10 Gb/s Indoor Optical Wireless Systems Employing Beam Delay, Power, and Angle Adaptation Methods...

JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 12, JUNE 15, 2012 1843

10 Gb/s Indoor Optical Wireless SystemsEmploying Beam Delay, Power, and AngleAdaptation Methods With Imaging Detection

Mohammed T. Alresheedi and Jaafar M. H. Elmirghani

Abstract—In this paper, we propose a mobile optical wirelesssystem that employs beam delay adaptation, and makes use of ourpreviously introduced beam angle and power adaptation multi-beam spot diffusing configuration in conjunction with an imagingreceiver. Our ultimate goal is to improve the bandwidth, reducethe effect of intersymbol-interference, and increase the signal-to-noise ratio (SNR) when the transmitter operates at a higher datarate under the impact of multipath dispersion, background noise,and mobility. A significant reduction in the delay spread can beachieved compared to a conventional diffuse system (CDS) whenan imaging receiver replaces a nonimaging receiver at the room’scorner, where the delay spread is reduced from 2.4 ns to about 0.35ns. Our proposed system, beam delay, angle, and power adapta-tion in a line stripmultibeam spot diffusing configuration (BDAPA-LSMS), offers a reduction in delay spread by a factor of morethan 10 compared with only the beam angle and power adaptationLSMS. An increase in channel bandwidth from 36 MHz (CDS) toabout 9.8 GHz can be achieved when our methods of beam delay,angle, and power adaptation coupled with an imaging receiver areemployed. These improvements enhance our system and enable itto operate at a higher data rate of 10 Gb/s. At a bit rate of 30 Mb/s,our proposed BDAPA-LSMS achieves about 50 dB SNR gain overconventional diffuse systems that employ a nonimaging receiver(CDS). Moreover, our simulation results show that the proposedBDAPA-LSMS at a bit rate of 10 Gb/s achieves about 32.3 dBSNR at the worst communication path under the presence of back-ground noise and mobility while achieving a bit error rate below

.

Index Terms—Angle and power adaptation, beam delay, gigabitmobile optical wireless systems, imaging receivers, signal-to-noiseratio (SNR).

I. INTRODUCTION

R ECENTLY, optical wireless (OW) communication hasgained increasing attention as a potential technology for

the implementation of LANs. The use of the optical medium asa means for indoor wireless communication was proposed al-most three decades ago. Gfeller and Bapst first proposed andinvestigated indoor OW using IR radiation [1]. IR communica-tions refer to the use of free space propagation of light waves in

Manuscript received June 17, 2011; revised December 05, 2011, January 30,2012; accepted March 05, 2012. Date of current version April 09, 2012. Thework of M. T. Alresheedi was supported by a scholarship from King Saud Uni-versity, Riyadh, Saudi Arabia.The authors are with the School of Electronic and Electrical Engi-

neering, University of Leeds, Leeds, LS2 9JT, U.K. ([email protected];[email protected]).Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/JLT.2012.2190970

the near infrared band as a transmission medium for communi-cations. The behavior of IR signals is similar to that of signalsin the visible spectrum which are absorbed by dark objects anddirectionally reflected by shiny surfaces. One of the prime mo-tivators for reconsidering the use of IR radiation in the wirelesscontext is the demand for greater transmission bandwidths. Be-cause of the nature of light, free space IR links offer numerousadvantages over their RF counterparts including an abundantunregulated spectrum, freedom from fading [1], [2], and a de-gree of privacy at the physical layer as optical signals are con-fined to the room in which they originate (hence, the possibilityof frequency reuse). Despite these advantages, there are somelimitations including: eye safety considerations which restrictthe maximum transmit power [3], [4], multipath propagationwhich leads to an increased delay spread, and directive noisesources (background noise) which reduce the signal-to-noiseratio (SNR). In addition to these limitations, OW networks relyon a fiber (or some other) distributed network that feeds accesspoints since optical signals are blocked by walls and other ob-jects.Recently, many researchers have suggested and studied

the use of visible light (white-light emitting diodes (LEDs))for indoor communications [5]. Compared with conventionalIR wireless communications, white LED OW can use higherpower levels and also can minimize the shadowing as the whiteLED lights are distributed within a room. Achieving high datarates is challenging due to the low modulation bandwidth ofwhite LEDs which is few megahertz [6]. There are, however,some approaches to improve the modulation bandwidth ofwhite LEDs using different equalization schemes includingthe use of simple ON–OFF keying (OOK) predistortion to-gether with a simple first-order RC equalization circuits [7]or postequalization at the receiver [8]. Another approach hasalso been proposed to achieve high-speed transmission rates,up to 513 Mb/s by utilizing discrete multitone modulation incombination with quadrature amplitude modulation [9]. Such acomplex modulation scheme will complicate the transmitter’sand receiver’s designs. Transmission of OOK over an equal-ized channel is simpler compared to the advanced modulationscheme considered, since the latter requires extensive signalprocessing at the transmitting and receiving ends. IR opticalcommunications can offer much higher transmission rates thanvisible light communication (up to Gb/s). This is due to thewider modulation bandwidth of laser sources used in IR OWinstead of white LEDs.OW transmission links can be classified into two categories:

direct line of sight (DLOS) and non-LOS (diffuse systems).DLOS can only be established by having a direct path between

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1844 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 12, JUNE 15, 2012

the transmitter and the receiver, where such links can improvepower efficiency and minimize multipath dispersion. However,this class of systems needs to be carefully aligned in order to setup the link. On the other hand, diffuse transmission links allowthe system to operate even when barriers are placed between thetransmitter and the receiver which may still allow an indepen-dent path. Diffuse systems rely on diffuse reflections from thewalls and ceiling. Although they offer full mobility and do notrequire a direct LOS between the transmitter and the receiver,they suffer from multipath dispersion. A proven technique totackle the signal dispersion caused by multipath propagationis to replace the diffuse system by one that produces multiplenarrow beams casting small diffusing spots in different direc-tions in a room [3], [4]. The multiple diffusing spots can be im-plemented using computer generated holograms (CGHs) withstatic beam intensities (as in [10]) or can be produced using anumber of transmitters (as in [11]).The influence of ambient light noise and multipath dispersion

