Real-time optimal tracking angles of photodiodes for MC-VLC in indoor mobile scenarios☆
Introduction
Next significant revolution in data connections is the Internet of things (IoT) with the popularization of mobile-phone, computer and sensors, which demands better data transmission performance with the growing amount of network traffic and connections generated by various IoT devices [1], [2]. Emerging applications such as virtual/augmented reality (VR/AR) are requiring low latency and high computing capabilities for real-time interactions [3]. The development trend shows that the remarkable demand of next-generation indoor mobile real-time data transmission are high spectral-efficiency, high-speed and high-density deep-coverage.
Visible light communications (VLC), as a complementary wireless technology theoretically has the enormous potential to satisfy the requisites because of the numerous base stations and huge spectrum resource reaching to THz [4], [5]. Meanwhile, the flourishing light emitting diodes (LEDs) and increasingly tight radio frequency (RF) resources cause that VLC is widely concentrated recently [6], [7]. Besides, compared with conventional wireless communications VLC has the advantages of environmental protection, inherent security capability, high immunity to electromagnetic interference and license-free operation [8], [9].
Among two typical LED on the market generating white light, multi-color LED has higher color rendering, larger equivalent bandwidth index and is safer to the human eye than pc-LEDs [10]. So multi-color LED utilized to be the transmitter naturally to achieve multiple-input multiple-output (MIMO) called MC-VLC is the object of our works. The basics of the QLED based VLC systems are introduced in reference [11]. The illumination-adapted transceiver are designed for VLC systems utilizing QLED as transmitter in reference [12]. A fast-adaptive color-collaborative signal constellation is proposed for chromaticity-changeable multicolor visible light communications (VLC) systems [13]. Multi-color LEDs at fixed power ratio, human eyes do not perceive the fast modulation of the light emitted by the multi-color LEDs, which simultaneously achieves high-speed communication and efficacious illumination [14]. The extensively installed of Multi-color LEDs in different size indoor area providing the possibility of achieving high-density deep-coverage [15], [16], [17].
Recently, the effect of mobility of the receiver containing position and orientation on single-photodiode (PD) VLC systems performance has been thoroughly investigated. For the position mobility of receiver, the channel impulse responses for each point over the user movement trajectories are obtained based on non-sequential ray tracing and laboratory measurements in [18], [19]. The ergodic capacity of a mobile VLC scenario is evaluated in [20] for randomly distributed user locations. In [21], the statistics of signal to noise ratio (SNR) is derived for random waypoint mobility model. The impact of random receiver orientation on visible light communications channel is researched [22]. Meanwhile the mobility and flexibility of multi-PDs MC-VLC systems is also vital for industrialization of IoT and VR/AR.
However, and two challenges at the mobile scenarios urgently need to be confronted summarized as follows:
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Infection of wide-spectrum interference (WSI) for MC-VLC. Wide-spectrum interference (WSI) caused by overlap among the spectra of different color LEDs when considering the realistic filters decreases the reliability of the MC-VLC systems.
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Influence of the alignment and availability for PDs with wide field of view (FOV). The wide-FOV PDs are employed to reduce the interruption probability and improve the receiver mobility, whose availability and alignment style greatly influence the WSI and target signal (TS) of MC-VLC system.
So for MC-VLC when the receiver randomly moves, a real-time optimal tracking angles (ROTAs) of PDs is proposed to adapt the future application, which ascertains the trade-off alignment style of PDs to minimize the total WSI and ensure the reliable transmission of TS. Actually, the incline angle of PDs and LEDs both greatly influence the WSI and TS of MC-VLC. The tracking angles (TAs) of PDs is chose as the optimized object to avoid damaging the lighting quality of multi-color LEDs, the indicator of interference signal ratio (ISR) is defined to represent the WSI.
Focusing on the WSI problem at the physical layer, MC-VLC develops from wavelength-division multiplexing (WDM) [23], [24], [25] to color-shift keying (CSK) [26], [27], [28], [29], the advancement of CSK is considering multi-color cross talk rather than independently modulated for each color. At device design, researchers propose a joint design of multiple optical filters for MC-VLC by properly selecting the passband bandwidth and center wavelength of each filter to mitigate the WSI among different color LEDs [30]. However, for the previous research of MC-VLC, the receiver position and angle of irradiance and incidence are always fixed and the WSI never decreases to minimal [31].
The main contributions of this paper are summarized as follows:
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ROTAs is proposed to quickly ascertain the optimal tracking angles to minimize the total WSI of MC-VLC and ensure the reliable transmission of TS, achieving the trade-off alignment style of PDs.
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The optimization problem is formulated, and the ROTAs and ES algorithm are proposed. The analytical solution of ROTAs converges on the numerical solution of ES, which have ultra low complexity.
