초록 ▼

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

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.

대표청구항 ▼

[ What is claimed is:] [1.] 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 tra

[ What is claimed is:] [1.] 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; andsaid 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.