1. MULTI-BAND CSMA/CA- BASED COGNITIVE RADIO NETWORKS Jo Woon Chong, Youngchul Sung, and Dan Keun Sung School of EECS KAIST IWCMC 2009 1

2. Outline  Introduction  Proposed RawPEACH MAC Scheme  For Multi-band CSMA/CA System  Markov Chain Analysis  For The Operation of Secondary User in RAWPEACH Networks  Numerical Results  Conclusion and Comment 2

3. Introduction  In IEEE 802.11e, QoS is classified according to various classes of service.  However, the absolute guarantee of QoS for higher priority users in not still provided due to its dependence on contention-based collision resolution  Propose a new flexible MAC scheme based on CSMA/CA  Provide strict QoS guarantee to certain high priority users (primary users)  Embedding channelization into the CSMA/CA operating in multiple bands 3

4. Introduction (cont’d) 4  Random access protocol with PrE-Arbitrated CHannelization (RawPEACH)  The evolution of the conventional CSMA/CA to provide QoS guarantee to certain users in the network by incorporating multi-band operation and channelization  Analyze the performance of the proposed mixed MAC scheme  Using a new CSMA/CA model based on a Markov chain capturing the primary user channel activity and the number of bands

5. Proposed RawPEACH MAC Scheme 5 Number of primary users: N p Number of secondary users: N s

6. RawPEACH – The Operation of PU 6  Orthogonal physical channel in multiple frequency hopping sequences in multiple frequency bands  Latin square, which exploit frequency diversity to avoid channel fading and interference.  In this scheme,  Each primary user transmits its frame over one primary frame interval T f,p  and hops to a different band according to the assigned hopping pattern for the next frame interval.

7. RawPEACH – The Operation of PU 7 1.If the number, N P, of primary users is larger than that, N CH, of frequency bands, the orthogonality among primary users cannot be maintained 2.The RawPEACH protocol needs to employ admission control to maintain the orthogonality among the primary users in the network

8. RawPEACH - The Operation of SU 8  Secondary users are provided only with best-effort services  be required not to interfere with the operation of primary users in cognitive radio networks  Assume that all the secondary users sense all N CH frequency bands at the beginning of every secondary time slot with length T f,s. When a particular band is sensed to be used by a primary user, the secondary users do not transmit their frames in the band at that time.

9. RawPEACH - The Operation of SU 9  The performance of the secondary users is controlled by various design parameters  such as the arbitrary inter-frame space (AIFS), the contention windows (CW), the frame lengths of primary and secondary users, etc.

10. RawPEACH - The Operation of SU 10  If all the channels are busy due to the transmission of primary users the secondary users freeze their back-off counter, and wait until at least one of the primary users ceases to transmit the frame  If at least one among N CH channels is sensed to be idle all the secondary users decrease the values of their back- off counters by one  If more than one secondary user transmit their frames simultaneously on the same primary user-free channel the transmission of the secondary users fails

11. RawPEACH 11  The overall operation can be viewed as a single CSMA/CA protocol  all the users in the network sense the channel after AIFS from the frame boundary of their own

12. Markov Chain analysis for SU 12 1.State S i,j means “a secondary user is in the i th backoff stage and j th backoff counter value” 2.Assume that the probability of each frequency band being busy due to the primary user transmission is identical and independent, and is equal to P p. 3.the probability P b that all channels are busy is given by P p NCH, where N CH denotes the number of channels Freeze counter Tx successes Tx fails

13. Markov Chain analysis for SU 13 Calculate the stationary probability(b ij ) and the transmission probability( τ ) to find the collision probability(p)

14. Markov Chain analysis for SU 14 N 1ch s is the number of secondary users in one free-channel The collision probability(p)  the probability that at least one other secondary user transmits data simultaneously with the given secondary user. the probability that the channel is busy due to a primary user although other secondary users do not transmit

15. Markov Chain analysis for SU 15  Normalized throughput per band  Calculate the total system throughput is based on a band-by-band approach. Successful transmission Idle Collision  The normalized throughput S per band

16. Numerical Result 16

17. Numerical Result (cont’d) 17

18. Conclusion 18  Proposed a new combined MAC scheme  Primary user and secondary user  Evaluate the throughput performance of the proposed scheme  Markov Chain  Future work  OFDM/OFDMA based WLAN standards

19. Comments 19  Modeling a system using Markov Chain  Stochastic Process  Introduce a new idea/model to a conventional scheme