Secured Indoor Powerline Communication Using CDMA Technique

Transcription

1 Secure Inoor Powerlne Communcaton Usng CDMA Technque Mohame Sherf Omer AbuElHassan an Razal gah Wreless Communcaton Centre, Faculty of Electrcal Engneerng Unverst Teknolog Malaysa 83 UTM Skua Johor an Abstract - Wth the rap growth of home networks, there s an ongong nee for an economcal an relable communcatons system that can be mplemente n any bulng. Powerlne channel has been consere as a meum not only for low-rate, control communcatons, but also for hgh-spee ata communcatons, such as home networkng an Internet access. Communcaton over the power lne has become an opportunty for the power strbutors to mplement new servces. The focus of ths paper s to aress the challenges n PLC such as nose an securty. The technques to overcome these challenges are presente. Keywors: Powerlne communcaton, CDMA, Couplng Crcut, Securty. Introucton Powerlne communcaton (PLC) s a technque whch proves the ablty to transfer ata over stanar AC wrng, uses the exstng publc power wrng system network to carry nformaton. It s somehow a kn of "wreless" communcaton because PLC technology can supersee the nstallaton of ecate wrng n some applcatons. Varous applcatons use PLC technology from power company equpment controllng to computer networkng. The esgn an mplementaton of nterface crcut that can transfer the ata wthn the avalable range wll be consere, that means many applcatons can be use usng PLC. Powerlne networkng uses exstng electrcal wrng can be use to create a home network. Snce most homes have plenty of power outlets, then ths technology can be consere as an easy an eventually less expensve than other types of networkng, as t s alreay exsts. PLC has several avantages whch can lea to use t as communcaton channel. Usng AC power lnes to transmt ata elmnates the cost of nstallng specal wrng between strbute system elements an can be use for all type of communcatons.. PLC Challenges Power lnes an ther assocate networks are not esgne for communcatons use. They are a hostle envronment that makes the accurate propagaton of communcaton sgnals ffcult. The bggest challenges face n PLC are nose, attenuaton, nterference an securty. The man reason s that powerlne where esgne to elver power not ata, most esgn effort where only one to mnmze the crcut resstance between the power njecton pont an the loa. Powerlne s alreay establshe, therefore, many plugs nstalle aroun the bulng an ths make powerlne s unsecure. To esgn sutable crcuts such as couplng crcut, power lne moem, etc., the behavour of powerlne must be stue to avo the above problems. 3. Inoor PLC Channel ose From the basc approach prove n [] an extene n [], powerlne nose can be generally classfe nto three types: ) Colore backgroun nose: Ths nose s manly cause by summaton of numerous nose sources wth low power, an also consstent wth the loa capacty of strbute transformer. Its power spectral ensty (PSD) vares over tme n terms of mnutes or even hours. Fgure shows the best, average an worst cases of colore backgroun nose PSD. The ynamc range was up to 4 B over the MHz banwth. Its feature appears to be whte nose. Generally, backgroun nose PSD can be wrtten as [3]: b c. f ( f ) = (W/Hz) () where b, c an are constant an f s frequency. The maxmum, mnmum an the average values for the parameters of b, c an n equaton () are shown below epenng on measurement over MHZ [3]: At maxmum: b = - 55, c = - 4, = -.4 At mnmum: b = - 85, c = - 5, = -.6 Average: b = - 7, c = - 6, = /7/$5. 7 IEEE Authorze lcense use lmte to: UIVERSITY TEKOLOGI MALAYSIA. Downloae on January, 9 at 3:43 from IEEE Xplore. Restrctons apply.

