Power Efficient Downlink Resource Allocation for Hybrid RF/VLC Wireless Networks

In this paper, an indoor visible light communication (VLC) system is considered. The system consists of multiple VLC access points that assist in providing high data rate downlink to multiple users. We propose Nth best node selection algorithm for indoor VLC system. The Nth best node selection analysis hold significance at times when the best node is not available; hence, the user has to switch to second or third best generally the Nth best. We derive exact closed form expressions for outage probability, coverage probability, average symbol bit error rate and ergodic capacity.

Cross-layer analysis has been gaining an increasing attention as a powerful tool to study and assess different quality-of-service (QoS) mechanisms in wireless networks. Regarding the physical and data-link layers, in this paper we provide a cross-layer study for visible light communication (VLC) systems operating under statistical QoS constraints, which are inflicted as limits on the delay violation and buffer overflow probabilities. We assume that the VLC access point (AP) is unaware of the channel conditions, thus the AP sends the data at a fixed rate. Under this assumption, and considering an ON-OFF data source, we employ the maximum average data arrival rate at the AP buffer and the non-asymptotic bounds on buffering delay as the main performance measures. Through numerical results, we illustrate the impacts of different physical and data-link parameters on the system performance.

Since indoor visible light communication (VLC) systems can offer several potential advantages over their radio frequency and infrared counterparts, there has been a growing interest in VLC systems. Influenced by the complicated optical propagation environment, multipath effect existed which may result in intersymbol interference (ISI). Therefore, the bit error ratio (BER) performance is degraded excessively due to the effects of ISI. In this paper, we evaluate the performance of a nonlinear MAP (maximum a-posteriori probability) equalizer in indoor VLC environment. Moreover, Forward error correction (FEC) coding and interleaving is used. It will be shown that MAP equalization is well behaved in VLC systems. Besides, the systems with encoder and interleaver provide notable performance gain at the expense of higher computational complexity.

We propose and experimentally demonstrate a novel integrated passive optical network (PON) and indoor visible light communication (VLC) system based on Nyquist single carrier frequency domain equalization (N-SC-FDE) modulation with direct detection. In this system, a directly modulated laser and a commercially available red light emitting diode are served as the transmitters of the PON and VLC, respectively. To enable high spectral efficiency, high-speed transmission, and flexible multiple access with simplified optical network unit-side digital signal processing, multilevel, multiband quadrature amplitude modulations 128/64/16 are implemented here. VLC N-SC-FDE signals are successfully delivered a further 30 cm indoor distance after transmitting over a span of 40 km single mode fiber (SMF) together with 3 sub-band PON signals. As a proof of concept, a 10 Gb/s PON and 500 Mb/s VLC integrated system for three wired users and one wireless user is successfully achieved, which shows the promising potential and feasibility of this proposal to extend multiple services from metropolitan to suburban areas.

Optimizing SNR for indoor visible light communication via selecting communicating LEDs

Due to directional propagation of light signals, visible light communication (VLC) channel quality is sensitive to the distance and the angle between a VLC access point (AP) and a VLC terminal. When a terminal is mobile, VLC channel gain varies with the position of the terminal. Considering rotations of a terminal during mobility, channel variations are even more severe. As a result, data rates need to be adapted according to variable link qualities. The commonly used feedback-based adaptive modulation and coding (AMC) scheme cannot catch up with channel variations in VLC, resulting in staircase-shaped adaptation results. Smoother adaptation can be achieved by the seamless rate adaptation (SRA) scheme via rate compatible modulation (RCM). However, SRA does not provide an effective way to increase symbol distances, so the improvement on spectral efficiency is small. To address the shortcomings in the existing schemes, rateless adaptation (RLA) is developed for VLC systems in this paper based on spinal codes. With RLA, smooth rate adaptation is accomplished without channel state information (CSI) feedback, and spectral efficiency is also greatly improved. Simulation results show that, in mobile scenarios, RLA achieves at least 46% improvement over AMC and 19% improvement over SRA in terms of spectral efficiency.

Visible Light Communications (VLC) technology is restricted by the transmission coverage, which is short by nature. This is imposed by the lighting range which barely reaches a couple of hundred meters. The number of applications of VLC technology is therefore limited by this specific characteristic of the light propagation. As a result, VLC cannot be used in long and medium distance communication systems. The technology is suitable for exploitation in optical wireless personal area networks (OWPAN) in which the mobile terminal (MT) and the VLC access point (VLC AP) are placed in the same room. It is then essential that the access point is fed by a backhaul network. In this paper, we propose an access network in which the backhaul or backbone network exploits fibre optic (FO) technology to feed the VLC access point with data to be retransmitted. The channel is analyzed for a few parameters of the entire system including the FO attenuation factor, α, the transmission range, L, and the indoor VLC wall, ceiling and floor reflection coefficient, ρ.

This paper investigates the effect of light emitting diodes (LEDs) positioning and allocation in the channel analysis performance for an indoor intra-vehicle visible light communication (VLC) system. The MATLAB simulation results focus on the received power and the signal to noise ratio (SNR) within a sports utility vehicle. Furthermore, this work aims to validate by investigating two different scenarios, one utilizing two sources of power and the other using three sources of power with various locations, how LED’s spatial positioning affects the VLC system and the probability of error. Proving the demand for considering LEDs layout positioning while designing a VLC system.

With the recent successful standardization of broadband power line communication (PLC) (IEEE 1901, ITU-T G.9960/61) and visible light communication (VLC) (IEEE 802.15.7), there is an excellent opportunity to consider their integration. In particular, there is inherent benefit to leveraging existing power line infrastructure to provide connectivity while exploiting energy-efficient LED illumination systems for wireless downlink. The ubiquity of LED lighting together with power line networks leads us to conclude that VLC will be a strong complementary wireless technology to indoor PLC much in the way that Wi-Fi currently supports broadband Ethernet connections. This paper will survey some aspects of both PLC and VLC and present new proposals for their integration.

