Oct 3, 2014

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Does Wireless AP Mode Interfere With P2P mode? Can both modes be activated at the same time?

Amazon I am amazed that nobody on Google knows whether wireless AP mode and P2P mode can be operational at the same time. So I've decided to write an article about it.

When the wireless module is in AP (short for access point) mode, also known as a hotspot in an 802.11 network operating in the infrastructure mode, it means the module acts as a Wi-Fi hotspot so that wireless clients can connect to it.

When the wireless module is in P2P mode, also known as direct mode, it means the module can send data directly to another P2P device wirelessly, or can receive data directly from another P2P device wirelessly. In the context of this article, we enable P2P mode so we can use WiFi Direct.

Wi-Fi Direct is actually not an IEEE standard but a Wi-Fi Alliance technical specification called "Wi-Fi Peer-to-Peer (P2P) Specification". It allows Wi-Fi devices to connect to each other and form groups, usually one-to-one, but also one-to-many.

In order to use WiFi Direct, the wireless module must have P2P mode activated.

There are actually legitimate use cases for this. Suppose I have a monitor that allows a smartphone to use Miracast to connect to it. While the smartphone is using Miracast to mirror its screen to the monitor, I want the monitor to be an access point so that another smartphone can connect to the monitor and communicate with it.

Miracast uses WiFi Direct to work.

Let's read on to find out if a wireless module can be in both AP mode and P2P mode simultaneously.

First you need to know how AP mode and P2P mode work.

Both AP mode and P2P mode are based on the IEEE 802.11 family, and traditional WiFi and WiFi Direct have the same scan process for two devices to discover and communicate with each other. After the scan process, the WiFi Direct device would execute a new Discovery algorithm, which the traditional WiFi access point would not execute.

This difference makes it possible for both ends to recognize each other's role as an access point, a WiFi client, or as a WiFi Direct device. That's how a WiFi client will only discover WiFi access points, and a WiFi Direct device will only discover other WiFi Direct devices.

For more information on the scan sequence in traditional Wireless LANs go to http://www.cacs.louisiana.edu/~perkins/csce575/papers/80211_tutorial-veriwave.pdf.

If the Wi-Fi's hardware chipset has one physical hardware device, then the chipset can only listen on one single frequency and channel (e.g. 2.4GHz channel 6) for packets for an access point and packets for a WiFi Direct device.

This means the two signals will definitely interfere with each other, delaying the wireless transmission. However, technically speaking, it could work; a wireless module can have AP mode and P2P mode activated concurrently.

If the wireless chipset supports two physical hardware devices, then one device can listen on 2.4GHz for traditional WiFi clients, and one device can listen on 5GHz for WiFi Direct traffic. Then the two transmissions will not interfere with each other at all.

So what's the problem?

The big question is even if it is technically possible to switch on the AP mode and P2P mode of a wireless module, if no vendors manufacture such wireless modules, then there's nothing you can do about it.

Our company has sent inquiries to many Wi-Fi module vendors and they responded saying they don't carry modules that support the concurrent combination of AP mode and P2P mode.

So if you cannot find such a module and you really want this to work, simply buy two Wi-Fi modules. One will be in AP mode and the other will be in P2P mode.

The following is the Q&A section.

What frequencies does WiFi Direct operate on?

Per http://www.wi-fi.org/knowledge-center/faq/does-wi-fi-direct-work-on-80211-abgn, Wi-Fi Direct products can work on 802.11 a, g and n Wi-Fi standards. Users can match Wi-Fi Direct products just like any other Wi-Fi CERTIFIED products.

All Wi-Fi Direct devices operate in the 2.4 GHz frequency band and can connect to 802.11g and some 802.11n devices. In addition, some Wi-Fi Direct devices work in the 5 GHz frequency band to connect to 802.11a and some 802.11n devices. Many devices operate in both frequency bands.

What is WiF Direct's data rate?

Per http://www.popularmechanics.com/technology/how-to/tips/how-does-wi-fi-direct-work-12203369, Wi-Fi Direct can move data at up to 250 megabits per second.

Questions? Let me know!
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