If the pandemic taught us anything, it taught us the importance of high-speed connectivity in our daily lives. Restrictions on travel, schools being closed forcing remote learning, and offices transitioning to remote or hybrid work schedules caused an explosion of the use of virtual meeting applications. These applications deliver real-time voice, video, and collaboration tools that require both low latency and high bandwidth to function adequately.
While the promised 5G cellular services will provide many of these features, many cellular systems do not have the capacity for the increased data usage inherent in these applications nor do many of the carriers provide for unmetered, unlimited data usage. When coupled with the need to support multiple simultaneous high-bandwidth users, what the typical consumer needed was a low-cost, high-speed communications mechanism that had few data restrictions and was unmetered. This is the capability that Wi-Fi® provides.
The Evolution of Wi-Fi
The IEEE 802.11™ wireless local area network (WLAN) working group is responsible for the development of new WLAN standards.
In conjunction with the IEEE 802.11 working group, a non-profit industry consortium known as the Wi-Fi Alliance® is responsible for taking the 802.11 standards, certifying product compliance, and promoting those standards for use by the consumer.
Wi-Fi devices are divided in to two basic classes: access points (AP) and stations (STA). APs are the base stations that are attached to the wide-area network (a.k.a., Internet) feed and provide access to the consumer devices such as handsets (mobile phones), tablets, laptops, etc. that are the STA devices. The performance of the connections between the APs and the STAs is determined by a number of factors including modulation type, channel width, number of spatial streams, and radio frequency.
In general, Wi-Fi operates in the unlicensed Industrial, Scientific and Medical (ISM) frequencies in the 2.4, 5, and new 6 GHz range. The 2.4 GHz ISM band is filled with a number of additional services including Bluetooth®, Zigbee, WirelessHART, DECT telephones, and several other communications mechanisms that all compete for spectrum. The 5 GHz band is relatively free of contention, with some exceptions. Also, some versions of Wi-Fi operate in only one of the frequency ranges, whereas others operate in multiple frequency bands.
In an effort to aid the consumer sort out all of the different “flavors” of Wi-Fi, the Wi-Fi Alliance has developed a simpler naming convention (See Table Above).
The Wi-Fi 7 standard is still undergoing modification and is expected to be ratified in two subsequent releases towards the end of 2023 and early 2024.
Channel width, Modulation and Spatial Streams… Oh my!
One of the first limiting factors in the data transmission capacity of a single AP to STA link is the width of the radio channel. The 2.4 GHz band is available as an unlicensed frequency range. In the U.S., there are 11 Wi-Fi channels spaced 5 MHz apart starting at 2412 MHz. These channels are defined to be 20 MHz per channel meaning that only channels 1, 6, and 11 do not overlap, as shown in Figure 1. Adjacent channels can cause interference with each other, which can significantly impact the performance.
The 5 GHz band is much wider than the 2.4 GHz band but has a gap in the middle of the band and, in the U.S., must employ dynamic frequency selection and transmit power control capabilities to avoid interference with existing military and weather-radar applications. Wi-Fi 4 introduced 40 MHz channels in the 5 GHz band. Additionally, Wi-Fi 5 opened up the option for 80 MHz and even 160 MHz channels (Figure 2). Because of the 500 MHz total frequency allocation to the 5 GHz band (as compared to the 80 MHz in the 2.4 GHz band), it is possible to have up to twelve 40 MHz channels, six 80 MHz channels, or two 160 MHz channels and combinations thereof, as long as the selected channels do not overlap each other.
With the addition of the 6 GHz band (Figure 3) and its 1200 MHz of frequency, Wi-Fi 6e introduced an option for 320 MHz channels in that band! The uses of this increased channel size coupled with new modulation techniques are how Wi-Fi 6e can achieve multi-gigabit transfer rates between the STA and the AP. However, 6 GHz suffers from reduced range and susceptibility to blocking of the signal from walls, etc.
Another aspect of the newer Wi-Fi versions is increasing the number of radio carriers and symbol rate (essentially the number of bits/sec) through the introduction of quadrature amplitude modulation (QAM). With QAM, phase shift is introduced to the modulation and combined with amplitude so that each carrier can be in one of four phases representing 00, 01, 10, and 11 bit patterns that are replicated on each of the carriers (Figure 4).
Wi-Fi 4 introduced multiple-input/multiple-output (MIMO) operation, also referred to as spatial streaming. Another capability known as channel bonding was introduced in Wi-Fi 4 to combine multiple individual channels into a single, unified data stream. With channel bonding, dual 20 MHz channels could be combined into what is effectively a single 40 MHz channel even if a single, contiguous 40 MHz channel is unavailable.
