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Title:MEHANIZMI REŠEVANJA PROBLEMA SKRITEGA VOZLIŠČA V IEEE 802.15.4/ZIGBEE BREZŽIČNIH SENZORSKIH OMREŽJIH
Authors:Pešović, Uroš (Author)
Čučej, Žarko (Mentor) More about this mentor... New window
Files:.pdf MAG_Pesovic_Uros_2010.pdf (4,29 MB)
 
Language:Slovenian
Work type:Master's thesis (m2)
Organization:FERI - Faculty of Electrical Engineering and Computer Science
Abstract:V magistrski nalogi opisujemo energetsko učinkovite metode dostopa do prenosnega medija (MAC), ki se uporabljajo v brezži čnim senzorskih omrežjih (BSO). Brezžična senzorska omrežja so sestavljena običajno iz velikega število senzorjev, ki s komunikacijskega vidika predstavljajo vozlišča. BSO se uporabljajo v različnih aplikacijah daljinskega upravljanja in zaznavanje, kot so na primer: varovanje in hišna avtomatizacija, okoljski nazor in nadzor v zdravstveni oskrbi, vojaška uporaba, itd. Pogosto so, na določenem območju, razporejeni brez vnaprejšnjega načrtovanja. V takšnih omrežjih potrebujemo mehanizme, ki omogočajo samoorganizacijo, za komunikacijo z centralnim vozliščem, ki predstavlja podatkovni ponor. Eden od glavnih ciljev pri snovanju brezžičnih senzorskih omrežij je zmanjšanje skupne porabe energije, da bi omogočili nekaj mesecev ali celo let avtonomnega delovanja pri baterijskem napajanju. Poraba energije v BSO je odvisna od različnih dejavnikov, kot so: lastna poraba procesorja in senzorja, oddajna moč, količine prometa, itd. Porabo električne energije bomo lahko omejimo s skrbno izbiro komponent, z nižanjem oddajne moči in z ustreznimi komunikacijskim protokoli, ki omogočajo uporabo dolgih obdobij nedejavnosti, ko so naprave v načinu spanja. Dosedanje raziskave na tem področju so bile usmerjene k možnostim posodobitev protokolov MAC plasti v IEEE 802.15.4 WPAN (Wireless Personal Area Networks). Protokoli dostopa do prenosnega medija, uporabljenih v tovrstnih omrežjih, temeljijo na pristopu mediju z izogibanjem trčenj CSMA/CA (Carrier Sense Medium Access with Collision Avoidance). Glavna pomanjkljivost tega protokola je nesposobnost za spopadanje s problemom skritih vozlišč, ki pa je zelo pogost v vseh tipih brezžičnih omrežij. Trki paketov povzročajo nepotrebne izgube energije in degradacija zmogljivosti omrežij. Z uporabo RTS/CTS usklajevalnih mehanizmov, znanih iz IEEE 802.11 omrežij, je mogoče problem skritih vozlišč v celoti odpraviti. Mehanizem te vrste dostopa do medija zagotovi posredno sinhronizacijo med vozlišči, kar lahko zelo pove ča učinkovit uporabe prenosnega medija. V prvem delu magistrske naloge smo raziskali količino bitnih napak v paketih, v odvisnosti od interferenčnih paketov. Obstoječa dognanja upoštevajo vpliv interference enako kot šume ozadja. S simulacijami pa smo pokazali, da je bolje, če vpliv interference na količino bitnih napak, obravnavamo ločeno. Na podlagi meritev in simulacij smo izdelali empirični model, ki smo ga nato uporabili drugem delu raziskav. V drugem delu raziskav smo raziskali učinke skritih vozlišcč na interference paketov ob uporabi standardnih CSMA/CA mehanizmih dostopa mediju, ki se uporabljajo v omrežjih tipa IEEE 802.15.4/ZigBee. Rezultati simulacij kažejo, v primeru prisotnosti skritih vozliš č, hudo poslabšanje energetske učinkovitosti ter zmogljivosti omrežja iz stališča prepustnosti in zakasnitev paketov. Na koncu smo raziskovali učinkovitost ideje, da bi uporabili znane RTS/CTS mehanizme rokovanja tudi v BSO. Rezultati simulacij kažejo,da predlagani mehanizem pomaga popolnoma prepreči trčenja zaradi skritih vozlišč. Prav tako se je izkazalo, da v pogojih, kjer so prisotna skrita vozlišča pride do izboljšanja zmogljivosti omrežja, še posebej v pogojih velikega prometa. Zaznali pa smo tudi nekaj pomanjkljivosti. Glavna pomanjkljivost tega mehanizma je v velikem povečanju zakasnitev v pogojih povečanega prometa, kar omejuje njegovo uporabnost. To nam predstavlja tudi motivacijo za nadalje delo, ker bomo raziskovali nove mehanizme dostopa do prenosnega medija, ki bodo imeli boljše lastnosti v pogojih delovanja v omrežjih skritimi vozlišči.
Keywords:Skrito vozlišče, Brezžično senzorsko omrežje, IEEE 802.15.4, ZigBee, MAC, RTS/CTS
Year of publishing:2010
Publisher:[U. Pešović]
Source:Maribor
UDC:004.451.6:[621.397.12:681.586]
COBISS_ID:14087446 Link is opened in a new window
NUK URN:URN:SI:UM:DK:QM69UQOR
Views:2184
Downloads:170
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Categories:KTFMB - FERI
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Secondary language

