More Pressure on WiFi

As if we really needed more pressure put onto our public WiFi spectrum, both Verizon and AT&T are now launching Licensed Assisted Access (LAA) broadband for smartphones. This is the technology that allows cellular carriers to mix LTE spectrum with the unlicensed 5 GHz spectrum for providing cellular broadband. The LAA technology allows for the creation of ‘fatter’ data pipes by combining multiple frequencies, and the wider the data pipe the more data that makes it to the end-user customer.

When carriers combine frequencies using LAA they can theoretically create a data pipe as large as a gigabit while only using 20 MHz of licensed frequency. The extra bandwidth for this application comes mostly from the unlicensed 5 GHz band and is similar to the fastest speeds that we can experience at home using this same frequency with 802.11AC. However, such high-speed bandwidth is only useful for a short distance of perhaps 150 feet and the most practical use of LAA is to boost cellphone data signals for customers closest to a cell tower. That’s going to make LAA technology most beneficial in dense customer environments like busy downtown areas, stadiums, etc. LAA isn’t going to provide much benefit to rural cellphone towers or those along interstate highways.

Verizon recently did a demonstration of the LAA technology that achieved a data speed of 953 Mbps. They did this using three 5 GHz channels combined with one 20 megahertz channel of AWS spectrum. Verizon used a 4X4 MIMO (multiple input / multiple output) antenna array and 256 QAM modulation to achieve this speed. The industry has coined the new term of four-carrier aggregation for the technology since it combines 4 separate bands of bandwidth into one data pipe. A customer would need a specialized MIMO antenna to receive the signal and also would need to be close to the transmitter to receive this kind of speed.

Verizon is starting to update selected cell sites with the technology this month. AT&T has announced that they are going to start introducing LAA technology along with 4-way carrier aggregation by the end of this year. It’s important to note that there is a big difference between the Verizon test with 953 Mbps speeds and what customers will really achieve in the real world. There are numerous factors that will limit the benefits of the technology. First, there aren’t yet any handsets with the right antenna arrays and it’s going to take a while to introduce them. These antennas look like they will be big power eaters, meaning that handsets that try to use this bandwidth all of the time will have short battery lives. But there are more practical limitations. First is the distance limitation and many customers will be out of range of the strongest LAA signals. A cellular company is also not going to try to make this full data connection using all 4 channels to one customer for several reasons, the primary one being the availability of the 5 GHz frequency.

And that’s where the real rub comes in with this technology. The FCC approved the use of this new technology last year. They essentially gave the carriers access to the WiFi spectrum for free. The whole point of licensed spectrum is to provide data pipes for all of the many uses not made by licensed wireless carriers. WiFi is clearly the most successful achievement of the FCC over the last few decades and providing big data pipes for public use has spawned gigantic industries and it’s hard to find a house these days without a WiFi router.

The cellular carriers have paid billions of dollars for spectrum that only they can use. The rest of the public uses a few bands of ‘free’ spectrum, and uses it very effectively. To allow the cellular carriers to dip into the WiFi spectrum runs the risk of killing that spectrum for all of the other uses. The FCC supposedly is requiring that the cellular carriers not grab the 5 GHz spectrum when it’s already busy in use. But to anybody that understands how WiFi works that seems like an inadequate protection, because any of the use of this spectrum causes interference by definition.

In practical use if a user can see three or more WiFi networks they experience interference, meaning that more than one network is trying to use the same channel at the same time. It is the nature of this interference that causes the most problems with WiFi performance. When two signals are both trying to use the same channel, the WiFi standard causes all competing devices to go quiet for a short period of time, and then both restart and try to grab an open channel. If the two signals continue to interfere with each other, the delay time between restarts increases exponentially in a phenomenon called backoff. As there are more and more collisions between competing networks, the backoff increases and the performance of all devices trying to use the spectrum decays. In a network experiencing backoff the data is transmitted in short bursts between the times that the connection starts and stops from the interference.

