Issue link: https://read.uberflip.com/i/1428356
LoRaWAN Fragmented Data Block Transport v1.0.0 Specification ©2018 LoRa Alliance™ Page 16 of 30 The authors reserve the right to change specifications without notice. 6 Introduction 386 387 This appendix proposes a simple Forward Error Correction (FEC) code to be used for 388 fragmented transport of large binary files over LoRaWAN. As all radio link, a LoRaWAN link 389 exhibit a certain ratio of lost frames. Adding FEC in the file fragmentation process allows an 390 end-device to autonomously recover the full file even in the presence of lost frames without 391 having to systematically request the missing fragments. 392 The transmitter of the fragmented binary file can select to add an arbitrary redundancy to the 393 transmission content through this FEC. 394 For example a 10% redundancy added by the fragmentation transmitter allows the receiver 395 performing the defragmentation to loose roughly 10% of the incoming frames and still be 396 able to reconstruct the binary file. 397 398 399 Fragmentation may be used for many different applications, for example: 400 • Broadcasting a firmware upgrade to a group of end-devices (Network -> end-devices 401 downlink multicast) 402 • Fragmenting a huge data block in several smaller messages before sending it up to 403 the network (end-device -> Network uplink) and make sure all the data has been 404 successfully received. Example: A sensor collects frequent data for a long time, and 405 then compresses it into one huge block that is sent using fragmentation, as soon as 406 the server is able to reconstruct the full block the end-device receives a notification 407 and stops transmitting. 408 409 410 The coding scheme proposed here is directly derived from the 1963 thesis of Robert 411 Gallager describing Parity-Check code: This thesis can be accessed at 412 http://www.inference.phy.cam.ac.uk/mackay/gallager/papers/ldpc.pdf 413 414