Merged master 8748
This commit is contained in:
Jordan Sherer
@@ -0,0 +1,186 @@
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White Paper: FT8 for DXpeditions
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-----------------------------------
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Joe Taylor, K1JT - October 27, 2017
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Assumptions:
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1. WSJT-X will have two distinct options that enable the maximum-rate
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QSO exchanges described below. Fox must select "Fox"; all Hounds must
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select "Hound".
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2. There will be an announced basic dial frequency for each band, say
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f0=14082 kHz for 20m. This is the basic Channel.
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3. Fox always transmits in the 1st sequence, 200-800 Hz above f0.
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4. Hounds call in 2nd sequence, 1000-5000 Hz above f0. Hounds
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transmitting below f0+1000 Hz will not be answered.
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5. If found necessary, additional Channels may be defined in which
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Hounds can transmit. (However, I suggest that CQ-by-call-area may
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be easier to implement and use; and the software could be made to
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prevent Hounds in the wrong area from transmitting.)
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6. Ideally, Fox and Hounds should all use CAT control configured with
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*Split Operation* set to *Rig* or *Fake It*, and transceiver dial
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frequencies should best be calibrated to within a few Hz. (WSJT-X
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provides tools that make this fairly easy to do.)
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When Fox is running a pileup, QSOs will look something like the
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following exchanges. Here I've assumed the Fox callsign is KH1DX,
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his locator AJ10:
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------------------------------------------------------------------------
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Fox Hounds
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------------------------------------------------------------------------
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1. CQ KH1DX AJ10
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2. KH1DX K1ABC FN42, KH1DX W9XYZ EN37, ...
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3. K1ABC KH1DX -13
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4. KH1DX K1ABC R-11
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5. K1ABC RR73; W9XYZ <KH1DX> -17
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6. ... no copy from W9XYZ ...
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7. W9XYZ KH1DX -17
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8. ... no copy from W9XYZ ...
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9. G4AAA KH1DX -11
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10. KH1DX G4AAA R-03
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11. G4AAA RR73; DL3BBB <KH1DX> -12
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12. KH1DX DL3BBB R-09
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13. DL3BBB RR73; DE <KH1DX>
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14. ...
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------------------------------------------------------------------------
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All messages except those containing "<...>" are standard FT8 messages
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(i3bit=0, iFreeText=0). Hounds transmit only standard messages.
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Fox transmits standard messages and also special messages with
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i3bit=1. The special messages contain a callsign whose completed QSO
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is being acknowledged; a callsign for the next station to be worked; a
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hash code corresponding to the Fox callsign; and a signal report.
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Users will see the Fox callsign enclosed in angle brackets, <KH1DX>.
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The 72-bit message payload contains two 28-bit callsigns, a 10-bit
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hash code, and a 6-bit signal report. If no call has been queued up
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by Fox for the next QSO, the acknowledgment message takes the
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abbreviated form shown in line 13 above.
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When a Hound receives a message with i3bit=1, the decoder interprets
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the remaining 72 bits as described above. If the 10-bit hash code
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matches that for Fox's callsign, the message is displayed as in the
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QSO exchanges shown above. Otherwise the message is considered a
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false decode and is not displayed.
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Station Setup and Operation for FOX
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-----------------------------------
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A wide Rx bandwidth (up to 5 kHz) is selected. The basic dial
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frequency is set 1 kHz above f0 (thus 14083 kHz in my example) and the
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audio TxFreq somewhere between -200 and -800 Hz. (Yes, negative
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numbers are OK. *Split Operation* will reset the Tx dial frequency as
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needed and will keep the generated Tx audio frequency between 1500 and
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2000 Hz.) Hounds with audio TxFreq set to N Hz will be received by Fox
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at N-1000 Hz.
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WSJT-X at Fox will maintain and display a list of all decoded Hounds
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calling Fox in the past 2 to 4 Rx cycles. The list might look
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something like this (but typically will be much longer):
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----------------------------
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Call Grid Rpt Freq
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----------------------------
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AA2UK FM29 -11 240
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AD9H EN61 +02 1260
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K0TPP EM48 -15 1980
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N2BJ EN61 +11 540
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N4NDR EL98 -17 4620
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NX4E EM70 +00 3780
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ON3LA JN29 -10 3300
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PD9BG JO21 -21 2100
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PJ4/KA1XYZ FK60 -07 1020
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VE1SKY FN74 +03 1620
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WB2REM EL97 -13 3060
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...
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----------------------------
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Fox can choose to have the list sorted on any column.
