Assignment 1

Due Date: 4/27/2016

Design a wireless acoustic communication channel on an android phone with

• Data rate – number of bits communicated per second – at least 500 bps
• Bit error rate – Ratio of the number of bits correctly received to the number of bits sent – less than 2%

 
Components

• Sender: An android app that
  • Takes a file or a short message as input and convert it to actual bits
  • Modulates the bits to a signal that can sent
  • Send the signal over an acoustic channel
• Receiver: An android app that
  • Receives the acoustic signal
  • Decodes the signal to bits
  • Display the message

 
Prerequisites

• Make sure your system has Java jdk and jre installed
• Install android studio:
  http://developer.android.com/sdk/index.html

 
Project Implementation Steps

• Sender app:
  
  Add a textbox to your app to enter a message or filename as input. Have a send button which will invoke a send function on click:
  
  
  • The send function should first convert the message or file to a bit array of 0's and 1's, and add a header. The header in this case will have the source, destination, and length of the message.
  
  
  • Then choose a frequency in which you are going to operate. The frequency available to you is 0-20 KHz, as the speaker and microphone in your phone will support only this range. However, it is wise to check the frequency response of the speaker/microphone pair and choose an appropriate frequency. Usually a frequency from 1-12 KHz will be suitable. Generate a carrier wave (Sine wave) of this frequency.
  
  
  • Write a modulate function which modulates the data bits using a modulation scheme like ASK, PSK, etc. The modulation scheme will determine your data rate.
  
  
  • You can just send the resulting signal using the speaker. However, to identify the start of the data at the receiver, your data should be preceded by a preamble. A preamble is a sequence of bits known by both the sender and the receiver. The receiver looks for the preamble and once it identifies the preamble, it decodes the data that proceeds it. A preamble is a signal that can be easily identified at the receiver. So, choose an appropriate pattern of some length as your preamble.
  
  
  • Now use the AudioTrack api to send the signal through the speaker.


• Receiver app:
  
  
  • Write a recorder using the AudioRecord api. It should record samples from the microphone and store it in a buffer.
  
  
  • Process the samples in the buffer to identify the preamble.
  
  
  • Once you identify the start of the preamble, you can start decoding the data that proceeds it. Decoding the header gives the length of the data. Then decode the entire data.
  
  
  • Convert the bits to a string and display it in a textbox.


• Sophisticated Techniques:
  
  The above steps detail the basic components for your communication channel. However, you can use more sophisticated techniques to make your channel more efficient. Here are some suggestions:
  
  At the sender:
  
  
  • Use a preamble that has a high detection accuracy, but a shorter length
  
  
  • Use a good modulation scheme to increase your data rate
  
  
  • Use better coding techniques to reduce the bit error rate at the receiver as you increase your data rate
  
  At the receiver:
  
  
  • You can design some filtering techniques to filter the environment noise
  
  
  • Do some channel estimation to improve the decoding process

 
Report

 
Extra Credit