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Author: Terry Ngo
If you ask users in developed countries about their home Wi-Fi connections, they are likely to tell you that it seems to be getting worse rather than better lately. Some might even say, “It’s terrible!” Even residents in the White House face Wi-Fi issues. Before the 50th Super Bowl, First Lady Michelle Obama complained in an interview with the BBC: “The signal is not very good. It has upset the girls.”
More than 80% of households in the U.S. and 50% of the global population live in urban areas, where the quality of Wi-Fi connections is steadily declining. The reason seems obvious: there are more people (and things) using Wi-Fi than there were 10 years ago, and that number continues to grow. Today, there are 6.4 billion devices globally that access Wi-Fi and are in use. By 2020, that number is expected to soar to 20.8 billion—equivalent to 2.8 mobile devices for every person on Earth. So, the “highway” of Wi-Fi is certainly going to get crowded, and it will continue to get more congested.
However, this virtual traffic jam cannot simply be blamed on the need to accommodate more vehicles—the roads themselves are also causing conflicts. Three major changes in the market have made the situation worse.
First, each household in your neighborhood may not only have one router, but many communities also use public Wi-Fi networks simultaneously. Second, as users demand higher speeds, the virtual lanes on the Wi-Fi highway need to become wider, which means fewer lanes. Finally, cellular network operators are also shifting traffic to the Wi-Fi spectrum—imagine if everyone who used to commute by train suddenly switched to private cars.
The following discusses why Wi-Fi has succeeded but is suffering as a result—and what engineers can do to improve it.
Wi-Fi operates in an unlicensed spectrum. This means that while the Federal Communications Commission (FCC) typically requires a license to use the spectrum in the U.S., spectrum regulators in other countries (such as Japan’s Ministry of Internal Affairs and Communications) have similar requirements, but they also leave some relatively open bands. Users only need to meet technical requirements such as power limits and do not need to apply for special permission. There are several such bands, and home Wi-Fi networks primarily operate in the 2.4 GHz and 5 GHz bands, as these are the few bands that meet both coverage and bandwidth requirements. The 2.4 GHz band performs best: it easily penetrates walls and furniture, and at the same power level, the 2.4 GHz signal generally propagates further than the 5 GHz signal.
In the U.S., the FCC has authorized about 80 MHz of bandwidth in the 2.4 GHz band for Wi-Fi use. The working channel width under the IEEE 802.11 standard is about 20 MHz or 22 MHz, so you can only use 3 non-overlapping channels simultaneously, namely channels 1, 6, and 11. The situation is slightly different in Europe, but only 3 non-overlapping channels are allowed to be used simultaneously out of 13 channels; in Japan, 4 non-overlapping channels are allowed out of 14 channels.
So when you search for available networks on your phone or computer in the U.S., if you can see more than 3 2.4 GHz routers (which is likely if you don’t live in a suburb), or if you only see 3 routers but none on channels 1, 6, or 11, then there is interference.
Due to walls and furniture blocking signals, the coverage of the 5 GHz band is relatively small in homes, but in North America, the 5.180–5.825 GHz band has 24 non-overlapping channels, each 20 MHz wide, while Europe and Japan have 19. For our crowded wireless highway, the number of these additional channels is substantial. However, about half of these channels (even more in North America) are primarily allocated for weather and military radar. To allow Wi-Fi to enter this radar-priority spectrum requires special technology. So far, most consumer routers have ignored these channels. But they are important, and we will discuss them later.
In both bands, there are some channels that do not interfere with each other. As more and more routers come online and more devices connect to them, interference becomes common. In the Wi-Fi world, when two conversations conflict, all devices pause their conversations and try again after a while. The length of time they wait is determined by an exponentially increasing delay known as “backoff.” The more conflicts there are, the more backoff occurs, and Wi-Fi becomes slower and more unstable.
Today, channel congestion in many areas is so severe that the 2.4 GHz band is nearly incapable of high-speed data transmission. Several broadband service providers (including AT&T, British Telecom, and Comcast) no longer use the 2.4 GHz band for video or voice transmission, and almost all smartphone manufacturers, including Apple, no longer recommend using smartphones on the 2.4 GHz band. The latest variant of the Wi-Fi standard, IEEE 802.11ac, is the fastest, and Wi-Fi only operates in the 5 GHz band, although most Wi-Fi devices include both bands to be compatible with older mobile devices.
Therefore, on the Wi-Fi highway, signals do not affect traffic on some roads as they pass through. But it is not just devices that cause congestion; the network itself does as well.
Shifting Wi-Fi communication from the 2.4 GHz band to the 5 GHz band was initially beneficial in alleviating congestion, but it also sacrificed coverage, so many consumers have turned to simpler improvements like network extenders or mesh networks to cover every room in their homes with Wi-Fi. These extenders or mesh networks are placed at the edge of the router’s coverage area, where the signal gradually fades. These devices receive all transmissions and then rebroadcast the content at a higher power, sometimes using a different channel. Now, even more Wi-Fi signals overlap in the same frequency range.
