Federal Office for CommunicationsFrequency Management

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

René Tschannen, OFCOMBrussels, 25th January 2010

3 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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”

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

Relevant immunity standards

Background Measurements Theoretical Studies Conclusions

4 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Radiated power of mobile handsets

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

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

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

In this typical example 90% of the active mobile handsets have an output power of ≤14 dBmEIRP

2 dBmEIRP= 1.6 mW

14 dBmEIRP= 25 mW

23 dBmEIRP=200 mW

24 dBmEIRP=250 mW

25 dBmEIRP=316 mW

Background Measurements Theoretical Studies Conclusions

Accordingly 10% of the active mobile handsets have an output power of >14 dBmEIRP

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+2.15dBm

ERP=EIRP–2.15dBm

5 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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

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

Background Measurements Theoretical Studies Conclusions

separation distance

= interference radius

victim

immunityfield strength

PTx

interferer

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

6 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Measurement setupsInterferer

Background Measurements Theoretical Studies Conclusions

Viewer

coaxial cable

analogue TV orTV set with integrated STB

RFin

TV setDVB-C STB

coaxial cable

SCART or HDMI

RFin

Viewer

TV setDVB-C STB

coaxial cable

RFin RFout

RFin

coaxial cable

Viewer

Cable Modem PC

coaxial cable

ETHERNET

CATV distribution network

PTx level increased until interferenceobserved

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)

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

7 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Measurement resultsBackground Measurements Theoretical Studies Conclusions

• 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 connectors two 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

lousy device

very good device

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

8 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Background Measurements Theoretical Studies Conclusions

Interferer

TV setDVB-C STB

RFin RFout

RFin

coaxial cablecoaxial cable

CATV distribution network

broadband amplifier

RFin RFout

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

Interference cases

Interference cases and the results of our measurements:a) insufficient shielding of the cable distribution network

Is not an issue, if the network is properly implemented

b) 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 !

c) 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 regulatory requirement 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 interference occurs it is 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.

9 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Findings from the measurementsBackground Measurements Theoretical Studies Conclusions

How likely is co-channel interference?

• The wanted signal level in a CATV-network should be sufficient (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 only b) the interference radius is small (a few meters) => interference is

home-made and thus under the control of the user c) 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 available from other parties are based 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)

10 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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

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.

Background Measurements Theoretical Studies Conclusions

High cable penetration in Switzerland > 85%

11 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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

832 857852847842837 862 MHz

854846838830 862 MHz

K66

UL1 IMT-UL

DVB-C

UL5UL4UL3UL2 UL6

K67 K68 K69

A certain CATV-receiver is interfered, when:• this CATV-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 channelch67, ch68, and ch69 are interfered from 2 IMT channels each

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%6969686867676666 SKSKSKSKS ppppppppp 16.2005.0

66

22

11 eep DrS

32.4005.0696867

2

1 eppp SSS601

69686766 KKKK pppp

12 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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)

Background Measurements Theoretical Studies Conclusions

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

13 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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

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 !! !

14 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

BTS LTE

CATV-Receiver

UE LTE

7 LTE cells with randomly distributed UE and CATV-Receivers

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

Background Measurements Theoretical Studies Conclusions

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

the probability of co-channel interference is calculated

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 power was identified as 13.8 dBmEIRP and

the probability of co-channel interference is in the same order of magnitude !

15 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

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

Background Measurements Theoretical Studies Conclusions

16 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Conclusions (2)OFCOMs view • It is politically justifiable to introduce IMT in the 800 MHz

band without risking many customer complaints about interferences in CATV-networks/-devices

Background Measurements Theoretical Studies Conclusions

17 cable TV receivers affected by new radio services in the 800 MHz bandRené Tschannen, OFCOM

Thank you for your attention…

… are there any questions?

Background Measurements Theoretical Studies Conclusions