The Evolution of Wi-Fi networks: from IEEE 802.11 to Wi-Fi 6E

This is the first article in a 6-part series featuring articles on Next-Gen Wi-Fi Applications and Solutions. The series focuses on the improvements Wi-Fi 6/6E and its applications bring to enhance the performance of the next-gen wireless networking devices. This series is sponsored by Mouser Electronics. Through the sponsorship, Mouser Electronics shares its passion for technologies that enable smarter and connected applications.

Over the past 24 years, IEEE 802.11, commonly referred to as Wi-Fi, has evolved from 2 Mbps to multi-gigabit speeds, a 1,000-fold increase in throughput. The standard has continuously advanced itself by introducing new protocols such as 802.11n, 802.11ac, and 802.11ax (Wi-Fi 6). 

There is a deep history of the widely accepted wireless communication technology that has led it to the point where it currently is. In this article, we explore the origins and the evolution of Wi-Fi as the most prevalent wireless communication technology of present times.

Fig. 1: The growth of Wi-Fi raw data transfer rates

The evolution of Wi-Fi Standards 

Since Wi-Fi was first released to consumers in 1997, its standards have been continually evolving, resulting in faster speeds and network/spectrum efficiency for users. As capabilities were added to the original 802.11 standards, they became known by their amendment (802.11b, 802.11g, etc.). 

Table 1 lists different standards, year of release, frequency bands, bandwidth, and max theoretical data rates achieved. Typical data rates are lower than theoretical ones based on several factors, including the signal degradation with distance, modulation rate, forward error correction coding, bandwidth, Multiple Input Multiple Output (MIMO) multiplier, guard interval, and error rates. The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the same basic protocol for wireless communication.

Table 1. The evolution of Wi-Fi standards.

IEEE 802.11-1997 Standard

802.11-1997 was the first wireless standard in the family, which was released in 1997. This standard defined the protocol and compatible interconnection of data communication equipment in a local area network (LAN) using Carrier Sense Multiple Access protocol with Collision Avoidance (CSMA/CA). CSMA/CA is a network access method in which a channel’s idleness is checked before beginning the data transmission.

802.11-1997 supported three physical layer technologies, including infrared, operating at 1 Mbps, a Frequency Hopping Spread Spectrum (FHSS) supporting 1 Mbps, and an optional 2 Mbps data rate or a Direct Sequence Spread Spectrum (DSSS) supporting both 1 Mbps and 2 Mbps data rates. This protocol was not widely accepted because of interoperability issues, cost, and insufficient throughput.

IEEE 802.11b Standard

802.11b products appeared on the market in mid-1999. They had a maximum theoretical data rate of 11 Mbps and used the same CSMA/CA medium access method defined in the original standard. The dramatic increase in throughput of 802.11b, along with substantial price reduction, led to the wide acceptance of 802.11b as a wireless local area networking technology. 

802.11b used the ISM unlicensed frequency band from 2.4 GHz to 2.5 GHz. The protocol was a direct extension of DSSS and used Complementary Code Keying (CCK) as its modulation technique. 802.11b was used in a point-to-multipoint configuration where an access point communicates with mobile clients within the range of the access point. 

This range depended on the radio frequency environment, output power, and sensitivity of the receiver. 802.11b had a channel bandwidth of 22 MHz and operated at 11 Mbps but could have scaled back to 5.5 Mbps, then to 2 Mbps, and 1 Mbps (adaptive rate selection) in order to decrease the rate of re-broadcasts that resulted from errors. The 802.11b standard shared the same frequency bandwidth as that of other wireless standards. Thus, within the home, wireless devices such as microwave ovens, Bluetooth® devices, and cordless phones caused interference with Wi-Fi, resulting in data transfer rates taking a hit.

IEEE 802.11a Standard

The 802.11a used the same core protocol as the original standard, however, operated at a frequency of 5 GHz. It used a 52-subcarrier Orthogonal Frequency Division Multiplexing (OFDM) and had a maximum theoretical data rate of 54 Mbps. In practical usage scenarios, the Wi-Fi standard achieved a throughput of mid-20-Mbps. 

