802.11h 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 802.11h?** 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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How many subcarriers are used in 802.11h OFDM?** 52 subcarriers are used: 48 for data and 4 pilot subcarriers, identical to 802.11a. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the purpose of pilot subcarriers in 802.11h?** Pilots help with channel estimation and phase tracking to ensure accurate data recovery. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How does DFS impact PHY transmissions?** DFS requires the PHY to suspend transmissions and perform radar detection before using certain channels, ensuring regulatory compliance. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How does TPC affect PHY power settings in 802.11h?** TPC algorithms adjust the transmit power dynamically to reduce interference and save energy. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Can 802.11h PHY dynamically change channels?** Yes, DFS enables automatic channel switching when radar signals are detected. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What is the FFT size used in 802.11h PHY?** A 64-point FFT is used, matching 802.11a specifications. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How does the PHY layer handle error detection in 802.11h?** Error detection is managed via convolutional coding and CRC checks at higher layers. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Is 802.11h PHY backward compatible with 802.11a?** Yes, 802.11h extends 802.11a PHY with added regulatory features but maintains full compatibility. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`Reference links ` .. _phy_80211h_step17: .. tab-set:: .. tab-item:: Reference links * Reference links