Differences

This shows you the differences between two versions of the page.

--- lora_rf [2023/11/15 15:36] – river
+++ lora_rf [2024/07/31 14:45] (current) – river
@@ Line 1: / Line 1: @@
-====== LoRa: RF Paramaters, Power, Regulations ======
+====== LoRa: RF Parameters, Power, Regulations ======
-Spreading factors:
+===== Parameters =====
-According to SX1276 datasheet:
-At SF 6, SNR of -5dB is required
-At SF 12, -20dB.
-.5dB change between SFs.
-===== Experimental Data =====
+==== Spreading factor (SF)====
-During a test with Heltec Wireless Tracker, I received on the edge of the usable range:
+According to SX1276 datasheet:
-RSSI: -123dBm, SNR:-17.3dB
+  * At SF 6, SNR of -5dB is required
+  * At SF 12, -20dB.
-SNR(dB) = sig(dB) - noise(dB)
+  * 2.5dB change between SFs.
--noise = SNR - sig
-noise = sig - SNR
-noise = -123dBm + 17.3dB = -105.7dBm
-Meshtastic was on the default LongFast setting, which uses:
-TX power 27dBm (500mW).
-SF 11
-Link budget (from meshtastic docs): 148.5dB
-"The link budget used by these calculations assumes a transmit power of 17dBm and an antenna with 0dB gain"
-SF 11 requires -17.5dB SNR, so SNR was just acceptable by spec.
-In a later test, with VeryLongSlow, lowest RSSI seen with connection was -124dB and -6.0dB SNR, so not better.
 ===== Data Rate =====
@@ Line 40: / Line 22: @@
 This is all assuming the channel is fully utilised by this system, without interference or any retransmissions needed. With CSMA, actual channel utilisation will be much less than 100%, perhaps 50%  - 80% depending on number of nodes and details of CSMA algorithm. It would be safer to design a system that is useful at about 2kB/h.
+N.B. Headers have yet to be allowed for. I have also not allowed for any network / mesh management overhead, or admin messages.
 With good clear line of sight over the water it may be possible to use a smaller spreading factor, which would give higher data rate and reduce interference with Meshtastic or other systems using slower spreading factors. In case SF7 was usable, we would get x10 data rate, so 20kB/h.
@@ Line 46: / Line 30: @@
 What can be done with 2kB/h?
-N.B. Headers have yet to be allowed for.
 SMS messages.
 A custom weather report message might be squashed into 15 - 20 bytes.
 ====== Regulation ======
@@ Line 69: / Line 50: @@
 Further limits on usage in relation to LoRa one may see are probably just rules of The Things Network.
-The Things Network uses channels defined by LoRaWAN people, with max 16dBm (40mW) eirp. Most of the frequencies I see in the linked ofcom document though are max 25mW or 10mW erp. (40mW eirp is around 25mW erp though, maybe that is it.)
+The Things Network uses channels defined by LoRaWAN people, with max 16dBm (40mW) eirp. Most of the frequencies I see in the linked Ofcom document though are max 25mW or 10mW erp. (40mW eirp is around 25mW erp though, maybe that is it.)
 ===== 433 MHz UK / EU =====
@@ Line 90: / Line 71: @@
 ===== LoRa WAN =====
-LoRa WAN is a network built ontop of LoRa. The standard does not apply to general LoRa use, but maybe of interest to see what frequencies, bandwidth, etc. they use.
+LoRa WAN is a network built on top of LoRa. The standard does not apply to general LoRa use, but maybe of interest to see what frequencies, bandwidth, etc. they use.
 [[https://lora-alliance.org/wp-content/uploads/2020/11/lorawan_regional_parameters_v1.0.3reva_0.pdf]]
@@ Line 98: / Line 79: @@
 [[https://unsigned.io/website/loramon/|LoRaMon]] - LoRa packet sniffer using RNode code on LILYGO boards.
+===== Bibliography =====
+[[https://arxiv.org/pdf/1607.08011.pdf|Understanding the Limits of LoRaWAN]]
+[[https://www.etsi.org/deliver/etsi_en/300200_300299/30022001/03.01.01_60/en_30022001v030101p.pdf|ETSI Short Range Devices, Technical characteristics and methods of measurement]] (e.g. how to measure duty cycle)