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 method of allocating channels in a wireless communication system, the method comprising:
 coordinating a measurement interval with a plurality of transceivers during which each 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 one 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 each of the plurality of transceivers transmits a predetermined test signal.  
     
     
       12. The method of claim 11, wherein the test signal is a probe signal.  
     
     
       13. The method of claim 10, further comprising the step of receiving a measurement of the amplitude of at least one probe signal from each of the plurality of transceivers, and
 wherein the step of allocating the channel is further based in part on the measurements of the at least one probe signal amplitude.    
     
     
       14. The method of claim 13, 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 amplitude; and   communicating the maximum transmit power to the at least one of the plurality of transceivers for which the channel is allocated.    
     
     
       15. 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.    
     
     
       16. 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.    
     
     
       17. The method of claim 10, wherein the step of coordinating the measurement interval comprises synchronizing the measurement interval to substantially a same time period.  
     
     
       18. 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.  
     
     
       19. The method of claim 10, wherein the step of receiving the signal strength measurement comprises receiving a signal strength measurement of a signal from a network distinct from the wireless communication system.  
     
     
       20. The method of claim 10, wherein the step of receiving the signal strength measurement comprises receiving a signal strength measurement of a television signal.  
     
     
       21. 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 signal strength measurement of a channel from the list of proposed channels from the first transceiver.    
     
     
       22. The method of claim 21, 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.  
     
     
       23. The method of claim 10, wherein the step of allocating the channel to at least one of the plurality of transceivers comprises:
 comparing each of the signal strength measurements to a predetermined threshold;   determining an allocation list based in part on the comparisons; and   allocating a channel from the allocation list.    
     
     
       24. The method of claim 23, wherein the allocation list is determined based at least in part on a regulatory database of emitters.  
     
     
       25. A method of accessing channels in a wireless communication system, the method comprising:
 synchronizing a measurement interval with a plurality of transceivers during which each of the plurality of transceivers halts transmissions;   measuring a signal strength of a signal from a network distinct from the wireless communication system during the measurement interval; and   receiving a channel allocation based at least in part on the signal strength.    
     
     
       26. The method of claim 25, further comprising the step of communicating the signal strength to a central controller, wherein the channel allocation is received from the central controller.  
     
     
       27. The method of claim 25, further comprising the step of receiving a channel allocation list from a central controller, and
 wherein the step of measuring the signal strength comprises measuring the signal strength in each channel of the channel allocation list.    
     
     
       28. The method of claim 25, wherein the step of measuring the signal strength comprises measuring a signal strength in a channel outside of a bandwidth of the channel.  
     
     
       29. The method of claim 25, further comprising receiving a test interval assignment from the central controller.  
     
     
       30. The method of claim 29, further comprising transmitting a predetermined probe signal during the test interval assignment.  
     
     
       31. The method of claim 30, wherein the predetermined probe signal comprises at least one continuous wave (CW) signal.  
     
     
       32. The method of claim 30, wherein the predetermined probe signal comprises a BPSK waveform.  
     
     
       33. The method of claim 29, further comprising:
 receiving a test signal transmitted by one of the plurality of transceivers during the test interval;   determining a metric value based on the received test signal; and   communicating the metric value to the central controller.    
     
     
       34. The method of claim 33, wherein the metric value comprises an amplitude of the received test signal.  
     
     
       35. The method of claim 25, further comprising the steps of:
 receiving a test interval assignment from the central controller;   determining a test channel frequency; and   transmitting a predetermined test signal during the test interval assignment and at the test channel frequency.    
     
     
       36. The method of claim 25, further comprising the step of performing at least one transmitting or receiving information over the allocated channel.  
     
     
       37. The method of claim 25, further comprising the step of transmitting a signal of a predetermined waveform type over the allocated channel.  
     
     
       38. The method of claim 37, wherein the predetermined waveform type comprises an orthogonal frequency division multiplex (OFDM) signal.  
     
     
       39. The method of claim 37, further comprising the step of amplitude modulating the signal of a predetermined waveform type.  
     
     
       40. A method of accessing channels in a wireless communication system, the method comprising:
 coordinating a test interval with a plurality of transceivers;   receiving a first test signal transmitted by one of the plurality of transceivers during at least a first portion of the test interval;   determining a metric based on the received test signal; and   receiving a channel allocation based at least in part on the metric.    
     
     
       41. The method of claim 40, wherein the test signal is a probe signal.  
     
     
       42. The method of claim 40, further comprising:
 determining a test channel frequency; and   receiving the first test signal during the first portion of the test interval and at the test channel frequency.    
     
     
       43. The method of claim 40, further comprising transmitting a second test signal during at least a second portion of the test interval.  
     
     
       44. The method of claim 40, further comprising:
 determining a test channel frequency; and   transmitting a second test signal during at least a second of the test interval and at the test channel frequency.    
     
     
       45. The method of claim 40, wherein receiving the first test signal comprises receiving a plurality of continuous wave (CW) tones.  
     
     
       46. The method of claim 40, wherein receiving the first test signal comprises receiving a BPSK waveform.  
     
     
       47. The method of claim 46, wherein the BPSK waveform comprises a pseudo random sequence.  
     
     
       48. The method of claim 46, wherein the BPSK waveform comprises a signal having a bandwidth that is approximately equal to a channel allocation bandwidth.  
     
     
       49. The method of claim 40, wherein the step of determining the metric comprises determining an amplitude.  
     
     
       50. The method of claim 40, wherein determining the metric comprises the steps of:
 sampling the received first test signal to generate a plurality of samples; and   performing FFT processing on the samples.    
     
