Digital Voice Systems AMBE-3000 Especificações descarregar pdf (Página 43)

AMBE-3000F™ Vocoder Chip Users Manual

Version 3.4, April, 2014

itial Design Considerations

Figure 18 Typical Echo Path

The echo canceller can be activated either through the hardware pin, or through the packet interface.

4.5.3 DTMF Dual Tone Multiple Frequency, Detection and Generation

The AMBE-3000F™ Vocoder Chip is capable of detecting, transmitting, and synthesizing DTMF tones. When the encoder

detects DTMF tones the voice data field will contain the DTMF tone data. Additionally, the encoder passes the DTMF data in-

band (within the regular voice data bits) so that normal DTMF tones pass seamlessly from the encoder to the decoder for

synthesis. The decoder synthesizes a DTMF tone in response to reception of an in-band DTMF tone frame or reception of a

control packet with the DTMF word set. When this voice data is received by an AMBE-3000F™ Vocoder Chip decoder, it

will regenerate the inband tone. The AMBE-3000F™ Vocoder Chip can also generate “Dual Tones” at many different

frequencies. Each tone packet generates 20 milliseconds of output tones. The length of the output tones can be extended by

repeating the tone packet. DTMF may be enabled or disabled through a control packet. DTMF is enabled by default.

The AMBE-3000F™ Vocoder Chip can also generate Single Frequency Tones. This can be done by using the TONE_IDX

Field (see Table 103 TONE Field Format. Each packet with TONE_IDX generates 20 m

illiseconds of output tones. The

length of the output tones can be extended by repeating the packet. Tones that can be generated by the AMBE-3000F™

Vocoder Chip are shown in Table 104 TONE Index Values.

4.5.4 Soft Decision Error Correction

Significant improvement in FEC performance can be added by setting up a receiver so that the demodulator is making a finer

estimation of the received energy prior to sending it to the decoder, this is called soft-decision decoding. To use Soft Decision

Error Correction use the CHAND4 (ID 0x17) field in the channel packet. The AMBE-3000F™ Vocoder Chip utilizes a 4-bit

soft decision decoder. The bits are defined as follows:

Decision Value (Binary) Interpretation

0000 Most confident 0

0111 …

1000 …

1111 Most confident 1

Table 10 Soft Decision Error Correction

The user must implement circuitry at the receive end of the channel for making a finer (4 bit) estimation of the received energy.

The AMBE-3000F™ Vocoder Chip uses a different channel data field (CHAND4) to specify channel data represented by 4

soft decision (SD) bits. The decoder will make the decision of whether or not a 1 or a 0 is represented by the SD bits.

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Digital Voice Systems AMBE-3000 Especificações Página 43