Language:English
Title:HIDDEN NODE AVOIDANCE MECHANISM FOR IEEE 802.15.4/ZIGBEE WIRELESS SENSOR NETWORKS
Abstract:HIDDEN NODE AVOIDANCE MECHANISM FOR IEEE 802.15.4/ZIGBEE WIRELESS SENSOR NETWORKS Key words: Hidden node, Wireless sensor network, IEEE 802.15.4, ZigBee, MAC, RTS/CTS UDK: 004.451.6:[621.397.12:681.586] This master thesis describes techniques for energy efficient access to the transmission medium (MAC) used in Wireless Sensor Networks (WSN). Wireless sensor networks typically consist of a large number of sensors, which from communications aspects are called nodes. These networks are used in a variety of applications such as security and home automation, environmental and health care monitoring, military applications and many others. They are often deployed without pre-planning in a given area. They need mechanisms, which enable the self-organization, to communicate with a central node, which is called data sink. One of the main objectives in wireless sensor networks is to reduce overall energy consumption to achieve a months or even years of autonomous work powered with single battery. Energy consumption in WSN depends on the various factors such as consumption of processor and sensor, transmitting power, amount of traffic, etc. Energy consumption can be reduced by careful selection of low power devices and the relevant communication protocol, which use long periods of inactivity to take full advantage of low power sleep modes of the device. Current research is aimed at possible updates of Medium Access Control (MAC) layer in IEEE 802.15.4 Wireless Personal Area Networks (WPAN). MAC protocols used in such networks based on the approach to collision avoidance Carrier Sense Medium Access with Collision Avoidance (CSMA/CA). The main disadvantage of this protocol is the inability to deal with the problem of hidden nodes, which is a very common problem in all wireless networks. Consequence of this problem is a packet collisions that cause unnecessary energy loss and degradation of network performances. Using RTS/CTS handshake mechanisms, known from the IEEE 802.11 networks, the packet collisions caused by hidden nodes, can be totally eliminated. This type of media access mechanism provides indirect synchronization between nodes, which can lead to very effective use of the transmission medium. Amount of bit errors in packets as a function of interfering packets was studied, in order to understand the nature of packet collision. State of the art knowledge treats interference effect on the same way as the background noise. Simulations shown that the impact of interference on the amount of bit errors needs to be taken separately from background noise. Based on the measurements and simulations an empirical model was developed which was used in later stages of research. In second part of research examines effects which hidden node caused collisions have on the network performances in case of standard CSMA/CA medium access mechanisms, used in IEEE 802.15.4/ZigBee networks. The simulation results indicate severe degradation of energy efficiency and network performances which were caused by hidden nodes where network throughput is significantly reduced and packet delivery time is increased. At the end, effectiveness of the proposed RTS/CTS handshake mechanisms was examined on the prevention of the hidden nodes caused collisions in the WSN. The simulation results show that the proposed mechanism helps to completely prevent collisions due to hidden nodes. Also network performances will be improved, especially in conditions of high network traffic. The main disadvantage of this solution is in the large increase in delay at high load traffic conditions, which limits its usefulness. This is also our motivation to continue research work to develop the new MAC mechanisms, which will have better features in the WSN operating conditions in the presence hidden nodes.
Keywords:Hidden node, Wireless sensor network, IEEE 802.15.4, ZigBee, MAC, RTS/CTS


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