Distributed Coordinated Spectrum Sharing
MAC Protocol for Cognitive Radio
Advisor ：Wei-Yeh Chen
Student ：楊
于
世

Reference

Hao Nan; Tae-In Hyon; Sang-Jo Yoo; , “Distributed
Coordinated Spectrum Sharing MAC Protocol for Cognitive
Radio ,” in Ireland Dublin DySPAN 2007. 2nd IEEE
International symposium, pp. 240 - 249 , April 2007.
1
Outline

Introduction

Background and hidden incumbent device problem

Avoid method

Simulation

Conclusion
2
Introduction

By adding the available channel list(表;列舉) into the RTS
and CTS, the communication pair can know which data sub
channels are available.

We proposed an ENNI (exchanging of neighbor nodes
information) mechanism to deal with the hidden incumbent(現
在的) device problem.
3
Hidden incumbent device problem
Hidden node
problem
A
B
C
D
Collision
A
B
C
D
Data transmission
Expose node
problem
Overhearing
Hidden node and expose(暴露) node problem in
single channel environment
4
Avoid method

It has to send the RTS which includes the time duration(持續)
that other node should defer to the receiver.

Upon receiving the RTS, it sends the CTS to notify(通知) the
neighbor node around to defer(延遲) their transmission as
well in order to avoid the possible collision.

The structure that records(紀錄) the time duration called NAV
(network allocation vector), which is included in both of the
RTS and CTS.
5
A
B
C
D
Time
RTS
Channel 3
CTS(2)
RTS
Channel 2
CTS(2)
Channel 2
Collision
Multi-channel hidden terminal problem
6
Avoid method(1)

MMAC (multi channel MAC) protocol to handle the multi
channel hidden terminal problem.

In MMAC, periodically(定期地) transmitted beacons
divide(劃分) time into beacon intervals(間格).

It uses the ATIM (ad hoc traffic indication messages) window
to negotiate(通過) the channel during each beacon interval,
and use the ATIM-RES (ATIM reservation(保留)) and ATIMACK to notify the nodes in the vicinity of sender and receiver.
7
Transmission
initiation
Channel sensing
Add the available
channel list into
the RTS
N
Have the same
channel?
Compare the ACL
of source with
overhearing
node’s own one
Y
Choose one among
the same channels
end
Set the NAV of the
data channel and
send it back to the
source by CTS
Both sender and
receiver switch to
the agreed channel
to begin the
transmission
General channel selection procedure of multiple
channel protocols. ACL (available channel list)
8
incumbent system
interference area
SC3
DN-3
SC1
D
SC1:DATA
SN-1
S
SC1:ACK
SC1:ACK
SC1:ACK
SC1:DATA
SC4
SN-2
SC2
DN-4
Incumbent System Device
Sender/Receiver’s neighbor nodes
Hidden incumbent device problem
9
Avoid method(2)

Receiver transmits a short pulse(脈衝) during the slot time if
the channel corresponding(相同的) to the slot is used by
incumbent systems around themselves.

This kind of the pulse reports is generated(產生) by the
neighbor node, the distance is very short.

The propagation(增加) delay can be ignored. Therefore, there
is no need to use the synchronization.
10
11
Avoid method(3)

The time duration of time slot of 802.11 is greater than that of
the pulse. Thus, any pulse appears with the range of
specific(特殊的) time slot will be regarded(當作) as the
appearance of the incumbent device on that sub data channel.

Because the pulse does not need to be decoded, sender can
know which sub channel has already been used.

If no pulse were detected(發現), there is no need to transmit
the RTSu (RTS updated) packet to the destination node.
12
Simulation(1)

The appearance of the incumbent devices, channel will be idle
for a relatively(相對) long time interval.

The type of appearance duration follow the exponential(指數
的) distribution function.
13
ON/OFF model
14
Calculate

We use the Eq. 9 and Eq. 10 to calculate the TimeON (time
duration of the incumbent system).
15
Simulation(2)
X軸:目前設備在次資料頻道上所使用的機率
Y軸:主要使用者的鄰近節點的干擾影響
16
Simulation(3)
17
Conclusion

隱藏終端問題

單通道與多通道隱藏終端問題

如何避免隱藏終端

避免的方法
18