And this means that when the cellular companies use the 5 GHz spectrum they will be interfering with the other users of that frequency. That’s what WiFi was designed to do and so the interference is unavoidable. This means other WiFi users in the immediate area around an LAA transmitter will experience more interference and it also means a degraded WiFi signal for the cellular users of the technology – and they reason they won’t get speeds even remotely close to Verizon’s demo speeds. But the spectrum is free for the cellular companies and they are going to use it, to the detriment of all of the other uses of the 5 GHz spectrum. With this decision the FCC might well have nullified the tremendous benefits that we’ve seen from the 5 GHz WiFi band.

Why is my WiFi Slow?

Wi-FiOne of the universal complaints in the broadband world is that WiFi networks operate poorly. So today I thought I’d talk a bit about how WiFi functions. I think it’s probably different than what most people expect.

Most people know that there are two frequencies used for WiFi today – 2.4 GHz and 5 GHz. The 2.4 GHz band covers 80 megahertz of total bandwidth and is divided into 11 channels in the US. That may sound like a lot, but one 802.11 connection requires five consecutive channels. In practical terms this means that almost all WiFi gear in the US is preset to only offer channels 1, 6, and 11 and that means that only three non-overlapping transmissions can occur at the same time. The WiFi in Japan covers a wider spectrum footprint, up to channel 14, meaning they can use four non-overlapping signals simultaneously.

In practical use if you can see three or more WiFi networks you are experiencing interference, meaning that more than one network is trying to use the same channel at the same time. It is the nature of this interference that causes the most problems with WiFi performance. When two signals are both trying to use the same channel, the WiFi standard causes all competing devices to go quiet for a short period of time, and then both restart and try to grab an open channel. If the two signals continue to interfere with each other, the delay time between restarts increases exponentially in a phenomenon called backoff. As there are more and more collisions between competing networks, the backoff increases and the performance of all devices trying to use the spectrum decays. Your data is transmitted in short bursts each time you make a connection and before the restart cycle repeats.

If you’ve ever been in a hotel where you can see ten or more other WiFi signals, the reason for slow speeds is that there are huge conflicts between competing devices. People generally assume that the hotel has a poor Internet connection, but they could have a fast connection and the slo speeds are due to so many devices trying to connect simultaneously. Each WiFi device is rapidly turning on and off repeatedly trying to get open access to a channel. Your device will grab a channel for a short time and then get kicked off due to interference. Congestion has become so bad on the 2.4 GHz band that AT&T and Comcast no longer use 2.4 GHz for video or voice. Almost all smartphone makers no longer recommend using their smartphones at 2.4 GHz.

WiFi has improved dramatically with the introduction of the 5 GHz spectrum. In North America this spectrum swath has 24 non-overlapping channels. However, more than half of these channels are reserved for weather and military radar. However, this still provides a lot more potential paths to add to the three paths provided by the 2.4 GHz spectrum. Unfortunately the 5 GHz band shares the same WiFi characteristics as the 2.4 GHz spectrum and has the identical interference issues. But with more open channels there is still an increased chance of finding a free channel to use.

And interference between devices is not the only culprit of poor WiFi speeds. The network configuration can also contribute to poor performance. Some of the biggest sources of interference are range extenders or mesh networks that are used to try to get better signals. Range extenders listen to all WiFi transmissions and then retransmit them at a higher power level, and usually using a different channel. This creates even more WiFi signals in the intermediate environment competing for an open channel. When you can see your neighbor’s WiFi network, if they are using range extenders they might be always trying to use most of the available WiFi channels.

In a lot of the US we now also see a lot of public hotspots. For example, Comcast is in my neighborhood and I can walk and maintain a WiFi signal is most places from WiFi public signals that are transmitted from every Comcast home WiFi router. These public signals are always on, meaning that the WiFi router is using at least one channel at all times.

Probably the biggest new culprit for poor WiFi performance comes from our quest for greater speeds. The 802.11ac standard operates by merging together a lot of WiFi channels, and divides the whole WiFi spectrum into just two 160 MHz-wide channels. This means that only two devices using this 802.11ac can use up all of your home WiFi bandwidth. This standard was intended to be used to operate in short high-bandwidth bursts, but as people use this for gaming or watching 4K video the channels stay occupied all of the time.

