Decision processes in Communications Multi-path Access Systems applied within ITS

Transcription

1 Dcision procsss in Communications Multi-path Accss Systms applid within ITS M. Svitk* & T. Zlinka* Faculty of Transport Scincs, Czch Tchnical Univrsity of Pragu, Praha 1, Czch Rpublic *Corrsponding authors: ABSTRACT: Th papr prsnts multi-path communications accss systms dcision procsss applid within ITS (Intllignt Transport Systm. A comptnt dcision procss basd on prcisly quantifid systm rquirmnts using a prformanc indicators tolranc rang rprsnts a critical part of th ITS accss communications systm. Th goal of th dscribd procss is to kp th communications srvic continuously availabl with no influnc on changing conditions in tim and srvd spac. Eithr th family of CALM standards basd systm or th spcifically dsignd and configurd L3/L2 switching rprsnt rlvant a solution for such a multi-path accss communication systm. Th mthod of diffrnt paths srvic quality valuation and th slction of th bst possibl activ communications accss path ar introducd. Th proposd approach is basd on Kalman filtring, which sparats a rasonabl part of nois and also allows th prdiction of th individual paramtrs nar futur bhavior. Th prsntd classification algorithm applid to th filtrd masurd data combind with dtrministic paramtrs is traind using training data, i.., a combination of th paramtrs vctors tim lin and rlvant dcisions. Th classification procss rsults ar dpndnt on th siz and quality of th training sts. KEY WORDS: Intllignt transport systms, prformanc indicators, localization, navigation, multi-path accss, dcision procsss 1 INTRODUCTION Th first stp in addrssing th ITS applications is th analysis and stablishmnt of prformanc rquirmnts on tlmatics applications don in co-opration with th ndusrs and organizations lik th Railways Authority, Road and Motorways Dirctorats, Air Traffic Controls. Th nxt stp rprsnts a dcomposition of th systms rquirmnts to th individual subsystms of th tlmatics chain. Th list of rprsntativ tlmatic prformanc indicators was dvlopd and is widly accptd in structur (Svitk, 2005 or (Svitk & Zlinka, 2006: Safty - risk analysis, risk classification, risk tolrability matrix, tc. Rliability - th ability to prform rquird functions undr givn conditions for a givn tim intrval Availability - th ability to prform rquird functions at th initialization of th intndd opration Intgrity - th ability to provid timly and valid alrts to th usr whn a systm must not b usd for th intndd opration 3

2 Continuity - th ability to prform rquird functions without unschduld intrruptions during th intndd opration Accuracy - th dgr of conformanc btwn a platform s tru paramtrs and its stimatd valus, tc. A substantial part of th prformanc paramtrs analysis rgarding th tlmatics application is rprsntd by th dcomposition of ths paramtrs to individual subsystms of th tlmatics chain, including a proposal for th macro-functions of individual subsystms and information rlations btwn macro-functions. Part of th analysis is th stablishmnt of rquirmnts on individual functions and information linkag so that th whol tlmatics chain should comply with th abov dfind prformanc paramtrs. Th compltd dcomposition of prformanc paramtrs nabld th dvlopmnt of a mthodology for a follow-up analysis of tlmatics chains according to various critria - optimization of th information transfr btwn a mobil unit and th procssing cntr, maximum us of th xisting information and tlcommunication infrastructur, and so on. On of th critria appropriat for transport-tlmatics applications with a Global Navigation Satllit Systm (GNSS is synthsis of th tlmatics systm with minimizd prformanc rquirmnts on a locator, as wll as a communications solution rsulting in th prformanc paramtrs of th tlmatics application to b maintaind. This synthsis dos not rlat only to th tchnical or tchnological part of th solution bcaus th safguarding of prformanc paramtrs of tlmatics applications is to b nsurd by organizational and lgislativ instrumnts as wll. Th transport tlmatics fild dals not only with its own tchnologis of th ITS systms but particularly with organizational, conomic, managrial and othr implmnting instrumnts of such systms, including th valuation of th impact of ITS systms on th carriag of prsons and goods, th accptanc of th approach by drivrs, passngrs, and th incras in th capacity of goods transport. 2 COMMUNICATIONS SOLUTION Tlmatic sub-systm rquirmnts Mobility of th communication solution rprsnts on of th crucial systm proprtis, namly in th contxt of, frquntly, vry spcific systm rquirmnts. Th following communications prformanc indicators quantify communications srvic quality (Svitk & Zlinka, 2006, (Svitk & Zlinka, 2007 or (Zlinka & Svitk, 2007: Availability Srvic Activation Tim Man Tim to Rstor (MTTR Man Tim Btwn Failur (MTBF VC availability Dlay is an accumulativ paramtr and it is influncd by Intrfacs rats Fram siz Load / congstion of all in-lin activ nods (switchs Packt/Frams Loss, and Scurity Prformanc indicators applid for such communications applications must b transformabl into tlmatic prformanc indicators structur and vic vrsa. Th indicators transformability simplifis systm synthsis. Th additiv impact of th communications prformanc indicators vctor tci on th vctor Δtmi of tlmatic prformanc indicators can 4

