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SCR Synchronization

SCR Synchronization. Authors:. Date: 2010-02-25.

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SCR Synchronization

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  1. SCR Synchronization Authors: Date: 2010-02-25 John Stine is employed by The MITRE Corporation but represents himself in this presentation. The MITRE Corporation is a not for profit company and has no economic interest in the outcome of the 802 standards process. The author's affiliation with The MITRE Corporation is provided for identification purposes only, and is not intended to convey or imply MITRE's concurrence with, or support for, the positions, opinions or viewpoints expressed by the author. MITRE Public Release #10-0513 John A. Stine, Self

  2. Abstract • The Synchronous Collision Resolution (SCR) protocol provides special mechanisms to enable directional communications, QoS, energy conservation, and channel management that depend on network synchronization • This presentation identifies simple mechanisms to synchronize networks using SCR • Synchronization to a reference (e.g. an access point) • Selection of a synchronization reference • Synchronization transfer • Synchronization among references John A. Stine, Self

  3. The Larger Story John A. Stine, Self

  4. Review John A. Stine, Self

  5. A paradigm not a specific design Characteristics of Synchronous Collision Resolution Common Multiple technologies can coexist here • Time slotted channels with common time boundaries • Nodes with packets to send contend in every slot • Signaling is used to arbitrate contention • Signaling resolves time, space, and frequency CR Signaling Transmission Slot … John A. Stine, Self

  6. Proposed Signaling and Epoch Design • Energy conservation • Coexistence • Reservations for streams • Channelization • Designed to support • Directional access • Prioritized access Broadcast Priority/QoS … 1 2 n CBR … C E C E C E C E C E C E Contention Phases Priority Phases Packet Transmissions CR Signaling Transmission Slot … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch John A. Stine, Self

  7. Division of MAC Functionality • SCR puts as much functionality as possible into signaling • Signaling should be independent of messaging so that it can be the foundation of coexistence • The signals used should be the most effective at propagating and being detected by a plurality of technologies Involves the exchange of management frames Messaging Involves the transmission and detection of RF energy Signaling John A. Stine, Self

  8. Assumptions • All stations know • The number of transmission slots per epoch • The duration of transmission slots • The signaling design • Any specialized signaling sequences Synchronization will involve specialized signaling sequences John A. Stine, Self

  9. Access Points are good time references Concept of Operations • Access points establish networks • Subscriber stations • Search and find access points • Point their antennas toward the access point • Associate with the access point John A. Stine, Self

  10. Concept of Operations • Subscriber stations (The TV and the projector) • Are set to receive inputs from a known channel • Search for and synchronize to those stations • Search process also supports antenna pointing John A. Stine, Self

  11. Syncnronization John A. Stine, Self

  12. Goals of Synchronization • The purpose of synchronization is to make the slots in which signaling occurs unambiguous • Stations are synchronized when their transmission slots align to within xmsec and are in the same epoch and synchronization epoch (x = 1 in our design) Synchronization Epoch John A. Stine, Self

  13. 1 2 3 4 m-1 m 1 2 Signaling will be used to align epochs (Will in effect align seconds) CBR Epoch 1 2 3 4 m-1 m 1 2 CBR Epoch Messaging must be used for time of day synchronization (Aligns to which second of the day) John A. Stine, Self

  14. Goals of Synchronization - 2 • Different synchronization tasks • Synchronization to a reference (e.g. an access point) • Synchronization transfer • Synchronization among references John A. Stine, Self

  15. Starting Assumptions • Stations can synchronize to the leading edge of received signals • Stations will synchronize to a network before participating in contentions • Our signaling design will provide a set of signals that • Uniquely identifies a reference • Enables stations to synchronize to the reference • Avoids the need to send any packets John A. Stine, Self

  16. Main Assumption tS • Criteria • Propagation of signals is likely less than 30 meters so p 100 ns • If stations can synchronize to rs 900 ns of the leading edge of a received signal then our signal design will work trs tp tsy John A. Stine, Self

  17. Signaling for Syncrhonization John A. Stine, Self

  18. Additions to the Epoch Design to Support Synchronization No reservations allowed. All slots require contention • The first y transmission slots (y  2) of every epoch are set aside to support synchronization • Do not allow reservations in these slots • The first slot is used to send signals that enable synchronization • The additional slots are used to shift epochs • The technique also prevents contention starvation No restrictions on slot use … … … 1 y y+1 m-1 m 1 CBR Epoch John A. Stine, Self

