Digital Standard GPS SMIQ
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The simulation of Doppler-shifted GPS signals can be used to check the receiver characteristics under
more realistic conditions than with zero Doppler. In contrast to the real system, however, the set Doppler
frequency is fixed and must eventually be changed manually.
4. GPS signals with modified carrier frequency and symbol rate
Additional settings for carrier frequency and symbol rate can be made to perform more comprehensive
receiver tests. However, these settings may result in signals that do not conform to GPS.
The basic carrier frequency without Doppler shift can be freely set under FREQ. The actual frequency
output physically is yielded by the following equation
Doppler
fFREQf +=
and is displayed under RESULTING FREQUENCY.
The symbol rate used for zero Doppler is set under SYMBOL RATE. Taking into account a Doppler
shift, the actual symbol rate is determined by the following equation
÷
÷
ø
ö
ç
ç
è
æ
+∗=
FREQ
f
ff
Doppler
SymbolSymbol
rZeroDoppleresulting
1
and is given under RESULTING SYMBOL RATE.
Selecting the appropriate parameters enables the characteristics of the receiver (such as dependence
of receiver synchronization on the symbol rate/carrier frequency ratio, etc.) to be easily checked.
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