Adjacent Satellite Interference

A Case Study

SUIRG Annual ConferenceJuly 11- 13, 2006

Stockholm

C or Ku-Band Satellite dishEMR5520/5020

PAL TV

RG-6 Plenum

PAL ChannelModulator #1

PAL ChannelModulator #2

Tivella STB#2

Tivella STB#1

NetworkSwitch

Combiner

RG-6

EDS IP Addition-DownlinkA. Porter 11.4.2004

VideoOut

VideoOut

AudioOutLeft

AudioOutRight

AudioOutLeft

AudioOutRight

Ethernet Ethernet

Eth2/LAN2

Satellite In ForEMR5020.PCI1 forEMR5520

Installer Laptop computer

Eth1/LAN1

CAT5e

CAT5eCross Over

Cable

Block Diagram

Receive Only Site

2.4M Antenna

User Application

• IP streaming based BTV satellite network

• The IP streaming network is broadcast on a 2.75MHz carrier allowing for two IPTV channels using 1.2 MB of data each.

• The Skystream EMR-5000\5520 receives the DVB carrier, decapsulates the IP data and forwards Multicast on to the LAN.

• The Set Top Box decodes the Multicast IPTV streams and outputs analog audio and video for viewing on a normal PAL TV set

Bench Mark Parameters

• Receive Signal is at 3727.5MHz, RHCP (LNB Output=1422.6MHz)

• Signal Strength of > -65dBm for the Skystream Receiver

• Signal Lock

• Eb/No of > 6dB (indicated on the Skystream Receiver)

• LNB Offset of < 1 (indicated on the Skystream Receiver)

• Reed Solomon Uncorrected Errors less than 5 over a period of 1Hr

10°

0°

Fuchsstadt

SpeedLink40: Forward link - User terminal antenna size IX (902) at 62.0°E , 5.97 GHz Up, 3.75 GHz Down Data rate: 3041 kbps, User terminal availability: 99.900% Uplink beam: IZ1 (NW), Downlink beam: IH2 (EH)

<2.4m2.4m to 2.8m2.8m to 3.2m3.2m to 3.7m>3.7m

Coverage Map – Installed Sites

ChennaiPune

Mumbai

Gurgaon

<2.4M

2.4M to 2.8M

2.8M to 3.2M

3.2M to 3.7M

>3.7M

Recommended Antenna Size

2.4M Reference Site - BangaloreCarrier as seen on 2.4M Receiver Statistics

Low Eb/No = 3dB

Very High Uncorrecte

d Errors

Possible Causes

- Terrestrial Interference

- Lower Gain in Rx chain

Next Step: Try the same setup on a 3.8M Antenna

3.8M Test - BangaloreCarrier as seen on 3.8M Receiver Statistics

Good Eb/No = 7.4dB

Uncorrected Errors = 0

Works fine - Both TV Channels received properly

2.4M vs 3.8M- BangaloreCarrier as seen on 2.4M Carrier as seen on 3.8M

• 3.8M Results is in line with expectations

• 2.4M Carrier ‘shape’ is suspicious. However no reasons attributed

Next Step: Install 2.4M setup at Chennai and study performance

2.4M Client site - ChennaiCarrier as seen on 2.4M Receiver Statistics

Neglect this spike. It was a characteristic of the receiver when the LNB is powered from receiver.It was proved that this has no bearing on the results

• Similar results as in Bangalore

• Carrier parameters are as expected

• Low Eb/No and High Number of errors

Terrestrial Interference is ruled outSuspect Antenna Orientation, Cabling, Link Budget Errors

Link Budget Analysis

• C/N Measured on 2.4M at Bangalore is 7.9dB.This is as expected from the Link Calculations.

• Eb/No measured is significantly lesser than Link Calculations.

• Suspect Interfering signals, but source is not known.

• Suspect that locations Bangalore and Chennai lie in weaker signal zone as per coverage map.

Next Step: Install 2.4M setup at Pune which is in a stronger signal region

2.4M Client site - PuneCarrier as seen on 2.4M Receiver Statistics

• C/N and Eb/No is better by about 1dB

• Eb/No is below spec of 6dB

• Uncorrected Errors are High

• Suspect Rx signal level is too low for the IP Receiver

Next Step: Use a Line Amplifier in Rx chain to improve signal level

2.4M - Bangalore with Line Amp

• Signal Level has improved

• Eb/No is still at 3dB

• Uncorrected Errors are High

• Suspect Interfering Signal (Most Probably from Adjacent 2º Satellite)

Carrier as seen on 2.4M Receiver Statistics

Next Step: Check for Signals in Adjacent Satellites

Adjacent Satellite PlotsPlots of signals 1422.6MHZ on 2.4M

SAT0 - Sat. of Interest SATW - Sat. 2º WestSATE - Sat. 2º East

• SATW shows a large Carrier at the same frequency as our Downlink

• 3dB Beamwidth of 2.4M Antenna is 2.2º.

• Suspect strongly that SATW signal is the source of Interference

Next Step: Switch Off SAT0 signal and make measurements

Measurements with Carrier OffPlot on 2.4M Plot on 3.8M

• 2.4M plot shows potential spurious signals

• 3.8M plot is relatively clean

• 3dB Beamwidth of 3.8M is 1.5º may not pick up signals from Adjacent 2º Satellite

Comparision of SignalsSignals seen on 2.4M Prodelin Antenna

Carriers on SATW. Taken at 20MHz span centered around1422.6 MHz

Plot seen on SAT0 with Carrier ‘OFF’

Conclusion

Next Step: Shift to a new Downlink Frequency

• Problem is repeated at 3 Geographically different locations. Terrestrial Interference is ruled out

• Rx signal levels and C/N as per Link CalculationsAntenna Orientation, Cabling issues are ruled out

• Line Amplifier did not have any effectLow signal level is ruled out

• Signal Interference is the causeSource of Interference is strongly suspected to be from Adjacent Satellite

Results at New Frequency

• New Frequency is 3895.64MHz (LNB = 1254.35Mhz) , RHCP

• Eb/No =8.9dB and Uncorrected Errors = 0

• All results achieved with only change in Downlink Frequency

• No other change in Antenna position or any other equipment

Carrier as seen on 2.4M Receiver Statistics

• Satellite Operator decided to freeze on New Frequency and Level

• All 4 Client Locations were successfully installed after this

• The entire effort resulted in large delays and escalation of costs

• Troubleshooting effort was complicated as many parties were involved needing close co-ordination.

• Same problem may occur in future if frequency in Adjacent Satellite is re-allocated without taking our application into account.

• Urgent need to review the use of 2.4M Antennas with 2-degree spacing Satellites

• Similar Case studies on other Satellites, Applications and Antennas needs to be published with a view to reducing troubleshooting effort

Closing Observations

THANK YOU