[Music]
and Welcome to our last session before
lightning talks this afternoon um if
you're not sure it is Saturday afternoon
um please welcome Philipe
whoa please please say farewell to me um
please welcome Filipe Taris who's here
to talk about Wi-Fi is it just blinking
lights Wi-Fi RF other kinds of dark arts
please welcome
philippin hello
everyone so let's just get a quick
introduction through um I do a bit of
statistics and testing at a company
called moris micro we design Wi-Fi chips
but it's not your conventional Wi-Fi
it's actually Wi-Fi Halo which is
basically a longer range lower power
version of Wi-Fi basically for embedded
devices um I have a Blog where you can
read about my ramblings um I also do a
bit of pixel art on the side you can
look at that uh and if you're on fattye
you can find me
there all
right um this would be the updated title
of the talk um risky Devils of un proven
technology I haded together in the
kitchen yesterday and just a picture of
what that looked like that was me in my
apartment room making sure things worked
just before the
talk um all right
so let's cover the statement of the talk
right um is Wii just blinking lights so
let's start talk about light for a
second um
um the basis of light is something
called a photon um this little guy there
uh with a cool hat because he goes fast
um so the way light works is depending
on the different kinds of light that you
have you have something called
wavelength which basically describes how
fuzzy the light is um and of course
light is always going at the speed of
light um you have all of these different
kinds of light you have light that's
used in Wi-Fi Halo which is like about
30 cm in that fuzziness uh you have
light that's used on 2.4 GHz Wi-Fi which
is your standard Wi-Fi and that's about
8 is 8 cm um and then if you go all the
way down and further down and further
down in size you finally have visible
light which is much much much smaller um
about 500 50
nanom um but yes it's all light the
light that's used in your um phone to
communicate with the cell towers light
that's used on uh hem radios and like
there you can see all
photons um and of course light has a bit
of a relationship with
frequency uh which is basically just
it's the inverse of the time that it
takes for the Photon to move that uh
wavelength
amount all right so we have established
that Wi-Fi is in fact light and a lot of
other things are light as well um but
what exactly is Wi-Fi so Wi-Fi is
defined by this standard called dat 21
standard which defines a bunch of things
and over the years it just has been
added and added and added to and every
time you see a new release of something
Wi-Fi 4 Wi-Fi 5 Wi-Fi 6 Wi-Fi 7 uh it
goes on and on and every time it's just
a bunch of new things that gets added to
the same old standard called
a211 um and at its score that standard
basically defines there is something
called the physical layer which
basically defines how do we generate
light how do we see that light how how
that light behaves in general and then
there's something called the medium
access layer um which basically defines
how we control the chaos that's
generated by trying to communicate just
with light PES and blinking lights
um so if we were to break down what is
happening when you're using some Wi-Fi
device to communicate you basically have
your browser that's doing something
there um and it's sending something to
the kernel of the operating system and
that goes through the driver which
basically generates 8 to 11 frames which
is the data unit that's used used when
you are using any Wi-Fi technology um
that gets communicated to whatever Wi-Fi
Hardware you have by any kind of bus
that can be a multiple uh different uh
protocols in this case I just has
exemplified there with USB bus uh and
finally your Wi-Fi Chip is going to do
some magic and it's plugged to an
antenna and you get some light
um and finally and this is the most
complicated bit what exactly are we
saying when we say Wi-Fi is blinking
lights why say blinking um it's a very
specific kind of
blinking um and I'm going to cover a
quick example
of how that blinking pattern would
behave if you were to send something
over blinking lights uh somewhat in a
Wi-Fi standard for Pon AAU for example
if we take the p
that is represented by some uh s uh
number so it's there in binary uh eight
bits and then the first thing that we do
is basically split that in two so we get
the first part which is just five the
second one is zero and then we represent
that in multiple different ways but
people in the RF space usually like to
do it in one very specific way which is
this they create a cartisian plane and
they say I'm going to put the five on
one of the axis and the zero on the
other one so they split the information
into two and one goes to the xaxis the
other one goes into y AIS one of these
points is whatever information you want
to send um however this is just a
preference of from the people that work
with this thing if you wanted you could
represent in a number of ways you could
use a complex number which has two parts
you assign five to one of them zero to
the other one doesn't matter which
direction um you could use a vector
anything that has two components would
do it just fine um but the important
thing here is actually that when you
want to send that as light there is an
interesting property that you can use um
which is basically if you have something
that is oscillating in a sine wave and
something that's oscillating in a cosine
wave they are something that we call
orthogonal that means you can mix them
together and then unmix them apart and
you can still retrieve the information
from both sides so what you can do is if
you want to send the five and zero from
earlier which if you combine them
