Efficient hardware implementation for signal reconstruction over multiple analog-to-digital, digital-to-analog conversions in a telecommunication system
View Patent ↗Method and apparatus for providing an improved quality voice band channel equalization in telecommunication systems employing v.90 transmission standard in which PCM modem signals passing through a digital-to-analog and analog-to-digital conversion processes between a central office switch and a multiple subscriber access system may be reconstructed with improved quality at the A/D converter side by variably adjusting the gain between the digital-to-analog conversion process at the central office switch and the analog-to-digital conversion process at the multiple subscriber access system, and low pass filtering the signal using a second order low pass notch filter to provide a boost of 6 dB at a frequency of 4 KHz.
1. A multiple subscriber carrier system supporting v.90 standard data transmission, comprising:
a variable gain control unit coupled to a central office switch for receiving a converted analog signal converted from a digital signal and gain controlling the converted analog signal;
a low pass filter coupled to the gain control unit for filtering the gain controlled analog signal; and
a μ-law analog to digital converter coupled to the filter for converting the filtered, gain controlled analog signal to a corresponding digital signal;
wherein said low pass filter is configured to increase the band edge gain of said gain controlled analog signal at a frequency of approximately 4 KHZ by approximately 6 dB.
2. The system of claim 1 wherein said digital signal and said corresponding digital signal output from said μ-law analog to digital converter are substantially the same.
3. The system of claim 1 wherein said low pass filter includes a second order low pass notch filter.
4. The system of claim 1 wherein said low pass filter includes a pole at approximately 4,065 Hz and a zero at approximately 4,216 Hz, and a quality factor of 40.9.
5. A method of providing a multiple subscriber carrier system supporting v.90 standard data transmission, comprising the steps of:
receiving an analog signal converted from a 64 Kbps pulse code modulated (PCM) signal;
gain controlling the analog signal;
filtering the gain controlled analog signal; and
converting the filtered, gain controlled analog signal to a corresponding digital signal;
wherein said filtering step includes the step of increasing the band edge gain of said gain controlled analog signal at a frequency of approximately 4 KHz by approximately 6 dB.
6. The method of claim 5 wherein said step of filtering includes the step of providing a low pass filter having a pole at approximately 4,065 Hz and a zero at approximately 4,216 Hz, and a quality factor of 40.9.