Algoritmi de rutare bazai pe informaiile de poziie ale nodurilor ntr-o reea ad-hoc

Proiect realizat n cadrul cursului Reele de Calculatoare i Internet"*Petru Andrei An 2 Master IISC

Introducere in retele de senzori wireless / ad-hocAlgoritmi de rutareGeneralitatiParametrii criticiAlgoritmul A: LARAlgoritmul B: DREAM

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Ce este un senzor wireless?SoC compus din:Procesor consum redusPutere de procesare limitataMemorieCapacitate redusaModul radioRata de transfer micaRaza de acoperire redusaSenzoriScalariCamere de captura, microfoaneSursa energie

SensorsProcessorRadioStoragePOWER

Fig. 1 modulele componente ale unui nodFig. 2 exemple de noduri WSN (incapsulat si SMD)*

Ce este o retea de senzori wireless?Este compusa din mai multi senzori wireless (noduri)

Proprietati:Puternic limitate dpdv energetic(compromis performanta/autonomie)Self-management, Self-organizingScalabile (numar mare de noduri)Heterogene (noduri organizateierarhic,dispozitive cu diferite capabilitati)AdaptabileSecuritate sporita

Fig. 3 retea WSN cu senzori distribuiti aleator*

Diferente intre WSN / WAN

Retelele de senzori sunt mai denseRetelele de senzori sunt predispuse la erori/failuresTopologia retelelor de senzori de schimba foarte desWSN trimite mesajele broadcast, pe cand in retelele ad-hoc comunicarea este point-to-pointNodurile din WSN pot sau nu sa aiba identificator unic global*

Aplicatii ale retelelor de senzori wireless

MonitorizareScop stiintific, aplicatii in ecologie.Informatii spatio-temporale in timp realAccesul la zone restrictionateSupraveghere si urmarireRecunoastereControlul perimetruluiMedii inteligenteAgriculturaProcese industriale*

Aplicatii ale retelelor de senzori wirelessMonitorizare

Fig. 4 o implementare WSN in scop de monitorizare a unui obiectiv*

Aplicatii ale retelelor de senzori wirelessSupraveghere si urmarire

Fig. 5 o implementare WSN in scop militar, de recunoastere*

Aplicatii ale retelelor de senzori wirelessFig. 6 implementari WSN in aplicatii consumer*

Algoritm de rutare -> serviciu Funcii:Defineste procedurile si infrastructura pentru transmiterea mesajelor/datelor intre nodurile reteleiAsigura flexibilitate si adaptabilitate reteleiUn algoritm de rutare eficient va contribui semnificativ la: autonomia generala a sistemului, confidentialitatea datelor transmiseFig. 7 frame-ul pachetului intr-o retea TDMAFig. 8 o retea WSN*

Ce folosesc informatiile de pozitie ale nodurilor in retea:

GPSR Greedy Perimeter Stateless RoutingLocation-aware long-lived route selectionDREAM Distance Routing Algorithm for MobilityLAR Location Aided RoutingFig. 9 GPSR (rutare geografica)Fig. 10 retea WANFig. 11 LAR (rutarea asistata de localizare)*

Parametrii critici pentru algoritmii de rutare:Eficienta de rutare (correct destination high hit rate)Evitarea buclelor de rutareAlegerea rutelor optimeViteza de rutarePerioada mica de convergenta a reteleiRata ridicata de transfer a pachetelor in reteaEficienta energeticaComplexitatea implementarii

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Foloseste doar informatii geo pentru descoperirea rutelor si se bazeaza pe un protocol de rutare on-deman (gen Ad-hoc on demand distance-vector routing)Daca emitorul cunoaste o pozitie anterioara a receptorului cat si viteza acestuia de deplasare, el va calcula o arie unde este posibil sa se afle receptorul in momentul actual (expected zone)Astfel, se va minimiza efectul de flood a pachetelor menite sa identifice rutelePachetele sunt trimise doar in expected zoneDaca un nod din exteriorul acestei zone primeste un astfel de pachet, il ignoraDaca nodul destinatie primeste pachetul, acesta raspunde cu pozitia sa curenta si viteza de deplasareAtunci cand un nod intra in retea, acesta nu cunoaste informatiile de pozitie a celorlalte noduri, motiv pentru care nodul face fall-back si va folosi protocolul fundamental de rutare (flood the entire network)

*Fig. 13 LAR (rutarea asistata de localizare)

Pentru ca LAR sa aduca un beneficiu peste traditionalul flood, reteaua trebuie sa fie stabila! LAR va fi eficient in cadrul retelelor dinamice (si/sau) cu noduri care dispar, insa eficienta va fi scazuta atunci cand apar noduri noi.

Avantaje:Se evita floodarea inutila a intregii retelePerformante ridicate chiar si in retele puternic dinamice

DezavantajeDaca reteaua nu este stabila, algoritmul este ineficientPerformantele sunt scazute in retelele in care fluxul de intrare a nodurilor noi este ridicat

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Fiecare nod isi cunoaste pozitiaFiecare nod isi comunica adresa si pozitia in reteaCand se trimite un pachet, acesta este inaintat numai pe directia nodului receptorApare efectul de distanta:Nodurile apropiate intre ele isi trimit informatii unul celuilalt mai des decat nodurile intre care exista o distanta mai mareCand un pachet este transmis de la nodul A catre nodul mai departat B, informatiile despre pozitia nodului B se detaliaza pe masura ce pachetul se propaga in reteaCand un nod isi schimba pozitia dez, acesta trimite mai frecvent informatii vecinilor sai*Fig. 12 GPSR (rutare geografica)

Frecventa de actualizare/notificare a informatiilor de pozitie a unui nod A catre nodul B este dependenta de distanta dintre aceste noduri. Informatiile de pozitie constau in coordonate, ci nu in cai de rutare!