Unfortunately the demands for WiFi are only increasing. The cellular carriers are still pestering the FCC to allow LTE-U, which would using WiFi to complete cellular calls. There are currently tests underway of the technology. We can also expect an increasing demand for WiFi from IoT devices. While most WiFi devices won’t use spectrum continuously, they still place demands on the channels and cause interference. There are also increasing use of devices that are always on, such as video surveillance cameras or smart home controllers like the Amazon Echo. A lot of experts look out five or ten years and expect WiFi to be unusable in a lot of places.

The Death of 2.4 GHz WiFi?

Wi-FiIt’s been apparent for a few years that the 2.4 GHz band of WiFi is getting more crowded. The very thing that has made the spectrum so useful – the fact that it allows multiple users to share the spectrum at the same time – is now starting to make the spectrum unusable in a lot of situations.

Earlier this year Apple and Cisco issued a joint paper on best network practices for enterprises and said that “the use of the 2.4 GHz band is not considered suitable for use for any business and/or mission critical enterprise applications.” They recommend that businesses avoid the spectrum and instead use the 5 GHz spectrum band.

There are a number of problems with the spectrum. In 2014 the Wi-Fi Alliance said there were over 10 billion WiFi-enabled devices in the world with 2.3 billion new devices shipping each year. And big plans to use WiFi to connect IoT devices means that the number of new devices is going to continue to grow rapidly.

And while most of the devices sold today can work with both the 2.4 GHz and the 5 GHz spectrum, a huge percentage of devices are set to default to several channels of the 2.4 GHz spectrum. This is done so that the devices will work with older WiFi routers, but it ends up creating a huge pile of demand in only part of the spectrum. Many devices can be reset to other channels or to 5 GHz, but the average user doesn’t know how to make the change.

There is no doubt that the spectrum can get full. I was in St. Petersburg, Florida this past weekend and at one point I saw over twenty WiFi networks, all contending for the spectrum. The standard allows that each user on each of these networks will get a little slice of available bandwidth, which leads to the degradation of everyone using it in a local neighborhood. And in addition to those many networks I am sure there were many other devices trying to use the spectrum. The WiFi spectrum band is also filled with uses by Bluetooth devices, signals from video cameras and is one of the primary bands of interference emitted by microwave ovens.

We are an increasingly wireless society. It was only a decade or so ago where people were still wiring new homes with Category 5 cable so that the whole house could get broadband. But we’ve basically dropped the wires in favor of connecting everything through a few channels of WiFi. For those that in crowded areas like apartments, dorms, or within businesses, the sheer number of WiFi devices within a small area can be overwhelming.

I’m not sure there is any really good long-term solution. Right now there is a lot less contention in the 5 GHz band, but one can imagine that in less than a decade that it will also be just as full as the 2.5 GHz spectrum today. We just started using the 5 GHz spectrum in our home network and saw a noticeable improvement. But soon everybody will be using it as much as the 2.4 GHz spectrum. Certainly the FCC can put bandaids on WiFi by opening up new swaths of spectrum for public use. But each new band of spectrum used is going to quickly get filled.

The FCC is very aware of the issues with 2.4 GHz spectrum and several of the Commissioners are pushing for the use of 5.9 GHz spectrum as a new option for public spectrum. But this spectrum which has been called dedicated short-range communications service (DSRC) was set aside in 1999 for use by smart vehicles to communicate with each other to avoid collisions. Until recently the spectrum has barely been used, but with the rapid growth of driverless cars we are finally going to see a big demand for the spectrum – and one that we don’t want to muck up with other devices. I, for one, do not want my self-driving car to have to be competing for spectrum with smartphones and IoT sensors in order to make sure I don’t hit another car.

The FCC has a big challenge in front of them now because as busy as WiFi is today it could be vastly more in demand decades from now. At some point we may have to face the fact that there is just not enough spectrum that can be used openly by everybody – but when that happens we could stop seeing the amazing growth of technologies and developments that have been enabled by free public spectrum.

LTE-U

Cell-TowerRecently, the NCTA asked the FCC to make sure that wireless carriers don’t interfere with WiFi spectrum. I wrote a blog a few weeks ago talking about all of the demands on WiFi, and the threat that the NCTA is warning about is another use of the already busy WiFi spectrum.