In this paper, we propose, design, and evaluate two indoor visible light communication (VLC) systems based on computer generated holograms (CGHs); a simple static CGH-VLC system and an adaptive CGH-VLC system. Each transmitter is followed by the CGH, and this CGH is utilized to direct part of the total power from the best transmitter and focus it to a specific area on the communication floor. This leads to reduction in inter-symbol interference and increasing in the received optical power, which leads to higher data rates with a reliable connection. In the static CG11H-VLC system, the CGH generates 100 beams (all these beams carry same data) from the best transmitter and directs these beams to an area of 2 m $\times2$ m on the communication floor. In the adaptive CGH-VLC system, the CGH is used to generate eight beams from the best transmitter and steer these beams to the receiver’s location. In addition, each one of these eight beams carries a different data stream. Whereas in the first system, a single photodetector is used (added simplicity), an imaging receiver is used in the second one to obtain spatial multiplexing. We consider the lighting constraints where illumination should be at acceptable level and consider diffusing reflections (up to second order) to find the maximum data rate that can be offered by each system. Moreover, due to the fact that each beam in the adaptive CGH-VLC system conveys a different data stream, co-channel interference between beams is taken into account. We evaluate our proposed systems in two different indoor environments: an empty room and a realistic room using simple on–off-keying modulation. The results show that the static CGH-VLC system offers a data rate of 8 Gb/s while the adaptive CGH-VLC system can achieve a data rate of 40 Gb/s.

For channel estimation in the relay-assisted multiple-input multiple-output and orthogonal frequency division multiplexing indoor visible light communication (VLC) system affected by light source, there is a problem that the received signal cannot be separated by simple filtering. To solve this problem, a channel estimation by PARATUCK2-PARAFAC-based noise compensation which introduces tensors to construct the suitable model of VLC is proposed. First, the transmitting pilots for channel estimation and noise estimation are constructed separately with the Hermitian symmetry structure. Then the tensor-based transmission model of the indoor VLC system is established, and the signals for channel and noise estimations are received. Finally, an asymptotic estimation for separating signals from different sources and noise is proposed by PARATUCK2-PARAFAC. Simulation results show that the proposed algorithm provides a more effective scheme for channel estimation comparing with the state-of-the-art algorithms.

In this paper, we consider an indoor Visible Light Communication (VLC) system with a placement technique with and without an overlap formed, using four and five Light Emitting Diodes (LED), placements on a room roof. To support the better received signal power, this paper evaluated the performance of LED overlap using the 3-Watt transmit power. We did a computer simulation using the dimension closed communication room $5 \times 5\times 3 m^{3}$ . In this paper, we found that the VLC system with an overlap was better than the one without an overlap. The result showed that the received power could reach the minimum Bit Error Rate (BER) threshold $\leq 10^{-3}$ around −18 dBm for VLC system without an overlap and −20 dBm for VLC system with an overlap. From the simulation, it obtained that communication link coverage with an overlap was about 25 m2.

In this paper, we consider an indoor visible light communication (VLC) system and evaluate its performance in terms of the signal to noise ratio for both line of sight and diffuse paths and consider objects within the room. We show that by rearranging the transmitter layout (i.e., position) on the ceiling the link performance can be improved.

In this paper, we investigate the use of a new modulation scheme recently introduced in the RF domain, called orthogonal time frequency space (OTFS) modulation, in an indoor visible light communication (VLC) setting. In particular, we consider VLC systems that employ dual-LED schemes for transmission. The following dual-LED schemes are considered: 1) non-DC biased (NDC) scheme, and 2) dual-LED complex modulation (DCM) scheme. The proposed NDC-OTFS scheme uses 2-dimension (2D) Hermitian symmetry operation to convert complex signals to positive, real-valued signals suitable for transmission in the optical domain, and the proposed DCM-OTFS scheme achieves this by exploiting the polar representation of complex signals. We obtain analytical upper bounds on the bit error performance of the proposed NDC-OTFS and DCM-OTFS schemes, which are found to be tight at high signal-to-noise ratios (SNR). Our analytical and simulation results show that the proposed NDC-OTFS and DCM-OTFS schemes achieve better performance, respectively, compared to NDC-OFDM and DCM-OFDM schemes known in the VLC literature. Further, using the ratio of the minimum distance of different normalized received signal sets as a metric, we quantify the spatial distribution of the SNR gain of the proposed NDC-OTFS/DCM-OTFS schemes compared to NDC-OFDM/DCM-OFDM schemes.

This paper considers a successive light interference cancellation and allocation algorithm (SLICA) practicing interference cancellation for an indoor visible light communication (VLC) system based on successive interference cancellation (SIC) technique. The interference among users is cancelled with the help of the proposed approach to reduce computational complexity. VLC has become the cornerstone of intelligence in the current scenario. The data services allocated to the users are demand based and rely on their channel conditions. The data is allocated to user by modulating light waves via illuminated LEDs. The receiving end has photodiode installed in it to recover back the data. Better performance rate is achieved with lesser interference with the proposed approach. To guarantee good (quality-of service) QoS, considerable simulations are carried out considering real- time scenario which further demonstrates the high level performance of the proposed approach over conventional approach. Based on the analysis, the SINR and interference level is demonstrated for the conventional and the proposed approach and there is a hike in the performance rate of SINR and interference level of about 20 – 30 % with the applied proposed approach. The prior motto of this study is to enhance the system throughput and improve per user average performance rate and reducing the complexity of the system. This contributes to the total efficiency of the optical indoor VLC network. Our proposed algorithm will provide a strong backbone for the 6G deployment.