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EC workshop cable TV receivers affected by new radio services in the 800 MHz band. René Tschannen, OFCOM Brussels, 25th January 2010. Background. Measurements. Theoretical Studies. Conclusions. Interference immunity level for CATV-networks and –equipment.

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ec workshop cable tv receivers affected by new radio services in the 800 mhz band

EC workshopcable TV receivers affected by new radio services in the 800 MHz band

René Tschannen, OFCOMBrussels, 25th January 2010

interference immunity level for catv networks and equipment
Background

Measurements

Theoretical Studies

Conclusions

Interference immunity level for CATV-networks and –equipment
  • EN 50083-8“Cabled distribution systems for television and sound signals. Electromagnetic compatibility for networks”
  • EN 50083-2“Cable networks for television signals, sound signals and interactive services. Electromagnetic compatibility for equipment”

Relevant immunity standards

CATV-networks and –equipment have a regulatory need to work up to an interference immunity level of 106 dBμV/m(= 0.2V/m)

radiated power of mobile handsets
Background

Measurements

Theoretical Studies

Conclusions

typical power distribution of mobile handsetsdata measured in an IMT rural cell in Australia 1)

In this typical example90% of the active mobile handsets have an output power of≤14 dBmEIRP

Accordingly10% of the active mobile handsets have an output power of>14 dBmEIRP

Radiated power of mobile handsets

user device uplink emission (e.i.r.p.) levels according to 3GPP specifications:

The maximum radiated power of a UMTS handset is 24 dBmEIRP

(as handsets have isotropic antennas the values given are in EIRP- and not in ERP) EIRP=ERP+2.15dBmERP=EIRP–2.15dBm

2 dBmEIRP= 1.6 mW

14 dBmEIRP= 25 mW

23 dBmEIRP=200 mW

24 dBmEIRP=250 mW

25 dBmEIRP=316 mW

1) ITU-R JTG 5-6 Doc. 5-6/88-E (Annex 14), published 3rd June 2009

interference radius
Background

Measurements

Theoretical Studies

Conclusions

Remember:24 dBmEIRP = max. radiation power of a UMTS handset14 dBmEIRP => 90% of all active handsets radiate a power ≤14 dBmEIRP

= regulatory interference immunity level

interferer

Interference radius

PTx

Field strength as a function of the separation distance between a LTE handset (interferer) and a CATV-receiver (victim) at a given radiation power PTx

separation distance

immunityfield strength

= interference radius

victim

In case a CATV-receiver complies with the immunity level of 106 dBμV/m then the interference radius is for 90% of the active LTE handsets ≤4.3m

If the immunity level of a device is better than 106 dBμV/m then the interference radius is reduced accordingly

measurement setups
Background

Measurements

Theoretical Studies

Conclusions

analogue TV orTV set with integrated STB

Viewer

coaxial cable

CATV distribution network

A

RFin

Viewer

TV set

DVB-C STB

SCART or HDMI

RFin

D

B

coaxial cable

PTx level increased until interferenceobserved

Viewer

TV set

DVB-C STB

coaxial cable

coaxial cable

C

RFin

RFout

RFin

PC

Cable Modem

ETHERNET

coaxial cable

Measurement setups

Interferer

UMTS signal with abandwith of 3.84 MHz(focus on UpLink 832-862 MHz)

Measurements have been conducted at two locations:- at a CATV-headend - in a private apartment

Analogue and digital reception has been studied

Separation distance between interferer and vitctim: 1.6m (to compare with studies from other organisations)

measurement results
Background

Measurements

Theoretical Studies

Conclusions

very good device

lousy device

Interpretation:less than 10% of active handsets have an interference radius >1.6m

Measurement results
  • Setups A & B:The immunity of the configurations under test was ≥10dB better than the regulatory immunity field strength limit of 106dBµV/m. The immunity could be further improved with better cables.
  • Setup C:When the signal was looped through the RFin/RFout connectorstwo devices did behave quite badly (due to built-in broadband amplifiers that pick-up interference)
  • Setup D: The device under test (cable modem) was a very poor one
interference cases
Background

Measurements

Theoretical Studies

Conclusions

TV set

CATV distribution network

DVB-C STB

coaxial cable

coaxial cable

RFin

RFout

RFin

Warning:Daisy-chaining the signal through the RFin/RFout connectors of domestic equipment can cause a signal qualitydegradation up to 30dB !!

broadband amplifier

RFin

RFout

Interference cases

Interferer

Interference cases and the results of our measurements:

  • insufficient shielding of the cable distribution network

 Is not an issue, if the network is properly implemented

  • isufficient shielding of the cables between the wall socket and the receiver equipment

 Critical as cable qualities differ substantially. Measured shielding effectiveness varied between 30-105dB ! => use good shielded cables only !

  • insufficient shielding of the receiver equipment

 If a „loop-through“ of the signal via built-in broadband amplifiers was avoided: The immunity of the devices was better than the current regulatoryrequirement of 106dBμV/m(exception: cable modem)

There are some CATV-devices on the market that show quite a good immunity ! => request to industry to improve the immunity of all CATV-products

If interferenceoccurs itis mainly localised within a short distance to the victim and it is co-channel only !Interference is thus under the control of the user of a mobile LTE handset.

findings from the measurements
Background

Measurements

Theoretical Studies

Conclusions

 How likely is co-channel interference?

