Method and system for detecting non-linear devices

Abstract

To assist with the detection of unfiltered device(s), a system observes how the received noise changes between two links as the transmit signal is changed. Harmful unfiltered nonlinear devices will generate significant noise that depends on the transmitted signals; therefore, this additional noise can be quantified to some extent by comparing the observed noise for two different transmit signals. The total noise can be determined from the SNR if the received signal is known. The received signal may be read directly in some non-standard systems, or it may be determined from the known transmit signal and channel attenuation, which is sometimes the case in standard-compliant links, but often with a relatively large error. To circumvent this problem, certain embodiments of this invention only consider the change in noise between two links with the same channel attenuation. This differential comparison makes it unnecessary to accurately know the channel attenuation.

The invention claimed is: 
     
       1. An unfiltered device detection method, implemented by an unfiltered device detection system, comprising:
 initiating a first link with a first power spectral density (PSD) profile; 
 obtaining and storing, in a memory, first signal to noise ratio (SNR) and transmit power levels based on the first link; 
 initiating a second link with a second PSD profile different than the first PSD profile; 
 obtaining and storing, in a memory, second SNR and transmit power levels based on the second link; and 
 identifying, by processing circuitry, at least one unfiltered device by comparing the first SNR and transmit power levels to the second SNR and transmit power levels, 
 wherein the comparison of the first SNR and transmit power levels to the second SNR and transmit power levels is made to determine a ratio of a noise on the first link, N 1 , to a noise on the second link, N 2 , as follows:
     N 1 / N 2=( S 1* SNR 2)/( S 2* SNR 1), 
 
 where S 1  and S 2  are the respective transmit power levels on the first link and second link, and SNR 1  and SNR 2  are the respective SNR values on the first link and second link, and 
 the at least one unfiltered device is determined to be present when the value of N 1 /N 2  is above a predetermined threshold value. 
 
     
     
       2. The method of  claim 1 , further comprising determining an upper SNR boundary. 
     
     
       3. The method of  claim 1 , further comprising one or more of generating a report and formulating an instruction. 
     
     
       4. The method of  claim 3 , wherein the instruction is to install a micro filter. 
     
     
       5. The method of  claim 1 , further comprising determining whether a noise change is one or more of reasonable and significant. 
     
     
       6. The method of  claim 1 , further comprising determining whether a noise change bound across monitored subcarriers is one or more of reasonable and significant. 
     
     
       7. The method of  claim 1 , further comprising determining whether the SNR and transmit power levels are observable. 
     
     
       8. The method of  claim 1 , wherein the steps are performed for either a link over a communications channel or for packet transmission. 
     
     
       9. The method of  claim 1 , wherein the unfiltered device is one or more of a telephone, answering machine and fax machine. 
     
     
       10. An unfiltered device detection system comprising:
 a memory; and 
 processing circuitry configured to:
 initiate a first link with a first power spectral density (PSD) profile; 
 obtain and store into the memory first signal to noise ratio (SNR) and transmit power levels based on the first link; 
 initiate a second link with a second PSD profile different than the first PSD profile; 
 obtain and store, in the memory, second SNR and transmit power levels based on the second link; and 
 
 identify at least one unfiltered device by comparing the first SNR and transmit power levels to the second SNR and transmit power levels, 
 wherein the comparison of the first SNR and transmit power levels to the second SNR and transmit power levels is made to determine a ratio of a noise on the first link, N 1 , to a noise on the second link, N 2 , as follows:
     N 1/ N 2=( S 1* SNR 2)/( S 2* SNR 1), 
 
 where S 1  and S 2  are the respective transmit power levels on the first link and second link, and SNR 1  and SNR 2  are the respective SNR values on the first link and second link, and
 the at least one unfiltered device is determined to be present when the value of N 1 /N 2  is above a predetermined threshold value. 
 
 
     
     
       11. The system of  claim 10 , the processing circuitry being further configured to determine an upper SNR boundary. 
     
     
       12. The system of  claim 10 , the processing circuitry being further configured to generate a report and formulate an instruction. 
     
     
       13. The system of  claim 12 , wherein the instruction is to install a micro filter on a communications channel. 
     
     
       14. The system of  claim 10 , the processing circuitry being further configured to determine whether a noise change is one or more of reasonable and significant. 
     
     
       15. The system of  claim 10 , the processing circuitry being further configured to determine whether a noise change bound across monitored subcarriers is one or more of reasonable and significant. 
     
     
       16. The system of  claim 10 , the processing circuitry being further configured to determine whether the SNR and transmit power levels are observable. 
     
     
       17. The system of  claim 10 , wherein the system detects unfiltered devices for either a link over a communications channel or for packet transmission. 
     
     
       18. The system of  claim 10 , wherein the unfiltered device is one or more of a telephone, answering machine and fax machine.