Designing for Coexistence

1. Designing for Coexistence Authors: Date: 2008-11-11 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. John A. Stine, Self

2. Patent Statement • Methods described in this presentation are covered in claims in patents and patents pending. • The MITRE Corporation is a not for profit company that does not own the patents and has no economic stake in the outcome of the 802 standards activity John A. Stine, Self

3. Abstract • The VHT 60 PAR scope includes the intent of providing mechanisms for coexistent use of spectrum • This presentation provides a taxonomy of spectrum sharing techniques based on design intent • Provides an overview of a contention-based technique to arbitrate use of spectrum shared by multiple technologies • This same technique provides solutions for many hard problems we want to solve in the VHT 60 standard John A. Stine, Self

4. Spectrum Compatibility - 1 • Many terms cover part of the problem space • Electromagnetic compatibility (EMC) – “The condition that prevails when telecommunications equipment is performing its individually designed function in a common electromagnetic environment without causing or suffering unacceptable degradation due to unintentional electromagnetic interference (EMI) to or from other equipment in the same environment.” (NTIA Red Book) • Coexistence – “The ability of one system to perform a task in a given shared environment where other systems have an ability to perform their tasks and may or may not be using the same set of rules.” (IEEE 802.15.2) • Cooperation – Differentiated from coexistence by whether a protocol is used to arbitrate sharing of spectrum (Peha 2009) • Dynamic Spectrum Access (DSA) – A variety of technologies that allow different systems to dynamically access spectrum based on its availability. One of those technologies is cognitive radio (CR). John A. Stine, Self

5. Spectrum Compatibility - 2 • To bring order to the design space I propose a taxonomy based on design intent • Reactive design – design efforts in reaction to the unintentional interference that occurs when systems operate in proximity to each other (The traditional EMC efforts) • Non-cooperative design – design without overt consideration of what other systems the DSA system must be compatible • Cooperative design – design with a deliberate effort to make systems compatible with known peer or incumbent systems John A. Stine, Self

6. Taxonomy-1 Non-cooperative design Cooperative design • In non-cooperative design • The technologies branch are static techniques to at least mitigate and hopefully prevent interference • The strategies branch are dynamic techniques that usually depend on some form of sensing to inform use decision • Where you would find most cognitive radio and policy driven technologies Technologies Strategies Targeted cooperation Design to rules Signal space Temporal Spatial Power Antennas Redesign Design Compliant Managed Policy driven approaches Collaborative Dynamic Static Collaborative Independent John A. Stine, Self

7. Taxonomy-2 Non-cooperative design Cooperative design • Targeted cooperation is where most coexistence work lies • In the design branch new systems are designed to coexist with an incumbent • The dynamic branch encompasses CR where design is specified by policy • In the redesign branch existing systems are modified to coexist • Progress is constrained by “tyranny of the incumbent” Technologies Strategies Targeted cooperation Design to rules Signal space Temporal Spatial Power Antennas Redesign Design Compliant Managed Policy driven approaches Collaborative Dynamic Static Collaborative Independent John A. Stine, Self

8. Taxonomy-3 Non-cooperative design Cooperative design • In design to rules, the rules of sharing are established first • The collaboration branch encompasses systems designed together • The managed branch encompasses technical methods that support a third party manager that manages which systems may use spectrum • The compliant branch encompasses approaches where rules are written and then any technologies that can follow the rules are allowed to use the spectrum Technologies Strategies Targeted cooperation Design to rules Signal space Temporal Spatial Power Antennas Redesign Design Compliant Managed Policy driven approaches Collaborative Dynamic Static Collaborative Independent John A. Stine, Self

9. Challenges in Creating Rules for Compliant Design-1 • Likely to be a contention-based design • Non-exclusive licensing rules of the 3650-3700 band are an example • Prefer techniques that allow different technologies to play together • “restricted” protocols which are only capable of avoiding interference with other co-frequency devices using the same protocol, can only use the lower 25 MHz • “unrestricted” protocols that prevent interference among different contention technologies may use the whole band • What are the alternative “unrestricted” protocols • Listen-before-talk • ? John Doe, Some Company

10. Challenges in Creating Rules for Compliant Design-2 • What’s wrong with listen-before-talk • Suffers from all the same problems as carrier sensing protocols • Hidden terminals • Exposed terminals • Deafness • Muteness • Still suffers “tragedy of the commons” • Can I beat the other guy’s backoff scheme • Returns the sharing problem to “tyranny of the incumbent” • You have to be able to sense my signal and I don’t have to sense yours • You better not send any signals I interpret incorrectly Returns the compatibility problem to targeted cooperation John A. Stine, Self

11. Creating Rules • The focus of creating rules should be the design of a generic mechanism that • Arbitrates the fair use of time, space, and frequency • Uses the simplest possible signals for detection and arbitration • Allows open ended design of all other aspects of the system in the arbitrated periods of spectrum use • New technologies should only have to play by the rules to participate We propose that synchronous collision resolution is such a mechanism John A. Stine, Self

