Method and apparatus to provide communication protection technology for satellite earth stations

Abstract

An interference signal canceling system for communications protection is described for canceling interference signals from earth station received signals using a two input adaptive cancellation network. The present invention addresses terrestrial, co-channel and adjacent satellite interference sources resulting from emitting, isolated, frequency re-use and polarized sources. Main and auxiliary signals are derived directly or by coherent conversion to intermediate frequency using an auxiliary antenna, cross-polarized feed, or auxiliary squinted feed. Filters set receive and canceling bands. Cancellation combines the main signal with a phase, amplitude and time modulated sample of the auxiliary signal. A receiver correlates the auxiliary signal with a sample of the combined output to minimize interference. A control drives the modulator from internal measurements, or satellite receiver measurements, i.e., BER, C/No, SNR, etc., or both. The control searches the modulation space to locate interference nulls followed by null acquisition and tracking to maximize cancellation effects. The present invention is also configurable for multiple interferences using series and parallel arrangements.

We claim:  
     
         1 . A system for communication protection that reduces interference signals in L-band, C-band or Ku-band satellite down links resulting from terrestrial, co-channel or adjacent channel satellite interference signals resulting from a variety of sources, the system comprising: 
 Antenna or interface means for receiving the main satellite down link signal directly or by down conversion to a convenient intermediate frequency,    An auxiliary reference input port means for receiving and discriminating in band interference or jamming signals using either a separate auxiliary antenna, antenna feed or transmission line reference signal, used either directly or by down conversion to the same intermediate frequency,    Coherent and synchronized down conversion means for both main and auxiliary signals effectively using the same reference local oscillator from a common source for injection into the main conversion path and to the auxiliary conversion path, phase locking or injection locking the local oscillator of the auxiliary conversion path to the local oscillator of the main conversion path, or providing a common reference clock signal from a common source to all conversion paths using a separate phase lock loop (PLL) local oscillator circuit for each conversion path, etc.,    A group delay equalization network in the main and/or auxiliary paths to match the cumulative delays in the main and auxiliary signals so that the interference signal components substantially correspond in the frequency range or bandwidth of interest,    An auxiliary channel filter in the auxiliary signal path to select a segment of the channel or band and to discriminate against out-of-channel or out-of-band such that the signal output corresponds to the interference signal of interest,    An automatic gain control (AGC) in the auxiliary signal path to set the dynamic range of the auxiliary signal path to substantially match the signal levels of interference on the two signals to the gain and dynamic range of the signal modulator.    A reference coupler connected to the auxiliary input port following delay and gain control with a portion of the reference signal being provided for modulation and substantially representing the interference signal, the remaining portion of the reference signal being provided as a reference local oscillator for correlation with a sample of the system output error,    A summing coupler connected to the main input port following delay control with the input port coupled to the main received signal, the second input port coupled to a modulated sample of the auxiliary input signal, and the output port being the sum of the two signals providing the cancellation signal,    A channel filter in the post-cancellation error signal path to establish the bandwidth of the main channel and interference signal and the bandwidth of the cancellation process either coupled to the output port of the summing coupler after cancellation and whose output is provided to the input to the output coupler, or coupled to the error monitor port of the output coupler and whose output is provided to the correlating receiver as the error signal,    An output coupler coupled to the output of the summing coupler or the output of the channel filter receiving a signal corresponding to the sum of the main receive signals and the modulated auxiliary signal, and corresponding to the cancellation or error signal,    A correlating receiver having a first input coupled to the cancellation or error signal and a second input coupled to the auxiliary input reference coupler and responsive to these two signals where the reference signal serves as the local oscillator, the correlating receiver determining the phase and amplitude relationship between the reference and error signals, and providing a two port output conveying a measure of the error signal correlated to the reference signal in a defined bandwidth, either as quadrature (I/Q) signals, or as magnitude and phase signals,    A system control having two inputs corresponding to the two output ports of the correlating receiver and responsive to error or cancellation signal magnitude and phase, applying the interference detection and suppression algorithm by providing two output ports to a signal modulator to modulate the auxiliary reference signal to cancel the interference, an output port to optimize the delay mismatch between the main received and the auxiliary reference signals, an output port to set the gain and dynamic range of the auxiliary reference signal into the process, and an output port consisting of a system data bus to communicate between control functions in other channels or bands and in an integrated manner with the satellite receiver to receive performance measurements of the channel,    A signal modulator with input port connected to the reference coupler and output port connected to the second input port of the summing. coupler, electrically coupled to the system control, and responsive to the amplitude and phase controls for adaptive adjustment of the auxiliary signal to generate the canceling signal that is equal in level and opposite in phase with respect to the interference in the main channel.    
     