Avantaje:Permite o scalabilitate ridicata a reteleiAlgoritmul are o eficienta de rutare buna

DezavantajeTrebuie rezolvata problema achizitiei informatiilor de pozitie pentru fiecare nod (prin GPS = cost ridicat dpdv al eficientei energetice)

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P. Bahl and V. N. Padmanabhan. Radar: An in-building RF-based user location and tracking system. In Proc. IEEE INFOCOMM, paginile 775784, 2000.N. Bulusu, J. Heidemann, and D. Estrin. GPS-less low cost outdoor localization for very small devices. IEEE Personal Communications, 7(5):28-34, 2000. Special Issue on Smart Spaces and Environments.S. Capkun, M. Hamdi, and J.-P. Hubaux. GPS-free positioning in mobile ad-hoc networks. In Proc. of 34th HICSS, volume 9, pagina 9008, 2001.B. Kusy, M. Maroti, G. Balogh, P. V Olgyesi, J. Sallai, A. Nadas, A. Ledeczi, and L. Meertens. Node density independent localization. In Proc. of IPSN, paginile 441-448, 2006.K. Pister L. Doherty and L. EI Ghaoui. Convex optimization methods for sensor node position estimation. In Proc. of IEEE INFOCOMM, paginile 1655-1663, 2001.R. Nagpal, H. E. Shrobe, and J. Bachrach. Organizing a global coordinate system from local information on an ad hoc sensor network. In Proc. of IPSN '03, paginile 333-348, 2003.D. Niculescu and B. Nath. SpotON: An indoor 3-d location sensing technology based on RF signal strength. Technical Report Report #200002-02, Department of CSE, University of Washington, Feb. 2000.D. Niculescu and B. Nath. Ad hoc positioning system (APS). In Proc. of GLOBECOMM, volume 5, paginile 2926-2931, 2001.D. Niculescu and B. Nath. Ad hoc positioning system (APS) using aoa. In Proc. of IEEE INFOCOMM, paginile 1734-1743, 2003.A. Savvides, C. C. Han, and M. B. Srivastava. Dynamic fine-grained localization in ad-hoc networks of sensors. In Proc. of MobiCom, paginile 166-179, 2001.A. Savvides, H. Park, and M. B. Srivastava. The n-hop multilateration primitive for node localization problems. Mobile Networks and Applications, 8(4):443-451, 2003.A. Vargas. The OMNeT++ discrete event simulation system. In Proc. of ESM), paginile 319-324, 2001.

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*Algoritmi de rutare bazai pe informaiile de poziie ale nodurilor ntr-o reea ad-hoc

Proiect realizat n cadrul cursului Reele de Calculatoare i Internet"

*http://www.linuxonly.nl/docs/1/74_Geographical_routing_protocols.html*The Location Aided Routing Protocol (LAR, [Ko00]) only uses geographical information for route discovery. It is based on an on-demand protocol, like AODV. If the sender knows where the destination was at some time and it knows its speed, it can determine in which area the destination is now. This area is called the expected zone. LAR uses this to limit the flooding of route discovery packets. Packets are flooded within an defined area containing both the source and the expected zone. When a node outside this area recieves a packet, it ignores it. When the destination receives the route discovery packet, it returns it with its current location and speed, which can assist in future route discoveries.

When a node enters the network, it has no information about the geographical position of other nodes. LAR will then fall back to the underlying protocol, which floods the route discovery packet. For LAR to be an improvement over flooding, the network has to be stable. LAR will perform well for moving nodes and disappearing nodes, but not when a lot of new nodes are added to the network. Furthermore, connections in the network has to be stable. If nodes connect to many other nodes for a short time, location information will not be available or accurate enough to make use of LAR.*For LAR to be an improvement over flooding, the network has to be stable. LAR will perform well for moving nodes and disappearing nodes, but not when a lot of new nodes are added to the network. Furthermore, connections in the network has to be stable. If nodes connect to many other nodes for a short time, location information will not be available or accurate enough to make use of LAR.*The DREAM protocol was proposed in [Bas98]. It assumes that each node knows its own location. Each node then communicates its address and location through the network. When a packet is sent, it is sent to the direction of the receiving node.

DREAM makes use of what is called the distance effect: the greater the distance separating two nodes, the slower they appear to be moving with respect to each other. Neighbours close by are frequently informed of the location of a node; nodes which are farther away only occasionally receive this information. The further a packet travels to its destination, the more detailed the position of the destination becomes.

Furthermore, DREAM takes into account the mobility of the nodes. When a node travels fast, it frequently sends its location information to its neighbours.

DREAM is similar to HSLS in that the update frequency is dependant on the distance to a node, only it uses coordinates instead of routing paths. This makes it very well scalable, but introduces the problem of determining the location for each node.*

DREAM is similar to HSLS in that the update frequency is dependant on the distance to a node, only it uses coordinates instead of routing paths. This makes it very well scalable, but introduces the problem of determining the location for each node.**