OFDM review/basics as a baseline for understadning WIFI 6/802.11ax – part 1

How will 802.11ax change the wireless space? In order to understand how the standard will move forward an understanding of OFDM will be the first order of the day. 802.11ax is set to be a game changer, but what is the technology set to do?

One of the main features will be high efficiency…

802.11ax contains a new PHY protocol with higher modulation and coding schemes. In contrast to802.11ac, 802.11ax does not increase the number of theMIMO spatial streams and does not widen the channel. Thusthe nominal data rates are increased up to 9.6 Gbps, which isjust 37% higher than that of 802.11ac (rather small comparedto the 10x growth of 802.11n or 802.11ac!) [20]. The desiredincrease of the user throughput is achieved by more efficientspectrum usage.

The key feature of 802.11ax is the adoption of an OFDMA approach, an approach widely used in cellular networks, but brand new in Wi-Fi. The rationale is that the very wide chan-nels (80 MHz, 80+80 MHz and 160 MHz) introduced by802.11ac suffer from frequency selective interference, which significantly impairs the practically achievable rates. With OFDMA, adjacent subcarriers (tones) are grouped together into a resource unit (RU) and a sender can choose the best RUfor each particular receiver, which actually results in higher Signal-to-Interference-plus-Noise Ratio (SINR), Modulation and Coding Scheme (MCS) and throughput

reference https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8468986

Features of High Efficiency:

OFDMA – Orthogonal Frequency Division Multiple Access

reference image – http://telecompedia.net/ofdma/

1024 QAM – supposed to provide a 25% increase in data rate as compared to 256 QAM

Longer symbol – to help improve indoor efficiency and outdoor resiliency. A symbol is data that is modulated onto the carrier signal in bits. At its most basic level modulation is changing a signal into “useful data”.

Multi user MIMO – MU

guard interval – guard intervals are used to ensure that transmissions do not interfere with one another.

802.11ac is up to 6 times faster than 802.11n

802.11ax will support a larger number of users making it ideal for stadiums, lecture halls and conferences where a larger number of users are expected to use the wireless medium.

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