I'm not familiar with FHSS or DSSS, but pseudo random sequences from LFSRs are used as scramblers on serial links. The idea is to avoid long strings of 0s that will provoke clock recovery troubles. The transmitter XORs a pseudo random sequence with the data stream and the receiver does the same to get the data back.
The problem is to keep both ends in sync. There is a good section on scramblers in Lee and Messerchmitt: Digital Communication, page 440. I don't know how good that book is. It's one I picked up years ago. I've been happy with it. Mine says copyright 1988, 4th printing 1992. There are two types of scramblers: Frame Synchronous and Self Synchronizing. With a Frame Synchronous setup, you get a reset pulse from someplace else. (magic) It's usually a start-of-packet signal or a specific bit pattern used as a frame marker, anything both ends can agree on. The idea is to get back in sync occasionally in case you happened to get out of sync. So the questions are: Can both ends get the same reset pulse? Are the clocks at both ends running at the same speed? I'd expect it to work as long as both GPS systems are happy. You will probably have to correct for propagation delays, that is delay the receive clocking by X ns. The self synchronizing scramblers probably aren't appropriate for SS work. (But they might work fine if you know how to use them. I don't see it.) The idea is to feed the data bit on the wire into the LFSR rather than the output of the LFSR. If the data is received correctly, a garbage scrambler on the receive side will get in sync after N bits. If you get a single bit error on the wire, it will make a multi-bit error in the unscrambled data stream. That error pattern will be the polynomial used for the LFSR. (It's easy after you see it.) -- These are my opinions, not necessarily my employer's. I hate spam. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