can be further reduced by using an imaging receiver [10]. Pre-vious work has shown that multibeam transmitters and imagingreceivers can reduce the transmit power by more than 20 dBcompared with nonimaging receivers [12]. However, perfor-mance degradation can be induced due to transmitter mobility.The link performance can be significantly improved comparedto the other nonadaptive systems [13], [14] by adaptively dis-tributing the power among the beams in conjunction with diver-sity detection. In the power adaptive technique, the positionsof the spots are fixed so that when the transmitter and the re-ceiver are far from each other, the spots are only distributednear the transmitter: on the ceiling and on the corner adjacentto the transmitter. In this case, the fixed beam angle associatedwith beam power adaptation does not help much. To resolve thisproblem, as well as reduce the SNR and delay spread degrada-tion due to transmitter mobility, “delay, angle, and power adap-tation” are introduced here coupled with an imaging receiver toprovide a degree of freedom in order to optimize the receivedsignal through the optimization of the position of spots (redis-tribute spots near the receiver position regardless of the trans-mitter position), the power associated with each spot, and thedelay between the beams.We show in this paper that beam delayadaptation, beam angle adaptation, and beam power adaptationcan significantly improve the SNR as well as the channel band-width in a real environment (mobility, ambient light noise, andmultipath propagation).We model four OW configurations: CDS, line strip multi-

beam system (LSMS), beam delay and power adaptive LSMS(BDPA-LSMS), and beam delay, angle, and power adaptiveLSMS (BDAPA-LSMS) in conjunction with an imaging re-ceiver. For comparison purposes, CDS with a nonimagingwide field-of-view (FOV) receiver is modeled and comparedto our systems. All the systems are discussed, analyzed, andsimulated at 30 Mb/s to facilitate comparison with results inthe literature. The BDPA-LSMS and BDAPA-LSMS are alsosimulated at 10 Gb/s and 12.5 Gb/s bit rates. At 30 Mb/s,BDAPA-LSMS offers almost 35 dB SNR gain over the LSMSand almost 50 dB SNR gain over CDS imaging receiver in aworst case channel. Moreover, the proposed system providesabout 70 dB SNR gain over a CDS nonimaging receiver ata 6 m horizontal separation between the transmitter and thereceiver. The proposed BDAPA-LSMS can also reduce the

Fig. 1. Physical structure of the imaging receiver.

delay spread by a factor of 10 compared to the “beam angle andpower adaptation” LSMS [15]. Our results show an increase inchannel bandwidth from 4.2 GHz (power adaptation in LSMSwith angle diversity [23]) to about 7.9 GHz (BDPALSMScoupled with imaging receiver). Furthermore, at 10 Gb/s, theproposed BDAPA-LSMS offers 32.3 dB SNR in the presenceof background shot noise, multipath dispersion, and mobility.The receiver structure is given in Section II. Section III presentsthe propagation environment. The proposed BDAPA-LSMS isdiscussed in Section IV. Simulation results and conclusions aredrawn in Sections V and VII respectively.

II. IMAGING RECEIVER

In contrast to the single wide FOV receiver, angle diversityreceivers utilize multiple nonimaging concentrators that arepointed in different directions. The main drawbacks of this ap-proach are the large size and high cost of the multiple receiverconcentrators associated with the angle diversity receiver.The imaging receiver provides an appropriate alternativesolution that can reduce the impact of multipath dispersionas well as ambient background noise. An imaging receiveroffers some potential advantages over a nonimaging receiver.First, a common imaging concentrator can be shared amongall photodetectors, reducing the size and cost compared withangle diversity receivers. Second, a single planar array is usedfor all photodetectors which can facilitate the use of a largenumber of pixels. The photocurrents received in each pixel canbe amplified separately, and can be processed using differentmethods such as selection and maximum ratio combining(MRC) techniques in order to maximize the power efficiencyof the system.All photodetectors are laid out in a single detector array seg-

mented into equal-sized rectangular-shaped pixels with nogaps among them, as shown in Fig. 1. Therefore, the area of eachpixel is the photodetector’s area, which is equal to the exit areadivided by the number of pixels. The detector array is segmentedinto 200 pixels in this study and we employ an imaging concen-trator with the parameters in [12]. The transmission factor of theconcentrator is given by

(1)

where is the reception angle measured in radians. Our imagingreceiver has a refractive index , the entrance area is

ALRESHEEDI AND ELMIRGHANI: 10 GB/S INDOOR OPTICAL WIRELESS SYSTEMS 1845

Fig. 2. Reception area associated with the detector array when the receiver isplaced at the center of the room.

cm , and its concentrator’s acceptance semiangle isrestricted to in order to view the whole ceiling (whenthe receiver is at the center of the room). The exit area of theimaging receiver is . The detector array isassumed to fit exactly into its corresponding concentrator’s exitarea. Therefore, the detector array has a photosensitive area of 2cm and each pixel has an individual area of 1 mm , since thereare no gaps among them. Note that as becomes large, the pixelarea becomes much smaller than the area of the detector array.The photodetector has a responsivity of 0.6 A/W. It should benoted that, to the best of our knowledge, there are no commercialhigh-speed 200 pixel detector arrays, but if a PIN detector as in[16] is used as the building block of the array, then its detectorrise time will be in the picosecond range.In our analysis, when the receiver is placed at the center of

the room, it sees the whole ceiling [200 pixels (10 20)] andeach reception area is cast onto a single pixel. The receptionarea can be found by calculating the reception angleswith respect to the receiver normal along the directions asshown in Fig. 2. These angles can be calculated as

(2)

where , and are the horizontal separation along the-axis, -axis, and the reception area height, respectively.Furthermore, the reception area observed by each pixel varieswhen the imaging receiver moves. The calculation of thereception angles under receiver mobility is given indetail in [15].

