Optical energy-constrained slot-amplitude modulation for dimmable VLC. Suboptimal detection and performance evaluation

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference

Optical energy-constrained slot-amplitude modulation for dimmable VLC: suboptimal detection and performance evaluation

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference

A two phase framework for visible light-based positioning in an indoor environment: performance, latency, and illumination

Recently with the advancement of solid state lighting and the application thereof to Visible Light Communications (VLC), the concept of Visible Light Positioning (VLP) has been targeted as a very attractive indoor positioning system (IPS) due to its ubiquity, directionality, spatial reuse, and relatively high modulation bandwidth. IPSs, in general, have 4 major components (1) a modulation, (2) a multiple access scheme, (3) a channel measurement, and (4) a positioning algorithm. A number of VLP approaches have been proposed in the literature and primarily focus on a fixed combination of these elements and moreover evaluate the quality of the contribution often by accuracy or precision alone. In this dissertation, we provide a novel two-phase indoor positioning algorithmic framework that is able to increase robustness when subject to insufficient anchor luminaries and also incorporate any combination of the four major IPS components. The first phase provides robust and timely albeit less accurate positioning proximity estimates without requiring more than a single luminary anchor using time division access to On Off Keying (OOK) modulated signals while the second phase provides a more accurate, conventional, positioning estimate approach using a novel geometric constrained triangulation algorithm based on angle of arrival (AoA) measurements. However, this approach is still an application of a specific combination of IPS components. To achieve a broader impact, the framework is employed on a collection of IPS component combinations ranging from (1) pulsed modulations to multicarrier modulations, (2) time, frequency, and code division multiple access, (3) received signal strength (RSS), time of flight (ToF), and AoA, as well as (4) trilateration and triangulation positioning algorithms. Results illustrate full room positioning coverage ranging with median accuracies ranging from 3.09 cm to 12.07 cm at 50% duty cycle illumination levels. The framework further allows for duty cycle variation to include dimming modulations and results range from 3.62 cm to 13.15 cm at 20% duty cycle while 2.06 cm to 8.44 cm at a 78% duty cycle. Testbed results reinforce this frameworks applicability. Lastly, a novel latency constrained optimization algorithm can be overlaid on the two phase framework to decide when to simply use the coarse estimate or when to expend more computational resources on a potentially more accurate fine estimate. The creation of the two phase framework enables robust, illumination, latency sensitive positioning with the ability to be applied within a vast array of system deployment constraints

Investigation and Implementation of Dicode Pulse Position Modulation Over Indoor Visible Light Communication System

A visible light communication (VLC) system with green technology is available and enables users to use white LEDs for illumination as well as for high data rate transmission over wireless optical links. In addition, LEDs have advantages of low power consumption, high speed with power efficiency and low cost. Therefore, a great deal of research is considered for indoor VLC, as it offers huge bandwidth whilst using a significant modulation technique. This thesis is concerned with the investigation and implementation of the dicode pulse position modulation (DiPPM) scheme over a VLC link using white LED sources. Novel work is carried out for applying DiPPM over a VLC channel theoretically and experimentally including a comparison with digital PPM (DPPM) in order to examine the system performance. Moreover, a proposal of variable DiPPM (VDiPPM) is presented in this thesis for dimming control. The indoor VLC channel characteristics have been investigated for two propagation prototypes. Two models have been proposed and developed with DiPPM and DPPM being applied over the VLC channel. A computer simulation for the proposed models for both DiPPM and DPPM systems is performed in order to analyse the receiver sensitivity with the effect of intersymbol interference (ISI). Both systems are operating at 100 Mbps and 1 Gbps for a BER of 10-9. An improvement in sensitivity being achieved by the DiPPM compared to the DPPM VLC system. The system performance has been carried out by Mathcad software. The predicted DiPPM receiver sensitivity outperforms DPPM receiver at by -5.55 dBm and -8.24 dBm, at 1 Gbps data rate, and by -5.53 dBm and -8.22 dBm, at 100 Mbps, without and with guard intervals, respectively. In both cases the optical receiver sensitivity is increased when the ISI is ignored. These results based on the received optical power required by each modulation scheme. Further work has been done in mathematical evaluation carried out to calculate the optical receiver sensitivity to verify the comparison between the two systems. The original numerical results show that DiPPM VLC system provides a better sensitivity than a DPPM VLC system at a selected BER of 10-9 when referred to the same preamplifier at wavelength of 650 nm and based on the equivalent input noise current generated by the optical front end receiver. The results show that the predicted sensitivity for DPPM is greater than that of DPPM by about 1 dBm when both systems operating at 100 Mbps and 1 Gbps. Also, it is show that the receiver sensitivity is increased when the ISI is limited. Experimentally, a complete indoor VLC system has been designed and implemented using Quartus II 11.1 software for generating VHDL codes and using FPGA development board (Cyclone IV GX) as main interface real-time transmission unit in this system. The white LEDs chip based transmitter and optical receiver have been constructed and tested. The measurements are performed by using LED white light as an optical transmitter faced to photodiode optical receiver on desk. Due to the LED bandwidth limitation the achieved operating data rate, using high speed LED driver, is 5.5 Mbps at BER of 10-7. The original results for the measurements determined that the average photodiode current produced by using DiPPM and DPPM optical receivers are 8.50 μA and 10.22 μA, respectively. And this in turn indicates that the DiPPM receiver can give a better sensitivity of -17.24 dBm while compared to the DPPM receiver which gives is -16.44 dBm. The original practical results proved the simulation and theoretical results where higher performance is achieved when a DiPPM scheme is used compared to DPPM scheme over an indoor VLC system

