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ANT+ Packet collisions

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Total Posts: 3

Joined 2016-03-11

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Hi all! I'm using a USB ANT+ dongle with https://github.com/half2me/antgo my Golang based ANT+ decoder.
I'm working with a Speed & Cadence Sensor
I've made it log all ANT+ data so I can better debug problems, and I have quite an interesting situation.
I use continous scanning mode:
Here is an excerpt of my log: (See the image, where I've marked the problematic packet)

[#][timestamp][type][Channel][ANT ID][Device Type] [...]
[CAD]: CadenceEventTime -> CumulativeCadenceRevolutionCount
[SPD]: SpeedEventTime -> CumulativeSpeedRevolutionCount

[ 1382] [17:25:03:116] [BRD] CH 0 [27012] [S&C] [CAD] 43272 -> 1453 | [SPD] 43131 -> 4984
[ 1383] [17:25:03:140] [BRD] CH 0 [13280] [S&C] [CAD] 06825 -> 1351 | [SPD] 06818 -> 5247
[ 1386] [17:25:03:363] [BRD] CH 0 [27012] [S&C] [CAD] 43272 -> 1453 | [SPD] 43131 -> 4984
[ 1387] [17:25:03:388] [BRD] CH 0 [13280] [S&C] [CAD] 06825 -> 1351 | [SPD] 06818 -> 5247
[ 1390] [17:25:03:609] [BRD] CH 0 [27012] [S&C] [CAD] 43272 -> 1453 | [SPD] 43131 -> 4984
[ 1391] [17:25:03:628] [BRD] CH 0 [20381] [S&C] [CAD] 09005 -> 1445 | [SPD] 08883 -> 4504
[ 1395] [17:25:03:883] [BRD] CH 0 [13280] [S&C] [CAD] 07521 -> 1352 | [SPD] 07364 -> 5250
[ 1397] [17:25:04:104] [BRD] CH 0 [27012] [S&C] [CAD] 43938 -> 1454 | [SPD] 43901 -> 4988
[ 1398] [17:25:04:125] [BRD] CH 0 [13280] [S&C] [CAD] 07521 -> 1352 | [SPD] 07364 -> 5250
[ 1401] [17:25:04:349] [BRD] CH 0 [27012] [S&C] [CAD] 44604 -> 1455 | [SPD] 44492 -> 4991
[ 1405] [17:25:04:864] [BRD] CH 0 [20381] [S&C] [CAD] 10255 -> 1447 | [SPD] 10085 -> 4510
[ 1406] [17:25:04:866] [BRD] CH 0 [13280] [S&C] [CAD] 00260 -> 44611 | [SPD] 44968 -> 5230
[ 1407] [17:25:04:869] [BRD] CH 0 [13280] [S&C] [CAD] 08218 -> 1353 | [SPD] 08092 -> 5254
[ 1410] [17:25:05:091] [BRD] CH 0 [27012] [S&C] [CAD] 45279 -> 1456 | [SPD] 45277 -> 4995
[ 1413] [17:25:05:338] [BRD] CH 0 [27012] [S&C] [CAD] 45279 -> 1456 | [SPD] 45277 -> 4995
[ 1414] [17:25:05:358] [BRD] CH 0 [20381] [S&C] [CAD] 10255 -> 1447 | [SPD] 10085 -> 4510
[ 1417] [17:25:05:589] [BRD] CH 0 [27012] [S&C] [CAD] 45945 -> 1457 | [SPD] 45854 -> 4998
[ 1418] [17:25:05:610] [BRD] CH 0 [13280] [S&C] [CAD] 08914 -> 1354 | [SPD] 08805 -> 5258
[ 1421] [17:25:05:832] [BRD] CH 0 [27012] [S&C] [CAD] 45945 -> 1457 | [SPD] 45854 -> 4998
[ 1422] [17:25:05:854] [BRD] CH 0 [13280] [S&C] [CAD] 09610 -> 1355 | [SPD] 09522 -> 5262
[ 1425] [17:25:06:103] [BRD] CH 0 [13280] [S&C] [CAD] 09610 -> 1355 | [SPD] 09522 -> 5262
[ 1428] [17:25:06:325] [BRD] CH 0 [27012] [S&C] [CAD] 46611 -> 1458 | [SPD] 46432 -> 5001
[ 1429] [17:25:06:349] [BRD] CH 0 [13280] [S&C] [CAD] 10317 -> 1356 | [SPD] 10242 -> 5266
[ 1431] [17:25:06:573] [BRD] CH 0 [27012] [S&C] [CAD] 46611 -> 1458 | [SPD] 46432 -> 5001
[ 1434] [17:25:06:822] [BRD] CH 0 [27012] [S&C] [CAD] 47266 -> 1459 | [SPD] 47190 -> 5005
[ 1435] [17:25:06:841] [BRD] CH 0 [13280] [S&C] [CAD] 10317 -> 1356 | [SPD] 10242 -> 5266
[ 1436] [17:25:07:066] [BRD] CH 0 [27012] [S&C] [CAD] 47266 -> 1459 | [SPD] 47190 -> 5005
[ 1437] [17:25:07:084] [BRD] CH 0 [20381] [S&C] [CAD] 12129 -> 1450 | [SPD] 12086 -> 4520
[ 1438] [17:25:07:089] [BRD] CH 0 [13280] [S&C] [CAD] 11013 -> 1357 | [SPD] 10957 -> 5270
[ 1440] [17:25:07:311] [BRD] CH 0 [27012] [S&C] [CAD] 47266 -> 1459 | [SPD] 47190 -> 5005
[ 1441] [17:25:07:335] [BRD] CH 0 [13280] [S&C] [CAD] 11013 -> 1357 | [SPD] 10957 -> 5270

If you look at Device ID 13280, at 17:25:04:866 there is a packet which does not belong there. If you look at the RED boxed numbers, it seems to be something that was supposed to be for Device ID 27012.
The checksums are good though, so I have no idea how this happens. Could it be possible that the checksums match, yet the packets get mixed up anyway?      

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Total Posts: 3

Joined 2016-03-11

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Also just noticed the timestamps: usually 1msg / bike @every 200ms.
Look at the time between the bad message and the next one, which is perfectly valid ~4ms      
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Total Posts: 658

Joined 2012-09-14

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How often have you seen this issue before? Would you be able to pull the ANT Version Message from the USB stick?      
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Total Posts: 3

Joined 2016-03-11

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@Harrison the more bikes that are in range, the more often these anomalies occur. With 12 bikes in the room, I've gotten a bad packet like this every 1-2 minutes.