What is WiFi?

Wireless internet has become ubiquitous in our daily lives.  We seek it out in public spaces, curse it when it is slow, and we set it up in a new home before we even bother calling the electrical company.  Yet, beyond a way to acquire cat videos, what IS WiFi?

Good Question.

A Wireless Access Point (WAP) such as a router allows wireless devices to connect and send information to it.  If this WAP is connected via Ethernet to the internet, it can pass requests to the internet and send the response back to the wireless device.  If a WAP is configured without access to the internet it can still moderate device-to-device (also known as peer-to-peer or P2P) requests.  This is how you can use the Solstice Pod to collaborate with other users on a display without any device being connected to the internet.

WiFi is commonly referred to as a 2.4GHz technology.  This means that communications occur within the 2.4GHz ISM band on a carrier frequency between 2400MHz and 2500MHz.  The 802.11 specification quickly evolved to also cover the 5GHz ISM band, with the requirement that dynamic frequency selection (DFS) be employed at certain frequencies within that band to avoid interference with weather radar stations.  DFS enabled access points will automatically jump to frequency channels with low interference.

Channels?

Though a WiFi device is said to operate at 2.4GHz, it really may be operating anywhere between 2.41GHz and about 2.46GHz. This ISM band is traditionally divided into up to 14 channels, each 20MHz wide and centered around a frequency 5MHz higher or lower than the neighboring channel.  This density means that the channels overlap with their immediate neighbors, such that using channels 1 and 2 at the same time would force the channels to share a fair bit of bandwidth.  Due to overlap, channels 1, 6, and 11 are the only ones that should be used concurrently where three channels are required.    Channels 12-14 are not commonly used in North America due to restrictions at 2500MHz.

Dual band devices that can communicate with routers at either 2.4GHz or 5GHz may effectively utilize many more channels than a single band device, increasing the likelihood of finding a channel with low interference.

What Sort of Interference?

So many sorts.  2.4GHz is a wireless communication sweet spot because it uses an available ISM band, is a low enough frequency to pass through most walls and common barriers, and yet it is a high enough frequency to move acceptably large amounts of information.  As a result, radios for most common wireless protocols (including Bluetooth, ANT, and ZigBee) all use that 2.4GHz band.  Even though they use different protocols, any device listening on a 2.4GHz channel must sort through all that noise to find messages meant for them.

In more familiar terms, this is like trying to have a conversation with a friend.  If you are in a quiet café, you can have a fluid discussion and express complicated thoughts.  If you are in a noisy restaurant, you have much more trouble communicating even though none of the people around you are actually trying to join your conversation.  Your sentences must be shorter and more concise, and may need to be repeated several times to be understood.  You may be able to get the same point across, but the rate at which you can convey data is far slower.

Beyond other wireless devices communicating in the same ISM band, interference at 2.4GHz comes from things you would not expect, like your microwave oven or a nearby car alarm.  The 5GHz space is much less crowded, making it ideal for wireless communication from an interference perspective, but it suffers decreased range and cannot overcome common attenuators like brick as well.

Although the numbers vary by transmitter and receiver, you can expect to get about 100m of range from a 2.4GHz signal in a noiseless, line of sight application.  Under the same circumstances, you could see 30-50m of range from a 5GHz signal.  In a typical residential environment, 2.4GHz and 5GHz ranges are commonly reduced to 10-15m and 2-3m respectively.  This may be acceptable in a small office space with an open floor plan, but can be very frustrating in a large building with thick walls between rooms.

Yet, this can be entirely positive for some applications.  Large trade shows like InfoComm are moving to only offering 5GHz internet access points to exhibitors because the speeds are higher and the decreased range means less interference from neighboring booths.  Not all personal devices (like smartphones) are 5GHz enabled, but the vast majority of commercial technologies recognize the benefits of using a dual band WiFi module.

Why Don’t I get Gigabit Download Speeds from a GigaHertz Router? 

While higher carrier frequencies generally enable higher data transfer rates because they are in bands that allow a wider bandwidth, the resultant speed seen by a user has many factors.  2.4GHz just means that if you measured the carrier wave used to communicate between devices, you would see a peak 2.4 billion times per second.    It does not mean that a user should expect to see 2.4 billion bits of useful data delivered per second.

The practical data rate of WiFi started at just 1Mbps with the introduction of the standard in 1997, using direct sequence spread spectrum (DSSS) modulation.  As the WiFi alphabet soup has grown over the years, achievable data rates have increased from 802.11b (50Mbps) to 802.11ac (800Mbps) and are speculated to break the gigabit boundary with the release of new standards like 802.11ax as early as 2018.

Liar, my 802.11ac Router Never Provides 800Mbps

That’s entirely possible.  Achievable data rates are much like achievable signal ranges – they are tested under perfect conditions.  If you could connect one wireless device to your router in a noiseless environment, you may very well get your cat video downloaded at 800Mbps.  If you are you using your access point in a more standard situation, your results will be worse.  When you connect multiple wireless devices to the same access point, they all have to share that “achievable data rate” pipeline to send and receive messages.  When you are listening to music through a wireless speaker, letting your phone automatically update apps over WiFi while browsing the internet with several tabs open, that same cat video will take significantly longer to download.  Add in neighbors with their own wireless routers set to the same default channels as yours and non-wireless interference at 2.4GHz, and that achievable 800Mbps speed slows to a crawl.

Of course, competing to get a slice of 800Mbps is still going to render better results than trying to compete with other devices with only 1MHz to go around.  Since its inception nearly 20 years ago, the 802.11 standard has improved standard wireless transmission speeds by defining ways to use more channels and more frequency bands, and by helping maximize data efficiency in both packet and antenna configuration.


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