802.11h PHYs
What is the PHY in IEEE 802.11h?
The PHY in 802.11h is based on the 802.11a OFDM physical layer, operating in the 5 GHz band with additional regulatory features like DFS and TPC.
Does 802.11h use a different modulation scheme than 802.11a?
No, 802.11h uses the same OFDM modulation types as 802.11a: BPSK, QPSK, 16-QAM, and 64-QAM.
What is Dynamic Frequency Selection (DFS) in 802.11h PHY?
DFS enables devices to detect radar signals and dynamically switch channels to avoid interference in the 5 GHz band.
How does Transmit Power Control (TPC) affect 802.11h PHY?
TPC adjusts the transmit power to minimize interference while maintaining link quality, complying with regional regulations.
What is the channel bandwidth used in 802.11h?
802.11h typically uses 20 MHz channels, similar to 802.11a, with channel switching based on DFS.
What is the OFDM symbol duration in 802.11h?
Each OFDM symbol is 4 microseconds long, consisting of a 3.2 microsecond data part and a 0.8 microsecond guard interval.
How many subcarriers are used in 802.11h OFDM?
52 subcarriers are used: 48 for data and 4 pilot subcarriers, identical to 802.11a.
What is the purpose of pilot subcarriers in 802.11h?
Pilots help with channel estimation and phase tracking to ensure accurate data recovery.
What coding rates are supported by 802.11h PHY?
Convolutional coding rates of 1/2, 2/3, and 3/4 are supported for error correction.
Is the PHY preamble in 802.11h different from 802.11a?
No, 802.11h uses the same short and long preambles as 802.11a for synchronization and channel estimation.
How does DFS impact PHY transmissions?
DFS requires the PHY to suspend transmissions and perform radar detection before using certain channels, ensuring regulatory compliance.
What role does the SIGNAL field play in 802.11h PHY frames?
It indicates modulation, coding rate, and payload length for proper demodulation and decoding.
Does 802.11h support variable modulation within a single PHY frame?
No, modulation and coding are fixed per PHY frame but can be adapted frame-to-frame based on link quality.
What is the guard interval in 802.11h PHY and why is it important?
The 0.8 µs guard interval prevents inter-symbol interference from multipath propagation.
How does TPC affect PHY power settings in 802.11h?
TPC algorithms adjust the transmit power dynamically to reduce interference and save energy.
Can 802.11h PHY dynamically change channels?
Yes, DFS enables automatic channel switching when radar signals are detected.
What is the FFT size used in 802.11h PHY?
A 64-point FFT is used, matching 802.11a specifications.
How does the PHY layer handle error detection in 802.11h?
Error detection is managed via convolutional coding and CRC checks at higher layers.
Is 802.11h PHY backward compatible with 802.11a?
Yes, 802.11h extends 802.11a PHY with added regulatory features but maintains full compatibility.
What is the impact of 802.11h PHY on overall network throughput?
Regulatory features like DFS can introduce delays, but PHY efficiency remains comparable to 802.11a.
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