wide area broadcast over wifi

Question

I want to find a solution to broadcast voice over WiFi for the people in a march. Since Android and IPhone is the most popular devices among the people in the march, it would be great if i can find a solution for audio broadcast over wifi with limited budget.

I know that people in occupy movement use different app on their cell, but it is not suitable in a march in my city. As the authority in my country may temporarily shutdown the data over mobile network to disable the app.

If i can develop an app to gather the broadcast message (SSID) from a powerful wifi AP with a long-length directional antenna, I should able to deliver message among the people in the march. Is it a possible solution?

Also, is it possible to modify the AP to allow any device to join the AP without further acknowledgment and broadcast message to all devices in that network?

Any idea or opinion is welcome. Many Thanks.

Answer 1

This will be difficult, especially with a large number of users. Since you only need to send audio in one direction, that will at least be a bit easier.

First, you're going to want to put that AP in the middle of the crowd with an omnidirectional antenna. Perhaps, in a backpack or something. Each phone on that network needs to "hear" when other phones are transmitting, or it will be a mess. Even though your application is one-way, 802.11 isn't.

Now, when you write your application, use UDP packets sent to the broadcast address. No need for TCP packets, as they will clog up your network anyway.

Use a simple voice codec, such as AMR. The codecs available vary from platform to platform. See this document for a list on Android: http://developer.android.com/guide/appendix/media-formats.html

Honestly, the easiest solution would be to go buy a small FM transmitter, since many phones have receivers in them anyway.