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Return Path Field Training

Return Path Field Training. Presented By: Fawad Faheem Return Path Maintenance. Overview. Introduction Modulation Schemes Return Path Noise DOCSIS Specifications. Introduction. What is Return Path? Why do we use Lower Spectrum? Different Standards (DOCSIS / EURODOCSIS). m(t). Sin.

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Return Path Field Training

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  1. Return Path Field Training Presented By: Fawad Faheem Return Path Maintenance

  2. Overview • Introduction • Modulation Schemes • Return Path Noise • DOCSIS Specifications

  3. Introduction • What is Return Path? • Why do we use Lower Spectrum? • Different Standards (DOCSIS / EURODOCSIS)

  4. m(t) Sin • Modulation schemes being used in R/P? • a) QPSK b) 16-QAM • BPSK • One bit is transmitted in one symbol m(t)Sint Block Diagram For Bpsk (t) = m(t) Sin t

  5. QPSK The input binary bit stream {dk}, dk = 0,1,2,..... arrives at the modulator input at a rate 1/T bits/sec and is separated into two data streams dI (t) and dQ (t) containing odd and even bits respectively. dI(t) = d0, d2, d4 ,... dQ(t) = d1, d3, d5 , ...

  6. DI Sin Digital bit stream (t) = DI Sin t + DQ Cos t  90o Cos DQ Block Diagram Qpsk (t) = DI Sin t + DQ Cos t = A Cos (t + I) Where A= √ (DI)2 + (DQ)2  = Tan-1 (DQ/DI)

  7. Reason for using QPSK and it's specs

  8. Return Path Noise being the biggest challenge to interactive services in HFC

  9. LEAKAGE Amount of RF signal that escapes out of the cable due to one of the following reasons. • Cable cracks. • Loose connectors • Damaged Connectors • Corrosion of connectors Types of Leakages: There are two types. 1) Egress. 2) Ingress

  10. Egress: Egress is RF signal leakage out of the Cable System Ingress: Ingress refers to RF Noise that leaks into the cable system. RF signal emitted from surroundings enters into the system to follow any path that provides least resistance

  11. Possible causes of noise from distribution plant and their fixing

  12. Studies have revealed that almost 95% of the ingress comes from customer premises. Possible causes are:

  13. CPD (Common path distortion) • 1) Because this distortion arises at points in the plant where both forward and reverse signals are present ,it is called as common path distortion. • 2) This type of noise is spurious in nature (whole noise floor raises) and are composed of distortion products of downstream signals.

  14. Second and Third Order Beats

  15. Possible causes • These usually include poorly installed connectors, corrosion, dissimilar metals used in connectors, or kinks and cracks in rigid coax, weather shielding, oxidation etc.

  16. DOCSIS Specifications Downstream

  17. DOCSIS Specifications Upstream

  18. How to Improve C/N?

  19. Plant Statistics • Plant leakage has been a Big Problem. • Missing HPF’s should be looked after • Weather protection of passives by using heat shrinks • Documentation and improvement in troubleshooting techniques

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