CEN DSRC / ITSCEN DSRC / ITS-G5 coexistence...-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40...

World Class Standards

CEN DSRC / ITS G5CEN DSRC / ITS-G5 coexistencecoexistence

Basic RF properties

Dieter Smely© ETSI 2011. All rights reserved

Workshop; July 2011 | Ispra

Workshop, Coexistence between CEN DSRC and ITS-G5

Workshop; July 2011 | Ispra


Index

Signal properties

Interference mechanismInterference mechanism

Coexistence considerations

Coexistence methods

Power coexistence

Time sharing coexistence

Mitigation area identification

Example: Isolation estimation

Workshop, Coexistence between CEN DSRC and ITS-G5 2


Signal PropertiesSignal Properties



CEN DSRC features

Used for road tolling and access applications

Small low price retrofit onboard units (OBU)Small low price retrofit onboard units (OBU)

Roadside units (RSU) with defined antenna footprint( ) p

Workshop / Coexistence between CEN DSRC and ITS-G5 4


CEN DSRC signal propertiesRSU

The RSU is using amplitude shift keying (ASK) with a data rate of 500 kBit/s to modulate the down link (DL) (2 µs per bit).( ) ( µ p )

1 0

0.0

1.0

2.0

x10-3

-2.0

-1.0

20181614121086420µs

OBUThe OBU acts as a variable reflector to a constant DL (passive back scatter technology). By changing the phase of the reflected signal the uplink (UL) isBy changing the phase of the reflected signal the uplink (UL) is generated. The modulation type of this UL is phase shift keying with two states (2-PSK) and a data rate of 250 kBit/s.In addition either a 1 5 MHz or a 2 MHz sub carrier PSK modulation is


In addition, either a 1.5 MHz or a 2 MHz sub carrier PSK modulation is used to shift the UL in frequency.


CEN DSRC signal in frequency domainDSRC frequency utilization for 1 5 MHz sub-carrier frequency (U1-0 CEN EN 12253 )

DSRC frequency utilization for 1,5 MHz sub-carrier frequency (U1-0, CEN EN 12253 )

7950

GH

z

8000

GH

z

8050

GH

z

8100

GH

z

8150

GH

z

7975

GH

z

8025

GH

z

8075

GH

z

8125

GH

z

8030

GH

z

8040

GH

z

8020

GH

z

8010

GH

z

7960

GH

z

7970

GH

z

7980

GH

z

7990

GH

z

8080

GH

z

8090

GH

z

8070

GH

z

8060

GH

z

8130

GH

z

8140

GH

z

8120

GH

z

8110

GH

z

Channel 1 Channel 2 Channel 3 Channel 4

5. 5. 5. 5. 5.5. 5. 5. 5.5. 5.5.5.5. 5. 5. 5. 5. 5.5.5. 5. 5.5.5.

UL

DL

DL

Car

rier

UL

UL

DL

DL

Car

rier

UL

UL

DL

DL

Car

rier

UL

UL

DL

DL

Car

rier

UL

DSRC frequency utilization for 2 MHz sub-carrier frequency (U1-1, CEN EN 12253 )

5.79

50 G

Hz

5.80

00 G

Hz

5.80

50 G

Hz

5.81

00 G

Hz

5.81

50 G

Hz

5.79

75 G

Hz

5.80

25 G

Hz

5.80

75 G

Hz

5.81

25 G

Hz

5.80

30 G

Hz

5.80

45 G

Hz

5.80

20 G

Hz

5.80

05 G

Hz

5.79

55 G

Hz

5.79

70 G

Hz

5.79

80 G

Hz

5.79

95 G

Hz

5.80

80 G

Hz

5.80

95 G

Hz

5.80

70 G

Hz

5.80

55 G

Hz

5.81

30 G

Hz

5.81

45 G

Hz

5.81

20 G

Hz

5.81

05 G

Hz

Channel 1 Channel 2 Channel 3 Channel 4


UL

DL

DL

Car

rier

UL

UL

DL

DL

Car

rier

UL

UL

DL

DL

Car

rier

UL

UL

DL

DL

Car

rier

UL


Overlapping of CEN DSRC DL in MLFF

Lane Width

Multilane free flow (MLFF)Several, but not all, MLFF implementations use one RSU

10m Tolling Zone

pper lane with overlapping antenna footprints and synchronised modulation.

