Tunable Pulse Amplitude and Position Modulation Technique for Reliable Optical Wireless Communication Channels

Transcription

1 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 Tuable ulse Amplitude ad ositio Modulatio Techique for Reliable Optical Wireless Commuicatio Chaels Yu Zeg, Roger.J.Gree, Shaobo Su ad Mark.S.eeso Commuicatios ad Sigal rocessig Research Group, School of Egieerig, Uiversity of Warwick, Covetry, Uited Kigdom {yu.zeg, roger.gree, s.su.1, mark.leeso}@warwick.ac.uk Abstract Modulatio techiques have attracted icreasig attetio i optical wireless commuicatios. asic schemes such as o off keyig (), pulse amplitude modulatio (AM) ad pulse positio modulatio (M) have bee validated as suitable for the optical wireless chael. This paper starts from the aalysis of these three modulatio schemes i terms of their power ad badwidth requiremets. As a result, a ew tuable hybrid modulatio techique is proposed. The proposed modulatio scheme takes the real time chael coditios ito accout, which is differet from other schemes. y employig amplitude ad positio modulatio selectively, a guarateed system performace ca be secured, without compromisig power ad badwidth efficiecy. This is also a ew approach to realize reliable optical wireless liks. Idex Terms tuable modulatio techique, papm, optical wireless, reliable commuicatio chaels I. INTRODUCTION High-speed wireless optical commuicatio liks have become more popular for persoal mobile applicatios such as DAs ad mobile phoes. This is a cosequece of the icreasig demad from the persoal iformatio service boom. Compared to the radio frequecy domai, optical wireless commuicatio offers much higher speeds ad bit rates per watt. As stated by the official ifrared stadards body, the IrDA [1], optical commuicatio ejoys much lower power cosumptio tha luetooth, with a iheret security feature whilst i ie of Sight (OS) applicatios. The oly drawback is that ifrared radiatio caot peetrate walls as radio frequecies do. Nevertheless, the optical chael is somewhat oisy for real time applicatios; it suffers from thermal oise, shot oise ad periodic backgroud ambiet oise. Due to the ature of persoal mobile commuicatio, the established optical lik is exposed to a dyamic ased o Adaptive ulse Amplitude ad ositio Modulatio for Optical Wireless Chaels, by Y. Zeg, R.J. Gree ad M.S. eeso which appeared i the roceedigs of the IET Iteratioal Coferece o Access Techologies 6, Cambridge, UK, Jue 6. 6 IET. eviromet with various oise sources. I optical commuicatio applicatios, there are always trade offs betwee system performace ad costs. There is thus a pressig eed to desig a modulatio techique for the real time situatio. I this paper, the characteristics of basic modulatio schemes are aalyzed. The combied power ad badwidth requiremets suggest that the basic modulatio schemes caot provide reliability whe deployed i a real time chael, resultig i compromised system performace. Startig from actively tuig the modulatio scheme parameter, a hybrid modulatio scheme is proposed. Extesive simulatios of operatio i severe oise iterferece have bee carried out to validate the ew scheme. A fuzzy logic cotrol module has bee developed to realise the tuig mechaism. The simulatio results idicate that the ew scheme ca provide icreased immuity agaist chael oise fluctuatio at a relatively low cost. The scheme obtaied formed a basis to support reliable mobile optical wireless commuicatio applicatios. The rest of this paper is orgaized as follows: Sectio II reviews the basic modulatio schemes suitable for optical wireless chael. Sectio III itroduces the ew tuable modulatio scheme, ad carries out comparative simulatios with the basic schemes. Sectio IV develops a fuzzy logic cotrol module for the proposed modulatio scheme. Sectio V addresses the reliability prospect of the proposed modulatio schemes. Sectio VI cocludes the paper. II. MODUATION SCHEMES A. Optical Chaels The optical chael is geerally optimal while employig itesity modulatio ad direct detectio (IM/DD) []. Whe the backgroud oise is low, the chael ca be modeled as a oisso process. I the presece of substatial backgroud light, the additive white Gaussia oise (AWGN) model is more appropriate [3]. I terms of calculatio complexity, the Gaussia approximatio is much simpler tha more accurate momet geeratig fuctio based approaches. 7 ACADEMY UISHER

