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

Unary Coding Design for Simultaneous Wireless Information and Power Transfer with Practical M-QAM

Relying on the propagation of modulated radio-frequency (RF) signals, we can achieve simultaneous wireless information and power transfer (SWIPT) to support low-power communication devices. In this paper, we proposed a unary coding based SWIPT encoder by considering a practical M-QAM. Markov chains are exploited for characterising coherent binary information source and for modelling the generation process of modulated symbols. Therefore, both mutual information and the average energy harvesting performance at the SWIPT receiver are analysed in semi-closed-form. With the aid of the genetic algorithm, the sub-optimal codeword distribution of the coded information source is obtained by maximising the average energy harvesting performance, while satisfying the requirement of the mutual information. Simulation results demonstrate the advantage of the SWIPT encoder. Moreover, a higher-level unary code and a lower-order M-QAM results in higher WPT performance, when the maximum transmit power of the modulated symbol is fixed

Joint Dimming Control and Optimal Power Allocation for THO-OFDM Visible Light Communications

Layered or hybrid optical orthogonal frequency division multiplexing (OFDM) has been proposed for use in optical communications due to its excellent spectral and power efficiencies, especially in visible light communications (VLC). However, most of the current works concentrate on transmitter and receiver design as well as the quality of service in communication networks. In this paper, we propose a spectrum-efficient dimmable triple-layer hybrid optical OFDM (DTH-OFDM) scheme to tackle the illumination requirements, considering different practical indoor VLC scenarios from low illumination to high illumination intensities. In the proposed DTH-OFDM scheme, the required dimming level is achieved by jointly adjusting the dimming factors and direct current bias. We investigate the comprehensive performance analysis of the proposed DTH-OFDM in detail, including probability density function, bit error rate (BER), spectral and energy efficiencies. In addition, a joint dimming control and optimal power allocation problem for DTH-OFDM is formulated and solved using convex optimization under the constraints of light emitting diode (LED) nonlinearity, dimming target and communications reliability. Numerical results show that, the proposed DTH-OFDM can offer continuous and arbitrary dimming target with higher spectral efficiency and lower BER compared with its counterparts, as well as an enhanced tolerance to the LED nonlinearity

Unary Coding Design for Simultaneous Wireless Information and Power Transfer With Practical M-QAM

Relying on the propagation of modulated radio-frequency (RF) signals, we can achieve simultaneous wireless information and power transfer (SWIPT) to support low-power communication devices. In this paper, we proposed a unary coding based SWIPT encoder by considering a practical M-QAM. Markov chains are exploited for characterising coherent binary information source and for modelling the generation process of modulated symbols. Therefore, both mutual information and the average energy harvesting performance at the SWIPT receiver are analysed in semi-closed-form. With the aid of the genetic algorithm, the sub-optimal codeword distribution of the coded information source is obtained by maximising the average energy harvesting performance, while satisfying the requirement of the mutual information. Simulation results demonstrate the advantage of the SWIPT encoder. Moreover, a higher-level unary code and a lower-order M-QAM results in higher WPT performance, when the maximum transmit power of the modulated symbol is fixed

Power and spectrally efficient integrated high-speed LED drivers for visible light communication

Recent trends in mobile broadband indicates that the available radio frequency (RF) spectrum will not be enough to support the data requirements of the immediate future. Visible light communication, which uses visible spectrum to transmit wirelessly could be a potential solution to the RF ’Spectrum Crunch’. Thus there is growing interest all over the world in this domain with support from both academia and industry. Visible light communication( VLC) systems make use of light emitting diodes (LEDs), which are semiconductor light sources to transmit information. A number of demonstrators at different data capacity and link distances has been reported in this area. One of the key problems holding this technology from taking off is the unavailability of power efficient, miniature LED drive schemes. Reported demonstrators, mostly using either off the shelf components or arbitrary waveform generators (AWGs) to drive the LEDs have only started to address this problem by adopting integrated drivers designed for driving lighting installations for communications. The voltage regulator based drive schemes provide high power efficiency (> 90 %) but it is difficult to realise the fast switching required to achieve the Mbps or Gbps data rates needed for modern wireless communication devices. In this work, we are exploiting CMOS technology to realise an integrated LED driver for VLC. Instead of using conventional drive schemes (digital to analogue converter (DAC) + power amplifier or voltage regulators), we realised a current steering DAC based LED driver operating at high currents and sampling rates whilst maintaining power efficiency. Compared to a commercial AWG or discrete LED driver, circuit realised utilisng complementary metal oxide semiconductor (CMOS) technology has resulted in area reduction (29mm2). We realised for the first time a multi-channel CMOS LED driver capable of operating up to a 500 MHz sample rate at an output current of 255 mA per channel and >70% power efficiency. We were able to demonstrate the flexibility of the driver by employing it to realise VLC links using micro LEDs and commercial LEDs. Data rates up to 1 Gbps were achieved using this system employing a multiple input, multiple output (MIMO) scheme. We also demonstrated the wavelength division multiplexing ability of the driver using a red/green/blue commercial LED. The first integrated digital to light converter (DLC), where depending on the input code, a proportional number of LEDs are turned ON, realising a data converter in the optical domain, is also an output from this research. In addition, we propose a differential optical drive scheme where two output branches of a current DAC are used to drive two LEDs achieving higher link performance and power efficiency compared to single LED drive