The emergence of public hotspots— Wi-Fi that the public or a small group of users (such as subscribers to a certain internet service) can access—has made matters worse. In 2005, Spanish Wi-Fi provider Fon Wireless first proposed the concept of community hotspots, which are hotspots attached to private routers. Community hotspots have become increasingly common worldwide. Today, U.S. internet providers like AT&T, Comcast, and Verizon are rapidly rolling out these hotspots, adding this feature to users’ home wireless gateways, which all users can access. Juniper Research in England predicts that by 2017, one-third of global home gateways will embed a second network identifier and allow sharing part of the Wi-Fi spectrum of that gateway, often without the household residents being aware of it.
Mobile operators have largely exhausted their unique spectrum, and the congestion of Wi-Fi is likely to worsen. These wireless operators plan to shift 60% of mobile data transmission to the unlicensed spectrum used by Wi-Fi over the next three years.
The technology to achieve this shift is called LTE-Unlicensed (LTE-U) or Licensed Assisted Access (LAA), which utilizes 4G LTE radio devices and routers to send and receive data over the same 5 GHz frequencies as Wi-Fi. While operators downplay the interference to Wi-Fi users, organizations like CableLabs, Google, and Microsoft have stated that LTE-U and LAA will definitely exacerbate Wi-Fi channel congestion and weaken Wi-Fi service. In the U.S., Verizon and T-Mobile have begun trials of LTE-U deployment to assess its impact on Wi-Fi. Operators in Europe and Asia are also planning similar trials.
However, the most important thing is that the latest variant of the Wi-Fi standard, IEEE 802.11ac, has indeed reduced the number of channels on the wireless highway.
IEEE 802.11ac can meet the growing speed demands—fast enough to transmit high-definition video, and mobile devices can only transmit at high speeds for a limited time, extending battery life. The previous generation Wi-Fi standard, 802.11n, could transmit 450 megabits of data per second, while this new generation standard can transmit 1.3 gigabits of data per second.
To transmit data at such speeds, 802.11ac needs to combine channels. In the highest performance configuration of IEEE 802.11ac Wave 3, all available Wi-Fi spectrum is integrated into two channels, each 160 MHz wide. This means that only two pairs of devices can communicate simultaneously on the widest channel without interference. So, if one of your neighbors is using one of the channels to watch a movie, and another neighbor is using the other channel, then you might be out of luck. Suddenly, those additional non-conflicting channels that make 5 GHz superior to 2.4 GHz have disappeared.
As many regions deploy such advancements, Wi-Fi connections may soon go from “annoying” to “completely broken.” In 2013, the UK’s communications regulator (OFCOM) released a study—”The Future Role of Spectrum Sharing for Mobile and Wireless Data Services”—predicting that by 2020 (only 4 years from now), Wi-Fi and mobile internet channels will become severely congested.
For the past 15 years, technology standard setters and router manufacturers have been working to increase speeds, but to date, they have overlooked these issues. In particular, they have yet to recognize the fact that: 802.11ac can provide wider channels, but the number of channels is fewer, and its widespread rollout will make congestion issues extremely severe.
However, there is a short-term fix. Remember that part of the 5 GHz spectrum that is radar-priority and requires special technology for Wi-Fi use? Today’s consumer Wi-Fi router manufacturers have ignored these channels. Opening these frequencies to consumers would have a significant impact.
In 2007, the FCC and other global regulators opened this additional spectrum to Wi-Fi traffic. Regulators realized that radar (such as Doppler weather radar systems that warn of low-level wind shear at airports) is not present everywhere and does not operate around the clock. Therefore, the Wi-Fi community can migrate Wi-Fi communications to these frequencies, as long as devices using these channels can implement a mechanism called “Dynamic Frequency Selection” (DFS) that does not interfere with radar signals.
DFS acts like a high-speed traffic cop—when it detects radar signals on a protected channel, it quickly switches all Wi-Fi traffic to another channel. It has some rules to follow: before declaring a channel free to use, it must listen for radar signals for at least 60 seconds, and it must continue to listen while Wi-Fi traffic is using that channel. Even if the mechanism detects a radar pulse for just 1 microsecond, the Wi-Fi transmitter must clear the channel within 10 seconds and refrain from using it for half an hour.
In the past three to four years, the vast majority of wireless mobile devices released have radio devices capable of operating in these bands and have the software required for feedback from the DFS host instructions. However, for these devices, the DFS host needs to be embedded in the router to tell them when they can use radar-priority channels and when they need to clear and pause.