CEN DSRC RSU CEN DSRC RSU

yTo avoid signal cancellation in the overlap region, different carrier frequencies are used in

10mTolling Zone

qadjacent lanes.The OBU uses a broadband envelop detector. Therefore it

Lane Width

pcan demodulate the sum signal of several RSUs.



ITS-G5 signal propertiesAll ITS-G5 stations use the physical layer described in IEEE 802.11p which is currently in the progress of being merged with all other IEEE 802.11 standards.Signal properties ValueChannel bandwidth 10 MHzCarrier spacing 156,25 kHzNumber of used carriers 52 (including 4 pilots) (OFDM)Symbol duration 8 µs (including 1 6 µs cyclic prefix)Symbol duration 8 µs (including 1,6 µs cyclic prefix)Modulation 2 PSK, 4 PSK, 16 QAM and others

1.0

0.0

-1.0

x10-3

Workshop / Coexistence between CEN DSRC and ITS G5 8

876543210µs


ITS –G5 Signal in frequency domain (from ES 202 663 )Channel Centre frequency IEEE 802.11 Channel Default data rate TX power limit TX powerChannel

typeCentre frequency IEEE 802.11

CH numberChannel spacing

Default data rate TX power limit TX power density limit

G5CC 5 900 MHz 180 10 MHz 6 Mbit/s 33 dBm EIRP 23 dBm/MHzG5SC2 5 890 MHz 178 10 MHz 12 Mbit/s 23 dBm EIRP 13 dBm/MHzG5SC1 5 880 MHz 176 10 MHz 6 Mbit/s 33 dBm EIRP 23 dBm/MHzG5SC3 5 870 MHz 174 10 MHz 6 Mbit/s 23 dBm EIRP 13 dBm/MHzG5SC4 5 860 MHz 172 10 MHz 6 Mbit/s 0 dBm EIRP -10 dBm/MHzG5SC5 As required in EN 302 571 for the

band 5 470 MHz to 5 725 MHzseveral dependent on channel

spacing30 dBm EIRP (DFS master) 17 dBm/MHz23 dBm EIRP (DFS slave) 10 dBm/MHz

NOTE: With respect to emission limits (power limit / power density limit), the more stringent requirement applies.



Interference mechanismInterference mechanism

ITS_WG4#13, Coexistence between CEN DSRC and ITS-G5 10


Different possible interference scenariosDifferent possible interference scenarios

ITS-G5 transmitter to CEN DSRC OBU receiver

ITS-G5 transmitter to CEN DSRC RSU receiver

CEN DSRC RSU transmitter to ITS-G5 receiver



Interference from ITS-G5 to CEN DSRC OBUThe CEN DSRC DL and the interfering ITS-G5 signal sum up in the CENThe CEN DSRC DL and the interfering ITS G5 signal sum up in the CEN DSRC OBU receiver. Since the OBU uses an envelope detector, the interference signal is treated as additional noise.

2.0

-2.0

-1.0

0.0

1.0

0

x10-3

RSU DL

86420µs

1.0

0.010-3

ITS signal-1.0

x

876543210µs

g

-2

0

2

x10-3

sum signal


µs


Interference from ITS-G5 to CEN DSRC RSU

BlockingThe CEN DSRC UL and the interfering ITS-G5 signal sum up in the CEN DSRC RSU receiverRSU receiver. The RSU sensitivity at the antenna for a left hand circular polarised CEN DSRC UL is about -110 dBm to -120 dBm. Therefore the input low noise amplifier or the input mixer can be saturated by a much stronger interference p p y gsignal even it is not in the CEN DSRC UL frequency band.The interference level that causes this so called blocking, strongly depends on the CEN DSRC implementation.

Spurious and unwanted emissionsIf the ITS-G5 unwanted emissions in the CEN DSRC UL frequencyIf the ITS G5 unwanted emissions in the CEN DSRC UL frequency band exceed -120dBm, interference to the CEN DSRC UL will start to happen.



Interference from CEN DSRC RSU to ITS-G5

In theory blocking and interference by unwanted emissions of the CEN DSRC RSU can also happen to ITS-G5 stations.

But...... since the antenna food print of the CEN DSRC stations is very small, the

ibl i t f d t th ITS G5 i ti illpossible interference area compared to the ITS-G5 communication range will be very small.... since the input sensitivity of the ITS-G5 station is only in the order of -80 to -90 dBm it will be less sensitive to interference signals compared to CEN-90 dBm it will be less sensitive to interference signals compared to CEN DSRC.... measurements showed no interference from CEN DSRC to ITS-G5.

