Lesson plan
JPL sequence
JPL sequences or JPL codes consist of two linear feedback shift registers (LFSRs) whose code sequence lengths L a and L b must be prime (relatively prime). In this case the code sequence length of the generated overall sequence L c is equal to: : L_c = L_a \cdot L_b = (2^n - 1)(2^m - 1) It is also possible for more than two LFSRs to be interconnected through multiple XORs at the output for as long as all code sequence lengths of the individual LFSR are relatively prime to one another. JPL sequences were originally developed in the Jet Propulsion Labs, from which the name for these code sequences is derived. Areas of application include distance measurements utilizing spread spectrum signals for satellites and in space technology. They are also utilized in the more precise military P/Y code used in the Global Positioning System (GPS). However, they are currently replaced by the new M-code. Due to the relatively long spreading sequences, they can be used to measure relatively long ranges without ambiguities, as required for deep space missions. By having a rough synchronziation between receiver and transmitter, this can be achieved with shorter sequences as well. Their major advantage is, that they produce relatively long sequences with only two LFSRs, which makes it energy efficient and very hard to detect due to huge spreading factor.…
Article summary
JPL sequences or JPL codes consist of two linear feedback shift registers (LFSRs) whose code sequence lengths L a and L b must be prime (relatively prime). In this case the code sequence length of the generated overall sequence L c is equal to: : L_c = L_a \cdot L_b = (2^n - 1)(2^m - 1) It is also possible for more than two LFSRs to be interconnected through multiple XORs at the output for as long as all code sequence lengths of the individual LFSR are relatively prime to one another. JPL sequences were originally developed in the Jet Propulsion Labs, from which the name for these code sequences is derived. Areas of application include distance measurements utilizing spread spectrum signals for satellites and in space technology. They are also utilized in the more precise military P/Y code used in the Global Positioning System (GPS). However, they are currently replaced by the new M-code. Due to the relatively long spreading sequences, they can be used to measure relatively long ranges without ambiguities, as required for deep space missions. By having a rough synchronziation between receiver and transmitter, this can be achieved with shorter sequences as well. Their major advantage is, that they produce relatively long sequences with only two LFSRs, which makes it energy efficient and very hard to detect due to huge spreading factor.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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