine tRNA is not, and the importance of having cmo5U is different for the different tRNAs. In addition, we found that cmo5U is important for efficient reading of G-ending codons, which is surprising considering the wobble hypothesis, which states that uridine should read G-ending codons. The dominant +1 frameshift suppressor sufY suppresses the hisC3737 +1 frameshift mutation. We have demonstrated that sufY induces frameshifting at CCC-CAA (Pro-Gln), when tRNAPro[cmo5UGG] occupies the P-site. sufY mutants accumulate novel modified nucleosides at the wobble position of tRNAs that should normally have (c)mnm5s2U34. The presence of an extra sidechain (C10H17) on the wobble nucleoside of tRNAGln[(c)mnm5s2U] leads to slow decoding of CAA codons, inducing a translational pause that allows the P-site peptidyl-tRNAPro[cmo5UGG] to slip into the +1 frame. We have characterized 108 independent frameshift suppressor mutants in the gene encoding tRNAPro[cmo5UGG]. The altered tRNAs are still able to read all four proline codons in the A-site, but induce frameshifts after translocation into the P-site. Some of the mutations are in regions of the tRNA that are involved in interactions with components of the P-site. We hypothesize that the ribosomal P-site keeps a “grip” of the peptidyl-tRNA to prevent loss of the reading frame.
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Hur tolkar du? : En studie om reklambilder utifrån sändar- och mottagarperspektiv. / How do you interpret? : A study of advertising images based on the transmitter and recipient perspective.Yusuf, Farah, Jaykar, Ida, Emilsson, Isabelle January 2008 (has links)
The study aims to gain a better understanding and explore how a selected group (receivers) perceive two elected advertising images from Indiska and Vila and then compare their opinions to what Indiska and Vila themselves want to communicate. We base the study on theories of encoding / decoding, which deals with how the companies charge their advertising images with values and how recipients decodes these values. A qualitative study was carried out based on analytical induction (planning, collection and analysis). Through the analytical method of induction, we created categories based on the collected data and put them in relation to each other. The result showed that the overall impression of the images' and the context are of great importance for how our respondents perceive the advertising images. The overall impressions convey emotion that reinforces the expression and the message. The respondents partially perceived the transmitters' message in the pictures, but some elements did not match the transmitters' intention. We also made a reception analysis to find out whether the nursery place of our respondents made a difference in how they interpreted the advertising images. Although we could not reveal any significant difference between these groups, we still believe that social, cultural and economic background matters when it comes to interpretation.
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On Optimal Link Activation with Interference Cancelation in Wireless NetworkingYuan, Di, Angelakis, Vangelis, Chen, Lei, Karipidis, Eleftherios, Larsson, Erik G. January 2013 (has links)
A fundamental aspect in performance engineering of wireless networks is optimizing the set of links that can be concurrently activated to meet given signal-to-interference-and-noise ratio (SINR) thresholds. The solution of this combinatorial problem is the key element in scheduling and cross-layer resource management. In this paper, we assume multiuser decoding receivers, which can cancel strongly interfering signals. As a result, in contrast to classical spatial reuse, links being close to each other are more likely to be active concurrently. Our focus is to gauge the gain of successive interference cancellation (SIC), as well as the simpler, yet instructive, case of parallel interference cancellation (PIC), in the context of optimal link activation. We show that both problems are NP-hard and develop compact integer linear programming formulations that enable to approach global optimality. We provide an extensive numerical performance evaluation, indicating that for low to medium SINR thresholds the improvement is quite substantial, especially with SIC, whereas for high SINR thresholds the improvement diminishes and both schemes perform equally well.
