IEEE 802.11ax

What is 802.11ax Wi-Fi?

Wi-Fi experiences a seismic change approximately every five years – and 802.11ax is the latest generation of Wi-Fi that bridges the performance gap towards ten gigabit speeds. The new Wi-Fi standard will deliver faster network performance, connect more devices simultaneously and transition Wi-Fi from a ‘best-effort’ endeavor to a deterministic wireless technology that has become the de-facto medium for internet connectivity. With an expected four-fold capacity increase over its 802.11ac Wave 2 predecessor, 802.11ax deployed in dense device environments will support higher service-level agreements (SLAs) to more concurrently connected users and devices with more diverse usage profiles.

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802.11ax offers a range of technical enhancements to optimize spectral efficiency, increase throughput and reduce power consumption. These include:

OFDMA and MU-MIMO

Orthogonal frequency-division multiple access (OFDMA) and multi-user multiple-in multiple-out (MU-MIMO) are techniques that increase reliability and efficiency in the unlicensed Wi-Fi spectrum. In contrast to previous generations of Wi-Fi, OFDMA enables Wi-Fi to become deterministic, as devices consistently receive more attention with minimal contention. This helps stabilize Wi-Fi performance, especially in higher density environments.

Each Wi-Fi channel is divided into smaller sub-channels known as Resource Units. The AP decides how to allocate the sub-channels, as each individual RU (or sub-channel) can be addressed to different clients that are serviced simultaneously. This technique improves the average throughput (per user) by creating a narrower, albeit dedicated sub-channel. Moreover, OFDMA boosts spectral efficiency and reduces latency, while supporting heterogeneous users (i.e., IM, email or light web browsing versus large downloads).

It is important to note that OFDMA and MU-MIMO provide complementary techniques to concurrently serve multiple users. More specifically, OFDMA is best utilized when multiple connections transmit limited amounts of data. OFDMA which is effective at all ranges – close, medium and far – offers lower latency and can be used to mitigate OBSS interference issues. Meanwhile, MU-MIMO best serves multiple user with full buffer traffic and is most effective at close-to mid-range.

Uplink MU-MIMO

With 802.11ax, OFDMA and MU-MIMO are supported in downlink (from AP to stations) and uplink (from stations to AP). It should be noted that the AP schedules the transmissions in both directions. This contrasts with pre-802.11ax networks (especially in uplink direction), where resource allocation is contention-based, with individual stations making the decision to appropriate the medium and transmit data. As stations increase, so does contention.

Sub-carrier spacing and MAC/PHY enhancements

With 802.11ax, sub-carrier spacing is reduced, thereby enabling a 4X jump in the number of available data-tones and significantly increasing maximum PHY rates. Moreover, additional data tones help support multiple users in conjunction with OFDMA. 802.11ax also optimizes spectral efficiency with more tones/channel, reduces overhead, bolsters outdoor operation and facilitates a quantum jump in highest achievable PHY rates. In addition, 802.11ax APs maintains two separate network allocation vectors (NAVs) to prevent misbehavior and collisions. Last, but certainly not least, 802.11ax features a 1024-QAM constellation (in contrast to 256-QAM for 11ac), enabling a 25% physical data rate increase that in combination with other 802.11ax techniques offer up to 4x the capacity.

Target Wake Time

First introduced in the IEEE 802.11ah standard, target wake time (TWT) enables scheduled sleep and power-on (awake) times, along with pre-negotiated wake times between AP and clients to avoid on-the-air contention amongst client devices. This helps make air utilization more efficient and enhances the battery life of client devices.

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802.11ax 

一般無線技術

說明:

802.11ax 是最新 Wi-Fi IEEE 無線標準。這項新標準在多方面都有重大進展。  拓展多輸出多輸入 (MU-MIMO) 技術,相較於 802.11ac Wave 2 的四個串流,新標準可同時透過最多八個串流進行傳輸。此外,新標準透過 MU-MIMO 附帶正交分頻多工存取 (OFDMA) 技術,讓每個 MU-MIMO 串流再進一步分為四個串流,使每位使用者的有效平均輸送量大幅提升四倍。

以 1024-QAM 引入新的調變和編碼組合,讓每個封包可傳輸更多資料,提升輸送量。此外,這也改善了實體和 MAC 層的整體效率及電池電源管理。

如果早期的標準有如超市的一個收銀台前排了長長人龍,802.11ac 的 MU-MIMO 則像是增設了四個收銀台,可同時服務四倍顧客。802.11ax 進一步擴增為八個收銀台,服務八倍顧客。有了 OFDMA 之後,現在收銀台可在有空時一次為多位顧客結帳。想想看,如果收銀台可以同時服務多名顧客,當第一位顧客決定回到店內快速拿項商品,收銀台就能先服務下一位顧客。

為何這項技術值得關注:

人潮眾多的體育館或繁忙的機場目前多半都部署了 Wi-Fi,動輒有成千上萬部裝置爭奪頻寬,目前的 802.11ac 標準已不敷使用。802.11ax 可在高使用密度的環境中,將每位使用者的平均輸送量提升 4 倍。

若將最新標準結合 Ruckus 超高密度技術套件,必能協助您提供最佳使用體驗。