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IEEE 802.11ac is a wireless networking standard in the 802.11 family (which is marketed under the brand name Wi-Fi), developed in the IEEE Standards Association process,〔 providing high-throughput wireless local area networks (WLANs) on the 5 GHz band.〔 The standard was developed from 2011 through 2013 and approved in January 2014.〔(【引用サイトリンク】 Official IEEE 802.11 Working Group Project Timelines )〕 This specification has expected multi-station WLAN throughput of at least 1 gigabit per second and a single link throughput of at least 500 megabits per second (500 Mbit/s). This is accomplished by extending the air interface concepts embraced by 802.11n: wider RF bandwidth (up to 160 MHz), more MIMO spatial streams (up to eight), downlink multi-user MIMO (up to four clients), and high-density modulation (up to 256-QAM). ==New technologies== New technologies introduced with 802.11ac include the following:〔 * Extended channel binding * * Mandatory 80 MHz channel bandwidth for stations (vs. 40 MHz maximum in 802.11n), 160 MHz available optionally * More MIMO spatial streams * * Support for up to eight spatial streams (vs. four in 802.11n) * Downlink Multi-user MIMO (MU-MIMO, allows up to four simultaneous downlink MU-MIMO clients) * * Multiple STAs, each with one or more antennas, transmit or receive independent data streams simultaneously * * * “Space Division Multiple Access” (SDMA): streams not separated by frequency, but instead resolved spatially, analogous to 11n-style MIMO * * Downlink MU-MIMO (one transmitting device, multiple receiving devices) included as an optional mode * Modulation * * 256-QAM, rate 3/4 and 5/6, added as optional modes (vs. 64-QAM, rate 5/6 maximum in 802.11n) * * Some vendors offer a non-standard 1024-QAM mode, providing 25% higher data rate compared to 256-QAM * Other elements/features * * Beamforming with standardized sounding and feedback for compatibility between vendors (non-standard in 802.11n made it hard for beamforming to work effectively between different vendor products) * * MAC modifications (mostly to support above changes) * * Coexistence mechanisms for 20/40/80/160 MHz channels, 11ac and 11a/n devices * * Adds four new fields to the PPDU header identifying the frame as a Very High Throughput (VHT) frame as opposed to 802.11n's High Throughput (HT) or earlier. The first three fields in the header are readable by legacy devices to allow coexistence Meru Networks has suggested that 802.11ac makes a wireless network employing the Single Channel Architecture substantially more effective. Traditional 802.11 networks are deployed as a Multiple Channel Architecture 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IEEE 802.11ac」の詳細全文を読む スポンサード リンク
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