2 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 3 Usig the Gaussia model, the output curret at the receiver, y(t), is give by + y( t) x( τ ) h( t τ ) + ( t) (1) Where x(t) is the optical power of the trasmitted sigal, h(t) represets the factor of multi-path dispersio ad (t) represets the white Gaussia oise. Also, x(t) must satisfy: 1 T x( t) ad lim x t dt T T ( ) () T Where is the average optical power costrait of the trasmitter. These costraits greatly ifluece the choice of modulatio scheme.. O Off Keyig The modulatio scheme is used for its easy implemetatio. The trasmitter, operatig at a bit rate R b, emits rectagular pulses of duratio 1/R b ad itesity to geerate bit oe, ad o pulse to geerate bit zero. The badwidth required by is roughly R b 1/T, the iverse of the pulse width. Assumig matched filterig with a maximum likelihood receiver, the bit error rate () of a system is []: Q (3) N R b Where N is the power spectral desity of the white Gaussia oise ad Q(x) is the customary Q-fuctio of digital telecommuicatios. y ivertig (3), the power requiremet for easily see to be: 1 N R Q ( ) (4) b As x R, ad Q(x) is mootoically decreasig, the iverse Q -1 (x) {,1} R is straightforward to obtai via a built i MATA fuctio [4]. Furthermore, the modulatio scheme ca be regarded as a bechmark to other modulatio schemes, which ca make compariso amog differet modulatio schemes easy. Fig. 1 shows the badwidth ad power efficiecies of the, -AM ad -M modulatio schemes. C. level ulse Amplitude Modulatio For -AM, usually represets amplitude levels. That is, oe of possible amplitude levels trasmitted from the trasmitter to represet a specific value. The badwidth requiremet of -AM is[]: The is: R 1 log log b AM (5) Figure 1. Normalized power requiremet ad badwidth requiremet for, -AM ad -M o IM/DD chael AM AM Q 1 log N R b Thus the power requiremet of -AM schemes is: AM (6) 1 1 N R Q ( AM ) (7) log To compare with the system, whe achievig the same : (8) AM The ower requiremet of the -AM is therefore: 1 log AM (9) The above equatio is with the assumptios of high Sigal to Noise Ratio (SNR), moderate values of ( ), ad a give. D. level ulse ositio Modulatio I -M, trasmitted optical sigals are represeted by the locatio of the pulse withi a clock cycle. As a result, sychroizatio betwee trasmitter ad receiver is required or assumed whe comparig M schemes with other schemes[5]. I additio, represets pulse slots umbers. Note that this is differet from -AM, though they all use. The power requiremet of a - M system ca be approximated by[]: log M (1) The badwidth requiremet for -M is: log M (11) 7 ACADEMY UISHER

3 4 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 Sugiyama ad Nosu have reported multiple-pulse positio modulatio (MM) ad overlappig pulse positio modulatio (OM) as relatives of M[6]. oth improve the badwidth or power requiremet at a cost of code calculatio redudacy [7]. Alahmari discovered a hybrid modulatio scheme: level pulse positio modulatio (M), that has a.6 icrease i the spectral efficiecy with the same power requiremet [8]. I additio to the above modulatio schemes, there are others such as quadrature amplitude modulatio (QAM), quadrature phase shift keyig, ad biary phase shift keyig (Q/SK). However, accordig to the combied power ad badwidth requiremet, they are ot strog cadidates for the optical wireless chael. The -AM ad -M modulatio schemes have bee validated as suitable for the optical wireless chael as basic modulatio techiques. The presece of a gap betwee -AM ad -M suggests that it is possible to utilize a ew modulatio scheme to provide a bridge betwee the two modulatio schemes. It must satisfy both the -AM