1. 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 IEEE INFOCOM 2011 Mini-conference

2. ECE 5560, Fall 2006 22 Outline Cognitive Radio (CR) Networks The Rendezvous Problem in CR Networks Rendezvous Protocol using Asynchronous Channel Hopping (ACH) Performance Evaluation Conclusion

3. ECE 5560, Fall 2006 3 Static Frequency Allocation 3 Source: D. Staelin, April 2010. Broadcast TV 470-806 MHz ZigBee 802.15.4 ISM (915 MHz) Wi-Fi, BlueTooth, Zigbee ISM (2.4 GHz)

4. ECE 5560, Fall 2006 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. 4 TV white space Over-crowded unlicensed bands Under-utilized licensed (TV) bands

5. ECE 5560, Fall 2006 55 Outline Cognitive Radio (CR) Networks The Rendezvous Problem in CR Networks Rendezvous Protocol using Asynchronous Channel Hopping (ACH) Performance Evaluation Conclusion

6. 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 6 Ch 2 Ch 1 Ch 0 Control Data Control Data Vacate control channel 6 Licensed bands

7. ECE 5560, Fall 2006 77 Outline Cognitive Radio (CR) Networks The Rendezvous Problem in CR Networks Rendezvous Protocol using Asynchronous Channel Hopping (ACH) Performance Evaluation Conclusion

8. ECE 5560, Fall 2006 Channel hopping (CH) can create rendezvous. 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 8 Requirements for CH-based Rendezvous Protocols 88

9. ECE 5560, Fall 2006 Random channel hopping: no TTR bound Common channel hopping: clock syn. Sequence-based channel hopping (Dyspan08): single rend. 9 Related Work on CH-based Rendezvous Protocols 99

10. ECE 5560, Fall 2006 10 Optimal Asynchronous CH System (1) Optimal asyn. CH scheme Max # of rend. channels, N Min sequence period, N 2 slots No clock syn. An array-based design Assumption of the Tx/Rx role Tx and Rx use different methods Not applicable to ad hoc networks 10 Tx: column- based CH seq. Rx: row-based CH seq. 0 1 2 3 4 5 6 7 8 Column-wise assignment Row-wise assignment

11. ECE 5560, Fall 2006 11 Optimal Asynchronous CH System (2) Every node has a unique ID ID seq.: a = {a1,a2} Bit seq.: A = a + {0,0} + {1,1} Two nodes are able to generate two distinct bit sequences. If a ≠ b Then A ≠ Shift (B, k) 11 ID + ID extended to Bit seq. A B A B A B “0” only seq. + “1” only seq.

12. ECE 5560, Fall 2006 12 Optimal Asynchronous CH System (3) Bit seq. extended to CH seq. A = {1, 0, 0, 0, 1, 1} B = {1, 1, 0, 0, 1, 1} Every node uses the same method: Bit “1”  two column-based CH seqs. Bit “0”  two row-based CH seqs. N rend. channels achieved within O(N 2 ) slots. TTR bounded by N 12 Column-based CH seq. u Row-based CH seq. v A  Node 1’s CH seq. B  Node 2’s CH seq.

13. ECE 5560, Fall 2006 13 Outline Cognitive Radio (CR) Networks The Rendezvous Problem in CR Networks Rendezvous Protocol using Asynchronous Channel Hopping (ACH) Performance Evaluation Conclusion

14. ECE 5560, Fall 2006 14 Comparisons of CH Schemes 14 # of rend. channels Mean TTR Bounded TTR Asyn. operation Common CHNO(1)YesNo Random CHNO(N)O(N)NoYes Seq.-based Rend 1O(N2)O(N2)Yes Asyn QCH2O(1)Yes Optimal Asyn. CH NO(N)O(N)Yes

15. 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

16. 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

17. 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 17 Questions? Thank you

18. ECE 5560, Fall 2006 18 Backup Slides

19. ECE 5560, Fall 2006 19 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. 19 TV band licensed users vs. unlicensed users WiFi vs. BlueTooth vs. Zigbee Cellular vs. Cellular

20. ECE 5560, Fall 2006 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. Which channel to rendezvous given N channels ? Jammer on X channels 20