System and method for reuse of communication 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 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 in 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 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 identity 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 as 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 of 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 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 and 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 of allocating channels in a wireless communication system, the method comprising:
 coordinating a measurement interval with a plurality of transceivers during which at least a first transceiver of the plurality of transceivers halts transmissions;   receiving a signal strength measurement made during the measurement interval from each of the plurality of transceivers; and   allocating a channel to at least a second transceiver of the plurality of transceivers based at least in part on the signal strength measurements.   
     
     
       11. The method of claim 10, further comprising the step of coordinating a test interval for each of the plurality of transceivers, during which at least one of the plurality of transceivers transmits a predetermined signal. 
     
     
       12. The method of claim 11, wherein the predetermined signal is a probe signal. 
     
     
       13. The method of claim 11, wherein each of the plurality of transceivers transmits the predetermined signal during the test interval. 
     
     
       14. The method of claim 11, wherein the signal strength measurement is a measurement of the predetermined signal by at least one of the plurality of transceivers. 
     
     
       15. The method of claim 10, further comprising the step of receiving a measurement of at least one predetermined signal from at least one of the plurality of transceivers, and
 wherein the step of allocating the channel is further based in part on the measurement of the at least one predetermined signal.   
     
     
       16. The method of claim 15, further comprising the steps of:
 determining a maximum transmit power associated with the allocated channel based on the measurements of the at least one signal; and   communicating the maximum transmit power to the second transceiver.   
     
     
       17. The method of claim 15, wherein the step of receiving the measurement of the at least one predetermined signal from the at least one of the plurality of transceivers comprises receiving a measurement of the amplitude of the at least one predetermined signal from each of the plurality of transceivers, wherein the step of allocating the channel is further based at least in part on the measurements of the at least one predetermined signal amplitude. 
     
     
       18. The method of claim 10, further comprising the step of:
 determining whether at least one of the plurality of transceivers is mobile, and   wherein allocating the channel is based in part on the mobility of the transceiver.   
     
     
       19. The method of claim 10, further comprising the step of:
 determining whether the at least one of the plurality of transceivers is elevated, and   wherein the step of allocating the channel is based in part on whether the at least one of the plurality of transceivers is elevated.   
     
     
       20. The method of claim 10, wherein the step of coordinating the measurement interval comprises synchronizing the measurement interval to substantially a same time period. 
     
     
       21. The method of claim 10, wherein the step of coordinating the measurement interval comprises coordinating a duration of the measurement interval such that each of the plurality of transceivers operates within the measurement interval for not more than one percent of operating time. 
     
     
       22. The method of claim 10, wherein the step of receiving the signal strength measurement comprises receiving a signal strength measurement of a signal sent by a transmitter that is not a part of the wireless communication system. 
     
     
       23. The method of claim 10, wherein the step of receiving the signal strength measurement comprises receiving a signal strength measurement of a television signal. 
     
     
       24. The method of claim 10, wherein the step of receiving the signal strength measurement comprises:
 providing a list of proposed channels to a first transceiver; and   receiving the measurement of the channel from the list of proposed channels from the first transceiver.   
     
     
       25. The method of claim 24, wherein the step of allocating the channel to at least one of the plurality of transceivers comprises allocating at least one channel from the list of proposed channels to the first transceiver. 
     
     
       26. The method of claim 10, wherein the step of allocating the channel to at least one of the plurality of transceivers comprises:
 comparing the signal strength measurement to a predetermined threshold;   determining an allocation list based in part on the comparison; and   allocating a channel from the allocation list.   
     
     
       27. The method of claim 26, wherein the allocation list is determined based at least in part on a regulatory database of emitters. 
     
     
       28. The method of claim 26, wherein the transmission power is determined based at least in part on a regulatory database. 
     
     
       29. The method of claim 10, wherein the second transceiver is the first transceiver. 
     
     
       30. A wireless communication device comprising:
 a processor configured to coordinate a measurement interval with a plurality of transceivers during which each of the plurality of transceivers halts transmissions; and   a transceiver configured to receive a signal strength measurement made during the measurement interval from at least a first transceiver of the plurality of transceivers;   wherein the processor is further configured to allocate a channel to at least a second transceiver of the plurality of transceivers based at least in part on the signal strength measurement.   
     
     
       31. The device of claim 30, said processor further configured to coordinate a test interval for each of the plurality of transceivers, during which at least one of the plurality of transceivers transmits a predetermined signal. 
     
     
       32. The device of claim 31, wherein the predetermined signal is a probe signal. 
     
     
       33. The device of claim 30, wherein receiving the signal strength measurement comprises:
 providing a list of proposed channels to a first transceiver; and   receiving the measurement of the channel from the list of proposed channels from the first transceiver.   
     
     
       34. The device of claim 33, wherein allocating the channel to at least one of the plurality of transceivers comprises allocating at least one channel from the list of proposed channels to the first transceiver. 
     
     
       35. The device of claim 31, said processor further configured to allocate the channel further based in part on a measurement of the at least one predetermined signal. 
     
     
       36. The device of claim 35, said processor further configured to determine a maximum transmit power associated with the allocated channel based on the at least one measurement of the at least one signal, and to communicate the maximum transmit power to the second transceiver. 
     
     
       37. The device of claim 36, wherein the step of receiving the measurement of the at least one predetermined signal from the at least one of the plurality of transceivers comprises receiving a measurement of the amplitude of the at least one predetermined signal from each of the plurality of transceivers, wherein the step of allocating the channel is further based at least in part on the measurements of the at least one predetermined signal amplitude. 
     
     
       38. The device of claim 30, said processor further configured to determine whether at least one of the plurality of transceivers is mobile;
 wherein allocating the channel is based in part on the mobility of the transceiver.   
     
     
       39. The device of claim 30, said processor further configured to determine whether the at least one of the plurality of transceivers is elevated;
 wherein the step of allocating the channel is based in part on whether the at least one of the plurality of transceivers is elevated.   
     
     
       40. The device of claim 30, wherein coordinating the measurement interval comprises synchronizing the measurement interval to substantially a same time period. 
     
     
       41. The device of claim 30, wherein coordinating the measurement interval comprises coordinating a duration of the measurement interval such that each of the plurality of transceivers operates within the measurement interval for not more than one percent of operating time. 
     
     
       42. The device of claim 30, wherein receiving the signal strength measurement comprises receiving a signal strength measurement of a signal sent by a transmitter that is not a part of the wireless communication system. 
     
     
       43. The device of claim 30, wherein receiving the signal strength measurement comprises receiving a signal strength measurement of a television signal. 
     
     
       44. The device of claim 30, wherein the allocating the channel to at least one of the plurality of transceivers comprises:
 comparing the signal strength measurement to a predetermined threshold;   determining an allocation list based in part on the comparison; and   allocating a channel from the allocation list.   
     
     
       45. The device of claim 44, wherein the allocation list is determined based at least in part on a regulatory database of transmitters. 
     
     
       46. The device of claim 44, wherein the transmission power is determined based at least in part on a regulatory database. 
     
     
       47. The device of claim 30, wherein the second transceiver is the first transceiver. 
     
     
       48. The device of claim 31, wherein each of the plurality of transceivers transmits the predetermined signal during the test interval. 
     
     
       49. The device of claim 31, wherein the signal strength measurement is a measurement of the predetermined signal by at least one of the plurality of transceivers. 
     
     
       50. A system comprising a plurality of wireless communication devices, at least one of said plurality of wireless communication devices comprising a device as recited in claim 30.