论文研究-LED Power Optimization and Angle Parameters Analysis for In....pdf-资料库

中国科技论文在线 http://www.paper.edu.cn LED Power Optimization and Angle Parameters Analysis for Indoor Visible Light Communication Systems DING Yingrui, LI Lihua** (School of Information and Communication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876) Abstract: The transmit power and half power semi-angle (HPSA) of LEDs as well as receiver's field of view (FOV) affect the performance of indoor visible light communication systems. In this paper, a novel linear programming (LP) method is proposed to optimize transmit power of LEDs. System performance with different HPSA and FOV is also investigated. Simulation results show that a significant improvement of illumination and communication quality as well as a remarkable reduction of power consumption is achieved after the proposed LP optimization. What's more, the influence of various HPSA and FOV on VLC system is found to be double-sided. Key words: visible light communication; power allocation; linear programming 0 Introduction Visible light communication is receiving increasing attention nowadays due to the trend toward solid state lighting[1]-[4]. However, the performance of a VLC system is often not satisfactory due to reasons such as inter-symbol interference (ISI), fluctuation of received signal power and illuminance. The performance is affected by multiple factors, such as LEDs' transmit power and HPSA as well as receivers' FOV. Therefore it is necessary to optimize these parameters to obtain satisfactory communication and illuminance performance for users at different position within the room environment. Recently, much work has been done on optimizing VLC system parameters. A novel genetic algorithm is utilized to optimize transmit power of a large number of LEDs[5]. However, this method is flawed in complexity and accuracy of result. Receiver's FOV and its effect on communication data rate is analyzed[6]. It is shown that high data rate is achievable with a small receiver FOV. But the illuminance performance is not considered which is important for VLC systems. The optimization of HPSA of LEDs is investigated to improve transmission bandwidth[7]. A VLC system employing spotlight is analyzed which shows that using a narrow HPSA enables high data rate and low channel distortion[8]. Generally, these analysis focus on a single parameter and some optimization scheme is not efficient. To improve system performance further and more efficiently, we need to take multiple factors that affects system performance into consideration and 5 10 15 20 25 30 35 find better methods to optimize system parameters. In this paper, we apply a novel linear programming method to optimize the transmit power of every LED. After that, we analyze VLC system performance with different HPSA and FOV. The VLC system performance is evaluated using the fluctuation of received power, uniformity illuminance ratio (UIR), mean rms delay spread and system power consumption. 40 1 System Model An indoor visible light communication scenario is shown in Fig. 1. A room with size of 5m 5m 3m was used. The reflectivity of walls, ceiling and floor is 0.5, 0.8 and 0.2 respectively. Sixteen LED arrays are uniformly distributed on the ceiling[5]. Each LED array is filled with 49(7 7) LEDs. The space between LEDs is 4cm. The initial transmitted power and center Brief author introduction:丁颖睿 (1990-)，男，硕士研究生，主要研究方向：室内可见光通信 Correspondance author: 李立华（1976-），女，副教授，主要研究方向：室内可见光通信，MIMO 技术，中继和协作通信. E-mail: lilihua@bupt.edu.cn - 1 - 

中国科技论文在线 http://www.paper.edu.cn 45 luminous intensity of each LED is 0.452W and 23.81cd respectively. The photo-detector area of a receiver is 1 . The responsivity of a receiver is 0.54A/W. The receiver plane is divided into elements of size 25cm 25cm. A virtual receiver lies in the center of each element which is used to evaluate communication and illumination performance on the receiver plane. We simulate three order reflections here[9]. The reflecting surface is divided into small reflectors with 20cm 20 cm area. 50 Fig. 1 Indoor visible light communication system scenario 1.1 Illumination Property The brightness of an illuminated surface is measured by illuminance. The illuminance 55 at receiver from LED can be calculated as[10]: (1) where is the illuminance of line-of-sight (LOS) path. is the illuminance undergoing reflect path. 1.2 Received Optical Power 60 The received power at receiver from LED is calculated as[9]: (2) where is the channel DC gain on direct path, is channel DC gain on reflect path, is the maximum transmit power of every LED. 1.3 Electrical SNR 65 We assume AWGN noise model here, the electrical SNR of receiver is expressed as: (3) where is the responsivity of receiver, is the number of LEDs, is the shot noise variance, noise are omitted here for brievity[10]. is the thermal noise variance. The parameters for the shot noise and the thermal 70 2 Power Optimization and Angle Analysis 2.1 MIMO Characteristic Channel Matrix In order to evaluate system performance, we build a multiple-input multiple-output characteristic channel. The multiple input are LEDs. The multiple output are virtual - 2 - 2cm,,rijEij,,,,,,rijdijrefijEEE,,dijE,,refijE,,rijPij,,,,,,()rijdijrefijlPHHP,,dijH,,refijHlPi2,,122tNrijjishotthermalRPSNRRtN2shot2thermaltNrN