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Polar codes for compress-and-forward in binary relay channelsBlasco-Serrano, Ricardo, Thobaben, Ragnar, Rathi, Vishwambhar, Skoglund, Mikael January 2010 (has links)
We construct polar codes for binary relay channels with orthogonal receiver components. We show that polar codes achieve the cut-set bound when the channels are symmetric and the relay-destination link supports compress-and-forward relaying based on Slepian-Wolf coding. More generally, we show that a particular version of the compress-and-forward rate is achievable using polar codes for Wyner-Ziv coding. In both cases the block error probability can be bounded as O(2-Nβ) for 0 < β < 1/2 and sufficiently large block length N. / <p>© 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111207</p>
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Exploiting diversity in wireless channels with bit-interleaved coded modulation and iterative decoding (BICM-ID)Tran, Huu Nghi 23 April 2008
<p>This dissertation studies a state-of-the-art bandwidth-efficient coded modulation technique, known as bit interleaved coded modulation with iterative decoding (BICM-ID), together with various diversity techniques to dramatically improve the performance of digital communication systems over wireless channels.</p>
<p>For BICM-ID over a single-antenna frequency non-selective fading channel, the problem of mapping over multiple symbols, i.e., multi-dimensional (multi-D) mapping, with 8-PSK constellation is investigated. An explicit algorithm to construct a good multi-D mapping of 8-PSK to improve the asymptotic performance of BICM-ID systems is introduced. By comparing the performance of the proposed mapping with an unachievable lower bound, it is conjectured that the proposed mapping is the global optimal mapping. The superiority of the proposed mapping over the best conventional (1-dimensional complex) mapping and the multi-D mapping found previously by computer search is thoroughly demonstrated.</p>
<p>In addition to the mapping issue in single-antenna BICM-ID systems, the use of signal space diversity (SSD), also known as linear constellation precoding (LCP), is considered in BICM-ID over frequency non-selective fading channels. The performance analysis of BICM-ID and complex N-dimensional signal space diversity is carried out to study its performance limitation, the choice of the rotation matrix and the design of a low-complexity receiver. Based on the design criterion obtained from a tight error bound, the optimality of the rotation matrix is established. It is shown that using the class of optimal rotation matrices, the performance of BICM-ID systems over a frequency non-selective Rayleigh fading channel approaches that of the BICM-ID systems over an additive white Gaussian noise (AWGN) channel when the dimension of the signal constellation increases. Furthermore, by exploiting the sigma mapping for any M-ary quadrature amplitude modulation (QAM) constellation, a very simple sub-optimal, yet effective iterative receiver structure suitable for signal constellations with large dimensions is proposed. Simulation results in various cases and conditions indicate that the proposed receiver can achieve the analytical performance bounds with low complexity.</p>
<p>The application of BICM-ID with SSD is then extended to the case of cascaded Rayleigh fading, which is more suitable to model mobile-to-mobile communication channels. By deriving the error bound on the asymptotic performance, it is first illustrated that for a small modulation constellation, a cascaded Rayleigh fading causes a much more severe performance degradation than a
conventional Rayleigh fading. However, BICM-ID employing SSD with a sufficiently large constellation can close the performance gap between the Rayleigh and cascaded Rayleigh fading channels, and their performance can closely approach that over an AWGN channel.</p>
<p>In the next step, the use of SSD in BICM-ID over frequency selective Rayleigh fading channels employing a multi-carrier modulation technique known as orthogonal frequency division multiplexing (OFDM) is studied. Under the assumption of correlated fading over subcarriers, a tight bound on the asymptotic error performance for the general case of applying SSD over all N subcarriers is derived and used to establish the best achievable asymptotic performance by SSD. It is then shown that precoding over subgroups of at least L subcarriers per group, where L is the number of channel taps, is sufficient to obtain this best asymptotic error performance, while significantly reducing the receiver complexity. The optimal joint subcarrier grouping and rotation matrix design is subsequently determined by solving the Vandermonde linear system. Illustrative examples show a good agreement between various analytical and simulation results.</p>