ad -M requiremets, or at least share the features of the two modulatio schemes if such scheme exists. From [9] the properties of a potetial modulatio scheme, ulse Amplitude ad ositio Modulatio (AM) ca be foud. E. ulse Amplitude ad ositio Modulatio I AM modulatio, the iformatio is represeted both by the amplitude ad by the positio of the pulse. AM is thus also a multi-level modulatio scheme. It ca be expressed as M--AM, where M is the umber of amplitude levels, ad is the umber of pulses withi a clock cycle. The badwidth requiremet of the M-- AM is[9]: The power requiremet is: log M M AM (1) M M AM (13) log M Sice M--AM has two variables, a family of dimesioal curves ca be obtaied as show i Fig.. The vertical curves are costat pulse umbers, with amplitude level M icreasig from to 16, ad the horizotal curves are costat amplitude levels, with pulse umbers icreasig from to 16. M--AM modulatio covers the space above the -AM, ad -AM modulatio schemes, with the lower bottom edge beig of most iterest from the poit of power ad badwidth efficiecy. The curve joitly formed by M-- AM ad --AM crosses the -M at 4-M, ad reaches the upwards ear side of the (-AM). I Fig., a family of curves formed a matrix to cover the space above, -AM ad -M. This leads to the desig of a ew hybrid modulatio scheme: the tuable AM. Figure. Normalized power requiremet ad badwidth requiremet for, -AM, -M ad M--AM o IM/DD chael III. TUNAE MODUATION TECHNIQUE A. Tuable AM The tuable AM sigal set ca be writte as: 1 i x ( t) A c p( t it / ) (14) i Where is the umber of slots, A is the amplitude thresholds, A1/M, is the average sigal power, c i is the code word of -M, p(t) is the rectagular pulse of duratio T/ with uity height. The of the tuable AM scheme is bouded by its pairig -AM ad -M. The upper boud is give by (6), usig the method i (8), from (1) ad (11), upper ad the lower boud is give by the followig: Tuable M Tuable AM Q Q 1 log log M ( M 1) M N R b AM N R b (15) (16) The coditio for switchig betwee differet pulse umbers depeds o the requiremet of the expected power ad the badwidth efficiecy. I aother words, the fewer the umber of pulses the lower the badwidth requiremet ad the greater the umber of pulses the lower the power cosumptio. Switchig amog differet modulatio levels is depedet o the circumstaces i which the modulatio scheme is used. For power limited mobile applicatios, it is likely the system will switch to higher-level M for a reduced power requiremet ad thus exted the battery life. For badwidth-limited applicatios i high-speed data commuicatios, power is ot the major restrictio but better badwidth efficiecy ad speed are preferable. I this case the lower level of the modulatio scheme will 7 ACADEMY UISHER

4 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 5 be applied. The tuable AM scheme provides the flexibility of varyig modulatio levels without the cosiderable complexity of MM or OM.. Chael with variable As evideced by (4), the reflects the chael coditio. Whe the is icreasig, R b will reduce to maitai the same power cosumptio (battery life), ad vice versa. For multi level AM ad M, there is the possibility of maitaiig costat whilst the chages by alterig modulatio levels. I ay free space liks, the coditios will costatly chage as a result of obstacles, optical turbulece ad the like. As a bechmark, ca chage from 1-6 to 1 -, i a costat power situatio. For each scheme, Table I lists the relevat performace. The first row idicates the level chage eeded to maitai the bit rate at the maximum for the chael. The secod row shows the resultig multiplicatio factor from the bit rate without adaptatio to that whe the system adapts. It should be oted that M is uable to fully compesate for the poor, as 16-M was the maximum complexity cosidered. The resultig accuracy i the bit rate is a show as a percetage i the third row, whilst the fourth row explicitly states the umber of levels chaged i the adaptatio. I Table I, the -AM ad tuable AM are similar i performace, but, by plottig the