Bidirectional trunk amplifier and cable modem for cable hybrid fiber and coax network which utilizes an upstream pilot signal

Abstract

A method of utilizing a bidirectional amplifier in a cable hybrid fiber and coax (HFC) and a cable modem utilizing an upstream signal. The invention provides an upstream pilot signal from the cable modem and automatically controls the gain of the signal so that the headend receives a constant level upstream pilot signal from each terminal. A cable modem for bidirectional services in the HFC network has a saw filter, a mixer & AGC, a LPF, a tuner, a gain controller, a downstream demodulator, an upstream modulator, a media access controller (MAC), a CPU, a programmable attenuator, a pilot signal generator and a switch connecting the tuner and the pilot signal generator under the control of the CPU. A bidirectional trunk amplifier for bidirectional services in the HFC network, has a directional filter (DF) which separates the upstream signals from the downstream signals, a pad, having characteristics approximately equivalent to the frequency characteristics of the coaxial cable, for compensating the attenuated value of the coaxial cable and matching the input level, an equalizer for compensating the frequency deviation occurring in the line, an amplifier for amplifying the input signal to a desired level, and a level controller for controlling the slope and the automatic gain.

What is claimed is:  
     
         1 . A cable modem for bidirectional services in an HFC (Hybrid Fiber and Coax) network, comprising: 
 a central processing unit (CPU);    a tuner for downconverting upconverted downstream signals into IF (Intermediate Frequency) signals having constant frequency, by utilizing RF (Radio Frequency) signals;    a saw filter for filtering a specified band frequency of the IF signals received from the tuner;    a mixer and AGC (Automatic Gain Controller) for converting the filtered IF signals into base band signals and for outputting a gain control signal;    a LPF (Low Pass Filter) for passing only low band signals and removing high band signals from the signals generated by the mixer and AGC;    a gain controller for controlling the level of the signals received from the mixer and AGC so that the level of the signals output by the mixer and AGC is constant;    a downstream demodulator for recovering and converting the base band signals from the LPF into pre-modulated digital signals by demodulating the modulated signals;    a MAC (Media Access Controller) for dividing the demodulated signals into control signals and data signals and for transmitting upstream data signals to the transceiver under the control of the CPU;    an upstream modulator for modulating the upstream data signals received from the MAC to be transmitted to the headend;    a programmable attenuator for controlling the level of the modulated upstream signals;    a pilot signal generator for generating a pilot signal; and    a switch for connecting said tuner and said pilot signal generator under the control of the CPU.    
     
     
         2 . The apparatus as set forth in  claim 1 , wherein said pilot signal generator comprises: 
 an oscillator which generates a radio frequency upstream pilot signal;    a multiplier which multiplies the radio frequency upstream pilot signal to a desired frequency and outputs a multiplied upstream pilot signal;    an AGC (automatic gain control) which outputs a level control signal;    a level controller which controls the level of the multiplied upstream pilot signal in accordance with the level control signal to maintain the multiplied upstream pilot signal at a constant level;    a radio frequency amplifier which amplifies the level controlled multiplied upstream pilot signal and outputs an amplified upstream pilot signal; and    a BPF (band pass filter) which receives the output of the radio frequency amplifier and passes only the amplified upstream pilot signal.    
     
     
         3 . The apparatus as set forth in  claim 2 , wherein said pilot generator is included in one of a plurality of terminals in a last cell of a tree structure.  
     
     
         4 . The apparatus as set forth in  claim 2 , wherein said pilot generator is inactive when a pilot signal is not required, so as not to cause interference with other signals.  
     
     
         5 . The apparatus as set forth in  claim 1 , wherein said head-end requests said pilot generator to generate the pilot signal when required.  
     
     
         6 . The apparatus as set forth in  claim 2 , wherein said radio frequency amplifier performs the automatic gain control by utilizing the signal of said pilot generator.  
     
     
         7 . The apparatus as set forth in  claim 2 , wherein the pilot signal generated by said pilot signal generator is constant.  
     
     
         8 . The apparatus as set forth in  claim 5 , wherein the upstream data signals received by said head-end have a constant level.  
     