2 -4 Backgroun ose & Frequency -5-6 Backgroun ose X: 6 Y: Frequency Fgure : Maxmun, average, an mnmum of backgroun ose ) arrow ban nose: It s manly prouce by the horzontal scannng sgnals of the TV set an montors, the peak on the power spectrum graph appears at the horzontal scannng sgnal an ts harmonc frequency ponts. The repeatng frequency s usually 5 to Hz []. 3) Impulse ose-ranom Pulse ose: It s manly occurre when the protecton swtch turnng off or on. Each pulse nose wll affect a very broa ban. Its arrval tme s ranom, an t can last from several μs to several ms. the pulse wave shape s lke ampng sne wave or serre ampng sne wave. Swtchng O/OFF of applances s unprectable []. Fgure shows the sample of mpulse nose wth + the mpulse ampltue, A = max( A, A ).The mpulse wth tw, an the arrval tme t arr,. The stance between two mpulse events s escrbe by the nterarrval tme t IAT or mpulse stance.the stance between two mpulse t t IAT events s escrbe by the s gven by []. t IAT = t w + t = t arr, + t arr, + η () The tran of mpulses mptran (t) can be escrbe by the tme behavour an gven by [], mptran t t ( t) = A mp * tw, arr =, η (3) Fgure : Impulse nose 4. Attenuaton A power lne s a transmsson lne esgne for transmttng commercal power of 5 Hz an 6 Hz frequences, not a lne esgne for communcatons. For ths reason, the sgnal attenuaton characterstcs are affecte to a greater extent by cable types or wrng methos an loas connecte to the cable termnals (electrc equpment, wall outlets, etc.), as compare to lnes of coaxal cable or twst par cable, etc., whch are use for normal wre communcatons. Dstance on the power lne s one of the major factors n sgnal attenuaton ncreases. Reflecton from the termnals of branch lnes on the power lne also s one of the major factors n sgnal attenuaton ncreases. In power lnes, cable types are generally fferent n major lnes an branch lnes; therefore, they have fferent characterstc mpeances, causng msmatchng. Bascally, reflecton s assume to be relate to the stance from the branch lne to the termnals; however, snce the number of branches an the stance vary an they are ntrcately combne n the actual power lne confguraton, as was prevously state, reflecton occurs on varous frequences. When these conce, a great amount of unexpecte sgnal attenuaton wll occur on certan frequences. Power Best Worst Average Dstance Fgure 3: Attenuaton Authorze lcense use lmte to: UIVERSITY TEKOLOGI MALAYSIA. Downloae on January, 9 at 3:43 from IEEE Xplore. Restrctons apply.

3 Fgure 3 shows the relatonshp between transmtte power (P) an stance () at the best, average an worst channel cases. As shown n the fgure the transmtte power ecreases when stance ncreases. It s possble to avo attenuaton by ncrease the transmtte power. The receve sgnal powers, S for the best an worst case at a stance, from the transmtter are gven by [4]:.4* S ( ) = P * [W] (4), best S ( ) P * worst.* = [W] (5) 5. Shannon s Theory for the Powerlne Channel The ablty to transfer ata can be estmate for a channel wth knowlege of the essental use n Shannon s formula, S C = B * log + (6) C ncates the maxmum ata rate n (bts/s) for whch a theoretcally error-free transmsson s possble normally cannot be acheve by techncally realzable an also proftable systems n practce..e., the use of [8] s not mmeately feasble for powerlne channels, snce the sgnal to nose rato s not constant wthn the banwth B, but may vary substantally. In practce therefore the transmtte sgnal-power ensty spectrum S rr ( f ) an a frequency-epenent nose-power spectral S nn ( f ) ensty must be taken nto account, so that equaton (6) has to be mofe as follows []: f Srr ( f ) C f S f = log + (7) f nn( ) u where f = f u B In orer to be able to use equaton (7) the transmsson power ensty spectrum S tt ( f ), the channel transfer functon H(f) as well as nose power ensty spectrum S nn ( f ) recever shoul be etermne. The receve sgnal power ensty spectrum s then: S Srr ( f ) = Stt ( f ) * H ( f ) (8) E( f ) K( f, ) tt f ) * ( = (9) where E s electrcal fel strength, an B s avalable ban wth, K(f,) s ecouplng factor. B