Unary-coded dimming control improves ON-OFF keying visible light communication

An ideal visible light communication (VLC) system should facilitate reliable data transmission at high throughputs, while also providing flicker-free illumination at the user-defined dimming level. In this spirit, we conceive a unary code aided dimming scheme for ON-OFF keying (OOK) modulated VLC systems. The proposed unary-coded scheme facilitates joint dimming and throughput control, while relying on iterative decoding. It is demonstrated that the proposed unary-coded dimming scheme provides attractive throughput gains over its contemporaries and it is also capable of approaching the theoretical throughput limit. Furthermore, we design novel joint dimming-forward error correction coding schemes, which significantly outperform their compensation time dimming-based counterparts in terms of the attainable bit error rate performance as well as the throughput. Finally, in the quest for approaching the capacity, we also optimize our system using EXTRINSIC information transfer charts and demonstrate an SNR-gain of upto 6 dB over the compensation time dimming-based classic benchmarker

Unary-coded dimming control improves ON-OFF keying visible light communication

An ideal Visible Light Communication (VLC) system should facilitate reliable data transmission at high throughputs, while also providing flicker-free illumination at the user-defined dimming level. In this spirit, we conceive a unary code aided dimming scheme for On-Off Keying (OOK) modulated VLC systems. The proposed unary-coded scheme facilitates joint dimming and throughput control, while relying on iterative decoding. It is demonstrated that the proposed unary-coded dimming scheme provides attractive throughput gains over its contemporaries and it is also capable of approaching the theoretical throughput limit. Furthermore, we design novel joint dimming-Forward Error Correction (FEC) coding schemes, which significantly outperform their compensation time dimming based counterparts in terms of the attainable Bit Error Rate (BER) performance as well as the throughput. Finally, in the quest for approaching the capacity, we also optimize our system using EXtrinsic Information Transfer (EXIT) charts and demonstrate an SNR-gain of up to 6 dB over the compensation time dimming based classic benchmarker

Research Data: Unary-Coded Dimming Control Improves ON-OFF Keying Visible Light Communication

An ideal Visible Light Communication (VLC) system should facilitate reliable data transmission at high throughputs, while also providing flicker-free illumination at the user-defined dimming level. In this spirit, we conceive a unary code aided dimming scheme for On-Off Keying (OOK) modulated VLC systems. The proposed unary-coded scheme facilitates joint dimming and throughput control, while relying on iterative decoding. It is demonstrated that the proposed unary-coded dimming scheme provides attractive throughput gains over its contemporaries and it is also capable of approaching the theoretical throughput limit. Furthermore, we design novel joint dimming-Forward Error Correction (FEC) coding schemes, which significantly outperform their compensation time dimming based counterparts in terms of the attainable Bit Error Rate (BER) performance as well as the throughput. Finally, in the quest for approaching the capacity, we also optimize our system using EXtrinsic Information Transfer (EXIT) charts and demonstrate an SNR-gain of upto 6 dB over the compensation time dimming based classic benchmarker.</span

Pattern Recognition

Pattern recognition is a very wide research field. It involves factors as diverse as sensors, feature extraction, pattern classification, decision fusion, applications and others. The signals processed are commonly one, two or three dimensional, the processing is done in real- time or takes hours and days, some systems look for one narrow object class, others search huge databases for entries with at least a small amount of similarity. No single person can claim expertise across the whole field, which develops rapidly, updates its paradigms and comprehends several philosophical approaches. This book reflects this diversity by presenting a selection of recent developments within the area of pattern recognition and related fields. It covers theoretical advances in classification and feature extraction as well as application-oriented works. Authors of these 25 works present and advocate recent achievements of their research related to the field of pattern recognition