Journal of Kerbala University, Vol. 7 No.2 Scientific. 2009

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1 Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 Opical Repeae fo fee- space lase communicaion Sysem Rayed N. Ali, Jassim M. Jassim, Jalib A. Al-dahash, Niza S. Al-zubaidi Depamen of lase Physics Univesiy of Babylon, Babylon- Iaq. Absac: The aim of his pojec is o design and consuc an opoeleconic epeae o be uilized o exend he ange of a lase fee space communicaion sysem. I consiss of an opical eceive, an eleconic pocessing uni, and an opical ansmie. This epeae is expeced o exend he ange of he lase communicaion sysem seveal folds depending on he numbe of he uilized epeaes. Inoducion: Any Communicaion sysem consiss of hee main unis, a ansmie, popagaion medium and eceive. The pupose of he sysem, he ange beween he infomaion souce and is desinaion in addiion o he cos and many ohe facos dicae he powe equiemens of he communicaion sysem. Opical communicaion sysem have many pomising advanages ha make hem he pope choice o many applicaions. Lase souce added poweful ool o opical communicaion sysem which inceases hei capabiliy especially in fee space communicaions including he emoe sensing as a ype pf indiec o passive communicaions. Fee space, o unguided opical communicaion sysem have many impoan applicaions, specially, when one o boh eminals (ansmie eceive) has o be mobile is found vey ineesing in moden miliay applicaions since i povides a highly secued communicaion channels [1]. Theoy: A physical model fo a lase communicaion sysem can be summaized as follows: An infomaion signal is coded o he modulao foma (PCM, PPM, FM, AM, ec) and applied o a modulao. The modulaed lase beam is collimaed by an opical anenna (efacing o eflecing opics) and ansmied, hough an opical wave guide (fee- space, opical fibe), o a eceive uni. The eceive uni has also, is own opical anenna, bu is ole now is gaheing and condensing he eceived opical powe. While he ansmie opical anenna woks as a collimao, especially in he fee space lase communicaion sysem (FSLCS). The eceived opical signal is condensed on opical anenna (deeco), which ansfoms he colleced opical enegy ino an elecical signal. This signal is hen pocessed and decoded o egain he oiginal ansmied signal. In any communicaion sysem he elaionship beween he ansmied and eceived signal powe is descibed by a communicaion ange equaion. This equaion povides a chaaceizaion of popagaion in he communicaion channel, fee space popagaion loss, and aenuaion losses in he sysem componens. The lase beam is heefoe, uilized as a signal caie. The powe of his caie suffes fom diffeen losses and degadaion hough is passage fom he souce o he eceive pocessing uni. Opical signal powe losses in a lase ansmie uni can be descibed by he ansmie sysem ansmiance,, which is given as P P L (1) Whee P L is he lase souce powe, and P is he ansmie unie opical powe. The ansmiance of he ansmie unie implicily includes any losses of he lase beam powe due o he unis opical componens. Diffacion causes beam divegence, in he fa field, which is invesely popoional o he apeue diamee of he ansmie opical anenna. A a disan poin (Z), assuming a unifomly illuminaed cicula apeue, he inensiy pe unie sold angle ceneed a 178

2 Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 (Z), in he eceive plane, can be expessed in he em of he Bessel funcion of he fis ode as [], u J1 I z I o u Whee u d d - Tansmie apeue diamee - Half angle fom cene of ansmie apeue o poin (Z) a he eceive plane - Lase wavelengh d And I o P A he eceive plane, he powe eceived abou he cene of he diffacion paen, is he spaial inegal of I (R) ove ecepion angle ( ) muliplied by he amospheic ansmiance faco ( a ) o accoun fo aenuaion losses in he amosphee [3]. If he eceive opical anenna diamee (d) is locaed a a lage disance (R) fom he ansmie, and ceneed on he opical axis, hen i can be shown ha minimum powe a he eceive apeue is given as d d PMIN R 0.3 a P 3 R If a phoodeeco, of diamee (d p ), is placed a he focal poin of a eceive anenna and he opics of his anenna is assumed o be diffacion limied which poduce a spo size of diamee (d A ) given as ;.44 d A F d A he eceive anenna focal plane (F ), hen he caie signal powe a he deeco suface is given as: dd Pc 0.3 a Pl 4 R Whee ( ) epesens he eceive ansmiance. This quaniy includes he ansmiance (o eflecance when using eflecing opics) of all opical pas of he eceive anenna and deeco window. The opical deeco is an enegy ansduce ha conves he opical signal o an elecical one. The deecion capabiliy and he enegy ansfe efficiency of his ansduce ae elaed by seveal deeco paamees such as he deeciviy, quanum efficiency and esponsiviy.if he opical signal is sinusiodally modulaed, and is modulaion index ( m=1). Then he aveage signal cuen is given by [4]; e is Pc 5 hc Whee: - The deeco quanum efficiency -he opical signal wavelengh P - The opical signal caie powe in (W) colleced by he deeco. c A - is he deeco cuen esponsiviy in W Fom elaion (4) & (5) he ange equaion can be epesened as; 179

