802.11ax PHYs ============== .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the PHY in IEEE 802.11ax?** The PHY (Physical Layer) in 802.11ax is responsible for transmitting and receiving data over the wireless medium, supporting higher efficiency, multiple antennas, and advanced modulation techniques. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What modulation does 802.11ax use?** 802.11ax uses OFDMA with advanced modulation schemes including BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM, and up to 1024-QAM for higher throughput. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is OFDMA in 802.11ax?** Orthogonal Frequency Division Multiple Access (OFDMA) divides channels into smaller subchannels (Resource Units), allowing multiple users to transmit simultaneously, improving efficiency and reducing latency. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How many subcarriers are used in 802.11ax OFDM?** 802.11ax uses up to 256 subcarriers in a 20 MHz channel, compared to 52 in 802.11a, enabling finer frequency granularity and more efficient spectrum use. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What are pilot subcarriers in OFDM?** Pilot subcarriers are reference signals embedded within OFDM symbols to assist in synchronization, channel estimation, and phase tracking, similar to previous standards but optimized in 802.11ax. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What coding technique is used in 802.11ax PHY?** 802.11ax uses Low-Density Parity-Check (LDPC) codes which provide more powerful error correction and improve data reliability over convolutional codes used in 802.11a. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is convolutional coding?** 802.11ax generally replaces convolutional coding with LDPC, which offers improved error correction performance and efficiency. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is interleaving in 802.11ax?** Interleaving is used in 802.11ax to spread bits over multiple subcarriers to mitigate the effect of burst errors, similar to earlier standards but optimized for higher subcarrier counts. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What data rates are supported by 802.11ax PHY?** 802.11ax supports a wide range of data rates from under 1 Mbps up to several Gbps, depending on channel width, number of spatial streams, and modulation (up to 1024-QAM). .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Which modulation corresponds to the lowest data rate?** The lowest rates in 802.11ax use BPSK with low coding rates on narrow Resource Units. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Which data rate uses 1024-QAM?** The highest data rates in 802.11ax use 1024-QAM combined with multiple spatial streams and wide channels for maximum throughput. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the OFDM symbol duration in 802.11ax?** The OFDM symbol duration is extended to 12.8 microseconds with a 0.8 or 3.2 microsecond guard interval, to improve robustness especially in dense and multipath environments. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is a guard interval?** A guard interval in 802.11ax reduces inter-symbol interference by providing time buffers between OFDM symbols; 802.11ax supports both standard (0.8 µs) and extended (3.2 µs) guard intervals. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the FFT size used in 802.11ax?** 802.11ax uses a 256-point FFT for 20 MHz channels, allowing for increased subcarrier count and spectral efficiency. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How wide is the 802.11ax channel in MHz?** 802.11ax supports flexible channel widths of 20, 40, 80, and 160 MHz, enabling scalable throughput. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Why is OFDM suitable for 5 GHz PHY in 802.11ax?** OFDM, combined with OFDMA and longer guard intervals, effectively handles multipath and interference common in dense 5 GHz deployments, improving efficiency. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Is the 802.11ax PHY half-duplex or full-duplex?** 802.11ax PHY is still half-duplex, but it introduces uplink and downlink OFDMA for simultaneous transmissions on different subchannels. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Does 802.11ax PHY support MIMO?** Yes, 802.11ax supports MU-MIMO (Multi-User MIMO) for both uplink and downlink, allowing multiple clients to communicate simultaneously using multiple antennas. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the function of the PHY preamble in 802.11ax?** The preamble includes multiple training fields for synchronization, channel estimation, and spatial stream training, optimized for OFDMA and MU-MIMO. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the SIGNAL field in the PHY header?** The SIGNAL field conveys modulation, coding, resource allocation, spatial streams, and length information, allowing dynamic adaptation per user. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the service field in 802.11ax PHY?** The service field is used for scrambler initialization and reserved for future enhancements, similar to prior standards. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the tail field in PHY?** The tail field terminates the LDPC decoder state, aiding in accurate error correction. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Can PHY parameters change dynamically in 802.11ax?** Yes, 802.11ax features dynamic modulation, coding, resource unit assignment, and spatial stream adjustments based on real-time channel conditions. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How does 802.11ax handle multipath effects?** Longer OFDM symbols and guard intervals, combined with advanced channel estimation, reduce multipath interference significantly. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What limits the range of 802.11ax PHY?** Like earlier 5 GHz standards, range is limited by higher frequency propagation characteristics, though advanced coding and MIMO improve effective range. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Does PHY impact latency in 802.11ax?** PHY efficiency improvements, especially OFDMA and MU-MIMO, reduce latency by allowing simultaneous transmissions and better resource allocation. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is spectral efficiency in PHY terms?** Spectral efficiency is greatly enhanced in 802.11ax through higher order modulations, OFDMA, MU-MIMO, and flexible channel widths. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How does PHY relate to MAC in 802.11ax?** PHY transmits data over the air, while MAC manages resource allocation, scheduling, and coordination to leverage PHY’s advanced features like OFDMA and MU-MIMO. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Is the 802.11ax PHY backward compatible?** Yes, 802.11ax PHY is backward compatible with earlier standards (802.11a/b/g/n/ac), allowing operation on the same bands with fallback modes. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Is 802.11ax PHY still used today?** Yes, 802.11ax is the current mainstream Wi-Fi PHY, widely deployed for its improvements in throughput, efficiency, and dense environment performance. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`Reference links ` .. _phy_step17: .. tab-set:: .. tab-item:: Reference links * Reference links