3 b xprssd by Eq. 1, howvr, only undr th condition that th probability lvls of all studid phnomna ar on th sam lvl and all prformanc indicators ar xprssd xclusivly by paramtrs with th sam physical dimnsions in th dscribd cas in tim or to tim convrtibl variabl (Svitk & Zlinka, 2007: Δ tmi = TM tci (1 Transformation matrix construction is dpndnt on th dtaild communication solution and its intgration into th tlmatic systm. Th probability of ach phnomna apparanc in th contxt of othr procsss is not dply valuatd in th introductory priod, whn th spcific structur of transformation matrix is idntifid. Howvr, ach TM lmnt is consquntly valuatd in svral stps, a procss basd on th dtaild analysis of th particular tlmatic and communications configuration and its apparanc probability in th spcific contxt of th whol systm prformanc. This approach rprsnts a subsqunt itrativ procss managd with th goal to rach a stag whr all minor indicators (rlations ar liminatd and th maor indicators ar idntifid undr th condition that rlvant tlmatic prformanc indicators ar kpt within th givn tolranc rang. Dtails of itrativ mthod ar discussd in (Svitk & Zlinka, 2007 or (Zlinka & Svitk, Th mthod is dsignd as broadly as possibl with th clar aim to b applid in th widst possibl rang of tlmatic applications. This mthod can also b succssfully usd for idntification of CALM critria, i.., th tolranc rang of ach prformanc indicator, to b abl to dcid which altrnativ accss tchnology is, in a spcific tim and spac, valuatd as th bst possibl altrnativ. 2.1 COMMUNICATIONS SOLUTION STRUCTURE Figur 1: Tlmatic chain diagram Figur 1 prsnts a typical tlmatic sub-systm chain diagram (spcifically th solution for th pilot proct Airport (Svitk & Zlinka, 2007 and (Zlinka & Svitk, Th outdoor unit consists of GNSS (Global Navigation Satllit Systm GPS (Global Positioning Systm/Galilo Snsing Systm (SS, On Board control and display Unit (OBU and Wirlss mobil communication units (WL i. Th trrstrial communication part consists of a st of mobil cllular Bas Stations (BS i as wll as th trrstrial ntwork basd on L2 switchs/nods (TN i intrconnctd with Srvrs (S i. On cor tchnology can b slctd as th cor solution, if possibl. Howvr, som aras nd to b covrd by altrnativ solutions. W will discuss th principls of procdurs which support th slction of th bst possibl communications solution quantifid by prformanc indicators and by som othr paramtrs,.g., srvic costs, as wll. Th tchnical implmntation is dscribd by th standard CALM, vn though altrnativ solutions ar also availabl,.g., basd on L3/L2 switching principls. 5

4 Th typical gnral transport tlmatic accss solutions with th combination of a wid rang of accss tchnologis is shown on Fig. 2 (Wall, Figur 2: Transport tlmatics communications accss solutions 2.2 MULTI-PATH ACCESS BASED ON CALM AND L3/L2 SWITCHING. Th family of standards ISO TC204, WG16.1 Communications Air-intrfac for Long and Mdium rang (CALM rprsnts a widly concivd concpt of switching to th bst availabl wirlss accss altrnativ in a givn tim and ara. Th substitution procss of xisting paths by th altrnativ wirlss accss solution is undrstood as th scond gnration of th handovr principl. Both gnrations of th handovr action ar startd basd on an valuation of th prformanc indicators st. BER (Bit Error Rat or packt RTD (Round Trip Dlay ar typical but not th only possibl prformanc indicators usd for dcision procsss in data ntworks. Switching to th altrnativ path is rlvant only if availabl tools of th lowr layr ar alrady unabl to rsolv prformanc limits. Simultanous action on mor layrs can b countrproductiv action. Scond gnration handovr action can b vokd also by th idntification of a mor suitabl altrnativ,.g., by th apparanc of an altrnativ srvic with bttr cost conditions, vn though th xisting altrnativ is tchnically sufficint and saf. An adaptiv communications control systm has th following architctur: 1st layr Cllular Layr (CL - rprsnts th fd-back control procsss of paramtrs lik transmittd powr, typ of applid modulation, tc. Th goal of procsss on this layr is to kp th givn st of managd paramtrs, for xampl Bit Error Rat (BER or Round Trip Dlay (RTD, within th rquird limits 2nd layr th first gnration of handovr (1HL - rprsnts th samlss switching procss btwn diffrnt clls of th sam mobil ntwork. Such an approach is applid in mobil systms lik GPRS, EDGE, UMTS, Mobil WiMax (IEEE or WiFi (IEEE , via th amndmnt IEEE r. Th 1HL layr shars rlvant information with th CL layr (dlivrd usually as on systm so that thr is no risk of countrproductiv simultanously opratd procsss on both layrs - of cours only in th cas it is corrctly dsignd and opratd 6