Other data rates it supported included 6 Mbps, 9 Mbps, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, and 48 Mbps. Even though both the protocols were released in the same year, 802.11a was not interoperable with 802.11b as they operated in different unlicensed ISM frequency bands. The 5 GHz band gave 802.11a an advantage in terms of data transfer rates since the 2.4 GHz was getting crowded due to the occupation of spectrums by other devices. 

But operating at a higher frequency also reduced the operating range of the devices using 802.11a. The solution was to go for more powerful antennas, which had the potential to boost the range by a bit; however, their use was largely limited to routers deployed in big organizations owing to the requirement of powerful antennas and high price.

Of the 52 OFDM subcarriers, 48 were for data, and 4 were pilot subcarriers with a carrier separation of 312.5 kHz. Each of these subcarriers could be Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 16 Quadrature amplitude modulation (QAM), or 64QAM. The bandwidth of the channel was 20 MHz with an occupied bandwidth of 16.6 MHz. The symbol duration was 4µsec which includes a guard interval of 0.8 µsec. OFDM advantages included reduced multipath effects in reception and increased spectral efficiency. Table 2 lists the different modulations supported by 802.11a and their respective theoretical data rate.

Ultimately, 802.11a products were not widely accepted because of their high cost, low range, and incompatibility with 802.11b. 

Table 2. 802.11a modulation rates and data rates for 20 MHz channel spacing.

IEEE 802.11g Standard

802.11g became available in the summer of 2003. It used the same OFDM technology introduced with 802.11a. 802.11g combined the best of both 802.11b and 802.11a to make users interested in investing in a device supporting the wireless communication protocol. 

The Wi-Fi standard supported a maximum data transfer rate of 54 Mbps like the 802.11b while working at 5 GHz frequency to offer a higher range like the 802.11a. The 802.11g protocol was backward compatible with 802.11b (i.e. 802.11b devices could connect to an 802.11g access point, limited by the capabilities of the device supporting the older protocol). 802.11g was able to handle dual-band or dual-mode access points using 802.11a and 802.11b/g.

IEEE 802.11n Standard

If 802.11g was the first Wi-Fi standard good enough for commercial use, 802.11n was when things really started getting better. With 802.11n, Wi-Fi became even faster and more reliable. This was achieved by adding Multiple-Input and Multiple-Output (MIMO) and 40 MHz channels to the physical layer (PHY) and frame aggregation to the Media Access Control (MAC) layer. 

MIMO is a method for multiplying the capacity of a radio link using multiple transmit and receive antennas to exploit multipath propagation. These antennas need to be spatially separated so that the signal from each transmit antenna to each receive antenna has a different spatial signature so the receiver can separate these streams into parallel independent channels. 

Channels operating with a bandwidth of 40 MHz, double the channel width, and provide twice the Physical (PHY) data rate over a single 20 MHz channel used in the previous generation of Wi-Fi. 802.11n draft allowed up to 4 spatial streams with a maximum theoretical throughput of 600 Mbps. 

Table 3. 802.11n modulation and data rates for a single stream

20 MHz channels had 56 OFDM subcarriers, 52 were for data and 4 were for pilot tones with a carrier separation of 312.5 kHz. Each of these subcarriers could be based on BPSK, QPSK, 16QAM, or 64QAM. The total symbol duration is 3.6 µSec or 4 µSec, which includes a guard interval of 0.4 µSec or 0.8 µSec, respectively. Table 3 lists different modulation and coding schemes for a single stream (for multiple streams, the data rate is multiple of the number of streams). 

802.11n supports frame aggregation where multiple MAC Service Data Units (MSDUs) or MAC Protocol Data Units (MPDUs) are packed together to reduce the overheads and average them over multiple frames, thereby increasing the user-level data rate. Also, 802.11n is backward compatible with 802.11g, 11b, and 11a. 

