Synchronous Collision Resolution MAC Design and Performance Assessment

1. Synchronous Collision Resolution MAC Design and Performance Assessment Date: 2009-11-17 Authors: 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 #09-4802 John A. Stine, Self

2. Abstract • The Synchronous Collision Resolution (SCR) protocol provides a technology agnostic mechanism to arbitrate contention access that also provides special mechanisms to • Enable directional communications, • Differentiate services – priority access and reservations for streaming • Energy conservation • Channel management • This presentation seeks to quantify the performance of these mechanisms by • Defining the duration of a signaling slot • Presenting a contention, framing, and epoch design • Determining the efficiency of payload transmission 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 • Time slotted channels with common time boundaries • Nodes with packets to send contend in every slot • Signaling is used to arbitrate contention • Packet transmissions occur simultaneously CR Signaling Transmission Slot … John A. Stine, Self

6. Purpose of Collision Resolution Signaling • Prune the set of contenders to a subset which can transmit without colliding John A. Stine, Self

7. Arbitrating Space and Time • Signaling with Echoing • Resolves to a subset of contenders where interfering nodes are at least one radio range away from destinations • Demonstration • Survivor Density ~ 0.5-0.8 John A. Stine, Self

8. Significant Take Aways • SCR arbitrates time, space, and frequency • Signaling can be the common arbitration mechanism and made independent of the rest of the frame • Multiple technologies can coexist • Technologies can evolve with fewer legacy constraints Common Multiple technologies can coexist here CR Signaling Transmission Slot John A. Stine, Self

9. Summary of Additional Features • Supports directional contention and antenna adaptation • Supports channel management • Supports SDMA, CDMA, and FDMA • Provides quality of service • Prioritized access • Reservations for streaming • Provides multiple mechanisms for energy conservation • Default dozing • Opportunistic dozing • Coordinated dozing John A. Stine, Self

10. Signal Duration John A. Stine, Self

11. Criticial Assumptions About Signaling • The presence of signals is detected and there is no requirement to recover symbols or bits (PHY) • A signal is detected as present when receiving many signals (PHY) • The signaling slot in which a signal was sent is unambiguous (PHY or MAC) John A. Stine, Self

12. Timing Parameters Table 1. Design Choices Table 2. Modem Capabilities and Physics John A. Stine, Self

13. Signaling Slot Assumptions November 2009 • Assume the signal slot size is selected as • Assume signal transmission or signal reception starts at the beginning of a signaling slot • Assume required sensing time, tsf, can be specified • ts is selected to account for PHY limitations in sending and sensing signals, propagation times, and synchronization differences • tg is selected to account for PHY transitions between receiving and transmitting states, propagation times, and synchronization differences ts tg ts tg tsignaling slot tsignaling slot John A. Stine, Self

14. Late Signal Transmission • We select the minimum time to sense a signal, tsf, such that tsf > tsn and tsftss • Observations John A. Stine, Self

15. Early Signal Transmission • Observations • Recall late signal transmission observations Largest tsn Smallest tss John A. Stine, Self

16. Design Equations – Specified Sensing Time Ensures tsf > tsn Ensures tss≥tsf Ensures tsf > tsn John A. Stine, Self

17. Some Numbers Modem Capabilities and Physics John A. Stine, Self

18. Contention Design John A. Stine, Self

19. We Commit to Signaling with Echoing • Supports directional contention • Resolves to a subset of contenders where interfering nodes are at least one radio range away from destinations • Eliminates the need for an RTS-CTS exchange John A. Stine, Self

20. Assumptions in the Contention Design • Stations will be one of two types • A station that commits its antenna to a direction • A station that participates in multiple directions (Typically base stations) • Stations that commit to a direction send all signals and receive only in that direction John A. Stine, Self

21. Assumptions in the Contention Design -2 • Stations that participate in multiple directions • Send priority phase signals and echoes in all of those directions • Listen for signals in all of those directions • Send contention signals directionally (In multihop environments) • Signal transmission power on the narrow band of a signal can compensate for the absence of directional gain John A. Stine, Self

