Anatomy of an Access Point

There are three main components to a Wi-Fi Access Point, each of which are critical to its function:

Radio
Antenna
The CPU

There are many different ways to split the three components above, but every Wi-Fi solution has all three components.

What is a Wi-Fi Access Point? It's made up of some key components that are common between manufacturers. All manufacturers are vying to produce better and better access points, with more features - in this blog we'll introduce you to the basics of what makes an AP an AP!

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The Wi-Fi Radio Chipset

A Wi-Fi Radio is a purpose-built computer chip that has two key responsibilities:

Transmitting: creating the signal pattern sent out over the RF Spectrum
Receiving: Interpreting the signal pattern received by listening on the RF Spectrum

It can only serve one role at any point in time, although it can switch extremely quickly between those roles. Most of the time, a radio is in listening mode. When it transmits it uses energy to create the signal, usually at a set amount of mW.

A Wi-Fi radio will support a particular set of Wi-Fi protocols and while two radios can be from different vendors, they must support the same combination of features to communicate.

These capabilities are usually “baked” into the chipset, so to use newer protocols requires new hardware on both sides with that support.

(Let’s not discuss software defined radios or firmware upgrades here…)

An enterprise access point can (and usually does) have multiple radios that operate mostly independently of each other. Given the limits of RF, each radio operates on its own distinct channel to avoid problems.

There are actually only a few Wi-Fi chip vendors in the world: Broadcom, Atheros and intel are the most known, but other vendors like MediaTek also make chipsets used in clients and APs.

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The RF Antenna

The antenna is the simplest of the three components but no less critical.

The antenna is used both to amplify and shape the signal transmitted by the radio. It doesn’t usually add any more energy than what the radio uses.

Using an antenna to direct the signal allows the same amount of energy produced by a radio to be spread in all directions (omni-directional), only in a certain direction (directional) or even be focussed in a narrow single direction (beam forming) for improved signal and effective distance. Although for simple antenna designs bigger usually means more amplification, antennas can take many shapes and sizes.

Older devices usually had one antenna per radio, but newer Wi-Fi devices can use multiple antennas (MIMO) with a single radio to do fancy things like transmit to multiple receivers at once, or send multiple streams of data over different paths.

One fact missed in many marketing statements is that the signal is only as good as what is on both ends.

A small client with a single, small antenna is not going to see the benefits when connecting to a fancy new access point, whether it looks like a spider or not…

Antenna Cables - a Necessary Evil?

As most APs have internal, fixed antennas, it can be easy to assume that they always have to be together. It’s not an absolute requirement and antenna cables are a common way of placing the antenna in a suitable location where an AP can’t easily go.

An antenna cable does reduce the signal strength, but the impact can be managed and the trade-off can be useful.

Antennas can be quite some distance from their associated radios, with 10m antenna cables not uncommon.

The impact on the signal is dependent on the quality of both the cable and the installation process. It’s critical to ensure good connections between the components, otherwise problems can occur.

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AP Placement: Location Grade Wi-Fi

The Central Processor (CPU)

An access point often needs to do multiple things beyond just using its radio. While also being a transceiver, an AP is also a switch, a stateful server, a firewall and a few other things. The most significant cost of an AP goes into its processing capabilities, to perform such varied tasks as:

Network packet switching (i.e. unwrapping and rewrapping frames between mediums and paths)
Client session management, to enable roaming and other stateful features
Network security enforcement (traffic filtering, session encryption)
Spectrum monitoring, looking for issues that might affect radio performance.

Although it’s easy to think of a single device taking on all these duties, it’s just as possible to separate some (or even all) of these duties and centralise or distribute them. Each Wi-Fi hardware vendor will have their points of difference in the processing rather than the radio or antenna.

Wireless controllers are an example of centralised components that do everything but the RF-related work, making the AP “light weight”.

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