Browse Prior Art Database

GOLAY SEQUENTIAL CODE TONE ONLY DECODING SENSITIVITY IMPROVEMENT

IP.com Disclosure Number: IPCOM000005686D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-26
Document File: 4 page(s) / 144K

Publishing Venue

Motorola

Related People

Robert B. Schneider: AUTHOR [+2]

Abstract

Paging sensitivity for GSC pagers can be improved by discarding framing errors in the decoding algorithm. Framing errors are those which occur at bit transitions in a sequential data stream.

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MOTOROLA Technical Developments Volume 7 October 1987

GOLAY SEQUENTIAL CODE TONE ONLY DECODING SENSITIVITY IMPROVEMENT

by Robert B. Schneider and Allen J. Weidler

Paging sensitivity for GSC pagers can be improved by discarding framing errors in the decoding algorithm. Framing errors are those which occur at bit transitions in a sequential data stream.

   As is well known in a GSC transmission, the GSC digital word is sampled at a rate of 4 times per bit (4 phases) and stored into alternate registers 23 bits long for a total of 92 bits. Since pagers typically correlate to 3 errors per phase on the average, good word correlation is limited to no more than 12 errors total. When any one of these phases is being sampled during bit transitions, it can be corrupted by noise. Samples are more sensitive to noise at the transitions. This corrupted data causes loss of paging sensitivity depending upon when it is sampled.

   A more sensitive and predictable algorithm can beobtained if the worst phase is discarded due to its poten- tial of having framing errors. Only the best 3 phases would be used in the correlation for good data. Since there are now 3 phases in which correlation is computed, good correlation is accomplished to no more than 9 errors in 69 samples instead of 12 errors in 92 samples.

For explanation purposes, the algorithm is illustrated in flow charts in the following figures. The flow charts are self-explanatory wherein:

   FIGS. 1 and 2 show the data structure and program flow diagrams for a GSC word correlator which uses the best 3 of 4 phases sampled from a data stream. FIG. 2A illustrates correlator initialization so that the first 88 samples of 92 samples are prepared. FIG. 2B illustrates taking the last 4 samples and determining the errors in each phase of 23 bits. FIG. 2C shows the addition of each 3 phases of errors neglecting the 4th phase. Final- ly, FIG. 2D shows which phase is chosen for correlation if one exists.

   A mathematical statistical model has been used to quantize the relative sensitivity increase obtained with this correlation method. The following discussion illustrates this statistical model used to compute the pro- posed decoding function.

GSC PROBABILITY MODELS

X = number of bit errors F = number of framing errors P = probability...