IEEE 802.11ac Standard

802.11ac revved up the Wi-Fi standard by providing gigabit speeds per second and this is achieved by extending the 802.11n concepts which include wider bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), downlink multi-user MIMO (up to 4 clients) and high-density modulation (up to 256 QAM).  802.11ac supports 256 QAM at 3/4, 5/6 coding rate (MCS8/9) which requires 6 dB tougher system-level EVM (-34 dB) requirements.

802.11ac worked exclusively in the 5 GHz band, so dual-band access points and clients continued to use 802.11n at 2.4 GHz. The first wave of 802.11ac compatible devices released in 2013, supported only 80 MHz channels and up to 3 spatial streams delivering up to 1300 Mbps at the physical layer. The second wave of products, or 802.11ac wave 2 products, were released in 2015, supporting more channel bonding, more spatial streams, and Multi-User, Multiple-Input, Multiple-Output (MU-MIMO), a significant advancement of 802.11ac. 

While MIMO directed multiple streams to a single user, MU-MIMO can direct spatial streams to multiple clients simultaneously, thus improving network efficiency. 802.11ac also uses a technology called beamforming. With beamforming, the antenna transmits the radio signals in such a way that they are directed at a specific device, rather than having the signals spread in all directions. 

When done properly, this causes constructive interference resulting in the strengthening of signals in a particular region where the Wi-Fi client is present. 802.11ac routers are backward compatible with 802.11b, 11g, 11a, and 11n which means all the legacy clients just work fine with 802.11ac routers. Fig. 2: OFDM vs OFDMA resource allocation

IEEE 802.11ax Standard (Wi-Fi 6)

802.11ax, also popularly known as the Wi-Fi 6, is the sixth generation of Wi-Fi built on the strengths of 802.11ac, which provides more wireless capacity and reliability. 802.11ax achieves these benefits by using denser modulation schemes (1024 QAM & OFDMA), reduced subcarrier spacing (78.125 kHz), and schedule-based resource allocation. 

Unlike its predecessor, the 802.11ac, 802.11ax is a dual-band technology working in the 2.4 GHz and 5 GHz frequencies. It offers an upgrade in terms of speed even for the lower frequency band. 802.11ax is designed for maximum compatibility, coexisting efficiently with 802.11a/g/n/ac clients. 802.11ax uses OFDMA, which allows resource units (RUs) that divide the bandwidth according to the needs of the clients and provide multiple individuals with the same user experience at faster speeds. 

With 802.11ac, the Wi-Fi channel was broken down into a collection of smaller OFDM sub-channels. At any given point in carriers in each PLCP Protocol Data Unit (PPDU). However, with OFDMA (802.11ax), individual groups of subcarriers are individually allocated to clients as resource units on a per-PPDU basisFig. 2 shows a comparison between resource allocation in OFDM and OFDMA schemes.

Table 4. 802.11ac vs 802.11ax

Earlier 802.11 standards used CSMA/CA method wherein wireless clients first sensed the channel and attempted to avoid collisions by transmitting only when they sensed the channel to be idle. Although this clear assessment and collision avoidance served well, its efficiency decreased when the number of clients grew very large. 

802.11ax protocol solves this problem through OFDMA and schedule-based resource allocation. 802.11ax access points dictate when the device will operate, thus handling clients more efficiently. Resource scheduling also significantly reduces the power consumption during sleep time, which improves the battery life of clients. Table 4 lists the differences between 802.11ac and 802.11ax protocols. 

The new Wi-Fi standard also supports the transmission of multiple streams to a single client or multiple clients simultaneously. In addition to increasing peak data rates, efforts have been made to improve spectral efficiency which characterizes how well the system uses the available spectrum. 

Multi-user techniques, such as MU-MIMO and OFDMA, have been improved to increase the network efficiency and network capacity. While the previous standards supported MU-MIMO for downlink connections, Wi-Fi 6 supports 8x8 connections for both uplink and downlink.

IEEE 802.11ax Standard (Wi-Fi 6E)

In April 2020, the Federal Communication Commission, the body that governs radio communication in the United States, opened the 6 GHz band for unlicensed uses.^[1] This move led to the inclusion of the newly added frequency to WiFi 6.