<p>Further, by combining the ideas of multi-D mapping and subcarrier grouping, a novel power and bandwidth-efficient bit-interleaved coded modulation with OFDM and iterative decoding (BI-COFDM-ID) in which multi-D mapping is performed over a group of subcarriers for broadband transmission in a frequency selective fading environment is proposed. A tight bound on the asymptotic error performance is developed, which shows that subcarrier mapping and grouping have independent impacts on the overall error performance, and hence they can be independently optimized. Specifically, it is demonstrated that the optimal subcarrier mapping is similar to the optimal multi-D mapping for BICM-ID in frequency non-selective Rayleigh fading environment, whereas the optimal subcarrier grouping is the same with that of OFDM with SSD. Furthermore, analytical and simulation results show that the proposed system with the combined optimal subcarrier mapping and grouping can achieve the full channel diversity without using SSD and provide significant coding gains as compared to the previously studied BI-COFDM-ID with the same power, bandwidth and receiver complexity.</p>
<p>Finally, the investigation is extended to the application of BICM-ID over a multiple-input multiple-output (MIMO) system equipped with multiple antennas at both the transmitter and the receiver to exploit both time and spatial diversities, where neither the transmitter nor the receiver knows the channel fading coefficients. The concentration is on the class of unitary constellation, due to its advantages in terms of both information-theoretic capacity and error probability. The tight error bound with respect to the asymptotic performance is also derived for any given unitary constellation and mapping rule. Design criteria regarding the choice of unitary constellation and mapping are then established. Furthermore, by using the unitary constellation obtained from orthogonal design with quadrature phase-shift keying (QPSK or 4-PSK) and 8-PSK, two different mapping rules are proposed. The first mapping rule gives the most suitable mapping for systems that do not implement iterative processing, which is similar to a Gray mapping in coherent channels. The second mapping rule yields the best mapping for systems with iterative decoding. Analytical and simulation results show that with the proposed mappings of the unitary constellations obtained from orthogonal designs, the asymptotic error performance of the iterative systems can closely approach a lower bound which is applicable to any unitary constellation and mapping.</p>
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Iterative low-complexity multiuser detection and decoding for coded UWB systemsSathish, Arun D. 07 1900 (has links)
In general, ultra wideband (UWB) signals are transmitted using ~'eIYshort pulses m tiIae
domain, thus promising very high data rates. In this thesis, a recei'ler structure is proposed for
decoding multiuser information data in a convolutionally coded UWB system. The proposed
iterative receiver has three stages: a pulse detector, a symbol detector, and a channel decoder.
Each of these stages outputs soft values, which are used as a priori information in the next
iteration. Simulation results show that the proposed system can provide performance very close
to a single-user system. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering. / "July 2006." / Incluldes bibliographic references (leaves 29-31)
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Investigation of LDPC code in DVB-S2Ge, Hanxiao January 2012 (has links)
As one of the most powerful error-correcting codes, Low-density parity check codes are widely used in digital communications. Because of the performance of LDPC codes are capable to close the shannon limited extraordinarily, LDPC codes are to be used in the new Digital Video Broadcast-Satellite-Second Generation(DVB-S2) and it is the first time that LDPC codes are included in the broadcast standard in 2003. In this thesis, a restructured parity-check matrices which can be divided into sub-matrices for LDPC code in DVB-S2 is provided. Corresponded to this restructured parity-check matrix, a reconstructed decoding table is invented. The encoding table of DVB-S2 standard only could obtain the unknown check nodes from known variable nodes, while the decoding table this thesis provided could obtain the unknown variable nodes from known check nodes what is exactly the Layered-massage passing algorithm needed. Layered-message passing algorithm which also known as "Turbo-decoding message passing" is used to reduce the decoding iterations and memory storage for messages. The thesis also investigate Bp algorithm, lambda-min algorithm, Min-sum algorithm and SISO-s algorithm, meanwhile, simulation results of these algorithms and schedules are also presented.
