System and method for reuse of communications spectrum for fixed and mobile applications with efficient method to mitigate interference

Abstract

A communications system network that enables secondary use of spectrum on a non-interference basis is disclosed. Each secondary transceiver measures the background spectrum. The system uses a modulation method to measure the background signals that eliminates self-generated interference and also identifies the secondary signal to all primary users via on/off amplitude modulation, allowing easy resolution of interference claims. The system uses high-processing gain probe waveforms that enable propagation measurements to be made with minimal interference to the primary users. The system measures background signals and identifies the types of nearby receivers and modifies the local frequency assignments to minimize interference caused by a secondary system due to non-linear mixing interference and interference caused by out-of-band transmitted signals (phase noise, harmonics, and spurs). The system infers a secondary node's elevation and mobility (thus, its probability to cause interference) by analysis of the amplitude of background signals. Elevated or mobile nodes are given more conservative frequency assignments that stationary nodes.

1. A method for a network of secondary communication devices consisting of transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel, 
 each secondary transceiver communicating the signal level to the central controller, and 
 the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value, 
 wherein a portion of the secondary transceivers and secondary base stations in a region distant from where the channel is being used sequentially transmit a short duration probe signal with a certain power level (P_probe), 
 the secondary transceivers and secondary base stations within a primary region where the channel is being used measure the probe signal amplitude value (P_received) and send these values to the central controller, and 
 the central controller determines the maximum power level for each secondary transceivers and secondary base stations in the distant region by the formula: P_transmission (dBm)=P_probe (dBm)−P_received (dBm)+constant, with the value of the constant depending on the maximum interference level allowed in the primary region plus a safety margin, and 
 the above steps are repeated at regular intervals. 
 
     
     
       2. The method according to  claim 1 , further comprising the step of:
 using high processing gain probe waveforms such as, but not limited to, direct sequence waveforms, single or multiple continuous wave (CW) tones. 
 
     
     
       3. The method of  claim 2 , wherein the high processing gain probe waveform is either multiple CW waveforms or combinations of narrowband waveforms, each with energy in a frequency zone within the NTSC six MHz channel width and minimal energy at other frequencies in the channel, the frequency zone being in the lower and upper guard bands, between the video carrier and the color-subcarrier, or between the color-subcarrier and the sound carrier. 
     
     
       4. A method for a network of secondary communication devices consisting of transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel, 
 each secondary transceiver communicating the signal level to the central controller, 
 the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value, 
 wherein a modulation scheme where each secondary transceiver and secondary base station transmits and receives data for a certain time period, then simultaneously halts transmissions, making measurements of the background signals for a time period, and then either transmitting or receiving probe signals. 
 
     
     
       5. A method for a network of secondary communication devices consisting of transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel, 
 each secondary transceiver communicating the signal level to the central controller, 
 the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value, 
 wherein proximate primary receivers are identified to each secondary transceivers and secondary base stations by having each secondary transceiver and secondary base station measure the strength of all strong signals within a certain range of the spectrum, and 
 those signals with a power level above a threshold value declare that these are proximate nodes, and 
 determine the proximate radio's receive frequency using well-known standards information, and 
 restricting the secondary transceiver's or secondary base station's transmit frequency list from harmonically related values, adjacent channel values, or image related values compared to the primary signal. 
 
     
     
       6. A method for a network of secondary communication devices consisting of transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel, 
 each secondary transceiver communicating the signal level to the central controller, and 
 the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value, 
 wherein proximate primary receive only radios are identified to each secondary transceivers and secondary base stations by having each secondary transceivers and secondary base stations measure the strength of the primary receiver's local oscillator leakage, and 
 and those signals above a threshold value declare that these is a proximate receive-only node, and 
 determine the proximate receiver's frequency using well-known standards information, and 
 restricting the secondary transceivers or secondary base station's transmit frequency list from harmonically related values, adjacent channel values, or image related values compared to the primary signal. 
 
     
     
       7. A method for a network of secondary communication devices to share the analog TV spectrum consisting of the steps of,
 each secondary transceivers and secondary base stations measuring the strength of the background TV signal strength, and 
 if the primary TV signal strength is greater than a certain level above the noise level but less than another higher level, then 
 the secondary system will use a waveform with energy between 1.5 MHz above the channel start frequency and 4.5 MHz above the channel start frequency to avoid interference caused by the analog video and sound carriers. 
 
     
     
       8. A method for a network of secondary communication devices consisting of transceivers, base stations and a central controller to identify which device is causing Interference to a primary user comprising of the steps of, 
       a method to unambiguously marking the secondary system's signal when received by the primary receiver such as, but not limited to, amplitude modulating the secondary signal, and
 provide a method for the affected primary user to communicate with the secondary system's central controller and communicate the primary receiver's location and the channel frequency, and 
 the central controller determine the closest secondary transceiver or secondary base station to the primary node and the likely frequencies being transmitted that might cause the interference, and 
 command the secondary transceiver or secondary base station to transmit data, and 
 sequentially reducing the power of the closet secondary transceiver or base station until the primary user reports that the problem is resolved, and 
 if the interference to the primary receiver continues, determine the next closest secondary transceiver or secondary base station to the primary node and repeating the previous step until the secondary node causing the Interference is located. 
 
