Audio Network

Data transmission over sound waves written in JavaScript without any dependencies. All you need is just microphone, speakers and the browser!

If you want to try AudioNetwork by yourself I would recommend to first open Demo - simple because Demo - full features might be little scary for the first time. You can also watch YouTube video that shows how to transmit data over sound between two laptops:

This project is still under development. Documentation is also planned but... little later :)

How can I transmit something over sound?

First of all you need to have two devices. One for sending, one for receiving data. It should work with any device (PC, Mac, tablet, smartphone) with browser that supports Web Audio API. Next you need to open Demo - simple at both devices and follow steps below:

[Receiver] - Before you load demo page you need to be quiet :) Receiving device needs to listen to 'silence' around you when there is no signal in the air. It's indicated by IDLE_INIT state and it ends when FIRST_SYNC_WAIT state will come. If you fell that your silence wasn't good enough you can always use RESET button to start again.
[Transmitter] - All you need to do is to click on SYNC button.
[Receiver] - When SYNC transmission is in progress state should change to FIRST_SYNC. After about 2 seconds it should switch to IDLE. At this point we are ready to send some data!
[Transmitter] - Now you can put some data to textarea and click on Send packet button. After short moment your data will appear on the receiver's side.

By default PSK-2 modulation is used so you can use only symbols 0 and 1 but it's enough to send data bit by bit. For example to send ASCII a character (0x61) you need to put inside textarea 0 1 1 0 0 0 0 1. Please remember to always put one space between each symbol but whole text needs to be without trailing and leading spaces.

If at any point you will see FATAL_ERROR state you need to click on RESET button and start all points again.

AudioNetwork needs raw microphone output without any filter applied. You can verify that by opening Sound settings in your operating system. When you enter your microphone properties you might need to un-check all filters. The worst scenario is when your microphone has some hardware filter that you can't disable. In this case you need to throw it away and buy a new one ;)

How to add sound transmission to my project?

Audio Network is available at GitHub and npm so you can just run one of the commands below:

git clone https://github.com/robertrypula/AudioNetwork.git
cd AudioNetwork
npm install
gulp serve

npm install audio-network

In both cases at build directory you will find minified and unminified js file with whole library. Pick one and include it into your HTML file. For example:

<script src="node_modules/audio-network/build/audio-network-v1.0.4.min.js"></script>

Now you can access AudioNetwork object at global JavaScript scope. It's the entry point for all components:

var physicalLayer, transmitAdapter, receiveAdapter;

physicalLayer = new AudioNetwork.PhysicalLayer.PhysicalLayer({
    // config
}),
transmitAdapter = new AudioNetwork.PhysicalLayerAdapter.TransmitAdapter(physicalLayer),
receiveAdapter = new AudioNetwork.PhysicalLayerAdapter.ReceiveAdapter(physicalLayer);

Below you can find Demo - simple source code:

html
js

To work properly Web Audio API requires running your HTML file via web server (http://localhost...) like Apache or some Node stuff like gulp-webserver (I'm using it and it works great). In case of local machine normal http connection would work. Unfortunately when you will want to go live you have to provide https. It's because in some browsers accessing microphone is not allowed when site is not hosted over https. You can read more about this here

In case you are curious about long namespaces: Under the hood AudioNetwork works on simple Injector implementation. For example AudioNetwork.PhysicalLayer.PhysicalLayer is just alias for AudioNetwork.Injector.resolve('PhysicalLayer.PhysicalLayer'). Other public classes/services that have aliases you can find here

More about full features demo

Full feature demo is growing with AudioNetwork library core. It's developer sandbox for all new features.

Demo is divided into two sections - Receive and Transmit (blue bar with white text). You can show or hide stuff by clicking on View type buttons at Initialize section.

Receive section

Here you can find lots of information like input spectrum, constellation diagrams, power chart.

At Receive section you can also check current status of ReceiveAdapter.

ReceiveAdapter is wrapper for lower level PhysicalLayer's object rx events.

The most important thing in this adapter is its state. You can find it at the top of the orange box (capital letters text like IDLE_INIT, FIRST_SYNC_WAIT, etc). Other important area to look is output of RX adapter - PACKETS. Here you can find any potential packet that will be found in the air. I wrote potential because integrity of incoming packets is not verified so some of them might be corrupted. It's because it's not PhysicalLayer responsibility to deal with it. In some future release of AudioNetwork packet verification will be added. This would be in next layer in the network stack - DataLinkLayer (like in OSI model).

Orange box is kind of developer debug box - it will be replaced to some nicer UX in the future...

