802.11u PHYs
==============

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        **What is the PHY layer in IEEE 802.11u?**

        The PHY layer in 802.11u defines the physical transmission method for data over the wireless medium, typically based on existing 802.11 PHYs.

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        **Does 802.11u introduce a new PHY?**

        No, 802.11u extends MAC and higher layers but uses PHYs defined in other 802.11 standards like 802.11a/b/g/n/ac.

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        **Which frequency bands do 802.11u PHYs operate in?**

        PHYs used by 802.11u operate in 2.4 GHz and 5 GHz bands, depending on the underlying 802.11 standard.

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        **What modulation schemes are supported by PHYs in 802.11u?**

        Modulation depends on the underlying PHY; common schemes include DSSS, OFDM, BPSK, QPSK, QAM variants.

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        **Does 802.11u support OFDM PHY?**

        Yes, 802.11u can use OFDM PHYs, as defined in 802.11a/g/n/ac standards.

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        **What is the typical channel bandwidth for PHYs under 802.11u?**

        Channel bandwidths vary from 20 MHz to 160 MHz, depending on the PHY (e.g., 802.11n uses 20/40 MHz).

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        **How does PHY impact 802.11u performance?**

        PHY characteristics like modulation, coding, and bandwidth determine throughput and range for 802.11u communications.

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        **Are 802.11u PHYs compatible with legacy devices?**

        PHY compatibility depends on the underlying standard; 802.11u works with PHYs that may support backward compatibility.

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        **Can 802.11u PHYs support MIMO?**

        Yes, if the underlying PHY (like 802.11n or ac) supports MIMO, then 802.11u benefits from it.

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        **What is the role of PHY in 802.11u roaming and network selection?**

        PHY provides the basic connectivity, while 802.11u extends higher layers for roaming decisions; good PHY quality improves user experience.

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        **Does 802.11u define power levels for PHY transmissions?**

        No, power levels follow regional regulations and PHY specifications of the underlying 802.11 standard.

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        **Are PHY parameters dynamically adjustable in 802.11u?**

        Dynamic adjustment is handled by the PHY and MAC layers of the underlying 802.11 standard, not specifically by 802.11u.

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        **Which PHY rate adaptation methods work with 802.11u?**

        Rate adaptation algorithms are PHY-specific, and 802.11u uses those defined in the underlying PHY standard.

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        **Does 802.11u support multiple PHY types simultaneously?**

        Yes, 802.11u can operate over different PHYs, depending on the hardware and network configuration.

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        **What PHY layer error correction is used in 802.11u?**

        Error correction follows the underlying PHY’s methods, such as convolutional coding and LDPC in newer standards.

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        **How does PHY layer affect 802.11u's quality of service?**

        Higher PHY data rates and reliability improve QoS by enabling faster, more stable connections.

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        **Is PHY layer security enhanced in 802.11u?**

        Security enhancements are primarily at MAC and higher layers; PHY layer security is inherited from the underlying PHY standard.

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        **What PHY parameters are critical for 802.11u interworking with cellular networks?**

        Frequency bands, modulation schemes, and channel bandwidth must be compatible for seamless handoff and interoperability.

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        **Can 802.11u PHY support fast handoffs?**

        Fast handoffs rely on PHY speed and MAC protocols; faster PHYs help reduce delay during handoff procedures.


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        Topics in this section,

                * :ref:`Reference links <phy_u_step17>`


.. _phy_u_step17:

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    .. tab-item:: Reference links

       * Reference links