The implementation of DFS host technology is not complex. Radar pulses are difficult to detect because they are very fast, with each pulse lasting only about 0.5 microseconds and can appear at very low power levels (as low as 62–64 dBm). Integrating radar detection tools can consume up to 17% of bandwidth because the router must listen for at least 60 seconds before concluding that it can transmit, and it must continue to listen during normal transmission.
Currently, DFS host technology is available only in expensive routers that only large enterprises would install. In Europe and Japan, this technology is migrating to low-cost consumer routers. However, whether it is the expensive enterprise version or the cheap consumer version, they are not very smart: when they detect radar, they switch traffic to a default channel in the non-DFS part of the 5 GHz band—a crowded frequency. Moreover, they do not return to using radar-priority channels until the user restarts the router. In commercial environments, it is often possible to set the restart to occur daily, but in home environments, users may go weeks or even months without realizing that the router is performing poorly and needs to be reset. So even routers with DFS capabilities often remain off the fast lane, at least most of the time.
However, solutions to Wi-Fi congestion still exist in these DFS channels. The key is to create a cheaper but more efficient radar detection technology. My colleagues and I at Ignition Design Lab in San Jose, California, believe we have found such a method.
We designed an enhanced router called Portal, which includes a full-spectrum radio scanner, a CPU dedicated to radar detection and channel management, and standard router hardware. The scanner continuously searches the entire 5 GHz band for radar, Wi-Fi traffic, and general interference. Existing radar detection technology allows radar detection and communication devices to share the main processor with Wi-Fi devices, while this method of completely separating the detection system from the Wi-Fi radio transceiver solves many problems.
With this standard hardware configuration, the radio device can only see the situation in a single channel within the DFS band at a time, so the DFS host can only monitor one specific DFS channel at a time. When the DFS host radio device first monitors a DFS channel, the FCC requires that the radio device must stop any signal transmission on any channel for at least 60 seconds to confirm that it is not interfering with the receiving device searching for radar. To avoid this pause, most radio devices are designed to only search for open DFS channels when the router is reset.
Another radio device specifically designed for detecting radar signals eliminates this barrier. It can also periodically search all channels. So, when a radar pulse is detected on a channel that is currently transmitting data, the system will simultaneously know whether another DFS channel has radar pulses, and if not, it can migrate the data flow there instead of to a pre-set default channel. Moreover, when the DFS host requests the router to abandon a channel due to radar traffic, after the required 30-minute waiting period, it can automatically return and recheck that channel without interrupting the ongoing transmission.
At the same time, the dedicated CPU can minimize the number of false radar alerts, reducing the frequency of Wi-Fi traffic evacuating channels. Today, when the router’s processor is handling a large amount of Wi-Fi traffic, such as when you are watching a video online, your child is gaming, and other family members are listening to music or browsing social media, it does not have the extra processing power to analyze whether the radio energy it detects on a protected channel matches radar signal patterns. Therefore, it can be overly cautious and make mistakes—if it detects any interference (which could just be the Wi-Fi traffic from a neighbor’s router), it will evacuate that channel until the router is reset.
We are trying to make the channel allocation process smarter, not only collecting radar information but also gathering various interference data and sending this information along with general Wi-Fi and radar traffic pattern data to a cloud server; our software analyzes the data on the cloud server and adjusts the behavior of Portal, which we call network self-optimization.
With this system, we can determine the best channels available for Wi-Fi devices in different locations. For example, we know that at 8 PM in Europe, DFS channels will be limited for user use, and the default DFS channel—channel 100—will become very busy. So we can switch one user’s traffic to channel 132 and their neighbor’s traffic to channel 154. This coordination will have a significant impact on Wi-Fi communication quality.
Our technology has been approved by the FCC and will launch the first products in North America and Europe in late summer and fall, respectively. We are also collaborating with some Wi-Fi device manufacturers and internet providers, hoping to eventually integrate our hardware into their Wi-Fi routers and gateways.
It is essential to launch this comprehensive intelligent Wi-Fi resource management system before Wi-Fi goes from unreliable to unavailable.
Because our colleagues in the communications industry have not managed the way Wi-Fi devices use the 2.4 GHz spectrum, this spectrum is now nearly exhausted. However, because we can migrate to the 5 GHz spectrum, consumers have not truly realized that the 2.4 GHz band is already full. But when the 5 GHz spectrum is also exhausted, we will have nowhere to turn, at least in the near term.
In the long run, new technologies will be developed to migrate some traffic to other types of communication networks that are incompatible with current Wi-Fi. The FCC has a few bands that could be considered for reallocation, including small amounts of 5.9 GHz, 4.9 GHz, and 3.5 GHz bands. But the process of spectrum reallocation could take years or even decades. Moreover, these frequency ranges include radar and other priority uses (such as public safety communications). Therefore, even if these bands are approved, intelligent use of DFS technology will be required.
For this reason, finding robust, affordable technology to utilize all channels on the wireless highway is the only way to solve the data congestion problem.
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