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A Cognitive MAC Protocol for QoS Provisioning in Overlaying Ad Hoc Networks

A Cognitive MAC Protocol for QoS Provisioning in Overlaying Ad Hoc Networks. Advisor ： Wei-Yeh Chen Student ： 王璽農

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A Cognitive MAC Protocol for QoS Provisioning in Overlaying Ad Hoc Networks

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  1. A Cognitive MAC Protocol for QoS Provisioning inOverlaying Ad Hoc Networks Advisor：Wei-Yeh Chen Student：王璽農 L. C. Wang, A. Chen, and D. S. L Wei, “A Cognitive MAC Protocol for QoS Provisioning in Overlaying Ad Hoc Networks,” in Proc. 4th IEEE CCNC, Las Vegas, Nevada, pp. 1139 -1143, January 2007.

  2. Outline • Abstract • Introduction • The cognition cycle(4-stages) • Simulation(NS-2) & Results • Conclusion

  3. Abstract • One fundamental issue for a CR network is how CR users establish an overlaying ad hoc link on licensed and unlicensed bands. • On licensed band, the CR functions aim to detect the presence of primary users and vacate the occupied spectrum to avoid the interference. • On the unlicensed band, the CR functions have to improve the efficiency and fairness of spectrum usage as well as support the QoS.

  4. Introduction • The fixed spectrum allocation(靜態分配) may not be always effectively used everywhere. • In the literature, most of studies for MAC protocol design focus on the dynamic spectrum selection(動態選擇). • The main contribution is to propose a CR device while coexisting with the legacy users on both licensed and unlicensed bands.

  5. The cognition cycle • Observe-stage • Plan-stage • Decide-stage • Act-stage

  6. Establish Neighbor-List(1/2) • we suggest a neighbor list establishment to record the information of the primary and CR users. • we partition the observed frames into three categories and store the observed information into three tables: • Primary user information table (PIT) • Reservation Information Table (RIT) • Contention Information Table (CIT)

  7. Establish Neighbor-List(2/2) • A CR user is designed to observe the status of frame transmissions around its neighborhood for a period of Tobv. • The duration of Tobv must be longer than the maximum repetition period between two successive delay-sensitive frame. • rt-nodes = CR users sending delay-sensitive • nrt-nodes = non-real-time frames <BACK>

  8. Contention Resolution • One of conditions is to prevent the CR users from interfering the existing legacy system, and one is to efficiently and fairly access the unused spectrum during a short time. • we suggest three improved approaches as follows: • Gating mechanism(管控機制) • Linear back-off algorithm(線性退避演算法) • Stall avoidance scheme(攤位避免計劃)

  9. Gating mechanism(1/2) • When a CR user is requested for transmission, the gating mechanism first checks whether a legacy user occupies the channel or not. • If so, the transmission of this CR user is deferred. • Otherwise, the optimal transmission probability p is calculated.

  10. Gating mechanism(2/2) • Apply the p -persistent algorithm to determine whether the frame can be transmitted or not. • If the frame is granted for transmission, the CR user immediately sends the frame. • Otherwise, the frame will be deferred and again contend for the channel access. <BACK>

  11. Linear back-off algorithm • To expedite the channel access for delay-sensitive flows. • If the request of the delay-sensitive traffic flow is collided, the CW size (CWrt) increases according to the following principle: • CWrt = min(CWmax, CWmin × (N_att − 1)) <BACK>

  12. Stall avoidance scheme(1/2) • To improve the fairness for the access in short time, we develop a scheme aiming to reduce the transmission delay of the nrt-nodes with excessive buffered frames. • But the specific goal is to minimize the variance of the transmission delay.

  13. Stall avoidance scheme(2/2) • The suggested stall avoidance scheme with respect to the nrt-nodes is described as follows.(預定起始值的訊框緩衝最大值=Qthreshold) • CWstall< CWmin • The request of a delay-sensitive traffic flow still contends for the channel access with CWmin, the stalled non-real-time frame with CWstallcan have a higher probability to win the channel contention. <BACK>

  14. Invitedreservation procedure • The invited reservation procedure is designed for supporting the delay-sensitive flows. • 接收器負責發送CTS用來控制訊框，讓訊框傳輸以及對於隨後的訊框延遲來保留時槽，rt-CTS訊框用來禁止其他用戶的傳輸，因隱藏節點的問題導致碰撞緩和。由於CR接收器學習了在觀察階段中主要用戶的頻譜使用時間，隨著動態的調整讓程序能夠保留在沒有干擾主要使用者的情況下。 <BACK>

  15. Distributed frame synchronization mechanism • One important issue is to develop a distributed approach to ensure the frame synchronization among all the CR users. • The basic idea of the proposed distributed synchronization algorithm (rt-CTS, ACK). • Therefore, all the stations can access the channel in the designated period without influencing the transmissions in the reserved time.

  16. CR MAC & traditional CSMA/CA MAC

  17. CR MAC & traditional CSMA/CA MAC

  18. CR MAC & traditional CSMA/CA MAC

  19. CR MAC & traditional CSMA/CA MAC

  20. Conclusion • 此文提出了一個感知MAC協定，建立一個CR ad hoc網絡中配置QoS的傳統無線系統。研究設計的機制可以補充傳統CSMA / CA的MAC協定的不足，以實現目標的感知無線網絡。

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