User`s manual

AMBE-20x0™-HDK Development Board
User’s Manual (Preliminary)
Page 4
DVSI Confidential Proprietary
Section 1 – Introduction
AMBE-2000™ Vocoder Chip Applications
AMBE-2000™ Vocoder Chip Applications
Cellular Telephony and PCS
Satellite Communications
Digital Mobile Radio
Secure Communications
Voice Multiplexing
Voice Mail
Multimedia Applications
Video Conferencing
Documentation
Table 2 AMBE-2000™ Applications
Data Rates from 2000bps to 9600bps
The total coded bit rate is the sum of two components, the Speech Data bit rate and the Forward Error
Correction (FEC) Data bit rate. The addition of FEC data to the speech data allows the decoder to be
able to correct a limited amount of errors within each frame should they arrive corrupted. If the channel
is expected to have more errors then more bits should be dedicated to FEC. At the same time, voice
quality will increase if the number of speech bits is increased.
The channel interface is responsible for outputting the compressed data from the encoder and inputting
compressed data to the decoder. In addition to these most basic functions, the channel interface is also
capable of reporting certain events, such as the detection of a DTMF tone. The channel interface can
also control certain selectable functions of the AMBE-2000™, such as the voice-coding rate.
The Voice coding rate as well as the FEC coding rate can be selected individually on the AMBE-2000™
HDK. These rates are selected by using the dipswitches. The board is designed with 32 pre-configured
voice/FEC rates. If rates other than these are desired then an embedded channel software command
protocol can be used to configure voice and FEC rates in 50 bps increments.
FEC
FEC is a standard portion of most digital transmission systems. FEC reduces the number of
transmission errors, extends the operating range, and reduces the power requirements for
communications systems. System throughput is increased by eliminating the need for packet
retransmissions.
The AMBE-20x0™ HDK demonstrates two different Forward Error Correction (FEC) schemes built into
the the AMBE-2000
TM
and AMBE-2020
TM
chips. These schemes may be used together or independently
offering a wide variety of FEC choices. This gives the user the flexibility to optimize their system for the
best possible performance.
The two FEC methods in the AMBE-20x0™ HDK are block codes and convolutional codes. The chips
also use an interleaving scheme that spreads around the important bits in each frame to reduce the
likelihood that all of these bits get corrupted in one frame. The chip can keep track of the number of bit
errors in the current decoded frame, the current bit error rate. The FEC methods in the chips can be
used in many different ways offering a very flexible tool for the designer.
.