together represents the p in Pyon uh
what you can do is just have one of
these sides uh multiply a sine wave and
the other one multiply a cosine wave mix
them together and then through the magic
of mathematics you get them both back
together uh on the other end um and
that's how the blinking is done in Wi-Fi
um so essentially instead of just being
onoff blinking it's actually more of a
multiple different levels
blinking um and this thing is called
quadrature amplitude modulation
quadrature because it actually this
property where you have signs and
cosiness can be mixed together and un
mixed uh is basically a 90° phase
difference and that's called a
quadrature um amplitude because when you
multiply things by different values
you're basically making them smaller or
bigger so amplitude and modulation
because anything that's being used to
generate waves in this sense is uh
modulation
scheme um I'll just cover a bit of
encryption because on Wi-Fi Technologies
all right you can have the sequence of
btes you can convert them to something
and then send them through an antenna
all good and all fine however very often
you do want to do that uh secretly or
with some encryptions laed on um so I'll
just cover really quickly uh what the
core principle of encryption is I won't
go too in depth but it's just enough to
get anyone curious um so what is
encryption when we say something is
encrypted are you making it garbled are
you hiding something is it a magic that
you do that only allows you to to see
the result in nobody else um it's
actually
random uh pseudo random to be precise
and the core principle is just if you
have a sequence of numbers let's call
them B1 B2 B3 whatever uh and you have a
sequence of random numbers R1 R2 R3 what
you can do is just sum every single
number with every single random number
and the result is also a random number
let's say that I had three and then
someone gives me a random number I sum
that to three and then I tell the result
to someone they can't tell that I had
three initially because I summ a random
number could be anything right so that's
the fundamental fundamental principle of
encryption and the way that this
actually works is you have this things
called Soo random number generators that
can take a seed um and that essentially
means that they generate a infinite
sequence of sud sudo random numbers that
you can just add to bytes and that's
your encrypted traffic so if if you
actually looked at what bytes are being
transferred in encrypted traffic is all
random bytes one of the big issues in
making things secure is making sure that
random is actually close to actual
random um so close that you cannot
actually use any techniques to retri
information from
that
um all
right and now is the part of the talk
where I do what Matt didn't in talk
before and I'm going to show you a demo
of how of this stuff works interestingly
enough using micro python so it's a nice
compliment
um so the idea here is pretty simple you
have all of this stuff um you can
generate of all of this waves that
somewhat are analog to uh Wi-Fi
and can you actually do it though can
you actually do something that is doing
some communication using this quadrature
amplitude modulation stuff um and
sending some information over as light
and can you actually see how that light
behaves instead of just being invisible
Hocus Pocus light that nobody can see um
the plan for that is using a Raspberry
Pi Peele um which you can Flash with
micropython and then adding some LEDs to
generate light on that and then some
light sensitive resistors to actually
detect that light on the other end and
we want to send some information over
and you want to see what it looks like
um
and because I like to make things very
complicated when they could be very
simple uh I actually built this out of
individual LEDs I could just have used a
normal RGB LED but I actually slapped
together real LED is one of each color
just for the for the fun of it um very
good soldering practice skills
um and then I did the same thing for all
the all the ldrs and that's for
detecting the light that's coming out of
those
LEDs um the problem is though I actually
wanted to detect what color was that
light on because for the fun of it I
wanted to do all of those schemes on top
of some color modulation I wanted to see
some color going around so how do you do
that these guys can only basically
detect
light but they can't say okay which
color is that
[Music]
so H I went to Office Works looking for
some filters and they had these in there
and what happened next was
murder and that's what I get um very
nice F third uh light sensitive
resistors um
however it didn't go too according to
plan so what you guys are seeing here is
basically for every single combination
that I can have with those RGB LED uh
that I created slapping together
different
LEDs on the x-axis this is the response
that I get from the different uh
ldrs so one of them is pretty good that
blue one seems to pick up some frequency
the yellow one also pretty good some
seems to pick around somewhere however
that red one and the yellow one are
pretty similar so they are not really
picking up different things and that's
because blue and green are really
similar even computers are confused as
to what is blue and what is green
um however we don't care too much about
that um because they are just this
similar enough that we can sort of
reconstruct um the the original color of
the light from that So the plan is we
get some information in this case just
some random bits uh we do some quad
amplitude modulation which just means I
multiply cosiness and SS and then I
generate something out of that and then
I want to send that as different colors
and to do that basically I can set up um
all the different colors that we can see
as a single spectrum and I can just
