Data compression of voiceband modem signals

The development of an integrated data-compression system for speech and voiceband modem signals is described. The integrated source coder performs a quadrature decomposition of a bauded signal prior to quantization. A detection algorithm is used to determine the presence and the carrier frequency of the bauded signal. The coder is currently implemented with a TMS 32020 digital signal processor in a basic exchange radio system to provide wireless digital access for rural subscribers. Performance of the integrated source coder was evaluated in the lab and in a field trial. Using a radio link in the lab, the coder support the following data communication standards: 300 b/s Bell 103, CCITT V.21; 1200 b/s Bell 212A, CCITT V.22; 2400 b/s CCITT V.22 bis; and 2400 b/s CCITT V.24 ter. Tests were also conducted for the transmission of facsimiles between a dozen of the popular low-priced telecopiers. The reproduction quality of the system for various types of documents and drawings were near transparent.<
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