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Turbo Equalization for HSPA / Turboutjämning för HSPAKonuskan, Cagatay January 2010 (has links)
New high quality mobile telecommunication services are offered everyday and the demand for higher data rates is continuously increasing. To maximize the uplink throughput in HSPA when transmission is propagated through a dispersive channel causing self-interference, equalizers are used. One interesting solution, where the equalizer and decoder exchange information in an iterative way, for improving the equalizer performance is Turbo equalization. In this thesis a literature survey has been performed on Turbo equalization methods and a chosen method has been implemented for the uplink HSPA standard to evaluate the performance in heavily dispersive channels. The selected algorithm has been adapted for multiple receiving antennas, oversampled processing and HARQ retransmissions. The results derived from the computer based link simulations show that the implemented algorithm provide a gain of approximately 0.5 dB when performing up to 7 Turbo equalization iterations. Gains up to 1 dB have been obtained by disabling power control, not using retransmission combining and utilizing a single receiver antenna. The algorithm has also been evaluated considering alternative dispersive channels, Log-MAP decoding, different code rates, number of Turbo equalization iterations and number of Turbo decoding iterations. The simulation results do not motivate a real implementation of the chosen algorithm considering the increased computational complexity and small gain achieved in a full featured receiver system. Further studies are needed before concluding the HSPA uplink Turbo equalization approach.
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Exploiting diversity in wireless channels with bit-interleaved coded modulation and iterative decoding (BICM-ID)Tran, Huu Nghi 23 April 2008 (has links)
<p>This dissertation studies a state-of-the-art bandwidth-efficient coded modulation technique, known as bit interleaved coded modulation with iterative decoding (BICM-ID), together with various diversity techniques to dramatically improve the performance of digital communication systems over wireless channels.</p>
<p>For BICM-ID over a single-antenna frequency non-selective fading channel, the problem of mapping over multiple symbols, i.e., multi-dimensional (multi-D) mapping, with 8-PSK constellation is investigated. An explicit algorithm to construct a good multi-D mapping of 8-PSK to improve the asymptotic performance of BICM-ID systems is introduced. By comparing the performance of the proposed mapping with an unachievable lower bound, it is conjectured that the proposed mapping is the global optimal mapping. The superiority of the proposed mapping over the best conventional (1-dimensional complex) mapping and the multi-D mapping found previously by computer search is thoroughly demonstrated.</p>
<p>In addition to the mapping issue in single-antenna BICM-ID systems, the use of signal space diversity (SSD), also known as linear constellation precoding (LCP), is considered in BICM-ID over frequency non-selective fading channels. The performance analysis of BICM-ID and complex N-dimensional signal space diversity is carried out to study its performance limitation, the choice of the rotation matrix and the design of a low-complexity receiver. Based on the design criterion obtained from a tight error bound, the optimality of the rotation matrix is established. It is shown that using the class of optimal rotation matrices, the performance of BICM-ID systems over a frequency non-selective Rayleigh fading channel approaches that of the BICM-ID systems over an additive white Gaussian noise (AWGN) channel when the dimension of the signal constellation increases. Furthermore, by exploiting the sigma mapping for any M-ary quadrature amplitude modulation (QAM) constellation, a very simple sub-optimal, yet effective iterative receiver structure suitable for signal constellations with large dimensions is proposed. Simulation results in various cases and conditions indicate that the proposed receiver can achieve the analytical performance bounds with low complexity.</p>
<p>The application of BICM-ID with SSD is then extended to the case of cascaded Rayleigh fading, which is more suitable to model mobile-to-mobile communication channels. By deriving the error bound on the asymptotic performance, it is first illustrated that for a small modulation constellation, a cascaded Rayleigh fading causes a much more severe performance degradation than a
conventional Rayleigh fading. However, BICM-ID employing SSD with a sufficiently large constellation can close the performance gap between the Rayleigh and cascaded Rayleigh fading channels, and their performance can closely approach that over an AWGN channel.</p>
