Performance Evaluation of Inter-vehicle Packet Relay for Fast - - PowerPoint PPT Presentation

Performance Evaluation of Inter-vehicle Packet Relay for

Fast Mobile Road-vehicle Communication

Ryoichi SHINKUMA

Visiting scholar, WINLAB, Rutgers Assistant professor, Kyoto University, Japan

*Takayuki YAMADA, and Tatsuro TAKAHASHI

Kyoto University

* Presently, with NTT Network Innovation Laboratories.

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• Background & goal
• Problems of road-vehicle communication

in fast mobile environments

• Our inter-vehicle packet relay technique
• Simulation results
• Conclusion

Outline

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Background & goal Background:

• Road-vehicle communication on highways

–Applications: safety services, location-aware services, content delivery etc –Requirements:

• High throughput
• Wide communication coverage

Goal:

• To satisfy the above requirements

AP

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Problems of road-vehicle communication in fast mobile environments

• Mobile stations (MSs) have to connect to

fixed roadside access points (APs).

• Large relative speed between MSs and APs

causes ...

1.Time-varying fading caused by large Doppler shift 2.Wide dynamic range of path loss 3.Short period of being within coverage of an AP

AP

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10 20 30 40 50 60 10 20 30 40

• Max. transmission rate [Mbps]

Eb / N0 [dB]

0 km/h 20 km/h 40 km/h 60 km/h 80 km/h 100 km/h 120 km/h

Problems of IEEE802.11a WLAN in fast mobile environments

Time-varying fading by Doppler shift Long frame transmission Not correctly compensated !

IEEE802.11a,1500 Bytes

• As moving speed

increases, transmission rate decreases

fading One frame duration

Rx power Time

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Relative speed per hop decreases

VMS > V

RS >> (VMS

• VRS

) – Reducing Doppler shift – Reducing dynamic range of path loss Proposed method:

Inter-vehicle packet relay technique

Receiving packets via other, slower vehicles

MS AP RS MS

VMS VMS VRS

RS: Relay Station

Channel-quality improvement => Increased throughput and coverage

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Simulation parameters

p12 p23

Lane 1 (RSs)

AP1 AP2 AP3

Parameters

Frequency band 5GHz Moving speed of MS/RS 100 / 80 km/h Data length 1500 Bytes RS interval (crowded and not) 100 / 400 m Transmission power 12 dBm AP interval 100 ~ 2000 m Noise figure 10 dB AP / vehicle height 6 / 1.5 m Overhead per frame 96 μsec Lane width 3.5 m Overhead for handover 100 msec Route selection phase 5 msec

IEEE802.11a WLAN

Lane 2 (MS) VRS VMS

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Simulation model

p1 p2

Lane 1 (RSs) Lane 2 (MS)

AP1 AP2 AP3

Choice!

• The observed MS ran from P1 to P2

, adaptively choosing a communication route that maximizes the throughput from an AP to the MS (including direct route from AP)

• RSs ran with constant speed and equal intervals.

VRS =80km/h VMS =100km/h

100~2000m 100/400 m

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Geometric propagation model

AP

Received signal= + a direct path + a road reflection path + several delay paths

Sharply fluctuated

• 140
• 120
• 100
• 80
• 60
• 40

200 400 600 800 1000

Loss [dB] Position [m]

(AP) ITU-R LoS lower bound Free space 2 paths + 3 delay paths 2 paths

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1 1.2 1.4 1.6 1.8 2 2000 1500 1000 500 250 100

Normalized connected time AP interval [m]

DRS = 100 [m] DRS = 400 [m]

Simulation result: connected time (coverage metric)

Normalized by conventional method only using direct route

22 sec 33 sec 36 sec

• Time during

which frame success rate of the MS exceeds 5%

• Frame success

rates of both links of two-hop routes have to be over 5%

Increased communication coverage

DRS : RS interval Conventional method

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Simulation result: average throughput (quality metric)

• Average throughput

θAV is given by

– All possible default positions of RSs are considered

Increased average throughput

( ) ( )

. 1

12 23

∫

− =

RS

D RS AV

dx p t p t Nl D θ t(p): time when MS is at position p DRS : RS interval N: number of success frames l: data length

1 1.2 1.4 1.6 1.8 2000 1500 1000 500 250 100

Normalized throughput AP interval [m]

DRS=100m DRS=400m

1.9 Mbps 2.2 Mbps 2.8 Mbps

Conventional method

Normalized by conventional method only using direct route

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Conclusion

• Inter-vehicle packet relay technique for road-

vehicle communication in fast mobile environment

Reducing relative speed – Improved channel quality – Increased throughput and communication coverage

• Future work

– Testing our method in multi-user environment

• MAC
• Route selection algorithm

[IEEE Globecom06, IEICE Trans vol.E90-B no.9, IEEE CCNC08]

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Thank you for your attention.

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Problems in multiple access environment

What problems are caused?

Frame collision Interference

Solutions to avoid the frame collision are

[Between neighboring areas] – To assign different channels to neighboring areas [Within coverage of a single AP] – To use point coordination function (PCF) – To limit number of hops to two

But … there is still an interference problem.

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Interference problem

• Comparison with conventional method

– Additional interference by RSs between neighboring areas

• Features of our method

– Seldom choosing the RSs near the border and far from AP due to low transmission rate – Ability to shorten MSs' transmission time per frame by choosing RS-MS links of high transmission rate Lane 1 (RS’s lane) Lane 2 (MS’s lane)

AP1 AP2

Ch1 Ch2

Overlapped zone

Here, seldom chosen due to low transmission rate Shorter than the Direct

Transmission rate of RS-MS links are higher than that of the direct link Area of interference with neighboring channel Uplink

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Evaluation results : Interference between neighboring areas

Normalized by conventional method only using direct route

Our method does not cause additional interference between neighboring areas.

AP interval: 1000 m

0.6 0.8 1 1.2 2000 1500 1000 500 250 100

Normalized total transmission time AP interval [m]

DRS=100 m DRS=400 m 0.2 0.4 0.6 0.8 1 100 200 300 400 500

Transmission time [sec] Position [m]

(AP) DRS=100m DRS=400m Direct only

Total transmission time in overlapped zone Total transmission time of MS and RSs at each position

Overlapped zone

(border)