Cellular carriers are using LTE technology to deliver 4G data. Cellular carriers today deliver 4G data and voice using spectrum for which they have paid billions (at least in the US and Europe). But in urban areas the LTE spectrum is already stressed and the demand for the existing spectrum is growing far faster than the carriers can find new spectrum to offload the extra demand.

The cellular carriers have had their eye on the 5 GHz unlicensed band of spectrum that is used for WiFi. This is a big swatch of spectrum that in some markets is larger than the band that some carriers have for LTE. Recently, various carriers have been experimenting with using this public spectrum to deliver LTE. Huawei and NTT demonstrated this capability last August; Qualcomm showed this capability at the CES show earlier this year. It’s rumored that T-Mobile plans to run a trial of this technology this year.

This new technology is being called LTE-U (for Unlicensed). NCTA filed at the FCC on behalf of their cable company members who use this WiFi spectrum to deliver WiFi for various uses such as distributing data wirelessly around a home or to bring data to settop boxes. They are worried that if the cellular companies start using the spectrum that they will swamp it and make WiFi useless for everybody else, particularly in urban areas where WiFi is under the most pressure.

That certainly is a valid concern. As my recent blog noted, the list of companies and technologies that are planning on using WiFi spectrum is large and growing. And there is already notable stress on WiFi around crowded places like large hotels, convention centers, and stadiums. The fear is that if cellular carriers start using the spectrum this same crowding will spread to more places, making the spectrum useless to everyone.

The cellular carriers argue that the swath of WiFi is large enough to allow them to use it without hurting other users. They argue that nobody can use all of the 400 MHz of spectrum in that band all at once. While that is true, it doesn’t take a huge pile of LTE-U customers at one time to locally overdraw the WiFi spectrum in the same manner that they are overloading the cellular spectrum today.

Engineers tell me that LTE uses the spectrum more efficiently today than does most WiFi technologies. This is due to the fact that the LTE specifications very neatly limit the bandwidth that any one customer can draw while most WiFi applications will let a user grab all of the bandwidth if it’s available. This means you can fit a lot more LTE customers into the spectrum that might be assigned to one WiFi customer.

There is a characteristic of WiFi that makes it incompatible with the way that LTE works. WiFi has been designed to share spectrum. When one customer is using WiFi they can grab a huge swath of spectrum. But when another customer demands bandwidth the system dynamically decreases the first connected customer to make room for the second one. This is very different than how LTE works. LTE works more like a telephone network and if there is enough bandwidth available to handle a customer it will assign a band to the customer or else deliver a ‘busy signal’ (no bars) if there us not enough bandwidth. The problem with these two different operating systems is that LTE would continually grab spectrum until it’s all used and the WiFi users are shut out, much like what you might get in a busy hotel in the evening.

The LTE providers say they have handled this by introducing a new protocol called LAA (Licensed Assisted Access) which introduces the idea of coexistence into the LTE network. If it works properly, LAA ought to be able to coexist with WiFi in the same manner that multiple WiFi customers coexist. Without this change in protocol LTE would quickly gobble all of the free WiFi spectrum.

But this still doesn’t answer the concern that even with LAA there could be a lot of people trying to grab bandwidth in environments where the WiFi is already stressed. Such a network never shuts anybody out like an LTE system will, but rather will just keep subdividing the bandwidth forever until the amount each customer gets is too small to use.

It will be interesting to see what the FCC says about this. This was discussed years ago and the FCC never intended to let licensed cellular holders snatch the public WiFi spectrum. I will also be curious to see if wireless carriers try to charge customers for data usage when that data is being delivered over a free, unlicensed swath of spectrum. And how will customers even know that is where they are getting their data?

I hope the FCC doesn’t let the wireless carriers run rampant with this, because I think it’s inevitable that this is going to cause huge problems. There are already places today where WiFi is overloaded, and this new kind of data traffic could swamp the spectrum in a lot more places. The wireless carriers can make promises all day about how this won’t cause problems, but it doesn’t take a huge number of LTE-U users at a cell site to start causing problems.

