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Browse Prior Art Database

SELECTABLE BANDWIDTH DECODING

IP.com Disclosure Number: IPCOM000007019D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-18
Document File: 3 page(s) / 130K

Publishing Venue

Motorola

Related People

Tim Laflin: AUTHOR

Abstract

Radio receivers in the past used a single bandwidth data limiter filter. The result of this sin- gle bandwidth was a trade-off between falsing and sensitivity had to be made. Ifthe low pass data filter was narrow enough to provide good sensitivity it would band limit noise to appear data like to the baud rate detector. If the data filter was wide enough to pass enough noise that the baud rate detector did not false, the sensitivity during data decoding decreased. Selectable bandwidth decoding is a desir- able mode of operation for certain types of data decoding devices.

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MOTOROLA INC. Technical Developments Volume 20 October 1993

SELECTABLE BANDWIDTH DECODING

by Tim Laflin

  Radio receivers in the past used a single bandwidth data limiter filter. The result of this sin- gle bandwidth was a trade-off between falsing and sensitivity had to be made. Ifthe low pass data filter was narrow enough to provide good sensitivity it would band limit noise to appear data like to the baud rate detector. If the data filter was wide enough to pass enough noise that the baud rate detector did not false, the sensitivity during data decoding decreased. Selectable bandwidth decoding is a desir- able mode of operation for certain types of data decoding devices. There are a great number of cod- ing schemes transmitted to radio receivers on the same carrier frequency; therefore, the receiver must make a decision which coding scheme to receive and which coding schemes to ignore. The one cri- teria which may be used for this application is to determine ifthe radio channel has desired informa- tion by a means ofbaud rate detection. It is assumed that if a signal is present and has a transmission (baud) rate of the receiver's desired rate, then the receiver should attempt to decode all such informa- tion. It became apparent while conducting tests on a radio frequency data receiver, that having band limited noise presented to a baud rate detection agorithm caused much greater that expected false detection of baud rate. It is possible to calculate the probability of falsely .detecting a specific baud rate with unfiltered Gaussian white noise presented to the baud rate detector. The false rate that was meas- ured from the test receiver was much greater than the number calculated for Gaussian white noise. The only explanation for this phenomenon was that the receiver was band limiting the noise. This phenom- ena, increased falsing, was verified by varying the bandwidth ofthe low pass data filter. The false detec- tion of baud rate went up as the bandwidth of the filter approached the data rate. When the bandwidth of the data filter (the -3db point) was the same as the data rate the false rate was nearly 100%. This meant that almost every time the baud rate detec- tion algorithm examined the band limited data it

8 Motorola. Inc. 1993

made the decision that a valid data rate was present, even though only Gaussian white noise was presented to the data filter. This presents a problem for the radio receiver designer. For maximum sensitivity while data decoding, the data filter needs to be set at the data rate. If the data filter is set at the data rate, then the receiver...