  19. Additions to the Epoch Design to Support Synchronization - 2 Special rules and signaling to support distinguishing synchronization signaling Stations sending the synchronization signals may also send management frames or packets • Enable a special signaling design in the first slot to support synchronization activities • Unique signals for different types of references Sync Signaling Transmission Slot … … … 1 y y+1 m-1 m 1 CBR Epoch John A. Stine, Self

  20. Additions to the Epoch Design to Support Synchronization - 3 Transmission slot used for sending the reference synchronization signal • Establish an epoch cycle for periodic transmission of synchronization reference signaling • Provide a unique reference signaling sequence which stations search for and synchronize to • These would be sent in the first transmission slot of an epoch repeated every w epochs (Select w to match desired time interval, e.g. quarter second) • All stations must hear and be synchronized to the synchronization reference signal to participate in the contentions within the following synchronization epoch … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch CBR Epoch 7 6 w-6 5 w-7 w-5 4 w-4 3 w 1 2 w-3 w-2 w-1 Synchronization Epoch John A. Stine, Self

  21. Distinguishing Synchronization Signals • Use different signals for synchronization to make it easier to discern synchronization signals from generic contentions and to differentiate contention signals from echoes (i.e. E from C) • Possible variations of simple signals • Tones (vary by frequency and duration) • Chirps (vary by frequency, duration, and slope of frequency rise) John A. Stine, Self

  22. Types of References • Designated reference • A station configured to be a reference • Ad hoc reference • A station that cannot detect a neighboring reference and elects itself as the reference • Device reference • A station that has output for a device on the network • Used to support direct transfer • Arbitrating reference • A station seeing two designated or ad hoc references that assists in synchronizing one to the other John A. Stine, Self

  23. Rules for Contentions in the First Transmission Slots of Epochs - 1 • Regular contentions do not use the CBR priority phase • Signals in the priority phase are used to indicate a synchronization signal and the type of reference Reserved for synchronization use … 1 2 n … C E C E C E C E C E C E Contention Phases Priority Phases C E C E C E Type of Reference Sync Indicator John A. Stine, Self

  24. Rules for Contentions in the First Transmission Slots of Epochs - 2 • Signaling rules provide precedence of references • Follow-on signaling varies by reference type 00 – A stations between two references assisting their time shift 01 – A station that will send an identifier signal for a device to find and to synchronize to 10 – A station that takes on the role of an ad hoc references in the absence of a reference 11 – A station that is configured to be a designated reference C E C E C E Sync Indicator Type of Reference 1 = signal, 0 = don’t signal Designates type of reference Guidance from the reference(varies by type of reference) C E C E C E C E C E C E C E C E John A. Stine, Self

  25. Designated and Ad Hoc Reference Signals Designates type of reference Guidance from the reference(varies by type of reference) • Current quarter second counts the quarter second (00 is the second boundary) • References (Types 11 and 10) indicate the quality of their signal • Quality of reference follows when not directing a shift ( Shift signal = 0) • Quality indicator • 00 – Internal clock only • 01 – Synchronized to multiple peer references • 10 – Neighbor to a reliable reference • 11 – Reliable reference at this station (e.g. GPS) C E C E C E C E C E C E C E C E Sync Reference Identifier Type of Reference Shift Current Quarter Second Type of Shift or Reference Quality John A. Stine, Self

  26. Designated and Ad Hoc Reference Signals - 2 Designates type of reference Guidance from the reference(varies by type of reference) • References (Types 11 and 10) can adjust the epoch timing • Shift signal sent to indicate a cooperative adjustment will be made • After shift signal, type of shift indicates shift • 00 – Transmission slot 2 will be skipped this epoch • 01 – Transmission slot 2 will be skipped every other epoch • 10 – Transmission slot 2 will be skipped every epoch • 11 – Epoch 2 will be skipped this synchronization epoch C E C E C E C E C E C E C E C E Sync Reference Identifier Type of Reference Shift Current Quarter Second Type of Shift or Reference Quality John A. Stine, Self

  27. Device Reference Signals Designates type of reference Guidance from the reference(varies by type of reference) • Additional slots used to send a device ID • Echoing of device IDs is not necessary so there are a possible 210 = 1024 possible IDs • Sent in the first transmission slot of an epoch but not the first epoch of a synchronization epoch C C C E C E C E C C C C C C C C Sync Reference Identifier Type of Reference Device ID John A. Stine, Self

