0 1 00:00:00,450 --> 00:00:04,500 In this video, I'm going to show you the LoRa modulation and the LoRa frame. 1 2 00:00:04,620 --> 00:00:08,850 We know that the modulation is made with Chirp. It's a sweep frequency, 2 3 00:00:08,850 --> 00:00:13,920 and the difference between the bottom frequency and the top one represents the Bandwidth. 3 4 00:00:14,650 --> 00:00:15,760 In the LoRa frame, 4 5 00:00:15,760 --> 00:00:21,110 there is first a preamble, and an optional Header. At the tail of the frame, 5 6 00:00:21,130 --> 00:00:24,160 there is a CRC to check if there was an error in the frame. 6 7 00:00:24,310 --> 00:00:29,380 And finally, the most important part is what we call the PHY Payload. 7 8 00:00:29,860 --> 00:00:32,740 This is the LoRaWAN message carried by the frame. 8 9 00:00:33,010 --> 00:00:38,710 The preambule part, header, the presence or not of the CRC can be configured the way we want. 9 10 00:00:39,100 --> 00:00:45,100 The only requirement is that this information should be the same on the transmitter and on the receiver. 10 11 00:00:45,580 --> 00:00:51,340 So if you want to use the LoRa modulation and comply with the LoRa frame format, then you can do your own 11 12 00:00:51,340 --> 00:00:52,990 configuration of these fields. 12 13 00:00:53,170 --> 00:00:59,770 However, if you aim to use the LoRaWAN protocol on top of the LoRa modulation, then you don't have the 13 14 00:00:59,770 --> 00:01:02,980 choice and these fields must have a specific value. 14 15 00:01:03,420 --> 00:01:04,020 Right. 15 16 00:01:04,030 --> 00:01:08,740 So for this transmission, I have programmed a simple LoRa message of the string: 16 17 00:01:08,740 --> 00:01:17,170 "Hello". I'm using SF12, 125kHz bandwidth, 868.1Mhz channel, 17 18 00:01:17,410 --> 00:01:24,190 And for the frame, I've selected the preamble of 8 symbols, with a header and a CRC. About the 18 19 00:01:24,190 --> 00:01:24,780 preamble. 19 20 00:01:24,790 --> 00:01:31,900 We just need to remember that the specification says that there is always 4.25, so 4 plus a quarter 20 21 00:01:31,900 --> 00:01:35,140 of a symbol in addition to the number of preambule configuration. 21 22 00:01:35,710 --> 00:01:40,380 So in our case, that will make 12.25 symbols overall. 22 23 00:01:40,630 --> 00:01:46,570 There is probably a good reason for this additional 4.25 symbols, but I've got no idea where it comes from. 23 24 00:01:46,570 --> 00:01:48,700 To be exact, 24 25 00:01:48,700 --> 00:01:54,650 in these 4.25 symbols, there will be 2 upchirps and 2.25 downchirps. 25 26 00:01:55,150 --> 00:01:57,850 That makes indeed 4.25. 26 27 00:01:58,000 --> 00:01:58,590 Great. 27 28 00:01:58,600 --> 00:02:05,200 So first to try this LoRa modulation, I'm going to use the transceiver of a LoRa device to send a hello 28 29 00:02:05,200 --> 00:02:06,010 characters. 29 30 00:02:06,010 --> 00:02:13,330 And on the other side, I'm going to use an SDR. An SDR is a Software Defined Radio managed by an application. 30 31 00:02:13,630 --> 00:02:19,690 The one I'm using for this demonstration is the ADAM-PLUTO mainly used for education, and the software 31 32 00:02:19,690 --> 00:02:22,640 that I use is the Open Source SDR Angel. 32 33 00:02:23,890 --> 00:02:28,750 Okay, so in the SDR Angel software, I need to configure my receiver. 33 34 00:02:28,960 --> 00:02:31,960 So 868.1 Mhz. 34 35 00:02:33,580 --> 00:02:40,420 And I will decrease the gain because in my situation, my LoRa device is very close from my receiver. 35 36 00:02:40,420 --> 00:02:41,200 I start it. 36 37 00:02:42,160 --> 00:02:42,850 Here we go. 37 38 00:02:42,880 --> 00:02:45,850 We can perfectly see the LoRa modulation here. 38 39 00:02:46,330 --> 00:02:49,540 I will try to stop the visualization when the frame starts. 