Code Design for Visible Light Communications Under Illumination Constraints

Visible light communication (VLC) uses the same LEDs which are an efficient source of illumination to transmit information concurrently using optical direct-detection. As a result of modulating the LED to convey information, there may be a perceived change in the light perception which besides being annoying, may produce physiological consequences under prolonged exposure. The aim of this research is to propose code design methodologies for controlling the effects of light intensity flickering, brightness control, and color shifts due to the modulation, encoding information bits in organized optical symbol sequences, and improving the coding gain by the use of the Viterbi algorithm. In order to mitigate the effect of intensity flickering presented in On-Off Keying modulation, five codes are designed with two proposed algorithms using finite-state machines (FSMs) for constraining the runs of zeros or ones. The codes are compared with the codes proposed in the IEEE 802.15.7 standard on VLC (Manchester code, 4B6B code, and the 8B10B code) in terms of flicker mitigation using the perceived flicker index (PFI) (a mathematical measure of flicker introduced in this study) and error-rate performance. The designed codes show asymptotic coding gains between 1:25 and 6 dB with a low sacrifice in PFI. To avoid color shifts in color-shift keying (CSK) modulation, four codes were designed from optimally CSK constellations and two classes of codes where one class is based on FSMs and the other on trellis-coded modulation (TCM) according to the desired color perception constraint. The designed codes show asymptotic coding gains between 1:5 to 3:5 dB with respect to uncoded transmission. For brightness control, variable-weight multipulse pulse-position modulation (VW-MPPM) is introduced as an alternative for increasing the spectral efficiency by the selection of multipulse pulse-position modulation symbols of diverse weight to attain the desired dimming level. Combining VM-MPPM symbols with Huffman codes and TCM, two designed codes are compared with MPPM codes for dimming level of 0:67 and 0:40 showing an asymptotic coding gain of 0:94 and 1:29 dB, respectively. Finally, we show the trade-offs between coding gain improvement and their effects on light perception

Study of MIMO techniques for optical wireless communications

With its huge spectral resource, optical wireless communication (OWC) has emerged as a promising complementary technology to the radio frequency (RF) communication systems. OWC provides data communications for a variety of user applications and it can be deployed using simple, low-cost, low-power and energy-efficient component. In order to enhance capacity, reliability and/or coverage of OWC, multiple-input-multiple-output (MIMO) systems are employed to exploit additional degrees of freedom, such as the location and angular orientation of optical sources and detectors. However, the implementation of MIMO systems is faced with challenges such as the strong correlation and multipath propagation in indoor OWC channels, system synchronisation, as well as inter-channel interference (ICI) due to multiple parallel data transmission. This dissertation investigates MIMO OWC systems which utilises transmission techniques with reduced complexity. A detailed study and performance evaluation of the techniques in terms of capacity, spectral efficiency and error rates is conducted through theoretical analysis, simulation and experiments. The system performance is investigated under different constraints imposed by impairments such as interference, synchronization and channel correlation. Optical spatial modulation (OSM) is studied as a low complexity technique using multiple light sources to enhance system capacity. A generalised framework for implementing OSM with energy efficient pulse position modulation scheme is devised. This framework supports other variants of OSM, and it can be adapted to satisfy varying system requirement such as spectral and energy efficiencies. The performance of the OWC system is investigated in indoor line-of-sight (LOS) propagation. The error performance of the system is analysed theoretically and matched by simulation results. Also, the system performance is evaluated with experiments to demonstrate feasibility. Furthermore, the performance of OSM MIMO techniques in the realistic indoor scenario is considered by taking into account the multiple reflections of the transmitted signal from room surfaces. This is motivated by the recent drive towards high-speed Gigabits per second (Gbps) data communication, where the inter-symbol interference (ISI) caused by the multipath propagation may pose a major bottleneck. A model of the multipath-induced ISI is presented to account for signal spreading and then applied to formulate the error performance analysis. The impact of multipath-induced power penalty and delay spread on system performance is demonstrated using their spatial distributions across the coverage area. Additionally, the impact of timing synchronization problems on the error performance of different variants of the OSM MIMO techniques is investigated. While most works related to SM have assumed a perfect synchronization among the multiple transmitter and receiver elements, such assumption pose a challenge in practical deployment. Hence, the need to examine the impact of synchronisation error that can result from clock jitters and variations in propagation delay. Synchronisation error analyses of OSM schemes are presented, and the tolerance of each scheme to timing synchronization errors is demonstrated. To further enhance system capacity, this thesis also explores spatial multiplexing MIMO technique with orthogonal frequency division multiplexing (OFDM). The central objective is to propose and apply techniques to address the correlation of the indoor optical wireless channel and the frequency selectivity due to the limited bandwidth of LEDs. To address these two effects, a joint coding of paired information symbols was applied in a technique termed pairwise coding (PWC). This technique is based on rotated symbol constellation and it offers significant performance improvement. The error performance of the proposed system is evaluated through simulation and experimental demonstration. PWC proved to be effective over varying degrees of bandwidth limitation and under different channel conditions