User`s manual

AMBE-2000™ Vocoder Chip
User’s Manual Version 4.9
DVSI Confidential Proprietary, Subject to Change Page 60
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8.5 Expanded Tone Detection and Generation
The AMBE-2000™ is capable of detecting and generating single tones as well as dual tones. The single tones span from
156.25 Hz to 3812.5 Hz in 31.25 Hz steps.
Tone Index
(Decimal)
Tone Type
Freq #2
(Hz)
Freq #1
(Hz)
0-4 Invalid N/A N/A
5 Single N/A 156.25
6 Single N/A 187.5
7 Single N/A 218.75
……… …………. ………… ……………
122 Single N/A 3812.5
123-127 Invalid N/A N/A
128 DTMF “1” 1209 697
…………. ………….. …………. …………
143 DTMF “D” 1633 941
144 Call Progress 440 350
145 Call Progress 480 440
146 Call Progress 620 480
147-254 Invalid N/A N/A
255 No Tone N/A N/A
8.6 Soft Decision Decoding
In modern communication systems the transmitter transmits information in the form of symbols. The demodulator
takes the received signal and tries to decide which symbol was transmitted. In other words, the demodulator is
making a decision based on the received signal. For instance, in a binary system, the symbols could be represented
by a 1 and a 0. Because of interference and many other factors, these signals can be misinterpreted because of
channel degradation. Significant improvement in FEC performance can be added by setting up the receiver so that
the demodulator is making a finer estimation of the received energy prior to the decoder, this is called soft-decision
decoding. The link below describes this in more detail.
http://www.mathworks.com/access/helpdesk/help/toolbox/commblks/usersguide/tutor135.shtml
The AMBE-2000™/2020 utilizes a 4-bit soft decision decoder. The bits are defined as follows:
Decision Value (Binary) Interpretation
0000 Most confident 0
0111 Least confident 0
1000 Least confident 1