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

• US 20020002052A1
• Filed: 06/11/2001
• Published: 01/03/2002
• Est. Priority Date: 06/13/2000
• Status: Active Grant

• Current Assignee: Shared Spectrum Company
• Original Assignee: Shared Spectrum Company
• Inventors: McHenry, Mark Allen
• Granted Patent: US 7,146,176 B2
• Time in Patent Office: Days
• US Class Current: 455/447
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 72/54 based on quality criteria

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.

Claims

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, and

each secondary transceiver communicating the signal level to the central controller, and

the central controller determines which channels each node may potentially use by comparing the primary signal level to a threshold value.

2. The method according to claim 1, further comprising the step of:

the central controller using amplitude thresholds to decide if each secondary transceiver and secondary base station is within a region where the channel is being used by primary users, is in a region distant from where the channel is being used by primary users, or an intermediate region.

3. The method according to claim 1, further comprising the step of:

having a portion of the secondary transceivers and secondary base stations in the “

distant region”

sequentially transmit a short duration probe signal with a certain power level (P_probe),

the secondary transceivers and secondary base stations within the “

primary region”

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.

4. The method according to claim 3, 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.

6. The method according to claim 1, further comprising the step of:

a modulation scheme where each secondary transceiver and secondary base station transmits and receives data for a certain time period, then simultaneously halting transmissions, making measurements of the background signals for a time period, and then either transmitting or receiving probe signals.

7. The method according to claim 1, further comprising the step of:

identifying proximate primary receivers 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.

8. The method according to claim 1, further comprising the step of:

identifying proximate primary receive only radios 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 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.

11. The method according to claim 1, further comprising the step of:

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.

5. A waveform specifically for use in combination with NTSC analog TV signals consisting of multiple CW waveforms or combinations of narrowband waveforms with energy in certain frequency zones within the NTSC six MHz channel width and minimal energy at other frequencies in the channel.

9. 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.

10. 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.

12. A system to use the TV spectrum on a secondary basis, comprising:

of a distributed network of fixed or mobile secondary transceivers that measure the TV signal power levels, and

a communicate system that sends this information to a central controller, and

a central controller that thresholds this information to determine which secondary transceivers are located in regions where the primary TV signal is too weak for viewing, thus allowing the secondary transceivers to be able to transmit on this frequency without causing significant interference to the primary TV receivers.