With the Wi-Fi Alliance launch of the second generation of the 802.11ac certification program, the Wi-Fi industry has taken another huge step forward in increasing the speed of Wi-Fi – and more importantly a big step in improving the efficiency of Wi-Fi networks.

When it was officially approved in 2014, the IEEE 802.11ac standard introduced a number of features that were welcomed by Wi-Fi vendors and consumers alike; these included:

  • 5 GHz only operation
  • Wider channels
  • More MIMO spatial streams (i.e. more antennas)
  • 256-QAM modulation
  • Multi-user MIMO (MU-MIMO)

Creating a Wi-Fi Alliance certification program requires assembling a test bed of devices that provide multiple independent implementations of the 802.11ac Wave 2 technology. Because the test bed is composed of real products, development of the certification program reflects the highest risk/reward trade-offs of the technology capabilities in the standard.

The first version of the Wi-Fi Alliance (known as Wave 1) was focussed on the features that had the lowest implementation risk:

  • 80MHz channels, because it was a straightforward extension of the 40 MHz capabilities in existing 11n devices
  • 3 spatial streams, because the products could re-use much of existing 802.11n 3-streams
  • 256-QAM, because it was relatively easy to do

This enabled the first release of the Wi-Fi Alliance certification program to achieve data rates of 1.3 Gbps with very low risk, effectively doubling the rate that was achieved with 802.11n.

802.11-maximum-data-rateThe maximum speeds of 802.11-based devices

The Wi-Fi Alliance has now released the second generation of the certification program for 802.11ac (known as Wave 2).  The second generation adds the following features:

160 MHz channels

When Wi-Fi first started back in the late 1990s, it used 20 MHz channels.  As Wi-Fi was primarily used in the 2.4 GHz ISM band which has limited spectrum, 20 MHz channels worked very well. But as Wi-Fi has grown in popularity and more and more performance has been required, the bandwidth requirements have gradually increased. Increasing bandwidth helps to increase speed. 802.11n introduced 40 MHz bandwidth, 802.11ac introduced 80 and 160 MHz bandwidth.

A number of countries have allowed 80 and 160 MHz channels, however the available spectrum has been limited. In early 2013, the FCC increased the available spectrum for 802.11ac and similar actions have been taken throughout the world.

Overall, the regulatory environment has been supportive of Wi-Fi moving to 160 MHz channels and the Wi-Fi industry continues to devote effort to increase the available spectrum simply because we need the capacity.

Up to 4 spatial streams

In a MIMO environment, multiple antennas are used at a receiving station and at a transmitting station (known as the access point or AP). In order to transmit and receive various signals simultaneously, a common multiplexing technique known as spatial multiplexing is used.

Basically, when wireless signals are being transmitted simultaneously from different antennae, each signal is transmitted via a spatial stream within the given spectral channel to avoid collisions.

MU-MIMO support

MIMO stands for multiple input, multiple output and refers to the way bandwidth is broken up by a router and pushed to individual devices. Most modern routers presently use SU-MIMO (single user MIMO). With these routers, only one device can receive data at any given time. This means that if you have one person watching Netflix and another watching YouTube, if you were to start both those streams at the exact same time, one device would get priority while the other has to wait until the first has buffered a few bits of data for itself.

Usually, you won’t notice a slowdown.  Even though SU-MIMO routers can only open up one stream at a time, they do so in very rapid succession, which to the naked eye looks like a solid stream of data.

MU-MIMO (multiple user MIMO) routers, on the other hand are able to break up this bandwidth into separate, individual streams that each share the connection evenly, no matter the application. MU-MIMO routers come in three flavors: 2×2, 3×3, and 4×4, which refers to the number of streams that they can create for each device in your household.

SU-MIMO vs MU-MIMOSU-MIMO vs MU-MIMO operation

The main benefit is that instead of each stream being periodically (albeit very briefly) interrupted, a MU-MIMO router can keep its signal constant for those four devices, and fairly distribute the bandwidth to each without compromising the speed of any of the others at the same time.

Imagination is a proud member of the Wi-Fi Alliance

We are already seeing strong ecosystem demand for the new Wi-Fi 11ac Wave 2 features in building the next generation of connected devices for such applications. This is why we’ve designed the Ensigma Explorer RPU architecture to support a wide range of high-performance Wi-Fi protocols (including 802.11ac and 802.11ax) for applications such as 4K video and high-end audio streaming.

03 - Creator Ci40 dev board - full specsThe Creator Ci40 IoT hub implements 802.11ac 2×2 Wi-Fi

Ensigma Explorer RPUs can be integrated inside the main SoCs or can be used to build standalone high-performance wireless chips that deliver a wide range of connectivity standards, including Wi-Fi, Bluetooth and LTE. One recent device to use Ensigma is the Creator Ci40 dev board – a high-end IoT hub that integrates 802.11ac 2×2 connectivity inside the cXT200 applications processor.

About the author: Richard Edgar

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Richard Edgar is Director of Communications Technology for Imagination Technologies. Richard has worked in the Wi-Fi industry for far too long at various semiconductor and equipment manufacturers developing various short-range wireless solutions. Richard represents Imagination in various industry bodies for short range wireless technologies. When not obsessing about wireless technologies, Richard enjoys church bell ringing, archery and shouting at his children.

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