LiFi Systems Research Articles

Photovoltaic Solar Cells for Outdoor LiFi Communications

Increasing demand of wireless devices contributes to radiofrequency (RF) congestion. Light Fidelity (LiFi) promises to be an interesting alternative by using the visible part of the electromagnetic spectrum instead of the RF part as nearly all existing wireless transmission systems do. A basic LiFi system is composed of one intensity-controlled light-emitting diode (LED) and one receiver device sensitive to very high-frequency (thus invisible to human sight) modulations of the luminous intensity. In most cases, the photoreceptor is a silicon photodiode of PIN (P-type intrinsic N-type) or APD (Avalanche photodiode) conception. Recently, a few studies suggest that photovoltaic (PV) modules could be used to implement outdoor LiFi transmissions, i.e., under direct sunlight exposure. In this paper, we propose to compare the behavior of a PV module and a commercial APD-based photodetector (without any optical lens or colored filter) for experimental LiFi transmissions on both indoor and outdoor conditions. The performance of the two solutions is quantified in terms of various frequency responses like attenuation, signal-to-noise ratio, or bit-error rate. The results show that, while the photodiode exhibits very good performance in indoor conditions, its frequency response is rapidly deteriorating when a sunlight exposure of more than 200 W/m $^2$ is superimposed over the LiFi signal. We demonstrate that a PV module in $V_{oc}$ (open-circuit voltage) condition still operates a LiFi transmission under additional solar illumination.

Complex Signal Mapping for Improving Spectral Efficiency of Li-Fi Systems

Light fidelity (Li-Fi) systems based on the orthogonal frequency division multiplexing (OFDM) scheme have gained more attention in the communications circles, as a means to provide high spectral efficiency and ensure stricter data rate requirements for visible light communication (VLC) systems. However, common OFDM schemes employ Hermitian symmetry to obtain a real-valued signal which is necessary in intensity modulation and direct detection (IM/DD) optical systems, at the expense of doubling the required bandwidth. In this paper, a novel transmission scheme for an OFDM-based Li-Fi system is proposed to tackle the issue in question. A new approach to complex signal mapping (CSM), based on the pairing function method, has been developed for Li-Fi systems. It does not require Hermitian symmetry and, hence, saves about 50% of the required bandwidth. Unlike existing OFDM-based VLC approaches, the proposed scheme employs CSM to ensure a real and positive signal without Hermitian symmetry in order to fully utilize the bandwidth available to Li-Fi networks. Simulation results show that the proposed scheme significantly outperforms other systems in terms of spectral efficiency. The CSM-OFDM based Li-Fi system also achieves a good peak-to-average power ratio (PAPR) reduction with acceptable bit-error-rate (BER) performance, compared to conventional approaches.

Bidirectional Optical Spatial Modulation for Mobile Users: Toward a Practical Design for LiFi Systems

Among the challenges of realizing the full potential of light-fidelity (LiFi) cellular networks are user mobility, random device orientation, and blockage. In this paper, we study the impact of those challenges on the performance of LiFi networks in an indoor environment using measurement-based channel models, unlike existing studies that rely on theoretical channel models. In our paper, we adopt spatial modulation (SM) and consider two configurations for the user equipment (TIE). A multidirectional receiver (MDR) structure is proposed, in which the PDs are located on different sides of the TIE, e.g., a smartphone. This configuration is motivated by the fact that conventional structures exhibit poor performance in the presence of random device orientation and blockage. In fact, we show that the MDR outperforms the benchmark structure by over 10 dB at bit-error ratio (BER) of 3.8 × 10 -3 . Moreover, an adaptive access point (AP) selection scheme for the SM is considered, where the number of APs is chosen adaptively in an effort to achieve the lowest energy requirement for a target BER and spectral efficiency. The user performance with random orientation and blockage in the entire room is evaluated for sitting and walking activities, for which the orientation-based random waypoint (ORWP) mobility model is invoked. Furthermore, we demonstrate that the proposed adaptive technique with SM outperforms the conventional spatial multiplexing system. We also study the performance of the underlying system on the uplink channel where we apply the same techniques used for the downlink channel. It is shown analytically that the multidirectional transmitter (MDT) with adaptive SM is highly energy efficient.

