LoRa nxKm Walkabout

Introduction

LoRa (Long Range) is a very popular protocol for long range communication between low powered battery operated devices (Ref.1). In the previous three posts I looked at sending a packet using a pair of adjacent 915MHz LoRa transceivers, simulating the LoRa symbols and receiver symbol correlation with Scicos (Ref.2/4). In this post I go on a walkabout to see how far I can travel from a balcony mounted transceiver and still receive a message correctly.

Walkabout Configuration

Fig.1 LoRa Walkabout Configuration
ParameterSeparation Distance m
RSSI = -510 m (adjacent)
RSSI = -7210 m (inside apartment)
RSSI = -7950m (Outside Facing)
RSSI = -88100m (1st Block North)
RSSI = -104200m (2nd Block North)
RSSI = -108300m (3rd Block North)
RSSI = -110400m (4th Block North)
RSSI = -115500m (5th Block North)
RSSI = -114600m (6th Block North)
Obstructed Church, Houses & Trees
Fig.4 RSSI Receive Signal Strength Indicator vs. Separation Distance

Figure 1 shows the walkabout configuration. An RPi4B is used as a base unit and is connected to a desktop computer via VNC viewer. A PiTop with RPi3B is used as the portable terminal. A Python program rfm9x_node1/2_ack.py is run on each unit (Ref.5). Each node receives a startup message, then packets 1,2,3….etc until the program is terminated. There is no output on the OLED display but just on the Terminal Program. Figure 4 shows the reception results. At 600m the path was obstructed by a church, several houses and trees. Without these obstructions I am pretty sure I could have gone out to at least 1Km without packet loss.

An RTL-SDR is used to capture the packet transmission with SDR# and is saved as an IQ baseband file for playback and study.

LoRa Signal Capture

Fig.5. LoRa Packet & ACK
Fig.6 LoRa ACK
Fig.7 YouTube Video LoRa nxKm Walkabout


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References

#1. – “LoRa Alliance”
https://resources.lora-alliance.org/technical-specifications/rp002-1-0-4-regional-parameters

#2. – “LoRa Scicos Simulation_b”
https://jeremyclark.ca/wp/telecom/lora-scicos-simulation_b/

#3. – “LoRa 915MHz Transceiver Packet Test”
https://jeremyclark.ca/wp/telecom/lora-915mhz-transceiver-packet-test/

#4. – “LoRa Scicos Simulation_a”
https://jeremyclark.ca/wp/telecom/lora-scicos-simulation_a/

#5. – “Python Code for RFM95W”
https://github.com/adafruit/Adafruit_CircuitPython_RFM9x

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.