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Research and Experimentation of LoRa in Heavy Multipath

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Recently published research (July 2019) has described a model for Bit Error Rate (BER) analysis of the LoRa PHY over a Rayleigh flat fading channel. Rayleigh flat fading channels are observable in environments where there’s a lot of multipath interference (e.g. dense urban, indoor, etc).
The LoRa PHY experiences significant degradation of sensitivity in Raleigh flat fading channels
Experimentation in an environment exhibiting Raleigh flat fading validates the model from the research.
Haystack XR2 encoding for LoRa was observed to yield roughly 30 dB gain to Packet Error Rate (PER) vs. default LoRaWAN encoding, in said experiment.
Haystack XR2 encoding for LoRa can yield enormous gains to efficiency, Quality of Service (QoS), and channel density for LoRa deployments in dense urban, indoor, or other environments where multipath dominates.

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Research and Experimentation of LoRa in Heavy Multipath

  1. 1. Research and Experimentation of LoRa in Heavy Multipath JP Norair CTO, Haystack Technologies 16 January 2020 1
  2. 2. Synopsis 2 • Recently published research (July 2019) has described a model for Bit Error Rate (BER) analysis of the LoRa PHY over a Rayleigh flat fading channel. Rayleigh flat fading channels are observable in environments where there’s a lot of multipath interference (e.g. dense urban, indoor, etc). • The LoRa PHY experiences significant degradation of sensitivity in Raleigh flat fading channels • Experimentation in an environment exhibiting Raleigh flat fading validates the model from the research. • Haystack XR2 encoding for LoRa was observed to yield roughly 30 dB gain to Packet Error Rate (PER) vs. default LoRaWAN encoding, in said experiment. • Haystack XR2 encoding for LoRa can yield enormous gains to efficiency, Quality of Service (QoS), and channel density for LoRa deployments in dense urban, indoor, or other environments where multipath dominates.
  3. 3. About LoRa® and LoRaWAN® 3 • LoRa is a type of modulation and encoding developed into a product line by Semtech. • LoRa is a Chirp Spread Spectrum modulation technology. It has features that make it perform well in ISM channels with unpredictable interferers. • LoRaWAN is a simple MAC layer that uses the default features of Semtech’s LoRa transceiver product line (SX127x, SX126x). • Since 2015, much research on LoRa has been conducted by 3rd party researchers in academia and industry. This presentation cites the following research paper below, which itself cites many other works related to performance analysis of LoRa. ‣ Jules Courjault, Baptiste Vrigneau, Olivier Berder. Fast performance evaluation of LoRa communications over Rayleigh fading channels. International Workshop on Mathematical Tools and technologies for IoT and mMTC Networks Modeling, IEEE Wireless Communications and Networking Conference (WCNC), Apr 2019, Marrakech, Morocco. hal-02181133 ‣ https://hal.archives-ouvertes.fr/hal-02181133
  4. 4. About Haystack LoRa XR2 4 • XR2 is a proprietary PHY-layer encoding and bit- framing technology developed by Haystack Technologies. It utilizes the highest performing short-block-length error correction technology currently known to science • LoRa XR2 includes customizations made specifically for LoRa modulation. It can repair a data frame even when every LoRa symbol in the frame is demodulated with bit errors. • XR2 is implemented in firmware. ‣ Streaming, real-time decoder on Cortex M4 ‣ Even better performance on Cortex M33 Haystack LoRa XR2 PHY Ground-to-Ground Range
 (Urban Environment) 0.64 miles / 1 km Data Rate Support 1.33-60 kbps (variable) “Real World” Link Budget 155 dB Forward Error Correction Yes: Haystack XR2 Code Auto-negotiated Encoding Rate Yes: 0.5-0.8 Packet Size Variable: up to 203 bytes Auto-negotiated TX power Supported MAC & Upper Layers DASH7
