24 Jul 2017

Wi-Fi Spectrum Needs and the role of Wi-Fi assurance

Narayan Menon, CTO & Founder of XCellAir, looks at the growing use of Wi-Fi and how this will impact the requirements for additional spectrum and the forthcoming standards.

In today’s increasingly connected world, Wi-Fi is no longer a nice to have – for many consumers, it is an absolute necessity. Today’s users consume Wi-Fi every day, all day, and for tasks which five years ago did not require wireless connections. Consumer reliance on the internet has meant that there are demands for a Wi-Fi connection almost everywhere; on public transport, in shopping malls, in restaurants and even in open spaces like public parks. Wi-Fi is also now commonly deployed in the home, often as part of a broadband package from a cable MSO or an internet service provider.

And this demand for Wi-Fi is not going away. The recent Wi-Fi Spectrum Needs report from the Wi-Fi Alliance shows that not only is more spectrum required to meet consumer Wi-Fi demands, but due to the rise of connected devices, standardisation and the growing use cases for Wi-Fi, a seamless experience is also needed.

This means the demand for future Wi-Fi is about more than just extra spectrum. Being able to efficiently manage Wi-Fi becomes just as, if not, more important. But what impact can Wi-Fi management have on these areas? Can better Wi-Fi management fulfil the growing consumer demand for Wi-Fi, and help alleviate the pressures on Wi-Fi spectrum availability?

More spectrum is required

Today, there is simply not enough spectrum to cope with the ever-growing demands of Wi-Fi services. With more devices and more services utilising Wi-Fi, the spectrum currently available is not enough to meet future consumer demands. According to the Wi-Fi Alliance’s ‘Wi-Fi Spectrum Needs’ report, by 2025, between 500MHz and 1GHz more spectrum is required to accommodate the “Busy Hour” – the hour in which a Wi-Fi network sees the most traffic. But in some cases, much more is needed – between 1.3 and 1.8GHz more spectrum than what is available today may be needed.

The recent FCC spectrum auction puts this additional spectrum required into perspective – not only was it a huge undertaking for ‘just’ 70MHz of spectrum, but it also cost telcos and broadcasters $19.77 billion. So, while the additional spectrum required represents huge value and opportunity to regulators, there is also the challenge of opening up that much spectrum, especially in support of unlicensed technologies like Wi-Fi.

The report also outlines that to meet the demands for future Wi-Fi, spectrum also needs to be assigned with sufficient contiguity, so that wide channels of 160MHz, or perhaps even wider, can be constructed with ease. These wider channels would have the potential for higher data rates, and can meet consumer demands for Wi-Fi more efficiently. If, for example, offering spectrum in multiples of 160MHz became best practice, then it would offer the best speed potential for consumer devices. If not designed contiguously, then this would not only restrict the growth of Wi-Fi, it may also impact the economic benefits associated with spectrum regulation. But given spectrum availability today, even with sufficient contiguity, putting together 160MHz channels will be difficult. In fact, in the 5GHz band, only one, or maybe two 160MHz channels are possible, which means forming these channels, and making them best practice, simply requires more spectrum.

But while demand for Wi-Fi is increasing, simply throwing spectrum at the problem isn’t the solution. Tools that help manage Wi-Fi utilisation are also crucial. Findings from our own research, modelling common urban scenarios in which public Wi-Fi is in everyday use, demonstrates the impact poor Wi-Fi management has on valuable network capacity. According to the findings, 92% of access points do not adjust their operating frequency, no matter how badly performance is degraded by interference. The findings also revealed that on average, two channels worth of bandwidth in the highly populated 2.4GHz band is unused at any given time, despite congestion and interference. Each channel equates to 50MBps of idle bandwidth totalling 100MBps unused. In practical terms, this is enough latent capacity to concurrently stream 25 HD videos, or more than 3000 HD voice calls.