III. PROPAGATION ENVIRONMENT

A. Simulation Setup

In order to present the benefits of our methods (beam delayadaptation, beam angle adaptation, transmit power adaptation,spot diffusing, and imaging reception) in indoor OW systems,propagation simulations were conducted in an empty midsizedroom with floor dimensions of 8 m 4 m (length width) andceiling height of 3 m. It was proven that plaster walls reflectlight rays in a form close to a Lambertian function [1]; therefore,walls (including ceiling) and floor are modeled as Lambertianreflectors of the first order with reflectivity coefficients of 80%

and 30%, respectively. Reflections from doors and windows areconsidered completely the same as reflections from walls. Thereflection elements have been treated as small transmitters thatdiffuse the received signals from their centers in the form of aLambertian pattern with a radiation lobe mode number .Previous research has found that most of the transmitted poweris within the first and second reflections, but when it goes be-yond the second order it is highly attenuated [1], [3]. Therefore,reflections up to the second order are considered in our simu-lator.A simulation tool similar to the one developed by Barry et

al. [17] is used to produce the impulse responses, power distri-bution, and to calculate the delay spread. To model the reflec-tions, the room reflecting surfaces were divided into a numberof equally sized square reflecting elements. The accuracy of thereceived pulse shape and the optical signal power are controlledby the size of the surface elements. For all geometries (the mul-tispot channels and the traditional diffuse link), surface elementsof 5 cm 5 cm for the first-order reflections, and 20 cm 20 cmfor the second-order reflections were used. These dimensionshave been selected in order to keep the computation within rea-sonable time and measure.To verify the improvements achieved under mobility, four

configurations were considered: CDS with nonimaging wideFOV receiver, LSMS, BDPA-LSMS, and BDAPA-LSMS inconjunction with imaging receiver. The transmitter was placedin an upright position at two different locations on the commu-nication floor (CF), i.e., (2 m, 4 m, 1 m) and (2 m, 7 m, 1 m),and emitted 1 W total optical power with an ideal Lambertianradiation pattern. CGHs can be used to produce static multi-beam intensities. Beam delay, angle, and power adaptationamong the beams can be implemented using liquid crystal(LC) devices. These devices have microsecond to millisecondresponse times [18] which are adequate given that the beamdelay, angle, and power adaptation have to be carried out at therate at which the environment changes (human motion) not atthe system’s bit rate. A feedback channel can be provided byusing one of the beams at a low data rate.

B. Channel Characteristics and Ambient Light Modeling

In OW communication links, intensity modulation with directdetection (IM/DD) is considered to be the most viable approach.The indoor OW IM/DD channel can be fully characterized byits impulse response and it can be modeled as a basebandlinear system [19] given by

(3)

where is the received instantaneous current in thephotodetector at a particular position due to reflecting ele-ments, is the absolute time, Az and El are the directions of ar-rival in the azimuth and elevation angles, is the total numberof receiving elements, is the transmitted instantaneous op-tical power, denotes convolution, is the photodetector re-sponsivity ( A/W) and finally, is the back-ground noise which is independent of the received signal and


is modeled as white and Gaussian. By simulating the OW im-pulse response, several parameters can be derived, such as 3dB channel bandwidth, SNR, and delay spread. Indoor OW issubject to multipath dispersion due to nondirected transmissionwhich can cause intersymbol-interference. Root-mean-squaredelay spread is a good measure of signal pulse spread due totemporal dispersion of the incoming signal and is given by [4]

(4)

where the time delay is associated with the received power( reflects the impulse response behavior) and is

the mean delay given by

(5)

The discretization is the result of dividing the reflecting surfacesinto small elements. Since the positions of the transmitter, re-ceiver, and the reflecting elements are fixed, the received opticalpower and the delay spread can be considered deterministic forgiven transmitter and receiver locations.In order to evaluate our proposed systems under ambient light

noise, eight halogen spotlights were chosen, which result in oneof the most stringent optical spectral corruptions to the receiveddata stream. “Philips PAR 38 Economic” (PAR38) was inves-tigated where each PAR38 emits an optical power of 65 W ra-diated in the form of a narrow beamwidth which is modeled asa Lambertian radiant intensity with order [3]. Thespotlights are placed on the ceiling at positions (1 m, 1 m, 3 m),(1 m, 3 m, 3 m), (1 m, 5 m, 3 m), (1 m, 7 m, 3 m), (3 m, 1m, 3 m), (3 m, 3 m, 3 m), (3 m, 5 m, 3 m), and (3 m, 7 m, 3m). These lamps produced a well-illuminated environment. Wedo not consider the interference of daylight through windowsin this study. Moreover, an imaging receiver is used to reducethe impact of background noise as well as multipath dispersion.More simulation parameters are given in Table I.

IV. TRANSMITTER CONFIGURATIONS

In this section, four different transmitter configurations(CDS, LSMS, BDPA-LSMS, and BDAPA-LSMS) in conjunc-tion with an imaging receiver are presented, evaluated, andcompared in order to identify the best geometry for indoorOW under mobility. In addition, the proposed systems arecompared with the CDS nonimaging wide FOV receiver. Tohelp visualize the transmitter configurations, Fig. 3 shows theOW communication architectures used in our proposed systems(LSMS, BDPA-LSMS, and BDAPA-LSMS) combined withimaging receivers and also CDS with wide FOV receiver.

A. CDS

The CDS is the basic configuration used in diffuse transmis-sion and reception and has been widely discussed [1], [2]. Itdoes not rely on a direct path between the transmitter and thereceiver. Although it offers full mobility and does not requirea direct LOS between the transmitter and the receiver, it suf-fers from multipath dispersion. The pure diffuse system uses asingle beam transmitter with a wide FOV receiver, as shown inFig. 3(a). The receiver collects the signal after it has undergone

TABLE ISIMULATION PARAMETERS

one or more reflections from the ceiling, walls, and room ob-jects. For comparison purposes, a conventional diffuse systemwith wide FOV nonimaging receiver was simulated to producethe 3 dB channel bandwidth and SNR.

B. LSMS

The LSMS achieves performance improvements over theCDS by employing multiple beams. Multibeam spot diffusingmethods have been investigated in [3] and [12]. The LSMSin conjunction with angle diversity reduces the impact ofbackground noise as well as multipath dispersion.Furthermore, the LSMS can be further enhanced by replacing

angle diversity with an imaging receiver. The LSMS is assumedto produce equal intensity beams, 80 1, aimed at the middle ofthe ceiling in the form of a line strip with 10 cm spacing betweenadjacent spots on the ceiling when the transmitter is at the centerof the room, as shown in Fig. 3(b) with equal beams’ intensity.These spots operate as secondary transmitters. The positions of


Fig. 3. OW communication architectures for our proposed systems. (a) CDS with nonimaging wide FOV receiver. (b) LSMS and BDPA-LSMS with imagingreceiver. (c) BDAPA-LSMS with imaging receiver.

the spots change according to the transmitter movement. Theanalysis of LSMS mobility is detailed in [20].