cost ormalized to the adaptive target, as show i Fig. 3, it becomes apparet that tuable AM is more efficiet. To demostrate the beefit of the tuable modulatio scheme, Fig. 4 shows the data rates obtaiable for the differet modulatio schemes over a 5 Mbps direct OS optical lik, whilst the varies from 1-6 to 1 - ad the required optical power is fixed. From Fig. 4, it is clear that uder severe coditios, tuable AM ad -AM provide a better prevetio from droppig the R b tha -M ad, which suffer a extremely large pealty. IV. AYING FUZZY OGIC CONTRO A. Fuzzy logic cotrol Fuzzy logic (F) is a superset of covetioal (oolea) logic that has bee exteded to hadle the cocept of partial truth, that is truth values betwee "completely true" ad "completely false" [1]. F icorporates a simple, rule-based IF X AND Y THEN Z Figure 3. Cost compariso of tuable AM, AM ad M approach to a solvig cotrol problem rather tha attemptig to model a system mathematically. The stadard defiitios i fuzzy logic are: truth (ot x) 1. - truth (x) truth (x ad y) miimum (truth(x), truth(y)) truth (x or y) maximum (truth(x), truth(y)) Traditioal cotrol systems are based o mathematical models to defie a relatioship that trasforms the desired state ad observed state of the system ito iputs that will alter the future state of that system. Fuzzy machies work the same way, but the decisio ad the meas of choosig that decisio are replaced by fuzzy sets ad rules. Fuzzy cotrol, which directly uses fuzzy rules, has the purpose of ifluecig the operatio of a system by chagig iputs to that system via rules that model how the system operates [11].. Applyig Fuzzy logic cotrol The System status ca be modeled as membership fuctios i F. The rules set i the F system will come from the requiremets of the ideal system. While varies across the rage, F ca be used to set up rules accordig to differet circumstaces such as applicatios which eed prologed battery power, while the system power cosumptio is the mai cocer. I a system where data rate is more vital tha others, such as i a bak or govermet offices, the selectio of system TAE I. COMARISON OF ADATIVE ACCURACY ETWEEN -AM, -M AND TUNAE AM ( ) -AM -M Tuable AM evel chage Adaptive Target (.4) Accuracy (%) Cost (level) Figure 4. Compariso of R b recovery betwee tuable AM, AM, M ad modulatio schemes uder differet coditios. 7 ACADEMY UISHER

5 6 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 status will be weighted more towards R b to satisfy the eed for high performace data trasmissio. The followig sectio will develop a fuzzy logic cotrol model for the tuable modulatio system. The example model will stabilise the by establishig a set of rules properly rather tha purely cotrol parameters affectig the i terms of performace, such as dealig with the badwidth or power budget. Assumig the system beig discussed is possessed of a tuable modulatio techique, the is affected by several factors, which are stated i (15) ad (16). This produces a highly oliear characteristic. It ca be ackowledged that the will be affected ot oly by oise ad trasmitted sigal power but also by the system modulatio state. A cotroller i the system eeds to kow the curret level ad eeds to be able to set the state. Therefore, the cotroller's iput will be the level differece (compared to 1-6, expressed i d) ad its output will be the rate, or the tred at which the M or is chagig. Sice the level teds to oscillate aroud the desired level, it is also worth cosiderig addig aother iput, the level's rate of chage, to slow dow the state chage whe the is close to the right level. The rules for the fuzzy cotroller for this model are the followig. 