Reducing Scanning Latency in WiMAX Enabled VANETs

Syed Hassan Ahmed, Safdar Hussain Bouk and Dongkyun Kim

Presenter: Sungwon Lee (PhD Student)

School of Computer Science & Engineering, Kyungpook National University,

Daegu, Republic of Korea.

Agenda

• Introduction.o VANETs.

o WiMaX. (802.16)

• WiMaX in VANETs.

• Handover Issues.

• Scanning Delay.

• Scanning in Conventional 802.16.

• Proposed Scheme.

• Results.

Introduction

Vehicular Ad-hoc Networks (VANETs)

• VANETs mostly have three applications:o Road Safety Applications.

o Traffic Efficiency Applications.

o Value-added applications.

• IEEE 802.11p:o Dedicated for vehicular environment.

o No channel scanning required.

o However, data transfer speed and coverage is noticeably insufficient.

o Non-safety applications are not supported by 802.11 stack smoothly.

o Vehicles may have multiple interfaces such as WiMaX, LTE, etc..

WiMaX in VANETs

Image from: Msadaa, Ikbal Chammakhi, Pasquale Cataldi, and Fethi Filali. "A comparative study between 802.11p and mobile WiMAX-based V2I communication networks." In Next Generation Mobile Applications, Services andTechnologies (NGMAST), 2010 Fourth International Conference on, pp. 186-191. IEEE, 2010.

Introduction…

WiMaX

• IEEE 802.16 Std is introduced in 2004.

• It supports Line of Sight (LoS) and Non-LoS both with advanced speed and range.

• IEEE 802.16e amendments made in 2005 are even more efficient and are supporting more dynamic topologies likewise VANETs.

• Mobile WiMaX have several issues:o Routing.

o MAC Layer issues.

o Transport.

o Handover.

Handover Issues in WiMaX

• For seamless connectivity MS moving from one RSU to another RSU requires to perform handover.

• The overall handover latency:• Scanning Delay [90%].• Authentication.• Association.

• One solution is to broadcast neighbor RSU list periodically and let MS decide target RSU, but it will be cost extra time.

Scanning in Conventional 802.16

• Scanning is performed for each available channel within a network. (e.g. 16 in case of WiMaX).

• 802.16e supports sending Probe by MS and wait for DL message from target RSU.

• S-RSU provides list of neighbors to MS and then each channel is listened by MS.

• Synchronization and association is performed later.

• Extra latency occurs due to this procedure.

• Main Objective is to reduce overall handover delay by re

ducing scanning delay.

• Network assisted handover.

• MS is required to share its destination with S-RSU.

• Each S-RSU maintains a table:

• MS’s arrival time.

• Speed.

• Moving direction.

• S-RSU autonomously selects T-RSU on the basis of MS movi

ng direction.

• T-RSU is updated with MS’ ID and its arrival time.

• MS is provided with the dedicated channel info of T-RSU

before it reaches exit point of S-RSU.

Proposed Solution

Proposed Solution• MS moving from X –Y and Y-Z.

• Connection time (Tc) is calculated by:

,where Tr is the transmission range and Vs is the MS’s Speed.

• S-RSU calculates one Th value for each MS by:

Dist is the remaining distance of Tr and d is the remaining distance between MS and S-RSU

• Time required for covering the Remaining Tr distance:

TrTc

Vs

Dist Tr d

DistTh

Vs

• S-RSU periodically calculates Th to start HO Process.

Proposed Solution…

• Seamless Data Communication (DC) is ensured.

• DATA-ReQ and DATA_Res are included in DC.

• S-RSU informs MS about HO process initiation.

• MS only listen to the channel of T-RSU and performs association directly.

• Thus joins new T-RSU without extra delays.

Simulation Environment

• Network Simulator 2.

• Varying speed of MS: 8m/s to 20m/s.

Results

• Total time required tofinish scanning.

• Conventionally, a vehicle should continue scanning until it finds its T-RSU.

• More speed doesn’t allow MS to select appropriate T-RSU.

• Proposed scheme allows T-RSU selection by S-RSU.

• No effect on varying speed.

Results..

• Scanning iterations.

• The existing solutionrequires the scanning to be performed multiple times, especially when the moving speed is slow.

• Proposed scheme provides dedicated channel info for scanning.

• Only one channel is scanned in our scheme.

Future Work• Future work includes the implementation of our sch

eme for overall network throughput in case of multi

ple vehicles with various speed.

• Adapting the same concept in future network hand

overs is challenging, however, it can be beneficial.

• More advanced QoS metrics can be introduced to

evaluate the performance of proposed scheme.

Thanks for Listening…

Q/A Session

Contact: Syed Hassan Ahmed. PhD Research Scholar,

Kyungpook National University.Email: hassan@monet.knu.ac.kr

Website: http://shahmed.infoSkype: hassan_knu