As WLAN access point and device vendors work toward product launches at the end of 2018, we will publish a series of blogs covering all aspects of 802.11ax technology. This first one introduces the motivation and main features of 802.11ax.
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如何改善今天的Wi-Fi？
When deciding how to improve Wi-Fi beyond the current release, 802.11ac, the IEEE and Wi-Fi Alliance surveyed Wi-Fi deployments and behavior in order to identify obstacles to wider use and causes of dissatisfaction among user communities. The conclusion was to focus more on performance under “typical” field conditions, a departure from previous upgrades that advanced peak data rates under “excellent” field conditions. With 802.11ax, peak performance and average and worst-case performance under real-world conditions will see improvements.
重叠的覆盖范围
Real-world conditions have changed over the years, due in no small part to Wi-Fi’s extraordinary success. Access points are everywhere, indoors and outdoors. In many areas, congestion has become a serious problem.
其中一些拥挤的地区是繁忙的机场和火车站，多住所公寓和学校和大学设置。所有这些领域都是通过接入点的覆盖范围重叠，无论是在同一网络中管理还是不协调，都提供了许多数据饥饿的客户端设备。
To advance Wi-Fi and meet user expectations, IEEE and Wi-Fi Alliance set out to improve performance for everyone, especially in areas of overlapping coverage.
物联网要求
用于手机和PC的互联网服务不是Wi-Fi的唯一用途。越来越多的东西互联网（物联网）传感器正在许多地方使用Wi-Fi进行连接，但几个限制限制了其采用。为了帮助移动市场，802.11AX中的新功能允许有效地分配低数据速率连接，提高IOT传感器电池寿命，并扩展Wi-Fi信号的范围。
无线互联网服务提供商（Wisps）也使用Wi-Fi进行户外点对点链接，802.11AX中的新功能将扩展范围，增加数据速率，并降低干扰的影响。
Rolling Out Wave 1 and Wave 2
We are seeing some parallel development of 802.11ax, similar to the development of 802.11n and 802.11ac. The Wi-Fi Alliance started work on certification tests before the IEEE had finished the underlying specification. Faced with commercial pressures, access point and device vendors are expected to release “pre-standard” equipment ahead of the Wi-Fi Alliance certification, but the industry has managed this before, so we don’t expect any interoperability issues. Another consequence of time-to-market pressures is that 802.11ax will be split: the initial wave 1 release will be followed 1-2 years later by wave 2.
802.11AX主要特征
More than 50 features are in the IEEE 802.11ax standard, but not all will be certified and make it to market. Here is a high-level summary of anticipated commercial features (including both wave 1 and wave 2 features).
- Downlink and uplink OFDMA：正交频率分割多址（OFDMA）增加用户数据速率并减少延迟，尤其是对于具有短帧或低数据速率要求（例如IoT设备）的大量设备。它是一种多用户能力，其中可以在频域中划分传输，其中不同的子载波组用于不同目的地的帧。OFDMA在提高网络容量时特别有效，其中有许多设备，短帧或低数据速率流。对于Wi-Fi联盟11AX认证，Uplink和下行链路都是强制性的。
- Downlink and uplink multi-user MIMO:Multi-user Multiple-Input, Multiple-Output (MU MIMO) is a second multi-user capability, originally introduced in 802.11ac for downlink traffic. It improves network capacity by allowing multiple devices to transmit simultaneously, making use of multipath spatial channels. 802.11ax improves on 802.11ac by increasing the size of downlink multi-user MIMO groups, allowing more efficient operation. Uplink multi-user MIMO will be added during wave 2 of the 11ax certification.
- Transmit beamforming:现有的功能,一个访问点使用everal transmit antennas to land a local maximum signal on a receiver’s antennas. It improves data rates and extends range. While 802.11ac access points incorporated up to 4 antennas (although the specification allowed more), 8-antenna 802.11ax access points are expected to ship in 2019.
- 高阶调制: The highest modulation level is extended from 256-QAM to 1024-QAM. This increases data rates under good conditions (high SNR) and results in a better user experience. Peak rates improve by 25% over 802.11ac.
- OFDM符号：正交频分复用（OFDM）符号是802.11的RF构建块。出于技术原因，Subcarrier间距，符号持续时间和FFT大小都在802.11AX中更改，以允许小OFDMA子信道的有效操作。这是对OFDMA操作所必需的，并且它会降低每符号开销并增加网络容量。
- Outdoor operation：许多功能改善了户外性能。最重要的是一种新的数据包格式，现在重复最敏感的字段以获得鲁棒性。其他功能包括延长冗余的更长的保护间隔和模式，以允许错误恢复。
- Reduced power consumption: Existing power-save modes are supplemented with new mechanisms, allowing longer sleep intervals and scheduled wake times to reduce the power consumption of client devices. Also, for IoT devices, a 20MHz-channel-only mode allows for simpler, less power-hungry chips that support only that mode.
- Spatial re-use: When contending for a transmit opportunity, a device is allowed to transmit over the top of a distant transmission, which would previously have forced it to wait. This increases network capacity by allowing more simultaneous transmissions in a given geographic area.
未来几年对Wi-Fi和挑战具有很大的承诺。Wi-Fi必须继续提高性能，克服自己成功引起的未经许可的乐队拥堵，并尽可能吸引IOT开发人员。该行业正在响应802.11AX的要求。新标准将推动Wi-Fi，直到2024年和接下来的802.11 PHY修正案。
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