C. BDPA-LSMS

In contrast to the LSMS, where the transmitter distributes thetotal power among the beams equally as well as switches all thebeams at the same time, the BDPA-LSMS is based on adaptiveapproaches that adapt the delay between the beams as well asadjusting the distribution of the transmitter power among thebeams. Instead of distributing the transmit power (1 W) equallyamong 80 beams (12.5 mW per beam) as in the LSMS, theBDPA-LSMS transmitter varies the power distribution amongthe beams and introduces delay between the beams in order tomaximize the SNR and reduce the delay spread at the receiver.Beam delay adaptation helps reduce the delay spread, hence in-creasing the 3 dB channel bandwidth. The multipath profilesobserved by the receiver are relayed to the transmitter and arestored for each spot at each given location. Instead of switchingON all the beams at the same time and increasing the delayspread, beam delay adaptation switches ON the beam that has

the longest journey to travel first, and then switches ON the otherbeamswith different differential delay so that all the beamsreach the receiver at the same time. The transmitter and receiverare synchronized and at the start of a frame, the transmitter in-dividually turns on each spot, and then the receiver calculatesthe SNR after combining signals using MRC and also computesthe power received from the pixel that has the highest SNR andcalculates the delay of the maximum received power withrespect to the start of the frame. The transmitter turns on thesecond beam after a predetermined time delay . The receiverreceives this second pulse at time ( and, hence, deter-mines . The difference between and , i.e., , isthe difference in delay the two beams experience in the channel.The individual receivers’ varying response times may add ajitter element to this value if their response is slow or if they arenot implemented on a common integrated platform; the lattermay reduce variability. BDPA-LSMS combines the benefits ofhaving power adaptation to maximize the receiver SNR as wellas differential beam delays to reduce the impact of multipathdispersion. Beam delay and power adaptation is based on in-formation about the time delay and signal quality of each beam


Fig. 4. Beam delay and power adaptation algorithm.

fed back to the transmitter by the receiver at each location. Thebeam delay and power adaptation algorithm, which is depictedin Fig. 4, adapts the transmission power and the delay among thebeams for a single transmitter and a single receiver as follows.1) Switch ON the line strip (LSMS), beams, with cmspacing between adjacent spots. Equally distribute the totalpower among the beams and compute the received poweras well as the SNR at each pixel.

2) Individually turn on each spot, compute the power receivedat the receiver as well as calculate the SNR at each pixels( pixels) and the SNR after combining the signalsusing MRC weights.

3) Use the SNR in step 2 as the SNR associated with the spot.4) Repeat steps 2 and 3 for all the spots.5) The receiver calculates the differential delay betweenthe received pulse due to each spot and the next.

6) The receiver sends a control feedback signal at low rate tothe transmitter about the differential delay between adja-cent beams and the SNR associated with each spot.

7) Redistribute the power among the beams according to theratio of SNRs:


Fig. 5. Block diagram of the beam delay, angle, and power adaptation algorithm.

8) Introduce a differential delay between the beams at thetransmitter to compensate for the differential beam spreadas seen by the receiver.

9) SwitchON the beamwith the longest journey first, and thenswitch ON the other beams with a differential delay so thatall the beams reach the receiver at the same time.

At the transmitting end, if the transmitter is implementedusing discrete or array sources, then electronic control can beused to switch ON these sources with nanosecond delays whichis implementable in electronics. If a hologram is used to gen-erate the beams in a spatial light modulator, then stored framescorresponding to different spot outputs can be loaded; however,the time allowed for this operation is challenging with currenttechnology (liquid crystal devices typically have microsecondnot nanosecond response time, although nanosecond responsetimes have been demonstrated [21], [22]). Having identified thedelays (for example, when a set of discrete sources are used)the transmitter can then switch the beams with the required de-lays using electronic control. The transmitter can be simplifiedif fewer sources are used instead. The penalty incurred in linkperformance will be small; however, this warrants further study.

D. BDAPA-LSMS

An excessively large distance between the nearest diffusingspot on the ceiling or walls and the receiver can lead to signif-icant performance degradation. In order to reduce the impactof this problem as well as enhance the channel bandwidth atthe receiver, we introduce beam delay, angle, and power adap-tation LSMS coupled with an imaging receiver. Beam angle andpower adaptation help identify the optimum locations of spotsand increase the power to spots nearest to the receiver, hencemaximizing the SNR. Although the SNR is maximized, limi-tations remain in channel bandwidth due to multipath disper-sion as well as time delay between the signals from the spotswithin the selected receiver’s FOV. Switching ON all the beamsat the same time increases the delay spread, hence limiting the 3

dB channel bandwidth. Beam delay adaptation introduces a dif-ferential delay between the beams to ensure that all thebeams reach the receiver at the same time. The beam delay,beam angle, and beam power adaptations can be implementedusing an adaptive hologram that produces spots whose locationsand intensities can be varied with transmission angles inthe directions. Most of the adaptive holographic switches areLC based [22]. One of the most important advantages of theseswitches is that they do not suffer from the power fan out loss.A high switching speed is important for data applications withswitching times reported down to 10 s [25]. The 2-D LC devicecan implement a further 2-D shutter stage which can be used forbeam delay adaptation (however there are switching speed lim-itations, where the typical LC adaptation speeds are in the orderof tens to hundredths of microseconds [18]). Other implementa-tion approaches can also be considered, for example, where thebeams are produced by an array source. Here, the delay adap-tation is implemented through array element delayed switching(hence the switching speed limitations are reduced or removed)and beam power adaptation is achieved through varying the in-tensity per array element. The LC device in this case has the solerole of beam angle adaptation (beam steering). The implemen-tation choices and their optimization warrant further study andare beyond the scope of this paper.The beam angles can be varied (between ) with

respect to the transmitter’s normal in both directions ( ). Theadaptive hologram first produces a single spot which is scannedalong the range of rows and columns in the ceiling and wallsto identify the best SNR location at the receiver. The receivedmultipath profiles are stored for each spot at each given loca-tion. The resultant power profile is the sum of the powers dueto the ( in our case) impulse responses. Instead ofswitching ON all the beams at the same time at the optimum lo-cation and increasing the delay spread, beam delay adaptationswitches ON the beam that has the longest journey to travel first,and then switches ON the other beams with different differential


