Effective Cooperative Channel Sensing for CR Ad Hoc Networks

2008. 2. 19

Wireless Network Lab.

Copyright Wireless Networks Lab. CSE. SNU. All rights reserved.ⓒ

Wireless Networks Lab. 2

Introduction• CR ad hoc networks

– should protect PU’s transmission– should disseminate the channel information including the st

art 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 node’s activity w

ould affect the PU’s transmission

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

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 don’t use it for their channel sensing

• PU detection delay can be longer

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.

PU is on.

No PU

No

PU

PU is on.

Wireless Networks Lab. 6

Example of Disseminating PU Detection

AB

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.

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

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 node’s 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

Wireless Networks Lab. 9

Example of Proposed Scheme

AB

C

D

node A detects the activity of PUnode A sends detection info. by control packet.

ci,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 A’s detection on ith channel.

ci,B = 2c

i,C = 1c

i,D = 0

PU is on ith channel