GPS signal - 地球科學討論

關於GPS signals的東東
我看到書裡面的文章寫到：

Each GPS satellite transmits two spread spectrum, L-band carrier signals--
an L1 signal with carrier frequency f1=1575.42MHz and an L2 signal with
carrier frequency f2=1227.6MHz. These two frequencies are integral multiples
f1=1540*f0 and f2=1200*f0 of a base frequency f0=1.023MHz.
為什麼上面所列的L1 and L2 signals 會和f0有一個倍數關係？
而f0=1.023MHz作為一個base frequency是有何用意？

The L1 signal from each satellite uses binary phase-shift keying(BPSK),
modulated by two pesudorandom noise (PRN) codes in phase quadrature, designated
as the C/A-code and P-code. The L2 signal from each satellite is BPSK modulated
by only the P-code.
What is "binary phase-shift keying(BPSK)"??
What is "pesudorandom noise(PRN)"??
What are "C/A-code" and "P-code"??
為何L1 signal有 C/A-code and P-code來modulate, 但對於L2 signal卻只有P-code??
thanks!!

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