Wi-Fi Theory Pt.1

Applications and SDRs

Let's start with the history of Wi-Fi and how it all started. Well you have multiple entities that played apart in the creation of Wi-Fi such as the Wi-Fi alliance and IEEE (Institutue of Electrical and Electronics Engineering). The Wi-Fi alliance is responsible for ensuring the devices (Access Points, Clients, etc.) are meeting the standards established by the IEEE. IEEE establishes the different standards using a variety of working groups, and these working groups are responsible for the frequency, modulation and associated data rates. The IEEE has only recently started calling the technology Wi-Fi and sometimes you will see it as 802.11. These terms are interchangeable in how they are used. For example, Wi-Fi 1 or Wi-Fi 2 is not something you grew up hearing but instead these are 802.11 a, 802.11b, 802.11g, 802.11n, etc. Often you hear people try to say that Wi-Fi stands for Wireless Fidelity but in reality it was just a cool marketing name that the alliance came up to better advertise the technology, hence the title of the blog.

Below are the associated and released 802.11 technologies and their associated Wi-Fi generation names:

• 802.11 b - released in 1999 (retroactively Wi-Fi 1)

• 802.11 a - released in 1999 (retroactively Wi-Fi 2)

• 802.11g - released in 2003 (retroactively Wi-Fi 3)

• 802.11n - released in 2009 Wi-Fi 4

• 802.11ac - released in 2013 Wi-Fi 5

• 802.11 ax - released in 2021 Wi-Fi 6

• 802.11be released in 2024 Wi-Fi 7

  Now there are other Wi-Fi standards such as 802.11ad which is meant for high speed internet at 60GHz. Now this has its problems due to the limited range these signals are able to propagate at. Key point to remember when talking frequency is the higher the frequency the higher the data rates but usually come at cost with the short range. That is where technology like 802.11ah, a sub-GHz technology,

  come into play but are specifically meant for IoT (Internet of Things) devices.

If you are in the United States you also are familiar with the FCC (Federal Communications Commission) which is responsible for the break down of the RF spectrum in the United States. The most commonly used frequency bands are below:

• 2.4GHz

• 5GHz

• 6GHz

These bands are also associated with what is known as the ISM (Industrial Scientific Medical) band. Each one of these characteristics have their specific use cases. The first two Wi-Fi technologies (a & b) were distinct in which frequency ranges they occupied. The 802.11b opted for the 2.4GHz range which had increased range much slower than the 802.11a which operated at 5GHz. As technology continued to develop, these bands were eventually used together as seen in today's Wi-Fi where you can have them as separate networks (e.g., FreeWiFi and FreeWiFi5GHz) where the 5GHz is usally in the SSID (Service Set Identifier) commonly referred as the Network name or something similar. Don't worry we will break these different identifiers down in a later blog.

History of Wi-Fi

Modulation & Bandwidth

Now that we have talked about the history of Wi-Fi and the common operating bands for the Wi-Fi technology, let's further break down the modulation schemes and bandwidths of these technologies. First let's talk about FHSS (Frequency Hopping Spread Spectrum) which is exactly as the name implies a Frequency that hops around to help accommodate for interference and data transmission. Frequency hopping is also known to provide security in a way, that your central frequency (or channel number in the case of Wi-Fi) is never going to be the same. This had its downsides such as being slow (in comparison to the new modulation and access schemes) and would often drop packets when interference was met. This was common when Wi-Fi first started taking off as running a mircowave would possibly take down your network for one burrito.

Now this technology is largely irrelevant in Wi-Fi technologies for today's standards. DSS (Direct Sequence Spread Spectrum) and OFDM (Orthogonal Frequency Division Multiplexing) are the standards for today's Wi-Fi. DSS and FHSS are both types of spread spectrum but for DSS instead of spreading across multiple channels it relied on spreading across the given bandwidth for a single channel. This distinction allowed for more reliable connections during downloads or uploads. OFDM blows these out of the water with its reliability and support for channel bonding. OFDM is used today's cellular technologies as well (4G, LTE, & 5G)due to the reliability. How does it achieve this? Well OFDM uses a pilot channel that the clients (Wi-Fi device) uses to center point the signal and then has subcarriers (or tones) within the frequency spectrum that allow the data transmissions. The signals are Orthogonal meaning they do not interfere with each other. This technology enables further enhancements throughout Wi-Fi such as MIMO (Multiple Inputs Multiple Outputs).

