In Wi-Fi, Sometimes Less Is More

“The Voice of Cincinnati Goes ‘round the World!”

That’s a quote from an ad in the Cincinnati Enquirer May 2, 1934, the day Powel Crosley Jr.’s WLW radio station officially began broadcasting with 500,000 watts (W). 

Crosley was already billing WLW as “The Nation’s Station” when it was operating at 50,000 watts and could be heard in Florida.  Now, WLW had the most powerful transmitter in the world, and it immediately caused problems. 

When WLW increased its power, interference with CFRB's broadcasts occurred hundreds of miles away in Toronto. WLW attempted to mitigate this by adopting a directional antenna system and adding towers, but the problem persisted, leading to complaints, including a lawsuit from WOR in Newark, NJ, operating on yet another clear-channel station.

Within a few short years, the Federal Communications Commission (FCC) announced new regulations and clear channels were limited to 50,000 W. The age of superpower broadcasting was over. Rather than a few giants broadcasting over huge territories, the future of broadcast radio would be many smaller stations offering the same content, i.e., national broadcast networks.

Those who have been around IT a while may recognize a similarity between the WLW story and the early days of Wi-Fi. Early Wi-Fi deployments generally tried to cover as much territory as possible with the least number of access points (APs), just like Crosley and his superpowered broadcasting.

Wi-Fi was always intended to be a local communication system. Unlike broadcast radio where the system could service a whole continent, Wi-Fi was built to serve buildings, so the power levels have always been rather small, initially capped at 100 milliwatts (mW).

Although the power levels are objectively low, maximum power was still the de facto standard in the early days. When lack of signal is perceived to be the source of poor performance, increased power seems like an obvious answer. But just like with broadcast radio, more powerful Wi-Fi may cause worse problems than it solves.

Unlike broadcast radio receivers, Wi-Fi clients are transmitters just like the APs and talk back on the same channel. And just as with broadcast radio, two transmitters can’t use the same channel at the same time without interfering with each other. So, Wi-Fi is a shared medium, where every transmitter, APs and clients both, must ensure no other transmission is occurring before utilizing the channel.

Initially, Wi-Fi was built around the 2.4 GHz Industrial, Scientific and Medical Band (ISM), with 13 channels spaced 5 MHz apart. Unfortunately, 802.11 Wi-Fi also defined 22 MHz wide channels, which means that only three 2.4 GHz channels can be used in the same space without interfering with each other.

Even at maximum power, it was often unlikely that three APs could provide the required coverage, but adding the necessary additional APs meant multiple APs on the same channel interfering with each other was all but certain.

Maximizing the power of an AP also maximized its service area and generally meant maximizing the number of clients that would utilize that AP. As Wi-Fi became more popular and the number of clients in an area increased, the time any one client could use the channel decreased. This led to not just poor performance for any clients that had poor signal, but for all the radios using the channel. 

The easiest answer to this problem was more APs operating on different channels. But of course, there are only so many channels to go around, and hence there are only so many APs that can serve the same territory. 

In addition to the problem of increasing numbers of transmitters trying to operate in any given space, the energy available to transmitters also became a problem.

As smaller and more mobile clients like smartphones proliferated, battery power became an increasing concern. One significant way to reduce battery usage is to decrease transmit power. But having disparate transmit powers between APs and the clients they serve can cause yet more problems, like only one side being able to receive transmissions. 

This sort of power mismatch can cause noticeable problems in real-time communications like voice, where the signal from a powerful AP can reach a client, but the return signal from the lower power client never makes it back to the AP.

The solution to these problems was lower transmit power at the AP. Reducing the power limited the number of attached clients and improved the speeds at which data moved, all of which increased the efficient sharing of the channel. Smaller service areas also meant more channel reuse across a space and less interference caused by neighboring APs.

Lower power systems are the norm today, with standard AP power generally less than a quarter of the original maximum. Even with the addition of dozens of channels in the 5 GHz UNII bands, the current client density and client power limitations still require the small service cells that lower power brings. 

Smaller AP cells require more APs to provide the desired overall coverage. This proliferation of APs necessitated centralized management and control, which developed into systems commonly referred to as wireless controllers today. Wireless controllers can take the form of dedicated on-site systems, virtual controllers on local APs, AP coordination systems, or cloud-based systems. Regardless of the form it takes, one of the major functions of all wireless controllers is dynamic transmit power control.

The dynamic power controls available for APs today don’t solve all problems however, as the systems still must be configured to account for many variables, such as:

• Regulatory limits: Maximum allowed transmit power can vary by channel in the 5GHz band, and in the 6GHz band, it can vary depending on channel width.
• Receive sensitivity: The receive sensitivity of clients is highly variable, so a power and associated receive signal that works for one device may be inadequate for a different radio.
• Communication between transmit power and received signal: While standards like 802.11 are a sort of common language, many manufacturers have developed their own dialects.  Manufacturers often use different notation to both configure and display AP transmit power.

So, what have we learned from the ancient history of broadcast radio and more recent history of Wi-Fi? Primarily, that radio communications are complex, and often in unexpected ways. Even with all the lessons we’ve learned and the advanced tools we’ve developed to deal with this complexity, designers and engineers still must account for all the nuances of radio when deploying and maintaining wireless communication networks.

These variables can be difficult to account for without expert assistance. Whether you’re deploying Wi-Fi for the first time, upgrading an older network, or just wondering if your network is doing what you expect, CDW can help your organization optimize your wireless experience with services such as:

• Site surveys: A wireless site survey helps identify the best spots to place wireless access points for optimal efficiency, reliability and performance.
• Network assessments: Through this engagement, a CDW expert examines an organization’s current network operations to see what upgrades may be needed.
• Network design: CDW wireless engineers help organizations design and build high-performance, dependable wireless networks .