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I am doing some research into GNSS (Global Navigation Satellite Systems) and have come across various signals listed as having the in-phase or quadrature channels modulated with BPSK(2) or BPSK(10), etc. However, I am struggling to find a definition of BPSK that includes this additional parameter.

What does the (n) signify in BPSK(n)?

I understand the basic concept of BPSK - Binary Phase Shift Keying and have implemented this in very basic tests by multiplying the LO by 1 or -1 for a 1 or 0 chip respectively.

It has been suggested by a colleague that the n is simply the chip rate and that BPSK(1) is a chip rate of 1MHz, BPSK(2) 2MHz, BPSK(10) 10MHz, etc. as mentioned in the comments by Jim Clay.

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I am very familiar with BPSK, and I have never seen BPSK(n), BPSK(2), or BPSK(10). Could you provide a quote that gives the context? – Jim Clay Feb 6 '13 at 19:37
As a couple of examples, see the characteristics table in… where various signals are described as BPSK(1) [GPS L1 C/A which is what I understood as BPSK], BPSK(2) or BPSK(10); or Figure 2 in – Darran Feb 6 '13 at 19:44
Both of those signals are CDMA. A quick review didn't indicate explicitly what the numbers mean, but it appears to me that they probably indicate the chip rate that is used. I saw a reference in a Galileo paper that seemed to suggest that BPSK(5) meant a BPSK signal at 5*fo chip rate. – Jim Clay Feb 6 '13 at 19:58
Yuck, more tower of babel terminology rampant in the literature. >< – Mohammad Feb 6 '13 at 20:18
Sorry, but I find it a bit ironic to start a question about unexplained acronym, BPSK(n), with an unexplained acronym, GNSS. – Hilmar Feb 7 '13 at 5:34

1 Answer 1

up vote 3 down vote accepted

While I do not have proof, it seems pretty clear, given the "Characteristics of Compass signals reported as of May 2008 compared to GPS-L1CA" table at the Wikipedia page that you offered as an example, that the "(n)" notation refers to the chip rate. You will notice that there is one BPSK(1) signal that has a chip rate of 1.023 Mchips/s. There are four BPSK(2) signals listed, and all of them have a chip rate of 2.046 Mchips/s, which is twice 1.023 Mchips/s. There are also three BPSK(10) signals that have a chip rate of 10.23 Mchips/s which is, of course, 10 times 1.023 Mchips/s.

It appears that the "(n)" notation means that the signal has a chip rate of $n*f_o$, and in the case of the Compass signals $f_o$ is 1.023 Mchips/s.

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