89601B/BN-BHJ WLAN 802.11n/ac Modulation Analysis, 89601B/BN-BHX WLAN 802.11ax Modulation Analysis

WLAN Technology Overview

WLAN products and systems started with 802.11b, 802.11g and 802.11a standard amendments, all of which provided throughput enhancements over the original 802.11 standard introduced in 1997. To meet the requirements of new applications and the need for higher data rates, WLAN technology continued to evolve by integrating the latest technologies. The goal was clear: to continuously improve spectrum utilization, throughput and user experience. 802.11n, the High Throughput (HT) amendment to the 802.11 standard, improved throughput through the adoption of Single-User Multiple-Input Multiple-Output (SU-MIMO) with up to 4 spatial streams and wider bandwidth (40 MHz). This improvement was further extended in 802.11ac, the Very High Throughput (VHT) amendment to the 802.11 standard, with new and enhanced technologies including up to 8x8 SU-MIMO, wider channel bandwidth (up to 160 MHz), new downlink Multi-User MIMO (MU-MIMO) technology, and 256-QAM modulation.

While still in the early stages of development, the next-generation 802.11 standard, 802.11ax or High Efficiency (HE) WLAN, is taking things one step further. 802.11ax promises to add significantly higher efficiency, capacity and coverage for a better user experience, especially for dense deployment scenarios in both indoor and outdoor environments (e.g., stadiums, airports and shopping malls). Unlike 802.11ac, 802.11ax operates in both 2.4- and 5-GHz bands and employs technology building blocks like Orthogonal Frequency Division Multiple Access (OFDMA) for high efficiency, 8x8 MU-MIMO for high capacity, and uplink scheduling for increased capacity, efficiency and better user experience. Other technologies, such as 1024-QAM modulation, are used to improve throughput.

802.11ax devices will be required to be backward compatible and coexist with legacy IEEE 802.11 devices operating in the same band. Table 1 compares key physical layer (PHY) technologies of 802.11n, ac and ax.

IEEE 802.11ax Overview

As previously mentioned, 802.11ax introduces various new technologies. This brief overview focuses solely on transmit modes, or PPDU formats, and the multi-user technologies—OFDMA and MU-MIMO—used in 802.11ax. PPDU Formats

There are four different transmit modes, known as physical layer convergence procedure (PLCP) protocol data unit (PPDU) formats, defined for 802.11ax. These modes include: HE SU PPDU, HE extended-range SU PPDU, HE MU PPDU, and HE trigger-based Uplink (UL) PPDU. Each is used as follows:

• HE SU PPDU format is used when transmitting to a single user.
• HE extended range SU PPDU format is used when transmitting to a single user, but further away from the Access Point (AP) such as in an outdoor scenario.
• HE MU PPDU format is used when transmitting to one or more users. It is similar to SU format, except that an HE-SIG-B field is present.
• HE trigger-based PPDU format is used for uplink OFDMA and/or MU-MIMO transmission. It carries a single transmission and is sent as an immediate response to a Trigger frame sent by the AP.

The 802.11ax frame, similar to that of 802.11n and 802.11ac, starts with the preamble. The first part of the preamble consists of legacy (non-HE) training fields, while the second part is the HE preamble. The legacy portion of the preamble includes the L-STF, L-LTF and L-SIG; each is easily decodable by legacy devices and is included for backward compatibility and coexistence with the legacy devices. The HE preamble can only be decoded by 802.11ax devices.