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There are three things that customers care most about when it comes to using Wi-Fi: 1. High data, 2. High capacity (i.e. multiple, simultaneous users), and 3. Good range. Of course, there are other considerations, like easy to connect and easy to install. There has been great progress on the first, and ease of installation is getting better with distributed Wi-Fi in a box (which also indirectly addresses the range issue). There is also the murkier issue of avoiding interference from neighbors, which may or may not contribute to a slow Wi-Fi issue.

While higher data rate may seem to be the most important issue, let’s first look at capacity – multiple users using Wi-Fi at the same time.

Most people today have a router, and everyone connecting to that router is using the same Wi-Fi channel. Which also means that those users are sharing the same bandwidth and the same raw data rate. When people are using a repeater, that bandwidth gets shared even more – you talk with your repeater on the same channel as your repeater talks with your router, effectively doubling the traffic on that same channel.

Here is where distributed Wi-Fi comes in and makes dramatic improvement. Every node on the network can talk on its own frequency band with the end user, while simultaneously communicating on other frequency bands with the main router connecting to the Internet.

To put this in perspective, consider that the first Wi-Fi effectively used 3 channels (in the 2.4 GHz band) to stay away from using the same channel as the neighbors. Today, “modern Wi-Fi” uses 40 MHz-wide channels and effectively supports 10 of those channels in the 2.4 GHz and the 5 GHz bands, making it not only easier to stay away from the neighbors, but also to optimize usage in a home by enabling different users using different channels and also allowing a wireless infrastructure in the home for distributed Wi-Fi with multiple access points.

Distributed Wi-Fi ­– Not As Simple As It Sounds

If talking about different channels in Wi-Fi makes it sound as simple as digital radio and changing channels with a push of a button, the reality is a little harsher. Cheap Wi-Fi radio technology causes easy bleeding from one channel into another, particularly when using high or maximum output power. This bleeding effectively kills the neighboring channels, drastically reducing overall capacity.

The real name of the game in Wi-Fi today is making sure that channels are well-separated, to stop the bleeding. Suddenly, building a Wi-Fi product is not only about the Wi-Fi chip. Now it’s also about the “front-ends” – the amplifiers and filters between the Wi-Fi chip and the antenna that make or break the capacity of the distributed Wi-Fi system.

Higher Data Rates Do Count

So back to raw data rates. Our appetite for ever higher data rates seems insatiable. So, let’s take a look at where we came from and where are we going, as shown in the following table:

It’s important to note that this table focuses on raw data rate. But of course, we all know that in real life usage, there is often a significant difference between raw data rate and actual throughput, which can be half or even less of the raw data rate. In light of that, it’s good to know that while IEEE 802.11ax (planned for 2019) does include a modest increase in raw data rate, its main intention is to increase the actual throughput by a factor of 4 as compared to IEEE 802.11ac. This capacity improvement will result through splitting up MIMO communication streams and assigning them to different users for throughput optimization.

Bluetooth On Steroids?

Another example of the race for more bandwidth is the 60 GHz family of IEEE 802.11 standards (originally under WiGig, but now back in the Wi-Fi Alliance). The first one (IEEE 802.11ad) has been available for several years but has not yet been widely adopted – and the next generation is already in the works, as shown here:

Unfortunately, there is a problem with 60 GHz – it cannot penetrate walls, and therefore it “stays” in the room.

But wait, is this really a problem? If it stays in the room, that means it does not interfere with the usage of the same channel/frequency in the other rooms, much less the neighbors. Sounds kind of ideal, doesn’t it? One may really wonder: if 60 GHz 8011.ad has existed for years, why hasn’t the market jumped on it yet?

Something Is Wrong

To understand this, let’s compare it to our road system. We have freeways connecting cities, big through-roads connecting neighborhoods, and the small streets in the neighborhoods. There is a hierarchy. And this hierarchy makes sense. You don’t have freeways in neighborhoods or small streets connecting large cities. But for Internet in our homes, the situation is different.

The Internet, or the cloud, has very high-speed interconnects (100 Gb/s or more), comparable with large freeways. But the exit lane, the pipe to our home called the “local loop” (or the “small cell” in wireless lingo), is usually 100 Mb/s at best, although 1 Gb/s fiber and 10 Gb/s DOCSIS® 3.1 are starting to emerge. Then we have the option of a distributed Wi-Fi network in our house or building, for instance 802.11ac at 1 Gb/s or even a wired 10 Gb/s Ethernet cable. And finally, with the connection with the end node (the TV, game station, tablet, smart phone), we’re again at something like 1 Gb/s, although this could even be 7 Gb/s if we use IEEE 802.11d (WiGig).

Something is wrong with this. Where’s the hierarchy? The high speed in the home is not served by the access to the home. We have freeways inside the house, but only a small street provides access to the house. And even inside the house, there is no real hierarchy. Take a look at this visual representation:

Out-of-balance (100 Mb/s – 1 Gb/s – 7 Gb/s)

WiGig Doesn’t Help In This Scenario

It’s no surprise, then, that WiGig (IEEE 802.11ad) hasn’t really taken off yet. Why build a higher multi Gb/s highway in your room, if it connects via a 1 Gb/s pipe to a 100 Mb/s local loop, single lane road? It’s also no

surprise that in this context, the expectations for the tens of Gb/s (IEEE 802.11ay) should not be too high. Higher data rates to the end nodes are great, but if the infrastructure does not support it, then what’s the point?

So, the fact that the step from IEEE 802.11ac to IEEE 802.11ax is a very moderate step in terms of data rate, and a step more focused on higher capacity in the home (multiple users at the same time) makes a lot of sense. But the real hurdle is getting more data to (and from) the home.

Streaming And Bursting Affect Data Rates

To complicate matters further, there are effects to consider from streaming and bursting. There is another factor also, that makes this all even more convoluted. There is a difference between streaming and bursting. To stream a movie, you typically need a lot of continuing bandwidth for quite some time, say a continuous 20 Mb/s for high quality. That sounds quite doable with a 100 Mb/s pipe to your home. However, this 100 Mb/s has a somewhat statistical character. If everyone on the street is watching a movie, then the 100 Mb/s to your house quickly drops to significantly lower rates. Streaming a movie on a Saturday evening can be a challenging experience, as you are not the only one on the street (or in your small cell). It is no different than everyone in the house taking a shower at the same time, causing the pressure of the water system to drop.

Burst is another statistical effect. You can compare it to someone opening all the taps in the home to get as much water flowing as possible. If someone tries to download a movie as fast as possible (to watch it later, for example), it causes a real burst of data consumption as the system tries to get as close as possible to the 100 Mb/s to one house, instantaneously. For a short time, this should be no problem. But of course, it is not sustainable, as the rest of the neighborhood would degrade quickly. From a statistical perspective, the chance that everyone on the street would try to download a movie at the same time is probably not that high, but the fact that bursts have an effect on the available bandwidth is clear.

Part 2 - What Needs To Happen? Coming soon.

Cees Links was the founder and CEO of GreenPeak Technologies, which is now part of Qorvo. Under his responsibility, the first wireless LANs were developed, ultimately becoming household technology integrated into PCs and notebooks. For more information, please visit www.qorvo.com.

 

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