Distributed Prioritized on Demand Contention March 2008 doc.: IEEE 802.22-yy/xxxxr0 July 2008 Distributed Prioritized on Demand Contention IEEE P802.22 Wireless RANs Date: 2008-07-14 Authors: Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org. > Steve Shellhammer, Qualcomm Steve Shellhammer, Qualcomm

Abstract Propose a new contention algorithm for spectrum sharing July 2008 Abstract Propose a new contention algorithm for spectrum sharing The new algorithm benefits from the broadcast nature of the wireless channel significantly reducing the communication overhead Employs a new adaptive back-off algorithm to further reduce the communication overhead Steve Shellhammer, Qualcomm

Adaptive on Demand Contention July 2008 Adaptive on Demand Contention One of the spectrum sharing techniques described in the IEEE 802.22 draft [1] for self coexistence between different 802.22 WRANs Contention destination (CD) is defined as the WRAN currently occupying the channel Contention sources (CS) are defined as any WRAN that wishes to share the channel Each CS will randomly generate a contention number (CN) The CS will try transmitting the CN during the SCW (self-coexistence-window) through contention with other CS’s After all CN’s are received at CD, the CD decided on the winning CS that has the largest CN Steve Shellhammer, Qualcomm

Adaptive On Demand Contention July 2008 Adaptive On Demand Contention Generate a contention number Generate a random back-off Sense the channel busy Freeze the back-off free Decrease the back-off no Back-off = 0 ? yes Transmit packet yes Collision ? Steve Shellhammer, Qualcomm

July 2008 Disadvantage Have to complete transmission of every CS and then choose the one with the highest contention number. Large probability of collision due to the same size of random back-off window. Broadcast nature of the wireless channel is not utilized Longer scheduling time. If there are M CS’s, then at least M SCW frames are required to complete the process. Hence the algorithm does not scale well If the winning CS only needs to transmit x frames with x small, then at least M-x frames are wasted till a new CS acquires the channel (where M is the number of CS’s) Steve Shellhammer, Qualcomm

Dynamic Prioritized Contention (DPC) July 2008 Dynamic Prioritized Contention (DPC) Objective: to decrease the scheduling time via providing the CS with higher CN (higher priority) a smaller random back-off. Size of random back-off window is based on the contention number (inversely proportional) Every CS can listen to other CS’s contention number. If a CS finds that its contention number is less than another CS’s contention number, it will stop trying to send the packet Steve Shellhammer, Qualcomm

Proposed Algorithm Diagram July 2008 Proposed Algorithm Diagram Generate a contention number Generate a back-off based on contention number no Sense the channel busy Sensed a bigger contention number? free yes Decrease the back-off Stop trying to transmit in this slot no Back-off = 0 ? yes Transmit packet yes Collision ? Steve Shellhammer, Qualcomm

Generating the Random Back-off in DPC July 2008 Generating the Random Back-off in DPC CNmax: the size of contention number window RBmax: the size of random back-off window For each CS i CN(i)=Uniformly distributed ~{0,1,…,CNmax-1) ModRBmax=RBmax-round[CN(i)*(RBmax-1)/(CNmax-1)] CSBackoff(i)=Uniformly distributed ~{0,1,…,ModRBmax-1}; Steve Shellhammer, Qualcomm

July 2008 Advantage The CS with higher contention number (higher priority) will transmit the packet probably earlier, because it has a smaller size of random back-off window. The CS will stop trying to transmit after it hears a higher contention number, so that the probability of collision is sharply decreased. This advantage is significant in the case of large number of CS’s Steve Shellhammer, Qualcomm

Simulation Results Maximum contention number Maximum back-off Window July 2008 Simulation Results Maximum contention number CNmax=220 Maximum back-off Window RBmax=24 Steve Shellhammer, Qualcomm

July 2008 Steve Shellhammer, Qualcomm

July 2008 Conclusions The previous algorithm requires at least a number of frames equal to the number of contention sources. Hence does not scale well The proposed algorithm scales well with increasing the number of contention sources (requires 1 or 2 frames on average) This reduces the delay significantly for a WRAN to acquire the channel Reduces the throughput loss when the current CD only needs to transmit for a few frames Steve Shellhammer, Qualcomm

July 2008 References [1] Draft Standard for Wireless Regional Area Networks IEEE P802.22™/ DRAFTv1.0 Steve Shellhammer, Qualcomm