中国科技论文在线 http://www.paper.edu.cn receivers. So the illuminance channel can be expressed as: 75 (4) where is the illuminance from LED to receiver using Eq. (1). The received illuminance of virtual receivers is: (5) where is the scaling vector for LEDs. 80 Similarly, the power channel is defined as: (6) where is the channel DC gain from LED to receiver . It can be calculated using Eq. (2). The received power of all virtual receivers is: (7) 85 where is the transmitted optical power vector, is the received power vector. 2.2 LED Power Optimization The transmitted power of every LED is optimized by a scaling factor , . The corresponding scaling vector for all LEDs is . As a result, the transmitted optical power vector , . 90 Communication performance is one of the key factors to be considered when designing a VLC system. We use a fixed target power vector (8) to represent the minimum received power for virtual receivers. The target power is predefined according to the communication requirements of different receivers. 95 A minimum illuminance vector is applied to ensure the illumination requirements is satisfied according to illumination standards. The received illuminance of a virtual receiver should be larger than the minimum illuminance. For all receivers, the target illumination vector is (9) The values for and can be modified to adjust to different illumination and 100 communication requirement flexibly. Then we minimize the gap between actual received power and the target power vector as well as the gap between and the target illuminance vector , that is: 105 - 3 - 111212122212ttrrrtNNNNNNlllllllllL,,,,ijdijrefijlEEjilly=Lxlx111212122212ttrrrtNNNNNNhhhhhhhhhH,,,,ijdijrefijhHHjippy=Hxpxpyia01ia12[,,]tTNaaaalPpxalxa1[,,]tTppNbbpbrNpbrN1[,,]rTllNbblblbpbpypblylbmin11||||,||||lPplHabLabs.t.lPpHablLab

中国科技论文在线 http://www.paper.edu.cn , (10) where is the maximum transmitted power of all LEDs. Using the linear scalarization method, we transfer the problem as follows: 110 , (11) 115 where represents the mean value. This optimization problem is a linear programming problem since the objective function and the constrains are all linear in the scaling vector . Linear programming problems have polynomial-time solutions. The running time is , where is the number of bits in the input[11]. As a comparison, the complexity of a full-search method is exponential, that is , 120 where is the number of all scaling levels. 2.3 System Performance with Different HPSA and FOV The performance of a VLC system is influenced by LEDs' HPSA and receivers' FOV. However it is difficult to find the optimal HPSA and FOV especially when considering reflections of indoor objects. Here we use an exhaustive search method which is followed by the proposed LP 125 optimization method to investigate the influence of HPSA and FOV values on VLC systems. We assume there are discrete HPSA values and FOV values. For all HPSA and FOV pairs, problem (11) is solved with fixed target power and target illumination . Four indicators are utilized to evaluate system performance. Fluctuation of received power is used to evaluate the uniformity of received power[5]. It is given by . 130 UIR is used to judge illuminance performance. It is expressed as . Channel root mean square delay spread is used to measure ISI [10]. Power consumption is also used as the last indicator. 3 System Performance We assume 500Mb/s data rate for each position within the indoor environment. OOK-NRZ 135 modulation scheme is used. Modulated OOK signal has rectangular pulse with duration equal to the bit period. The receiver filter has a raised-cosine spectrum with 100% excess bandwidth. To ensure BER< , SNR should be larger than 13.6dB. Using Eq. (3), the corresponding received power is 1.97 W. To achieve uniform performance in all positions, each element in the target power vector is set to be =1.97 , . According to standards of ISO, 140 illuminance of 300lx to 1500lx is needed for office work, we set =400, . 3.1 Optimized and Non-optimized System Performance In this part, the optimized and non-optimized system performance is compared. LEDs' HPSA - 4 - 01ia1,,tiN1tNiallliaPPallPmin11||||||||()()lPEEplplHabLabbbs.t.lPpHablLab01ia1,,tiN1tNiallliaPP()Ea3.52()tONkkStNSMKMKpblb(max()min())/max()pppyyymin()/mean()llyy610510pib5101,,riNlib1,,riN

