Digital Acoustic Software Radio

This website is designed to be used as a tool for learning about digital communication systems. It introduces the concepts behind digital acoustic software radio and explains how to acoustically characterize a room, how the modulator and demodulator work, and how to measure the performance of a communication system. The website also provides access to the Matlab code used in the project and to sample data transmission audio files.

What is Digital Acoustic Software Radio?

The term "Digital Acoustic Software Radio" refers to a broad class of communication techniques, the specific channel, and the implementation methodology of the communication system. The first broad category of techniques is analog communication, which includes amplitude modulation (AM) and frequency modulation (FM). Techniques such as binary phase shift keying and binary frequency shift keying fall into the second broad category, digital communication. In the case of digital techniques, a sequence of binary numbers are transmitted by taking a base signal varying certain parameters, such as the signal phase or the signal frequency. The channel of a communication system refers to the medium through which the signal is transmitted. An acoustic channel uses sound waves in the audible spectrum range of 100 Hz to 20,000 Hz to transmit the data signal. The implementation methodology refers to the architecture of the communication transceiver itself. In the past, communication systems have been implemented using specialized analog hardware components. The majority of a software radio system is implemented either with software or reconfigurable digital hardware.

Why Software Radio?

Traditionally, communication transceivers were implemented using custom analog hardware. This is costly and essentially a one shot approach as new hardware is needed for different transmission techniques. In the last few years there has been a move toward replacing as much of the analog hardware as possible with either software or reconfigurable digital hardware. The key tenet behind this movement is reusability. Software and digital hardware is easier to reuse and modify than analog hardware. To utilize a new communication technique the system merely has to be reprogrammed, not replaced. With the advent of very fast and very cheap DSP's and other off the shelf digital components, software radio has become feasible.

Why Acoustic?

Transmitting the signals acoustically has two distinct advantages over using a traditional electromagnetic communication link. First, acoustic waves can be broadcast and received through standard computer sound cards, speakers, and microphones whereas using electromagnetic waves requires the use of antennas and at least some specialized analog hardware. By using sound waves, the entire system can be implemented by nearly everyone as sound cards and speakers come standard with most computers. Second, using audible transmissions enhances the study of communication systems. The students can literally hear how the different communication techniques affect the transmitted signal and, because acoustic waves can be scaled directly to RF waves, students learn about the nature of RF waves simultaneously.

Why Digital?

A previous project focused on implementing analog communication techniques using acoustic software radio. That team covered the major analog techniques, amplitude modulation and frequency modulation. This project focuses entirely on digital communication techniques. Fundamentally, digital communication has a number of advantages over analog communication. These include the ability to use repeater stations without accumulating noise, the ability to detect and correct errors, and the ability to encrypt data. Digital also offers a richer source of communication techniques from which to choose, increasing the opportunities to learn.

Who was Involved?

This project was completed to satisfy the MQP requirements of the Worcester Polytechnic Institute in Worcester, Massachusetts. The team consisted of three undergraduate students majoring in Electrical and Computer Engineering. The students were David Bresnick, Ian Ferguson, and Meggan Marcantonio. The project was advised by Professor Donald R. Brown.

What Equipment was Used?

The software modules were coded using Matlab 7 and run on two Dell Inspiron 6800 laptops (1.70 GHz Intel Pentium M, 512 MB of RAM). All audio playing and recording were done via M-Audio FireWire 410 external sound cards. Alesis M1 Active speakers broadcast the audio signals and a AKG C414 B-ULS omni-directional microphone. Additionally, two Belkin F6H500 battery backup systems were used to remotely power the communication system and two carts were used to transport the equipment.

What is an MQP?

The Major Qualifying Project (MQP) is a part of the Worcester Polytechnic Institute Plan. The goal of the MQP is to "demonstrate application of the skills, methods, and knowledge of the discipline to the solution of a problem that would be representative of the type to be encountered in one's career" (WPI 2004-2005 Undergraduate Catalog).