The performance of turbo codes can often be improved by improving the weight spectra of such codes. Methods of producing the weight spectra of turbo codes have been investigated and many improvements were made to refine the techniques. A much faster method of weight spectrum evaluation has been developed that allows calculation of weight spectra within a few minutes on a typical desktop PC. Simulation results show that new high performance turbo codes are produced by the optimisation methods presented. The two further important areas of concern are the code itself and the decoding. Improvements of the code are accomplished through optimisation of the interleaver and choice of constituent coders. Optimisation of interleaves can also be accomplished automatically using the algorithms described in this work. The addition of a CRC as an outer code proved to offer a vast improvement on the overall code performance. This was achieved without any code rate loss as the turbo code is punctured to make way for the CRC remainder. The results show a gain of 0.4dB compared to the non-CRC (1014,676) turbo code. Another improvement to the decoding performance was achieved through a combination of MAP decoding and Ordered Reliability decoding. The simulations show a performance of just 0.2dB from the Shannon limit. The same code without ordered reliability decoding has a performance curve which is 0.6dB from the Shannon limit. In situations where the MAP decoder fails to converge ordered reliability decoding succeeds in producing a codeword much closer to the received vector, often the correct codeword. The ordered reliability decoding adds to the computational complexity but lends itself to FPGA implementation.

In wireless communication, MIMO (multiple input multiple output) is one of the promising technologies which improves the range and performance of transmission without increasing the bandwidth, while providing high rates. High speed hardware MIMO decoders are one of the keys to apply this technology in applications. In order to support the high data rates, the underlying hardware must have significant processing capabilities. FPGA improves the speed of signal processing using parallelism and reconfigurability advantages. The objective of this thesis is to develop an efficient hardware architectural model for the universal lattice decoder and prototype it on FPGA. The original algorithm is modified to ensure the high data rate via taking the advantage of FPGA features. The simulation results of software, hardware are verified and the BER performance of both the algorithms is estimated. The system prototype of the decoder with 4-transmit and 4-receive antennas using a 4-PAM (Pulse amplitude modulation) supports 6.32 Mbit/s data rate for parallelpipeline implementation on FPGA platform, which is about two orders of magnitude faster than its DSP implementation.

Fountain codes have recently gained wide attention in the communications research community due to their capacity-approaching performance and rateless properties that allow them to seamlessly adapt to unknown channel statistics. This thesis of fers two key contributions. For the first, we consider the problem of low complexity decoding of Luby Transform (LT) and Raptor codes, which are classes of Fountain codes. We introduce a decoding method which has a significantly reduced compu tational load compared to the commonly used alternative of message-reset decoding with a flooding schedule. This method combines the recently proposed technique of informed dynamic scheduling combined with incremental decoding. Simulation re sults for the example of the binary symmetric channel show complexity reductions (in terms of the total required number of decoding iterations) by 87% compared to conventional message-passing decoding and 54% compared to a recently proposed incremental decoding scheme for Raptor codes. Having proposed our novel decoding method, we then focus on applying rateless codes to free-space optical (FSO) transmission systems. FSO systems enable high speed communication with relatively small deployment costs. However, FSO systems suffer a critical disadvantage, namely susceptibility to fog, smoke, and similar con ditions. A possible solution to this dilemma is the use of hybrid systems employing FSO and radio frequency (RF) transmission. As for the second contribution of this thesis, we propose the application of rateless coding for such hybrid FSO/RF sys tems. The advantages of our approach are (i) the full utilization of available FSO and RF channel resources at any time and (ii) very little feedback from the receiver. In order to substantiate these claims, we establish the pertinent capacity limits for hybrid FSO/RF transmission and present simulation results for transmission with off-the-shelf Raptor codes, which achieve realized rates close to these limits under a wide range of channel conditions.

The cooperative communication is one of technologies which can explore the space diversity to resist fading channel. The spatial diversity is achieved by allowing various terminals behaving or a virtual antenna array and forwarding signal for a source terminal in cooperative manner. Under the existence of multiple sources, resource allocation to each source user is even more crucial to enhance the system performance and achieve higher diversity gain. In this work, we proposed a multiuser relaying strategy for a cooperative network with multiple sources sharing the radio resource provided by the cooperative relays simultaneously. Different from the existing work, the set of relays forwards signals of all source users over a common channel to raise spectral efficiency. With full channel information available at relays, the set of sub-optimal precoders and decoders was proposed in terms of maximal the average SNR over all users, subject to eliminating the multiple access interference (MAI) at each destination and satisfying total power constraint among all relays. It shows from the simulation results that, compared with the conventional cooperative strategy and direct transmission, the proposed scheme provides pronounced improvement on the outage capacity. Keywords: user cooperation, multiple access, resource allocation