中国科技论文在线 is 80 degree and receivers' FOV is 55 degree[5]. http://www.paper.edu.cn The non-optimized received power varies between -4.59 dBm and -0.70dBm as in Fig. 2(a). 145 Fig. 2(b) shows the optimized power distribution using linear programming, varying between -9.97dBm and -8.54dBm. Comparing with the non-optimized case, fluctuation of received power drop from 59.1% to 28.0% after LP optimization. It equals to a 31.1% decrease. The non-optimized illuminance is shown in Fig. 2(c), varies between 1612.6lx and 2360.5lx. Fig. 2(d) shows the optimized illuminance LP, varies between 400lx and 453.0lx. The uniformity 150 illuminance ratio is improved from 0.78 to 0.94 after optimization meanwhile the illuminance is sufficient for indoor lighting. In Fig. 2(e), the average rms delay spread without optimization is 1.68ns, the minimum and maximum rms delay spread is 1.34ns and 2.14ns respectively. After LP optimization, the average rms delay spread is 1.49ns, the minimum and maximum rms delay spread is 0.90ns and 1.99ns as in Fig. 2(f). What's more, system power consumption drop from 155 354.4W to 80.5W. (a) (b) (c) (d) (e) (f) Fig. 2. Performance comparison of non-optimized case, and linear programming. (a) Non-optimized received power. (b) Optimized received power using LP. (c) Non-optimized illuminance. (d) Optimized illuminance using LP. (e) Non-optimized rms delay spread. (f) Optimized rms delay spread. 3.2 HPSA,FOV and System Performance Based on the proposed LP optimization method, we analyze system performance with different HPSA and FOV. The HPSA varies between 25 degree and 90 degree and the FOV varies - 5 - 160 165

中国科技论文在线 http://www.paper.edu.cn between 10 degree and 60 degree, both with an interval of 5 degree. 170 In Fig. 3(a), as LEDs' HPSA increase, the fluctuation of received power shows different trends. When FOV is between 30 degree and 45 degree, power fluctuation is high due to a tradeoff between uniform power and illuminance. When FOV varies from 50 degree to 60 degree, received power fluctuation is small. UIR performance is shown in Fig.3(b). Since the UIR should be over 0.7 [10], the illuminance performance is satisfactory after LP optimization regardless of LED HPSA and receiver FOV. Fig. 3(c) shows average rms delay spread performance. The average rms delay 175 spread will increase when FOV or HPSA grow wider. So narrow HPSA and FOV is helpful for reducing multipath induced ISI. Fig. 3(d) shows system power consumed. The power demand drops quickly as HPSA increase. The large power consumption when receivers' FOV is small is caused by the decrease of received power of a receiver. 180 The results show that a wide LED HPSA can reduce power consumption significantly at the cost of increased inter-symbol interference. A narrow FOV reduces multipath components however the received signal power is not stable at different locations which degrades communication quality. 185 (a) (b) (c) (d) 190 Fig. 3. System performance with different HPSA and FOV. (a) Fluctuation of received power. (b) Uniformity illuminance ratio. (c) Average RMS delay spread. (d) System power consumption. 4 Conclusion In this paper, we propose a linear programming method to optimize the transmit power of LEDs considering both communication and illumination. Compared with the non-optimized case, 195 fluctuation of received power decrease to a large extent, all users within the room can have almost identical communication quality. The UIR is improved which enables more uniform illuminance distribution. The average rms delay spread is reduced which alleviates the performance loss due to multipath propagation. The system power consumption also drops significantly after the proposed optimization. The influence of LED HPSA and receiver FOV on VLC systems is also investigated. - 6 -