Interference from the CEN DSRC OBU to an ITS-G5 station has no practical relevance because of the low output power level of the passive backscatter technology used in the OBUpassive backscatter technology used in the OBU.



Coexistence considerationsCoexistence considerations

ITS_WG4#13, Coexistence between CEN DSRC and ITS-G5 15


Power coexistence limits evaluated by STF 395

Within a CEN DSRC Tolling Zone the electric field strength of a fi d ITS G5 t ti h ll t

Lane Width (*)

fixed ITS-G5 station shall not exceed 0,11V/m (-52 dBm).

10m Tolling Zone (**)

At the CEN DSRC RSU antenna the field strength of a fixed ITS-G5 station shall not exceed 0 21 V/m

CEN DSRC RSU CEN DSRC RSU

station shall not exceed 0,21 V/m (-46 dBm).

10mTolling Zone (**)

Lane Width*) The width of the CEN DSRC tolling zone is given by the number of parallel lanes. Usually one RSU is used per lane.

(*)

**) Mobile enforcement vehicles will not have a fixed Tolling


) gZone position or RSU position.


How to achieve coexistence

Detect Identify the position of the mitigation areaDetect

A

Identify the position of the mitigation area

And

Avoid Avoid interference by a set of Coexistence Methodsy



Coexistence MethodsCoexistence Methods



CEN DSRC RSU

Fixed tolling stationCEN DSRC RSUmounted ongantry

RTTT

mobileITS-G5 RTTT

OBUstation

Interference can only happen when the CEN DSRC OBU is inside the tolling zone.



CEN DSRC RSU

Power coexistence mitigation areas40

CEN DSRC RSUmounted ongantry

35

30

dBm

EIR

P

25 dB

33 dBm17

0 m

Pathloss coefficient n=1.8

25

20

15ut p

ower

lim

it / d 25 dBm

70 m

B is

olat

ion

B is

olat

ion

mum

mum

mobileITS-G5 RTTT15

10

5

ITS-

G5

Out

p

10 dBm 75 d

B

82 d

Bm

inim

min

imstationRTTTOBU

0

-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200Distance to CEN DSRC tolling station / m

schematically - not true scale!



Power coexistence mitigation areas40

35

30

dBm

EIR

P

25 dB

33 dBm17

0 m

Pathloss coefficient n=1.8

( ) 6 8-10-dlog18P ⋅=25

20

15ut p

ower

lim

it / d 25 dBm

70 m

B is

olat

ion

B is

olat

ion

mum

mum

( ) 6.810dlog18PTX =

15

10

5

ITS-

G5

Out

p

10 dBm 75 d

B

82 d

Bm

inim

min

im

0

-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200Distance to CEN DSRC tolling station / m

10 dBm ITS-G5 output power level assures coexistence (Non interference mode).

Higher power levels are possible at more than 20 m distance to the tolling station or when a time sharing method is used alternatively


station or when a time sharing method is used alternatively.


Principles of time sharing coexistenceTime sharing can work when ITS-G5 is in Low Duty Cycle (LDC) operation.R

SU

RX

/ TX

TX RX TX X retry RX ....

Additionally to the channel load, ITS-G5 channel usage timing constraints g gmust be specified.

ITS-

G5

activ

ity ....(*)

STF 411 is dealing with LDC methods.

STF 420 on ITS-G5 channel configurationX

2520151050

STF 420 on ITS-G5 channel configuration could consider this topic.

OB

U

RX

/ TX XTXRX TXRX ....

*) Interference will usually happen in CEN DSRC down link.2520151050


time / ms) Interference will usually happen in CEN DSRC down link.


Proposed LDC operation35

Bm

30

25

20

ower

lim

it / d

B

tati

15

10

5

-G5

outp

ut p

o

Additionally to the channel load, the maximum ITS-G5 channel activity time ta

0ITS-

time

and the minimum idle time ti should be specified.

Because of CSMA/CS, an ITS-G5 station monitors the channel continuously. This can be used to determine whether the channel was idle for at least time tThis can be used to determine whether the channel was idle for at least time ti

or active for time ta. The experiments here at JRC will help to find out whether CSMA/CS sensitivity is sufficient to ensure coexistence.


During idle time, the channel can still be used with a power level of less than 10 dBm.


