Francisco J. Escribano

Chaos-Coded Modulations Over Rician and Rayleigh Flat Fading Channels

In this brief, we analyze a kind of chaos-coded modulations over both Rician and Rayleigh frequency non-selective uncorrelated fading in the presence of additive white Gaussian noise. We provide bounds both for the case when perfect channel-state information (CSI) is available at the decoder and when there is no CSI. We show that the bounds proposed can be tight enough to give reason of the behavior of these systems in a flat fading channel. We compare the results with a related trellis-coded modulation and show that the degradation in performance can be at least as low as with conventional coded modulation systems.

Interleaver Design for Parallel Concatenated Chaos-Based Coded Modulations

It is a well known property that turbo-like systems owe their success to the principle of reducing error event multiplicities rather than just minimizing related error distances. It has also been shown that Parallel Concatenated Chaos-Based Coded Modulations exploit further this principle, and this article explains how to take advantage of their typical error event structure to heuristically build interleavers with improved error floor properties. Simulations will prove the validity of the approach, as well as its limits and trade-offs.

Turbo-like structures for chaos encoding and decoding

In this paper, we explain how to build a turbo-like structure with binary inputs and chaotic outputs for efficient coding and decoding in additive white Gaussian noise (AWGN). We analyze the convergence of the decoding algorithm, the performance in the error floor region and explain minimum distance properties of the resulting codes.

Design of a New Differential Chaos-Shift-Keying System for Continuous Mobility

Conventional differential chaos-shift-keying systems (DCSK) are not the most suitable for supporting continuous-mobility scenarios. Therefore, in this paper an improved continuous-mobility differential chaos-shift-keying system (CM-DCSK) is presented that provides greater agility and improved performance in fast fading channels without accurate channel estimation while still being simple compared to a conventional DCSK system. A new DCSK frame signal is designed to reach this goal. In our new frame design, each reference sample is followed by a data carrier sample. This modification of the system design reduces the hardware complexity of DCSK because it requires a shorter wideband delay line and significantly improves the performance over fast fading channels while keeping the non-coherent nature of the transmission system. Once the design is explained, the bit error rate performance is computed over a multipath fast fading channel and compared to the conventional DCSK system. Simulation results confirm the advantages of this new noncoherent spread-spectrum design that can support mobility.

Chaos-Based Turbo Systems in Fading Channels

The growing demand for ubiquitous wireless communication services requires powerful coding and modulation schemes to counteract the signal degradation in the air interface, preferably without resorting to costly hardware. Previous work has demonstrated that chaos-based coded modulations could be robust in the flat fading channel. This paper illustrates that, as the flat fading channel quality degrades, parallel concatenated chaos-based coded modulations can provide better error performance than non-chaotic counterparts. Therefore, this joint coding and modulation approach may contribute to power saving in common adverse channel conditions. Moreover, it is shown that it is possible to manage its spectral efficiency while keeping its robustness under fading.

Improving the Performance of Chaos-Based Modulations Via Serial Concatenation

This paper proposes a serially concatenated system with an outer convolutional channel encoder and an inner chaos-based coded modulator. With the help of the principles of symbolic dynamics, the chaotic modulation can be described in terms of a trellis. Owing to this, we show that the resulting system can be designed and analyzed following developments made for serially concatenated channel codes (SCCCs) or bit-interleaved coded-modulation systems. We show how the iterative decoding algorithm used in this concatenated framework can be analyzed through the well-known extrinsic information transfer chart device and how the bit error rate can be bounded using the transfer function of the convolutional channel encoder. Comparison with a related SCCC system in both additive white Gaussian noise and frequency-nonselective fading channels shows that this kind of chaos-based systems keeps the potential advantages of coded-modulation-based systems. We are thus confident that the principles shown here can lead to the design of competitive chaotic discrete communication systems.

Evaluation of channel coding and decoding algorithms using discrete chaotic maps

In this paper we address the design of channel encoding algorithms using one-dimensional nonlinear chaotic maps starting from the desired invariant probability density function (pdf) of the data sent to the channel. We show that, with some simple changes, it is straightforward to make use of a known encoding framework based upon the Bernoulli shift map and adapt it readily to carry the information bit sequence produced by a binary source in a practical way. On the decoder side, we introduce four already known decoding algorithms and compare the resulting performance of the corresponding transmitters. The performance in terms of the bit error rate shows that the most important design clue is related not only to the pdf of the data produced by the chosen discrete map: the own dynamics of the maps is also of the highest importance and has to be taken into account when designing the whole transmitting and receiving system. We also show that a good performance in such systems needs the extensive use of all the evidence stored in the whole chaotic sequence.

Parallel concatenated chaos coded modulations

In this article we propose a parallel concatenated encoder similar to a turbo trellis coded modulation, but where the constituent encoders are chaos coded modulators. We show that, even when the uniform error property does not hold for the kind of constituent chaos coded modulations employed, it is still possible to draw a reasonable bound for the bit error probability at the error floor region based on the interleaver structure. The simulations validate the bounds and show that the dynamics of the underlying chaotic maps, rather than the quantization level of the constituent encoders, is the most important factor to account for the error rate behaviour at the error floor region.

Competitive decoders for turbo-like chaos-based systems

Recent work has shown that chaos-based communication systems can yield performances as good as their non-chaotic counterparts in additive white Gaussian noise (AWGN), and behave even better in flat-fading channels. However, much of this work relies on computer simulations and there is still a need to study in depth the implementation issues of such systems. The authors address for the first time a fixed-point arithmetic implementation of the iterative decoding algorithm for a recently proposed and successful class of parallel concatenated chaos-based coded modulations. The novel digital signal processor (DSP) results demonstrate that it is possible to implement in standard hardware competitive chaos-based communication systems.

ITERATIVELLY DECODING CHAOS ENCODED BINARY SIGNALS

In the present article we propose a new soft-input softoutput (SISO) decoding module for a chaos-channel encoded binary signal. When the chaos based channel encoder is used as inner encoder and a convolutional encoder is used as outer encoder in a serial concatenation scheme, the signal can be thus iterativelly and jointly decoded by means of the corresponding SISO decoders. This allows the transfer of bit extrinsic information for a nal Maximum a Posteriori (MAP) decoding of the bit information. We believe that the design of this new chaos based SISO decoding module opens a road for new developments to make chaos based communications more robust and efcient.