While there are still interference issues to be resolved, new specifications for Wi-Fi in the 6-GHz band will bring instantly better wireless performance.
Eve Danel | LitePoint
Wi-Fi technology turns 20 this year, and it has proven to be successful beyond the wildest expectations. The recent announcement by the FCC to consider allowing 1,200 MHz of spectrum in the 6 GHz band for unlicensed use, as well as similar work in the E.U., promises to free up enough spectrum to move Wi-Fi forward into a new era of high performance.
In late 2018, the FCC released a notice of proposed rulemaking to promote new opportunities for unlicensed use in portions of the 1,200 MHz of spectrum in the 5.925-7.125 (6 GHz) band. Wi-Fi users should rejoice, as Wi-Fi in the 6-GHz band could become a reality in 2020. To understand why this event is cause for celebration, we examine the reasons that make the 6 GHz band compelling for unlicensed use and why additional spectrum is so badly needed to sustain Wi-Fi growth.
Cisco’s annual Mobile Visual Networking Index (VNI) forecasts that by 2022, Wi-Fi will carry 51% of global IP traffic, more than any other wired or wireless access technology, while the total number of Wi-Fi hotspots (including home spots) is expected to reach 549 million by 2022.
Wi-Fi carries more internet traffic than any other wireless technology. And this took place despite an available frequency range of less than 600 MHz (70 MHz in the 2.4-GHz band, 500 MHz in the 5-GHz band). But a study commissioned by the Wi-Fi Alliance predicts an 800-MHz spectrum shortfall to handle traffic by 2020, with that shortfall growing to 1.12 GHz by 2025. The study stresses the importance of making available continuous spectrum to enable 160-MHz-wide channels (or future 320 MHz). The 6-GHz band and its 1,200 MHz of contiguous spectrum can fulfill the growth requirements, and this is why the FCC is currently considering it.
Why is more spectrum needed?
The availability of unlicensed spectrum in the 2.4-GHz and 5-GHz bands has driven Wi-Fi growth. It has lowered the barrier of entry for new-comers and enabled low-cost deployments that have made Wi-Fi a ubiquitous local network connectivity technology.
But it has also contributed to its woes, as unlicensed spectrum is being shared by a multitude of devices (including non-Wi-Fi equipment using Bluetooth, Zigbee and others) and forced the technology to make compromises as it coexists with many users. Additional unlicensed spectrum will address the two main problems that users face:
Congestion – The low number of Wi-Fi channels available today forces many users to share available bandwidth and creates congestion.
Restricted 80-MHz and 160-MHz channel availability – Today the limited amount of contiguous spectrum makes it difficult to enable 80-MHz or 160-MHz channels, yet high data throughput can only come when wide channels are available.
In Wi-Fi networks using Wi-Fi 5 (802.11ac) or older Wi-Fi versions using OFDM (orthogonal frequency-division multiplexing) access technology, all devices connected on the same channel split its capacity. When connected on a channel with a high number of devices, users will experience low data throughput, as each one of them waits their turn to transmit (or receive) data. Congestion is caused by devices connected on the same access point and sharing the same channel.
Though it may be less intuitive, congestion is also caused by devices in neighboring networks, on the same channel, or on an overlapping channel. All these devices compete for access to the same RF channel spectrum. Channel congestion is particularly problematic in dense urban areas, airports, or stadiums where there are Wi-Fi signals from hundreds of access points and client devices.
The 2.4-GHz and 5-GHz frequency bands support a limited number of non-overlapping 20-MHz and 40-MHz channels. Wi-Fi 5 and Wi-Fi 6 (802.11ax) standards added support for an 80-MHz and 160-MHz channel width to allow for higher data speed. But in practice, the wider channels are rarely deployed. Only six 80-MHz and two 160-MHz channels are currently available in the 5-GHz band.
In dense environments or large enterprises, it’s hard to find an 80-MHz or 160-MHz channel free from interference caused by devices on overlapping channels. In response, network administrators often choose to disable these capabilities, thereby restricting the data speed available on their network.
When considering the case of a two-antenna (MIMO streams) client station typically used with phones, laptops, and tablets, the max achievable speed on a 40-MHz Wi-Fi 5 deployment is only 400 Mbps, while a Wi-Fi 6 deployment can only hit a maximum of 574 Mbps at the physical layer. At the TCP layer — i.e. usable data throughput — the results are in the range of 60% to 70% of the above numbers.
