1,997 research outputs found
Permutation Trellis Coded Multi-level FSK Signaling to Mitigate Primary User Interference in Cognitive Radio Networks
We employ Permutation Trellis Code (PTC) based multi-level Frequency Shift
Keying signaling to mitigate the impact of Primary Users (PUs) on the
performance of Secondary Users (SUs) in Cognitive Radio Networks (CRNs). The
PUs are assumed to be dynamic in that they appear intermittently and stay
active for an unknown duration. Our approach is based on the use of PTC
combined with multi-level FSK modulation so that an SU can improve its data
rate by increasing its transmission bandwidth while operating at low power and
not creating destructive interference for PUs. We evaluate system performance
by obtaining an approximation for the actual Bit Error Rate (BER) using
properties of the Viterbi decoder and carry out a thorough performance analysis
in terms of BER and throughput. The results show that the proposed coded system
achieves i) robustness by ensuring that SUs have stable throughput in the
presence of heavy PU interference and ii) improved resiliency of SU links to
interference in the presence of multiple dynamic PUs.Comment: 30 pages, 12 figure
Super-orthogonal space-time turbo codes in Rayleigh fading channels.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.The vision of anytime, anywhere communications coupled by the rapid growth of
wireless subscribers and increased volumes of internet users, suggests that the
widespread demand for always-on access data, is sure to be a major driver for the
wireless industry in the years to come. Among many cutting edge wireless
technologies, a new class of transmission techniques, known as Multiple-Input
Multiple-Output (MIMO) techniques, has emerged as an important technology
leading to promising link capacity gains of several fold increase in data rates and
spectral efficiency. While the use of MIMO techniques in the third generation (3G)
standards is minimal, it is anticipated that these technologies will play an important
role in the physical layer of fixed and fourth generation (4G) wireless systems.
Concatenated codes, a class of forward error correction codes, of which Turbo codes
are a classical example, have been shown to achieve reliable performance which
approach the Shannon limit. An effective and practical way to approach the capacity
of MIMO wireless channels is to employ space-time coding (STC). Space-Time
coding is based on introducing joint correlation in transmitted signals in both the
space and time domains. Space-Time Trellis Codes (STTCs) have been shown to
provide the best trade-off in terms of coding gain advantage, improved data rates and
computational complexity.
Super-Orthogonal Space-Time Trellis Coding (SOSTTC) is the recently proposed
form of space-time trellis coding which outperforms its predecessor. The code has a
systematic design method to maximize the coding gain for a given rate, constellation
size, and number of states. Simulation and analytical results are provided to justify the
improved performance. The main focus of this dissertation is on STTCs, SOSTTCs
and their concatenated versions in quasi-static and rapid Rayleigh fading channels.
Turbo codes and space-time codes have made significant impact in terms of the
theory and practice by closing the gap on the Shannon limit and the large capacity gains provided by the MIMO channel, respectively. However, a convincing solution
to exploit the capabilities provided by a MIMO channel would be to build the turbo
processing principle into the design of MIMO architectures. The field of concatenated
STTCs has already received much attention and has shown improved performance
over conventional STTCs. Recently simple and double concatenated STTCs
structures have shown to provide a further improvement performance. Motivated by
this fact, two concatenated SOSTTC structures are proposed called Super-orthogonal
space-time turbo codes. The performance of these new concatenated SOSTTC is
compared with that of concatenated STTCs and conventional SOSTTCs with
simulations in Rayleigh fading channels. It is seen that the SOST-CC system
outperforms the ST-CC system in rapid fading channels, whereas it maintains
performance similar to that in quasi-static. The SOST-SC system has improved
performance for larger frame lengths and overall maintains similar performance with
ST-SC systems. A further investigation of these codes with channel estimation errors
is also provided
Trellis phase codes for power-bandwith efficient satellite communications
Support work on improved power and spectrum utilization on digital satellite channels was performed. Specific attention is given to the class of signalling schemes known as continuous phase modulation (CPM). The specific work described in this report addresses: analytical bounds on error probability for multi-h phase codes, power and bandwidth characterization of 4-ary multi-h codes, and initial results of channel simulation to assess the impact of band limiting filters and nonlinear amplifiers on CPM performance
Convolutional coding techniques for data protection
Results of research on the use of convolutional codes in data communications are presented. Convolutional coding fundamentals are discussed along with modulation and coding interaction. Concatenated coding systems and data compression with convolutional codes are described
EXIT charts for system design and analysis
Near-capacity performance may be achieved with the aid of iterative decoding, where extrinsic soft information is exchanged between the constituent decoders in order to improve the attainable system performance. Extrinsic information Transfer (EXIT) charts constitute a powerful semi-analytical tool used for analysing and designing iteratively decoded systems. In this tutorial, we commence by providing a rudimentary overview of the iterative decoding principle and the concept of soft information exchange. We then elaborate on the concept of EXIT charts using three iteratively decoded prototype systems as design examples. We conclude by illustrating further applications of EXIT charts, including near-capacity designs, the concept of irregular codes and the design of modulation schemes
Turbo receivers for interleave-division multiple-access systems
In this paper several turbo receivers for Interleave-Division Multiple-Access (IDMA) systems will be discussed. The multiple access system model is presented first. The optimal, Maximum A Posteriori (MAP) algorithm, is then presented. It will be shown that the use of a precoding technique at the emitter side is applicable to IDMA systems. Several low complexity Multi-User Detector (MUD), based on the Gaussian approximation, will be next discussed. It will be shown that the MUD with Probabilistic Data Association (PDA) algorithm provides faster convergence of the turbo receiver. The discussed turbo receivers will be evaluated by means of Bit Error Rate (BER) simulations and EXtrinsic Information Transfer (EXIT) charts
On Optimal TCM Encoders
An asymptotically optimal trellis-coded modulation (TCM) encoder requires the
joint design of the encoder and the binary labeling of the constellation. Since
analytical approaches are unknown, the only available solution is to perform an
exhaustive search over the encoder and the labeling. For large constellation
sizes and/or many encoder states, however, an exhaustive search is unfeasible.
Traditional TCM designs overcome this problem by using a labeling that follows
the set-partitioning principle and by performing an exhaustive search over the
encoders. In this paper we study binary labelings for TCM and show how they can
be grouped into classes, which considerably reduces the search space in a joint
design. For 8-ary constellations, the number of different binary labelings that
must be tested is reduced from 8!=40320 to 240. For the particular case of an
8-ary pulse amplitude modulation constellation, this number is further reduced
to 120 and for 8-ary phase shift keying to only 30. An algorithm to generate
one labeling in each class is also introduced. Asymptotically optimal TCM
encoders are tabulated which are up to 0.3 dB better than the previously best
known encoders
Advanced channel coding for space mission telecommand links
We investigate and compare different options for updating the error
correcting code currently used in space mission telecommand links. Taking as a
reference the solutions recently emerged as the most promising ones, based on
Low-Density Parity-Check codes, we explore the behavior of alternative schemes,
based on parallel concatenated turbo codes and soft-decision decoded BCH codes.
Our analysis shows that these further options can offer similar or even better
performance.Comment: 5 pages, 7 figures, presented at IEEE VTC 2013 Fall, Las Vegas, USA,
Sep. 2013 Proc. IEEE Vehicular Technology Conference (VTC 2013 Fall), ISBN
978-1-6185-9, Las Vegas, USA, Sep. 201
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