     
       51. The method of claim 40, wherein determining the metric comprises the steps of:
 sampling the received first test signal to generate a plurality of samples; and   coherently integrating the samples over a coherence time.    
     
     
       52. A method of accessing channels in a wireless communication system, the method comprising:
 receiving a channel allocation list;   synchronizing a measurement interval with a plurality of transceivers during which each of the plurality of transceivers halts transmissions;   measuring a received signal metric during the measurement interval;   associating the received signal metric with a channel from the channel allocation list; and   determining a channel allocation from the channel allocation list based at least in part on the received signal metric.    
     
     
       53. The method of claim 52, wherein measuring the received signal metric comprises:
 determining a channel from the channel allocation list; and   determining the received signal metric based in part on a signal received outside of a bandwidth of the channel.    
     
     
       54. The method of claim 53, wherein the signal received outside of the bandwidth of the channel comprises a signal received at a harmonic of the channel.  
     
     
       55. The method of claim 53, wherein the signal received outside of the bandwidth of the channel comprises a signal received at frequency determined based on a cross product of a primary signal with a secondary signal.  
     
     
       56. The method of claim 53, wherein signal received outside of the bandwidth of the channel comprises a signal received at a predetermined frequency offset from the channel.  
     
     
       57. The method of claim 56, further comprising the step of restricting transmitted power based at least in part on the received signal metric.  
     
     
       58. The method of claim 56, further comprising the step of changing to another frequency.  
     
     
       59. The method of claim 56, wherein the predetermined frequency offset is a harmonically-related frequency offset.  
     
     
       60. The method of claim 56, wherein the predetermined frequency offset comprises an adjacent channel offset.  
     
     
       61. The method of claim 56, wherein the predetermined frequency offset comprises a local oscillator frequency offset.  
     
     
       62. The method of claim 56, wherein the predetermined frequency offset comprises an IF image related offset.  
     
     
       63. The method of claim 56, wherein the predetermined frequency offset comprises a transmit/receive pair frequency offset.  
     
     
       64. A system comprising:
 a plurality of transceivers, each of the plurality of transceivers configured to halt transmissions during a measurement interval; and   a controller configured to receive a signal strength measurement made during the measurement interval from each of the plurality of transceivers;   the controller further configured to allocate a channel to at least one of the plurality of transceivers based at least in part on the signal strength measurements.    
     
     
       65. The system of claim 64, wherein the controller is one of the plurality of transceivers.  
     
     
       66. The system of claim 64, said controller further configured to coordinate a test interval for each of the plurality of transceivers, during which each of the plurality of transceivers transmits a predetermined test signal.  
     
     
       67. The system of claim 64, said controller further configured to receive a measurement of the amplitude of at least one probe signal from each of the plurality of transceivers, and to allocate the channel based in part on the measurements of the at least one probe signal amplitude.  
     
     
       68. The system of claim 67, said controller further configured to:
 determine a maximum transmit power associated with the allocated channel based on the measurements of the at least one signal amplitude; and   communicate the maximum transmit power to the at least one of the plurality of transceivers for which the channel is allocated.    
     
     
       69. The system of claim 64, wherein the step of coordinating the measurement interval comprises synchronizing the measurement interval to substantially a same time period.  
     
     
       70. The system of claim 64, wherein the signal strength measurement comprises a measurement of a signal from a network distinct from the wireless communication system.  
     
     
       71. The system of claim 64, said controller further configured to allocate the channel based at least in part on a regulatory database of emitters.  
     
     
       72. A transceiver configured to:
 coordinate a measurement interval with at least one other transceiver during which each of the transceivers halts transmissions;   receive a signal strength measurement made during the measurement interval from the at least one other transceiver; and   allocate a channel to the at least one other transceiver based at least in part on the signal strength measurements.    
     
     
       73. The transceiver of claim 72, further configured to communicate the signal strength to a central controller, wherein the channel allocation is received from the central controller.  
     
     
       74. The transceiver of claim 72, further configured to measure the signal strength in a channel outside of a bandwidth of the channel.  
     
     
       75. The system of claim 72, further configured to perform at least one transmitting or receiving information over the allocated channel.  
     
     
       76. The system of claim 72, further configured to transmit a signal of a predetermined waveform type over the allocated channel.  
     
     
       77. A device configured to:
 receive a channel allocation list;   synchronize a measurement interval with a plurality of transceivers during which each of the plurality of transceivers halts transmissions;   measure a received signal metric during the measurement interval;   associate the received signal metric with a channel from the channel allocation list; and   determine a channel allocation from the channel allocation list based at least in part on the received signal metric.    
     
     
       78. The device of claim 77, further configure to measure the received signal metric by:
 determining a channel from the channel allocation list; and   determining the received signal metric based in part on a signal received outside of a bandwidth of the channel.    
     
     
       79. The device of claim 78, wherein the signal received outside of the bandwidth of the channel comprises a type selected from the group consisting of: a signal received at a harmonic of the channel, a signal received at frequency determined based on a cross product of a primary signal with a secondary signal, and a signal received at a predetermined frequency offset from the channel.  
     
     
       80. The device of claim 78, wherein the signal received outside of the bandwidth of the channel comprises a signal received at a predetermined frequency offset from the channel, wherein the predetermined frequency offset is selected from the group consisting of: a harmonically-related frequency offset, an adjacent channel offset, a local oscillator frequency offset, an IF image related offset, and a transmit/receive pair frequency offset.