delay so that all the beams reach the receiver at the sametime. The block diagram of our proposed system is shown inFig. 5. The BDAPA-LSMS algorithm adapts the beam delays,angles, and powers for a single transmitter and a single receiveras follows.1) The adaptive hologram generates a single spot which scansthe walls and ceiling by changing the beam angle asso-ciated with the spot between and 90 in steps of2.86 [in each step, the spot moves 10 cm which resultsin a total of 8000 possible locations (40 80 locations inthe ceiling, 40 20 locations in the wall m and80 20 locations in the wall m)]. Pedestriansmove typically at a speed of 1 m/s. If each SNR compu-tation is carried out in 10 s [22], then the total adaptiontime when the receiver moves is 80 ms which is lower thanthe 1 s available. We propose that the receiver periodically(namely at 1 second intervals) reevaluates its SNR andif this has changed significantly (compared to a thresholdvalue), then this change initiates transmitter adaptation. Assuch the holograms can adapt every 1 s. The 80 ms adapta-tion time, therefore, represents an overhead of 8% in termsof transmission time. It should be noted that this adapta-tion has been done at the rate at which the environmentchanges, for example, the rate at which humans move notat the system’s bit rate. Therefore, when the system is sta-tionary, it can achieve 10 Gb/s, and when it is on the move,it can achieve 92% of this data rate, i.e., 9.2 Gb/s. Holo-grams based on LC devices capable of adapting within mil-lisecond times are feasible. We estimated the power con-sumption if our algorithm is implemented in an embeddedsystem. For example, if the Microchips 32 bits microcon-troller is used as processor (PIC32MX110F016B) [26], thepower consumption is found to be 72 mW. Therefore, theenergy consumption is 5760 J within 80 ms.

2) The receiver computes the SNR at each step and sends acontrol feedback signal at low rate to the transmitter aboutthe SNR associated with each step.

3) The transmitter records the transmission anglesthat maximize the receiver’s SNR, and determines the spotlocation .

4) The transmitter deploys a line strip (80 1, equal intensi-ties) with its center at the location that maximized the SNR.

5) Starting with a minimum angle of 0.28 between thebeams, all the beams spots touch each other in the linestrip, and each beam spot has a diameter of 1 cm.

6) The transmitter individually turns on each spot; the re-ceiver computes the power received and calculates theSNR at each pixels ( pixels) and the SNR aftercombining the signals using MRC weights.

7) The receiver uses the SNR in step 6 as the SNR associatedwith the spot.

8) The transmitter and receiver repeat steps 6 and 7 for all thespots.

9) The receiver calculates the differential delay betweenthe received pulse due to each spot and the next.

10) The receiver sends a control feedback signal at low rateto the transmitter about the differential delay between thepulses due to adjacent beams and the SNR associated witheach spot.

11) The transmitter redistributes the power among the beamsaccording to the ratio of SNRs.

12) The transmitter introduces a differential delay between thebeams to compensate for the spread due to the differentialbeam arrival times as seen by the receiver. Note that mostof the power is collected by the receiver through the lineof sight with each spot (significantly lower power throughreflections). Therefore, adjusting the differential beam de-lays helps reduce the delay spread at the receiver.

13) The transmitter switches ON the beam with the longestjourney first, and then switches ON the other beams witha differential delay so that all the beams reach the receiverat the same time. It should be noted that beams with thesame delay (due to room symmetry) are switched ON atthe same time.

14) The transmitter increases the angle between the beams insteps of 0.57 (notice that the angles between the beamsare equal), and steps 6 to 13 are repeated.

15) The algorithm stops when the angle between the beamsreaches 2.86 .

16) The transmitter is specified so that it operates at the op-timum beam delays, angles, and powers.

In order to regularly perform beam delay, angle, and poweradaptation, the medium access control protocol should includea repetitive training period. This training should be used at thelow rate at which the channel changes. It has to be noted that theBDAPA-LSMS algorithm is developed for the single-user sce-nario where the spots nearest to the receiver are allocated withmore power. In a multiuser scenario, the optimum transmissionpower of the beams that maximizes the receiver SNR may bedifferent for the different users’ receivers. Different methodscan be used to resolve this situation. For example, opportunisticscheduling [27] can be used to select the optimum beam powersfor a given set of users for a given time duration. The SNRmeasured by the receiver is conveyed to the transmitter via afeedback channel at a low data rate for reliability. This can be adiffuse channel implemented, for example, by using a separatesource or by using one of the beams. An important observationhere is that the design of the holograms and their implementa-tion through LC devices is not ideal. The input power may not beall allocated to spots; it may partially leak through resulting ina form of noise where data are not directed at the correct spatialorientations desired (spots). The impact of such noise (a formof background noise) is of interest in the overall design and isnot considered here.

V. SIMULATION RESULTS

In this section, we investigate the performance of the pro-posed multibeam configuration BDAPA-LSMS in the presenceof background noise and multipath dispersion. Our proposedsystems are discussed and compared (impulse response, 3 dBbandwidth, and SNR) with the CDS and LSMS in two differentlocations when the transmitter is placed on the CF: at (2 m, 4 m,1 m) and (2 m, 7 m, 1 m).

A. Delay Spread Distribution

For delay spread assessment, the transmitter is stationary atthe center of the room (2 m, 4 m, 1 m) and the receiver moves


Fig. 6. Delay spread of four configurations: CDS, LSMS, beam angle andpower adaptation LSMS, and BDAPA-LSMS when the transmitter is placed at(2 m, 4 m, 1 m) and the receiver moves along m line.

along the m line. At each given location, the spots are au-tomatically optimized based on the methods (beam delay, angle,and power), in order to reduce the delay spread as well as tomaximize the SNR at the receiver.Fig. 6 compares the delay spread of the CDS, LSMS, angle

and power adaptive LSMS, and BDAPA-LSMS in conjunctionwith an imaging receiver. The CDS nonimaging channel re-ceiver is also considered. The CDS nonimaging receiver showsmuch more signal delay spread (over large period) due to itsdiffuse transmission and the wide receiver FOV ( ).The CDS configuration delay spread is reduced from almost 2.4to 0.35 ns when an imaging receiver replaces the nonimaging re-ceiver. This reduction in delay spread is attributed to the narrowFOV associated with each pixel, which results in a limited rangeof received signals. The multibeam transmitter, LSMS, reducesthe delay spread to almost 0.14 ns. There is a significant reduc-tion in delay spread to almost 0.02 ns when beam angle andpower adaptations are introduced. This result is in agreementwith previous findings [15]. Our proposed BDAPA-LSMS re-duces the delay spread by a factor of 10 compared with the beamangle and power adaptive LSMS reported in [15].A smaller time bin of 0.01 ns was also considered for higher

data rates in our proposed systems which results in a slightlyhigher delay spread compared to that obtained using a 0.5 nstime bin. Note that if one ray dominates the impulse response(due to angle and power adaptation), then the impact of a smallertime bin is reduced. Fig. 7 shows the delay spread of our pro-posed beam angle and power adaptation LSMS with differenttime bins of 0.5 and 0.01 ns. A smaller time bin (0.01 ns) re-sulted in a slightly higher delay spread compared with a timebin of 0.5 ns.