Design and Implementation of LiFi Communication system

Visible Light Communication technology is considered complimentary to Radio Frequency (RF) technology. More specifically, Light Fidelity (LiFi) based Visible Light Communication system appears to have enhanced wireless capability to realize IoT, 5G Cellular System conforming to requirements such as high data rate, low latency, connectivity etc. Recent developments in solid-state lighting technology have significantly influenced LiFi system Architecture. In view of these developments, we propose to carry out a study on feasibility of deploying LiFi technology along with the existing RF infrastructure. We emphasize to look for designing full-duplex LiFi Indoor communication module, utilizing multiple White Light Emitting Diode (WLED) based lighting equipment and integrate the module with network edge devices such as PC, smart phones for establishing efficient communication systems.

Windowing Techniques for Reducing PAPR of OFDM in Li-Fi Systems

Abstract In this paper, Li-Fi system based on orthogonal frequency division multiplexing (Li-Fi-OFDM) is presented. In these systems, light-emitting diodes (LEDs) are used to send information data using intensity modulation. LEDs have a limited dynamic range and the voltage-current characteristic shows a nonlinear behavior. Li-Fi-OFDM signal is used to drive these transmitter LEDs. However, LEDs chip overheating and nonlinear distortions occur, due to high peak-to-average power ratio (PAPR) of the OFDM signal. The proposed approach develops a new PAPR reduction method of OFDM in Li-Fi systems based on time-domain windowing techniques. Several windows such as rectangular, Hanning and raised cosine methods have been applied to the OFDM time-domain signal in order to reduce its PAPR while maintain acceptable bit error rate (BER) performance at receiver side. The simulation results of the work have shown the advantages of the offered method; the proposed scheme achieves a significant PAPR reduction compare to the unwindowed signals. Our proposed system also slightly improves the BER performance for all windowing methods employed.

Impact of Device Orientation on Error Performance of LiFi Systems

Most studies on optical wireless communications (OWC) have neglected the effect of random orientation in their performance analysis due to the lack of a proper model for the random orientation. Our recent empirical-based research illustrates that the random orientation follows a Laplace distribution for the static user equipment (UE). In this paper, we analyze the device orientation and assess its importance on system performance. The reliability of the OWC channel highly depends on the availability and alignment of line-of-sight (LOS) links. In this paper, the effect of receiver orientation, including both polar and azimuth angles on the LOS channel gain are analyzed. The probability of establishing the LOS link is investigated and the probability density function (PDF) of signal-to-noise ratio (SNR) for a randomly oriented device is derived. By means of the PDF of SNR, the bit-error ratio (BER) of DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) in additive white Gaussian noise (AWGN) channels is evaluated. A closed-form approximation for the BER of UE with random orientation is presented which shows a good match with Monte-Carlo simulation results. Furthermore, the impact of UE's random motion on the BER performance has been assessed. Finally, the effect of random orientation on the average signal-to-interference-plus-noise ratio (SINR) in a multiple access points (AP) scenario is investigated.

LIGHT FIDELITY: A WAY OF DATA TRANSMISSION

Li-Fi is a very efficient, simple and cheaper network that can be used for wireless data transmission. It is considered to be better than the trending technology, i.e. Wi-Fi, in terms of cost and efficiency of usage. Li-Fi complies with the IEEE standard 802.15.7. The paper focuses on explaining the concept and meaning of Li-Fi technology. In this paper we have explained the different components necessary for constructing a Li-Fi system. Its features, different applications and future uses are also discussed in brief. The use and importance of LED light in the working of Li-Fi is also described. The VLC technology (for increasing the transmission speed) used in Li-Fi has been explained briefly.