22. Base Station Contention Signaling • Typically in multihop environments contention signaling is directional and echoing is in all directions a node might receive • In our scenarios most traffic is to and from base stations which puts base stations at a disadvantage • Thus base stations transmit and echo signals in all directions they might receive Base station is at a disadvantage unless it signals in all direction it might receive John A. Stine, Self

23. Priority Phase Design • Provides support for • 2 levels of peer-to-peer prioritized access • Separate broadcast priority to support channelization • Two step state-based reservations for streaming • Rapid return to dozing states when using coordinated dozing Broadcast Priority/QoS … 1 2 n CBR … C E C E C E C E C E C E Priority Phases Contention Phases John A. Stine, Self

24. How to Design Signaling to Resolve to a Single Contender • Recall that contending nodes signal in a phase with a specified probability • Nodes survive a signaling phase if • They transmit a contention signal • They do no transmit a contention signal and hear neither a contention signal nor an echo • Nodes that do not survive a signaling phase stop contending • The objective of signaling design is to select the number of phases and their associated contention probabilities to most efficiently resolve contentions John A. Stine, Self

25. How to Design Signaling to Resolve to a Single Contender • Let px be the probability that a contending node will signal in phase x • A transition matrix may be populated where the element k,s corresponds to the probability that s of k contending nodes survive the signaling phase John A. Stine, Self

26. How to Design Signaling to Resolve to a Single Contender (3) • The transition matrix of the signaling process with n phases may be calculated • The probability that just 1 of k contending nodes survives signaling is • It is easy to optimally select a set of probabilities that maximizes the probability that there will be 1 survivor when there are some k = k1 contenders at the beginning but this problem formulation may result in a lower probability that one survivor remains when there are k < k1 contenders. P(one survivor) k k1 Improvement at k1 may results in decreased performance at k < k1 John A. Stine, Self

27. How well does signaling isolate just one survivor? (3) • A redefined optimization problem • Let qn be the set of px for an n phase CRS design • Let kt be a target density of contending nodes • Let m be the total number of signaling slots allowed (in this case n = m) • Let S(qn,kt,m)be the probability that there will be only one surviving contender 4, 5, 6 , 7, 8, and 9 phase designs optimized for a 50 contender density Comparison of 9 phase designs optimized for various target densities of contenders John A. Stine, Self

28. What Should the Target Density Be? • Maximum contenders occur in only very congested environments • Nodes only contend if they use the same priority phase to gain access • Nodes with CBR reservations never have to contend Maximum of 2 contenders Maximum of 21 contenders Maximum of 9 contenders John A. Stine, Self

29. Assorted Designs Signaling with 7 Phases Signaling with 5 Phases Signaling with 9 Phases Signaling with 8 Phases Signaling with 6 Phases John A. Stine, Self

30. Determining when one design is better than another • Throughput computation • Threshold payload size computation (The size of the payload that warrants using more signaling phases) (Given other values solve for tp) Signaling Phases kt POne_Survivor at kt of each design Signaling Phases kt Payload size threshold in ms between contention designs at kt John A. Stine, Self

31. Threshold Curves Signaling designs for kt = 5 Signaling designs for kt = 15 Signaling designs for kt = 25 Shows payload where using more contention phases is appropriate Signaling designs for kt = 10 Signaling designs for kt = 20 John A. Stine, Self

32. Epoch Design John A. Stine, Self

33. Epoch design goal • Support expected realtime streams • Seeking a transmission slot size and repetition rate Broadcast Priority/QoS … 1 2 n CBR … C E C E C E C E C E C E Contention Phases Priority Phases Protocol Data Unit ACK 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

34. Resource reservation process (1) • Contenders with a real time stream first contend using the QoS or broadcast priority • If packet exchange is successful, that node may use the CBR priority in the same ordinal transmission slot of every subsequent CBR Epoch. Broadcast Priority/QoS CBR C E C E C E … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch John A. Stine, Self

35. Resource reservation process (2) • Because of these two steps, nodes using the CBR priority win without having to do any further signaling • The process may be repeated by a node to reserve as much bandwidth as is needed. • Nodes hold reservations on a “use-it or lose-it” basis (Unused slots are immediately available). • It is best if contiguous slots are reserved since signaling can be reduced Reserves 2 slots per frame … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch John A. Stine, Self

