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I'm able to use Wi-Fi to connect a Windows PC to a smart TV (Android-based). I does that while the PC is connected to the WLAN but the TV is neither connected to Ethernet nor to the WLAN.

--> I'm wondering how does the PC open a Wi-Fi connection with the TV.

  • The PC documentation just says: To use a wireless display, ensure that both your computer and the external display support the Miracast feature. A snake biting its tail.

  • Windows documentation says: On your PC, make sure Wi-Fi is turned on and indicate a Miracast connection can be set with shortcut Win-K.

  • The TV documentation doesn't describe the Android-based functions and has just a legal mention about "Miracast" and "Wi-Fi" being trademarks, but no explanation and no other occurrence of Miracast.

Does the PC use a second Wi-Fi adapter? Does it mean the PC has some pre-requirements to perform such mirroring/casting? Or does it share the same Wi-Fi adpater and some form of multiplexing between two Wi-Fi connections?

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  • try to create a hotspot on your PC and then connect your TV to it with the administrative command netsh wlan start hostednetwork on cmd
    – Dong Li
    Commented May 31 at 12:33
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    @FrankThomas Miracast is over Wi-Fi. In fact the Wi-Fi Alliance is who now certifies Miracast implementations. Bluetooth is a separate radio technology than Wi-Fi, and requires separate radio hardware. Bluetooth's radio layer barely has enough bandwidth for stereo audio (A2DP), so there's no way it can do video. Some laptops have combo wireless modules that contain both a Wi-Fi radio chipset and a Bluetooth radio chipset on the same M.2 module, but that's just a convenience to support coexistence and antenna-sharing, and it isn't required by Windows or any other OS.
    – Spiff
    Commented May 31 at 16:33

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Miracast was a technology the Wi-Fi Alliance once promoted for transmitting video over a LAN or over a Wi-Fi Direct link.

Wi-Fi Direct was a way to make direct device-to-device radio connections between Wi-Fi capable devices, without requiring them to be on the same Wi-Fi network, and without requiring either of them to leave the Wi-Fi network they're on. That is, it could multiplex the Wi-Fi radio so that it could maintain your connection to your WLAN while simultaneously making a direct radio connection to the other Wi-Fi Direct device. In the case of Miracast, that Wi-Fi Direct link was typically between a laptop and a nearby smart TV, and video was streamed from the laptop to the TV over that link.

For more information about Miracast and Wi-Fi Direct, including, last time I checked, a searchable database of products which have been certified as supporting those and other Wi-Fi-related technologies, see the Wi-Fi Alliance.

It seems to me that Miracast struggled to find a sustainable market niche. Multiplexing Wi-Fi radios was hard to get right, so interoperability was always a frustrating disappointment. Big players like Google and Apple wanted to provide more reliable, less frustrating user experiences even if it meant sacrificing interoperability, so they focused on fixing what they had the power to fix, which meant refining their own proprietary ecosystem technologies like Chromecast and AirPlay.

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    @mins I seem to recall Miracast was originally developed as a proprietary or semi-proprietary technology by one or a small handful of vendors, and was then taken to the Wi-Fi Alliance. I don't think it was ever developed or controlled by an open standards body, just semi-proprietary corporate consortia like the Wi-Fi Alliance. If the specification has been openly published, you'd probably have to get it from the Wi-Fi Alliance.
    – Spiff
    Commented May 31 at 16:58
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    @mins Wi-Fi Direct is neither traditional BSS nor IBSS mode. It's its own thing. It was specifically designed to allow you to make direct device-to-device radio links between devices that might be on different BSSes or even different network altogether, without making either device leave whatever network they are on.
    – Spiff
    Commented May 31 at 17:41
  • Thanks for your clear explanations, I appreciate. I found a good document on Wi-Fi Direct and the link with Miracast. It seems there is a requirement for the PC to be compatible with Wi-Fi Direct, but no special requirement for the other participants to the direct link. This requirement is to be able to play the role of "Group Owner", that is to emulate some access point functions in software.
    – mins
    Commented May 31 at 17:59

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