5 3rd layr th scond gnration of handovr (2HL - is mostly dpndnt only on idntification of th srvic prformanc indicators. Cllular systms ar not usually dsignd as opn systms with appropriat application intr-facs (API so that thr is mostly not a potntial for th intrconnction with th managmnt of ths lowr layrs. It is crtain that th ffctiv managmnt of th 2HL layr can b rachd much mor asily if 1HL and LC layrs shar rlvant information with th managd layr 2HL Communications accss systms usd in transport tlmatics ar: Cllular systms, including 2.5G GSM and UMTS Mobil Wirlss Broadband (MWB with clls usually much largr than UMTS clls today namly communications systms basd on IEEE Std and th up-coming IEEE Std WiFi (IEEE basd diffrnt altrnativs - a, b, g and cllular mod option (802.11r DSRC (5.8GHz M5 basd on standard IEEE p IR (Infra Rad communications solutions IEEE x basd solutions: Blutooth 15.1, UWB (Ultra Wid Band , ZigB Millimtr wav tchnology (62-63GHz usd in conunction with radar signals at similar frquncis Satllit communications xclusivly applid for mrgncy and spcial applications W-USB (Wirlss USB Othr mdia to com Only som of prsntd systms hav cllular architctur. In th cas that th systm is not cllular w can omit th 1HL layr of th prsntd modl. In CALM standard vrtical dcomposition to th individual subsystms is applid for ach communications accss path. Each layr can shar th support of mor altrnativ accss solutions in on subsystm, whn it is possibl and ffctiv. Howvr, managmnt rmains xclusivly and strictly in th horizontal layrs architctur. Th 1HL layr is undrstood only as an optional xtnsion of L2 with no principal influnc on th whol systm architctur. Rlvant information ndd for qualifid dcisions is shard btwn layrs xclusivly via rlvant control systm structurs. CALM architctur is discussd in (Wall, 2006 and (Zlinka & Svitk, CALM applis th xclusivly still not widly sprad IPv6 protocol which allows, du to its xtnsiv abilitis, to continuously rmotly trac activ applid altrnativs. Handovr is accomplishd in CALM xclusivly on th L2 of th TCP(UDP/IP modl, i.., out of TCP/IP comptncs. Handovr comptncs givn to this L2 is a suitabl altrnativ for most of th wirlss solutions. Th authors valuatd CALM an orintation as appropriat approach, howvr, connctd with quit an xtnsiv R&D rprsnting a rmarkabl tim priod. As a rspons to th urgnt nd of an accptabl solution th authors proposd an altrnativ approach basd on L3/L2 TCP/IP switching opratd in a spcific configuration and sttings. This solution is undrstood as only an intrim and, in functionality, limitd substitution, howvr, with a much lss dmanding and thrfor fastr implmntation. 7