sweep through that Spectrum according to
my wave and that's going to generate a
bunch of colors I can detect that on the
other end and I can figure out what that
what the original information that was
sent was in the first place
um demo time let's hope this works so
what I have here is I actually put all
of that micr controller stuff inside my
bag because it's nice and dark in there
probably quite warm as well they
probably like that
um and I put a camera in
there now if this
works we should just be able to see
inside my bag what's what's going
on all right and my program here is just
a quick micropython program that does a
couple things first it tries to
calibrate the medium because if I do
this inside my bag it's going to be
different if I do it outside somewhere
it's going to be different in every
single place so I'm just going to run
every single color and I'm going to
register what the response is what's
happening with the those different
frequencies of light um and that's going
to calibrate the system so it knows what
is what and after that I'm going to do
something where I send a couple bits at
a time um so instead of the example that
we had with like four bits uh like a a 8
bit number from like the p in Pyon being
split into four bit numbers and then
that being translated into two sine
waves what I'm going to do is just use a
two bit number and then one bit goes
into each one of the axes which means
that it can be either one side or the
other side same for the other axis one
side or the other side that leaves us
with basically four different points uh
so it's just a two bit number that's
being transferred uh um let's see what
it looks
like all right that's the
calibration and now it's sending stuff
and then I wrote a quick program to
actually visualize what's happening
there in a nice way and hopefully this
works all right so what we should be see
what we should be seeing here is
basically each one of the four different
configurations so basically each one of
the four different edges of a square um
being read by the the uh ldrs in here
and that's going to be one of uh each
one of the four corners you can see
there is a lot of variation it's flowing
around a lot but it does follow corner
to corner to corner to corner so this
what you seeing here at the bottom is
what Wi-Fi would would look like if you
could actually see
it and
then back to the
slides all right there are a couple
things that I sort of glossed over in
this they're a bit more complicated um
and two that didn't make it they're are
particularly important in actually
making Wi-Fi work work is or ofdm and
interference ofdm is just a way of
instead of having this let's say two
bits of information being transferred at
time you have multiple channels of those
happening at the same time so you could
have eight different channels each one
two bits across all of them being sent
at the same time and the way that that's
being done is by separating out
different frequencies of light and
creating different channels from those
uh um the end result of that is that
everything basically looks like a
buzzing Mass because there's just like
so much information being transferred
across such a large range of different
uh waves of light um but it's the main
reason that Wi-Fi works so well and you
can get so much data through um the
second thing that's pretty important is
interference um there is a lot in there
I cannot go into detail into any depth
um but
basically the thing is there is not a
single uh just a single Wi-Fi device in
here for example or a single radio
device there multiple different devices
with multiple different protocols for
example Wi-Fi and Bluetooth live with
each other and they use the same
frequencies um so all of this stuff you
need to come up with ways of making sure
people are not talking over each other
um
and still you get uh uh data
through and other than that there is a
million other things they are also
important in Wi-Fi uh from understanding
uh how the chips are made and all the uh
analog uh Magic that goes into making uh
RF chips uh and a bunch of other things
and that's it um I'll take some
questions
now all
right than fipe
all right yeah we have heaps of time for
questions um so please put your hands
up preferably up the back so I get to
like walk closer to the fresh
air um H how is our signal attenuation
like calibrated for in the real world
because um when like things move like
the um like the amplitude changes right
yep so remember that thing that I talked
about just now called fdm that allows
you to send multiple different signals
at the same time what you can do is send
known signals so you're sending multiple
signals at the same time right so one of
these signals or multiple of these
signals can be something that you know
what's in there already it's not data
just for example just a sine wave in the
known frequency just something that you
know um and then when you're reading
that information you can basically know
what the information should be in those
places and when when you read that and
it's different you can basically
computer okay what happened to that
information so it's coming out different
now right so you can know both like in
terms of oh the signal is being Reduce
by attenuation or like there's some
weird effects that can also happen where
uh signals at different frequencies are
being uh attenuated at different levels
and then that sort of like creates a
squished signal or a smoosh signal right
and you can create multiple of those uh
they are called traveling Pilots um
multiple of those at multiple different
frequencies and then you can basically
understand how the shape of your signal
changed when it was transmitted across
the
medium thank
you up
the something I don't understand about