1. If ( is ok) the (state is o_chage). If ( is low) the (M is chage_fast) 3. If ( is high) the ( is chage_fast) 4. If ( is ok) ad (rate is egative), the (M is chage_slow) 5. If ( is ok) ad (rate is positive), the ( is chage_slow) These rules are show as a fuzzy iferece diagram i Fig. 5. Accordig to the rules set above, the system performs a self-adaptatio whe degrades more tha a certai threshold. Sice high states are usually ot acceptable from the commuicatio system desig poit of view, the system states will be chaged based o a calculatio withi available cadidate states. This ca be dealt with by settig the low membership fuctio to be more ifluetial o the high value settigs. The surface of M ad demaded versus the chage rate, ad the relative differece is show i Fig. 6. C. Discussio The modulatio requiremet will be derived accordig to the fuzzy logic cotrol output, which ca be set at a value betwee -1 ad 1. For the tuable AM scheme, M ca be chaged whe the fuzzy cotroller has a positive output, ad chages whe the output is egative. The operatio could be iverted, depedet o the importace give to M ad. The system uder such a cotrol mechaism ca perform a search amog modulatio variables, which provides a added flexibility whe dealig with the chagig eviromet. It is also feasible to maipulate other factors, which affect the whole but every effort is made to keep the system Figure 5. The rules of fuzzy cotroller to chage the system status ad stabilise the performace stable. Utilizig fuzzy systems i a dyamic cotrol eviromet reduces potetial stability problems, ad this is the beefit of applyig fuzzy logic cotrol over a modulatio chael. V. REIAE COMMUNICATIONS The reliability or robustess of a commuicatio chael usually refers to the adaptatio ability of the system itself uder severe coditios. Researchers have bee seekig techiques to combat causes of system istability with the maistream beig focused o the codig theorem [1]. As stated by arry i 1994 [], modulatio schemes other tha the basic oes are eeded i the optical wireless eviromet. Followig a comprehesive aalysis by ark [13], trellis-coded multiple pulse positio modulatio (MM) stads out from the simulatio results. The capacity of the itesity modulatio chael remaied a ope problem util recet work by Hrailovic ad Kschishag [14]. Apart from error correctio codes, attempts have bee made to fid alterative techiques to realize reliability ad robustess [1]. Amog these, the tuable d e tr d a M rate er level Figure 6. System state chagig tred o the basis of fuzzy cotrol rules 5 7 ACADEMY UISHER

6 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 7 modulatio scheme is very promisig. From a system desig poit of view, the desired reliability oe system ca provide maily depeds o the system models. As for the optical wireless model, three importat issues are: the power requiremet, the badwidth requiremet, ad the achievable. The problem with codig is that the codes desiged for a specific commuicatio lik usually have a limited variatio rage, although adaptive codig techiques have bee used i the latest commuicatio systems [15]. There is the possibility of employig modulatio techiques i cojuctio with codig [16]. The system model used i this paper shows the coectio to codig patters. That is, the system model will determie the code desig process to accommodate the system requiremets. The detailed codig desig issues are out of the scope of this paper, so we leave it to aother discussio. Fig. 7 illustrates the possible system states of a tuable M--AM modulatio scheme. As demostrated by the figure, the system adopts differet states accordig to the real system. There are two poits to be clarified: 1. How fast does the system eed to respod to the chage?. How frequetly does the system eed to perform amplitude or slot umber chages? Over-actively chagig i a small time scale will result i a fluctuatio i data rate, ad ustable trasmissio. This raises aother importat issue: the quality of service (QoS). The QoS usually refers to cotrol mechaisms that ca provide a differet priority to differet users or data flows. [17] I commuicatio systems, the, data rate, power requiremets ad badwidth requiremets form a combied priority bak istead of oe mai priority header i computer etworks. The priorities are set accordig to differet circumstaces. The ad data rate i most applicatios are more certai tha other parameters. Accordig