【正文】 oks clearly unfocused and thus the signal from all the transmitting elements of the LEA is directed to typically one or few pixels. This suggests that at short distances, the system can offer large ”multiplexing” gains by using the transmitting elements to signal independent bitstreams or equivalently realizing ”parallel” channels. On the other hand, at large distances, there can only be a ”diversity” gain where by the same bits are signaled on each of the transmit elements. These distance dependent gains in visual MIMO is in contrast to the RF MIMO channel, where the rich scattering channel matrix typically allows a continuous tradeoff between diversity and multiplexing gains [24], [27].Fig. 4. Distance dependent Multiplexing and Diversity modesV. VISUAL MIMO CHANNEL CAPACITYTo quantify the perspective dependent multiplexing and diversity gains in visual MIMO we use the channel capacity of the visual MIMO channel as a metric which is given as, where W is the receiver sampling rate (camera framerate), d is the threshold multiplexing distance from equation (6). SNRcam。 j) which can expressed as,where, s, f, lk are the pixel edge length, camera focal length and diameter of kth transmit element (considering a circular transmitting element) respectively. The amount of concentration of the signal per pixel is also dependent on the amount of blur in the image due to the lens. Typically, lens blur is modeled as a Gaussian function [12] and the amount of blur in the image is quantified by its standard deviation (blur). The lens essentially acts like a filter with the blur function as its impulse response. Thus the image of the transmit element can be viewed as a result of the projected image convolving with the blur function over the detector area.I(:) is an indicator function indicating whether a pixel (i。 j), characterized by hk(i。i。i。i。i。 viewing angle between each transmit element kand receiving pixel (i。i。i。 j) from each transmit element k to the pixel(i。 j) represents the concentration ratio of the kth transmit element of an LEA on pixel (i。 3 : : :K) emitting a light beam of power Pin。 j) of the noise matrix N representing the noise current at each pixel is given aswhere q is the electron charge, R is the responsitivity of the receiver characterized as the optical power to current conversion factor, Pn is the background shot noise power per unit area, s is the square pixel side length and W is the sampling rate of the receiver (equates to the frame rate of the camera).The optical signal from the kth transmit element (k =1。 j) representing the channel between the kth transmit element and pixel (i。 j) in each pixel with image coordinates (i。參考文獻(xiàn)：[1]王亞超，寧濱，基于無線傳感器網(wǎng)絡(luò)的城軌列車運(yùn)行能耗數(shù)據(jù)采集系統(tǒng)設(shè)計(jì)[D]，.[2]林一多，高德云. 基于 ARM 的無線傳感器網(wǎng)絡(luò) MAC 協(xié)議設(shè)計(jì)與實(shí)現(xiàn) [J].計(jì)算機(jī)應(yīng)用，2010,30（5）:11451148.[3]林彬，基于 WIFI 的無線傳感器網(wǎng)絡(luò)檢測(cè)系統(tǒng)的設(shè)計(jì)[D]..[4黃茂芹，基于FPGA的實(shí)時(shí)無線傳感器網(wǎng)絡(luò)系統(tǒng)設(shè)計(jì)[D]，電子科技大學(xué) 電子與通信工程，.[5]曾強(qiáng)，張志杰，WIFI無線傳感器網(wǎng)絡(luò)的設(shè)計(jì)與實(shí)現(xiàn)[D]，中北大學(xué)，.[6]王賽博，劉素凱，毛先柏，無線傳感器網(wǎng)絡(luò)綜述[J]，信息通信，.[7]秦邵華，無線傳感器多信道通信技術(shù)的研究[D]，山東大學(xué)，.[8]孫宇,基于嵌入式 Linux 的無線傳感器網(wǎng)絡(luò)基站軟件設(shè)計(jì)與實(shí)現(xiàn) [D],吉林大學(xué),.[9][D].北京:北京交通大學(xué),2008[10] ARM 的無線測(cè)控系統(tǒng)[J].(4):156157.[11] ARM 的無線數(shù)據(jù)采集系統(tǒng) [J].廣東技術(shù)師范學(xué)院學(xué)報(bào)，:2528.[12] Camera calibration toolbox for matlab. [13] Free space optics:technology insight. .[14] Irda. ://[15]Mipav.[16] Stan moore astronomy. [17] , , N. B. Mandayam, J. Silva, K. Dana, and . Challenge: Mobile optical networks through visual mimo. In MobiCom ’10: Proceedings of the sixteenth annual international conference on Mobile puting and networking, pages 105–112, New York, NY, USA, 2010. ACM.外文文獻(xiàn)： Characterizing Multiplexing and Diversity in Visual MIMOAbstract Mobile optical wireless has so far been limited to very short ranges for high data rate systems. It may be feasible to overe the data rate limitations over large transmission range in optical wireless through camera receivers and light emitting transmitter arrays through a concept what we call ”visual MIMO”. In this concept multiple transmit elements of a light emitting array (LEA) are used as transmitters to municate to the individual pixel elements of the camera which act as multiple receive elements to create the visual MIMO channel. Multiplexing information over parallel data channels albeit be very similar to RF MIMO in concept, the visual MIMO approach dramatically differs in its characterization. In visual MIMO since the received signal is essentially the image of the transmitting element, the perspective distortions in the visual channel dominate over some of the important properties of a RF wireless channel such as distance based attenuation and multipath fading. Some of the prominent perspective distortions include the reduction in the size of the image with distance and skew/rotation in the image due to angular view. Further lens blur (typically due to focus imperfection or jerks while capturing the image) can also significantly depreciate the image quality. In this paper we will detail how MIMO techniques such as multiplexing and diversity are characterized based on the effect of perspective distortions. Based our visual MIMO channel model we will derive the analytical channel capacity of the visual MIMO channel and using the same we illustrate the significance of parameters such as distance, viewing angle and blur in characterizing multiplexing and diversity in visual MIMO.I. INTRODUCTIONHigh data rate mobile optical wireless munications, has so far been limited to very short transmission ranges of less than 10m [3]. To achieve transmission ranges greater than a few tens of meters in optical wireless requires highly directional light beams with very narrow angleofview [2]. Optical wireless channels are characterized by large path loss and high background noise typically from sunlight or other ambient light sources in vicinity [16]. Further the low transmit power levels in optical channels (due to output power regulations in optical sources such as LEDs and LASERs)