1. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 1 Issues and Enhancements on Coexistence Beaconing Protocol for Inter-cell Discovery and Communications in IEEE 802.22 IEEE P802.22 Wireless RANs Date: 2007-06-01 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 Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl 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.patcom@iee.org >

2. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 2 Introduction This presentation is to identify a number of critical issues on the current CBP mechanisms (in D0.3) used for inter-cell discovery and communication. We propose fundamental remedies to resolved these issues respectively. We describe an Enhanced Coexistence Beaconing Protocol (CBP) that allows reliable, efficient, scalable, and backward-compatible cross-channel inter-cell communications for IEEE 802.22 systems.

3. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 3 What is CBP? The Coexistence Beaconing Protocol – CBP. The CBP is a best-effort (contention based) protocol based on coexistence beacon transmissions. Coexistence beacons are transmitted during a contention window, the Self Coexistence Window, at the end of an upstream sub-frame. CBP packets can be transmitted by CPEs and BSs.

4. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 4 Issue 1 - Directional Antenna at the CPE

5. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 5 CBP Communications Require Neighbor- cell CPEs to exist The “face-to-face CPEs” case: –Beacons can be transmitted and received by the face-to- face CPEs associated with different neighbor cells. The “back-to-back CPEs” case: –Beacons transmitted by the BSs can be received by CPEs associated with the neighbor cells

6. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 6 CBP Communications Fail without a Neighbor-cell CPE Beacons from WRAN2 will never be received by WRAN1. Without knowing the existence of WRAN2, WRAN1 will interfere WRAN2’s operation and sensing. WRAN2 may decide to switch channel, which however may not be always possible.

7. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 7 Proposed Remedy The CPE in the cell-overlapping area shall employ an Omni- directional antenna or multiple directional antennas for CBP transmission, if there exists no neighbor-cell CPE.

8. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 8 Issue 2 – WRAN Cells Discovery / Detection CBP packets are transmitted in non-deterministic instances. The CPEs of a cell would have to be continuously quiet for a number of super-frames to monitor CBP transmission for one single channel. –No more than 4 super-frames of waiting time as specified in the draft. The current mechanism leads to long delay and low system efficiency especially when a set of channels need to be monitored during normal WRAN operation. –1.92 seconds for 3 channels (N±1)

9. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 9 Latency of WRAN Discovery In the v0.3 draft – WRAN discovery takes no more than 4 super- frames. –However, there is neither a specification nor a demonstration on how such latency is achieved. Note that – CBP is a contention-based best effort transmission protocol –Self-coexistence Windows are scheduled where CBP packets from multiple neighbor cells are transmitted using a contention-based medium access mechanism –Collisions occurs depending on the size of the contention window and the number of contending cells that are transmitting CBP packets. –Latency and reliability of successful transmission is hard to managed and guaranteed. –It becomes more difficult if self-coexistence windows are not synchronized across neighbor WRAN cells across different channels.

10. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 10 Proposed Remedies A CBP packet for announcing the existence of a WRAN on a certain channel shall be transmitted in a deterministic (prior arranged) time instance, which shall be well-known (standardized) in IEEE 802.22. Such an announcement CBP packet shall be transmitted by a non-contention-based (collision-free) mechanism. IEEE 802.22 systems shall be able to complete the WRAN discovery process for a large set of channels in a reasonably small time scale. Self-coexistence windows shall be synchronized across different channels.

11. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 11 Proposed Remedy – Channel Hosting

12. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 12 Proposed Remedy – Channel Hosting A CBP packet for announcing the existence of a WRAN on a certain channel – the Hosting CBP packet – is transmitted periodically in a deterministic (prior arranged) time instance, which is well-known in IEEE 802.22. The hosting CBP packets for different channels are transmitted during the self-coexistence windows in a non-contention-based (collision-free) manner. IEEE 802.22 systems is able to complete the WRAN discovery process for a large set of channels (e.g. 32 channels or more) within one super-frame, and for each channel it takes very short time (1 symbol). Super-frames (therefore Self-coexistence windows) are synchronized across different channels. More explanations later.

13. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 13 Issue 3 – Inter-cell Communication for Adjacent- channel Sensing quiet period coordination In draft version 0.3, the sensing quiet periods for incumbents detection are only required to be synchronized among WRAN cells that are operating on the same channel (through co-channel inter-cell communication). There is no specification on sensing quiet period coordination/synchronization for WRAN cells that are operating on the adjacent channels (i.e. N±1). However, it could be a serious issue that WRAN cells operate without such cross-channel synchronization, as shown in the next slides.

14. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 14 Adjacent-channel Sensing quiet period coordination Non-coordinated adjacent-channel sensing can cause interference to “hidden” incumbents for an intolerable period of time (violating the FRD) Sensing periods False positive due to interference of WRAN2 during the sensing period

15. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 15 Adjacent-channel Sensing quiet period coordination (cont’d) More seriously, close-by CPEs operating on the adjacent channels can interfere the sensing performance of a sensing CPE. This scenario can lead to interference to “hidden” incumbents for an ever longer period of time. Sensing periods

16. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 16 Adjacent-channel Sensing quiet period coordination (cont’d) Coordinated adjacent-channel sensing can avoid WRAN cells from interfering to “hidden” incumbents for an intolerable period of time

17. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 17 Proposed Remedy WRAN cells operating on the adjacent channels shall communicate to coordinate their quiet periods for incumbent detection. The quiet periods shall be synchronized by the operating WRAN cells on the adjacent channels.

18. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 18 Issue 4 – Inter-cell Communication for Cross-Channel Spectrum Sharing In draft version 0.3, there is no mechanism being specified that supports CBP-based inter-cell communication to be effectively performed across channels. We have shown the necessity of enabling cross-channel inter-cell communication for adjacent-channel quiet period synchronization. In the next slide, we will show the above requirement for effective cross-channel communications also holds for cross-channel spectrum sharing.

19. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 19 Cross-Channel Spectrum Sharing Coordination WRAN1 operates on Channel M and WRAN2 on Channel N. Channel M and N are the only vacant channels. When an incumbent pops up on channel M, WRAN1 has to switch to and share channel N with WRAN2. For a smooth channel switching, it is desirable to coordinate the spectrum sharing between WRAN1 and WRAN2 before the channel switching of WRAN1 from channel M to N takes place.

20. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 20 Proposed Remedy WRAN cells operating on different channels shall communicate to coordinate their spectrum sharing activities. An effective cross-channel CBP mechanism shall be defined.

21. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 21 Enhanced Cross-channel CBP To resolved the mentioned issues of inter-cell discovery and inter-cell coordination using CBP, we propose and enhancement to the current CBP that efficiently and reliably supports cross-channel communications. The following slides present the enhanced Cross- channel CBP

22. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 22 Single Channel CBP WRAN cells on the same operating channel can transmit or receive CBP packets during the synchronized CWs using the best effort contention-based protocols to communicate with one another. Analogy: Professors share the same office and discuss with one another

23. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 23 Cross Channel CBP: the problem Similar to the single-channel CBP operation, during a CW, the CBP-participating CPEs of a WRAN can either stay on their operating channel or tune to another channel occupied by a neighboring WRAN cell. Communications between two neighboring cells can succeed ONLY when at least two CBP-participating CPEs from each cell are tuned to the same channel during a CW where one of them is transmitting and the other is receiving.

24. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 24 Cross-Channel CBP: the problem An analogous problem: University professors occupying temporarily assigned offices visit one another’s offices in a non- deterministic manner (asynchronously).

25. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 25 Slotted Self-Coexistence Window (SCW) Instead of being utilized as contention windows, SCWs are slotted. Each slot is one OFDMA symbol. A typical size of a slotted CBP window is 3 slots. The advantage of CBP Window Slotting is to enable efficient management of CBP communications. Analogy: The meeting time is partitioned into sessions.

26. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 26 More on Channel Hosting A CBP packet for the announcement of a WRAN’s existence on a certain channel – the Hosting CBP packet – is transmitted periodically in one of the SCW slots, whose time instance and duration are well-known in IEEE 802.22. The well-known position of the Hosting Slot can be determined by Modulo Scheduling. For example, Slot Number (in every super-frame) == the 1 st slot of Frame {Channel-Number mod 16}. Time to discover one channel: 1 symbol duration –VS. 640ms required by the current CBP mechanism. Analogy: Each professor hosts their office hours that are well known to every one. The time to check if a office is occupied by someone is very short.

27. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 27 More on Channel Hosting Therefore the hosting CBP packets for different channels are transmitted during the self-coexistence windows in a non-contention-based (collision-free) manner. A WRAN cell is able to complete the WRAN discovery process for a large set of channels (almost all channels) within one super-frame. –There are a few channels that use the same slot position for channel hosting as the one being used by the discovering WRAN. We refer this situation as “concurrent hosting”. –Since frequency separation is very large (e.g. 16x6MHz), concurrent hosting should be feasible between neighbor cells.

28. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 28 More on Channel Hosting – Modulo Scheduling

29. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 29 CBP Framing CBP Framing provides a scalable management mechanism for cross-channel CBP-based inter-cell communication. A CBP Frame is a group of CBP Windows in 16 consecutive data frames, and is piloted with a Hosting Beacon in a Hosting Slot. Similar to a regular data frame, a CBP frame consists of a MAP and the Payload. The MAP of a CBP frame is carried by the Hosting Beacon, and specifies the payload in the CBP frame. The Payload is the SCW slots scheduled by the MAP in the CBP Frame. Analogy: During his office hour, a professor announces his meeting schedule (MAP) in meeting slots (SCW slots) for the upcoming 5 business days (16 consecutive frames).

30. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 30 CBP Framing

31. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 31 Scheduling of SCW Slots in a CBP Frame There are three types of slots in a CBP frame –Hosting (announcement) slot (H) Reserved for the transmission of the Hosting CBP packet. It is always at the beginning of a CBP frame. Contains information of channel hosting and SCW slot scheduling (MAP), which can received by WRAN cells on every channel. –Presentation (reservation) slot (P) Reserved for a WRAN cell to perform contention-free CBP packet transmission Other WRAN cells can received the packet during this slot. Each WRAN cell can reserve its own P slot. –Discussion (contention/free-to-talk) slot (D) Used for contention-based inter-cell communication and regular WRAN system maintenance (CBP based ranging, etc.). Ensure backward compatibility with the current CBP mechanism.

32. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 32 Scheduling of SCW Slots in a CBP Frame P(x): Reserved Presentation Slot for CBP transmission of WRAN cell x.

33. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 33 Reservation Life-time of Presentation Slot To prevent a WRAN cell from holding a Presentation Slot, a Reservation Life-time of the Presentation Slot shall be initialized. The reservation of the Presentation Slot of a WRAN on a Channel expires at the end of a corresponding Reservation Life-time. Typically the Life-time is a (to be defined) number of super-frames. After the Life-time is expired, the Presentation Slot of a WRAN is removed.

34. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 34 Cross-channel Inter-cell Communication WRAN cell “A” to receive CBP packets from a nearby WRAN cell “B” –Tune to the operating channel of WRAN B – Ch(B) – during the hosting slot of Ch(B); –Receive and decode the CBP frame MAP of Ch(B) – H(B); –Identify the presentation slot of WRAN B – P(B); –If P(B) exists, receive CBP packets from WRAN B at slot P(B); –Else, try to receive CBP packets from WRAN B during the discussion slots on Ch(B) WRAN cell “A” to transmit CBP packet to a nearby WRAN “B” –If presentation slot is required for the CBP packet transmission, reserve one – P(A). –Transmit the CBP frame MAP – H(A) – on its operating channel – Ch(A) – during the hosting slot of Ch(A); –If there is presentation slot – P(A) – reserved for WRAN A, transmit the CBP packet during P(A); –Else, transmit the CBP packet during the discussion slot on Ch(A).

35. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 35 Cross-channel Inter-cell Communication

36. doc.: IEEE 802.22-07/0274r0 Submission June 2007 Wendong Hu, STMicroelectronicsSlide 36 Conclusion This presentation identifies a number of import issues on the current CBP mechanism (in D0.3) used for inter-cell discovery and communication. We proposed fundamental remedies to resolved these issues respectively. Moreover, we proposed a Enhanced Coexistence Beaconing Protocol (CBP) that allows efficient, reliable, scalable, and backward-compatible cross-channel inter-cell communications for IEEE 802.22 systems.