     
     
       9. A method for a network of secondary communication devices consisting of transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel, 
 each secondary transceiver communicating the signal level to the central controller, and 
 the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value, 
 wherein each secondary transceivers arid secondary base stations measures the strength of multiple signals from several other stationary transmitters and by analysis of these signal level amplitudes and if there is significant co-channel interference determines if the secondary transceiver or secondary base station is moving or elevated, and 
 
       if the secondary transceiver or secondary base station is moving or elevated, then the node will use more conservative spectrum assignments that include one or more of the following: reducing the node's maximum transmitted power, Increasing the repetition rate of the node's probing and primary signal level measurements, and use of another channel. 
     
     
       10. A method for a network of secondary communication devices comprising transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users, the method comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel,   each secondary transceiver communicating the signal level to the central controller, and   the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value,   wherein a portion of the secondary transceivers and secondary base stations in a region distant from where the channel is being used sequentially transmit a short duration probe signal with a certain power level (P — probe),   the secondary transceivers and secondary base stations within a primary region where the channel is being used measure the probe signal amplitude value (P received) and send these values to the central controller, and   the central controller determines the maximum power level for each secondary transceivers and secondary base stations in the distant region by the formula: P transmission (dBm)=P — probe (dBm)−P received (dBm)+constant, with the value of the constant depending on the maximum interference level allowed in the primary region plus a safety margin, and   the above steps are repeated at regular intervals.   
     
     
       11. The method according to claim 10, further comprising the step of:
 using high processing gain probe waveforms such as, but not limited to, direct sequence waveforms, single or multiple continuous wave (CW) tones.   
     
     
       12. The method of claim 11, wherein the high processing gain probe waveform is either multiple CW waveforms or combinations of narrowband waveforms, each with energy in a frequency zone within the NTSC six MHz channel width and minimal energy at other frequencies in the channel, the frequency zone being in the lower and upper guard bands, between the video carrier and the color-subcarrier, or between the color-subcarrier and the sound carrier. 
     
     
       13. A method for a network of secondary communication devices comprising of transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users, the method comprising the steps of: each secondary transceiver and secondary base station measuring the primary signal level in the channel,
 each secondary transceiver communicating the signal level to the central controller,   the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value,   wherein each secondary transceiver and secondary base station transmits and receives data for a certain time period, then simultaneously halts transmissions, makes measurements of the background signals for a time period, and then either transmits or receives probe signals.   
     
     
       14. A method for a network of secondary communication devices comprising transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users, the method comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel,   each secondary transceiver communicating the signal level to the central controller,   the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value,   determining a proximate radio's receive frequency using well-known standards information, and   restricting the secondary transceiver's or secondary base station's transmit frequency list from harmonically related values, adjacent channel values, or image related values compared to the primary signal,   wherein proximate primary receivers are identified to each secondary transceiver and secondary base station by having each secondary transceiver and secondary base station measure the strength of all strong signals within a certain range of the spectrum, each signal with a power level above a threshold value indicating a proximate nodes.   
     
     
       15. A method for a network of secondary communication devices comprising transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users, the method comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel,   each secondary transceiver communicating the signal level to the central controller, and the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value,   wherein proximate primary receive only radios are identified to each secondary transceiver and secondary base station by having each secondary transceivers and secondary base stations measure the strength of the primary receiver's local oscillator leakage, those signals above a threshold value indicating a proximate receive-only node,   determining the proximate receiver's frequency using well-known standards information,   restricting the secondary transceivers' or secondary base station's transmit frequency list from harmonically related values, adjacent channel values, or image related values compared to the primary signal.   
     
     
       16. A method for a network of secondary communication devices to share the analog TV spectrum, the method comprising:
 each secondary transceiver and secondary base station measuring the strength of the background TV signal strength, and   if the primary TV signal strength is greater than a certain level above the noise level but less than another higher level, then   using, by the secondary system, a waveform with energy between 1.5 MHz above the channel start frequency and 4.5 MHz above the channel start frequency to avoid interference caused by the analog video and sound carriers.   
     
     
       17. A method for a network of secondary communication devices comprising transceivers, base stations and a central controller to identify which device is causing interference to a primary user, the method comprising:
 marking the secondary system's signal when received by the primary receiver by amplitude modulating the secondary signal,   providing a method for an affected primary user to communicate with the secondary system's central controller and communicate the primary receiver's location and the channel frequency,   determining, at the central controller, the closest secondary transceiver or secondary base station to the primary node and the likely frequencies being transmitted that might cause the interference,   commanding the secondary transceiver or secondary base station to transmit data,   sequentially reducing the power of the closet secondary transceiver or base station until the primary user reports that the problem is resolved, and   if the interference to the primary receiver continues, determine the next closest secondary transceiver or secondary base station to the primary node and repeating the previous step until the secondary node causing the interference is located.   
     
