In this series, we’ll be taking an in-depth look at the evolution of the IEEE 802.11 standard and its latest iteration: Wi-Fi 6 (802.11ax). We’ll start with a high-level overview of various Wi-Fi 6 building blocks and then take a closer look at each. Specific topics include OFDMA, OFDM vs. OFDMA, OFDMA vs MU-MIMO, Long OFDM Signal, 1024-QAM, BSS Coloring and Target Wake Time (TWT). We’ll also explore IEEE and WFA commercial activities, along with multiple W-Fi 6 use cases.
2.4GHz & 5 GHz and Wi-Fi 6
Before getting into the nuts and bolts of Wi-Fi 6, let’s first take a brief trip down memory lane. 802.11 has steadily evolved over the past 20 years, with industry engineers working on the ever-changing standard since the early 1990s. The first iteration was published in 1997 and 20 years later, Wi-Fi 6 (802.11ax) is on the cusp of being ratified, while Wi-Fi 6 products are already being manufactured, sold and shipped. The first iteration of 802.11 supported only 2.4 GHz, although support for the 5 GHz band was subsequently added to Wi-Fi 4 (802.11n). Perhaps not surprisingly, Wi-Fi 5 (802.11ac) only supported the 5 GHz band. The thinking behind this decision was to encourage people to move towards 5 GHz because it was a much cleaner frequency.
However, Wi-Fi 6 (802.11ax) supports both 2.4 GHz and 5 GHz. This is primarily due to the proliferation of 2.4 GHz IoT devices that are hitting the market today. In addition, the FCC is slated to open the 6 GHz unlicensed spectrum for Wi-Fi 6 (802.11ax). Regarding channelization, the IEEE 802.11 standard began with 20 MHz and subsequently expanded to 40 MHz for Wi-Fi 4 (802.11n) and up to 160 MHz for Wi-Fi 5 (802.11ac) as well as (802.11ax). Today, we don’t see very many 160 MHz applications, although with 6 GHz, this might become a reality.
It should also be noted that Wi-fi 6 (802.11ax) supports 20 MHz-only clients, which is especially important for the IoT. Indeed, 11ax supports 20MHz-only clients because the Wi-Fi 6 (802.11ax) draft amendment was written with IoT devices in mind as they are low cost, consume little power and pack very small batteries. Using management frames, client stations will be able to inform a Wi-Fi 6 (802.11ax) AP that they are operating as 20 MHz-only clients. A 20 MHz-only device can transmit/receive in either the 2.4 or the 5 GHz band. Moreover, the Wi-Fi 6 standard implements a protocol in which the 20 MHz-only devices communicate only on the primary 20 MHz channels.
Essentially, this means a 40 MHz channel could potentially be extended to 80 and 160 MHz. All 20 MHz packet exchanges of these clients are in the primary 20 MHz. One can have a packet exchange of normal clients in the upper secondary – as well as additional mixing and matching. More specifically, ‘normal’ clients would be named as the primary, along with 20 MHz-only clients. It is important to understand that 20 MHz-only devices are only required to operate in the primary 20 MHz channels.
Peak PHY Rates & Spectrum Utilization
The peak 802.11 PHY rate supported 2 Mbps per second, which has increased to 10 Gbps per second for Wi-Fi 6 (802.11ax). Although there is a lot of industry chatter about high throughput, what really matters is how efficiently the wireless spectrum is utilized. Yes, high throughput sells products because it’s easy for everyone to understand, but again, what really matters is how well the standard exploits available spectrum. One way of quantifying this is with link spectral efficiency. For example, the first 802.11 Wi-Fi standard pushed 0.1 bps/Hz. In sharp contrast, Wi-Fi 6 pushes a staggering 62.5 bps/Hz.
It should be noted that overall spectrum performance is also indicated by the name of the standard. Wi-Fi 4 (802.11n) was known as HT or a high throughput, followed by Wi-Fi 5 (802.11ac) which was referred to as VHT, or very high throughput. Continuing this naming pattern, Wi-Fi 6 (802.11ax) is designated HE for high efficiency. As we’ll further discuss in this series, spectrum efficiency is one of the most important features of the new Wi-Fi 6 (802.11ax) standard.