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Fox selects a Hound to call next by clicking on a line. Or he can hit
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"F1" to have the program select a caller according to one of these
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criteria (maybe others as well?):
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- Weakest caller
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- Strongest caller
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- Strongest one below -N dB (with N selectable)
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- Choose a call at random
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- Random choice with S/N between snrMin and snrMax dB.
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After a particular Hound has been called, Fox's Auto-Sequencer looks
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for a response containing "R+rpt" originating from that same callsign.
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If such a message is received, Fox's next transmission will be the
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special "acknowledge-and-call-next" type, with i3bit=1. If the
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expected message is not received, as in example line 6 above, the
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report is sent to the same station again. If the second attempt fails
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and another Hound callsign has been queued up, the QSO is aborted and
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the next Hound is called.
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Station Setup and Operation for Hounds
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--------------------------------------
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Dial frequency is set to f0, 14082 kHz in my example. Rx bandwidth and
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displayed range on the Wide Graph can be anything convenient, say 200
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to 2600 Hz. (Signal from Fox will be expected between 200 and 800
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Hz.) Enter callsign and locator of Fox on WSJT-X main window as *DX
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Call* and *DX Grid*. Choose a TxFreq offset of 1000 + 60*N for some N
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in the range 1 to 80 (maybe even higher?). Move TxFreq as desired,
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hoping to find a clear slot, by using Shift+F11 and Shift+F12.
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- Hit F1 to call Fox in your next Tx sequence. Yes, you must hit F1
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repeatedly, in order to keep calling.
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- The Auto-sequencer will watch for a decoded message that contains
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"MyCall DXcall rpt" or "MyCall <DXcall> rpt". When one of these is
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received, your next transmission will be "DXcall MyCall R+rpt",
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sent automatically.
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- After you send the "R+rpt" message, AutoSeq will watch for a
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message that starts with "MyCall RR73; ...". When that is
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received, you're in his log, and you'll be prompted to log the QSO.
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Random thoughts
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---------------
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Fox's decoder has access to signals in a 4 kHz (maybe even 5 kHz?)
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window. At 60 Hz intervals, that's enough for around 65 (or 80?)
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non-overlapping Hound signals. If the pileup becomes too deep, more
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spectrum might be used; but note that WSJT-X can't access more than 5
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kHz at one time. A better solution might be for Fox to call "CQ n
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KH1DX AJ10", where n is a single digit indicating call area. The
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decoder could then limit the list of eligible calls to those in the
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specified call area. After decoding such a CQ, the software at Hound
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could refuse to transmit unless MyCall falls in the specified call
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area. (Other special CQ formats can be imagined that would limit the
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eligible Hound callsigns even further.)
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We haven't thought much, yet, about logging issues for Fox. I imagine
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we could do what's necessary to join a N1MM+ logging network, if that's
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deemed desirable.
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A few questions:
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Q1: Should the Auto-Sequencer allow for other cases in which a QSO has
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been initiated by Fox, but one of next two messages is not copied by
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either Fox or Hound? For example, what if K1ABC does not copy message
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#5? Should he keep sending his message "KH1DX K1ABC R-11" ? If Fox
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receives this message again, should he acknowledge again? And poor
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W9XYZ, who never received an acknowledgment, will probably keep
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sending "KH1DX W9XYZ R-19", or whatever. If Fox eventually copies the
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message, should the program remember that W9XYZ had been called, and
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thus send him an acknowledgment?
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Q2: Should we provide a stack for several to-be-called callsigns,
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rather than just one? Should re-ordering of calls in the stack be
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permitted?
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Q3: Can we handle WSJT-X "Type 1" and "Type 2" compound callsigns, for
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Hounds?
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@@ -1,233 +0,0 @@
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program ldpcsim168
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! End to end test of the (168,84)/crc12 encoder and decoder.
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use crc
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use packjt
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parameter(NRECENT=10)
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character*12 recent_calls(NRECENT)
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character*22 msg,msgsent,msgreceived
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character*8 arg
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integer*1, allocatable :: codeword(:), decoded(:), message(:)
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integer*1, target:: i1Msg8BitBytes(11)
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integer*1 msgbits(84)
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integer*1 apmask(168), cw(168)
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integer*2 checksum
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integer*4 i4Msg6BitWords(13)
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integer colorder(168)
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integer nerrtot(168),nerrdec(168),nmpcbad(84)
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logical checksumok,fsk,bpsk
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real*8, allocatable :: rxdata(:)
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real, allocatable :: llr(:)
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data colorder/0,1,2,3,28,4,5,6,7,8,9,10,11,34,12,32,13,14,15,16,17, &
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18,36,29,42,31,20,21,41,40,30,38,22,19,47,37,46,35,44,33,49,24, &
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43,51,25,26,27,50,52,57,69,54,55,45,59,58,56,61,60,53,48,23,62, &
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63,64,67,66,65,68,39,70,71,72,74,73,75,76,77,80,81,78,82,79,83, &
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84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104, &
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105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125, &
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126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146, &
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147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167/
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do i=1,NRECENT
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recent_calls(i)=' '
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enddo
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nerrtot=0
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nerrdec=0
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nmpcbad=0 ! Used to collect the number of errors in the message+crc part of the codeword
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nargs=iargc()
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if(nargs.ne.3) then
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print*,'Usage: ldpcsim niter #trials s '
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print*,'eg: ldpcsim 10 1000 0.84'
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print*,'If s is negative, then value is ignored and sigma is calculated from SNR.'
