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 ProcessingExamples 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 ProcessingBasis 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 ProcessingDSP 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 1/100th 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.