Efficient OFDMA for LiFi Downlink

Light-fidelity (LiFi) relies on visible light communication to provide multiuser access in a small cell. For higher throughput, this paper studies the resource allocation problem for an orthogonal frequency-division multiplexing access scheme for LiFi downlink transmissions and presents a joint design of the bias level, power and subcarrier allocation. Decomposing the original optimization into subproblems, we first develop an efficient algorithm for the bias optimization, along with its performance analysis in terms of convergence properties and the global optimality. We then propose several power and subcarrier allocation strategies, including an optimal algorithm and a near-optimal simplified method, to satisfy different complexity and accuracy requirements. Finally, we present two algorithms to jointly optimize the bias, power, and subcarrier, and analyze the convergence properties in terms of both the objective and the solution. Comprehensive simulation results under practical LiFi system setups illustrate the effectiveness of the proposed algorithms.

Robust and Low-Complexity Timing Synchronization for DCO-OFDM LiFi Systems

Light fidelity (LiFi), using light emitting devices such as light emitting diodes (LEDs) which are operating in the visible light spectrum between 400 and 800 THz, provides a new layer of wireless connectivity within existing heterogeneous radio frequency wireless networks. Link data rates of 10 Gbps from a single transmitter have been demonstrated under ideal laboratory conditions. Synchronization is one of these issues usually assumed to be ideal. However, in a practical deployment, this is no longer a valid assumption. Therefore, we propose for the first time a low-complexity maximum likelihood-based timing synchronization process that includes frame detection and sampling clock synchronization for direct current-biased optical orthogonal frequency division multiplexing LiFi systems. The proposed timing synchronization structure can reduce the high-complexity two-dimensional search to two low-complexity one-dimensional searches for frame detection and sampling clock synchronization. By employing a single training block, frame detection can be realized, and then sampling clock offset (SCO) and channels can be estimated jointly. We propose three frame detection approaches, which are robust against the combined effects of both SCO and the low-pass characteristic of LEDs. Furthermore, we derive the Cramer–Rao lower bounds (CRBs) of SCO and channel estimations, respectively. In order to minimize the CRBs and improve synchronization performance, a single training block is designed based on the optimization of training sequences, the selection of training length, and the selection of direct current (DC) bias. Therefore, the designed training block allows us to analyze the trade-offs between estimation accuracy, spectral efficiency, energy efficiency, and complexity. The proposed timing synchronization mechanism demonstrates low complexity and robustness benefits and provides performance significantly better than achieved with existing methods.

Feasibility of LiFi in the Contemporary World � A Survey on the Dichotomy of its Production and Distribution Mechanisms

LiFi is expected to garner a market share of US $14.91 Billion by 2022. Our research is an endeavor to finding out whether the dichotomy of production and distribution of LiFi systems would bring positive change in the future of this nascent technology. To undertake it, we analyze the standardization efforts, the consumer market acceptance and the trends in the production of the components of LiFi. Partly, because the technology forwards the Green Communication Goal, and eradicates the Radio Frequency Bottleneck. Keywords: Consumer Market, Feasibility, Light Fidelity, LiFi, Market Trends, Optical Wireless Communication, Visible Light Communication

Optimization of Load Balancing in Hybrid LiFi/RF Networks

Light fidelity (LiFi) uses light emitting diodes (LEDs) for high-speed wireless communications. Since an LED lamp covers a small area, a LiFi system with multiple access points (APs) can offer a significantly high spatial throughput. However, the spatial distribution of data rates achieved by LiFi fluctuates because users experience inter-cell interference from neighboring LiFi APs. In order to guarantee a quality of service (QoS) for all users in the network, an RF network is considered as an additional wireless networking layer. This hybrid LiFi/RF network enables users with low levels of optical signals to achieve the desired QoS by migrating to the RF network. With regard to moving users, the hybrid LiFi/RF system dynamically allocates either a LiFi AP or an RF AP to users based on their channel state information. In this paper, a dynamic load balancing scheme is proposed, which considers the handover overhead in order to improve the overall system throughput. Joint optimization algorithm (JOA) and separate optimization algorithm (SOA), which jointly and separately optimize the AP assignment and resource allocation, respectively, are proposed. Simulation results show that SOA can offer a better performance/complexity tradeoff than JOA for system load balancing.

