Wireless Communication System Using Hybrid Cooperative and Noncooperative Sensing

1. A spectrum sensing method in a communication system comprising: sensing a shared spectrum with a cognitive radio that is one of a plurality of cognitive radios; switching the cognitive radio, non interfering cognitive radios of the plurality of cognitive radios and cooperative secondary users to a non-cooperative mode; keeping a record of a number of times a result of spectrum sensing of the cognitive radio of the plurality of cognitive radios matches a result of cooperative sensing; setting a threshold in a shift register value to determine when to switch between cooperative and non-cooperative sensing modes based on comparing the shift register value to the threshold; and sending a control message to provide the non-cooperative cognitive radios of the plurality of cognitive radios access to the spectrum.

2. The method of claim 1 wherein the spectrum is a wireless radio frequency spectrum.

3. The method of claim 1 , wherein the switching is performed, regardless of a cooperative sensing result.

4. The method of claim 1 , wherein the keeping includes keeping a record in a shift register.

5. The method of claim 1 , wherein the plurality of cognitive radios include cooperative and non-cooperative cognitive radios in a same network.

6. The method of claim 1 further comprising avoiding interference from a non-cooperative cognitive radio to a primary system and cooperative cognitive radios by sending a broadcast message.

7. The method of claim 1 further comprising: avoiding interference from a non-cooperative cognitive radio to a primary system and cooperative cognitive radios by sending a broadcast message from the non-cooperative cognitive radio to neighboring cognitive radios whenever the non-cooperative cognitive radio senses that the spectrum is available.

8. The method of claim 7 further comprising: sending reply messages from neighboring cognitive radios to the non-cooperative cognitive radio in response to the broadcast message.

9. The method of claim 7 further comprising: sending reply messages from neighboring cognitive radios to the non-cooperative cognitive radio in response to the broadcast message, wherein respective reply messages contain information on whether transmission from the non-cooperative cognitive radio causes harmful interference.

10. The method of claim 1 further comprising: avoiding interference to a primary user or cooperative cognitive radios by using two antennas for each cognitive radio, wherein one antenna is for transmission over a certain channel and the other antenna is for sending a control message.

11. The method of claim 10 , wherein control messages comprise broadcast messages and reply messages.

12. A spectrum sensing apparatus in a communication system comprising: a cognitive radio that includes a sensor to sense a shared spectrum, the cognitive radio being one of a plurality of cognitive radios in the communication system; a switch configured to change an operational mode to a non-cooperative mode of the cognitive radio and a portion of the plurality of cognitive radios that are not interfering with a primary system and cooperative cognitive radios; a shift register disposed in the cognitive radio to keep record of a number of times a result of spectrum sensing of the cognitive radio matches a result of cooperative sensing; comparator circuity configures to compare the shift register value to a threshold to determine if the switch should change the mode between cooperative and a non-cooperative sensing; and a plurality of transmitter antennas configured to send a control message to provide a non-cooperative cognitive radio access to the shared spectrum.

13. The apparatus of claim 12 , wherein the plurality of tramitter antennas include two antennas that respectively send broadcast messages and reply messages.

14. The apparatus of claim 12 , wherein the spectrum is a wireless radio frequency spectrum.

15. A non-transitory computer-readable storage medium including computer executable instructions, wherein the instructions, when executed by a computer, cause the computer to perform a method of sensing, the method comprising: sensing a shared spectrum with a cognitive radio that is one of a plurality of cognitive radios; switching the cognitive radio,non interfering cognitive radios of the plurality of cognitive radios, and cooperative secondary users to a non-cooperative mode; keeping a record of a number of times a result of spectrum sensing of the cognitive radio of the plurality of cognitive radios matches a result of cooperative sensing; setting a threshold in a shift register value to determine when to switch between cooperative and non-cooperative sensing modes based on comparing the shift register value to the threshold; and sending a control message to provide the non-cooperative cognitive radios of the plurality of cognitive radios access to the shared spectrum.

16. The method of claim 15 , wherein the switching is performed, regardless of a cooperative sensing result.

17. The method of claim 15 , wherein the keeping includes keeping a record in a shift register.

18. The methods of claim 15 further comprising: avoiding interference to a primary user or cooperative cognitive radios by using two antennas for each cognitive radio, wherein one antenna is for transmission over a predetermined channel and the other antenna is for sending control messages, wherein the control messages include broadcast messages and reply messages.

19. The method of claim 15 further comprising: avoiding interference from a non-cooperative cognitive radio to a primary system and cooperative cognitive radios by sending a broadcast message from the non-cooperative cognitive radio to neighboring cognitive radios whenever the non-cooperative cognitive radio senses that the spectrum is available.

20. The method of claim 15 further comprising: sending reply messages from neighboring cognitive radios to the non-cooperative cognitive radio in response to the broadcast message, wherein respective reply messages contain information on whether transmission from a non-cooperative cognitive radio causes harmful interference.