6 3 ACCESS PATHS EVALUATION AND THE DECISION PROCESS ON POTENTIAL SEAMLESS SWITCHING TO THE ALTERNATIVE SOLUTION Th following paragraphs dscrib on of th potntial approachs to th dcision procsss, which ar much lss discussd than th switching approachs and thir managmnt. Th proposd mthodology is basd on following principls: Masurd paramtrs ar procssd by th Kalman filtr. Such a procss sparats a rasonabl part of nois and also allows for th prdiction of th individual paramtrs nar futur bhavior A st of masurd paramtrs xtndd by dtrministic paramtrs, for xampl conomical critria is availabl togthr as a vctor x Basd on tim lins of vctor x, it is fasibl to classify th bst possibl tchnology slction. Th classification algorithm is traind using th tim lins of training vctors x and th rlvant slctd paths - s for xampl (Svitk, 2006 This solution dos not ncssarily rquir 2HL communication with th othr layrs, but nvrthlss, it would b a much mor fficint solution if such communication is at last partially possibl in futur implmntations. 3.1 ESTIMATION AND PREDICTION OF MEASURED PERFORMANCE DATA VECTOR P(N Lt us dfin paramtr vctor p( in th tim intrval n. W will suppos that th dynamics of paramtr p( volut basd on th following modl (it is supposd that p(n-1 is know: p ( = A( p( n 1 + b( + q( (2 whr A( is a transition matrix, b( is th dtrministic vctor of constant paramtrs and q( is th vctor of Gaussian nois with th following proprty: E[ q( ] = 0 cov[ q(, q( i ] = 0 for n i (3 cov[ q(, q( i ] = Q( i for n = i Th quations (2 and (3 rprsnt "th volution form of an unknown paramtrs vctor". In many cass w cannot masur th vctor of an unknown paramtr p( dirctly, howvr, w can masur anothr vctor z( that dpnds on unknown paramtrs as follows: z ( = D( p( + r ( + w( (4 whr D( is a transition matrix, r( is a dtrministic vctor of constant paramtrs and w( is th vctor of Gaussian nois with th following proprty: E[ w( ] = 0 cov[ w(, w( i ] = 0 for n i (5 cov[ w(, w( i ] = W ( i for n = i Th quations (4 and (5 rprsnt "th volution form of a masurmnt vctor". Th algorithm for th stimation of a vctor pˆ ( of unknown paramtrs togthr with its covarianc matrix S( can b summarizd: pˆ( = pˆ ( ˆ n + H( ( z( r ( D( n p( (6 S n = S ( H( D( S ( n ( 8

7 whr ( pˆ is an xtrapolatd stimat from th last stp, S n is a covarianc matrix of xtrapolation and H( is th Kalman gain. All th mntiond paramtrs ar possibl to b rcursivly computd from th last stimatd paramtrs charactrizd by p ˆ( n 1, S( n 1 according to th form: pˆ ( = A( pˆ( n 1 + b( S ( = A( S( n 1 A( T + Q( T ( D( S ( D( + W( 1 T H( = S ( D( Equations (6 and (7 ar undrstood as "th Kalman filtring algorithm". Now, w suppos th non-linar volution of an unknown paramtr vctor (2 and a masurmnt vctor (4 through known non-linar functions f(. and h(.: ( f ( p( n 1 + b( q( p = + (8 z ( = h( p( + r ( + w ( (9 Th main ida is to linariz th quations (8 and (9 with th hlp of th first two componnts of Taylor sris in th xtrapolatd valu pˆ ( (xtndd Kalman filtring: ( ˆ 1 f ( p f ( p( n 1 = f p ( ( ( n 1 ˆ + p p ( (10 2 p h( p( n 1 = h ( pˆ ( ( p 1 h + 2 p p=pˆ ( ( p( n 1 ˆ ( p p=pˆ ( Basd on th quations (10 and (11 non-linar quations (8 and (9 ar transformd into a linar form and Kalman filtring could b usd. Kalman filtring can b startd by th first masurmnt z(1. Th initial paramtrs should b st up as: pˆ S ( 1 = H( 1 ( z( 1 r( 1 H 1 T ( D( 1 W( 1 T 1 ( D 1 W 1 D 1 1 T 1 ( 1 = D( 1 W( 1 D( 1 ( 1 = ( ( ( 1 ( (7 (11 ( SWITCHING AS A CLASSIFICATION PROCESS Lt us introduc th vctor x as th vctor carrying information about th valus of prformanc paramtrs in a sampl tim. Th itms of vctor x ar ithr dtrministic or random procsss with th hlp of th Kalman filtring dscribd abov. D Lt us dfin th classification problm as an allocation of th fatur vctor x R to on of th C mutually xclusiv classs knowing that th class of x taks th valu in Ω = { ω 1,...,ω C } with probabilitis P( ω 1,..., P( ωc, rspctivly, and x is a ralization of a random vctor charactrizd by a conditional probability dnsity function p( x ω, ω Ω.This allocation mans th slction of th bst suitd tlcommunication tchnology basd on knowldg of x vctor. A non-paramtric stimat of th ω-th class conditional dnsity providd by th krnl mthod is: N ˆ 1 ω ω x x i f ( x ω = K, N D (13 ω h ω i= 1 hω 9