3 Jounal of Kebala Univesiy, Vol. 7 No. Scienific spl R d d is O d 1 d R 0.65 s o Whee: s P a m m 7 L W oe Is he sysem opical o- eleconic signal ansfeabiliy in ( ). is A Fo he case of a PIN phoodiode wih a FET opeaion amplifie, he minimum deecable signal cuen may be given as [5]; 4kT is min ei p 8 RL Whee: I Is he phoocuen. p P c Is he cicui bandwidh T Tempeaue K Bolzmanns consan R L load esiso The fis em of Eqn. (8) epesens he sho noise, while he second em epesens hemal noise. A maximum opical communicaion sysem ansfeabliy can, heefoe epesened by max i oe s min 6 Telecommunicaions sysems include signal epeaes ha consised of a deeco, amplifie, and a signal egeneao ha esoed he shape and inensiy of he pulse and lase souce eplicaes and einfoces he signal opically [6], is shown in figue (1). 9 Figue (1) Schemaic diagam fo lase communicaion sysem wih Opical epeae 180

4 Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 Repeaes: In he case of fee space opical communicaion, he ange beween he ansmie and eceive is limied by he diec viewing wihin a line of signal, and fo a high capaciy digial sysem, hen epeaes ae used o exend he ange of he oveall sysem. Repeaes usually designed wih he same opical componens as he eminal equipmen, Tha is i consiss of a deeco, low noise,an amplifie and auomaic gain conol gain, heshold deecion and egeneaion, and a lase ansmie cicuiy,as shown in he figue ( ). Deeco Pe-amp AGC Theshold deecion Dive LD Figue ( ) Schemaic diagam fo Opical epeae The aenuae an dispesed opical pulse ain is deeced and amplified in he eceive uni. This consiss of a phoodiode followed by a low noise peamplifie. he elecical signal hus acquied is given a fuhe incease in powe level in a main amplifie pio o eshaping in ode o ode o compensae fo he ansfe chaaceisic of popagaion medium and he amplifie using an equalize. Depending on he phoodiode uilized, auomaic gain conol (AGC) may be povided a his sage fo boh he phoodiode bias cuen and he main amplifie. Accuae iming (Clock) infomaion is hen obained fom he amplified and equalized wavefom using a iming exacion cicui such as a eining cicui on phase locked loop. This enables wihin he bi inevals of he oiginal pulse ain. This funcion of he epeae cicui is o econsiue he oiginally ansmied pulse ain, ideally wihou eo. Lase Tansmie: Elecically, a semiconduco lase behaves as a diode wih a volage un-on knee geae han 1 V. When he lase is biased wih a sufficien cuen so ha lasing occus, a fuhe incease in injeced cuen esuls in a popoional incease in lase opical oupu. Fo epesenaive lase diodes, he fequency esponse of opical powe oupu due o a change in lase cuen is fla ou o a esonance a a vey high fequency [7]. This esonance is due o lase elaxaion pocesses. In his pape, he diode is o be opeaed a a maximum modulaion fequency of a few megahez, wih a ise ime (depending on lase cuen se-poin) of appoximaely 15 ns. The lase cuen is modulaed beween wo pe-se values I h and I pk.the heshold cuen I h bias he lase o a poin whee is jus begins lasing. I pk is he cuen necessay o geneae a given opical oupu powe. Fo a 1 Wa a empeaue 5 o C semiconduco lase, epesenaive values fo and ae 300 ma and 1. A, especively. o mainain consan opical powe oupu, i is desiable o make he injeced lase cuen independen of empeaue. Theefoe, he lase is diven wih a high impedance cuen souce. The lase is also fied wih a hemo-elecic (TE) coole so as o mainain consan lase chip empeaue so ha opical powe emains consan a consan cuen and he wavelengh consan a 810 nm. The cicui in figue ( 3) is capable of deliveing 100 ma o a lase load a full opical powe modulaion fequencies of 10 MHz, elaed he inpu signal i have ampliude abou 30μA. 181