12. Rule Design The Original Sins • Recommended starting point • Defining channels (mechanisms should allow the arbitration and use of contiguous channels) • Division of time into periods (aka slots) common for all channels • Recommended approach • Use Synchronous Collision Resolution • Given the starting point, can simultaneously arbitrate the use of time, space, and channel • Absolutely fair unless you design it to be unfair for purposes of service differentiation John Doe, Some Company Slide 12 John A. Stine, Self

13. A paradigm not a specific design Characteristics of SCR used for Spectrum Arbitration • Time slotted channels with common time boundaries • Nodes with packets to send contend in every slot • Signaling is used to arbitrate contention • Unique signals assigned to each channel(e.g. tones) CR Signaling Transmission Slot … John A. Stine, Self

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

15. Collision Resolution Signaling Example - 1 Red = contender Gray = non-contender All contending nodes do a random number draw and those beneath a specified threshold transmit a signal. Signalers and those that do not hear the signal survive this phase of the signaling In this example all nodes start off as contenders John A. Stine, Self

16. Collision Resolution Signaling Example - 2 Signaling and attrition proceeds for several iterations with the threshold for signaling changing for each phase John A. Stine, Self

17. Collision Resolution Signaling Example - 3 John A. Stine, Self

18. Collision Resolution Signaling Example - 4 John A. Stine, Self

19. The end result of collision resolution signaling When all nodes are in range of each other – one surviving node In a multihop environment as shown – a set of surviving nodes separated by the range of their signals The range of signaling’s effect can be extended by using echoing (See subsequent slides) Collision Resolution Signaling Example - 5 Demonstration John A. Stine, Self

20. How effective is CRS in resolving contention ? • It is a function of design, # of signaling phases, threshold probabilities for signaling • We have a simple design methodology that yields the performance illustrated Comparison of 9 single-slot phase designs optimized for various target densities of contenders 4, 5, 6 , 7, 8, and 9 single-slot phase designs optimized for a 50 contender density > 99% of the transmissions slots can be resolved to one transmitter for all practical densities of contenders! John A. Stine, Self

21. Signal Echoing • One hop signaling may result in deadlock • Two survivors repeatedly win the contention but attempt to send to the same destination thus blocking each other • Most likely to occur in lightly loaded and less dense networks • Signal echoing will break this deadlock John A. Stine, Self

22. Signal Echoing John A. Stine, Self

23. Echoing Example Red = contender Gray = non-contender Blue square = echoer 19 contenders after echoing 75 contenders after contention Demonstration John A. Stine, Self

24. Spatial Reuse-1 • Simulations of signaling without echoes reveal • The density of survivors levels off at about 1.4 survivors per signaling area (the area covered by the range of a signal) • Depending on signaling effectiveness, survivors are separated by at least the range of their signals Density of range to the nearest surviving neighbor when the average contending neighbor density is10 Simulated survivor densities using a 9-phase CRS design, kt = 50 John A. Stine, Self

25. Spatial Reuse-2 25 • Simulations of signaling with echoes reveal • The density of survivors decreases with contender density • Average separation range increases with the density of the contenders 20 2 10 15 5 8 Simulated survivor densities using SUMA version of signaling Density of range to the nearest surviving neighbor using SUMA version of signaling John A. Stine, Self

26. Arbitrating Channels among Technologies Channels systems want Channels systems receive Signaling Schedule • Stations may contend for multiple channels • Signals contain the tones of the channels a station wants to use • A station may win the right to use a subset of the channels it initially contends to use Station of system A Station of system B Station of system C The signals in this scenario John A. Stine, Self

27. Features Useful to the VHT 60 Goals • Synchronous Collision Resolution has additional features • Creates the conditions for effective CDMA use and other channelization schemes • Enables multiple antenna adaptation schemes • Differentiates prioritization of access among nodes • Supports resource reservations without scheduling • Provides multiple mechanisms to enhance energy conservation SCR creates the access conditions that allow most PHY technologies to perform at their best and will enable the very high throughput sought John A. Stine, Self

28. The Hurdles in Designing the Rules • Methods to synchronize different technologies • Agreement on • The features to include in the signaling • Precedence in arbitration • Boundaries on slots and channels • The common signals • The synchronization bounds The Original Sins John A. Stine, Self

29. Conclusion • Listen before talk methods of sharing suffer shortcomings and do not solve the contentious issues in spectrum sharing across technologies • We have proposed a method of sharing that • Does not suffer listen-before-talk’s failure modes • Enables sharing across all RF spectrum’s dimensions • Avoids the “tyranny of the incumbent” problem • This technique can also serve as a very effective contention-based access mechanism for high throughput applications John A. Stine, Self

30. References • 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. • 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. • J. A. Stine, “Exploiting smart antennas in wireless mesh networks,” IEEE Wireless Comm Mag. Apr 2006. John A. Stine, Self

31. Backup John A. Stine, Self

32. How well does signaling isolate just one survivor? • Consider a signaling design where all phases have one slot • 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

33. How well does signaling isolate just one survivor? (2) • 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

34. 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 single-slot phase designs optimized for a 50 contender density Comparison of 9 single-slot phase designs optimized for various target densities of contenders John A. Stine, Self