qim is how do you um how do you
determine if a sine wave is the sign or
the cosine how do you how do you lock
that phase to begin with so you mean
like when you're doing the the reading
of the signal yes right so the way it
works is a bit interesting it's based on
sort of like all the if if you want to
look into the math later like you look
into convolution and that kind of thing
um but the basic idea is just you have
your signal uh you do like let's go back
from the beginning actually so you have
the the two different sides you multiply
one by uh cosine the other one by a sign
you sum them together you get some
signal right now you want to you want to
know what was in there in the first
place the way that you do it is very
simple is you get that signal and you
just multiply Again by a cosine and the
other one by a sign and that's going to
give you an approximation of what the
original values are but it's not going
to be perfect you're going to get like
it's going to be basically if it was a
one there before it's going to be like a
waving one essentially and then you pass
that through some filters you get the
one back um but yeah if you want to look
into the math later look into
convolution and that kind of thing
all
right uh just a bit curious is this by
any chance related to the fast forear
transformation because it seems
similar it is in multiple ways
especially the thing about ofdm um so
fundamentally the way that ofdm works is
it's actually a fre trans form right so
um yes very much related and if you are
getting to fdm it's just a fast free a
transform
yeah with that synchronization thing
again like so what if you sampled it at
like a 90° phase difference again so
then you'd have like the cosine when you
multiply it by a sign it would look like
a cosine right mhm so how do you
differentiate between both of them then
if you sample it like 90° phase
difference yep so that because of that
is very important to have
um there's something called cohes
coherence and it's very important to
have synchronized signals when you're
dealing with Wi-Fi or any kind of radio
signal that actually uses this stuff um
there are multiple ways that you can
deal with it but basically what you do
is start if you phase lock the two
systems so you are always like you never
you can never like do the decoding at a
90° angle otherwise you get the
incorrect information so before you send
an information you need to make sure
like either you have very accurate
clocks on board of both systems or you
send some form of like U pilot signal
that allows you to initialize a specific
instant in time and then do like the UR
decoding synchronized way but that's one
of the main drawbacks of like any kind
of system that uses this kind of
thing do we have any more um
questions oh oh hey
are there Wi-Fi systems C say that use
visible light because I've heard of
thing called
lifi which kind of Lights the room while
it's doing the Wi-Fi thing is that can
you talk about that not not like actual
Wi-Fi um there are sort of like um and
by actual Wi-Fi I mean not something
that why was like written in the
standard but if you look into research
papers there are people doing for
example um headlights on cars and doing
actual like Wi-Fi Pro call communication
using those
headlights um and a bunch of other
things like for maritime signals but
there is no like broad application Wi-Fi
like visible light
communication
okay how bright would my Wi-Fi antenna
be if it was a 500 anomet
LED well um the usual power on Wi-Fi
systems rang from like 20 dbm to 30
dbm um so that's like at most one watt
I'm not exactly sure how bright that
looks but yeah it would be a one watt uh
LED all right do we have any more
questions oh
hey so the choice of frequencies in
practice we have the 2.4 and 5 GHz
except except that these are the fre
range uh bands is there any other
reasons be reason behind the different
frequencies um there are two main
reasons possibly a few others but the
two most important ones is first this
ofdm thing basically makes you use a
bunch of different frequencies right so
the more frequencies that you want to
use the more frequencies you need to be
to have available so if you're using
like one Hertz you cannot go like below
zero Hertz right so you're spaced to one
side is basically between 0 Herz and 1
Hertz if you're using 2.4 gz you can use
anything from 0 to 2.4 to over 2.4 right
so one the first reason is just if you
want to have more of those waves at the
same time usually you need a higher
frequency so you can have a higher what
we call bandwidth um so for example in
2.4 it's goingon to have like 40
megahertz and 80 megahertz systems if
you go much further up you get bigger
channels
uh and with those bigger channels you
can get like wider and more information
at the same time that's one second thing
that you have different things is for
example you have a 5G uh wi-fi system
right if you put it in this room and you
go into the Next Room your signal is
actually going to be much lower than if
you had a 2.4 uh gahz Wi-Fi because the
higher the frequency the more it gets
reflected by stuff and everything else
so yeah those are the two main reasons
you have like different frequencies one
is like sometimes you want the higher
penetration you cannot get like the the
higher bandwidth but sometimes you do
want the higher bandwidth and you lose a
bit of pentation so it's a bit of
a balancing
game all right do we have time for one
more
question no if anyone here is feeling a
little bit lost be reassured this was
just a fourth year engineering
telecommunications
subject so so it's okay it's also the
middle of the afternoon and we're about
to go into a break and then into um
lightning talks this afternoon so uh
please join me
with please join with me in thanking
Filipe
[Applause]