Novel low computational complexity technique for visible light communication systems

In visible light communication (VLC) system, the Orthogonal Frequency Division Multiplexing (OFDM) technique has been widely used to achieve a high data rate transmission. However, OFDM will cause high peak-to-average power ratio (PAPR) in the VLC system. In this paper, we propose and experimentally demonstrate a new interleaved Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-S OFDM) method. We compare the interleaved DFT-S technique to other PAPR reduction techniques, such as Clipping OFDM and conventional DFT-S. The experimental results show that interleaved DFT-S achieve FEC threshold for an overall 2.0Gb/s 32QAM signal over the 1.05m transmission. In addition, interleaved DFT-S presents significant PAPR reduction, low complexity and optimal BER performance, when compared to other techniques.

The filtered‐orthogonal frequency division multiplexing (F‐OFDM) scheme has gained attention as a promising solution in the field of visible light communication (VLC) systems. One crucial aspect in VLC is the conversion of the complex F‐OFDM signal into a real signal that corresponds with direct detection and intensity modulation. Traditionally, achieving a real F‐OFDM signal has involved imposing Hermitian symmetry (HS) on the samples of the Inverse Fast Fourier transform (IFFT), which requires 2N‐point IFFT and obtains an N‐point FFT, thus adding complexity. In this study, a novel approach is presented and implemented, aiming to enhance spectral efficiency and reduce system complexity by generating a real F‐OFDM signal without relying on HS. This approach is then compared with HS‐free (HSF)‐OFDM, direct current biased optical OFDM, and asymmetrically clipped optical OFDM. The suggested method offers a remarkable improvement of ~50% in the required IFFT/FFT volume. Consequently, this method reduces hardware complexity and power usage compared with the traditional F‐OFDM method. Moreover, regarding error rates, the proposed method demonstrates better spectral efficiency than HSF‐OFDM.

We proposed two kinds of visible light communication(VLC) systems which respectively based on 64QAM/square geometrical shaping(SGS) 128QAM time domain hybrid modulation scheme (SGSHY) and 64QAM/128QAM time domain hybrid modulation scheme (REGHY). These two systems can operate around specific forward error correction (FEC) threshold and maximize the achievable information rate (AIR) of the system. The principles of SGSHY and REGHY are proposed in detail, which has very low computation complexity compared with probabilistic shaping. The SGSHY outperforms REGHY at high peak to peak voltage (Vpp). Experimental results show that at high Vpp like 1.4 V, which means the system is suffering from high nonlinear distortion, the AIR of SGSHY outperforms that of REGHY by 0.12Gb/s at the 2×10–2 FEC threshold. The AIR of the REGHY is at most 0.36Gb/s higher than that of 64QAM at 0.8V Vpp and 7% FEC threshold, while the (achievable information rate) AIR of SGSHY is at most 0.40Gb/s higher than that of 64QAM at 1.4 V Vpp and 20% FEC threshold.

In order to realize the video image transmission and the excellent lighting function of the visible light communication system, a LED-based visible light communication method and system is proposed. Based on the field programmable gate array (FPGA) hardware, the RS channel coding is applied to the visible light communication system. A pulse position decision algorithm is proposed, which is applied to the receiver of the visible light communication system to meet the error-free decision of the signal. The design of the system is based on the analog-to-digital conversion circuit, which provides a large signal dynamic range for the pulse position decision algorithm, and designs the LED driver based on the bias circuit to realize the fast broadband modulation of the signal. The test results show that the combined application of pulse position decision algorithm and Reed-Solomon codec can reduce the error of system signal and meet the real-time and reliable transmission of signal. The system can display the received video in real time from the receiver, and the whole system communication distance up to 5 m.