Changes to Unlicensed Spectrum

Wi-FiEarlier this year in Docket ET No. 13-49 the FCC made a number of changes the unlicensed 5 GHz band of unlicensed spectrum. The docket was intended to unify the rules for using the 5 GHz spectrum. The FCC had made this spectrum available over time in several different chunks and had set different rules for the use of each portion. The FCC was also concerned about interference with some parts of the spectrum with doppler radar and with several government uses of spectrum. Spectrum rules are complex and I don’t want to spend the blog describing the changes in detail. But in the end, the FCC made some changes that wireless ISPS (WISPs) claim are going to kill the spectrum for rural use.

Comments filed by WISPA, the national association for WISPs claim that the changes that the FCC is making to the 5725 – 5850 MHz band is going to devastate rural data delivery from WISPs. The FCC is mandating that new equipment going forward use lower power and also use better filters to reduce out-of-band emissions. And WISPA is correct about what that means. If you understand the physics of wireless spectrum, each of those changes is going to reduce both the distance and the bandwidth that can be achieved with this slice of spectrum. I didn’t get out my calculator and spend an hour doing the math, but WISPA’s claim that this is going to reduce the effective distance for the 5 GHz band to about 3 miles seems like a reasonable estimate, which is also supported by several manufacturers of the equipment.

Some background might be of use in this discussion. WISPs can use three different bands of spectrum for delivering wireless data – 900 MHz, 2.4 GHz and 5 GHz. The two lower bands generally get congested fairly easy because there are a lot of other commercial applications using them. Plus, those two spectrums can’t go very far and still deliver significant bandwidth. And so to the extent they use those spectrums, WISPs tend to use them for customers residing closer to their towers. They save the 5 GHz spectrum for customers who are farther away and they use it for backhaul between towers. The piece of spectrum in question can be used to deliver a few Mbps to a customer up to ten miles from a transmitter. If you are a rural customer, getting 2 – 4 Mbps from a WISP still beats the heck out of dial-up.

Customers closer to a WISP transmitter can get decent bandwidth. About the fastest speed I have ever witnessed from a WISP was 30 Mbps, but it’s much more typical for customers within a reasonable distance from a tower to get something like 10 Mbps. That is a decent bandwidth product in today’s rural environment, although one has to wonder what that is going to feel like a decade from now.

Readers of this blog probably know that I spent ten years living in the Virgin Islands and my data connection there came from a WISP. On thing I saw there is the short life span of the wireless CPE at the home. In the ten years I was there I had three different receivers installed (one at the end) which means that my CPE lasted around 5 years. And the Virgin Islands is not a harsh environment since it’s around 85 degrees every day, unlike a lot of the US which has both freezing winters and hot summers. So the average WISP will need to phase in the new CPE to all customers over the next five to seven years as the old customer CPE dies. And they will need to use the new equipment for new customers.

That will be devastating to a WISP business plan. The manufacturers say that the new receivers may cost as much as $300 more to comply with the filtering requirements. I take that estimate with a grain of salt, but no doubt the equipment is going to cost more. But the real issue is the reduced distance and reduced bandwidth. Many, but not all, WISPs operate on very tight margins. They don’t have a lot of cash reserves and they rely on cash flow from customers to eke out enough extra cash to keep growing. They basically grow their businesses over time by rolling profits back into the business.

If these changes mean that WISPs can’t serve customers more than 3 miles from an existing antenna, there is a good chance that a lot of them are going to fail. They will be faced with either building a lot of new antennas to create smaller 3-mile circles or else they will have to abandon customers more than three miles away.

Obviously spectrum is in the purview of the FCC and some of the reasons why they are changing this spectrum are surely valid. But in this case they created an entire industry that relied upon the higher power level of the gear to justify a business plan and now they want to take that away. This is not going to be a good change for rural customers since over time many of them are going to lose their only option for broadband. While it is important to be sensitive to interference issues, one has to wonder how much interference there is out in the farm areas where these networks have been deployed. This impacts of this change that WISPA is warning about will be a step backward for rural America and rural bandwidth.