It is know that the LORD (Layered Orthogonal Lattice Detector) and the sphere decoding achieve performance equaling that of ML. However, both detectors have different disadvantage. When the transmit antenna number is greater than three antennas, it is difficult to apply the LORD. Therefore, we consider using the sphere decoding together with the LORD. The complexity of the sphere decoding highly depends on the initial radius. In this thesis, we intend to reduce the sphere decoding complexity by using LORD.

Fountain codes have recently gained wide attention in the communications research community due to their capacity-approaching performance and rateless properties that allow them to seamlessly adapt to unknown channel statistics. This thesis of fers two key contributions. For the first, we consider the problem of low complexity decoding of Luby Transform (LT) and Raptor codes, which are classes of Fountain codes. We introduce a decoding method which has a significantly reduced compu tational load compared to the commonly used alternative of message-reset decoding with a flooding schedule. This method combines the recently proposed technique of informed dynamic scheduling combined with incremental decoding. Simulation re sults for the example of the binary symmetric channel show complexity reductions (in terms of the total required number of decoding iterations) by 87% compared to conventional message-passing decoding and 54% compared to a recently proposed incremental decoding scheme for Raptor codes. Having proposed our novel decoding method, we then focus on applying rateless codes to free-space optical (FSO) transmission systems. FSO systems enable high speed communication with relatively small deployment costs. However, FSO systems suffer a critical disadvantage, namely susceptibility to fog, smoke, and similar con ditions. A possible solution to this dilemma is the use of hybrid systems employing FSO and radio frequency (RF) transmission. As for the second contribution of this thesis, we propose the application of rateless coding for such hybrid FSO/RF sys tems. The advantages of our approach are (i) the full utilization of available FSO and RF channel resources at any time and (ii) very little feedback from the receiver. In order to substantiate these claims, we establish the pertinent capacity limits for hybrid FSO/RF transmission and present simulation results for transmission with off-the-shelf Raptor codes, which achieve realized rates close to these limits under a wide range of channel conditions.

The advent of turbo codes in 1993 represented a significant step towards realising the ultimate capacity limit of a communication channel, breaking the link that was binding very good performance with exponential decoder complexity. Turbo codes are parallel concatenated convolutional codes, decoded with a suboptimal iterative algorithm. The complexity of the iterative algorithm increases only linearly with block length, bringing previously unprecedented performance within practical limits. This work is a further investigation of turbo codes and other concatenated schemes such as the multiple parallel concatenation and the serial concatenation. The analysis of these schemes has two important aspects, their performance under optimal decoding and the convergence of their iterative, suboptimal decoding algorithm. The connection between iterative decoding performance and the optimal decoding performance is analysed with the help of computer simulation by studying the iterative decoding error events. Methods for good performance interleaver design and code design are presented and analysed in the same way. The optimal decoding performance is further investigated by using a novel method to determine the weight spectra of turbo codes by using the turbo code tree representation, and the results are compared with the results of the iterative decoder. The method can also be used for the analysis of multiple parallel concatenated codes, but is impractical for the serial concatenated codes. Non-optimal, non-iterative decoding algorithms are presented and compared with the iterative algorithm. The convergence of the iterative algorithm is investigated by using the Cauchy criterion. Some insight into the performance of the concatenated schemes under iterative decoding is found by separating error events into convergent and non-convergent components. The sensitivity of convergence to the Eb/Ng operating point has been explored.