The exponential rise in wireless communication demands and allied applications have revitalized academia-industries to develop an efficient and potential solution. Furthermore, the high-pace increasing scarcity of radio spectrum has also alarmed researchers to achieve better Quality of Service (QoS) centric solution. To meet such demands Visible Light Communication (VLC) systems have gained global attention; however, up surging high rate, range and reliability (3R) needs demand better performance. Towards these goals, Multiple Input Multiple Output (MIMO) based VLC systems is an efficient approach; though its efficacy under Multiple Users (MU) conditions remains least explored. Enabling MIMO-MU based VLC can achieve 3R objectives effectively; however, factors like multipath attenuation, interferences and varied impairment-affects makes classical approached confined. The MIMO-MU VLC systems require robust error, noise or interference resilient transmission even under adverse conditions such as non-linear LED, multipath attenuation and interference. Towards these objectives, in this paper a highly robust MIMO-MU VLC system is developed that incorporates an augmented MIMO channel design and combined pre-coding and post equalization schemes. To alleviate major interference probability in MIMO-MU environment, proposed model incorporates time (delay)-multiplexing based data transmission followed by signal adaptive precoding and Volterra Kernel based Hybrid-equalizer. This approach enables interference and noise removal as well as LED non-linearity handling under MIMO-MU VLC communication. The use of a Volterra Kernel based Decision Feedback Equalization with both linear as well as non-linear equalization enables proposed VLC system to exhibit low Bit Error Rate with low modulation index and taps, that optimizes trade-off between performance as well as complexity.

In this paper, we have studied a multi - LED matrix optical sensing technology for high speed transmission in a visible light communication system based on an optical camera CCD sensor. In order to improve transmission capacity in visible light communication, data must be transmitted from different LEDs at the same time and received. However, a system environment with multiple LEDs may cause interference between adjacent LEDs. Generally, since a visible light communication system generally uses a luminance modulation method, when a plurality of LEDs transmit data at the same time, it is difficult to accurately detect each LED due to light scattering interference of an adjacent LED. To solve this problem, we proposed a spatial filtering technique to group multiple LEDs and to reduce the interference of grouped LED matrix. We also propose a pixel image processing technique for detecting each LED. This technology accurately recognizes each matrix of LEDs in a multi-matrix LED environment and improves system performance by increasing the throughput of the MISO-OCVLC (Optical Camera Visible Light Communication) system.

Modern hospitals are beginning to adopt E-HEALTH as efficient complements to the traditional healthcare services. To support the E-HEALTH services, a locatable, radiation-free and high-capacity communication system is urgently needed in hospitals. Power line communication (PLC) system can use the ubiquitous power line network to power the light-emitting diode (LED) lights while serving as the backbone network for the indoor visible light communication (VLC) systems naturally. In this paper, an integrated broadband power line and visible light communication systems with OFDM modulation is proposed for the indoor hospital applications. This gives a brand-new solution to replace the conventional wireless communication systems in hospitals.

SummaryWith the development of new generation lighting sources, visible light communication (VLC) system has become a complementary solution to traditional radio frequency wireless system. However, the error performance of VLC system is degraded because of multipath effects and interference from other lighting sources that, in turn, reduce the communication range. This work targets the issue of performance degradation of VLC systems in terms of communication range and demonstrates a VLC system design that utilizes forward error correction (FEC) codes as the main tool to fix this issue. Furthermore, the work also covers practical implementation of the proposed VLC system using UART modules programmed in MATLAB. The hardware results demonstrate that the communication range of the proposed VLC system is enhanced up to 0.5 m. Over and above, it is also shown through simulations that the coding gain of the proposed design is more when compared with existing VLC system(s).

Multiple-input multiple-output (MIMO) technique is now used in most new broadband communication system, and orthogonal frequency division multiplexing (OFDM) is also utilized within current 4^th generation (4G) of mobile telecommunication technology. With MIMO and OFDM combined, visible light communication (VLC) system’s diversity gain is increase, yet system capacity for dispersive channels is also enhanced. Moreover, with the emerging massive MIMO-OFDM VLC system, there are significant advantages than smaller systems’ such as channel hardening, further increasing of energy efficiency (EE) and spectral efficiency (SE) based on law of large number. This paper addresses one of the major technological challenges, system architecture design, which was solved by semispherical beehive structure (SBS) receiver and so that diversity gain can be identified and applied in Massive MIMO VLC system. Simulation results shows that the proposed design clearly presents a spatial diversity over conventional VLC systems.

This paper proposes an asymmetric frequency shift keying (AFSK) modulation technique for visible light communications (VLC) systems. AFSK is derived from the normal FSK in response to the non-negative aspect of VLC technology. AFSK provides VLC systems with a low cost and low complexity modulation technique that mitigates flickering and dimming for both square and rectified sine waves signals. The binary version of AFSK is analyzed and a general expression is proposed to its carrier frequency based on the original FSK. Simulated results of selected AFSK constellation sizes which perform better than on-off keying are presented. We also present M-ary FSK (MFSK) modulation in the VLC channel.

