Stanislav Zvanovec

Channel Characteristics of Visible Light Communications Within Dynamic Indoor Environment

Visible light communications (VLC) is a new emerging technology, which provides both data transmission and illumination by utilizing the visible range (370-780 nm) of the electromagnetic spectrum. In order to maximize the available data rate and enhance the users mobility within an indoor environment, it is essential to characterize the communication channel. In this paper, we present both analytical and experimental results for a VLC system affected by movement of people for different indoor conditions (i.e., furnished office room, empty hall, and corridor). VLC systems utilize multiple light-emitting diodes mounted in the ceiling and the configuration is based on the nondirected line of sight. We consider random movement of people within the room, focusing on the impacts of shadowing and blocking on mobility and link system performance by investigating changes in the channel characteristics using the cumulative distribution function of the received power distribution and the delay profile. We demonstrate the behaviour of communication channels for different scenarios from corridor, the most robust against people movement induced fading, to the office rooms and halls, the most vulnerable to the received power fluctuation.

UHF RF Identification of People in Indoor and Open Areas

The performance of an ultra-high-frequency RF identification (ID) system operating at 869 MHz, intended for the ID of persons in both indoor and open areas, has been validated using the propagation models, as well as the series of practical measurements. A two-ray propagation model and the 3-D ray-tracing model were used for calculations of all important system parameters in open and indoor areas, respectively. For the application mentioned above, a novel (electrically small and, at the same time, low-profile) wearable TAG antenna was designed. It was used in order to carry out the necessary tests as well. The antenna in question is based on an artificial-like surface. The latter provides an important screening effect and avoids detuning. Another virtue of the surface used is represented by the fact that it ensures the minimum loss of the antenna efficiency (resulting from the presence of a nearby human body). The simulations and measurements show that the optimized system can guarantee a reliable ID at distances up to 9 m in open areas and up to 16 m in corridors.

Multi-band carrier-less amplitude and phase modulation for bandlimited visible light communications systems

Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370-780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems.

Experimental characterization and mitigation of turbulence induced signal fades within an ad hoc FSO network.

Optical beams propagating through the turbulent atmospheric channel suffer from both the attenuation and phase distortion. Since future wireless networks are envisaged to be deployed in the ad hoc mesh topology, this paper presents the experimental laboratory characterization of mitigation of turbulence induced signal fades for two ad hoc scenarios. Results from measurements of the thermal structure constant along the propagation channels, changes of the coherence lengths for different turbulence regimes and the eye diagrams for partially correlated turbulences in free space optical channels are discussed. Based on these results future deployment of optical ad hoc networks can be more straightforwardly planned.

A European view on the next generation optical wireless communication standard

Optical wireless technology uses light for mobile communications. The idea is to simultaneously combine the illumination provided by modern high-power light-emitting diodes (LEDs) with high-speed wireless communications. There have been numerous practical demonstrations of this concept, and the technology is now well matured to be deployed in practice. Independent market analysts forecast a high-volume market for mobile communication devices connected to the ubiquitous lighting infrastructure. This paper aims to make optical and wireless industries aware of the requirement for standardization in this area. The authors present the view of the European COST 1101 research network OPTICWISE towards a next-generation optical wireless standard aiming at data rates from 1 Mbit/s to 10 Gbit/s. Besides key technical insights, relevant use cases and main features are described that were recently adopted by the IEEE 802.15.7r1 working group. Moreover, a channel model is introduced to enable assessment of technical proposals.

A Multi-CAP Visible-Light Communications System With 4.85-b/s/Hz Spectral Efficiency

In this paper, we experimentally demonstrate a multiband carrierless amplitude and phase modulation format for the first time in VLC. We split a conventional carrierless amplitude and phase modulated signal into m subcarriers in order to protect from the attenuation experienced at high frequencies in low-pass VLC systems. We investigate the relationship between throughput/spectral efficiency and m, where m = {10, 8, 6, 4, 2, 1} subcarriers over a fixed total signal bandwidth of 6.5 MHz. We show that transmission speeds (spectral efficiencies) of 31.53 (4.85), 30.88 (4.75), 25.40 (3.90), 23.65 (3.60), 15.78 (2.40), and 9.04 (1.40) Mb/s (b/s/Hz) can be achieved for the listed values of m, respectively.

Route diversity analyses for free-space optical wireless links within turbulent scenarios.

Free-Space Optical (FSO) communications link performance is highly affected when propagating through the time-spatially variable turbulent environment. In order to improve signal reception, several mitigation techniques have been proposed and analytically investigated. This paper presents experimental results for the route diversity technique evaluations for a specific case when several diversity links intersects a common turbulent area and concurrently each passing regions with different turbulence flows.

FSO Detection Using Differential Signaling in Outdoor Correlated-Channels Condition

In this letter, we introduce a detection technique based on differential signaling scheme for outdoor free space optical communications. This method requires no channel state information (CSI) and does not suffer from the computational load compared with the conventional receivers, where adjusting dynamically the detection threshold level (either based on CSI knowledge, or by using pilots) leads to increased computational time and reduced link throughput. This letter shows that the performance of the proposed technique only depends on the correlation of propagating optical beams. Especially under highly correlated-channels condition the fluctuation of the detection threshold level in the receiver is significantly small. We also show experimentally that under weak turbulence regime the variance of detection threshold level reduces for the correlated channel.

Quantized Feedback-Based Differential Signaling for Free-Space Optical Communication System

We propose a quantized feedback-based differential signaling scheme for 2 × 1 free space optical (FSO) multiple-input single-output communication systems. The analytical bit error rate (BER) for the proposed differential signaling scheme is derived and compared with the existing differential signaling scheme for FSO systems. The asymptotic BER of the proposed scheme is also determined and it is shown by using the asymptotic BER expression that the proposed scheme achieves full spatial diversity of two. Moreover, the effect of the feedback error on the performance of the proposed scheme is studied and it is demonstrated by simulation-based and analytical results that the proposed scheme significantly outperforms a previously proposed differential signaling scheme in terms of turbulence fades reduction for tolerable feedback errors.

Experimental verification of long-term evolution radio transmissions over dual-polarization combined fiber and free-space optics optical infrastructures.

This paper describes the experimental verification of the utilization of long-term evolution radio over fiber (RoF) and radio over free space optics (RoFSO) systems using dual-polarization signals for cloud radio access network applications determining the specific utilization limits. A number of free space optics configurations are proposed and investigated under different atmospheric turbulence regimes in order to recommend the best setup configuration. We show that the performance of the proposed link, based on the combination of RoF and RoFSO for 64 QAM at 2.6 GHz, is more affected by the turbulence based on the measured difference error vector magnitude value of 5.5%. It is further demonstrated the proposed systems can offer higher noise immunity under particular scenarios with the signal-to-noise ratio reliability limit of 5 dB in the radio frequency domain for RoF and 19.3 dB in the optical domain for a combination of RoF and RoFSO links.