Reducing Scanning Latency in WiMAX Enabled VANETs
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Reducing Scanning Latency in WiMAX Enabled VANETs
- 1. 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.
- 2. Agenda • Introduction. o VANETs. o WiMaX. (802.16) • WiMaX in VANETs. • Handover Issues. • Scanning Delay. • Scanning in Conventional 802.16. • Proposed Scheme. • Results.
- 3. 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..
- 4. WiMaX in VANETs Image from: Msadaa, Ikbal Chammakhi, Pasquale Cataldi, and Fethi Filali. "A comparative study between 802.11 p and mobile WiMAX-based V2I communication networks." In Next Generation Mobile Applications, Services and Technologies (NGMAST), 2010 Fourth International Conference on, pp. 186-191. IEEE, 2010.
- 5. Introduction… WiMaX • IEEE 802.16 Std is introduced in 2004. • It supports Line of Sight (LoS) and Non-LoS both with adv anced speed and range. • IEEE 802.16e amendments made in 2005 are even more efficient and are supporting more dynamic topologies lik ewise VANETs. • Mobile WiMaX have several issues: o Routing. o MAC Layer issues. o Transport. o Handover.
- 6. 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.
- 7. Scanning in Conventional 802.16 • Scanning is performed for eac h available channel within a n etwork. (e.g. 16 in case of Wi MaX). • 802.16e supports sending Pro be by MS and wait for DL me ssage from target RSU. • S-RSU provides list of neighb ors to MS and then each chan nel is listened by MS. • Synchronization and associati on is performed later. • Extra latency occurs due to this procedure.
- 8. • 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
- 9. 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 t he remaining distance between MS and S-RSU • Time required for covering the Re maining Tr distance: Tr Tc Vs Dist Tr d Dist Th Vs • S-RSU periodically calculates Th to sta rt HO Process.
- 10. 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.
- 11. Simulation Environment • Network Simulator 2. • Varying speed of MS: 8m/s to 20m/s.
- 12. Results • Total time required to finish 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.
- 13. Results.. • Scanning iterations. • The existing solution requires 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.
- 14. 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.
- 15. 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.info Skype: hassan_knu
Editor's Notes
- Good afternoon Everyone ! I would like to appreciate the efforts of all session chairs for arranging such an informative event. My name is Sungwon Lee and I am pursuing my PhD from Kyungpook National University, Republic of Korea. Unfortunately, my lab mate Mr. Hassan couldn’t receive the visa to come here and present his work. That’s why I have been assigned to present this work on behalf of actual authors. Before I start my presentation, I would like to declare that I will try to answer any query, however, if you have some in-depth questions, please feel free to contact Mr. Hassan. Let’s come to the paper, whose title is “Reducing Scanning Latency in WiMAX Enabled VANETs”.
- This is the agenda of today’s presentation. First of all, I will briefly introduce, VANETs and WiMaX, because most of us have already conceptual information of these terms. Then I will use one slide for showing integration of WiMaX in VANETs. Beside the other issues, one of the key issue targeted in this paper is handover issue. With in handover, we have several steps. I will show later. What is scanning, and how it effects the handover process? It will be answered in coming slides. Then I will try to explain the proposed work and results.
- Just because this paper deals with vehicular environment, we cannot avoid talking about 802.11p. Before that we have some known applications for VANETS. VANETs mostly have three applications: 1. Road Safety Applications. 2. Traffic Efficiency Applications. 3. Value-added applications. IEEE 802.11p: This protocol is Dedicated for vehicular environment. No channel scanning required in IEEE 802.11p and this makes it to skip association and authentication steps. Thus we can say that 802.11p provides Less secure communication. Also data transfer speed and coverage is noticeably insufficient. It is find not suitable for particularly Non-safety applications. On other hands we have several research projects supporting the fact that Vehicles may have multiple interfaces such as WiMaX, LTE, etc..
- In this slide we can easily see the difference between deploying 802.11 and 802.16 infrastructures. This figure has been taken from other resource, reference is given downside. We can see the difference in terms of coverage area. In case of 802.11p, we only can cover about 1.5 KM, so it means in order to cover 13 Km road strip, we may require more than 3 RSUs. However, in case of WiMaX we only require 2 RSUs covering the doubled road segment, i.e. 26 KM. Because of its wide coverage range such as 20km.
