bch time about iridium-toolkit

[Sec42]

Not sure what you mean by "bch". If you mean the time in the IBC frames: to our current knowledge that references the time of the start of the signal (preamble) of the start of the frame that contains the IBC packet.

And of course you then need to take the travel time of the signal from satellite to the receiver into account.

I have some changes to reassembler.py in the works that will hopefully clarify this a bit.

[schneider42]

Addendum: It specifies the time at the start of the 90 ms L-Band frame that contained the IBC frame. The slot value tells you in which DL slot the IBC frame was sent.

The following code show cases the exact calculation. Please take into account that the time the signal took to reach you is not compensated.

iridium-toolkit/reassembler.py

Lines 520 to 536 in 39f1200

	def process(self,q):
	q.uxtime=datetime.datetime.utcfromtimestamp(q.time)
	# correct for slot:
	# 1st vs. 4th slot is 3 * (downlink + guard)
	q.itime+=datetime.timedelta(seconds=q.slot*(3 * float(8.28 + 0.1))/1000)
	# correct to beginning of frame:
	# guard + simplex + guard + 4*(uplink + guard) + extra_guard
	q.itime+=datetime.timedelta(seconds=(1 + 20.32 + 1.24 + 4 * float(8.28 + 0.22) + 0.02)/1000)
	# correct to beginning of signal:
	# our timestamp is "the middle of the first symbol of the 12-symbol BPSK Iridium sync word"
	# so correct for 64 symbols preamble & one half symbol.
	q.itime+=datetime.timedelta(seconds=(64.5/25000))
	# no correction (yet?) for signal travel time: ~ 2.6ms-10ms (780-3000 km)