Basic RF properties. World Class Standards. Dieter Smely. Workshop; July 2011 Ispra. ETSI All rights reserved

Transcription

1 CEN DSRC / ITS-G5 coexistence Basic RF properties Workshop; July 2011 Ispra Dieter Smely ETSI All rights reserved Workshop, Coexistence between CEN DSRC and ITS-G5

2 Index Signal properties Interference 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

3 Signal Properties Workshop, Coexistence between CEN DSRC and ITS-G5 3

4 CEN DSRC features World Class Standards Used for road tolling and access applications Small low price retrofit onboard units (OBU) Roadside units (RSU) with defined antenna footprint Workshop / Coexistence between CEN DSRC and ITS-G5 4

5 RSU CEN DSRC signal properties World Class Standards The RSU is using amplitude shift keying (ASK) with a data rate of 500 kbit/s to modulate the down link () (2 µs per bit) x OBU The OBU acts as a variable reflector to a constant (passive back scatter technology). By changing the phase of the reflected signal the uplink () is generated. The modulation type of this 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 used to shift the in frequency. 10 µs 12 Workshop / Coexistence between CEN DSRC and ITS-G

6 CEN DSRC signal in frequency domain DSRC frequency utilization for 1,5 MHz sub-carrier frequency (U1-0, CEN EN ) Channel 1 Channel 2 Channel 3 Channel 4 Carrier Carrier Carrier Carrier 7950 GHz 7960 GHz 7970 GHz 7975 GHz 7980 GHz 7990 GHz 8000 GHz 8010 GHz 8020 GHz 8025 GHz 8030 GHz 8040 GHz 8050 GHz 8060 GHz 8070 GHz 8075 GHz 8080 GHz 8090 GHz 8100 GHz 8110 GHz 8120 GHz 8125 GHz 8130 GHz 8140 GHz 8150 GHz DSRC frequency utilization for 2 MHz sub-carrier frequency (U1-1, CEN EN ) Channel 1 Channel 2 Channel 3 Channel 4 Carrier Carrier Carrier Carrier 7950 GHz 7955 GHz 7970 GHz 7975 GHz 7980 GHz 7995 GHz 8000 GHz 8005 GHz 8020 GHz 8025 GHz 8030 GHz 8045 GHz 8050 GHz 8055 GHz 8070 GHz 8075 GHz 8080 GHz 8095 GHz 8100 GHz 8105 GHz 8120 GHz 8125 GHz 8130 GHz 8145 GHz 8150 GHz Workshop / Coexistence between CEN DSRC and ITS-G5 6

7 10 m 10 m World Class Standards Overlapping of CEN DSRC in MLFF Multilane free flow (MLFF) Several, but not all, MLFF implementations use one RSU per lane with overlapping antenna footprints and synchronised modulation. To avoid signal cancellation in the overlap region, different carrier frequencies are used in adjacent lanes. The OBU uses a broadband envelop detector. Therefore it can demodulate the sum signal of several RSUs. Lane Width Tolling Zone CENDSRCRSU CENDSRCRSU Tolling Zone Lane Width Workshop / Coexistence between CEN DSRC and ITS-G5 7

8 ITS-G5 signal properties World Class Standards All ITS-G5 stations use the physical layer described in IEEE p which is currently in the progress of being merged with all other IEEE standards. Signal properties Channel bandwidth Carrier spacing Number of used carriers Symbol duration Modulation Value 10 MHz 156,25 khz 52 (including 4 pilots) (OFDM) 8 µs (including 1,6 µs cyclic prefix) 2 PSK, 4 PSK, 16 QAM and others 1.0 x µs Workshop / Coexistence between CEN DSRC and ITS G5 8

