A DSP based laboratory system for exploring digital communication concepts

Abstract

One problem with digital communication laboratories is the lack of flexibility. Current laboratories either use specialized equipment with little or no ability to change system parameters or extremely general equipment with limited modulation types and pulse shaping options. One solution to this problem is to use digital signal processing (DSP) techniques. DSP systems are extremely flexible and provide the ability to implement a wide range of modulation types and pulse shapes. By using complex baseband signal processing techniques and two channels of output, both one- and two-dimensional constellations can be generated. Combining the signal processing capabilities of a DSP system with a simple user interface implemented on a desktop computer provides an attractive, simple and flexible laboratory tool. This system allows the student to generate various modulation types and view the corresponding signal constellations and eye patterns on an oscilloscope. Modulated signals can be generated by connecting the system outputs to a quadrature modulator. The user interface allows the student to change the modulation type or the pulse shape with a single keystroke. This functionality provides a friendly user interface which encourages more experimentation and increases the value of the laboratory experience. This paper presents the system design and user interface. Problems encountered during the design and equipment selection criteria are discussed. Preliminary implementation results are presented.