802.11n technology revolutionized Wi-Fi with the introduction of channel bonding, MIMO (Multiple Input, Multiple Output), and frame aggregation technologies that collectively improved Wi-Fi throughput by more than eight times above the previous standard. 802.11ac incrementally improves on all of these features.
802.11ac, approved in 2013, is the latest extension to the IEEE Wireless LAN standard. It defines wireless technology for Very High Throughput (VHT) networks, providing connection speeds that reach up to several Gigabits per second. The Super Gigabit Wi-Fi standard - 802.11ac – is being widely adopted across the industry. By implementing new technologies and expanding existing capabilities, this feature-packed standard promises to deliver a huge performance boost.
802.11ac achieves its raw speed increase by pushing on three different dimensions:
- Increasing the bandwidth from the maximum of 40 MHz in 802.11n up to 80 MHz or even 160 MHz in 802.11ac (for 117% or 333% speed-ups, respectively)
- Higher modulation, now using optional 256 quadrature amplitude modulation (QAM), up from 802.11n’s maximal 64QAM (for a 33% speed burst at shorter, yet still usable, ranges)
- More multiple inputs, multiple outputs (MIMO) spatial streams (SS). Whereas 802.11n stopped at four spatial streams, 802.11ac goes all the way to eight (for another 100% speed up).
802.11ac has entered the commercial market in two distinct phases, dubbed Wave 1 and Wave 2. 802.11ac Wave 1 products entered the marketplace in 2013 and have been highly successful so far. These technologies improve Wi-Fi throughput from 450Mbps to 1.3Gbps. Wave 2 products began shipping in 2015 and can enhance throughput to a theoretical maximum of 3.47Gbps. Across the industry, many people are waiting for the wave II 802.11ac chipsets, which will bring the long anticipated MU- MIMO functionality.
MU-MIMO enables the AP to transmit data to multiple clients simultaneously using beamforming. MU-MIMO is a radical new technology that attempts to support higher density deployments by servicing multiple endpoint devices concurrently. In addition, several channel bonding improvements enhance overall throughput by utilizing wider portions of the 5GHz band as well as enabling more flexible use of the spectrum.
Devices using the 802.11ac Wave 2 standard have started to ship in earnest, and interoperability certification has begun, which will lead to accelerating adoption in 2016 and 2017. 802.11ac Wave 2 uses downlink MU-MIMO (multi-user MIMO) to send data to up to four clients1 simultaneously, reducing contention and improving overall network throughput substantially.
Benefits of MU-MIMO under 802.11ac Wave 2
It provides up to 3X higher aggregate throughput to a Wi-Fi network by making use of beamforming to differentiate among client devices, sending data simultaneously to groups of up to four clients simultaneously.
Reduces wait time for MU-MIMO-enabled clients, which can increase throughput for all clients in a mixed environment of SU and MU users. Improved video streaming with fewer stutters and pauses under high network loads, for example in crowded hotspots. Faster downloads for all using the network, but especially for MU-MIMO-enabled clients. It also allows the use of lower-cost client devices with fewer antennas and less powerful Wi-Fi computational engines, potentially reducing power consumption in battery-operated handsets and tablets.
802.11ac Wave 2 supports the existing bonding methods of 802.11n and 802.11ac Wave 1 (up to 80MHz wide), along with added options for 160MHz wide channels. Wider bonding allows for higher throughput between two wireless devices. To increase the number of bonding options for 160MHz, Wave 2 introduces a new feature called 80+80 that allows non-adjacent bonding of the 80MHz wide channels.
To support 80+80 channel bonding with four spatial streams, a 4x4 (four transmitting antennas, four receiving antennas) 80MHz MIMO transceiver would have to duplicate its entire signal processing core to service the second channel. This is because spatial stream processing has to be treated separately on a non-contiguous second channel. The alternative is to divide up the four existing processing resources between the two channels to support 80+80MHz in a 2x2 configuration. This is the path being taken by many chip manufacturers. The result is the utilization of a wider band, but without any additional throughput.
Like all 802.11 standards, Wave 2 technology has been specifically drafted to support the operation of all predecessor technologies so that Wave 2 APs will work with all existing Wi-Fi clients in the field. However, Wave 1 clients are only SU-MIMO capable. They are not forward compatible with Wave 2 APs and therefore not able to participate in MU-MIMO communications. This is because they lack the beamforming feedback and group forming protocols needed to form MU-MIMO groups.
The benefits of Wave 2 will certainly come to bear within the lifespan of a deployment installed today. Organizations must pay close attention to the potential value and impact of these products, as it is simply a matter of time before they will need to consider Wave 2 in their technology plans
What is after 802.11 ac wave 2?
802.11ax, the next evolution of the 802.11ac standard, will increase the maximum modulation rate to 256-QAM and will use OFDMA (orthogonal frequency division multiple access) to direct different subcarriers to different intended users, increasing the number of clients that can receive data simultaneously in a 5 GHz network. The standard increases the power spectral density (PSD) per user, and therefore increases overall network throughput. The standard will also add uplink MU-MIMO.
- Peak data rates for a single device could reach as high as 10 Gbps to 14 Gbps under 802.11ax.
- UL OFDMA and higher PSD increase the UL link budget by 9 dB, increasing range.
- The standard could increase the maximum number of MU-MIMO streams and antennas from four to eight, requiring as many as 16 antennae for simultaneous dual-band operation in an AP.
- The standard could add MU-MIMO to the 2.4 GHz band.
The IEEE is expected to approve the 802.11ax standard in 2019, but devices using Draft 802.11ax could ship in late 2017.