While the Wi-Fi Spectrum Needs report outlines the impact various aspects have on spectrum availability, such as connected devices, standards, latency and speed, Wi-Fi assurance can help to alleviate some of these pressures. The rise of connected devices

The increase in internet connected devices is no doubt playing a huge role in spectrum availability. According to Ofcom’s Communication Market report, there has been an increase in the use of smartphones and tablets, and the decrease in use of desktops and laptops to connect to the internet. In fact, the use of desktops has halved, whereas the use of smartphones has doubled, making smartphones the most important way for consumers to connect to the internet. The increasing use of smartphones is good news for Wi-Fi spectrum availability, in comparison to older, slow-speed devices that can drain a channel and cause congestion. This is because given their high-speed, smartphones send current data quickly (given good coverage), leaving the channel for other devices to use. So as the world moves away from slower devices to become a predominantly smartphone and high-end laptop world, Wi-Fi resources will tend to be used more efficiently.

However, ensuring solid Wi-Fi coverage is also critical, as a lack of coverage means devices are unable to access spectrum that is currently available - let alone extra spectrum. If, for example, a channel is clear and not congested, poor coverage can prevent devices from accessing that perfectly good channel. Furthermore, devices with poor coverage transmit at slow, instantaneous bit rates, meaning they take longer to submit their data when they get their turn. This creates a counter-intuitive congestion-build effect, as devices keep coming back for more channel time.

Airtime allocation therefore becomes increasingly important. By allocating airtime across different Service Set Identifiers (SSIDs) and devices in an equitable manner, airtime management ensures that the right amount of bandwidth is allocated to the right device, at the right time. Essentially, it makes sure that slow devices, or devices with poor coverage don’t hog too much of a channel – and by limiting the airtime given to slow devices, it means healthier devices aren’t starved of channel capacity.

But when it comes to more spectrum, and wider channels of the future, smartphones will be unable to take full advantage of the spectral efficiency and performance. This is due to standards, and the MIMO (multiple input, multiple output) capabilities of not only current devices, but future devices too.

The impact of standards on spectrum

When it comes to Wi-Fi standards, 802.11ac is here today; Wave 2 of this standard will come to dominate in the next few years, and we are likely to see products with 802.11ax being shipped by 2020. With each iteration of these standards comes greater MIMO, which increases performance and is a big part of the ‘headline’ throughput numbers quoted by the standards bodies. For example, the current state-of-the-art is 8x8 MIMO to achieve the headline performance numbers of 802.11ac Wave 2.

But the benefits of increased MIMO are limited to device capabilities. Today’s smartphones are typically single antenna devices with 1x1 MIMO. With some larger phones, two antennas become realistic. Laptops and tablets form a natural second group, based mostly on size, where 2x2 MIMO will be common until 2020. Only high-end laptops (and a small subset at that) support the latest 4x4 configuration.

But smartphones and similar portable devices cannot power or house 8x8 antenna configurations. Which means you simply can’t rely on the air interface to provide spectral efficiency – you need to leverage more intelligent spectrum usage schemes. Some of this is coming in in 802.11ax, with additional scheduling capabilities, local spectrum management schemes and power control managing dense Wi-Fi systems cohesively. But broader, more coordinated management across access points, working in combination with the standards progression, will still be needed to take full advantage of the additional spectrum, and to service the expected demand.

Latency vs speed

When it comes to measuring the performance of Wi-Fi, the argument of latency vs speed comes into action. For some consumers, speed will be a defining factor, with a slow speed impacting applications like video streaming. For others, latency will be more important, where voice, virtual reality and gaming are all very latency sensitive with delays dramatically disrupting the consumer experience.

The Wi-Fi Spectrum Needs report however, looks at metrics related to capacity only. Specifically, the percentage of offered traffic that is carried, plus a measure of AP utilisation. Both areas relate to data rates and latency. A network that can carry all the traffic offered and where the AP utilisation is within normal bounds will be able to deliver the maximum data rates that a device can access according to its signal level.