  5. 5. LoRaWAN® Fades in Multipath 5 Jules Courjault, Baptiste Vrigneau, Olivier Berder. Fast performance evaluation of LoRa communications over Rayleigh fading channels. International Workshop on Mathematical Tools and technologies for IoT and mMTC Networks Modeling, IEEE Wireless Communications and Networking Conference (WCNC), Apr 2019, Marrakech, Morocco. hal-02181133 LoRaWAN Sensitivity in a Multipath Environment • The latest research on the LoRa PHY validates numerically what we have been observing for years, in practice. • In most real-world conditions, there is multipath interference. The mathematic model for this is called “Rayleigh flat fading.” LoRa PHY is not immune to multipath. In flat fading environments, it has similar degradation as most other types of digital modulation. • Without a good error correcting code, Bit Error Rate (BER) corresponds directly to Packet Error Rate (PER). ‣ To yield 1% packet loss in an exemplary 24 byte frame, under RFF conditions, LoRaWAN® requires a BER of 0.005% (5*10-5) ‣ The red line on the chart shows: BER = 5*10-5.
 (i.e. 12.5 dB SNR is required at SF12).
  6. 6. LoRa XR2 Performs in Multipath 6 ~30 dB XR2 PER
 SF11 • The observed Packet Error Rate (PER) for an exemplary 24 byte frame, encoded via Haystack XR2 @ SF11, has been overlaid onto the previous chart. • LoRa XR2 at SF11 was observed, in an environment dominated by multipath, to have roughly 30 dB better performance than LoRaWAN at SF12 as modeled according to the research. • Environments dominated by multipath include: ‣ Dense urban ‣ Indoor ‣ Outdoor, where transmitter and receiver are operating close to the ground (e.g. 1m elevation) ‣ Scattering in the upper atmosphere LoRaWAN vs LoRa XR2:
 Sensitivity in a Multipath Environment Jules Courjault, Baptiste Vrigneau, Olivier Berder. Fast performance evaluation of LoRa communications over Rayleigh fading channels. International Workshop on Mathematical Tools and technologies for IoT and mMTC Networks Modeling, IEEE Wireless Communications and Networking Conference (WCNC), Apr 2019, Marrakech, Morocco. hal-02181133
  7. 7. Experiment: Airport Parking Lot 7 L Fixed device Red = dead spot Green = coverage X X X X X X X XX X X X X X X X X X XX XX X X X X X X X X L Fixed device Green = coverage 300 m LoRaWAN: SF12 / 500 kHz / Default Settings
 20 dBm @ 915 MHz LoRa XR2: SF11 / 500 kHz / 1/2 Rate
 20 dBm @ 915 MHz The results of the experiment corroborate the BER model from the aforementioned research.
 It also shows a roughly 30 dB improvement in QoS for the LoRa network encoded with Haystack XR2. Airport Parking Lot Area
  8. 8. Packet Efficiency Comparison • In AWGN environments (e.g. open space), XR2 SF11 offers similar QoS vs LoRaWAN SF12 yet ~3 dB greater energy efficiency. • In Rayleigh flat fading environments, however, XR2 SF11 offers enormous gains to QoS vs LoRaWAN SF12. • In Rayleigh flat fading environments, XR2 SF9 still offers better QoS vs LoRaWAN SF12, yet ~8 dB greater energy efficiency. 8 133.12 ms 262.14 ms 50.18 ms 163.84 ms 50.18 ms 131.07 ms 12.54 ms 12.54 ms 38.92 ms 49.16 ms LoRaWAN® Default Settings SF12 @ 500 kHz Haystack XR2 SF11 @ 500 kHz 1/2 Rate (A) 3/4 Rate (B) (A) (B) Haystack XR2 SF9 @ 500 kHz 1/2 Rate (A) 3/4 Rate (B) (A) (B) Preamble 24 Byte Frame Time-on-Air (Ratio) 395.26 ms (1.00) 214.02 ms (0.54) 181.25 ms (0.46) 61.70 ms (0.16) 51.46 ms (0.13) Conclusions
  9. 9. Conclusions and What’s Next 9 • Versus LoRaWAN, Haystack LoRa XR2 can yield enormous gains to efficiency, Quality of Service (QoS), and channel density for LoRa deployments in dense urban, indoor, or other environments where multipath dominates. • In environments where AWGN dominates, Haystack LoRa XR2 still yields a roughly 3dB improvement to efficiency and channel density, vs. LoRaWAN. • Ricean models describe environments where there is some compromise between AWGN environments (i.e. line of sight) and Rayleigh flat fading environments. We expect Haystack LoRa XR2 to perform markedly better than LoRaWAN in these environments, although not so dramatically better as it does in Rayleigh flat fading environments.
  10. 10. For more info on XR2 error correction: https://www.haystacktechnologies.com/xr-error-correction/ HayTag 2.0 Demo Kits with XR2 error correction: https://www.haystacktechnologies.com/demo-kits/ Other questions? info@haystacktechnologies.com

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