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COMPRESSION AND RELIABLE TRANSMISSION OF CONTINUOUS DATA SIGNALS

IP.com Disclosure Number: IPCOM000007680D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-15
Document File: 5 page(s) / 277K

Publishing Venue

Motorola

Related People

Kevin Baum: AUTHOR [+3]

Abstract

A common problem encountered in digitizing an analog signal is minimizing the bandwidth required to accurately represent the signal. This min- imization process is generally referred to as data compression.

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MO7VROLA Technical Developments

8

COMPRESSION AND RELIABLE TRANSMISSION OF CONTINUOUS DATA SIGNALS

by Kevin Baum, Christopher Clanton and Jeff Smolinske

PROBLEM SOLVED BY THE INVENTION

  A common problem encountered in digitizing an analog signal is minimizing the bandwidth required to accurately represent the signal. This min- imization process is generally referred to as data compression.

  Many algorithms have been developed specili- tally for the purpose of compressing speech signals, such as Adaptive Differential Pulse Code Modula- tion (ADPCM) and Linear Predictive Coding (LPC) techniques. Unfortunately, these algorithms can rarely provide an accurate representation of data signals, such as those signals generated by modems and FAX machines. Specialized algorithms for coding data signals exist, but they require additional bandwidth for error control ifthe transmission path is noisy.

  The first section of this article describes an inven- tion by which continuous data signals are optimally compressed such that the signal representation requires very low bandwidth. The second section describes a novel scheme for reliably transmitting the representation over a noisy digital channel. The combination of these inventions produces an algo- rithm that outperforms the prior art in terms of bandwidth required and degree of reliability offered.

1. The appearance of easily identifiable tones that are present in the initial transmissions of data devices. These tones are not present during a typ- ical voice call.
2. The fact that the frequency spectrum of the data signals is limited in such a way that the sampling rate required is lower than what would be imme- diately expected.

  The invention, hereafter referred to as the modem-coder or MoCoder, is the result of combin- ing several known concepts in an attempt to take advantage of these properties.

  Figure 1 is a block diagram of a MoCoder imple- mentation in a system that also supports transmis- sion of digital voice, such as the TeleDensity" sys- tem. The data signal is: converted to digital form using standard A/D hardware such as a PCM codec. The PCM samples are passed to a digital tone detec- tor. The tone detector determines whether the spe- cial tones associated with data signals are present. If the special tones are not present, the signal is pre- sumed to be a voice signal, and the data is routed to a voice coder via a detector-driven switch. If the special tones are present, the signal is presumed to be a data signal and the switch routes the digital samples to the MoCoder digital signal processing chain, starting with the bandpass filter block shown in Figure 1. MoCoder processing is described in the following paragraphs. Transmitter operation is described first. The receiver operation is similar to the transmitter's, and is described briefly at the end ofthis section.

  Initially, linear samples (sampling rate R) that represent the data signal are bandpass-filtered. The high (Fhigh) an...