802.11ac PHYs
What is the PHY in IEEE 802.11ac?
The PHY (Physical Layer) in 802.11ac is responsible for transmitting and receiving data over the wireless medium using advanced radio technologies.
What modulation does 802.11ac use?
802.11ac uses OFDM with modulation types including BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM for higher data rates.
What is OFDM in 802.11ac?
OFDM divides the wireless channel into multiple orthogonal subcarriers that transmit data simultaneously, improving throughput and robustness.
How many subcarriers are used in 802.11ac OFDM?
Depending on channel width, 802.11ac uses 52 subcarriers for 20 MHz channels, up to 234 subcarriers for 80 MHz, and 468 subcarriers for 160 MHz channels.
What coding technique is used in 802.11ac PHY?
It uses convolutional coding and optionally LDPC (Low-Density Parity-Check) coding for enhanced error correction.
What is LDPC in 802.11ac?
LDPC is an advanced error-correcting code that improves data reliability and throughput compared to traditional convolutional coding.
What data rates are supported by 802.11ac PHY?
802.11ac supports data rates from around 6.5 Mbps up to several Gbps depending on channel width, MIMO streams, and modulation.
Which modulation corresponds to the highest data rate in 802.11ac?
256-QAM modulation combined with multiple spatial streams and wide channels achieves the highest throughput.
What is the channel width in 802.11ac?
802.11ac supports 20 MHz, 40 MHz, 80 MHz, and optionally 160 MHz channel widths for wider bandwidth and higher speeds.
What is MU-MIMO in 802.11ac?
Multi-User MIMO allows simultaneous data transmission to multiple devices using multiple antennas, increasing network efficiency.
How many spatial streams does 802.11ac support?
Up to 8 spatial streams can be used to increase throughput, depending on device capabilities.
What is beamforming in 802.11ac?
Beamforming focuses the radio signal toward specific clients to improve signal quality and range.
What is the OFDM symbol duration in 802.11ac?
Similar to 802.11a/n, around 4 microseconds per OFDM symbol, including a guard interval.
What is the guard interval in 802.11ac?
802.11ac supports both standard 800 ns and optional short 400 ns guard intervals for reduced latency and increased throughput.
What FFT size is used in 802.11ac?
The FFT size scales with channel width: 64 points for 20 MHz, 128 for 40 MHz, 256 for 80 MHz, and 512 for 160 MHz.
How does 802.11ac PHY handle multipath effects?
OFDM, beamforming, and advanced error correction reduce multipath interference in dense environments.
Is 802.11ac PHY full-duplex?
No, 802.11ac operates in half-duplex mode like other Wi-Fi standards.
What is the PHY preamble in 802.11ac?
The preamble contains training fields used for synchronization, channel estimation, and beamforming feedback.
How does 802.11ac PHY support backward compatibility?
It supports backward compatibility with 802.11a/n devices via mixed mode operation.
Does 802.11ac use dynamic rate adaptation?
Yes, it dynamically adjusts modulation, coding, and spatial streams based on channel conditions.
What limits the range of 802.11ac?
Like 802.11a/n, 802.11ac uses 5 GHz, which has shorter range and less wall penetration compared to 2.4 GHz.
Is 802.11ac PHY widely used today?
Yes, it remains common in many modern Wi-Fi devices and access points for high-speed wireless networking.
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