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WLAN Standards

Every day, more and more things are connecting to the internet.  In addition to computers and phones, things like refrigerators and light bulbs and thermostats and toys are now connecting to our wireless local access networks (WLANs).  They all share the same bandwidth by following protocols set by the IEEE 802.11 set of standards. Below is a short history of 802.11:

802.11a, released in 1997, defined requirements for an orthogonal frequency division multiplexing (OFDM) communication system) operating in the 5 GHz band with a maximum data rate of 54 Mbit/s.  Though superceded by subsequent amendments, you'll still see the term in use to indicated basic compliance with 5 GHz, 54 Mbit/s systems.

802.11b, also released in 1997, uses direct sequence spread spectrum (DSSS) modulation. It has a maximum raw data rate of 11 Mbit/s, and defines operations at 2.4 GHz.  This frequency is commonly used for bluetooth communications , which leads to some problems with interference as the number of devices sharing a network increases.

802.11g (2003) uses the same OFDM transmission as 802.11a, but operates in the 2.4 GHz band. It has a maximum data rate of up to 54 Mbit/s, which eases the crowding problem of 802.11b. 

802.11n (2009) allows for the use of multiple antennas at both input and output (see our tutorial article on MIMO for more information on this method). This standard incorporates a huge jump in the maximum data rate from 54 Mbit/s to 600 Mbit/s and can be used in the 2.4 GHz or 5 GHz frequency bands.

802.11ac (2013) operates on the 5 GHz band, and uses MU-MIMO (multi-user MIMO) and OFDM techniques. It has multi-station throughput of at least 1 gigabit per second and single-link throughput of at least 500 megabits per second (500 Mbit/s). The standard allows for wider RF bandwidth (up to 160 MHz), and up to eight MIMO spatial streams.

802.11ax (scheduled for public release 2019) is still in development, but is predicted to have a top speed of around 10 Gb/s. It will operate in the 2.4 GHz and 5 GHz< ranges, and make use of MIMO, MU-MIMO, and OFDMA (a new muliti-user version of OFDM). Though the standard isn't fully released, many suppliers are already developing 802.11ax-specific components. Hardware must be backward compatible, of course.

You'd think that with IEEE 802 committee setting these standards, that we would enjoy perfect WiFi at the International Microwave Symposium.  Sadly, it costs significant money to configure the best equipment for events...

Our friends over at Keysight have sent along a couple of videos from Application Engineer Martha Zemede to help us work with the new standard. First, here's an overview of 802.11ax. Many of the acronyms that are used can be found in the Microwaves101 acronym glossary.

The second video addresses some of the challenges in designing and testing for the 802.11ax standard, using Keysight's 89600 VSA software.  By cramming information more efficiently into the same bandwidth (up to 18 simultaneous users in 40 MHz bandwidth!), hardware improvements are needed: the challenges are improved linearity, and lower phase noise. Check it out!

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Author : Unknown Editor

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