5 Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 Lase eceive: Figue ( 3) Lase ansmie cicui. As a deeco fo he lase pulses an avalanche phoodiode (6188) is employed in he eceive unie, (see figues (4, a and b)). I woks as an envelope deeco and conves he lase ligh pulses ino elecical pulses. When he phoons is inciden, he hole -elecon Pais ha is foming in he depleion egion. Aveage value of such inne gain depends on he eceive avalanche phoodiode supply volage.receive avalanche phoodiode (6188)epesens a cuen geneao [8]. The geneaed cuen pulse is led o he load esiso of he eceive avalanche phoodiode (R =3.9 k ohm) whee he volage pulse is obained. Figue (4,a), cicui of Receive uni. Figue (4,b) Ove view of he Receive uni 18

Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 Simulaion Resuls: 1- The figue ( 5 ) shows he signal modulaed on lase diode wih specificaion, Pulse duaion = 50 ns, PRT = 100ns Vp= 4.

6 Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 Simulaion Resuls: 1- The figue ( 5 ) shows he signal modulaed on lase diode wih specificaion, Pulse duaion = 50 ns, PRT = 100ns Vp= 4.5 v Ip =150mA. Figue (5 ) modulaing signal Empiical Resul: The figue ( 6 )shown he synchonizaion beween he opical signal of main lase souce and he opical signal egeneaion fom opical epeae in Laboaoy, he delay ime beween singles esuls fom elecical componens delay ime and he ime geneaed new opical signal. The figue ( 6 ) he synchonizaion beween opical signal 183

7 Jounal of Kebala Univesiy, Vol. 7 No. Scienific. 009 Conclusions: This cicuis demonsaes he successful applicaion of Receive opical signal,pocessing his signal and dive high powe lase diode (1W) a modulaed fequency (10 MHz). Refeences 1 -William D. Walon andeik L. Johnsson" Fee Space Opics Communicaion Sysem Tesing in Smoke and Fie Envionmens" Naional Insiue of Sandads And Technology, (006) - Pa, W. K.," Lase communicaion sysems" John Wiley and Sons, Ine,NY,(1969). 3- Xiaoming Zhu and Joseph M. Kahn," Fee-Space Opical Communicaion Though Amospheic Tubulence Channels " IEEE TRANSACTIONS ON COMMUNICATIONS, vol. 50, no. 8, AUGUST( 00). 4 - Yaiv,A.," Opical Eleconics in Moden Communicaions" New You Oxfo pess 5 d Ediion, (1997). 5- Douglas A. Ross, "Opoeleconic Devices and Opical Imaging Technigues" The Macmillan Pess LED.,London, (1979). 6-D. Don M. Booson "Lase Communicaion in Space "Communicaions and Infomaion Technology 6 Sepembe ( 007). 7 - Mac T. Thompson, " High Powe Lase Diode Dive Based on Powe Convee Technology" IEEE TRANSACTIONS ON POWER ELECTRONICS, vol. 1, no. 1, JANUARY (1997). 8 - Cova, S. e ai, Avalanche phoodiodes fo nea infaed phoon-couning, SPIE Poc. vol. 388 (1995). 184

A Cooperative MIMO Mobile Multihop Relay for Cellular Networks

A Cooperative MIMO Mobile Multihop Relay for Cellular Networks Poceedings of he 6h WSEAS In. Conf. on Eleconics, Hadwae, Wieless and Opical Communicaions, Cofu Island, Geece, Febuay 16-19, 7 116 A Coopeaive MIMO Mobile Mulihop Relay fo Cellula Newoks Jong-Moon Chung¹,