Hi Martin, > Many thanks for your reply.
You're more than welcome! USRPs in ground stations are fun stuff! > The ground station is intended to primarily support future educational > CubeSat projects > so it's difficult to say exactly what communications protocols will be used > but you are > right to assume common amsat modes. Well, in that case, a slight case of overdimensioning can't be bad – would be stupid if you found out in a year that had you spent a few kronor more, things would be working. > Currently we are developing a 1U cubesat that will use a 9.6 kbps > GFSK/ASM+Golay/Reed > Solomon configuration. Well, if you're in the "business" of building your own satellites, then by all means, just slap a PC of some kind (intel NUC? or any micro-ATX board, maybe with a Ryzen 5 even?) on there – really can't hurt if you've got a little headroom for doing more advanced stuff such as attitude tumble estimation, better doppler prediction / correction, or simply more modes (and simultaneous modes). Regarding the Golay code: is that the classical perfect binary Golay (23,12)-code, for hard decoding? If you pick a PC over a Pi, you get higher memory bandwidth, and can implement Maximum-Likelihood decoding (it doesn't get any better ;) ) simply by having a precomputed table of 2²³ 12-bit words; that's 16 MB of RAM when you put each 12 bit info word into a 16 bit machine word (if you implement it in a packed manner, it's only 12 MB) of a lookup table, and a single memory access would then give you the fully decoded 12 bits. Not that you're anywhere near computational trouble with the 9600 bits a second doing a traditional decoder. In fact, Daniel Estévez, himself of GNU Radio and satellite observation/gr-satellites fame [10], has a nice article on algebraic decoding of the (24,12) Golay [11] and the (23,12), too [12] (note that you can solve the 1-bit-reduced error correction capability by actually trying to decode both parity hypotheses). > However it might be of interest in the future to add support for reception of > higher > frequencies and data rates (say amateur S-band for example) which would mean > adding > another SDR to the same PC and there I'm worried about creating a bottleneck > in terms of > computing power. Go do a bit of "receiver shopping" in gr-satellites. In fact, Daniel even has guidance for teams developing ground stations for smallsat missions [13]. Best regards, Marcus [10] https://github.com/daniestevez/gr-satellites/ [11] https://destevez.net/2018/05/algebraic-decoding-of-golay2412/ [12] https://destevez.net/2018/05/using-a-golay2412-decoder-for-golay2312/ [13] https://github.com/daniestevez/gr-satellites/blob/master/satellite_teams.md _______________________________________________ USRP-users mailing list -- [email protected] To unsubscribe send an email to [email protected]