B. Impulse Response and 3 dB Channel Bandwidth

The bandwidth achieved by the four configurations whenthe transmitter is stationary at the center of the room and thereceiver moves along the m line is depicted in Fig. 8.The results show that the proposed BDAPA-LSMS providesthe largest bandwidth compared with the other systems. This isdue to four factors. First, introducing delay among the beamssignificantly reduces the delay spread, hence increasing the

Fig. 7. Delay spread of beam angle and power adaptation LSMS using differenttime bins: 0.5 and 0.01 ns, when the transmitter is placed at (2 m, 4 m, 1 m) andthe receiver moves along m line.

channel bandwidth. Second, through optimizing the spots’ po-sitions at an area on the ceiling and/or walls, where the receivercan collect a strong signal through DLOS components. Third,allocating high power levels to the spots nearest to the receiver,which results in a strong received power. Finally, employingan imaging receiver significantly reduces the impact of thebackground noise. Our simulation results show that the CDStransmitter in conjunction with an imaging receiver increasesthe communication channel bandwidth from the 36 MHzoffered by the CDS nonimaging wide FOV receiver, which isin agreement with [28], to almost 330 MHz (see Fig. 9). Themultibeam transmitter in conjunction with an imaging receiverincreases the communication channel bandwidth from thebandwidth offered by the CDS to almost 1.1 GHz, which is ingood agreement with that reported in [15] (see Fig. 8). Previouswork [4] has shown that adopting a multibeam transmittercoupled with a 7 FOV angle diversity receiver can provide3 dB channel bandwidths of more than 2 GHz. Furthermore,recent work has demonstrated an experimental 1.25 Gb/s OWline-of-sight system with an angle diversity receiver [29]. How-ever, these studies do not use beam delay and power adaptationsin conjunction with the imaging receiver. When beam poweradaptation coupled with an angle diversity receiver replaces theconventional LSMS, there is significant bandwidth improve-ment to approximately 4.2 GHz [23]. Moreover, beam angleand power adaptation in conjunction with an angle diversityreceiver increases the channel bandwidth up to 7.2 GHz [23].Introducing beam delay with only power adaption and an

imaging receiver increases the channel bandwidth to 7.9 GHz(see Fig. 8). Previous work has shown that beam angle andpower adaptation coupled with an imaging receiver achieved 8.2GHz [15]. Our proposed system, BDAPA-LSMS, increases the3 dB channel bandwidth to 9.8 GHz [24] as shown in Fig. 9. Thisincrease in channel bandwidth enables our proposed system tooperate at higher data rates, i.e., 10 and 12.5 Gb/s (to the best ofour knowledge this is the highest data rate (feasibility) reportedfor an indoor mobile OW system employing any method). In anoptical direct detection system, the optimum receiver bandwidthis 0.7 times the bit rate. As such, a 12.5 Gb/s data rate requiresan 8.75 GHz receiver bandwidth (the 0.7 figure is based on Per-sonik’s optical receiver design [30]).


Fig. 8. 3 dB channel bandwidth of three configurations: CDS, LSMS, andBDAPA-LSMS when the transmitter is placed at (2 m, 4 m, 1 m) and thereceiver moves along m line.

In our proposed systems unlike diffuse systems, the third-order reflections are very small in comparison given that thefirst-order reflections from the spots are very strong [23]. Hence,the impact of higher order reflections is very small when ouradaptation techniques are introduced. This is an important dis-tinction between our proposed systems and conventional diffusesystems where, in the latter, third-order reflections may play asignificant role at high data rates.

C. SNR Performance Analysis

Indoor OW communication links are strongly impaired by theshot noise in the receiver’s electronics induced by ambient light.OOK is the simplest modulation technique for OW systems.OOK employs a rectangular pulse with duration equal to the bitperiod.The SNR associated with the received signal can be computed

by taking into account and , the powers associated withlogic 1 and 0, respectively. The SNR is given by [31]

(6)

where and are the noises associated with the signal andcan be computed from

(7)

where represents the preamplifier noise component,represents the background shot noise component, and and

represent the shot noise associated with the received signal( and ), respectively. This signal-dependent noiseis very small and can be neglected based on the experimentalresults reported in [32]. In this study, we used the p-i-n FETtransimpedance preamplifier used in [12]. The gate leakage and

Fig. 9. Impulse response and frequency response of CDS and BDAPA-LSMSwhen the transmitter is placed at (2 m, 4 m, 1 m) and the receiver is at the cornerof the room (1 m, 1 m, 1 m). (a) CDS wide FOV nonimaging receiver. (b) CDSwith 200 pixels imaging receiver. (c) BDAPA-LSMS with 200 pixels imagingreceiver.


noise of the FET were neglected. Therefore, the preampli-fier shot noise is given by [12]

(8)

where is the Boltzmann’s constant, is the absolute tem-perature, is the feedback resistance, , and isthe bit rate. The first term in (8) represents thermal noise fromthe feedback resistor, whereas the second term in (8) representsthermal noise from the FET channel resistance. is the noisefactor of the FET channel, is the transconductance of theFET, is the detector capacitance, and isFET gate capacitance. We assumed that the receiver bandwidthis equal to the bit rate and .These assumptions require the condition ,

where is the open-loop voltage gain. The photodetector ca-pacitance is proportional to the photodetector area i.e.,, where is the fixed capacitance per unit area. Therefore,

the preamplifier shot noise can be rewritten as

(9)

This preamplifier is used for a bit rate of 30 Mb/s. In our cal-culations, we chose the same parameters values used in [12]:

K, A/W, ms,and, pF/cm . Higher bit rates of 10 Gb/s and 12.5 Gb/sare also considered. We used the p-i-n FET receiver design in[33]. The background shot noise component can be calculatedfrom its respective associated power level as

(10)

where , and BW represent the electron charge, receivedbackground power, and receiver bandwidth, respectively.Substituting (7) into (6), the SNR can be written as

(11)In the imaging receiver, we consider two schemes: selection

combining, i.e., select best combining (SC) and MRC. SC im-plements a simple diversity approach. The receiver simply se-lects the branch with the largest SNR among all the branches.The SC SNR is given by (12), shown at the bottom of the page,where is the number of pixels. In contrast to the SC ap-proach, MRC utilizes all the branches. The output signals of allthe branches are combined through an adder circuit. Each input

to the circuit is added with a weight (proportional to its SNR) inorder to maximize the SNR