A computationally efficient ranging scheme that estimates time of arrival (TOA) by a low complexity minimum mean square error (MMSE) and a matrix pencil techniques is proposed for IEEE 802.15.4a chirp spread spectrum system. In TOA estimation, it is known that accurate channel delay can be estimated by the MMSE technique. However, the major drawback of the MMSE is its high computational complexity, which grows with number of signal samples. In this paper, thus, a computational efficient MMSE technique based on the chirp spectrum characteristic is proposed for a low complexity ranging algorithm. The proposed TOA estimation method consists of two-step signal processing: proposed low complexity MMSE-based channel impulse response (CIR) estimation and the channel delay tracking by matrix pencil algorithm. The proposed TOA estimation method not only has low computational complexity, but also achieves small ranging error. The effectiveness of the proposed algorithm is demonstrated by simulation results.

The need to exchange data wirelessly has increased as the growth of the number of mobile devices. Visible light communication (VLC) is a promising technology to alleviate the growing traffic problem. However, the occlusion problem is a difficulty in VLC system. In order to solve the problem, an anti-occlusion VLC system has been proposed in this article. In this VLC system, we propose the channel cooperative selection mechanism, which is based on the best-response dynamics and best response strategies of the game theory. This mechanism uses bit error ratio (BER) as the utility function to optimize system performance. In addition, the system provides three candidate communication channels, including direct channel, indirect channel, and mixed channel, to active users who will select the optimal communication channel. Moreover, the anti-occlusion VLC system has many application scenarios, such as the office, which has practical significance. For verifying the validity of the proposed mechanism, we accomplish the simulation results in terms of BER and throughput in different communication cases. It is demonstrated that the proposed channel cooperative selection mechanism in VLC systems offers superior performance in environment of obstructions.

Visible Laser Light Communication System (VLLC) is a wireless communication system, using laser as the medium. In the data transfer process, it is possible to have optical interference where 2 laser beams coincide with one point on the reflector. Research on the effect of laser source interference has been carried out by several researchers including mitigation actions to reduce its effects. This experiment uses 2 optical distance sensors that produce a laser with a wavelength of 650 nm with a power <=4.1 mW and with the direction of the laser beam both of them cross each other. To determine the effect of the interference of two laser beams when crossing the communication process in the visible light communication system, a reflector is used which can capture the two laser beams and the reflector can be shifted gradually so that a condition can be obtained where the two laser beams meet at one point. From the measurements made at the points after the laser beam crossing, the measurements at the point where the beam crossed, and the measurements at the points before the beam crossing, it was obtained data, at the exact point where the laser beam crossed the interference occurred, which is indicated by unstable output voltage of the two lasers, so that communication at the point of intersection is disrupted. However, if outside the point of contact both before and after the point of contact, interference and communication systems will not occur.

We investigate the performance of visible light communication (VLC) system with a pulse width modulation (PWM) dimming control scheme. Under this scheme, the communication quality in terms of number of transmitted bits and bit error rate (BER) of less than 10(-3) should be guaranteed. However, for on-off-keying (OOK) signal, the required data rate becomes 10 times as high as the original data rate when the duty cycle of dimming control signal is 0.1. To make the dimming control scheme easy to be implemented in VLC system, we propose the variable M-QAM OFDM VLC system, where M is adjusted according to the brightness of LED light in terms of duty cycle. The results show that with different duty cycles the required data rates are not higher than the original value and less LED lamp power is required to guarantee the communication quality, which makes the dimming control system that satisfies both communication and illumination requirements easy to be implemented and power-saving.

We propose a configuration of a wavelength division multiplexing (WDM)-visible light communication (VLC) system using orthogonal frequency division multiplexing (OFDM) modulation and an adaptive Nyquist windowing of the OFDM signal in the receiver. Based on this configuration, we demonstrate a 750-Mb/s WDM-VLC transmission based on RGB light-emitting diode (LED) with a distance of 70 cm. The measured bit error rate (BER) for all channels are under the pre-forward error correction limit of 3.8 \times 10-3. The BER performances of all the channels of the proposed WDM-VLC system show considerable improvement compared with those of the system without Nyquist windowing.