By Frank R. Koperda, Scientific-Atlanta, Inc
Past studies have quantified the behavior of interference and ingress in the reverse path (e.g., 5 - 40 MHz) of Hybrid Fiber Coaxial cable (HFC) plants. Unfortunately, the speculation of a hostile environment has been confirmed The studies show the detrimental impact of ingress and impulse noise on the transmission quality, and confirm its unpredictable nature. Preventive measures can be applied to improve cable plants' quality for digital services, but the real challenge is to design a network architecture that survives adverse conditions. Achieving high signal quality is even more important when telephony service is added because it demands high system reliability and fault tolerance. This paper focuses on the selection of various transmission schemes for this potentially hostile environment. It shows the advantages FDMA (Frequency Division Multiple Access) has over the wideband burst mode TDMA (Time Division Multiple Access). The requirements and mechanism for providing reliable telephone service will be discussed and analyzed. A reliable RF channel protection algorithm and family of channel hopping algorithms that achieve acceptable telephone service will be discussed System capacity can be estimated given a desired service quality as measured by blocking probability.