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.

What is claimed is: 
     
       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 wireless transceiver in communication with one or more remote transceivers in a secondary network coexisting with a primary user associated with a primary signal, comprising:
 a radio transceiver transferring data between active ones of the remote transceivers during a first time period in one of a plurality of channels of the secondary network;   a controller to coordinate the transfer of data between the active ones of the remote transceivers, to coordinate the first time period between the one or more remote transceivers, and to select one of the plurality of channels in which to operate the secondary network,   wherein, the controller, coupled to the radio transceiver, monitors a presence or an absence of the primary signal within a monitored one of the plurality of channels;   wherein, the controller, via the radio transceiver, communicates to active ones of the remote transceivers to enter a receive-only mode to receive signals during a second time period in the monitored one of the plurality of channels, and   in the presence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, denies the transfer of data in the secondary network by the remote transceivers in the monitored one of the plurality of channels, and   in the absence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, communicates to active ones of the remote transceivers to operate the secondary network in the monitored one of the plurality of channels.   
     
     
       11. The wireless transceiver of claim 10, wherein when the controller, via the radio transceiver, communicates to the active ones of the remote transceivers to enter the receive-only mode, the controller enables synchronization of the second time period among all of the plurality of transceivers. 
     
     
       12. The wireless transceiver of claim 10, wherein during the second time period, the controller receives measurements of background signals in a communication channel not used by the remote transceivers. 
     
     
       13. The wireless transceiver of claim 10, wherein during the second time period, the controller receives measurements of background signals in a communication channel used by the remote transceivers. 
     
     
       14. The wireless transceiver of claim 10, wherein during the second time period, the controller restricts transmission by at least one of the remote transceivers on a channel associated with the primary signal. 
     
     
       15. The wireless transceiver of claim 14, wherein the controller restricts transmission by the at least one of the remote transceivers on the channel associated with the primary signal by reduction of the at least one of the remote transceivers' maximum transmitted power. 
     
     
       16. A method of communication by a wireless transceiver with one or more remote transceivers in a secondary network coexisting with a primary user associated with a primary signal, comprising:
 transferring, by a radio transceiver, data between active ones of the remote transceivers during a first time period in one of a plurality of channels of the secondary network;   a controller to coordinate the transfer of data between the active ones of the remote transceivers, to coordinate the first time period between the one or more remote transceivers, and to select one of the plurality of channels to operate the secondary network,   wherein, the controller, coupled to the radio transceiver, monitors a presence and an absence of the primary signal within a monitored one of the plurality of channels;   wherein, the controller, via the radio transceiver, communicates to active ones of the remote transceivers to enter a receive-only mode to receive signals during a second time period in the monitored one of the plurality of channels, and
 in the presence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, denies the transfer of data in the secondary network by the remote transceivers in the in the monitored one of the plurality of channels, and 
 in the absence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, communicates to active ones of the remote transceivers to operate the secondary network in the monitored one of the plurality of channels. 
   
     
     
       17. The method of claim 16, wherein when the controller, via the radio transceiver, communicates to the active ones of the remote transceivers to enter the receive-only mode, further comprising enabling synchronization of the second time period among all of the plurality of transceivers. 
     
     
       18. The method of claim 16, wherein during the second time period, receiving, by the controller, measurements of background signals in a communication channel not used by the remote transceivers. 
     
     
       19. The method of claim 16, wherein during the second time period, receiving, by the controller, measurements of background signals in a communication channel used by the remote transceivers. 
     
     
       20. The method of claim 16, wherein during the second time period, restricting, by the controller, transmission by at least one of the remote transceivers on a channel associated with the primary signal. 
     
     
       21. The method of claim 20, wherein the restricting transmission by the at least one of the remote transceivers on the channel associated with the primary signal includes reducing of the at least one of the remote transceivers' maximum transmitted power. 
     
     
       22. A remote transceiver in communication with a base station wireless transceiver in a secondary network coexisting with a primary user associated with a primary signal, comprising:
 a radio transceiver transferring data between the remote transceiver and the base station wireless transceiver during a first time period in one of a plurality of channels of the secondary network;   a controller to coordinate the transfer of data between the remote transceiver and the base station wireless transceiver, to coordinate the first time period based on a communication from the base station wireless transceiver, and to select one of the plurality of channels to operate the secondary network based on the communication from the base station wireless transceiver,   wherein, the base station wireless transceiver monitors a presence or an absence of the primary signal within a monitored one of the plurality of channels; and   wherein, the remote transceiver enters a receive-only mode to receive signals during a second time period in the monitored one of the plurality of channels based on the communication from the base station wireless transceiver, and
 in the presence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, denies the transfer of data in the secondary network by the remote transceiver in the monitored one of the plurality of channels, and 
 in the absence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, operates the secondary network in the monitored one of the plurality of channels. 
   
     
     
       23. A method of communication by a remote transceiver in communication with a base station wireless transceiver in a secondary network coexisting with a primary user associated with a primary signal, comprising:
 transferring, by a radio transceiver, data between the remote transceiver and the base station wireless transceiver during a first time period in one of a plurality of channels of the secondary network;   coordinating, by a controller, the transfer of data between the remote transceiver and the base station wireless transceiver, coordinating the first time period based on a communication from the base station wireless transceiver, and selecting one of the plurality of channels to operate the secondary network based on the communication from the base station wireless transceiver,   wherein, the base station wireless transceiver monitors a presence or an absence of the primary signal within a monitored one of the plurality of channels; and   entering, by the remote transceiver, a receive-only mode to receive signals during a second time period in the monitored one of the plurality of channels based on the communication from the base station wireless transceiver, and
 in the presence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, denying the transfer of data in the secondary network by the remote transceiver in the monitored one of the plurality of channels, and 
   in the absence of the primary signal in the monitored one of the plurality of channels, the controller, via the radio transceiver, operating the secondary network in the monitored one of the plurality of channels.