In this article, we propose an index modulation system suitable for optical communications, where the intensity of the light is modulated along the time, space and frequency dimensions, building a Frequency-Hopping Spatial Multi-Pulse Position Modulation (FH-SMPPM). We analyze its performance from the point of view of its efficiency in power and spectrum, and its implementation complexity and required receiver latency. We analyze its error probability in the case of the non-turbulent free-space optical (FSO) channel. We derive formulas for the average symbol and bit error probabilities, and the simulation results show that they are tight enough for a wide range of signal-to-noise ratios and system parameters. We compare FH-SMPPM with other proposed index modulated systems of the same nature, and we highlight its distinctive advantages, like the flexibility to build an appropriate waveform under different constraints and objectives. Moreover, FH-SMPPM shows to be better performing in BER/SER and/or offer advantages in efficiency with respect to those alternatives, thus offering the possibility to be adopted for a variety of contexts.

The massive deployment of light-emitting diode (LED) lightning infrastructure has opened the opportunity to reuse it as visible light communication (VLC) to leverage the current RF spectrum crisis in indoor scenarios. One of the main problems in VLC is the limited dynamic range of LEDs and their nonlinear response, which may lead to a severe degradation in the communication, and more specifically in the bit error rate (BER). This is aggravated by the extensive usage of multicarrier multiplexing, based on optical orthogonal frequency division multiplexing (O-OFDM), characterized by a high peak-to-average power ratio. Here, we present a chaos-based coded modulation (CCM) setup specifically adapted to the LED nonlinearities. It replaces the usual modulation, while keeping the multicarrier O-OFDM structure unchanged. First, we obtain a semi-analytical bound for the bit error probability, taking into account the LED nonlinear response. The bound results particularly tight for the range of signal-to-noise ratio of interest. Then, we propose a method to design the modulator based on optimization techniques. The objective function is the semi-analytical bound, and the optimization is applied to a parameterization of the CCM conjugation function. This appropriately shapes the chaotic waveform and leads to BER improvements that outperform classical counterparts under ideal predistortion.

Chaos-based coded modulation (CCM) systems have been shown to be competitive against important wireless channels impairments, like fading. Nonetheless, these systems have not been tested yet in a real-world scenario, and their performance has only been explored using theoretical and numerical bounds, and validated by simulation. In this proposal, we take advantage of the availability of Software-Defined Radio (SDR) hardware and open source GNU Radio software libraries to carry on a full proof-of-concept. The implementation issues and tradeoffs for such CCM systems are addressed and detailed. The performance results, compared against classical counterparts, validate experimentally what had previously been shown by simulation, and exhibit gains against classical counterparts.

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.

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.