IEEE INFOCOM 2011 Mini-conference
Asynchronous Channel Hopping for
Establishing Rendezvous in Cognitive
Radio Networks
Kaigui Bian and Jung-Min “Jerry” Park
Department of Electrical and Computer Engineering
Virginia Tech
{kgbian, jungmin}@vt.edu
April 11, 2011
Shanghai, China
1
2
Outline
Cognitive Radio (CR) Networks
The Rendezvous Problem in CR Networks
Rendezvous Protocol using Asynchronous Channel Hopping (ACH)
Performance Evaluation
Conclusion
ECE 5560, Fall 2006
3
Static Frequency Allocation
Broadcast TV
470-806 MHz
ZigBee 802.15.4
ISM (915 MHz)
5560, Fall
Source:ECE
D. Staelin,
April2006
2010.
Wi-Fi, BlueTooth,
Zigbee
ISM (2.4 GHz)
4
Opportunistic Spectrum Sharing (OSS) Paradigm
Unused TV bands (around 700 MHz in U.S.) = TV white space (TVWS)
Cognitive Radio (CR) is an enabling technique for realizing OSS.
Unlicensed (secondary) users cause NO interference to licensed
(incumbent or primary) users.
Over-crowded
unlicensed bands
TV white space
ECE 5560, Fall 2006
Under-utilized
licensed (TV) bands
5
Outline
Cognitive Radio (CR) Networks
The Rendezvous Problem in CR Networks
Rendezvous Protocol using Asynchronous Channel Hopping (ACH)
Performance Evaluation
Conclusion
ECE 5560, Fall 2006
6
The Rendezvous Problem
Rendezvous = control channel
Needed for link setup, control information exchange, etc
In OSS, vacate any licensed channel where primary users appear.
Multiple rendezvous = robustness of rendezvous
SERIAL
ETHERNET
Ch 2
Licensed
bands
Ch 1
SERIAL
ETHERNET
Ch 0
Control
Data
Control
Data
Vacate control channel
ECE 5560, Fall 2006
7
Outline
Cognitive Radio (CR) Networks
The Rendezvous Problem in CR Networks
Rendezvous Protocol using Asynchronous Channel Hopping (ACH)
Performance Evaluation
Conclusion
ECE 5560, Fall 2006
8
Requirements for CH-based Rendezvous Protocols
Channel hopping (CH) can create rendezvous.
C0 C1 C2 C1 C1 C2 C0 C2
C1 C2 C0 C1 C2 C0 C1 C2
C2 C0 C1 C1 C0 C1 C2 C2
Multiple rendezvous channels per node pair
Robust to link breakage caused by primary users
Bound for time-to-rendezvous (TTR)
Small channel access delay
Independence of clock synchronization
ECE 5560, Fall 2006
9
Related Work on CH-based Rendezvous Protocols
Random channel hopping: no TTR bound
C0 C1 C2 C1 C2 C0
…...
C1 C2 C0 C2 C0 C1
…...
Common channel hopping: clock syn.
C0 C1 C2 C0 C1 C2 C0 C1 C2
C0 C1 C2 C0 C1 C2 C0 C1 C2
Sequence-based channel hopping (Dyspan08): single rend.
C0 C0 C1 C2 C1 C0 C1 C2 C2 C0 C1 C2
C0 C0 C1 C2 C1 C0 C1 C2 C2 C0 C1 C2
ECE 5560, Fall 2006
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Optimal Asynchronous CH System (1)
N = 3, U = {0, 1, …, 8}
Optimal asyn. CH scheme
Max # of rend. channels, N
2
Min sequence period, N slots
No clock syn.
An array-based design
Assumption of the Tx/Rx role
0
1
2
3
4
5
6
7
8
column = {1, 4, 7}
row = {0, 1, 2}
Tx and Rx use different methods
Not applicable to ad hoc networks
Column-wise
assignment
Tx: columnbased CH seq.
Rx: row-based
CH seq.