     
       18. A method for a network of secondary communication devices comprising transceivers, base stations and a central controller sharing a radio frequency channel with existing primary users with minimal interference to the primary users, the method comprising the steps of:
 each secondary transceiver and secondary base station measuring the primary signal level in the channel,   each secondary transceiver communicating the signal level to the central controller, and   the central controller determining which channels each node may potentially use by comparing the primary signal level to a threshold value,   wherein each secondary transceiver and secondary base station measures the strength of multiple signals from several other stationary transmitters and by analysis of these signal level amplitudes and if there is significant co-channel interference determines if the secondary transceiver or secondary base station is moving or elevated, and   if the secondary transceiver or secondary base station is moving or elevated, using more conservative spectrum assignments that include one or more of the following: reducing the node's maximum transmitted power, increasing the repetition rate of the node's probing and primary signal level measurements, and use of another channel.   
     
     
       19. A method for a plurality of transceivers to communicate using at least one channel in the broadcast television frequency bands, the method comprising:
 each transceiver measuring background TV signal strength;   determining whether the measured TV signal strength is greater than a first level and less than a second level, the second level being higher than the first level; and   if the measured TV signal strength is greater than the first level and less than the second level, using a waveform with energy above a start frequency of the at least one channel.   
     
     
       20. The method of claim 19, wherein the first level is at least the noise level and the second level is not greater than a threshold value used to identify the channel as available for use. 
     
     
       21. A method for a plurality of cooperative transceivers and a central controller to communicate using a radio frequency channel, the method comprising:
 providing a means for a non-cooperative node to identify the non-cooperative node's location and the channel on which interference is received;   identifying a first cooperative node and associated likely frequency being transmitted that might cause the interference;   commanding the identified first node to transmit data;   sequentially reducing the power of the identified first node until the non-cooperative node reports that the interference is decreased; and   if the interference to the non-cooperative node continues, repeating the previous step until a node causing the interference is located.   
     
     
       22. The method of claim 21, wherein the first node is the closest of the plurality of transceivers to the non-cooperative receiver. 
     
     
       23. The method of claim 21, wherein the non-cooperative node's location and the channel on which interference is received is communicated to the central controller. 
     
     
       24. A system comprising a plurality of transceivers, each transceiver configured to measure background TV signal strength in at least one channel; said system configured to:
 determine whether the measured TV signal strength is greater than a first level and less than a second level, the second level being higher than the first level; and   if the measured TV signal strength is greater than the first level and less than the second level, configure the system to use a waveform with energy above a start frequency of the at least one channel to communicate among the plurality of transceivers.   
     
     
       25. The system of claim 24, wherein the first level is at least the noise level and the second level is not greater than a threshold value used to identify the channel as available for use. 
     
     
       26. A system comprising:
 a plurality of cooperative transceivers; and   a central controller;   at least one of said cooperative transceivers or said central controller configured to provide a means for a non-cooperative node to identify the non-cooperative node's location and a channel on which interference is received;   said central controller further configured to:
 identify a first of the plurality of cooperative transceivers and an associated likely frequency being transmitted that might cause the interference; and 
 command the identified first cooperative transceiver to transmit data; 
   said identified first cooperative node configured to sequentially reduce the power of the commanded transmission until the non-cooperative node reports that the interference is decreased and, if the interference to the non-cooperative node continues, sequentially reduce the power of the commanded transmission until a node causing the interference is located.   
     
     
       27. The system of claim 26, wherein the first node is the closest of the plurality of transceivers to the non-cooperative receiver. 
     
     
       28. The system of claim 26, wherein the non-cooperative node's location and the channel on which interference is received is communicated to the central controller. 
     
     
       29. A device comprising:
 a communication module configured to measure background TV signal strength in at least one channel; and   a processor configured to:
 determine whether the measured TV signal strength is greater than a first level and less than a second level, the second level being higher than the first level; and 
   if the measured TV signal strength is greater than the first level and less than the second level, configure the communication module to use a waveform with energy above a start frequency of the at least one channel to communicate with a plurality of transceivers.   
     
     
       30. The device of claim 29, wherein the first level is at least the noise level and the second level is not greater than a threshold value used to identify the channel as available for use. 
     
     
       31. The device of claim 29, wherein said communication module comprises a tuner, a programmable modem, or a combination thereof. 
     
     
       32. A device comprising:
 a communication module configured to communicate with a plurality of cooperative transceivers;   a processor configured to:
 provide a means for a non-cooperative node to identify the non-cooperative node's location and a channel on which interference is received; 
 identify a first of the plurality of cooperative transceivers and an associated likely frequency being transmitted that might cause the interference; and 
 command the identified first cooperative transceiver to transmit data at sequentially reduced power until the non-cooperative node reports that the interference is decreased and, if the interference to the non-cooperative node continues, sequentially reduce the power of the commanded transmission until a node causing the interference is located. 
   
     
     
       33. The device of claim 32, said communication module further configured to receive the non-cooperative node's location and the channel on which interference is received. 
     
     
       34. The device of claim 32, wherein said communication module is a tuner, a programmable modem, or a combination thereof.