Wi-Fi: The Transmission and Reception of Wireless
Internet
Introduction
Since the introduction of the internet in the late 1980s, it has become deeply
engrained in our daily life. The first iteration of internet connection used wires a as
a method of data transfer. Using wires is a safe and effective way for connecting to
the internet but it limits us to physically plugging devices into the wall. It was the
introduction of wireless communication that changed the way we access the
internet by introducing a wire-free connection. Wi-Fi is a wireless communication
technology that allows an electronic device to exchanged data wirelessly with the
internet.
The Wi-Fi process is broken down into 3 major steps: Conditioning, Transmission,
and Reception. These steps are always followed whether you transmitting from a
router (Wi-Fi producing device) to a device or from a device back to the router.
Step 1: Conditioning
The first step in the process is known as data conditioning. Computers at the base
level operate on large strings of 1’s and 0’s. These strings are known as binary code
and this is how all computer communication/function is defined. Every graphic or
text on a web page boils down to binary code. When a user views pages on the
internet your device is taking the binary code sent to it via the Wi-Fi connection and
then translates it into the web page you see. Before these strings are to be
transferred over Wi-Fi they need to be conditioned for transmission based on the
properties of radio-frequency transmission. Radio frequency transmission is a
method of wireless data transmission through the generation of electro-magnetic
waves (Variations in the electro-magnetic field of the air). Encoding and carrier
modulation are what define the conditioning step.
Encoding
Encoding is the process of using these 1’s and 0’s to define how the wave will
transfer the data. Since an electromagnetic wave travels with a certain
frequency (rate that the wave oscillates) we can encode our 1’s and 0’s into
the wave by defining 2 slight variations to this frequency as representations
of the binary code. The top of figure 1 shows defining a 1 and 0 as different
frequencies.
Carrier modulation
Carrier modulation is the process of taking carrier (a wave of a pre-defined
frequency) and then making these slight variations. For Wi-Fi the carrier
wave has a frequency of 2.4 Gigahertz and to transmit the signal we make
small frequency changes to this 2.4 Gigahertz signal. The bottom of figure 1
shows the carrier wave modulated signal. The carrier wave is required
because different wireless communications use different carrier waves as to
not interfere with each other. This way a Wi-Fi signal will not cause
distortion to other wireless communications.
Figure 1: Visual representation of Conditioning
The entirety of this step is accomplished digitally on the router. It is this final carrier
modulated electro magnetic wave that is then sent to the antenna on the router for
the next step of transmission.
Step 2: Transmission
Transmission is the second step in the process and it is the most complex. This is
where the transfer of the wave through the air via an antenna takes place. Located
somewhere on all routers and cell-phones are antennas for transmission and
reception of an electromagnetic waves. You may not see them externally on cellphones or other devices but they are located internally. These antennas facilitate
changes in the electro-magnetic field in the form of waves that travel through the
channel (medium of information transfer). It is the antenna and channel which
dictate the transmission of information in Wi-Fi.
The Antenna
The antenna is a relatively simple component of transmission. Essentially an
antenna is a piece of strait metal. The antenna operates on the basic physics
property that changes in current induce changes in the electromagnetic field
around the current. So to transmit via an antenna current is varied in the
same way that the conditioned wave is varied. These variations in current
supplied to the antenna create variations in the electromagnetic field. These
variations manifest as electromagnetic waves that are representative of the
conditioned signal. These waves then proceed to propagate through the
channel. Figure 2 displays an antenna producing electro magnetic waves.
Figure 2: Antenna creating electro magnetic waves
The Channel
The channel is the most unpredictable part of the entire process. Since air is
not uniform and changes depending on weather conditions, there are
random distortions and attenuations (reductions in power). We also have to
account for materials in the channel such as walls and other objects. Since
Wi-Fi transmission distance not very far, only about 30-50 meters, the typical
channel consists of things in the general vicinity of the router. Routers are
always located in buildings to protect them from the elements so your
channel will include walls and objects inside the building. Since Wi-Fi is
transmitted at a high frequency the wave will pass through walls and objects
not made of metal. Metal walls and objects are conductive and therefore
absorb the wave. So when transmitting its imperative that the router is in a
central location for best distribution of Wi-Fi and that no large metal objects
are located near it.
It is these two components to transmission that define how the signal will be
transmitted to your device. Since there is no physical connection in Wi-Fi this is the
step that most errors occur and why it subject to lost connections on a regular basis.
After the wave is transmitted and passed through the channel it is then received by
your device.
Step 3: Reception
Reception the third and final step in the process of Wi-Fi and it the most straight
forward part of the process. When the electromagnetic wave finally reaches the
device there is another antenna that captures the signal using the reverse of the
transmission method. Once the signal is captured, it is then decoded based on how it
was encoded. These are the two steps that define reception.
The Antenna
The purpose of the antenna at the receiving device is the opposite of the
antenna at the transmitting device. Instead of using current to produce
electromagnetic waves, this antenna uses the transmitted waves to induce
current in the antenna. This is accomplished by the principal that changes in
the electromagnetic field induce current in metal. This is the reverse of the
principal used in the transmission antenna. This reversibility allows us to use
the same antenna for transmission and reception.
Figure 3: Iphone 4 antenna. Located on the rim of the phone
Decoding
Decoding is a relatively simple process because the device already knows
how the signal is conditioned. Once the antenna converts the electromagnetic
wave into a current wave the phones processor looks for our 1’s and 0’s
definitions in the waveform. Once the processor sorts through possible
distortions in the signal caused by the channel, the defined changes in the
waveform are then converted back to binary code.
It is this binary code that is received from the router through the Wi-Fi transmission
that is used by the phone to recreate the web page. It is after this step that the
process is complete for the Wi-Fi transmission of one web page.
Conclusion
Even though Wi-Fi seems to be transparent and everywhere it is actually based on
the physical interactions of electronics. The interactions boil down to the
conditioning of the information for transmission, the actual transmission, and the
reception of the signal. It is Wi-Fi that has allowed us to have a wealth of knowledge
at our fingertips.