8 ( whr K is a krnl function that intgrats to on, hω is a smoothing paramtr for ω-th ω ω class, N ω stands for th sampl count in class ω and x 1,...,x Nω is th indpndnt training data. Th dnsity stimat dfind by (13 is also calld th Parzn window dnsity stimat with th window function K(. It is a wll-known fact that th choic of a particular window function is not as important as th propr slction of smoothing paramtr. W us th Laplac krnl dfind by th following Laplac dnsity function: 1 x μ ( f L x; μ, σ = xp (14 2 σ σ whr x R, μ R, σ (0,. Th product krnl is usd with a vctor of smoothing paramtrs hω = ( h 1ω,...,hD ω for ach class ω. Th product krnl dnsity stimat with Laplac krnl is thn dfind as N ω ω D ˆ 1 1, ( xp. = 1 = 1 2 f x ω = x xi N ω i hω, h (15 ω, Smoothing vctors h ω ar optimizd by a psudo-liklihood cross-validation mthod using th Expctation-Maximisation (EM algorithm. To rank th faturs according to thir discriminativ powr th standard btwn-to within-class varianc ratio is mployd. This mthod is basd on th assumption that D individual faturs hav Gaussian distributions. Th fatur vctor x R taks th valu to on of C mutually xclusiv classs Ω = { ω 1,...,ω C }. Th probabilistic masur Q d, i, ( d, ω i, ω of two classs sparability for th fatur d (d-th componnt of fatur vctor is dfind as ( σ i + σ Q ( ω, ω = η d, i, d, i, (16 μ μ whr ω i and ω ar classs and symbol η = 3.0 dnots th ral constant spcifying th intrval takn into account (probability that th obsrvation of a normally distributd random variabl falls in [ μ 3.0 σ, μ σ ] is Th smallr th valu of th masur Q i,,d, th bttr th sparation of th inspctd classs mad by th fatur d is. For Q i,, d < 1 both classs ar compltly sparabl. Th masur is similar to th widly usd Fishr critrion. For multi-class problms, th two-class contributions ar accumulatd to gt a C-class sparability masur Q(d for th fatur d: C ( = Q ( d,i, Q d i= 1 C i = 1 d, i,. All th faturs in th training data ar thn sortd according to thir Q(d masurs. Th function Q(d is similar to a significanc masur of th d-th componnt of a fatur vctor. Th subst of n first faturs is slctd as an output of this individual fatur slction mthod. Th drawback of th mthod is th assumption of unimodality and th fact that only linar sparability is takn into account. On th othr hand, th individual fatur slction mthod basd on th btwn-to within-class varianc ratio is vry fast. Th prsntd classification approach is ffctivly applicabl for rlvant dcision procsss usd to slct th bst possibl altrnativ accss from th st of availabl paths. Th dcision is basd on th valuation of both random, as wll as dtrministic, procsss. Th introducd approach nabls continuous dcision procsss training. Th prsntd mthod allows implmntation to b startd with no information flow btwn th layr 2HL and layrs 1HL and CL. Howvr, th proposd solution is dlibratd i (17 10

