Hello, everyone. My name is Fusang zhang.
I would like to share our recent work on behalf of all authors.
The title of our paper is
"Exploring LoRa for Long-range Through-wall Sensing".
This is the outline of this talk. It consists of five parts.
Let's begins with background and motivation.
Wireless sensing has attracted significant amounts of attentions in recent years
and various wireless signals have been explored for contactless sensing,
including WiFi, RFID, FMCW radar, ultrasound,
60GHz radar, UWB, and visible light.
Many new applications have been enabled,
such as localization, activity recognition, vital sign monitoring and etc.
While promising in many aspects,
one key limitation of current wireless sensing technologies
is the short sensing range.
The table shows the sensing capabilities of existing wireless technologies
in terms of operational range and through-wall capability.
We can see that long-range through-wall sensing is still missing.
This work explores exciting new opportunities
to significantly increase the sensing range with the introduction of LoRa.
LoRa is one of the major low-power wide-area network (LPWAN) technologies
that aim to sustain connections among IoT devices over a long distance.
The transmission range can be up to a few kilometers in urban areas.
LoRa devices operate in the license-free radio bands and have low cost.
So, we want to ask can we use LoRa to achieve long-range contactless sensing?
Next, let's see how to utilize LoRa signal for sensing
LoRa adopts the Chirp Spread Spectrum (CSS) modulation technique,
which encodes data as frequency varying chirps.
The chirp waveform can be represented as this Equation.
where fc is the central frequency, k is the sweep rate of the chirp,
B is the bandwidth, and T is the chirp duration.
We analyze the received signal when the target moves.
We obtain the received signal as the R(t).
The signal consists of two parts,
the former part is frequency changing band signal and phase error.
The later part is signal change induced by target movement.
So, we need to remove chirp band signal and phase error.
Note that the LoRa gateway is typically equipped with two antennas.
The two antennas share the same clock, and thus have the same phase offsets.
So we employ the ratio of received signals to eliminate the errors.
Thus we can successfully obtain the sensing signals for target movement
with accurate amplitude and phase.
Then we can calculate the distance and orientation of the moving target.
By measuring the phase change, we obtain the movement distance
And by measuring phase rotation direction,
we obtain the movement orientation
Next, we conduct extensive empirical study
to investigate the Lora sensing capability.
We build a LoRa sensing prototype
which is composed of one LoRa transmitter and one LoRa receiver.
The LoRa transmitter is Semtech product with an Arduino broad.
Our LoRa gateway is based on USRP and GNU Radio.
For LoRa long-range sensing,
We consider both small-scale motion and large-scale motion in our experiments.
We place the metal plate at a distance of 10m to 50m
at a step size of 5m from the transceivers.
We can see that LoRa signal is capable of sensing
even a subtle 5mm displacement at a distance of 25m away.
We also study the lora sensing granularity, and the impact of various factors.
Because of time, if you are interested, please refer to our paper
Finally, we demonstrate two sensing applications
The demo shows that the human respiration can be sensed
when the target is 25 meters away.
Human walking can be tracked even when the target is 30 meters away.
In summary, our work explores the sensing model, techniques and applications of LoRa
to achieve long-range through-wall human sensing.
We believe the proposed LoRa sensing system
would enable a large range of new applications.
Thanks for your attention.