9 ITS G5 Signal in frequency domain (from ES ) Channel Centre frequency IEEE Channel Default data rate TX power limit TX power type CH number spacing density limit G5CC MHz MHz 6 Mbit/s 33 dbm EIRP 23 dbm/mhz G5SC MHz MHz 12 Mbit/s 23 dbm EIRP 13 dbm/mhz G5SC MHz MHz 6 Mbit/s 33 dbm EIRP 23 dbm/mhz G5SC MHz MHz 6 Mbit/s 23 dbm EIRP 13 dbm/mhz G5SC MHz MHz 6 Mbit/s 0 dbm EIRP -10 dbm/mhz G5SC5 As required in EN for the several dependent on channel 30 dbm EIRP (DFS master) 17 dbm/mhz band MHz to MHz spacing 23 dbm EIRP (DFS slave) 10 dbm/mhz NOTE: With respect to emission limits (power limit / power density limit), the more stringent requirement applies. Workshop / Coexistence between CEN DSRC and ITS-G5 9

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

11 Different 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 Workshop / Coexistence between CEN DSRC and ITS-G5 11

12 Interference from ITS-G5 to CEN DSRC OBU The CEN DSRC 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. x RSU µs x ITS signal µs x sum signal µs Workshop / Coexistence between CEN DSRC and ITS-G5 12

13 Interference from ITS-G5 to CEN DSRC RSU Blocking The CEN DSRC and the interfering ITS-G5 signal sum up in the CEN DSRC RSU receiver. The RSU sensitivity at the antenna for a left hand circular polarised CEN DSRC 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 signal even it is not in the CEN DSRC frequency band. The interference level that causes this so called blocking, strongly depends on the CEN DSRC implementation. Spurious and unwanted emissions If the ITS-G5 unwanted emissions in the CEN DSRC frequency band exceed -120dBm, interference to the CEN DSRC will start to happen. Workshop / Coexistence between CEN DSRC and ITS G5 13

14 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 possible 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 DSRC.... measurements showed no interference from CEN DSRC to ITS-G 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 OBU. Workshop / Coexistence between CEN DSRC and ITS G5 14

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

16 10 m 10 m World Class Standards Power coexistence limits evaluated by STF 395 Within a CEN DSRC Tolling Zone the electric field strength of a fixed ITS-G5 station ti shall not exceed 0,11V/m (-52 dbm). Lane Width ( * ) Tolling Zone ( ** ) At the CEN DSRC RSU antenna the field strength of a fixed ITS-G5 station shall not exceed 0,21 V/m (-46 dbm). CENDSRCRSU CEN DSRC RSU Tolling Zone ( ** ) *) 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 Zone position or RSU position. Lane Width ( * ) Workshop, Coexistence between CEN DSRC and ITS-G5 16

17 How to achieve coexistence World Class Standards Detect Identify the position of the mitigation area A And Avoid Avoid interference by a set of Coexistence Methods Workshop, Coexistence between CEN DSRC and ITS-G5 17

18 Coexistence Methods Workshop, Coexistence between CEN DSRC and ITS-G5 18

19 Fixed tolling station CEN DSRC RSU mounted on gantry World Class Standards mobile ITS-G5 station RTTT OBU Interference can only happen when the CEN DSRC OBU is inside the tolling zone. Workshop, Coexistence between CEN DSRC and ITS-G5 19

20 ut power limit / dbm EIRP ITS-G5 Outp dbm 170 m CEN DSRC RSU mounted on gantry World Class Standards Power coexistence mitigation areas 25 dbm mobile ITS-G5 station 70 m 10 dbm minim mum 75 db isolation Pathloss coefficient n=1.8 RTTT OBU minim mum 82 db isolation Distance to CEN DSRC tolling station / m schematically - not true scale! Workshop, Coexistence between CEN DSRC and ITS-G5 20

21 40 Power coexistence mitigation areas ut power limit / dbm EIRP ITS-G5 Outp dbm 170 m 25 dbm 70 m P TX =18 log 10 dbm ( d -10 ) minim mum 75 db isolation Pathloss coefficient n=1.8 minim mum 82 db isolation Distance 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. Workshop, Coexistence between CEN DSRC and ITS-G5 21