C0
C1
C2
C0
C1
C2
C0
C1
C2
C1
C1
C1
C2
C2
C2
C0
C0
C0
C1
C1
C1
C2
C2
C2
C0
ECE 5560, Fall 2006
C0
C1
C0
C0
C2
Row-wise
assignment
C0
C1
C2
C0
C1
C2
11
Optimal Asynchronous CH System (2)
ID extended to Bit seq.
Every node has a unique ID
ID seq.: a = {a1,a2}
Bit seq.: A = a + {0,0} + {1,1}
ID
Two nodes are able to generate
A
two distinct bit sequences.
B
If a ≠ b
Then A ≠ Shift (B, k)
A
B
A
B
ECE 5560, Fall 2006
+
“0” only seq.+“1” only seq.
12
Optimal Asynchronous CH System (3)
Bit seq. extended to CH seq.
Every node uses the same method:
A = {1, 0, 0, 0, 1, 1}
B = {1, 1, 0, 0, 1, 1}
Bit “1” two column-based CH seqs.
Bit “0” two row-based CH seqs.
Column-based
CH seq.
Row-based
CH seq.
u
v
N rend. channels achieved within O(N2) slots.
TTR bounded by N
Bit seq A = a + {0, 0} + {1, 1}
= {1, 0, 0, 0, 1, 1}
ANode 1’s CH seq.
BNode 2’s CH seq.
Bit seq B = b + {0, 0} + {1, 1}
= 5560,
{1, Fall
1, 2006
0, 0, 1, 1}
ECE
13
Outline
Cognitive Radio (CR) Networks
The Rendezvous Problem in CR Networks
Rendezvous Protocol using Asynchronous Channel Hopping (ACH)
Performance Evaluation
Conclusion
ECE 5560, Fall 2006
14
Comparisons of CH Schemes
# of rend.
channels
Mean
TTR
Bounded
TTR
Asyn.
operation
Common CH
N
O(1)
Yes
No
Random CH
N
O(N)
No
Yes
Seq.-based
Rend
1
O(N2)
Yes
Yes
Asyn QCH
2
O(1)
Yes
Yes
Optimal Asyn.
CH
N
O(N)
Yes
Yes
ECE 5560, Fall 2006
15
Simulation Results
Comparisons of asyn. CH protocols using network simulation in NS-2
Primary users occupy X < N channels at random
RCH (random CH): N rend. channels possible
Optimal Asyn. CH: N rend. channels guaranteed
SR (sequence-based rendezvous): 1 rend. channel
ECE 5560, Fall 2006
16
Outline
Cognitive Radio (CR) Networks
The Rendezvous Problem in CR Networks
Rendezvous Protocol using Asynchronous Channel Hopping (ACH)
Performance Evaluation
Conclusion
ECE 5560, Fall 2006
17
Conclusion
Addressed the rendezvous problem in MAC protocol design for
CR networks
An array-based CH systems for rendezvous (control channel)
establishment
Robustness: max number of rend. channels
Bounded time-to-rendezvous (TTR)
Asynchronous rendezvous
Questions?
Thank you
ECE 5560, Fall 2006
18
Backup Slides
ECE 5560, Fall 2006
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Coexistence Problem
Horizontal coexistence among unlicensed networks that have equal
priority to access spectrum.
Vertical coexistence among networks that have different priorities to
access spectrum.
Coexistence
Vertical
coexistence
Horizontal
coexistence
WiFi vs. BlueTooth
vs. Zigbee
Heterogeneous
coexistence
Homogeneous or
self coexistence
Cellular vs. Cellular
ECE 5560, Fall 2006
TV band licensed users
vs. unlicensed users
Incumbent
coexistence
20
Other Applications of Multiple Rendezvous CH Schemes
Jamming resistant rendezvous
Attack model: a jammer randomly picks X out of N
channels to launch the jamming attack
The maximized number of pair-wise rendezvous channels
guarantees the maximized jamming resistance.
SERIAL
ETHERNET
Which channel to
rendezvous given N
channels ?
Jammer on X channels
ECE 5560, Fall 2006
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