Characterizing Signal Leakage from an All-Digital Cable Network

Transcription

1 Characterizing Signal Leakage from an All-Digital Cable Network for CCTA Technical Training Sessions August 14, San Juan, PR Presenter: Mario Sebastiani 1

2 Seminar Summary Topics review for all-digital HFC network: Is it necessary to patrol for leakage? Is the leakage spec the same as for analog? Can QAM signals cause harmful interference? Can off-air digital ATSC impair QAM signals? Is CW/Video carrier necessary for patrolling? What frequency should I troubleshoot egress? Are vendors providing digital leakage gear? 2

3 Technical Training Outline Examine reasons for a patrolling leakage program Demystify leakage characteristics & requirements Analyze leakage symptoms & measurements Concerns of leakage in an all-digital network? Characterising Signal Leakage in an All-Digital Cable Network (Courtesy of SCTE live learning, 2010) Demonstration of QAM carrier impaired by analog or digital signals with MER/BER measurements 3

4 What is Leakage/Egress? Definition: - Undesired emission of RF energy generated by the coaxial plant - Modulated RF signals radiating or leaking out of the cable network 4

5 Leakage & Ingress Leakage - RF energy leaking out of the coaxial environment Ingress - RF or electrical energy that enters the coaxial environment 5

6 Why do we monitor for leakage? 6

7 Reason #1 to Monitor for Leakage Prevent Off-Air Interference 7

8 Off-Air Interference Broadcast TV signals Radio Mobile Communications Public Services Emergency Services Aircraft Communications 8

9 NCTA/EIA Spectrum Plan Bande de retour Bande FM Bande moyenne Fréquences Hertzienne (TV) (usage limité) Bande supérieure Fréquences aéronautiques (restrictions d utilisation) Bande Hyper Fréquences Hertzienne (TV) (usage limité) 9

10 Frequency Allocation-Cable & Off-Air EIA/NCTA Traditionnel Standard Terrestre EIA/NC Traditionnel Standard Terrestre T A Bande T 99 A T * A * B Bande * C basse Bande D moyenne E MHz 19 F Bande basse Bande FM radio et télévison par câble G H XX I A A Bande haute 97 A XX

11 Frequency Allocation-Cable & Off-Air FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC) Bande moyenne Bande haute FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC) Désignation du canal Porteuse audio (MHz) Désignation du canal Porteuse audio (MHz) EIA/NCTA Traditionnel Standard Terrestre EIA/NCTA Traditionnel Standard Terrestre 98 A J Bande 99 A K super 14 * A W * B AA Radio Astronomie 16 * C BB D * EE E * FF F GG G HH H Bande Q hyper 22 I Q Q Q Q Q Q Q * fréquences aéronautiques 11

12 Reason # 2 to Monitor for Leakage Regulatory compliance requirements for spectrum management, public interest and public safety (FCC,IC, Burtel,TATT,Broadcom, etc ) 12

13 Frequency Allocation-Cable & Off-Air FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC) Bande moyenne Bande haute FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC) Désignation du canal Porteuse audio (MHz) Désignation du canal Porteuse audio (MHz) EIA/NCTA Traditionnel Standard Terrestre EIA/NCTA Traditionnel Standard Terrestre 98 A J Bande 99 A K super 14 * A W * B AA Radio Astronomie 16 * C BB D * EE E * FF F GG G HH H Bande Q hyper 22 I Q Q Q Q Q Q Q * fréquences aéronautiques 13

14 Spectrum Chart Aeronautical Service Bands 108MHz 139MHz Off-Air Aircraft Radio & Navigation Cable CH 98 CH 99 CH 14 CH 15 CH 16 QAM Freq. 111MHz 117MHz 123MHz 129MHz 135MHz 14

15 Spectrum Chart (cont d) Aeronautical Service Bands 324MHz 336MHz Off-Air Aircraft Radio & Navigation Cable QAM Freq. CH MHz CH MHz 15

16 FCC/IC Regulations & Procedures for Leakage Measurement < 54 MHz & > 216 MHz = 30m > 54 MHz & < 216 MHz = 3m Use a calibrated half-wave dipole antenna Antenna must be elevated 3 meters off the ground and positioned 3 meters from the leakage source 16

17 Patrolling for Leakage 20µVm 3 meters 30 meters 2 µvm 17

18 µv/m Standard unit of measure for Leakage 50 Ohm off air measurement Voltage developed in 1 meter of infinitely thin section of wire submerged in a leakage field, produces 1µV of energy 18

19 Polarization Angle Dipole Monopole 19

20 Leakage Antennas-Dipole 20

21 Cumulative Leakage Index (CLI) CLI is the net effect of the combination of all the leaks in the system added together These cumulative leaks form an invisible cloud of unwanted RF energy over the cable system 21

22 Required Actions All leaks 20 µv/m must be logged and fixed Only leaks above 50 µv/m are used in CLI calculation All measurements taken outside MHz must be converted as if they were taken within the band 22

