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 

一般的なワイヤレス技術

概要:

802.11ax は最新の Wi-Fi IEEE ワイヤレス規格です。この新規規格は、さまざまな点で非常に進化しています。  マルチ入出力 (MU-MIMO) 技法を拡大し、802.11ac Wave 2 の 4 ストリームから、最大 8 ストリーム まで同時送信できるようになっています。さらに、MU-MIMO をベースに直交周波数分割多元接続 (OFDMA) 技術を採用し、MU-MIMO の各ストリームを 4 つの追加ストリームに分割して、ユーザーごとの有効平均スループットを 4 倍に増やします。

1024-QAM によるモジュレーションとコーディングの新規セットを採用することで、パケットごとの送信データを増やし、スループットを向上させます。また、物理的および MAC レイヤーの全体的な効率を高め、バッテリー電力管理を改善します。

旧規格を 1 つしかないスーパーのレジに長い列を作って並ぶ買い物客に例えるとすれば、802.11ac の MU-MIMO はそれを 4 つのレジに増やして 4 列の買い物客に対応できるようになったようなものでした。802.11ax ではそれをさらに 8 つのレジに増やして 8 列の買い物客に対応できるようになりました。さらに OFDMA では、手が空いているときに 1 つのレジで複数の買い物客に対応できるようになっています。最初の買い物客が何かを取りにレジをちょっと離れている間に、次の買い物客に対応できるといったことを想像してみてください。

利点:

Wi-Fi は現在、何十万ものデバイスが帯域幅を奪い合ってる満員のスタジアムや混雑した空港に導入されており、現在の 802.11ac 規格による対応は苦戦を強いられています。802.11ax は、高密度環境でユーザーごとの平均スループットを 4 倍に増加させます。

この最新規格をラッカスの超高密度テクノロジー スイートと組み合わせることで、最高のエンドユーザー体験を提供できます。