+
+
+
Data Over Audio
+
+
+
+
+
+
Data Over Audio
+
-
+
+
\ No newline at end of file
diff --git a/index.js b/index.js
index 07ca2f6..7122175 100644
--- a/index.js
+++ b/index.js
@@ -14,6 +14,7 @@ var MAX_BITS_DISPLAYED_ON_GRAPH = 9;
var MAX_DATA = 300;
var pauseTimeoutId;
var sampleIntervalId;
+var HAMMING_ERROR_CORRECTION = true;
// 20 to 20,000 - human
var TEXT_TO_SEND = "Hello World!";
@@ -36,6 +37,7 @@ var PAUSE_AFTER_END = true;
var PACKET_SIZE_BITS = 10;
const packetBits = [];
+const packetDecodedBits = [];
let packetDataByteCount = -1;
function handleWindowLoad() {
@@ -49,6 +51,11 @@ function handleWindowLoad() {
sentDataTextArea = document.getElementById('sent-data');
samplesPerBitLabel = document.getElementById('samples-per-bit');
document.getElementById('pause-after-end').checked = PAUSE_AFTER_END;
+ document.getElementById('error-correction-hamming').checked = HAMMING_ERROR_CORRECTION;
+ document.getElementById('error-correction-hamming').addEventListener('change', event => {
+ HAMMING_ERROR_CORRECTION = event.target.checked;
+ showSpeed();
+ })
document.getElementById('pause-after-end').addEventListener('change', event => {
PAUSE_AFTER_END = event.target.checked;
if(!PAUSE_AFTER_END) resumeGraph();
@@ -131,6 +138,47 @@ function showSpeed() {
document.getElementById('bits-per-duration').innerText = bitsPerSegment;
document.getElementById('data-transfer-speed-bits-per-second').innerText = baud.toFixed(2);
document.getElementById('data-transfer-speed-bytes-per-second').innerText = bytes.toFixed(2);
+ if(HAMMING_ERROR_CORRECTION) {
+ const effectiveBaud = baud * 4 / 7;
+ const effectiveBytes = effectiveBaud / 8;
+ document.getElementById('effective-speed-bits-per-second').innerText = effectiveBaud.toFixed(2);
+ document.getElementById('effective-speed-bytes-per-second').innerText = effectiveBytes.toFixed(2);
+ } else {
+ const effectiveBaud = baud;
+ const effectiveBytes = effectiveBaud / 8;
+ document.getElementById('effective-speed-bits-per-second').innerText = effectiveBaud.toFixed(2);
+ document.getElementById('effective-speed-bytes-per-second').innerText = effectiveBytes.toFixed(2);
+ }
+}
+function nibbleToHamming(nibble) {
+ if(nibble.length !== 4) return [];
+ return [
+ nibble[0] ^ nibble[1] ^ nibble[3],
+ nibble[0] ^ nibble[2] ^ nibble[3],
+ nibble[0],
+ nibble[1] ^ nibble[2] ^ nibble[3],
+ nibble[1],
+ nibble[2],
+ nibble[3]
+ ]
+}
+function hammingToNibble(hamming) {
+ if(hamming.length !== 7) return [];
+ const error_1 = hamming[0] ^ hamming[2] ^ hamming[4] ^ hamming[6];
+ const error_2 = hamming[1] ^ hamming[2] ^ hamming[5] ^ hamming[6];
+ const error_3 = hamming[3] ^ hamming[4] ^ hamming[5] ^ hamming[6];
+ let error = (error_3 << 2) | (error_2 << 1) | error_1;
+ if(error !== 0) {
+ // don't mutate the array
+ hamming = hamming.slice();
+ hamming[error - 1] ^= 1; // flip
+ }
+ return [
+ hamming[2],
+ hamming[4],
+ hamming[5],
+ hamming[6]
+ ];
}
function getFrequency(bit) {
@@ -175,9 +223,19 @@ function sendBits(bits) {
.padStart(PACKET_SIZE_BITS, '0')
.split('')
.map(Number);
+
bits.unshift(...packetLength);
logSent(bits.join(''));
+ if(HAMMING_ERROR_CORRECTION) {
+ const encodedBits = [];
+ for(let i = 0; i < bits.length; i+= 4) {
+ const nibble = bits.slice(i, i + 4);
+ while(nibble.length < 4) nibble.push(0);
+ encodedBits.push(...nibbleToHamming(bits.slice(i, i + 4)));
+ }
+ bits = encodedBits;
+ }
var audioContext = getAudioContext();
const channels = getChannels();
const oscillators = [];
@@ -387,21 +445,36 @@ function processSegmentReceived() {
packetBits.push(...bitValues);
- if(packetBits.length >= 10) {
+ const encodingRatio = HAMMING_ERROR_CORRECTION ? 7/4 : 1;
+ if(HAMMING_ERROR_CORRECTION) {
+ packetDecodedBits.length = 0;
+ for(let i = 0; i < packetBits.length; i += 7) {
+ const hamming = packetBits.slice(i, i + 7);
+ const nibble = hammingToNibble(hamming);
+ packetDecodedBits.push(...nibble);
+ console.log(i, hamming, nibble);
+ }
+ } else {
+ packetDecodedBits = packetBits;
+ }
+
+ if(packetDecodedBits.length >= 10) {
// we can evaluate how many bytes are comming
- const dataLengthIndex = Math.floor(10 / channelCount);
+ const encodedBitsNeeded = Math.ceil(10 * encodingRatio);
+ const dataLengthIndex = Math.floor(encodedBitsNeeded / channelCount);
if(dataLengthIndex === segmentIndex) {
// we just got the bits we needed
- packetDataByteCount = 1 + packetBits
+ packetDataByteCount = 1 + packetDecodedBits
.slice(0, PACKET_SIZE_BITS)
.reduce((value, bit) => (value << 1) | bit);
+ document.getElementById('decoded-byte-count').innerText = packetDataByteCount;
// let's get the end time
- const totalBits = (packetDataByteCount * 8) + PACKET_SIZE_BITS;
+ const totalBits = Math.ceil(((packetDataByteCount * 8) + PACKET_SIZE_BITS) * encodingRatio);
const segments = Math.ceil(totalBits / channelCount);
const duration = segments * FREQUENCY_DURATION;
const streamEnded = streamStarted + duration;
console.log({
- tenBitNum: packetBits
+ tenBitNum: packetDecodedBits
.slice(0, PACKET_SIZE_BITS).join(''),
packetDataByteCount,
PACKET_SIZE_BITS,
@@ -419,7 +492,7 @@ function processSegmentReceived() {
});
}
// remove phantom bits
- const totalBits = (packetDataByteCount * 8) + PACKET_SIZE_BITS;
+ const totalBits = Math.ceil(((packetDataByteCount * 8) + PACKET_SIZE_BITS) * encodingRatio);
if(packetBits.length > totalBits) {
const excess = packetBits.length % totalBits;
packetBits.length = totalBits;
@@ -427,7 +500,15 @@ function processSegmentReceived() {
}
}
- received(bitValues.join('') + '\n');
+ document.getElementById('decoded-data').value = packetDecodedBits.reduce((all, bit, i) => {
+ if(i !== 0 && i % 8 === 0) return all + ' ' + bit;
+ return all + bit;
+ }, '');
+ document.getElementById('received-data').value = packetBits.reduce((all, bit, i) => {
+ if(i !== 0 && i % 8 === 0) return all + ' ' + bit;
+ return all + bit;
+ }, '');
+
}
function resetGraphData() {
frequencyOverTime.length = 0;