Fountain codes have recently gained wide attention in the communications research community due to their capacity-approaching performance and rateless properties that allow them to seamlessly adapt to unknown channel statistics. This thesis of fers two key contributions. For the first, we consider the problem of low complexity decoding of Luby Transform (LT) and Raptor codes, which are classes of Fountain codes. We introduce a decoding method which has a significantly reduced compu tational load compared to the commonly used alternative of message-reset decoding with a flooding schedule. This method combines the recently proposed technique of informed dynamic scheduling combined with incremental decoding. Simulation re sults for the example of the binary symmetric channel show complexity reductions (in terms of the total required number of decoding iterations) by 87% compared to conventional message-passing decoding and 54% compared to a recently proposed incremental decoding scheme for Raptor codes. Having proposed our novel decoding method, we then focus on applying rateless codes to free-space optical (FSO) transmission systems. FSO systems enable high speed communication with relatively small deployment costs. However, FSO systems suffer a critical disadvantage, namely susceptibility to fog, smoke, and similar con ditions. A possible solution to this dilemma is the use of hybrid systems employing FSO and radio frequency (RF) transmission. As for the second contribution of this thesis, we propose the application of rateless coding for such hybrid FSO/RF sys tems. The advantages of our approach are (i) the full utilization of available FSO and RF channel resources at any time and (ii) very little feedback from the receiver. In order to substantiate these claims, we establish the pertinent capacity limits for hybrid FSO/RF transmission and present simulation results for transmission with off-the-shelf Raptor codes, which achieve realized rates close to these limits under a wide range of channel conditions. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Evaluation of soft output decoding for turbo codes is presented. Coding theory related to this research is studied, including convolutional encoding and Viterbi decoding. Recursive systematic convolutional (RSC) codes and nonuniform interleavers commonly used in turbo code encoder design are analyzed. Fundamentals such as reliability estimation, log-likelihood algebra, and soft channel outputs for soft output Viterbi algorithm (SOVA) turbo code decoding are examined. The modified Viterbi metric that incorporates a-priori information used for SOVA decoding is derived. A low memory implementation of the SOVA decoder is shown. The iterative SOVA turbo code decoding algorithm is described with illustrative examples. The performance of turbo codes are evaluated through computer simulation. It has been found that the SOVA turbo code decoding algorithm, as described in the literature, did not perform as well as the published results. Modifications to the decoding algorithm are suggested. The simulated turbo code performance results shown after these modifications more closely match with current published research work. / Master of Science

<p>Sammanfattning</p><p> </p><p>Syfte: Att undersöka två läsmetoders effekter på tolv elever från skolår 2, 3 och 4 avseende fonologisk och ortografisk läsförmåga, läsflyt, läsförståelse och RAN (Rapid Automatic Naming) samt jämföra resultaten med en grupp elever som fått traditionell specialundervisning under samma tid.</p><p> </p><p>Metod: 52 elever genomförde en screening med avseende att mäta läsflyt och läsförståelse. Av dessa valdes 12 elever ut som hade svårigheter i läsflyt och korrekt läsning, fyra elever från varje skolår, 5 pojkar och 7 flickor. Eleverna delades i två lika stora grupper som tränade ordavkodning med två olika metoder i en-en-undervisning, 20 minuter tre gånger per vecka i sex veckor. De 18 eleverna fick utföra ytterligare fem läs- och skrivtest före och efter interventionen.</p><p> </p><p>Resultat: De båda interventionsgrupperna förbättrade sina resultat på flera test mer än gruppen som fick traditionell specialundervisning. Elever som tränat Rydaholmsmetoden fick bättre resultat i alla högläsningstest utom ett. Elever som tränat datorprogrammet Hitta ord fick bättre resultat i nonsensordtestet samt de båda tystläsningstesten.</p><p> </p><p>Diskussion: Resultatet skulle kunna tydas så att Rydaholmsmetoden tränar artikulation, ordmobilisering och läsflyt i högläsning medan datorprogrammet Hitta Ord tränar den ortografiska och fonologiska läsningen mer. Vidare skulle studiens resultat kunna tolkas så att en-en-undervisning är effektivare än traditionell specialundervisning.</p> / <p>Abstract</p><p>Aim: To investigate two reading methods effect on twelve students from school year 2, 3 and 4 in phonologic and orthographic reading, reading fluency and RAN comparing to traditional special education.</p><p> </p><p>Method: 52 students were tested in reading fluency. Twelve students with reading problems were elected, four students from each class, 5 boys and 7 girls. They were divided in two groups and had an intervention in two different word reading program in a one-to-one-torturing for 20 minutes three times a week in six weeks. A group of six students, were chosen as a comparing group. All 18 students were testing the same battery of tests before and after the six weeks.</p><p> </p><p>Result: The result showed that both intervention groups were improved their result more than the group trained with traditional special education. Rydaholms method group improved more in all loud reading tests except Nonsen word reading test while the computer trained group improved more in both cilent reading test and made a small improve in Nonsen word reading test.</p><p> </p><p>Discussion: The result could interpret that Rydaholm method trained articulation, word mobilization and loud reading fluency more while the computer based program trained orthographic and phonological reading more. The result could also interpret that one-to-one-torturing improve reading ability more than traditional special education in this reading abilities.</p><p> </p>