     
         2 . The system of  claim 1 , wherein the system controller and signal modulator are responsive to align the signal modulator to suppress interference using the outputs of the correlating receiver.  
     
     
         3 . The system of  claim 1 , wherein the system controller and signal modulator are responsive to align the signal modulator to suppress interference using the information on satellite signal processing performance provided by the satellite receiver.  
     
     
         4 . The system of  claim 2 , wherein the system controller, signal modulator, delay equalizer and AGC are responsive to align modulators and equalizers to suppress interference from moving and varying interference sources resulting in dynamically adaptive operation.  
     
     
         5 . The system of  claim 1 , wherein the system is responsive to terrestrial interference.  
     
     
         6 . The system of  claim 1 , wherein the system is responsive to co-channel interference.  
     
     
         7 . The system of  claim 1 , wherein the system is responsive to adjacent satellite interference.  
     
     
         8 . The system of  claim 1 , wherein the system is responsive to frequency re-use interference.  
     
     
         9 . An interference cancellation system composed of a number of systems of  claim 1  configured in a serial arrangement wherein the leading system defines the cancellation channel bandwidth and configured to cancel multiple uncorrelated interference signals each defines separately by an auxiliary reference signal, and providing interference cancellation in a common channel of operation for a satellite receiver.  
     
     
         10 . An interference cancellation system composed of a number of systems of  claim 1  configured in a parallel arrangement wherein each system defines a separate and distinct channel bandwidth and configured to cancel multiple correlated or uncorrelated interference signals defines separately by multiple auxiliary reference signals or a reference signal in multiple channels, and providing interference cancellation for multiple satellite receivers.  
     
     
         11 . An interference cancellation system composed of a number of systems of  claim 1  configured in a combination of the serial and parallel arrangements of claims  9  and  10 , wherein each system leg defines a separate and distinct channel bandwidth, each system element within each leg defines a separate interference component within the channel bandwidth, each system element is defined separately by auxiliary reference signals, and providing interference cancellation for multiple satellite receivers.  
     
     
         12 . A method for canceling an interfering signal using the system in  claim 1  and providing an output from a main received signal and an auxiliary reference signal, the method comprising: 
 A sample of an interference signal from an auxiliary input used as a reference signal;  
 A sample of a main receive signal composed of the desired receive signal and interference signal combined with a modulated variant of the reference signal, and providing an error signal corresponding to the interference;  
 A correlation between the reference and error signals to generate a set of control signals for operation of modulators and equalizers;  
 Adjusting the auxiliary signal gain and level to match the dynamic range of the interference in both the main and the reference signals;  
 Adjusting the delay mismatch between the main and reference signals to match the delay or time of the interference in both the main and reference signals;  
 Adjusting the amplitude and phase of the modulated reference signal over the control space of the modulators using a coarse or sparse scan of both dimensions to detect cancellation or null settings;  
 Adjusting the amplitude and phase of the modulated reference signal using varying control resolution and following a down hill gradient to optimize the cancellation of the interference.  
 
     
     
         13 . A method for canceling an interfering signal using the system in  claim 1  and providing an output from a main received signal and an auxiliary reference signal, the method operates in conjunction with the method in  claim 12  and comprising: 
 A sample of the signal processing performance measurement of the satellite receiver as a secondary error signal;  
 Adjusting the delay, amplitude and phase of the modulated reference signal using varying control resolution and following a down hill gradient to further optimize the cancellation of the interference.