(13)

The SNR computed using MRC is

(14)

giving

(15)

The SNR (SC and MRC) of the proposed systems: CDS,LSMS, and BDAPA-LSMS in conjunction with an imaging re-ceiver compared with the CDS nonimaging system, operatingat 30 Mb/s, when the transmitter is placed at (2 m, 4 m, 1 m)and (2 m, 7 m, 1 m), and the receiver moves along them line is depicted in Figs. 10 and 11. The SNR calculationswere performed for seven different locations along the -axisat a constant m which scans the peaks and troughs ofbackground noise, based on SC and MRC. Our simulation re-sults indicate that fluctuations in the CDS SNR are mitigatedby more than 20 dB SNR improvement at the worst case sce-nario (6 m horizontal separation between the transmitter andthe receiver) when the CDSMRC imaging receiver replaces thenonimaging receiver. This result is in agreement with previousfindings [12]. This significant improvement in the SNR level isattributed to the ability of the imaging receiver to select thosepixels that observe the minimum background noise in additionto the reduction in the noise level that is collected by the smallpixels due to their narrow FOV. A significant improvement canbe achieved by employing the multibeam LSMS configuration,which provides 18 dB SNR gain over the CDS imaging re-ceiver. This improvement in the SNR is due to the fact thatthe LSMS has the ability to uniformly cover its surroundingsthrough spot diffusing, when the transmitter is stationary at thecenter of the room, which gives the receiver an option to collectthe signal from the nearest diffusing spot. However, degrada-tion in the CDS and LSMS imaging receiver SNR is observedwhen the transmitter is mobile, as depicted in Fig. 11 [trans-mitter moved away from the receiver toward the edge (2 m, 7m, 1 m)]. However, this SNR degradation, which is attributed

(12)


Fig. 10. OWCDS, LSMS, and BDAPA-LSMS systems SNR at 30Mb/s, whenthe transmitter is placed at (2 m, 4 m, 1 m) and the receiver moves alongm line; the imaging receiver has a pixel FOV of 11.3 .

Fig. 11. OWCDS, LSMS, and BDAPA-LSMS systems’ SNR at 30Mb/s, whenthe transmitter–receiver separation is 6 m; the imaging receiver has a pixel’sFOV of 11.3 .

to transmitter mobility, can be reduced by replacing the CDSand the LSMS with our proposed BDAPA-LSMS. Our pro-posed BDAPA-LSMS with an imaging receiver achieves about35 dB SNR gain over LSMS and 50 dB SNR gain over the CDSimaging receiver in the worst case scenario [24]. The results de-picted in Figs. 10 and 11 show that the BDAPA-LSMS SNR iscompletely independent of the transmitter location. Therefore,a significant improvement in SNR is obtained at every trans-mitter and receiver location. It should be noted that if a singlebeam system is used, the improvement in the channel bandwidthand the SNR may be desirable; however, such a system can beaffected by beam blockage and shadowing, and may violate eyesafety regulations if all the transmit power is allocated to thesingle beam.Significant improvement in SNR and channel bandwidth is

achieved as shown in Fig. 8, which confirms that our proposedsystem is useful in increasing the data rate. Fig. 12 shows theSNR of the BDPA-LSMS, beam angle and power adaptiveLSMS, and BDAPA-LSMS operating at 10 and 12.5 Gb/s whenthe systems operate under background noise and multipathdispersion impairments. The transmitter is placed at (2 m, 7 m,

Fig. 12. SNR of beam power adaptation LSMS, beam angle and power adap-tation LSMS, BDPA-LSMS, and BDAPA-LSMS systems at 10 and 12.5 Gb/s,when the transmitter is placed at (2 m, 7 m, 1 m) and the receiver moves along

line; the imaging receiver has a pixel’s FOV of 11.3 and 7.1 .

1 m) and the receiver moves at a constant m along the-axis over the CF.Fig. 12 shows that BDPA-LSMS offers about 9 dB SNR gain

in the worst case scenario over the LSMS that uses beam poweradaptation only. This is due to the fact that beam delay andpower adaptation helps to increase the 3 dB channel bandwidth,hence increasing the SNR at the higher data rates. Note thatthe SNR, as defined in (6), takes into account the eye opening,hence dispersion. Furthermore, our proposed BDAPA-LSMScoupled with an imaging receiver (with a pixel FOV of 11.3 )achieves a consistent 25 dB SNR at 10 Gb/sin the presence of background shot noise and multipath disper-sion. Our proposed system provides approximately 3 dB SNRgain over beam angle and power adaptation. Since our methods(beam delay, angle, and power adaptation) are able to identifythe optimum location of the spots as determined by the receiver,we reduce the acceptance semiangle of our imaging receiver to45 and increase the number of pixels to 256 (our imaging re-ceiver has a pixel FOV of 7.1 and a pixel area of 0.99 mm ),in order to enhance the link budget at higher data rates. Ourproposed system, BDAPA-LSMS, coupled with an imaging re-ceiver having a pixel’s FOV of 7.1 provides 32.3 and 29.2 dBSNR at 10 and 12.5 Gb/s, respectively, in the presence of back-ground shot noise, multipath dispersion, and mobility. The SNRimprovement obtained through the combination of beam delayangle and power adaptations, spot diffusing, and imaging re-ceiver allows us to reduce the transmit power below the current1 W level.To investigate our proposed system with respect to eye safety

regulations, we used a total transmit power of 80 mW (1 mWper beam) and introduced a limitation in the power adaptationalgorithm so that the power per beam is not increased beyond0.5 mW (which is an eye safety limit). We have also reducedthe size of the spot from a diameter of 1 cm to 0.5 cm whichallows more flexibility in clustering the spots closely if needed.The SNRs achieved in our proposed system in this case wereabout 12.5 and 9.5 dB at 10 and 12.5 Gb/s, respectively, underthe impact of background noise, multipath dispersion, and mo-bility (see Fig. 13). At 12.5 Gb/s, the SNR is still greater than 9.5dB . Therefore, forward error correction (FEC)


Fig. 13. SNR of our proposed system operating at 30 Mb/s, 10 Gb/s, and 12.5Gb/s, with a total transmit power of 80 mW.

can be used to further reduce the BER from to inour proposed system. The higher data rates (12.5 and 10 Gb/s)in our BDAPA-LSMS system are, therefore, shown to be fea-sible through the combination of multiple transmit beams, beamdelay adaptation, beam angle adaptation, beam power adapta-tion, and imaging receivers.