Data rate enhancement of optical camera communications by compensating inter-frame gaps

Optical camera communications (OCC) is a convenient way of transmitting data between LED lamps and image sensors that are included in most smart devices. Although many schemes have been suggested to increase the data rate of the OCC system, it is still much lower than that of the photodiode-based LiFi system. One major reason of this low data rate is attributed to the inter-frame gap (IFG) of image sensor system, that is, the time gap between consecutive image frames. In this paper, we propose a way to compensate for this IFG efficiently by an interleaved Hamming coding scheme. The proposed scheme is implemented and the performance is measured.

Vehicular Management using a Li-Fi Communication System Powered by BIPV (Building Integrated Photo-Voltaics)

Objectives: Many vehicular accidents take place in India which are primarily due to lack of traffic discipline. Our aim is to minimize the accidents by creating an efficient communication system. Methods/Statistical Analysis: In our proposed system, we have used light as the carrier to create a fast and reliable communication system where OOK modulation technique is used, unlike other systems where RF is used. The LED’s are positioned in the headlights and taillights of the car which also contain the photodetector to receive light signal. The circuitry have designed and simulated in PROTEUS. Findings: It was found that by replacing all the windows of the car with BIPV, the system can run independently. Theoretically it can work up to 20m with a low bit error rate and this can be achieved by using an array of LED’s or increasing the intensity of the LED. It was observed that by hindering the intensity of the LED, the range decreased and hence the validity of the relation between Intensity of LED and range was established. It was found that the data from individual cars were being transmitted immediately with no delay. It will help conserve energy and also act as a builtin glass for the vehicle thus allowing sufficient sunlight to enter. Application/Improvements:This system can be used for vehicular communication to detail about speed, position and traffic. In the future, automatic braking and intelligent synchronization can be implemented.

Smart traffic management using a building integrated photovoltaic (BIPV) powered Li-Fi system on IoT

The conventional glass can be replaced with building integrated photovoltaics (BIPV) which serve as a power source as it provides better insulation and clean energy. In the proposed system, car windows and sunroofs are replaced with BIPV, to power the Li-Fi system. Streetlights are used to transmit information to a vehicle which acts as a master node and further transmits this data to other nearby vehicles. Each vehicle acts as a transceiver, a network for sending and receiving data related to traffic, road conditions and regarding braking. As information is sent at the speed of light, Li-Fi communication is both faster and more accurate for short distance communication than the existing systems using RF. All the data are processed using IoT. Proteus simulations are shown. The size and capacity of the BIPV glass to be used is calculated based upon the current requirements of the individual components.

Smart traffic management using a building integrated photovoltaic (BIPV) powered Li-Fi system on IoT

The conventional glass can be replaced with building integrated photovoltaics (BIPV) which serve as a power source as it provides better insulation and clean energy. In the proposed system, car windows and sunroofs are replaced with BIPV, to power the Li-Fi system. Streetlights are used to transmit information to a vehicle which acts as a master node and further transmits this data to other nearby vehicles. Each vehicle acts as a transceiver, a network for sending and receiving data related to traffic, road conditions and regarding braking. As information is sent at the speed of light, Li-Fi communication is both faster and more accurate for short distance communication than the existing systems using RF. All the data are processed using IoT. Proteus simulations are shown. The size and capacity of the BIPV glass to be used is calculated based upon the current requirements of the individual components.

Novel user allocation scheme for full duplex multiuser bidirectional Li-Fi network

A novel user allocation scheme for a full duplex multi-user bidirectional Li-Fi system is proposed. The users are allocated into separate color clusters and the user data is transmitted through the allocated color beams from the RGB (red, green, and blue) light emitting diodes (LEDs) in the form of predefined frame structure. At the receiving end, primary user separation is achieved by a color sensor that is capable of distinguishing the colors. Similarly, for uplink data transmission, the modulation of the user data is performed using a different color from the one used to retrieve the data and transmitted through the RGB LED, resulting in a bidirectional VLC link with minimal interference. Simulations demonstrate that the proposed user allocation scheme is efficient and robust with significant performance in the bidirectional Li-Fi system.