Radio frequency (RF) signals propagate through most materials that we are surrounded by while light is blocked by many of these materials. This feature makes wireless networks based on light (which are also referred to as LiFi networks) inherently more secure. However, it can also lead to sudden link failure if the legitimate data link is blocked because of user movements or changes in device orientation. In this paper, the secrecy capacity has been analysed with the consideration of imperfect channel state information, random device orientation and probability of link blockage for the case of a single eavesdropper. It has been found that the secrecy capacity almost doubles in a standing activity as opposed to a sitting activity and that the density of blocking objects degrades the secrecy capacity in single access point networks. It is evident that environmental factors and user behaviour have a significant impact on the secrecy performance and, thus, need to be considered for robust physical layer security (PLS) design in LiFi networks.
OLEDs and other organic optoelectronic devices combine many attractive features. However, they are generally thought to be slow, limiting their range of possible applications. We demonstrate that by careful study of the factors limiting their bandwidth, and appropriate design in terms of device size, operating field and emitter lifetime exceptionally fast OLEDs can be made with modulation bandwidths up to 245 MHz, opening up new potential applications in communications, spectroscopy, sensing and ranging. In particular, we demonstrate visible light communication in which a single OLED transmits data at a rate exceeding 1 gigabit per second.
We demonstrate high-speed LiFi data communication of over 20 Gbit/s using visible light from a laser-based white light emitting surface mount device (SMD) product platform that offers 10-100X the brightness of conventional LED sources. Equipped with high power blue laser diodes that offer over 3.5 GHz of 3 dB bandwidth, the laser-based white light SMD modules exhibited a signal-to-noise ratio (SNR) above 15 dB up to 1 GHz. The high SNR was combined with high order quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM) to maximize the bandwidth efficiency. In this work, we present a laser based white light SMD module configured with a single 3W blue laser diode mounted on heat-sink, optically coupled to a collimating optic, achieving a LiFi data rate of up to 10 Gbit/s. Moreover, we demonstrate wavelength division multiplexing (WDM), from a white light SMD module configured with two blue laser diodes separated in peak wavelength to serve as separate communication channels. Using WDM, the dual laser SMD module enabled LiFi data rates of over 20 Gbit/s by simultaneously transmitting data over both channels.
A record data rate for visible light communications (VLC) using a transistor outline (TO) packaged Gallium Nitride (GaN) laser diode is reported. Using a system 3 dB bandwidth of 1.4 GHz data transmission at 15 Gb/s is reported. This is achieved due to the use of orthogonal frequency division multiplexing (OFDM) in combination with a high system signal to noise ratio (SNR) and adaptive bit loading extending the effective bandwidth to 2.5 GHz. To the best of authors knowledge this is the highest reported data rate for single channel VLC.
Proc. SPIE. 10128, Broadband Access Communication Technologies XI
KEYWORDS: Light emitting diodes, Modulation, Interference (communication), Receivers, Monte Carlo methods, Signal processing, Wireless communications, Data communications, Orthogonal frequency division multiplexing, Signal detection
Light-fidelity (LiFi) uses energy-efficient light-emitting diodes (LEDs) for high-speed wireless communication, and it has a great potential to be integrated with fibre communication for future gigabit networks. However, by making fibre communication wireless, multiuser interference arises. Traditional methods use orthogonal multiple access (OMA) for interference avoidance. In this paper, multiuser interference is exploited with the use of non-orthogonal multiple access (NOMA) relying on successive interference cancellation (SIC). The residual interference due to imperfect SIC in practical scenarios is characterized with a proportional model. Results show that NOMA offers 5 -10 dB gain on the equivalent signal-to-interference-plus-noise ratio (SINR) over OMA. The bit error rate (BER) performance of direct current optical orthogonal frequency division multiplexing (DCO-OFDM) is shown to be significantly improved when SIC is used.
Solid state lighting systems typically use multiple Light Emitting Diode (LED) die within a single lamp, and multiple lamps within a coverage space. This infrastructure forms the transmitters for Visible Light Communications (VLC), and the availability of low-cost detector arrays offers the possibility of building Multiple Input Multiple Output (MIMO) transmission systems. Different approaches to optical MIMO are being investigated as part of a UK government funded research programme, ‘Ultra-Parallel Visible Light Communications’ (UPVLC). In this paper we present a brief review of the area and report results from systems that use integrated subsystems developed as part of the project. The scalability of these approaches and future directions will also be discussed.
Motivated by the looming radio frequency (RF) spectrum crisis, this paper aims at demonstrating that optical wireless communication (OWC) has now reached a state where it can demonstrate that it is a viable and matured solution to this fundamental problem. In particular, for indoor communications where most mobile data traffic is consumed, light fidelity (Li-Fi) which is related to visible light communication (VLC) offers many key advantages, and effective solutions to the issues that have been posed in the last decade. This paper discusses all key component technologies required to realize optical cellular communication systems referred to here as optical attocell networks. Optical attocells are the next step in the progression towards ever smaller cells, a progression which is known to be the most significant contributor to the improvements in network spectral efficiencies in RF wireless networks.