23 Reason #3 to Monitor for Leakage Improves System Performance Reduces Repeat Service Calls Locate Physical Problems 23

24 Common Causes 70% of all leakage is caused by problems between the tap and entry to the house Aging and environmental stress Physical trauma to cables or connectors Loose drop connectors Inferior quality coaxial cable, passives, or connectors Loose hard line connectors 24

25 Other Causes of Leakage Improperly installed connectors Cracks in the distribution and feeder cable Animal chews Poorly-shielded drop cable Bad connectors at the tap Bad/loose port terminators Corroded connectors 25

26 Other Causes (Cont d) Customer installed equipment Damaged amplifier housing or loose lids Loose tap plates Broken tap ports Poor installation of splices and connectors Poorly-shielded customer premise gear 26

27 Tools Dipole Monopole 27

28 Signal Phasing 28

29 Standing Waves 29

30 Electrical Noise 30

31 Characterizing Signal Leakage from an All-Digital Cable Network Ron Hranac and Ray Thomas (Comcast) have conducted field tests on the subject a couple of years ago SCTE live Learning presentation on the subject erence/recordingdefault.aspx?c_psrid=e D50D

32 Characterizing Signal Leakage from an All-Digital Cable Network Field tests were conducted in the Denver, Co area using an analog CW carrier and a 256 QAM carrier CW test frequency was Ch. MHz Digital test with 256QAM 147Mhz Digital test with power -6dBc from CW (video) Testing leakage carrier in between 2 QAMs Minimum spectrum protection for CW vs QAM 32

33 Characterizing Signal Leakage from an All-Digital Cable Network Review the characteristics of the analog and digital carriers Review type of modulation Where the RF energy is located Historical test instruments to measure leakage Troubleshooting gear MER/BER performance behavior being deteriorated by signal ingress 33

34 Typical Analog & Digital Carriers 34

35 Analog Video Carrier 35

36 Analog A/V Carriers MHz Video Carrier -10 Audio Carrier Amplitude Modulation db Sous-porteuse couleur 4.2 MHz FM Modulation +/- 25 KHz MHz MHz MHz 4.5 MHz 36

37 Analog C/I Objective Table MHz Red designates Visible interference Green designates Non-visible interference db MHz 4.5 MHz 37

38 Analog Carrier with Modulation 38

39 Typical Digital QAM Carriers 39

40 Characterizing Signal Leakage from an All-Digital Cable Network Conclusion from Hranac/Comcast test results: Leaks from digital QAM carriers can cause harmful interference to terrestrial users just like analog carriers Terrestrial RF energy can impair on QAM signals depending on the level of the ingress Patrol leakage program should apply to alldigital systems The compliance spec for all-digital networks is similar as for analog cable systems 40

41 Characterizing Signal Leakage from an All-Digital Cable Network Summary and conclusion of SCTE tests (cont d): A CW carrier is still the most cost/efficient method for testing and troubleshooting leakage The minimum frequency offset allocation to a QAM is 1 MHz The frequency range for leakage detectors can be from 108MHz ~147MHz (Aeronautical band) Allocating CW carrier between 2 QAM carriers will impair on both QAM carriers Video carrier from analog modulator may be used 41

42 Characterizing Signal Leakage from an All-Digital Cable Network Summary and conclusion of SCTE tests (cont d): Some manufacturers are working on or already supplying leakage detection tools for digital QAM carriers Cost efficiency of digital leakage instrumentation will accelerate its deployment in all-digital cable systems 42

43 Leakage Downstream Ingress Facts Being leakage compliant with rules and regulations increases the figure of merit of the HFC network Higher MER levels throughout the RF plant - greater signals reliability The average MER objective at the subscriber tap of 33dB ~ 35dB 43

44 MER TARGET - THE CLIFF EFFECT P Operating margin Zone Risk Zone RS-FEC Crash Zone Upstream 16 QAM >22dB 22dB - 20dB <17dB Objective UP/Downstream 64 QAM >28dB 28dB - 26dB <23dB P- BER CER Downstream 256 QAM >33dB 33dB - 31dB <28dB 1 x x

45 Constellation Performance Good MER Bad MER 45

46 QAM EVS Troubleshooting in-channel ingress is easy with QAM EVS mode Typical ingress areas Loose connector Broken shields Tap plate loose Home wiring CSO/CTB from house amp Sweep inter-mod 46

47 Digital signals work well until very close to the point of failure Measurement of digital carriers is critical in determining the system margin BER Signal level MER Pre/Post BER CER (Codedword Error Rate) The BER helps to find problems related to point of failure. Gray lines designate marginal signal quality Black lines is a sign of macro-blocks and picture pixelling 47

48 BER/CER BER Pre: before FEC repair Post: after FEC repair ERRORS Corr = corrected codewords uncor = uncorrectable codewords err sec = errored seconds sev sec = severely errored seconds Codeword Error Rate: Objective = 9x10 ⁷ 48

49 MER/BER Demonstration Impairment simulation affected by leakage 49

50 Characterizing Signal Leakage from an All-Digital Cable Network Thank you, Gracias, Danki, Merci to the CCTA members Mario Sebastiani: Serving the industry since 1978 with pride, integrity and commitment 50

51 Tools Dipole Monopole 51

52 Some of Incospec s Associates 52