It is obvious that spectrum availability limits will quickly hamper Wi-Fi technology evolution. Meanwhile, broadband access speeds (DOCSIS, passive optical network, fiber to the home) keep rising at a rapid pace, and applications like video streaming, VR/AR and gaming require more and more bandwidth. Additionally, Wi-Fi is a critical enabler of 5G technology; it likely will be widely used for mobile-traffic offload and providing 5G indoor coverage via FWA (Fixed Wireless Access). In the near future, with no improvements to the spectrum availability, the Wi-Fi network may well become a bottleneck as all services are ultimately accessed via Wi-Fi.
Wi-Fi 6 and the 6-GHz band
It is important not to confuse Wi-Fi 6 and Wi-Fi in the 6-GHz band,
as these are two separate, but interconnected, topics.
Wi-Fi 6 is the Wi-Fi Alliance’s new consumer-friendly name for the IEEE 802.11ax standard. The 802.11ac standard has also been renamed Wi-Fi 5; 802.11n is now Wi-Fi 4. The purpose of this new naming scheme is to make it easier for the general public to identify device generations without remembering the complex 802.11 alphabet soup.
IEEE 802.11ax has been defined to operate in the 2.4-GHz and 5-GHz bands, and many device manufacturers are already shipping Wi-Fi 6 equipment operating in these bands. Now the stage is set for operation from 5.925-7.125 GHz. Wi-Fi 6-compliant devices operating in the 6-GHz band could become available as early as 2020.
Wi-Fi 6 is already a revolutionary standard as it introduces orthogonal frequency-division multiple access (OFDMA). OFDMA is a real disruptor in the way Wi-Fi operates because it allows multiple users to transmit simultaneously. Unlike with OFDM, the technology used for older Wi-Fi generations, OFDMA Wi-Fi channel bandwidth (20, 40, 80 or 160 MHz) is divided amongst multiple users who simultaneously transmit on smaller sub-channels called resource units (RU). 802.11ax is big step toward addressing network congestion. Its impact often gets compared to upgrading from a single-lane road (OFDM) to a multi-lane freeway (OFDMA).
But OFDMA only becomes effective with wide adoption of Wi-Fi 6 technology in client devices and access points. Indeed, each time a legacy device (11ac, 11n or older) transmits in the network, the transmission reverts back to standard OFDM mode with a single transmission occupying the entire spectrum. Only Wi-Fi 6 devices are capable of participation in an OFDMA transmission. The truth is that until most consumer devices employ Wi-Fi 6, users may not notice much performance improvement over older technologies.
On the other hand, the introduction of the 6-GHz band for Wi-Fi use provides instant gratification for all Wi-Fi 6 users. With enough spectrum to safely deploy 80-MHz or 160-MHz-wide channels and green-field deployments alleviating concerns of backward compatibility, the 6-GHz frequency band could become the VIP Lounge for Wi-Fi 6 users, where high throughput rates and congestion-free network access can be instantly achieved.
A deeper look at the 6-GHz frequency band
The 6-GHz frequency band, also called mid-band spectrum, spans 5.925 GHz to 7.125 GHz. It is divided into four bands:
UNII-5: 5925-6425 MHz (500 MHz)
UNII-6: 6425-6525 MHz (100 MHz)
UNII-7: 6525-6875 MHz (350 MHz)
UNII-8: 6875-7125 MHz (250 MHz)
The mid-band spectrum is currently for licensed users who have deployed services in these frequencies. For example, users include point-to-point microwave links and mobile TV pickups at sporting events relaying signals back to a studio. There are currently around 100,000 microwave links in the U.S. The operators of these links are common carriers (AT&T, Verizon, etc.), industrial and business entities (utilities, railroad, oil and gas) and public safety agencies (safety, emergency services, transportation).
These incumbents have concerns about coexistence and possible signal interference with unlicensed services. FCC rulings will likely include mechanisms to mitigate interference from Wi-Fi operation in the 6-GHz band, either by having devices operate indoors only at low power levels or by having AFC (Automated Frequency Coordination) mechanisms in place.
While these coexistence processes are still being finalized, Wi-Fi chip and device makers are already planning to offer products soon after the regulatory bodies grant their final approval. The IEEE incorporated definitions for the new 6 GHz frequency band channels in the latest draft of the 802.11ax standard.
In the U.S. a plethora of new channels could soon be added to Wi-Fi devices, immediately alleviating congestion and enabling the highest data speed in Wi-Fi 6 devices operating in the 6-GHz band.
59 x 20 MHz channels
29 x 40 MHz channels
14 x 80 MHz channels
7 x 160 MHz channels
All in all, Wi-Fi in the 6-GHz band means instant performance increases for Wi-Fi 6 users. While there are still interference issues to be resolved, opening up 6-GHz frequency bands for Wi-Fi is the right move to ensure this widely used wireless technology can deliver the performance needed for future applications and networks.