A cross layer multihop data delivery protocol with fairness guarantees for vehicular networks
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A Cross-Layer Multihop Data Delivery Protocol With Fairness Guarantees for Vehicular Networks. Gokhan Korkmaz, Eylem Ekici, and Fusun Ozguner Department of Electrical and Computer Engineering, Ohio State University. IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, TVT 2006. Outline. Introduction

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A cross layer multihop data delivery protocol with fairness guarantees for vehicular networks

A Cross-Layer Multihop Data Delivery Protocol With Fairness Guarantees for Vehicular Networks

Gokhan Korkmaz, Eylem Ekici, and Fusun Ozguner

Department of Electrical and Computer Engineering, Ohio State University

IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, TVT 2006


Outline
Outline Guarantees for Vehicular Networks

  • Introduction

  • Controlled Vehicular Internet Access (CVIA)

  • Simulation

  • Conclusion


Introduction
Introduction Guarantees for Vehicular Networks

  • As mobile wireless devices became the essential parts of our lives, “anytime, anywhere” connectivity gains a growing importance.

  • Inasmuch as an average user spends hours in the traffic everyday, Internet access from vehicles is in great demand.


Introduction1
Introduction Guarantees for Vehicular Networks

  • DSRC(Dedicated Short Range Communication) is one of the ITS(Intelligent Transport System) standards that allows high-speed communications between vehicles and the roadside, or between vehicles.

  • DSRC systems use the IEEE 802.11 protocol as their MAC layer.

  • Multihopping with the IEEE 802.11 protocol suffers from several problems, leading to low throughput and starvation of packets originating from vehicles far away from gateways.

2R

2R

2R


Goal Guarantees for Vehicular Networks

  • To increase the end-to-end throughput.

  • Achieving fairness in bandwidth usage between vehicles.

  • Mitigating the hidden node problem .

  • Avoiding contention.


Network assumption
Network Assumption Guarantees for Vehicular Networks

  • Vehicular network that accesses the Internet through fixed IGWs (Internet gateways) along the road.

  • Gateways send periodic service announcements to indicate the availability of the service in their service area.

  • The uplink and the downlink packets are transmitted over two frequency-separated channels.


Network assumption1
Network Assumption Guarantees for Vehicular Networks

  • Vehicles are equipped with GPS devices used for time synchronization and obtaining vehicle positions.

  • Vehicle positions obtained via GPS are exchanged among one-hop neighbors.


Basic idea
Basic Idea Guarantees for Vehicular Networks

  • Divides the time into slots and the service area of the gateway into segments.

  • Controls time slots the vehicles are allowed to transmit in, how the vehicles access the channel, and to which vehicles the packets are sent.


Cvia overview
CVIA-Overview Guarantees for Vehicular Networks

Segment Length=R

S6 S5 S4 S3 S2 S1

Slot1 Slot2 Slot3 Slot4 Slot5 Slot6 Slot7 time

VTR (Virtual Transmission Radius)

VTR length N=5

Slot Length=Tslot


Cvia overview1
CVIA-Overview Guarantees for Vehicular Networks

the direction of packet dissemination

Si-

Si

Si+

S6 S5 S4 S3 S2 S1

S6 S5 S4 S3 S2 S1

Si+:The neighboring segment in the same direction of the packet dissemination.

Si-:The neighboring segment in the opposite direction of the packet dissemination.


Cvia overview2
CVIA-Overview Guarantees for Vehicular Networks

Segment Length=R

S6 S5 S4 S3 S2 S1

Interference parameter (r):


Cvia overview3
CVIA-Overview Guarantees for Vehicular Networks

S6 S5 S4 S3 S2 S1

Active segment:Siis active in TSj if (i mod r)=(j mod r)

For example, r=2

when the current time slot is T5 , the segments S1, S3, and S5 become active.

Interference parameter (r):

when the current time slot is T6 , the segments S2, S4, and S6 become active.


