White Light Constrained Multi-Primary Modulation for Visible Light Communication

The application of visible light communication (VLC) systems is to transmit data while maintaining efficient and good quality illumination service. In order to meet standard lighting requirements when multi-colored modulation techniques are used, such as color shift keying (CSK), the color fluctuation becomes a relevant issue. This paper presents a multi- primary (multi-color) modulation technique which provides reliable data transmission while keeping a strong constraint on the light color illuminated by every symbol of the modulation alphabet. The number of possible primary color combinations that ensure white light are calculated for a given set of multi-color light sources. The system performance in terms of bit error rate for different constellation is evaluated and compared against other multi-color VLC schemes in the literature, considering a range of channel impairments due to the optical front-end components

Trace-Orthogonal PPM-Space Time Block Coding Under Rate Constraints for Visible Light Communication

Visible light communications (VLC) represents a new frontier of communications allowing high data-rate Internet access, specially in indoor environments, where the use of light emitting diodes (LEDs) is growing as a viable alternative to traditional illumination. As a result, LED output intensity can be varied faster than human eye can perceive, thus guaranteeing simultaneous wireless communications and illumination. One of the key challenges is the limited modulation bandwidth of sources that is typically around several MHz. The use of multiple input and multiple output (MIMO) techniques in optical wireless system helps to increase the capacity of the system and thus improve the system performance. In this paper, we investigate the use of an optical MIMO technique jointly with pulse position modulation (PPM) in order to improve the data rates without reducing the reliability of the link. PPM is known to be signal-to-noise ratio efficient modulation format, while it is bandwidth inefficient so the use of MIMO can compensate that drawback with reasonable complexity. Furthermore, an offline tool for VLC system planning, including error probability and transmission rate, has been proposed in order to solve the tradeoff between transmission rate and error rate. Finally, several numerical results and performance comparisons are reported

LAST: a framework to Localize, Access, Schedule and Transmit in Indoor VLC Systems

The need allowing indoor access to the Internet services requires to reduce the electromagnetic pollution. Recently, the scientific community is looking for alternatives to the use of radio frequency communication, leading to propose and study the new paradigm of visible light communications. In order to present a system implementing transmission and access procedures, we propose a logical stream starting from user localization, so as to decide which LEDs can provide access, thus basically performing a space-division multiple access by scheduling data on the basis of the bits to be transmitted. For this aim, a two-bands access scheme is proposed, and implemented through the use of a separated channel where signaling specifies where, in the wavelength domain, the reception must be operated by the different users. A multipleinput multiple-output scheme is considered for data transmission, in order to increase rate with a reliable error rate performance. Performance is evaluated for what concerns localization and access tasks, so as to show the effectiveness of the proposed scheme. Performance comparison with the recent literature has been also reported

Space-time multichannel adaptive filtering scheme for VLC color cross-talk equalization

In the emerging framework of visible light communications, the limitation of modulation bandwidth of light emitting diodes (LEDs) transmitters is counterbalanced by the use of red-green-blue (RGB) LEDs since they exhibit higher modulation bandwidth. Using RGB LEDs allows to exploit the spatial multiplexing aspects, that is obtaining parallel channels for transmission. In this context, we used at the receiver RGB-tuned photodiodes (PDs). Hence each PD can, in principle, detect only the information its tuning is matched to. The drawback of increasing spectral efficiency is the presence of cross-talk at the single PD due to the signals emitted by the remaining colors when a perfect color filtering is not applied. In this paper we consider amplitude shift keying (ASK) modulation, investigate the issue of the spatial (color) interference and we present a blind multichannel adaptive equalizer able to mitigate the temporary intersymbol interference (ISI) and also the spatial (color) ISI, this latter partially suppressed using suitable color filters. We analyze also the convergence of the adaptive algorithm and compare its performance with the literature

Quasi trace-orthogonal space-time block coding for underwater MIMO-PPM acoustic communications

The achievement of an optimal trade-off between reliability and rate has always been one of the most challenging issues in underwater acoustic links. In this context, the implementation of suitable transmission techniques on Multiple-Input Multiple-Output (MIMO) architectures results to be an efficient solution to improve the communication performance. Following this direction, we investigate a space-time block coding scheme for MIMO-PPM (Pulse Position Modulation) systems that is able to provide a satisfactory compromise between rate and reliability

On the MIMO multipath channels spatial correlation in shallow water communications

Acoustic communications in underwater environment are considerably influenced by the physical characteristics of the medium. This is even more true in the polar regions where the presence of icebergs and icy water layers represent an additional dependence to the signal propagation. Considering a MIMO scenario, we investigate how the channels spatial correlation is conditioned in the case of both frozen and fluid water surface. More, we evaluate the impact of the medium changes on the signal delay spread

Channel reciprocity analysis for bi-directional shallow water acoustic communications

In underwater acoustic networks (UWANs) with bidirectional communication links, channel state information (CSI) plays an important role since having a good channel knowledge allows system performance enhancements. Two communicating nodes can use the information obtained by their respective channel estimation in order to adjust the transmission parameters to the channel characteristics. However forward channel estimation is generally different from the backward one. In this paper we investigate the acoustic channel reciprocity in a shallow water communication