Viavi 87339, Руководство по эксплуатации

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Testing
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3.2.2.A Fading and Multi-path Model Implementation
The GPSG-1000 firmware implements independent multi-path models for each satellite
channel. Each channel supports a two-state (good/bad) Rician fading model with
independently configurable fading and shadowing in each state. This underlying model
can also be simplified to support a Rayleigh fading model.
In Rician fading the power of the received signal varies as the dominant line-of-sight
component is partially canceled by delayed reflections of itself, particularly when the
delays experienced by the reflected rays are time-varying.
In Rayleigh fading the power of the received signal varies according to the Rayleigh
statistical distribution (i.e. as the radial component of the sum of two uncorrelated
Gaussian random variables). This is generally considered as a good model for scenarios
where the signal has been highly scattered and there is no dominant line-of-sight
component. This situation typically occurs in urban environments, and during propagation
through the atmosphere.
Shadowing simulates the effect of occasionally losing the line-of-sight signal due to
obstruction of the signal by nearby objects. This can occur due to the motion of the
satellite across the sky taking the apparent position of satellite behind buildings of other
objects, but is typically caused by motion of the user. The effect is that the multi-path
environment can be described as a two state system, with different behavior in the “good”
or non-obstructed state and “bad” or obstructed state.
Fading is modeled as being uncorrelated between satellites and frequencies, whereas
shadowing in uncorrelated between satellites, but correlated across frequencies.
There is no support for simulating multi-path ray delay in the current firmware, so the
model is best considered as simulating a very complex multi-path environment with many
multi-path rays and none dominant.
The GPSG-1000 firmware models the line-of-sight component as having 0 dB power, with
the power of the multi-path components relative to this level.