The evolution of Wi-Fi is accelerating: we have just seen an uptake of Wi-Fi 6 and Wi-Fi 6E access points (AP) and client devices, and the Wi-Fi 7 standards are already on the verge of being released by the IEEE. Wi-Fi 7 is projected to support 36 Gbps per access point, about 3.75 times as fast as Wi-Fi 6, while ensuring backward compatibility and coexistence with legacy devices in the 2.4, 5, and 6 GHz unlicensed bands.

Let’s look at the features we can find in Wi-Fi 7. But first… some Wi-Fi basics.

The starting point of Wi-Fi is a frequency. Up until Wi-Fi 6, there were two groups (or “bands”) of frequencies that could be used for Wi-Fi: one around 2.4 GHz, and another around 5 GHz. In practice, only a portion of frequencies in each band are used: in the 2.4 GHz band, this equates to about 80 MHz, compared to about 600 MHz on the 5 GHz band. These groups of frequencies are called the spectrum. The actual size of the spectrum depends on the regulators in different countries.

The next step is to “translate” a frequency into computer speed, expressed in bits per second. To do that, a complicated technique is used called quadrature amplitude modulation, or QAM. Wi-Fi 5 used 256QAM, meaning that 256 signals could be derived from the frequencies. Wi-Fi 6 supports 1024QAM and, as a result, can carry more bits, and hence delivers a higher throughput.

Then, we need to choose a Wi-Fi channel in one of the bands. This refers to a small group of frequencies, known as the “channel width”. In the 2.4 GHz band, typically, a channel width of 20 MHz is used, while on the 5 GHz band, 40 or 80 MHz are used. The wider the channel width, the higher the throughput.
Figure 1 shows the channels, depending on the possible channel widths. Please note that the spectrum of the three bands is not drawn to scale.

Figure 1: Wi-Fi bands, spectrum, channels and channel width

Wi-Fi transmits data from one device to another using specific Wi-Fi channels. To further boost the throughput, we can use a technique where we transmit not only a single stream of data across that channel but use several streams of data in parallel. We refer to this as “spatial streams”. In the specification of Wi-Fi devices, you may read about a 2x2 MIMO. MIMO, which stands for multiple in, multiple out, and is a synonym for spatial streams. A 2x2 MIMO means that two spatial streams are transmitted, and two spatial streams are received. This way, you can double the throughput, or quadruple it if you use a 4x4 MIMO. The only catch is that both the Wi-Fi access point and the client device (like your smartphone) need to support those spatial streams.

Figure 2: Using multiple spatial streams in parallel

With those principles in mind, now let’s compare the different generations of Wi-Fi.
Table 1 shows that Wi-Fi 6 has a data rate (considering the maximum number of spatial streams) of 9.6 Gbps, which is 39% higher than the data rate of Wi-Fi 5. This is primarily due to the increase in QAM from 256QAM (Wi-Fi 5) to 1024QAM (Wi-Fi 6). Wi-Fi 6E supports the same underlying technologies as Wi-Fi 6. The only difference is the addition of the 6GHz band for Wi-Fi 6E.

So, here comes the quantum leap of Wi-Fi 7.

•    The channel width doubles from 160 MHz to 320 MHz, doubling the data rate.
•    The QAM is improved from 1024QAM to 4096QAM, which adds another 20% to the data rate.

Table 1: Comparison of Wi-Fi generations

Wi-Fi 7 however also introduces several truly disruptive techniques that take things further.
Probably the most important is multi-link operations (MLO). MLO allows spectrum to be concatenated from various bands. There are a number of very interesting use cases:

• Use it for multi-band link aggregation to reach a higher throughput. Combining a 4x4 MIMO with 40 MHz channel bandwidth at 2.4 GHz with an 8x8 MIMO with 160 MHz channel bandwidth at 5 GHz and an 8x8 MIMO with 320 MHz at 6 GHz, yields a total of 36 Gbps!
• Select the best link (using the 2.4 GHz, 5 GHz, or 6 GHz band) for lowest latency. 
• Reach a higher efficiency, which is especially beneficial if one link has a large amount of traffic or interference. 
• Load balance traffic across bands.
• Enable simultaneous downlink and uplink transmission.

Another great technique is called “puncturing the spectrum”. This involves segmenting the bandwidth into smaller pieces, called resource units (RU). In case of interference, the affected RU can be omitted, while keeping the other RUs. So, while the resulting bandwidth is smaller than the total bandwidth, a connection can still be maintained on it thanks to the puncturing. Without puncturing, the whole bandwidth would be lost. In addition, this increases channel availability and provides a better user experience in terms of throughput and latency.

And while end-users are anticipating the first Wi-Fi 7 APs and client devices to appear on the market, the IEEE is already working on the candidate features of Wi-Fi 8!
Stay tuned…