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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.

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First Claim