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return
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endif
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call getarg(1,arg)
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read(arg,*) max_iterations
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call getarg(2,arg)
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read(arg,*) ntrials
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call getarg(3,arg)
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read(arg,*) s
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fsk=.false.
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bpsk=.true.
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! don't count crc bits as data bits
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N=168
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K=84
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! scale Eb/No for a (168,72) code
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rate=real(72)/real(N)
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|
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write(*,*) "rate: ",rate
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write(*,*) "niter= ",max_iterations," s= ",s
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|
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allocate ( codeword(N), decoded(K), message(K) )
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allocate ( rxdata(N), llr(N) )
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! msg="K1JT K9AN EN50"
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msg="G4WJS K9AN EN50"
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call packmsg(msg,i4Msg6BitWords,itype) !Pack into 12 6-bit bytes
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call unpackmsg(i4Msg6BitWords,msgsent) !Unpack to get msgsent
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write(*,*) "message sent ",msgsent
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|
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i4=0
|
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ik=0
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im=0
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do i=1,12
|
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nn=i4Msg6BitWords(i)
|
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do j=1, 6
|
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ik=ik+1
|
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i4=i4+i4+iand(1,ishft(nn,j-6))
|
||||
i4=iand(i4,255)
|
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if(ik.eq.8) then
|
||||
im=im+1
|
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! if(i4.gt.127) i4=i4-256
|
||||
i1Msg8BitBytes(im)=i4
|
||||
ik=0
|
||||
endif
|
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enddo
|
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enddo
|
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|
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i1Msg8BitBytes(10:11)=0
|
||||
checksum = crc12 (c_loc (i1Msg8BitBytes), 11)
|
||||
! For reference, the next 3 lines show how to check the CRC
|
||||
i1Msg8BitBytes(10)=checksum/256
|
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i1Msg8BitBytes(11)=iand (checksum,255)
|
||||
checksumok = crc12_check(c_loc (i1Msg8BitBytes), 11)
|
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if( checksumok ) write(*,*) 'Good checksum'
|
||||
|
||||
mbit=0
|
||||
do i=1, 9
|
||||
i1=i1Msg8BitBytes(i)
|
||||
do ibit=1,8
|
||||
mbit=mbit+1
|
||||
msgbits(mbit)=iand(1,ishft(i1,ibit-8))
|
||||
enddo
|
||||
enddo
|
||||
i1=i1Msg8BitBytes(10) ! First 4 bits of crc12 are LSB of this byte
|
||||
do ibit=1,4
|
||||
msgbits(72+ibit)=iand(1,ishft(i1,ibit-4))
|
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enddo
|
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i1=i1Msg8BitBytes(11) ! Now shift in last 8 bits of the CRC
|
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do ibit=1,8
|
||||
msgbits(76+ibit)=iand(1,ishft(i1,ibit-8))
|
||||
enddo
|
||||
|
||||
write(*,*) 'message'
|
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write(*,'(11(8i1,1x))') msgbits
|
||||
|
||||
call encode168(msgbits,codeword)
|
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call init_random_seed()
|
||||
call sgran()
|
||||
|
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write(*,*) 'codeword'
|
||||
write(*,'(21(8i1,1x))') codeword
|
||||
|
||||
write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
|
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do idb = 6,-6,-1
|
||||
db=idb/2.0-1.0
|
||||
sigma=1/sqrt( 2*(10**(db/10.0)) )
|
||||
ngood=0
|
||||
nue=0
|
||||
nbadcrc=0
|
||||
nberr=0
|
||||
do itrial=1, ntrials
|
||||
! Create a realization of a noisy received word
|
||||
do i=1,N
|
||||
if( bpsk ) then
|
||||
rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
|
||||
elseif( fsk ) then
|
||||
if( codeword(i) .eq. 1 ) then
|
||||
r1=(1.0 + sigma*gran())**2 + (sigma*gran())**2
|
||||
r2=(sigma*gran())**2 + (sigma*gran())**2
|
||||
elseif( codeword(i) .eq. 0 ) then
|
||||
r2=(1.0 + sigma*gran())**2 + (sigma*gran())**2
|
||||
r1=(sigma*gran())**2 + (sigma*gran())**2
|
||||
endif
|
||||
rxdata(i)=0.35*(sqrt(r1)-sqrt(r2))
|
||||
! rxdata(i)=0.35*(exp(r1)-exp(r2))
|
||||
! rxdata(i)=0.12*(log(r1)-log(r2))
|
||||
endif
|
||||
enddo
|
||||
nerr=0
|
||||
do i=1,N
|
||||
if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
|
||||
enddo
|
||||
nerrtot(nerr)=nerrtot(nerr)+1
|
||||
nberr=nberr+nerr
|
||||
|
||||
! Correct signal normalization is important for this decoder.