ow t s possble to calculate S tt ( f ), S nn ( f ) an also C epenng on system components parameter such as avalable banwth. C C C r(t) Fgure 4: Basc structure of echo-moel efnton Fgure.4 shows the echo moel that affect by the echo elay an attenuaton. The basc behavour of a transmsson channel ncorporatng echoes can be escrbe by an mpulse response []: h( t) = c * δ ( t ) () = where the coeffcents enote the echo elays an the factors C s the echo attenuaton. From Fgure 4, the transfers functon can be rewrte as, h( t) = = c * e j πf 6. Couplng Crcut () To be able to esgn an optmum couplng crcut, approprate components must be chosen an ther operaton must be unerstoo. The components of the couplng crcut are: () Couplng capactors [5]: These are extensvely use n power lne communcatons, most commonly to couple the PLC sgnal to the power lne but also as a part of more sophstcate, hgherorer flters. Couplng capactors carry the communcaton current an thus have to be hghfrequency capactors (self resonant frequency has to be hgher than the moulaton frequency). Conversely, they have to flter the power voltage (roppe across the component), as well as voltage surges an therefore nee to be hgh-voltage capactors. () Isolaton transformer: use to solate hgh voltage. Couplng crcut s as a protectng crcut use as nterface crcut between powerlne an moem crcut. The common LC hgh pass flters must have some large nuctve components when they are workng at lower frequences. In orer to Authorze lcense use lmte to: UIVERSITY TEKOLOGI MALAYSIA. Downloae on January, 9 at 3:43 from IEEE Xplore. Restrctons apply.

4 elmnate the flter tself to prouce some harmonc ntermoulaton proucts, the RC- type hgh pass flter s aopte [6]. Fgure 5: Couplng Crcut Fgure 6 shows the sgnal of powerlne before couplng by applyng kv, 6 Hz: 5 5 Here, the scontnuous-phase frequency-shft keyng (DPFSK) s chosen for moulaton n smulaton. Equaton () an (3) gve the expresson of the DPFSK output sgnal an Fgure 8 shows the schematc of the DPFSK as escrbe n [7], where s calle the mark (bnary ) frequency an s calle the space (bnary ) frequency. S( t) = Ac [ wc + θ ( t)] = S( t) = Ac [ w + θ] () for t n the tme nterval when a bnary s beng sent S( t) = Ac [ wc + θ ( t)] = S( t) = Ac [ w + θ] (3) for t n the tme nterval when a bnary s beng sent. Ampltue Fgure 9 shows the DSFSK output usng Matlab smulnk: Tme Fgure 6:.Powerlne sgnal before couplng crcut Fgure 7 shows the powerlne sgnal after couplng. It shows that the couplng crcut has successfully remove the AC voltage. Ampltue Tme Fgure 7:.Powerlne sgnal after couplng crcut 7. FSK Moulaton Frequency shft keyng (FSK) moulaton s a form of FM moulaton where the frequency of the carrer wave s vare by the bnary nput stream. As the bnary nput sgnal changes from a logc to a logc, an vce-versa, the FSK output shfts between two frequences: a mark or logc frequency an a space, or logc frequency. Oscllat or F Oscllat or F Swtc h FSK Output DATA IPUT Fgure 8: DPFSK schematc Ampltue Tme Fgure 9: FSK Output 8. Sprea spectrum Technques DS-CDMA The nvestgatons show that the powerlne must be regare as a slghtly tme-varant an frequency-selectve channel. These propertes wll have an effect on the selecton of a sute transmsson scheme. The man problem that powerlne s alreay establshe wthn the bulngs, an there are many plenty s (plugs) strbute aroun the bulng, an ths wll cause a bg problem..e.f computer network s use over noor powerlne, that means any one can access ths network. All these reasons lea to a system esgn whch s base on the sprea spectrum technque to overcome the mentone problems. By spreang the sgnal over a we frequency range s that the nfluence by jammers wth small banwth s very low. By usng DS-CDMA or rect sequence sprea spectrum,ata wll be more secure. Wth rect sequence sprea spectrum (DSSS), each bt n the sgnal represente by multple bts n transmtte sgnal, usng spreang coe sprea the sgnal across a wer frequency ban n rect Authorze lcense use lmte to: UIVERSITY TEKOLOGI MALAYSIA. Downloae on January, 9 at 3:43 from IEEE Xplore. Restrctons apply.

