Mitigation of Side-Effect Modulation in Optical OFDM VLC Systems

Side-effect modulation (SEM) has the potential to be a significant source of interference in future visible light communication (VLC) systems. SEM is a variation in the intensity of the light emitted by a luminaire and is usually a side-effect caused by the power supply used to drive the luminaires. For LED luminaires powered by a switched mode power supply, the SEM can be at much higher frequencies than that emitted by conventional incandescent or fluorescent lighting. It has been shown that the SEM caused by commercially available LED luminaires is often periodic and of low power. In this paper, we investigate the impact of typical forms of SEM on the performance of optical OFDM VLC systems; both ACO-OFDM and DCO-OFDM are considered. Our results show that even low levels of SEM power can significantly degrade the bit-error-rate performance. To solve this problem, an SEM mitigation scheme is described. The mitigation scheme is decision-directed and is based on estimating and subtracting the fundamental component of the SEM from the received signal. We describe two forms of the algorithm; one uses blind estimation while the other uses pilot-assisted estimation based on a training sequence. Decision errors, resulting in decision noise, limit the performance of the blind estimator even when estimation is based on very long signals. However, the pilot system can achieve more accurate estimations, thus better performance. Results are first presented for typical SEM waveforms for the case where the fundamental frequency of the SEM is known. The algorithms are then extended to include a frequency estimation step and the mitigation algorithm is shown also to be effective in this case

A Comparison of CP-OFDM, PCC-OFDM and UFMC for 5G Uplink Communications

Polynomial-cancellation-coded orthogonal frequency division multiplexing (PCC-OFDM) is a form of OFDM that has waveforms which are very well localized in both the time and frequency domains and so it is ideally suited for use in the 5G network. This paper analyzes the performance of PCC-OFDM in the uplink of a multiuser system using orthogonal frequency division multiple access (OFDMA) and compares it with conventional cyclic prefix OFDM (CP-OFDM), and universal filtered multicarrier (UFMC). PCC-OFDM is shown to be much less sensitive than either CP-OFDM or UFMC to time and frequency offsets. For a given constellation size, PCC-OFDM in additive white Gaussian noise (AWGN) requires 3dB lower signal-to-noise ratio (SNR) for a given bit-error-rate, and the SNR advantage of PCC-OFDM increases rapidly when there are timing and/or frequency offsets. For PCC-OFDM no frequency guard band is required between different OFDMA users. PCC-OFDM is completely compatible with CP-OFDM and adds negligible complexity and latency, as it uses a simple mapping of data onto pairs of subcarriers at the transmitter, and a simple weighting-and-adding of pairs of subcarriers at the receiver. The weighting and adding step, which has been omitted in some of the literature, is shown to contribute substantially to the SNR advantage of PCC-OFDM. A disadvantage of PCC-OFDM (without overlapping) is the potential reduction in spectral efficiency because subcarriers are modulated in pairs, but this reduction is more than regained because no guard band or cyclic prefix is required and because, for a given channel, larger constellations can be used

Advances in Visible Light Communication

Peer reviewed: TrueAcknowledgements: We extend our sincere gratitude to all the authors who submitted their work to this Special Issue and to the dedicated Photonics editorial staff for their invaluable assistance.Publication status: Publishe

MIMO-OFDM Visible Light Communications

Visible light communication is emerging as an important new technology for indoor high-speed data transmission. Illumination in most indoor scenarios is provided by multiple luminaires located on the ceiling. When these luminaires are used as data transmitters, they can be configured as an optical multiple-input multiple-output (MIMO) system to achieve high data rate transmission. In this thesis, new front-end designs for optical MIMO receivers have been developed. These designs are shown to provide significant angular diversity and therefore can be used in compact portable devices

A Review of Advanced Transceiver Technologies in Visible Light Communications

Visible Light Communication (VLC) is an emerging technology that utilizes light-emitting diodes (LEDs) for both indoor illumination and wireless communications. It has the potential to enhance the existing WiFi network and connect a large number of high-speed internet users in future smart home environments. Over the past two decades, VLC techniques have made significant strides, resulting in transmission data rates increasing from just a few Mbps to several tens of Gbps. These achievements can be attributed to the development of various transceiver technologies. At the transmitter, LEDs should provide high-quality light for illumination and support wide modulation bandwidths. Meanwhile, at the receiver, optics systems should have functions such as optical filtering, light concentration, and, ideally, a wide field of view (FOV). The photodetector must efficiently convert the optical signal into an electrical signal. Different VLC systems typically consider various transceiver designs. In this paper, we provide a survey of some important emerging technologies used to create advanced optical transceivers in VLC

Signal demodulation using a radial basis function neural network (RBFNN) in a silicon photomultiplier-based visible light communication system

A silicon photomultiplier (SiPM) contains an array of microcells that can each detect individual photons. Consequently, it can arguably result in the most sensitive receiver in visible light communication (VLC). However, each microcell needs a period of several nanoseconds to recover after detecting a photon. This creates a non-linear response and introduces a unique form of inter-symbol interference. In this paper, we first show that this interference splits each element of the received signal constellation into multiple clusters. This observation motivates the investigation into the use of a Radial Basis Function Neural Network (RBFNN) to deal with the impact of the nonlinearity. Both the training procedures and the performance of the RBFNN are explained and discussed in detail. The influence of the number of the RBFNN centers, the widths of the centers, the constellation size and the period of the transmitted signal samples on the system performance are investigated. In addition, two different RBFNN-based data demodulation methods are introduced. The simulation results suggest that the new RBFNN-aided receivers reduce the negative impacts of the SiPM nonlinearity and can result in lower bit error rates (BERs) for a wide range of irradiances on the SiPM

DCO-OFDM channel sounding with a SiPM receiver

Orthogonal Frequency-Division Multiplexing (OFDM) is a popular modulation scheme, which requires a linear channel. Unfortunately, the most sensitive receivers for visible light communications, silicon photomultipliers (SiPMs), have a non-linear response. Despite this incompatibility, results from an easily implemented method of combining OFDM and SiPMs are shown to successfully limit the bit error rate to below the limit required by forward error correction

Indoor Visible Light Positioning: Overcoming the Practical Limitations of the Quadrant Angular Diversity Aperture Receiver (QADA) by Using the Two-Stage QADA-Plus Receiver

Visible light positioning (VLP), using LED luminaires as beacons, is a promising solution to the growing demand for accurate indoor positioning. In this paper, we introduce a two-stage receiver that has been specifically designed for VLP. This receiver exploits the advantages of two different VLP receiver types: photodiodes and imaging sensors. In this new receiver design a quadrant angular diversity aperture (QADA) receiver is combined with an off-the-shelf camera to form a robust new receiver called QADA-plus. Results are presented for QADA that show the impact of noise and luminaire geometry on angle of arrival estimation accuracy and positioning accuracy. Detailed discussions highlight other potential sources of error for the QADA receiver and explain how the two-stage QADA-plus can overcome these issues