The resulting standard carries all the features of the previously released protocol, and due to the expansion of operating frequency, it is named WiFi 6E. 

A direct effect of an increase in the width of the communication channel is a further reduction in interference when compared to WiFi 6. WiFi 6E is backward compatible with all the previous generations of WiFi. As more countries gradually open up the 6 GHz standard for unlicensed use, WiFi 6E will continue to make its way to newer markets.

IEEE 802.11be Standard (WiFi 7) 

Expected to be released sometime in 2024, WiFi 7 is the true successor to the present gen WiFi 6/6E standard that aims to operate in the 6 GHz band and bump up the raw data rates to 46.1 Gbps. 

The standard is expected to bring features like improved multi-access point coordination which could practically let active access points request idle access points to turn down their output power to minimize the interference caused by the devices not currently in use. WiFi 7 also implements joint transmission technology that lets two or more access points coordinate and agree to offer service to a single device when feasible.

The use of 360 MHz wide channels, a modulation order of 4096-QAM, and 16 spatial streams are just some more reasons to be excited about the upcoming WiFi standard. We’ll be bringing articles about WiFi 7 in the future as more details surface.

The upcoming articles from Next-Gen Wi-Fi Applications and Solutions Series will explore Wi-Fi 6/6E and its enabling technologies in-depth, trying to explore where the innovation is headed.

Wi-Fi 6/6E and RF solutions by Qorvo for next-gen networking applications

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Qorvo QPF4230 Wi-Fi® Front End Module (FEM), Qorvo QPF4230EVB-01 Evaluation Board, Qorvo QPQ1906 Wi-Fi®/IoT bandBoost Filter, Qorvo QPQ1906EVB-01 Evaluation Board

Conclusion

The developments in Wi-Fi connectivity have been over multiple fronts with data transfer rates, and range leading the way. To improve the performance and efficiency of consumer, commercial and industrial products, Original Equipment Manufacturers (OEMs) must make use of the true potential of the current-gen wireless networking technology and upgrade to the best hardware available in the market.

This article was initially published by Mouser and Qorvo in an e-magazine. It has been substantially edited by the Wevolver team and Electrical Engineer Ravi Y Rao. It's the first article from the Next-Gen Wi-Fi Applications and Solutions Series. Future articles will introduce readers to some more interesting applications of the technology in various industries.

• The introductory article provided an overview of wireless communication and the subsequent articles of the series. 
• The first article explored the origins and the evolution of WiFi to showcase how the wireless local area networking standard improved over time.
• The second article was focused on recent trends and the design philosophy behind WiFi 6/6E. The article explains why even with a marginal improvement in raw data rates, WiFi 6/6E is the biggest upgrade yet.
• The third article dives into the technicalities of WiFi 6/6E. It explains the 6 enabling technologies of WiFi 6/6E including OFDMA, BSS Coloring, TWT, Beamforming, 8X8 MU-MIMO, and 1024-QAM.
• The fourth article is a comparison between WiFi and 5G based on some of the key performance parameters. It tries to form a perspective regarding which technology is suitable for different use cases.
• The fifth article features a discussion on where the wireless communication industry is headed to. Concepts like mesh WiFi networks are explored with excerpts from an interview with Cees Links, General Manager of the Low Power Wireless Business Unit in Qorvo and one of the leading pioneers of WiFi. 
• The final article introduces the readers to the concept, benefits, and applications of BAW filters in WiFi, 5G, and other RF communication systems designs.
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About the sponsor: Mouser Electronics

Mouser Electronics is a worldwide leading authorized distributor of semiconductors and electronic components for over 1,100 manufacturer brands. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.

References

[1] FCC Opens 6 GHz Band to Wi-Fi and Other Unlicensed Uses, Federal Communication Commission, [Online], Available from: https://www.fcc.gov/document/fcc-opens-6-ghz-band-wi-fi-and-other-unlicensed-uses