DECENTRALIZED CONGESTION CONTROL FOR ITS G5 · Basics How to shape the network traffic?...

DECENTRALIZED CONGESTION CONTROL FOR ITS‐G5ETSI STF469

Dieter Smely 6th ITS Workshop, Feb. 2014, Berlin, Germany

© ETSI 2013. All rights reserved

Overview

Introduction

Basics

Solutions

Conclusions

2 © ETSI 2011. All rights reserved Dieter Smely , STF469

Introduction

What is Decentralized Congestion Control (DCC)?What is Decentralized Congestion Control (DCC)?DCC shapes the ITS‐G5 ad hoc network traffic.

Why to shape the network traffic?To ensure proper operation of safety applications.To ensure proper operation of safety applications.Since high channel loads cause ...• ... long channel access delays andg y• ... packet collisions, which cause radio range degradation

Therefore, for safety relevant systems, y ycritical channel loads must be avoided!


Basics

How to shape the network traffic?How to shape the network traffic?

Decentralized Congestion Control (DCC)g ( )• IEEE 802.11 (MAC and PHY Layer)

• Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)• Enhanced Distributed Coordination Function (EDCA)• Quality of Service (QoS) and Access Categories (AC)

• ETSI TC ITS • Cross layer extension to IEEE 802.11


Basics

IEEE 802.11 CSMA/CA and QoS for broadcast packetsIEEE 802.11 CSMA/CA and QoS for broadcast packets

lot t

ime

3 µsarbitration interframe space

Message prioritization by PHY timing parameters.

AIFS[i] sl 13

timebusy medium transmission

CW random number of slots

EDCA mechanismcontention window

AC CW i CW AIFSAC CWmin CWmax AIFSAC_VO 3 7 58 µsAC_VI 7 15 71 µsAC_BE 15 1 023 110 µs

4 priorities (access categories) historically called:VO ... voiceVI ... videoBE best effort


AC_BK 15 1 023 149 µsBE ... best effortBK ... background

Basics

EDCA limitations for broadcast packetsEDCA avoids most packet collisions up to moderate channel loads.For high channel loads the probability increases that the CWs end simultaneously for several nodes.both nodes can transmit at the same time.

ETSI TC ITS DCC• DCC avoids this channel overload by ...• ... message rate control, and in future• ... by additional transmit power control, and later on


y p ,• ... by offloading data traffic to other channels.

Basics

Control input to the DCC algorithmControl input to the DCC algorithm

• Local measurement simple to implement:• Local measurement simple to implement: • Local Channel Busy Ratio (CBR)

• Global knowledge improves fairness and safety: • CBR disseminationCBR dissemination• Message rate dissemination• Transmit power level dissemination


Basics

CBR determination principle*) and accuracy

RSSI threshold

Busy

timeRSSI ... Received Signal Strength Indicator


*) IEEE 802.11 specifies a more complex CBR determination.

Specification

How to specify DCC?f b d bl b h l

0 81,0

• Specification based on a testable system behaviour limit.• Proposal: Upper CBR limit vs. node number

0,00,20,40,60,8

CBR

0 100 200 300 400 500 600 700

Number of ITS‐S

• For a message length of 1 ms themessage rate limit is:

5101520

sage Rate

[Hz]

• For a message length of 1 ms the message rate limit is:


05

0 100 200 300 400 500 600 700

Mess [

Number of ITS‐S

Implementation examples ...

1,0

State Machine (Toff proportional to CBR)

0,4

0,6

0,8

CBR

0,0

0,2

0 100 200 300 400 500 600 700

Number of ITS‐S

Limit Limit Cycle+ Limit Cycle‐

Number of ITS‐S

Continuous PI controller with upper and lower rate limits

0,81,0

0,00,20,40,6,

CBR

CBR Limit Continuous PI controller


Any other algorithm that matches the limit!PI ... proportional integral

0 100 200 300 400 500 600 700Number of ITS‐S

Single channel with local DCC information

Facilities LayerCAM DENM Service Appl.

DCC Facility

Message generation parameters

y

aram

.

Network and Transport Layer

Traffic class prioritizationDCC parm. evaluational

DC

C p

a

. .DCC queues

Power control

Local CBR

evaluation

CEN DSRC coexistence

inte

rna

Flow controlcoexistence

DCC Access

Access Layer11 © ETSI 2011. All rights reserved Dieter Smely , STF469

PHY / MAC / DRIVERS / RADIO (Chipset)

Multi channel with global DCC information

Facilities LayerCAM DENM Service Appl.

DCC Facility

Message generation parameters

DCC Facility

Global DCC

Neighbour TableChannel DCC param.

y

aram

.

Global DCC TX param.

y

Network and Transport Layer

Traffic class prioritization

Global CCRX param.

DCC parm. evaluational

DC

C p

a

DCC parm. evaluation

Traffic class prioritization...

.

.

.

.

.

.

.

.

.DCC queues

Power control

Local CBR

evaluation

CEN DSRC coexistence

inte

rna evaluation

Local CBR

.

.

.

.

.

.

.

.

.

.

.

.DCC queues

Power controlCEN DSRC coexistence


DCC AccessDCC Access


Access Layer12 © ETSI 2011. All rights reserved Dieter Smely , STF469

PHY / MAC / DRIVERS / RADIO (Chipset)

Conclusions

IEEE 802.11 CSMA/CA plus EDCA works fine for moderate network loads.For safety related applications the network load has to b ll d b ddi i l l i hbe controlled by an additional DCC algorithm.The first implementation step will be done by a l l CBR t d t t llocal CBR measurement, and a message rate control.To improve fairness and safety, information sharing between the ITS Ss will be necessary later onbetween the ITS‐Ss will be necessary later on. A coordinated power control will be necessary when high penetration rates are reached


high penetration rates are reached.In addition, multi‐channel DCC can be used.

Decentralized Congestion Control for ITS‐G5

Dieter Smely

Kapsch TrafficCom AGAm Europlatz 2 | A-1120 Vienna | Austria

Tel.: +43 50 811 2217Fax: +43 50 811 2209

E-mail: [email protected] kapschtraffic comwww.kapschtraffic.com

www.kapsch.net

Thank you!

© ETSI 2011. All rights reserved14

DECENTRALIZED CONGESTION CONTROL FOR ITS G5 · Basics How to shape the network traffic?...

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