5 research outputs found
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Implementation of Turbo Codes on GNU Radio
This thesis investigates the design and implementation of turbo codes over the GNU radio. The turbo codes is a class of iterative channel codes which demonstrates strong capability for error correction. A software defined radio (SDR) is a communication system which can implement different modulation schemes and tune to any frequency band by means of software that can control the programmable hardware. SDR utilizes the general purpose computer to perform certain signal processing techniques. We implement a turbo coding system using the Universal Software Radio Peripheral (USRP), a widely used SDR platform from Ettus. Detail configuration and performance comparison are also provided in this research
On the Error Statistics of Turbo Decoding for Hybrid Concatenated Codes Design
In this paper we propose a model for the generation of error patterns at the output of a turbo decoder. One of the advantages of this model is that it can be used to generate the error sequence with little effort. Thus, it provides a basis for designing hybrid concatenated codes (HCCs) employing the turbo code as inner code. These coding schemes combine the features of parallel and serially concatenated codes and thus offer more freedom in code design. It has been demonstrated, in fact, that HCCs can perform closer to capacity than serially concatenated codes while still maintaining a minimum distance that grows linearly with block length. In particular, small memory-one component encoders are sufficient to yield asymptotically good code ensembles for such schemes. The resulting codes provide low complexity encoding and decoding and, in many cases, can be decoded using relatively few iterations
Repeat--punctured turbo codes and superorthogonal convolutional turbo codes.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.The use of error-correction coding techniques in communication systems has become
extremely imperative. Due to the heavy constraints faced by systems engineers more
attention has been given to developing codes that converge closer to the Shannon
theoretical limit. Turbo codes exhibit a performance a few tenths of a decibel from the
theoretical limit and has motivated a lot of good research in the channel coding area in
recent years.
In the under-mentioned dissertation, motivated by turbo codes, we study the use of three
new error-correction coding schemes: Repeat-Punctured Superorthogonal Convolutional
Turbo Codes, Dual-Repeat-Punctured Turbo Codes and Dual-Repeat-Punctured
Superorthogonal Convolutional Turbo Codes, applied to the additive white Gaussian noise
channel and the frequency non-selective or flat Rayleigh fading channel. The performance
of turbo codes has been shown to be near the theoretical limit in the AWGN channel. By
using orthogonal signaling, which allows for bandwidth expansion, the performance of the
turbo coding scheme can be improved even further. Since the resultant is a low-rate code,
the code is mainly suitable for spread-spectrum modulation applications. In conventional
turbo codes the frame length is set equal to the interleaver size; however, the codeword
distance spectrum of turbo codes improves with an increasing interleaver size. It has been
reported that the performance of turbo codes can be improved by using repetition and
puncturing. Repeat-punctured turbo codes have shown a significant increase in
performance at moderate to high signal-to-noise ratios. In this thesis, we study the use of
orthogonal signaling and parallel concatenation together with repetition (dual and single)
and puncturing, to improve the performance of the superorthogonal convolutional turbo
code and the conventional turbo code for reliable and effective communications.
During this research, three new coding schemes were adapted from the conventional turbo
code; a method to evaluate the union bounds for the AWGN channel and flat Rayleigh
fading channel was also established together with a technique for the weight-spectrum
evaluation
Repeat-punctured turbo coded cooperation.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2008.Transmit diversity usually employs multiple antennas at the transmitter. However, many
wireless devices such as mobile cellphones, Personal Digital Assistants (PDAs), just to name
a few, are limited by size, hardware complexity, power and other constraints to just one
antenna. A new paradigm called cooperative communication which allows single antenna
mobiles in a multi-user scenario to share their antennas has been proposed lately. This
multi-user configuration generates a virtual Multiple-Input Multiple-Output system, leading
to transmit diversity. The basic approach to cooperation is for two single-antenna users to use
each other's antenna as a relay in which each of the users achieves diversity. Previous
cooperative signaling methods encompass diverse forms of repetition of the data transmitted
by the partner to the destination. A new scheme called coded cooperation [15] which
integrates user cooperation with channel coding has also been proposed. This method
maintains the same code rate, bandwidth and transmit power as a similar non-cooperative
system, but performs much better than previous signaling methods [13], [14] under various
inter-user channel qualities.
This dissertation first discusses the coded cooperation framework that has been proposed
lately [19], coded cooperation with Repeat Convolutional Punctured Codes (RCPC) codes
and then investigates the application of turbo codes in coded cooperation.
In this dissertation we propose two new cooperative diversity schemes which are the
Repeat-Punctured Turbo Coded cooperation and coded cooperation using a Modified
Repeat-Punctured Turbo Codes. Prior to that, Repeat-Punctured Turbo codes are introduced.
We characterize the performance of the two new schemes by developing the analytical bounds
for bit error rate, which is confirmed by computer simulations. Finally, the turbo coded
cooperation using the Forced Symbol Method (FSM) is presented and validated through
computer simulations under various inter-user Signal-to-Noise Ratios (SNRs)
ON TURBO CODES AND OTHER CONCATENATED SCHEMES IN COMMUNICATION SYSTEMS
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.SateUite Research Centre
Department of Communication and Electronic Engineerin