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Characteristics of the Signal

 Multipath Fading Dominates the Mobile Radio Channel

– Fade rate is a function of the doppler frequency, V/λλ

λλ

– E.g., for 860 MHz at 60 mph, fade rate is roughly 75 Hz

– Amplitude is assumed to be Rayleigh-distributed

– Channel can be time-dispersive due to delay spread

 Radio Specifications are Typically for Mean Signal

– Ideally, corresponds to a particular delivered audio quality (DAQ)

– Additional margin is needed to operate in fading

– Delay spread performance often poorly addressed or ignored

 E.g., Typical P25 Phase I Radio (C4FM):

– 12.5 kHz channel

– Static sensitivity = -118 dBm (5% BER)

– Fading sensitivity = -105 dB

m (DAQ = 3.4)

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Audio Note VINDICATOR Manual do Utilizador Página 12