5 proporton an ths coe generate by pseuoranom nose [7]. Fgure shows DSSSS usng P coe: (). Fgure : Pseuoranom coe By usng FSK moulaton as frst moulaton, the FSK output wll be the nput to the DSSS. Fgure shows the FSK spreang sgnal by usng DSSSS..e, DSSS output: Fgure : FSK spreang sgnal 9. Error Control Methos To avo the sgnal errors, the couplng crcut an hgh pass flter s not enough, because there are some errors can be etecte uo to mpulse nose an other factors, therefore error control wll be goo soluton bese the other components. Forwar Error Correcton (FEC) s use to etect an correct errors at the recevng en wthout callng for retransmsson. Wth FEC, a number of bts are ae to the message. These extra bts are coe n a way that allows for a certan number of errors per message to be etecte an correcte.. Summary Due to the nherent characterstcs of the lowvoltage power lne, the transmtte sgnal s serously pollute for the nfluence of nose, attenuaton. In ths paper,the optmze methos to enhance the communcaton relablty of the lowvoltage PLC have been presente. A metho for DSFSK moulaton also has been presente. The metho s uncomplcate, fast an easy to mplement, thus t s sutable for low-cost archtectures, elmnatng the nee for hgh-spee processng harware. The emoulaton metho s also rect. The applcaton of sprea spectrum technology has been presente, whch s effectve n mprovng the nose-resstng ablty of the communcaton system. An also solve the major problem of powerlne by usng pseuo nose ranom to make t secure. Decreasng of the sprea spectrum carrer frequency ban of the crcuts use an the amplfcaton of transmsson power can effectvely counter lne attenuaton. Effectve couplng crcut has been presente to wthstanng v-5/6hz an also some noses. FEC use to etect an correct the errors can be etecte ue to mpulse nose; also channel capacty has been scusse. By usng hgh frequency above MHz up to 3 MHz the nose an also nterference can be overcome.. References [] Manfre Zmmermann an Klaus Dostert Analyss an moelng of mpulsve nose n broa-ban powerlne communcatons, IEEE Trans. Electromagn. Compat., vol. 44, no., pp 49-58, Feb.. []Hal Hrasnca,Abelfatteh Hane,Ralf Lehnert, Broaban Powerlne Communcaton etworks, John Wley, 4. [3] T. Esmalan, P. Gulak, an F. Kschschang, A screte multtone power lne communcatons system, Proc. of ICASSP '. vol. 5, pp , Jun.. [4] X H Zhang, L Y Zhang, B Zou an Z L DuThe Desgn of Vrtual Low-Voltage Power Lne ose Generator, IOP Publshng Lt, 6. [5] Osama Blal, Er Lu, Yangpo Gao an. Tmo O. Korhonen Desgn of broaban couplng crcuts for powerlne communcaton,, n Proc. of ISPLC Zaragoza, Span, 4. [6] Yang Xaoxan, Zheng Tao, an Zhang Baohu, Measurement an research of channel nose strbute characterzaton n low voltage networks, n Proc. of Transmsson an Dstrbuton Conference an Exhbton: Asa an Pacfc Dalan, Chna, 5. [7]Wllam Stallng, Data an Computer Communcaton, Prentce Hall, 4. [8] Mohamma Sharaw Coes an Moulaton for sprea spectrum an broaban wreless communcatons, M. Sc. Thess, Oaklan Unversty, US,. Authorze lcense use lmte to: UIVERSITY TEKOLOGI MALAYSIA. Downloae on January, 9 at 3:43 from IEEE Xplore. Restrctons apply.