22 Principles of time sharing coexistence RSU RX / TX TX RX TX X retry RX... Time sharing can work when ITS-G5 is in Low Duty Cycle (LDC) operation. Additionally to the channel load, ITS-G5 channel usage timing constraints ITS-G5 activity (*)... must be specified. STF 411 is dealing with LDC methods. OBU RX / TX RX TX X RX TX... STF 420 on ITS-G5 channel configuration could consider this topic *) Interference will usually happen in CEN DSRC down link. time / ms Workshop, Coexistence between CEN DSRC and ITS-G5 22

23 Proposed LDC operation ITS- -G5 output po ower limit / db Bm t i t a time World Class Standards Additionally to the channel load, the maximum ITS-G5 channel activity time t a and the minimum idle time t i 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 t i or active for time t a. 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. Workshop, Coexistence between CEN DSRC and ITS-G5 23

24 Mitigation area identification Part 1 Workshop, Coexistence between CEN DSRC and ITS-G5 24

25 90 Isolation estimation methods - principle isolation / db Isolation Pathloss coefficient n=1.8 Fading margin +/- 6dB = log g( ( d ) Distance to beacon / m Due 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. Workshop, Coexistence between CEN DSRC and ITS-G5 25

26 Example: CEN DSRC signal detector Expected maximum ( * ) isolation to a CEN DSRC signal while passing the RSU CEN DSRC RSU mounted on gantry Pathloss coefficient n=1.8 Fading margin +6dB 80 lation / db iso Distance to beacon / m *) Because of fading, the isolation between detector and RSU might differ from the isolation to the victim. Workshop, Coexistence between CEN DSRC and ITS-G5 26

27 Example: CEN DSRC signal detector The TX power level and the antenna characteristics of CEN DSRC are standardised*. CEN DSRC RSU mounted on gantry -55 tector threshold / dbm CEN DSRC de Pathloss coefficient n=1.8 Fading margin +6dB polarization margin +3dB minim mum 75 db isolation 70 m -72 dbm detector RX level threshold minim mum 82 db isolation 170 m -79 dbm Distance to beacon / m *) Outside the main lobe of the RSU antenna the TX power level is 18 dbm EIRP. Workshop, Coexistence between CEN DSRC and ITS-G5 27

28 Example: CEN DSRC signal detector Example of combination with power coexistence areas ( * ) CEN DSRC RSU mounted on gantry tector threshold / dbm CEN DSRC de Pathloss coefficient n=1.8 Fading margin +6dB polarization margin +3dB 10 dbm minim mum 75 db isolation 70 m -72 dbm 25 dbm detector RX level threshold ITS-G5 TX power limit minim mum 82 db isolation 170 m 33 dbm -79 dbm ITS TX power limit / dbm EIRP Distance to beacon / m *) As another option LDC could be combined with a CEN DSRC signal detector. Workshop, Coexistence between CEN DSRC and ITS-G5 28

29 Summary Non 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 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). Workshop, Coexistence between CEN DSRC and ITS-G5 29

30 Thank you for your attention Workshop, Coexistence between CEN DSRC and ITS-G5 30

31 Abbreviations CEN Comité Européen de Normalisation CSMA/CA Carrier Sense Multiple Access with Collision Avoidance CH Channel CVIS Cooperative Vehicle-Infrastructure Systems DAA Detect And Avoid Down Link DSRC Dedicated Short Range Communication EIRP Equivalent Isotropic Radiated Power EN European Norm ETC Electronic Toll Collection ETSI European Telecommunication Standard d Institute t IEEE Institute of Electrical and Electronics Engineers ITS Intelligent Transport System ITS-G5 acronym for the 5,9 GHz vehicular adhoc network PHY LDC Low Duty Cycle LHCP Left Hand Circular Polarized MLFF Multi Lane Free Flow OBU OnBoard Unit OFDM Orthogonal Frequency Division Multiplex PHY PHYsical (OSI layer) RF Radio Frequency RSU RoadSide Unit RX Receive TS Technical Specification TX Transmit UpLink World Class Standards Workshop / Coexistence between CEN DSRC and ITS-G5 31