US 6,154,499 A · Communication systems using nested coder and compatible channel coding

Abstract

A communication network, comprising data transmission and data receiving systems and operations, for carrying reliable voice communications, particularly for mobile communications applications involving land-mobile, aeronautical and maritime systems. Because the quality of the links in such systems may vary, the present invention combines a nested codec with a channel coder at the transmission side of the link and a decoder at the reception side. The nested codec will transmit at a constant rate, which is the highest bit rate possible in the system, but according to channel conditions, will reconstruct voice at different bit rates. Thus, for example, transmission will always occur at a rate of 3600, but the reconstruction of the transmitted signal will be at 2400 or 1200 bps, depending on the quality of the signal. Notably, the lower two rates are subsets of the higher rate, thus defining their "nested" characteristic. Moreover, the rate reductions from the constant maximum rate occur automatically at the receiver, without transmitter control, based on the detected degraded conditions at the receiver. Because the rates are nested, they are a known multiple of the lowest rate.

Claims22

Dependent claims

A voice communication system having a transmitter for sending encoded voice signals in a digital bit stream over a communications medium to a receiver and being capable of providing automatic rate reduction under degraded conditions without transmit side control, said transmitter comprising a voice encoder and a channel encoder and said receiver comprising a channel decoder and a voice decoder,

said voice encoder comprising:
a nested voice codec which is responsive to input speech signals for generating a plurality of levels of encoded speech signals comprising a basic level and at least one other level, said basic level containing speech signals sufficient to reproduce at least an intelligible content of speech;
said channel encoder comprising:
an encoder operative to encode said basic level and said at least one other level and to transmit at a constant data rate, said constant data rate being a full rate for said at least one other level and said basic level being at a subrate comprising an integral subset of said full data rate, said encoder for said basic level providing a higher level of error correction than said at least one other level;
and
said receiver comprising:
a channel state estimator operative to estimate a channel state condition and to produce a channel state selector signal, whereby said voice decoder is responsive to said selector signal for variable rate processing of a received signal and for decoding said received signal at said basic level when channel conditions are at a first quality level and said at least one other level when channel conditions are at a second quality level, where said first quality level is degraded with reslect to said second level.

4 more elements

A receiver for receiving a voice signal which is encoded by a nested voice codec into a basic level and at least another two higher nested levels and is transmitted, following channel encoding, unique word and framing bit generation, and modulation, at a predetermined constant bit rate comprising:

a demodulator for demodulating said voice signal and producing a demodulated output;
a detector for detecting a unique word and framing bits in said demodulated output;
a channel decoder for decoding said demodulated output and producing a channel decoded output;
a voice decoder for decoding a voice content of said channel decoded output;
and
a channel state estimator operative to estimate a channel state condition and to produce a channel state selector signal, whereby said voice decoder is responsive to said selector signal for variable bit rate processing of the voice content of said channel decoded output comprising decoding the voice content of said channel decoded output at said basic level when channel conditions are at a first quality level and at one of said at least another two higher nested levels when channel conditions are at a second quality level, where said first quality level is degraded with respect to said second level.

3 more elements

A method of voice communication for conveying high quality speech signals between a transmitter and a receiver via a communications channel and being capable of providing automatic rate reduction under degraded conditions without transmit side control, comprising:

encoding said speech signals by generating a plurality of levels of encoded speech signals comprising a basic level and at least one other level, said basic level containing speech signals sufficient to reproduce at least an intelligible content of speech;
channel encoding said plural level encoded signals whereby said basic level is provided with a high level of error correction than said at least one other level;
and
transmitting said channel encoded signals in a digital bit stream at a constant bit rate over a communications medium;
receiving said transmitted digital bit stream;
channel decoding said received digital bit stream by variable bit rate processing said transmitted digital bit stream,
estimating a channel state condition and producing a channel state selector signal and
selectively decoding said channel decoded signals at said basic level when channel conditions are at a first quality level and said at least one other level when channel conditions are at a second quality level, where said first quality level is degraded with respect to said second level, into a voice signal in response to said selector signal.

5 more elements

Dependencies are inferred from the claim text.

Communication systems using nested coder and compatible channel coding

Life of this patent

Communication systems using nested coder and compatible channel coding

Life of this patent

Abstract

Claims22