Wi-Fi 5 came in “Wave 1” and “Wave 2” variants. Wave 1 boosted the number of streams to 4 × 4 (four concurrent transmit (TX) and receive (RX) sessions), upped the modulation to 256 QAM, and allowed the channel bonding to extend to 80 MHz. In Wave 2, the MIMO approach was extended to multi-user MIMO (MU-MIMO) to allow for multiple users on multiple antennas. However, MU-MIMO only worked in the download (AP to STA) direction and not bi-directionally. Wave 2 was extended to 160 MHz channels with 4 spatial streams for a combined performance of 3.4 Gbits/sec. It is important to realize that all of these enhancements come at a cost. The required signal to noise ratio (SNR) and receiver sensitivity for a 256 QAM modulated signal effectively limits the performance to an unobstructed, line of sight of 20 feet or less. Otherwise, Wi-Fi 5 drops back to 64 QAM, which makes it no better than Wi-Fi 4 other than the channel bonding increase to 160 MHz.
Wi-Fi 6 and 6e increased the modulation again, to 1024 QAM, and boosted the number of spatial streams to 8x8. Another enhancement for Wi-Fi 6/6e was the introduction of orthogonal, frequency division multiple access (OFDMA) multiplexing of the data to multiple STAs simultaneously within a single radio frame. In Wi-Fi 5, data was distributed to each STA one at a time. But with OFDMA, multiple STAs can be serviced simultaneously in a single radio frame. This is a huge win for facilities with multiple simultaneous users because the users do not have to wait for the previous data transfer to complete before the next transfer can commence. Another enhancement for Wi-Fi 6 is the addition of bi-directional MU-MIMO rather than the downlink-only MU-MIMO found in Wi-Fi 5.
Wi-Fi 6e is an extension of all the Wi-Fi 6 goodness into the 6 GHz frequency band. This new unlicensed band provides for considerable additional bandwidth. However, at the time of writing, there are few APs and even fewer STAs that have support for these new frequencies. This will no doubt increase over time. However, in the short run if you have 6e-capable devices, you likely have that entire spectrum to yourself.
Finally, in order to compensate for the SNR degradations and receiver sensitivity issues, an additional technique known as beam-forming was introduced in Wi-Fi 5 and enhanced in Wi-Fi 6. With beam-forming, multiple antennas can be combined to “steer” the signal in a specific direction while increasing the signal strength to the destination STA. This technique yields better range and SNR by allowing the modulation to stay in the higher mode QAM more of the time.
The Elephant in the Room – Wi-Fi 7
Even though Wi-Fi 6/6e has not been in wide-scale deployment for very long, we are already hearing about the next coming standard based on IEEE 802.11be, known as Wi-Fi 7. The Wi-Fi 7 standard is not expected to be ratified until 2024 and then devices will need to be certified for compatibility. So realistically we could start expecting to see certified devices sometime in mid-2024.
Wi-Fi 7 will have several enhancements over Wi-Fi 6. First, the number of spatial streams doubles again to 16 simultaneous streams. The modulation scheme also increases to 4096 QAM with backward compatibility to 1024/256/64 QAM as needed. These changes scale the throughput of Wi-Fi 7 from Wi-Fi 6’s theoretical 9.6 Gbps to a whopping 46.1 Gbps! Naturally, these rates are theoretical numbers and not what you could realistically expect to achieve. This increased capacity also earns Wi-Fi 7 the moniker of Extremely High Throughput (EHT).
If you are considering upgrading your Wi-Fi infrastructure, waiting for Wi-Fi 7 is probably not a solid strategy unless you are already using Wi-Fi 6 or 6e. Wi-Fi 6 is already faster than the links that most Internet service providers can deliver to the premises. Upgrading from Wi-Fi 6 to 6e is likely not worth the investment unless you already have a number of devices that can use the 6 GHz spectrum, or you are seeing significant interference from other Wi-Fi sources in the 2.4 GHz and 5 GHz bands. Upgrading from Wi-Fi 5 or earlier to Wi-Fi 6 may be worth the investment if your facility or home has multiple simultaneous users — especially if they are all streaming content or frequently using high-bandwidth applications like virtual meetings.
Wi-Fi is not targeted at solving the carrier’s “last-mile” problem but rather the last 100-foot problem. The carrier gets the Internet to your home/facility and then Wi-Fi solves how to get the WAN connection from the point of demarcation to the users. Additionally, Wi-Fi is not really competition for the 4G/5G cellular system as the cellular carrier has greater range and relatively limitless digital roaming — for a fee — at least until unmetered, unlimited cellular data becomes prevalent. In the meantime, Wi-Fi provides the most cost-effective way to provide connectivity within the home/facility at data rates that rival wired solutions.