Calculating Fade Margin

2.7.2.1 Using the Rayleigh Fading Assumption. If we assume fading is entirely due to multipath conditions, we then can describe the worst-case fading with a Rayleigh distribution. A Rayleigh fading distribution is plotted in Figure 5.2.

For Rayleigh fading, the link margins given in Table 2.6 are required versus time availability. Extrapolation from Table 2.6 can be made for any time availability. For example, a link requiring 99.95% time availability would require a 33-dB margin. This tells us that if the minimum unfaded C/N for the link were specified as 20 dB, the link would require 20 dB + 33 dB or a

Fade Margin

Figure 2.16. Fade margins A1 as a function of path length d with unobstructed LOS (without precipitation attenuation). Typical values are for 1% of the time of a month with severe fading. (From Planning and Engineering of Radio Relay Links, 8th ed., Siemens-Heyden; copyright ©1978 Siemens Aktiengesellschaft, FRG; Ref. 12.)

Figure 2.16. Fade margins A1 as a function of path length d with unobstructed LOS (without precipitation attenuation). Typical values are for 1% of the time of a month with severe fading. (From Planning and Engineering of Radio Relay Links, 8th ed., Siemens-Heyden; copyright ©1978 Siemens Aktiengesellschaft, FRG; Ref. 12.)

TABLE 2.6 Fade Margins for Rayleigh Fading

Time Availability (%)

Fade Margin (dB)

+1 -2

Responses

  • mathias
    How to calculate fade margin from availability figure?
    7 years ago
  • evan
    What is db fade margin satellite?
    7 years ago

Post a comment