filtering

DSP Trick: Filtering in QAM transmitters and receivers

Subject: Re: DSP Tricks
From: Allan Herriman
Date: 1999/04/22
Newsgroups: comp.dsp
THIS WORK IS PLACED IN THE PUBLIC DOMAIN

Name: Filtering in QAM transmitters and receivers. When *NOT* to do what the textbooks tell you to do.

Category: Hardware architecture, or implementation

Application: QAM receivers (with hardware emphasis)

Advantages: The textbook descriptions of QAM receivers sometimes miss practical details. "Optimal" solutions may not be the best ones...

DSP Trick: FIR Filtering in C

Subject: DSP Trick: Filtering
From: rainer.storn@infineon.com
Date: 1999/04/21
Newsgroups: comp.dsp
THIS WORK IS PLACED IN THE PUBLIC DOMAIN

Name: Filtering in C

Category: Programming Trick

Application: FIR-Filtering

Advantages: Simple and fast

Introduction:

This is more like a trick in C but might also be applicable in DSP environments. It allows to compute FIR-filtering in a fast manner when the filter length contains a factor of, let's say 4 (other factors are also possible).

Filtering Tricks

Interpolation

3.1 Basics

3.1.1 What are "upsampling" and "interpolation"?

"Upsampling" is the process of inserting zero-valued samples between original samples to increase the sampling rate. (This is called "zero-stuffing".) Upsampling adds to the original signal undesired spectral images which are centered on multiples of the original sampling rate.

Decimation

2.1 Basics

2.1.1 What are "decimation" and "downsampling"?

Loosely speaking, "decimation" is the process of reducing the sampling rate. In practice, this usually implies lowpass-filtering a signal, then throwing away some of its samples.

"Downsampling" is a more specific term which refers to just the process of throwing away samples, without the lowpass filtering operation. Throughout this FAQ, though, we'll just use the term "decimation" loosely, sometimes to mean "downsampling".

Multirate Basics

1.1 What does multirate mean?

Multirate simply means "multiple sampling rates". A multirate DSP system uses multiple sampling rates within the system. Whenever a signal at one rate has to be used by a system that expects a different rate, the rate has to be increased or decreased, and some processing is required to do so.

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