Autonomous Target Assignment: A Game Theoretical Formulation Gurdal Arslan & Jeff Shamma Mechanical and Aerospace Engineering UCLA AFOSR / MURI

2 max Global Utility ( assignment ) Setup for Target Assignment Problem

3 Global Utility Example Global Utility = Utility generated at target j E [ total value of ( destroyed target – vehicles lost ) ] No engagement here Independent engagements (for example)

4 Joint Optimization Can be formulated as an integer programming problem - Computationally hard - Relaxation techniques available for suboptimal solutions Decentralized implementation - Requires global information - Agreement issues can arise Global Utility Assignment Profile :

5 Game Theory Formulation Vehicles are self-interested players with private utilities A vehicle need not know other vehicles’ utilities. Individual utilities depend on local information only. Vehicles negotiate an agreeable assignment.

6 Autonomous Target Assignment Problem Design - Vehicle utilities - Negotiation mechanisms so that vehicles agree on an assignment with high Global Utility using - low computational power - low inter-vehicle communication

7 Agreeable Assignment - Nash Equilibrium An assignment is a ( pure ) Nash equilibrium if no player has an incentive to unilaterally deviate from it. Example : Pure Nash equilibria : (1,1), (2,2), (3,3) Mixed Nash equilibria : ([ ], [ ]) ,10,0 1,20,0 3,

8 Utility Design Vehicle utilities should be aligned with Global Utility Ideal alignment : – Only globally optimal assignments should be agreeable – Not possible without computing globally optimal assignments Relaxed alignment ( factoredness in Wolpert et al ) : – Globally optimum assignment is always agreeable (pure Nash)

9 Aligned Utilities - Team Play For every vehicle, Example : Not localized - Each vehicle needs global information - Low Signal-to-Noise-Ratio (Wolpert et al. 2000) 21 2, 20, 0 1, Suboptimal Nash

10 Aligned Utilities - Wonderful Life Utility (Wolpert et al. 2000) Marginal contribution of vehicle # i to Global Utility, i.e., Localized : - Equal marginal contribution to engagements within range - Signal-to-Noise-Ratio is maximized no engagement

11 Aligned Utilities - Wonderful Life Utility (Wolpert et al. 2000) Aligned : Leads to a Potential Game with potential Convergent negotiation mechanisms for potential games

12 A Misaligned Utility Structure Equally Shared Utilities : Hence Global optimum may not be Nash agreeable A pure Nash agreeable assignment may not exists at all !

13 Negotiation Mechanisms At step k, vehicle # i proposes a target based on the past proposal profiles Is there a reasonable negotiation mechanism that leads to a Nash equilibrium ? Adopt learning methods in repeated games

14 Fictitious Play (FP) Empirical frequencies of past proposals Vehicle # i proposes the best response to Initial proposals are random target # 1target # 2

15 Convergence of FP in Potential Games Convergent to a (possibly mixed) Nash equilibrium Believed to be generically convergent to a pure Nash May be trapped at a suboptimal Nash 21 2, 20, 0 1,

16 Stochastic FP Randomness may help avoid a suboptimal assignment Positive probability of convergence to any pure Nash equilibrium in almost all potential games Conjecture : Stochastic FP converges to one of the pure Nash equilibria almost surely, in almost all potential games.

17 Stochastic FP with Utility Measurements Empirical average payoff for past proposals Propose the target with largest empirical average payoff target # 1target # 2

18 Stochastic FP with Utility Measurements Advantage : Don’t need to keep track of empirical frequencies Conjecture : Converges to one of the pure Nash equilibria almost surely, in almost all potential games. Convergence may be slower than FP

19 Near Optimum Performance Example: 40 uniform weapons negotiate 40 non-uniform targets

20 Simulation Environment Consists of entities and a battlefield

21 Entity Types Entities can be of different types Each entity type represented by a data structure For example: type = ‘uav’ side = ‘blue’ attributes = {‘radius’ ‘pkill’ ‘SARscanrate’ … } states = {‘health’ ‘location’ ‘heading’ ‘nstores’ … } routine = ‘uav_rule’;

22 Entity Rules How an entity type interacts and performs tasks For example, routine for `uav’ type : If UAV is alive – Find all SAM’s within radius – If no missile is launched & UAV has ammo Target closest live enemy

23 State Space State space consists of - states of all entities - environment states number of iterations left, etc. Simulation state is updated essentially based on the entity rules At each step, simulation state is displayed using visualization tools.

24 Simulation Scalable: One routine for each entity type Easy to modify, introduce new types, rules, etc.

25 Extensions & Issues Investigate other negotiation mechanisms - Gradient based mechanisms - Replicator dynamics - Finite Memory - Asynchronous mechanisms Explore applications - Traffic management - Routing in communication networks