Findings from the measurements
  • The wanted signal level in a CATV-network should besufficient (e.g. >55 dBμV for a 256QAM modulated OFDM-signal) to get a reasonable C/I-ratio
  • For use in sharing studies a realistic working level for the interfering LTE-signal is 14dBm(90th percentile value)
  • Avoid daisy-chaining the signal through the RFin/RFout connectors of domestic equipment
  • Use only connection cables with a good shielding effectiveness
  • It was observed that a) interference occurs in co-channel onlyb) the interference radius is small (a few meters) => interference ishome-made and thus under the control of the userc) the likelihood that mobile handsets radiate with high PTx levels is relatively low what reduces the risk of interference (power distribution of LTE UE)
  • Criticism:In the view of OFCOM the measurements currently availablefrom other parties arebased on theoretical absolute worst case conditions (use of extreme PTx levels for the interferer, assumption of permanent co-channel constellations and a too low wanted signal level in the cable distribution network)
slide9
Background

Measurements

Theoretical Studies

Conclusions

Probability of co-channel interference from IMT handsets (uplink) into CATV-receivers (statistical approach)

High cable penetration in Switzerland > 85%

Assumptions for the theoretical modelling for Switzerland:

  • Active IMT handsets (UE) per km2 and per 5 MHz: . . . . . 2.16 1) = D
  • Typical call duration: . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 min
  • Total number of CATV-receivers in SUI: . . . . . . . . . . . . . 2‘800‘000
  • CATV-receivers in use during busy hour: . . . . . . . . . . . . 30% (840’000)
  • Number of channels on the cable: . . . . . . . . . . . . . . . . . . 60
  • Daily usage of the CATV-receivers: .. . . . . . . . . . . . . . . . 4 h
  • Interference distance between UE and CATV-receiver. . <5 m = r

1) This density is conservative (i.e. is high). A large percentage of indoor mobile traffic will be operated by femto-cells in future. Femto-cells will hardly being operated in the UHF-band.Furthermore, the 3.4-GHz-band was not considered by the calculations.

calculating the probability of co channel interference statistical approach
Background

Measurements

Theoretical Studies

Conclusions

The probability that at least one IMT handset causes co-channel interference into a particular CATV-receiver is

= 1.97 * 10-5~0.002%

Calculating the probability of co-channel interference(statistical approach)

A certain CATV-receiver is interfered, when:

  • thisCATV-receiver is in use (active)
  • and an active IMT handset is located within a distance of <5 m
  • and the channel on the cable and the IMT channel collide

ch66 is interfered from 1 IMT channel

ch67, ch68, and ch69 are interfered from 2 IMT channels each

number of interfered catv receivers statistical approach
Background

Measurements

Theoretical Studies

Conclusions

During main traffic hours there will be about 17 interferences on average all over Switzerland

Number of interfered CATV-receivers(statistical approach)

Distribution (CDF) of the interferences throughout Switzerland at a given point of time. Interference distance ≤ 5 m

For Switzerland:With a probability of 90% less than 23 interference cases are in place at a given point of time

(of a total of 2‘800‘000 devices whereas 840‘000 are in use during busy hours)

number of annual interferences for an individual catv receiver statistical approach
Background

Measurements

Theoretical Studies

Conclusions

With a probability of nearly 90% a particular Swiss CATV-receiver will be interfered throughout one year once at most !!

!

Number of annual interferences for an individual CATV-Receiver (statistical approach)

Distribution (CDF) of the number of the annually interferences perCATV-receiver and year. Interference distance ≤ 5 m

another approach to cross check the reliability of the statistical results monte carlo simulation
Background

Measurements

Theoretical Studies

Conclusions

the probability of co-channel interference is calculated

Another approach to cross-check the reliability of the statistical results („Monte Carlo“-simulation)

A single “shot”:

  • A certain CATV-Receiver is placed randomly in the centre cell
  • The active IMT handsets are with a given density equally positioned over all 7 cells (on the same channel)
  • Is there an active IMT User Equipment within a distance of <5m?
  • The interference from the closest UE to the chosen CATV-Receiver is calculated

Such “shots” are repeated 5 million times

7 LTE cells with randomly distributed UE and CATV-Receivers

The supplementary „Monte Carlo“-simulation fully confirmed the results that we have previously obtained with a pure statistical investigation !=> the 90th percentile of the mobile handset output powerwas identified as 13.8 dBmEIRP and the probability of co-channel interference is in the same order of magnitude !

conclusions 1
Background

Measurements

Theoretical Studies

Conclusions

Conclusions (1)

Outcome from Measurements

  • Interference is limited to co-channel only
  • The likelihood that mobile handsets radiate high PTx levels is low what reduces the risk of interference
  • The interference radius is in a range of a few meters, therefore „home-made“ and under the control of the user

Outcome from Theoretical Studies

  • Two independent theoretical approaches (statistical model & MC-simulation) have shown that the probability of co-channel interference between LTE UE and CATV-Receivers is very low

Conclusion

  • The probability of co-channel interference is a very important factor that has to be taken into account in discussions about „IMT  CATV“-interference
conclusions 2
Background

Measurements

Theoretical Studies

Conclusions

Conclusions (2)

OFCOMs view

  • It is politically justifiable to introduce IMT in the 800 MHzband without risking many customer complaints about interferences in CATV-networks/-devices
slide16
Background

Measurements

Theoretical Studies

Conclusions

… are there any questions?

Thank you for your attention…

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