9 to b opn for futur xtnsions in information rsourcs to lt th dcision procss improv by th application of potntially availabl information, lik th status of layrs 1HL and CL. 4 CONCLUSION Th main goal of our rsarch is to introduc a nw gnration of Intllignt Transport Srvics (ITS which can b continuously availabl (on a dfind probability lvl. Du to th rgular complxity of aras covrd by tlmatic srvics w hav concntratd on th wirlss accss solution dsignd as samlss switchd combination of mor indpndnt accss solutions, i.., a multi-path accss systm. Th procss of accss solution switching has bn th subct of intnsiv R&D and diffrnt approachs hav alrady bn publishd. On of altrnativs a family of standards CALM - rprsnts a promising rspons to ITS rquirmnts. Howvr, du to th complxity of th proposd solution it is invitabl that a quit rmarkabl amount of tim to rsolv all issus can b xpctd. Th proposd altrnativ approach, basd on L3/L2 TCP/IP switching opratd undr a spcific configuration and sttings, is undrstood only as a potntial intrim and, in functionality, a limitd substitution, howvr, with much lss dmanding and thrfor fastr implmntation conditions compard, for xampl, to th ons of CALM. Th mthod of diffrnt paths valuation and th dcision procss background has not bn as widly discussd as th cor switching altrnativs. On of th possibl approachs was studid and th cor principls of th proposd solution ar prsntd. Th masurd paramtrs of all availabl altrnativ accss paths ar procssd by th Kalman filtr with th aim of sparating a rasonabl part of th data nois. Th Kalman filtr also allows for th prdiction of th individual paramtrs nar futur bhavior. Th filtrd flow of th masurd paramtrs vctors can thn b xtndd by dtrministic paramtrs, for xampl th conomical critria. Th rsultant vctor x tim lin allows th classification of th bst possibl tchnology slction from thos for which th rlvant tim lin of vctors x is availabl. Th classification algorithm is basd on th training procdur using rlvant training data i.. a lin of training vctors x and rlvant to data slctd paths. Du to th fact that only linar sparability is takn into account, th individual fatur slction mthod basd on th btwn-to within-class varianc ratio rprsnts a vry swift approach. Th prsntd classification approach is applicabl for rlvant dcision procsss on th top layr of th communications systm managmnt to slct th bst possibl accss altrnativ from th st of availabl paths. Th dcision is basd on an valuation of both random, as wll as dtrministic procsss, and th introducd approach nabls continuous dcision procsss training, as wll as th futur information rsourcs xtnsion obtaind namly from potntially availabl lowr layrs of th multilayr adaptiv communications managmnt systm. REFERENCES Svitk, M., Architctur of ITS Systms and Srvics in th Czch Rpublic. Intrnational Confrnc Smart Moving 2005, Birmingham, England. Svitk, M., Intllignt Transport Systms - Architctur, Dsign mthodology and Practical Implmntation. Ky-not lsson, 5th WSEAS/IASME Int. Conf. on Systms Thory and Scintific Computation, Malta. 11

10 Svitk, M., Zlinka, T., Communications Tools for Intllignt Transport Systms. Procdings of 10th WSEAS Intrnational Confrnc on Communications, Athns, pp ISSN , ISBN Svitk, M., Zlinka, T., Communications Solutions for ITS Tlmatic Subsystms. WSEAS Transactions on Businss and Economics, Issu 4 (2006, Vol. 3, Athns, pp , ISSN Svitk, M., Zlinka, T., Tlcommunications solutions for ITS. Towards Common Enginring &Tchnology for Land, Maritim, air and Spac Transportation ITCT 2006, CNISF, Paris, pp Svitk, M., Zlinka, T., Communication solution for GPS basd airport srvic vhicls navigation. EATIS 97 ACM-DL Procdings, Faro (Portugal, ISBN # Svitk, M., Zlinka, T., Communication solution for Vhicls Navigation on th Airport trritory. Procdings of th 2007 IEEE Intllignt Vhicl Symposium, Istanbul, Turky, pp , IEEE Catalogu numbr 07TH8947, ISBN Svitk, M., Zlinka, T., Communications Environmnt for Tlmatic Subsystms. Procdings of 11-th World Multi-Confrnc on Systmic, Cybrntics and Informatics, Volum II, IIIS/IFSR, Orlando, FL, pp , ISBN-10: , ISBN-13: Svitk, M., Zlinka, T., Communications Challngs of th Airport Ovr-ground Traffic Managmnt. Procdings of th 11th WSEAS Intrnational Multi-confrnc CSCC, Volum Advancs in Communications, Agion Nikolaos, Crt Island, Grc, pp , ISSN , ISBN Zlinka, T., Svitk, M., Communications Schm for Airport Srvic Vhicls Navigation. Procdings of Intrnational Confrnc TRANSTEC Pragu, Czch Tchnical Univrsity, Faculty of Transport Scinc and Univrsity of California, Santa Barbara, Praha, pp , ISBN Zlinka, T., Svitk, M., Communication Schm of Airport Ovr-ground Traffic Navigation Systm. Procdings of th Intrnational Symposium on Communications and Information Tchnologis - ISCIT IEEE Sydny, IEEE Catalogu No. 07EX1682(C, ISBN , Library of Congrss Wall, N., CALM - why ITS nds it. ITSS 6 (Sptmbr. Zlinka, T., Svitk, M., CALM - Tlcommunication Environomnt for Transport Tlmatics. Tchnology & Prosprity, Vol. XI, spcial dition (Nov./06, ISSN Svitk, M., Dynamical Systms with Rducd Dimnsionality. Nural Ntwork World dition, II ASCR and CTU FTS, Praha, ISBN: , EAN: