153 research outputs found
Towards Fully Optimized BICM Transceivers
Bit-interleaved coded modulation (BICM) transceivers often use equally spaced
constellations and a random interleaver. In this paper, we propose a new BICM
design, which considers hierarchical (nonequally spaced) constellations, a
bit-level multiplexer, and multiple interleavers. It is shown that this new
scheme increases the degrees of freedom that can be exploited in order to
improve its performance. Analytical bounds on the bit error rate (BER) of the
system in terms of the constellation parameters and the multiplexing rules are
developed for the additive white Gaussian Noise (AWGN) and Nakagami- fading
channels. These bounds are then used to design the BICM transceiver. Numerical
results show that, compared to conventional BICM designs, and for a target BER
of , gains up to 3 dB in the AWGN channel are obtained. For fading
channels, the gains depend on the fading parameter, and reach 2 dB for a target
BER of and .Comment: Submitted to the IEEE Transactions on Communication
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
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
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
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
Telemetering and telecommunications research
The New Mexico State University (NMSU) Center for Space Telemetering and Telecommunications systems is engaged in advanced communications systems research. Four areas of study that are being sponsored concern investigations into the use of trellis-coded modulation (TCM). In particular, two areas concentrate on carrier synchronization research in TCM M-ary phase shift key (MPSK) systems. A third research topic is the study of interference effects on TCM, while the fourth research area is in the field of concatenated TCM systems
Improved closed-form bounds on the performance of convolutional codes with correlated Rayleigh fading
New bounds on the probability of bit error are presented for a coded communication system with binary antipodal modulation and soft-decision maximum-likelihood decoding over a correlated Rayleigh-fading channel. The bounds are closed-form expressions in terms of the code\u27s transfer function; they are illustrated by considering a system using convolutional encoding. A long-standing conjecture regarding the worst-case error event in correlated Rician fading is proven for the special case of correlated Rayleigh fading, and it is used in the development of some of the new bounds. The bounds are shown to be tighter than previously developed closed-form bounds for communications using convolutional codes in correlated Rayleigh fading
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