By Diana Linton, Justin Stiles, Esteban Sandino, Roger Stafford, Vinod Dani, Jay Liew, Keith Auzenne; Charter Communications
This paper will present the results of the practical application of PMA in an HFC plant. The primary focus will be on OFDM operation in HFC plant roll-off areas as a practical mechanism to gain additional network capacity by increasing the modulation order and bit loading capacity of individual subcarriers for those CMs reporting higher RxMER values. The paper will discuss first the observed roll-off characteristics between 1.0 GHz and 1.2 GHz for a representative HFC plant segment configured with a mix of 1.2 GHz amplifiers and 1.0 GHz passives, and the worsening conditions impacting this portion of the HFC spectrum as the number of cascaded 1.0 GHz passives increases. It will discuss next the maximum expected MER and modulation orders at various tap locations throughout the cascade, and how an initial optimization of OFDM parameters for operation in roll-off areas using only flat modulation profiles can deliver limited capacity gains prior to a PMA deployment. Finally, the paper outlines how a full PMA approach is used to correctly identify physical channel conditions as seen by individual customer modems, and how this data is used to dynamically select the most appropriate OFDM profiles for optimal roll-off operation of modems connected throughout the cascade. Expected overall capacity gains when applying a PMA approach that enables efficient operation of OFDM carriers in roll-off areas will be discussed.