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

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

Introduction  In IEEE e, 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

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

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

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.

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

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.

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.

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

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

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

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

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

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

Numerical Result 16

Numerical Result (cont’d) 17

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

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