to Fig. 7, the system will beefit from the tuig oly whe the appropriate selectio is preset. This is ot the same case with fixed mode modulatio schemes, where the optimal fit is ot applicable. To summarise, startig from the system requiremets, chael reliability depeds o correlatios betwee cadidate modulatio patters formed by possible system states. A itetioally-desiged codig scheme ca improve the performace, but ot ecessarily optimize the modulatio scheme itself. A properly egieered modulatio scheme shows the potetial system versatility to cope with ucertai costraits arisig from the real chael coditios. VI. CONCUSIONS We have ivestigated a real system model ad proposed a tuable modulatio techique for high speed optical wireless commuicatio chaels. The resultig tuable M--AM scheme has excellet potetial to combat the variatio without compromisig Figure 7. System states versus amplitude (M) ad pulse slot umber () betwee power ad badwidth requiremets. This is differet from other modulatio schemes i terms of its tuability. The proposed scheme ca provide adaptive fuctioality for the real time chael at a relatively low cost. This provides the system with the freedom to adapt to chagig eviromets, rather tha usig same modulatio schemes for every applicatio. Whe both power ad badwidth efficiecy are cosidered, by movig amogst the matrix of amplitude levels ad pulse slot umbers, the proposed modulatio scheme ca ameliorate system performace degradatio. I compariso with coded schemes, the proposed tuable scheme achieves a simple system structure ad less calculatio redudacy. This work offers the prospect of a practical adaptive modulatio scheme for high-speed persoal mobile commuicatio applicatios. We have applied a specially-desiged fuzzy logic cotrol system to the proposed tuable modulatio scheme. The test system realized real time patter selectio to miimize the variatio. Accordig to the results, the proposed tuable modulatio scheme is very promisig i providig a reliable optical wireless commuicatio chael. Nevertheless, the results preseted i this paper are by o meas a claim to limit the system model to - dimesio modulatio patters; a multi-dimesioal system model ca be derived usig the model discussed i part IV. ACKNOWEDGMENT The authors would like to thak Dr. Xiaomig Jia from the Warwick hysics Departmet for thoughtful discussios, ad also thaks the aoymous reviewers for their costructive suggestios. REFERENCES [1] [] J. R. arry, Wireless ifrared commuicatios. osto, Mass. ; odo: Kluwer Academic, [3] J. M. Kah, W. J. Krause, ad J.. Carruthers, "Experimetal characterizatio of o-directed idoor 7 ACADEMY UISHER

7 8 JOURNA OF COMMUNICATIONS, VO., NO., MARCH 7 ifrared chaels," Commuicatios, IEEE Trasactios o, vol. 43, pp , [4] S. J. Chapma, MATA programmig for egieers. acific Grove, Calif. ; odo: rooks/cole-thomso earig,. [5] M. D. Audeh, J. M. Kah, ad J. R. arry, "erformace of pulse-positio modulatio o measured o-directed idoor ifrared chaels," Commuicatios, IEEE Trasactios o, vol. 44, pp , [6] H. Sugiyama ad K. Nosu, "MM: a method for improvig the bad-utilizatio efficiecy i optical M," ightwave Techology, Joural of, vol. 7, pp , [7] D. C. M. K. ee, J.M. Audeh, M.D., "Trellis-coded pulse-positio modulatio for idoor wireless ifrared commuicatios," Commuicatios, IEEE Trasactios o vol. 45, pp , 1997 [8] A. S. Alahmari, "Turbo Coded ulse ositio Modulatio for Optical Commuicatios," hd Thesis, School of Electrical ad Computer Egieerig, Georgia Istitute of Techology, 3. [9] H. ark, "Coded modulatio ad equalizatio for wireless ifrared commuicatios," School of Electrical ad Computer Egieerig, Georgia Istitute of Techology, 1997, pp [1] J. Harris, A itroductio to fuzzy logic applicatios. Dordrecht ; odo: Kluwer Academic,. [11] D. Driakov, H. Helledoor, ad M. Reifrak, A itroductio to fuzzy cotrol. erli ; New York: Spriger- Verlag, [1] F. Gfeller ad W. Hirt, "A robust wireless ifrared system with chael reciprocity," Commuicatios Magazie, IEEE, vol. 36, pp. 1-16, [13]. Hyucheol ad J. R. arry, "Trellis-coded multiplepulse-positio modulatio for wireless ifrared commuicatios," Commuicatios, IEEE Trasactios o, vol. 5, pp , 4. [14] S. Hrailovic ad F. R. Kschischag, "Capacity bouds for power- ad bad-limited optical itesity chaels corrupted by Gaussia oise," Iformatio Theory, IEEE Trasactios o, vol. 5, pp , 4. [15] G. W. K. Marsh, J.M., "Chael reuse strategies for idoor ifrared wireless commuicatios," Commuicatios, IEEE Trasactios o vol. 45, pp , [16] J. J. Grubor, V. ager, K.