GPS 中A/D位数为什么只要3位？

我是做GPS的新手，我有个疑问为什么GPS 中A/D位数为什么只要3位?我查的资料都说对信噪比损失小，但理论原因是什么呢?请高手予以解答?是A/D的原因呢，还是GPS信号的原因。QQ：214649117.email:jarronaaron@163.com

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.

thanks

说的很好，谢谢呀