     
         9 . A bidirectional trunk amplifier for bidirectional services in a HFC (Hybrid Fiber and Coax) network, comprising: 
 a directional filter (DF) for separating an upstream signal from a downstream signal;    a pad, having characteristics approximately equivalent to the frequency characteristics of a coaxial cable, for compensating for attenuation in the coaxial cable and input level matching, after receiving the signals from said DF;    an equalizer for compensating for frequency deviation in the coaxial cable with respect to signals received from said pad;    an amplifier for amplifying the equalized signal to a desired level;    a level controller for automatically controlling the slope and the gain of the amplified signals.    
     
     
         10 . The apparatus as set forth in  claim 9 , wherein said level controller automatically controls the gain of the amplified signals so as to provide a stable upstream signal.  
     
     
         11 . The apparatus as set forth in  claim 9 , wherein said level controller comprises: 
 a gain block for controlling the gain-of the signal received from the amplifier;    a slope block for controlling the slope of the signal received from the gain block;    an amplifier for amplifying the gain-controlled signal and the slope-controlled signal;    a directional splitter for separating said signals into main and sub signals; and    an AGC&ASC (Automatic Slope Controller) for controlling the gain block and the slope block.    
     
     
         12 . An HFC (Hybrid Fiber and Coax) network which includes an amplifier, said amplifier comprising: 
 a directional filter (DF) for separating an upstream signal from a downstream signal;    a pad, having characteristics approximately equivalent to the frequency characteristics of a coaxial cable, for compensating for attenuation in the coaxial cable and matching the input level, after receiving the signals from said DF;    an equalizer for compensating for frequency deviation in the coaxial cable with respect to signals received from said pad;    an amplifier for amplifying the equalized signal to a desired level; a level controller for controlling the slope and the automatic gain of the amplified signals;    wherein said amplifier may be applied to trunk amplifiers and to any bidirectional amplifier included in the HFC network.    
     
     
         13 . The apparatus as set forth in  claim 9 , wherein upstream pilot signals are utilized for the stability of the upstream transmission line.  
     
     
         14 . The apparatus as set forth in  claim 9 , wherein the upstream bidirectional amplifier is automatically gain controlled.  
     
     
         15 . The apparatus as set forth in  claim 7 , wherein said cable modem provides a constant pilot signal.  
     
     
         16 . The apparatus as set forth in  claim 13 , wherein said upstream pilot signal is selected from the upstream frequency band in order to provide a constant level of the upstream signal to the terminal.  
     
     
         17 . The apparatus as set forth in  claim 15 , wherein said cable modem generates a pilot signal only when said headend requires it.  
     
     
         18 . A cable modem for bidirectional services, the modem comprising: 
 a pilot signal generator which generates an upstream pilot signal; and    a modulator which modulates an upstream signal, said upstream signal including said upstream pilot signal.    
     
     
         19 . The cable modem as set forth in  claim 18 , wherein said pilot signal generator comprises means for controlling the level of said upstream pilot signal.  
     
     
         20 . The cable modem as set forth in  claim 18 , wherein said pilot signal generator generates a pilot signal only when a pilot signal request signal is received from a headend external to the modem.  
     
     
         21 . The cable modem as set forth in  claim 18 , wherein said pilot signal generator comprises: 
 an oscillator which generates a radio frequency upstream pilot signal;    a multiplier which multiplies the radio frequency upstream pilot signal to a desired frequency and outputs a multiplied upstream pilot signal;    an AGC (automatic gain control) which outputs a level control signal;    a level controller which controls the level of the multiplied upstream pilot signal in accordance with the level control signal to maintain the multiplied upstream pilot signal at a constant level;    a radio frequency amplifier which amplifies the level controlled multiplied upstream pilot signal and outputs an amplified upstream pilot signal; and    a BPF (band pass filter) which receives the output of the radio frequency amplifier and passes only the amplified upstream pilot signal as said upstream pilot signal.    
     
     
         22 . The cable modem as set forth in  claim 18 , wherein said modem further comprises a downstream demodulator for demodulating a downstream signal.  
     
     
         23 . A bidirectional trunk amplifier for bidirectional services in a HFC (Hybrid Fiber and Coax) network, comprising: 
 means for receiving an upstream pilot signal; and    a level controller which controls the level of an upstream signal according to the level of said upstream pilot signal.    
     
     
         24 . A bidirectional trunk amplifier for bidirectional services in a HFC (Hybrid Fiber and Coax) network, comprising: 
 a directional filter for separating downstream signals from upstream signals; and    a level controller for controlling the level of the downstream signals in accordance with a downstream pilot signal contained within said downstream signals and for controlling the level of the upstream signals in accordance with an upstream pilot signal.