Now let's talk about bandwidth or how much frequency is being occupied by the Wi-Fi channels. First we will start with 2.4GHz because each frequency range has its own channel numbers and corresponding bandwidths. The most common frequency channel numbers for 2.4 are 1, 6, 11, and 14 (Channel 14 is not available worldwide) and that is because these are the non-overlapping channels for the 2.4 GHz spectrum.

Each channel is ~ 20MHz (closer to 22MHz in total bandwidth) but some devices might allow for a maximum of 40MHz to increase throughput but depending on the environment your router might not choose this option to due to noise and interference.

Now with 5GHz and 6GHz you get into various channels and bandwidths and this is because of something I mentioned earlier, channel bonding. Now because these higher frequencies have less range than 2.4 the risk of interference is lower so taking more of the spectrum has less affect on the surrounding networks or other signals propagating at these frequencies. These higher frequencies use what is called DFS (Dynamic Frequency Selection) and LPI (Low Power Indoor) The purpose behind DFS is to ensure that weather or military radars are not interfered with. Over half of the 5GHz sprectrum is comprised of DFS channels in the United States. LPI is specific for 6GHz and Wi-Fi 6e which allows users to allocate up to 160MHz and with Wi-Fi 7 that number increases to 320 MHz for even faster data transmission.

Now to get some hands-on experience before we continue on with Wi-Fi Theory Part 1. Well there are some useful applications out there that you can use to see this information for yourself. This is not a sponsor nor am I affliated with these companies or products in anyway. The first application I recommend to people for Windows is the Wi-Fi Analyzer app for people who just want to see how their Wi-Fi network looks in comparison to their neighbors Wi-Fi or potential interference your network. The paid version gives you upgrades to better visualize these overlapping channels and from there you can manually change your Access Point (AP) settings to choose a less congested channel. It's a one time charge of $9.99 to upgrade, which I guess is not too bad and beats most subscription based platforms. Now I have a screenshot below of the application but keep in mind that your Network Interface Card (NIC) must be compliant with the given spectrum you are looking at. For example, if I am using a NIC that does not support Wi-Fi 6 or better I cannot look at the 6GHz band.

Now moving on to SDRs (Software Defined Radios) you can use a variety of SDRs just as long as they support the 2.4GHz to 6GHz range to view a live snapshot of the RF environment. Now you have to take into account that your SDR is not going to decode any of the information and you are just looking at the raw RF environment so seeing information like SSIDs is not something native to most SDR applications. I would say the most popular SDR for Wi-Fi based tinkering is the HackRF One by Great Scott Gadgets, which supports frequency ranges of 1MHz to 6GHz. Not just the frequency range which makes this SDR popular but also the fact that this SDR can transmit. Tinkering with Wi-Fi becomes a bit more fun with transmit capabilities.

Now there is the ever-so popular Flipper Zero which has really helped SDRs take off in the capabilities that this little device can do. It has also further gamify the cybersecurity realm with some of its native "tamagatchi" like and leveling up features. Natively this device does not support Wi-Fi but you can buy the Wi-Fi dev board ~50 USD for this capability. Never underestimate the power of the Raspberry Pi either which I believe is far superior to the Flipper Zero but requires more user knowledge and in tinkering to fully package for Wi-Fi exploring.

I will perhaps do a deeper dive on both the HackRF One and Flipper Zero to show case their capbilities in a future Youtube video. That's right, I have been thinking about it for awhile and think that I should also showcase some of the these unique tools and softwares on Youtube. I think video tutorials in combination with this blog will take us all to newer heights. So stay tuned for part 2 where I break down the identifiers for further explore the HackRF One and Flipper Zero to explore the unique technology that is Wi-Fi.

Wi-Fi Frequencies

Frequency Hopping Spread Spectrum

DSS and OFDM

Bandwidth - 2.4GHz

Bandwidth - 5 & 6GHz

Wi-Fi Analyzer

HackRF One

Flipper Zero & Raspberry Pi