|
||||
! rxav=sum(rxdata)/N
|
||||
! rx2av=sum(rxdata*rxdata)/N
|
||||
! rxsig=sqrt(rx2av-rxav*rxav)
|
||||
! rxdata=rxdata/rxsig
|
||||
! To match the metric to the channel, s should be set to the noise standard deviation.
|
||||
! For now, set s to the value that optimizes decode probability near threshold.
|
||||
! The s parameter can be tuned to trade a few tenth's dB of threshold for an order of
|
||||
! magnitude in UER
|
||||
if( s .lt. 0 ) then
|
||||
ss=sigma
|
||||
else
|
||||
ss=s
|
||||
endif
|
||||
|
||||
llr=2.0*rxdata/(ss*ss)
|
||||
nap=0 ! number of AP bits
|
||||
llr(colorder(168-84+1:168-84+nap)+1)=5*(2.0*msgbits(1:nap)-1.0)
|
||||
apmask=0
|
||||
apmask(colorder(168-84+1:168-84+nap)+1)=1
|
||||
|
||||
! max_iterations is max number of belief propagation iterations
|
||||
call bpdecode168(llr, apmask, max_iterations, decoded, niterations)
|
||||
! if( niterations .eq. -1 ) then
|
||||
! norder=3
|
||||
! call osd168(llr, norder, decoded, niterations, cw)
|
||||
! endif
|
||||
! If the decoder finds a valid codeword, niterations will be .ge. 0.
|
||||
if( niterations .ge. 0 ) then
|
||||
call extractmessage168(decoded,msgreceived,ncrcflag,recent_calls,nrecent)
|
||||
if( ncrcflag .ne. 1 ) then
|
||||
nbadcrc=nbadcrc+1
|
||||
endif
|
||||
|
||||
nueflag=0
|
||||
nerrmpc=0
|
||||
do i=1,K ! find number of errors in message+crc part of codeword
|
||||
if( msgbits(i) .ne. decoded(i) ) then
|
||||
nueflag=1
|
||||
nerrmpc=nerrmpc+1
|
||||
endif
|
||||
enddo
|
||||
|
||||
write(37,*) niterations, ncrcflag, nueflag
|
||||
nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1
|
||||
if( ncrcflag .eq. 1 ) then
|
||||
if( nueflag .eq. 0 ) then
|
||||
ngood=ngood+1
|
||||
nerrdec(nerr)=nerrdec(nerr)+1
|
||||
else if( nueflag .eq. 1 ) then
|
||||
nue=nue+1;
|
||||
endif
|
||||
endif
|
||||
endif
|
||||
enddo
|
||||
snr2500=db+10*log10(10.417/2500.0)
|
||||
pberr=real(nberr)/(real(ntrials*N))
|
||||
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,snr2500,ngood,nue,nbadcrc,ss,pberr
|
||||
|
||||
enddo
|
||||
|
||||
open(unit=23,file='nerrhisto.dat',status='unknown')
|
||||
do i=1,168
|
||||
write(23,'(i4,2x,i10,i10,f10.2)') i,nerrdec(i),nerrtot(i),real(nerrdec(i))/real(nerrtot(i)+1e-10)
|
||||
enddo
|
||||
close(23)
|
||||
open(unit=25,file='nmpcbad.dat',status='unknown')
|
||||
do i=1,84
|
||||
write(25,'(i4,2x,i10)') i,nmpcbad(i)
|
||||
enddo
|
||||
close(25)
|
||||
|
||||
|
||||
|
||||
end program ldpcsim168
|
||||
Reference in New Issue
Block a user