But what the report doesn’t take into consideration is channel utilisation. While deploying additional APs (albeit within limits, and in a dense deployment) can help overcome high AP utilisation, high channel utilisation cannot be overcome in the same way. Channel utilisation can only be improved in two ways - by adding more spectrum, or by better radio resource management.

So, while more spectrum will be able to fulfil these needs, benchmarking utilisation and the impact of different service types also becomes key. As noted in the report, Wi-Fi is generally adequate up until certain thresholds are exceeded for different applications. After this, the user experience degrades. What Wi-Fi assurance, and specifically, automated optimization can do, is track these metrics, so that when thresholds are exceeded, the access point is switched to a clear piece of Wi-Fi spectrum to use in that location, which means knowing what the right thresholds are, choosing the best new configuration when making the change, and doing so quickly ensure the service is uninterrupted.

In addition to choosing the cleanest portion of spectrum (or channel) within a specific band, load balancing between spectrum bands also comes into play here – for example, moving devices between the 2.4 GHz and 5 GHz radio. Multiple scenarios exist where this can alleviate challenges in delivering reliable Wi-Fi and dramatically increase performance. First, many 5GHz capable devices end up latching onto and staying on 2.4GHz which is 3x slower. Simply moving these devices to 5 GHz gives a huge boost in performance. Second, the congestion itself may be because you’re simply doing a lot over Wi-Fi, so balancing the load on the AP across both bands will alleviate the strain.

While the report was based on 70% utilisation, which is more than adequate, it is worth noting that 70% utilisation in the 2.4GHz band is different from the same level in 5GHz, as there is typically more bandwidth volume left over in 5GHz, given the wider bandwidth it provides. As more spectrum is ultimately is opened for Wi-Fi usage, this challenge becomes even greater, as routers will feature at least three, if not four different radios. Today, there are already many tri-band routers on the market in anticipation of new technologies like WiGig. Effectively, using all the radios available will be critical to truly taking advantage of any new spectrum band.

Ultimately, being able to effectively manage the utilisation of spectrum becomes increasingly important as the types of services and devices that will consume Wi-Fi increase in number and diversity of need. For example, some IoT devices may not need much bandwidth, but have reliable connectivity with low latency, while others, like security cameras for example, need all three. OTT video services today, are already latency sensitive – consumers do not want to wait for the next episode of House of Cards to buffer and load, or be interrupted mid-episode. As more services that use Wi-Fi come to light, population density will increase, which will lead to much more contention – and being able to alleviate congestion and manage how a service is provided to a device based on its applications needs will become critical. Successfully managing spectrum

There is no doubt that additional Wi-Fi spectrum is needed for the future. With advancements like 5G, IoT and smart cities all having an element of Wi-Fi to them, having more spectrum available to deliver services will always be the foundation of wireless.

However, spectrum is not an infinite resource, and allocation is a largely political, unpredictable and potentially expensive process – which means there is so much more to consider than simply campaigning for more of it. Effectively assuring reliable, high performance Wi-Fi through automated management and optimisation, utilising spectrum in the right way, will make more room for new services, new devices, and new users.

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About the author

Narayan Menon is the CTO & Founder, XCellAir. He drives the Engineering team and the technology strategy at XCellAir. Part of his passion lies in ideating new technology concepts and developing them through to commercial solutions. Previously, Narayan was at InterDigital, running next-generation R&D projects in a variety of areas in the wireless field. Narayan loves to communicate and share ideas, and work collaboratively with others in the industry to move the technology ball forward.

XCellAir brings order to the potential chaos of using unlicensed spectrum when deploying a dense radio network of Wi-Fi access points and cellular small cells. Based in San Diego, CA, XCellAir provides a cloud-based Quality of Experience (QoE) solution that automates the management and optimization of these networks. XCellAir enables wireless service providers to meet the challenges and capture the opportunity presented by the insatiable thirst for data and ubiquitous connectivity.

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