Cvia overview4
CVIA-Overview Guarantees for Vehicular Networks

S6 S5 S4 S3 S2 S1

Inbound temporary router ( ):The vehicle closet to Si-.

All packets entering a segment go through.

Outbound temporary router ( ):The vehicle closet to Si+.

All packets leaving the segment go through .

Si- Si Si+


Cvia overview5
CVIA-Overview Guarantees for Vehicular Networks

the direction of packet dissemination

S6 S5 S4 S3 S2 S1

Si-Si Si+

1. deliver packet train to .

2. gather local packets.

3. move out packet train to .


Cvia state diagram
CVIA- Guarantees for Vehicular NetworksState diagram

End of active slot

New active slot

tg

tu

Routers

are selected

End of

packet train


CVIA Guarantees for Vehicular Networks


Cvia inactive
CVIA - Guarantees for Vehicular NetworksInactive

Vehicles in inactive segments do not access the channel.

Siis active in TSj if (i mod r)=(j mod r)

i = , ∆d:The distance of the vehicle to the gateway.

j = , ∆t:The time passed since an absolute reference point.

Vehicles obtain their positions and synchronize their clocks using GPS.

Vehicles learn the positions of gateways from a digital road map database or

the service announcement packets broadcast periodically by gateways.

Δd

R

S5 S4 S3 S2 S1


CVIA Guarantees for Vehicular Networks


Cvia vehicle position update phase
CVIA - Guarantees for Vehicular NetworksVehicle Position Update Phase

Si-Si Si+

tu:A time interval reserved for position update packets (PUPs).

tPUP:The duration of a PUP.

Vehicles pick a random waiting time (RWT) from [0,tu-tPUP).

After an RWT, vehicles access the channel using DCF method of the IEEE 802.11 protocol.

The length of a PUP is short, RTS/CTS handshake is not used before sending PUP.


CVIA Guarantees for Vehicular Networks


Cvia temporary router selection phase
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

Si-Si Si+

New and are selected by .

The selected routers are called and until they become active.

Use “router lifetime” and “safe area” concept.


Cvia temporary router selection phase1
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

Temporary router must stay inside the segment for an amount of time called the router lifetime.

When and are selected at the beginning of TSj .

is responsible for

1. Receiving packet train relayed by .

2. Gathering local packets.

3. Creating a new packet train and sending this train out of Si to .

Si-Si Si+


Cvia temporary router selection phase2
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

Slotj Slotj+1Slotj+2… Slotj+r time

Temporary router must stay inside the segment for an amount of time called the router lifetime.

When and are selected at the beginning of TSj .

is responsible for

1. Receiving packet train relayed by .

2. Gathering local packets.

3. Creating a new packet train and sending this train out of Si to .

becomes active immediately and stays active until the end of TSj .

lifetime of is Tslot


Cvia temporary router selection phase3
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

Temporary router must stay inside the segment for an amount of time called the router lifetime.

When and are selected at the beginning of TSj .

is responsible for

1. Receiving packet train coming from in TSj+1.

2. Selecting and announcing and at the beginning of TSj+r .

3. Relaying the packet train to in TSj+r .

Si-Si Si+


Cvia temporary router selection phase4
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

Slotj Slotj+1Slotj+2… Slotj+r time

Temporary router must stay inside the segment for an amount of time called the router lifetime.

When and are selected at the beginning of TSj .

is responsible for

1. Receiving packet train coming from in TSj+1.

2. Selecting and announcing and at the beginning of TSj+r .

3. Relaying the packet train to in TSj+r .

becomes active throughout TSj+1 and TSj+r .

lifetime of is (r+1)Tslot


Cvia temporary router selection phase5
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

xmargin+,v= (∆tpu,v+1∙Tslot)∙Vmax

xmargin-,v= (∆tpu,v+ (r+1) ∙Tslot)∙Vmax

∆tpu,v:The elapsed time since the last powsition update from vehicle v.

Temporary router must be away from the segment border for a certain amount of distance (xmargin)

to stay inside to stay inside the segment during the router lifetime.

xmargin+:measured from the segment borders associated with (lifetime=1∙Tslot) .

xmargin-: measured from the segment borders associated with (lifetime=(r+1)∙Tslot).