  28. Arbitrating Reference Signals Designates type of reference Guidance from the reference(varies by type of reference) • Arbitrating references direct designated and ad hoc references to adjust (Applicability assumed since guidance is synchronized) • Adjustments • Shift type indicates shift unit • 00 – Tenths of microseconds (i.e. 100 nanoseconds) (Subsequent shift sizes are signed) • 01 – Microseconds • 10 – Transmission slots • 11 – Epochs • Shift size as large as 28 = 256 units (27 signed shifts for tenths of microseconds) C C C E C E C E C C C C C C C C Sync Reference Identifier Type of Reference Shift Type Shift Size John A. Stine, Self

  29. Rules for Contentions in the First Transmission Slots of Epochs - 3 • Designated and Ad Hoc References send their signals in the first transmission slot of the first epoch of a synchronization epoch • Device and arbitrating references may send their signals in the first transmission slot of any epoch but not the first epoch of a synchronization epoch • First transmission slots not used by timing references may be used for non-CBR contentions Synchronization Epoch 7 6 w-6 5 w-7 w-5 4 w-4 3 w 1 2 w-3 w-2 w-1 In any but #1 John A. Stine, Self

  30. Summary of Signaling for Synchronization Designated and Ad Hoc Reference • Type of Reference • 00 – A stations between two references assisting their time shift • 01 – A station that is the source to a device • 10 – A station that takes on the role of an ad hoc • 11 – A station that is configured to be a designated reference • Type of Shift • 00 – Transmission slot 2 will be skipped this epoch • 01 – Transmission slot 2 will be skipped every other epoch • 10 – Transmission slot 2 will be skipped every epoch • 11 – Epoch 2 will be skipped this synchronization epoch • Reference Quality • 00 – Internal clock only • 01 – Synchronized to multiple peer references • 10 – Neighbor to a reliable reference • 11 – Reliable reference at this station (e.g. GPS) • Shift Type • 00 – Tenths of microseconds • 01 – Microseconds • 10 – Transmission slots • 11 – Epochs • Shift Size: 28 possible shifts, (27 signed shifts for microseconds) • Device ID: 210 possible IDs Arbitrating Reference Device Reference John A. Stine, Self

  31. Protocol Rules for Syncrhonization John A. Stine, Self

  32. Network Participation • A station may participate in a network if it is a reference or is synchronized to a reference • A station may only contend if it has synchronized itself to a reference station or participated in a contention in the current synchronization epoch • A station exiting a low energy state must synchronize itself to a reference signal prior to participating in the network • A station that does not hear a reference for r epochs must execute the procedure for network entry and reference selection • All stations should be either a reference or a direct one-hop neighbor to a reference John A. Stine, Self

  33. Network Entry and Reference Selection • Begin searching for a synchronization reference • If multiple references are found, synchronize to the best reference • If this station is a designated reference • After finding the best reference (it could be the station itself if it has access to GPS) synchronize to that reference • If neighboring references conflict first serve as an arbitrating reference until neighboring references are synchronized • Begin serving as a reference in the same slots as the best reference • If no reference is found, begin serving as a reference • If this station is not a designated reference and no reference is found, follow ad hoc reference procedures John A. Stine, Self

  34. Selecting the Best Synchronization Reference • Given a choice of references a station will prefer references by the following criteria • A reference from which the station can receive packets • The reference with the highest quality in the order • Reliable reference at the reference station (e.g. GPS) • Neighbor to a reliable reference • Synchronized to multiple peer references • Internal clock only • The reference more advanced in time John A. Stine, Self

  35. Ad Hoc Reference Selection • After a station fails to find a neighboring designated or ad hoc reference initiate process to become an ad hoc reference • Randomly select a time within the window of x seconds to become a reference • While waiting to become a reference continue to search for a reference and if found end this process and synchronize to that reference • If no reference is found in the wait • If within two hops of a reference synchronize to the best two hop reference (Used to support mesh or ad hoc networking) • Start sending an ad hoc reference signal • Execute the ad hoc reference maintenance procedure John A. Stine, Self

  36. Ad Hoc Reference Maintenance • In all reference signaling listen to the reference signals and echoes when this ad hoc reference is silent • Listen in the reference type signaling field and resign as an ad hoc reference if a neighboring station is a designated reference • Listen in the quality field and resign as an ad hoc reference of a neighboring station is a better quality reference • Listen in the quarter second field and resign as an ad hoc reference if a neighboring station is 1 or 2 quarter seconds ahead • On a periodic basis refrain from signaling in the guidance fields • Listen during the guidance fields and resign as an ad hoc reference if a neighboring station is a reference John A. Stine, Self

