Evolution of 802.11 Physical layers

Today most of us know 802.11 ac or 802.11ax, which is used commonly with wireless. Let’s learn the Evolution of Wireless PHY’s and understand the first 802.11 Physical layers (PHY) supported and how wireless evolved to 802.11ax.

The physical layer in Wireless is represented as PHY.

Multiple radios + Antennas known as Radio Chains.

Spatial streams are the partitioning /breaking down of stream of data bits into multiple streams transmitted simultaneously by multiple radio chains by AP or User device (Laptop etc.).

802.11 Prime.

802.11 Prime was the first ratified Standard of 802.11 in 1997.

802.11 Prime was the first/oldest Physical layer (PHY) of wireless currently supported by Modern wireless Devices.

Honestly, I was not aware of 802.11 Prime until I started my journey to achieve CWAP certification.

802.11 Prime uses Direct Sequence Spread Spectrum (DSSS). In addition, 802.11 Prime uses a channel of 22MHz wide and operated only at 2.4GHz.

802.11 Prime supported data rates only 1 and 2 Mbps and supported only a single spatial stream.

802.11b

The High Rate/Direct Sequence Spread Spectrum Physical layer (PHY) came in 1999, known as 802.11b.

802.11b supported advanced Modulation techniques allowing support for data rates of 5.5 Mbps and 11 Mbps.

802.11b supported data rates are 1, 2, 5.5, and 11 Mbps.

802.11b also uses 22 MHz wide channels and is supported only in 2.4GHz.

802.11b supports only a single spatial stream.

We may not see the usage of 802.11 Prime and 802.11b today in most of the networks.

802.11a

The first Orthogonal Frequency Division Multiplexing (OFDM) was supported in 5GHz Band operations and was made available in 1999.

OFDM was the first to use 20 MHz channels instead of 22 MHz channels.

OFDM supported data rates 6,9,12,18,24,36,48, and 54 Mbps.

802.11a supports only single Spatial streams.

802.11g

The Extended Rate PHY(ERP), also known as 802.11g, was introduced in 2003.

The ERP uses OFDM modulation and uses a 20 MHz channel in the 2.4GHz band.

All ERP /802.11g devices support backward compatibility with HR/DSSS and DSSS.

802.11g supported data rates 6,9,12,18,24,48,36 and 54 Mbps using OFDM.

802.11g also supports data rates 1, 2, 5.5, and 11 Mbps to support backward compatibility DSSS and HR/DSSS.

802.11n

The High Throughput (HT) PHY was introduced in 2009.

802.11n provides wider channels by combining two 20MHz channels into one 40 MHz channel.

Two 20 MHz channels forming a 40 MHz channel are named Primary channel and Secondary channel.

For example, channel 52 (Primary) and channel 56(Secondary) can form a 40 MHz channel.

Access points use Primary channels to send Management Frames like Beacon, etc.

More details on Beacon can be seen in the Article.

https://www.wirelessnewbies.com/post/wireless-trouble-shooting

802.11n supports 20 MHz or 40 MHz channels.

Access Point operating on 40 MHz channel can still serve the clients on 20 MHz channel using Primary channel.

802.11n is supported both in 2.4GHz and 5GHz bands.

Enabling 802.11n in 2.4GHz is not recommended in Campus Access point (Multiple Access points can see each other) deployment, as we have only three channels 1,6, and 11.

There are a lot more features like Multiple inputs/Multiple outputs (MIMO) got introduced with 802.11n.

Spatial Multiplexing is used with MIMO to send Multiple spatial streams of data across the channel using Multiple radio chains.

802.11n introduced two methods of Frame aggregation (A-MSDU and A-MPDU).

802.11n introduced support of Short Guard Interval.

Guard interval is a time between symbols in a frame to avoid interframe symbol interference.

All the above features helped to provide higher data rates and better speeds using 802.11n.

802.11ac

802.11ac is known as very High Throughput (VHT) PHY and got introduced in 2013.

802.11 ac supports 80MHz and 160 MHz channels.

802.11 ac supports most of the features supported by 802.11n. we can see 802.11ac is fine-tuned and enhanced features of 802.11n

80MHz and 160 MHz channels are achieved by combining 4*20 MHz (80MHz) and 8*20MHz (160 MHz).

802.11ac is supported only 5GHz and not in 2.4GHz.

To understand why 802.11ac is not supported in 2.4GHz because we need 4 *20 MHz to support 80MHz, and unfortunately, we have only three channels in 2.4GHz.

802.11n vs. 802.11ac

802.11ax

The High-Efficiency Wireless PHY, also known as 802.11ax or WI-FI6, got introduced in 2019.

802.11ax came up with a new modulation known as orthogonal Frequency Division Multiple Access. (OFDMA)

OFDMA allows dividing the channel into multiple Resource units (or sub-channels) that can be used to communicate (in both directions) with Multiple Stations simultaneously.

You can see the difference between OFDM and OFDMA transmission.

Using OFDMA, Complete Channel /Frequency can communicate to a single client or multiple clients simultaneously as we can divide a channel into multiple Resource Units.

802.11ax/WI-FI 6 supports 1024-QAM, whereas 802.1lac supported only 256-QAM.

For more details about 802.11ax, please refer to the article.

https://www.wirelessnewbies.com/post/wireless-frames-exchange-between-access-point-wi-fi-6-user-device-with-wpa3-personal-ssid