A central coordinating entity (the AP in 802.11ax) assigns RUs for reception or transmission to associated stations. OFDMA segregates the spectrum in time-frequency resource units (RUs). Therefore, bandwidth occupied by a single OFDMA transmission is between 2.03125 MHz and ca. Each tone consists of a single subcarrier of 78.125 kHz bandwidth. To meet the goal of supporting dense 802.11 deployments, the following features have been approved.Ĭentrally controlled medium access with dynamic assignment of 26, 52, 106, 242(?), 484(?), or 996(?) tones per station. Therefore, unlike 802.11ac, 802.11ax also operates in the unlicensed 2.4 GHz band. 802.11ax addresses frequency bands between 1 GHz and 6 GHz. The 802.11ax amendment brings several key improvements over 802.11ac. In 802.11ax, it takes 12.8 microseconds (both without guard intervals). This introduces OFDM symbols that are four times longer: in 802.11ac, an OFDM symbol takes 3.2 microseconds to transmit. Since the available bandwidths have not changed and the number of subcarriers increases by a factor of four, the subcarrier spacing is reduced by the same factor. To support OFDMA, 802.11ax needs four times as many subcarriers as 802.11ac. By doing so, an 80 MHz channel can be split into multiple Resource Units, so that multiple clients receive different types of data over the same spectrum, simultaneously. With OFDMA, multiple clients are assigned to different Resource Units in the available spectrum. With 802.11ax, a similar multiplexing is introduced in the frequency domain: OFDMA. By doing so, the interference between clients is reduced, and the overall throughput is increased, since multiple clients can receive data simultaneously. MU-MIMO allows the access point to form beams towards each client, while transmitting information simultaneously. In 802.11ac (802.11's previous amendment), multi-user MIMO was introduced, which is a spatial multiplexing technique.
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