  37. Reference Directed Time Adjustments • When a reference station receives guidance to adjust its timing it determines a shifting plan to come into alignment (Done so as not to disrupt ongoing streaming traffic) • It shifts largest increments first, whole quarter seconds by changing the quarter second count and then shifts within synchronization epochs by: • Skipping Epoch 2 • Skipping transmission slot 2 every epoch • Skipping transmission slot 2 every other epoch • Skipping transmission slot 2 the first epoch • Repeated as necessary • Ultimately puts the new quarter second mark within the first slot of the synchronization epoch • Starts next reference signal on the mark John A. Stine, Self

  38. Arbitrating Synchronization of References • Stations that are neighbors of multiple references may assist in synchronizing them • Algorithm • Select the best reference and determine the adjustment that other references must achieve • Synchronize to a reference needing adjustment • Randomly select an epoch in the synchronization epoch (x 1 < x w) and send the reference adjustment signal in its first transmission slot • Send the adjustment signal • Wait for the adjustment to be made and repeat the process as necessary • 00 – Tenths of microseconds • 01 – Microseconds • 10 – Transmission slots • 11 – Epochs John A. Stine, Self

  39. Reference Signaling for a Device • Three scenarios • An isolated station that is the source of a stream to a device • A station that is associated with a network • A networked device (e.g. a projector) • A dedicated device (e.g. a disk drive) • All device ID signals sent in a first transmission slot in an epoch after thefirst in a synchronization epoch • In the first scenario the source is told the device ID and then it operates on its own clock and periodically sends the synchronization reference signal with the device ID • In the other scenarios the source first synchronizes to the network and then starts sending the device reference signal • The second scenario may be preceded by coordination through the network John A. Stine, Self

  40. Using the synchronization mechanisms to conserve Energy John A. Stine, Self

  41. Opportunistic Periodic Dozing  Inactivity indicates a low load so doze Sync Signaling Transmission Slot … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch CBR Epoch Start dozing as soon as possible  9 8 7 6 w 4 3 2 5 1  Synchronization Epoch Doze until the last transmission slot of epoch w of the synchronization epoch, wakeup and wait for the synchronization signal Duty cycles much less than 1% are possible John A. Stine, Self

  42. Conclusion • Synchronization is necessary for signaling to work • A signaling and framing design and accompanying algorithms are provided for synchronization • Signaling can be used • To provide a synchronization reference • To synchronize references • To assist direct connectivity between devices and source stations • Synchronization can be achieved without messaging • The proposed synchronization design also supports very effective energy conservation John A. Stine, Self

  43. References John A. Stine, Self

  44. References • J. A. Stine, “Exploiting processing gain in wireless ad hoc networks using synchronous collision resolution medium access control schemes,” Proc. IEEE WCNC, Mar 2005. • J.A. Stine, “Cooperative contention-based MAC protocols and smart antennas in Mobile Ad Hoc Networks,” Chapter 8 in Distributed Antenna Systems: Open Architecture for Future Wireless Communications, Auerbach Publications, Editors H. Hu, Y. Zhang, and J. Luo. 2007. • K. H. Grace, J. A. Stine, R. C. Durst, “An approach for modestly directional communications in mobile ad hoc networks,” Telecommunications Systems J., March/April 2005, pp. 281 – 296. • J. A. Stine, “Modeling smart antennas in synchronous ad hoc networks using OPNET’s pipeline stages,” Proc. OPNETWORK, 2005. • J. A. Stine, “Exploiting smart antennas in wireless mesh networks,” IEEE Wireless Comm Mag. Apr 2006. • J. M. Peha, “Sharing Spectrum through Spectrum Policy Reform and Cognitive Radio,” TBP Proc. of the IEEE, 2009. • J. A. Stine, “Enabling secondary spectrum markets using ad hoc and mesh networking protocols,” Academy Publisher J. of Commun., Vol. 1, No. 1, April 2006, pp. 26 - 37. • J. Stine, G. de Veciana, K. Grace, and R. Durst, “Orchestrating spatial reuse in wireless ad hoc networks using Synchronous Collision Resolution,” J. of Interconnection Networks, Vol. 3 No. 3 & 4, Sep. and Dec. 2002, pp. 167 – 195. • J.A. Stine and G. de Veciana, “A paradigm for quality of service in wireless ad hoc networks using synchronous signaling and node states,” IEEE J. Selected Areas of Communications, Sep 2004. • J. A. Stine and G. de Veciana, “A comprehensive energy conservation solution for mobile ad hoc networks,” IEEE Int. Communication Conf., 2002, pp. 3341 - 3345. • K. Grace, “”SUMA – The synchronous unscheduled multiple access protocol for mobile ad hoc networks,” IEEE ICCCN, 2002. John A. Stine, Self

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