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The optimal tracking angles adapts to the relative offset angle between the transmitter and the receiver denoted by . The better BER performance is achieved by the system with ROTAs at different .
The remainder of this paper is arranged as follows: Section 2 mainly introduces the system model in indoor mobile scenarios and multi-spectra interference. Section 3 detailedly indicates the ROTAs problem, angle constraint and the analytical solution of ROTAs. We also bring forward the design method of ROTAs in mobile scenario and then analyze the complexity. Simulation results and performance comparison of ROTAs and MC-VLC with fix angles of incidences are illuminated in Section 4 and conclusions are drawn out in Section 5.
Note that the key notations of whole paper are listed in Table 1 for conciseness.
Section snippets
System model and background knowledge
In indoor mobile scenarios, a VLC system that utilizes multi-color LEDs as the transmitter is introduced. The WSI caused by overlapping spectra is analyzed and the point-to-point channel gain for mobile scenarios is derived. And then system model contains WSI for mobile scenarios is established.
Real-time optimal tracking angle of PDs
Recently, to achieve higher communication speed and better lighting color quality, a new type of LED device named quadrichromatic LED (QLED) has been recommended as the substitution to RGB LEDs [34]. Here, mainly aiming at QLED based VLC, we propose the ROTAs to obtain the optimal tracking angles (OTAs) denoted by , which achieves the trade-off of WSI and TS.
In this section, the ROTAs problem is resolved through combining the projections of on and plane denoted by and
Simulation result
In this section, we present comprehensive simulation results to examine the performance of the ROTAs for QLED based VLC. The OTAs denoted by at different decided by are obtained through two methods, which are analytic solution of ROTAs and numerical solution of ES. Finally, the BER performance of QLED based VLC system with ROTAs and without ROTAs at different are compared. The coefficients to convert the luminous flux to the forward current vector of RGBY is
Conclusion
In this work, the real-time optimal tracking angles (ROTAs) of PDs for QLED based VLC is proposed to achieve trade-off of wide-spectra interference and target signal. The ROTAs is a real-time technology to quickly obtain minimizing the total ISR, which is based on the alternative tracking angles sets. We formulated optimization problem, and the analytical solution of ROTAs converge on the numerical solution in our simulation situation. And optimal tracking angle obtained by ROTAs adapts to
Yumeng Zhang received her B.S. degree (June 2017) from Beijing Institute of Technology (BIT), Haidian District, Beijing (100000), China. She is currently pursuing the M.S. degree with the Information Engineering University (IEU), Zhengzhou, Henan Province (450000). Her main research interests are in the areas of wireless communication theory, visible light communications and signal processing.
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Cited by (1)
Performance Analysis of Mobile Receivers with Optimal Tilt Angle in Visible Light Communication System
2021, 2021 IEEE 6th International Conference on Computer and Communication Systems, ICCCS 2021
Yumeng Zhang received her B.S. degree (June 2017) from Beijing Institute of Technology (BIT), Haidian District, Beijing (100000), China. She is currently pursuing the M.S. degree with the Information Engineering University (IEU), Zhengzhou, Henan Province (450000). Her main research interests are in the areas of wireless communication theory, visible light communications and signal processing.
Yijun Zhu (M14) received his B.Eng. (June 1999), MSc (June 2002) and Ph.D. (June 2010) degree from the Information Engineering University (IEU), Zhengzhou, Henan Province (450000), China. During 2011, he is a visitor in the Department of Electrical and Computer Engineering, McMaster University. Now, he is with the NDSC. His main research interests are in the areas of wireless communication theory, visible light communications, and signal processing.
Yanyu Zhang received the B.S. degree in Communication Engineering, the M.S. degree in Communication and Information System and the Ph.D. degree in Information and Communication Engineering from the Information Engineering University (IEU) , Zhengzhou, China, in 2009, 2012, and 2016, respectively. He is currently a Lecturer at NDSC of China. His research interests lie in the finite alphabet signal processing for radio frequencies or optical wireless communications with current focus on the fundamental structure establishment and energy-efficient designs for multiuser finite-alphabet signals.
Chao Wang received the B.S. degree in communication engineering in from Tianjin University in 2011, the M.S. degree in information system engineer, and Ph.D. degree in information system engineer from the Information Engineering University (IEU), Zhengzhou, China, in 2014 and 2018, respectively. He is currently a Lecturer at NDSC of China. His research interests are optical wireless communications and signal processing.
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The work of Y.M. Zhang, Y.J. Zhu, Y.Y. Zhang and C. Wang is supported by the National Key Research and Development Project, China (2018YFB1801903) and in part by the National Natural Science Foundation of China (NSFC) under Grant 61671477, 61901524.
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Member, IEEE.