EE302 Lesson 19: Digital Communications Techniques 3

7-5: Digital Signal Processing The Basis of DSP  Once signal is digitized, it can now be manipulated by digital signal processing (DSP)  Digital signal processing (DSP) is the use of a fast digital computer to perform processing on digital signals.  Any digital computer with sufficient speed and memory can be used for DSP.

7-5: Digital Signal Processing Examples of DSP  Audio signal processing  Audio compression  Digital image processing  Video compression  Speech processing and speech recognition  Digital communications  Radar and Sonar processing  Computer generated animation  Medical imaging

7-5: Digital Signal Processing Figure 7-36: Concept of DSP

7-5: Digital Signal Processing Basis of DSP  An analog signal to be processed is fed to an A/D converter, where it is converted into a series of binary numbers and stored in a read-write random-access memory (RAM).  A program, usually stored in a read-only memory (ROM), performs mathematical and other manipulations on the data.  Most digital processing involves complex mathematical algorithms that are executed in real time.  The processing results in another set of data words which are also stored in RAM.  They can be used in digital form or fed to a D/A converter.

7-5: Digital Signal Processing DSP Applications  The most common DSP application is filtering. A DSP processor can perform bandpass, low-pass, high-pass, and band-reject filter operation. With DSP, filters can have characteristics far superior to analog filters  Data compression is a process that reduces the number of binary words needed to represent a given analog signal. If a video signal contained frequencies up to 4 MHz, the sampling rate would have to be at least 8 MHz. With an 8-bit A/D converter, 8 Mbytes/sec of data would be produced. One minute of video would require 480 Mbytes of data. Data can be compressed to 1/100 th of its original size Current algorithms for photography and video compression are MPEG-2 and MPEG-4 MP3 is a current compression algorithm for music

7-5: Digital Signal Processing DSP Applications  Spectrum analysis is the process of examining a signal to determine its frequency content. Fast Fourier Transform (FFT) permits real-time signal spectrum analysis  Signal averaging is the process of sampling a recurring analog signal transmitted in the presence of noise. The signal is repeatedly converted to digital and the average is taken. Result is a noise-free version of the signal.  Signal Synthesis it is now possible to generate a signal with any waveform Software Defined Radios (SDR) are now a reality

7-5: Digital Signal Processing Navy Next-Generation Mobile Software Radio (SDR)  Solicitation for contract closed 9 Jan 2008  Requirements: RF frequency coverage should be 2 MHz to 2 GHz continuous, with programmable bandwidths to at least 40 MHz.