-D., "Rate-adaptive multiple sub-carrier-based trasmissio for broadbad ifrared wireless commuicatio," Optical Fiber Commuicatio Coferece, 6 ad the 6 Natioal Fiber Optic Egieers Coferece, Califoria, USA, pp. 1, 5-1 March 6 [17] QoS : Measuremet ad evaluatio of telecommuicatios quality of service Wiley, 1 Yu Zeg received the.sc degree i Applied hysics from eijig Jiaotog Uiversity, eijig, Chia, i 1 ad M.Sc degree i Advaced hotoic ad Commuicatios from Uiversity of Warwick, Covetry, UK, i 3. He is curretly workig toward the h.d degree i electrical ad electroic egieerig at the Uiversity of Warwick. His research iterests iclude adaptive modulatio schemes, chael codig ad chael optimizatio for optical wireless. Mr. Zeg is a Studet Member of the IEEE ad IET. Roger J Gree received the.sc. degree i electroics from UMIST, Machester, U.K., i 1973 ad the h.d. degree i commuicatios i He was a Research Egieer at GEC Avioics, asildo, U.K., from 1976 to 1978 ad took academic posts startig i He became the rofessor of Electroic Commuicatio Systems at Warwick i September 1999, ad Head of the Divisio of Electrical ad Electroic Egieerig i August 3, with research iterests i photoics, video ad imagig. He has published over 18 papers i the field of optical commuicatios, optoelectroics, video, ad imagig, ad has several patets. Some 45 h.d. research studets have worked successfully uder his supervisio. He leads the Commuicatios ad Sigal rocessig Research Group, which is the largest i the School of Egieerig at Warwick. He curretly serves o two IEEE committees cocered with commuicatios ad sigal processig. He is a member of the Smart Optics Faraday artership at Warwick, a member of the UK ESRC grats eer Review College, ad a evaluator for proposals i the EU Framework 6 activities. rofessor Gree is a Fellow of the IET, a Chartered Egieer, ad a Seior Member of the IEEE. Shaobo Su received the.eg degree i telecommuicatio egieerig from eijig Uiversity of osts ad Telecommuicatios, eijig, Chia, i 4 ad M.Sc degree i Advaced hotoic ad commuicatios from Uiversity of Warwick, Covetry, UK, i 5. I 6, he worked i the R & D cetre of Ericsso i eijig, Chia, as a Itegratio ad Verificatio Egieer carryig out telecom hardware ad software testig. He is curretly workig toward the h.d degree i electrical ad electroic egieerig at the Uiversity of Warwick. His research iterests iclude optical commuicatio systems ad optical receivers. Mark S eeso is a Associate rofessor i the Divisio of Electrical ad Electroic Egieerig, ad a member of the Commuicatios ad Sigal rocessig Research Group. He received the degrees of.sc. ad.eg. (with First Class Hoors) i Electrical ad Electroic Egieerig from the Uiversity of Nottigham, UK, i 1986, ad the h.d. degree i ovel optical modulators i the Egieerig Departmet from the Uiversity of Cambridge, UK, i 199. From 199 to 199, he worked i the IT Divisio of a large Uited Kigdom bak carryig out commuicatio etwork simulatios. He the held several academic appoitmets prior to joiig Warwick i March. His curret research iterests are maily at the systems level i the commuicatios area, particularly the aalysis ad simulatio of both subsystems ad etworks. He has published over 85 joural ad coferece papers, ad has bee a member of the ESRC peer review college sice Jauary 3. He is curretly supervisig three hd studets (followig seve successfully completios). Dr eeso is a member of the UK Istitute of hysics, a Chartered hysicist, a member of the IEEE ad a Fellow of the Higher Educatio Academy. 7 ACADEMY UISHER