1 / 20

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

dinah
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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。

More Related