- The IEEE 802.16 Std is introduced in 2004. It supports Line of Sight (LoS) and also 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. These features make WiMaX best solution as compared to 802.11p.0 However, Mobile WiMaX requires several secure communication steps and have several issues such as: Routing. MAC Layer issues. Transport. Handover. Our paper focuses on Handover issues.
- For seamless connectivity MS moving from one RSU to another RSU requires to perform handover. The overall handover latency is caused by the following factors: Scanning Delay which contributes up to 90% in overall handover latency. Other factors are also involved in handover process in 802.16e such as: 1. Authentication. 2. Association. But these factors are not that much cause of increased latency. One solution to reduce latency is to broadcast neighbor RSU list periodically and let MS decide target RSU, but it will be cost extra time. But still MS has to decide the target RSU and it will cost us Extra delay.
- Previously, the Scanning is performed for each available channel within a network. (e.g. 16 channels in case of WiMaX). Usually 802.16e supports sending Probe message from MS and wait for Down-Link message from target RSU. Then Serving RSU provides the list of neighbors to MS and then each channel is listened by MS for best Target RSU selection. After all that time consuming process, the Synchronization and association is performed later. Worst part is that during all this process, the data communication is suspended. Hence extra latency occurs due to this procedure.
- Our Main Objective is to reduce overall handover delay by reducing scanning delay. We therefore, proposed our Network assisted handover scheme to support seamless connectivity. In our scheme, MS is required to share its destination with S-RSU, which will help RSU to determine the moving direction of this MS. Each S-RSU maintains a table: MS’s arrival time in its transmission range. Its Speed. Moving direction. S-RSU autonomously selects T-RSU on the basis of MS moving direction. Selected T-RSU is updated with MS’ ID and its arrival time which can be easily calculated on the basis of moving speed of the vehicle and distance to the target RSU. In the end MS is provided with the dedicated channel info of T-RSU before it reaches exit point of S-RSU.
- We can see in the figure 2 where MS is moving from point X to Y and then following route from Y to Z. We define connection time as a time of MS being spent in any RSU. The Connection time (Tc) is calculated by: Read first equation ,where Tr is the transmission range and Vs is the MS’s Speed. S-RSU calculates one threshold (Th) value for each MS by: Read second equation , where Dist is the remaining distance of Tr and d is the remaining distance between MS and S-RSU. This threshold value determines the time when a serving RSU should start handover process on behalf of MS. We used the value obtained in Dist for calculating time required for covering the Remaining Tr distance: Each S-RSU periodically calculates Th to start HandOver Process.
- In this slide, we mention that how our scheme works: Just like mentioned before, that we aim to provide Seamless Data Communication (DC). In this figure you can see that data communication is not suspended and in the meanwhile due to our scheme, serving RSU is capable of selecting and starting handover process with Target RSU. After receiving channel information from the selected target RSU and providing it with upcoming vehicle’s information such as ID Speed, now S-RSU informs MS about HO process initiation. Remember that in the meanwhile data communication is not interrupted at all. Now as has received the info about handover and knows the channel to scan, therefore, it only listens to the channel of Target RSU and performs association directly. This procedure will not interrupt data communication for long time and thus now vehicle will be continuing communication with new RSU.
- We have used NS2 two for simulations and in addition to that, we vary the speed of MS for more realistic evaluation. Also in future work, we will allow multiple MS into the given network environment with same characteristics. Such as different speed and path ways etc. Read From Table
- This figure shows the time required to perform scanning by each MS during the overall handover process w.r.t speed. Previously, an MS is allowed to scan every channel of neighboring RSUs. If vehicle is moving faster, it will have less chance to select best Target RSU. However, in our scheme network assistance allows serving RSU to select target RSU, thus no extra effort required for selecting an appropriate target RSU.
- Similarly this figure shows the No. of scanning iterations performed by each MS during entire handover process. More iteration means more time consuming and more computation power, time etc…. Conventionally, an MS is allowed to scan every channel of neighboring RSUs and thus will cost extra time specially in case of slow speed because more chances to search for best T-RSU. However, in our scheme network assistance allows serving RSU to select target RSU, thus no extra effort required and vehicle will just scan one channel.
- Read from the slide.
- Thank you very much for your considerations and patience As I said, I will try to answer the questions but if you have any in-depth questions, Please feel free to contact Mr. Hassan. Thanks once again.