James O. Neel

Using game theory to analyze wireless ad hoc networks

The application of mathematical analysis to the study of wireless ad hoc networks has met with limited success due to the complexity of mobility and traffic models, the dynamic topology, and the unpredictability of link quality that characterize such networks. The ability to model individual, independent decision makers whose actions potentially affect all other decision makers renders game theory particularly attractive to analyze the performance of ad hoc networks. In this article we describe how various interactions in wireless ad hoc networks can be modeled as a game. This allows the analysis of existing protocols and resource management schemes, as well as the design of equilibrium-inducing mechanisms that provide incentives for individual users to behave in socially-constructive ways. We survey the recent literature on game theoretic analysis of ad hoc networks, highlighting its applicability to power control and waveform adaptation, medium access control, routing, and node participation, among others.

Performance Evaluation of Cognitive Radios: Metrics, Utility Functions, and Methodology

Performance evaluation of cognitive radio (CR) networks is an important problem but has received relatively limited attention from the CR community. Unlike traditional radios, a cognitive radio may change its objectives as radio scenarios vary. Because of the dynamic pairing of objectives and contexts, it is imperative for cognitive radio network designers to have a firm understanding of the interrelationships among goals, performance metrics, utility functions, link/network performance, and operating environments. In this paper, we first overview various performance metrics at the node, network, and application levels. From a game-theoretic viewpoint, we then show that the performance evaluation of cognitive radio networks exhibits the interdependent nature of actions, goals, decisions, observations, and context. We discuss the interrelationships among metrics, utility functions, cognitive engine algorithms, and achieved performance, as well as various testing scenarios. We propose the radio environment map-based scenario-driven testing (REM-SDT) for thorough performance evaluation of cognitive radios. An IEEE 802.22 WRAN cognitive engine testbed is presented to provide further insights into this important problem area.

Convergence of cognitive radio networks

In this paper, we examine the conditions and behavior of several common convergence dynamics from game theory and show how they influence the structure of networks of cognitive radios. We then apply these to previously proposed distributed power control algorithms and describe how they impact network complexity.

Game theoretic analysis of a network of cognitive radios

Cognitive radio is an enhancement on traditional software radio design where observations of the operating environment are combined with knowledge of the radios available hardware and software capabilities to form decisions as to how to modify the radios behavior to produce a desired level of performance. This paper addresses how the insertion of cognitive radio technology into a network will impact performance and demonstrates how techniques from game theory can be used to analyze the network as a first step of shaping the decisions of the radios to achieve optimal network performance.

Performance of Distributed Dynamic Frequency Selection Schemes for Interference Reducing Networks

One of the more commonly envisioned algorithms for cognitive radios is spectrum filling via dynamic frequency selection. Applying the cognitive radio design framework, we formalize a low complexity distributed ad-hoc dynamic frequency selection algorithm that converges to near-minimal interference frequency re-use patterns. We then examine the performance of this algorithm in the presences of practical considerations such as intra-network policy variations and timing issues and show that while this leads to situations that violate the framework, the steady-state and convergence properties of the framework are still preserved

A game theory perspective on interference avoidance

We show that the fixed power, synchronous interference avoidance (IA) scheme of (C. Rose et al, IEEE Trans. on Wireless Comm., vol.1, no.3, p. 415-427, 2002) employing the (greedy) eigen-iteration can be modeled as the recently developed potential game of (D. Monderer et al, Journal of Games and Economic Behavior, vol.14, no.0044, p.124-143, 1996). Motivated by the fact that receivers can make small mistakes, we consider the convergence of the eigen-iteration when noise is added in a manner similar to (P. Anigstein, IEEE Trans. On Inf. Theory vol.49, no.4, 2003). Further, we restrict ourselves to a class of signal environments that we call levelable environments. Applying game-theory, we obtain a convergence result similar to that of the Anigstein method, for levelable environments: arbitrarily small noise assures that the eigen-iteration almost surely converges to a neighborhood of the optimum signature set.

Interference Reducing Networks

When cognitive radios operate in a network, each links adaptations impact the decisions of other cognitive radios which spawns an interactive decision processes. The existence of these interactive processes could potentially limit the deployment of cognitive radios as it is difficult to guarantee that the resulting behavior will avoid a tragedy of the commons, much less provide optimal performance. This paper proposes a novel design framework that ensures that cognitive radio interactions are beneficial and reduce sum network interference with each adaptation. Five different approaches to implementing algorithms that satisfy this framework are presented ¿ two of which rely on collaboration and three which permit autonomous adaptations.

Virginia Tech Space-Time Advanced Radio (VT-STAR)

With the integration of the Internet and multimedia applications in next generation wireless communications, the demand for reliable high data rate services is rapidly growing. Traditional wireless communications systems use a single input single output (SISO) channel, meaning one antenna at each side of the link. Information theory research has shown an enormous potential growth in the capacity of wireless systems by using multiple element array (MEA) technology at both ends of the link. Space-time coding exploits the spatialtemporal diversity provided by the multiple input multiple output (MIMO) channel, significantly increasing both the system capacity and the reliability of the wireless link. The Virginia Tech Space-Time Advanced Radio (VT-STAR) system presents a visual demonstration of the capabilities of space-time coding techniques. The VT-STAR system has integrated an MPEG-2 video stream to show a representation of the effect of the wireless channel on a video transmission in real-time. Core algorithms are implemented on Texas Instruments TMS320C67 Evaluation Modules (EVM). Data conversion between the digital and analog domains is performed by TI THS5661 EVM and TI THS1206 EVM for the transmitter and receiver, respectively. The radio frequency subsystem is composed of multi-channel transmitter and receiver chains implemented in hardware. The capabilities of the MIMO channel are demonstrated in a non-line of sight (NLOS) indoor environment. Real-time monitoring of physical layer parameters, such as the bit error rate and diversity advantage, as well as a video display are presented on an attached personal computer.

Game theoretic analysis of joint link adaptation and distributed power control in GPRS

In this paper, using non-cooperative game theory, we present a joint link adaptation and power control algorithm for GPRS (general packet radio service). We propose a utility model and analytically verify the existence of a Nash equilibrium (NE) in the network. We then propose a solution method and validate our work by simulating a seven-cell distributed system. Non-unique NE are shown to exist. The effects of the key parameters of the game are evaluated. We introduce three figures of merit (FOMs) that express the tradeoff between throughput and energy efficiency for the entire network. The FOMs are used to calculate the optimal values of penalty function parameters and to compare different NE. The proposed scheme is finally compared with another multirate power control technique.

Inter-Cell Interference Coordination/Avoidance for Frequency Reuse by Resource Scheduling in an OFDM-Based Cellular System

This paper proposes and evaluates a new method for mitigating inter-cell interference. We show that the proposed method results in a minor degradation of block error rate under low traffic loading but results in significant improvements for high traffic loads. We also propose and compare two options for resource re-allocation following allocation conflicts: immediate (synchronous) re-allocation and round-robin re-allocation. Simulation results indicates that round-robin reallocation results in good BLER performance when the traffic load is high.