ASK-based spatial multiplexing RGB scheme using symbol-dependent self-interference for detection

We propose a vsible light communication scheme utilizing red, green and blue lightemitting diodes (LEDs) and three color-Tuned photodiodes. Amplitude shift keying modulation is considered, and its effect on light emission in terms of flickering, dimming, and color rendering is discussed. The presence of interference at each photodiode generated by the other two colors is used to improve detection since interference is symbol-dependent. Moreover, the capability of the photodiodes to follow the LEDs speed is considered by analyzing the possibility of equalizing the received signal, and also self-interference mitigation is proposed. The system performance is evaluated both with computer simulations and tests on an Arduino board implementation

Mutual information of a 3x3 RGB MIMO VLC scheme based on Amplitude Shift Keying

Visible Light Communications (VLC) are a new key in the Internet access as well as, a possible enabler of Internet of Things. This kind of systems can allow, in principle, high data rate by stressing the bandwidth and also the spatial dimension. We deal in this work with a 3×3 VLC system characterized by red, green and blue LEDs at the transmitter and three photodiodes at the receiver. Each photodiode is tuned on a different color. In this paper we analyze the mutual information expression when thermal noise is present and we distinguish two different approaches. The first one considers the effect of interference of colors, while the second one aims at equalizing, from a spatial/color point of view, the channel. More, we show the numerically evaluated mutual information and the effect of some system parameters

Trace-orthogonal pulse position modulation space time block coding for underwater links

The need for underwater reliable connections requested to provide different services as sea monitoring, devices control and camera images/videos may lead to require also large rate values. Due to the very limited bandwidth achieving few Khz, space diversity techniques can aid in this twofold mission. In this paper we investigate the use of an underwater acoustic MIMO technique, and jointly adopt the Pulse Position Modulation (PPM), in order to improve the data rates without reducing the reliability of the link. PPM is known to be power efficient modulation format while it is bandwidth inefficient so the use of MIMO can compensate that drawback with reasonable complexity. The performance has been evaluated on the basis of signal recordings for what concerns interference. © 2014 IEEE

Near-sea multi-target opportunistic multiple-input multiple-output detection

The passive radar uses opportunistic illuminators, such as FM radio or TV transmitters, cellular telephone base stations, etc., to detect and track moving targets. Due to the fact that the radar itself does not transmit any power, it is undetectable. The other advantages of passive radar include its low power consumption, low cost and potential ability to detect stealth targets, due to the multistatic geometry and low frequencies used as weel as, it reduces electromagnetic pollution. This paper tackles with the problem of detecting targets close to the coastal and present on the sea surface by using opportunistic signals as The receiving operations aim at detecting the possible presence of reflective objects by stressing the diversity properties of the multiple-input multiple-output configuration due to multiple transmissions related to different communication services. © 2014 IEEE

Merging color shift keying and complementary pulse position modulation for visible light illumination and communication

The rising need of indoor broadband services without increasing the electromagnetic pollution has led the scientific community to look for smart spectrum usage. From this, it stems the need of emerging paradigm of visible light communications. In the context of the IEEE 802.15.7 Task Group activities, a new modulation format named color shift keying (CSK), based on sending signals spaced in the domain of the wavelength and able to both support the communication and the illumination of indoor environments, has been proposed. In this paper, we propose a transmission/reception scheme based on CSK modulation that also makes use of a modulation format that descends from the pulse position modulation by taking care of illumination level to be granted. The aim of this contribution is twofold: to propose the receiver architecture for that kind of transmission and to evaluate its performance by performing also comparisons with other contributions in the literature. The proposed scheme is robust with respect to optical interference and presents high rate and low bit error rate at the cost of a limited increasing of complexity of the receiver with respect to other approaches

Merging color shift keying and complementary pulse position modulation for visible light illumination and communication

The ever increasing need to be able to take advantage of broadband services without the need to increase the electromagnetic pollution, has led the scientific community, in recent years, to look for alternatives to the use of a radio frequency communication. From this, it stems the need of budding paradigm of visible light communications. In the context of the activities of the IEEE 802.15.7 Task Group, a new modulation format named Color Shift Keying (CSK), based on sending signals spaced in the domain of the wavelength able to both support the communication and the illumination of indoor environments has been tackled. In this paper, a transmission scheme based on the use of the CSK modulation which also makes use of a modulation format that descends from the Pulse Position Modulation (PPM) has been proposed. The aim of this contribution is also proposing the receiver architecture for that kind of transmission and then evaluate its performance in terms of Bit Error Rate (BER) of Transmission Rate by performing also comparisons with the literature. The proposed scheme is robust with respect to optical interference and presents high rate and low BER at the cost of a bit complexity increasing with respect to other approaches. © 2014 AEIT

On the mutual information of the VLC channel in the presence of external ambient lighting

Visible Light Communications (VLC) represent a new frontier of communication allowing high data-rate Internet access, specially in indoor environments, where the use of Light Emitting Diodes is growing as a viable alternative to traditional illumination. As a result, by properly modulating light, it is possible to guarantee coexistence with illumination. One of the key challenges is the limited modulation bandwidth of sources that is typically tens of MHz. In this context, when VLC link must be optimized by using, for example, adaptive modulations, channel capacity is evaluated according to the hypothesis of Gaussian distributed input. In this paper we derive the mutual information expression when thermal noise, shot noise and ambient lighting are present so as to show the difference with the conventional Gaussian approach. More, we show the numerically evaluated mutual information when different input distributions have been taken into account. © 2015 IEEE

Camera communication deblurring: A semiblind spatial fractionally-spaced adaptive equalizer with flexible filter support design

In Optical Camera Communication systems an important issue is the spatial intersymbol interference (blurred images) that can arise when Multi-Input Multi-Output techniques are applied. However, the transmitted symbols are described with very high resolution, due to the high number of pixels composing the camera. To take advantage of this characteristic, in this paper we use a semiblind spatial fractionally-spaced adaptive equalizer to counteract the blur introduced by the optical channel. We formulate the adaptive algorithm in a way that permits to design the support of the Finite Impulse Response filter with flexibility. The choice of the support is related to the spatial shape of the blur encountered, by following an heuristic approach. The equalizer performances in terms of Bit Error Rate are presented in the numerical results showing performance improvement. We also show the behaviour of the equalizer when different filter supports are used. © 2016 IEEE

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

A space-time RLS algorithm for adaptive equalization. The camera communication case

This paper presents a novel space-time recursive least-squares adaptive algorithm, which performs filter coefficients updates in space and postponed filtering in time. The algorithm is used for intersymbol interference suppression in optical camera communications, which is a subgroup of visible light communication systems. Optical camera communications uses image sensor receivers, as those available in smartphones, tablets, and laptops, to detect changes in light intensity in order to allow data transmission. The achievable data transmission rate of optical camera communication systems is nowadays constrained by the frame-per-second rate achieved by those devices, so that the spatial dimension, e.g., multiple-input multiple-output techniques, are typically exploited. Spatial intersymbol interference could arise and image blurring can be an issue especially when the link distance grows and/or when the receiver is in mobility. We present here a semiblind spatial fractionally spaced equalizer that uses a novel space-time recursive least-square adaptive algorithm to counteracts the blur introduced by the optical channel. Numerical results show how the bit error rate can be drastically reduced in both motion and out-of-focus blur scenarios