Cvia temporary router selection phase6
CVIA - Guarantees for Vehicular NetworksTemporary Router Selection Phase

v1

v2

If vehicle v’s distance to segment borders is more than xmargin+,v, the vehicle can safely be selected as .

If vehicle v’s distance to segment borders is more than xmargin-,v , the vehicle can safely be selected as .

Among the vehicles inside the safe area, selects

the vehicle closest to Si+ as and

the vehicle closest to Si- as

Distance to segment border

xmargin+,v

xmargin-,v

v1

v1,v2

Si-Si Si+


CVIA Guarantees for Vehicular Networks


Cvia intra segment packet train movement phase
CVIA - Guarantees for Vehicular NetworksIntra-segment Packet Train Movement Phase

Si-Si Si+

delivering the packet train coming from Si-to .

To avoid contention, has the highest access priority and

waits only SIFS duration before accessing the channel.


CVIA Guarantees for Vehicular Networks


Cvia local packet gathering phase
CVIA - Guarantees for Vehicular NetworksLocal Packet Gathering Phase

Si-Si Si+

Vehicles directly send their packets to .

Each vehicle starts this phase with a random backoff counter.

has the highest channel access priority in this phase.


Cvia local packet gathering phase1
CVIA - Guarantees for Vehicular NetworksLocal Packet Gathering Phase

100 packets

S5 S4 S3 S2 S1

Si-Si Si+

20 packets

20 packets

20 packets

40 packets

20 packets

60 packets

80 packets

20 packets

100 packets

20 packets

  • accesses the channel and ends the LPG phase in 2 cases:

  • When the total number of packets queued up in reaches .

  • When the time left in the active slot is just enough to move out all packets in the queues.


CVIA Guarantees for Vehicular Networks


Cvia inter segment packet train movement phase
CVIA - Guarantees for Vehicular NetworksInter-segment Packet Train Movement Phase

Si-Si Si+

forms a packet train and moved to before the end of TSj.

There is only one in Si+, does not need to specify the vehicle ID of the destination in the data train.


CVIA Guarantees for Vehicular Networks


Cvia state diagram download
CVIA- Guarantees for Vehicular NetworksState diagram-Download


Cvia state diagram download1
CVIA- Guarantees for Vehicular NetworksState diagram-Download


Cvia state diagram download2
CVIA- Guarantees for Vehicular NetworksState diagram-Download


Cvia download local packet distriburion and intra segment packet train movement phase
CVIA - Guarantees for Vehicular NetworksDownloadLocal Packet Distriburion and Intra-segment Packet Train Movement Phase

Si-Si Si+

delivering the packet train coming from Si-to .

Some packets leave the train, and a shorter train keeps moving away from the gateway.


Performance evaluation
Performance Evaluation Guarantees for Vehicular Networks


Performance evaluation1
Performance Evaluation Guarantees for Vehicular Networks


Performance evaluation2
Performance Evaluation Guarantees for Vehicular Networks


Performance evaluation3
Performance Evaluation Guarantees for Vehicular Networks


Performance evaluation4
Performance Evaluation Guarantees for Vehicular Networks

Fairness Index (FI) =

Thri:the throughput of segment i


Performance evaluation5
Performance Evaluation Guarantees for Vehicular Networks

In LPG phase, the contention-based

channel access is used.

Probability of packet collision ≈ 0.3

Probability of packet dropping ≈ 0.310

≈ 5×10-6


Conclusion
Conclusion Guarantees for Vehicular Networks

  • Mitigates the hidden node problem.

  • Avoids contention while moving packets among road segments.

  • Provides fairness among segments by controlling the contents of the packet trains.

  • Unnecessary RTS/CTS overhead while moving packets among road segments.

  • The throughput gain obtained using the proposed CVIA protocol is higher for short payload scenario.


Thanks~~~ Guarantees for Vehicular Networks


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