39 40 00:02:50,860 --> 00:02:51,420 Great. 40 41 00:02:51,430 --> 00:02:52,270 Perfect. 41 42 00:02:52,540 --> 00:02:54,460 Here we can see the preambules. 42 43 00:02:54,670 --> 00:02:56,510 They are 8 upchirps. 43 44 00:02:56,530 --> 00:03:01,900 One, two, three, four, five, six, seven and eight. 44 45 00:03:02,290 --> 00:03:04,470 Then there are another 2 upchirps. 45 46 00:03:04,480 --> 00:03:07,630 One, two. And finally two. 46 47 00:03:07,630 --> 00:03:09,370 And a quarter downchips. 47 48 00:03:09,370 --> 00:03:10,540 One, two. 48 49 00:03:10,540 --> 00:03:13,210 And this little bit here. Right, 49 50 00:03:13,330 --> 00:03:18,250 of course, it's very difficult with this representation to analyze the frame and its content. 50 51 00:03:18,460 --> 00:03:21,310 So we're going to use a little pluggin. 51 52 00:03:21,340 --> 00:03:24,250 This plugin is called ChirpChat demodulator. 52 53 00:03:29,650 --> 00:03:33,760 The first thing I need to do is to configure the parameters used for the transmission: 53 54 00:03:34,270 --> 00:03:38,530 The most important one are the SF12 and the bandwidth. 54 55 00:03:39,460 --> 00:03:45,550 Then, now, when I run the demodulator, I can see the Raw Payload of the LoRa packet. 55 56 00:03:46,030 --> 00:03:51,670 This is exactly the same "Hello" string that I sent with my device and we can check on each transmission the 56 57 00:03:51,670 --> 00:03:55,930 CRC status to see if there was some errors during the modulation process. 57 58 00:03:56,440 --> 00:03:58,690 That obviously happened when the RSSI, 58 59 00:03:58,720 --> 00:04:03,600 so the power of the signal received is very low, or if the SNR is low as well. 59 60 00:04:03,610 --> 00:04:05,590 But that's not my case here. 60 61 00:04:05,920 --> 00:04:06,520 Okay. 61 62 00:04:06,520 --> 00:04:09,640 So now I would like to present a second demonstration. 62 63 00:04:10,000 --> 00:04:13,840 Let's say that for some reason we would like to debug a transmission. 63 64 00:04:14,290 --> 00:04:20,320 For example, you have doubts about the value sent by your device and you want to visualize the LoRa 64 65 00:04:20,380 --> 00:04:21,380 packet around you. 65 66 00:04:21,400 --> 00:04:27,640 It's a kind of LoRa sniffer that we want with the same purpose as an oscilloscope when we do some electronic 66 67 00:04:27,640 --> 00:04:28,320 debugging. 67 68 00:04:28,330 --> 00:04:31,600 And what is a LoRa packet sniffer? a gateway? 68 69 00:04:31,630 --> 00:04:35,570 Yes, because a gateway is able to demodulate any LoRa packet. 69 70 00:04:35,590 --> 00:04:42,310 And the nice thing with a gateway is that it can demodulate many channels and all spreading factors at 70 71 00:04:42,310 --> 00:04:43,930 the same time. 71 72 00:04:44,530 --> 00:04:50,470 So, for this last demonstration, I'm going to use a gateway and look at the Log to see what happens. 72 73 00:04:50,650 --> 00:04:51,730 On my gateway, 73 74 00:04:51,730 --> 00:04:55,060 to see the Log I need to connect thanks to a serial link. 74 75 00:04:58,570 --> 00:05:00,450 And I can now see all packet. 75 76 00:05:00,460 --> 00:05:01,390 It's uplink, 76 77 00:05:01,390 --> 00:05:06,170 if it comes from my device, and it's downlink, if it's sent to my device. 77 78 00:05:06,190 --> 00:05:12,970 Of course, if I send the "hello" string then my gateway can demodulate the packet and print the characters 78 79 00:05:12,970 --> 00:05:13,690 in the Log. 79 80 00:05:14,470 --> 00:05:15,150 Great. 80 81 00:05:15,160 --> 00:05:23,830 So now we don't just want to send "hello" with a LoRa modulation, but instead we need to send all the information 81 82 00:05:23,830 --> 00:05:25,120 of the LoRaWAN protocol. 82 83 00:05:25,660 --> 00:05:27,820 That's what we're going to do in the next video.