Home Network Basis: Transmission Environments and Wired/Wireless Protocols

3.7. Noise Environment

Transmission characteristics have been extensively field-tested for the purpose of implementing cable modem and other digital services [5]. In the reverse channel frequency band between 5 and 40 MHz, ingress noise level is relatively high. It was found that ingress spectral contents are confined to narrow frequency ranges. Sources of ingress include short-wave broadcasts, HAM band transmission, and CB traffic. In general, the spectral energy density decreases as frequency increases. Figure 3.11 shows one example of many field-collected measurements. There are seven visible plots representing minimum, first decile, first quartile, third quartile, ninth decile, 99th level, and maximum, respectively, in Figure 3.11. In real ...