Differential pulse code communications system having dual quantization schemes |
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| 申请号 | US3781686D | 申请日 | 1972-11-13 | 公开(公告)号 | US3781686A | 公开(公告)日 | 1973-12-25 |
| 申请人 | BELL TELEPHONE LABOR INC; | 发明人 | CHING Y; | ||||
| 摘要 | A differential pulse code communications system is disclosed wherein the transmitter quantizes differential signals on two quantizing scales having different numbers of levels. The combined signal is transmitted to a receiver which may either utilize the higher quality signal or re-transmit either the lower and/or higher quality signal, without re-quantization and the error associated therewith, to yet another receiver; the quality of the signal re-transmitted being determined by the bandwidth of the re-transmission channel. | ||||||
| 权利要求 | 1. A transmitter for transmitting coded differential signals at fixed periodic intervals comprising a transmitter input terminal for receiving an input message signal, quantizing means for encoding differential input signals to first digital signals each having one of a first predetermined number of quantizing levels, a digital accumulator connected to said quantizing means to add each quantizing level of said first digital signal to previously accumulated quantizing levels, a delay network connected to said digital accumulator to delay said accumulated first digital signal at least one of said fixed periodic intervals, first subtraction means connected to said transmitter input terminal, the output of said delay network, and the input of said quantizing means to produce a differential input signal to said quantizing means at each of said fixed periodic intervals by subtracting the delayed signal from said input message signal, second subtraction means connected to said transmitter input terminal and the output of said digital accumulator to produce a second differential signal at each of said fixed periodic intervals by subtracting said accumulated first digital signal from said input message signal, a transmitter output terminal, signal combining means connected to said second subtraction means, said quantizing means and said transmitter output terminal to produce a second digital signal at said transmitter output terminal having one of a second predetermined number of quantizing levels representing the combination of each of said first digital signals and each of said second difference signals, whereby said second predetermined number of quantizing levels of said second digital signal at said transmitter output terminal is greater than said first predetermined number of quantizing levels, and a signal having said first predetermined number of quantizing levels may be derived from said second digital signal. 2. A transmitter in accordance with claim 1 wherein said first digital signal having one of said first predetermined number of quantizing levels is represented by a first predetermined number of bits, said second difference signal is represented by a second predetermined number of bits, and said signal combining means combines said first predetermined number of bits and said second predetermined number of bits to produce said second digital signal. 3. A transmitter in accordance with claim 1 wherein said input message signal is an analog signal, an analog-to-digital converter is connected between said transmitter input terminal and said first subtraction means to convert said analog signal at said transmitter input terminal to digital format, one input of said second subtraction means is connected to the output of said analog-to-digital converter, and a second input of said second subtraction means is connected to said digital accumulator. 4. A transmitter in accordance with claim 3 wherein said signal combining means is a parallel-to-serial converter that transforms the combination of the parallel output of said quantizer and the parallel ouput of said second subtraction means to serial digital format. 5. a receiver for receiving coded differential signals having one of a first predetermined number of quantizing levels at fixed periodic intervals comprising a receiver input terminal for receiving digital differential signals, a digital converter connected to said receiver input terminal to convert each of said received digital differential signals to a first digital signal having one of a second predetermined number of quantizing levels, said second predetermined number of quantizing levels being less than said first predetermined number of quantizing levels, a digital accumulator connected to said digital converter for adding the quantizing level of said second digital signal to previously accumulated quantizing levels, a delay network connected to said digital accumulator to delay said accumulated second digital signal at least one of said fixed periodic intervals, a receiver output terminal, and a digital adder connected to said receiver input terminal, the output of said delay network, and said receiver output terminal to add the quantizing level of said received digital differential signal to the delayed accumulated second digital signal, whereby a signal having said first predetermined number of quantizing levels and a signal having said second predetermined number of quantizing levels may be derived from the signal at said receiver output terminal. 6. A receiver in accordance with claim 5 wherein a digital-to-analog converter is connected between the output of said digital adder and said receiver output terminal to convert the digital signal at the output of said digital adder to analog format. 7. A receiver in accordance with claim 6 wherein a serial-to-parallel converter is connected between said receiver input terminal, said digital adder and said digital converter to convert the serial digital differential signals at said receiver input terminal to a parallel digital format. 8. A differential pulse code communications system for transmitting and receiving coded differential signals at fixed periodic intervals comprising a transmitter input terminal for receiving an input message signal, quantizing means for encoding differential input signals to first digital signals each having one of a first predetermined number of quantizing levels, a first digital accumulator connected to said quantizing means and to add each quantizing level of said first digital signal to previously accumulated quantizing levels, a first delay network connected to said first digital accumulator to delay said accumulated first digital signal at least one of said fixed Periodic intervals, first subtraction means connected to said transmitter input terminal, the output of said delay network, and the input of said quantizing means to produce a differential input signal to said quantizing means at each of said fixed periodic intervals by subtracting the delayed signal from said input message signal, second subtraction means connected to said transmitter input terminal and the output of said first digital accumulator to produce a second differential signal from said input message signal at each of said fixed periodic intervals by subtracting said accumulated first digital signal from said input message signal, a transmitter output terminal, signal combining means connected to said second subtraction means, said quantizing means and said transmitter output terminal to produce a second digital signal at said transmitter output terminal having one of a second predetermined number of quantizing levels representing the combination of each of said first digital signals and each of said second difference signals, said second predetermined number of quantizing levels being greater than said first predetermined number of quantizing levels, a receiver input terminal, a transmission medium interconnecting said transmitter output terminal and said receiver input terminal for transmitting said second digital signal having one of said second predetermined number of quantizing levels to said receiver input terminal, a digital converter connected to said receiver input terminal to convert the received digital signal at said receiver input terminal to a third digital signal having one of said first predetermined number of quantizing levels, a second digital accumulator connected to said digital converter for adding the quantizing level of said third digital signal to previously accumulated quantizing levels, a second delay network connected to said second digital accumulator to delay said accumulated third digital signal at least one of said fixed periodic intervals, receiver output terminal, and a digital adder connected to said receiver input terminal, the output of said second delay network, and said receiver output terminal to add the quantizing level of said received digital signal at said receiver input terminal to the delayed accumulated third digital signal, whereby a signal having said first predetermined number of quantizing levels and a signal having said second predetermined number of quantizing levels may be derived from the signal at said receiver output terminal. 9. A differential pulse code communications system in accordance with claim 8 wherein said input message signal is an analog signal, an analog-to-digital converter is connected between said transmitter input terminal and said first subtraction means to convert said input message signal to analog format, one input of said second subtraction means is connected to the output of said analog-to-digital converter, a second input of said second subtraction means is connected to said first digital accumulator and a digital-to-analog converter is connected between said digital adder and said receiver output terminal to convert the digital signal at the output of said digital adder to analog format. |
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