KEYWORDS: Light emitting diodes, Receivers, Orthogonal frequency division multiplexing, Transmitters, Signal processing, Visible radiation, Received signal strength, Databases, Systems modeling, Superposition
Visible light positioning (VLP) has attracted much attention in both academic and industrial areas due to the extensive deployment of light-emitting diodes (LEDs) as next-generation green lighting. Generally, the coverage of a single LED lamp is limited, so LED arrays are always utilized to achieve uniform illumination within the large-scale indoor environment. However, in such dense LED deployment scenario, the superposition of the light signals becomes an important challenge for accurate VLP. To solve this problem, we propose a forward and correctional orthogonal frequency division multiplexing (OFDM)-based VLP (FCO-VLP) scheme with low complexity in generating and processing of signals. In the first forward procedure of FCO-VLP, an initial position is obtained by the trilateration method based on OFDM-subcarriers. The positioning accuracy will be further improved in the second correctional procedure based on the database of reference points. As demonstrated in our experiments, our approach yields an improved average positioning error of 4.65 cm and an enhanced positioning accuracy by 24.2% compared with trilateration method.
KEYWORDS: Light emitting diodes, Orthogonal frequency division multiplexing, Free space optics, Modulation, Signal to noise ratio, Visible radiation, Complex systems, Free space optical communications, Telecommunications, Free space
A modulation format, polarity separating optical orthogonal frequency division multiplexing (PSO-OFDM), is proposed to mitigate the light-emitting diode (LED) nonlinearity for visible light communication systems. A polarity separator is used to divide the OFDM signal in time domain x(t) into two parts: x+(t) and x−(t), which will be transmitted parallelly from the different LEDs and overlap linearly in free space to realize PSO-OFDM. The experimental results demonstrate that PSO-OFDM has high spectral efficiency and suffers less nonlinear distortions than other methods. Employing PSO-OFDM, the modulation index and bit error rate performance can be significantly enhanced.
On bandwidth-limited visible light communication (VLC) transmission systems, direct current (DC) component loss, DC-unbalance of code, and severe high-frequency attenuation cause baseline wander (BLW) and data-dependent jitter (DDJ) phenomena, which deteriorate signal quality and result in a higher bit error rate (BER). We present a scheme based on hybrid run length limited codes and pre-emphasis techniques to decrease the intersymbol interference caused by BLW and DDJ phenomena. We experimentally demonstrate, utilizing 1-binary-digit-into-2-binary-digits (1B2B) codes and postcursor pre-emphasis techniques, that the impacts of BLW and DDJ on on–off keying nonreturn-to-zero VLC systems are alleviated and a 130 Mb/s data transmission rate with a BER performance of <10−4 can be achieved.
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.
KEYWORDS: Telecommunications, Visible radiation, Mobile communications, Transceivers, Signal to noise ratio, Light emitting diodes, Systems modeling, Lithium, Diodes, Avalanche photodetectors
Various patterns of device-to-device (D2D) communication, from Bluetooth to Wi-Fi Direct, are emerging due to the increasing requirements of information sharing between mobile terminals. This paper presents an innovative pattern named device-to-device visible light communication (D2D-VLC) to alleviate the growing traffic problem. However, the occlusion problem is a difficulty in D2D-VLC. This paper proposes a game theory–based solution in which the best-response dynamics and best-response strategies are used to realize a mode-cooperative selection mechanism. This mechanism uses system capacity as the utility function to optimize system performance and selects the optimal communication mode for each active user from three candidate modes. Moreover, the simulation and experimental results show that the mechanism can attain a significant improvement in terms of effectiveness and energy saving compared with the cases where the users communicate via only the fixed transceivers (light-emitting diode and photo diode) or via only D2D.
KEYWORDS: Color difference, Optical tracking, Video, Detection and tracking algorithms, Particle filters, RGB color model, Machine vision, Computer vision technology, Visual process modeling, Computing systems
Visual tracking under illumination changes is a challenging task for numerous computer vision applications. We propose a robust and efficient tracking algorithm based on maximum color difference histogram (MCDH) and a well-designed min-max-ratio (MMR) similarity metric. Appearance model is essential to the tracker’s robustness under illumination changes. We propose a new feature descriptor MCDH, calculated by exploiting the maximum color difference information within the eight-neighborhood of each pixel in the object region, to build the object appearance model. Unlike the traditional histogram-based algorithms, the MCDH is efficiently extracted by employing the local integral histogram which is propagated in a specially designed local image region. The similarity metric plays an important role on accurately locating the target. However, the existing metrics are not suitable for comparisons of MCDHs due to many zero-valued bins in MCDH. Therefore, we propose a new MMR metric, defined as the average ratio between the minimum and maximum of a MCDH bin pair. The combination of proposed components enables the tracker to be robust to illumination changes with high computational efficiency. Experiments demonstrate superior performance of the proposed tracking algorithm compared with 10 state-of-art tracking methods when illumination varies.
Current generalized multi-protocol label switching (GMPLS) based control plane is still facing some technical
challenges in terms of feasibility, scalability, and performance, which prevent it from being deployed in the next-generation
all-optical network. Sensor Technology is proposed to be used in this paper for enhancement of control plane
on performance monitoring and fault management. Two models are presented for integration of control plane and sensor
networks, as well as a new routing-based mechanism for notification of the performance and fault information.
Experimental results show the difference between the two models and the advantages of the presented routing-based
notification mechanism.
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