The 802.11ac working group standardized the standard for Very High Throughput( VHT), a gigabit WLAN, in 2013. It is a further development of 802.11n, which also operates with OFDM multiplexing in the 5 GHz band, the UNII band. In 802.11ac, a physical layer( PHY) with a data throughput of 6.93 Gbit/s is specified. 802.11ac technology is also marketed under the name5GWiFi, in reference to the 5th generation mobile communications technology( 5G).
802.11ac transmits over multiple connections, with at least 500 Mbit/s transmitted per connection; theoretically, a stream can reach a data rate of 866 Mbit/s. The transmission speed is determined by the Modulation and Coding Scheme( MCS). It depends on the channel width, the modulation method, the number of radio channels and the code rate.
The WLAN according to 802.11ac works like 802.11n with BPSK, QPSK and quadrature amplitude modulation( QAM), 16QAM and 64QAM, but can also work with 256QAM, in which each symbol is coded with 8 bits.
Radio channels and data rates
The radio channels have a channel width of 20 MHz, 40 MHz, 80 MHz and 160 MHz. 160 MHz channels can also be established by channel bundling, channel bundling, of two adjacent 80 MHz channels.
In the 5 GHz band, only two 160 MHz channels are available. In the first version of 802.11ac for car-to-car communication specified by the Wireless Access for Velicalur Environment(WAVE 1) working group, three streams are available, transmitted using single-user MIMO( SU-MIMO). The achievable data rate is 433 Mbit/s at a bandwidth of 80 MHz. The resulting data rate for the three streams is thus 1.3 Gbit/s. In the Wave 2 version, the number of streams was increased to four. Transmission in the downlink is in multi-user MIMO( MU-MIMO) and uses beamforming. The achievable data rates are 3.4 Gbit/s (4x866 Mbit/s) with a bandwidth of 160 MHz (2x80 MHz). With 8x8 MIMO, data rates of up to 6.936 Gbit/s are theoretically possible.
To further increase the data rate, 802.11ac works with a maximum of eight spatial streams( SS) and multi-user MIMO (MU-MIMO). The maximum data rate that can be achieved with this is 6.9 Gbit/s. The guard interval( GI) is 400 ns or 800 ns.
The standard provides for compatibility with other 802.11 devices as well as coexistence of multiple 802.11 devices. Compared to the ISM band at 2.4 GHz, the 5 GHz band has the advantage that it is used much less and thus less interference can form. The disadvantage is the smaller expansion, which is due to free space attenuation. The further development of 802.11ac is 802.11ax, with which data rates of more than 10 Gbit/s can be realized
Since only a few parallel 160 MHz frequency bands are available in the 5 GHz frequency band, the development of gigabit WLANs is shifting to the 60 GHz band. The 802.11ad and 802.11ay working groups are dealing with this issue.
The 802.11ac frame
The 802.11ac frame consists of a preamble, which is the same as the 802.11n frame, and 802.11ac-specific data fields. The preamble has three data fields: Short Training Field( L-STF), Long Training Field( L-LTF), and Signal( L-SIG). The first two data fields are for frequency offset and timing synchronization, and the SIG field contains packet length information. The 802.11ac-specific data fields are labeled Very High Throughput (VHT), followed by the abbreviation for their contents: VHT-SIG or VHT-LTF. They indicate the packet length or the payload length, or are used for frequency selection.
The connection of the Access Point
Since data rates of well over 1 Gbit/s are transmitted via the 802.11ac access point, the connection of the access point must also be able to handle corresponding data rates. The connection must therefore support data rates of several gigabits per second. This connection to a fast Ethernet can be made via link aggregation using Link Aggregation Control Protocol( LACP) or via the Ethernet standard 802.3bz, which transmits data rates of 2.5 Gbit/s and 5 Gbit/s via existing STP cables ofcategoryCat 5e and Cat 6. In addition, this standard supports power transmission via Power over Ethernet( PoE).
According to certification by the WiFi Alliance, 802.11ac corresponds to WiFi 5.