4743

4462

كارشناسي ارشد

مخابرات

اصفهان،دانشگاه صنعتي اصفهان، دانشكده برق و كامپيوتر

1388

ده،105،[I]ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

فرامرز هندسي، ابوالقاسم زيد آبادي نژاد

17/8/88

پژمان خديوي، مهدي مهدوي، مسعود رضا هاشمي

مهندسي برق و كامپيوتر

ID4462

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Enhancing IEEE 802 11 protocol with beam forming Azam Samie Ghahfarrokhy azam samie@ec iut ac ir Date of Submission April 25 2009 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Faramarz Hendessi hendessi@cc iut ac irAbolghasem Zeidaabadi Nezhad zeidabad@cc iut ac irAbstractIn recent decades rapid growth of wireless Ad Hoc networks has led to network connectivity with completelack of central control and wired backbone Increasing demand for accessing information has made undeniablyessential increase in the wireless Ad Hoc networks This expansion is impossible without efficient use ofbandwidth and network capacity increment In addition to limited bandwidth in all wireless networks powerlimited batteries in wireless Ad Hoc networks result in power consumption constraint Many solutions havebeen proposed to solve these problems Conventionally Omni directional antennas are used Omni directionalantennas spread energy over a large region of space while small portion is received by the intended receiver Furthermore Omni directional transmission results in higher interference and lower network capacity Therefore the battery is used inefficiently and the network lifetime decreases It causes not only unnecessaryinterference to other nodes but also network capacity reduction It is shown that directional antennas reduce interference and consequently increase network capacity Besides directional antennas significantly enhance power consumption Nevertheless using directionalantennas in wireless Ad Hoc networks inherently introduce new kinds of problems arising from directivity andsome other serious challenges Thus directional transmission sometimes decays network throughput Asolution to this problem is to modify traditional protocols or design a new protocol which is suitable for supportof directional antenna features Therefore there is a strong demand for the design of a new protocol which willbe efficient enough In this thesis the effort is made to modify IEEE 802 11 standard and enhance network throughput andreduce power consumption reduction by using multi beam directional antennas In the proposed scheme eachnode is equipped with a switched beam antenna system which can switch between M fixed beam patterns Theantenna system can operate in two separate modes Omni and Directional Neighbor s information such asappropriate beam for communication minimum transmission power level deafness status is maintained inNeighbor Table Initially the Neighbor Table is empty and it is continuously updated upon overhearing anytransmission Transmission will take place based on this information There is no need for acquiring thisinformation in the upper layer or use additional hardware Each node keeps maximum admissible power andNAV duration for each of its beams dynamically through the Angle Table If the channel is busy and requiredtransmission power is less than admissible power in that direction new communication is allowed Simulationresults in NS 2 show remarkable performance improvement in comparison with IEEE 802 11 protocol Key Words 1 Ad Hoc Networks 2 Power control 3 Network throughput 4 IEEE 802 11 5 Directional antennas 6 Medium Access Control

فرامرز هندسي، ابوالقاسم زيد آبادي نژاد

پژمان خديوي، مهدي مهدوي، مسعود رضا هاشمي