Transmit section

At Transmit section there is not that much as at Receive section. You will find there only few buttons to send SYNC signal, PACKET and individual symbols (0, 1, ...). Number of unique symbols is determined by PSK symbol size (you need to switch view type to Complex to see that). At Packet textarea please remember to always put one space between each symbol but whole text needs to be without trailing and leading spaces.

Features

Dependency free library
Unit test friendly. Build-in Dependency Injector (tests are planned in the future)
Multiple channel support for parallel transmission without collisions
OFDM (Orthogonal Frequency-Division Multiplexing) support per each channel. This helps to save bandwidth and pack more data into one burst. It's the same technique as used in many existing standards like LTE, Wi-Fi, DAB, DVB.
Constellation Diagram, that helps to easily verify phase and amplitude of carrier frequency in the realtime.
Spectrum Analyzer of incoming signal is based on AnalyserNode for Web Audio API.
Adapter classes (ReceiveAdapter and TransmitAdapter) that acts as easy-to-use wrappers over raw PhysicalLayer class with lower level tx and rx methods. If you want you can also write your own adapter class and attach PhysicalLayer to it. AudioNetwork is shipped with PSK adapters but you can write any other modulation like PWM.
ReceiveAdapter internally has state machine with states listed here. The idea is to extract potential packets from raw carrier details data that rx method provides.
Auto phase correction. PSK modulation is ultra sensitive to frequency offsets. Even if transmitter and receiver frequencies are de-tuned by 0.05 Hz it will rotate symbol at constellation diagram every 20 seconds. It means that we will not be sure what symbol we are reading. Fortunately Adapter classes adds SyncPreamble (symbol with zero phase offset relative to reference) before each packet. ReceiveAdapter takes that SyncPreamble and restores symbol alignment before each packet. During packet transmission it may still rotate but at least at the beginning of the packet symbols are aligned at both sides - sender and receiver
Auto frequency correction. Similar to point above. PSK is ultra sensitive to frequency offsets so basically we need to fine-tune receiver to sender. This feature looks how fast constellation point rotates and corrects receiver's reference carrier frequency to minimize this effect.
Auto detection of signal and noise levels. ReceiveAdapter after reset first listens to ambient noise to set averageIdlePower (during IDLE_INIT state). Then it waits for sender for synchronization signal which is basically symbol zero transmitted for few seconds. During sync transmission receiver stores averageFirstSyncPower at FIRST_SYNC state. After those steps receiver calculates powerThreshold and it's ready for packets from sender. All above is needed to propperly determine signal and noise power levels. Without it we will not be able to decode packet.

Known limitations

Currently Guard Interval needs to be few times longer than Symbol Duration (two or tree times longer). It's because ReceiveAdapter, when restoring packet symbols, is 'clocked' by carrier frequency power changes.

Few more words about the project

Internally AudioNetwork library uses Web Audio API for retrieving audio data from the microphone and sending audio data to the speakers. To be more precise it is using ScriptProcessorNode. ScriptProcessorNode fires event when new portion of samples arrives (from mic) or new portion of samples is required (for speakers). Basically AudioNetwork library is analysing/providing raw arrays of sound samples inside audio events handlers. In other words all DSP is performed by internal AudioNetwork's classes or services written in pure JavaScript.

Apart from ScriptProcessorNode two other Web Audio API nodes were used. First was GainNode for connecting other nodes together and the second was AnalyserNode. AnalyserNode was used only to show some 'nice' visual stuff to the user. We can switch between time domain (to see raw samples) and frequency domain (spectrum analyzer like on FM radio display). It's optional and not required when we want to just send or receive data.

If somebody is familiar with Web Audio API one question may now come - why I didn't use OscillatorNode for sound generation or AnalyzerNode's FrequencyData output for detecting carrier frequencies? Well... I could, but the main goal for this project was to use PSK (Phase Shift Keying) modulation to send/receive data and learn a bit about modern wireless communication techniques. Those two goals even forced me to write everything from scratch because AnalyserNode's frequency domain data output (it is using FFT - Fast Fourier Transform) provides only amplitude information without any phase information. It turned out that the only way to achieve PSK modulation was to implement own Discrete Fourier Transform with amplitude/phase or use some DSP library. I wanted to dig into the details so I picked the first option :) Wikipedia about DFT looks ultra scary but in the code there is no rocket science. Basic implementation of Discrete Fourier Transform is very simple. We will not find there any mathematical tricks like used in FFT. If you don't believe me, check this class CarrierRecovery.

There's no rose without a thorn... CarrierRecovery class code is simple but when we would like to create more of its instances, to have more carrier frequencies, we will reduce overall performance pretty fast. It is not good but at least it's closer to KISS design principle ;)

Licence

The MIT License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

tushroy/AudioNetwork