VI. HIGH DATA RATE OW COMMUNICATIONS’ CHALLENGESAND POSSIBILITIES

Achieving high data rate IR communications is possibleusing our proposed system. Since the adaptive transmitter(tracking system) is able to track the receiver, even with smallFOV imaging receivers, the link budget is increased. However,the fabrication and testing of a high-speed OW receiver arrayare very challenging tasks. To the best of our knowledge, thereis no commercial high-speed receiver to date that has speciallybeen designed for mobile indoor OW (we will design such areceiver in the future). At a data rate of 10 Gb/s, most of thecomponents will probably be adopted from the optical fiberdomain, which is not ideal for OW, thus making the receiverfabrication a challenging task. This is especially the case forcustom OW components such as the concentration lens, thesmall detector, and its narrow FOV.

VII. CONCLUSION

Mobility can degrade the performance of the CDS, LSMS,and BDPA-LSMS. In this paper, we introduced a beam delayadaptation approach and examined its use with our two pre-viously introduced methods: beam angle adaptation and beampower adaptation. We have examined these methods (in con-junction with an imaging receiver) to improve the OW systembandwidth and reduce the impact of background noise and mul-tipath dispersion. The SNR results show that beam delay, angle,and power adaptations in conjunction with an imaging receivercan help reduce the impact of background noise, multipathdispersion, and mobility-induced impairments. At a bit rate of30 Mb/s, our proposed BDAPA-LSMS offers SNR improve-ments of 35 dB over LSMS and 50 dB over CDS in a worstcase scenario. This improvement is achieved by introducingfive methods: beam delay adaptation, beam angle adaptation,beam power adaptation, multibeam transmitters, and imaging

receivers. Beam angle adaptation can help the transmitter targetits diffusing-spot at an area where the receiver can collect astrong signal through direct-LOS components. Beam delayadaptation helps reduce the delay spread, hence increases the 3dB channel bandwidth. Beam power adaptation can enable thetransmitter to allocate more power to the spots nearest to thereceiver, thus increasing the SNR at the receiver. Our proposedmethods coupled with an imaging receiver are shown to be ex-tremely effective in increasing the channel bandwidth from 36MHz (CDS) to about 9.8 GHz (BDAPA-LSMS with an imagingreceiver). Furthermore, the proposed BDAPA-LSMS offers animprovement in the SNR of more than 50 dB compared with theCDS nonimaging wide FOV receiver. Our simulation resultsshow that the BDAPA-LSMS system achieves about 29.2 dBSNR level at 12.5 Gb/s. To investigate our proposed systemwith respect to eye safety regulations, we used a total transmitpower of 80 mW (1 mW per beam) and introduced a limitationin the power adaptation algorithm so that the power per beamis not increased beyond 0.5 mW (which is an eye safety limit).The SNRs achieved in our proposed system in this case wereabout 12.5 and 9.5 dB at 10 and 12.5 Gb/s, respectively, underthe impact of background noise, multipath dispersion, andmobility. FEC can be used to further reduce the BER from

(at these SNRs) to in our proposed system.

ACKNOWLEDGMENT

M. Alresheedi would like to thank King Saud University inSaudi Arabia for supporting him during his research.

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Mohammed T. Alresheedi received the B.Sc. degree in electrical engineeringfromKing SaudUniversity, Riyadh, Saudi Arabia, in 2006, and theM.Sc. degreein communication engineering from Leeds University, Leeds, U.K., in 2009,where he is currently working toward the Ph.D. degree in electronic and elec-trical engineering.His research interests include adaptive techniques for optical wireless (OW),

OW systems design, and indoor OW networking.

JaafarM. H. Elmirghani received a B.Sc. degree (first-class hons) in electricalengineering from the University of Khartoum, Sudan, in 1989 and the Ph.D.degree in 1994 from the University of Huddersfield, U.K., for work on opticalreceiver design and synchronization.He is currently the Director of the Institute of Integrated Information Systems,

University of Leeds, Leeds, U.K., and a Professor of communication networksand systems in the School of Electronic and Electrical Engineering, Universityof Leeds. Before joining Leeds in 2007, he was the Chair in optical communica-tions at the University ofWales, Swansea, U.K., during 2000–2007. He has pub-lished more than 350 technical papers, co-edited the book Photonic SwitchingTechnology—Systems and Networks (IEEE Press, 1998) and leads a number ofresearch projects. His research interests include communication networks, wire-less, and optical communication systems.Mr. Elmirghani is a Fellow of the Institute of Engineering and Technology

(IET) and a Fellow of the Institute of Physics. He was the Chairman ofthe IEEE U.K. and Ireland Communications Chapter, the Chairman of theIEEE Comsoc Transmission Access and Optical Systems Committee, andthe Chairman of the IEEE Comsoc Signal Processing and CommunicationElectronics Committee. He was a member of the IEEE ComSoc TechnicalActivities Council, an Editor of the IEEE Communications Magazine, andhas been on the technical program committee of 29 IEEE International Con-ference on Communications (ICC)/Global Communications (GLOBECOM)conferences since 1995 including ten times as the Symposium Chair. He wasthe Founding Chair of the Advanced Signal Processing for CommunicationSymposium which started at IEEE GLOBECOM’99 and has continued since atevery ICC and GLOBECOM. He was also the Founding Chair of the first IEEEICC/GLOBECOM Optical Symposium at GLOBECOM’00, and the FuturePhotonic Network Technologies, Architectures and Protocols Symposiumwhere he has been the Chair to date. He received the IEEE Communica-tions Society 2005 Hal Sobol Award for exemplary service to meetings andconferences, the IEEE Communications Society 2005 Chapter AchievementAward, the University of Wales Swansea Inaugural “Outstanding ResearchAchievement Award” in 2006, and the IEEE Communications Society SignalProcessing and Communication Electronics Outstanding Service Award in2009. He is currently an Editor of the IET Optoelectronics, editor of the Journalof Optical Communications, the Co-Chair of the GreenTouch Core Switchingand Routing Working Group, an Adviser to the Commonwealth ScholarshipCommission, a member of the Royal Society International Joint Projects Panel,and a member of the Engineering and Physical Sciences Research Council(EPSRC) College. He has been awarded in excess of 20 million in grants todate from EPSRC, the European Union, and industry, and has held prestigiousfellowships funded by the Royal Society and British Telecommunications.

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