Differential pulse code communications system having dual quantization schemes |
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| 申请号 | US3781685D | 申请日 | 1972-11-13 | 公开(公告)号 | US3781685A | 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 in which a digital difference signal having a higher number of quantization levels is transmitted to a distant receiver wherein the received higher grade quality digital signal is degraded, for re-transmission, to a digital signal having a lesser number of quantization levels without introducing an additional quantization error component into the system. In the transmitter, the transmitted higher grade quality difference signals are degraded to the lower grade quality digital signals before being digitally accumulated for subtraction from the input signal. At the receiver, the higher grade quality transmitted difference signals are similarly degraded to the lower grade quality digital signals and digitally accumulated. The higher grade quality reconstruction of the input signal is obtained by summing the received higher grade quality difference signal plus the accumulated lower grade quality digital signals. The lower grade quality digital difference signal derived from the higher grade quality digital signal may be re-transmitted to another distant location with a quantization error equivalent to the error introduced by quantizing the input signal to a difference signal having the fewer number of quantization levels. | ||||||
| 权利要求 | 1. A transmitter for transmitting coded differential signals comprising a transmitter input terminal for receiving an input message signal, sampling and quantizing means for sampling and encoding a differential input signal to a first digital signal having one of a first predetermined number of quantizing levels, a transmitter output terminal connected to the output of said sampling and quantizing means, a level converter connected to the output of said sampling and quantizing means to convert said first digital signal to a second digital signal having one of a second predetermined number of quantizing levels, said seocnd predetermined number of quantizing levels being less than said first predetermined number of quantizing levels, a digital accumulator connected to said level converter for adding the quantizing level of said second digital signal to previously accumulated quantizing levels of said second digital signals, a delay network connected to said digital accumulator to delay said accumulated second digital signal one sample time, and means connected to said transmitter input terminal, the output of said delay network, and the input of said sampling and quantizing means to produce said differential input signal by subtracting the delayed signal from said input message 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 transmitter output terminal. 2. A transmitter for transmitting coded differential signals in accordance with clain 1 wherein said input message signal is an analog signal, and a digital-to-analog converter is connected between said delay network and said means to produce said differential input signal for converting said delayed accumulated second digital signal to analog format. 3. A transmitter for transmitting coded differential signals in accordance with claim 2 wherein a parallel-to-serial converter is connected between said sampling and quantizing means and said transmitter output terminal to convert said first digital signal to serial digital format for transmission. 4. A receiver for receiving coded differential signals of a message signal comprising a receiver input terminal for receiving at predetermined sampling periods a transmitted differential signal having one of a first predetermined number of quantizing levels, a level converter connected to said receiver input terminal to convert said received digital differential signal to a second 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 level converter for adding the quantizing level of said second digital signal to previously accumulated quantizing levels of said second digital signal, a delay network connected to said digital accumulator to delay said accumulated second digital signal at least one of said predetermined sampling periods, a digital adder having a first input connected to said receiver input terminal and a second input connected to said delay network to sum said received digital differential signal and said delayed accumulated second digital signal, and a receiver output terminal connected to the output of said digital adder 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. 5. A receiver for receiving coded differential signals in accordance with claim 4 wherein said message signal is an aNalog signal, 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. 6. A receiver for receiving coded differential signals in accordance with claim 5 wherein a serial-to-parallel converter is connected to said receiver input terminal, said first input of said digital adder, and said level converter to convert said received digital differential signal to parallel digital format. 7. A differential pulse code communications system for transmitting and receiving coded differential signals comprising a transmitter input terminal for receiving an input message signal, sampling and quantizing means for sampling and encoding a differential input signal to a first digital signal having one of a first predetermined number of quantizing levels, a transmitter output terminal connected to the output of said sampling and quantizing means, a first level converter connected to the output of said sampling and quantizing means to convert said first digital signal to a second 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 first digital accumulator connected to said first level converter for adding the quantizing level of said second digital signal to previously accumulated quantizing levels of said second digital signal, a first delay network connected to said first digital accumulator to delay said accumulated second digital signal one sampling time, means connected to said transmitter input terminal, the output of said first delay network, and the input of said sampling and quantizing means to produce said differential input signal by subtracting the delayed signal from said input message signal, a receiver input terminal, a transmission medium interconnecting said transmitter output terminal and said receiver input terminal for transmitting the signal at said transmitter output terminal to said receiver input terminal, a second level 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 second predetermined number of quantizing levels, a second digital accumulator connected to said second level converter for adding the quantizing level of said third digital signal to previously accumulated quantizing levels of said third digital signal, a second delay network connected to said second digital accumulator to delay said accumulated third digital signal one sample time, a digital adder having a first input connected to said receiver input terminal and a second input connected to said delay network to sum the received digital difference signal and said delayed accumulated third digital signal, and a receiver output terminal connected to the output of said digital adder whereby a signal having a 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. 8. A differential pulse code communications system in accordance with claim 7 wherein said input message signal is an analog signal, a first digital-to-analog converter is connected between said first delay network and said means to produce said differential input signal to convert said delayed accumulated second digital signal to analog format, and a second digital-to-analog converter is connected between said digital adder and said receiver output terminal to convert the signal at the output of said digital adder to analog format. |
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