中国科技论文在线 http://www.paper.edu.cn 200 It is also shown that a wide LED HPSA enables lower power consumption however at the cost of increased inter-symbol interference. A narrow FOV can reduce received multipath components but lead to unstable communication quality at different indoor locations. References 205 210 215 220 225 230 235 240 [1] T. Fath and H. Haas. Performance comparison of mimo techniques for optical wireless communications in indoor environments[J]. IEEE Trans. Commun, 2013, 61(2): 733-742. [2] M. Biagi, T. Borogovac, and T. Little. Adaptive receiver for indoor visible light communications[J]. Lightwave Technology, Journal of, 2013, 31(23):3676-3686. [3] I. Stefan and H. Haas. Analysis of optimal placement of led arrays for visible light communication. Vehicular Technology Conference (VTC Spring), 2013, 1-5. [4] L. Zeng, D. C. O'Brien, H. L. Minh, G. E. Faulkner, K. Lee, D. Jung, Y.Oh, and E. T. Won. High data rate multiple input multiple output (MIMO) optical wireless communications using white led lighting[J]. IEEE J. Select. Areas Commun., 2009, 27(9):1654-1662. [5] J. Ding, Z. Huang, and Y. Ji. Evolutionary algorithm based power coverage optimization for visible light communications[J]. IEEE Commun. Lett., 2012 ,16(4):439-441 [6] T. Komine and M. Nakagawa. Fundamental analysis for visible-light communication system using led lights[J]. IEEE Trans. Consum. Electron., 2004, 50(1):100-107 [7] D. Wu, Z. Ghassemlooy, H. Le Minh, S. Rajbhandari, M. khalighi, and X. Tang. Optimization of lambertian order for indoor non-directed optical wireless communication. Communications in China Workshops (ICCC), 2012 1st IEEE International Conference on, 2012, 43-48 [8] T. Borogovac, M. Rahaim, and J. B. Carruthers. Spotlighting for visible light communications and illumination. Globecom Workshop, 2010, 1077-1081. [9] Alqudah, Y. A. and Kavehrad, Mohsen. MIMO characterization of indoor wireless optical link using a diffuse-transmission configuration[J]. Communications, IEEE Transactions on, 2013, 51(9):1554-1560. [10] Komine, T. and Lee, J. H. and Haruyama, S. and Nakagawa, M. Adaptive equalization system for visible light wireless communication utilizing multiple white LED lighting equipment[J]. Wireless Communications, IEEE Transactions on, 2009, 8(6):2892-2900. [11] N. Karmarkar. A new polynomial-time algorithm for linear programming. Proceedings of the Sixteenth Annual ACM Symposium on Theory of Computing, ser. STOC'84, 1984, 302-311. 室内可见光通信系统 LED 灯源功率优化及角度参数分析丁颖睿，李立华（北京邮电大学信息与通信工程学院，北京 100876）摘要：室内可见光通信系统的性能受到 LED 灯源发送功率，LED 灯源半功率角（HPSA）以及接收器视角（FOV）的影响。本文提出了一种新颖的线性规划优化方法来优化 LED 灯源发射功率，此外分析了不同 LED 半功率角，不同接收器视角对系统通信，照明性能的影响。仿真结果表明采用本文优化算法，系统照明和通信质量有显著提升,同时系统消耗的功率显著下降，此外，仿真结果还表明 LED 灯源半功率角，接收器视角对可见光通信系统性能的影响是双面的，需要权衡。关键词：可见光通信；功率分配；线性规划中图分类号：TN929.12 - 7 -

资料库

论文研究-LED Power Optimization and Angle Parameters Analysis for In....pdf

相关推荐

开发技术

热门标签

最新资料