1. Effective Cooperative Channel Sensing for CR Ad Hoc Networks 2008. 2. 19 Wireless Network Lab. Copyright Wireless Networks Lab. CSE. SNU. All rights reserved.

2. Wireless Networks Lab.2 Introduction CR ad hoc networks –should protect PUs transmission –should disseminate the channel information including the start of PU Primary user (PU) –The transmission range and activity time is not known to CR node can vary according to the type of PU –The transmission range is limited The available channels are varied according to the location Vacating channel is preferable only when the CR nodes activity would affect the PUs transmission

3. Wireless Networks Lab.3 Example of CR Ad Hoc MAC Scheme node A detects the PU. node A will not report the detection but sends channel availability for data channel negotiation. PU is on the ith channel node B detects the PU independently. A B

4. Wireless Networks Lab.4 Problems of CR Ad Hoc MAC Schemes Using 1 bit channel occupancy information –provides only the channel availability –uses only for negotiation of data channel Even though neighbors can overhear this information, they dont use it for their channel sensing PU detection delay can be longer

5. Wireless Networks Lab.5 Example of Clustering for PU Detection Some CR nodes detect the PU. All CR nodes report the sensing results to the cluster head. PU is activated Cluster head combines all sensing results. Cluster head notifies the presence of the PU. Cluster Head PU is on. No PU PU is on.

6. Wireless Networks Lab.6 Example of Disseminating PU Detection A B C D node A detects the activity of PUnode A floods the presence of the PU. PU is on. PU is on ith channel node B floods the received presence of the PU blindly. node C also floods the received presence of the PU blindly.

7. Wireless Networks Lab.7 Problems of Previous Schemes Using 1 bit channel status dissemination scheme –Provides only the presence of PU –blind flooding of PU detection The difference of channel state among nodes is ignored The number of available channels will be reduced even though there exist more empty channels per each node

8. Wireless Networks Lab.8 Dissemination of PU Detection Proposed 2 bits channel status dissemination scheme –expresses the 4 step urgency level of sensing per channel for encouraging neighbors to sense certain channels for disable neighbors from using certain channels for its sensing –However, CR nodes channel availability only depends on its sensing result Receiving the detection information from other nodes is used only for judging the sensing priorities of channels

9. Wireless Networks Lab.9 Example of Proposed Scheme A B C D node A detects the activity of PUnode A sends detection info. by control packet. c i,A = 3 node B forwards the detection info. node C notifies that it can not use ith channel. node D is not affected by the As detection on ith channel. c i,B = 2 c i,C = 1 c i,D = 0 PU is on ith channel