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发表于 2008-11-18 16:32:57
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GPS is a CDMA signal. In order to receive the
maximum of signals, it is desirable to have comparable signal strength from
all visible satellites at the receiver. Under this condition, the dynamic range of
a GPS receiver need not be very high.
An ADC with a few bits is relatively
easy to fabricate and may operate at high frequency. Another advantage of using
fewer bits is that it is easier to process the digitized data, especially when they
are processed through hardware.
The disadvantage of using fewer bits is the
degradation of the signal-to-noise ratio. Spilker(11) indicated that a 1-bit ADC
degrades the signal-to-noise ratio by 1.96 dB and a 2-bit ADC degrades the
signal-to-noise by 0.55 dB. Many commercial GPS receivers use only 1- or 2-
bit ADCs.
The only time that a high number of bits in ADC is required in a GPS receiver
is to build a receiver with antijamming capability. |
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