Mitigation area identification

Part 1



90

Isolation estimation methods - principle85

80

75

70

65isol

atio

n / d

B Pathloss coefficient n=1.8Fading margin +/- 6dB

( )dlog189.47 ⋅+=Isolation

60

55

( )g

50

-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200Distance to beacon / m

Due to fading the isolation can vary by ±6 dB around its expected valueDue to fading, the isolation can vary by ±6 dB around its expected value.

To ensure coexistence, the worst case minimum isolation is essential.

The use of an RF signal detector can directly estimate this minimum isolation


The use of an RF signal detector can directly estimate this minimum isolation.


Example: CEN DSRC signal detectorExpected maximum(*) isolation to a CEN DSRC signal while passing the RSUExpected maximum(*) isolation to a CEN DSRC signal while passing the RSU

CEN DSRC RSUmounted ongantryg y

95

90

85

Pathloss coefficient n=1.8Fading margin +6dB

80

75

70latio

n / d

B

70

65

60

55

iso

2001901801701601501401301201101009080706050403020100Distance to beacon / m

55

50

Workshop , Coexistence between CEN DSRC and ITS-G5 26

*) Because of fading, the isolation between detector and RSU might differ from the isolation to the victim.


Example: CEN DSRC signal detectorThe TX power level and the antenna characteristics of CEN DSRC are standardised*.


The TX power level and the antenna characteristics of CEN DSRC are standardised .

g y

65

-60

-55

d / d

Bm

B is

olat

ion

mum

B is

olat

ion

mum

detector RX level threshold

-75

-70

-65

tect

or th

resh

old


75 d

B

min

im82

dB

min

im-72 dBm

-85

-80

75

CEN

DSR

C d

e Fading margin +6dBpolarization margin +3dB

mm

-79 dBm

-90

2001901801701601501401301201101009080706050403020100

Distance to beacon / m

170

m

70 m


*) Outside the main lobe of the RSU antenna the TX power level is 18 dBm EIRP.


Example: CEN DSRC signal detectorExample of combination with power coexistence areas (*)


Example of combination with power coexistence areas

g y

65

-60

-55

d / d

Bm

70

60

50

ITS

B is

olat

ion

mum

B is

olat

ion

mum

detector RX level threshold ITS-G5 TX power limit

-75

-70

-65

tect

or th

resh

old 50

40

30

TX power lim

it /


33 dBm75

dB

min

im82

dB

min

im-72 dBm

-85

-80

75

CEN

DSR

C d

e 30

20

10

/ dBm

EIRP

Fading margin +6dBpolarization margin +3dB

m

25 dBm

m

10 dBm

-79 dBm

-90

2001901801701601501401301201101009080706050403020100

Distance to beacon / m

0170

m

70 m


*) As another option LDC could be combined with a CEN DSRC signal detector.


SummaryNon interference mode with 10 dBm ITS-G5 TX power level

no identification of CEN DSRC Toll Station needed

Non interference mode can also be implemented by use of the proposed LDC operation.

no identification of CEN DSRC Toll Station needed

Combination of power coexistence method and time sharingCombination of power coexistence method and time sharing coexistence (LDC) is possible in one device, but also can coexist from a system view perspective.

The actual isolation from the victim can be directly estimated by use of an RF detector (no indirect position based estimation).



Thank you for your attentionThank you for your attention



AbbreviationsCEN Comité Européen de NormalisationCSMA/CA Carrier Sense Multiple Access with Collision AvoidanceCH ChannelCVIS Cooperative Vehicle-Infrastructure SystemsDAA Detect And AvoidDL Down LinkDSRC Dedicated Short Range CommunicationEIRP Equivalent Isotropic Radiated PowerEN European NormETC Electronic Toll CollectionETSI E T l i ti St d d I tit tETSI European Telecommunication Standard InstituteIEEE Institute of Electrical and Electronics EngineersITS Intelligent Transport SystemITS-G5 acronym for the 5,9 GHz vehicular adhoc network PHY LDC Low Duty CycleLHCP Left Hand Circular PolarizedLHCP Left Hand Circular PolarizedMLFF Multi Lane Free FlowOBU OnBoard UnitOFDM Orthogonal Frequency Division MultiplexPHY PHYsical (OSI layer)RF Radio FrequencyRF Radio FrequencyRSU RoadSide UnitRX ReceiveTS Technical SpecificationTX TransmitUL UpLinkUL UpLink


CEN DSRC / ITSCEN DSRC / ITS-G5 coexistence...-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40...

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Transcript of CEN DSRC / ITSCEN DSRC / ITS-G5 coexistence...-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40...