<p>In the next step, the use of SSD in BICM-ID over frequency selective Rayleigh fading channels employing a multi-carrier modulation technique known as orthogonal frequency division multiplexing (OFDM) is studied. Under the assumption of correlated fading over subcarriers, a tight bound on the asymptotic error performance for the general case of applying SSD over all N subcarriers is derived and used to establish the best achievable asymptotic performance by SSD. It is then shown that precoding over subgroups of at least L subcarriers per group, where L is the number of channel taps, is sufficient to obtain this best asymptotic error performance, while significantly reducing the receiver complexity. The optimal joint subcarrier grouping and rotation matrix design is subsequently determined by solving the Vandermonde linear system. Illustrative examples show a good agreement between various analytical and simulation results.</p>
<p>Further, by combining the ideas of multi-D mapping and subcarrier grouping, a novel power and bandwidth-efficient bit-interleaved coded modulation with OFDM and iterative decoding (BI-COFDM-ID) in which multi-D mapping is performed over a group of subcarriers for broadband transmission in a frequency selective fading environment is proposed. A tight bound on the asymptotic error performance is developed, which shows that subcarrier mapping and grouping have independent impacts on the overall error performance, and hence they can be independently optimized. Specifically, it is demonstrated that the optimal subcarrier mapping is similar to the optimal multi-D mapping for BICM-ID in frequency non-selective Rayleigh fading environment, whereas the optimal subcarrier grouping is the same with that of OFDM with SSD. Furthermore, analytical and simulation results show that the proposed system with the combined optimal subcarrier mapping and grouping can achieve the full channel diversity without using SSD and provide significant coding gains as compared to the previously studied BI-COFDM-ID with the same power, bandwidth and receiver complexity.</p>
<p>Finally, the investigation is extended to the application of BICM-ID over a multiple-input multiple-output (MIMO) system equipped with multiple antennas at both the transmitter and the receiver to exploit both time and spatial diversities, where neither the transmitter nor the receiver knows the channel fading coefficients. The concentration is on the class of unitary constellation, due to its advantages in terms of both information-theoretic capacity and error probability. The tight error bound with respect to the asymptotic performance is also derived for any given unitary constellation and mapping rule. Design criteria regarding the choice of unitary constellation and mapping are then established. Furthermore, by using the unitary constellation obtained from orthogonal design with quadrature phase-shift keying (QPSK or 4-PSK) and 8-PSK, two different mapping rules are proposed. The first mapping rule gives the most suitable mapping for systems that do not implement iterative processing, which is similar to a Gray mapping in coherent channels. The second mapping rule yields the best mapping for systems with iterative decoding. Analytical and simulation results show that with the proposed mappings of the unitary constellations obtained from orthogonal designs, the asymptotic error performance of the iterative systems can closely approach a lower bound which is applicable to any unitary constellation and mapping.</p>
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A behavioural and neurobiological investigation of basic reading processesCummine, Jacqueline 15 September 2009 (has links)
There are competing theories in the literature regarding the extent to which the translation of print to speech involves single or multiple routes. Regardless of the number of routes in a model, all models of reading must account for both sight vocabulary (SV) processing, which specializes in mapping whole-word representations, and phonetic decoding (PD) processing, which specializes in mapping sub-word representations. The purpose of the present work was to examine two hypotheses regarding the relationship between SV and PD: independence versus redundancy. Both behavioural and functional Magnetic Resonance Imaging (fMRI) experiments were conducted and the results supported the hypothesis that SV and PD are behaviourally and neurobiologically independent processes. Furthermore, in the interest of advancing all models of basic word recognition, the neurobiological representations of some of the sub-systems within SV and PD routes were explored and the contribution that particular brain regions make to the completion of naming particular stimuli was evaluated. Finally, basic and applied areas of research were integrated to demonstrate how diagnostic stimuli developed from basic reading research can inform us about impaired reading performance following traumatic brain injury.
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