36. Resource reservation process (3) • A single signaling period can capture multiple consecutive slot reservations • Subsequent signals after the CBR signal convey a binary number of the quantity of consecutive slots that are reserved (no more than to the end of the epoch) … n Bit 0 Bit 1 CBR Bit m … … C E C E C E C E C E Reserved Number of reserved slots Protocol Data Unit ACK CR Signaling Multiple Transmission Slots … … … 1 2 3 4 m-1 m 1 2 3 4 m-1 m 1 2 CBR Epoch CBR Epoch John A. Stine, Self

37. Payload sizes for MSDUs • We are seeking the best transmission slot duration Number of fragments John A. Stine, Self

38. Payload sizes for MSDUs (2) Most payload durations are less than 200 ms (those larger are shaded) Values were selected to allow an analysis and not based on any particular PHY John A. Stine, Self

39. Choosing an Epoch Rate • Assume a multiple of 60 epochs per second in order to accommodate 60 fps video • Recall 200 ms payload size from previous slide for MSDU delivery With a payload duration of 200 ms a 5-phase signal design is appropriate 120 epochs per second with 20 transmission slots per epoch meets our 200 ms criteria providing 2400 transmission slots per second Shaded regions indicate designs where signaling exceeds 50% of a slot duration John A. Stine, Self

40. What video rates will this scheme support • Assumptions • A node cannot reserve the first slot of an epoch • At 120 epochs per second, each epoch needs to support the transmission of 34 video slices • Since contiguous slots can support more payload, the protocol will attempt to send the video slices consecutively within a contiguous set of transmission slots • An RTS at the beginning identifies the destinations of the stream • As proposed by Cordeiro in IEEE 802.11-09/0709r1, slices are normally distributed and scalable with mslice = 15.798 Kbytes and sslice = 1.350Kbytes at an average 515 Mbps video rate John A. Stine, Self

41. What video rates will this scheme support (2) • The maximum bits that must be sent per epoch for the average video rate B can be determined by • The time required to send 34 slices with confidence is John A. Stine, Self

42. Transmission Slots Required per Epoch per Video Rate per Date Rate NF = Not Feasible Assumes 34 slices per epoch in support of 60 frames per second and a 3s guard for peek bursts John A. Stine, Self

43. Maximum Video Ratesby Date Rates and Slots per Epoch Assumes 34 slices per epoch in support of 60 frames per second and 3s guard for peek bursts John A. Stine, Self

44. So What is the Efficiency • For a 1500 Byte MSDU • For a maximum sized packet • For a video stream John A. Stine, Self

45. Conclusion • This presentation • Proposed an SCR design for VHT that supports • Directional contention access • Quality of service • Use of multiple channels, FDMA or CDMA • Energy conservation • Provided a design methodology that will allow revision to the design as details of technology capability become better known • The design is as high as 40% efficient for data transmissions and can be better than 80% efficient for streaming video transmission • The design does not depend on any particular PHY and will support the coexistence of multiple PHYs John A. Stine, Self

46. The Larger Story John A. Stine, Self

47. Backup John A. Stine, Self

48. Desired (not necessary) characteristics of signals • Short • Contributes to efficiency • Easily distinguished from noise and other transmissions • Allows operation in noisy environments where physical layer capabilities can reject interference • Have unique characteristics that are associated with the signaling slot in which they are sent • Reduces overhead requirements to prevent slot of transmission ambiguity • Provides security preventing some cases of malicious DoS John A. Stine, Self

49. Directional Signaling • Assumes sources know the direction to destinations • Uses an echo design • Signaling rules • Rules the same as those for signal echoing designs except • Contenders send priority signaling in all directions they might possibly receive • Contenders send CRS signals in the direction of their destinations • Non-contenders echo in all directions they might possibly receive • Contenders defer directionally after receiving echoes • In AP network, all non-AP stations can permanently point toward the AP John A. Stine, Self

50. 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