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Cognitive radio simultaneous spectrum access/one-shot game modelling

The aim of this paper is to assess simultaneous spectrum access situations that may occur in Cognitive Radio (CR) environments. The approach is that of one-shot, non-cooperative games describing CR interactions. Open spectrum access scenarios are modelled based on continuous and discrete reformulations of the Cournot game theoretical model. CR interaction situations are described by Nash and Pareto equilibria. Also, the heterogeneity of players is captured by the new concept of joint Nash-Pareto equilibrium, allowing CRs to be biased toward different types of equilibrium. Numerical simulations reveal equilibrium situations that may be reached in simultaneous access scenarios of two and three users.

Analysis of cognitive radio scenes based on non-cooperative game theoretical modelling

A noncooperative game theoretical approach for analysing opportunistic spectrum access (OSA) in cognitive radio (CR) environments is proposed. New concepts from game theory are applied to spectrum access analysis in order to extract rules of behaviour for an emerging environment. In order to assess OSA scenarios of CRs, two oligopoly game models are reformulated in terms of resource access: Cournot and Stackelberg games. Five CR scenes are analysed: simultaneous access of unlicensed users (commons regime) with symmetric and asymmetric costs, with and without bandwidth constraints and sequential access (licensed against unlicensed). Several equilibrium concepts are studied as game solutions: Nash, Pareto and the joint NashPareto equilibrium. The latter captures a game situation where players are non-homogeneous users, exhibiting different types of rationality, Nash and Pareto. This enables a more realistic modelling of interactions on a CR scene. An evolutionary game equilibrium detection method is used. The Nash equilibrium indicates the maximum number of channels a CR may access without decreasing its payoff. The Pareto equilibrium describes a larger range of payoffs, capturing unbalanced as well as equitable solutions. The analysis of the Stackelberg modelling shows that payoffs are maximised for all users if the incumbents are Nash oriented and the new entrants are Pareto driven.

An Adaptive Combiner-Equalizer for Multiple-Input Receivers

Where multiple-input receivers are concerned diversity combining is one of the most efficient techniques against fading effects. In this paper we propose a multipleinput adaptive combiner-equalizer. The novelty of the solution lies in the unified combining-equalization approach - the two classical operations being performed simultaneously and not sequentially. Our simulations show significant performance in terms of outage probability for both indoor and outdoor conditions, while complexity is lower than for a classical MRC implementation. The concept of unifying certain operations along the transmission chain is feasible today more than ever as it can be easily implemented on SDR (Software Defined Radio) platforms.

The Adaptive Potential of reconfigurable MEMS in MIMO Antenna Technology

Part of a detailed study of adaptive radio techniques, the work presented in this paper focuses on the potential of MEMS (Micro-Electro-Mechanical Systems) in reconfigurable antenna array technology. After identifying the main challenges and benefits of multiple antenna systems, we have analyzed the four mechanisms in which a multiple antenna system can improve upon the throughput of a traditional wireless network: beamforming, beam-steering, transmit and receive diversity, and spatial multiplexing. In this paper we propose a unified technology for both the MEMS and the metallic pixel-patches that form the reconfigurable antenna array, thus aiming at a less expensive one, that can be unitarily controlled, as a single entity. This will in turn reduce the computational complexity of the control module. We have designed, simulated and analyzed reconfigurable MEMS antenna arrays at 40 GHz, 2.4 and 5 GHz. Reconfigurability of the operating frequency and of polarization are discussed. Based on our observations we can set the premises for new adaptive strategies.

Towards Cognitive Antenna Systems based on antenna-channel co-evolution

The paper discusses critical issues and challenges for the present generation of smart antennas, identifying multireconfiguration capabilities that can be addressed by evolutionary computing. A bio-inspired model called Cognitive Antenna System-CAS is proposed. Evolutionary algorithms are pointed at as a means of modelling and implementing cognitive mechanisms in such a system, based on the proposed antennachannel co-evolution concept.

The Impact of Novel RF MEMS and SDCs on Smart Antenna Technologies

This paper evaluates the impact of the newest micro & nanotechnologies on smart antenna systems. After analyzing the key features of the main mobile wireless systems of the present - UMTS, CDMA2000, WiMax 802.16e, and MBWA 802.20, we have identified some common issues, requirements and limitations. Dwelling on the SDC -Software-Defined Component perspectives we have analyzed the impact of novel RF MEMS on reconfigurable circuits, namely on smart antenna systems. This lead us to imagine a software-defined autonomous antenna - SDAA, which includes the RF module. This in turn, integrated on a SDR platform, will prototype the idea of extending the SDR concept over the RF module. This paper introduces our proposed SDR & SDAA architecture and its benefits.

