1. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 1 CBP Overview and Updates IEEE P802.22 Wireless RANs Date: 2007-06-21 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 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 2 Abstract This presentation gives an overview of CBP and explains the rules for scheduling SCW in Active (Tx) and Passive (Rx) mode to enable the required coordination among 802.22 cells for coexistence and sensing. Most of the features described here are already part of the MAC normative text, but some details and additional information may have to be added to clarify and guarantee the proper operation of the protocol

3. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 3 WRAN Cell Discovery WRAN Cell Discovery is done through CBP and it is needed for: –Self-coexistence –Exchange information about sensing quiet periods (QP) When do we need tight coordination of Sensing QPs? –Assumption: to reliably sense channel N, QPs are needed in N-1, N and N+1 –For in-band sensing: Cells operating in channels N, N+/-1 and N+/-2 shall synchronize their QPs E.g. BS X operating in channel N shall synchronize its QPs for sensing with other BSs operating in N+/-1 and N+/-2. This ensure that the BS X can perform reliable sensing in the operating channel N and its adjacent channels (N+/-1) Synchronization of QP is done through CBP

4. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 4 QP coordination for in-band sensing NN+1N+2N-1N-2 Other neighboring BSs: A, B BS X operating in ch N X X A X X X X X B AB A B AB X needs to synchronize its QP with B (in N+-2) to do in-band sensing in N+-1 X needs to synchronize its QP with A to do in-band sensing in N

5. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 5 QP coordination for out-of-band sensing BS A operating in channel N wants to perform out-of-band sensing in channel N+Δ (Δ >1) –Scenario 1: there is another BS B operating in N+ Δ A needs to discovery B, and obtain B’s schedule of QPs A’s out-of-band sensing in N+ Δ shall be done during the QPs scheduled by B A doesn’t need to worry about other cells in N+ Δ +/-1 (the rule for in-band sensing will ensure their QPs are synchronized with B) –Scenario 2: there is no BS operating in N+ Δ A must scan N+ Δ +/-1 If B is found in either channel (N+1 or N-1), A can use the B’s QPs –If B in N+1 and C in N-1 are discovered, A has to use the overlapping QPs of B and C to sense N (B and C will have overlapping QPs according to the N+/-1+/-2 rule)

6. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 6 QP coordination for out-of-band sensing N+Δ Other neighboring BSs: B, C, D BS A operating in ch N and wants to do out-of-band sensing in ch N+Δ B B C B B B B B C CD C A scans the adjacent channels N+Δ+/-1 and uses B/C’s overlapping QPs B and C are sync (N+-1+-2 rule) N … N+Δ+1N+Δ-1N+Δ+2 C B A scans ch N+Δ to get B’s QP schedule through CBP A uses B’s QPs to do out-of- band sensing A scans the adjacent channels N+Δ+/-1 A uses B’s QPs to do out-of- band sensing A scans N, N+ Δ+/-1 and finds no BS A can do out-of-band sensing in N.

7. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 7 QP coordination requirements: Cells operating in channel N, N+/-1, and N+/-2 shall discover each other Cells operating in channel N, N+/-1, and N+/-2 shall synchronize their QPs when needed to ensure reliable sensing –To do sensing in channel N, a cell shall have its QP synchronized with other cells operating in channel N+/-1 –To do sensing in channel N+/-1, a cell shall have its QP synchronized with other cells operating in channel N+/-2

8. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 8 QP coordination requirements: (cont.) A cell does not need to synchronize its QPs for sensing with the QPs of other cells operating beyond N-/+2. –In order to perform out-of-band sensing, the cell only needs to know the schedule of the QP (if any) in the desired channel to perform out-of-band sensing during these periods

9. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 9 QP Scheduling Advertisement QP schedule for in-band sensing (N, N+/-1) is included in the SCH and carried by CBP packets When a cell receives a CBP packet from a neighboring cell, it will have the information needed to know whether it should synchronize its QP with the QPs of the neighboring cell

10. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 10 When Network Discovery in Performed? Discovery procedures will be performed during two stages: –At Network Initialization Network Discovery are one of the steps in the initialization procedures for BS and CPEs –During Normal Operation CBP is used in both cases

11. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 11 Network Discovery during initialization The BS and CPE shall perform a network discovery procedure by scanning the wireless medium for CBP packets and SCH during initialization and before data transmission –In case of the BS, this procedure is performed before the selection of the operating channel and it will include all the available channels Therefore, based on the channel selected, the BS will know whether it needs tight coordination of its QPs with other cells –For CPEs, this procedure shall include, at least, the BS’s operating channel (N) and channels N+/1 and N+/-2 The initial scanning time per channel depends on the minimal frequency of CBP transmissions (currently, it will take at most 4 frames) Since this is performed once, at initialization, this level of delay should not be an issue As neighbouring cells are discovery, the BS shall adjust its QPs accordingly

12. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 12 Network Discovery during normal operation During normal operation, the BS will schedule transmissions/receptions of CBP frames within Self- coexistence windows (SCW) to enable the needed coordination among neighboring cells When scheduling a SCW, the BS indicates which CPE will transmit or listen for CBP packets –Active Mode: CPE transmits a CBP packet –Passive Mode: CPE scans the channel indicated by the BS for CBP transmissions

13. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 13 Scheduling of the SCW The BS must follow some basic rules to schedule transmission/reception of CBP packets in order to efficiently coexist with neighboring cells –CBP packets carry the schedule of the quiet periods (QP) for sensing –CBP packets carry information related to coexistence mechanisms

14. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 14 (1) Minimal Frequency of CBP transmissions The BS shall schedule one SCW in Active mode at least every 4 frames –At least one CBP packet is transmitted (in the operating channel) at every 4 frames –The BS could also schedule CBP transmissions more or less often if needed (e.g., depending upon the contention level) This is unlikely though, given that the load of self-coexistence information exchange will probably be neither very high nor time critical This ensures a cell can be discovered by neighboring cells.

15. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 15 (2) Minimal frequency of SCW in Passive mode The BS shall schedule at least 3 SCWs in passive mode within a superframe period –Within every 3 SCWs, the BS shall request CPEs to listen for CBP packets in a way that ensures that channels N, N+1 and N-1 are scanned at least once. –By using the information collected during initialization procedures and the min. freq. of CBP transmissions, the BS can schedule the SCW to ensure the successful reception of CBP from neighbouring cells The BS shall schedule at least 2 SCW in passive mode within a channel detection time period –Within these 2 SCWs, the BS shall request CPEs to listen for CBP packet to ensures that channels N+2 and N-2 are scanned at least once.

16. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 16 Additional Network Discovery Features The BS can schedule Self-Coexistence Quiet Periods (not for sensing) –During this time, both CPEs and the BS shall search for CBP packets or BS SCH transmitted by overlapping 802.22 terminals belonging to other 802.22 cells –This is scheduled in the same way as the explicit scheduling of QP for sensing (using CHQ-REQ message), but it is used only to scan for neighboring cells There is no need for coordination of self-coexistence QP amongst cells Scanning during idle time –If a CPE is not expecting any transmission/reception from the BS and it has not been requested by the BS to perform any other procedure, then it can use its idle time to scan for other neighboring cells.

17. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 17 CBP Packet Format PreambleCBP Data 1CBP Data 2 (opt.) 1 OFDM Symbol (4 repetitions) 1 OFDM Symbol (Data + Pilots) 1 OFDM Symbol (Data + Pilots) Default CBP packet = 2 symbols (Preamble + CBP Payload) By default, CBP Payload carries the SCH Optionally a third symbol may be added to carry extra information

18. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 18 Self-Coexistence Window (SCW) CBP packets are transmitted during the SCW SCW are scheduled by the BS at the end of the frame –Across all sub-channels –Fixed size in the time domain: 3 OFMD symbols long 3 OFDM symbols Time frequency

19. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 19 Contention Based Access Multiple CPEs may contend for transmission of CBP during a SCW –Within a cell, the BS selects which CPE(s) will transmit CBP, therefore it has full control over the contention level e.g. BS may select the CPEs based on location information so that there is no collisions –Contention may happen amongst nearby CPEs in neighboring cells that are requested to transmit CBP when these cells are operating on the same channel. A random backoff mechanism can reduce the collision probability in this case

20. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 20 Access Mechanism for CBP transmissions For the default 2 symbol CBP packet size: –CPE performs the random backoff mechanism within the SCW before transmitting the CBP packet (explained in the next slide) For the optional 3 symbol CBP packet size: –CPE starts transmission directly in the first symbol

21. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 21 Random Backoff during SCW CPE selects a random Contention Window (CW) in the range [0, CWmax] CPE performs carrier sensing in the SCW Backoff slots within the first symbol of the SCW –Not related to incumbent sensing, but rather detection of another WRAN signal (energy detection with much higher signal level) If the medium is busy, freeze the CW counter and defer to the next SCW CPE decrements its CW counter if the medium is idle

22. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 22 CBP Access during the SCW (Example) CW1, CW2, and CW3 are backoff intervals at nearby CPEs 1, 2, and 3 CWmax = 9 CW1=3 CW2=9 CW3=6 CBP packet Rx xx+1x+2 SCW at Frame i … … … Rx xx+1x+2 SCW at Frame i+1 Rx CBP packet CW2=6 CW3=3 … … … … … … xx+1x+2 SCW at Frame i+2 Rx CBP packet Rx CW2=4

23. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 23 Conclusions The minimal CBP transmission/reception requirements also ensure that –a WRAN cell operating in channel N will discover other cells operating in N+/-1 and N+/-2 channels and therefore synchronize their QP for sensing Simple Backoff mechanism can reduce the collision probability when multiple overlapping CPEs are sharing the same SCW.

24. doc.: IEEE 802.22-07/0306r1 Submission June 2007 Dave Cavalcanti, PhilipsSlide 24 References