LoRa Scicos Simulation_a


LoRa ParameterRegion/Country Specific
900MHz ISM Freq Band
North America (902-928MHz)
Europe (863-870MHz)
R Data RateUS(902-928): 980bps – 21900bps
EU(863-870): 250bps – 11000bps
BandwidthUS(902-928): 125KHz, 500KHz
EU(863-870): 125KHz, 250KHz
Tx PowerUS(902-928): 2dBm – 28dBm
EU(863-870): 2dBm – 16dBm EIRP
SF Spreading Factor7,8,…..12
Number Symbols 2^SF128(2^7),……4096(2*12)
Fig.1 LoRa Specifications (LoRa Alliance Ref.1)
Fig.2 Rpi3B LoRa 915MHz Transceiver

LoRa (Long Range) is a very popular protocol for long range communication between low powered battery operated devices (Ref.2). It is part of the new IoT Internet of things and uses Chirp Spread Spectrum. LoRa is a specification for the Physical Layer only (Ref.3), whereas LoRaWAN is a specification for higher layers (Ref.4). Figure 1 shows some of the basic parameters. Figure 2 shows a LoRa 915MHz Transceiver mounted on a RaspberryPi4.

Pulsed Chirp FM Systems

Fig.3 Generate Symbol Structure
Fig.4 Symbol S1(000) & Symbol S2(001)
Fig.5 LoRa Tx
Fig.6 ChirpUp
Fig.7 ChirpDown
Fig.8 LoRa Tx vs. Random Data Symbols
Fig.9 LoRa Spec BW=VCOmax-VCOmin=100Hz

LoRa uses Spread Spectrum Chirp modulation. The number of symbols is equal to 2^SF. So for example SF=3, there are 8 unique spreading symbols representing 3bits (Ref.5). If we consider a VCO being driven over it’s bandwidth by a signal from -1 to 1, then each symbol is staggered over this interval. Figure 3 shows the symbols being created in ScicosLab and read into Scicos using a Structure V. Figure 4 shows the first Symbol S1 starting at -1 and going linearly to +1. The second Symbol starts at -0.75 and continues to 1.0, resets to -1 and continues back to -0.75.

Figure 5 shows the LoRa Transmitter which consists of a VCO being driven over it’s bandwidth by input structure V. Simple units are chosen for convenience, Fo=100Hz, Fmin=50Hz, Fmax=150Hz. Random data symbols are read in. Note the Tx Spectrum=VCO bandwidth of 100Hz. Figure 6 shows a Chirp Up, Figure 7 shows a Chirp Down, Figure 8 shows random data symbols, and Figure 9 shows the Transmit Spectrum = VCO Bandwidth.

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#1. – “LoRa Alliance”

#2. – “LoRa”

#3. – “AN1200.22 LoRa Modulation Basics”

#4. – “The Things Network”

#5. – “How LoRa Modulation Works”, Visual Electric

#6. – “Spread Spectrum Systems”, R.C. Dixon,
John Wiley & Sons, 1976, ISBN 0-471-21629-1

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.