Spectral efficiency improvement for the under-11GHz Broadband Wireless Access

Our evaluation is performed in the context of a study of adaptive radio techniques, in the attempt to improve link availability and transmission quality of BWA (broadband wireless access) systems, and to achieve an efficient use of radio resources. As part of an evaluation of coexistence issues in the under-11 GHz bands, we have analysed several adaptive techniques currently in use in IEEE 802.16 and IEEE 802.11 (a, b, g) standards. This paper is focused on the spectral efficiency and BER performance of the 802.16 FEC block. One of our goals was to study the effect of the interleaving process on the spectrum efficiency for different environments modelled by different radio channels. Another goal was to measure the system throughput and the delay introduced by the interleaver in the presence of noise, these enabling us to investigate from which BER and/or SNR threshold the interleaver can increase the overall spectrum efficiency. In the end, we identify six evaluation criteria for an adaptive FEC (forward error correction) scheme that can improve the performance, in terms of throughput, in an 802.16 SC system. The detailed observations will enable us to set the premour evaluation is performed in the context of a study of adaptive radio techniques, in the attempt to improve link availability and transmission quality of BWA (broadband wireless access) systems, and to achieve an efficient use of radio resources. As part of an evaluation of coexistence issues in the under-11 GHz bands, we have analysed several adaptive techniques currently in use in IEEE 802.16 and IEEE 802.11 (a, b, g) standards. This paper is focused on the spectral efficiency and BER performance of the 802.16 FEC block. One of our goals was to study the effect of the interleaving process on the spectrum efficiency for different environments modelled by different radio channels. Another goal was to measure the system throughput and the delay introduced by the interleaver in the presence of noise, these enabling us to investigate from which BER and/or SNR threshold the interleaver can increase the overall spectrum efficiency. In the end, we identify six evaluation criteria for an adaptive FEC (Forward Error Correction) scheme that can improve the performance, in terms of throughput, in an 802.16 SC system. The detailed observations will enable us to set the premises for new adaptive strategies at the PHY and MAC layer is set for new aadaptivedaptive strategies at the PHY and MAC layer.

A Strategic Interaction Model of Punishment Favoring Contagion of Honest Behavior

The punishment effect on social behavior is analyzed within the strategic interaction framework of Cellular Automata and computational Evolutionary Game Theory. A new game, called Social Honesty (SH), is proposed. The SH game is analyzed in spatial configurations. Probabilistic punishment is used as a dishonesty deterrence mechanism. In order to capture the intrinsic uncertainty of social environments, payoffs are described as random variables. New dynamics, with a new relation between punishment probability and punishment severity, are revealed. Punishment probability proves to be more important than punishment severity in guiding convergence towards honesty as predominant behavior. This result is confirmed by empirical evidence and reported experiments. Critical values and transition intervals for punishment probability and severity are identified and analyzed. Clusters of honest or dishonest players emerge spontaneously from the very first rounds of interaction and are determinant for the future dynamics and outcomes.

A Relevant Equilibrium in Open Spectrum Sharing: Lorenz Equilibrium in Discrete Games

A new game theoretical solution concept for open spectrum sharing in cognitive radio (CR) environments is highlighted – the Lorenz equilibrium (LE). Both Nash and Pareto solution concepts have limitations when applied to real world problems. Nash equilibrium (NE) rarely ensures maximal payoff and it is frequently Pareto inefficient. The Pareto set is usually a large set of solutions, often too hard to process. The Lorenz equilibrium is a subset of Pareto efficient solutions that are equitable for all players and ensures a higher payoff than the Nash equilibrium. LE induces a selection criterion of NE, when several are present in a game (e.g. many-player discrete games) and when fairness is an issue. Besides being an effective NE selection criterion, the LE is an interesting game theoretical situation per se, useful for CR interaction analysis.

A Game Theoretical Perspective on Small-Cell Open Capacity Sharing in Cognitive Radio Environments

Small-cell, open capacity sharing scenarios in Cognitive Radio (CR) environments are studied from a game theoretical (GT) perspective. Simultaneous capacity requests in small-cell scenarios are modelelled as strategic interactions between CRs and analysed as resource access games. CR capacity access competition is modelled based on discrete reformulations of the Bertrand GT model. Detected equilibria describe stable game situations. Numerical simulations identify situations where Nash equilibrium (NE) is both fair and Pareto efficient or where there are multiple NE solutions to choose from, indicating a flexible range for CR strategies. Adding to the analysis are the joint Nash-Pareto solutions (intermediate between Nash and Pareto) capturing heterogeneous behaviour of players. Stable and equitable states are detected even when players have different biases.