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Optimal Data Rate Selection for Vehicle Safety Communications

Optimal Data Rate Selection for Vehicle Safety Communications. ACM Workshop VANET 2008 Daniel Jiang, Qi Chen, Luca Delgrossi Mercedes-Benz Research and Development North America, Inc. Sep 15 th 2008. Contents. 1. Overview of Data Rate in 802.11p. 2. Theory and Methodology.

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Optimal Data Rate Selection for Vehicle Safety Communications

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  1. Optimal Data Rate Selection for Vehicle Safety Communications ACM Workshop VANET 2008 Daniel Jiang, Qi Chen, Luca Delgrossi Mercedes-Benz Research and Development North America, Inc. Sep 15th 2008

  2. Contents 1. Overview of Data Rate in 802.11p 2. Theory and Methodology 3. Simulation Results and Summary

  3. Data Rate Selection In VANET Communications 54Mbps Data Rate choicesFor IEEE 802.11p(Mbps) 27 24 18 12 9 6 4.5 3 The best selection of data rate depends on the scenario Choose 11 6 1 100m 200m 300m Data rate vs. operating distance for MAC 802.11 a/b/g • Is there a data rata most suitable for DSRC? • If so, how do we find out the most suitable one?

  4. Influential Parameters of a DSRC Scenario Data Rate Packet Size Vehicle Density Transmission Power Number of Lanes Message Frequency Influential Parameters of a DSRC Scenario

  5. Data Rate Supported in IEEE 802.11p • Impact of the Data Rate Selection • Higher rate leads to shorter MAC Frame transmission duration • Higher rate makes MAC frame reception more difficult and prone to errors IEEE802.11p OFDM PHY Parameters

  6. Contents 1. Overview of Data Rate in 802.11p 2. Theory and Methodology 3. Simulation Results and Summary

  7. Methodology of Finding the Most Suitable Data Rate 3-step procedure to figure outthe most suitable data rate: Step 1 (Make different parameter combinations) Create scenarios with different combinations of transmission parameters Step 2 (Compare combinations ) Compare the performance of different combinations Step 3 (Choose best combination) Select the combination with highest performance Challenges: How to select representative values of the 6 influential parameters. How to make sure scenarios with different parameters can be compared fairly? What’s the criterion of highest performance?

  8. Concept of Communication Density Data Rate Data Rate Packet Size Packet Size Vehicle density Vehicle density Transmission power Transmission power Number of Lanes Number of Lanes Message frequency Message frequency Communication Density 4 into 1 CD = Transmission Power * Message Frequency * Nr. Lanes * Vehicle Density Communication Density • A system can be now defined by a triplet • <CD value, Packet Size, Data Rate> • A system is defined by 6 parameters • <Vehicle Density, Number of Lanes, Message Frequency, CD value, Packet Size, Data Rate> Packet Size

  9. Understanding of Communication Density • Channel load at a location is determined by the number of transmission sensible there and their durations. • Number of sensible transmissions is related to the number of nodes around the location and their transmission power and frequency. • (CD is a simple metric value, please see Communication Density paper in Movenet2007) • The duration of a sensible transmission is determined by the MAC frame size and the data rate being used. Node B Node A Node C T2 T1 Channel Busy Channel Clear t1 t2 t CSMA Channel Status of Node A

  10. Use CD to Measure the Channel Load • Channel load is determined by a triplet <CD, data rate, message size>CD = Transmission Power * Message Frequency * Nr. Lanes * Vehicle Density • Power, Message Frequency and Vehicle Density are inter-changable • CD is additive. Two groups of nodes with CD1 and CD2 are mixed together, their total CD = CD1 + CD2 How to measure? Attach a reference group, If the reference groupkeeps the same performance, the tested group shall produce the same level of load to the reference group Both groups yield the same Channel Load as long as their CD values are the same

  11. Transmission Performance Under a Channel Load Level • Performance of a transmission is determined by a triplet <CD, size, data rate>, together with the power being used. • Performance degrades under high channel load Range= 500m Range= 100m Range= 300m Tested Group Reference Group

  12. Answers to the Challenges • How to select representative values of the 6 influential parameters? • (using Communication Density as a metric to combine 4 parameters) • How to make sure scenarios with different parameters can be compared fairly? • (use an attached reference group to test if the tested group generates the same level of channel load, even though its parameters have been selected in different combinations) • What’s the criterion of highest performance? • (the best transmission performance in the tested group, in terms of successful reception probability)

  13. Contents 1. Overview of Data Rate in 802.11p 2. Theory and Methodology 3. Simulation Results and Summary

  14. Simulation Settings Simulator Environment

  15. Simulation Settings (Cont.) • 9 channel load levels • System CD level: (3 options) 200, 400, 800 • Packet Size (3 options): 100B, 200B, 500B [6Mbps] Data Rate [100B, 200B, 500B] [200, 400, 800] Communication Density Packet Size

  16. Defining Parameter Combinations • In each channel load level, parameters are varied in combinations of <range, message frequency, lanes, vehicle density,data rate, messagesize> • Data rate: (5 options) 3, 4.5, 6, 9, 12 Mbps • Transmission Range: (3 options)100m, 300m, 500m For each channel load level with <CD,size,6Mbps> System Load is divided into 3 groups Making 15 different combination of the parameters of the study group Varying with15 combinations System Load Using reference group to test the study group maintains the same channel load contribution

  17. Transmission Performance in a Given Channel Load Performance of Study Group Performance of Reference Groups

  18. Simulation Result Study Group Range = 100m Study Group Range = 300m Study Group Range = 500m Best combination with 4.5Mbps Best combination with 4.5Mbps Best combination with 6Mbps Performance of reference group1 matches to each other Performance of reference group 2matches to each other

  19. Simulation Result (Cont.)

  20. Summary • 6Mbps is the most optimum data rate for DSRC communications across a general spectrum overall channel load and transmission powers. This result removes one dimension for future research. • Triplet <total CD values, message size, data rate> is an simple but effective value to indicate channel load level. • Proposed new methodology “COMBINE, COMPARE, CHOOSE” allows the further optimization study of communications parameters.

  21. Questions and Discussions

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