Method and apparatus for adaptive rate communication system

• US 5,940,439 A
• Filed: 02/26/1997
• Issued: 08/17/1999
• Est. Priority Date: 02/26/1997
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wood, Clifford Allan, Kleider, John Eric, Campbell, William Michael
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Corrielus, Jean B
• Application Number:
  US08/806,783
• Time in Patent Office: 902 Days
• Field of Search: 375/285, 375/296, 375/254, 375/346, 375/348, 375/224, 375/225, 375/227, 375/228, 375/260, 375/240, 375/242, 375/265, 375/221, 375/358, 455/63, 455/67.3, 455/226.1, 455/226.3, 455/296, 455/126, 455/69, 455/67.1, 371/5.1, 370/249, 714/204, 704/200, 704/201
• US Class Current: 375/225
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0014 by adapting the source coding
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/0038 Blind format detection for detection of modulation format H04L27/0012
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27

Abstract

A system is disclosed for an adaptive rate voice system to provide improvements in coded operation over changing communication channel (50) conditions. This adaptive rate system efficiently determines optimal voice/channel coding rates , coding strategies and modulation/demodulation for optimum voice quality and intelligibility. A system state estimator (100), channel status estimator (110) and channel status monitor (120) provides feedback in the system to optimize the communication channel. The system maintains a continuous link despite changing channel conditions and minimizes delays through the system. Even though simple in design, it provides relatively low complexity and powerful channel coding operation. Operating conditions are thus extended for CDMA and portable communication systems. Voice intelligibility is preserved in extremely noisy or even hostile channel conditions.

Claims

1. An adaptive voice coding communication system comprising a transmitter for transmitting voice coded signals through a communication channel, and a receiver for receiving the voice coded signals from the channel, wherein the transmitter comprises:

a voice coder for compressing and digitizing audio signals from an audio source at a voice coding rate;

a channel coder for encoding signals from the voice coder at a channel coding rate;

a modulator for modulating and transmitting the voice coded signals provided by the channel coder at a symbol rate and modulation method; and

a channel status monitor for changing the voice coding rate, the channel coding rate, the symbol rate and the modulation method in response to a channel status indicator provided by the receiver over a feedback channel, the transmitter providing system status bits to the receiver prior to changing the voice coding rate, the channel coding rate, the symbol rate and the modulation method, and

wherein the receiver comprises;

a demodulator for demodulating the voice coded signals at the symbol rate and a demodulation method that corresponds with the modulation method, the demodulator determining a symbol error rate from the received signal;

a channel decoder for decoding signals provided by the demodulator at a channel decoding rate that corresponds with the channel coding rate, the channel decoder determining a bit error rate;

a voice decoder for decompressing signals provided by the channel decoder and synthesizing audio signals in accordance with a voice decoding rate that corresponds with the voice coding rate, the voice decoder determining a spectral distortion indicator from the signals decoded by the channel decoder;

a system state estimator for setting the symbol rate, demodulation rate, channel decoding rate, and voice decoding rate of the receiver in response to system status bits provided by the transmitter; and

a channel status estimator for providing the channel status indicator to the transmitter'"'"'s channel status monitor when a current channel state differs from a previous channel state, the system state estimator coupled to the channel status estimator and determining the current channel state by computing a new symbol rate, demodulation rate, channel decoding rate, and voice decoding rate from the symbol error rate, bit error rate, and spectral distortion indicator.

2. A system as claimed in claim 1 wherein the transmitter provides initial system status bits to the system state estimator over the communication channel, the initial system status bits instructing the system state estimator to set an initial symbol rate, demodulation rate, channel decoding rate, and voice decoding.

3. A method of communicating voice coded signals through a communication channel comprising the steps of:

in a transmitter;

compressing and digitizing audio signals from an audio source at a voice coding rate;

encoding the compressed and digitized audio signals at a channel coding rate;

modulating and transmitting the encoded signals at a symbol rate and modulation method;

changing the voice coding rate, the channel coding rate, the symbol rate and the modulation method in response to a channel status indicator provided over a feedback channel;

providing system status bits to a receiver prior to changing the voice coding rate, the channel coding rate, the symbol rate and the modulation method,

and in the receiver

demodulating received voice coded signals at the symbol rate and a demodulation method that corresponds with the modulation method;

determining a symbol error rate from the received voice coded signals;

decoding the demodulated signals at a channel decoder;

determining a bit error rate from the demodulated signals;

decompressing signals and synthesizing audio signals in accordance with a voice decoding rate that corresponds with the voice coding rate;

determining a spectral distortion indicator from synthesized audio signals;

setting the symbol rate, demodulation rate, channel decoding rate, and voice decoding rate of the receiver in response to system status bits provided by the transmitter;

providing the channel status indicator to the transmitter when a current channel state differs from a previous channel state; and

determining the current channel state by computing a new symbol rate, demodulation rate, channel decoding rate, and voice decoding rate from the symbol error rate, bit error rate, and spectral distortion indicator.

4. A method as claimed in claim 3 further comprising the steps of:

the transmitter providing initial system status bits over the communication channel; and

setting an initial symbol rate, demodulation rate, channel decoding rate, and voice decoding in response to the system status bits.